Controlled and automatic fabrication of ultra small SnO2-CdS nano-heterojunction via continuous flow method designed for photochemical treatment of dye contaminated natural water resources

Abstract

Contaminated organics such as dyes represent a most important and rising source of environmental pollution. A capable approach to remedy this utilizes semiconductors to catalytically photodegrade the stable bonds in these toxic dye molecules. Heterostructured photocatalysts composed of two dissimilar semiconductors can conquer difficulties of rapid electron-hole recombination and inefficient light harvesting whilst reducing dependency on either constituent independently. At present fabrication of scalable, non-agglomerated, and monodispersed semiconductor photocatalysts by using continuous flow microreactor technology pays severe concern since it presents a range of advantages compared to the conventional batch reactor technology. In this contribution, we advance the prior art by introducing a simplistic, commercial, and environmentally benign continuous flow microreactor synthetic approach for designing a SnO2-CdS nano-heterojunction at a reasonably low reaction temperature and very short reaction period. Up-to-date, very few researchers are able to prepare the heterojunction nanocomposites such as SnO2-CdS through a microfluidic approach and as well the corresponding ultra-low particle size is not reported either. A PTFE (polytetrafluoroethylene)-based helical tubular microreactor is being exploited that comprises a compact structure and offers improved heat and mass transport as well as better intermixing among the reactants. Heterostructure formation is confirmed by X-ray diffraction (XRD), FTIR spectroscopy, and transmission electron microscopy (TEM) analysis. Mott-Schottky (M−S) and Diffused Reflectance (DRS) analyses jointly demonstrate that the heterostructured nanomaterial, comprising a narrow bandgap semiconductor (CdS) and a wide band-gap semiconductor (SnO2), possesses significant potential as a photocatalyst. Furthermore, when applied in the degradation of Congo red (CR) dye under simulated solar conditions, it clearly exhibits superior photocatalytic activity compared to its individual SnO2 and CdS components. The efficient charge separation in this heterostructure is confirmed by the time resolved spectroscopic study. It is monitored that a strong type-II interaction is exhibited in the heterostructure and a plausible mechanism has been utilized to clarify this behaviour.