Thermally Reduced Graphene Oxide Membranes Revealed Selective Adsorption of Gold Ions from Mixed Ionic Solutions

The recovery of gold from water is an important research area. Recent reports have highlighted the ultrahigh capacity and selective extraction of gold from electronic waste using reduced graphene oxide (rGO). Here, we made a further attempt with the thermal rGO membranes and found that the thermal rGO membranes also had a similarly high adsorption efficiency (1.79 g gold per gram of rGO membranes at 1000 ppm). Furthermore, we paid special attention to the detailed selectivity between Au³⁺ and other ions by rGO membranes. The maximum adsorption capacity for Au³⁺ ions was about 16 times that of Cu²⁺ ions and 10 times that of Fe³⁺ ions in a mixture solution with equal proportions of Au³⁺/Cu²⁺ and Au³⁺/Fe³⁺. In a mixed-ion solution containing Au³⁺:Cu²⁺:Na⁺:Fe³⁺:Mg²⁺ of printed circuit board (PCB), the mass of Au³⁺:Cu²⁺:Na⁺:Fe³⁺:Mg²⁺ in rGO membranes is four orders of magnitude higher than the initial mass ratio. A theoretical analysis indicates that this selectivity may be attributed to the difference in the adsorption energy between the metal ions and the rGO membrane. The results are conducive to the usage of rGO membranes as adsorbents for Au capture from secondary metal resources in the industrial sector.