Highly efficient photocatalytic degradation of organic pollutants by mesoporous graphitic carbon nitride bonded with cyano groups

Constructing high-performance visible-light responsive photocatalyst to remediate organic pollutants from wastewater is of great challenge in recent years. In this study, by using SiO2 clusters as a template, mesoporous graphitic carbon nitride nano-clusters (NC MCN) were fabricated as a high-activity photocatalyst. The confined growth of carbon nitride in the presence of SiO2 clusters introduced extra structural defects to the carbon nitride framework including nitrogen vacancies and cyano groups, which was confirmed by employing different characterization analyses. These structural defects created midgap states below the conduction band, which improved light-harvesting efficiency and suppressed electron-hole recombination. Thus, NC MCN showed high photocatalytic activity toward degradation of both tetracycline and rhodamine B under visible light irradiation. Complete degradation of 15 mL solution of 15 ppm tetracycline was achieved in 30 min compared to the bulk catalyst (taking more than 3 h). Furthermore, NC MCN demonstrated high stability after reusing for 8 consecutive photodegradation cycles. The total organic carbon concentration at different reaction time showed a rising and falling trend, which illustrate photodegradation process, i.e. adsorption, photodegradation, and mineralization. By liquid chromatography-mass spectroscopy analysis, the produced intermediates during the tetracycline degradation were proposed, which showed the formation of smaller molecules in just 15 min. The toxicity of the intermediates was analyzed using quantitative structure-activity relationship estimation and the outcomes exhibited that the toxicity of the solution reduced as the reaction time increased. This comprehensive study from photodegradation process to mineralization of TC demonstrated NC MCN as a promising photocatalyst for sustainable treatment of wastewater.