CdS-TiO2/AC和CdO-TiO2纳米复合光催化剂性能和机理研究/STUDIES ON PHOTOCATALYTIC ACTIVITY AND MECHA

2019-01-10 23:40:43

TiO2 photocatalytic band CdS CDO



半导体光催化具有室温深度反应和可以直接利用太阳能作为光源来驱动反应等独特性能,而成为一种理想的环境污染治理技术和洁净能源生产技术。宽禁带半导体 TiO2作为光催化剂,性质稳定、无毒价廉、效率高,常温常压下即可操作,几乎可以无选择地氧化分解各种有机物;但仅能被紫外光激发;加之为了追求纳米级光催化剂的高活性,制备出的催化剂光吸收带边往往会因量子尺寸效应而进一步蓝移,因此如何高效利用可见光进行光催化反应已引起人们的兴趣。本课题开创了共沉淀法结合超临界流体干燥组合技术制备CdS-TiO2/AC,CdO-TiO2纳米复合光催化材料,筛选了制备工艺条件,优化了使用工艺条件,并对催化剂结构进行了XRD,IR,TEM测试,考察其光催化活性,讨论了光催化反应机理,取得了如下创新结论。
1. 负载型CdS-TiO2/AC纳米复合光催化剂最佳制备工艺:溶胶-凝胶法结合沉淀法,CdS复合量为1.75 wt. %,m(TiO2)/m(AC)=1/3, 110℃干燥,加入0.1v%H2O2作氧化剂,紫外光下降解1000 mg•L-1丙烯酸溶液6 h的降解率为97.9%;CdS复合量为24.59 wt. %,350℃煅烧1h,加入0.17v%H2O2作氧化剂,可见光下6 h 的降解率为95.3%。XRD结果表明CdS高度分散在锐钛矿TiO2晶格中,UV-Vis DRS结果表明:复合实现了TiO2光吸收向可见光转移。
2. 非负载型CdO-TiO2纳米复合光催化剂最佳制备工艺:共沉淀法结合超临界流体干燥组合技术,CdO%=5at.%,500℃煅烧1h, 加入0.1v%的H2O2作氧化剂,紫外光下降解3000 mg•L-1丙烯酸溶液6 h的降解率为94.4%。
3. 比较了采用不同干燥方式制备的CdO-TiO2 纳米复合光催化剂性能,得出采用共沉淀法结合超临界流体组合技术(SCFD)制备的光催化剂催化活性最好,XRD结果表明CdO高度分散在锐钛矿TiO2晶格中,催化剂粒径在10nm左右;IR结果表明CdO少量掺杂的情况下,复合粒子里也可观测到CdO纳米粒子的存在。
4. 探讨了复合半导体中宽能带隙、低能导带的半导体微粒和窄能带隙、高能导带的半导体微粒复合体系CdS-TiO2/AC或CdS-TiO2和宽能带隙、高能导带的半导体微粒和窄能带隙、低能导带的半导体微粒复合体系CdO-TiO2体系紫外光和可见光下不同的光催化机理。



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.