Nitrogen-deficient g-C3Nx/POMs porous nanosheets with P-N heterojunctions capable of the efficient photocatalytic degradation of ciprofloxacin

Abstract

The direct shedding of piperazine rings is critical for the degradation of antibiotic persistent organic pollutants. In this work, nitrogen-deficient g-C₃N₄ loaded with polyoxometalates porous photocatalysts with P-N heterojunctions were carried out through the formation of chemical bonds between the nitrogen-deficient C⁺ in g-C₃N_x and the bridging oxygen in polyoxometalates (POMs), including phosphomolybdic acid (PMA), phosphotungstic acid (PTA) and silicotungstic acid (STA). The adsorption and photocatalysis experiments confirm the ability of the g-C₃N_x/POMs nanosheets to efficiently remove ciprofloxacin via the synergistic effects of adsorption and photo-catalysis. Approximately, g-C₃N_x/POMs-30 exhibits the optimal degradation ability, and the degradation rates of g-C₃N_x/PMA-30, g-C₃N_x/PTA-30 and g-C₃N_x/STA-30 could respectively reach 93.1%, 97.4% and 95.6% within only 5 min under visible light. The free radical scavenging experiment and ESR free radical capture experiments confirm that ·OH and ·O₂^- are free radicals that effectively degrade CIP. According to the results of the LC-MS analysis, the intermediates produced after CIP degradation and the efficient degradation pathway are proposed. The direct shedding of piperazine rings in the decarboxylation and defluorination process leads to the most efficient degradation of CIP into the small molecules.

Keywords: Adsorption; Ciprofloxacin; Nitrogen-deficient g-C(3)N(x); POMs; Photo-catalysis; P–N heterojunctions.