Construction of carbon quantum dots sensitized porous carbon nitride/titanium dioxide nanosheets for enhancing visible light photocatalytic degradation of tetracycline

Porous carbon nitride/titanium dioxide nanosheets (pCN/TNs) were synthesized by annealing the mixtures of urea, oxalic acid, and prepared titanium dioxide nanosheets, and it was then modified by carbon quantum dots (CQDs) to produce CQD-pCN/TNs. The novel CQD-pCN/TNs composites possessed excellent photocatalytic performance for the degradation of tetracycline (TC) with 86.2% under 120 min visible light irradiation, which was improved by 54%, 32.2%, and 20.7% compared to the systems with CNs, TNs, or pCN/TNs, respectively. The study on the catalytic mechanism revealed that the enhanced photocatalytic activity was attributed to the expanded absorption wavelength range by CQDs and the inhibited electron-hole recombination by heterojunction structure. The redshift effect could be compensated by increasing the absorption of visible light for the constructed 1% CQD-pCN/TNs. However, excessive redshift of absorption wavelength band could reduce the photocatalytic activity. The •O2-, h+, •OH, and 1O2 could be generated, and the former two played major roles, while the latter two played supporting roles in the degradation of TC. Furthermore, the CQDs could promote the production of more reactive species. TC molecule was broken down into small molecules via ring-opening reactions or/and the cleavage of the main carbon bond. The antibacterial activities of treaded solutions and eco-toxicities were detected and predicted by bacteriostatic test and ECOSAR model. This work offered a new sight for the design of excellent photo-catalysts for organic pollutants degradation.