Simultaneous Recovery of Metal Ions and Electricity Harvesting via K-Carrageenan@ZIF-8 Membrane

The spent lithium-ion batteries contain significant amounts of valuable metals such as lithium and cobalt. However, how to effectively recover these valuable metals and minimize environmental pollution simultaneously is still a challenge. In this work, a natural biopolymer K-Carrageenan is introduced into a stable metal-organic framework ZIF-8 to form a composite (KCZ) membrane for selectively separating Li⁺ from Co²⁺ and simultaneously harvesting the concentration gradient energy efficiently. The prepared KCZ membrane shows an Li⁺ ionic conductivity of up to 1.70 × 10^-5 S cm^-1, 5 orders of magnitude higher than 1.1 × 10^-10 S cm^-1 for pristine ZIF-8, with an Li⁺ flux of 0.342 mol m^-2 h^-1 and a selectivity of about 8.29 for Li⁺ over Co²⁺. Moreover, this asymmetric KCZ/anodic alumina oxide membrane exhibits a good output power of up to 3.54 μW when employed as a concentration-gradient energy-harvesting device during the separation process. Hence, the KCZ membrane shows great potential in application for advanced separation and simultaneous concentration gradient energy harvesting.