Microporous and Mesoporous Materials 232 (2016) 174e183
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Microporous and Mesoporous Materials journal homepage: www.elsevier.com/locate/micromeso
Synthesis and characterization of zeolite based nanoecomposite: An environment friendly slow release fertilizer Ambreen Lateef a, Rabia Nazir b, *, Nadia Jamil a, Shahzad Alam c, Raza Shah d, Muhammad Naeem Khan b, Murtaza Saleem e a
College of Earth and Environmental Sciences, University of the Punjab, Lahore 54500, Pakistan Applied Chemistry Research Centre, Pakistan Council of Scientific and Industrial Research Laboratories Complex, Ferozepur Road, Lahore 54000, Pakistan Pakistan Council of Scientific and Industrial Research Laboratories Complex, G-5/2 Islamabad, Pakistan d H.E.J Research Institute of Chemistry, International Center for Chemical and Biological Sciences, University of Karachi, Karachi 75270, Pakistan e Department of Physics, School of Science and Engineering, Lahore University of Management Sciences, Lahore 54792, Pakistan b c
a r t i c l e i n f o
a b s t r a c t
Article history: Received 5 March 2016 Received in revised form 8 May 2016 Accepted 12 June 2016 Available online 14 June 2016
The research deals with assessing the feasibility of using nano-zeolite as support material for the provision of nine out of thirteen primary, secondary and micro-nutrients on slow release basis. The nanozeolite (NZ) and nano-composite (ZNC), synthesized using simple chemical approach, were characterized by different techniques including FT-IR, powder XRD, SEM/EDX, AFM and TGA/DSC. Physical characterization was also performed by using standard methods. The lab studies showed that there is considerable increase in water retention capacity, water absorbency, equilibrium water content and swelling ratio of ZNC as compared to the NZ which is favorable for maintaining water level in the soil. The nano-composite prepared is safe to use as compared to conventional fertilizers as indicated by salt index value. Nutrients slow release studies carried out in water and soil confirmed the long term availability of all the doped nutrients to the plant over the full crop cultivation period that is suitable for promoting germination, growth, flowering and fruiting. Hence, the results obtained showed that the prepared nanocomposite materials can be safely used as environment friendly fertilizer. © 2016 Elsevier Inc. All rights reserved.
Keywords: Nano-zeolite Zeolite based nano-composite Slow release fertilizer Macro and micro-nutrients
1. Introduction Agriculture practices are very important for people all over the world for providing food but unfortunately these methods are facing several international challenges now days. One such challenge is massive increase in the population which had put enormous burden on the agronomic productions that need to be enhanced with same limited resources of land and water. This resulted in significant rise in fertilizers’ usage to enhance soil health
Abbreviations: AFM, Atomic Force Microscopy; DSC, Differential Scanning Calorimetry; EDX, Energy-dispersive X-ray Spectroscopy; EWC, Equilibrium Water Content; FTIR, Fourier Transforms Infrared Spectroscopy; HDTMA, Hexa Decyl Trimethyl Ammonium; SI, Salt Index; SR, Swelling Ratio; SRF, Slow Release Fertilizer; SEM, Scanning Electron Microscope; SMZ, Surface Modified Zeolite; TGA, Thermal Gravimetric Analysis; TDS, Total Dissolved Solids; TH, Total Hardness; WR, Water Retention; WA, Water Absorbance; XRD, X-ray Diffraction; ZNC, Zeolite Based Nano-composite. * Corresponding author. E-mail address:
[email protected] (R. Nazir). http://dx.doi.org/10.1016/j.micromeso.2016.06.020 1387-1811/© 2016 Elsevier Inc. All rights reserved.
that can expedite fast increase in yield per hectare [1]. However, this uncontrolled use of fertilizers had not only caused decline in land quality but owing to their high solubility which results in 40e75% leaching losses, they contribute less towards plant growth and more towards environmental issues [1e3] which directly or indirectly lead to various health concerns [4]. Furthermore, this incurs in huge wastage of fertilizers accounting for economic loses. All these issues together can put enormous financial burden on the society which is not only a matter of serious concern for developing countries which are striving for survival but also for developed countries in attaining sustainability. Therefore, there is a dire need to change agronomic practices by designing new environmental friendly fertilizers that can also enhance crop yield by facilitating maximum nutrient uptake. Application of nanotechnology in this area can help in promoting sustainable agriculture by provision of slow or controlled release fertilizers, herbicides and pesticides [5e7]. Several researches have been carried out in this context which dealt with the development of nanoparticles or nano-composites to facilitate
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plant growth either by direct uptake or by slow release of nutrients [8]. Total of 16 nutrients are required by the plants out of which 13 are usually taken up from the soil. Nano-fertilizers have helped in provision of these essential nutrients to the soil on continues basis by slow release. This gradual release promotes enhanced delivery of nutrients to the plants that further accelerates early germination, fast growth and high nutritional level [9]. Zeolite, in general, is known to support crop cultivation by improving soil condition through enhancing nutrients and water utilization efficacy, biological activity and fertility and minimizing ammonia volatilization and soil salinity [10e14]. Additional advantage of zeolite is that it enhances the nutrient retention capacity of soil which leads to increased availability of nutrients to the plants for longer period of time because of its slow disintegration and decomposition rate in soil [5]. Considering all these advantages of zeolite, the material has recently gained much attention and is being used to deliver fertilizer to the plants at slow rate after some structural modifications [15e19]. Not much of the work is cited on applicability of nano-zeolite as slow-release fertilizer, the few studies that have been carried out are conducted by Subramanian et al. [20,21]. They showed that these nano-zeolites release nutrients over a much longer period of time when compared with conventional fertilizers thereby reducing nutrients’ leaching losses considerably [22]. High pore density, enhanced surface area and anion exchange capacity of nano-zeolites favors the retention of anions [20,23,24]. The only drawback associated with the use of these fertilizers is related with their incapability in loading cations in considerable amounts on to its porous structure. For this purpose various structural modifications were performed to increase both cation and anion uptake capacities either by use of surfactants [21,22] or by prolonged thermal treatment [20]. These additional treatments not only add up to the cost of fertilizers but also the use of surfactants put extra burden on the environment [25,26]. Therefore, the need is to design simple and cost-effective ways for the synthesis of nano-zeolite that can enhance the nutrient uptake capacity in addition to reducing the environmental impacts caused by use of conventional and environmental hazardous materials. The current research is henceforth aimed to develop simple methodology for synthesis of nano-composite of zeolite that not only facilitates the enhancement in ion exchange capacity but also acts as a material that can act as a continues source of both macro and micro-nutrients throughout the period of crop growth. 2. Experimental 2.1. Chemicals All chemicals used in the study are of analytical grade. Sodium phosphate monobasic dihydrate (NaH2PO4$2H2O), magnesium sulphate heptahydrate (MgSO4$7H2O), aluminum sulphate heptahydrate (Al2(SO4)3$7H2O), and ethylene glycol (C2H6O2) were taken from Merck, Germany. Sodium hydroxide (NaOH), calcium phosphate (Ca3(PO4)2), zinc sulphate heptahydrate (ZnSO4$7H2O) potassium chloride (KCl) and sodium silicate solution (Na2SiO3) were procured from DAEJUNG while sodium chloride (NaCl), sodium nitrate (NaNO3), ferrous chloride tetrahydrate (FeCl2$4H2O), nitric acid (HNO3) and hydrochloric acid (HCl) were supplied by SigmaAldrich. 2.2. Synthesis of zeolite nano-composite (ZNC) Two-step approach was adopted to synthesize ZNC; in first step zeolite was prepared that was impregnated with nutrients in second step.
175
2.2.1. Synthesis of nano-zeolite (NZ) Nano-zeolite (NZ) was synthesized by simple co-precipitation method [27]. Sodium silicate solution (220 g/300 ml distilled water) and ethylene glycol (25 ml) were taken in a three necked round bottom flask fitted with reflux condenser and quick fit dropping funnels. The contents were stirred for 30 min while maintaining the temperature at 50e60 C to get homogenous mixture. To this aluminum sulphate (78.7 g/250 ml) and sodium hydroxide (30 g/ 250 ml) solutions were added drop-wise along with stirring and heating (50e60 C). When dropping was completed pH was adjusted to neutral using 1 N HCl followed by filtration, oven drying at 105 C and annealing at 650 C to result in grey colored zeolite. 2.2.2. Synthesis of zeolite nano-composite (ZNC) The zeolite based nano-composite (ZNC) was synthesized by simple impregnation of nutrients in NZ. To the suspension of NZ in distilled water (200 g/l) 5% solution of each of macro (N, P, K, Ca, Mg, S) and micro-nutrients (Fe, Zn, Cu) in the form of their salts (NaH2PO4$2H2O, MgSO4$7H2O, Ca3(PO4)2, ZnSO4$7H2O, KCl, NaNO3 and FeCl2$4H2O) were added and allowed to stir for 3 h to attain maximum impregnation of these nutrients into NZ. The resulting suspension was vacuum filtered, oven dried (105 C) and fine grinded in blender at 12,000 rpm. The prepared zeolite was stored in air-tight container till further use. 2.3. Characterization 2.3.1. Physical properties The physical properties including pH (ASTM D 4959-00), conductivity (ASTM D1125-14), moisture content (ASTM 4643-08), bulk and tap densities (ASTM D2854-70), methylene blue (MB) value (ASTM C1777-15), ash content (ASTM D2866-70) and cation exchange (CEC) and anion exchange (AEC) capacities of NZ and ZNC were determined by standard methods [28]. 2.3.2. Fourier transform infrared spectroscopy (FT-IR) The material characterization was done using FT-IR Thermo Nicolet spectrometer series by scanning the sample pallet made with KBr in the range of 4000e400 cm1. 2.3.3. Powder X-ray diffraction (XRD) Powder XRD analysis was carried out using PANanalytical X’pert pro diffractometer by a Philips X-ray generator. Diffraction data was acquired by exposing powder samples to Cu-Ka X-rays radiation, which has a characteristics wavelength of 1.5418 A . X-rays were generated from a Cu anode supplied with voltage of 40 kV and a current of 40 mA. The data were collected over a range of 20e80 2q with a step size of 0.05 and nominal time per step is 0.5 s. 2.3.4. Scanning electron microscopy (SEM) and energy dispersive xray spectroscopy (EDX) Gold coated pallets of the samples were used to acquire the SEM images on Nova NanoSEM 450 while powder samples spread on carbon tape were used to determine the elemental composition using EDX, Nova 450 at 5.00 kV. 2.3.5. Atomic force microscopy (AFM) The topographic images of atomic force microscopy were recorded with AFM 5500 (Agilant, USA). Silicon nitride probe with a triangle soft cantilever (Veeco, model MLTC-AUHM) having a nominal value of the spring constant of 0.01 and 0.1 N/m used in the non-contact topography measurements. Ethanolic solution of sample (100 mg/ml) was vortexed for 1 min followed by sonication (KQ 500-DE) for 30 min. From this 10 ml solution was taken and
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deposited on a freshly cleaved mica surface to obtain images using AM in tapping mode.
2.3.6. Thermal gravimetric analysis Thermo gravimetric analysis (TGA and DSC) was carried out using a SDT-Q600 (Germany) instrument; 3 mg of sample was taken in an alumina cup and scan was recorded at heating rate of 20 C/min over the range of 50e1000 C to find the thermal stability of material.
2.4. Salt index (SI) 1.0 g each of ZNC and sodium nitrate were taken in separate beakers and200 ml of distilled water was added in each of the beaker. After 24 h, the conductivities of solutions were taken using conductivity meter CM-40S TOA and SI was calculated as ratio of these conductivities [29].
2.5. Swelling ratio (SR) and equilibrium water content (EWC) 1.0 g of ZNC and NZ was immersed in distilled water (200 ml) and allowed to swell for 24 h under ambient conditions of temperature and pressure. The contents were filtered and SR and EWC were calculated using Eqs. (1) and (2), respectively [29].
SR ¼
Ws Wd Wd
EWCð%Þ ¼
Ws Wd 100 Ws
(1)
2.8.1. Slow release studies in water Seven days slow release or leaching pattern of ZNC in water was determined by conducting experiment in glass column (3000 0.500 ) using 5.0 g of ZNC and pre-analyzed tap water (Table 1). The volume of water was maintained at 50 ml mark throughout the experiment. During the seven days period, water in increments of 25 ml was collected daily at 24 h time interval to determine the leakage of nutrients within span of 7 days [32]. 2.8.2. Slow release studies in soil 14 days column studies were done by employing glass column (6200 500 ) filled with 400 g of sieved soil mixed thoroughly with 10 g of ZNC.180 ml pre-analyzed tap water (Table 1) was added to the column to saturate the soil. 50 ml water was collected daily at 24 h interval from the column for the period of study. 100 ml water was then added to ensure constant moisture content in the column. The collected water samples were analyzed to check the release pattern of nutrients from nano-composite in soil. The experimental blank using just soil sample (400 g) was run under same set of conditions [33]. The collected samples (from above experiments) were analyzed for metals (Zn2þ, Fe2þ/3þ, Ca2þ, Mg2þ) by Perkin Elmer Flame Atomic Absorption Spectrometer (FAAS), (Na1þ, K1þ) by Flame Photometer Tenway PSP7, Holand, NO1 3 by Ion Selective Electrode 930 and PO3 4 by UV Visible Spectrophotometer. 2.9. Statistical analysis
2.6. Water absorbance (WA) studies These studies were carried out by taking 1.0 g of NZ and ZNC (W1) in pre-weighted petri-dishes (W2). These petri-dishes were kept in desiccator under moist environment for 5 days and reweighted (W3) to check the sample water absorption capacity (WC) by using Eq. (3) [30].
ðW3 W2 Þ 100 W1
Two types of slow release studies were conducted for ZNC to determine the nutrient leaching pattern in 1) water and 2) soil.
(2)
where, WS and Wd are the wet and dry weights of ZNC or NZ, respectively.
WC ¼
2.8. Slow release studies
(3)
The data was analyzed using Microsoft Excel and OriginPro 8.5 software. All the readings are reported as average of three. For slow release studies the readings for blank are adjusted prior to simulation of results in order to get the true picture of nutrients released only from ZNC. 3. Results and discussion This research defines a simple method to synthesize ZNC using impregnation approach to load both macro (primary and secondary) and micro nutrients onto NZ in the ratio of 5%. The synthesized materials (both NZ and ZNC) were characterized using FT-IR, SEM/ EDX, AFM, powder XRD, TGA and DSC to get insight into their structure, morphology, chemical composition, particle size and thermal stability. Physical characterization was also performed using standard methods. To find the applicability of the ZNC as slow
2.7. Water retention (WR) studies Water retention capacity (WR) was measured using preweighted cups A (WA) and B (WB) with sieved bottom. 50.0 g sieved soil from field was taken in cup A and in cup B 2.0 g of ZNC was taken after mixing with 50 g soil followed by addition of 30 ml distilled in each cup. Water was allowed to seep through them and cups were reweighed (WA1 and WB1) after 24 h. The cups were then kept in a glass box and weighted (WA2 and WB2) daily for next 30 days allowing 24 h interval between the readings [31]. The following equation (Eq. (4)) was used to calculate water retention.
WR ¼
W2 100 W1
(4)
Table 1 Water analysis. Parameters
Results
pH Conductivity (ms/cm) at 25 C TDS (mg/l) TH (mg/l) Ca2þ(mg/l) Mg2þ (mg/l) Zn2þ (mg/l) Cl1 (mg/l) Na1þ (mg/l) K1þ (mg/l) PO3 4 (mg/l) NO1 3 (mg/l)
7.8 290.50 413.3 0.7 0.36 0.34 0.04 17.75 2.1 1.0 2.4 0.9
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release fertilizer, related studies like SI, SR, EWC, WA, WR and nutrient slow release studies were also performed.
Table 2 Physical parameters of NZ and ZNC. Parameters
NZ
ZNC
pH Moisture content (%) Conductivity (ms/cm) at 25 C Bulk density (mg/m3) Tap density (mg/m3) Cation exchange capacity (meq/g) MB value Ash content (%)
6.97 2.5 508.27 0.89 1.5 2.45 60 91.37
6.0 4.48 555.23 1.2 1.8 1.37 65 94.27
3.1. Synthesis of ZNC Simple co-precipitation method was used to prepare NZ which was further used to synthesize ZNC by simple impregnation of macro- and micro- nutrients. Zeolite in general has a porous structure [34] and use of templating agent further promotes increase in porosity and surface area. Hence, when impregnation is done nutrients penetrate into the pores and from one pore to
Fig. 1. FT-IR spectra of NZ (A) and ZNC (B) showing peak shifting in ZNC due to doping.
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another pore, ensuring more adsorption of nutrients and therefore enhanced availability to the plants. These nutrients will be released from ZNC depending upon the pore size, adsorption level, and binding capacity or impregnation level [35]. 3.2. Characterization 3.2.1. Physical parameters Experiments were performed to determine physical parameters i.e. pH, moisture, conductivity, bulk density, tap density, CEC, AEC, MB value, loss on ignition and ash content for both NZ and ZNC. The results obtained are tabulated in Table 2. NZ is a neutral material as observed from its pH value, but there is a small increase in acidity of ZNC probably due to incorporation of non-metallic moieties. Significant increase in conductivity of ZNC from 508.27 to 555.23 mS/cm has taken place owing to inclusion of
3.2.2. Fourier transform infrared spectroscopy (FT-IR) Fig. 1 gives the comparison of FT-IR spectra of NZ and ZNC. The peaks in the range of 3400e3200 cm1 are due to extra bridging of hydroxyl ion or due to moisture incorporated in the porous structure of zeolite as affirmed from physical characterization as well. The peaks arising at 1060.85 and 786.96 cm1 are assigned to bending and stretching of AleO and SieO in zeolite structure [39]. The peak shifting is in FI-TR spectra of ZNC to 3034.03, 1070.49, 796.60, 594.06, 557.43 and 507.28 positions which may be attributed to incorporation of nutrients in the zeolite structure hence, supporting the doping of nutrients on the NZ as available in the literature [40].
B
A
20
30
40
50
60
metals and ionic salts into zeolite porous structure. This incorporation of salts has also resulted in increase in both tap and bulk densities. Very high moisture content is indicated by the studies which is accordance with the previous studies that state that nano-zeolites with high Si/Al ratio are usually characterized with high moisture content because of enhance hydrophobicity induced by silica [28]. The lower MB value is recorded in case of ZNC (60) as compared to NZ (65) because of impregnation of metals into the NZ structure. The NZ has cation exchange capacity (CEC) of 2.45 meq/g which is comparable with the clinoptilolite [28] and anion exchange capacity is 0.01 meq/g which is very low; while ZNC has cation and anion exchange capacities of 1.37 and 1.96 meq/g. The decrease is observed in CEC of ZNC as compared to NZ owing to incorporation of cations into NZ matrix. Low anion exchange capacity is observed in case of NZ making it specifically cation exchanger [36]. But for ZNC equally good AEC is observed hence it can be claimed as amphoteric ion exchanger [37] which makes it better material for agricultural purposes [38].
70
80
2
Fig. 2. Powder XRD of NZ (A) and ZNC (B) showing amorphous nature of samples.
3.2.3. Powder x-ray diffraction (XRD) Powder XRD patterns of NZ and ZNC scanned in range of 2q ¼ 20e80 are shown in Fig. 2. The low crystalline structure of NZ
Fig. 3. SEM images of NZ and ZNC at resolution of 10 mm (A & B) and at 1 mm (C & D), respectively.
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Fig. 4. EDX analysis of (A) NZ and (B) and ZNC showing composition of elements in table inset.
spectrum is matched with sodium aluminum silicate having cubic crystal system and CCDC No: 01-074-1183. The ZNC spectra (Fig. 2B) when compared with NZ represents that basic structure of zeolite is not changed just a slight decline in the intensities resulted which is due to incorporation of nutrients into NZ [41]. The presence of low intensity broadened peaks is also indicative of small particle size of the samples prepared [42,43].
Fig. 5. AFM images in (A) 2D and (B) 3D of ZNC showing particle size in range of 3e6 nm.
3.2.4. Scanning electron microscopy (SEM)/energy dispersive x-ray spectroscopy (EDX) and atomic force spectroscopy (AFM) After structural characterization, SEM analysis was conducted to get insight into the morphology of the samples prepared. The micrographs of NZ and ZNC (Fig. 3A and B) corresponds to the spongy nature of prepared samples. Increase in the particle size, reduction in porosity and appearance of white colored coating on the particles in case of ZNC spongy appearance shows doping effect. Compositional analysis of elements was done by EDX which is presented in Fig. 4. The chemical formula derived from this composition (Fig. 4 inset table) by fitting in the values in general formula of zeolite (i.e. [AlxSiyO2xþ2y]x where x y) points to the formation of high silicon zeolite i.e. [AlSi6O12].Na2. The charge (x) is stabled by incorporation of an added cation (Na1þ, K1þ, Ca2þ, etc) as mentioned in the literature [44,45]. The Si/Al ratio hence obtained is 6.15 for the NZ and 10.7 for ZNC (Fig. 4 inset Table) which also points towards the incorporation of other metallic and nonmetallic impurities and amount of Si or Al exchanged [46]. This study is also in accordance with ion exchange capacity studies discussed earlier. Particle size of ZNC was determined using AFM by taking both 2D and 3D images as presented in Fig. 5. The 2D image (Fig. 5A) depicts the narrow distribution of particles in size range of 3e6 nm with majority of particles having size of 6.05 nm as confirmed from 3D image (Fig. 5B). The increase in particle size as affirmed from SEM (Fig. 3) and AFM (Fig. 5) images is also attributed to high Si/Al ratio in ZNC [47].
is indicated (Fig. 2A) with low intensity peaks arising at 2q values of 23.32 , 25.82 , 28.89 , 31.59 and 33.85 corresponding to (311), (222), (400), (311) and (421) hkl diffraction planes, respectively. The
3.2.5. Thermogravimetric analysis To determine the stability and thermal degradation pattern of samples prepared, TGA and DSC analysis were conducted which are
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Fig. 6. TGA (black line) and DSC (blue line) spectra of NZ showing minor weight loss. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)
given in Figs. 6 and 7 as interlinked spectra. The TGA of NZ (Fig. 6) thermogram is characterized by one single slope with continuous but smooth weight loss which is typical of the spectra recorded for zeolites [28,48]. The initial weight loss occurring around 100 C is attributed to loss of water physically adsorbed which approximately accounts for wt. loss of 2.5% that is line with the moisture obtained in physical characterization studies (Table 1). This is followed by further incremental decrease up to 500 C associated with loss of matrix bound water [28]. The total weight loss is approximately 8.9%. As temperature raises, breakdown of hydroxyl ion increases
but in overall the de-hydroxylation process of zeolite is slow and occurs in temperature range of 500e800 C [45]. The weight loss of NZ occurred till 981.86 C accounting for 85.32% residue. The different Si/Al ratio of zeolite were found responsible for the thermal stability of zeolite; in general the zeolites with ratio up to 6 shows more stability than zeolites with lower ratio [46]. This trend of NZ thermal degradation when compared with ZNC thermogram (Fig. 7) is observed to be nearly same except that small incremental steps can be seen owing to dehydration resulting from weight loss of physically bound water (124.97 C; Wt. loss 4.56%), matrix bound
Fig. 7. TGA (black line) and DSC (blue line) spectra of ZNC showing incremental weight loss. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)
A. Lateef et al. / Microporous and Mesoporous Materials 232 (2016) 174e183
WR of Soil WR of Soil+ZNC
100
80
WR (%)
60
40
20
181
water (482.16 C; Wt. loss 6.38%) and oxidation of metallic species accompanied by decomposition of nitrates, sulphates and phosphates resulting in evolution of gaseous moieties (Residue 82.07% at 919.62 C) [49]. This kind of almost linear behavior is consistent with earlier studies [45]. Overall both the samples showed high stability. The results of residue obtained in both the cases are in accordance with loss on ignition and ash content studies performed earlier. DSC curves of NZ and ZNC are given in Figs. 6 and 7 which are characterized by having dehydroxlation endotherms in range of 50e600 C with first low temperature peaks appearing around 100 C in both samples and other shallow peak appeared with minima at 596.30 C corresponding to △H ¼ 87.83 J/g for NZ. In case of ZNC another high temperature board endothermic peak with minima at 920 C with high △H ¼ 825.21 J/g value which probably accounts for decomposition of non-metallic moieties.
0 0
5
10
15
20
25
30
3.3. Salt index (SI)
No. of Days Fig. 8. Water retention capacity of soil without ZNC and with ZNC.
SI is also calculated to assess the probable potential of prepared fertilizer to cause plant injury; higher the potential larger the
2þ/3þ Fig. 9. Slow release pattern of percentage release of nutrients (NO1 , Zn2þ, Ca2þ and Mg2þ) in tap water for seven days studies. 3 , P2O5, K2O, Na2O, Fe
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3.5. Water retention (WR)
damage caused to plant leading to less crop yield. The acceptable range for SI is terms of electrical conductivity should be less than 2 mmhos/cc which in case for ZNC comes around 0.5 mmhos/cc [50]. The SI expressed in terms of ratio to NaNO3 (taken as 100), conductivity comes out to be very low for both the NZ and ZNC, when compared with urea which has very high SI value. The low value shows that the prepared fertilizer is safe for plant use and is also suitable for the seed row placement in agriculture, hence can result in high yield crops as well [51].
WR, another significant property for SRF, is essential for agriculture in arid and desert areas for saving water to improve plants’ health [54]. Fig. 8 presents water holding capacity of ZNC mixed with soil and soil without ZNC as control. The soil mixed with ZNC has water retention capacity of 94.04 and 69.14% on 3rd and 20th day while soil without ZNC has 75.01 and 55.5%, respectively. The rate of water retained in case of soil alone is approx. 18% less than that of soil þ ZNC indicating ZNC has higher water holding capacity which is in accordance with the absorbency studies. This retained water helps in enhancing water availability, making it available to soil and consequently to plants as per requirement [11].
3.4. Water absorbance (WA), swelling ratio (SR) and equilibrium water content (EWC) WA [52], SR [53], EWC [29] are essential features for the SRF. The results of experiment for NZ and ZNC for all these three parameters are 49, 63%; 3.28, 3.53 g/g and 76.63, 77.92%, respectively. Small increase in all the three parameters was observed in case of ZNC as compared to NZ. Zeolite, in general, has high porosity due to which it can hold water more than half of its weight. Water can penetrate into porous structure of ZNC and provides moisture to plants in dry areas to improve yield [44]. In addition to that presence of water also enhances the slow release of nutrients to the crops [52].
P2O5 0.7
3.6. Slow release studies These studies were conducted both in tap water (Fig. 9) and in soil (Fig. 10) separately to check the impact of these two on the slow release pattern. In both the cases, the studies were conducted in triplicates and the data is presented as average of percentage of nutrient released out of total available nutrients present in ZNC (Fig. 4). The results hence obtained helps in getting know-how
Na2O
K2O
Zn 0.05
0.10
0.20
2+
0.19 0.18 0.6
0.09
0.17 0.16
0.04
0.08
0.15
0.5
0.14
0.07
Amount released (%)
0.13 0.03
0.12
0.4
0.06
0.11 0.10 0.3
0.05
0.09
0.02
0.08 0.04
0.07 0.2
0.06 0.03
0.05
0.01 0.04
0.1
0.02
0.03 0.02 0.01 0
2
4
6
8
10
12
14
16
0.01 0
2
4
No. of Days
6
8
10
12
14
16
0
2
4
15
Ca
6
8
10
12
14
16
0
2
4
No. of Days
No. of Days Mg
2+
8
10
12
14
1-
16
Fe
NO3
0.040
2+
6
No. of Days 2+/3+
0.6
50 0.035
0.5 40
0.030
10
0.4
Amount released (%)
0.025 30
0.3
0.020 20 0.015
0.2
5
10
0.010
0.1
0.005
0
0.0
0 0
2
4
6
8
No. of Days
10
12
14
16
0
2
4
6
8
No. of Days
10
12
14
16
0
2
4
6
8
No. of Days
10
12
14
16
0
2
4
6
8
10
No. of Days
2þ/3þ Fig. 10. Slow release pattern of percentage release of nutrients (NO1 , Zn2þ, Ca2þ and Mg2þ) in soil for 14 days studies. 3 , P2O5, K2O, Na2O, Fe
12
14
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about the exact release of specific nutrients present in the fertilizer and also their availability to the plant on daily basis. These kind of studies are an acceptable approach for selecting the suitability of fertilizer to a crop as reported in literature [18,55]. 7-day release studies performed in pre-analyzed tap water (Table 1) shows a set 2þ/3þ pattern for release of nutrients i.e. NO1 3 , P2O5, K2O, Na2O, Fe and Mg2þ (Fig. 9) i.e. initially the release is little faster which decreases with the time period except for magnesium and nitrate. In case of magnesium gradual decrease in percentage of release was observed with increase in time while for nitrate the incremental increase with increase in time is noticed. 14 days nutrient release studies carried out in case of soil (Fig. 10) exhibited the same trend as was observed in case of tap water except that the concentration of nutrients released is little higher than that in water. The results obtained are well in accordance with previous studies carried out and the trend observed favors continues supply of nutrients to plants thereby preventing leaching loses that are commonly observed with tradition fertilizers [55]. In addition to that availability of high nutrient content in start also supports early seed sprouting and germination of plant which facilitates the growth of healthy plant. After the initial high dose to the plant, continues release supplied by ZNC helps in early flowering and fruiting leading to high yield crops. The release of nutrients from the fertilizer having porous structure depends upon the pore size and difference in chemical composition of nutrients [35]. 4. Conclusion The study is based on synthesis on zeolite based nanocomposite material as a potential environmental friendly slowrelease fertilizer having average particle size of 6.05 nm. The porous structure of nano-zeolite was effectively utilized to incorporate essential macro and micronutrients that are released slowly to the plant depending upon their affinity to the zeolite. The synthesized materials were characterized using physical parameters, powder XRD, FT-IR, AFM, SEM/EDX, TGA and DSC to get insight into the properties, morphology and structure. Water absorbance, swelling ratio, equilibrium water content, salt index and water retention studies showed good water holding capacity that can enhance soil condition without imparting negative impacts. Further the slow release studies confirm the gradual supply of nutrients to the plants over a large period of time that helps in reducing leaching impacts of the traditional fertilizers. Acknowledgment The financial support of PCSIR Labs Complex, Lahore, Pakistan and Higher Education Commission (HEC), Pakistan under Indigenous PhD Fellowship for 5000 Scholars, Phase - ll is greatly acknowledged for this study. References [1] R. Liu, R. Lal, Sci Total Environ 514 (2015) 131e139. [2] M.E. Trenkel, International Fertilizer Industry Association, 2010. n, M.G. Martin, J.G. Herna ndez, J Control Release 34 [3] J.N. del Pino, I.A. Padro (1995) 25e29. [4] E. Rodriguez, R. Sultan, A. Hilliker, Ef Agric Trap 3 (2004) 28e32. [5] V. Rai, S. Acharya, N. Dey, Implications of nanobiosensors in agriculture, J Biomater Nanobiotech 3 (2012) 315. [6] S. Mura, G. Seddaiu, F. Bacchini, P.P. Roggero, G.F. Greppi, Ital J Agron 8 (2013) 18. [7] S. Baruah, J. Dutta, Env Chem Lett 7 (2009) 191e204. [8] M. Naderi, A. Danesh-Shahraki, Int J Agric Crop Sci 5 (2013) 2229e2232.
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