Fabrication and characterization of amidoxime-grafted silica composite particles via emulsion graft polymerization

Abstract

This study deals with the synthesis and characterization of polyacrylonitrile (PAN)-grafted silica composite particles by emulsion graft polymerization using potassium persulphate as the initiator and Tween 80 as the surfactant for potential application in wastewater treatment. The commercially available silica particles (37-70 micron) were first functionalized with vinyltriethoxysilane that were subsequently employed for the grafting of PAN via emulsion polymerization. The effect of various experimental parameters, such as varying the amount of the monomer, initiator, and the emulsifier in the feed on the grafting (%) has been investigated in detail. The maximum grafting (296%) was achieved with 6% (w/v) monomer, 0.15% (w/v) initiator, and 1% (w/v) emulsifier concentration. The nitrile groups of the PAN-grafted silica composite particles were converted into amidoxime by treating with hydroxylamine. The synthesized products in all the preparation steps were carefully characterized by various analytical tools, i.e., Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and X-ray diffraction analysis (XRD). In FTIR spectrum of the silica-grafted PAN, the appearance of the characteristic peak at 2245 cm-1 that corresponds to CN stretching confirms the successful grafting of PAN onto the modified silica particles; while the transformation of nitrile into amidoxime functionality was verified by the appearance of peaks at 1642 cm-1 and 920 cm-1. Further verification of the grafting of PAN and amidoxime formation also comes from the SEM micrographs and the XRD profiles. Finally, the obtained amidoxime-grafted silica composite particles were evaluated as an adsorbent for Cu+2 ions from the simulated wastewater for potential application in wastewater treatment. The maximum adsorption capacity of 130 mg/g was achieved at pH 5 in 2 hrs.