Rapid and template-free synthesis of copper(I) oxide-graphitic carbon nitride heterojunction for photocatalytic degradation of orange II dye in water

Herein, we report the synthesis of a p-n heterojunction catalyst comprising Cu₂O and g-C₃N₄ via a novel rapid, template-free and facile one-pot approach. The pristine semiconductors and their composite were characterised by X-ray diffraction (XRD), N₂ adsorption-desorption isotherms (BET), UV–vis diffuse reflectance spectroscopy, transmission electron microscopy (TEM), field emission scanning electronic microscopy (FESEM) and energy dispersive X-ray spectrometry (EDX). From the Mott-schottky plot, the flat-band potential and carrier density were estimated. Band gap energies of 2.03 and 2.65 eV were calculated for Cu₂O and g-C₃N₄ respectively, which indicate that both catalysts possess excellent optical absorption in the visible region of the solar spectrum. The p-n heterojunction produced a type-II band alignment which promotes the efficient separation of photogenerated electron-hole pairs. The photocatalytic property of the material was evaluated by employing it for the degradation of orange II dye in water. Different mass ratios of Cu₂O-g-C₃N₄ such as 1:1, 3:2, 7:3 and 9:1 were employed in the degradation process. However, Cu₂O-g-C₃N₄ with mass ratio 9:1 displayed the best photocatalytic performance, giving a removal efficiency that is 3.6 times higher than the pristine Cu₂O. The decolourisation and mineralisation efficiencies were 85% and 60% after 4 h of treatment. Scavenger studies further revealed the photogenerated holes as the main oxidant species in the photocatalytic reaction.