异质结型复合光催化剂的制备及模拟太阳光催化制氢和光催化剂修饰贮氢合金研究

【作者】 朱裔荣；

【导师】 唐有根； 阎建辉；

【作者基本信息】 中南大学 ， 应用化学， 2008， 硕士

【摘要】 本论文首先制备了掺杂型锆酸盐和钛酸盐异质结复合光催化剂，并以贵金属及金属氧化物对其进行了修饰。采用XRD、SEM、IR、TG-DTA、UV-Vis、FS等技术对其进行了表征。以草酸为电子给体，光催化分解水产氢评价了催化剂的活性。研究了光催化剂活性的影响因素及连续使用效果，并探讨了异质结光催化剂的活性机理及光生载流子分离机理，为丰富钙钛矿异质结型复合氧化物的研究提供一些实验数据和理论参考。其次，将光催化剂与贮氢合金复合制成可光充电的光催化贮氢合金电极（记作PHSA），以电化学充放电性能作为评价手段，考察了光催化剂修饰和光照处理对贮氢合金电化学性能影响方面做了一些初步的研究。（1）溶胶包覆法制备的异质结SrZr_0．95Y_0．05O₃-TiO_2-xN_x复合光催化剂在模拟太阳光条件下有较好的光催化产氢活性，其催化活性明显高于纯的SrZr_0．95Y_0．05O₃和TiO₂。详细研究了不同条件下制备的复合催化剂，得出了最佳的工艺条件：给电子体浓度为30～70mmol／L，溶液pH值为2～4，氮源剂为三乙胺，N／Ti摩尔比为8：100，TiO₂复合含量为70wt％，焙烧温度为400℃，焙烧气氛为空气气氛。不同方法进一步负载铂后，其产氢量均得到提高，其中以光还原法的负载效果最佳，在最佳负载量1wt％下，平均产氢速率达到2．1mmol·g·cat^-1h^-1。同时还探讨了Pt载异质结复合光催化剂的稳定性和可能的光催化机理。（2）采用固相烧结法在不同条件下制备了氮掺杂改性SrTiO₃，并考察了模拟太阳光下的产氢活性。得到了固相法制备的最佳实验条件：氮源剂为六次亚甲基四胺（HMT），SrTiO₃与HMT质量比为1：3，焙烧温度为450℃。在此条件下，采用氢还原和光还原法负载铂使光催化产氢活性得到较大的提高，其中氢还原法比光还原法负载铂效果更好，两者最佳负载量均为2wt％，平均产氢速率分别为1．15和0．38 mmol·g·cat^-1h^-1。此外，采用氢还原法负载NiO、CoO和ZnO也取得了较为理想的产氢效果，探讨了负载物的不同处理方法对光催化剂产氢活性的影响，发现氧化物的负载先氢还原后氧化处理较直接氧化处理有更高的光催化活性；同时还研究了三种负载物的最佳负载量、产氢活性变化规律及其异质结作用机理。（3）对（2）中所制各的最佳条件的氮掺杂SrTiO₃以溶胶包覆法使其与TiO₂进行复合，并采用氢还原法于复合催化剂表面进一步沉积Pt和Pd。从TiO₂复合含量、焙烧温度、负载量方面考察了异质结复合催化剂模拟太阳光下的光催化产氢活性。结果表明，当复合催化剂中TiO₂的质量百分含量为70％，焙烧温度为400℃，Pt和Pd负载量均为2wt％时，平均产氢速率分别达到5．1和5．4mmol·g·cat^-1h^-1。（4）将（3）中所制备的Pt载复合光催化剂修饰贮氢合金制备成可光充电的PHSA，电化学充放电测试表明，光催化剂对贮氢合金的修饰，其充放电性能并没有得到改善。将PHSA紫外光处理后其活化性能、最大放电容量、高倍率放电性能以及循环性能均明显优于无光照的处理，而纯贮氢合金经光照处理其充放电性能基本上没有变化。光照处理PHSA与纯贮氢合金相比，光催化剂添加量为5％时其首次活化的容量明显要高，活化达到的最大容量也略高，但循环性能有所降低。更多还原

【Abstract】 Doping zirconate and titanate heterojunction composite photocatalysts were prepared firstly and noble metal or metal oxide was further modified. These photocatalysts were characterized by X-ray diffraction, scanning electron microscope, fourier transform infrared, thermogravimetry and differential thermal analysis, ultraviolet visible diffuse reflectance absorption spectra, fluorescence spectra. The photocatalytic generation of hydrogen in oxalic acid solution was used as the probe reaction to evaluate the photocatalytic activity of the photocatalyst. The influencing factors of photocatalytic activity and continuous usage property of photocatalysts were investigated. We also studied the mechanism of photocatalytic activity and photo-generated carrier separation of photocatalyst. These can afford some experimental data and theoretical references for enriching the research on perovskite heterojunction composite oxides. Secondly, the photocatalytic hydrogen storage alloy （PHSA） was made by the combination of photocatalyst with hydrogen storage alloy. The electrochemical test was used as a means to evaluate their charge-discharge properties. The effect of photocatalyst modification and UV light treatment on the electrochemical property of hydrogen storage alloy was discussed.SrZr_0.95Y_0.05O₃-TiO_2-xN_x heterojunction composite photocatalyst prepared by sol coating method had high activity under simulated sunlight irradiation. The photocatalytic activity of composite particles was higher than that of pure TiO₂ and pure SrZr_0.95Y_0.05O₃. The composite catalysts prepared under different conditions were systematically investigated and the optimum conditions were obtained as follows: the concentration of electron donor was 30-70mmol/L, the pH value was 2-4, the nitrogen source regent was triethylamine, the molar ratio of N/Ti was 8:100, the content of TiO₂ in composite catalyst was 70mass%, the calcination temperature was 400℃and the calcination atmosphere was air. After further loading Pt by different methods, the photocatalytic activity of hydrogen generation was all greatly improved, and the in situ photoreduction method showed the optimized activity of hydrogen generation. The average rate of hydrogen generation was up to 2.1 mmol·g·cat^-1h^-1when the optimum loaded content was 1 mass %. Meanwhile, we also discussed the stability of Pt loaded heterojunction composite photocatalyst and possible photocatalytic mechanism. Nitrogen doped SrTiO₃ were prepared by solid sintering method under different conditions. The photocatalytic hydrogen generation activity of catalysts was discussed. The optimal preparation condition was obtained by experiments: the nitrogen source was HMT, the mass proportion of SrTiO₃ and HMT was 1:3, and the calcination temperature was 450℃. Under this condition, the photocatalytic activity of hydrogen generation was both greatly improved after losding Pt on nitrogen doped SrTiO₃ by hydrogen reduction method and photoreduction method respectively, and the photocatalytic activity of photocatalysts prepared by hydrogen reduction method was better than that prepared by photoreduction method. The average rates of hydrogen generation were respectively up to 1.15 and 0.38 mmol-g-caf’h"1 when the optimal loaded content were both 2mass%. Moreover, the good result of hydrogen generation was achieved by loading NiO, CoO and ZnO with hydrogen reduction method. The effect of different treatment methods of loading NiO on hydrogen generation activity of nitrogen doped SrTiO3 was also studied. The result demonstrated that the NiO loaded composite catalyst showed higher photocatalytic activity when NiO was loaded by hydrogen reduction treatment firstly and then oxidation treatment than NiO was loaded by direct oxidation treatment. The optimal loaded contents, the law of hydrogen generation and heterojunction mechanism of three loadings were also discussed.The nitrogen doped SrTiO₃ obtained from above further combined with TiO₂ by sol coating method to form heterojunction composite catalyst, and noble metal Pt and Pd particles were further modified by hydrogen reduction method. Photocatalytic hydrogen generation was used as the probe reaction to evaluate the photocatalytic activity of photocatalysts under simulated sunlight irradiation in detail from the aspects of different contents of TiO₂ in the composite particles, different calcination temperatures, and different contents of Pt and Pd. The result demonstrated that the average rates of hydrogen generation were respectively up to 5.1 and 5.4mmol·g·cat^-1h^-1 when the optimal loaded contents of Pt and Pd were both 2mass%.The photo-charge PHSA was made·by the modification of Pt loaded composite catalyst on hydrogen storage alloy. The electrochemical charge-discharge test demonstrated that the charge-discharge property didn’t improve when the photocatalyst was modified on hydrogen storage alloy. The activation property, biggest discharge capacity, high-rate discharge property and cycle property of the PHSA with light treatment was superior to that of the PHSA without light treatment, and whereas the charge-discharge property of pure hydrogen storage alloy with light treatment was almost the same as that without light treatment. The capacity of first activation and the biggest activation capacity of PHSA with light treatment were slightly higher and the cycle property decreased when compared to pure hydrogen storage alloy.更多还原