Reactive oxygen species: New insights into photocatalytic pollutant degradation over g-C3N4/ZnSe nanocomposite

This work reports the synthesis of g-C3N4, ZnSe and their nanocomposite for photocatalytic degradation of the congo red (CR) dye under visible-light irradiation. For the as-synthesized materials, their phase and morphology were confirmed by using powder X-ray diffraction (XRD) and transmission electron microscopy (TEM), respectively. In addition, other spectroscopic techniques including energy dispersive X-ray (EDX), X-ray photoelectron spectroscopy (XPS), UV-visible diffuse reflectance (DRS) and electron spin resonance (ESR) were also used to study their physiochemical and optoelectronic properties. Based on the valence band (VB) positions from XPS and bandgap energies from UV-visible DRS, alignment of energy levels vs. standard hydrogen electrode (SHE) was drawn which exhibited the formation of type-II heterostructure. The acquired degradation results reveal that the nanocomposite degrades 95.69% of the CR dye during 1 h of visible-light illumination, which is 1.57 and 1.81-folds higher than the degradation efficiency of bare ZnSe and g-C3N4, respectively. The promising results while using nanocomposite might be attributed to efficient interfacial charge transfer based on their typeII alignment. It has also been confirmed via ESR spectroscopy that the superoxide anion radical (O-center dot(2)-) acts as the primary oxidant for the CR degradation. The photocatalyst reusability and sustainability have also been investigated.