Efficient removal of organic pollutants on sponge-type inorganic adsorbent derived from spent cotton fiber/layered double hydroxides

For the whole life cycle of the textile industry, the disposal of printing and dyeing wastewater and the reuse of spent fibers were two of the main environmental problems. In this work, activated carbon fiber/layered double oxides (ACF/LDO) were prepared by the pyrolysis of spent cotton fiber/layered double hydroxides (LDH) composite. Compared to 2D structure LDH, 3D hierarchical ACF/LDO was formed by introducing activated carbon nanofibers as a skeleton. ACF/LDO had excellent adsorption properties for organic dye and the maximum adsorption capacity of acid red 27 (AR27) exceeded 800 mg/g. Due to the memory effect of LDH, the interconversion of ACF/LDO to ACF/LDH was observed during the adsorption and regeneration process. Meanwhile, the shrinkage and expansion of adsorbent occurred, which was similar to that of a sponge absorbing water. During the adsorption process, the average pore diameter of the adsorbent increased as ACF/LDO was converted to ACF/LDH, which increased the diffusion of organic dye inside the pores. On the contrary, the specific surface area and pore structure were restored during the regeneration process. Therefore, this composite displayed excellent adsorption capacity and repeatability, with no significant decrease was observed in adsorption capacity even after five consecutive cycles. The adsorption mechanism revealed that the removal of AR27 was dominated by electrostatic attraction and π-π interactions. The experiment provided a new strategy of treating wastewater with waste fiber.