Impact of CdS/SnO2 heterostructured nanoparticle as visible light active photocatalyst for the removal methylene blue dye

Abstract

An efficient and recyclable CdS/SnO2 heterostructure containing various proportions of CdS (0–10) wt % was synthesized for photocatalytic degradation of methylene blue dye under UV and natural sunlight radiations. Mesoporous SnO2 nanoparticles of surface area 19.2 m2/g and particle size 34 nm with well definite slit pore structure were synthesized by sol-gel route using span as structure and pore directing agent. The physicochemical properties of the novel nanoparticles were investigated by X-ray diffraction [XRD], N2-adsorption-desorption isotherm, diffuse reflectance spectra [DRS], X-ray photoelectron spectroscopy [XPS], photoluminescence [PL] and high resolution transmission electron microscope [HRTEM]. CdS quantum dots of size 9 nm, surface area 26.5 m2/g and wide mesoporous size (pore radius = 119.2 Å) were incorporated homogeneously on the surface of SnO2 forming an efficient heterojunction that cause a remarkable reduction in the band gap energy of SnO2 from 3.52 to 2.53 eV. These novel heterostructures facilitate the electron transfer from CB of CdS of more negative potential (-0.52 eV) to that of SnO2 of less negative potential (-0.04 eV), thus enhancing the separation efficiency of the charge carrier and increasing the life time of the reactive radicals. It is emphasized that the photocatalytic reactivity of SnCd5 is more than twice that of SnO2 and CdS nanoparticles. Experiments with different quenchers indicate that the electrons conduction band and superoxide radicals are the predominant reactive species on SnCd5 hybrid nanoparticles, however, hydroxyl radical and positive holes are more efficient on pure SnO2 surface. The as-synthesized SnCd5 nanoparticles exhibits an excellent photocatalytic stability and the catalyst retains 83 % of its reactivity after five consecutive cycles revealing that there is no deterioration in the catalyst structure.