Enhancing Internal Electric Field of Metal-Free Donor–Acceptor\nConjugated Photocatalysts for Efficient Photocatalytic Degradation\nof Tetracycline and CO<sub>2</sub> Reduction

Constructing\nalternating donor–acceptor (D–A) units\nwithin g-C<sub>3</sub>N<sub>4</sub> represents an effective strategy\nfor enhancing photocatalytic performance through improved charge carrier\nseparation while concurrently addressing energy shortages and facilitating\nwastewater remediation. Here, a series of D–A-type conjugated\nphotocatalysts (CNBTC-X) are prepared using g-C<sub>3</sub>N<sub>4</sub> as an acceptor unit and different masses of 5-bromo-2-thiophenecarboxaldehyde\n(BTC) as a donor unit by a one-step thermal polymerization. CNBTC-50\npresents higher photocatalytic properties for CO<sub>2</sub> reduction\ncoupled with tetracycline (TC) removal than those of g-C<sub>3</sub>N<sub>4</sub>, CNBTC-10, CNBTC-30, and CNBTC-70. The introduction\nof the unique electron-donor–acceptor structure effectively\ndrives the separation and transfer of photoinduced carriers while\nreducing the internal carrier transfer hindrance. Photocatalytic experiments\nreveal that the CNBTC-50 photocatalyst achieves up to 94.6% TC removal\nunder visible light irradiation conditions. Compared with that of\nthe pristine g-C<sub>3</sub>N<sub>4</sub>, the photocatalytic degradation\nreaction rate constant of CNBTC-50 is significantly increased by about\n3.87 times. The study examines the influence of various reaction parameters\non degradation activity, including catalyst concentration, pH, and\nTC concentration. Additionally, LC–MS is utilized to perform\na comprehensive analysis of the intermediates and pathways involved\nin TC degradation. Furthermore, CNBTC-50 demonstrates remarkable photocatalytic\nCO<sub>2</sub> reduction activity, achieving rates of 20.83 μmol\ng<sup>–1</sup> h<sup>–1</sup> (CO) and 9.36 μmol\ng<sup>–1</sup> h<sup>–1</sup> (CH<sub>4</sub>), which\nare 10.68 and 5.98 times more efficient than those of g-C<sub>3</sub>N<sub>4</sub>, respectively. This work aims to offer valuable guidance\nfor the rational design of nonmetal D–A-structured catalysts\nand effectively integrates reaction systems to couple CO<sub>2</sub> reduction with antibiotic removal.