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g-C3N4基复合材料的制备及可见光光催化分解水制氢性能研究
丁小玲
学位类型硕士
导师李英宣
2016-05-24
学位授予单位中国科学院大学
学位授予地点北京
学位专业材料工程
关键词氢能 光催化剂 金属硫化物 类石墨相氮化碳 可见光光催化
摘要

氢能是一种理想的绿色能源,具有高燃烧值和无污染两大优点,其开发利用备受各个领域科研工作者的重视。目前工业上制氢的途径很多,如水电解制氢、天然气水蒸气催化转化制氢、煤炭气化制氢等,但是这些制氢方法存在成本高、耗能多以及污染大等缺陷。利用丰富的太阳能光催化分解水制取氢气是一种兼顾能耗、资源和环境的最有前途和最为理想的氢能开发技术。此技术实用化的关键在于开发高效的具有可见光响应的光催化剂。基于半导体光催化剂的发展现状,本论文结合n型聚合物半导体g-C3N4和硫化物构建了一系列新型的复合半导体光催化材料体系,并研究了该系列光催化剂在可见光催化分解制氢方面的性能,为半导体光解水制氢材料的发展提供了新的思路、实验依据和理论支持。本论文主要研究内容如下:(1)采用两步还原法制备了新型三元复合光催化剂CdS/Au/g-C3N4。通过X射线衍射(XRD)、高分辨透射电镜(HRTEM)、X射线能谱(EDX)、紫外-可见漫反射(UV-vis DRS)、光致发光光谱(PL)等表征手段分析了复合材料的结构、形貌和光学性质,并以CH3OH为电子给体,评价了材料的可见光分解水制氢活性。结果表明,CdS包裹Au纳米粒子周围形成核壳型结构,并负载在g-C3N4表面上。CdS/Au/g-C3N4比g-C3N4和Au/g-C3N4具有更好的可见光吸收能力和光生电子-空穴分离效率,进而拥有最佳的产氢效率。通过对反应机理的分析得出, Z型光催化体系和CdS与g-C3N4形成了异质结结构对CdS/Au/g-C3N4三元复合催化剂的光学以及催化性能的提高起关键作用。(2)同样采用两步还原法合成了CdxZn1-xS/Au/g-C3N4复合光催化剂。通过XRD、场发射扫描电镜&能谱仪(FESEM & EDX)、HRTEM、DRS、PL 和光电流等表征手段分析了光催化材料的结构、形貌和光学性质。结构表明,CdxZn1-xS固溶体包裹在Au纳米粒子的周围,且与g-C3N4半晶体材料形成异质结结构;CdxZn1-xS固溶体的引入提高了材料的可见光吸收强度,并拓宽了其吸收范围;与g-C3N4和Au/g-C3N4相比,三元复合光催化剂具有更低的光生电子-空穴复合率。以葡萄糖为电子给体,可见光下产氢结果表明,Cd0.8Zn0.2S/Au/g-C3N4复合光催化剂在葡萄糖浓度为0.1 mol×L-1下的光催化制氢活性最高,其产氢速率(123.21 mmol×g-1×h-1)分别是Pt/g-C3N4和CdS/Au/g-C3N4的7.26倍和1.23倍。进一步分析葡萄糖的气相氧化产物发现,CdS的复合有利于降低气相产物中CO的产生,而形成CdxZn1-xS固溶体后,产物中的CO2的比例进一步降低,说明复合CdxZn1-xS固溶体不仅能够提高材料的光催化性能,而且能够进一步降低气相产物中的副产物的产量。该发现为制备高选择性的光催化材料提供了新的途径。另外,循环伏安法测试和质谱(MS)实验结果表明,葡萄糖氧化过程中产生的中间液相产物是葡萄糖酸。

其他摘要

Hydrogen (H2) is an ideal green energy source to solve the energy crisis and environmental pollution because it has advantages of high combustion value and non-pollution. The development and utilization of hydrogen has been paid much attention by many researchers in various fields. At present, there are a large of ways to produce hydrogen in the industry, such as water electrolysis hydrogen production, coal gasification, etc., but these methods have many drawbacks such as high cost, many energy consumption and severe pollution. Photocatalytic splitting water on the semiconductors utilizing abundant solar energy has been considered to a promising approach for clean, cost-effective hydrogen production. The key of this technology is the development of high efficient visible-light-induced semiconductor photocatalysts, which have many defects, such as poor solar energy utilization, low quantum efficiency and easily deactivation. These badly restrict the commercialization application of photocatalytic H2-production technology. Therefore, to design and develop new photocatalysts with high efficiency have extremely urgent in the environmental photocatalytic field. Based on the development of the semiconductor photocatalysts, this thesis combined the polymer semiconductor g-C3N4 with sulfide to build a series of new type of semiconductor photocatalytic material systems, and study the visible-light photocatalytic water splitting H2-production.This work was mainly composed of two parts:In the first part, we succeeded in preparation of a new ternary composite photocatalyst CdS/Au/g-C3N4 by using reduction methods. The photacatalyst was characterized by X-ray diffraction (XRD), high resolution transmission electron microscopy (HRTEM), X-ray energy dispersive spectrum (EDX), ultraviolet-visible diffuse reflection spectrum (UV-vis DRS), photoluminescence spectrum (PL) and its performance for H2 production was evalulated using methanol as an elector donor. results showed that the Au/CdS particle is a core (Au)-shell (CdS) structure and supported on the g-C3N4 surface. The CdS/Au/g-C3N4 has higher visible-light absorption and photogenerated electron-hole separation efficiency than those of g-C3N4 and Au/g-C3N4U, thereby exhbitting the highest activity for H2 production. Based on the mechanism analysis, it can be concluded that the Z-scheme system and heterojunction structure of CdS and g-C3N4 are key factor for the enhanced optical and catalytic performance of CdS/Au/g-C3N4.In the second part, we synthesized a series of CdxZn1-xS/Au/g-C3N4 compound photocatalysts. The obtained photocatalysts were characterized by many means, such as field emission scanning electron microscopy & energy dispersive spectrum (FESEM & EDX), XRD, EDX, HRTEM, DRS, PL, etc. The structure showed that Au nanoparticles are coated with CdxZn1-xS solid solution, and the heterojunction structure was formed at the CdxZn1-xS-g-C3N4.interface. The DRS results showed that CdxZn1-xS/Au/g-C3N4 have wider visible-light absorption region. The photocatalytic H2-production over CdxZn1-xS/Au/g-C3N4 photocatalysts with glucose as an elector donor had been studied. Results showed that the activity of photocatalytic H2-production over Cd0.8Zn10.2S/Au/g-C3N4 photocatalysts was obviously promoted in 0.1 mol×L-1 glucose aqueous solution, as compared with the pure water system. The H2 evolution rate (123.21 mmol×g-1×h-1) is 7.26 and 1.23 times higher than that of Pt/g-C3N4 and CdS/Au/g-C3N4, respectively. By analysizing the gas phase oxidation products of glucose, it was found that photochemical deposition of CdS retard the CO production and the deposition of CdxZn1-xS further decreased CO2 production. These results suggested that the deposition of CdxZn1-xS can not only improve the photocatalytic performance, but also reduce the oxidation prducts. In addition, the liquid production for the glucose oxidation is gluconic acid.

文献类型学位论文
条目标识符http://ir.xjipc.cas.cn/handle/365002/4576
专题环境科学与技术研究室
作者单位中国科学院新疆理化技术研究所
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丁小玲. g-C3N4基复合材料的制备及可见光光催化分解水制氢性能研究[D]. 北京. 中国科学院大学,2016.
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