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a b s t r a c tHigh sorption capacity, high sorption rate, and fast separation and regeneration for qualified sorbents used in removing heavy metals from wastewater are urgently needed. In this study, a polyampholyte hydrogel was well designed and prepared via a simple radical polymerization procedure. Due to the remarkable mechanical strength, the three-dimensional polyampholyte hydrogel could be fast separated, easily regenerated and highly reused. The sorption capacities were as high as 216.1 mg/g for Pb(II) and 153.8 mg/g for Cd(II) owing to the existence of the large number of active groups. The adsorption could be conducted in a wide pH range of 3e6 and the equilibrium fast reached in 30 min due to its excellent water penetration for highly accessible to metal ions. The fixed-bed column sorption results indicated that the polyampholyte hydrogel was particularly effective in removing Pb(II) and Cd(II) from actual industrial effluent to meet the regulatory requirements. The treatment volumes of actual smelting effluent using one fixed bed column were as high as 684 bed volumes (BV) (7736 mL) for Pb(II) and 200 BV (2262 mL) for Cd(II). Furthermore, the treatment volumes of actual smelting effluent using tandem three columns reached 924 BV (31,351 mL) for Pb(II) and 250 BV (8483 mL) for Cd(II), producing only 4 BV (136 mL) eluent. Compared with the traditional high density slurry (HDS) process with large amount of sludge, the proposed process would be expected to produce only a small amount of sludge. When the treatment volume was controlled below 209.3 BV (7103 mL), all metal ions in the actual industrial effluent could be effectively removed (<0.01 mg/L). This wok develops a highly practical process based on polyampholyte hydrogel sorbents for the removal of heavy metal ions from practical wastewater.

A ethylenediaminetetra-acetic acid (EDTA) cross-linked chitosan and N,N-methylenebis(acrylamide) (MBA) cross-linked polyacrylamide based double network hydrogel was successfully synthesized via a two-step method and then employed for heavy metal ion adsorption. Various adsorption conditions, such as pH, ionic strength, adsorbent dosage, and contact time were investigated. CTS/PAM gel have a theoretical maximum Cd(II), Cu(II), and Pb(II) sorption capacities of 86.00, 99.44, and 138.41 mg/g, respectively, at experimental conditions. The adsorption process of CTS/PAM gel on the heavy metal ion was identified to be endothermic and follows an ion-exchange reaction. The application of this gel adsorbent was demonstrated using practical industrial effluent. We found that it could effectively treat practical wastewater with all kinds of heavy metals. At an adsorbent dosage of 8 g/L, the total metal ions concentration declined from 448.5 to 5.0 mg/L. Simultaneously, the CTS/PAM gel exhibited remarkable mechanical strength and good recyclability. This study shows that CTS/PAM gel offers great potential for practical application in the removal of heavy metal ions from contaminated aquatic systems.

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Development of mechanically strong and adhesive hydrogels with self-recovery and self-healing properties is important for many applications but has proven to be very challenging. Here, we reported a double-network design strategy to synthesize a fully physically cross-linked doublenetwork (DN) hydrogel, consisting of the first gelatin network and the second poly(N-hydroxyethyl acrylamide) network where both networks were mainly cross-linked by hydrogen bonds. The resultant gelatin/pHEAA hydrogels exhibited high mechanical property (tensile stress of 1.93 MPa, tensile strain of 8.22, tearing energy of 4584 J/m 2 ), fast self-recovery at room temperature (toughness/stiffness recovery of 70.2%/ 68.0% after 10 min resting), and good self-healing property (self-healed tensile stress/strain of 0.62 MPa/3.2 at 60 °C for 6 h). More importantly, gelatin/pHEAA hydrogels also exhibited strong surface adhesion on different hydrophilic solid surfaces, as indicated by high adhesion energy (i.e., interfacial toughness) of 645 J/m 2 on glass, 867 J/m 2 on Al, 702 J/m 2 on Ti, and 579 J/m 2 on ceramics. Surface adhesion can be largely retained after multiple, repeatable adhere on/peel off actions. Reversible and strong mechanical properties in bulk and on solid surfaces are likely attributed to reversible hydrogen bondings and physical coordinate bonds between the networks and between networks and surfaces. This work demonstrates our design principle that multiple physical bonds in both networks offer excellent mechanical recoverability, self-healing, and self-adhesive properties, while DN structure provides strong and tough mechanical properties via efficient energy dissipation by sacrificed bonds, which offers a new possibility to develop next-generation hydrogels with desirable properties used for soft robotics, wearable electronics, and human−machine interfaces.