G-C3N4 with gradient vacancies to enhance spatial charge carriers transfer and separation for photodegrading antibiotics under visible light

[Display omitted] •VC, N-CN6 constructed of gradient VN and surface VC was prepared.•The VC, N-CN6 can completely photodegrade tetracycline within 3 min.•The kinetic constant of VC, N-CN6 is 45.9-fold higher than pristine g-C3N4. Antibiotic pollution has potential toxicities to living organisms and the ecological environment and draws great concern of researchers. Photocatalytic degradation of antibiotics by g-C3N4 shows an unsatisfied activity due to the low utilization efficiency of photogenerated electrons and severe charge recombination. A main reason is the neglect of the utilization of electrons at the depth of the material surface. Herein, we report local microenvironment rearranged g-C3N4 (VC, N-CN6) with intrinsic gradient concentration nitrogen (VN) and carbon vacancy (VC) via KBH4 etching followed by water oxidation, enabling a complete photocatalytic degradation (≥99.6%) of TC within 3 min under visible light. This photoactivity has a universality, and can completely visible-light photodegrade sulfadiazine and ciprofloxacin in a short time. Such an extraordinary activity is ascribed to cooperation between gradient VN modulating utilization of internal electron and VC enhancing reactive species generation. Additionally, photodegraded pathways, intermediates, and risks of TC photocatalytic degradation were elucidated by the HPLC-MS and quantitative structure-effect relationship mathematical model. This work enriches the toolbox to engineer the local microenvironment of photocatalysts to upgrade the utilization of internal photoexcited electrons and heighten TC photocatalytic degradation efficiency.