Boosting the catalytic activity of a step-scheme In_(2)O_(3)/ZnIn_(2)S_(4) hybrid system for the photofixation of nitrogen

梯型In_(2)O_(3)/ZnIn_(2)S_(4)杂化体系的构建及其光催化固氮增效

In this study,a step-scheme photocatalytic system comprising one-dimensional In_(2)O_(3)nanorods and two-dimensional ZnIn_(2)S_(4)nanosheets was developed for the catalytic photofixation of nitrogen.The effects of the combination of In_(2)O_(3)with ZnIn_(2)S_(4)on the crystallinity,microstructure,optical absorption,and charge transfer behavior of the In_(2)O_(3)/ZnIn_(2)S_(4)hybrid photocatalysts were investigated.Benefiting from the synergistic effects of the photogenerated vacancies and a step-scheme charge separation mechanism,the In_(2)O_(3)/ZnIn_(2)S_(4)hybrid photocatalyst exhibited significantly enhanced catalytic activity compared to those of bare In_(2)O_(3)and pure ZnIn_(2)S_(4),and an optimized 50 wt%In_(2)O_(3)/ZnIn_(2)S_(4)hybrid sample was found to exhibit superior catalytic activity for the photofixation of N2,fixing 18.1±0.77 mg·L-1 of ammonia after exposure to simulated sunlight for 2 h.Crucially,the results of trapping experiments and electron paramagnetic resonance investigation to identify the active species confirmed that the catalytic nitrogen photofixation performance was highly correlated with the presence of·CO_(2)-radicals rather than photogenerated electrons,especially when methanol was used as a hole scavenger.In summary,the reported In_(2)O_(3)/ZnIn_(2)S_(4)hybrid photocatalysts exhibit both stability and high activity for the photofixation of N_(2),making them promising catalysts for sunlight-driven artificial N_(2)fixation.

工业化固氮合成氨主要采用Haber-Bosch法.然而,该工艺条件苛刻,需要氮气与氢气在高温高压和使用催化剂的条件下反应,耗费大量能源,同时产生温室气体.与Haber-Bosch法不同,光催化固氮不需要使用氢气,而是利用清洁的太阳能和水直接提供固氮反应所需的还原电子和质子,反应耗能低且绿色无污染,是一种理想的固氮方法.然而,目前光催化固氮合成氨受限于光催化剂载流子分离效率低、氮气吸附和活化难,总体固氮效率仍然很低.大量研究证明,构建梯型异质结是一种改善光催化活性的有效手段,这是因为梯型异质结体系不仅有效分离光生载流子,而且保留了光生空穴和电子的强氧化还原能力.另外,表面缺陷不仅可以充当吸附位点,有效调控表面N2分子的吸附特性,还可以起到活化N2分子的作用.本文设计了富含空位的In_(2)O_(3)/ZnIn_(2)S_(4)梯型异质结,系统考察了复合体系中组分配比对晶型结构、微结构和光学吸收等的影响,并通过XPS谱研究了In_(2)O_(3)和ZnIn_(2)S_(4)之间存在强的相互作用,这为光生载流子的高效分离奠定了基础.同时,结合XPS、Raman和EPR测试揭示了材料中表面空位的成功构筑.在此基础上,深入研究了In_(2)O_(3)/ZnIn_(2)S_(4)梯型异质结在室温常压下光催化固氮合成氨的活性.研究结果表明,所有的梯型异质结均展现出明显的光催化固氮活性,其中50 wt%In_(2)O_(3)/ZnIn_(2)S_(4)梯型体系具有最高的光催化固氮活性,自然光照射2 h产生的氨气浓度达到18.1±0.77 mg·L-1,分别是In_(2)O_(3)和ZnIn_(2)S_(4)的21.0和2.72倍.并且该复合体系具有较高的光催化稳定性,在连续循环使用6次时,产生氨气浓度仍然可达到16.3±0.86 mg·L^(-1).荧光光谱测试、光电化学测试和表面光电压测试证明了电荷的有效分离和转移.综上,构建In_(2)O_(3)/ZnIn_(2)S_(4)梯型体系后,所制备的In_(2)O_(3)/ZnIn_(2)S_(4)活性得到增强,这主要归因于空位对氮气的吸附和活化作用以及梯型异质结中载流子的高效分离机制.另外,研究表明·CO_(2)-物种是光催化固氮合成氨的主要活性物种.