Adsorption of p-nitrophenol onto activated carbon prepared from fir sawdust: isotherm studies and error analysis

Abstract

Fir sawdust was employed for the preparation of activated carbons by potassium hydroxide (KOH), phosphoric acid (H₃PO₄) and zinc chloride (ZnCl₂) activations. The three adsorbents have been abbreviated BAC, AAC and SAC. The nitrogen adsorption–desorption experiments were performed at 77 K to determine the physical surface properties of these three adsorbents. The chemical properties were depicted by the point of zero charge (pH_PZC) measurement and by Fourier Transform Infrared (FTIR) spectra. Characterization of the fir sawdust activated carbons suggests that their structures are highly dependent on the activation agent molecules. In this research, in order to evaluate the performances of the fir sawdust activated carbons, a series of batch experiments were conducted for the adsorption of p-nitrophenol from aqueous solution at initial concentrations in range of 50–250 mg/L. The equilibrium data were fitted by non linear regression with two-parameter models: Langmuir, Freundlich and Jovanovic and three-parameter models: Redlich–Peterson, Vieth–Sladek, Koble–Corrigan and Brouers–Sotolongo. Five error functions were used to compare the accuracy of the fit. The equilibrium data of p-nitrophenol onto BAC were better described by Langmuir isotherm and by Freundlich isotherm for AAC and SAC. The maximum adsorption capacity of p-nitrophenol was found for SAC (q_m = 318.67 mg/g) and this can be attributed to the basic nitrogen-containing groups and graphitic structure. The results proved that zinc chloride-activated carbon was a successful adsorbent for p-nitrophenol removal from wastewater.