Highly efficient removal of trace metal ions by using poly(acrylic acid) hydrogel adsorbent

Abstract Hydrogels as metal ions adsorbents are commonly applied in wastewater treatment field. However, low swelling ratio (SR) of ever reported hydrogel adsorbents prevents adsorptive sites from effectively exposing to metal ions, leading to unpleasant removal efficiency for trace metal ions. Designing high SR for hydrogel adsorbents can increase contact area between adsorbents and metal ions, being favorable for the internal adsorption sites exposure to metal ions. Thus, improved adsorption performance for removing trace metal ions can be achieved by endowing high SR for hydrogel adsorbents. In the present work, poly(acrylic acid) hydrogel adsorbent achieves high SR up to 8130 g/g by employing calcium hydroxide (Ca(OH) 2 ) nano-spherulites as cross-linkers, which can effectively adsorb various trace metal ions including Cu 2+ , Cd 2+ , Cr 6+ , Fe 3+ , Mn 2+ , Ni 2+ , Zn 2+ , Ce 3+ and Ag + . The removal ratios reach 46.8% for Cu 2+ (initial concentration C 0  = 0.16 mg/L), 57.1% for Cd 2+ (C 0  = 0.56 mg/L), 26.9% for Cr 6+ (C 0  = 0.52 mg/L), 5.3% for Fe 3+ (C 0  = 0.56 mg/L), 52.7% for Mn 2+ (C 0  = 0.55 mg/L), 52.5% for Ni 2+ (C 0  = 0.59 mg/L), 58.4% for Zn 2+ (C 0  = 0.65 mg/L), 70% for Ce 3+ (C 0  = 0.7 mg/L) and 45.3% for Ag + (C 0  = 1.08 mg/L) by using such adsorbent, respectively. This work develops a potential hydrogel adsorbent for the efficient removal of trace metal ions.