Preparation characterization and photocatalytic activity of polycrystalline ZnO/TiO2 systems. 2. Surface, bulk characterization, and 4-nitrophenol photodegradation in liquid-solid regime

Electron spin resonance spectroscopy (ESR), Fourier transform infrared spec troscopy (FTIR), and monitoring of pyridine (py) and boric acid trimethyl e ster (BATE) adsorption for determining surface acidity and basicity, respec tively, were used to carry out further characterization of mixed ZnO/TiO2 p olycrystalline solids prepared by different methods. Moreover, the powders were tested in a batch photoreactor for a probe reaction, i.e., 4-nitrophen ol photodegradation in aqueous medium. ESR results indicated the presence o f signals attributable to Zn+ species in ZnO/TiO2 (anatase) solids, while i n ZnO/TiO2 (rutile) samples the presence of zinc induced only the formation of signals probably due to Ti3+ centers. FT-IR spectra showed no significa nt differences of the surface hydroxylation degree of the various photocata lysts, whereas the surface acidic properties generally decrease by increasi ng the amount of ZnO, Coupling of ZnO and TiO2 semiconducting powders was n ot so beneficial, as expected on the basis of the intrinsic electronic prop erties, to enhance the photoreactivity for the studied reaction, although s ome of the powders showed photoactivities slightly higher than those of bar e TiO2 and ZnO. Nevertheless, some of the samples (the mixed particles ZnO/ TiO2 (rutile)) appear promising from an application point of view because n o filtration tvas needed after the occurrence of the photoreactivity tests to separate them from the solution because they decanted easily. The minera lization of 4-nitrophenol was checked by determining the total organic carb on (TOC) and a complete photooxidation occurred in few hours in the presenc e of some of the samples.