Studies On Photocatalytic Activity And Mechanism Of CdS-TiO₂/AC And CdO-TiO₂ Nanocomposite Photocatalysts

Semiconductors for photocatalytic degradation has become an ideal contaminated environment treatment technology and clean energy production technology, because of its unique peculiarity of completing reaction deeply under room temperature and using solar light for irradiation. Wide band conductor TiO₂ is of non-toxicity, high activity, cheap, can operate under normal temperature and pressure and also can degrade various organic compounds without selection. But it can only be irradiated under ultraviolet light, Furthermore, the blue shift of nanometer TiO₂ also results in the decrease of photocatalytic activity due to the quantum size effects; meanwhile traditional photocatalytic suspending system has a lot of problems such as the reuse of TiO₂ and the causation of secondary contamination. Thus, the efficient use of visible light has received considerable attentions. In this dissertation, the nanocomposite photocatalyst was prepared by supercritical fluid combination technique and chose the condition of preparation technology and optimized the condition of use. The catalysts prepared were characterized by means of TEM, XRD, FT-IR, the preparation and photocatalytic mechanism of photocatalytic reactions were also explored. Its photocatalytic activity for degradation of acrylic acid industrial waste water was also assessed. Some innovation conclusions were gained.1. The optimal preparation technologies of CdS-TiO₂/activated carbon (AC) supported nanocomposite photocatalysts were: sol-gel method combined with precipitation method, with CdS coupling amounts of 1.75 wt. %, m(TiO₂)/m(AC)=1/3, dried at 110℃, using 0.1v% H₂O₂ as oxidation, the photodegradation ratio of acrylic acid solution with concentration of 1000 ppm for 6 hours was 97.9% under Ultraviolet (UV) irradiation; while with CdS coupling amounts of 24.59 wt. %, calcined at 350℃for 1 hour, using 0.17v% H₂O₂ as oxidation, the photodegradation ratio of acrylic acid solution under visible light irradiation reached 95.3%. XRD results show that CdS was finely dispersed in anatase TiO₂ crystal lattice, and UV/Vis diffuse reflectance spectra (UV/Vis DRS) showed that red shift of TiO₂ can be observed.2. The optimal preparation technologies of CdO-TiO₂ nonsupported nanocomposite photocatalysts were: co-precipitation method combined with Supercritical Fluid Dry (SCFD) Combination technology, CdO%=5at.%, calcined at 500℃for 1 hour, using 0.1v% H₂O₂ as oxidation, the photodegradation ratio of acrylic acid solution with concentration of 3000 ppm for 6 hours was 94.4% under Ultraviolet (UV) irradiation.3. The photocatalytic activities of CdO-TiO₂ nanocomposite photocatalytic catalysts prepared by different dry methods were compared, and an conclusion can be made that photocatalyst prepared by co-precipitation method combined with Supercritical Fluid Dry (SCFD) Combination technology had the highest photocatalytic activity, XRD results show that CdO is finely dispersed in anatase TiO₂ crystal lattice and the particle size of this catalyst is about 10nm; IR results show that even under low doping amount CdO nanoparticles can be observed.4. The photocatalytic mechanism under ultraviolet or visible light irradiation of CdS-TiO₂/AC supported or CdS-TiO₂ nonsupported nanocomposite conductor system and CdO-TiO₂ nanocomposite conductor system were also discussed in this paper. CdS/TiO₂ nanocomposite conductor was the combination of conductor with wide band gap and low condution band combined with conductor with narrow band gap and high conduction band, while CdO-TiO₂ nanocomposite conductor was the combination of conductor with wide band gap and high condution band combined with conductor with narrow band gap and low conduction band.