Selective adsorption and mechanism of Au (III) onto thiourea functionalized cuprous oxide

Thiourea-modified Cu2O (Cu2O-TU) was prepared by a facile route and used for the selective recovery of gold in acidic solution. X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) analysis elucidated that Au (III) ions were adsorbed onto the surface of Cu2O-TU via the electrostatic attraction of surface protonated amines groups (-NH3+) with AuCl4- and the chelating interaction of pyrrole-type nitrogen as well as CS groups in the pH range of 1.0 – 5.0. Subsequently, partial adsorption of Au (III) was reduced to Au (I) and Au (0), while pyridine-type nitrogen was oxidized to -NO, which accelerated the adsorption rate of Au (III). The adsorption equilibrium time was about 2 min and the adsorption capacity was 79.7 mg·g−1 at a pH value of 2.0 in 40 mg·L−1 Au (III) solution. The fitted result of gold adsorption by the Langmuir model was 1529.4 mg·g−1 at 318 K. The experimental data conformed to the pseudo-second-order model, indicating that the adsorption process was chemisorption. After 5 cycles, the capability of adsorption only decreased by 7.43%, which provided a great possibility for its application in solutions. Besides, Cu2O-TU showed specific and selective adsorption ability for Au (III) in the outdoor environment.