Biomolecule-mediated CdS-TiO2-reduced graphene oxide ternary nanocomposites for efficient visible light-driven photocatalysis

Abstract

We report an environmentally friendly synthetic strategy to fabricate reduced graphene oxide (rGO)-based ternary nanocomposites, in which glutathione (GSH) acts both as a reducing agent for graphene oxide and sulfur donor for CdS synthesis under modified hydrothermal (MHT) conditions. The report becomes interesting as pH variation evolves two distinctly different semiconducting nanocrystals of anatase/rutile TiO₂ and hexagonal yellow/cubic red CdS, and their packaging makes them suitable photocatalysts for dye degradation. Herein, a titanium peroxo compound, obtained from commercial TiO₂, is hydrolyzed to TiO₂ nanostructures without any additives. The yellow colored CdS-TiO₂-rGO (YCTG), one of the ternary photocatalysts, shows maximum efficiency compared to the corresponding red ternary CdS-TiO₂-rGO or binary photocatalysts (CdS-rGO, TiO₂-rGO and CdS-TiO₂) for dye degradation under visible light irradiation. Systematic characterizations reveal that TiO₂ presents at the interface of rGO and CdS in YCTG and thus makes a barrier that inhibits the direct interaction between rGO and CdS. This leads to a relatively higher bandgap value for CdS in YCTG (2.15 eV vs. 2.04 eV for CdS-rGO) but with better photocatalytic activity simply by diminishing the possibility of the charge-recombination process. In the present situation, rGO in the YCTG also supports faster dye degradation through higher dye adsorption and rapid internal electron transfer (CdS→TiO₂→rGO) in the YCTG nanocomposite. Thus, a simple aqueous phase and a greener synthetic procedure results in a low-cost, highly effective visible light-responsive material for environmental application.