【Angew.Chem.】突破2.7%转换效率！三模态共价有机框架实现光催化从水和空气高效制备纯
文章标题： -Bridge Modulation in Three-Motif Covalent Organic Framework for Efficient Photosynthesis From Water and Air
通讯作者： Hailong Wang, Jong-Beom Baek, Jianzhuang Jiang
文章概要
引言
过氧化氢（）作为一种绿色、高能量密度的重要化工原料，在医疗、环保和工业等领域应用广泛。当前工业主要依赖的蒽醌法存在高能耗、依赖贵金属催化剂以及大量挥发性有机溶剂等严重缺点。相比之下，太阳能驱动的光催化技术被视为一种极具前景的清洁替代路线，但在金属氧化物催化剂中普遍存在的高副反应和高重组率严重限制了生产效率。近年来，具有高结晶度和良好孔隙结构的金属共价有机框架（COFs）在光催化制备领域备受关注。然而，如何合理整合多模态活性催化位点以抑制光生载流子的快速复合，并同时利用水和空气实现全反应的高效转化，依然是当前RET化学和光催化领域面临的巨大技术瓶颈。
(a) Schematic molecular skeletons as electron-donor (D) as water oxidation reaction (WOR) site, electron-acceptor (A) as oxygen reduction reaction (ORR) site and π-bridge as well as molecular skeletons. (b) D–A–π–A strategy for enhanced H2O2 production (c) Schematic motif engineering to construct two- and three-motif COFs with D–A–A, D–A–π–A, D–A–π–π, and D–π–π–A arrangement, respectively.
(a) The structure and synthetic route of three-motif USTB-66 (D–A–π–A lattice). (b) The structures of TTA, TBPB, and TFPA. (c) The structures of three-motif USTB-65 (D–A–A lattice), two-motif USTB-67 (D–A–π–π lattice), and two-motif USTB-68 (D–π–π–A lattice).
主要实验及结论
为了打破这一制备瓶颈，研究团队精心设计并合成了一系列兼具氧化和还原双重活性的新型亚胺键结合的三模态共价有机框架催化材料（USTB-65 ~ USTB-68）。该体系创新性地将三苯胺单元作为电子给体（D）兼作水氧化反应（WOR）位点，同时引入苯并噻二唑和三嗪单元作为电子受体（A）兼作两电子氧还原反应（ORR）位点。通过在其D–A–A晶格结构中特意插入苯环作为-桥键，成功构建了具备D–A––A交替排列的USTB-66材料。微观形貌与光谱结构表征进一步确证了其完美的二维六方晶格蜂窝状多孔形貌及高达1612 的超高比表面积。
PXRD patterns of USTB-65 (a), USTB-66 (b), USTB-67 (c), and USTB-68 (d). Optimized AA-stacked unit cell models of USTB-65 (e), USTB-66 (f), USTB-67 (g), and USTB-68 (h). The TEM (i), HRTEM (j, k) images of USTB-66. (l) N2 adsorption (solid) and desorption (hollow) curves and pore size distribution of USTB-66.
(a) The electronic absorption spectrum of TPTCA in DMF and the corresponding excitation process. Excitation is predicted by TDDFT, with the red orbital representing the electron distribution and the blue orbital representing the hole distribution. (b) UV–vis diffuse reflectance spectrum of USTB-65 to USTB-68. (c) The increasing trend of H2O2 production rate photocatalyzed by USTB-65 to USTB-68 within one hour. (d) Comparison of photocatalytic H2O2 yields of USTB-65 and USTB-66 with those of selected COF-based photocatalysts. (e) Photocatalytic performance comparison among USTB-65 to USTB-68. (f) Flow reactor with a solar concentrator assembled with USTB-66 column for continuous H2O2 manufacturing. Conditions: photocatalyst (200 mg), H2O (2.0 L), air, and sunlight. (g) Schematic of photocatalyst column filled with USTB-66.
ESP maps of the corresponding fragments for USTB-65 (a), USTB-66 (b), USTB-67 (c), and USTB-68 (d). Temperature-dependent two-dimensional PL contour plots forUSTB-65 (e), USTB-66 (f), USTB-67 (g), and USTB-68 (h). Surface potential mappings ofUSTB-65 (i), USTB-66 (j), USTB-67 (k), and USTB-68 (l) obtained by KPFM.
凭借独特的激子结合能优化与显著增强的内置电场，USTB-66在纯水和环境空气饱和的极其温和条件下，展现出了惊人的光催化制氢氧性能，其产率高达11.2 ，并在550 nm处取得了27.3%的优异表观量子产率，太阳能到化学能转换效率（SCC）更是达到了惊人的2.71%。研究团队利用飞秒瞬态吸收光谱（fs-TA）结合理论计算深入阐明了其光物理机制，证实了–桥调制能显著延长电荷分离态寿命并实现清晰的逐步电荷转移。此外，团队利用室外太阳能聚光器组装的宏观流体反应器进行放大实验，在连续照射24小时后成功制备出浓度高达81.1 mM的过氧化氢溶液，充分验证了该材料的工业化实用潜力。
(a) The fs-TA spectra of TPTCA (N2 atmosphere) upon 380 nm excitation. (b) The fs-TA spectra of USTB-65 (N2 atmosphere) upon 380 nm excitation. (c) The fs-TA spectra of USTB-66 (N2 atmosphere) upon 380 nm excitation. (d) The fs-TA spectra of USTB-67 (N2 atmosphere) upon 380 nm excitation. (e–h) The corresponding excited-state electron distributions (red: electrons, blue: holes), indicating the photo-induced electron transfer. (i) In-situ DRIFTS spectra of USTB-66 in H2O2 photosynthesis. (j) Plausible WOR and ORR pathway for photocatalytic production of H2O2.
总结及展望
本研究成功提出了一种基于多模态活性单元集成与-桥空间调制的共价有机框架光催化剂构筑策略。通过对三模态骨架进行精细的能带电子结构调制，协同解决了光 captures 效率、激子 dissociation 难易度以及界面载流子转移动力学等系列核心难题。这不仅大幅刷新了空气条件下光催化全分解水制备过氧化氢的性能记录，也为未来从分子和晶格工程角度理性构筑高效、鲁棒的太阳能化学转化和异相光催化体系开辟了全新的设计范式。