【作者】 程俊；

【导师】 徐航勋；

【作者基本信息】 中国科学技术大学 ， 高分子化学与物理， 2025， 博士

【摘要】 随着全球能源危机和环境问题的日益严峻,构建绿色可持续的能源体系成为了人们不断追求的目标。太阳能作为地球上最为丰富的清洁能源,其高效开发与利用是实现能源转型的关键路径。通过模仿自然光合作用,开发高效的光催化全解水制氢和光合成过氧化氢等人工光合成技术,已成为能源化学领域的重要研究方向。共价有机框架(COFs)作为一种新型晶态多孔高分子材料,因其高度可调的化学与电子结构、长程有序的永久孔道及优异的电荷传输性能等优势,在人工光合成领域表现出巨大的应用潜力。本论文立足于COFs构筑的基本原理,设计并合成了一系列用于光催化全解水和光合成过氧化氢的高效COFs基光催化剂。通过结合实验表征与理论计算,重点探究了 COFs的光生电荷分离与传输行为,并揭示了表面催化反应机理,最终建立了 COFs结构与性能之间的构-效关系。具体研究内容如下:(1)基于COFs多样化的键合方式,开发了两类含有相同供体-受体结构的亚胺键和碳碳双键连接的COFs。研究表明,键合方式的变化导致了二者光催化水分解活性的显著差异。其中,碳碳双键连接的COFs在可见光照射下实现了光催化全解水反应,在420 nm下的表观量子效率达2.53%。相比之下,亚胺键连接的COFs则并不具备全解水活性。综合表征证明,碳碳双键在调节COFs的能带结构和电荷分离与迁移方面发挥了至关重要的作用。此外,通过原位表征与理论计算阐明了 COFs光催化全解水的反应机理。进一步研究显示,COFs的光催化活性与其结晶度之间也存在重要关联。这项研究代表了晶态无金属COFs用于光催化全解水的首个成功范例。(2)基于COFs可调节的框架尺寸,在上个研究的基础上,开发了一系列不同框架尺寸的碳碳双键连接的COFs,并实现了高效光合成过氧化氢全反应。多维度的实验表征证明,COFs框架尺寸的扩展可以促进其介电常数的升高,进而削弱激子束缚效应,提升光生激子的分离效率。此外,延长的共轭骨架也为COFs中自由光生电荷的高效传输提供了良好的通道。基于此,最大框架尺寸的COFs表现出最优的光合成过氧化氢性能,在模拟太阳光下的太阳能到化学能转化效率高达1.41%,超过了以往报道的所有COFs基材料。这项研究阐明了 COFs框架尺寸与电荷分离行为的关系,为COFs基光催化剂的框架设计提供了指导。(3)基于COFs可编程的拓扑构型,在前两个研究的基础上,开发了一系列不同拓扑构型(hcb、sql和hxl)的碳碳双键连接的大框架尺寸COFs,并用于研究拓扑效应对光合成过氧化氢性能的影响。尽管具备相似的化学组成和能带结构,但hxl拓扑COFs表现出明显优于其他拓扑的光催化活性。综合表征与理论计算证实,hxl拓扑构型可以大幅降低COFs的电荷有效质量,并显著改善光生电荷的传输行为。此外,结合对比实验、原位表征和理论计算,深刻理解了 COFs光合成过氧化氢的反应路径与本征活性位点。这项研究不仅揭示了 COFs中拓扑效应引导的电荷输运动力学,还为开发高效光合成过氧化氢催化剂建立了分子工程策略。更多还原

【Abstract】 With the escalating global energy crisis and worsening environmental challenges,building a green and sustainable energy system has become a vital objective.Solar energy,the most abundant clean energy source on Earth,plays a pivotal role in achieving energy transitions through its efficient development and utilization.Inspired by natural photosynthesis,the development of artificial photosynthesis technologies,such as photocatalytic overall water splitting for hydrogen production and photocatalytic hydrogen peroxide synthesis,has emerged as a critical research focus in energy chemistry.Covalent organic frameworks(COFs),as a novel class of crystalline porous polymeric materials,exhibit exceptional potential in artificial photosynthesis due to their highly tunable chemical and electronic structures,long-range ordered porosity,and superior charge transport properties.This dissertation focuses on mimicking natural photosynthesis using COFs.Guided by the fundamental principles of COFs design,a series of high-performance COFs-based photocatalysts were developed for photocatalytic overall water splitting and hydrogen peroxide synthesis.Combining experimental characterization and theoretical calculations,the study investigated the photoinduced charge separation and transport behaviors of COFs and revealed surface catalytic reaction mechanisms,ultimately establishing structure-property relationships.The key findings are summarized as follows:(1)Based on the diverse bonding modes of COFs,two types of COFs with identical donor-acceptor structures but different linkages,imine and sp2 carbon linkages,were developed.The results demonstrate significant differences in their photocatalytic water-splitting activities.The sp2 carbon-linked COFs exhibited optimal band structures for achieving photocatalytic overall water splitting,with an apparent quantum efficiency of 2.53%at 420 nm,whereas the imine-linked COFs lacked activity for overall water splitting.Comprehensive characterizations demonstrated that sp2 carbon linkage played a pivotal role in tuning the band structures and enhancing charge separation and transport.Furthermore,in situ characterization and theoretical calculations clarified the underlying reaction mechanisms of COFs in overall water splitting.Additional studies established a crucial correlation between COFs crystallinity and photocatalytic performance.This work marks the first successful demonstration of highly crystalline,metal-free COFs for achieving photocatalytic overall water splitting.(2)Leveraging the tunable pore sizes of COFs,a series of sp2 carbon-linked COFs with varying pore sizes were developed to achieve high-performance photosynthesis of hydrogen peroxide.Multidimensional experimental characterization revealed that increasing the pore size enhanced the dielectric constant,thereby reducing exciton binding energy and improving the separation efficiency of photogenerated excitons.Additionally,the extended conjugated framework provided an optimal pathway for efficient charge transport within the COFs.Consequently,COFs with the largest pore size exhibited optimal photocatalytic hydrogen peroxide activity,achieving a solar-tochemical energy conversion efficiency of 1.41%under simulated sunlight,surpassing all previously reported COF-based materials.This study clarifies the relationship between COFs pore size and charge separation behavior,providing guidance for pore engineering in COFs-based photocatalysts.(3)Building on the programmable topologies of COFs,a series of sp2 carbonlinked COFs with distinct topologies(hcb,sql,and,hxl)and large pore sizes were synthesized to investigate the impact of topology on hydrogen peroxide photosynthesis performance.Despite their similar chemical compositions and band structures,the hxl topology COFs exhibited significantly enhanced photocatalytic activity compared to other topologies.Combined experimental characterizations and theoretical calculations demonstrated that the hxl topology notably improved charge transport efficiency.Moreover,through comparative experiments,in situ characterizations,and theoretical studies,this research provided a comprehensive understanding of the reaction pathways and intrinsic active sites for hydrogen peroxide photosynthesis.This work not only elucidates the topological effects guiding charge transport dynamics in COFs but also introduces a molecular engineering strategy for designing high-performance photocatalysts for hydrogen peroxide synthesis.更多还原