A metal-free catalyst based on g-C3N4 functionalized with cyamelurate-like groups: Catalytic properties and mechanism of a new heterogeneous Fenton-like catalyst

We prepared fragments of polymeric g-C3N4 sheets functionalized with cyamelurate-like functional groups, evaluated their Fenton-like catalytic properties and proposed a reaction mechanism for the formation of hydroxyl radicals on the surface of the materials in presence of H2O2. The controlled fragmentation/functionalization of g-C3N4 was characterized by a variety of techniques including SEM, TEM, FTIR and potentiometric titration. The performance of the catalysts proved to be dependent on both the cyamelurate-like functional groups and the conjugated structure of the polymeric g-C3N4 sheets, with the kinetics of the catalyzed reaction being faster at higher pH. In addition, in the absence of the contaminant, no significant consumption of hydrogen peroxide was observed. The reaction mechanism of oxidizing radicals formation was elucidated using cyclic voltammetry and EPR spectroscopy in parallel with theoretical calculations based on the estimate of the reaction Gibbs free energy of HO• and HOO• radicals formation, generated through the reaction of surface functional groups and hydrogen peroxide. In a broader context, the results showed may contribute to the development of strategies for studying and elucidating the reaction mechanisms involving metal-free catalysts, one of the main challenges in the area and, enabling the surface designing of metal-free catalysts for different oxidation reactions.