Bio-Based aerogel beads with multistage pore network structure for Cr(VI) removal using ice template method

Abstract

Hexavalent chromium (Cr(VI)) poses a significant ecosystem risk due to its high mobility and stability. Nanoadsorbents possess high adsorption capacity but complex solid–liquid separation procedures. It is an unresolved challenge to design an adsorbent with both capabilities. Here, we covalently linked metal–organic frameworks (MOFs) and ethylene imine polymer (PEI) to chitosan hydrogel beads (3 mm). Assists with the ice template method to construct a multistage pore network structure of aerogel beads (CTS-U-E) for purifying Cr(VI) wastewater. The rich multistage pore network and high specific surface area of CTS-U-E (130.91 m² g⁻¹) enable fast adsorption kinetics and excellent selectivity. Its maximum adsorption capacity of 471.5 mg g⁻¹ is 2.47 times greater than that of commercial adsorbents and exceeds most reported nanoadsorbents. Impressively, after six cycles of adsorption tests, the Cr(VI) removal rate of CTS-U-E still reached 79 %. CTS-U-E is considerably more cost-effective than commercial activated carbon and resin, owing to its inexpensive raw materials and superior recycling capabilities. Density functional theory reveals that the strong affinity of N, O, and methylene for Cr(VI) results in their role as natural anchor points for efficient Cr(VI) adsorption. The reaction of Cr(VI) with amines to form highly active intermediates may further lead to ultra-high Cr(VI) removal. This study inspires a promising route for developing high-adsorption materials for Cr(VI) wastewater treatment and offers new insights into adsorption mechanisms.