Antibacterial and lead ions adsorption characteristics ...

International Journal of Biological Macromolecules 111 (2018) 1140–1145

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International Journal of Biological Macromolecules journal homepage: https://www.journals.elsevier.com/ijbiomac

Antibacterial and lead ions adsorption characteristics of chitosan-manganese dioxide bionanocomposite Yasir Anwar Department of Biological Sciences, Faculty of Science, King Abdulaziz University, P. O. Box 80203, Jeddah 21589, Saudi Arabia

a r t i c l e

i n f o

Article history: Received 6 November 2017 Received in revised form 2 January 2018 Accepted 14 January 2018 Available online xxxx Keywords: Chitosan Antibacterial MnO2 nanoparticles Bio-nanocomposite

a b s t r a c t In the current study, a facile and an eco-friendly manganese oxide nanoparticles dispersed in chitosan (CS-MnO2) nanocomposite was synthesized. A chemical precipitation method was used for the product synthesis. The product characterization was performed using various spectroscopic techniques such as X-ray scattering, scanning electron microscopy, Fourier transform infrared spectroscopy, thermogravimetric analysis and zeta potential which confirmed its successful formation. The CS-MnO2 nanocomposite was evaluated in the Pb2+ ions adsorption from it aqueous solution. The CS-MnO2 showed an approvable accomplishment for the removal of Pb2+ ions and evidence was provided from the adsorption experiments. The efficiency of adsorbent did not change much even after 5 cycles of reuse. Therefore, CS-MnO2 would serve as promising adsorbent. Additionally, the CSMnO2 nanocomposite showed low to moderate antibacterial efficacy against Escherichia coli and Staphylococcus aureus by inhibiting nearly 50% of the bacterial growth. Colony forming units method was used in the antibacterial studies which showed that the bio-nanocomposite had moderate antibacterial activity against the stated strains of bacteria. © 2018 Elsevier B.V. All rights reserved.

1. Introduction Water, the elixir of life, is becoming a competitive resource due to expeditious increase in population, draining water resources, global warming and climatic changes. Inspite of competing demands, the available water is polluted by a discharge of wide range of toxic inorganic and organic chemicals causing a serious threat [1–9]. Heavy metals like Pb, Cd, Ni, Cr, Hg, Zn, Co even though present in earth crust when exceeded above their acceptable level is usually associated with toxicity. They are lead into environment through effluents from manufacturing of chemical, pharmaceutical, leather, paints, battery industry, pesticides and fertilizers [10]. These toxic metal ions due to their higher affinity with hemoglobin easily accumulates in the human body generating lots of diseases like nervous and reproductive system disorders, hypertension, kidney and liver detoriation, metabolic disorders, convulsions and death [11, 12]. Thus the eradication of heavy metals from the water body is of prime importance due to their steadfastness and safe disposal. Numerous methods of heavy metal ions removal have been developed for effluents and wastewaters purification [13–16]. However, a lot of these processes are unacceptable because of either high cost or low ability to remove the pollutants. Besides, the water quality is also affected by certain bacteria. Therefore, nanomaterial with antibacterial properties is the need of the day [17–20].

E-mail address: [email protected].

https://doi.org/10.1016/j.ijbiomac.2018.01.096 0141-8130/© 2018 Elsevier B.V. All rights reserved.

Manganese oxides (MnO2) with different types of crystalline structures like α, β, γ, δ have been studied of late due to their oxidation property, environmental friendly nature, high activity, low cost, ease of handling, and convenient preparation [21]. Due to these advantages, they are used in wide range of applications like batteries, sensors, molecular sieves, catalysts and adsorbents [22, 23]. The only disadvantage of nanoparticles in catalysis is their agglomeration with an amount of assertive time due the high surface energy and van der Waal forces [8, 24–26]. As an aftereffect of this aggregation, their high surface area decreases and all the faces of nanoparticles are not available to activate a specific reaction. Hence functionalization of MnO2 with polymers could be one of effective way to prevent aggregation and make available most of the catalyst surface for reaction. Chitosan (CS) is a polysaccharide containing unbranched chains of β-(1 → 4)-2-acetoamido-2-deoxy-D-glucose synthesized mainly by deacetylation of chitin extracted from crustacean shell [27]. The interesting properties of CS like cationicity, high adsorption capacity due to –OH and –NH2 functional groups availability, low price, biocompatibility, nontoxicity, adsorption properties and biodegradability make them widely studied for biosensors, tissue engineering, separation film, water treatment, agriculture, drug delivery systems, catalysis [2, 9, 18, 19, 28]. Backbone of the CS hoists amino and hydroxyl group which makes it a good adsorbent for heavy metals and dyes [29, 30]. The wide application of CS is restricted due to its poor mechanical and thermal stability. It is well known that combining nanomaterial with certain polymers improve its various properties. Different metal oxides

Y. Anwar / International Journal of Biological Macromolecules 111 (2018) 1140–1145

have been incorporated into CS matrix for making it an efficient adsorbent of the metal ions. Mostly, iron oxide has been used as a nanomaterial in CS because of its easy magnetic-assisted removal after completion of the adsorption process. In numerous studies, MnO2 has been used as efficient adsorbent for the toxic Pb2+ ions from the polluted water. Therefore, we intend to prepare CS-MnO2 bio-nanocomposite which may display high Pb2+ ions removal characteristics as well as antibacterial properties. In this article, a bio-nanocomposite material of CS-MnO2 using the synergy of CS and MnO2 is devised. Pb2+ adsorption by CS-MnO2 and its reusability were studied. The nanocomposite showed high adsorption of Pb2+ from aqueous solution, simple separation, and economical water treatment with moderate antibacterial qualities. The mixing of MnO2 into the CS matrix overcame the problem of the aggregation of the nanoparticles, recollection and repeated use limitation of MnO2. The bio-nanocomposite removed Pb2+ ions by adsorption and could be regenerated without the aid of base or acid and producing pollutants as by-products and also by killing the bacteria. The CS-MnO2 composite was synthesized by chemical precipitation method and studied by X-ray scattering technique (XRD), Fourier transform infrared spectroscopy (FT-I.R), thermogravimetric analysis (TGA). The antibacterial activity of the bio-nanocomposite against Escherichia coli (E. coli) was explored.

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added to 100 mL of 1% (v/v) aqueous acetic acid, where MnO2 ionized into Mn4+ cations. Afterwards, CS (1 g) was added to this dispersion. The product was sonicated for 1 h. The stirring of the solution was continued until it became clear without aggregate of the particles. Then pH of solution was increased to pH 10 by addition of 1 M NaOH where CSMn-OH complex was precipitated which was then heated at 80 °C for 5 h and stored for further experiments of metal ions adsorption, swelling and antibacterial studies. 2.1.2. Adsorption of Pb2+ ions Pb2+ cation was taken as model heavy metal ion in this study. The Pb2+solution was prepared by dissolving (Pb(NO3)2) in aqueous solution. To examine the effect of the adsorbent concentration in the solution, experiments were conducted at room temperature by adding varying amounts of the CS, MnO2, CS-MnO2, i.e., 0.02, 0.04, 0.06, 0.08 and 0.1 g, into the 10 mL of 100 mg/L Pb2+ solution at a neutral pH with the stirring rate of 250 rpm for 24 h. After shaking, the suspension was centrifuged and supernatant was analyzed for the residual Pb2+concentrations using atomic absorption spectrophotometer or ICP analyses. The adsorption of Pb2+ was calculated as follows: Pb

2þ

adsorption ð%Þ ¼ ½C0 −Ct =C0 100

where C0 is the initial concentration of the Pb2+ ions in solution and Ct is the Pb2+ ions concentration in the solution at time t. The average value was reported based on triplicate experiments.

2. Experimental 2.1. Materials For the current research work, following chemicals and reagents were used. Manganese nitrate tetrahydrate (Mn(NO3)2.4H2O), acetic acid (CH3COOH), sodium hydroxide (NaOH), chitosan (CS) with 85% degree of acetylation and high molecular weight and lead nitrate (Pb (NO)3) were purchased from Aldrich of analytical grade and used without further purifiction. Peptone, beef extract, and agar powder of bacteriological grade were obtained from reputable supplier. The bacterial strains of Escherichia coli (E. coli) O157:H7 and Staphylococcus aureus were used as a model for evaluation of the antibacterial activities supplied by King Fahad Hospital, Jeddah. 2.1.1. Preparation of CS-MnO2 composite MnO2 nanoparticles were prepared by thermal decomposition of Mn (NO3)2.4H2O at 350 °C for 2 h. After its preparation, MnO2 (0.25 g) was

2.1.3. Antibacterial activity There are two different methods of evaluation of the antibacterial activities of a material. One is the colony forming units and another is zone inhibition method. In this study, a suitable method of colony forming units was followed for determination of the bactericidal activities of the CS, CS-MnO2 bio-nanocomposite. A nutrient agar (DIFCO 0001) containing 5 g/L peptones, 3 g/L beef extract, and 15 g/L agar in distilled water at pH 7 was prepared and E. coli was grown in it. The antibacterial activity of the CS, and CS-MnO2 bio-nanocomposite was evaluated through colony forming count (CFU) method. Small pieces of freezedried CS, andCS-MnO2 samples were sterilized at 80 °C for 15 min. 9 mL of the growth medium for E. coil was added to separate container and 0.03 g/mL of finely powdered samples of CS, and CSMnO2 were added to each of the container. A 1 mL fresh culture of

Scheme 1. Preparation route of CS-MnO2 in a pictorial way.

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E. coli was added to the containers and at the temperature of the container was maintained at 37 °C for 24 h. The sample's dilution was performed with the saline or saltish water and bacterial colonies were cultured in the dishes for different interval of times. The sample's dilution was performed with the saline or saltish water and bacterial colonies were cultured in the dishes for different interval of times. Similar procedure was used for testing of the antibacterial activity of CS and CS-MnO2 against Staphylococcus aureus. 2.1.4. Characterization The phase and crystallinity of the prepared bio-nanocomposite were determined by using a Thermo scientific X-ray diffractometer (XRD) with Copper Kα radiations. Fourier transform infrared spectroscopy was used for determining the interactions between CS chains and MnO2. A Jassco FT/IR-630 FT-I-R specctrometer was used for analyzing the samples. Thermogravimetric analyses on CS, MnO2 and CS-MnO2 were performed using TGA Q500 (TA instruments). Zeta potential analysis of 1 wt% of CS, MnO2, and CS-MnO2 dispersed in various buffer solutions (pH 2 to 12) was achieved using a Marvel Jetasizer Nano instrument. Pb2+concentrations was determined using AAS (atomic absorption spectrophotometer). The swelling characteristics of the samples were measured by first fully migitation of the samples in water followed by vacuum drying and calculating the percentage difference between the dried and completely wet samples. The swelling characteristics of the samples were measured by first fully migitation of the samples in water followed by vacuum drying and calculating the percentage difference between the dried and completely wet samples. 3. Results and discussion The formation of CS-MnO2 involved two steps (Scheme 1). Initially, CS and MnO2 nanoparticles were dispersed in acetic acid solution, where MnO2 ionizes into manganese cations (Mn4+). The Mn4+ ions coordinated with –OH and –NH2 groups of CS chains and precipitated as CS-Mn-OH3+ when pH of the solution was increased to 10 by the slow addition of NaOH.26 The precipitate obtained was heated for 5 h at 80 °C, where the Mn4+ ions transformed into MnO2. The homogeneous dispersion of Mn4+ in CS sol aided in the formation of CS-MnO2 composite. The feasible reactions of MnO2 evolution in alkaline medium could be as follow, Mn4þ þ OH− − →Mn−O−H3þ Mn−O−H3þ þ OH− − →MnO2 þ 2H2 O Fig. 1a shows XRD patterns of MnO2, CS, and CS-MnO2. The XRD pattern of MnO2 has nine peaks located at the 2θ = 12.5°, 17.9°, 28.6°, 37.0°, 41.9°, 49.6°, 55.6°, 60.0° and 69.9°. The peaks at the mentioned positions represent the (110), (200), (310), (211), (301), (411), (600), (521), and (002) planes of tetragonal phase of α-type MnO2. (JCPDSNo 40-0141). The broad peak in the XRD pattern of CS at 2θ = ~20° represents the amorphous nature of the biopolymer. The XRD pattern of CS-MnO2 has the broad peak arising from the amorphous CS and other small peaks from the MnO2 crystals. These results suggest that the MnO2 nanoparticles were present in the CS-MnO2 bio-nanocomposite. Fig. 1b depicts the FT-IR spectra of the three samples. The FT-IR spectrum of MnO2 has single distinct peak located at 516 cm−1. This peak corresponds to the stretching vibration of the bond between metal and oxygen. The band at 3500 cm−1 in MnO2 spectrum is due to OH stretching vibration of adsorbed water. The FTIR spectrum of pure CS has a peak at 3371 cm-1. This peak represents the stretching vibration mode of –NH2 and –OH groups. The band at 2873 cm−1 was attributed to the –CH group asymmetric stretching in polymer chain, 1662 cm−1 showed the amide I group (C\\O stretching along the N\\H deformation), 1578 cm−1 was due to –NH deformation, 1412 cm−1 showed the C\\N axial deformation (amine group), 1374 cm−1 was attributed

Fig. 1. XRD patterns (a) FTIR spectra (b) and TGA thermogragrams (c) of MnO2, CS and CSMnO2. (d) TEM image of CS-MnO2.

to the COO– group in carboxylic acid salt, 1157 cm−1 showed the special peak of β(1–4) glucosidic band in polysaccharide unit and 1037 cm−1 corresponds to the stretching vibration of C\\O\\C in glucose circle. In case of CS-MnO2 all peaks of CS and MnO2 were present but the peaks corresponding to hydroxyl, amino and amide groups were shifted


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indicating the chemical reaction of these groups in assembling MnO2 nanoparticles [31]. Fig. 1c shows the TGA thermograms of MnO2, CS, and CS-MnO2 bionanocomposite. The TGA thermogram of MnO2 show slight decrease of ~3% in weight upon subjecting to thermal treatment. Such a decrease in weight might be due to the moisture loss. The TGA thermogram of CS has strong decrease in weight around 390 °C followed by moderate weight loss until it became constant at 940 °C. These weight losses were due to thermal degradation of the CS polymer chains. The CS-MnO2 has similar trend of decreasing weight except that the final weight was slightly high as compare to the pure CS. The comparatively high final weight was due to incorporated nanomaterial. Fig. 2 shows the zeta potential of CS-MnO2 as a function of pH. It is clear that with the increasing pH the zeta potential shows decreasing trend. The isoelectric point of CS-MnO2 is around 4.9 which is slightly higher than MnO2 which could be due to the shifting of the slipping plane caused by the CS adsorption on the MnO2 surface [32]. At a neutral pH, the zeta potential is −6.2 mV and then with increasing pH it became more negative owing to the adsorption of hydroxyl groups on the surface of the MnO2 [33]. The adsorption behaviour of various concentrations of CS, MnO2 and CS-MnO2 at a neutral pH, contact time of 120 mins and Pb2+ concentration of 100 mg/L was studied for the removal of Pb2+ ions from the aqueous solutions as shown in Fig. 3. Experiments with CS, MnO2 and CS-MnO2 indicated from the plot of percentage of Pb2+ removal that these materials adsorbed Pb2+ 50.3, 79.3 and 88.7%, respectively, with a dosage of 0.02 g and further increase in the adsorbent dosage has no remarkable consequence on the Pb2+ removal. As expected the removal efficiency was higher by CS-MnO2 compared to CS and MnO2 alone which could be due to the synergy between CS and MnO2, negative zeta potential and higher surface area facilitating greater number of adsorption sites and thus maximum removal efficiency. Thus CS-MnO2 efficiently removed Pb2+ from simulated waste water by overcoming the shortcomings of aggregation of MnO2, solubility of CS when they are respectively used alone. In fact, CS has been widely used as adsorbent in various nanostructured form for the divalent metal ions especially Pb2+ ions. It has been found that the modification of the CS either by blending with nanomaterial or chemical modification of the CS greatly enhances its adsorption properties [34–37]. The important prerequisite of an adsorbent in an applied appliance point of view is its reusability because with time adsorbent disintegrates and loses its activity [29]. Therefore, the evaluation of resistance to detoriation and repeated use of the adsorbent is essential for the applied usage. The percentage of Pb2+ removal in 30 min for 5 times with the same adsorbent was studied as illustrated in Fig. 4. The after-effects adumbrated that the adsorbent conserved an acceptable action even

afterwards 5 cycles of reclaim. The slight abatement in ability may be acceptable due to a little depletion of the adsorbent during washing, inspite it could be assured that the CS-MnO2 has almost continued shelf action for the Pb2+ removal. Herein the use of CS in the composite played a major role in recovery and repeated use of MnO2 in comparison to bare MnO2 nanoparticles. Owing the clean nature of the materials involved and blooming chemistry, the low cost, high adsorption ability and several times repeated use; the CS-MnO2 could be a facile material with environmentally-friendly and acceptable action of self-regeneration. CS, and CS-MnO2 were tested for their antibacterial activity against bacterial strain E. Coli and S. aureus. The result of quantitative antibacterial assessment by CFU is explained in Fig. 5 and Table 1. According to the author's knowledge, not too many research works concerning the antibacterial activity of the MnO2 have been found in the literature. The two research works by Kunkaleker et al. suggest that the MnO2 does not show any antibacterial activity as revealed by performing the disc diffusion tests [38, 39]. Moreover, only the silver-doped MnO2 and other forms of the Mn2O3 samples showed good antibacterial activity [38]. The antimicrobial mechanism of CS was described in the literature that it forms the electrostatic bond through amine groups with the robustly electronegative bacterial cell wall surface [4, 17–20, 28–30, 40]. However, we could not clearly observe it here. Fig. 5 and Table 1 show that the CS-MnO2 has the comparatively good ability to kill both E. coli O157:H7 and S. aureus compare to the control (CS). The results identify

Fig. 2. Zeta potential of CS-MnO2 as a function of pH.

Fig. 4. Removal efficiency of Pb2+ by CS-MnO2 for continuous five cycles.

Fig. 3. Influence of amount of adsorbent (CS, MnO2 and CS-MnO2) on Pb2+ removal efficiency.

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Fig. 5. Nutrient agar plates showing antibacterial effect after 24 h of incubation in the presence of CS (a and c) and CS-MnO2 (b and d). The upper row petri dishes contain Staphylococcus aureus and lower contains E. coli colonies.

that the petri dish containing control (CS) has more colonies compare to the treated one. Which suggest that our sample exhibit prevention activity against these pathogenic bacteria. However, it was found that CS-MnO2 exhibit with inhibition of nearly 50% against E. coli O157:H7 and S. aureus. This activity may be attributed to the synergistic effect of the CS and MnO2 in the CS-MnO2 bionanocomposite. Our finding proposed that this metal oxide produce ions that are absorb by cell membrane. These metal ions interact with nucleic acids and proteins by changing cell structure. Also, it can affect enzyme activity by making the bacteria abnormal that leads to its death. However, studies have shown that metal oxide has weak antibacterial activity that is confirm by our study [41,42]. Apart from these CS-MnO2 might also develop species that are highly reactive such as hydrogen peroxide, superoxide's or hydrogen radicles. For that reason, the feasibility and development of these pathogenic bacteria is reduced as compared to the control one. CS-MnO2 showed comparatively enhanced antibacterial action which

conceivably attributed to the synergistic effect of CS and MnO2 nanoparticles. 4. Conclusions In this study, a novel CS-MnO2 composite were prepared by chemical precipitation method. The FT-IR and XRD spectra endorsed the establishment of composite. Zeta potential and TEM analysis ensured the binding of MnO2 nanoparticles on the CS surface. Various amounts of CS, and CS-MnO2 were used to evaluate the most able adsorbent for lead ions removal. The after-effects explained that the CS-MnO2 is most effective for adsorbing Pb2+ions. The results also showed that the repeated use of recycled composite (5 times) did not affect its adsorption ability significantly. The antibacterial effect of the CS, and CSMnO2 against E. coli and Staphylococcus aureus were studied and it was proved that the bio-nanocomposite of CS-MnO2 exhibited

Table 1 Shows growth characteristics of E. coli and Staphylococcus aureus in the presence of chitosan(CS) and chitosan-manganese dioxide(CS-MnO2). Strains used

Incubation (h)

Material used (CS) (Cfu/mL)

% Activity (CS)

Material used (CS-MnO2) (Cfu/mL)

% Activity (CS-MnO2)

E. coli O157:H7

12 24 12 24

98 × 10−4 133 × 10−4 82 × 10−4 118 × 10−4

0 0 0 0

58 × 10−4 75 × 10−4 46 57

40 58 36 61

Staphylococcus aureus


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