Hierarchically structural PAN/UiO-66-(COOH)2 nanofibrous membranes for effective recovery of Terbium(III) and Europium(III) ions and their photoluminescence performances

Metal organic frameworks (MOFs) as adsorbents are attracting wide attention due to their high porosity and rich functionalities. However, their intrinsic fragility and poor separability limited their practical applications. Herein, an intriguing MOF UiO-66-(COOH)2 nanoparticles with abundant carboxyl functional groups were embedded in polyacrylonitrile (PAN) nanofibers by colloid-electrospinning technique to construct flexible MOF nanofibrous membranes (NFMs) with hierarchical structure for effective recovery of lanthanide (Ln) ions and sustainable reutilization in photoluminescent applications. The MOF UiO-66-(COOH)2 contained twenty-four free carboxyl functional groups per crystal which could endow it with powerful affinity to Ln3+ ions. The resultant PAN/UiO-66-(COOH)2 NFMs with quite high UiO-66-(COOH)2 loading (up to 60 wt%) exhibited outstanding adsorption capacities and good recyclability for Ln3+ ions. The adsorption data could be better fitted by the Langmuir isotherm and pseudo-second-order kinetic models, and the maximum adsorption capacities of Terbium(III) (Tb3+) and Europium(III) (Eu3+) ions calculated from the Langmuir isotherm model were 214.1 mg/g and 191.9 mg/g, respectively. Moreover, it was found that the adsorbent could be well regenerated without obvious loss of adsorption capacities after three adsorption-desorption cycles. In addition, benefiting from the carboxyl ligands acting as excellent sensitizers for Tb3+ and Eu3+ ions, the flexible Ln3+-loaded PAN/UiO-66-(COOH)2-60 NFMs showed a series of characteristics including good photoluminescence properties and tunable emission colors, indicating their use as promising luminescent materials for luminescent patterning and optoelectronics.