3D-printed Al₂O₃ framework supported carbon-bridged tri-s-triazine of g-C₃N₄ for photocatalytic tetracycline oxidation

Powder-like g-C₃N₄ has been widely used as a photocatalyst but exhibits several drawbacks, including unrecyclable, high charge recombination, and limited light absorption. In this study, carbon-bridged g-C₃N₄ was successfully prepared and coated on a 3D-printed Al₂O₃ substrate for the photocatalytic oxidation of tetracycline. Oxamide (OD), malonamide (MD), and succinamide (SD) were used as carbon-containing linkers to react with precursors (melamine and urea) and produce carbon-bridged g-C₃N₄. Carbon substitution at the bridged N atoms of g-C₃N₄ improved light absorption, reduced charge recombination, and resulted in high photocatalytic tetracycline removal efficiency. Computational calculations were also employed, and Bader charge analysis supported the charge redistribution and charge transfer of the carbon-bridged g-C₃N₄ samples. Our results indicated that the degradation of tetracycline followed step-by-step oxidation, deamination, and mineralization to form CO₂ and H₂O. The 3D-printed Al₂O₃-supported carbon-bridged g-C₃N₄ exhibited a high removal rate of 85–90 % and stability for photocatalytic reactions and can be reused for at least 10 cycles. This study demonstrates that the 3D-printed Al₂O₃-supported carbon-bridged g-C₃N₄ catalyst is an efficient and effective catalyst support system for photocatalytic reactions.