Adsorption Mechanism of Oil-in-Water on a TiO₂/Al₂O₃-Polyvinylidene Fluoride (PVDF) Ultrafiltration Membrane

For the sake of gaining a clear idea of the adsorption mechanism involved with an oil emulsion-membrane system, Daqing crude oil emulsion and two types of polyvinylidene fluoride (PVDF) ultrafiltration membranes made in our laboratory were used as the objects to pursue the adsorption characteristics in this system. Several isotherm and kinetics models were used here to simulate the adsorption process; the effect of variables such as time, initial concentration, temperature, as well as scanning electron microscopy (SEM) and attenuated total reflectance-Fourier transform infrared (ATR-FTIR) spectra were investigated to assist in understanding the mechanism. The results show that the Redlich-Peterson model and the pseudo-first-order kinetic model are the best fitting models, with all of the models exhibiting correlation coefficient ( R²) values of >0.98, suggesting an endothermic adsorption process that involves a combination of chemical and physical mechanisms. Moreover, the thermodynamic parameters, such as Δ_r G_m^θ, Δ_r H_m^θ, and Δ_r S_m^θ were also calculated from the temperature dependence, indicating a nonspontaneous process, and increases in temperature had a negative effect on the oil-in-water (o/w) adsorption. Ultimately, further evidence is obtained from the microstructural and infrared spectral analyses.