Ag–ZnO heterojunction promotes the separation of photogenerated pairs and thus exhibits high catalytic activity under UV-visible light.

Using butyl titanate and absolute ethanol as raw materials, TiO2 was prepared by a hydrothermal method with different hydrothermal times, and the influences of hydrothermal time on the structure and photocatalytic performance of TiO2 were investigated. The obtained samples were characterized by XRD, SEM, TEM, BET, PL and DRS, separately. The results show that TiO2 forms anatase when the hydrothermal time is 12 h, forms a mixed crystal composed of anatase and rutile when the hydrothermal time is 24 h, and forms rutile when the hydrothermal time is 36 h. With the extension of hydrothermal time, anatase gradually transforms into rutile and the surface area decreases. Although TiO2-24 h and TiO2-36 h show lower photoinduced charge recombination and higher light source utilization, TiO2-12 h exhibits the highest photocatalytic activity owing to its largest surface area (145.3 m2/g). The degradation degree of rhodamine B and tetracycline hydrochloride reach 99.6% and 90.0% after 45 min.

The anatase/rutile mixed crystal TiO2 was prepared and modified with Ag decoration and SnO2 coupling to construct a Ag@SnO2/anatase/rutile composite photocatalytic material. The crystal structure, morphology, element valence, optical properties and surface area were characterized, and the effects of Ag decoration and SnO2 coupling on the structure and photocatalytic properties of TiO2 were studied. Ag decoration and SnO2 coupling are beneficial to reduce the recombination of photogenerated electrons and holes. When the two modification are combined, a synergistic effect is produced in suppressing the photogenerated charge recombination, making Ag@SnO2/TiO2 exhibits the highest quantum utilization. After 30 min of illumination, the degradation degree of tetracycline hydrochloride (TC) by pure TiO2 increased from 63.3% to 83.1% with Ag@SnO2/TiO2.

Pure and Sn/Ni co–doped TiO2 nanomaterials with anatase/rutile mixed crystal were prepared and characterized. The results show that pure TiO2 is a mixed crystal structure composed of a large amount of anatase and a small amount of rutile. Sn doping promotes the phase transformation from anatase to rutile, while Ni doping inhibits the transformation. Both single doping and co–doping are beneficial to the inhibition of photoinduced charge recombination. Sn doping shows the best inhibitory effect on photogenerated charge recombination, and increases the utilization of visible light, displaying the highest photocatalytic activity. The decolorization degree of methylene blue (MB) by Sn–TiO2 is 79.5% after 150 min. The reaction rate constant of Sn–TiO2 is 0.01022 min−1, which is 5.6 times higher than pure TiO2 (0.00181 min–1).

Pure and Cu doped anatase/rutile mixed TiO2 nanomaterials were fabricated through sol-gel method. The obtained photocatalysts were characterized by XRD, SEM, TEM, XPS, PL and DRS, and the influences of Cu doping on the structure and photocatalytic property were studied. The results show that when the molar ratios of Cu/Ti are 1% and 2%, Cu doping promotes anatase → rutile phase transformation. When the molar ratio of Cu/Ti is 4%, the phase transformation is inhibited. Cu element coexists in the form of Cu+ and Cu2+, and Cu doping facilitates the separation of photogenerated electrons and holes. TEM image shows that copper oxides are dispersed on TiO2 particles surface, which significantly reduces the optical absorption of ultraviolet region. The photocatalytic experiment results show that the photocatalytic activity of Cu–TiO2 is lower than pure TiO2, and the higher doping concentration, the lower photocatalytic activity.