利用地球上丰富的炭黑和NiS_2双助催化剂修饰提高CdS纳米片体系的可见光产氢活性(英文)

光催化产氢技术是目前解决能源和环境问题的最有潜力的方法之一,因此制备安全高效的光催化剂已成为目前的研究热点.在目前研究的各种光催化剂中,CdS光催化剂因为具有较窄的带隙(2.4 eV)和合适的导带位置,所以在可见光催化产氢领域受到广泛关注.然而,光生电子/空穴对易复合和光腐蚀作用极大地限制了CdS光催化剂的放大应用.因此,人们采用众多改性策略以提高CdS光催化剂的可见光产氢活性,其中构建CdS纳米结构和负载助催化剂被认为是最有效的方式.构建CdS纳米结构既可以缩短载流子的迁移路径,也可以减少CdS晶体中的缺陷.很多不同纳米结构的CdS光催化剂已经被开发,例如纳米线、纳米颗粒和纳米棒等.因为制备过程极为复杂繁琐,所以CdS纳米片的研究鲜见报道.本文采用乙酸鎘和硫脲为原材料,通过简单的溶剂热法合成了CdS纳米片.在CdS的各类助催化剂中,由于常用的Pt,Ag和Au等贵金属的高成本和低储量等问题严重限制了它们的实际应用,所以近年来众多非贵金属助催化剂(例如MoS_2,WS2,NiS,NiO和WC等)得到了广泛关注.由于非贵金属助催化剂存在弱电导率和低功函数等问题,影响了对光生电子的收集和利用.纳米碳材料具有极高的电导率、强可见光吸收、有效的载流子分离和较多的反应位点等优点,因此组合纳米碳材料和非贵金属助催化剂被认为是一种有效的解决方案.本文首次采用炭黑和NiS_2作为双助催化剂改性CdS纳米片,通过简单的溶剂热/沉淀两步法成功合成了廉价高效的CdS/CB/NiS_2三元光催化体系.光催化产氢性能测试表明,CdS-0.5%CB-1%NiS_2展现出最高的光催化效率(166.7μmol h~(-1)),分别是CdS NSs和CdS-1.0%NiS_2的5.16和1.87倍.X射线衍射、高分辨电子显微镜和X射线光电子能谱结果证实了CdS催化剂的片状结构,且炭黑和NiS_2成功负载在CdS纳米片表面.紫外-可见漫反射结果表明,随着炭黑和NiS_2的负载,复合催化剂的吸收边缘产生明显的红移,且对可见光的吸收增强.荧光光谱、阻抗和瞬态光电流曲线测试结果证明,炭黑和NiS_2的加入可以有效地促进光生电子/空穴对分离.极化曲线结果表明,加入炭黑和NiS_2可以降低CdS的产氢过电势,因此加速表面产氢动力学.总之,炭黑和NiS_2之间显著的协同效应极大地提高了可见光吸收,促进光生电子/空穴对分离,加速表面产氢动力学,最终得到了三元光催化体系极高的光催化产氢活性.

Improved visible-light photocatalytic H2 generation over CdS nanosheets decorated by NiS2 and metallic carbon black as dual earth-abundant cocatalysts

CdS nanosheets (NSs) photocatalysts modified with dual earth-abundant co-catalysts of metallic carbon black (CB) and NiS2 were synthesized by a two-step solvothermal/impregnation method. All the experiment results demonstrated that the co-loading of CB and NiS2 could significantly enhance the photocatalytic H2-evolution activity of CdS NSs. The photocatalytic performance of the as-prepared CdS/CB/NiS2 samples was tested under visible light (λ ≥ 420 nm) by using an aqueous solution containing 0.25 mol L–1 Na2S-Na2SO3 as the sacrifice agent. The CdS-0.5%CB-1.0%NiS2 composite photocatalysts exhibited the highest H2-evolution rate of 166.7 μmol h-1, which was ap-proximately 5.16 and 1.87 times higher than those of pure CdS NSs and CdS-1.0%NiS2, respectively. The possible mechanism for the enhanced H2-evolution activity of CdS/CB/NiS2 composite photo-catalysts was proposed. The results showed that the enhanced photocatalytic H2-evolution activities could be ascribed to the co-loading of metallic CB and NiS2 as co-catalysts onto the surface of CdS NSs. The excellent synergetic effect between the CB and NiS2 could obviously improve visible light absorption, promote separation of photogenerated electron-hole pairs and boost the H2-evolution kinetics, thus leading to an enhanced activity for H2 evolution. More interestingly, the metallic CB could not only act as a cocatalyst for H2 evolution, but also serve as a conductive electron bridge to promote the charge migration. This work not only demonstrates that loading CB as a co-catalyst is a promising strategy to further boost the photocatalytic activity of CdS/NiS2 composites, but also offers a new mechanistic insight into the construction of highly efficient and stable CdS NSs-based hybrid photocatalysts with dual earth-abundant co-catalysts for photocatalytic applications.