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.