Effect of Organic Acid-Modified Mesoporous Alumina toward Fluoride

Article pubs.acs.org/jced

Effect of Organic Acid-Modified Mesoporous Alumina toward Fluoride Ions Removal from Water Sukanya Kundu,† Ipsita Hazra Chowdhury,† Prasanta Kumar Sinha,‡ and Milan Kanti Naskar*,† †

Sol−Gel Division, ‡Materials Characterization and Instrumentation Division, Council of Scientific and Industrial Research, Central Glass and Ceramic Research Institute, Kolkata, 700 032, India S Supporting Information *

ABSTRACT: Mesoporous alumina (MA) was prepared via the sol−gel process at 40 °C/48 h followed by calcinations at 550 °C/5 h, in the absence of organic acids and in the presence of malic, tartaric, and citric acids (sample IDs: A-550, AM-550, AT-550, and AC-550, respectively). For fluoride ion adsorption on MA, the effects of different parameters such as contact time, concentration of adsorbate (F− ions), pH, temperature, and competing ions were studied. The adsorption kinetics of fluoride ions followed the pseudo-second-order model. The prepared MA showed the maximum F− ions adsorption capacity of 47.2, 49, 51.2, and 62.5 mg g−1 for the samples A-550, AM-550, AT-550, and AC-550, respectively. The adsorption efficiency of MA followed the order AC-550 > AT-550 > AM-550 > A-550, corroborating to their BET surface area and pore volume. The competing anions (PO43−, Cl− and SO42−) have a slight effect of reducing the F− ions adsoption in the order of PO43− > SO42− > Cl−. For interpretation of adsorption isotherms, both Langmuir and Freundlich models were used. The F− ions adsorption efficiency remained almost the same up to 3 cycles of the regenerated MA.

1. INTRODUCTION Groundwater contamination by fluoride ions coming from industrial effluents1−3 is a vulnerable environment topic throughout the world. Higher concentration of fluoride can be poisonous to human beings causing dental and skeletal fluorosis, and even neurological damages.4−6 Fluoride is normally discharged into the groundwater by the slow weathering of fluorine containing rocks and minerals.7,8 The waste products from ceramic and glass industries, electroplating, coal-fired power stations, etc. can be the other sources of fluoride.9 The industrial effluents cause 10 to 1000 mg L−1 fluoride concentration in natural waters.10 The removal process of fluoride ion concentrations in drinking water exceeding the World Health Organization’s guideline of 0.5 mg L−1 is known as defluoridation. The methods developed for water defluoridation include precipitation,11 electrocoagulation or electroflotation,12 membrane separation,13 ion exchange,14 electrodialysis,15 adsorption,16 and reverse osmosis.17 Adsorption is the most effective method among the other methods for removal of fluoride from impure water due to low cost, simplicity of design and procedure, and environment friendly technology. Different adsorbents for example, activated carbon, Al2O3, biosorbents, clays, and composite materials have been demonstrated for the F− ions adsorption.18−22 For the removal of fluoride ions, an efficient, robust, and sustainable material is required as adsorbent. Nanomaterials have received great interest in recent years because of their exceptional physical and chemical properties different from their bulk counterparts. Mesoporous materials © XXXX American Chemical Society

(pore dimension 2−50 nm) due to their high surface-to-volume ratio, superior accessibility, and ability to attach different chemical functionalities on their surface are universally essential in different areas of modern science and technology in the fields of electronics, catalysis, energy, environment, etc.23 Different mesoporous materials such as mesoporous zirconium phosphate, mesoporous Ti oxohydroxide, ordered and disordered mesoporous aluminas, etc., have been used for the removal of fluoride ions from water.24−26 Among these materials, alumina is found to be most efficient adsorbent material for fluoride removal because of its high thermal stability, high surface area, and low solubility in a wide pH range.27 In the present work, we have prepared mesoporous alumina (MA) by a facile sol−gel process in the presence of various organic acids such as malic, tartaric, and citric acids. The synthesized products have been exploited for study of the adsorption efficiency of fluoride ions from water. Here, to the best of our knowledge, for the first time we report the function of different organic acids in tuning the textural properties of mesoporous alumina toward adsorption efficiency for the removal of the toxic ion fluoride from contaminated water. The role of different experimental parameters such as contact time, adsorbent dose, pH, temperature, and competing anions was investigated for removal of fluoride ions from water. Received: February 6, 2017 Accepted: June 1, 2017

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DOI: 10.1021/acs.jced.7b00129 J. Chem. Eng. Data XXXX, XXX, XXX−XXX

Journal of Chemical & Engineering Data

Article

concentrations of F− ions (stirring at room temperature for 3 h). The Langmuir model as given below was used to fit the adsorption data:

2. EXPERIMENTAL SECTION 2.1. Materials. Aluminum isopropoxide and P123 block copolymer each purchased from Sigma-Aldrich, ethyl alcohol, malic, tartaric, and citric acids each purchased from Merck, and sodium fluoride purchased from Rankem were used. Ultrapure water was used during the experiment. 2.2. Preparation of MA. A 3.2 g portion of P123 was dissolved in 20 mL of ethanol under stirring followed by the addition of 1.38 mL HCl, 3.8 mmol of each organic acid (malic acid, tartaric acid, and citric acid) and 3.26 g of aluminum isoproxide. The above mixture was kept under stirring condition for 24 h at room temperature. After the mixture was stirred, it was put to a Petri dish at 40 °C in an air oven for 48 h to evaporate the solvent. The dried as-prepared gel sample was heat-treated at 550 °C for 5 h with a slow heating rate of 1 °C/min. The same procedure was repeated in the absence of any organic acid. The synthesized samples were marked as A550, AM-550, AT-550, AC-550, for the samples prepared in the absence of organic acid and in the presence of malic, tartaric, and citric acids, respectively. 2.3. Characterization. To confirm the characteristic vibration bands of the product, Fourier transform infrared spectroscopy (FTIR; Spectrum two, PerkinElmer) was recorded in the range of 4000−400 cm−1 with KBr pellet, and the resolution was maintained at 4 cm−1. The nitrogen adsorption−desorption isotherms were measured by a Quantachrome (ASIQ MP) instrument at 77 K. Before measurement, the powders were kept in vacuum at 250 °C for 4 h for outgassing. The surface area of the material was measured using the Brunauer−Emmett−Teller (BET) method within the range of relative pressure (P/Po) of 0.05−0.20, and the Barrett−Joyner−Halenda (BJH) method was used to calculate the pore size distribution. Pore volume was determined from the amount of nitrogen adsorption at the relative pressure (P/Po) of 0.99. Transmission electron microscopy (TEM) was used to examine the morphology of the particles using a Tecnai G2 30ST (FEI) instrument, operated at 300 kV. 2.4. Fluoride Ion Adsorption Test. For fluoride ion adsorption on MA, the effects of different parameters such as contact time, concentration of adsorbate (F− ions), pH, temperature, and competing ions were studied. For kinetics study, various concentrations of F− ions were added to the aqueous solutions using sodium fluoride. The pH of the each solution was maintained at 7. To study the kinetics of adsorption, 5 mg of MA samples from different sources (A550, AM-550, AT-550, AC-550) was added into 10 mL of F− solutions (20 mg/L). After a certain time, the solid and liquid were separated instantly and the supernatants were examined by Electrod Multi-Parameter Meter (model HQ40d) to calculate fluoride ion concentration. Before the effect of pH was studied, the mass titration method, developed by Noh and Schwarz,28 was used to examine the point of zero charge (pHpzc) of MA. In this method, different amounts of MA samples (0.005 to 0.3 g) were added into 10 mL of 0.01 N NaCl solutions each and the mixtures were stirred for 24 h. Finally, the pH of the solutions was measured. The pH was plotted against the mass of the MA samples, and the final pH approached an asymptotic value with increasing mass of MA. The pHpzc was the asymptotic value of the final pH. To perform the adsorption isotherm study, 5 mg of adsorbent was added into 10 mL solutions of various

qe = qmbCe/(1 + KLCe)

(1)

where Ce is the fluoride ion concentration at equilibrium (mg/ L), qe is the fluoride ions adsorbed per gram of the adsorbent at equilibrium (mg/g), qm is the (adsorption capacity)max in mg/g, and KLis the adsorption constant (L/mg). Another form of Langmuir isotherm is expressed as Ce/qe = Ce/qm + 1/KL ·qm

(2)

A plot of Ce/qe vs Ce will provide a straight line having slope 1/ qm, and intercept 1/KL·qm. The nonuniform distribution of heat of adsorption over the heterogeneous surface is represented by the Freundlich isotherm which is shown by the following equation: log qe = log K F + 1/nF log C e

(3)

where KF and nF are the Freundlich constant (mg/g) and the heterogeneity factor, respectively. A straight line is obtained from the plot of log qe vs log Ce, where slope and intercept are 1/nF and log KF, respectively. A favorable adsorption condition is confirmed from the value, nF > 1.

3. RESULTS AND DISCUSSION 3.1. Characteristics of MA Particles. 3.1.1. FTIR Study. The FTIR spectra of (a) A-550, (b) AM-550, (c) AT-550, and (d) AC-550 prepared in the absence of organic acid and in the presence of malic, tartaric, and citric acids, respectively, are shown in Figure 1. The peaks at 3457 and 1628 cm−1 matched

Figure 1. FTIR spectra of the samples: (a) A-550, (b) AM-550, (c) AT-550, and (d) AC-550.

with the stretching and bending vibrations of −OH bonds, respectively. The peaks at 859, 599, 1428, and 1520 cm−1 could be due to the characteristic band of Al−O−Al.29 The broad band at 400−900 cm−1 and weak peaks at 1428 and 1520 cm−1 could be attributed to the stretching vibrations of Al−O and AlO bonds, respectively.30 3.1.2. TEM Studies. The TEM images of (a) A-550, (b) AM550, (c)AT-550 and (d) AC-550 prepared in the absence of organic acid and in the presence of malic, tartaric and citric acids, respectively are shown in Figure 2. The highly porous microstructures are observed for all the samples. It is interesting to notice that the pores are not uniform, and the nature of the pore structure is mainly channel type. However, no significant B



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Table 1. Textural Properties of MA Samples

a

sample

SBET (m2 g−1)a

Vp‑Total (cm3 g−1)b

DBJH (nm)c

A-550 AM-550 AT-550 AC-550

238 247 357 424

0.83 0.83 0.88 1.18

11.40 10.08 8.15 7.42

BET surface area. desorption.

b

Total pore volume. cPore diameter by BJH

textural properties of the samples were influenced by the organic acids. The organic acids contain carboxylic and hydroxyl groups. During calcination these carboxylic and hydroxyl groups released as CO2 and H2O, respectively, which generates pores in the matrix leading to higher surface area of the samples. Among these acids, citric acid is a tricarboxylic acid, and malic and tartaric acids are dicarboxylic acids. Because of the presence of the extra carboxylic group in citric acid, AC-550 exhibited the highest surface area and pore volume. Dicarboxylic acids malic acid and tartaric acid have one and two hydroxyl groups, respectively. The extra hydroxyl group in tartaric acid leads to the higher surface area and pore volume for the sample AT-550 than that for AM-550. It is worth noting that the pore sizes decreased with increase in carboxylic and hydroxyl groups of organic acids. The effect of organic acids is important in tuning the textural properties of the samples. 3.1.4. Formation Mechanism. Scheme 1 shows the formation mechanism of mesoporous alumina in the presence

Figure 2. TEM images of the samples: (a) A-550, (b) AM-550, (c)AT550 and (d) AC-550.

changes in pore structure could be obtained by changing the organic acids in MA. 3.1.3. Textural Properties. Figure 3 represents the nitrogen adsorption−desorption isotherms of (a) A-550, (b) AM-550,

Scheme 1. Schematic Representation for the Formation of Mesoporous Alumina in the Presence of Tri-blockcopolymer P123 and Different Organic Acids

Figure 3. Nitrogen adsorption−desorption isotherms of the samples: (a) A-550, (b) AM-550, (c) AT-550, and (d) AC-550. Insets show the corresponding pore size distributions.

(c) AT-550, and (d) AC-550 prepared in the absence of organic acid and in the presence of malic, tartaric, and citric acids, respectively. The corresponding pore size distributions are shown in the inset of Figure 3. According to the IUPAC classification all the curves display type IV isotherm. This indicates mesoporous characteristic of the samples. The uptake of nitrogen steeply increased above the relative pressure (P/Po) of about 0.65. The textural properties such as pore diameter, total pore volume, and BET surface area of (a) A-550, (b) AM550, (c) AT-550, and (d) AC-550 samples are shown in Table 1. A maximum BET surface area of 424 m2 g−1 and pore volume of 1.18 cm3 g−1 was obtained for the sample AC-550 prepared in the presence of citric acid. The surface area (BET) and pore volume of different MA samples followed the order as AC-550 > AT-550 > AM-550 > A-550. Interestingly, the

of block copolymer P123 and different organic acids. The aluminum isopropoxide under hydrolysis and polycondensation at lower pH renders alumina sol. The [−Al(OH)−O− Al(OH)−]n moieties of alumina sol interact with P123 molecules as well as organic acids via hydrogen bonding and/ or van der Waals interaction. Thus, a network structure of Al− O−Al bond formation occurs via hydrogen bonding and/or van der Waals interaction with both the P123 molecules and organic acids which act as templating agents for the formation of mesoporosity in the products. Under slow evaporation of the C



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solvent a dried gel is formed comprising an alumina matrix and self-assembled templating agents. After heat-treatment, the template molecules are removed leading to the formation of a mesoporous structure. 3.2. Fluoride Ion Adsorption Study. Fluoride ion is one of the toxic elements in drinking water. It is a serious issue for its effective elimination from drinking water. The adsorption capacity of the adsorbents (MA samples) for the removal of fluoride ions was investigated by changing contact time, adsorbate concentration, pH, temperature, and competing ions. The change in adsorption of fluoride ions (initial concentration of 10 mg L−1 at pH 7) with contact time at 30 °C for the samples: (a) A-550, (b) AM-550, (c) AT-550, and (d) AC-550 is represented in Figure 4. The initial availability of Figure 5. Change in qe with Ce (adsorption isotherms obtained with different initial concentrations of fluoride ions for the samples at pH 7 and 30 °C): (a) A-550, (b) AM-550, (c) AT-550, and (d) AC-550.

reported that the pHpzc of activated alumina ranged from 6.2 to 8.9.38 The influence of pH on the adsorption capacity is attributed to the electrostatic or Coulombic interactions involving the MA surface and F− ions in aqueous solution. According to the value of pHpzc, the surface of MA is slightly basic and forms an Al−OH bond. Since the pH of the solution decreases, that is, pH < pHpzc, the MA surface becomes positively charged, and hence F− ions are adsorbed on the MA surface according to the following reaction mechanism: Figure 4. Change in adsorption of fluoride ions with contact time at pH 7 and 30 °C: (a) A-550, (b) AM-550, (c) AT-550, and (d) AC550.

−1

≡AlOH 2+ + F− → ≡ AlOH 2+ ··· F−

(6) (7) −

The electrostatic attractions favoring the adsorption of F ions become higher when the pH is far lower than pHpzc. However, the adsorption of F− ions decreases as the pH approaches to pHpzc due to less abundance of positive charges on MA. It is understood that with increasing pH above pHpzc, that is, pH > pHpzc, the adsorption of F− ions on MA decreased because of electrostatic repulsion of F− ions from the surface of MA having negatively charged hydroxide ions. The fluoride and hydroxide ions take part in competition to bind on the adsorbent surface which results in lowering fluoride ion adsorption.39 Interestingly, at pH 11 the adsorption of F− ions on MA suddenly increased. This phenomenon cannot be explained in terms of force of chemisorption due to electrostatic interactions. At higher pH, the adsorption of F− ions could be governed by physisorption due to van der Waals type of forces. Ducker et al. reported that at high pH, the repulsive double-layer force is screened, and the F− ions could be trapped within the MA particles.40 Medellin-Castillo et al. reported that at higher pH electrostatic attraction could not cause the adsorption of F− ions, but the other interactive force becomes prominent for the adsorption of F− ions.36 Figure 6b shows the adsorption of fluoride ions with temperature. The increase in adsorption with temperature could be attributed to the increase in kinetic energy.41 For the removal of fluoride ions, Langmuir and Freundlich isotherms are used and are shown in Figures S3 and S4, respectively, for (a) A-550, (b) AM-550, (c) AT-550, and (d) AC-550 each. Table 3 shows their respective kinetic parameters. Because of a higher regression value, the Freundlich isotherm model is best fitted for fluoride ion adsorption. The

(4) −1

(5)

≡AlOH 2+ ··· F− → ≡ Al ··· F + H 2O

abundant active sites on the surface of the adsorbent leads to the adsorption of 50% of fluoride ions in 5 min for all the MA samples.31 It was noticed that after 180 min, the maximum F− ions adsorptions were 53%, 52.3%, 56.3%, and 55.9% for A-550, AM-550, AT-550, and AC-550, respectively. The kinetics of F− ions removal was investigated (Figure S1, Supporting Information) as a pseudo-second-order model: t /qt = 1/k 2qe 2 + (1/qe)t

≡AlOH + H+ → ≡ AlOH 2+

−1

where qe, qt (mg g ), and k2 (g mg min ) are the amounts of adsorbed F− ions at equilibrium and time t (min), and second-order rate constant, respectively. The values of qe, k2, and R2 (regression coefficient) are shown in Table S1. Close to unit values of R2 indicate the pseudo-second-order model in which the chemisorption is the rate-determining step.32 For fluoride ion adsorption having various concentrations, the experiment was performed at pH 7 (contact time 3 h at 30 °C). By plotting Ce vs qe (Figure 5), it is evident that the adsorption capacity of different MA samples followed as AC550 > AT-550 > AM-550 > A-550. It could be corroborated with their BET surface area and pore volume. With increase in surface area, more abundance of active surface is available rendering higher adsorption efficiency. This result is much better than previously reported data33−37 (Table 2). The effect of pH on fluoride ions adsorption at 30 °C is shown in Figure 6a. It is observed that for all the samples, the maximum F− ions adsorption took place at pH 3−4 followed by decreasing the F− ions adsorption up to pH 8. It was explained by determining the pHpzc of MA. The pHpzc of MA samples was found to be 7.5, 7.8, 7.7, and 7.4 for the samples A-550, AM550, AT-550, and AC-550, respectively (Figure S2). It is D



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Table 2. Maximum Adsorption Capacity, Kinetics Performance, and pH Range of Fluoride Ion Adsorption by the Synthesized MA Samples Compared with the Reported Samples maximum adsorption capacity (mg/g) at 25 °C

sample ID nano crystalline γ-alumina Al2O3/CNTs alum-impregnated activated alumina bone char aluminum impregnated chitosan A-550 AM-550 AT-550 AC-550

32 at pH = 4 (at 30 °C) 28.6 at pH = 6 40.6 at pH = 6.5 11.9 at pH = 3 1.73 at pH = 6.5 47.2 49.0 51.4 62.4

k

kinetic performance pseudo-second-order

0.02678 (g mg

first order pseudo-second-order

0.101 0.053 0.028 0.043 0.023

min−1 (g mg−1 (g mg−1 (g mg−1 (g mg−1

−1

−1

min )

min−1) min−1) min−1) min−1)

pH range

ref

2−10 5−9 4−9 3−12 2−12 3−11

33 34 35 36 37 present work

Figure 6. Effects of (a) pH of the solution and (b) temperature, for the adsorption of fluoride ions on the samples (initial concentration of fluoride ions = 100 mg/L): (a) A-550, (b) AM-550, (c) AT-550, and (d) AC-550.

Table 3. Parameters Obtained from Langmuir and Freundlich Models, and Gibbs Free Energy Change sample ID

A-550

AM-550

AT-550

AC-550

qm (mg/g) KL (L/mg) R2 Freundlich KF nF R2 o ΔG at 30 °C (kJ/mol)

47.2 0.038 0.931 2.11 1.47 0.995 −1.99

49.0 0.030 0.853 3.50 1.66 0.971 −1.42

51.4 0.033 0.889 4.30 1.78 0.971 −1.93

62.4 0.025 0.762 3.63 1.56 0.963 −1.45

Langmuir

heterogeneity factor, nF is > 1 confirming the favorable adsorption. The change in Gibbs free energy (ΔGo) for the adsorption is calculated as ΔGo = −RT ln K

Figure 7. Effect of competing ions on fluoride ions adsorption by the samples.

(8)

F− ions on MA in the order of PO43− > SO42− > Cl−. It was reported that physicochemical properties of anions such as ionic radius, solubility, bulk diffusion coefficient, and hydration energy play important roles for selective adsorption of anions.42 It was noticed that for the samples AM-550, AT-550, and AC550 about 6−9% reduction of F− ions adsorption occurred; however, 16% reduction of F− ions adsorption resulted in the case of A-550. The effect of competing ions for the adsorption of F− ions on MA prepared in the absence of any organic acids is more prominent than that on the samples prepared using organic acids. To confirm the adsorption of fluoride ions on mesoporous alumina (MA), FTIR, EDS, N2 adsorption−desorption study, and XRD were performed on the fluoride ions adsorbed samples denoted as AF, AMF, ATF, and ACF for the

where, K, R, and T represent the thermodynamic equilibrium constant, universal gas constant (8.314 J mol−1 K−1), and Kelvin temperature, respectively. By plotting ln(qe/Ce) vs qe, and extrapolating to zero, K can be determined (Figure S5). The spontaneous adsorption of fluoride ions is confirmed by the negative values of ΔGo (Table 3).31 The effects of various competing ions (phosphate, sulfate, and chloride) upon F− ions adsorption were investigated. For this study, the initial F− ion concentration, pH, contact time, and temperature were maintained as 10 mg/L, pH 7, 3 h, and 30 °C, respectively. It is to be noted that the competing ions decreased the F− ions adsorption up to a certain extent (Figure 7). Some anions enhance the Coulombic repulsion forces in competition with F− ions for the active sites of MA, readily decreasing adsorption. The anions reduced the adsorption of E



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Figure 8. Maximum adsorption capacity values (qm) for the adsorption of fluoride ions on the samples (a) A-550, (b) AM-550, (c) AT-550, and (d) AC-550 in five consecutive cycles.

decrease of adsorption capacity for the consecutive fourth and fifth cycles.

corresponding samples of A-550, AM-550, AT-550, and AC550, respectively. The FTIR study shows that the wide peak of the Al−O bond shifted from 599 to 622 cm−1 which could be due to the influence of Al−F stretching vibrations in the F− ions adsorbed samples (Figure S6). The EDS study shows the presence of 2.13, 2.57, 3.03, and 3.35 atom % of F− ions for the samples AF, AMF, ATF, and ACF (Figure S7). It also illustrates that the adsorption capacity of F− ions on the MA samples follows in the order of AC-550 > AT-550 > AM-550 > A-550. The N2 adsorption−desorption study of the samples AF, AMF, ATF, and ACF shows the reduction in BET surface area and pore volume compared to the corresponding samples A-550, AM-550, AT-550, and AC-550 (Figure S8, Table S2). It is obvious that the adsorption of F− ions on the MA samples causes reduction in BET surface area and pore volume. Figure S9 represents the XRD patterns of (a) AC-550 (before adsorption), (b) ACF (after adsorption), and (c) regenerated AC-550 sample (NaOH treated ACF). Interestingly, the XRD pattern of the fluoride adsorbed sample (ACF) indicates an unidentified peak at 2θ around 18.2. It also demonstrates that after fluoride ions adsorption a new product is formed. The unidentified product after fluoride ions adsorption on MA disappeared when it was treated with 0.05 M NaOH solution. The same result was found for other MA samples. The TEM image of regenerated AC-550 (after NaOH treatment of ACF) sample shows that the porous microstructure remained almost the same as the parent AC-550 sample (Figure S10). TEM analyses for other MA samples revealed the same results. The XRD and TEM image of regenerated samples confirmed their structural stability. The recyclability and reusability of the regenerated samples, that is, NaOH treated AF, AMF, ATF, and ACF samples were studied keeping the F− ion concentration of 100 mg/L, contact time of 3 h, pH 7, and temperature at 30 °C. Figure 8 shows that, through up to three cycles, the maximum adsorption capacity (qm) remained almost the same followed by gradual

4. CONCLUSIONS In summary, we have synthesized mesoporous alumina (MA) using different organic acids (malic, tartaric, and citric acid), via the sol−gel process at 40 °C/48 h, and calcinations at 550 °C/ 5 h. The organic acids used in MA played a major role to enhance the BET surface area and pore volume governing the fluoride ion adsorption. The sample prepared with citric acid rendered favorable adsorption due to its maximum surface area. About 50% of fluoride ions were adsorbed within 5 min for all the samples. The adsorption of F− ions increased with increase in adsorbate amount, temperature, and with lowering pH of solution. The pseudo-second-order kinetics and Freundlich isotherm model fit well for the adsorption. The coexisting ions reduced the F− ions adsorption as PO43− > SO42− > Cl−. The maximum F− ions adsorption efficiency remained intact up to three cycles of the regenerated samples. By tuning surface textural properties of the materials, different toxic elements can be removed from drinking water.

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ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.jced.7b00129. Kinetic plots; pH vs percentage mass; Langmuir and Freundlich isotherms; FTIR, EDS, N2 adsorption studies; XRD patterns; plots of ln (qe/Ce) vs qe; TEM images; parameters of kinetic model of the adsorption of fluoride ions; textural properties of MA samples after fluoride adsorption (PDF) F



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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Tel.: +91 33 2473 3496 (ext. 3516). ORCID

Milan Kanti Naskar: 0000-0002-7447-4941 Funding

The work was funded by DST-SERB Project (Grant No. SR/ S3/ME/0035/2012), Government of India. S.K. and I.H.C. are thankful to AcSIR and UGC, Government of India, respectively for their fellowships. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS The authors would like to express their sincere gratitude to the Director of Central Glass and Ceramic Research Institute for his kind permission to publish this paper.

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Effect of Organic Acid-Modified Mesoporous Alumina toward Fluoride

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