Novel chitosan/lignin hydrogel prepared by the Mannich reaction for Pb(II) and Cu(II) removal from aqueous solution

Green and high-performance biomass-based adsorbents have a good application prospect for the removal of heavy metals. At present, the preparation of chitosan/lignin biomass adsorbents mainly adopts dissolution-drying method, and the obtained adsorbents show relatively poor adsorption performance for heavy metals. To overcome this problem, a novel chitosan/lignin hydrogel (CSL) is prepared by a simple one-pot method through the Mannich reaction. Research findings show that the hydrogels present higher adsorption selectivity for Pb(II) and Cu(II) than other common heavy metals. Among them, the optimal hydrogel CSL1 shows unexpectedly ultrafast adsorption rate for Pb(II) and Cu(II) with equilibrium time of only 1 min and 2 min. Meanwhile, the maximum adsorption capacities of CSL1 for Pb(II) and Cu(II) are 139.86 and 98.71 mg·g^-1, respectively. Compared with the reported adsorption materials related to chitosan or lignin, the CSL1 has the advantages of simple preparation process, considerable adsorption capacity, and short adsorption equilibrium time. Moreover, the adsorption mechanism is investigated by Fourier transform infrared spectroscopy (FT-IR) and X-ray photoelectron spectroscopy (XPS), and the results prove that the adsorption mechanism is chemical complexation. This work not only contributes to the advancement of hydrogel-based adsorbents, but also holds significant industrial potential for addressing water pollution issues and promoting sustainable development.