Poly(vinylidene fluoride) (PVDF)/titanium dioxide (TiO2) hybrid membranes were prepared using nano-TiO2 as the modifier, and characterized by Transmission Electron Microscope (TEM), Fourier transform infrared spectroscopy (FT-IR), scanning electron microscope (SEM), atomic force microscope (AFM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The characterization results demonstrated that nano-sized TiO2 particles dispersed homogeneously within the PVDF matrix, contributing to more hydroxyls and smoother surfaces. Moreover, permeate flux, retention factor, porosity, contact angle and anti-fouling tests were carried out to evaluate the effect of TiO2 concentration on the performance of PVDF membranes. Among all the prepared membranes, PVDF/TiO2 membrane containing 10 vol.% TiO2 exhibited the best hydrophilicity with an average pure water flux up to 237 L·m−2·h−1, higher than that of unmodified PVDF membranes (155 L·m−2·h−1). Besides, the bovine serum albumin rejection of the hybrid membrane was improved evidently from 52.3% to 70.6%, and the contact angle was significantly lowered from 83° to 60°, while the average pore size and its distribution became smaller and narrower.

Different composite films prepared by coupling ZnO and nitrogen-doped ZnO (N-ZnO) were used to photodegrade humic acids (HA). The catalysts exhibit an activity in the order of glass/ZnO/N-ZnO > glass/N-ZnO >glass/ZnO > glass/N-ZnO/ZnO when light is irradiated from the film to glass substrate. However, glass/ZnO/N-ZnO exhibits a lower activity than glass/N-ZnO/ZnO when light is illuminated from glass to film. Moreover, glass/ZnO/N-ZnO shows a lower activity when light is irradiated from glass to film than that irradiated in the opposite direction. These results suggest that it is not always the case that the presence of a heterojunction at interface of two semiconductors can definitely result in improving the photoactivity of the heterostructure although it can suppress the recombination of photogenerated charge carriers. They also indicate that photodegradation of HA is mainly via the oxidization by HO• (rather than directly by O2– and h+), which is produced mainly by the reactions with h+. This implies the importance of fabrication a right heterojunction at the interface between the composite materials when they are used for photocatalysis. We envision that this work will help to develop new photocatalysts, as well as to understand better the photocatalytic mechanism.Keywords: heterojunction; humic acid; hydroxyl radical; photocatalysis; zinc oxide;