Researchers have developed modified tungsten oxide (WO3) coupled with graphitic carbon nitride (g-C3N4) to significantly improve the photocatalytic recovery of gold from non-cyanide-based plating effluents. This innovative approach addresses the pressing issue of precious metals being discharged with wastewater, which poses both economic and environmental challenges.
The study focused on the creation of nCN/WO3 − x composites, synthesized through thermal treatment. The results revealed these composites demonstrated superior photocatalytic activity, surpassing their individual components. Among the various combinations, the 5.0CN/WO3 − x composite achieved impressive results, recovering approximately 69.4% of gold within 120 minutes under UV-vis light irradiation.
The researchers noted, "The highest photocatalytic activity of the 5.0CN/WO3 − x sample was attributed to the proper presence of defects, which can act as electron trapping sites and thereby restrain the recombination rate of charge carriers." This factor proves pivotal, as reducing the recombination rate of electrons enhances the overall efficiency of the photocatalytic process.
Gold recovery is increasingly important due to the rise of electronic devices and the subsequent generation of electronic waste, which often contains valuable metal ions. Presently, many industries use cyanide-based processes, raising environmental concerns. The novel method developed by these researchers offers a safer alternative, utilizing photocatalysis without toxic chemicals.
The methodology involved creating WO3 − x through acid precipitation followed by annealing, thereby controlling defect concentration. The coupling of g-C3N4 facilitates effective charge migration along the composite structure, improving light absorption and catalytic activity.
During experiments, the team observed significant gold recovery rates under UV-vis light. The WO3 and g-C3N4 components acted synergistically, allowing photogenerated electrons from the conduction band of WO3 to react with gold thiosulfate complexes, thereby converting them to metallic gold on the composite’s surface.
Notably, the recovery percentage increased with repeated reuse of the photocatalyst, demonstrating its longevity and effectiveness, bolstered by the fact, as stated by the researchers, "The photocatalytic gold recovery increased via the reused 5.0CN/WO3 − x composite, attributing to the presence of decorated gold, which can act as an electron sink to facilitate the unrestricted migration of hot electrons along its structure."
This suggests not only the resourceful use of materials but also the potential for recycling precious metals from industrial waste.
Overall, findings from this research applaud the performance of g-C3N4/WO3 composites, hinting at their applicability beyond just gold recovery. Future applications might include hydrogen production and dye degradation, showcasing the versatility and effectiveness of these composites in addressing various environmental challenges.
Such innovative approaches signal progress toward more sustainable industrial processes, marking significant steps forward in photocatalytic technology for waste management and resource recovery.