Selective and Light-Enhanced Au(III) Recovery by a Porphyrin-Based Metal–Organic Framework: Performance and Underlying Mechanisms

Recovering gold from unconventional sources, such as electronic waste, offers significant environmental and economic benefits. Exploiting materials and methods with high efficiency and selectivity is demanding. Herein, we reported a novel light-enhanced Au(III) recovery process using a porphyrin-based metal–organic framework (PCN-224). Our results showed that PCN-224 exhibited a remarkable Au(III) recovery capacity of up to 2613 mg/g when exposed to visible light irradiation, which was 3 times higher than that in the dark. Furthermore, light irradiation also improved the Au selectivity of PCN-224 against coexisting ions, including Zn2+, Mg2+, Cd2+, Ni2+, Hg2+, Cu2+, Pb2+, Al3+, and Fe3+. Based on characterization and kinetic analysis, an adsorption–reduction mechanism was proposed for the light-enhanced Au recovery, and porphyrin linkers played an essential role as active sites for both adsorption and reduction. To further protect the porphyrin linkers in PCN-224, acetic acid was introduced as a representative electron donor molecule in electronic waste, which could further enhance the Au(III) recovery capacity to 4946 mg/g. In addition, we demonstrated that PCN-224 and its light-enhanced feature also performed effectively in the actual leaching solution of waste electrical and electronic equipment, and the framework was successfully reused for at least six cycles. Overall, our discoveries could inspire the design of more outstanding materials and the artful use of clean energy to recover precious metals while minimizing the environmental impact.