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A solar-driven hydrogel composed of photothermal polydopamine (PDA) nanocoating, linear chitosan (CTS), and thermoresponsive poly(N-isopropyl acrylamide) (PNIPAM) crosslinking network was successfully synthesized to remove heavy metal ions from contaminated water. The as-prepared PDA/CTS/PNIPAM (DCN) hydrogel can achieve hydrophilic/hydrophobic phase transition driven by solar energy when the volume phase transition temperature (VPTT) was reached. The micromorphology, wetting behavior, swelling behavior, compression properties, photothermal responsiveness, and adsorption properties of hydrogels were studied one by one. The cross-linking of the controllable active nanogel (ANG) along with the modification of PDA endowed DCN hydrogel with a regular and interpenetrating porous structure, which enabled DCN to have excellent elasticity and withstand up to 80 % compressive deformation. And the hydrophilic groups of CTS and PDA reduced the water contact angle of DCN hydrogel to 13°, which was conducive to resisting the erosion of oil substances. The excellent photothermal conversion enabled DCN hydrogel to reach VPTT in only about 11 min under a simulated sunlight source. In addition, DCN hydrogel had excellent selective adsorption for Pb2+ and Cu2+, and the maximum theoretical adsorption capacities were 42.63 mg/g and 38.55 mg/g, respectively. It was also found that the volume phase transformation of hydrogel significantly enhanced its ability to resist external interference and effectively prevented the loss of heavy metal ions. [Display omitted] [ABSTRACT FROM AUTHOR]

Chitosan(CTS) has excellent adsorption capacity for heavy metal ions, the combination of chitosan with hydrogels provides a new development direction for chitosan-based adsorbents, and further improvement of adsorption can be achieved by modifying the chitosan on this basis. A semi-interpenetrating polymer network(semi-IPN) hydrogel was successfully synthesized for the removal of heavy metal ions by combining α-ketoglutaric acid grafting chitosan (KCTS) with polyacrylamide(PAM) cross-linked by N,N-methylenebis(acrylamide). This semi-IPN hydrogel had the porous structure with high specific surface area, which can expose more active sites and provide an interface for chitosan to fully contact waste water. And it had excellent selective adsorption for Cu(II), Pb(II), and Zn(II) in a mixture of five heavy metal ions. Many influencing factors affecting adsorption have been investigated, such as initial concentration of metal ions, adsorption time, pH of solution, ionic strength, and adsorbent dosage. The adsorption data were simulated well by the pseudo-second-order kinetic and adsorption isotherms were fitted well Langmuir isotherm model. At 30 °C and pH 5.0, the theoretical maximum adsorption capacities of Cu(II), Pb(II), and Zn(II) by KCTS/PAM hydrogel were 72.39, 61.41, and 51.89 mg/g, respectively. After five adsorption-desorption cycles, the adsorption capacity of Cu(II), Pb(II), and Zn(II) still maintained above 90% of initial adsorption capacity. XPS analysis illustrated that the adsorption mechanism of heavy metal ions was mainly due to coordination and ion exchange. [Display omitted] [ABSTRACT FROM AUTHOR]