【作者】 周志明；

【导师】 申燕；

【作者基本信息】 华中科技大学 ， 材料物理与化学， 2023， 博士

【摘要】 太阳能的开发利用能够帮助人类社会解决日趋严重的能源危机和环境问题。光催化和光电催化技术能够实现太阳能的有效利用和转化。设计高效的光催化剂是实现优异光催化和光电催化性能的关键因素。作为一种高结晶态有机多孔材料,共价有机框架（COFs）具有高比表面积、化学稳定性、良好的光吸收能力、结构多样性和可修饰性等性质,使其在光催化和光电催化领域备受关注。然而,由于存在光生载流子复合迅速、自身内阻较大以及表界面电荷分离和传输缓慢等关键科学问题,COFs在太阳能驱动水分解应用中受到一定的限制。针对上述问题,本论文通过对COFs进行功能化结构设计、表面修饰以及能带结构调节等策略制备一系列具有良好光活性的COFs光催化剂,以实现太阳能的有效利用和转化。本论文的主要研究内容如下:（1）设计并构筑了一种新型硫醚功能化的芘基COF（S₄-COF）。通过原位光沉积技术进一步制备搭载了尺寸均匀的金纳米颗粒（Au NPs）的复合光催化剂（Au@S₄-COF）用于高效光催化制氢。Au@S₄-COF展现出良好的光催化活性,析氢速率达1377μmol g^-1 h^-1,是纯S₄-COF的4.5倍。S₄-COF结构中硫醚基团的有序分布以及硫醚基团与Au NPs之间的特异性亲和力为优异的光催化性能提供了双重保证。尺寸均匀的Au NPs在S₄-COF上的有序分布可以显著加速电荷转移动力学并提高光生载流子的分离效率。这项工作为设计和开发高效COF基光催化剂以推进光催化在太阳能-氢能的转化提供了有价值的参考。（2）通过溶剂热法使用MoS₂修饰三嗪基COF（TTZ-COF）构建了COF基异质结（MoS₂/TTZ-COF）用于增强太阳能驱动光电化学水氧化。MoS₂/TTZ-COF实现更高的光电流密度和更强的光电化学活性,是纯TTZ-COF的2倍。MoS₂/TTZ-COF的入射光子转换效率和瞬态光电流响应均得到明显提升。COF基异质结的构建不仅可以有效地加速电荷分离和转移,而且能够增强光生电子-空穴对的分离以促进光电化学水氧化的过程。这项工作为开发COF基半导体光催化剂以推进太阳能驱动光电化学水分解提供了合理建议。（3）综合前两章研究内容中COFs结构的硫醚和三嗪功能化的设计思路,通过多组分策略构筑了一种新型含硫醚的三嗪基COF（TDB-COF）用于太阳能驱动全合成过氧化氢（H₂O₂）。在没有牺牲剂的情况下,TDB-COF实现有效光催化,H₂O₂的光合成产率为723.5μmol g^-1 h^-1,且展现良好的化学结构稳定性。紫外可见吸收光谱和光电测试结合表明硫醚基团的修饰不仅拓宽了TDB-COF的可见光吸收,而且可以促进光生载流子转移和界面电荷传输。实验研究和理论计算结合证实了硫醚基团的引入可以有效地调节TDB-COF的能带结构和增强O₂吸附,使其既能够氧化水反应生成H₂O₂,又能够氧还原生成H₂O₂,最终实现全光合成H₂O₂。这项工作为功能性COF的设计和开发提供了合理见解,为实现高效太阳能转化提供了重要参考。更多还原

【Abstract】 The development and utilization of solar energy can help human society resolve the increasingly serious energy crisis and environmental problems.Photocatalysis and photoelectrocatalysis technology can realize the effective utilization and conversion of solar energy.Designing efficient photocatalysts is a key factor to achieve excellent photocatalytic and photoelectrocatalytic performance.As a class of highly crystalline organic porous materials,covalent organic frameworks（COFs）have attracted massive attention in the fields of photocatalysis and photoelectrocatalysis because of their high specific surface area,chemical stability,good light absorption ability,structural diversity,and modifiability.However,COFs are limited in the application of solar-driven water splitting due to crucial scientific issues such as rapid recombination of photogenerated carriers,large internal resistance,and slowly interfacial charge separation and transport.In view of the above problems,this paper has prepared a series of COFs photocatalysts with good photoactivity through functional structure design,surface modification,and band structure adjustment of COFs to achieve the efficient utilization and conversion of solar energy.The main research contents of this paper are summarized as follows:（1）A novel thioether-functionalized pyrene-based COF（S₄-COF）was designed and constructed.The composite photocatalyst（Au@S₄-COF）supporting ultrafine gold nanoparticles（Au NPs）was further prepared by a facile in-situ photo-deposition technique,which was applied to efficient photocatalytic hydrogen production.Au@S₄-COF exhibits good photocatalytic activity with a hydrogen evolution rate up to 1377μmol g^-1 h^-1,which is ca.4.5-fold increase comparing with that of pure S₄-COF.The ordered distribution of the thioether groups in the structure of S₄-COF and the specific affinity between the thioether groups and Au NPs provide double assurances for the excellent photocatalytic performance.The ordered distribution of ultrafine Au NPs on S₄-COF can significantly accelerate the charge transfer kinetics and improve the separation efficiency of photogenerated carriers.This work provides valuable references for the design and development of efficient COF-based photocatalysts to promote the solar to hydrogen energy conversion through photocatalysis.（2）A two-dimensional（2D）COF-based heterojunction（MoS₂/TTZ-COF）was constructed by modifying the triazine-based COF（TTZ-COF）with MoS₂ via solvothermal method to enhance solar-driven photoelectrochemical（PEC）water oxidation.MoS₂/TTZ-COF achieves higher photocurrent density and stronger PEC activity,which is ca.2-fold increase comparing with that of pure TTZ-COF.The incident photon conversion efficiency and transient photocurrent response of MoS₂/TTZ-COF are both significantly improved.The 2D COF-based heterojunction construction can not only effectively accelerate charge separation and transfer but also boost the separation of photogenerated electron-hole pairs to facilitate the process of PEC water oxidation.This work provides reasonable suggestions for developing COF-based semiconductor photocatalysts to promote solar-driven PEC water splitting.（3）Combined with the design ideas of thioether and triazine functionalization on the COFs structures in the previous two chapters,a novel thioether-containing triazine-based COF（TDB-COF）was constructed through a multi-component strategy for solar-driven overall synthesis of hydrogen peroxide（H₂O₂）.In the absence of sacrificial agents,TDB-COF achieves efficient photocatalysis with a H₂O₂ photosynthesis yield of 723.5μmol g^-1h^-1 and exhibits good chemical structural stability.Ultraviolet-visible absorption spectra and photoelectric tests indicate that the modification of thioether groups can not only broaden the visible light absorption of TDB-COF but also promote the photogenerated carriers transfer and accelerate interface charge transport.Experimental research and theoretical calculation confirm that the introduction of thioether groups can effectively adjust the energy band structure of TDB-COF and enhance the O₂ adsorption,so that it could not only oxidize water to generate H₂O₂ but also reduce oxygen to produce H₂O₂,and ultimately achieving the overall H₂O₂ photosynthesis.This work provides reasonable insights for the design and development of functional COFs and important references for achieving efficient solar energy conversion.更多还原