【作者】 韩梅；

【导师】 杨柏；

【作者基本信息】 吉林大学 ， 高分子化学与物理， 2022， 博士

【摘要】 开发新材料、探索高效环保的能源产生方式是环境与能源相关研究领域的重要课题。光催化技术是指在催化剂和光的协同作用下进行能量转换的过程,是利用可再生太阳能的最引人注目的应用之一,具有十分广阔的应用前景和发展潜力。近年来,碳点（CDs）,作为一类新型碳基纳米材料被应用于光催化反应中。因此,基于CDs光催化材料的微、纳尺度结构设计与机理研究在光能转换方面具有重要意义。构筑CDs基杂化光催化材料能够实现对CDs结构、性质与功能的最大化利用。类石墨相氮化碳（g-C₃N₄）是理想的光催化材料之一,已被广泛研究,然而其仍存在着可见光利用率差、光诱导电子/空穴对的快速复合和比表面积小等劣势。设计并加以构建高效光催化体系是目前需要解决的关键科学问题。基于此,将CDs这类碳基纳米材料,用作能量转换单元和电子给体,并利用碳化聚合物点（CPDs）对g-C₃N₄进行一系列的修饰合成CPDs/g-C₃N₄杂化材料。本论文的创新之处在于:提出了一种新型、高效且简便的CDs/g-C₃N₄杂化材料合成策略;探索了杂化材料在光催化降解污染物、光解水产H₂以及对于促进聚酯类塑料降解的应用研究;研究了杂化材料在光解水产H₂的增强机理。具体来讲,本论文的研究工作可以归纳为如下三个部分:首先,开发一种一步热聚合法。相较于以往研究中的多步骤、耗能的合成方法,我们以简便的一步法有效地实现了基于本体g-C₃N₄的形貌调控,将其从块状结构向纳米片形貌进行转变;与此同时,将具有纳米尺寸的CDs原位集成到g-C₃N₄骨架中,从而形成了CDs植入g-C₃N₄纳米片的形貌,这种微、纳尺度结构改变了g-C₃N₄的本征电子结构,有益于满足促进光生载流子分离与输运的条件,并且能够窄化带隙、拓宽光谱响应范围,提升可见光区光吸收性能,提供更高比表面积值,最终实现对光催化性能的提升。接下来,提出一种CPDs/g-C₃N₄杂化光催化剂对聚对苯二甲酸乙二醇酯塑料进行催化转化的方法。该光催化反应同时实现了将水解产物乙二醇催化转化为乙醇酸、乙醇醛和乙醇等高附加值化学品与裂解水生成H₂的过程,所构筑的反应体系能够以光催化的手段促进碱性条件下聚酯水解反应速率。另外,水解所产生的对苯二甲酸盐可以经简单酸化处理即可回收高纯度单体,有望实现聚酯塑料的化学回收。所构筑的反应系统为同时生产高附加值有机化学品和H₂燃料提供了一个新颖的平台,推动聚酯塑料回收并使其具有成为制备化学品前体的可能性。最后,研究一种CPDs表面分子（简称为IPCA）对于光催化性能提升的机理。我们证实了IPCA能够从本质上增强CPDs/g-C₃N₄杂化体系对于太阳能驱动的催化产H₂活性。基于表面分子的研究,突破了以往研究中重点集中在碳核的局限性,推动了对CPDs结构及功能的认识。结合实验表征与理论计算结果,证明了CPDs与g-C₃N₄经过键合后形成稳定体系,其中,IPCA可以作为活性单元,参与杂化材料形成过程,产物有利于增加g-C₃N₄光响应范围,并且促进光生电子/空穴对重新分布,从而实现显著减少了能量浪费的载流子重组过程从而增强催化剂光活性,为利用表面分子来研究CPDs光催化的构效关系提供了新的思路,有助于设计开发高性能光催化剂。本论文致力于碳基杂化光催化剂的构筑及其在光催化领域的应用研究,从杂化材料的设计合成,到光催化反应的应用,再到针对于相关机理的探讨与验证。该过程不仅实现了将环保的碳基材料应用于多种面向能源与环境的催化转化反应中,同时也促进了对于催化反应机理的探索与理解,提升了环境友好型碳基催化剂的应用前景。更多还原

【Abstract】 Developing new materials to explore efficient and environmentally friendly energy generation is an important topic in the field of environment and energy related researches.Photocatalysis refers to the process of energy conversion under the synergistic effect of catalyst and light,which is one of the most eye-catching applications of renewable solar energy.It has very broad application prospects and development potential.In recent years,carbon dots（CDs）are used in photocatalytic reactions.Therefore,micro/nano scale structure design and mechanism research of CDs-based photocatalytic materials are of great significance in solar energy conversion.The construction of CDs-based hybrid photocatalysts can realize the maximum utilization of the structural properties and functions of CDs.Graphitic carbon nitride（g-C₃N₄）,as one of the ideal photocatalysts,has been widely studied.However,problems still exist including poor light utilization,rapid photoinduced electron/hole recombination rates and low specific surface areas.To design and prepare efficient photocatalytic system is the key scientific issue to be solved.Based on this,CDs were used as energy conversion units and electron donors and carbonized polymer dots（CPDs）was used to synthesize CPDs/g-C₃N₄ hybrid photocatalysts through a series of modification of g-C₃N₄.The innovation of this paper lies in:a new efficient and simple synthesis strategy of CDs/g-C₃N₄ hybrid was proposed;the applications in photocatalytic degradation of pollutants,water splitting for H₂production and polyester plastics degradation were explored;the mechanism of H₂production was studied.To be specific,the research work of this paper can be summarized into the following three parts:Firstly,we developed a one-step thermal polymerization method,which was compared with the multi-step energy-consuming ones in previous studies.We effectively realized the morphology regulation of g-C₃N₄ from the bulk structure to nanosheets.At the same time,nanoscale CDs was in-situ implanted into g-C₃N₄skeleton.This micro-nano structure changed the intrinsic electronic structure of g-C₃N₄,which was beneficial to promoting photogenerated carrier separation,and narrowing the band gap to broaden the spectrum range response,providing high specific surface areas,and finally achieving the improvement of photocatalytic performance.Next,a CPDs/g-C₃N₄ hybrid photocatalyst was proposed for the catalytic conversion of poly（ethylene terephthalate）plastics.The photocatalytic reaction also realized the catalytic conversion of ethylene glycol hydrolysate into high value-added chemicals such as glycolic acid,glycolaldehyde and ethanol;water splitting for H₂production and facilitating polyester hydrolysis.In addition,the terephthalic acid of high purity was expected to achieve the chemical recycling of plastic waste.The reaction system provides a novel platform for the simultaneous production of high value-added organic chemicals and H₂ fuels,promoting the recycling of polyester plastics and making them possible feedstocks for the production of chemicals.Finally,we studied the mechanism of a surface molecule（IPCA for short）on CPDs to improve the photocatalytic performance.We confirmed that IPCA can essentially enhance the activity of solar driven catalytic H₂ production over CPDs/g-C₃N₄catalyst.The research based on surface molecules breaks through the limitation of focusing on carbon core in previous studies,and promotes the understanding of CPDs structure and function.Experimental characterization and theoretical calculation results showed that the CPDs and g-C₃N₄ were chemically bonded to form a stable system.The IPCA unit can be used as an active site,involved in hybrid forming process.It contributed to increasing the light response and promoting the photogenerated electron/hole pairs for redistribution.A new way to study the structure-activity relationship of CPDs in photocatalysis by surface molecules is provided,which is helpful for the design and development of high performance photocatalysts.This paper is devoted to the construction of carbon-based hybrid photocatalysts and the applications in the field of photocatalysis,from the design and synthesis of composite materials,to the applications of photocatalytic reactions,and then to the related mechanism.This process not only realized the application of environmental friendly carbon-based materials in a variety of energy and environment-oriented catalytic conversion reactions,but also promoted the exploration and understanding of catalytic reaction mechanism,and promoted the application prospect of environmentally friendly carbon-based catalysts.更多还原