Enjun Wang

Improved visible light photocatalytic activity of titania doped with tin and nitrogen

Tin and nitrogen co-doped titania has been prepared by a hydrolysis precipitation method and studied by X-ray diffraction, X-ray photoelectron spectroscopy, diffuse reflectance UV-vis absorption spectra, and photoluminescence. The surface area has been determined by using the BET method. Tin is incorporated into the TiO2 crystal lattice in substitutional mode, while nitrogen is present as surface species. The resultant energy levels of tin doping and nitrogen surface states are located inside the bandgap, which are close to the conduction and valence bands, respectively. Hence, co-doping of tin and nitrogen can greatly enhance the absorption in the visible light region and inhibit the recombination of photogenerated charge carriers, leading to a higher photocatalytic activity for the co-doped catalyst than pure TiO2 and solely doped TiO2 with nitrogen or tin for degradation of 4-chlorophenol under both visible and UV-light irradiation. This indicates that co-doping simultaneously with two foreign elements is a feasible way to improve the photocatalytic activity of TiO2.

Structure of nitrogen and zirconium co-doped titania with enhanced visible-light photocatalytic activity.

Nitrogen and zirconium co-doped TiO2 (TiO2-N-x%Zr) photocatalysts were synthesized via a sol-gel method. The existing states of the dopants (N and Zr) and their corresponding band structures were investigated via XRD, Raman, BET, XPS, TEM, FT-IR, UV-vis DRS, and PL techniques. It was found that N existed only as a surface species (NOx) and Zr(4+) was doped in a substitutional mode; the doping of Zr(4+) ions and modification of N extended the absorption into the visible region and inhibited the recombination of electrons and holes. Moreover, the excess Zr(4+) ions existed as the ZrTiO4 phase when the content of Zr was sufficiently high, which could also contribute to the separation of the charge carriers. Therefore, the TiO2-N-x%Zr samples show enhanced visible-light photocatalytic activity compared with single-doped TiO2. These results offer a paradigm for the design and fabrication of optoelectronic functional materials such as solar cells and photocatalysts.

Improved visible-light photocatalytic activity of titania activated by nitrogen and indium modification

Nitrogen and indium co-modified TiO2 was prepared by a simple sol–gel method. Under visible-light irradiation, the modified catalysts exhibited much higher photocatalytic activity for 4-chlorophenol photodegradation than both the as-prepared TiO2 and nitrogen-doped TiO2. The structure and properties of the resultant catalysts were characterized by XRD, BET, XPS, UV-vis DRS and PL techniques. It was found that unique chemical species, such as N–O and O–In–Clx (x = 1 or 2), existed on the surface of the nitrogen and indium co-modified TiO2. The surface-state energy levels introduced by these surface species were located close to the valence and conduction bands, respectively, which could lead to significant absorption in the visible-light region and facilitate the separation of photogenerated electrons and holes. Thus, the visible-light photocatalytic activity of TiO2 can be greatly improved by nitrogen and indium modification. We envision the opportunities for using such a method to develop TiO2-based visible-light photocatalysts suitable for practical applications.