Influence of hydrogen peroxide in enhancing photocatalytic activity of carbon nitride under visible light: An insight into reaction intermediates

Carbon nitride is a known photocatalyst that can be activated under visible light irradiation. In this research, the combined effect of carbon nitride and hydrogen peroxide in photocatalytic degradation of methylene blue (MB) in water was investigated under visible light. Carbon nitride was synthesized by thermal polymerization of dicyandiamide and characterized by x-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), Energy dispersive x-ray (EDX), Fourier transform infrared spectroscopy (FTIR) and pore textural properties. The kinetic study of degradation of MB with carbon nitride and in presence of hydrogen peroxide showed complete degradation of MB before 45 min of time interval. The kinetic studies were also performed by varying the dose of photocatalyst and initial concentration of MB and it was shown that higher dose of photocatalyst and lower concentration of MB resulted in higher rate of degradation. The dual role of hydrogen peroxide can be related to the generation of additional highly reactive hydroxyl radicals in presence of photocatalyst and prevention of recombination of holes and electrons of carbon nitride thereby improving its photocatalytic activity. The pH study revealed that neutral pH of the solution results in the highest rate of degradation. Analysis of liquid chromatography-mass spectroscopy (LCMS) results helped to reveal the reaction steps of photocatalysis of MB and it was found that the four stages of photodegradation of MB were demethylation, ring shortening, ring opening and complete mineralization.