ABSTRACT
Corncob Activated Carbon (AC) was produced via chemical activation with phosphoric acid (H3PO4) for the hydrolysis step and potassium hydroxide (KOH) for the impregnation step. In this work, optimization and development of the model equations for the preparation conditions of AC, Design Expert 6.0.6 Stat-Ease, Inc USA software was used. For the optimization of the AC preparation conditions, a Central Composite Design (CCD) was used to investigate the effect of independent variables on the yield and adsorption capacity of the activated carbon samples. The independent variables used in this work were, phosphoric acid concentration, potassium hydroxide concentration, activation temperature (oC) and activation time (minute). Response Surface Methodology (RSM) technique was used to optimize the preparation conditions (H3PO4, KOH, temperature and time); with percentage yields of hydrolysate and activated carbon and adsorption capacity of AC as the targeted responses. The optimal conditions for the preparation of AC using CCD software were 358.15 oC, 116.90 minutes, 0.29 mg/l H3PO4, 0.09 mg/l KOH. This set of conditions gave hydrolysate yield of 76.9339 %, while activated carbon yield and Methylene Blue (MB) adsorption capacity were 21.84 % and 1.98 mg/g respectively. The specific surface area of the AC using Sear's method was 314.2 m2/g. Analysis of Variance (ANOVA) for hydrolysate yield, AC yield and adsorption capacity showed the developed models equations were significant. The experimental and predicted values of the hydrolysate yield, AC yield and adsorption capacity of adsorbent on adsorbate MB were in close agreement and the correlation coefficients R2-values of 0.9688, 0.9358 and 0.9134. The surface areas of selected ACs were 259.8 m2/g (AC8), 215 m2/g (AC9) and 314.2 m2/g (AC14) gave adsorption capacities of 1.92 gm/g, 1.97 mg/g and 1.98 mg/g of MB respectively. The Fourier Transform Infra-Red (FTIR) analysis of the AC samples produced showed the presence of O-H, C-H, C-Br, N-H, C-C, C-N, C=C and C≡C functional groups which aid in adsorbing adsorbate onto the adsorbent. Adsorption isotherm data were used to model the following Langmuir and Freundlich isotherms; the adsorption of Chromium ions on the selected AC produced was predicted by Langmuir and Freundlich isotherm models with R2 value of 0.9974 and 0.7691 respectively. The percentage chromium removal increases with increase in adsorbent dosage. The activated carbon samples produced can be effectively used for wastewater treatment.