Fabrication of an efficient ZIF-8 alginate composite hydrogel material and its application to enhanced copper(ii) adsorption from aqueous solutions

Abstract

A novel zeolitic imidazolate framework-8 (ZIF-8) alginate composite hydrogel material (PVA/SA@ZIF-8) is an alginate composite bead which was fabricated by grafting ZIF-8 on the surface of the sodium alginate hydrogel beads using an in situ growth method. The synthetic material was characterized by Fourier transform infrared spectroscopy, scanning electron microscopy, high resolution transmission electron microscopy, X-ray photoelectron spectroscopy, and thermogravimetric analysis. The PVA/SA@ZIF-8 bead was used to effectively adsorb Cu(II) from aqueous solutions. The initial concentration of copper ions, adsorbent dose, initial pH of copper ions solution, temperature, and contact time for the synthesis of the material were optimized. The adsorption isotherms and kinetics fitted to the Langmuir isotherm model (R² = 0.9992) and the pseudo-second-order kinetic model (R² = 0.9967) respectively. According to the Langmuir isotherm adsorption model, the maximum theoretical adsorption capacity of the adsorbent for Cu(II) was 166.94 mg g⁻¹. In addition, the recycling application of the adsorbent was possible as it was easily collected and reused after five adsorption-regeneration cycles. The results indicated the PVA/SA@ZIF-8 hydrogel has unlimited potential in the treatment of heavy metal wastewater. Moreover, the combination of sodium alginate hydrogel and metal–organic frameworks would broaden the potential application of hydrogel materials in other fields.