Integration of heterojunction and pore wall engineering on functionalized covalent organic frameworks for boosting...

The efficient photocatalytic removal of uranium, U (VI), by functionalized covalent organic frameworks (COFs) is promising, while precise regulation of their electronic structure and effective promotion of their charge-carrier separation remains a great challenge. Herein, the integrated strategies including pore wall and heterojunction engineering, for the first time, were employed to rationally construct a novel photocatalyst (NH₂-MX@Por-COF-OMe), for photocatalytic reduction of U (VI). Specifically, the functionalized COFs were in-situ grown on amino-functionated Ti₃C₂T_x MXene (NH₂-MX) substrate via stable imine covalent connection. In particular, three different substituted groups (-H, -Br, and -OMe), were designed to modify the pore walls of the COFs. The substituted groups can adjust the electronic structure of the COFs, and the strong electron-donating -OMe induces the most negative conduction band, beneficial for U (VI) photo-reduction. Meanwhile, the formed Schottky heterojunction between NH₂-MX and Por-COF-OMe, favors the rapid charge-carrier separation and accelerates the transfer of photogenerated electrons. As a result, the fabricated NH₂-MX@Por-COF-OMe photocatalyst exhibits excellent photo-reduction activity for U (VI) under light irradiation, with both high adsorption capability (q_m = 1858.7 mg/g, nearly twice the dark adsorption value of 943.3 mg/g), and fast reaction kinetics (removal of 98.3 % in 40 min, k = 0.098 min^-1), which significantly surpass those of pristine NH₂-MX (50.2 %, k = 0.004 min^-1) and Por-COF-OMe (60.3 %, k = 0.019 min^-1), respectively. The present work highlights the rational construction of COFs-based photocatalysts for efficient photocatalytic removal of U (VI) by the integrated pore wall and heterojunction engineering strategies.