Comparative study of TiO₂/CuS Core/shell and composite nanostructures for efficient visible light photocatalysis

An enduring impediment in the photocatalysis domain is the rapid recombination of photoinduced charge carriers. One viable strategy to realize efficient separation of photoinduced charge carriers is to design core/shell nanostructures. In this context, our work explains the substantial separation of photocarriers and enhanced light harvesting in TiO2 nanostructures following the realization of core/shell geometry with CuS. We demonstrate the design of the TiO2/CuS core/shell nanostructures, utilizing a surface-functionalizing agent, 3-mercaptopropionic acid, and offering commendable visible light driven photocatalytic performance for degradation of virulent organic pollutants of dye wastewater, like methylene blue (MB). To validate the merits of the TiO2/CuS core/shell nanostructures, we have also designed TiO2/CuS composite nanostructures under similar conditions (without utilizing the surface-functionalizing agent, 3-mercaptopropionic acid). Successful realization of TiO2/CuS nanostructures (core/shell and composite) was concluded from the PXRD, FESEM, TEM, HRTEM, EDS elemental mapping, and DRS studies. The resulting core/shell nanostructures have propitious photocatalytic performance (∼90%) over composite nanostructures (∼58%), which could be scrutinized in terms of core/shell geometry, maximizing the interfacial contact between TiO2 and CuS and enabling retardation in the recombination rate of the photoinduced charge carriers by confining electrons mainly in one component (core) and holes in the other component (shell). To have the best photocatalytic performance from the TiO2/CuS core/shell nanostructures, we also determined the optimum amount of photocatalyst (0.3 g/L) and organic pollutant dye concentration (0.003 g/L) required for visible light driven degradation of MB. A credible mechanism of the charge transfer process and mechanism of photocatalysis supported from trapping experiments in the TiO2/CuS nanostructures for the degradation of an aqueous solution of MB is also explicated. Degradation intermediates analysis performed using mass spectroscopy (MS) studies showed that MB dye degradation is initiated by a demethylation pathway. Our work also highlights the stability and recyclability of a core/shell nanostructures photocatalyst and supports its potential for environmental applications. We thus anticipate that our results bear broad potential in the photocatalysis domain for the design of a visible light functional and reusable core/shell nanostructures photocatalyst