Highly selective monitoring of metals by using ion ...

Highly selective monitoring of metals by using ion-imprinted polymers

Pankaj E. Hande, Asit B. Samui & Prashant S. Kulkarni

Environmental Science and Pollution Research ISSN 0944-1344 Volume 22 Number 10 Environ Sci Pollut Res (2015) 22:7375-7404 DOI 10.1007/s11356-014-3937-x

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Author's personal copy Environ Sci Pollut Res (2015) 22:7375–7404 DOI 10.1007/s11356-014-3937-x

REVIEW ARTICLE

Highly selective monitoring of metals by using ion-imprinted polymers Pankaj E. Hande & Asit B. Samui & Prashant S. Kulkarni

Received: 12 September 2014 / Accepted: 1 December 2014 / Published online: 7 February 2015 # Springer-Verlag Berlin Heidelberg 2015

Abstract Ion imprinting technology is one of the most promising tools in separation and purification sciences because of its high selectivity, good stability, simplicity and low cost. It has been mainly used for selective removal, preconcentration, sensing and few miscellaneous fields. In this review article, recent methodologies in the synthesis of IIPs have been discussed. For several applications, different parameters of IIP including complexing and leaching agent, pH, relative selectivity coefficient, detection limit and adsorption capacity have been evaluated and an attempt has been made to generalize. Biomedical applications mostly include selective removal of toxic metals from human blood plasma and urine samples. Wastewater treatment involves selective removal of highly toxic metal ions like Hg(II), Pb(II), Cd(II), As(V), etc. Preconcentration covers recovery of economically important metal ions such as gold, silver, platinum and palladium. It also includes selective preconcentration of lanthanides and actinides. In sensing, various IIP-based sensors have been fabricated for detection of toxic metal ions. This review article includes almost all metal ions based on the ion-imprinted polymer. At the end, the future outlook section presents the discussion on the advancement, corresponding merits and the need of continued research in few specific areas.

Keywords Ion-imprinted polymers . Solid-phase extraction . Contaminated water . Sensors . Preconcentration

Abbreviations DEHPA Di-(2-ethylhexyl) phosphoric acid PEIMPA Polyethylenimine methylenephosphonic acid DFO Desferrioxamine HEMA Hydroxy ethyl methacrylate MAC N-methacryloyl-(L)-cysteine MAGA N-methacryloyl-(L)-glutamic acid BAL British anti-Lewisite RAM Restricted accessed material DAAB Diazoaminobenzene TAR 4-(2-thiazolylazo) resorcinol IPTS 3-Isocyanatopropyltriethoxysilane DDDPA 1,12-Dodecanediol-O,O′-diphenyl-phosphonic acid 4-VP 4-Vinyl pyridine AAPTS 3-(2-Aminoethylamino)propyltrimethoxy silane TCPTS 3-Thiocyanatopropyltriethoxysilane SPANDS 2-(p-Sulphophenylazo)-1, 8-dihydroxynaphthalene-3,6-disulphonate MPTS 3-mercaptopropyltrimethoxysilane EGDMA Ethyleneglycol dimethacrylate MAH N-Methacryloyl-(L)-histidine 8-AOQ 8-Acryloyloxyquinoline PVDF Polyvinylidene fluoride CTAB Cetyltrimethylammonium bromide TEOS Tetraethoxysilicate SALO Salicylaldoxime IPN Interpenetrating polymer network MPS Methacryloxypropyltrimethoxysilane

Responsible editor: Philippe Garrigues P. E. Hande : A. B. Samui (*) : P. S. Kulkarni (*) Energy and Environment Laboratory, Department of Applied Chemistry, Defence Institute of Advanced Technology, Deemed University, Pune 411025, India e-mail: [email protected] e-mail: [email protected]

Introduction Every year, large quantities of toxic metals are released in the environment as industrial waste. These toxic metals have an

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adverse effect on the human being, wildlife and ecosystem. Some of these metals are Hg, Cd, Pb, As, Cr, Cu, Zn, Pd, Ni, Sn, Fe, Ag, U, etc. For instance, sources of toxic metal lead are gasoline industries, paints, batteries, explosives, etc. (Papanikolaou et al. 2005). Cd poisoning is mainly due to its release from fossil oil burning, use in phosphate fertilizers that appear in fruits and vegetables (Flick et al. 1971). Arsenic is released into the ecosystem due to the use of organoarsenic compounds as chemical warfare agents, use in pesticides and similar compounds to feed chicken and also its use in car batteries (Kapaj et al. 2006). Volcanoes, geological deposits of mercury, alkali and metals processing are the sources of the toxic metal mercury (Wang et al. 2004). Human beings are exposed to inorganic aluminium through industrial processes like metallurgy, food preservation, water purification, use of pharmacological and cosmetic products, etc. Mercury poisoning leads to memory loss, irritability, blindness and deafness, gingivitis, gastrointestinal irritation and kidney dysfunction (D’Itri and D’Itri 1977). Methyl mercury is the most toxic form of mercury and shows greater absorption in gastrointestinal tracts. Cadmium shows adverse effects on the human being such as kidney damage, renal necrosis and dysfunction, pulmonary edema and pneumonitis and lung cancers (Godt et al. 2006). Arsenic is highly toxic to human beings and shows serious consequences such as cancers of the lung, skin, bladder, kidneys and liver as it has been used as a chemical warfare agent (Bissen and Frimmel 2003). Lead poisoning shows serious toxic hazards such as memory and learning deficits, high blood pressure, damage to neurologic, hematologic and renal system, fertility damage, etc. (Needleman 2004). Aluminium poisoning leads to neurodegenerative diseases like Alzheimer’s dementia, Parkinson’s disease, amyotrophic lateral sclerosis, etc. in human beings, (Verstraeten et al. 2008). Inorganic aluminium is highly reactive as compared to the organic aluminium. Thus, it is more toxic than organic aluminium. Therefore, the WHO, USEPA and EU have put a stringent ban on the release of toxic metals into the environment. For example, Cr(VI) has a drinking water standard limit of 0.1 mg L−1, Hg has 0.002 mg L−1, Pb has 0.015 mg L−1 and As has 0.010 mg L−1 (US National Primary Drinking Water Standards). Various methods available for removal of toxic metals include chemical, physical and biological methods (Blais et al. 2008). The chemical methods are precipitation, solvent extraction and ion exchange. In chemical precipitation, metal ions are precipitated as metal hydroxide, sulphide, carbonate or phosphate (Baltpurvins et al. 1996; Charentanyarak 1999). However, it is costly, non-selective, generate waste products and not applicable at low concentration. Solvent extraction is based on the principle of the ability of solute to distribute between aqueous and the organic phase. However, it has limitation as non selectivity of metals (Lin et al. 2002; Belkhouche et al. 2005). Ion exchange is the process through

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which ions in a solution are transferred to a solid (e.g. synthetic resin) which release ions of a different type but of the same polarity. It means that ions in solution are replaced by different ions initially present in the solid (e.g. synthetic resin). Ion exchange resins such as synthetic (sulphonic, carboxylic, thiocarbamate, thiols, hydroxyl, amide groups), chelating (phosphonic, aminophosphonic, iminodiacetate, oxime groups), solvent impregnated (di-(2-ethylhexyl) phosphoric acid (DEHPA), polyethylenimine methylenephosphonic acid (PEIMPA)) and natural materials (zeolite, clay) are being used for removal of metal ions (Lin et al. 2000). It has limitations as not effective at higher concentrations, low pH, costly, difficult to regenerate synthetic resin. Micro-filtration, nano-filtration, ultra-filtration and reverse osmosis are the physical methods being used for water purification process. Micro-filtration is the process of filtration through a filter of 0.1–10 μm in absence of pressure. Nano-filtration is a pressure-driven process in which a filter of 1–10 Angstrom pore size is used for removal of metals from a metal solution (Frarès et al. 2005). In the ultra-filtration pressure-driven purification process, water and low molecular weight substances permeate a membrane (pore size 0.1–3 μm) while particles, colloids, and macromolecules are filtered (Hagen 1998). Because of a larger pore size in membranes of micro- and ultra-filtration techniques as compared with the diameter of metal ions, these techniques cannot be applicable to metal ions removal. Biological methods are ecofriendly and consist of biosorption of metals using agricultural biomass, bacteria, fungi, algae, sewage sludge, yeast, etc. (Kapoor and Viraraghavan 1995; GardeaTorresdey et al. 2004). In these methods, microorganisms possessing an abundance of functional groups passively adsorb metal ions. Such methods are mostly non-selective in nature. Membrane technologies nowadays, which include nanofiltration, reverse osmosis, ultra-filtration, are most widely used techniques for removal of metals. However, selective extraction of metal and its recovery can be easily achieved by using ionimprinted polymer technology (IIP). Ion-imprinted polymer is a technology used to create recognition sites in macromolecular matrix using a template molecule. The processes involved in the development of IIP are shown in Fig. 1. Basically, IIP is the development of the key-and-lock model. Ion-imprinted polymer is synthesised by using template (metal ion), monomer, crosslinker and initiator. After the formation of polymer, metal ion is extracted and cavities are created for specific metal ions. This imprinted polymer is used for selective extraction of metal ions. IIPs are different from molecularly imprinted polymers (MIPs) in case of template. In IIPs, metal ions are templates while in MIPs, molecules are templates. There are two approaches in imprinting technology, a covalent developed by Wulff and Sarhan (1972) and non-covalent or self-assembly approach introduced by Mosbach and co-workers (Arshady and Mosbach 1981). Rao et al. reviewed on metal ion-

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Fig. 1 Process involved in the development of IIP

imprinted polymers for preconcentration and selective recognition of metals (Rao et al. 2004, 2006). The IIPs for the environmental monitoring of inorganic pollutants were presented by Mafu et al. (2013). Recently, Branger et al. reviewed recent advances in IIPs, wherein focus was on synthetic strategies (Branger et al. 2013). Applications of IIP technology include wastewater treatment, biomedical applications, i.e. selective removal of metal from the human body (human serum or plasma) or analysis of metal from the human body, preconcentration, recovery of metals, and as a sensor. IIPs are stable, easy to synthesise, inexpensive and reusable, making them suitable for wide applications over other methods available towards selective removal of metal ions. Several techniques have been used for the development of IIP-like bulk polymerization (Singh and Mishra 2009a), suspension polymerization (Walas et al. 2008), emulsion polymerization (Zhu et al. 2011), dispersion polymerization (Birlik et al. 2007) and precipitation polymerization (Otero-Romaní et al. 2009a). After formation of a polymer, metal ions are leached using acid or chelating agent with the help of different techniques like Soxhlet extraction, physically assisted extraction and supercritical extraction (Cintas and Luche 1999; Ramos et al. 2007; Tobiszewski et al. 2009; Luque de Castro and Priego-Capote 2010). Analytical parameters such as relative selectivity coefficient (k′), adsorption capacity (q) have been used to study the performance of IIP sorbent. Distribution coefficient of the metal ion can be calculated by using Eq. (1) Kd ¼

C i −C f V Cf m

ð1Þ

where Kd represents the distribution coefficient; Ci andCf are initial and final concentrations of metal ions, respectively. V is the volume of the solution and m is the mass of the sorbent. The selectivity coefficient (k) for the binding of a metal ion in

the presence of competitor species can be obtained from Eq. (2). k¼

K dðtemplate metal ionÞ K dðinterferent metal ionÞ

ð2Þ

A relative selectivity coefficient (k′) can be calculated by using Eq. (3) 0

k ¼

k imprinted k non imprinted

ð3Þ

Adsorption capacity (q ) of IIP sorbent can be obtained from the Eq. 4 q¼

ðC i −C f ÞV m

ð4Þ

where q is the maximum adsorption capacity; Ci andCf are initial and final concentrations of metal ions, respectively; V is the volume of the metal solution (L); m is the weight of the sorbent respectively.

Thermodynamics of template-monomer and template-IIP recognition Physical approach of template-monomer recognition is very important in the development of ion-imprinted polymer (Nicholls et al. 2001). Thermodynamic study of templatemonomer recognition shows that extent of template complexation is governed by change in Gibbs free energy (Bittar et al. 1996; Nicholls 1998). Thermodynamic study of ligandreceptor (template) binding was done by Williams and expressed in terms of Eq. (5) (Williams et al. 1991). X ΔGbind ¼ ΔGtþr þ ΔGr þ ΔGh þ ΔGvib þ ΔGP þ ΔGconf þ ΔGvdw

ð5Þ


where ΔG bind , ΔG t + r, ΔG r, ΔG h , ΔG vib , ∑ΔG P, ΔG conf andΔGvdw are the Gibbs free energy changes for complex formation (bind), translational (t) and rotational (r), restriction of rotors upon complexation (r), hydrophobic interactions (h), residual soft vibrational modes (vib), sum of interacting polar group contributions (p), adverse conformational changes (conf), and unfavourable van der Waals interactions (vdw), respectively. ΔGbind expresses non-covalent monomer-template interactions. The ΔGt+r term in Eq. (5) reflects the change in translational and rotational Gibbs free energy associated with combining different entities in a complex. ΔGr reflects rigidity of template and thus, for better template-monomer recognition template should be less rigid. It has been reported that for the development of IIP, non-polar organic solvents are generally used, but sometimes water is also used as a polymerization solvent. In this case, hydrophobic moiety selective functional monomer is generally used and it shows hydrophobic effect which is reflected as ΔGh in Eq. (5). Term ∑ΔGP in Eq. (5) expresses the number and relative strengths of templatemonomer interactions. ΔGvib is directly related to the vibrational modes of adduct solution, which depends upon temperature of polymerization. ΔGconf andΔGvdw represent template conformation and van der Waals interaction for effective solvation during polymerization. In thermodynamic study of binding of template to IIP recognition sites, ΔGconf andΔGvdw should be neglected because the formation of a recognition site in IIP using monomer-template complex is thermodynamically controlled. Thus population of templates shows minimum conformational strain and maximum complementarity in IIP recognition sites. Thus, in case of rebinding of template to IIP, conformational strain and van der Waals interactions should not be taken into consideration. Thus, thermodynamic study of template-IIP recognition is expressed in terms of Eq. (6) X ΔGbind ¼ ΔGtþr þ ΔGr þ ΔGh þ ΔGvib þ ΔGP ð6Þ Some of the important points derived from the thermodynamics equations are the following: (i) The stability of the complex is enhanced with increasing interaction between monomer and template as this increases the ∑ΔGP, which helps in achieving better side fidelity. (ii) Having stoichiometric composition multivalent monomers offer energetic advantage due to less reduction in the degrees of freedom on complex formation (reduction of ΔGt+r). (iii) In aqueous media, hydrophobic effect can be utilized to compensate for the weakening of electrostatic interactions (maximising ΔGh), while rebinding the medium can be chosen to attenuate hydrophobic and electrostatic interaction.

Methodologies used for imprinting Various modifications in the imprinting methodologies have been carried out over the years for progressive development of


IIPs in order to enhance adsorption rate, adsorption capacity, selectivity, thermal stability and mechanical strength, etc. In the process of IIP development, some important methodologies caught the attention of researchers for obvious reasons. Some important landmarks arrived at are magnetic IIP, silicabased IIP, metal complexing agents-based IIP, biocompatible chelating agent-based IIP, ion-imprinted fibre, CNTs-based IIP, interpenetrating polymer network (IPN) gel-based IIP, restricted accessed material (RAM)-IIP, etc. These features have been discussed in detail in further part of this section. The attempts are always made to enhance adsorption capacity, selectivity by varying complexing moiety and design of adsorbent matrix. The disadvantage of solid-state extraction is that the size of powders is never sufficiently small and controlled. To avoid this, the synthesis of small size globules (microgel) can be achieved by using suspension polymerization method with a large excess of porogen. It was reported that the adsorption capacity, affinity constants and homogeneity of binding sites associated with polymers, prepared by this method, are clearly improved compared to another method such as bulk polymerization (Tamayo et al. 2003). It is obviously more suitable for preconcentration purposes. For removal of iron from the plasma of Beta thalassemia patient, Fe(III)-imprinted poly(hydroxyl ethyl methacrylate)–N-methacryloyl-(L)-cysteine (HEMA-MAC) monolith was synthesised (Serpil et al. 2008). The monolith has advantage over beads in that it can be recovered and reused many times without any decrease in adsorption capacity. Using suspension polymerization technique, nano-sized Cd(II)-IIP with neocuproine as complexing agent was made and successfully applied for cadmium removal from waste water, Caspian sea water, river water and tap water (Behbahani et al. 2013b). Magnetic metal IIP is one of the important landmarks in the development of metal IIPs due to its magnetic nature which helps in the selection of metals of interest in addition to other attributes. Several research articles have been reported on magnetic IIP (Ren et al. 2008, Candan et al. 2009, Luo et al. 2011). Surface ion-imprinted magnetic microspheres (Fe3O4@SiO4) was used for Pb(II) determination at trace level in water (Cui et al. 2012). The residual double bond on the methacryloxypropyltrimethoxysilane (MPS) was copolymerized with carboxyl-containing monomer. Subsequent to the development of magnetic core-shell system for making IIPs, new approaches have been designed and applied for metal ion detection. A typical core-shell magnetic ionimprinted polymer for the removal of Pb(II) is shown in Fig. 2 (Zhang et al. 2011a, b). Magnetic Cu(II)-IIP was reported for rapid enrichment of trace amount of Cu(II) (Luo et al. 2012). Further, Cu(II)-imprinted magnetic particles can be isolated by an external magnet. Synthesis method of IIP follows by first preparing Fe3O4 nanoparticles and then reacting the active surface of nanoparticles with γ-


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Fig. 2 A typical core shell magnetic ion-imprinted polymer for the removal of Pb(II)

aminopropyltriethoxysilane (APTES). Slight variation of the method was done by treating magnetic nanoparticles with tetraethoxysilicate (TEOS) which was followed by reacting with APTES (Sadeghi and Aboobakri 2012). The final amino functional magnetic nanoparticles were used for imprinting U(VI). To stabilize the surface active nanoparticles for ion imprinting, co-polymerization strategy was adopted in which methacryloylated APTES was first reacted with magnetic nanoparticles, leaving behind a reactive double bond which was co-polymerized with 4-vinyl pyridine (4-VP) (Tavengwa et al. 2013). The work on magnetic nanoparticles was extended to the area of detection of Hg(II). In this method, vinylfunctionalized Fe3O4 nanoparticles were co-polymerized with ethyleneglycol dimethacrylate (EGDMA) in the presence of Hg(II)-N-(pyridine-2-ylmethyl)prop-2-en-1-amine complex (Najafi et al. 2013). The magnetic IIPs have attracted more attention in recent years due to its superior properties over other IIPs. Therefore, magnetic IIPs are extensively studied during last few years (He et al. 2014; Liu et al. 2014; Guo et al. 2014; Tavengwa et al. 2014). Enlargement of surface area was also thought of for improving IIP performance. Nanoporous silica (MCM-41) was found to be stable with enlarged active surface area. It was modified by incorporating a dipyridyl ligand into EGDMA matrix in the presence of Au(II) for selective extraction at trace level (Ebrahimzadeh and Moazzen 2013). Co(II)-imprinted polymer for detection of Co(II) was synthesised similarly by

using mesoporous silica (SBA-15) with triglycine (Guo et al. 2013). Triglycine was responsible for complexing with Co(II). Surface imprinting on silica gel was attempted by using As(V) as a template, 3-(2-aminoethylamino)propyltrimethoxy silane (AAPTS) as a functional monomer and epichlorohydrin as a crosslinking agent (Fan et al. 2012). There are many more articles that have reported on silica-based IIPs (Zheng et al. 2006, He et al. 2007, Chang et al. 2008, Wang et al. 2009). Nanoporous carbon-based material was also developed in parallel with nanoporous silica for ion imprinting application using carbohydrate-derived Max-Planck Gesellsschaft 1, which was used in grafting IIP for exclusive detection of gold (Moazzen et al. 2013). Vinyl triethoxy silane was used for modification of nanoporous carbon support, which was further reacted with N-allyl-N-(pyridine-2-yl)pyridine-2-amineAu(II) complex in presence of EGDMA and AIBN. A unique sacrificial support for making IIP was developed by using yeast cells for imprinting of Sr(II) (Song et al. 2013). Biocompatible chitosan was used as a functional monomer and γ-(2,3-epoxypropoxy) propyltrimethoxy silane as a cross linking agent. Yeast cells were first reacted with TEOS to make hollow silica sphere on the former, which was further reacted to form Sr(II)-IIP. The monolayer adsorption capacity of Sr(II) was higher than other silicon adsorption system. High selectivity was also reported for above. The drawback seems that although approach and removal of the template was facilitated by this approach, the selectivity remains low around 2.5 to 13.5.


CNTs have undergone numerous studies in chemical, physical and material areas due to their excellent overall properties, which has prompted modification of the electrode substrate with MWCNTs for use in analytical sensing to a low detection limit (Beitollahi and Sheikhshoaie 2011). Cu(II)-IIP was prepared by using 1-(2-pyridylazo)-2-naphthol and methacrylic acid (Ashkenani and Taher 2012a). In chemically modified CPE, Cu(II)-IIP, graphite powder and a small amount of CNTs were used. The best selectivity was obtained with 5 % of CNTs in the matrix. Similarly, Hg(II)-IIP were modified by using MWCNTs for detection of Hg(II) (Fu et al. 2012, Rajabi et al. 2013). Hierarchically organic–inorganic sorbents were developed by using double imprinting approach, in which both metal imprinting as well as micelle imprinting can be done, for selective separation of Hg(II) from aqueous solution (Wu et al. 2007). The double-imprinting technique was also adopted for synthesis of Cd(II)-imprinted 3mercaptopropyltrimethoxysilane (MPTS)-silica coated stir bar (Zhang and Hu 2012). The removal of metal ion from the complex leaves behind cavities, which exhibits ionic recognition. On the other hand, removal of surfactant micelle leads to the formation of large pores which is responsible for excellent metal ion transport kinetics. Recently, fibres have been used as a grafting material for IIPs, which has some advantageous properties such as increased active surface area and less hindered approach. Cu(II)-imprinted fibres being used for selective removal of Cu(II) were developed by grafting acrylic acid onto the surface of polypropylene and subsequently modified with polyethylenimine (Li et al. 2011a, b). Typical synthesis of metal ion-imprinted fibre is shown in Fig. 3. Cellulosic cotton fibres have many advantages such as, easy availability, strong mechanical properties, and biodegradability. Due to these characteristic properties, various attempts have been made to functionalize cellulose. Functionalized cellulose acts as a very good metal complexing agent. Therefore, recently cellulosic cotton fibres were modified with thiourea and used for synthesising highly selective Hg(II) ion-imprinted thiourea modified cellulosic cotton chelating fibres (Monier et al. 2014). Interpenetrating polymer network (IPN) gel has excellent mechanical strength and high sorption capacity therefore; it can be repeatedly used as SPE in column as compared with

Fig. 3 Typical synthesis of metal ion imprinted fiber


ion-imprinted sorbents (Wang and Liu 2012). Cd(II)imprinted IPN gel was prepared for selective extraction of Cd(II) from aqueous solution by using Nhydroxymethylacrylamide (HMAM) and triethylene glycol divinyl ether (DVE-3) as functional monomer and crosslinker, respectively (Wang and Liu 2014). Thermosensitive ionimprinted hydrogel with IPN was synthesised for the selective recognition of Zn(II) from aqueous solution (Wang et al. 2014b). IPN has also been reported in synthesis of Cu(II)IIP recently (Wang et al. 2014a). A schematic for synthesis of IPN-based IIP is shown in Fig. 4. A new technique, viz., restricted accessed material (RAM)Cu(II)-IIP packed micro column SPE combined with ICPOES was attempted for the determination of copper in urine and serum samples (Cui et al. 2013). The advantage offered by this method is that the extraction and concentration are done directly from biological fluid without any further processing such as co-precipitation and digestion. The SPE and preconcentration by Hg(II)-imprinted diazoaminobenzene–vinylpyridine copolymer packed-bed columns was used for the first time towards removal of Hg(II) from aqueous solution (Liu et al. 2005).

Characterization methods of IIPs There are various common characterization tools being used for IIPs such as FTIR, elemental analyser, thermogravimetric analysis (TGA), XRD, SEM, TEM, BET, etc. FTIR is used to study presence of ligand in polymer matrix. Correct incorporation of ligand in polymer matrix can be verified by using elemental analysis. X-ray diffraction and energy dispersive Xray (EDX) have used for the determination of metal ion in IIP (Ahmadi et al. 2010; Arbab-Zavar et al. 2011). In case of the suspension or precipitation, co-polymerization SEM images are very essential because particle shapes can be determined by using SEM observations. Porous structure of polymer can also be observed by using this technique. In order to determine the surface area, pore volume and an average pore diameter of IIP particles, the Brunauer, Emmett and Teller (BET; Brunauer et al. 1938) method can be used (Godlewska-Żyłkiewicz et al. 2012, Pan et al. 2010b).


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Fig. 4 A schematic for synthesis of IPN-based IIP

TEM studies also been reported in case of the surface imprinted hybrid materials (Pan et al. 2010b, Milja et al. 2011). Magnetic characterization is very important in case of the magnetic IIPs (Zhang et al. 2011a, b, Candan et al. 2009). TGA study is used to check the thermal stability of IIPs (Baghel et al. 2007). Few landmark methodologies for characterization include photoacoustic spectroscopy. The photoacoustic spectroscopy originates from the formation of sound waves following light absorption in a material sample. Guo et al. used photoacoustic spectroscopy for the determination of Nd(III) inside the polymer matrix (Guo et al. 2009). Because of interferences, poor reproducibility and poor detection limits, the alternative method for some elements practised is the ‘Hydride generation atomic absorption spectroscopy (HGAAS)’. In the process of selective extraction and determination of selenium ions from aqueous media, the method has been found very useful (Khajeh et al. 2007a, b). Electrothermal atomic absorption spectrometry (ETAAS) was used for determination of thallium in aqueous solution (Zavar et al. 2011). The detection limit for this method was Table 1

0.02 ng mL−1, and the relative standard deviation for five replicates was 2.6 %. Flame atomic absorption spectrometer (FAAS), equipped with a deuterium lamp for background correction was used for absorbance measurement (Santos et al. 2014). The flame (wavelength, 213.9 nm) along with the flow rate used for the nebulizer was 5.0 mL min−1. A fluorescent sensor was designed for Hg2+ based on the Hg2+-induced conformational change of G-quadruplex with protoporphyrin IX (PPIX) as a signal reporter (Bai et al. 2014). The method is highly sensitive and selective and label-free in nature.

Applications Biomedical Currently, removal of metals from human body in medical applications is done by adopting only chelation therapy. In chelation therapy, various chelating agents are used for

List of common chelating agents for IIPs used for removal of excess metals present in human body and their adverse effects

Metal chelating Metals poisoning Toxicity of the metal chelating agent agents used in chelation therapy

Ref.

CaNa2EDTA

Pb

(Flora et al. 1995)

DPA

Pb

DMPS DMSA BAL

Hg As As

1. Causes redistribution of lead to the brain 2. Rapid decrease in plasma zinc concentrations 3. Hypocalcaemia 1. Prolonged treatment leads to anorexia 2. Nausea, vomiting 3. Causes skeletal, cutaneous and pulmonary abnormalities No major adverse effects It has no adverse effects but it is very difficult to remove metals from bones 1. It causes significant increase in brain arsenic 2. Administration of lead requires deep intramuscular injection that is extremely painful and allergic

(Rousseaux and Macnabb 1992)

(Aposhian 1983) (Hoover and Aposhian 1983) (Hoover and Aposhian 1983)

CaNa2EDTA calcium disodium ethylenediaminetetraacetic acid, DPA D-penicillamine, DMPS sodium 2,3 dimercaptopropane sulphonate, DMSA meso 2,3-dimercaptosuccinic acid, BAL British Anti Lewisite

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EDTA ethylenediaminetetraacetic acid, HEMA hydroxyl ethyl methacrylate, MAGA N-methacryloyl-(L)-glutamic acid, MAC N-methacryloyl-(L)-cysteine, TU thiourea

(Andaç et al. 2007) 0.45 0.5 % TU in 59.04 0.05 M HCl Hg(II)-imprinted poly(HEMA-MAC) beads

Hg(II)/ Cd(II), Hg(II)/ Zn(II): 14.7,21.5 Human serum

(Candan et al. 2009)

(Andaç et al. 2004) Human plasma Cd(II)/ Pb(II), Cd(II)/ Zn(II) : 7.8,1683 19.4

3.6 0.1 M TU

5.4 24.7 0.1 M TU Cd(II)-imprinted magnetic poly(HEMA-MAC) beads

Cd(II)-imprinted poly(HEMA-MAC) beads

Cd(II)/Pb(II), Cd(II)/Zn(II): 22.6, 160.7 Human plasma

(Serpil et al. 2008)

(Aslıyüce et al. 2010) Human plasma 0.075 32.7

Fe(III)/Cd(II), Fe(III)/Ni(II): 10.5, 2.3

(Yavuz et al. 2005)

Fe(III)-imprinted poly(HEMA-MAC) supermacroporous cryogel 0.1 M EDTA

Fe(III)/Cd(II), Fe(III)/Ni(II) : 42.6, 36.1 Human plasma

Fe(III)/Zn(II), Fe(III)/Cr(III): 17.3, 48.6 Human plasma

35.2

0.150

76.4 0.1 M EDTA Fe(III)-imprinted poly(HEMA-MAGA) monolith

Fe(III)-imprinted poly(HEMA-MAC) monolith (PHEMAC-Fe3+) 0.1 M EDTA

5.17

Adsorption Relative selectivity coefficient Leaching agent Surface area cap., mg g−1 of polymer beads/cryogel/ monolith, m2 g−1 Metal ion-imprinted polymer

List of IIPs and corresponding analytical parameters and performance in biomedical applications Table 2

treatment of metal poisoning (Flora 2009). Some commonly used chelating agents are shown in Table 1. The IIP technique can also be used for removal of metals from the human body. These polymers have been used in biomedical applications for determination and removal of metals like U(VI), Cu(II), Fe(III), Cd (II), and Hg (II) from human serum, human plasma, urine, etc. Most of the work on IIP technique in biomedical applications is done by Adil Danizlia and co-workers. Iron is essential for the human body, but excess of Fe(III) in human body causes toxic effects (Crichton 2009). Excess of iron in human body is due to genetic effects, accidental ingestion, repeated blood transfusion, inhalation of tobacco smoke or asbestos, certain types of anaemia overmedication of iron supplements and iron pills (Britton et al. 2002). For removal of excess of iron metal from human body using chelation therapy, the only drug used is desferrioxamine B (DFO) (Mahoney et al. 1989). But, the use of DFO has some limitations such as it is less effective when taken orally, shows toxicity with high concentrations and also very expensive (Britton et al. 2002). By taking all the above considerations, IIPs have been developed for selective removal of Fe(III) ions from human plasma (Yavuz et al. 2005; Serpil et al. 2008; Aslıyüce et al. 2010) as presented in Table 2. Most of the time, for preparation of IIPs, bulk polymerization technique is used. However, it has been reported that in bulk polymerization, there is formation of polymer in the block form that should be crushed. This prompted many to use suspension polymerization technique for preparation of IIPs. Fe(III)-imprinted poly(hydroxyl ethyl methacrylate)-N-methacryloyl-(L )glutamic acid (HEMA-MAGA) beads were employed for selective removal of iron from human plasma (Yavuz et al. 2005). Poly HEMA was used for extracorporeal therapy because of its superior properties such as hydrophilic character, good blood compatibility, minimal non-specific protein interactions, high mechanical stability and resistance towards microbial and enzymatic attacks. For the removal of iron from the plasma of Beta thalassemia patient, Fe(III)-imprinted poly(hydroxyl ethyl methacrylate)–N-methacryloyl-(L)-cysteine (HEMA-MAC) monolith was synthesised (Serpil et al. 2008). Fe(III)-imprinted poly(HEMA-MAC) monolith has advantage over beads in that it can be recovered and reused many times without any decrease in adsorption capacity. Polymer beads have large void volume and slow diffusional mass transfer in conventional bed columns as compared to polymer monolith. Instead of ion-imprinted monoliths, ionimprinted supermacroporous cryogel was also attempted for the purpose (Aslıyüce et al. 2010). Cryogel has some advantages such as low pressure drop, lack of diffusion resistance and a cheap material (Lozinsky et al. 2003). Therefore, blood can be directly applied without any treatment, and also itself being a cheap material, it can be disposed after use to avoid cross contamination in batches (Arvidsson et al. 2002; Noppe et al. 2007).


Analysed sample Ref.

7382


Cadmium is carcinogenic to human beings (Godt et al. 2006). The average amount of cadmium found in adult human is around 10 μg L−1. In case it exceeds 50 μg L−1, it is attributed to excessive cadmium exposure (Barnhart 1984). For the treatment of cadmium poisoning, chelation therapy is available in which British anti-Lewisite (BAL) and calcium disodium EDTA are used as chelating agents (Cantilena and Klaassen 1982). Cadmium-imprinted magnetic poly(HEMAMAC) beads were produced by the same procedure as Fe(III)imprinted poly(HEMA-MAGA) beads. However, magnetite was used to induce magnetic properties to imprinted beads (Candan et al. 2009). It was reported that magnetic beads have advantages in chromatographic separations using packed bed and conventional fluidized bed. Magnetic beads in fluidized bed show advantageous properties like low pressure drop, high feed-stream solid tolerances and in fixed bed, magnetic beads shows high mass transfer rates, no particle mixing and good fluid solid contact. The Cd(II)-imprinted poly(HEMAMAC) beads, for removal of Cd(II) from human plasma, was reported with enhanced selectivity coefficient in comparison to other reported Cd(II)-IIPs (Andaç et al. 2004). In this study, relative selectivity coefficient obtained for Cd(II) in presence of Zn(II) was 1683 which is very high as compared with other reported data. Mercury exists in three different oxidation states Hg(0), Hg(I) and Hg(II). In blood, elemental mercury is rapidly oxidised to mercurous form (Hg(I)) and then it is oxidised to mercuric (Hg(II)) form by catalase enzyme (Björnberg et al. 2005). Mercury is removed from the human body by using chelation therapy. Dimercaprol and D-acetyl-D,L-penicillamine have been used as metal chelating agents. For the selective removal of mercury from human serum using IIP, Hg(II)imprinted poly(HEMA-MAC) beads have been synthesised (Andaç et al. 2007). Hg(II) has very high affinity towards sulphahydryl group therefore, 0.5 % thiourea in 0.05 M HCl was used for removal of template from poly(HEMA-MAC) beads. Depleted uranium is released into the environment from the uranium enrichment processes of industries and military activities. Depleted uranium is toxic to human beings through its chemical and radiation action (Zamora et al. 1998; McDiarmid et al. 2000). For the detoxification and selective recognition of depleted uranium in human kidney cell, chitooligosaccharides-based uranium IIP was developed (Zhang et al. 2011a, b). It is observed that a new technique, viz., restricted accessed material (RAM)-Cu(II)-IIP was used for the determination of copper in urine and serum samples (Cui et al. 2013). In biomedical applications, mostly U(VI), Cu(II), Fe(III), Cd(II), and Hg(II) are removed by using IIP. These metals are normally observed in human serum, plasma and urine. Most of the studies were concentrated on removal of Fe(III) ion. Poly-HEMA-amino acid methacrylate combinations were used as monomers for the imprinting of above metals.

7383

Magnetic beads were also designed for removal of Fe(III). Selectivity coefficients were found to vary with different metal impurity combinations. Adsorption capacity for Cd(II) was found to be highest (5.4 mg g−1) among imprinted metal studies. The number of articles appeared in journals are scanty in nature. It needs concerted efforts to ensure minimum adverse effects on human body with maximum efficiency in selectivity, sensing and removal. The polymer used should be biocompatible and the process needs to be rapid in nature so that the process will be suitable for practical application. Removal of toxic metals from contaminated water and aqueous solutions These days, there is great concern over water contamination with toxic metals. Mostly in rural areas, people suffer from this contamination. There are various methods available for the adsorption of heavy metal ions from contaminated water. However, selective adsorption and preconcentration are very challenging tasks. IIPs have been used for selective removal of metals from aqueous solution. Mercury is one of the most studied toxic metals because of its topological and biochemical behaviour. There are various sources of mercury by which it is released into the ecosystem (Wang et al. 2004). Binding behaviour of metal ion depends upon complexing agent used for developing IIP. Therefore, different types of complexing agents being used for developing Hg(II)-IIP like diazoaminobenzene (DAAB) (Liu et al. 2005), 4-(2thiazolylazo) resorcinol (TAR) (Singh and Mishra 2010b), 3isocyanatopropyltriethoxysilane (IPTS) bearing thymine (T) (Xu et al. 2012), N-methacryloyl-2-mercaptoethylamine (Firouzzare and Wang 2012), 1-(2-thiazolylazo)-2-naphthol (Dakova et al. 2009), 3-mercaptopropyltrimethoxysilane (Wang et al. 2009), 1-pyrrolidinedithiocarboxylic acid (Yordanova et al. 2014), etc. Various Hg-IIP are listed in Table 3 with different parameters. The SPE and preconcentration by Hg(II)-imprinted diazoaminobenzene–vinylpyridine copolymer packed-bed columns was used for the first time towards removal of Hg(II) from aqueous solution (Liu et al. 2005). Adsorption study of Hg(II)-IIP showed higher adsorption capacity of 41 mg g−1, as compared to non-imprinted polymer having adsorption capacity of 11.72 mg g−1. It was reported that Hg(II)-imprinted polymer showed recoveries more than 95 % after use for 20 times in solid-phase extraction. Hierarchically organic–inorganic sorbents were developed by using double imprinting approach for selective separation of Hg(II) from aqueous solution (Wu et al. 2007). It has been reported that hierarchically hybrid materials have the ability to exhibit large number of functions in a small volume enabling optimization of complimentary properties between inorganic and organic components (Sanchez et al. 2005). Both Hg(II) and surfactant can make assembly resulting in honeycomb like structure. Adsorption of

VGA-AAS, GTA-AAS AFS

5.0 6.0

FAAS AAS HRCS-AAS FAAS ICP-OES FAAS

AAPTS

MAC

Crown ether

1-Vinylimidazole

APS

Chitosan

AAS

ETAAS

MAH

Pyrrolidinedithiocarbamate

Cr(III)

HG-AAS FAAS

Chitosan

AAPTS

As(III)

ICP-MS

ICP-MS FAAS

MPTS Neocuproine

1-Vinylimidazole, 4-VP or styrene

FAAS AAS

MPTS

6.0

FAAS

1-Vinylimidazole

6.0 6.0

UV-Vis S ICP-AES

SPANDS (2Z)-N,N′-bis(2-aminoethylic)but2-enediamide Diazoamino benzene

38.01

4.0

6.0

0.018

1.200

0.0013

69.28

16.1 6.18

– –

6.0

0.37

1.87

–

Cr(III)/Ni(II): 8.88

As(III)/ Fe(III): 502.33

As(V)/P(V): 5.67

–

– –

– 64

Cd(II)/Pb(II): 157.5 Cd(II)/Zn(II): 66.937

4.56

Cd(II)/Hg(II): 85.4

(Buhani et al. 2010)

(Segatelli et al. 2010)

(Liu et al. 2004)

(Singh and Mishra 2009b) (Zhai et al. 2007a, b)

(Gawin et al. 2010)

(Li et al. 2011b)

(Liu et al. 2011)

(Zhang et al. 2011a)

(Ricardo et al. 2012)

(Luo et al. 2013)

(Esen et al. 2009)


(Khajeh et al. 2011)

(Zhu et al. 2011)

(Chunxiang et al. 2009)

(Wang et al. 2009)

(Firouzzare and Wang 2012) (Dakova et al. 2009)

(Xu et al. 2012)

(Singh and Mishra 2010b)

(Liu et al. 2005)

Ref.

1.0 M HNO3 and 100 mM succinic acid

0.5 M HCl

6 M HCl

2 M HNO3

(Bayramoglu and Arica 2011)

(Birlik et al. 2007)

(Liu et al. 2011)

(Fan et al. 2012)

(Tsoi et al. 2012)

0.1 M HNO3 (Zhang and Hu 2012) HNO3 : HCl (1:1 M) (Behbahani et al. 2013b)

0.5 M HCl

0.4 M HNO3

0.1 M HNO3

1 M HNO3 0.5 M HCl

1 M HCl

Cd(II)/Zn(II): 7.4 Cd(II)/Hg(II): 62.1

–

2 M HCl 6 M HCl

Cd(II)/Zn(II): 11.6

Pb(II)/Co(II): 345.44

0.1 M HNO3

–

2 M HNO3 2 M HNO3

83.89

–

0.2 M HNO3 1 M HCl

Pb(II)/Cd(II): 64.9

Pb(II)/ Zn(II): 617.79

Pb(II)/Cu(II): 192.

Pb(II)/Cu(II): 7.41

2 M HCl 2 M HCl

Pb(II)/Co(II): 114.7.

3.0 M HNO3

1 M HNO3

TU 4 M HNO3

0.1 M HCl

0.5 M HCl–1 M TU

–

0.11 0.0044 0.2

5.0

Hg(II)/Cd(II): 100 Pb(II)/Co(II): 574

–

10.37

0.270 32.56

– 0.14 0.093

0.48

0.11

44.7

–

27.95 7.6

– – 19.66

2.01

–

0.20

19.61

–

5.5 7.0

6.0

6.7

6.8

ICP-MS

Salen

6.0

FAAS

TCPTS

6.0

4.0

6.4

7.5

39.0

0.092

116.9

Morin

6.1

ICP-AES GF AAS

DDDPA

4.0–9.0 –

92 22.7

0.35

Hg(II)/Zn(II): 46.6

– Hg(II)/Zn(II): 20.6 Hg(II)/ CH3Hg(I): 1633

Hg(II)/Co(II) : 70.6

28 6.4

Leaching agent

Hg(II)/CH3CH2HgCl: 84.0 0.1 M HCl+TU

25

41

Adsorption Relative selectivity cap., mg g−1 coefficienta

47

5.0

6.0

ICP-AES

AAS

3-Mercaptopropyltrimethoxysilane

Chitosan

0.50 0.006

0.0 3

7.5 7.0

8.0

N-Methacryloyl-2-mercaptoethylamine ICP-MS 1-(2-Thiazolylazo)-2-naphthol CVAAS

2.875

0.05

Limit of detection, μg L−1

7.0

8.0

pH

7384

As(V)

Cd(II)

Pb(II)

CVAAS

DAAB

TAR

Hg(II)

IPTS bearing thymine (T)

Detection technique

List of metal/complexing monomer in IIPs, corresponding analytical parameters and performance in selective removal of toxic metal ions from aqueous solution and contaminated water

Metal ion Ligand/complexing monomer

Table 3


ICP-OES FAAS ICP-AES

AAPTS

AAPTS

DBDA15C4

(1-(2-Pyridylazo)-2-naphthol)

PAR

Sn(IV)

8.0

9.7

33 1.3 2.37

24.78 24.2

– –

1.3

0.6

2 M HCl 4 M HCl

– –

– 78.3

4.0 M HNO3 6 M HCl

Fe(III)/Zn(II): 72.6

4 M HCl –

Fe(III)/Cr(III): 68.9

0.1 mM EDTA

6 M HCl

– –

0.1 M EDTA

HCl (50 %; v/v)

0.1 M HNO3

0.1 M EDTA

0.1 M HNO3

0.1 M HNO3

2 M HCl

2 M HCl

0.4 M HNO3 1 M HNO3

0.1 M HNO3

1.0 M HCl

0.05 M EDTA HNO3 Solution, 1 % (v/v) 1.6 M HCl 3 M HNO3

0.1 M HCl 1 M HNO3

0.2 g/L EDTA

1 M HCl

(Abedi and Ebrahimzadeh 2013)

(Khajeh and Sanchooli 2011)

(Chang et al. 2007)

(Karabörk et al. 2008)

(Xie et al. 2012)

(Zhai et al. 2008)

(Shakerian et al. 2012)

(Zhao et al. 2007)

(Shamsipur et al. 2014)


(Ren et al. 2008)



(Luo et al. 2011)

(Kang et al. 2013)

(Dam and Kim 2009) (Hoai et al. 2010)

(Birlik et al. 2007)

(Bi et al. 2007)

(Ebrahimzadeh and Moazzen 2013) (Jiang and Kim 2011)

(Singh and Mishra 2009a) (Tobiasz et al. 2009)

(Saraji and Yousefi 2009) (Dakova et al. 2007)

(Li et al. 2007)

(Vatanpour et al. 2011)

(Saraji and Yousefi 2009) (Otero-Romaní et al. 2009b)

6.0, 2.0 M HNO3, 3.0 M HCl 0.1 M HCl 2.0 M HNO3

Zn (II)/Cu(II): 53.1

Zn (II)/Pb(II): 42.6

Cu (II)/Co(II): 19.4

Cu (II)/Zn(II): 2.91

Cu (II)/Co (II): 23.3

Cu (II)/Zn (II): 16.1

Cu (II)/Ni (II): 133.92

–

Cu(II)/Cd(II): 25.2 Cu(II)/Ni(II): 43.48

Cu(II)/Ni(II): 122.7

–

– Cu(II)/Cd(II): 25.24

Cu(II)/Co(II) : 3.37 –

Ni(II)/Cu(II): 54.3 –

–

Ni(II)/Cu(II): 111.1

Ni(II)/Cu(II): 54.3 –

Ref.

Leaching agent

25.21

78.5 0.34

–

– 36.90

– 0.26

2.73

3.9

130

4.69

0.48

0.65

0.33

0.1

21.98 71.36

0.3 –

4.78

– 14.93

0.5

47.63

– –

–

– 0.83

76.4 22.24

0.1 –

3.0 l 0.310 1.03–1.07 9.55

1.6 0.63

88.62

1.3 1.98

Adsorption Relative selectivity cap., mg g−1 coefficienta


GFAAS

ICP-OES

3.0 3.0

ICP-AES ICP-AES

MAAP

4.0

3-Aminopropyltrimethoxysilane

2,20-Bipyridyl

6.0 4.0

ICP-AES

8-Hydroxyquinoline

5.0.

7.0

7.0

5.5.

7.0

7.0

5.0

4.5

5.6 6.5

7.0

4.5

6.0 6.2

6.0 6.8

8 7.0

FAAS

GFAAS

8-AOQ

AAPTS

FAAS FAAS

1-Hydroxy-4-(prop-2′-enyloxy)-9, 10-anthraquinone (AQ) 3,5,7,20,40-Pentahydroxyflavon

ICP-AES

AAS AAS

ICP-AES

AAS

Chitosan-succinate

MAA 4-VP, MAA

UV-Vis S

UV-Vis S

Glycine, diglycine, and triglycine

Chitosan

FAAS AAS

2,9-dimethyl-1,10-phenanthroline 4-VP, MAA

1,4-dihydroxy-9,10-anthraquinone

GTA-AAS FAAS

PAR Salen

Mn(II)

Fe(III)

Zn(II)

Cu(II)

–

–

UV-Vis S FAAS ETAAS

Chitosan

Dithizone PAR

6

6.5

GTA-AAS

1.6 0.26

Vinylbenzoate

8 9.0

FAAS ICP-OES

Dithizone 5-Vinyl-8-hydroxyquinoline


Ni(II)

pH

Detection technique

Metal ion Ligand/complexing monomer

Table 3 (continued)



Relative selectivity coefficient represents the highest relative selectivity coefficient reported for metal ion a

(Guo et al. 2013)

DAAB diazoaminobenzene, TAR 4-(2-thiazolylazo) resorcinol, IPTS 3-isocyanatopropyltriethoxysilane, CVAAS cold vapour atomic absorption spectrometry, VGA-AAS vapour generation accessory-atomic absorption spectrometer, GTA-AAS graphite tube atomizer-atomic absorption spectrometer, AFS atomic fluorescence spectrometry, AAS atomic absorption spectrometry, ICPMS inductively coupled plasma mass spectrometry, DDDPA 1,12-dodecanediol-O,O′-diphenyl-phosphonic acid, AAPTS 3-(2-aminoethylamino)propyltrimethoxy silane, APS 3-aminopropyltrimethoxysilane, ICP-AES inductively coupled plasma atomic emission spectrometry, GF-AAS graphite furnace atomic absorption spectrometry, FAAS flame atomic absorption spectrometer, HRCS-AAS high resolution continuum source atomic absorption spectrometer, TCPTS 3-thiocyanatopropyltriethoxysilane, SPANDS 2-(p-sulphophenylazo)-1,8-dihydroxynaphthalene-3,6-disulphonate, MPTS 3-mercaptopropyltrimethoxysilane, HGAAS hydride generation atomic absorption spectrometer coupled, MAH methacryloylamidohistidine, ETAAS electrothermal atomic absorption spectrometer, UV-Vis S ultraviolet visible spectrophotometer, PAR 4-(2-pyridylazo)resorcinol, DBDA15C4 5,6;14,15-dibenzo-1,4-dioxa-8,12-diazacyclopentadecane-5,14-diene, MAAP methacryloylamidoantipyrine, 8-AOQ 8-acryloyloxyquinoline, 4-VP 4-vinyl pyridine, MAA methacrylic acid

1.0 M HNO3

1 M HCl Co(II)/Ni(II) : 27.43 –

Cs(I)/Ni(II): 301 32.9

181.67

0.180 6.0

FAAS, ICP-OES 5.0

ICP-AES Chitosan

Triglycine

Cs(I)

Co(II)

Leaching agent Adsorption Relative selectivity cap., mg g−1 coefficienta Limit of detection, μg L−1 pH Detection technique Metal ion Ligand/complexing monomer

Table 3 (continued)

(Zhang et al. 2010b)


Ref.

7386

Hg(II) onto IIP depends on pH. It has been observed that adsorption of Hg(II) increases with the increase in pH. At low pH, H+ ions concentration is high therefore, H+ ions are adsorbed preferentially by imprinted polymer rather than adsorbing Hg(II). At higher pH value, H+ ions concentration decreases. Hence, adsorption of Hg(II) has been found to be maximum. As the pH is increased up to 10, OH− concentration increased and IIP adsorbed OH− ion rather than template ion. For the development of Hg(II)-imprinted polymer, sulphur-containing monomers are generally used as it has very high affinity towards Hg(II) ions. Considering Hg(II)–thymine (T) interaction, a new functional monomer, 3isocyanatopropyltriethoxysilane (IPTS) bearing thymine unit (T-IPTS) was synthesised and used for imprinting of Hg(II) (Xu et al. 2012). It was prepared by using the sol–gel process. Sol–gel process was used as it has various advantages such as ease of fabrication; ecofriendly reaction using solvents like ethanol or ultrapure water and mild polymerization reaction conditions having less probability of thermal decomposition and chemical decomposition. Comparative study of Hg-IIPVP (vinyl pyridine) and Hg-IIP-T showed that IIP-T has regular sphere morphology with a diameter of 300 nm while IIP-VP has irregular morphology. This indicates that IIP-T has advantages over IIP-4-VP such as increase in surface area, high binding capacity of templates and fast mass transfer. It was reported that adsorption capacity of IIP-T was two times higher than IIP-VP. Aminothiol class of molecules have been found to have dual functionality; thiol has the ability to complex with Hg(II), while on the other hand amine can be reacted to form a monomer. Recent synthesis of aminothiol monomer using 2-mercaptoethylamine was based on the above consideration for development of Hg(II)-IIP (Firouzzare and Wang 2012). Its thermogravimetric analysis study showed that polymerization process increased thermal stability of IIP up to 125°C. Hg(II)-IIP have some drawbacks such as long equilibration and elution time as compared to the ordinary resins. Thus, there is a limitation for its practical use and should be a subject of further investigations. Lead is one of the most toxic metals and shows adverse effects on human being (Body et al. 1991). So far, many Pb(II)-IIPs have been reported for selective removal of lead from contaminated water. A novel core-shell magnetic ionimprinted polymer was used for selective removal of lead (Zhang et al. 2011a). These magnetic sorbents possess large surface area and short diffusion route that increases extraction frequency. But the relative selectivity factor reported for this core-shell magnetic ion-imprinted polymer was comparatively low. Pb-IIP synthesised by using 1,12-dodecanediol-O,O′diphenyl-phosphonic acid (DDDPA) (complexing agent), 4VP (monomer) and trimethylolpropane trimethacrylate (crosslinker) showed very good adsorption capacity (116.9 mg g−1) and high relative selectivity coefficients as compared to other reported Pb(II)-IIP as shown in Table 3


(Zhu et al. 2011). Silica gel is one of the ideal supporting materials because of its high thermal stability, high mass exchange property and is a non-swelling inorganic material in nature. Thus, for the adsorption of lead from plant and water solutions, lead-imprinted amino-functionalized silica gel sorbent have been used (Zhu et al. 2009). Silica-based mesoporous material is well known as good solid support as it has stable mesoporous structure, good chemical and mechanical stability, and well-modified surface characteristics with large number of Si–OH active bonds on the pore walls (Kumar and Guliants 2010). Thus, mesoporous silica SBA-15 was used for synthesising Pb(II)-IIP (Liu et al. 2011). Apart from monomer as complexing agent there are various complexing agents like Morin (3,5,7,2′,4′-pentahydroxyflavone) (Khajeh et al. 2011), DDDPA (Zhu et al. 2011), AAPTS (Zhang et al. 2011a), Chitosan (Chunxiang et al. 2009) and crown ether (Luo et al. 2013), have been used for developing Pb(II)-IIP. These Pb(II)-IIPs have been successfully applied for selective removal of lead from sea water, environmental samples, lake water, saline water, etc. Annually, 15,000 t of cadmium is produced worldwide for nickel cadmium batteries, pigments, chemical stabilizers metal coatings and alloy (Hayes 1997). It accumulates in body and because of its low excretion rate selective removal and preconcentration of cadmium is very much important. WHO guideline for cadmium in drinking water is 3 μg L−1. Cd(II)IIP showed detection limit lower than these guideline values. According to literature Cd(II) is a well-studied metal ion by using IIP technology for its selective removal. Dual ligand monomer (2Z)-N,N′-bis(2-aminoethylic)but-2-enediamide, containing amide and amine functions respectively, was used for synthesising IIP for removal of cadmium from aqueous solution by using SPE with a view to enhance the imprinting efficiency (Zhai et al. 2007a, b). In order to increase adsorption capacity and selectivity, Nannochloropsis sp. biomass as metal ion chelating agent was used while using silica gel as supporting matrix (Buhani et al. 2010). Algae biomass from several algae species is reported to bind metal ions from aqueous medium as algae biomass is associated with several functional groups which can function as ligands to metal ions (Patel and Suresh 2008). 1-Vinylimidazole-based IIP was reported for Cd(II) binding (Segatelli et al. 2010). In this study, online preconcentration method was adopted by using optimization with the help of Doehlert design in duplicates. The response surface method (RSM) was employed to optimize the levels of the variables. Very good relative selectivity coefficient in the presence of lead (Cd(II)/ Pb(II)=157.5) was observed. Complexing agents like 3thiocyanatopropyltriethoxysilane (TCPTS) (Li et al. 2011a, b), Salen (Gawin et al. 2010), 2-(psulphophenylazo)-1,8-dihydroxynaphthalene-3,6disulphonate (SPANDS) (Singh and Mishra 2009b), (2Z)N,N′-bis(2-aminoethylic)but-2-enediamide (Zhai et al.

7387

2007a, b), Diazoamino benzene (Liu et al. 2004), MPTS (Zhang and Hu 2012), neocuproine (Behbahani et al. 2013b), etc. have been used for developing Cd(II)-IIP as shown in Table 3. Literature survey revealed that Cd(II)-IIP shows very good adsorption capacity in the pH range 6–7. Arsenic is very difficult to remove from wastewater because of its complex water chemistry. Generally, arsenic exists in two forms: pentavalent and trivalent. Pentavalent arsenate (H2AsO4− or HAsO42−) is easy to remove from wastewater because of its oxyanion as compared to trivalent arsenate (H3AsO3). WHO guideline value for arsenic is 10 μg L−1 in drinking water. IIP showed detection lower than WHO guidelines. Three types of adsorbents, viz., aluminium nanoparticles (Alu-NPs size, 98 %) uranyl binding between pH 1.0 and 3.0 during uranyl binding. Recently, the U(VI) magnetic ion-imprinted composite (MIIC) with a uniform core–shell was prepared by copolymerization of a ternary complex of uranyl ions with 4VP and acrylamide in presence of AIBN (Liu et al. 2014). The adsorption capacity of U(VI) magnetic IIP was 354.85 mg g−1, which was very much higher as compared with other reported IIP sorbents for the preconcentration of U(VI). Milja et al. synthesised aniline and 8-hydroxy quinoline functionalized


aniline-based ion-imprinted polymer for the selective removal and preconcentration of uranium (Milja et al. 2014). ICP-AES and UV–Vis spectrophotometry arsenazo (III) are the most commonly used detection techniques for uranium as listed in Table 4. Selective separation and preconcentration of Th(IV) is very difficult because of its complex matrix. For the preconcentration of Th(IV) using IIP, various complexing agents have been used like PMT-CAACP (Lin et al. 2010), N, N0-bis(3-allyl salicylidene)-o-phenylenediamine (He et al. 2013), CPMA (He et al. 2007), acryloyl-b-cyclodextrin (Ji et al. 2013), etc. as shown in Table 4. Separation of lanthanides is a challenging task because of its similar chemical properties, but lanthanide shows different physical properties like atomic and ionic radii. There are some traditional techniques for selective separation like ion exchange and liquidliquid extraction, respectively. Lanthanides can be separated by using IIPs. The IIP technology was found to be promising for preconcentration of erbium from the mixture of lanthanides (Kala et al. 2005); (Kala et al. 2004). Effect of γirradiation on selectivity of IIP for the preconcentration of Dy(III) have been studied (Biju et al. 2003). These γirradiated IIP showed 35–180-fold enhancement in selectivity coefficient as compared to NIP. Thorium is widely used in nuclear energy plants for the production of the electricity. IIP technology has also been reported for the selective preconcentration of other lanthanides like Ce(III) (Zhang et al. 2010a; Meng et al. 2014), Nd(III) (Jiajia et al. 2009), Lu(III) (Lai et al. 2012), Sm(III) (Shirvani-Arani et al. 2008), etc. Detailed parameters of these metal IIPs are shown in Table 4. Ag(I) preconcentration from aqueous media have been done by using ion-imprinted chitosan hydrogels (Song et al. 2012) and metal ion-imprinted polymers (Ahamed et al. 2013). Due to the high cost of the gold, its selective removal and preconcentration from mine stone attracted more attention recently. Preconcentration of gold was done by using imprinting technology. The speciality of the method was the grafting of IIPs on the surface of the nanoporous silica (MCM-41) and using it as a sorbent for gold extraction (Ebrahimzadeh and Moazzen 2013). Carbon-based material grafted with IIP is also used for selective extraction of gold (Moazzen et al. 2013). Preconcentration of Pd(II) is very important because it is a precious metal extensively used in metallurgy, chemical synthesis (catalysis), jewellery, etc. Various chelating agents, such as, ammonium pyrrolidinedithiocarbamate (APDC), dimethylglyoxime (DMG) and N,N′-diethylthiourea (DET) along with vinyl pyridine form complex with palladium and the study aimed at screening the best among the high performance solid phase extraction matrices in respect of Pd(II) preconcentration (Godlewska-Żyłkiewicz et al. 2010). Amine functionalized silica was synthesised in presence of Pd(II) by using sol–gel technique (Zheng et al. 2006). This method was used for analysis of trace Pd(II) in geological


sample. The effect of different polymerization methods on the performance of the Pd(II)-IIP was studied (Daniel et al. 2005a). The trend found was higher for bulk and precipitation polymerization as compared to emulsion polymerization in terms of selectivity, retention capacity and percent enrichment. Daniel et al. prepared ion-imprinted polymer material based on complexing agents dimethylglyoxime (Daniel et al. 2003) and quinoline derivatives (Daniel et al. 2005b) for the separation and preconcentration of Pd(II). Platinum metal has huge demand in electrical industries and jewellery. Its extraction from aqueous solution was achieved using acetaldehyde thiosemicarbazone based IIPs (Leśniewska and Kosińska 2011). IIPs are also reported for the preconcentration of the metal ions like Ru(III) (Zambrzycka et al. 2011; GodlewskaŻyłkiewicz et al. 2012), Sr(II) (Pan et al. 2010b; Song et al. 2013), Tl(III) (Arbab-Zavar et al. 2011; Darroudi et al. 2012), Zr(IV) (Chang et al. 2008), Se(IV) (Khajeh et al. 2007a, b), Y(III) (Sarabadani et al. 2014), etc. Tl(III) is widely used in industrial and medicinal applications. Because of the acute toxicity of Tl(III), its continuous separation and preconcentration is very important. An IIP mini-column was reported for online preconcentration of Tl(III) (Darroudi et al. 2012). The method designed integration of preconcentration with FAAS for detection of thallium from aqueous solution. In a medium with coexisting ions, the recovery of thallium was found to be more than 95 %. Preconcentration of metal ions is required for analysis and recovery of precious metals present in low concentrations. For uranium preconcentration nano-sized IIP, magneto nano-IIP, etc. were used. Gamma-irradiated IIP for lanthanides showed 35–184-fold enhancement in selectivity coefficient. Online preconcentration of metal ion using IIP in mini column showed very good results and hence, can be further studied for other metal ions on a large scale at the industry level. Sensing of metal ions IIPs play an important role in sensing of metal ions and show very low detection limit and high selectivity as compared to the conventional chemical sensors. For sensing of metal ions, there are various spectrometric methods available like atomic fluorescence spectrometry, AAS, UV–Visible spectrophotometry and ICP-MS but these techniques are costly, time consuming, and are not suitable for in situ testing and monitoring. On the other hand, electrochemical methods are most favourable because of its low cost, high sensitivity, and ease of operation. In sensing application, IIPs are used as a recognition element for electrochemical sensors such as potentiometric and voltammetric sensors (Kirowa-Eisner et al. 1999; Alizadeh and Amjadi 2011). In order to increase selectivity and sensitivity of metal ions, chemically modified electrodes have been used. Modifying agents used are organic chelating groups (Tonle et al. 2005; Marcolino Junior et al. 2007), clays

AcTSn TSd

ETAAS AAS

ICP-AES

Pd(II)

ICP-OES

APS

8-HQ

Ni(II)

FAAS

FAAS

N-allyl-N-(pyridin2-yl)pyridin-2-amine

Au(III)

ICP-OES

ICP-AES

UV–Vis S

4-VP

Ag(I)

4-VP

DCQ

Sm(III)

UV–Vis S

DMG

Acetylacetone

Lu(III)

ICP-AES

ICP-AES

DCQ

Chitosan

Nd(III)

ICP-AES

UV–Vis S Arsenazo I

DCQ

DBS

DCQ

Chitosan

DBS

DCQ

0.5 7.5

5.0

4.0

4.0

8.5

4.0

6.4

7.0

5.5

7.3

4.0

6.0

8.0

7.3

7.5

3.0

ICP-AES

3.5 4.5

UV–Vis S Arsenazo III

Ce(III)

Pt(IV) Ru(III)

6.5 4.0 6.0 3.0

UV–Vis S

UV–Vis S UV–Vis S UV–Vis S (S)-Arsenazo III ICP-AES

Quinoline-8-ol

APS Piroxicam MAA

7.0

PMT-CAACP

UV–Vis S (S)-Arsenazo III

SA

7.0

6.0

N,N0-bis(3-allyl salicylidene)o-phenylenediamine CPMA


DCQ

Dy(III)

Er(III)

Th(IV)


DCQ

6.0 8.0

5.0

ICP-AES UV–Vis S (S)-Arsenazo III UV–Vis S

7.0

pH

ICP-AES

DCQ formamidoxime

U(VI)

Detection technique

N,N′-ethylenebis(pyridoxylideneiminato) HAQ

Ligand /complexing monomer

12.40

–

23.11

0.16

0.36

2.5

1.5

0.050

746.3

50 % (v/v) HCl

–

U(VI)/ Cu(II): 300

2 M HCl. 50 % (v/v) HCl 50 % (v/v) HCl

– –

6 M HCl

Leaching agent

U(VI)/La(III): 102.4

–

Relative selectivity coefficienta

35.9

42.54

37.4

6.14 38.58 12.59

– 7.32 0.8 0.8

27.44

32.60

34.05

5

5

5

34.0 19.04

–

–

2 –

Adsorption cap., mg g−1


List of metal/complexing monomer in IIPs, corresponding analytical parameters and performance in selective preconcentration of metal ions

Metal ion

Table 4

(Leśniewska and Kosińska 2011) (Zambrzycka et al. 2011)

(Zheng et al. 2006)

(Daniel et al. 2003)

(Daniel et al. 2006)

(Ebrahimzadeh and Moazzen 2013) (Otero-Romaní et al. 2008)

(Ahamed et al. 2013)

(Shirvani-Arani et al. 2008)

(Lai et al. 2012)

(Jiajia et al. 2009)

(Pan et al. 2010a)


(Biju et al. 2003)

(Kala et al. 2004)

(Kala et al. 2005)

(He et al. 2007)

(He et al. 2013)

(Lin et al. 2010)

(Sadeghi and Aboobakri 2012) (Sadeghi and Mofrad 2007) (Shamsipur et al. 2007)

(Milja et al. 2011)

(Metilda et al. 2007a)

(Metilda et al. 2007a)

(Metilda et al. 2004)

(Gladis JM et al. 2004) (James et al. 2009)

(Fasihi et al. 2011)

(Ahmadi et al. 2010)

Ref.


Environ Sci Pollut Res (2015) 22:7375–7404 7391


Relative selectivity coefficient represents the highest relative selectivity coefficient reported for metal ion a

11 1.5

0.14 2.5

6.5 FAAS

ICP-AES

DCQ

APS Zr(IV)

HAQ 1-hydroxy-2-(prop-20-enyl)-9,10-anthraquinone, DCQ 5,7-dichloroquinoline-8-ol, SA succinic acid, PMT-CAACP 1-phenyl-3-methylthio-4-cyano-5-acrylicacidcarbamoyl-pyrazole, CPMA N-(ocarboxyphenyl)maleamic acid, DMG dimethylglyoxime, AcTSn acetaldehyde thiosemicarbazone, TSd thiosemicarbazide, 8-HQ 8-hydroquinone, DBS double-beam spectrophotometer

(Chang et al. 2008)

(Darroudi et al. 2012)

Zr(IV)/Nb(V): 50

6 M HCl

0.1 M HNO3

(Arbab-Zavar et al. 2011)

(Song et al. 2013) 0.1 M EDTA

5 M HNO3

Sr(II)/ Zn(II): 13.85 9.6

60.61

0.02 6.8

6.0 FAAS

ETAAS

Chitosan

DCQ Tl(III)

(Zambrzycka et al. 2011)

(Pan et al. 2010b) 0.01 M NH3 ·H2O ICP-AES Sr(II)

Chitosan

–

0.32 Allyl acetoacetate

7.5 AAS

AAS

AcTSn

6.5

0.25

58.5

Sr(II)/ Cs(I): 12.9

0.3 M TU in 0.5 M 1HCl

0.5 M HCl, 0.9 M TU Ru(III)/Co(II): 1.91

Ru(III)/Co(II): 9.4

Leaching agent Detection technique Ligand /complexing monomer Metal ion

Table 4 (continued)

pH


Adsorption cap., mg g−1

Relative selectivity coefficienta

(Godlewska-Żyłkiewicz et al. 2012)


Ref.

7392

(Grabec Švegl et al. 1998; Dias Filho and do Carmo 2006), silica and sol–gel (Walcarius et al. 2003; Cabello-Carramolino and Petit-Dominguez 2008), polymers (Sadeghi et al. 2012), SiO2–Al2O3 mixed oxide (Ghiaci et al. 2007), etc. Organic chelating agent provides moderate selectivity but shows instability. Zeolite and sol–gels provide good stability and adsorption capacity but shows very low selectivity. Perfluorinated polymer shows very low detection limit, which is based on ion exchange principle (Ugo et al. 1995). Therefore, it does not show selectivity. On the other hand, IIP as a modifying agent possesses all the advantages as above mentioned. IIP in sensor application have been reported for metal ions like mercury, lead, copper, dysprosium, cadmium, uranium, etc. The process involved in IIP-based chemical sensor is simple in which synthesised IIP is used to fabricate an electrode for an electrochemical cell as shown in Fig. 5. Mercurybased electrochemical sensors have been designed by using IIPs as modifying agents. For the development of these IIPs, stable complexing agents have been used. Stable ground-state complexing agent, 1-amino-8-naphthol-3,6-disodium sulphonate (ANDS) was reported for developing molecularly imprinted TiO2 thin film (Liu et al. 2006). This Hg(II)imprinted TiO2 thin film was used for fabricating graphite electrode. This electrode was used as electrochemical sensor for mercury. It was reported that this inorganic imprinted film can be repeatedly used over 200 times because of its stability. Another complexing agent, 5,10,15,20-tetrakis(3hydroxyphenyl) porphyrin has been used for developing Hg(II)-imprinted polymeric nanobeads (Rajabi et al. 2013). These Hg(II)-IIP nanobeads along with multiwalled carbon nanotubes (MWCNTs) were used to modify glassy carbon electrode. Modification of electrode substrate with MWCNTs for analytical sensing shows low detection limits, high sensitivities, resistance to surface fouling and reduction of overpotential. Simplicity and selectivity are important while developing sensors. A very simple and selective Hg(II)-IIPbased electrochemical sensor was reported for mercury ion sensing (Alizadeh et al. 2011b). The 4-vinyl pyridine acts as monomer as well as complexing agent. This Hg(II)-IIP was used along with graphite powder and melted n-eicosane for fabricating Hg(II)-IIP-carbon paste electrode. Recently, Hg(II)-ion-imprinted poly(2-mercaptobenzothiazole) films at the surface of gold nanoparticles/single-walled carbon nanotube nanohybrids has been developed for modifying glassy carbon electrode (PMBT/AuNPs/SWCNTs/GCE) (Fu et al. 2012). This electrode exhibited larger binding capacity, faster binding kinetics and higher selectivity for Hg(II) due to its larger surface to volume ratio and higher ratio of surface imprinted sites. The detection limit obtained for Hg(II)-(PMBT/AuNPs/SWCNTs/GCE) sensor was well below the WHO limit. All Hg(II)-IIP-based electrochemical sensors as mentioned above showed very good selectivity


7393

Fig. 5 Process involved in IIP based chemical sensor is simple in which synthesized IIP is used to fabricate electrode for electrochemical cell

over other metal ions, low detection limits and wide linear response range as shown in Table 5. These days, selective sensing of lead from wastewater is always a challenging task. An attempt was made to modify carbon paste electrode with synthesised nano-sized Pb(II)-IIP to make (Pb(II)-IIP-CPE) (Alizadeh and Amjadi 2011). This sensor showed lowest detection limit (6×10−10 M) for Pb(II) as compared to other sensors, which are developed by using modifying agents like bismuth, organic chelating groups, clay nanoparticles, etc. Pb(II)-IIP-CPE sensor showed no interference up to 200-fold molar excess of alkali metals, alkaline earth metals, Co(II), Zn(II), Ni(II), Cr(II), Hg(II) and Ag(II), respectively. Pb(II)-imprinted self-assembled monolayers (SAMS) gold electrode as an electrochemical sensor for Pb(II) have recently been developed but, its lower detection limit is higher than Pb(II)-IIP-CPE (Wang et al. 2012). On the other hand, they were able to improve the stability and life period of Pb(II)-imprinted membrane by storing it in dilute lead solution. Magnetic ion-imprinted polymer microsphere (Fe3O4@SiO2@IIPs) was synthesised for online monitoring of lead ions using colorimetric and electrochemical determination (Cui et al. 2012). The IIP nanoparticles in the CPE are h i gh l y s e l e c t i v e , h i g h l y eff i c i e n t a n d se l e c t i v e preconcentrators, and therefore, show very low limit of detection. Recently, voltammetric sensor was used for selective recognition and sensitive determination of lead ions using CPE modified with novel Pb(II)-IIP nanobeads based on dithizone, as a complexing ligand for Pb(II) ions (Bahrami et al. 2014). So far very less work have been reported on Pb(II)-IIP for sensing application as per literature; therefore, there is tremendous scope in this field. For Cd(II), similar methodology, viz. Cd(II)-imprinted polymer was synthesised using quinaldic acid and 4-VP. The polymer was then used as

modifying agent and mixed with carbon powder in the presence of melted n-eicosane in order to prepare a Cd(II) selective voltammetric sensor (Alizadeh et al. 2011a). The prepared electrode showing very good analytical characteristics was considered the first report on application of Cd(II)-imprinted polymer as a recognition element in the carbon paste electrode of voltammetric sensor for trace level Cd(II) determination. It was found that there is no interference of large number of anions and cations. Recovery of Cd(II) found to be around 100 %. Further, the electrode remains fully active even after 5 months of storage. In another report of Cd(II) determination, 1-(2-pyridylazo)-2-naphthol was used as complexing agents and methacrylic acid as the monomer (Ashkenani and Taher 2012a, b). Lower detection limit was found to be very low at 2.1–3.4 μg L−1. Developed Cd(II)-IIP-CPE sensor was used for analysis of cadmium in food and water samples which showed excellent recovery rate. Carbon paste electrode is the most commonly used electrode in sensing applications of IIPs. In order to detect copper from wastewater, Cu(II)-IIP-CPE have been developed to detect copper to a very low level in drinking water following the standard limit of 1.0–2.0 and 1.3 μg L−1 (WHO and USEPA) (Ashkenani and Taher 2012a, b). Ng et al. developed an optical sensor based on the Cu(II)-IIP for the sensing of Cu(II) using reflectance spectrometry (Ng and Narayanaswamy 2010). Recently, novel fluorescent Cu(II)IIP has been synthesised for Cu(II) optosensing (Pinheiro et al. 2012). In this study, novel fluorescent complexing monomer 4-[E-2(4′-methyl-2,2′-bipyridin-4-yl)vinyl] phenyl methacrylate (BSOMe) was synthesised for developing Cu(II)-IIPs. In this work, Cu(II) sensing is based on fluorescence quenching mechanism. Novel, highly efficient, and relatively cheap chemical conductance sensor was developed for the detection

PVC membrane electrode impregnated with Uranium-IIP. PVC membrane electrode impregnated with Dy(III)-IIP

U(IV) DCQ

8-hydroxy-quinoline sulphonic acid DCQ 6.0 M HCl

5.0 M HCl

0.5 M NaF

2.5×10−9–5.0×10−7 0.4×10−9–96×10−9 1.0×10−9–8.1×10−7

5.2×10−10 0.8×10−10 6.0×10−10

2.3×10

Potentiometry

2.0×10−8–1.0×10−2 2.0×10−6–1.0×10−1

2.0×10−8 2.0×10−6

(Wang et al. 2012)

(Alizadeh and Amjadi 2011)

(Fu et al. 2012)

(Alizadeh et al. 2011b)

(Rajabi et al. 2013)

(Liu et al. 2006)

Ref.

Tap water, river water and lake water Tap water, Persian gulf, Rice, tomato sauce Well water, hair sample

Mouth wash solutions

Tap and sea water

(Prasad et al. 2006)

(Metilda et al. 2007b)

(Ng and Narayanaswamy 2006)

(Zhihua et al. 2011)

(Ashkenani and Taher 2012a)

(Ashkenani and Taher 2012b)

(Alizadeh et al. 2011a)

Spiked environmental water (Bojdi K, et al. 2014)

Yellow river

Salt water and waste water

Natural water sample

Water sample

Ground water and waste water

Mercury nitrate solution

Analysed sample

7.0×10−8 to 1×10−6 Industrial waste water of and 1.0×10−6 to 1×10−4 yellow river 1.0×10−4 Aqueous solution

31.47×10−9–18.88×10−7

5.35×10−9 −8

17.79×10−9–17.79×10−7

−7

1.0×10 –5.0×10

−9

1.0×10−7–10×10−6

27.5×10−10

5.2×10

−10

0.3×10−10

2.0×10

3.00×10−7–5.00×10−5

1.00×10−8–7.00×10−4

5.0×10−9

−7

1.00×10−8–1.60×10−6

3.06×10−9

Spectrofluorometer 3.62×10−6

DPV

7.2–8.0 Potentiometry

7

5.0

5.0

DPASV

DPASV

– 5

DPASV

DPASV

DPASV

DPASV

DPASV

7

5.0

4.7

5.8

5.0

DPASV

DPASV

LSV

Limit of Linear response range, M detection, M

PMBT/AuNPs/SWCNTs/GCE poly(2-mercaptobenzothiazole)/gold nanoparticles/single-walled carbon nanotube/glassy carbon electrode, DPASV differential pulse anodic voltametry, CPE carbon paste electrode, LSV linear sweep voltametry, DPV differential pulse voltametry, PVC polyvinyl chloride, ANDS 1-amino-8-naphthol-3,6-disodium sulphonate

Dy(III)

Al(III)-IIP-Fluorescence sensor

4-VP, Acrylamide

Cu(II)-IIP -CPE

EDTA

1-(2-pyridylazo)-2-naphthol 3 M HCl

Cu(II)-IIP -CPE

1-(2-pyridylazo)-2-naphthol 3 M HCl

Cd(II)-IIP -CPE

2 M HCl

Quinaldic acid

4-(2-pyridylazo)resorcinol

2 M HCl

0.1 M EDTA

L-cysteine

salicyladehyde (CSA) Schiff-base

2 M HCl

MAA

0.2 M HNO3

0.1 M HCl

4-VP 2-Mercaptobenzothiazole

4

50 %(v/v) HCl

5,10,15,20-tetrakis (3-hydroxyphenyl) porphyrin, 2.5

4.7

M HClO4

ANDS

Cd(II)-IIP -CPE

Pb(II)-imprinted self-assembled monolayers (SAMS) gold electrode Pb(II)-IIP -CPE

Hg(II) imprinted (PMBT/ AuNPs/SWCNTs/GCE) Pb(II)-IIP -CPE

The graphitic electrode modified with imprinted TiO2 film Glassy carbon electrode modified with a ion-imprinted polymeric nanobeads and multi-wall carbon nanotubes Hg(II)-IIP-CPE

Detection method

7394

Al(III)

Cu(II)

Cd(II)

Pb(II)

Hg(II)

Leaching agent pH

List of IIPs analyzed by electrochemical method, corresponding analytical parameters and performance in sensing of toxic metal ions

Metal ion IIP-based electrode/sensor for sensing Complexing agent for of metal ion metal ions

Table 5



of Cu(II) ions in aqueous solutions. Cu(II)-IIP coated onto periodic microelectrode was fabricated for detection of Cu(II), to get conductance signals at 200 Hz (Zafar et al. 2014). Conductance sensors showed four times larger signals for Cu(II) in presence bivalent ions, and seven times larger sensitivity than monovalent ions. By merging imprinting technology with an optic fibre sensor, a fluorescence sensor can be realized. A fluorescence sensor along with Al(III)-IIP for the detection of Al(III) from aqueous solution is also reported (Ng and Narayanaswamy 2006). The IIP was realized by using acrylamide as monomer, 2-hydroxyethyl methacrylate as comonomer and ethylene glycol dimethracylate as crosslinker, respectively. Flow cell for fluorescence measurement is shown in Fig. 6. The synthesised MIP was characterized to have quantitative response over a range of Al(III) ion concentrations. Moreover, it can be regenerated within a very short period of time. Al-kindy et al. developed fluorescence sensor based on IIP for the monitoring of Al(III), wherein Morin was used as a chelating agent (Al-kindy et al. 2002). Polymers as coating materials can be combined with quartz crystal microbalances (QCMs) to develop sensor for detection of both ionic and neutral analytes in liquid phase. Various electrode QCMs have to be optimized to reduce electric field interferences to get the correct sensing. For the sensing of Cu(II) and Ni(II), QCMs were used as a sensor in combination with imprinted polymers (Latif et al. 2011). In potentiometric sensors, development of an electrical potential at the electrode surface takes place due to an ion exchange process between electrode surface and solution containing ions. These potentiometric sensors are called as ion selective electrodes (ISE), which are the most commercially available chemical sensors. An ion selective electrode, polyvinyl chloride membrane electrode modified with IIP is used for sensing of uranium and dysprosium (Prasad et al. 2006; Metilda et al. 2007b). The selectivity of the U(VI) sensor was found to be extremely good as compared to the ionophore-based sensor. Recently, IIP-based CPE sensor is reported for Eu(III) ion (Alizadeh and Amjadi 2013). There is sufficient scope for the development of electrochemical sensor based on IIP, because of its Fig. 6 Flow cell for fluorescence measurement

7395

superiority in selectivity, low detection limit, ease of operation, low cost and high stability. For the sensing of the alkaline earth metals, Mg(II), Ca(II), Sr(II) or Ba(II) ion-imprinted Au nano-composites were developed. The Au nanoparticles (NPs) composites were synthesised by electropolymerization of Au-coated glass support modified with thioaniline (crosslinking agent) and mercaptoethane sulphonic acid (complexing agent) (Ben-amram et al. 2012). Surface plasmon resonance (SPR) spectroscopy was applied for monitoring signal in binding processes of the analytes to respective imprinted sites. The SPR spectrum is sensitive to dielectric changes occurring due to the binding of the analytes to the surface. Rare earth metal ions, La(III) and Ce(III) were detected by using IIP-CPE in cyclic voltammetry (Li and Sun 2007). Details of few IIPs are given in Table 5. In the sensor applications, IIPs are used for fabricating electrodes, which are applied in the electrochemical cell. In sensing, electrodes are reported to be used for 200 times. Modification of electrode surface with MWCNT has shown low detection limit, high sensitivities, resistance to surface fouling and reduction of overpotential. Miscellaneous Apart from all the above applications of IIP, there are other fields of applications. Various thiazole derivatives show very high affinity towards metal ions and therefore, strong coordinate covalent bond is observed in between metal ion and these derivatives. Thus, in recent years thiazole compound containing vinylated group attracted more attention for synthesising metal IIPs. Novel Cu(II) ion-imprinted polymer was synthesised using 5-methyl-2-thiozylmethacrylamide for selective removal of Cu(II) from different salt matrices (Yılmaz et al. 2013). This IIP exhibits higher selectivity towards Cu(II) in presence of other metal ions with comparable ionic radii. Selective extraction of Zn(II) from different salt matrices was done by using Zn(II) ion-imprinted polymer (Zn(II)-IIP) nanoparticles (Shamsipur et al. 2014). Zn(II)-IIP have been developed by using diphenylcarbazone as complexing agent for


FAAS

Cow’s milk and their nutrition (Sadeghi and Aboufazeli 2013) Fish, vegetables and rice samples (Behbahani et al. 2013a) 1 M HCl, 0.1 M TU 2 M HCl 76.3 75.4 0.7 0.42 FAAS FAAS Dipyridile amine Diphenylcarbazone Pb(II) Pb(II)

6.0 6.0

(Zhang et al. 2010c)

(Najafi et al. 2013) Fish samples 0.1 M HCl, 0.1 M EDTA

Ethanol + acetic acid (9:1) Fly ash lixivium 4.09

147 0.03 N-(pyridin-2-ylmethyl)ethenamine (V-Pic) ICP-OES 8.0

7.3 8-Hydroxyquinoline Ga(III)

Hg(II)

3.03

(Yılmaz et al. 2013) Salt matrices 1 M HNO3 5.2 FAAS 5-Methyl-2-thiozylmethacrylamide Cu(II)

5.0–6.5 0.9

Analysed sample Limit of Adsorption Leaching agent detection, capacity, mg g−1 μg L−1 Detection pH technique Metal ion Ligand /complexing monomer

There exist huge health problems originating from metals poisoning. Only few articles appeared which report on treatment of metals poisoning using IIPs. These parameters indicate that there is sufficient scope of IIPs in biomedical applications. In biomedical applications, IIPs are reported for Cu(II), Fe(III), Cd(II) and Hg(II). However, biomedical treatment of poisoning for other toxic metals like Cr(VI), As(III), Pb(II), etc. has not been reported yet by using IIPs. This creates large scope for our future work. To enhance the binding ability, there has to be an extremely fast mechanism. This can be tried by using conjugate monomer concept without crosslinker. This will enable using monomer/monomer or monomer/polymer combination. Adsorption capacities of IIPs are generally based on the surface area of particles. The surface area increase can also be attempted by forming IIPs on nanoparticles or nanofibre. Some work has already been initiated. However, the area has to be vigorously pursued. Other nanoparticle-enhanced binding can be studied in large scale, in the future. For increasing adsorption rate, magnetic IIPs

List of IIPs and corresponding analytical parameters in miscellaneous applications

Future outlook

Table 6

removal and detection of Zn(II) in food samples (Behbahani et al. 2014). Result showed that the sorbents can be repeatedly used during 5 months with no significant decrease in their binding affinities. For the selective extraction and determination of Ga(III) in fly ash, IIPs modified with MWCNTS have been used (Zhang et al. 2010c). Novel magnetic sorbent was synthesised by grafting Hg(II)-IIP on Fe3O4 nanoparticles and used for selective separation and determination of Hg(II) ion in fish samples (Najafi et al. 2013). Recently, IIPs have been used for the determination of Cd and Pb in fresh fish (Barciela-Alonso et al. 2014). Cow’s milk and their nutrition containing lead was determined by using ion-imprinted magnetic nanoparticles (Sadeghi and Aboufazeli 2013). IIPs are also synthesised for the selective extraction and preconcentration of ultra trace quantity of lead from vegetables, rice, and fish samples (Behbahani et al. 2013a). Cobalt is one of the radioactive wastes generated during decontamination of nuclear reactor. In order to reduce this nuclear waste which has a longer half life period (t1/2 =5.27 years), IIPs were used and showed selectivity up to the parts per billion level (Bhaskarapillai 2009). Sea water containing Cu, Ni, Pb and Zn ions are determined by using ICP-OES in combination with IIP as SPE (Otero-Romaní et al. 2009a). Recently, new magnetic IIP nanoparticles have been synthesised for extraction and the determination of trace cadmium in diesel oil samples (Ebrahimzadeh et al. 2014). List of IIPs and corresponding analytical parameters in miscellaneous applications are shown in Table 6. There are various applications where IIP can be used extensively.


Ref.

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have been developed. The IIPs have the disadvantage over ion exchange resin in that the former has lower mass transfer rate and this can be the future scope of research. But, the other properties are superior over the ion exchange resins like selectivity and cost. The IIPs attracted the attention of researchers in recent years, in sensing applications, because of its low cost, high sensitivity, and ease of operation. For getting stability to IIPs, researchers started grafting IIPs on the surface of the solid support material like silica, membranes, etc. Not many options are available for arsenic and chromium. This must be pursued for water purification by sensing and removal from useful water. Acknowledgments The authors wish to acknowledge the financial support from DRDO (ERIP/ER/1003883/M/01/908/2012/D, R&D/ 1416, dated, 28-3-2012) New Delhi, India. P.E.H. acknowledges Defence Institute of Advanced Technology-DRDO, Pune for the Ph.D. research scholarship.

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