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Electron spin resonance spectroscopy (ESR), Fourier transform infrared spectroscopy (FTIR), and monitoring of pyridine (py) and boric acid trimethyl ester (BATE) adsorption for determining surface acidity and basicity, respectively, were used to carry out further characterization of mixed ZnO/TiO2 polycrystalline solids prepared by different methods. Moreover, the powders were tested in a batch photoreactor for a probe reaction, i.e., 4-nitrophenol photodegradation in aqueous medium. ESR results indicated the presence of signals attributable to Zn⁺ species in ZnO/TiO2 (anatase) solids, while in ZnO/TiO2 (rutile) samples the presence of zinc induced only the formation of signals probably due to Ti³⁺ centers. FT-IR spectra showed no significant differences of the surface hydroxylation degree of the various photocatalysts, whereas the surface acidic properties generally decrease by increasing the amount of ZnO. Coupling of ZnO and TiO2 semiconducting powders was not so beneficial, as expected on the basis of the intrinsic electronic properties, to enhance the photoreactivity for the studied reaction, although some of the powders showed photoactivities slightly higher than those of bare TiO2 and ZnO. Nevertheless, some of the samples (the mixed particles ZnO/TiO2 (rutile)) appear promising from an application point of view because no filtration was needed after the occurrence of the photoreactivity tests to separate them from the solution because they decanted easily. The mineralization of 4-nitrophenol was checked by determining the total organic carbon (TOC) and a complete photooxidation occurred in few hours in the presence of some of the samples.

Polycrystalline ZnO/TiO2 solids have been prepared with four different methods using home prepared TiO2 (anatase) or TiO2 (rutile) as supports and Zn(NO3)2·6H2O or Zn(CH3COO)2·2H2O as precursors for ZnO. The bulk and surface properties of the samples were investigated by means of TG-DTA, XRD, TEM, SEM-EDAX, XPS, BET surface area determination, and porosity measurements. XRD and TEM results indicate that no significant defect structures exist in any of the samples. The ZnO crystallinity and its enrichment on the surface of TiO2 particles were dependent on the preparation method. The surface areas generally decrease by increasing the amount of ZnO except when ZnO from Zn(CH3COO)2·2H2O was supported on TiO2 (rutile). The samples prepared from Zn(CH3COO)2·2H2O were more porous than those prepared from Zn(NO3)2·6H2O. This was confirmed by BET surface area determinations and SEM observations. XPS spectra indicate that the atomic ratio between OH^- and O^2- on the particles surface is similar for samples with the same ZnO content independent of the precursor used for the samples' preparation. Moreover a much higher segregation of ZnO was found for samples obtained by using the acetate precursor.

Iron(III) doped specimens (0.01–5% atomic Fe : Ti) have been prepared by impregnating polycrystalline “home prepared” TiO2 (mainly anatase) and have been studied for photocatalytic degradation of 4-nitrophenol in aqueous dispersions. Some structural and surface properties have been studied by X-ray diffraction, specific surface area and porosity measurements and FTIR monitoring of pyridine, ammonia and methanoic acid adsorption for surface acidity and basicity. Their surface properties were compared with a corresponding series of photocatalysts prepared by a coprecipitation method. Adsorption of pyridine and ammonia indicates the presence of surface acid Lewis sites, a low concentration of surface Brønsted sites being present only in the samples prepared by impregnation. The photocatalytic experiments indicated that the presence of iron ions does not influence or is detrimental for the occurrence of the 4-nitrophenol photodegradation.

The results show that there is not difference between the catalytic activities of two series of CuxMg1−xAl2O4 catalysts, despite a small but significant difference in cation distribution. The activity is mainly affected by the presence of CuO.

Two examples of photoreactions are reported in the present paper: namely the photoreduction of N2to NH3in the gas-solid regime and the complete photooxidation of phenol and nitrophenols in the gas-liquid-solid regime (aqueous oxygenated dispersions). Undoped pure and iron ion doped polycrystalline titania specimens were used as photocatalysts. The presence of the dopant, in the case of N2photoreduction, was essential for the occurrence of the photoprocess; it was, on the contrary, detrimental or indifferent in the case of phenol and nitrophenols photooxidation. The influence of several ions as Cl, SO42+, Fe2+, Fe3+, Ag+and of a compound such as H2O2added to the dispersion was also investigated and the different behaviour of TiO2(anatase) and TiO2(rutile) was ascribed to kinetic factors.

Photoinduced reduction of CO2by H2O to produce CH4and CH3OH has been investigated on wellcharacterized standard TiO2catalysts and on a Cu2+loaded TiO2catalyst. The efficiency of this photoreaction depends strongly on the kind of catalyst and the ratio of H2O to CO2. Anatase TiO2, which has a large band gap and numerous surface OH groups, shows high efficiency for photocatalytic CH4formation. Photogenerated Ti3+ions, H and CH3radicals are observed as reactive intermediates, by ESR at 77 K. Cu-loading of the small, powdered TiO2catalyst (Cu/TiO2) brings about additional formation of CH3OH. XPS studies suggest that Cu+plays a significant role in CH3OH formation.