Carbon-dot modified polyacrylonitrile fibers: Recyclable materials capable of selectively and reversibly adsorbing small-sized anionic dyes

Amine-rich carbon dot (CD) functionalized polyacrylonitrile fibers (PANF-g-CDs) were prepared by a facile hydrothermal method. These fibers are fluorescent and contain nano-sized pores. Dye adsorption experiments demonstrated that PANF-g-CDs preferred to adsorb small-sized anionic dyes with high aspect ratio, such as methyl orange (MO). The maximum adsorption capacity for MO reached 422 mg/g. The adsorption kinetics satisfied the pseudo second-order adsorption model, and the adsorption behavior was monolayer uniform adsorption. After adsorption, PANF-g-CDs could be separated conveniently just by taking it out from the solution. Moreover, the used PANF-g-CDs could be regenerated in an alkaline aqueous solution very rapidly within 30 min. Its adsorption performance was so stable that it did not show obvious performance loss even after ten adsorption-desorption cycles. In addition, the fluorescence of the fiber exhibited periodical change during the adsorption-desorption processes. Thus, this CD modified fibers with the combined advantages of simple synthesis, high dye-adsorption efficiency and selectivity, moderate dye-adsorption rate, fast dye-desorption, easy recyclability, stable adsorption performance and photoluminescent nature could be promising adsorbents for practical dyestuff wastewater treatment.