Adsorption and reduction of Cr(VI) in water by iron-based metal-organic frameworks (Fe-MOFs) composite electrospun nanofibrous membranes

Metal-organic frameworks (MOFs) are a new type of porous adsorbents, which has attracted widely attention in the removal of Cr(VI) from water. In the present study, iron-based MOFs (Fe-MOFs) were synthesized by solvothermal method, and then co-electrospun with polyacrylonitrile (PAN) to obtain composite electrospun nanofibrous membranes (PAN/MOFs ENFMs). Fe-MOFs could be in situ successfully immobilized in PAN nanofibers, and retain their adsorption properties. PAN/MOFs ENFMs could rapidly adsorb Cr(VI) in water, and the maximum theoretical adsorption capacities at pH 4.0 reached 127.70 mg/g. Meanwhile, part of adsorbed Cr(VI) could be reduced to less toxic Cr(III). The adsorption of Cr(VI) on both the Fe-MOFs particles and PAN/MOFs ENFMs were spontaneous processes, and their adsorption capacities were enhanced with the increase of temperature, while declined with the increase of solution pH. By contrast, PAN/MOFs ENFMs were less affected and could effectively adsorb Cr(VI) over a broader pH range. The adsorption processes were dominated by physical adsorption, meanwhile accompanied by chemical adsorption. Immobilizing MOFs in ENFMs is beneficial to solve the problems of easy aggregation and difficult recycle of powdery MOFs adsorbents, and provides a new technological option for the removal of Cr(VI) from water by the adsorption of MOFs.