Enhancing Internal Electric Field of Metal-Free Donor–Acceptor Conjugated Photocatalysts for Efficient Photocatalytic Degradation of Tetracycline and CO₂ Reduction

Constructing alternating donor-acceptor (D-A) units within g-C₃N₄ represents an effective strategy for enhancing photocatalytic performance through improved charge carrier separation while concurrently addressing energy shortages and facilitating wastewater remediation. Here, a series of D-A-type conjugated photocatalysts (CNBTC-X) are prepared using g-C₃N₄ as an acceptor unit and different masses of 5-bromo-2-thiophenecarboxaldehyde (BTC) as a donor unit by a one-step thermal polymerization. CNBTC-50 presents higher photocatalytic properties for CO₂ reduction coupled with tetracycline (TC) removal than those of g-C₃N₄, CNBTC-10, CNBTC-30, and CNBTC-70. The introduction of the unique electron-donor-acceptor structure effectively drives the separation and transfer of photoinduced carriers while reducing the internal carrier transfer hindrance. Photocatalytic experiments reveal that the CNBTC-50 photocatalyst achieves up to 94.6% TC removal under visible light irradiation conditions. Compared with that of the pristine g-C₃N₄, the photocatalytic degradation reaction rate constant of CNBTC-50 is significantly increased by about 3.87 times. The study examines the influence of various reaction parameters on degradation activity, including catalyst concentration, pH, and TC concentration. Additionally, LC-MS is utilized to perform a comprehensive analysis of the intermediates and pathways involved in TC degradation. Furthermore, CNBTC-50 demonstrates remarkable photocatalytic CO₂ reduction activity, achieving rates of 20.83 μmol g^-1 h^-1 (CO) and 9.36 μmol g^-1 h^-1 (CH₄), which are 10.68 and 5.98 times more efficient than those of g-C₃N₄, respectively. This work aims to offer valuable guidance for the rational design of nonmetal D-A-structured catalysts and effectively integrates reaction systems to couple CO₂ reduction with antibiotic removal.