ZnO/PUF composites with a large capacity for phosphate adsorption: adsorption behavior and mechanism studies

Phosphate is present in all kinds of industrial wastewater; how to remove it to meet the strict total phosphorus discharge standards is a challenge. This study used a one-step foaming technique to fill polyurethane foam (PUF) with ZnO, taking advantage of PUF's excellent features like its porous network, lightweight, hydrophilicity, and abundance of binding sites to create ZnO/PUF composites with high adsorption capacity and exceptional separation properties. The adsorption isotherms, kinetics, starting pH, and matrix impacts of ZnO/PUF composites on phosphate were examined in batch studies. The results showed that the composites had good adsorption performance for phosphate with a saturated adsorption capacity of 460.25 mg/g. The quasi-secondary kinetic and Langmuir models could better describe the adsorption process, which belonged to the chemical adsorption of monomolecular layers. The composites' ability to treat phosphates in complicated waters was shown by their ability to retain a high adsorption capacity in the pH range of 3-6. In column experiments, the composite also maintains a good affinity for phosphate during dynamic adsorption. Multiple characterizations indicate that the adsorption mechanism is a combined effect of ligand exchange and electrostatic interactions. Therefore, this study provides valuable insights for practical phosphorus-containing wastewater treatment.