Porous and ultrafine nitrogen-doped carbon nanofibers from bacterial cellulose with superior adsorption capacity for adsorption removal of low-concentration 4-chlorophenol

Abstract

Porous and Ultrafine Nitrogen-doped carbon nanofibers (NCNFs) were successfully obtained from bacterial cellulose (BC) by carbonization/activation in NH3/N2 atmosphere at higher temperatures. Thanks to the ammonia treatment, the as-obtained NCNFs have nanoarchitectures constructed of one-dimensional (1-D) nanofiber with ultrafine fibers, hierarchically porous structures, abundant nitrogen functionalities leading to the basic and hydrophobic surface, which render them as excellent adsorbents for the adsorption removal of organic pollutants from aqueous solutions. Their adsorption performance for low-concentration 4-chlorophenol (4-CP) were investigated systematically under different conditions. In comparison with the carbon nanofibers (CNFs) without ammonia treatment and commercial activated carbon (CAC), NCNFs displayed greatly enhanced adsorption capacity, short equilibrium time and wide pH range. NCNF-1000 prepared at 1000 °C had adsorption capacity of 4-CP up to 604.1 mg/g for the initial low-concentration of 100 mg/L, which was superior to the previously reported adsorbents. Analyses of the equilibrium adsorption and kinetic data revealed that the adsorption process of 4-CP onto NCNFs were fitted well with the Liu isotherm and pseudo-second-order kinetic models. The thermodynamic parameters (ΔH°, ΔS°, ΔG°) for 4-CP adsorption onto NCNFs confirmed that the essence of 4-CP adsorption was exothermic, feasible and spontaneous. The possible adsorption mechanism of 4-CP on NCNFs was proposed. The excellent adsorption performance of NCNFs for 4-CP were mainly ascribed to their maximum effective surface area, short mass transfer path and hydrophobic surface, which resulted from their nanoarchitectures with many exposed, shallow and accessible pores and a great deal of nitrogen functionalities.