Constructing molecular sieve-based MOFs nanofiber composites for separating Co(II) from wastewater

In addressing the crucial need for separating cobalt ions from leachate solutions of spent ternary lithium batteries (TLBs), this study focuses on the development of an innovative molecular sieve (MS)-based MOFs material, MS-MIL-53(Al), synthesized by combining MS with 2,5-dihydroxyterephthalic acid. Since the powdered MS-MIL-53(Al) material presents a granular powdery form, which is difficult to recover during the adsorption process, electrospun nanofibers denoted as MS-MIL-53(Al)/PAN, were fabricated and functionalized with hydroxylamine hydrochloride to create MS-MIL-53(Al)/AOPAN. Static adsorption experiments conducted with MS-MIL-53(AL)/AOPAN as the adsorbent in cobalt-containing wastewater revealed a maximum adsorption content of 65.3 mg/g for Co(II). Moreover, the material exhibited a tensile strength at the breaking point of 0.077 kPa, indicating its excellent mechanical properties. The adsorption process followed pseudo-second-order kinetics and the Langmuir isotherm model, showcasing a spontaneous, endothermic monolayer chemical adsorption behavior. XPS analysis highlighted the influence of hydroxy and amidoxime functional groups on Co(II) adsorption. Notably, MS-MIL-53(Al)/AOPAN displayed exceptional stability, retaining over 90 % of its adsorption capacity after five cycles, demonstrating its potential for efficient Co(II) separation in wastewater treatment. This study is the first to synthesize MOFs material using MS as the base material, showing potential cost reduction and enhanced adsorption capabilities, with implications for advancing the innovative use of MOFs.