Synthesis, characterization and statistical optimization of hydrophobic/oleophilic polystyrene Coated ZnO-cotton composite as vegetable oil adsorbent

Summary: Cotton being easily available, low cost and highly porous natural material is excellent candidate as adsorbent base. However, its super hydrophilicity hinders its applications as oleophilic adsorbent. In the present study, pristine cotton was impregnated with ZnO and stearic acid to provide it with rough surface and hydrophobic properties followed by dip coating of polystyrene for further enhancement of its oil adsorption capacity. The surface morphology of polystyrene coated ZnO impregnated non-woven cotton (PS@ZnO-NWCotton) and polystyrene coated ZnO impregnated woven cotton (PS@ZnO-WCotton) showed increased surface area, roughness and pores as compared to pristine cotton. FTIR spectra confirmed conjugation of polystyrene and ZnO with cotton. Different thermal degradation behavior of pristine cotton and PS@ZnO-NWCotton further confirmed the presence of ZnO and polystyrene onto cotton. PS@ZnO-WCotton exhibited lotus-effect high hydrophobicity with a water contact angle of 145±2o and super oleophilicity with an oil contact angle of 0 degree. Oil adsorption capacities of synthesized composites were found to have an inverse relationship with viscosity of adsorbate oil which could be due to easy mobility of lighter oils. Oil adsorption capacity of PS@ZnO-NWCotton for coconut oil was maximized by optimizing temperature, duration and oil/water ratio using central composite design (CCD). Good agreement was found between predicted values obtained by the model and the experimental values (R2 = 0.8904) for adsorption of coconut oil by PS@ZnO-NWCotton. Under the optimum conditions, the PS@ZnO-NWCotton adsorbed more than 12 times of its weight with acceptable reusability till third cycle. (author)