Surface electron-reservoir engineering of CQDs-modified Bi₁₉S₂₇Br₃ photocatalysts for efficient nitrate-to-ammonia...

Photocatalytic nitrate reduction to ammonia provides a sustainable route that integrates nitrogen-pollution remediation with green ammonia synthesis. However, the ammonia production efficiency of existing photocatalytic systems remains limited by insufficient light harvesting, severe recombination of photogenerated charge carriers, and inefficient surface adsorption and activation of nitrate. Herein, a surface electron-reservoir engineering strategy is proposed by anchoring zero-dimensional carbon quantum dots (CQDs) onto the surface of one-dimensional rod-like Bi₁₉S₂₇Br₃ through a facile hydrothermal method, yielding CQDs/Bi₁₉S₂₇Br₃ photocatalysts. Structural characterization studies demonstrate that the introduction of CQDs not only broadens the photoresponse range of Bi₁₉S₂₇Br₃ but also enables CQDs to serve as surface electron reservoirs that accept and temporarily store photogenerated electrons from Bi₁₉S₂₇Br₃ under illumination, thereby suppressing electron-hole recombination and improving the utilization efficiency of photogenerated electrons. Photocatalytic tests demonstrate that the optimized 5CQDs/Bi₁₉S₂₇Br₃ achieves an NH₃ production rate of 423.67 μmol g^-1 h^-1, with apparent quantum efficiencies of 0.24% and 0.17% under monochromatic irradiation at 380 and 400 nm, respectively. In situ FTIR results reveal that NO₃^- undergoes successive adsorption, stepwise deoxygenation, and proton-coupled electron-transfer processes on the surface of 5CQDs/Bi₁₉S₂₇Br₃, ultimately being converted into NH₄⁺via key intermediates such as *NO₂, *NO, and *NH₂OH.