【摘要】 氢能（H₂）因其高能量密度而被认为是一种有望解决全球能源危机,极具应用前景的可再生能源.光催化分解水制氢技术在能源研究领域受到广泛的关注,国内外研究者在探索和开发高效光驱动制氢的光催化剂方面做出了巨大努力.近年来,共价有机框架（COFs）因结晶性高、比表面积大和结构可设计性强等特性,而成为最具潜力的光催化有机多孔材料之一,并广泛应用于光催化分解水制氢.此外,由强共价键构筑而成的COFs,尤其是酰腙链接的COFs,通常展现出较好的结构稳定性,这有利于催化剂在光催化水分解过程中保持稳定的结构.然而,大多数纯COFs由于表面电荷传输缓慢以及光生载流子容易复合,使其光催化分解水性能不理想.如何加快电荷传输,促进光生载流子分离,进而提高COFs的光催化效率成为关键问题.本文制备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将精细金纳米颗粒（Au NPs）负载于S₄-COF上,制得Au@S₄-COF复合光催化剂,并用于光催化分解水制氢.通过傅里叶变换红外光谱、核磁共振波谱、X射线多晶衍射、扫描电子显微镜、透射电子显微镜、X射线光电子能谱等表征深入研究了S₄-COF的链接方式、晶型结构和形貌,证明了精细Au NPs均匀负载在S₄-COF表面.利用紫外-可见吸收光谱研究了S₄-COF和复合光催化剂Au@S₄-COF的光学性质,结果表明,与纯S₄-COF相比,Au@S₄-COF在可见光范围内光吸收能力增强.在可见光（λ>420 nm）照射下,以三乙醇胺作为电子牺牲剂进行光催化析氢实验.结果发现,在没有任何助催化剂的情况下,纯S₄-COF光催化制氢产率为302μmol g^-1 h^-1;而Au@S₄-COF复合光催化剂的光催化析氢活性明显提升,H₂析出速率为1377μmol g^-1 h^-1,约为纯S₄-COF的4.5倍.同时,Au@S₄-COF在循环实验中表现出稳定的光催化析氢性能,并在反应后完整地保持晶型结构.得益于S₄-COF结构中有序分布的硫醚基团与Au之间的配位相互作用,锚定在S₄-COF上的Au NPs具有超精细的尺寸分布,平均尺寸为3.8 nm.光致发光光谱、时间分辨光致发光波谱、线性扫描伏安、电化学阻抗谱、瞬态光电流响应等测试结果表明,锚定在S₄-COF光催化剂上的超细Au NPs可以显著加速光生载流子的分离并促进电荷传输.该策略不仅可以避免Au NPs在含硫醚的COFs上团聚,使复合光催化剂保持良好的稳定性,而且可以使催化剂具有均匀分散的有序结构,提高活性位点含量,从而提升光催化分解水性能.本文不仅证明了硫醚功能化的芘基COFs用于光催化分解水的可行性,而且为进一步设计和开发高效COFs基光催化剂以解决能源危机和环境污染问题提供了新思路.更多还原

【Abstract】 Covalent organic frameworks（COFs） have lately emerged as a blooming class of potential materials for photocatalytic water splitting because of their high crystallinity,huge surface areas,and structural versatility.However,the photo catalytic performance for most pure COFs face some limitations factors,such as the significant recombination of photogenerated carriers and slow charge transfer.Herein,a novel thioether-functionalized pyrene-based COF（S₄-COF） was efectively produced and chosen as a support for the immobilization of ultrafine gold nanoparticles（Au NPs）.S₄-COF photocatalyst with Au as co catalyst demonstrates remarkable photo catalytic activity with a H₂ generation rate of 1377 μmol g^-1 h^-1 under visible light（>420 nm）,which is ca.4.5-fold increase comparing to that of pure S₄-COF(302 umol g^-1 h^-1).Au NPs anchored on S₄-COF possess an ultrafine size distribution ranging from 1.75 to 6.25 nm with an average size centered at 3.8 nm,which benefits from the coordination interaction between thioether groups and Au.Meanwhile,the produced Au@S₄-COF can generate a stable photocatalytic H₂ generation during the four recycles and preserve its crystallinity structure after the stability testing.The Au NPs anchored on the S₄-COF photocatalyst can greatly accelerate the separation of photogenerated carriers and increase charge transfer because of the combined function of Au NPs and thioether groups.Such a method can not only prevent the aggregation of Au NPs onto thioether-containing COFs to achieve long-term photostability but also allow uniform dispersion for an ordered structure of photo catalysts.This work provides a rational strategy for designing and preparing COF-based photocatalysts for solar-driven H₂ production.更多还原