【作者】 刘悦；

【导师】 周欣；

【作者基本信息】 哈尔滨工业大学 ， 化学工程与技术， 2022， 博士

【摘要】 在“双碳”战略的大背景下,加快降低碳排放步伐、大力发展可再生能源,推进我国产业结构和能源结构调整已是大势所趋。半导体光催化技术具有节能廉价、条件温和等优势,在升级能源结构方面具有广阔的应用前景。开发高性能的光催化剂是该领域最重要的研究方向。本论文以来源广泛、化学稳定性高的锡基半导体材料为研究对象,通过引入缺陷能级和构筑内建电场等方式调控了SnS₂和Sn O₂催化剂的载流子行为。采用理论计算与实验验证结合的方法,深入分析了影响催化剂光生载流子分离效率的主要因素;探究了提高半反应速率和完成全反应过程的必要条件。经过掺杂离子和形成异质结等方法的改性后,锡基半导体催化剂的分解水产氢速率得到了显著的提升,并实现了SnS₂可见光范围内全分解水的目的。通过Cu²⁺掺杂策略成功制备了具有S^2-空位的SnS₂花球状光催化剂,抑制了光生载流子的体相内复合。水热反应过程中,Cu S前驱体溶解释放的Cu²⁺进入SnS₂的晶格内取代部分Sn⁴⁺的位置引起S^2-的空位缺陷。产生的硫空位会在催化剂内部形成稳定的缺陷能级,减小了催化剂的禁带宽度,增加了光生电子的转移路径,从而提高了光生载流子的载流子密度和分离效率;Cu²⁺和S^2-空位的引入降低了SnS₂的表面功函数,使光生电子更容易与水分子发生反应。最终,5%Cu/SnS_2-x样品在可见光下的产氢速率达到1.37 mmol h^-1 g^-1,超过掺杂前样品的6倍以上。通过二维纳米片自组装的方法构筑了一种面面结合的g-C₃N₄/SnS₂异质结,优化了锡基半导体催化剂光生载流子的迁移方向。异质结界面电荷重组和交错的能带结构促进光生载流子按照Ⅱ型异质结的机理进行转移,提高了光生电子-空穴对的分离效率,减小了体相内复合的几率;理论计算结果证明异质结体系具有更小的氢吸附自由能,增强了催化剂与水分子间的相互作用,反应中间体的吸-脱附速率更快,从而进一步将锡基半导体光催化剂的分解水产氢速率提高到1.69 mmol h^-1 g^-1。充分利用二维材料的结构优势及电荷传输各向异性,通过发泡-硫化法制备了连接紧密的Sn O₂/Cd S面内异质结催化剂,提高了异质结界面的导电能力。两相的异质结界面处分别出现了正负电荷累积,最终形成了指向Sn O₂的内建电场,驱动两相的光生载流子按照S型机制进行分离和转移。该异质结能够显著提高锡基催化剂的载流子分离效率同时确保具有较高能量的电子和空穴参与光催化反应。改性后的锡基催化剂表现出了更高的量子效率,分解水产氢速率达到了2.54 mmol h^-1 g^-1。设计并制备了一种高效的rGO/SnS₂/Ag纳米结构光催化剂,实现了SnS₂光生载流子的双向分离,并达到了可见光下将纯水分解为H₂和O₂的目的。在该体系中,rGO超薄纳米片通过C-S键与SnS₂紧密地面面结合,同时作为电子传输介质提取光生空穴;Ag单质纳米粒子以助催化剂的形式修饰在SnS₂的表面并诱导光生电子转移;理论计算结果发现三者的连接界面发生电子耦合,加速了载流子的界面传输,从而实现了更高的载流子分离效率和量子产率。最终,在各组分的协同作用下,rGO/SnS₂/Ag光催化剂的可见光区完全分解水产氢和产氧速率分别高达137和68μmol h^-1 g^-1。更多还原

【Abstract】 Under the background of the"double carbon"strategy,it is the general trend to accelerate the pace of reducing carbon emissions,vigorously develop renewable energy and promote the adjustment of Chinese industrial structure and energy system.Benefiting from energy-saving,low cost and mild conditions,semiconductor photocatalysis technology has broad application prospects in upgrading energy system.In this field,it is the most important research direction to develop and prepare photocatalysts with excellent performance.In this work,SnS₂ and Sn O₂semiconductor materials with wide sources and high chemical stability are explored,whose carrier behavior is regulated by introducing defect energy levels and constructing built-in electric field.By means of theoretical calculation and experimental verification,the main factors affecting the photogenerated carrier separation efficiency of the catalyst are deeply analyzed.The necessary and sufficient conditions for increasing the half reaction rate and completing the whole reaction process are explored from the perspective of kinetics and thermodynamics.After a series of modification methods such as doping ions and forming heterojunctions,the hydrogen production rate of water decomposition of tin based 2D semiconductor catalyst has been significantly improved,and the purpose of pure water decomposition in the visible light range has been realized.SnS₂ flower-like photocatalyst modified by vacancy was successfully prepared by Cu²⁺doping strategy,which inhibited the inside recombination of photogenerated carriers.During the hydrothermal reaction,Cu²⁺released by the dissolution of Cu S precursor entered the lattice of SnS₂ to replace position of Sn⁴⁺,resulting in formation of S^2-vacancy defects.The generated sulfur vacancy formed a stable defect energy level near the bottom of the conduction band of the catalyst,reduced the band gap and increased the transfer path of photogenerated electrons,thus improving the carrier density and separation efficiency of photogenerated carrier.The addition of Cu²⁺and S vacancy reduced the surface work function of SnS₂,making it easier for photogenerated electrons to react with water molecules.Finally,the hydrogen production rate of 5%Cu/SnS_2-x under visible light was 1.37 mmol h^-1 g^-1,which was more than 6 times higher than that of the sample before doping.A face-to-face bonded g-C₃N₄/SnS₂ heterojunction was constructed by self-assembly method,and the migration direction of photogenerated carrier inSn-based semiconductor catalyst was optimized.Heterojunction interface charge recombination and staggered energy band structure promoted the transfer of photogenerated carrier following the mechanism of type II heterojunction,improved the separation efficiency of photogenerated electron hole pairs and reduced the probability of recombination in bulk phase.Results of DFT revealed that thanks to the smaller hydrogen adsorption free energy of heterojunction system,the interaction between catalyst and water molecules was enhanced,and the adsorption-desorption rate of reaction intermediates was faster,so as to further improve the hydrogen production rate of water decomposition to 1.69 mmol h^-1 g^-1.Taking full advantage of the structural advantages of two-dimensional materials and the anisotropy of charge transfer,Sn O₂/Cd S in-plane heterojunction catalyst was prepared by foaming vulcanization method,which improved the conductivity of heterojunction interface.The positive and negative charges accumulated at the interface of the two-phase heterojunction,and finally formed a built-in electric field pointing to Sn O₂,driving the two-phase photogenerated carrier to separate and transfer following the mechanism S-scheme.This S-scheme heterojunction could significantly improve the carrier separation efficiency of tin based catalysts and ensure that electrons and holes with high energy to participate in photocatalytic reactions.The modified Sn-based catalyst showed higher quantum efficiency,whose hydrogen production rate of water decomposition reached 2.54 mmol h^-1 g^-1.An efficient 2D rGO/SnS₂/Ag nanostructure photocatalyst was designed and prepared,which realized bidirectional separation of photogenerated carriers inSnS₂,and achieved purpose of decomposing pure water into H₂ and O₂ under visible light.In this system,rGO nanosheets was closely combined with SnS₂ through C-S bond and worked as electron transmission medium exacting photogenerated holes.Ag nanoparticles were modified on surface of SnS₂ in the form of cocatalyst and induced the transfer of photogenerated electrons.The recombination of interfacial charges accelerated the interfacial transport of charge to achieve higher carrier separation efficiency and quantum yield.Therefore,under synergistic action of each component,overall water splitting hydrogen and oxygen production rates of rGO/SnS₂/Ag photocatalyst in the visible region were as high as 137 and 68μmol h^-1 g^-1。更多还原