One-pot, ligand-free, room-temperature synthesis of Au/Pd/ZnO nanoclusters with ultra-low noble metal loading and synergistically improved photocatalytic performances

Photocatalytic Gold Recovery from Industrial Gold Plating Effluent by ZnO Nanoparticles: Optimum Condition and Possible Applications

The comparative study of photocatalytic gold recovery from cyanide-based gold plating solution was explored via commercial and hydrothermally synthesized ZnO nanoparticles (NPs). The effects of hydrothermal temperatures on the properties and photocatalytic activities of synthesized ZnO NPs were investigated. In addition, the effects of operating parameters including types of hole scavenger, concentrations of the best hole scavenger, the initial pH of wastewater, and photocatalyst dosages were examined. The obtained results demonstrated that the commercial ZnO NPs exhibited a higher photocatalytic activity for gold recovery than that of the synthesized ones owing to their good crystal quality and the presence of non-lattice zinc ions and appropriate non-lattice oxygen ions. Via the commercial ZnO NPs, the gold ions were almost completely recovered from the cyanide-based gold plating effluent within 7 h at an initial pH of 11.0 in the presence of 10 vol % C2H5OH and 1.0 g/L of photocatalyst loading with a pseudo-first-order rate constant of 0.2637 h-1. Finally, the resultant gold-decorated ZnO NPs exhibited a higher photocatalytic property for color reduction from industrial wastewater and antibacterial activity than that of fresh ZnO NPs. The results obtained in this study possess benefits and pave the way for waste remediation and management for the plating industries.

Ni loaded SnS2 hexagonal nanosheets for photocatalytic hydrogen generation via water splitting

Herein we have prepared the Ni-decorated SnS₂ nanosheets with varying concentrations of Ni from 1 to 10 mol% (1, 2.5, 5, and 10 mol%) and studied their various physicochemical and photocatalytic properties. The chemical reduction technique was utilized to load the Ni nanoparticles on SnS₂ nanosheets. The synthesized Ni decorated SnS₂ (denoted as Ni-SnS₂) was characterized using different spectroscopic techniques such as X-ray diffraction, diffuse reflectance UV-vis and photoluminescence spectroscopy, field emission scanning electron microscopy (FESEM), and field emission transmission electron microscopy (FETEM). XRD revealed the formation of the highly crystalline hexagonal phase of SnS₂ but for nickel loading there is no additional peak observed. Further, the as-prepared Ni-SnS₂ nano-photocatalyst shows absorption behaviour in the visible region, and photoluminescence spectra of the Ni-SnS₂ nanostructures show band edge emission centred at 524 nm, and the peak intensity decreases with Ni loading. The FE-SEM and FE-TEM confirm the formation of hexagonal sheets having evenly distributed Ni nanoparticles of size ∼5-10 nm. BET surface area analysis was observed to be enhanced with Ni loading. The photocatalytic performance of the prepared Ni-SnS₂ nanosheets was evaluated for hydrogen generation via water splitting under a 400 W mercury vapour lamp. Among the prepared Ni-SnS₂ nanostructures, the Ni loaded with 2.5 mol% provided the highest hydrogen production i.e., 1429.2 μmol 0.1 g^-1 (% AQE 2.32) in four hours, almost 1.6 times that of pristine SnS₂ i.e., 846 μmol 0.1 g^-1. Furthermore, the photocatalytic performance of the catalyst is also correlated with the photoconductivity by measuring the photocurrent. The photoconductivity of the samples is revealed to be stable and the conductivity of 2.5 mol% Ni-SnS₂ is higher i.e. 20 times that of other Ni-SnS₂ and pristine SnS₂ catalysts.