ZnIn_(2)S_(4)/MOF-808微球结构S型异质结光催化剂的制备及其光还原CO_(2)性能研究

Enhancing photocatalytic CO_(2) reduction activity of ZnIn_(2)S_(4)/MOF‐808 microsphere with S‐scheme heterojunction by in situ synthesis method

近年来,能源过度消耗导致的温室效应引起人们广泛关注.通过不同半导体材料间能带交错排列构建异质结,用于将CO_(2)转化为高附加值产品是解决该问题的可行方法之一.其中, S型异质结的还原型光催化剂与氧化型光催化剂具有交错带结构,使各自存在的弱空穴与弱电子复合,极大提高光生载流子的透过率和电荷利用率,有效实现强电子-空穴对分离.在半导体中,ZnIn_(2)S_(4)由于能带结构适当、可见光响应范围广和化学性质稳定等优点,在CO_(2)减排领域表现出较好的性能.但其光吸收能力低、光生载流子分离效率低和光生电子的迁移过程缓慢,这些缺点导致单一ZnIn_(2)S_(4)在光催化领域的应用受限.在S前半导体研究中,MOF-808制备方法简单、比表面积大以及框架结构稳定,是一种理想的催化材料.因此,本文利用MOF-808与ZnIn_(2)S_(4)偶联形成合适的交错带结构,构建S型异质结以提高光催化CO_(2)还原活性.本文采用原位合成法设计由三维花球ZnIn_(2)S_(4)和八面体MOF-808组成的阶跃式异质结(S型异质结).通过调控反应温度与时间设计不同尺寸的ZnIn_(2)S_(4)微球,并探索制备条件对光催化CO_(2)还原活性的影响.结果表明,当ZnIn_(2)S_(4)微球直径为6μm时,与MOF-808偶联所构建的复合光催化剂的CO_(2)还原活性最高.并且通过调控MOF-808比例,制备的S型异质结ZM6-15%光催化剂的CO产率在辐照4 h后达到8.21μmol g^(-1)h^(-1),分为别MOF-808 (1.03μmol g^(-1)h^(-1))和ZnIn_(2)S_(4)(0.84μmol g-1h-1)的8倍和10倍左右,明显提高了光催化CO_(2)还原性能.X射线衍射、扫描电镜、透射电镜和X射线光电子能谱(XPS)等研究结果表明,ZnIn_(2)S_(4)微球表面被MOF-808八面体粘附,这种紧密粘附的结构有利于ZnIn_(2)S_(4)与MOF-808之间载流子的转移和分离,从而提高光催化CO_(2)的还原效果.此外,电子顺磁共振和紫外光电子能谱等测试结果表明ZnIn_(2)S_(4)中存在弱空穴,MOF-808中存在弱电子.在光照下,光生电子通过界面接触快速从MOF-808导带中迁移到ZnIn_(2)S_(4)价带中并被消耗,为光生电子提供快速传输途径,提高了电子利用率.最终,MOF-808中存在光生空穴具有最高的氧化能力,ZnIn_(2)S_(4)中存在光生电子具有最高的还原能力.原位XPS测试与密度泛函理论计算结果进一步证明了ZnIn_(2)S_(4)与MOF-808之间的S型电荷转移机制.原位红外技术分析结果表明,S型异质结ZnIn_(2)S_(4)/MOF-808光催化剂通过Carbene途径将CO_(2)光催化还原为CO (CO—→CO_(2)*→COOH*→CO*→CO).综上,本文为合理设计S型异质结光催化剂,以实现高效光催化CO_(2)还原活性提供了新思路.

The design of a heterogeneous structure for photocatalysts has attracted significant attention.In this study,a step-scheme(S-scheme)heterojunction was designed using an in‐situ synthesis method.The resulting heterojunction comprised 3D microspheres of ZnIn_(2)S_(4) and octahedral MOF-808(ZnIn_(2)S_(4)/MOF-808).During this process,we investigated the impact of the scale of the ZnIn_(2)S_(4) microspheres on performance by controlling the growth of the ZnIn_(2)S_(4) microspheres with various scales.The maximum catalytic activity was discovered to be achieved with ZnIn_(2)S_(4) microspheres of 6μm when coupled with MOF-808.Compared to pure ZnIn_(2)S_(4) and MOF-808,the fabricated S-scheme ZnIn_(2)S_(4)/MOF-808 heterojunction exhibited notably improved photocatalytic CO_(2) reduction performance.The performance of the CO yield of the optimized sample could reach 8.21mmol g^(‒1) h^(‒1),which was approximately 10 and 8 times higher than those of ZnIn_(2)S_(4)(0.84mmol g^(‒1) h^(‒1))and MOF-808(1.03mmol g^(‒1) h^(‒1)),respectively.Moreover,ultraviolet photoelectron spectroscopy,ESR,in situ X-ray photoelectron spectroscopy,and density functional theory calculations were used to study the charge transfer mechanism of the S-scheme heterojunction.In‐situ FT-IR investigation established the Carbene pathway as the source of CO production(CO_(2)→CO_(2)^(*)→COOH^(*)→CO^(*)→CO).This study provides an efficient method for designing an S-scheme heterojunction for photocatalytic CO_(2) reduction.