Adsorption of phenol and nitrophenols by carbon nanospheres: Effect of pH and ionic strength

In this paper, we report the adsorption of phenol and nitrophenols (2,4 dinitrophenol, 4-nitrophenol and 2-nitrophenol) on a novel carbon material: carbon nanospheres (CNS). CNS were prepared by the direct pyrolysis of benzene and characterized by N₂ adsorption-desorption, X-ray diffraction analyses (XRD), scanning and transmission electron microscopy (SEM and TEM) and Raman spectroscopy. Adsorption isotherms were obtained in the range 20-200 mg L¹ of phenolic compound, the effect of pH on adsorption was studied at acidic (3), neutral (7) and alkali (11) media. CNS showed a specific competitive adsorption mechanism and nonlinear adsorption isotherms were obtained with the tested phenolic compounds. The adsorption capacity of CNS followed the sequence: 2,4-dinitrophenol > 4-nitrophenol > 2-nitrophenol > phenol. The adsorption was favored under acidic conditions (pH 3), moreover, the presence of ionic salts (e.g. NaCl) in solution increased the ability of CNS to remove phenol and nitrophenols from aqueous solutions (pH 7). Maximum adsorption was obtained with 2,4-dinitrophenol, resulting in an adsorption capacity of 32.9 mggCN_S¹.