【作者】 刘兴；

【导师】 李越湘；

【作者基本信息】 南昌大学 ， 工业催化， 2013， 博士

【摘要】 作为光催化剂典型代表的TiO2,以其价廉、无毒、结构稳定、优良的物理、化学性质等众多优点,一直是光催化研究的热点。POM (polyoxometalate多金属氧酸盐)是除Ti02等半导体外,具有良好氧化还原能力和光电化学性质的另一类无机光催化剂。然而,POM和Ti02均只能利用紫外光,而太阳光中这部分光只占4%～6%,可见光却达到43-46%左右。染料敏化是一种拓展光催化剂激发波长范围、利用可见光的重要手段之一。染料敏化体系的一个重要问题就是稳定性问题,这也是制约染料敏化实际应用的重要因素。POM作为优良的电子受体,能够迅速转移染料激发态物种的电子,可以有效阻止敏化剂的降解,为构建高效、高稳定性的染料敏化制氢光催化剂或体系提供了可能。染料敏化体系的另一个重要问题是如何提高活性,通过金属离子或者非金属离子表面修饰Ti02可提高其敏化制氢活性。本论文研究了Eosin Y等占顿染料敏化POM及修饰后的Ti02光催化制氢,整个工作包括以下五个部分：(一)、研究了占吨染料(Eosin Y、 Erythrosin B、Rose Bengal)对完整Keggin结构的POM (SiW12O404-、PW12O403-等)的光敏化作用。实验以三乙醇胺为电子给体。可见光下,杂多蓝(POM-)的生成证明了染料与POM之间的电子转移。Pt共催化剂存在下,可见光照(λ≥420nm)20h,染料Eosin Y敏化PW12O403-和SiW12O404-显示了相对较高的产氢活性,平均产氢速率分别为53.3μmolh-1、51.8μmolh-1,表观量子效率分别为9.2%、8.9%。(二)、以EosinY(EY)敏化A13+取代的Keggin结构POMa-[AlSiW11(H2O)O39]5-(AlSiW,,)并用于可见光分解水制氢。Eosin Y与AlSiW11具有化学配位作用,这有利于它们之间的电荷转移,也大大提高了染料的光化学稳定性,抑制了EY的脱溴反应,因此体系显示了较高的制氢活性与很好的稳定性。结果表明,通过化学键(共价键或配位键)连接染料与POM分子可以提高光敏化体系的稳定性与活性。(三)、采用缺位的Keggin型POM SiW11O398-(SiW11)修饰TiO2,制备了SiW11/TiO2复合物。IR(红外光谱)、UV(紫外光谱)等光谱表征证明了SiW11与Ti02之的化学作用,SiW11的修饰促进了TiO2的晶化与晶粒尺寸的长大。Pt为共催化剂,EY敏化SiW11/TiO2具有高的可见光制氢的活性与稳定性,SiW11作为一个良好的电子传递剂,极大地促进了EY还原态自由基EY·-H(质子化形式)向Ti02导带的电子转移,有效抑制了EY·-的脱溴降解反应,从而大大提高了染料敏化体系的稳定性。考察了SiW11浓度、EY浓度以及Pt负载量等因素对光催化制氢的影响,优化的实验条件下,以上敏化体系在λ>420nm可见光下,20h得到了11.4%的平均表观量子效率。研究还讨论了光敏化电子转移的机理。(四)、制备了A13+偶联、Eosin Y敏化的Ti02催化剂。A13+偶联可以显著提高染料敏化Ti02催化剂的制氢活性。然而,此类催化剂的光催化稳定性却不甚如人意。考察了不同金属离子、不同含水量对光催化产生氢气的影响。以上产氢结果,再结合IR、XPS(X射线光电子能谱)、UV-Vis(紫外可见光谱)等的表征,发现催化剂在反应过程中存在水解、金属离子与TEOA络合、染料的降解等现象,从而导致光催化体系的活性降低,而在只有少量水(体积分数0.5%)存在的甲醇介质时能明显提高制氢稳定性。(五)、通过硫酸、磷酸处理TiO2,得到了S042-或P043-修饰的Ti02(记为S/TiO2、P/TiO2)。SO42-或PO43-与TiO2之间存在较强的化学配位作用。相比EY敏化TiO2,EY敏化S/TiO2、P/TiO2提高了可见光光催化制氢活性。S/TiO2与P/TiO2的导带较Ti02发生负移,键合的SO42-或P043-的诱导效应可使EY--H与S/TiO2、P/TiO2之间的氢键增强,以上均可增强光催化制氢活性。实验还考察了5042-与P043-浓度、EY浓度以及Pt负载量等因素对光催化制氢的影响。更多还原

【Abstract】 As a typical photocatalyst, TiO2is most frequently employed owing to its cheapness, nontoxicity, structural stability and intriguing physical and chemical properties etc.. POMs (polyoxometalates) are other kind of photocatalysts with intriguing redox ability as well as photoelectrochemical property. Howerover, both TiO2and POM can only be excited under ultraviolet (UV) light, which occupies only4%～6%in the solar spectra, for visible light, this number reaches to43～46%around. Dye sensitization is a good strategy to broaden the excitation wavelength range of photocatalyst and to utilize visible light.A significant problem in dye sensitization systems is the stability issue, which is also a key factor that limits their pratical applications. POMs are good electron acceptors, they can quickly transfer the electron from photoinduced dye species and suppress the decomposition of the sensitizers. So they are expected to conduct efficient and stable dye-sensitized photocatalysts or systems for hydrogen evolution. How to enhance the activities of dye sensitization systems are the other important challenge, modification of TiO2by metal ions or nonmetal ions could improve its photosensitized activity for hydrogen production.In this dissertation, xanthene dyes, such as EosinY, sensitized POMs and modified TiO2for photocatalytic hydrogen production were studied, and the whole work includes the following five sections:(I). Photosensitization of Keggin POMs (SiW12O404-、PW12O403-etc) with xanthene dyes (EosinY、Erythrosin B、Rose Bengal) were studied. Triethanolamine (TEOA) was used as electron donor in the experiments. The formation of heteropoly blue (POM-) under visible light illumination demonstrated that the electron transfer occurs between the dye and POM. In the presence of Pt as co-catalyst, Eosin Y sensitized PW12O3-or SiW12O4-system displays relatively high activity for hydrogen production with the average rates of53.3μmol h-1,51.8μmol h-1and the apparent quantum yields of9.2%,8.9%during20h irradiation (k>420nm), respectively. (Ⅱ). Eosin Y (EY)-sensitized a-[SiAlW11(H2O)O39]5-(AlSiW11)(an Al3+substituted Keggin POM) for the hydrogen evolution under visible light irradiation (λ>420nm) was investigated. EY can coordinate with AlSiW11. The coordination association between AlSiW11and EY is beneficial to the charge transfer between them and to promote the photochemical stability of EY. Thus, the system displays efficient and stable photocatalytic hydrogen evolution. The research suggests that a chemical association (coordination or covalence) between POM and dye must make contribution to improve stability and activity of dye sensitization system.(Ⅲ). TiO2was modified with a lacunary Keggin-type POM SiW11O398-(SiW11) to obtain SiW11/TiO2composite SiW11is bound at TiO2by a chemical interaction, which was demonstrated by FT-IR (Infrared spectroscopy) and UV (Ultraviolet spectroscopy). SiW11modification promotes TiO2crystallization as well as growth of the particles. EY sensitized SiW11/TiO2displays stable and efficient visible-light H2generation using Pt as a co-catalyst. SiW11, as an excellent electron relay, greatly facilitates the electron transfer from the reduced dye species EY’-H (the protonated form) to conduction band (CB) of TiO2and suppresses effectively the decomposition of EY·-. Thus, the stability of dye-sensitized system is enhanced. The factors which influenced the photocatalytic hydrogen evolution such as concentration of SiW11, concentration of EY and Pt loading content etc. were investigated. Under the optimal conditions, an average apparent quantum yield of11.4%was obtained from the above system during20h irradiation (λ>420nm). The photosensitized electron transfer mechanism was also discussed.(IV). An Al3+coupled and EY-sensitized TiO2photocatalyst was prepared. The coupling of Al3+can markedly improve the visible-light activity of dye-sensitized catalyst. Nevertheless, the stability of the as-prepared catalyst is poor. The effects of different metal ion and water content in photocatalytic system on hydrogen evolution were investigated. The results of hydrogrn evolution combined with IR, XPS (X-ray photoelectron spectroscopy) and UV-Vis specra, suggest that hydrolysis, complexing between Al3+and TEOA as well as degradation of dye result in a decreased activity of the photocatalytic system, the photocatalyst exhibits a enhanced activity and stability when water content is very low (0.5%volume fraction). (V). TiO2was modified by sulfate and phosphate (denoted as S/TiO2and P/TiO2) by simply sulfur or phosphoric acid treatment. The strong chemical coordination occurs between sulfate or phosphate and TiO2. EY sensitized S/TiO2and P/TiO2exhibit enhanced photocatalytic activity for hydrogen evolution upon visible light illumination compared to that of EY sensitized TiO2. The CB edges of S/TiO2and P/TiO2shift toward the negative, and the hydrogen bond interaction between EY·-H and S/TiO2or P/TiO2is enhanced due to the inducing effect of bound sulfate and phosphate, thus, photocatalytic hydrogen evolution is promoted. The factors which influenced the photocatalytic hydrogen evolution such as concentration of sulfate or phosphate, concentration of EY, and Pt loading content were investigated.更多还原