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

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 Delta H 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 Delta G 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 pre-dicted by the positive Delta S 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.

Automated summary

Novel ion-imprinted MIL-101(Cr) has been synthesized for selective recognition and removal of Pd2+ from aqueous solution. The adsorption behavior of Pd2+ on IPMIL-101(Cr) and NIMIL-101(Cr) was investigated, showing high removal efficiency and selectivity for Pd2+. The IPMIL-101(Cr) exhibited a maximum adsorption capacity of 193.2 mg.g-1 and followed a Langmuir isotherm. The adsorption process was endothermic and spontaneous according to the positive Delta H and negative Delta G values.