One step construction of N-vacancy-rich carbon doped g-C₃N₄/g-C₃N₄Z-type homojunction and its coupling with persulfate for tetracycline degradation

Abstract

Graphitic carbon nitride (g-C₃N₄) has been widely applied in advanced oxidation processes based on persulfate (PS) for photocatalytic degradation aqueous pollutants, yet it still suffers from limitations such as weak redox capability, low electrical conductivity and severe charge recombination. In this study, via building a confined environment, the doped-C and nitrogen vacancy (Nv) were simultaneously introduced in g-C₃N₄ through one-step calcination. Compared to CN-M derived from melamine, the urea-derived CN-U exhibits higher concentrations of doped-C and Nv, which leads to the different band structures. The valence band (VB) and conduction band (CB) of CN-M shift more positively than those for CN-U with ΔE_VB and ΔE_CB being 0.31 and 0.36 eV, respectively. As a result, a Z-type g-C₃N₄/g-C₃N₄ homojunction (CN-UM) derived from the mixture of urea and melamine was constructed with the minimum resistance, the lowest charge recombination rate and the high redox capacity retained. The tetracycline degradation efficiency and degradation rate constant by CN-UM coupling with PS reach 99% and 0.08989 min⁻¹, respectively, after irradiation for 60 min, along with the excellent cycling stability. The active species h⁺, ·O₂⁻, ·OH and

{\mathrm{S}\mathrm{O}}_{4^{\cdot -}}

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play roles during the degradation process, with the contributions from h⁺ and ·O₂⁻ higher than those from ·OH and

{\mathrm{S}\mathrm{O}}_{4^{\cdot -}}

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.

Keywords

graphitic carbon nitride / g-C₃N₄/g-C₃N₄ Z-type homojunction / carbon doping / nitrogen vacancy / tetracycline degradation

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