Bionanomaterial Scaffolds for Effective Removal of Fluoride

Research Article pubs.acs.org/journal/ascecg

Bionanomaterial Scaffolds for Effective Removal of Fluoride, Chromium, and Dye Anshu Kumar,†,§ Parimal Paul,*,†,§ and Sanna Kotrappanavar Nataraj*,‡,∥ Analytical Discipline and Centralized Instrument Facility, ‡Reverse Osmosis Membrane Division, and §Academy of Scientific and Innovative Research, CSIR−Central Salt and Marine Chemicals Research Institute (CSIR-CSMCRI), G. B. Marg, Bhavnagar 364 002, India ∥ Centre for Nano and Material Sciences, Jain University, Jain Global Campus, Kanakapura, Ramanagaram, Bangalore 562112, India Downloaded via UNIV OF BRITISH COLUMBIA on July 6, 2018 at 17:38:56 (UTC). See https://pubs.acs.org/sharingguidelines for options on how to legitimately share published articles.

†

S Supporting Information *

ABSTRACT: Here we demonstrate, chitosan−sodium alginate based bionanomaterial scaffolds (BMS) with in situ functionalized alumina hydroxide forming scaffold like structure and its application in removal of fluoride (F−), chromium (Cr(VI)), and dye from water. Further, the bionanomaterial scaffold surface was modified with silver nanoparticles (Ag NPs) to enhance the shelf life of the bionanomaterial scaffold (BMS). This Ag NP-coated BMS exhibited as high as ∼168 and ∼60 mg g−1 fluoride uptake efficiency at pH 4 and 7, respectively. Experiments were also carried out to check the chromium removal efficiency, and results showed ∼8.5 mg g−1 of Cr(VI) uptake capacity was achieved from contaminated water at room temperature. Further, over 99% Reactive Black 5 (RB-5) removal was achieved with remarkable surface regeneration properties. To test the end user affordability, the bionanomaterial was packed both in a columnlike filter cake and tea-baglike pouches in a series of experiments. This study demonstrates a viable and sustainable solution for removal of fluoride, chromium, and color contaminants from contaminated water streams. KEYWORDS: Fluoride removal, Bionanomaterial, Scaffolds, Sustainability, Biopolymers, Water Treatment

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INTRODUCTION Recent studies on drinking water quality have revealed that many parts of the world have been severely affected due to industrial activities. Also, water reservoirs contaminated with hazardous chemicals like heavy metals, dyes, and groundwater with fluoride raise serious concerns.1−4 More seriously, fluoride contamination in drinking water is increasingly becoming a global problem.5−7 More than 25 countries in the world are already affected by increased concentrations (>1.5 mg L−1) of fluoride in the groundwater. The western USA, parts of Mexico, Argentina, many parts of the African continent, India, Pakistan, Afghanistan, China, the Middle Eastern region, and parts of Australia are already experiencing severe fluoride contamination levels.8 India is one of the most affected countries, ∼15% of world’s geological distribution of fluoride deposits (12 M tons out of 85 M tons) is in India.9 In some parts of India, fluoride contamination levels have been recorded as high as 42.5 mg L−1.10 Recent estimates suggest that one-third of the 1.26 billion Indian population is vulnerable to fluorosis or likely to access water with higher levels (>2 mg L−1) of fluoride contamination (Figure S1).11 On the other hand, hexavalent chromium (Cr(VI)) is one of the harmful heavy metal ions listed by the Environmental Protection Agency (EPA).12 The Cr(VI) metal ion has been widely used or generated as waste in metal plating, leather © 2016 American Chemical Society

tanning, metal corrosion inhibition, and pigment production, etc., and the effluents from these industries contaminate groundwater.13 Recently, it has been reported that 89% of water samples from cities in America have Cr(VI) levels much higher than safety standards.14 It is extremely difficult to prohibit the use of Cr(VI) for important industrial purposes. Therefore, it is essential to develop a method or a process to remove and recover Cr(VI) ions from effluents.15 Further, many rivers and potable water streams in India are severely affected by discarded textile and dyeing industry wastewater.16,17 The main toxic pollutants in textile wastewater emanate from dyeing and finishing process steps. Reactive dyes are being used widely in textile industries for coloration of cellulose, viscose, nylon, and wool.18,19 The dyeing process in the textile industry consumes ∼90% of the overall water used; at the end, this water is contaminated with excessive dye. At present, several multistep defluoridation treatment methods are in use.20 Despite the fact that many adsorption/ absorption-based technologies have been tested for the removal of fluoride contaminated wastewater, simple and sustainable methods are still in demand. Activated alumina and bone char Received: September 15, 2016 Revised: October 28, 2016 Published: November 15, 2016 895

DOI: 10.1021/acssuschemeng.6b02227 ACS Sustainable Chem. Eng. 2017, 5, 895−903

Research Article

ACS Sustainable Chemistry & Engineering

Figure 1. (a) Schematic of the synthetic route of the CS-Alg-Al bionanomaterial scaffold (BMS) composite using aluminum precursor, Na-alginate, and chitosan biopolymers. (b) Photograph showing the as prepared nanomaterial paste immediately after the alkali assisted precipitation. (c and d) SEM micrographs showing dried BMS at different magnifications. (e−g) TEM micrographs showing distinct Al3+-alginate clusters in a continuous layer of chitosan biopolymer. (g inset) Presence of Ag nanoparticles on BMS.

are some of the commercially successful methods available to treat fluoride contaminated water.21−23Also, ion-exchange resins are being considered user-friendly and relatively stable fluoride chelating agents.24 In the recent past, membrane processes like nanofiltration, reverse osmosis, and electrodialysis are being used for fluoride removal.25−27However, many of the above-described processes are economically classified in the range of medium to very high cost.28 Therefore, here we demonstrate the use of a biopolymerbased (chitosan and sodium alginate) aluminum complex (CSAlg-Al), now onward referred as a bionanomaterial scaffold (BMS) as an efficient and sustainable material to remove fluoride (F), chromium (Cr(VI)), and dye from contaminated water. Here, we evaluate design of BMS and its structural and morphological properties formed as a result of a simple

precipitation reaction between biopolymers and alumina precursor. Further, BMS’s pollutant uptake properties as well as technology feasibility tests were conducted for selective removal of dye, F, and Cr(VI) from water.

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EXPERIMENTAL SECTION

Materials. Chitosan, sodium alginate, sodium borohydride, and Reactive Black 5 were purchased from sigma Aldrich. Aluminum sulfate was from Central Drug House (p) Ltd. India, silver nitrate was from s.d.fine-Chem Limited, Mumbai, sodium hydroxide was from Fisher Scientific, and sodium fluoride was from Qualigens Fine Chemicals, Mumbai. Fluoride contaminated groundwater samples were collected from different parts of the states of Gujarat and Rajasthan (India). Synthesis of Bionanomaterial Scaffold. A sodium alginate (0.75 g) solution was prepared using distilled water (40 mL), and in 896


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Figure 2. (a) FTIR spectra of sodium alginate, chitosan, and resulting BMS (CS-Alg-Al). (b) XRD patterns of as prepared bayerite form of H3AlO3 in BMS at RT (JPCDS no. = 98-002-6830). (c) Solid state UV−vis spectra of surface modified BMS to confirm the presence of AgNPs with inset confirming presence of AgNPs using TEM micrographs. (d) Plot of pH vs fluoride uptake efficiency of BMS with inset plot showing zeta potential of BMS vs pH.

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another beaker chitosan (0.75 g) was dissolved in dilute acetic acid. Chitosan solution was then added to alginate containing flask gradually with stirring for 1 h. After obtaining a homogeneous blend mixture, 100 mL of 0.5 M aluminum sulfate was added dropwise. After 3 h incubation, 140 mL of 2 M sodium hydroxide was added dropwise to precipitate the aluminum-alginate/chitosan bionanomaterial scaffold (BMS). The resultant precipitate was further stirred for 1 h and subsequently washed with copious amounts of water. Synthesis of Silver Nanoparticle on Bionanomaterial Scaffold. After redispersing BMS precipitate in water, 100 mL of 5 mM Silver Nitrate was added and incubated for 1 h. Afterward, 100 mL of 10 mM Sodium Borohydride was added dropwise at Cl− > NO3− > NO2−. Color and Chromium Removal Efficiency. The Reactive Black 5 dye (RB-5), which is commonly used for dying cellulosic fabric, easily dissociates to attain negatively charged moiety in water. The RB-5, was used as feed in high concentration (500 mg L−1) which instantaneously interacts with BMS in filter bed. A loosely packed lump of BMS (CS:Alg 50:50) was placed between microporous fabrics in a filtration chamber attached to a feed column that showed retention of >99% color from initial 500 mg L−1 feedstock as shown in Figure 3a. UV analysis of the permeate at different time intervals showed very high dye retention capacity of BMS. Initially, 99.99% removal efficiency of RB-5 was recorded which remained constant for a capacity of ∼240 mL permeate (Figure 3b). The 1 g active BMS filter bed sustained a high retention rate of dye (after 600 mL of feed, retention decreased to ∼97% up to ∼2 L of feed) tested under gravity. To alter the packing density of BMS during filtration, different compositions of parent scaffolds and tested for dye rejection performance (Figure S2). As a control composition CS:Alg in 90:10 ratios which initially showed high flux but later both rejection and fluxes declined drastically compared to CS:Alg(50:50) as shown in Figure 3c. It is assumed that anion exchange is coupled with the release of OH− ions on bayerite to form a scaffold complex (structure in Figure 3a). For chromium (VI) removal efficiency studies, 0.5 g BMS in the form of a filter was used (Figure 3d and SI Figure S3). Further, 5 and 10 mg L−1Cr(VI) contaminated brackish water feed was supplied to understand retention limit. From a feedstock of 5 mg L−1, the initial ∼600 mL of permeate carried 0.99 values in Table 1), which is in good agreement with the pseudo-secondorder kinetic fit. Further, the adsorption capacity analysis was evaluated based on Langmuir and Freundlich isotherms equations. Langmuir isotherm Ce C 1 = e0 + 0 qe Q Qb

(2)

Freundlich isotherm log(qe) = log(KF) +

1 log(Ce) n

(3) −1

Where, qe is the adsorbed fluoride at equilibrium (mg g ), Ce is the fluoride concentration at equilibrium, Q0 and KF are the measurements of the sorption capacity (mg g−1) based on Langmuir and Freundlich isotherms respectively, b is a constant 899


Research Article

ACS Sustainable Chemistry & Engineering Table 1. Summary of Kinetic Parameters and Isotherm Fitting of Fluoride on BMS K

H −3

1.9 × 10 1.2 × 10−4 1.2 × 10−5

R2

qe

0.8464 21.084 0.4114 57.8 0.1353 103.4 Freundlich Adsorption Isotherms

0.997 0.997 0.998

KF

1/n

R2

0.013

0.5803 Langmuir Adsorption Isotherms

0.914

KL

Qm (mg g−1)

R2

0.071

168

0.9967

related to the affinity of the binding sites, and 1/n is the adsorption intensity. Figure 4c and d gives corresponding Langmuir and Freundlich parameters along with correlation coefficients as are given in Table 1. The results indicate that the fluoride adsorption data fitted well with the Langmuir isotherm with a correlation coefficient between 0.99 and 1. Recovery and Reuse of BMS. From the Langmuir isotherm and the XRD of F− adsorbed, BMS clearly indicate that fluoride directly interacts with alumina resulting in ralstonitelike complex in irreversible adsorption.31 Also, steady uptake efficiency of anions at low pH ranges (2−6) indicates possible strong interactions of anions with BMS’s active aluminum sites. It is proposed based on XRD patterns (Figure 5a) that fluoride forms inner and outer-sphere complexes with the bayerite−bionanomaterial scaffold whereas Reactive Black has possible surface exchange reactions. XRD analysis confirms the stronger interaction between fluoride and alumina of BMS. The ralstonitelike complex identifies the aluminum fluoride hydrates or possibly anhydrous aluminum fluoride formation. Therefore, it is proposed that the bayeritelike BMS forms a double layer of hydroxide structure via entrapped sheets of aluminum coordinated by six OH− in the bionanomaterial scaffold, where two hydroxides are shared by neighboring aluminum centers of scaffold. These structural arrangements impose a trapping net for a range of anions. The cohesion between two consecutive sheets is ensured by interlayer hydrogen bonds. Therefore, the bayerite polymorph in the bionanomaterial scaffold strongly bonds with double coordinated Al−O interactions resulting in higher surface acidity. Higher surface acidity principally leads to increased positive surface charge which helps in capturing anions like reactive dye and fluoride through electrostatic interactions. Surface ion-exchange was evident from dye adsorption whereas the much stronger interaction between BMS and fluoride was established. On the other hand, dye adsorbed BMS was reactivated/ surface regenerated by washing in methanol which results in leaching of adsorbed RB-5 into solvent leaving active BMS as shown in Figure 5b. The FTIR studies on RB-5 adsorbed BMS and after washing the material recovered both dye and active material showing no significant interactions. The FTIR spectrum in Figure 5c confirms the weaker interaction (also see the structure in Figure 3a) between dye and BMS at ∼3450 cm−1, a sharp stretch assigned for O−H H-bonding. These weak hydrogen bonding interactions readily undergo the regenerative process. The RB-5 interaction with BMS is noticed in terms of −R−SO3− as SO stretching at around 1250−

Figure 5. (a) XRD pattern confirms formation of permanent bonding between F− and BMS resulting in ralstonitelike structure. (b) Surface activity of dye adsorbed BMS regenerated by washing in dye contaminated BMS in methanol and surface regenerated BMS tested for several cycles for dye removal efficiency. (c) Series of FTIR spectra showing the surface regeneration process.

1140 and 1070−1030 cm−1 which later disappears in recovered BMS leading to identical spectra of pristine BMS. Tea-Bag Experiments. It is important to demonstrate the robustness of BMS’s retention for fluoride, chromium, and dye contaminants from water samples. Hence, easy to use teabaglike pouches containing 1 g of BMS were prepared and tested for removal of RB-5 dye as shown in Figure 6a. To monitor the robustness, the timer was fixed next to 500 mg L−1 containing beaker. Once the BMS pouch was immersed, the time-dependent adsorption process was quantified under constant stirring conditions. From Figure 6b, it is clear that ∼4 h of stirring 100 mL RB-5 with 500 mg L−1 stock solution turned in to transparent solution. Further, sampling was done every 30 min to record the percent color adsorption by BMS. UV−vis spectrum recorded for each time interval has shown decreased intensity as shown in Figure 6c. The BMS containing pouch was then washed with methanol and repeatedly used for several cycles to quantify the recyclability of the BMS, for several cycles BMS shown excellent surface regeneration and reusability for 500 mg L−1 dye feedstock. Figure 6d indicates that in the first three 900


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Figure 6. (a and b) Photograph the BM−H3AlO3 complex in a tea-baglike experimental setup to show time-dependent Reactive Black (RB) dye removal. (c) UV−visible spectra taken different time intervals of feed stock containing RB-5 and the BMS tea bag indicates gradual reduction in color intensity as a function of time. The activity of BM−H3AlO3 is regenerated by washing with methanol and tested over several cycles for dye removal efficiency.

Figure 7. (a−d) Photographs of BMS before and after fluoride, Reactive Black 5, and chromium (VI) adsorption. (e−g) SEM images of pristine BMS, dye adsorbed BMS, methanol washed dye-BMS immediately after, and dried regenerated BMS. (h) TEM showing presence of AgNPs after use in dye removal and surface regeneration.

cycles >95% color removal was achieved in ∼5 h of stirring (Figure S5). It is interesting to note that BMS, in general, has shown different adsorption surface properties for F−, Cr(VI), and dye. Fluoride interacts strongly in irreversible complex formation while dye and chromium adsorbed surfaces were easily recovered, and BMS was reused as shown in Figure 7a−d. The surface morphologies of pristine and dye absorbed BMS are seen in Figure 7e−g; however, there was no significant change observed before and after washing of BMS during surface regeneration. In addition to this, the TEM micrograph in Figure 7h confirms the presence of Ag NPs even after several cycles of reuse and surface regeneration. Further, the structural stability of BMS was observed to be stable even after several

cycles of surface regeneration and reuse. The thermogravimetric (TGA) analysis shows higher structural stability compared to parent biopolymers as shown in Figure S6a. The solid UV, SEM, and TEM with energy dispersive X-ray diffraction (EDX) patterns show no significant changes in spectral patterns of BMS, dye-BMS, F-BMS, and surface regenerated BMS as seen in Figure S6b−d. There have been several adsorbents tested for dye, fluoride, and chromium (VI) removal in the recent past. To best of our knowledge, the present study is unique as it offers a comprehensive solution for the uptake of a series of anions and material reuse. A recent report lists out material references from activated alumina to layer-double hydroxide for F− uptake at different pH ranges.43 However, the present study showed an 901


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contaminated drinking water, particularly for rural and semiurban inhabitants.

exceptional uptake capacity on BMS compared to many reported adsorbents. In the present case, fluoride uptake recorded a range of 58−168 mg g−1 in the pH range of 2−10, which is much higher than that reported so far (see Table 2). In

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S Supporting Information *

Table 2 adsorbent TLAC MgO microspheres iron−silver oxide nanoadsorbent magnetic iron−aluminum oxide/graphene oxide nanoparticles pectin/Al2O3−ZrO2 core/shell bead electrospun alumina nanofibers porous 2-line ferrihydrite/ bayerite composites Al-doping chitosan−Fe(III) hydrogel nanozerovalent ironimmobilized alginate beads polyaniline-modified Mg/Al layered double hydroxide composites Fe@Fe2O3 core−shell nanowires oxygen furnace slag bionanomaterial scaffold bionanomaterial scaffold

removal

max sorption capacity (mg g−1)

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acssuschemeng.6b02227. Map showing fluoride contamination, XRD data, photographs, UV spectra of dye and Cr(VI) removal experiments, and oil−water separation experiment images (PDF)

ref

arsenic and fluoride fluoride fluoride

30.3 and 27.8

32

120 22.88

33 34

fluoride

64.72

35

ASSOCIATED CONTENT

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AUTHOR INFORMATION

Corresponding Authors fluoride

98.077

36

chromium (VI) and fluoride fluoride

6.8 and 1.2

37

123.03

38

fluoride

31.16

39

Cr(VI)

320.6 ± 3.87

12

Cr(VI)

393.70

40

Cr(VI)

7.78

41

reactive dyes fluoride

76.60 168

Cr(VI)

8.2

42 present study present study

*E-mail: [email protected] (P.P.). *E-mail: [email protected]; [email protected] (S.K.N.). Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS S.K.N. gratefully acknowledges the DST, Government of India, for the DST-INSPIRE Fellowship and Research Grant (IFA12CH-84). The help received from the Analytical Discipline and Centralized Instrument Facility and Technical Team at CSIRCSMCRI is greatly acknowledged. A.K. gratefully thanks UGC for financial assistance in the form of a fellowship. CSIRCSMCRI communication number: 012/2016.

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REFERENCES

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the case of fluoride, the bonded BMS forms a stable complex and no further regeneration treatment was conducted. Therefore, to address the disposal and value addition, F−− BMS was used as a separation media for oil−water emulsion (Figure S7).44 The BMS-F is hydrophilic in nature due to which it can be used as selective water absorbent from oil/water emulsion making BMS multifaceted nanomaterial.

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CONCLUSIONS In conclusion, the present study demonstrates preparation of bionanomaterial-based scaffolds modified with silver nanoparticles as a superadsorbent for removal of fluoride, chromium (VI), and dye contaminants from water. Extensive characterization-supported results reveal that (i) BMS shows remarkable F−, Cr(VI), and dye uptake efficiency, (ii) in cases of Cr(VI) and dye, the material can be easily recycled with high efficiency of regeneration, and (iii) fluoride-absorbed BMS forms a ralstonitelike permanent structure because of strong binding of F− with BMS. However, it can be used for separation of oil− water emulsions making use of its hydrophilic nature. The present study also demonstrates that BMS can be used in userfriendly modules with two different approaches: a column filter and tea-baglike pouches. The methods adopted are suitable and sustainable to provide an environmentally benign solution to producing safe drinking water from contaminated surface and underground water streams. Therefore, the present study may immensely contribute to solving endemic problems of 902


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Bionanomaterial Scaffolds for Effective Removal of Fluoride

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