Zirconium-based metal-organic framework (UiO-66) composite synthesized from polyethylene terephthalate (PET) waste was functionalized with chitosan (Cs) and ethylenediamine (ED) for the removal of Pd (II) ions from wastewater. The UiO-66 composite was created using a modulated solvothermal synthesis, followed by post-functionalization with Cs and ED, and its adsorption efficacy against Pd (II) was assessed utilizing batch adsorption studies. UiO-66-Cs-ED performed well in adsorption experiments, with a maximum Pd (II) removal efficiency of 96% at ideal conditions (pH 3, adsorbent dose of 15 mg, contact time of 10 minutes, and temperature of 25°C). The composite has a larger maximum adsorption capacity (282.3 mg g⁻¹) than UiO-66-ED (169.2 mg g⁻¹), according to the nonlinear Langmuir isotherm model. The FTIR spectra after adsorption revealed changes in important functional groups, including C-N (1260→1156 cm⁻¹), N-H (1622→1707 cm⁻¹), and -NH₂ (1100→934 cm⁻¹), demonstrating the interaction of Pd (II) ions with nitrogen-containing functional groups on the adsorbent’s surface. Furthermore, DFT results showed a more thermodynamically favorable interaction between Pd (II) and UiO-66-Cs-ED with a higher adsorption energy of -6.119 eV. The adsorption process exhibited swift kinetics, and following pseudo second-order model with a rate constant of 0.0335 g·mg⁻¹·min⁻¹. Thermodynamic metrics, including free energy changes (ΔG), standard enthalpy changes (ΔH), and standard entropy changes (ΔS), indicate that the adsorption process is endothermic and spontaneous. The composite removed more than 80 % Pd (II) ions from hydrous solution for five consecutive cycles without significantly losing its capacity and showing its potential to recovery Pd from electronic waste.
Netshivhandane et al. (Fri,) studied this question.