Synthesis of cadmium sulfide-reduced graphene oxide nanocomposites by pulsed laser ablation in liquid for the enhanced photocatalytic reactions in the visible light

The large-scale applications of cadmium sulfide (CdS) nanoparticles (NPs) as a photo-catalyst are limited by their poor stability (high aggregation tendency) and consequent reduction in the surface area and increased rate of recombination of photoinduced electron-hole pairs, despite its inherent positive feature of being visible light active. It has been reported that the photocatalytic performance of CdS can be considerably improved if CdS is made as a composite material with reduced graphene oxide (rGO) in an optimum ratio. In this work, for the first time, we adopted the technique of pulsed laser ablation in liquids (PLAL) to synthesize highly pure CdS NPs and the required CdS/rGO nanocomposites using high purity (99.9%) microstructured CdS and graphene oxide as chemical precursors. PLAL is a simple and rapid 1-step synthesis process (where the reaction time is reduced from several hours to a few minutes), which does not require high temperature, toxic chemicals, and the final treatment to remove the unwanted by-products. The optical and morphological characterizations revealed that the anchoring of CdS on rGO transformed the CdS/rGO composite into an efficient photo-catalyst by enhancing the following positive attributes required for a good photo-catalyst: (1) The inherent tendency of aggregation of CdS is considerably reduced; CdS NPs with an average grain size of 20nm are well placed on the rGO sheets; and hence, the surface area of the catalyst was significantly increased to provide more active sites. (2) The reduced rate of photoinduced electron-hole recombination manifested in the photoluminescence spectrum indicated the effective charge separation. (3) The enhanced light absorption in the visible/infrared region ensured the effectiveness of this material in naturally abundant solar radiation. In the CdS/rGO composite, the rGO sheets play the role of a supporting matrix, cocatalyst, and electron acceptor for CdS. To evaluate the photo-catalytic performance of CdS/rGO, we applied it as a visible light-driven photo-catalyst for degrading methylene blue dye and found that CdS/rGO nanocomposite was more efficient than pure CdS in the visible spectral region. Therefore, PLAL provides a simple and 1-step route to synthesize high-purity visible light-driven photo-catalysts and solar cell material.