Photoinduced recovery of gold using an inorganic/organic hybrid photocatalyst

Photorecovery of gold from solution using an amphiphilic photocatalyst based on a polyoxometallate (W₁₀O₃₂ ^4-)/ surfactant (dimethyldioctadecylammonium) hybrid was investigated. The prepared inorganic/organic hybrid dissolved in chloroform successfully photoreduced gold ions dissolved in water in a two-phase system under UV irradiation (λ > 320 nm). This resulted in the formation of gold colored films consisting of micrometer-sized hexagonal gold sheets with <111> crystal orientation at the liquid/liquid interface. The recovery can be performed at environmentally friendly pH values of 3-6. The recovery rate was dependent on the concentrations of the catalyst and a sacrificial agent (electron donor). SEM observations revealed that the catalyst has a morphology directing role in the formation of gold particles due to its preferential adsorption on gold. This makes gold nuclei formed at the interface grow into microsized large particles that can be readily collected via filtration. The hybridization of the polyoxometallate with the surfactant allows for the repeated use of the catalyst. Moreover, the addition of thiol compounds was found to significantly improve the recovery due to their covalent adsorption on gold and assistance with particle aggregation. The results show promising gold recovery feasibility using the hybrid catalyst as a new green process.