In this paper, TiO2 nanoparticles doped with different amounts of Zn were prepared by a sol-gel method and were mainly characterized by means of X-ray photoelectron spectroscopy (XPS), photoluminescence (PL), and surface photovoltage spectrum (SPS). The effects of surface oxygen vacancies (SOVs) of Zn-doped TiO2 nanoparticles on photophysical and photocatalytic processes were investigated along with their inherent relationships. The results show that the SOVs easily bind photoinduced electrons to further give rise to PL signals. The SOVs can result in an interesting sub-band SPS response near the band edge in the TiO2 sample consisting of much anatase and little rutile, except for an obvious band-to-band SPS response. Moreover, the intensities of PL and SPS signals of TiO2, as well as the photocatalytic activity for degrading phenol solution, can be enhanced by doping an appropriate amount of Zn. These improvements are mainly attributed to the increase in the SOV amount. It can be suggested that the SOVs should play an important role during the processes of PL, surface photovoltage, and photocatalytic reactions, and, for the as-prepared TiO2 samples doped with different amounts of Zn by thermal treatment at 550℃, the larger the SOV amount, the stronger the PL and SPS signal, and the higher the photocatalytic activity.

In this paper, Sn-doped TiO2 nanoparticles were prepared by a sol–gel method, and also were characterized by X-ray powder diffraction (XRD), X-ray photoelectron spectroscopy (XPS), infrared spectrum (IR), ultraviolet–visible diffuse reflection spectrum (UV-vis DRS), photoluminescence spectrum (PL), surface photovoltage spectroscopy (SPS) and electrical field induced surface photovoltage spectroscopy (EFISPS). The sample activity was evaluated by photocatalytic oxidation reactions of phenol solution. The effects of thermal treatment temperature and Sn amount on photoinduced charge property, mainly involving charge separation and bound excitons resulting from surface states, and photocatalytic activity of TiO2 nanoparticles were principally investigated. The results show that an appropriate calcination temperature and Sn dopant amount can greatly enhance the SPS responses of TiO2 nanoparticles related not only to the band-band transitions but also to the bound excitons, and obviously weaken the PL signal, while the photocatalytic activity remarkably raises. These demonstrate that the separation rate of photoinduced charges of TiO2 nanoparticles can be effectively improved by doping Sn, which is responsible for the obvious increase in the photocatalytic activity. Moreover, the existence of bound excitons related to surface states also favor the photocatalytic activity. In addition, it can be found that the SPS responses related to the bound excitons could easily exhibit in the TiO2 sample consisting of much of anatase and little of rutile, which is possibly ascribed to the heterojunction between the anatase and rutile phase.

In this paper, we examined the lifetimes of made-in-home ZnO and TiO2 nanoparticles in the gas phase photocatalytic oxidation of n-C7H16 or SO2, and especially investigated the deactivation mechanism by utilizing surface photovoltage spectrum (SPS) and X-Ray photoelectron spectroscopy (XPS) testing techniques and by considering semiconductor chemical properties. The results showed that ZnO could almost be deactivated in the gas phase photocatalytic oxidation of n-C7H16, while TiO2 could keep most of its activity. In the gas phase photocatalytic oxidation of n-C7H16 or SO2, ZnO and TiO2 both could almost be deactivated. The deactivation mainly resulted from semiconductor surface conduction type change from N-type before the photocatalytic reaction to P-type after the deactivation because of the adsorption of the oxidation products such as H2O, CO2 and SO3 on the semiconductor photocatalyst surface. In addition, the activity of the deactivated photocatalyst could be regenerated to a nearly full extent by washing and drying.

In this paper, ZnO nanoparticles were modified by depositing different amount of noble metal Ag or Pd on their surfaces with a photoreduction method. The as-prepared ZnO samples were principally characterized by X-ray photoelectron spectroscopy (XPS) and surface photovoltage spectroscopy (SPS), and their activity was evaluated by a photocatalytic degradation reaction of phenol solution. The effects of noble metal modification on surface composition, photoinduced charge transfer behavior and photocatalytic activity of ZnO samples were mainly investigated. The results show that, after an appropriate amount of Ag or Pd is deposited on the ZnO surfaces, the O 1s XPS spectrum shifts to higher binding energy, indicating that the content of surface hydroxyl oxygen (OH) increases. And the SPS intensity greatly decreases, indicating that the photoinduced electrons are easily captured by adsorbed oxygen via noble metal clusters so that the recombination of photoinduced electron and hole pairs is effectively inhibited. These are responsible for the enhancement in the photocatalytic activity. Moreover, the effects of Pd modification on photocatalytic activity is greater than that of Ag, which can be explained by means of surface hydroxyl content as well as charge separation situation.

Heterogeneous photocatalysis is a promising technique valuable for environmental purification. Nano-sized semiconductors such as ZnO and TiO2, which is one of the most basic functional materials, have emerged as effective photocatalyst materials. The surface photovoltage spectra (SPS) can be an effective method for quickly evaluating the photocatalytic activity of semiconductor materials since it can provide a rapid, non-destructive monitor of the semiconductor surface properties such as surface band bending, surface and bulk carrier recombination and surface states, mainly showing the carrier separation and transfer behavior with the aid of light, especially the electric-field-induced surface photovoltage spectra (EFISPS), in which SPS is combined with the electric-field-modified technique. In this review, the basic principles, measurement and applications of the SPS and EFISPS are mainly discussed together with some fundamental aspects like the electric properties of semiconductor surface and the principle of electric field effect. In particular, the applications of SPS to nano-sized semiconductors such as ZnO and TiO2 in heterogeneous photocatalysis are emphasized, which involve mainly evaluating the photocatalytic activity by analyzing semiconductor surface properties such as the separation efficiency of photoinduced carriers under illumination by the SPS measurement, highlighting our own contributions. The results show that the weaker the surface photovoltage signal is, the higher the photocatalytic activity is in the case of nano-sized semiconductor photocatalysts.