Preparation Of C₃N₄-Based Composite Photocatalysts With Controllable Morphologies And Their Efficient Visible-Light Photocatalytic Performance

The sustainable development of harmonious society and the great rejuvenation of our Chinese nation’s realization need us urgently to find a way out solving the environmental pollution and energy crisis. Semiconductor photocatalysis is a new photocatalytic technique, which can not only use the sunlight to oxidate oganic pollutants and air purification, but also can convert low density solar energy to high density chemical energy just like a imitated photosynthesis process as plants, and without any greenhouse gas release. These advantages make it have great potential both in environmental purification and energy crisis solving. But as the traditional semiconductor TiO₂ still has many drawbacks, such as low light response, low sunlight utilization, low quantum efficiency, easy to deactivation and so forth, which greatly inhibit the development of photocatalytic technique, it’s urgent to find out ways to overcome these shortages.Carbon nitride has a clear advangtage in simple fabrication process, cheap feedstocks, unique electronic properties and photoactive under visible light excitation, which make it gain more and more world-wide intention. Owning to the bulk layed structure, g-C₃N₄ possess less number of active sites, fast recombination of photoinduced carries and high mass transfer resistance.These drawbacks greatly limit the photoactivity of g-C₃N₄, so it’s necessary to improve the catalytic activity of g-C₃N₄. In this paper, stratagies were illustrated to enhance the catalytic efficiency and decrease the mass trasfer resistance, such as morphology control, heteropoly acid doping, noble metal decoration, heterojunction construction between several different semiconductor. More over, the fabrication method, characterization and catalytic mechanism were all studied in detail. Including:1. For the first time the carbon nitride nanotubes（C₃N₄ NTs） were fabricated via a quench method. The result shows that C₃N₄ NTs exhibit high photocatalytic activity toward organic pollutant degradation and hydrogen evolution. The enhanced photocataytic activity of C₃N₄ NTs owning to the improved quantun efficiency and mass transfer efficiency.2. For the first time the H₃PW₁₂O₄₀ hybrid C₃N₄ NTs（H3PW12O40/C₃N₄ NTs） composite were snthysized via a sovolthemal method by using H₃PW₁₂O₄₀ and C₃N₄ nanosheet as precursors. The surface-NH₂ was substuted by-OH during the high temperature and high pressure condition. The tubular nanostructure formation originate from the condensation of unbonded surface-OH groups during hydrothermal treatment. Based on the minerlization experiments tward MO and DEP, a detail photodegradation mechanism was also proposed.3. Platinum decorated C₃N₄ NTs materials were fabricated by using sovolthemal treatment. The as synthesized materials were applied in organic pollutants photodegradation, photoinduced water splitting and simultaneous photodegradation and hydrogen evolution experiments. The results show efficient photocaltalytic activity toward organic pollutant degradation and water spliting, most of all, the photodegradation and hydrogen evolution can be conducted in the same system.4. Based on the C₃N₄ NTs morphology, the C/X-TiO₂@C₃N₄ NTs（X=C、N、Cl、F） were successfully fabricated via a sol-gel process. The influence on the hydrogen evolution or organic degradation by constuct intermediate band was also studied in this paper. As for the simultaneous photodegradation and hydrogen evolution experiments, the enfluence towards the degradation rate and hydrogen mount with different concentration of electronic donator RB were studied in detail. The the approprite concentration of RB is 50 ppm according to the experimental result.5. Porous carbon nitride（pg-C₃N₄） was fabricated by calcinating the HCl and ethylene glycol co-treated melamine. The pg-C₃N₄ shows enhanced photo response, inhibited photo carries recombination rate and improved quantum compared with that of g-C₃N₄. The catalytic activity of as-prepared pg-C₃N₄-（EG+HCl） was evaluated by the multi-component phenolic wastewater（MPW） treatment.6. In order to further improve the catalytic activity of pg-C₃N₄, platinum particles were deposited on the surface of HD-pg-C₃N₄ by using a photoreduction method, pg-C₃N₄ and H2PtCl6·6H2O were used as precursors. The characterazition results show that Pt were uniformly dispersed on the surface of pg-C₃N₄, which effectively overcomed the aggrigation of Pt nanoparticles. The series of HD-Pt/pg-C₃N₄ composites show high performance and stability during the degradation of MO and PFP.