(Li J)) most common byproducts of the paint manufacture, dyeing, cosmetics, textile, paper, leather, and other industries, and it can poison the environment and endanger the safety of drinking water and foodstuffs [5,6]. Therefore, removal of organic dye from water is a major project for the development of a sustainable society [7].Adsorption is recognized as one of the most promising methods because of its high effectiveness, low cost, and popularity [8,9]. Polymeric adsorbents are widely used as materials for the removal of organic or inorganic contaminants from water or air because of their advantages such as high flexibility in the design of structures and properties; chemical stability in harsh environments, including strong acidic, alkaline, salty, and oxidizing solutions; feasible regeneration; and thermal durability [9][10][11]. Polyethylenimine (PEI) has a high amine density and accessible primary amine sites on the chain ends, which act as desirable building blocks for the construction of adsorbents. For instance, many excellent CO 2 adsorbents have been prepared by integrating PEI into porous materials, including silica [12], mesoporous carbon [13], titanate [14], polymeric supports [15], and other metal oxide nanocomposites [16]. In addition, because of the high positive charge density on the protonated PEI backbone or side chains, PEI-based adsorbents exhibit good adsorption capacity for acidic gas or anionic materials such as polyanions and negatively charged organic or inorganic matter, including various anionic dyes [16][17][18][19].Electrospinning is an effective approach to prepare ultrafine fibers; it uses an electrostatic force from an external high-voltage electrical field between a spinneret and a grounded collector to draw very fine (typically micro-to nanoscale) fibers from a liquid droplet [20]. The ultrafine fibers produced by electrospinning have very high specific ABSTRACT We prepared a nanofibrous adsorbent for anionic dye removal from aqueous solution by electrospinning a modified polyethylenimine (m-PEI) and polyvinylidene fluoride (PVDF) blend. The electrospun nanofibrous adsorbent was confirmed to be a nanoscale, porous material with a positively charged surface; these characteristics are quite beneficial for anionic contaminant adsorption. Experimental adsorption of an anionic dye, methyl orange (MO), demonstrates that this adsorbent can rapidly remove MO from aqueous solution; its maximum adsorption capacity was 633.3 mg g −1 , which is much higher than that of previously reported adsorbents. After immersion in a basic solution, the adsorbent was well regenerated and showed good recyclability. The adsorption performance of the nanofibrous adsorbent is greatly influenced by the temperature, initial MO concentration, and pH of the solution. We further found that MO adsorption onto the adsorbent can be described well by the pseudo-second-order kinetic model and Langmuir isotherm model. Weber-Morris plots suggested that the adsorption of MO onto the nanofibrous mat was affected...