Selective adsorption of palladium ions from wastewater by ion-imprinted MIL-101(Cr) derived from waste polyethylene terephthalate: Isotherms and kinetics

Abstract

Novel ion-imprinted (IP) MIL-101(Cr) was synthesized through post-modification for the selective recognition and removal of divalent palladium Pd2+ ions from an aqueous environment. Several techniques were used to confirm the successful preparation of the IPMIL-101(Cr) and its derivative non-ion imprinted polymer (NIMIL-101(Cr) adsorbent. The IPMIl-101(Cr) showed a highest removal of Pd2+ ions at pH 2.0 and the data fitted well with the Langmuir isotherm which gave the maximum adsorption capacity of 193.2 mg.g−1. The data revealed that the adsorption of Pd2+ ions increased with an increasing temperature, implying an endothermic process as supported by the positive ΔH values = 13.91 kJ.mol−1 and 11.80 kJ.mol−1 for the IPMIL-101(Cr) and NIMIL-101(Cr), respectively. In addition, the negative values of ΔG proved that the IPMIL-101(Cr) and NIMIL-101(Cr) materials spontaneously adsorbed Pd2+ ions. This interaction occurs at a higher degree of disorderness as predicted by the positive ΔS values = 10.27 kJ.K−1.mol−1 and 1.79 kJ.K−1.mol−1 for the IPMIL-101(Cr) and NIMIL-101(Cr). Adsorption kinetics showed a fast removal rate of Pd2+ ions onto the IPMIL-101(Cr) which fitted well with the pseudo-second-order model. Competing ions studies displayed that the IPMIL-101(Cr) adsorbent has high selectivity towards Pd2+ as the percentage removal reached more than 80% in the presence of various cations and anions. The IPMIL-101(Cr) adsorbent was regenerated and reused for five consecutive cycles without significant loss of the adsorption capacity. This work reveals the promising application of the IPMIL-101(Cr) for recovering and removing Pd2+ ions from industrial wastewater.