A highly efficient supramolecular adsorbent for precious metal: adsorption behavior of PdII by melamine cyanurate

Abstract

Melamine cyanurate (M-CA) was found to be a highly recoverable and selective supramolecular adsorbent for recovery of Pd^II ion. Adsorption of Pd^II by M-CA was fast in the first 30 min, with 93% adsorption efficiency, and equilibrium was reached within 1 h. Langmuir and Freundlich isotherm models were employed to correlate the experimental data. The adsorption of Pd^II by M-CA is well supported by a Langmuir isotherm model, with a high maximum adsorption capacity of 0.874 g_Pd g_M-CA⁻¹. M-CA was also capable of selective adsorption of Pd^II from a solution containing other metals. Pd adsorbed on M-CA was separated quantitatively by reductive treatment, and the M-CA could be recycled at least 3 times. We propose an in-plane adsorption mechanism for M-CA, which is a π–π stacked layered complex, based on the results of X-ray spectroscopy and computational calculations. This study demonstrates that M-CA is promising as a selective and highly efficient adsorbent for recovery of precious metals.