View of RECENT RESEARCH AND ANALYTICAL REVIEW ON REACTIVE AMPHIPHILIC MONTMORILLONITE NANOGELS AND HEAVY METALS WATER POLLUTANTS

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Peer Reviewed and Refereed Journal, ISSN NO. 2456-1037, IMPACT FACTOR: 7.98 (INTERNATIONAL JOURNAL) Vol. 04, Issue 05, May 2019 Available Online: www.ajeee.co.in/index.php/AJEEE

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RECENT RESEARCH AND ANALYTICAL REVIEW ON REACTIVE AMPHIPHILIC MONTMORILLONITE NANOGELS AND HEAVY METALS WATER POLLUTANTS

Dr. Mona Jaiswal

Lecturer Chemistry, Government Women's Polytechnic College, Jabalpur (M.P.) Abstract - The present work aims to reduce the surface tension of the water by using dispersed organophilic clay minerals to increase the adsorption of water pollutants (organic and inorganic) in the clay adits. Therefore, sodium montmorillonite (Na-MMT) was functionalized with amphophiles based on crosslinked nanogel polymers of N- isopropylacrylamide (NIPAm), sodium 2-acrylamido-2-methylpropanesulfonate (Na-AMPS), acrylamide (AAm), and acrylamidopropyl) trimethylammonium chloride solution (APTAC) using a surfactant-free technique. The chemical interactions between nanogels and Na- MMT and their chemical structure were confirmed by FTIR analysis. Intercalation and exfoliation of Na-MMT were confirmed by wide-angle X-ray diffraction. The morphology of Na-MMT nanogel composites was studied by TEM analysis. The adsorption capacities of the prepared Na-MMT nanogels for methylene blue dye, cobalt and nickel cations from water were investigated. The data showed that the Na-MMT nanogels reduced the surface tension of water and efficiently removed dyes and metal ions from the water.

1 INTRODUCTION

Water pollution, particularly from heavy metals and dyes, is a global problem affecting economic and environmental systems around the world. Industrial toxic waste is one of the main sources of these pollutants. Various techniques have been used to control water pollution, such as ion exchange, adsorbents, reverse osmosis [3], precipitation and coagulation techniques. Adsorbents have attracted a lot of attention due to the availability of different types of adsorbents, environmental friendliness, low cost and their high efficiency in removing organic and inorganic pollutants. The main adsorption mechanisms are based on complexation and ion exchange mechanisms. There are several important criteria that drive adsorbent selection and design, such as: B. rapid removal, ion selectivity and reusability. Recently, nanomaterial-based adsorbents have attracted much attention due to their high performance in adsorbing pollutants from aqueous environments such as carbon nanotubes, titanium dioxide, silica, and clay-polymer composites. Ionic polymer clay nanocomposites showed high performance in removing organic and organic pollutants. The efficiency of nanoclay-polymer composites has been influenced by the manufacturing process, the type of polymer composites, and the application technology such as membrane, nano-filter, etc.

Sodium montmorillonite (Na-MMT) has attracted a lot of attention in recent years for its application in the field of

water purification. The exfoliation of Na- MMT from multilayer films to dispersed monolayer composites plays an important role in the fabrication of nanocomposites for water treatment applications. Ion exchange, adsorption of organic compounds, and reactions with organic acid treatments are effective methods used to displace sodium cations between silicate layers to intercalate the silicate layers and convert layers to organophilic minerals. Crosslinking of reactive monomers is another preferred technique for dispersing clay slabs in the polymer composites. In previous work, exfoliation of Na-MMT sheets using a cross-linking technique enhanced the performance of Na-MMT to form an anti-corrosive thin film layer on the steel surfaces. The reactive anionic amphiphilic nanogels attracted much attention towards exophilized Na-MMt sheet monomers because of their high cation exchange capacities, surface area, surface reactivity, adsorption properties, and transparency in solution. 2-acrylamido-2- methylpropanesulfonic acid (AMPS) and N-isopropylacrylamide (NIPAm) have been described as good clay modifiers due to their ability to adsorb between sheets of Na-MMT. These polymers were chosen to modify Na-MMT because of them have sulfonate group, amido functional group potentially able to interact with Na-MMT surface. NIPAm microgel crosslinked with clay showed excellent surface effect...

The present work reports the functionalization of Na-MMT using a

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2 cross-linking technique to produce reactive amphiphilic dispersed Na-MMT sheets with the affinity to reduce the surface tension of water to increase clay adsorption of pollutants on their surfaces.

It has previously been reported that the addition of organic molecules to solid inorganic colloidal particles improves the material's ability to adsorb at the interface and forms an interfacial adsorption layer.

To achieve this goal, the present work aims to use anionic, cationic, and nonionic monomers to fabricate amphiphilic Na-MMT nanogels using a radical crosslinking technique. NIPAm was chosen as an amphiphilic nonionic monomer to copolymerize with acrylamide (AAm), sodium 2-acrylamido-2- methylpropanesulfonate (Na-AMPS), and acrylamidopropyl trimethylammonium chloride (APTAC) to exfoliate clay with nonionic, anionic, and amphoteric nanogels, respectively. NIPAm was chosen to produce nanogels due to its heat sensitivity at temperatures above the polymerization temperature to form reactive nanogels that have the ability to intercalate and exfoliate the Na-MMT. In addition, APTAC was selected for its ability to exchange Na cations from Na- MMT to form highly dispersed Na-MMT nanogels. The surface properties such as aggregation and adsorption at interfaces of the modified Na-MMT nanogels were investigated using surface tension measurements. The use of modified Na- MMT nanogels to absorb organic and inorganic pollutants in water.

2 EXPERIMENTAL 2.1 Materials

Sodium montmorillonite nanoclay (Na- MMT) with the tradename Nanometer PGV is purchased from Sigma-Aldrich Co. N- Isopropylacrylamide (NIPAm), sodium 2- acrylamido-2-methylpropanesulfonate (Na-AMPS), acrylamide (AAm), and acrylamidopropyl trimethylammonium chloride solution (APTAC; 75% by weight in H 2 O) monomers are sold by Aldrich Chemicals Co Received from Aldrich

Chemical Co. N, N-

Methylenebisacrylamide (MBA), Ammonium Persulfate (APS) and N, N, NO, NO-Tetramethylethylenediamine (TEMED) are used as crosslinkers, free radical initiators and activators for low temperature cross linking polymerization.

and they were obtained from Sigma-

Aldrich Co., respectively. Deionized water and ethanol are analytical grades used as solvents for cross linking polymerization.

Cobalt and nickel nitrate hexahydrate, manufactured by Sigma- Aldrich CO., are used to make stock solution at 100 ppm. Buffer solution (H3PO4/NaH2PO4) was prepared by titrating 0.1N NaH2PO4 against 0.1M HCl (for pH range 23) or against 0.1N NaOH (for pH range 712) to the required pH is reached. The pH was monitored with a pH meter.

2.2 Synthesis Procedure

Na-MMT clay was not easy to disperse in water solution. Therefore, a water/ethanol mixture (60/40% by volume) was used as a solvent to disperse Na-MMT. For this purpose, Na-MMT (2 g) is dispersed in water/ethanol (100 ml) and PVP (0.3 g) as a stabilizer at room temperature for 24 h.

The dispersed Na-MMT nanogels based on NIPAm were prepared using surfactant-free radical dispersion crosslinking polymerization using a temperature-programmed technique. For this purpose, NIPAm monomer (0.5 g) is dispersed in Na-MMT solution (water/ethanol 50 ml). The solution was first preheated to 40 8C for 30 min under a nitrogen atmosphere. APS (0.015 g/ml) was added to start the polymerization.

The reaction temperature was increased to 50 8C at a rate of 5 8C per 15 min. The NIPAm monomer (1.5 g), MBA (0.03 g) and 20 ml TEMED were dispersed in the remaining Na-MMT solution (water/ethanol 50 ml) and added dropwise over 1 h up to the reaction temperature. After 15 min, APS (0.02 g) dissolved in 2 mL of deionized water was injected into the reaction mixture. The reaction temperature was lowered to 45 8C to complete the stirring for 24 h. The dispersed Na-MMT/PNIPAm nanogel solution was centrifuged five times for 30 min at 12,000 rpm, washed with ethanol, and dried in vacuo at 30 8C

The same procedure was repeated to fabricate Na-MMT nanogels using PNIPAm/APTAC, PNIPAm/Na-AMPS, and PNIPAm/AAm as cationic, ionic, and nonionic nanogels. The remaining NIPAm (1.5 g) was mixed with anionic (APTAC and Na-AMPS) or non-ionic (AAm) monomers in an aqueous Na-MMT solution (50 mL). The molar ratio between the monomers NIPAm/APTAC,

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3 NIPAm/Na-AMPS and NIPAm/AAm was 1:1. The prepared Na-MMT nanogels were washed once each with water, ethanol, and acetone, the prepared particles were centrifuged (24,680 rpm, at 20 8C), and then dried in a vacuum oven at 35 8C.

The purity of the Na-MMT nanogels was confirmed by measuring that the surface tension of the supernatant was over 72.1 mN/m, indicating that the uncross linked monomers and polymers were completely removed from the Na-MMT nanogels.

3 CHARACTERIZATION

The interaction between Na-MMT and nanogels and their chemical structure were confirmed with a Fourier transform infrared (FTIR) spectrometer (Nicolet, NEXUS-670). Intercalation and exfoliation of Na-MMT galleries through nanogels was performed using wide-angle X-ray diffraction (WAX; Rigaku D/MAX-3C OD- 2988N X-ray diffractometer; CuKa radiation; l = 0.15418 at 40 kV and 30 mA

The morphology of the Na-MMT nanogel was observed under an electron microscope with a transmission electron microscope (TEM, JEOL JEM-2100F).

High-resolution HR-TEM images recorded at an acceleration voltage of 200 kV. The change in surface morphologies of Na- MMT nanogels after adsorption of heavy metal ions were observed under a scanning electron microscope (SEM, model JSM-T 220A, JEOL) at an accelerated voltage of 20kV.

Energy dispersive X-ray spectroscopy (EDX, SEM 3200 Hitachi electron microscope equipped with an EDX detector) was used to determine the Na-MMT nanogel composition after adsorption of heavy metal ions. Thermal stability and Na-MMT content were determined by thermogravimetric analysis (TGA-50 SHIMADZU) at a heating rate of 10 8C/min.

Zeta potentials, particle size (nm) and particle size distribution index (PDI) of the modified Na-MMT nanogel were measured in aqueous solution in the presence of KCl (0.001 M) at different aqueous pH solutions using a laser zetameter Malvern Instruments Model Zetasizer 2000 A UV/Vis double-beam spectrophotometer (model) was used to determine the absorbance of methylene blue dye (at 662 nm).

Atomic Absorption Spectroscopy (AAS; Perkin-Elmer 2380) was used to determine metals analysis by direct aspiration into an air-acetylene flame.

Surface activity, surface tension in aqueous solution, and interfacial tension between water and toluene are measured at 25 8C using the DSA-100 model drop shape analyzer.

4 CONCLUSIONS

The Na-MMT layers were exfoliated using a temperature-modified program for the cross linking polymerization technique to fabricate Na-MMT nanogels using anionic and nonionic monomers such as Na- AMPS, APTAC, AAm, and NIPAAm. The Na-MMT nanogel composites achieved a reduction in water surface tension from 72.1 to 30.1 mN/m. All dispersed Na- MMT nanogel composites have good surface activity except those made with PNIPAm/AAm nanogel. The ability of Na- MMT nanogels to reduce water surface tension reflects the increase in Na-MMT nanogel's ability to remove MB, Co, and Ni cations from water within 60 min. The prepared Na-MMT nanogels were desorbed and reused four times to remove the heavy metal from the water with the same efficiency.

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