Hierarchical porous carbon from semi-coke via a facile preparation method for p-nitrophenol adsorption

Abstract

Hierarchical porous carbon (PC) was prepared from semi-coke (SC) via a facile approach (K2CO3 catalytic steam activation) and used to adsorb p-nitrophenol (PNP) from aqueous solution. PC was characterized by elemental analysis, N2 adsorption-desorption, SEM, FT-IR spectra, Raman spectra, and XPS techniques. The results revealed that PC can process highly porous structures with a Brunauer–Emmett–Teller surface area of 121 m2 g−1. It is rich in oxygen functional groups on the surface and shows good affinity for p-nitrophenol, the maximum adsorption capacity being 192.13 mg g−1. Equilibrium adsorption data were fitted by the Langmuir, Freundlich, Redlich–Peterson, Liu, and Toth models. It was found that the Toth model presented the best fit. Kinetic studies showed that the data followed a pseudo second-order mode. Intra-particle diffusion studies showed that intra-particle diffusion was not the only rate controlling step. The negative enthalpy value ΔH° indicated that the adsorption process was exothermic. FT-IR and elemental analysis suggested that the adsorption mechanism of PNP onto PC was possible attributed to hydrogen bonding between polar functional groups on the PC surface and PNP. The spent PC was regenerated for four runs with acceptable adsorption capacity, which amounted to about 79.5% of the initial adsorption capacity. PC prepared from SC thus appears to be an effective adsorbent for removal of PNP from aqueous solutions.