Rational engineering of S-scheme CeO2/g-C3N4 heterojunctions for effective photocatalytic destruction of rhodamine B dye under natural solar radiations

Abstract

Constructing heterojunction to achieve efficient charge separation and transportation is a significant way to enhance the photocatalytic activity to solve many water crisis. In this novel research, rational sonochemical engineering of S-scheme CeO2/g-C3N4 heterojunctions was carried out by hybridizing CeO2 as oxidative photocatalyst (EVB = +2.37 eV) with g-C3N4 nanosheets as reductive photocatalyst (ECB= −1.2 eV) for removal of rhodamine B dye under natural solar radiations. The morphology, nanostructure, textural properties and optical characteristics of the solid samples were investigated using X-ray diffraction [XRD], N2-adsorption isotherms, diffuse reflectance spectrum [DRS], X-ray photoelectron spectroscopy [XPS], photoluminescence [PL], scanning electron microscope [SEM], mapping, selected area electron diffraction [SAED] and high resolution transmission electron microscope [HRTEM] analysis. The co-existence of CeO2 and g-C3N4 diffraction peaks and the depression in the surface area to half its value implied the strong interfacial interaction between the two semiconductors due to the remarkable difference in the point of zero charge of both semiconductors. CeO2 nanoparticles transported the heterojunction absorbability to deep visible region compared with pristine g-C3N4. With sonochemical incorporation of various proportions of CeO2 on g-C3N4 sheets, the photocatalytic performance was enhanced and optimized for the heterojunction containing 15 wt% CeO2 that mitigated 98.9% of RhB dye during three hours under natural solar radiations. RhB dye decomposed over heterojunction surface containing 15 wt% CeO2 with pseudo-first-order rate of 0.0312 min−1 which is 16.4 and 34.7 times higher than that of g-C3N4 and CeO2 nanoparticles, respectively. The exceptional enhancement of the photocatalytic performance of CeO2/g-C3N4 heterojunctions was ascribed to the strong absorbability of natural solar radiations, limiting the electron-hole recombination rate and production of S-scheme heterojunction with auspicious redox power. Scavenger experimental results and PL analysis of terephthalic acid directed the mechanism of the photocatalytic charge transportation to S-scheme route. The results emerged from this research work revealed that novel S-scheme CeO2/g-C3N4 heterojunctions with robust oxidative-reductive efficiency are capable for destructing various organic pollutants exist in wastewater.