Evaluation of CdS QDs/MWCNTs-supported AgNPs heterojunction nanocomposites for enhanced photocatalytic and antibacterial properties toward water remediation process

Heterojunction nanocomposites are considered as effective platforms for construction of photocatalysts. In this research, cadmium sulfide quantum dots (CdS QDs) and Ag nanoparticles (Ag NPs) simultaneously were synthesized and anchored on multi walled carbon nanotube (MWCNTs) for the fabrication of Ag-CdS QDs/MWCNTs ternary nanocomposites as a novel heterojunction photocatalyst for water remediation. The obtained nanostructures were characterized through several analysis to confirm the successful synthesis. Multifarious parameters including dye dosage, photocatalyst dosage, pH, contact time, light source, different dyes, H₂O₂ dosage, scavenger effect and inorganic anions were investigated for optimization. The function of Ag-CdS QDs/MWCNTs was studied against photodegradation of rhodamine B (RhB) as the water pollutant model. In optimum conditions, 98.8% of RhB was photodegraded after 35 min while it was exposed to natural sunlight. The highest adsorption capacity measured by Langmuir fitting was 28.74 mg g⁻¹. Moreover, the adsorption kinetics corresponded with the first-order kinetic model and the amount of rate of constant for Ag-CdS QDs/MWCNTs was 1.38 × 10⁻² min⁻¹. On the basis of radical quenching experiments, the effect of oxidizing types in the photodegradation of RhB was ordered as \({}^\cdot\text{OH}\) > \({}^\cdot{\text{O}}_{2}^{-}\) > \({\text{h}}^{+}\). After four catalyst reuse cycles, more than 82.4% RhB was removed, showing a cost-efficiency potential in the reusability of Ag-CdS QDs/MWCNTs. Furthermore, the ternary nanocomposite demonstrated noteworthy bactericidal activity against gram-positive (S. aureus and B. subtilis) and gram-negative (E. coli) bacteria strains.