Preparation of two-component Pickering emulsion hydrogels for the removal of zinc ions from aqueous solutions

Traditional liquid-solid extraction methods for the removal of zinc ions (Zn(II)) were generally limited by the leakage of extractant and low extraction capacity. The two-component Pickering emulsion hydrogels (PEHGs) in which the synergistic 2-ethylhexyl hydrogen-2-ethylhexylphosphate/tributyl phosphate (EHEHPA/TBP) was encapsulated in a semi-penetrating polymer network (SIPN) structured hydrogels polyacrylamide/sodium alginate (PAM/SA) were prepared by the Pickering emulsions polymerization route. The PEHGs were characterized by FTIR, SEM, TGA, and tensile mechanical measurements, and their self-healing properties were explored. The adsorption performance of PEHGs on Zn(II) was investigated. The results showed that the encapsulation of the extractant reached 95% due to the hydrogels network and nano-silica (nano-SiO₂) particle network in PEHGs-15. The critical crashing pressure of PEHGs-15 was 0.084 MPa, and the adsorption after 3 h of healing was only 86% of the original amount. The maximum adsorption capacity of PEHGs-15 on Zn(II) was 76.51 mg/g at pH 5. The functional groups of SA and EHEHPA/TBP enhanced the adsorption capacity of PEHGs-15 by chelating with Zn(II). After five adsorption-desorption cycles, the adsorption capacity of PEHGs-15 exceeded 85% of the initial one. The excellent mechanical properties, self-healing, and regenerative properties of PEHGs-15 offer the potential to remove Zn(II) from the solution.