A cerium (Ce) -based ammoniated tannin/polyvinyl alcohol hydrogel for effective and selective phosphate removal from natural water and real wastewater.

This paper presents the synthesis of a cost-effective, environmentally friendly, and highly efficient Cerium (Ce)-based polyvinyl alcohol/tannin hydrogel adsorbent modified with triethylene tetramine (Ce-PVA/TA/TETA). This material integrates components with exceptional phosphate affinity, making it ideal for phosphate removal applications. Specifically, the hydrogels were firstly prepared by using tannin and polyvinyl alcohol as raw materials. Subsequently, after HBO as crosslinking, the Ce was loaded into hydrogel by co-precipitation and Ce-PVA/TA was modified by triethylene tetramine amine to obtain Ce-PVA/TA/TETA with high adsorption efficiency and high selectivity. Triple modification with tannin hydrogelation, Ce loading and amination can significantly improve the affinity of the material to phosphate. This allows the Ce-PVA/TA/TETA hydrogel to maintain high phosphate adsorption capabilities across a wide pH range of 3.0-12.0. The Ce-PVA/TA/TETA hydrogel achieved a maximum phosphorus adsorption capacity of 110.88 mg/g within an equilibrium time of 120 min at 25 °C and pH = 3.0. The presence of co-existing ions had impact on phosphate adsorption. Both the pseudo-second-order model and the Langmuir model effectively described the kinetics and isotherms, respectively. The adsorption process was a monolayer chemical adsorption, which was dominated by the surface adsorption and particle internal diffusion. Besides electrostatic attraction, ligand exchange and internal diffusion mechanisms were involved in the phosphate adsorbing of Ce-PVA/TA/TETA based on Zeta potential, FTIR, and XPS analysis. Most importantly, the Ce-PVA/TA/TETA hydrogel can swiftly remove phosphate from natural water and wastewater at low doses, meeting regulatory standards. This underscores its promising potential for phosphate management and eutrophication control.