Highly efficient ZnO/WO₃ nanocomposites towards photocatalytic gold recovery from industrial cyanide-based gold...

Discharging the gold-contained wastewater is an economic loss. In this work, a set of ZnO/WO₃ was facile synthesized by hydrothermal method in order to recover gold from the industrial cyanide-based gold plating wastewater by photocatalytic process. Effect of ZnO contents coupled with WO₃ was first explored. Then, effects of operating condition including initial pH of wastewater, type of hole scavenger, concentration of the best hole scavenger and photocatalyst dose were explored. A series of experimental results demonstrated that the ZnO/WO₃ nanocomposite with 5 wt% ZnO (Z_5.0/WO₃) depicted the highest photocatalytic activity for gold recovery due to the synergetic effect of oxygen vacancies, a well-constructed ZnO/WO₃ heterostructure and an appropriate band position alignment with respect to the redox potentials of [Au(CN)₂]^- and hole scavengers. Via this ZnO/WO₃ nanocomposite, approximately 99.5% of gold ions was recovered within 5 h using light intensity of 3.57 mW/cm², catalyst dose of 2.0 g/L, ethanol concentration of 20 vol% and initial pH of wastewater of 11.2. In addition, high stability and reusability were observed with the best nanocomposite even at the 5th reuse. This work provides the guidance and pave the way for designing the ZnO/WO₃ nanocomposite for precious metal recovery from a real industrial wastewater.