Effective removal of cesium by ammonium molybdophosphate–polyethylene glycol magnetic nanoparticles

This study synthesizes a new adsorbent composite for the removal of Cs ions from waste effluents. The adsorbent is composed of polyethylene glycol-decorated ammonium molybdophosphate magnetic Fe3O4 nanoparticles (PEG–AMP MNs) and is prepared via coprecipitation by grafting ammonium phosphomolybdate onto the surface of Fe3O4 and coprecipitation with polyethylene glycol. The physical and chemical structure of the PEG–AMP MNs was investigated using various spectroscopic and analytical techniques, revealing that Fe3O4 was tightly bound to the AMP particles and that the composites exhibited superparamagnetic behavior. The Cs+ adsorption behavior of the adsorbent was investigated in a wide range of pH values and temperatures, using multiple Cs+ contact times and initial Cs+ concentration, and with interference from additional ionic species. The adsorbent achieved 99.8% removal of Cs+ in the solution pH range of 1–12 and maintained its stability after adsorption. Interfering ions had little effect on the amount of Cs+ adsorbed. The experimental data were fitted using Langmuir, Freundlich, Redlich-Peterson and Sips isotherms pseudo-first-order and pseudo-second-order kinetic models. The results showed that the adsorption data fitted well with pseudo-second-order kinetics and the Langmuir isotherm model, with a maximum adsorption capacity of 53.89 mg g−1 and equilibrium reached within 20 min. Thermodynamic experiments showed the adsorption process to be inherently endothermic. The mechanism of Cs+ adsorption by PEG–AMP MNs is proposed to primarily be a combination of weak electrostatic attraction and ion exchange between NH4+ and Cs+. More importantly, the encapsulation of a magnetic carrier allows for the efficient separation and recovery of Cs+ after adsorption.