Cu(II) and Cd(II) capture using novel thermosensitive hydrogel microspheres: adsorption behavior study and mechanism investigation

BACKGROUND At present, various kinds of hydrogel adsorbents are applied to the treatment of heavy metal ions in wastewater. In this work, we focused on the adsorption of cadmium [Cd(II)] and copper [Cu(II)] onto microspheres of a novel thermosensitive hydrogel (NH2-SA/PNIPA, aminated sodium alginate/poly-N-isopropyl acrylamide), studied the effect of temperature on the phase transition of the hydrogel in detail, and discussed the influence on the adsorption behavior of metal ions in the hydrogel. RESULTS The NH2-SA/PNIPA exhibited a higher adsorption efficiency under the conditions of interfering monovalent cationic and neutral pH. The adsorption capacities based on the Langmuir model were 57.2 mg g(-1) for Cu(II) and 100.5 mg g(-1) for Cd(II) at 20 degrees C, respectively. Higher temperature facilitated the adsorption process and also led to the volume shrinkage and hydrophobicity of NH2-SA/PNIPA. The metal ions had different hydration and hence different adsorption capacities, of 56.7 mg g(-1) for Cu(II) and 88.6 mg g(-1) for Cd(II) at 40 degrees C. The results of diffusion behavior analysis showed that the diffusion coefficients were approximate to 1 x 10(-11) m(2) s(-1). The adsorption performance of NH2-SA/PNIPA hardly decreased even after five cycles. In addition, the adsorption process was controlled mainly by the complexation reaction. CONCLUSION The novel hydrogel microspheres overcame the deficiency of conventional adsorbents and possessed high diffusibility. This work provides a theoretical basis and empirical evidence for enhancement of adsorbents for removing heavy metals in wastewater. (c) 2021 Society of Chemical Industry (SCI).