金属助催化剂的制备及其对CdS可见光分解水产氢性能的影响

发布时间：2018-08-27 05:48

【摘要】：太阳能光解水制氢在解决全球能源和环境问题中具有重要的研究价值。CdS具有可见光响应,但单独作为光催化剂存在产氢速率低及易发生光腐蚀的缺点。通常采用负载贵金属来提高产氢效率,但是却显著提高了催化剂的成本,限制了太阳能分解水产氢的实际应用。本文旨在减少贵金属Pt的用量并提高CdS光催化体系的产氢活性,主要采用两种技术路线：1)采用非贵金属镍(Ni)作为助催化剂。通过控制Ni纳米粒子的大小和结晶度提高体系的产氢活性；2)采用铂基二元金属助催化剂Pt@M(M=Pd,Ru),考察二元金属协同催化作用对体系产氢速率的影响。研究内容具体如下：一、Ni助催化剂对CdS可见光产氢活性的影响研究减小Ni的晶粒尺度：以CdS为基础光催化剂,进行非贵金属Ni纳米颗粒的控制沉积的研究。首先通过化学还原法制得Ni纳米颗粒,然后利用光解水反应产生的光生电子将其负载到CdS表面。采用透射电镜、粉末X射线衍射仪、紫外-可见漫反射光谱仪和荧光光谱仪对制备的光催化剂进行表征。透射电镜显示制得的Ni纳米颗粒直径约为3 nm,且均匀地沉积于CdS表面。Ni纳米粒子在光解水过程中,选择性地沉积于CdS的(100),(002)和(101)晶面制得的纳米Ni/CdS光催化剂表现出较高的分解水制氢活性。紫外-可见漫发射图显示,Ni的负载增加了CdS对可见光的吸收。在荧光图谱中,Ni/CdS发生了荧光淬灭现象,这是由于CdS表面沉积的Ni纳米粒子在CdS光催化分解水反应中充当了电子捕获阱的角色。以300 W氙灯为光源,(NH4)2SO3为牺牲试剂,对Ni/CdS进行了可见光分解水产氢性能的测试。结果表明Ni的最佳负载量为2.5%,产氢速率高达9.050 mmol·h-1·g-1,对应于λ=420 nm处的量子效率为9.4%；且Ni/CdS连续反应16.5 h后,催化活性未出现降低现象,显示了催化剂的稳定性。提高Ni的结晶度：通过化学还原法制备了高结晶度的Ni纳米颗粒,即在碱性条件下,采用水合肼N2H4·H2O在70℃将NiC12还原。在CdS发生分解水反应的同时,利用光生电子将制得的Ni纳米粒子沉积在CdS纳米棒表面,即采用光化学还原的方法将Ni纳米颗粒沉积于CdS纳米棒表面形成Ni/CdS光催化剂。采用透射电镜、粉末X射线衍射仪、紫外-可见漫反射光谱仪、比表面积及孔隙率分析仪和荧光光谱仪对光催化剂进行了表征。由XRD图得知高结晶度的Ni纳米粒子是fcc结构,透射电镜图显示Ni纳米颗粒的平均直径为10 nm。在光催化反应中,Ni纳米粒子选择性地沉积于CdS纳米棒的(100)、(002)和(101)晶面。Ni/CdS的BET比表面积为28.8 m2/g,高于单独的CdS纳米棒,证实了Ni纳米晶体沉积在CdS纳米棒表面。此外Ni/CdS在可见光区域的吸收有所增强,且Ni的沉积导致了CdS产生了荧光淬灭现象,说明Ni在光解水反应中充当电子捕获阱的角色,提高了载流子的利用效率。光催化分解水产氢实验表明负载量为4%时Ni/CdS表现出最高的产氢活性,高达25.848 mmol·h-1·-g-1,对应于λ-420 nm处的量子效率为26.8%,且在连续反应20 h后活性仍旧十分稳定。高结晶度的助催化剂Ni纳米粒子在提高CdS光催化活性方面很有成效。二、铂基二元金属助催化剂Pt@M(M=Pd, Ru)的合成及其对CdS可见光产氢活性的影响研究采用两步还原法分别制备了Pt@Pd和Pt@Ru二元金属纳米颗粒,并通过光化学还原法将其沉积在CdS表面,研究了其对CdS可见光分解水产氢性能的影响。采用X射线光电子能谱、透射电镜、紫外-可见漫反射及时间分辨荧光技术对光催化剂进行了表征。XPS结果证实了二元金属核壳结构的存在,TEM显示制得的铂钯和铂钌二元金属纳米粒子大小约为10 nm,分别形成了核壳结构的Pt@Pd和Pt@Ru。UV-Vis DRS显示核壳结构的助催化剂Pt@Pd和Pt@Ru负载到CdS表面,增加了其对可见光的吸收。以300 W氙灯为光源,以(NH4)2SO3为牺牲试剂,分别考察了单一助催化剂Pt、Pd和Ru及二元助催化剂Pt@Pd和Pt@Ru对CdS光分解水产氢性能的影响。实验表明,二元金属助催化剂的协同效应导致了光催化活性的提高,其中铂钯比为7：3时,产氢速率最高(26.9 mmol·h-1·g-1);铂钌比为7：3时,产氢速率最高(18.4 mmol·h-1·g1),均高于单一助催化剂的最高产氢活性。TRPL表明二元金属助催化剂延长了载流子的寿命,提高了光催化活性。
[Abstract]:Solar photolysis of water to produce hydrogen has important research value in solving global energy and environmental problems. CdS has visible light response, but as a single photocatalyst, it has the shortcomings of low hydrogen production rate and easy photocorrosion. Usually, noble metals are loaded to improve the hydrogen production efficiency, but the cost of the catalyst is significantly increased and the catalyst is limited too much. In order to reduce the amount of precious metal Pt and improve the hydrogen production activity of CdS photocatalytic system, two technical routes were adopted: 1) using non-precious metal nickel (Ni) as co-catalyst; 2) using platinum-based binary gold to improve the hydrogen production activity of the system by controlling the size and crystallinity of Ni nanoparticles; Pt@M(M=Pd,Ru) is a co-catalyst. The effect of binary metal synergistic catalysis on hydrogen production rate of the system was investigated. The main contents are as follows: 1. The effect of Ni co-catalyst on visible light hydrogen production activity of CdS was studied. The grain size of Ni was reduced. The controlled deposition of non-noble metal Ni nanoparticles was studied based on CdS photocatalyst. Ni nanoparticles were prepared by chemical reduction and then loaded onto CdS surface by photogenerated electrons produced by photolysis of water. The photocatalysts were characterized by TEM, powder X-ray diffraction, UV-Vis diffuse reflectance spectroscopy and fluorescence spectroscopy. The diameter of Ni nanoparticles was about 1. Ni nanoparticles were selectively deposited on the (100), (002) and (101) surfaces of CdS during the photolysis of water. The photocatalytic activity of Ni/CdS prepared on the (100), (002) and (101) surfaces of CdS was high. The UV-Vis diffuse emission spectra showed that the Ni loading increased the absorption of CdS to visible light. Fluorescence quenching occurred because Ni nanoparticles deposited on CdS surface acted as electron trapping traps in CdS photocatalytic water decomposition reaction. Using 300 W xenon lamp as light source, (NH4)2SO3 as sacrificial reagent, the hydrogen production performance of Ni/CdS in visible light aquatic decomposition was tested. The results showed that the optimum loading of Ni was 2.5%, and the hydrogen production rate was high. The quantum efficiency corresponding to lambda=420 nm is 9.4%, and the catalytic activity of Ni/CdS does not decrease after 16.5 hours of continuous reaction, showing the stability of the catalyst. To improve the crystallinity of Ni, high crystallinity Ni nanoparticles were prepared by chemical reduction method, that is, hydrazine hydrate N2H4.H2O was used in alkaline conditions. NiC12 was reduced at 70 C. When CdS was decomposed into water, the Ni nanoparticles were deposited on the surface of CdS nanorods by photoelectrons. The Ni nanoparticles were deposited on the surface of CdS nanorods by photochemical reduction to form Ni/CdS photocatalyst. Transmission electron microscopy, powder X-ray diffraction and UV-Vis diffuse reflection were used. The photocatalysts were characterized by spectroscope, specific surface area and porosity analyzer and fluorescence spectrometer. XRD showed that the highly crystalline Ni nanoparticles were FCC structure. TEM showed that the average diameter of Ni nanoparticles was 10 nm. In photocatalytic reaction, Ni nanoparticles were selectively deposited on (100), (002) and (101) CdS nanorods. The BET specific surface area of Ni/CdS is 28.8 m2/g, which is higher than that of CdS nanorods alone. It is confirmed that Ni nanocrystals are deposited on the surface of CdS nanorods. In addition, the absorption of Ni/CdS in the visible region is enhanced, and the deposition of Ni results in the fluorescence quenching of CdS, indicating that Ni acts as an electron trap in the photolysis of water reaction and enhances the absorption of Ni/CdS nanocrystals. The photocatalytic decomposition of water for hydrogen production showed that Ni/CdS exhibited the highest hydrogen production activity at 4% loading, up to 25.848 mmol H-1 g-1 and 26.8% quantum efficiency corresponding to lambda-420 nm. The activity remained very stable after 20 h of continuous reaction. Pt@Pd and Pt@Ru binary metal nanoparticles were prepared by two-step reduction method and deposited on CdS surface by photochemical reduction method. Their effects on CdS visible light decomposition aquatic products were studied. The photocatalyst was characterized by X-ray photoelectron spectroscopy, transmission electron microscopy, ultraviolet-visible diffuse reflectance and time-resolved fluorescence spectroscopy. XPS results confirmed the existence of binary metal core-shell structure. TEM showed that the prepared Pt-Pd and Pt-Ru binary metal nanoparticles were about 10 nm in size, forming core-shell structure P, respectively. T@Pd and Pt@Ru.UV-Vis DRS showed that the core-shell structure of the promoters Pt@Pd and Pt@Ru were loaded on the surface of CdS to increase their visible light absorption. The effects of single promoter Pt, Pd and Ru as well as binary promoters Pt@Pd and Pt@Ru on the photodecomposition of aquatic hydrogen by CdS were investigated using 300 W xenon lamp as light source and (NH4)2SO3 as sacrificial reagent, respectively. The results show that the synergistic effect of binary metal promoters leads to the enhancement of photocatalytic activity, in which the highest hydrogen production rate (26.9 mmol H 1 g 1) occurs when the Pt Pd ratio is 7:3, and the highest hydrogen production rate (18.4 mmol H 1 g 1) occurs when Pt Ru ratio is 7:3, which is higher than the highest hydrogen production activity of a single The lifetime of carriers increases the photocatalytic activity.
【学位授予单位】：河南大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：O643.36;TQ116.2

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