A green approach to recover Au(III) in aqueous solution using biologically assembled rGO hydrogels

• GO was reduced by Shewanella oneidensis MR-1 to prepare 3D rGO hydrogels.
• The rGO hydrogels exhibited excellent gold recovery from aqueous solution.
• RSM was used to obtain the optimized conditions for gold recovery.
• Precious metal could be preferentially recovered from mixed-ion-solution.

Recovery of precious metals from aqueous solution using environmentally benign methodologies is highly desirable. In this study, graphene oxide (GO) was reduced by Shewanella oneidensis MR-1 to prepare three dimensional reduced GO (rGO) hydrogels. The obtained rGO hydrogels were used to recover Au(III) from aqueous solution. This process was greatly affected by the concentration of GO in the solution, pH, reaction time, and Au(III) concentration, etc., and was optimized by using response surface methodology (RSM) for the maximum Au recovery. The optimal conditions obtained were: GO concentration of 0.279 mg mL−1, pH of 5.95, reaction time of 5.80 d, and Au(III) concentration of 4.41 mM, and an Au recovery efficiency of approximate 100% was achieved. It was also found that Au(III) was recovered through the reduction reaction, and small-sized and uniform Au(0) nanoparticles were assembled on the rGO surface after the Au recovery. Furthermore, the Au-recovering selectivity of this material was explored through comparing the recovery efficiencies of Au(III), Pd(II), Cu(II), Zn(II), and Ni(II) from an ion-mixed solution. It was demonstrated that precious Au(III) and Pd(II) could be preferentially recovered from water because of their more positive redox potential than other metal ions.

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