Selective adsorption of Au (III) from aqueous solution by a Cu-based bisligand metal organic framework adsorbent

A novel Cu-based bisligand metal organic framework adsorbent (Cu-BMOF) was prepared by hydrothermal method using 5-methyl-2-thiophenecarboxylic acid and 4,4-azopyridine as organic linkers. The samples were analyzed by scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD) and zeta potentiometry (Zeta). To investigate the adsorption performance of Cu-BMOF for Au(III), the effects of pH, temperature, adsorption time and initial concentration were explored. At 298 K and pH = 2, the maximum adsorption capacity of Cu-BMOF for Au(III) is 933 mg/g. Langmuir and quasi-second-order models can describe the adsorption process well. Au(III) adsorption on Cu-BMOF is a monolayer and irreversible chemisorption process. Thermodynamic studies show that the adsorption process of gold on Cu-BMOF is exothermic and spontaneous. The response surface method (RSM) was applied to optimize the adsorption efficiency. Under optimal conditions, the adsorption rate was 99.64%. X-ray photoelectron spectroscopy (XPS) results show that the adsorption mechanism of Cu-BMOF is the binding between Au (III) and the N, and S functional groups of Cu-BMOF. In addition, the affinity of Cu-BMOF for Au(III) is superior compared with that of coexisting ions in water. Cu-BMOF have promising applications in environmental protection and water purification.