氧化锌-硫化镉异质结构材料的设计、合成与光催化制氢研究

IMR OpenIR

	氧化锌-硫化镉异质结构材料的设计、合成与光催化制氢研究
	王学文
学位类型	博士
导师	逯高清 ; 成会明
	2011
学位授予单位	中国科学院金属研究所
学位授予地点	北京
学位专业	材料学
关键词	Zno-cds 异质结构光催化 Z型机制氢 Zno-cds Heterostructure Photocatalysis Z-scheme Hydrogen
摘要	"能源枯竭和环境污染是当今人类社会面临的主要问题，为了实现社会可持续发展，必须开发可循环使用的清洁能源。光催化分解水制氢可直接将太阳能转化为氢能。高效光催化制氢材料的设计和合成是光催化研究的重点内容。目前单相半导体催化材料主要采用掺杂和晶面控制等调控其电子结构，提高光响应和催化活性，但其发展受到材料本身的限制。而复合型催化材料不仅可拓展光谱响应范围，而且可通过载流子分离和转移的改善提高光催化活性。因此，本论文从复合型催化材料的设计出发，以直接Z型载流子转移机制为基础，设计并合成了ZnO-CdS异质结构光催化制氢材料。通过基元相的形貌结构控制、合成方法改进、极性界面优化及调控与增强载流子转移效率等方法提高ZnO-CdS异质结构的产氢速效率。根据Z型载流子转移机制的热力学规律，选择ZnO和CdS为基元相。采用溶液法合成了ZnO-CdS异质结构复合型光催化材料，研究了其光电化学和光催化制氢性能变化，发现ZnO-CdS异质结构表现出比CdS和ZnO高数倍到数十倍的光催化活性。其能带结构、基元相比例、界面组成及光生电子寿命等对光催化产氢效率都有影响，据此提出了在ZnO-CdS异质结构中的直接Z型载流子转移机制。为了解决溶液法制备的ZnO-CdS异质结构在光催化过程中的不稳定性和提高光催化产氢效率，发展了水热-热解硫化两步合成路径，制备以氧化锌棒为核、CdS纳米颗粒为壳的ZnO-CdS核壳棒状结构。该异质结构材料不仅光催化产氢速率明显提高，且具有良好的光催化稳定性。对共催化剂优化选择，当负载1 wt% RuO2纳米颗粒作为氧化反应位后，产氢速率可达到6.18 mol h-1 g-1。在ZnO-CdS异质结构中，ZnO和CdS界面间的载流子分离和转移对光催化活性的提高至关重要，因此研究了界面属性的变化对催化活性的影响。通过调节反应参数获得了（0001）和（000 ）极性面占不同比例的ZnO六棱盘，与CdS纳米颗粒复合后，发现极性界面比例高的ZnO disk-CdS异质结构有利于光生电子和空穴的分离，表现出更高的光催化产氢效率。通过模拟计算发现ZnO的（0001）和（000 ）极性面易吸附水分子且为金属性，有利于载流子在其表面的迁移。为了进一步提高光生电子和空穴的转移效率，引入金属相来调控复合型催化材料界面处的载流子转移过程。在ZnO-CdS异质结构基础上，设计和合成金属核增强载流子转移的复合型光催化材料Cd@ZnO-CdS，其中以金属镉作为核，ZnO-CdS异质结构为壳，金属镉是ZnO和CdS的连接桥梁，为两相间的载流子转移提供通道。该异质结构表现出非常高的光催化产氢速率（19.2 mol h-1 g-1）。"
其他摘要	"To keep sustainable development, searching renewable and clean energy has been a challenging yet very important research field due to the growing environmental concerns and increasing energy demand. Photocatalytic hydrogen evolution from water splitting under solar light irradiation is a direct route for converting solar light to hydrogen energy. It is very important to develop a photocatalyst with a high quantum yield. Compared to single-phase photocatalysts, which usually have less flexibility in changing their electronic structure by doping, facet optimization etc.. The multi-composition photocatalysts are becoming an important direction filed, which possesses significant advantages of extending light response range and promoting the separation of photoinduced charge carriers. In this dissertation, ZnO-CdS heterostructure photocatalysts are designed and synthesized based on a Z-scheme charge-carrier transport mechanism. Photocatalytic hydrogen evolution activity is improved through phase optimization, structure design, synthesis improvement, polar interface induction and improvment of the carrier transport process. ZnO and CdS are chosen for ZnO-CdS heterostructure photocatalysts based on the band energy requirement of a Z-scheme charge-carrier transport mechanism. ZnO-CdS heterostructures are prepared by a solution method and studied in the photoelectrical-chemical ability and photocatalytic hydrogen evolution. They are much higher than that of ZnO or CdS. The photocatalytic ability is affected by their band energy, phase proportion, interface and photoexcited electron lifetime. Therefore, a direct Z-scheme charge-carrier transport mechanism has been developed in the ZnO-CdS heterostructure. To improve the photocatalytic stability and activity of the ZnO-CdS heterostructures, a ZnO-CdS core-shell rod is designed and prepared via a two-step route (including hydrothermal and solid state reaction). Both photocatalytic stability and activity are greatly improved. And after loading 1 wt% RuO2 nanoparticles as oxidative sites, its hydrogen evolution rate reaches 6.18 mmol h-1 g-1. Photoexcited carrier transport under the interface of ZnO and CdS is a key step for improving photocatalytic activity. ZnO disks with different ratios of (0001) and (000 ) polar facets are prepared. After loading CdS nanoparticles, ZnO disk-CdS with more polar interfaces for promoting photoexcited electron and hole separation and transport, shows higher photocatalytic performance than that of ZnO rod-CdS. The first-principles calculations show that (0001) and (000 ) polar facets with feasible water absorption are metallic, which is helpful for the photoexcited charge-carrier transport on the surface. Photoexcited charge-carrier transport in heterostructure photocatalysts is improved by inducing a metal phase into the heterostructures. Cd@ZnO-CdS heterostructures are designed based on a metal Cd core to improve photoexcited charge-carrier transport for increasing photocatalytic hydrogen evolution. The Cd@ZnO-CdS heterostructure with a metal Cd core and ZnO-CdS heterostructure shell exhibits a very high photocatalytic hydrogen evolution rate at 19.2 mmol h-1 g-1."
文献类型	学位论文
条目标识符	http://ir.imr.ac.cn/handle/321006/64304
专题	中国科学院金属研究所
推荐引用方式 GB/T 7714	王学文. 氧化锌-硫化镉异质结构材料的设计、合成与光催化制氢研究[D]. 北京. 中国科学院金属研究所,2011.