Preparation And The Photocatalytic Activity Of TiO₂ Coated By Carbon With Doping Nitrogen

Among the numerous semiconductor photocatalysts, Ti O₂ has many good properties such as wide source, non-toxic, cheaper and higher catalytic efficiency. However, it has two kinds of chief shortcoming:（ a） The energy gap of Ti O₂ is wide（Eg = 3.0 3.2 e V）, so it can only be excitated by the ultraviolet that only accounts for 4% of the solar energy;（ b） The recombination between the photoinduced electron-hole is easier for pure Ti O₂ semiconductors and then leads a lower photocatalytic quantum efficiency.Many researchers had explored various methods to improve the photocatalytic activity of Ti O₂. Among them, it was found that the modification by doping C and N elements can increase the absorption range of light wavelength. Especially the modification can reduce the recombination between the photoinduced electron-hole pairs, since the graphitized carbon has a high electronic conduction that is good for separation of the electron-hole pairs.This work introduces a one-step process to obtain the materials of Ti O₂ coated by carbon with doping nitrogen. On this basis, some metal elements are loaded onto the materials in order to further improve its photocatalytic activity. The work mainly includes:（1） Using dopamine as the source of C and N and in the Tris- HCL aqueous solution（p H = 8.5）, Ti O₂ nanoparticles is dispersed thoroughly and dopamine is aggregated and polymerized on the surface of Ti O₂ under the effect of dissolved oxygen. After drying and calcination of the filter cake from the mixture above, the Ti O₂ materials coated by C with doping N can be finally obtained. The coated thickness can be controled by the dopamine amount.（2） Using phenol as C source, make it polymerize on the surface of Ti O₂ under ultraviolet light conditions to obtain Composites of Ti O₂（ C-Ti O₂） coated by carbon. Compared C-Ti O₂ with the Ti O₂ coated by C with doping N described above, it is found that the former has stronger fluorescence spectral response, which indicates that the electron-hole pairs in it recombine more easily and the corresponding hydrogen production capability is only about 80% of latter for the water-spliting under sunlight.（3） The thin layer of poly dopamine has a certain force binding to some metal ions and may reduce them somewhat. Hence, addition of some metal salts in to the reaction during coating poly dopamine, we can modify the Ti O₂ catalyst with metal ions（ Ag, Ni） based on nitrogen doped carbon coated. The best photocatalytic activity can be achieved when the load is 1 wt %.