Integration of thermoresponsive MIL-121 into alginate beads for efficient heavy metal ion removal

Metal-organic frameworks (MOFs) have been widely explored as adsorbents for heavy metal ions removal. However, the recovery and regeneration of powdery MOFs remains a huge challenge. In this work, MIL-121 (Al-based MOF) crystals were incorporated into biodegradable alginate matrix to form composite beads with enhanced recyclability and adsorption capacity. A systematic adsorption test for Cu2+ and Cd2+ was conducted and the optimal sample (with a MOF loading of 50 wt%) presented an adsorption capacity of 204.5 mg/g for Cu2+ and 88.7 mg/g for Cd2+. Moreover, the composite beads can be regenerated effectively by hot water (80 °C). The desorption is attributed to the carboxyl-rich MIL-121, which could release massive protons (H+) at elevated temperature. Compared with the traditional desorption using strong acids, this chemical-free thermal desorption strategy holds a great potential for adsorbent regeneration and practical wastewater treatment.