Photocatalytic degradation of tetracycline by N-CQDs modified S-g-C3N4 nanotubes and its product toxicity evaluation

Abstract

In this study, to improve the electron-hole pairs separation rate and enhance the antibiotic wastewater treatment efficiency, the sulfur doped g-C3N4 (SCN) nanotubes were modified with nitrogen-doped carbon quantum dots (N-CQDs) derived from pig manure by a simple solvothermal method, and SCN/N-CQDs composite photocatalyst was synthesized. SCN with hexagonal tubular structure has strong light scattering ability and abundant active sites. At the same time, the modification of N-CQDs extended the visible light response range, accelerated the separation of electron-hole pairs, and realized the efficient photocatalytic degradation of tetracycline (TC). The SCN/N-CQDs-1 showed the best photocatalytic performance, and degradation rate of TC could reach to 79.11% after 90 min of visible light irradiation, much higher than the degradation efficiency of pure SCN (58.33%). Among them, the generation of hole, hydroxyl radicals and superoxide radicals play an important role in the efficient degradation of TC. Furthermore, the intermediates produced during the degradation process were detected by ultra-performance liquid chromatography-mass spectrometry (HPLC − MS), and the possible TC degradation pathways were investigated. The repeatability and practicability of SCN/N-CQDs are proved by five cycle experiments. In addition, compared with the original toxicity, the inhibition rate of Escherichia coli (E. coli) colony growth was reduced by 91.315% after 90 min photodegradation. The results of biotoxicity analysis showed that SCN/N-CQDs leaching solution and its photodegradation wastewater did not produce biotoxicity to E. coli.