Carbon Defects as Highly Active Sites for Gold Detection and Recovery

The use of precious metals (PMs) in many areas, such as printed circuit boards, catalysts, and target drugs, is increasing due to their unique physical and chemical properties, but their recovery remains a great challenge in terms of zero-valent PMs as the final product. We report a highly hydrophilic carbon dot (CD) as a reductant (electron donor), in which the defects in CD served as efficient active sites for zero-valent PMs recovery with an electron-donating capacity of ~1.7 mmol g^-1. The reduction of gold follows a two-step dynamic model characterized by the formation of nano-gold nuclei (initial rapid electron transfer process) followed by an Ostwald ripening process (subsequent slow process). Finite element method (FEM) simulation shows that the reaction efficiency and confinement effect of AuCl₄ ^- ions are positively correlated with defect density, indicating that the quantitative control of carbon defect density is the key to enhancing reduction activity. Combining density functional theory (DFT) with XPS and FTIR technology, we found that the electron is transferred from CD to Au(III) via hydrogen bonding. This nano carbon material can be exploited to recover gold from e-waste water directly, with the characteristics of reducing energy consumption and avoiding environmental pollution.