Metal-free amorphous carbon nitride with N-vacancies for efficient photocatalytic decontamination: a case of peroxydisulfate-based nonradical oxidation mechanism

Abstract

Peroxydisulfate-based nonradical oxidation processes (PDS-NOPs) are appealing for wastewater purification due to their high efficiency and environmental friendliness. Herein, we design and synthesize metal-free amorphous carbon nitride (ACN) with N3_C-site vacancies for the photoactivation of PDS to eliminate pharmaceuticals and personal care products in wastewater. Integrated with electron paramagnetic resonance and radical scavenging tests, the nature of the nonradical pathways in PDS activation is unveiled to be an electron-transfer regime. The in situ Raman spectrum analysis and electrochemical test show that PDS molecules combine with positively charged nitrogen vacancies to form a metastable complex (i.e., ACN–PDS*) with high chemical potential. Then, the complex selectively extracts electrons from coexisting organic pollutants to trigger the oxidation reaction. In addition, the introduction of nitrogen vacancies not only enhances the surface affinity between the catalyst and PDS but also accelerates the transfer efficiency of photoinduced electrons. As a result, the ACN/PDS system shows high photocatalytic degradation efficiency of diclofenac (DCF) in the pH range of 4 to 10 with degradation rate constants in the range of 0.18 to 0.21 min⁻¹. In a variety of practical aqueous matrices, DCF can be entirely removed within 5 minutes when exposed to sunlight. Toxicity evaluation experiments show that the toxicity of DCF could be efficiently removed in the can/PDS system.