Boron-doped TiO 2 nanoparticles were prepared by the sol-gel method and characterized by XRD, TEM, XPS, FT-IR, and UV-vis spectroscopy. XRD results showed that the doping of boron ions could efficiently inhibit the grain growth and facilitate the anatase-to-rutile transformation prior to the formation of diboron trioxide phase. FT-IR and XPS results revealed that the doped boron was present as the form of B 3+ in B-doped TiO 2 samples, forming a possible chemical environment like Ti-O-B. The lattice parameters at different boron contents and calcination temperatures indicated that B 3+ was likely to weave into the interstitial TiO 2 structure. The photocatalytic activity of the B-doped TiO 2 nanoparticles was evaluated by the photoregeneration of reduced nicotinamide adenine dinucleotide (NADH). All B-doped TiO 2 nanoparticles calcined at 500 °C showed higher photocatalytic activity than pure TiO 2 sample in the photocatalytic reaction of NADH regeneration under UV light irradiation. When the molar ratio of B to Ti was 5%, the TiO 2 nanoparticles could photocatalytically reproduce 94% NADH.

To utilize visible light more efficiently in photocatalytic reactions, carbon-doped TiO2 (C−TiO2), nitrogen-doped TiO2 (N−TiO2), and carbon and nitrogen co-doped TiO2 (C−N−TiO2) nanoparticles with different nitrogen and carbon contents were prepared by a sol−gel method and characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and UV−vis spectroscopy. XRD results showed that the doping of C and N atoms could suppress the crystal growth of TiO2, and the effect of C doping was more pronounced than that of N doping. XPS, UV−vis spectroscopy, and lattice parameter analysis revealed that N atoms could incorporate into the lattice of anatase through substituting the sites of oxygen atoms, while most C atoms could form a mixed layer of deposited active carbon and complex carbonate species at the surface of TiO2 nanoparticles. The photocatalytic activities of obtained C−TiO2, N−TiO2, and C−N−TiO2 samples with different C and N contents were evaluated by methylene blue degradation under visible light irradiation. It was found that C−N−TiO2 nanomaterials exhibited the highest photocatalytic activity, which could be assigned to the synergistic effect of doped C and N atoms.

The influence of defects on the photoactivity of ZnO has been revealed. The defects can be formed via ball-milling treatment, and part of the defects can be repaired via annealing treatment. The photocatalytic activity of the ZnO sharply decreased as the ballmilling speed and milling time increased. After the annealing treatment, the photocatalytic activity recovered partly but could not return to the activity of the pristine ZnO. The bulk defects such as oxygen vacancies (V O ), zinc vacancies (V Zn ) and a lot of nonradiative defects were formed after the milling treatment. The annealing treatment can only repair part of the bulk defects and nonradiative defects. Thus, only part of the photoactivity was recovered. The species trapping experiments showed that the introduction of the bulk defects did not change the photocatalytic mechanism. The main oxidative species for the pristine ZnO, the milled ZnO, and the annealed ZnO are photogenerated holes and hydroxyl radicals.

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