Photoelectrocatalytic degradation of m-chloronitrobenzene through rGO/g-C3N4/TiO2 nanotube arrays photoelectrode under visible light: Performance, DFT calculation and mechanism

The photoelectrocatalytic (PEC) technology by combing photocatalysis and electrochemistry has attracted widespread concerns in the organic pollutant degradation due to its effective degradation performance. TiO2 nanotube arrays (TNAs) can be used not only as photocatalyst but also as electrode and is regarded as a popular photoelectrode in PEC system. However, the fast photogenerated carrier recombination and low visible light utilization of TNAs restrict practical application of PEC technology for organic pollutant degradation. In this work, the graphitic carbon nitride (g-C3N4) and reduced graphene oxide (rGO) were loaded on TNAs surface to prepare ternary photoelectrode (rGO/g-C3N4/TNAs) for PEC degradation of m-chloronitrobenzene (m-CNB) under visible light. The surface structure and composition analysis revealed that rGO and g-C3N4 were suc-cessfully deposited on TNAs surface. The good light absorption capacity of g-C3N4 and good conductivity of rGO inhibited the photogenerated carrier recombination of TNAs and g-C3N4. The rGO/g-C3N4/TNAs prepared with 60 mg/L graphene oxide (rGO/g-C3N4/TNAs-60) possessed wider visible-light absorption range, higher carrier density and photoconversion efficiency than other as-prepared photoelectrodes, which promoted PEC degra-dation efficiency of m-CNB. The cyclic degradation experiment indicated that rGO/g-C3N4/TNAs-60 photo -electrode had good reusability and stability. The radical scavenging experiments and electron paramagnetic resonance (EPR) spectra demonstrated that center dot OH, center dot O2- and h+ were major active species, and e- was auxiliary species for PEC degradation of m-CNB by rGO/g-C3N4/TNAs-60. The degradation pathways of m-CNB were proposed according to gas chromatography mass spectra and density functional theory calculation. The comprehensive toxicity of m-CNB was relieved after PEC degradation according to the toxicity prediction.

Automated summary

In this study, a ternary photoelectrode (rGO/g-C3N4/TNAs) was prepared by loading g-C3N4 and rGO on the surface of TNAs for the PEC degradation of m-chloronitrobenzene under visible light. The ternary photoelectrode showed enhanced degradation efficiency, wider visible-light absorption range, higher carrier density, and good reusability and stability. Active species such as center dot OH, center dot O2- and h+ were identified for the degradation of m-CNB by the rGO/g-C3N4/TNAs-60 photoelectrode.