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Preparation of Highly Cross-linked Magnetic Polymer Composite Particles and Application in the Separation of Arsenic from Water

M. K. Sharafat*
Depratment of Chemistry, University of Rajshahi, Rajshahi 6205, Bangladesh.

H. Ahmad
Depratment of Chemistry, University of Rajshahi, Rajshahi 6205, Bangladesh.

M. A. Alam
Depratment of Chemistry, University of Rajshahi, Rajshahi 6205, Bangladesh.

M. M. Rahman
Depratment of Chemistry, University of Rajshahi, Rajshahi 6205, Bangladesh.

Abstract/ Executive Summary:

Iron oxide magnetic particles have become a promising research field in separation technology because of their easy separation by external magnetic field and can be applied for the removal of toxic metals from waste water. Highly cross-linked Fe₃O₄/P(S-DVB) particles were prepared in this research by suspension polymerization of styrene (S) and divinylbenzene (DVB) in presence of nanosized Fe₃O₄ particles. At first Fe₃O₄ nanoparticles were prepared by co-precipitation of Fe₂+ and Fe₃+ from their alkaline aqueous solution. To stabilize the magnetic particles, the surface of the particles was modified with oleic acid. The morphology and surface structure were characterized by Fourier Transform IR(FTIR), Transmission Electron Microscope (TEM), Scanning Electron Microscope(SEM), and light microscope.The adsorption behavior of As(III) on composite polymer particles was evaluated and a comparative study with reference copolymer particles revealed that composite polymer particles possessed better adsorption capacity.

Keywords: Styrene; Divinylbenzene; Suspension polymerization; Highly cross-linked polymer.

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End Date:

Program Area: Risk Management in Agriculture

Commodity: Arsenic

Objectives:

Drinking As contaminated water over a long period causes skin, lung, bladder, and kidney cancer as well as pigmentation changes, skin thickening (hyperkeratosis) neurological disorders, muscular weakness, loss of appetite, and nausea. Since exposure to toxic metals, even at trace level, is believed to be a risk for human beings, thus, removing of undesirable metals from water system has become a challenging task. Recently adsorption technique is used in large scale which offers flexibility in design and operation, and in many cases it will generate high-quality treated effluent.

Methodology:

Chemicals and instruments Styrene of monomer grade, purchased from Fluka, Chemika, Switzerland, was distilled under reduced pressure. Crosslinking agent DVB from Sigma-Aldrich, Chemie (80% grade) was purified with aqueous 10% NaOH solution and subsequently dehydratd by stirring with anhydrous CaCl₂. Benzoyl peroxide (BPO) from BDH Chemicals Ltd. UK was recrystallized from methanol and preserved in the refrigerator before use.Polyvinyl alcohol (PVA) from Thomas Baker (Chemicals) Limited, India, of molecular weight 1.4×104 gmol-1 was used as polymeric stabilizer. As₂O₃ from May & Baker, UK, ferric chloride (FeCl₃), ferrous sulphateheptahydrate (FeSO₄.7H₂O), NH₄OH, Oleic acid and other chemicals were of analytical grade. Deionized water was distilled using a glass (Pyrex) distillation apparatus. TEM was performed with a JSEM-1230 microscope (JEOL, Tokyo, Japan) operating at a voltage of 100 kV, and optical image was obtained by a fluorescence microscope (IX71 Olympus, Japan) to see the particle morphology and size distribution. IR spectrophotometer, FTIR (Perkin Elmer, FTIR-100, UK), Double beam UV-visible spectrophotometer (Shimadzu, UV-1650pc), and microprocessor pH meter from Mettler Toledo (MP 220, Switzerland) Instruments were used in this study. Homogenizer (T 18 Digital Ultra Turrax, IKA, Germany) is used to homogenized the particles. B. Preparation of Fe₃O₄nanoparticles Nano-sized Fe₃O₄ particles were produced by co-precipitation of Fe2+ and Fe3+ from their aqueous solutions (molar ratio1:2) containing 25% NH₄OH. The reaction was carried out in a three necked round flask under a nitrogen atmosphere for 2h. Oleic acid was used as a stabilizer. The produced Fe₃O₄ particles were repeatedly washed by magnetic separation and subsequent redispersion in deionized distilled water to remove the residual electrolyte and excess oleic acid. C. Preparation of reference P(S-DVB) particles Styrene (5.3 g), DVB (0.4 g), PVA (1.25 g), toluene (1.50 g) were taken in 50 mL distilled water, homogenized at 10,000 rpm sonication for 3 min in ice-water bath to form monomer droplets. The homogenized mixture was polymerized in presence of BPO (2.6% w/w) based on monomer) at 75°C. D. Preparation of Fe₃O₄/P(S-DVB) composite particle Styrene (5.3 g), DVB (0.4 g), toluene (1.5 g) and 0.88 g (65% solid in n-octane) magnetic fluid were mixed to form the oil phase. PVA (1.25 g) and NaCl (1.5 g) were dissolved into 50 mL deionized water to form the water phase. Then the two phases were mixed together with ultrasonic treatment at 5,000 rpm sonication for 3 min prior to the polymerization in presence of BPO at 75°C. Preparation of Highly Cross-linked Magnetic Polymer Composite Particles and Application in the Separation of Arsenic from Water. .Porosity measurement Bulk density (loose) a property of particulate materials is the mass of many particles of the material divided by the volume they occupy. The occupied volume includes the space between particles as well as the space inside the pores of individual particles. This was measured at 26°C using a 5 mL graduated cylinder. Oven dried P(S-DVB) polymer and Fe₃O₄/P(S-DVB) composite particles were poured separately into the cylinder for each measurement. The weight and volume of the powder of copolymer and composite particles were recorded and the bulk density of them was obtained using the equation. The particle density or true density is the density of the particles that make up the powder. This density was measured using a densimetric bottle at 26°C. The volume of the densimetric bottle was first calculated using the appropriate density value of water. Then, 0.2 to 0.3 g of oven dried P(S-DVB) polymer and Fe₃O₄/P(S-DVB) composite particles were taken separately in the bottle for each measurement. Distilled water was added and the contents in the bottle were gently boiled for 10 min to remove any entrapped air. The increase in weight over the polymer powder and composite particles powder was used to obtain the volume of water in the bottle. The volume of the powder of polymer and composite particles in the bottle was obtained by subtracting the volume for each from the total volume of densimertic bottle. Equation (2) was used to calculate the particle density of P(S-DVB) polymer and Fe₃O₄/P(S-DVB) composite particles respectively. Both bulk density and particle density were measured in once The amount of pore space or porosity for P(S-DVB) polymer and Fe₃O₄/P(S-DVB) composite particles was measured by density measurement using equation. Adsorption behavior of arsenic The absorption behavior of arsenic on both polymer and composite particles were measured using UV-Vis spectrophotometer. For each measurement, a mixture of 30 mL of 40 ppm As(III) solution was prepared from 10.94 g purified particle solution (0.1g solid) and 1000 ppm arsenic stock solution. The mixture of arsenic-particle emulsion was allowed to stand for specific time at 25°C and pH was maintained at 9 with occasional stirring. Magnetic composite polymer particles were then separated applying external magnetic field followed by centrifugation at 12000 rpm whereas reference P(S-DVB) particles were separated only by centrifugation at 12000 rpm. The supernatant was transferred to arsenic generator and 5 mL conc. HCl, 2 mL KI solution and 0.5 mL SnCl₂ were added in it. The content of the flask was swirled and then allowed to stand for about 15 minutes to ensure complete reduction of arsenic to +3 state. The absorber tube was charged with 4.00 mL of the silver diethyldithiocarbamate. 5.0 g pure granulated zinc was added to the solution in the flask and then the hydrogen sulphide scrubber was immediately inserted. The evolution of arsine (AsH₃) was 99% completed within 40 min and additionally the mixture was heated for another 5 min in water-bath at 75°C to complete the reaction. The absorber solution was transferred and its absorbance was measured at the wavelength of 535 nm by a UV-visible spectrometer. The amount of arsenic adsorbed was calculated by subtracting the concentration in the medium from that of initial concentration. Calibration constant was used for this purpose.

Source of Information: Rajshahi University Journal of Science & Engineering ISSN 2309-0952 Vol. 44: 67-74, 2016

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Achievement/Findings:

Highly cross-linked magnetic polymer composite particles were prepared by a novel suspension polymerization of styrene and DVB in presence of nanosized Fe₃O₄ particles. The removal of As by magnetic composite particles was driven by both porosity and interaction with magnetic nanoparticles.

Knowledge Management: Journal