Adjustment the donor-acceptor COFs structure enhances the electron push-pull effect to induce electron transfer to Pt site and improve photocatalytic hydrogen evolution

Abstract

Photocatalytic hydrogen evolution is a pivotal approach towards achieving sustainable development and carbon neutrality. However, the limited light absorption capacity, sluggish electron transfer rate, and rapid electron-hole recombination efficiency often impede the advancement and practical implementation of photocatalytic hydrogen evolution technology. Covalent organic frameworks (COFs) are comprised of diverse molecular units and exhibit exceptional designability and topological properties. Notably, the cyclic chain structure synthesized from donor (D) and acceptor (A) units has achieved significant advancements in photocatalysis due to its superior design flexibility and enhanced photogenerated electron transport capabilities. In this study, 1,3,5-tris(4-aminophenyl)triazine (TAPT) and 1,3,5-tris(4-aminophenyl)benzene (TAPB) were employed as receptors to design a series of donor-acceptor (D-A) covalent organic frameworks using aldehyde from 1,3,5-benzenetricarboxaldehyde and aldehyde from 2,4,6-trihydroxybenzene-1,3,5-tricarbaldehyde as donors. The donor-acceptor structure of the COF was modified by altering the incorporation of hydroxyl groups and nitrogen elements. The photocatalytic hydrogen evolution performance of COF was further improved by significantly changing the light absorption capacity and surface electron distribution of COF when the reduction site was adjusted. Building upon this foundation, ascorbic acid was introduced to protonate the imide bond of COF, thereby further enhancing its photocatalytic hydrogen evolution ability. On this basis, the cocatalyst platinum (Pt) is further incorporated into the system, enabling the stable transfer of electrons to Pt. As a result, Pt functions as the active reduction site, thereby enhancing the catalytic reduction performance. Through experimental study and first-principles calculation analysis, the change of COF structure can adjust its light absorption capacity and energy band structure, and effectively improve the photogenerated electron transport capacity. Therefore, designing covalent organic frameworks with adjustable structures between donors and recipients emerges as a promising approach for optimizing photocatalytic hydrogen evolution technology.