Selective Separation of Pd(II) on Pyridine-Functionalized Graphene Oxide Prepared by Radiation-Induced Simultaneous Grafting Polymerization and Reduction

The recovery of precious metals like palladium (Pd) from secondary resources has enormous economic benefits and is in favor of resource reuse. In this work, we prepared a high efficiency pyridine-functionalized reduced graphene oxide (rGO) adsorbent for selective separation of Pd(II) from simulated electronic waste leachate, by one-pot γ-ray radiation-induced simultaneous grafting polymerization (RIGP) of 4-vinylpyridine (4VP) from graphene oxide (GO) and reduction of GO. The poly(4-vinylpyridine)-grafted reduced graphene oxide (rGO-g-P4VP) exhibits fast adsorption kinetics and high maximum adsorption capacity. The adsorption capacity is 105 mg g–1 in the first minute and reaches equilibrium within 120 min. The adsorption process follows the Langmuir model, from which the maximum adsorption capacity of Pd(II) is estimated to be 177 mg g–1. We also proved that the adsorption mechanism of Pd(II) on rGO-g-P4VP involves both ion exchange and coordination adsorption by XPS analysis. Most importantly, the loss of oxygen-containing groups due to reduction of GO not only facilitates the separation of adsorbent from aqueous solution but also reduces the electrostatic repulsion toward Pd(II)Cl42– in hydrochloric acid solution, leading to a higher adsorption selectivity of Pd(II) over some common metal cations in electronic waste including Fe(III), Cu(II), and Al(III) compared with poly(4-vinylpyridine)-grafted graphene oxide (GO-g-P4VP) prepared by atom transfer radical polymerization. Other precious metals like Pt(IV) and Au(III) can also be recovered easily and selectively by rGO-g-P4VP. This work demonstrates that rGO-g-P4VP prepared by the facile RIGP is a promising adsorbent for recovery of precious metals from secondary resources like electronic waste leachate.