Experimental and DFT studies on the selective adsorption of Pd(II) from wastewater by pyromellitic-functionalized poly(glycidyl methacrylate) microsphere

Palladium wastewater is produced from various industrial activities and seriously pollutes the environment. In here, a new adsorbent (PMDA-PGMA) was manufactured by functionalizing poly(glycidyl methacrylate) microspheres with pyromellitic acid and introduced to recover Pd(II) from wastewater. The main influencing factors including pH, palladium ionic content, reaction time and temperature were evaluated. The selectivity , reusability and sorption mechanism have been systematically examined. The pH 2 was optimal for Pd(II) adsorption and only 300 min was required to reach maximum adsorption capacity about 206.71 mg/g. The experimental data were is in tune with pseudo-secondary kinetics and Langmuir model well. So, the Pd(II) adsorption process was monolayer chemical adsorption. Thermodynamic parameters indicate that Pd(II) adsorption on PMDA-PGMA was an endothermic reaction . The main adsorption mechanism is ion exchange, electrostatic attraction and coordination between palladium ions and pyromellitic acid groups. Additionally, PMDA-PGMA can be easily regenerated by 10% thiourea and can be recycled at least five times. PMDA-PGMA exhibited good selective extraction ability for Pd(II) and effectively separated Pd(II) (≥95%) from laboratory wastewater in the presence divers metal ions . Density functional theory calculations show that PMDA-PGMA combines with Pd(II) through monodentate N atoms and bidentate O groups. The application prospect of PMDA-PGMA is encouraging in removing palladium from wastewater due to its high adsorption capacity and better reusability.