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Title: Fabrication of Silica/polymer composite materials by graft polymerization for environmental applications
Authors: Khan, Ijaz Ahmed
Keywords: Chemistry
Issue Date: 2019
Publisher: Quaid-i-Azam University, Islamabad.
Abstract: In this study, polymer/silica hybrid composites were developed using grafting techniques for potential applications as adsorbent, heterogeneous catalyst, and ion exchange resin. Two commonly used grafting techniques i.e., radiation-induced grafting and emulsion graft polymerization have been explored to modify the surface of the commercially available silica microparticles with different monomers to fabricate composite materials for environmental applications. The mesoporous silica particles with high surface area, tunable pore size, and narrow pore size distribution were modified by treating with vinyltriethoxysilane to introduce polymerizable vinyl functionality on the particle surface for in-situ polymerization of various monomers to achieve polymer/silica hybrid composites. Silica/poly(acrylonitrile) and silica/polystyrene hybrid composites were fabricated by in-situ grafting of acrylonitrile (AN) and styrene (St), from surface of the modified silica (MS) microparticles, respectively. Radiation induced grafting was achieved by using the Co-60 irradiator. Systematic and detailed studies have been carried out to investigate the influence of various grafting parameters, i.e., gamma absorbed dose and monomer concentration, on the grafting of acrylonitrile. Under the optimized conditions of 1:12 silica to monomer ratio (w/v) and 20 kGy absorbed dose, afforded the highest grafting (748 %, the value indicates the % increase in weight of the silica particles after the AN grafting). Radiation induced grafting in a solvent free system provided eco-friendly route by avoiding hazardous organic solvents. The emulsion graft polymerization AN was carried out with potassium persulfate as initiator and tween 80 as surfactant in aqueous medium. Systematic investigations were carried out to elucidate the effect of monomer, initiator, and surfactant concentration on the grafting. The optimized conditions were found to be 6% monomer, 0.15 % initiator, and 1 % surfactant concentration that afforded the highest grafting (296 %). The nitrile (-CN) groups of the grafted poly(acrylonitrile) were converted into amidoxime functionality by treating with hydroxylamine. The emulsion grafting route is free from the requirements of using higher monomer concentration, costly organic solvents, and special equipment. In 2nd study, styrene was grafted onto modified silica particles to afford silicagrafted- styrene composite via radiation induced grafting and subsequent sulfonation of the grafted polystyrene. The effect of grafting conditions, such as absorbed dose, monomer concentration, and the type of solvent used was investigated in detail. The structural and morphological investigations of the hybrid composites were carefully performed by Fourier transform infrared (FT-IR) spectroscopy, X-ray diffraction (XRD), field emission scanning electron microscopy (SEM), thermogravimetric analysis (TGA), and Brunauer–Emmett–Teller (BET) nitrogen adsorption-desorption isotherms. The amidoxime grafted silica materials prepared were evaluated as adsorbent for Cu(II) ions from the aqueous solution and were found to have higher loading capacities of 172 mg/g and 130 mg/g, respectively, for radiation-induced and emulsion grafted samples. The hybrid materials after loading with Cu(II) ions were also employed as heterogeneous catalyst for the reductive degradation of methylene blue (MB) in the presence of NaBH4 as reductant. The reduction process followed pseudo-first-order kinetics and the rate constant (k) was calculated 0.6224 min-1. The hybrid catalyst was found to be highly effective for the degradation of MB and can be easily recovered and reused several times with no appreciable loss of catalytic activity. The ion exchange capacity (IEC) of the fabricated silica-grafted-sulfonated styrene composite resin was evaluated by ion exchange titrations (back titration method). The IEC was found to be in the range of 0.43-2.97 meq/g depending on the degree of grafting. The facile fabrication method and high IEC value could lead to potential application of the fabricated resin in ion exchange resin in waste water treatment and metal recovery.
Gov't Doc #: 18841
Appears in Collections:PhD Thesis of All Public / Private Sector Universities / DAIs.

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