Synergistically homogeneous-heterogeneous Fenton catalysis of trace copper ion and g-C₃N₄ for degradation of organic pollutants

Using the bulk g-C₃N₄ as a precursor, four g-C₃N₄ nanosheets were further prepared by ultrasonic, thermal, acid, and alkali exfoliation. The structures of these materials were characterized by various techniques such as X-ray powder diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy, energy dispersive X-ray spectroscopy, transmission electron microscopy, and X-ray photoelectron spectroscopy. The synergistical Fenton catalysis of these materials with Cu²⁺ was evaluated by using rhodamine B as a simulated organic pollutant. The results showed that there existed a significant synergistical Fenton catalysis between Cu²⁺ and g-C₃N₄. This synergistic effect can be observed even when the concentration of Cu²⁺ was as low as 0.064 mg L^-1. The properties of g-C₃N₄ strongly influenced the catalytic activity of the Cu²⁺/g-C₃N₄ system. The coexistent of Cu²⁺ and the alkali exfoliated g-C₃N₄ showed the best catalytic activity. Hydroxyl radicals as oxidizing species were confirmed in the Cu²⁺/g-C₃N₄ system by electron paramagnetic resonance spectra. The synergistic catalysis may be attributed to the easier reduction of Cu²⁺ adsorbed on the g-C₃N₄. This study provided an excellent Fenton catalytic system, and partly solved the rapid deactivation of heterogeneous Fenton catalysts caused by the leaching of metal ions.