Synthesis of cadmium sulfide-tungsten trioxide nanocomposites for photo-catalytic degradation of organic pollutants and growth retardation of waterborne bacteria and biofilms

Nanocomposites of cadmium sulfide-tungsten trioxide (CdS@WO₃), with different CdS content (2.5 %, 5 % and 10 %) in WO₃ were synthesized by laser defect engineering in liquid (LDL). In the characterization studies, X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), transmission electron microscope (TEM) and high-resolution transmission electron microscope (HR-TEM) studies showed the perfect anchoring of CdS nanoparticles on the surface of bigger WO₃ nanoparticles in CdS@WO₃ nanocomposites. In the optical characterization, ultra-violet diffuse reflectance spectra (UV-DRS) indicated the narrowing down of band gap energy in CdS@WO₃, and consequent enhancement of visible light absorption compared to pure WO₃. Also photoluminescence (PL) implied the reduced charge recombination in CdS@WO₃, compared to that of pure WO₃, which can be attributed to the typical Z-scheme charge transfer between the composite partners. The LDL synthesized CdS@WO₃ nanocomposites were used as (i) a photocatalyst for the degradation of Rhodamine B dye in water, (ii) anti-microbial agent against multi drug-resistant Pseudomonas aeruginosa (MDR-PA) and Methicillin-resistant Staphylococcus aureus (MRSA) bacteria, (iii) biofilm growth retardation agent against biofilm-producing strains of MRSA and MDR-PA. In all the three applications CdS@WO₃ nanocomposite in general revealed a better performance than pure WO₃, particularly 5 % CdS content in the composite (5 %-CdS@WO₃), was the optimum for photocatalytic degradation and 10 % CdS content in CdS@WO₃ showed the best performance in antibacterial and biofilm growth retardation applications for both bacterial strains.