  Materials that are capable of extracting gold from complex sources,
especially electronic waste (e-waste) with high efficiency are needed for gold
resource sustainability and effective e-waste recycling. However, it remains
challenging to achieve high extraction capacity to trace amount of gold, and
precise selectivity to gold over a wide range of complex co-existing elements.
Here we report a reduced graphene oxide (rGO) material that has an ultrahigh
extraction capacity for trace amounts of gold (1,850 mg/g and 1,180 mg/g to 10
ppm and 1 ppm gold). The excellent gold extraction behavior is accounted to the
graphene areas and oxidized regions of rGO. The graphene areas spontaneously
reduce gold ions to metallic gold, and the oxidized regions provide a good
dispersibility so that efficient adsorption and reduction of gold ions by the
graphene area can be realized. The rGO is also highly selective to gold ions.
By controlling the protonation process of the functional groups on the oxidized
regions of rGO, it shows an exclusive gold extraction without adsorption of 14
co-existing elements seen in e-waste. These discoveries are further exploited
in highly efficient, continuous gold recycling from e-waste with good
scalability and economic viability, as exemplified by extracting gold from
e-waste using a rGO membrane based flow-through process.
