In Situ Fabrication of Magnetic Iron Oxide over Nano-hydroxyapatite

Article pubs.acs.org/jced

In Situ Fabrication of Magnetic Iron Oxide over Nano-hydroxyapatite Gelatin Eco-polymeric Composite for Defluoridation Studies Kalimuthu Pandi and Natrayasamy Viswanathan* Department of Chemistry, Anna University, University College of Engineering-Dindigul, Reddiyarchatram, Dindigul-624 622, Tamil Nadu, India ABSTRACT: This research work deals with the defluoridation studies of magnetic iron oxide (Fe3O4) fabricated nano-hydroxyapatite (n-HAp) gelatin (Gel) eco-polymeric composite. The developed hybrid Fe3O4@n-HApGel composite displays a high defluoridation capacity (DC) of 5009 mgF−·kg−1. Batch sorption experiments were performed to find the effect of various influencing parameters such as pH, contact time, competitor co-anions, initial fluoride concentration, and temperature. The structural, surface morphological changes, and elements present in the sorbent were studied using FTIR, XRD, and SEM with EDAX techniques. The equilibrium isotherm study was fitted with Langmuir isotherm model. The thermodynamic parameter values indicate the spontaneous and endothermic nature of fluoride sorption. The proposed mechanism indicates that the enhanced DC of magnetic composite is mainly due to electrostatic adsorption and complexation between fluoride ion and composite in addition to ion-exchange. The regeneration and reusability studies were performed for the effective utilization of the magnetic composite. The performance of Fe3O4@n-HApGel nanocomposite at field conditions was checked with the water sample collected from a nearby fluoride prevalent area.

1. INTRODUCTION The excessive ingestion of fluoride for a long period leads to fluorosis. World Health Organization (WHO) has authorized that the highest acceptable limit of fluoride content in drinking water is 1.5 mg·L−1.1 The main source of fluoride in groundwater is basically from the rocks and minerals, or it can appear as a toxic waste from industries. In India, the states such as Rajasthan, Gujarat, Tamil Nadu, Andhra Pradesh, Madhya Pradesh, Bihar, Punjab, and Uttar Pradesh are identified as high fluoride endemic areas due to the high amount of fluoride in groundwater because of mineral bearing metamorphic rocks.2 Since fluorosis is an incurable and irreversible disease, prevention is the best option to control fluorosis. One such preventive measure is defluoridation. Various defluoridation technologies such as precipitation, ionexchange process, electrodialysis, electrocoagulation, membrane separation, and adsorption have been adopted.3−8 Among the reported techniques, adsorption seems to be a useful technique because of its easy handling, selectivity, and cost-effectiveness. The searches for the new adsorption technologies involving the removal of toxic ions from water/wastewater have paid more attention to biosorption technique. In biosorption, the biological materials have the ability to accumulate the toxic ions from water/wastewater through metabolically interceded or physicochemical pathways. Chitin, chitosan, cellulose, alginate, and gelatin, etc., have been utilized for toxic ions removal.9−13 Gelatin is a biocompatible, biodegradable, and inexpensive biomaterial. In gelatin, there are numerous chemical groups such as amine, carboxyl, and carboxyl groups possess strong attraction toward toxic ions. However, gelatin exhibits poor mechanical strength, easy gel formation, and low specific © XXXX American Chemical Society

gravity, which limit its applications. A noticeable improvement in the mechanical properties of gelatin has been obtained in the form of polymeric composites.14−16 The enhanced surface area and high mechanical strength of the gelatin nanocomposite was utilized for toxic ion removal. The nanocomposite possesses a unique property for the separation of toxic ions from aqueous medium, but, because of its nanoscale, the separation and recycling is a challenge to modern industry. The magnetic adsorbents can keep away from such industrial bottlenecks through magnetic separation, and the adsorption process does not require a centrifuge or filter for the separation of adsorbents. Recently, magnetic nanoparticles have been synthesized in the presence of polymeric gels. The polymer gels having numerous advantages, viz., the nucleation and growth of iron oxide, can be controlled by the network of the polymer.17 Synthesis of magnetic polymeric materials has increased in recent years due to cost-effectiveness, environmentally friendliness, and easy separation of composite from aqueous medium. The synthesized magnetic polymeric materials were subjected to the removal of heavy metals, toxic anions, and dyes.18−25 The objective of this research study is to prepare magnetic iron oxide fabricated nano-hydroxyapatite gelatin eco-polymeric composite for defluoridation studies. The batch sorption experiments were carried out by varying the contact time, solution pH, coexisting anions, initial fluoride concentration, and temperature on fluoride removal. A comparative study was Received: August 28, 2015 Accepted: December 11, 2015

A

DOI: 10.1021/acs.jced.5b00727 J. Chem. Eng. Data XXXX, XXX, XXX−XXX

Journal of Chemical & Engineering Data

Article

2.4. Analytical Methods. The concentration of fluoride was measured using a Thermo Orion Benchtop multiparameter kit (Model: VERSA STAR92) using fluoride ion selective electrode having the relative accuracy of ±1 significant digit, detection limit of 0.02 mg·L−1, and the reproducibility of ±2%. The pH measurements were carried out with the same instrument using a pH electrode. All other water quality parameters were investigated using standard methods.27 2.5. Instrumentation Studies. The FTIR spectra of the composites were recorded using a JASCO-460 plus spectrometer operated at 1 cm−1 resolution in the range of 400−4000 cm−1 using KBr pellets. X-ray diffraction (XRD) measurement was obtained using X’pert PRO model instrument (PANalytical) to evaluate the crystalline phases present in the composite. The surface morphology of the composites was imagined by scanning electron microscopy (SEM) with the Vega3 Tescan model. The SEM images indicate the direct observation of the surface microstructures of the fresh and fluoride sorbed composites. The energy dispersive X-ray analyzer (EDAX) of the composites was determined using a Bruker Nano GMBH model. The pH at zero point of charge (pHzpc) of the composite materials was measured using the pH drift method.28 2.6. Statistical Tools. The computations of the obtained experimental results were carried out using Microcal Origin (Version 8.0) software. The best model and goodness of the fit were found out using the regression correlation coefficient (r), standard deviation (sd), and chi-square (χ2) analysis.

carried out for Fe3O4, Fe3O4@n-HAp composite, n-HApGel composite, and Fe3O4@n-HApGel composite to evaluate the fluoride removal capacity. The experimental results were fitted with isotherms and thermodynamic parameters. The effective utilization of the magnetic composite at field conditions was also tested by collecting the field fluoride water sample in a nearby fluoride rife area in Dindigul district of Tamilnadu.

2. EXPERIMENTAL SECTION 2.1. Materials. Gelatin was purchased from Central Drug House (New Delhi, India). Ferrous chloride tetrahydrate, ferric chloride hexahydrate, ammonium dihydrogen phosphate, calcium nitrate tetrahydrate, 25% ammonia solution, and sodium fluoride were purchased from Merck (Mumbai, India) with analytical grade and used without further purification. 2.2. In Situ Fabrication of Magnetic Fe3O4 on nHApGel Biocomposite. The magnetic Fe3O4@n-HApGel composite was prepared according to our previous report.26 About 2 g of gelatin was dissolved in 100 mL of double distilled water at 313 K and continuously stirred for 2 h. Then 20 mL of 1 M (NH4)2PO4 solution was added dropwise into the gelatin polymer solution for 15 min and stirred for 1 h at 313 K. The medium was adjusted to pH 10 using 25% ammonia solution. Thereafter, 20 mL of 1.67 M of Ca(NO3)2 solution was added to the preceding mixture over 20 min at the same temperature and then stirred for 2 h. Then a mixture of 10 mL of FeCl2· 4H2O (1.85 mmol) and FeCl3·6H2O (3.7 mmol) solution was slowly added into the aforementioned n-HApGel medium over 10 min; during addition the medium was maintained at pH 10. The formed magnetic Fe3O4@n-HApGel biocomposite was aged for 24 h in mother liquor and then filtered, washed with plenty amounts of distilled water to neutral pH, and dried at 353 K for 24 h in a hot air oven. The dried Fe3O4@n-HApGel composite was crushed to fine powder using a ball mill (IKA, Staufen, Germany). The fine powered composite was sieved to get uniform size for defluoridation studies. The synthesis of gelatin encapsulated nano-hydroxyaptite (n-HApGel) composite and magnetic Fe3O4@n-HAp composite was synthesized according to our previous reports.16,26 All of the synthesized composites were used for defluoridation studies. 2.3. Batch Defluoridation Experiments. The defluoridation studies were carried out in batch mode to investigate the effect of contact time, solution pH, competitive anions, initial fluoride concentration, and temperature. The adsorption studies were carried out by equilibrating 0.1 g of the magnetic composite with 50 mL of 10 mg·L −1 initial fluoride concentration solution at neutral pH. In a thermostat shaker, these contents were shaken with a constant speed of 200 rpm at 303 K. The magnetic composite was removed by external magnet, and then fluoride concentration was measured. The solution 0.1 M HCl/NaOH was used for pH adjustment. In the sorption isotherm experiments, the initial fluoride concentrations were varied from 8, 10, 12, and 14 mg·L−1 at three various temperatures, viz., 303, 313, and 323 K. The magnetic composite was separated by external magnet, and the fluoride concentration was measured. The defluoridation capacity (DC) can be calculated by C − Ce V × 1000 mgF· kg −1 DC = i m where Ci is the initial fluoride concentration (mg·L−1), Ce is the equilibrium fluoride concentration (mg·L−1), m is the mass of the sorbent (g), and V is the volume of the solution (L).

3. RESULTS AND DISCUSSION 3.1. Effect of Contact Time. To find the minimum contact time for the maximum DC of the materials, the experiments

Figure 1. Effect of contact time on the DCs of Fe3O4, Fe3O4@n-HAp composite, n-HApGel composite, and Fe3O4@n-HApGel composite in the presence of 0.1 g dosage, 10 mg·L−1 initial fluoride concentration with neutral pH at 303 K.

were carried out in the time range of 10−70 min with 10 mg· L−1 initial fluoride concentration and 0.1 g of adsorbent dosage with neutral pH at 303 K. The results showed that the DCs of Fe3O4@n-HApGel composite, n-HApGel composite, Fe3O4@ n-HAp composite, and Fe3O4 were found to be 5009, 4157, 2469, and 1050 mgF−·kg−1, and they have attained equilibrium within 20, 40, 30, and 60 min, respectively, which is shown in Figure 1. Among the sorbents, composites possess higher DC when compare to Fe3O4. Therefore, further studies were limited to the composites and then 20, 30, and 40 min of B



Article

Figure 5. XRD spectrum of fluoride sorbed Fe3O4@n-HApGel composite.

Figure 2. Effect of solution pH on the DCs of Fe3O4@n-HAp, nHApGel, and Fe3O4@n-HApGel composites with optimized contact time in the presence of 0.1 g dosage and 10 mg·L−1 initial fluoride concentration at 303 K.

5, 7, 9, and 11. Figure 2 demonstrates that the adsorption capacities of the composites were significantly affected by the solution pH. The outcome also reveals that the maximum DC was taking place at pH 3, and the DC diminished drastically while the pH was increased from pH 3 to 11. The pHzpc of nHApGel and Fe3O4@ n-HApGel composites were found to be 7.03 and 7.01 respectively. When the solution pH was below pHzpc, the fluoride ions were moved toward the positively charged surface of the composites, formed by the protonation of the hydroxyapatite hydroxyl groups, thus favoring fluoride adsorption onto the surface results in the increase in DC of the composites. At pH above the pHzpc value, the fluoride adsorption was very low because the composite surfaces were negatively charged, due to deprotonation of the hydroxyapatite hydroxyl groups, causing a mutual repulsion between fluoride ions and the composites surface.29 The final pH of the treated solution was found to be neutral in all of the composites. 3.3. Competitive Sorption of Fluoride on Composites. Some of the other common anions such as Cl−, NO3−, SO42−, and HCO3− ions might exist in drinking water in addition to fluoride, and they may battle with fluoride for the existing active sites of the composite during sorption. To estimate the DC of Fe3O4@n-HAp, n-HApGel, and Fe3O4@n-HApGel composites in the presence of other anions, 10 mg·L−1 initial fluoride solutions were transferred individually into 200 mg·L−1 initial concentrations of Cl−, NO3−, SO42−, and HCO3− ions. The influence of the different competitive anions on fluoride uptake of the composites at pH 7 is demonstrated in Figure 3. It was observed that all of the anions interfered a little with the fluoride sorption onto the composites, but bicarbonate caused momentous effect on the DC of the composites. The decline in the DC of the composites in the presence of HCO3− ion is mainly due to the increase in solution pH which diminishes the active sites for fluoride sorption. Among the composites, Fe3O4@n-HApGel composite possesses an enhanced DC compared to those of n-HApGel and Fe 3 O 4 @n-HAp composites. Hence, further studies were restricted to Fe3O4@ n-HApGel composite. 3.4. Characterization of the Magnetic Composite. The FTIR spectra of Fe3O4, Fe3O4@n-HApGel composite, and fluoride sorbed Fe3O4@n-HApGel composite are shown in Figure 4. As shown in figure, Fe3O4@n-HApGel and the fluoride sorbed Fe3O4@ n-HApGel composite possess common bands at 1461, 2926, and 3424 cm−1 which are due to the C−H bending, C−H stretching, and hydrogen bonded O−H

Figure 3. Effect of co-anions on the DCs of Fe3O4@n-HAp, nHApGel, and Fe3O4@n-HApGel composites in the presence of 0.1 g dosage, 200 mg·L−1 other anions concentration, 10 mg·L−1 initial fluoride concentration, and neutral pH with optimized contact time at 303 K.

Figure 4. FTIR spectra of (a) Fe3O4, (b) Fe3O4@n-HApGel composite, and (c) fluoride sorbed Fe3O4@n-HApGel composite.

equilibrium contact time were fixed for Fe3O4@n-HApGel, Fe3O4@n-HAp, and n-HApGel composites, respectively. 3.2. Influence of Solution pH on DCs of the Composites. The effect of solution pH was investigated for the composites such as Fe3O4@n-HAp, n-HApGel, and Fe3O4@n-HApGel at different various initial values of pH 3, C



Article

Figure 6. SEM micrographs of (a) Fe3O4@n-HApGel composite and (b) fluoride treated Fe3O4@n-HApGel composite and EDAX spectra of (c) Fe3O4@n-HApGel composite and (d) fluoride treated Fe3O4@n-HApGel composite.

Table 1. Freundlich, Langmuir, and Dubinin−Radushkevich Isotherm Parameters of Fe3O4@n-HApGel Composite temperature isotherms Freundlich

Langmuir

Dubinin−Radushkevich (D−R)

parameters

303 K

313 K

323 K

1/n n kF (mg·g−1) (L·mg−1)1/n r sd χ2 Qo (mg·g−1) b (L·g−1) RL r sd χ2 Xm (mg·g−1) E (kJ·mol−1) r sd χ2

0.264 4.679 3.467 0.987 0.024 0.101 3.873 1.257 0.237 0.997 0.012 0.013 3.468 8.344 0.994 0.060 0.024

0.289 5.035 3.761 0.990 0.018 0.072 4.155 1.965 0.451 0.999 0.009 0.010 4.617 8.516 0.992 0.049 0.035

0.342 5.475 4.279 0.990 0.009 0.155 6.415 2.442 0.571 0.998 0.016 0.006 4.897 8.699 0.996 0.051 0.019

1040, 960, 600, and 565 cm−1 indicating the formation of pure hydroxyapatite in the synthesized magnetic composite.30 The characteristic peak of Fe−O in Fe3O4 was observed at 590 cm−1.31 The Fe−O bond is present in the synthesized magnetic composite which signifies that the magnetic Fe3O4 was fabricated over n-HApGel composite. The band at 3424 cm−1 is recognized as the O−H stretching mode, caused by the hydroxyl groups in the synthesized composite. The decrease in the intensity of the band at 3424 cm−1 in the fluoride sorbed Fe3O4@n-HApGel composite was due to the exchangeable

Table 2. Thermodynamic Parameters of Fe3O4@n-HApGel Composite thermodynamic parameters −1

ΔG° (kJ·mol )

ΔH° (kJ·mol−1) ΔS° (J·mol−1·K−1)

temperature (K) 303 313 323

−5.97 −5.26 −4.71 8.49 39.00

stretching vibration of gelatin, respectively. The typical hydroxyapatite phosphate vibration bands appear at 1090, D



Article

Figure 7. Feasible defluoridation mechanism of Fe3O4@n-HApGel composite.

SEM analyses were performed to investigate the surface morphology details of before and after fluoride treated Fe3O4@ n-HApGel composite. The SEM micrographs of Fe3O4@nHApGel and fluoride sorbed Fe3O4@n-HApGel composite are shown in Figure 6a,b, respectively. It is observed that the nanocrystals of n-HAp and Fe3O4 are homogeneously dispersed in the gelatin polymeric matrix. Due to the enormous presence of hydroxyl groups in n-HAp and gelatin, hydrogen bonds may be formed between gelatin and n-HAp, which makes the combination of gelatin and n-HAp in a perfect manner. The SEM images of Fe3O4@n-HApGel composite before and after fluoride treatment show that the surface changes occurred in the sorbent. This is auxiliary supported by EDAX analysis, which reveals that Fe3O4@n-HApGel composite was composed of C, N, O, Ca, P, and Fe peaks (cf. Figure 6c) and the fluoride sorbed Fe3O4@n-HApGel composite possesses C, N, O, Ca, P, Fe, and F peaks, which confirms the adsorption of fluoride onto Fe3O4@n-HApGel composite (cf. Figure 6d). 3.5. Sorption Isotherms. To quantify the defluoridation capacity of Fe3O4@n-HApGel composite, three important isotherms, viz., Freundlich,36 Langmuir,37 and Dubinin− Radushkevich (D−R)38 have been adopted. The linear plot of log qe vs log Ce signifies the applicability of Freundlich isotherm. The obtained 1/n, n, and kF values are presented in Table 1. The n values lie between 1 and 10, and 1/ n values lie between 0 and 1 corresponding to the favorable conditions for fluoride sorption. A linear plot of Langmuir isotherm is acquired for the magnetic composite when Ce/qe is plotted against Ce which gives b and Qo values from intercept and slope, respectively. The calculated values of Qo and b are listed in Table 1. The RL values lie in the range between 0 and 1 indicating the favorable sorption. The linear plot of ln qe vs ε2 indicates the applicability of D−R isotherm. The values of KDR, Xm, and E are shown in Table 1. The E value range from 1.0 to 8.0 kJ·mol−1 indicating physical sorption and from 9.0 to 16.0 kJ·mol−1 for chemical sorption. The obtained E values are 9.576, 10.234, and 10.771 kJ·mol−1 for 303, 313, and 323 K, respectively, which indicates the defluoridation mechanism of Fe3O4@n-HApGel composite is purely chemical in nature. The higher r values and the lower sd values designate the suitable isotherm. The best isotherm fit was identified using low χ2 values. The calculated χ2 values are presented in Table 1. The best isotherm

Figure 8. Regeneration and reusability studies of the magnetic composite.

Table 3. Field Trial Results of Fe3O4@n-HApGel Composite water quality parameters

before treatment

after treatment

F− (mg·L−1) pH Cl− (mg·L−1) SO42− (mg·L−1) NO3− (mg·L−1) HCO3− (mg·L−1) total hardness (mg·L−1) total dissolved solids (mg·L−1)

3.73 8.27 348 298 39 137 432 913

1.31 8.11 276 255 31 103 404 857

hydroxyl ion present in the composite being replaced by the fluoride ion. The XRD patterns of fluoride sorbed magnetic Fe3O4@nHApGel nanocomposite are presented in Figure 5. The sharp peaks that appeared in the fluoride sorbed Fe3O4@n-HApGel nanocomposite at 2θ = 30.1°, 35.4°, 43.1°, 53.4°, and 62.5° values were due to Fe3O4, and the values of 2θ at 25.9°, 32°, and 39.8° corresponded to the XRD peak of n-HAp.32,33 The fluoride sorption on Fe 3O4@n-HApGel composite was confirmed by the calcium fluoride (CaF2) peaks that appeared at 2θ = 28.2°, 47.2°, 55.86°, and 68.76° and iron fluoride (FeF3) peaks that emerged at 23.8°, 34.4°, 41.0°, 53.2°, 65.0°, 70.3°, and 72.7°.34,35 E



Article

Table 4. Comparative Review of Fluoride Adsorption Capacity of Fe3O4@n-HApGel Composite serial no.

name of the adsorbent

adsorption capacity (mg·g−1)

ref

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17

Fe3O4@n-HApGel composite magnetic corn stover biochar zirconium-impregnated cellulose Fe/Zr-alginate microparticles magnetic nano-hydroxyapatite chitosan composite La3+ incorporated silica gel chitosan composite activated alumina 10% La-bentonite clay Fe−Al−Ce nanoadsorbent activated alumina doped cellulose acetate phthalate activated titanium rich bauxite iron oxide−hydroxide nanoparticles Fe3O4@n-HAp composite nano-hydroxyapatite gelatin composite Fe−Al-impregnated granular ceramic alginate bioencapsulated nano-hydroxyapatite composite lanthanum(III) and zirconium(IV) mixed oxides beads

5.01 4.11 4.95 0.98 4.77 4.90 1.45 4.24 2.20 2.30 4.10 1.66 2.47 4.16 3.56 3.87 4.97

present study 40 41 42 43 12 44 45 46 47 48 49 26 16 50 51 52

as shown in Figure 8. In each cycle the fluoride removal efficiency decreased gradually, and after four cycles the fluoride removal reached a minimum, suggesting that the magnetic composite is regenerable and can be effectively used up to four cycles. 3.9. Removal of Fluoride from Field Water Sample. The possible application of Fe3O4@n-HApGel composite for defluoridation of drinking water was practiced using a bore well water sample collected in a fluoride prevalent area. About 50 mL of fluoride water sample and 0.1 g of magnetic sorbent were shaken with constant time at room temperature, and the results are demonstrated in Table 3. The observed concentration of fluoride in the field water sample is 3.73 mg·L−1 which is higher than the guideline value recommended by WHO (i.e., >1.5 mg· L−1). After treatment with Fe3O4@n-HApGel composite, the fluoride concentration is reduced below the tolerance limit in the field fluoride water (cf. Table 3). Even though the concentrations of other anions are higher than the fluoride concentration in field water, Fe3O4@n-HApGel composite removes fluoride selectively. It is interesting to note that the level of other water quality parameters was also reduced. Hence, Fe3O4@n-HApGel composite can be efficiently employed for defluoridation of water. 3.10. Comparative Studies Based on Adsorption Capacity. The fluoride sorption capacity of Fe3O4@n-HApGel composite was compared with other fluoride adsorbent materials which were previously reported in the literature and have been shown in Table 4. The magnetic composite has perceptible fluoride sorption capacity when compared to the other adsorbents. Another added advantage is it can be easily removed using an external magnetic field.

fit model follows the order Langmuir > D−R > Freundlich for fluoride sorption onto Fe3O4@n-HApGel composite. 3.6. Thermodynamic Studies. The thermodynamic parameters are interconnected with the adsorption process, viz., standard free energy change (ΔG°), standard entropy change (ΔS°), and standard enthalpy change (ΔH°), were calculated by Khan and Singh method,39 and the calculated values are shown in Table 2. From the results the negative value of ΔG° indicates the spontaneous nature of fluoride removal. The positive values of both ΔH° and ΔS° show the fluoride sorption is endothermic and randomness occurred at the magnetic composite-solution interface. 3.7. Mechanism of Fluoride Uptake on Fe3O4@nHApGel Composite. The defluoridation of Fe3O4@nHApGel composite was administered by both adsorption and ion-exchange mechanism as shown in Figure 7. The fluoride ions in the solution get exchanged for the OH− ions present in n-HAp lattice of Fe3O4@n-HAp, n-HApGel, and Fe3O4@nHApGel composites by ion-exchange mechanism. The presence of positively charged Ca2+ ions in Fe3O4@n-HAp, n-HApGel, and Fe3O4@n-HApGel composites have an attractive tendency toward the negatively charged fluoride ions by means of electrostatic adsorption. The enhanced DC was observed by Fe3O4@n-HApGel composite over Fe3O4@n-HAp and nHApGel composites. The main reason could be the positively charged Fe3+ ions present in Fe3O4@n-HApGel composite attracts fluoride by means of electrostatic adsorption and complexation mechanism. 3.8. Regeneration Studies of the Magnetic Composite. The fluoride exhausted magnetic composite was desorbed by using dilute NaOH solution as regenerant. About 0.1 g of the fluoride sorbed magnetic Fe3O4@n-HApGel composite was treated with dilute NaOH solution (50 mL) with different concentrations ranging from 0.02 to 0.1 M for 1 h. From Figure 8, the fluoride desorption was increased from 0.02 to 0.1 M and maximum desorption of 91.0% was achieved at 0.1 M NaOH concentration as eluent. After regeneration, the magnetic composite was separated using the external magnet, washed with double distilled water, and dried in an oven and a fresh fluoride solution was added before each run. The defluoridation efficiency of Fe3O4@n-HApGel composite was found to be 91.0, 87.2, 82.6, 71.6, and 50.9% respectively for five cycles and

4. CONCLUSIONS This research work summarizes the defluoridation performance of Fe3O4@n-HApGel composite. The DC of Fe3O4@nHApGel composite decreased drastically when the solution pH was raised from pH 3 to 11. Except for bicarbonate, the adsorption capacity of the composites was not influenced by the presence of other competing anions. The adsorption isotherm process was fitted well with Langmuir isotherm, better than with D−R and Freundlich models. Fe3O4@n-HApGel composite possesses a higher DC than those of Fe3O4@n-HAp F



Article

and n-HApGel composites because it removes fluoride by ionexchange, electrostatic adsorption, and complexation. The thermodynamic parameters’ values indicate the spontaneous and endothermic nature of fluoride removal. The regeneration studies of magnetic composite indicate its reusability. The field trial results of Fe3O4@n-HApGel composite demonstrate that it can be effectively employed for defluoridation and it paves the way for the development of defluoridation technology.

■

(15) Wei, W.; Sun, R.; Jin, Z.; Cui, J.; Wei, Z. Hydroxyapatite-gelatin nanocomposite as a novel adsorbent for nitrobenzene removal from aqueous solution. Appl. Surf. Sci. 2014, 292, 1020−1029. (16) Pandi, K.; Viswanathan, N. In situ precipitation of nanohydroxyapatite in gelatin polymatrix towards specific fluoride sorption. Int. J. Biol. Macromol. 2015, 74, 351−359. (17) Philippova, O.; Barabanova, A.; Molchanov, V.; Khokhlov, A. Magnetic polymer beads: Recent trends and developments in synthetic design and applications. Eur. Polym. J. 2011, 47, 542−559. (18) Wan, Z.; Chen, W.; Liu, C.; Liu, Y.; Dong, C. Preparation and characterization of γ-AlOOH@CS magnetic nanoparticle as a novel adsorbent for removing fluoride from drinking water. J. Colloid Interface Sci. 2015, 443, 115−124. (19) Yan, H.; Yang, L.; Yang, Z.; Yang, H.; Li, A.; Cheng, R. Preparation of chitosan/poly(acrylic acid) magnetic composite microspheres and applications in the removal of copper(II) ions from aqueous solutions. J. Hazard. Mater. 2012, 229−230, 371−380. (20) Chai, L.; Wang, Y.; Zhao, N.; Yang, W.; You, X. Sulfate-doped Fe3O4/Al2O3 nanoparticles as a novel adsorbent for fluoride removal from drinking water. Water Res. 2013, 47, 4040−4049. (21) Zhuang, F.; Tan, R.; Shen, W.; Zhang, X.; Xu, W.; Song, W. Magnetic strontium hydroxyapatite microspheres for the efficient removal of Pb(II) from acidic solutions. J. Chem. Eng. Data 2014, 59, 3873−3881. (22) Shi, J.; Li, H.; Lu, H.; Zhao, X. Use of carboxyl functional magnetite nanoparticles as potential sorbents for the removal of heavy metal ions from aqueous solution. J. Chem. Eng. Data 2015, 60, 2035− 2041. (23) Mohseni-Bandpi, A.; Kakavandi, B.; Kalantary, R. R.; Azari, A.; Keramati, A. Development of a novel magnetite−chitosan composite for the removal of fluoride from drinking water: adsorption modeling and optimization. RSC Adv. 2015, 5, 73279−73289. (24) Gopalakannan, V.; Viswanathan, N. Synthesis of magnetic alginate hybrid beads for efficient chromium (VI) removal. Int. J. Biol. Macromol. 2015, 72, 862−867. (25) Fan, L.; Luo, C.; Li, X.; Lu, F.; Qiu, H.; Sun, M. Fabrication of novel magnetic chitosan grafted with graphene oxide to enhance adsorption properties for methyl blue. J. Hazard. Mater. 2012, 215− 216, 272−279. (26) Pandi, K.; Viswanathan, N. Enhanced defluoridation and facile separation of magnetic nano-hydroxyapatite/alginate composite. Int. J. Biol. Macromol. 2015, 80, 341−349. (27) APHA. Standard methods for the examination of water and waste water; American Public Health Association: Washington, DC, USA, 2005. (28) Lopez-Ramon, M. V.; Stoeckli, F.; Moreno-Castilla, C.; Carrasco-Marin, F. On the characterization of acidic and basic surface sites on carbons by various techniques. Carbon 1999, 37, 1215−1221. (29) Medellin-Castillo, N. A.; Leyva-Ramos, R.; Ocampo-Perez, R.; Garcia de la Cruz, R. F.; Aragon-Pina, A.; Martinez-Rosales, J. M.; Guerrero-Coronado, R. M.; Fuentes-Rubio, L. Adsorption of fluoride from water solution on bone char. Ind. Eng. Chem. Res. 2007, 46, 9205−9212. (30) Poinern, G. E. J.; Ghosh, M. K.; Ng, Y.; Issa, T. B.; Anand, S.; Singh, P. Defluoridation behavior of nanostructured hydroxyapatite synthesized through an ultrasonic and microwave combined technique. J. Hazard. Mater. 2011, 185, 29−37. (31) Poursaberi, T.; Hassanisadi, M.; Torkestani, K.; Zare, M. Development of zirconium (IV)-metalloporphyrin grafted Fe3O4 nanoparticles for efficient fluoride removal. Chem. Eng. J. 2012, 189−190, 117−125. (32) Cheng, F.-Y.; Su, C.-H.; Yang, Y.-S.; Yeh, C.-S.; Tsai, C.-Y.; Wu, C.-L.; Wu, M.-T.; Shieh, D.-B. Characterization of aqueous dispersions of Fe3O4 nanoparticles and their biomedical applications. Biomaterials 2005, 26, 729−738. (33) Jie, W.; Yubao, L. Tissue engineering scaffold material of nanoapatite crystals and polyamide composite. Eur. Polym. J. 2004, 40, 509−515.

AUTHOR INFORMATION

Corresponding Author

*Tel.: +91-451-2554066. Fax: +91-451-2554066. E-mail: [email protected]. Funding

We are thankful to the Department of Science and Technology, Science and Engineering Research Board (Grant No. SR/FT/ CS-43/2011 dt. 24-05-2012), New Delhi, India for the provision of financial support to carry out this research study. K. Pandi thanks the Council of Scientific and Industrial Research (CSIR), New Delhi, India for awarding the Senior Research Fellowship. Notes

The authors declare no competing financial interest.

■

REFERENCES

(1) WHO Report. Fluoride and Fluorides, Environmental Health Criteria 36; World Health Organisation: Geneva, Switzerland, 1984. (2) Hussain, J.; Sharma, K. C.; Hussain, I. Fluoride in drinking water in Rajasthan and its ill effects on human health. J. Tissue Res. 2004, 4, 263−273. (3) Lu, N. C.; Liu, J. C. Removal of phosphate and fluoride from wastewater by a hybrid precipitation-microfiltration process. Sep. Purif. Technol. 2010, 74, 329−335. (4) Meenakshi, S.; Viswanathan, N. Identification of selective ionexchange resin for fluoride sorption. J. Colloid Interface Sci. 2007, 308, 438−450. (5) Adhikary, S. K.; Tipnis, U. K.; Harkare, W. P.; Govindan, K. P. Defluoridation during desalination of brackish water by electrodialysis. Desalination 1989, 71, 301−312. (6) Vasudevan, S.; Lakshmi, J.; Sozhan, G. Studies on Mg-Al-Zn alloy as an anode for the removal of fluoride from drinking water in an electrocoagulation process. Clean: Soil, Air, Water 2009, 37, 372−378. (7) Min, B. R.; Gill, A. L.; Gill, W. N. A note on fluoride removal by reverse osmosis. Desalination 1984, 49, 89−93. (8) Karthikeyan, G.; Siva Ilango, S. Fluoride sorption using morringa indica-based activated carbon. Iran. J. Enviorn. Health, Sci. Eng. 2007, 4, 21−28. (9) Kousalya, G. N.; Rajiv Gandhi, M.; Viswanathan, N.; Meenakshi, S. Preparation and metal uptake studies of modified forms of chitin. Int. J. Biol. Macromol. 2010, 47, 583−589. (10) Zhou, D.; Zhang, L.; Guo, S. Mechanisms of lead biosorption on cellulose/chitin Beads. Water Res. 2005, 39, 3755−3762. (11) Zhang, L.; Xia, W.; Teng, B.; Liu, X.; Zhang, W. Zirconium cross-linked chitosan composite: Preparation, characterization and application in adsorption of Cr(VI). Chem. Eng. J. 2013, 229, 1−8. (12) Viswanathan, N.; Pandi, K.; Meenakshi, S. Synthesis of metal ion entrapped silica gel/chitosan biocomposite for defluoridation studies. Int. J. Biol. Macromol. 2014, 70, 347−353. (13) Pandi, K.; Viswanathan, N. A novel metal coordination enabled in carboxylated alginic acid for effective fluoride removal. Carbohydr. Polym. 2015, 118, 242−249. (14) Venditti, F.; Cuomo, F.; Ceglie, A.; Ambrosone, L.; Lopez, F. Effects of sulfate ions and slightly acidic pH conditions on Cr(VI) adsorption onto silica gelatin composite. J. Hazard. Mater. 2010, 173, 552−557. G



Article

(34) Khunur, M. M.; Risdianto, A.; Mutrofin, S.; Prananto, Y. P. Synthesis of fluorite (CaF2) crystal from gypsum waste of phosphoric acid factory in silica gel. Bull. Chem. React. Eng. Catal. 2012, 7, 71−77. (35) Standard X-ray Diffraction Powder Patterns; National Bureau of Standards Monograph 25, Section 10; U.S. Department of Commerce, National Bureau of Standards: Washington, DC, USA, 1972. (36) Freundlich, H. M. F. Over the adsorption in solution. Z. Phys. Chem. 1906, 57, 385−470. (37) Langmuir, I. The constitution and fundamental properties of solids and liquids. J. Am. Chem. Soc. 1916, 38, 2221−2295. (38) Karahan, S.; Yurdakoc, M.; Seki, Y.; Yurdakoc, K. Removal of boron from aqueous solution by clays and modified clays. J. Colloid Interface Sci. 2006, 293, 36−42. (39) Khan, A. A.; Singh, R. P. Adsorption thermodynamics of carbofuran on Sn(IV) arsenosilicate in H+, Na+ and Ca2+ forms. Colloids Surf. 1987, 24, 33−42. (40) Mohan, D.; Kumar, S.; Srivastava, A. Fluoride removal from ground water using magnetic and nonmagnetic corn stover biochars. Ecol. Eng. 2014, 73, 798−808. (41) Wang, J.; Lin, X.; Luo, X.; Long, Y. A sorbent of carboxymethyl cellulose loaded with zirconium for the removal of fluoride from aqueous solution. Chem. Eng. J. 2014, 252, 415−422. (42) Swain, S. K.; Patnaik, T.; Patnaik, P. C.; Jha, U.; Dey, R. K. Development of new alginate entrapped Fe(III)-Zr(IV) binary mixed oxide for removal of fluoride from water bodies. Chem. Eng. J. 2013, 215−216, 763−771. (43) Pandi, K.; Viswanathan. Synthesis and applications of ecomagnetic nano-hydroxyapatite chitosan composite for enhanced fluoride sorption. Carbohydr. Polym. 2015, 134, 732−739. (44) Ghorai, S.; Pant, K. K. Investigations on the column performance of fluoride adsorption by activated alumina in a fixedbed. Chem. Eng. J. 2004, 98, 165−173. (45) Kamble, S. P.; Dixit, P.; Rayalu, S. S.; Labhsetwar, N. K. Defluoridation of drinking water using chemically modified bentonite clay. Desalination 2009, 249, 687−693. (46) Chen, L.; Wu, H. X.; Wang, T. J.; Jin, Y.; Zhang, Y.; Dou, X. M. Granulation of Fe-Al-Ce nano-adsorbent for fluoride removal from drinking water by spray coating on sand in a fluidized bed. Powder Technol. 2009, 193, 59−64. (47) Chatterjee, S.; De, S. Adsorptive removal of fluoride by activated alumina doped cellulose acetate phthalate (CAP) mixed matrix membrane. Sep. Purif. Technol. 2014, 125, 223−238. (48) Das, N.; Pattanaik, P.; Das, R. Defluoridation of drinking water using activated titanium rich bauxite. J. Colloid Interface Sci. 2005, 292, 1−10. (49) Raul, P. K.; Devi, R. R.; Umlong, I. M.; Banerjee, S.; Singh, L.; Purkait, M. Removal of fluoride from water using iron oxide-hydroxide nanoparticles. J. Nanosci. Nanotechnol. 2012, 12, 3922−3930. (50) Chen, N.; Feng, C.; Li, M. Fluoride removal on Fe-Alimpregnated granular ceramic adsorbent from aqueous solution. Clean Technol. Environ. Policy 2014, 16, 609−617. (51) Pandi, K.; Viswanathan, N. Synthesis of alginate bioencapsulated nano-hydroxyapatite composite for selective fluoride sorption. Carbohydr. Polym. 2014, 112, 662−667. (52) Muthu Prabhu, S.; Meenakshi, S. Enriched fluoride sorption using chitosan supported mixed metal oxides beads: Synthesis, characterization and mechanism. J. Water Process Eng. 2014, 2, 96− 104.

H


In Situ Fabrication of Magnetic Iron Oxide over Nano-hydroxyapatite

Recommend Documents