Sonochemical synthesis of S-scheme CuO/CeO2 heterojunction for enhanced photocatalytic degradation of rhodamine B dye under solar radiations

CeO2 2 is renowned photocatalyst with 2.8 eV band gap energy and exceptional optical features. However, the slow charge transportation and the fast recombination of the electron-hole pair hindered the photocatalytic efficiency. In this pioneering research, S-scheme CuO/CeO2 2 heterojunctions were engineered sonochemically with rational compositions of CeO2 2 and CuO nanoparticles for enhanced the photocatalytic efficiency of CeO2 2 in destructing rhodamine B dye under full solar radiations. Diffuse reflectance spectrum [DRS], photoluminescence [PL], high resolution transmission electron microscope [HRTEM], selected area electron diffraction [SAED], N2 2adsorption-desorption isotherm, X-ray photoelectron spectroscopy [XPS] and X-ray diffraction [XRD] investigated the physicochemical properties of CuO/CeO2 2 heterojunction. Monoclinic CuO nanoparticles of 8 nm size are facilely incorporated in cubic CeO2 2 crystallites of 27.3 nm through substitution of Ce4+ 4 + by Cu2+ 2 + ions which ascribed to smaller ionic radii of Cu2+ 2 + compared with Ce4+ 4 + and Ce3+ 3 + ions. Homogeneous distribution of CuO nanoparticles on CeO2 2 surface was further investigated by SEM and TEM analysis. HRTEM, XRD, SAED and XPS analysis recorded the co-existence of crystalline peaks of CeO2 2 and CuO implying the successful construction of CuO/CeO2 2 heterojunction. The depression in the surface area of CeO2 2 from 91.4 to 83.6 m2/g 2 /g with incorporating 5 wt % of CuO revealed the deposition of CuO on CeO2 2 surface. XPS analysis implied the existence of Ce3+ 3 + and oxygen vacancies that provide more adsorption sites for oxygen, which are beneficial for enhancing the catalytic performance of catalysts. CuO nanoparticles with 1.3 eV band energy enhanced the visible light absorbability of the heterojunctions in deep visible region for broading the photocatalytic response. Significant reduction in photoluminescence signals intensity by 60 % with incorporation 5 wt % of CuO revealed the favorable reduction in the rate of electron-hole recombination. In particular, CeCu5 containing 5 wt % CuO expelled 96 % of RhB dye within 6-h under solar simulator compared with 13 % removal on pristine CeO2 2 and CuO surface. Hot radicals and positive holes degraded RhB dye molecules on the heterojunction surface as elucidated from scavenger experiments and PL analysis of terephthalic acid. The exceptional removal of RhB dye under solar radiation was ascribed to the alignment in the band structure of CeO2 2 and CuO nanoparticles and the successful production of an efficient S-scheme heterojunction with strong redox potential and better electron transportation and separation.