Construction of two-dimensional heterojunctions based on metal-free semiconductor materials and Covalent Organic Frameworks for exceptional solar energy catalysis

Abstract

Covalent organic frameworks (COFs) are newly developed crystalline substances that are garnering growing interest because of their ultra-high porosity, crystalline nature, and easy modified architecture, showing promise in the field of photocatalysis. However, it is difficult for pure COFs materials to achieve excellent photocatalytic hydrogen production due to their severe carrier recombination problems. To mitigate this crucial issue, establishing heterojunction is deemed an effective approach. Nonetheless, many of the metal-containing materials that have been used to construct heterojunctions with COFs own a number of drawbacks, including small specific surface area and rare active sites (for inorganic semiconductor materials), wider bandgaps and higher preparation costs (for MOFs). Therefore, it is necessary to choose metal-free materials that are easy to prepare. Red phosphorus (RP), as a semiconductor material without metal components, with suitable bandgap, moderate redox potential, relatively minimal toxicity, is affordable and readily available. Herein, a range of RP/TpPa-1-COF (RP/TP1C) composites have been successfully prepared through solvothermal method. The two-dimensional structure of the two materials causes strong interactions between the materials, and the construction of heterojunctions effectively inhibits the recombination of photogenic charge carrier. As a consequence, the 9% RP/TP1C composite, with the optimal photocatalytic ability, achieves a photocatalytic H2 evolution rate of 6.93 mmol g−1 h−1, demonstrating a 10.19-fold increase compared to that of bare RP and a 4.08-fold improvement over that of pure TP1C. This article offers a novel and innovative method for the advancement of efficient COFs-based photocatalysts.