Improved adsorptive separation of palladium ions from wastewater using metal-organic framework modified with poly(m-phenylenediamine)

• Synthesis of a novel PmPD/MIL-101(Cr) composite. • Mechanisms of Pd (II) ions adsorption using the PmPD/MIL-101(Cr) composite. • Investigation of adsorption isotherms for Pd(II) ions uptake using the PmPD/MIL-101(Cr) composite. • The PmPD/MIL-101(Cr) composite d demonstrated higher qm of 156.3 mg.g-1. • Effect of pH and coexisting ions on the adsorption efficiency of Pd(II) ions. A novel metal-organic framework decorated with poly(m-phenylenediamine) (PmPD/MIL-101(Cr) composite for adsorption of Pd ion from wastewater was synthesised. The structure of PmPD/MIL-101(Cr) composite was characterised by Fourier transform infrared spectrometer (FTIR), Brunauer-Emmett-Teller (BET), X-ray diffraction, simultaneous thermal analysis, scanning electron microscope and energy dispersive spectrometer (EDS). Adsorption experiments showed that the PmPD/MIL-101(Cr) composite efficiently removed Pd ions in acidic media of pH 1. Isothermal data best fitted the Langmuir model, with a maximum adsorption capacity of 156.3 mg·g⁻¹. Additionally, the adsorption of Pd (II) by PmPD/MIL-101(Cr) was endothermic and spontaneous with negative Gibbs free energy values and positive enthalpy value. The adsorption rate was very rapid and equilibrated within 50 minutes. The PmPD/MIL-101(Cr) composite maintained its efficiency of 46.87% in the presence sulphate ions. Stability test demonstrated that the composite can be reused for 5 consecutive cycles without significantly losing its performance. The present study provided an insight for the application of novel composite , PmPD/MIL-101(Cr) as a potential adsorbent for the recovery of Pd ion from wastewater.