Carbon-based binary organic photocatalysts for rapid dye degradation under weak light: performance and mechanistic study

Abstract

Congo red (CR), a stable benzidine diazo dye due to its azo bonds, resists natural photodegradation and poses a significant ecological threat. Herein, organic photocatalyst material PM7:ITC-2Cl@C was integrated with natural biochar to establish a high-performance photocatalyst coupling with adsorption. PM7:ITC-2Cl@C demonstrated complete degradation of 100 mg L⁻¹ CR in 10 min under indoor weak light, sustaining a degradation efficiency above 99% within 20 cycles. The removal efficiency of TOC content in a simulated aquatic environment containing 100 mg L⁻¹ of CR was over 81%. PM7:ITC-2Cl@C possesses broad photon utilization (450–760 nm) and sequential measurements confirm its remarkable electron–hole separation, and the catalyst surface with functional groups containing oxygen and hydrogen also aids radical generation. Additionally, the strong adsorption of biochar fosters an environment for effective interaction with active oxygen species, ensuring constant pollutant contacting. Moreover, radical quench measurements indicated h⁺, ˙OH, and ˙O₂⁻ as key reactive oxygen species. The potential degradation pathways of CR were explored via LC-MS and DFT analysis, while toxicity analysis revealed low toxicity in the intermediates, suggesting the promising prospects of this system. This approach demonstrates high-performance PM7:ITC-2Cl@C to significantly enhance the catalytic oxidative degradation process of dying wastewater.