摘要
In this work,a novel plasmon-assisted UV-vis-NIR-driven W_(18)O_(49)/Cd_(0.5)Zn_(0.5)S heterostructure photocatalyst was obtained by a facile ultrasonic-assisted electrostatic self-assembly strategy.The hybrid exhibits extraordinary H2 evolution activity of 147.7 mmol·g^(-1)·h^(-1) at room temperature due to the efficient charge separation and expanded light absorption.Our investigation shows that the unique Step-scheme(S-scheme)charge transfer and the‘hot electron’injection are both responsible for the extraordinary H2 evolution process,depending on the wavelength of the incident light.Moreover,by accelerating the surface reaction kinetics,the activity can be further elevated to 306.1 mmol·g^(-1)·h^(-1),accompanied by a high apparent quantum yield of 45.3% at 365±7.5 nm.This work provides us a potential strategy for the highly efficient conversion of the solar energy by elaborately combining a nonstoichiometric ratio plasmonic material with an appropriate active photocatalyst.
硫化锌镉(Cd_(1-x)Zn_(x)S,0<x<1)固溶体作为一种可见光响应光催化剂,因能带结构可调和光解水产氢活性优异而备受关注.如何进一步拓展Cd_(1-x)Zn_(x)S太阳光响应范围,提高光生电子与空穴利用效率是当前的研究热点.本文采用溶剂热法分别制备了Cd_(0.5)Zn_(0.5)S纳米棒和W_(18)O_(49)纳米颗粒,然后借助超声辅助静电自组装策略成功获得具有紫外-可见-近红外光响应的W_(18)O_(49)/Cd_(0.5)Zn_(0.5)S异质结.分析表明,W_(18)O_(49)晶格氧空位周围过量自由电荷的集体振荡,引起强烈的局域表面等离子体共振(LSPR)吸收现象,使其对500~800 nm范围的光产生明显吸收,使体系具有紫外至近红外光响应能力;而且W_(18)O_(49)作为一种氧化型半导体材料,可与还原型Cd_(0.5)Zn_(0.5)S半导体之间形成S-scheme异质结,在内建电场、能带弯曲和静电相互作用下有效促进了光生电子和空穴的分离,并能保留强的氧化还原能力.对比实验发现,常温下以Na_(2)S/Na_(2)SO_(3)为牺牲剂,全光谱照射下,20%-W_(18)O_(49)/Cd_(0.5)Zn_(0.5)S的产氢速率可达147.7mmol·g^(-1)·h^(-1),是Cd_(0.5)Zn_(0.5)S纳米棒单体的2.1倍;可见光下,复合样品的产氢活性约为Cd_(0.5)Zn_(0.5)S单体的1.89倍;近红外光下,Cd_(0.5)Zn_(0.5)S单体无产氢活性,而异质结的产氢速率约为0.2 mmol·g^(-1)·h^(-1).进一步对样品波长依赖性研究发现,当365、400、450 nm的入射光仅能引起W18O49和Cd0.5Zn0.5S的带间激发时,它们的复合样品比Cd_(0.5)Zn_(0.5)S表现出更优异的产氢活性;当λ=550、600、650 nm以及>800 nm的入射光仅能引起W_(18)O_(49)的LSPR效应时,Cd_(0.5)Zn_(0.5)S单体无活性,而W_(18)O_(49)/Cd_(0.5)Zn_(0.5)S仍具有较高的催化性能、但随着波长的增大产氢速率逐渐降低,与复合样品瞬态光电流强度的变化趋势吻合良好.以上结果表明,W_(18)O_(49)与Cd_(0.5)Zn_(0.5)S二者形成的S-scheme界面异质结有效抑制了光生载流子的表面复合,且当入射光不足以引起带间激发时,W_(18)O_(49)的LSPR效应产生的"热电子"可有效注入到Cd_(0.5)Zn_(0.5)S,从而引起表面催化反应.进一步研究发现,当将反应温度从25提高到60°C时,20%-W_(18)O_(49)/Cd_(0.5)Zn_(0.5)S在全光谱下的产氢速率可提高到306.1mmol·g^(-1)·h^(-1),表明温度对光催化产氢过程具有不可忽视的影响,可通过增强表面反应速率显著提高产氢活性.总之,本文通过一种简便方法获得了具有紫外-可见-近红外响应的S型W_(18)O_(49)/Cd_(0.5)Zn_(0.5)S异质结光催化剂,详细对比了不同波段下样品的光电特性及催化活性,最终在S-scheme电荷转移机制和LSPR"热电子"注入过程的协同作用下,复合样品活性比Cd_(0.5)Zn_(0.5)S单体有了明显提高.
基金
国家自然科学基金(21676213,22078261,11974276)
中国博士后科学基金(2016M600809)
陕西省自然科学基础研究计划(2020JM-422,2018JM5020).
