Efficient phosphate removal from water by multi-engineered PVA/SA matrix double network hydrogels: Influencing factors and removal mechanism

Development of environmentally friendly absorbent with superior adsorption performance and environmental adaptability is of great concern. In this study, multi-engineered polyvinyl alcohol (PVA)/sodium alginate (SA) matrix double network hydrogels (named as MGPA) were manufactured by freeze thawing and La(III)-ionic crosslinking and used for phosphate removal from water. Basic physicochemical parameters, swelling feature and other surface characters of as-prepared samples were firstly studied. The desired hydrogel displayed better mechanical properties, low swelling feature, and good separability, etc. Batch adsorption experiments have also shown that it has good adsorption performance at pH 3–12, making it widely operable. The adsorption behavior was further examined through adsorption kinetics and isotherms. The optimized MGPA-3 hydrogel (with 0.1 M La(III) in crosslinking) displayed the maximum experimental sorption capacity of ∼38.75 mg P/g and equilibrium time of 120 min, which was better than most of similar sorbents. It maintained good selectivity with the coexistence of anions and dissolved organic matters as well as in practical water treatment. Besides, superior environmental adaptability in dynamic adsorption studies and adsorption-desorption experiments were confirmed. Overall, electrostatic attraction, ligand/anion exchange, and Lewis acid-base interactions may jointly promote the pH-independent adsorption process for phosphate.