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.
