Adsorption of p-nitrophenol from aqueous solutions using nanographite oxide

Nanographite oxide prepared by a chemical oxidation method was characterized by SEM, XRD, FT-IR, zeta potential and BET surface area. The use of nanographite oxide as an adsorbent to remove p-nitrophenol from aqueous solutions was investigated. Adsorption experiments were carried out as a function of the contact time, initial p-nitrophenol concentration, pH, adsorbent dosage, and temperature. It was found that the nanographite oxide possessed a large surface area and was particularly effective for the removal of p-nitrophenol. The removal efficiency of p-nitrophenol decreased with an increase of the solution pH from 4.0 to 7.0 and an increase in the temperature. The adsorption of p-nitrophenol onto nanographite oxide reached equilibrium within 2 h. The maximum adsorption capacity of nanographite oxide for p-nitrophenol was 268.5 mg/g at 283 K and a natural pH. The Freundlich isotherm was the best choice to describe the adsorption behavior. The kinetic data were presented by the pseudo-second-order kinetic model. The parameters suggested that the adsorption process of p-nitrophenol onto nanographite oxide occurred via physisorption process and was exothermic in nature. Hydrogen-bonding, electron donor–acceptor and Lewis acid/base interactions were the main mechanisms affecting the adsorption capacity, while dispersive interactions were also found to influence the adsorption of p-nitrophenol through the influence of its deactivating functional groups on the aromatic ring. The results showed that nanographite oxide can be used as a new adsorbent which has higher adsorption capacity and faster adsorption rate for the removal of p-nitrophenol.