Poly-N-phenylglycine@multi-walled carbon nanotubes composite membrane for improvement of Au(III) adsorption

Poly-N-phenylglycine (PNPG) decorated with multi-walled carbon nanotube (MWCNT) composite membranes having high stability was easily prepared using ultrasound-aided vacuum-assisted filtration. The results showed that MWCNT bound to PNPG through non-covalent interactions. The PNPG@MWCNT composite membrane with a mass composition of P3.5M0.5 showed an approximately 20% higher adsorption efficiency than the pure PNPG membrane after 24 h adsorption in acidic Au(III) solution with pH = 1. The Au(III) adsorption capacity reached 1262.6 mg g−1 at pH 1, and the well-fitted pseudo-second-order kinetic and Langmuir isothermal models indicated that the adsorption process was mainly chemisorption and monolayer adsorption. More importantly, characterization data confirmed that the adsorption mechanism between the composite membrane and Au(III) included electrostatic interactions and redox reactions, thus electron transfer from PNPG to MWCNT promoted the adsorption capacity. Furthermore, the results of all competitive adsorption, repeatability, and gold recovery experiments in the leaching solution of waste printed circuit boards demonstrated the potential of the PNPG@MWCNT composite membrane in practical applications of gold recovery.