Modelling of a new form of nitrogen doped activated carbon for adsorption of various dyes and hexavalent chromium ions

Abstract This study reports a new form of nitrogen-doped activated carbon (AC5-600) produced from a blend of sawdust (SD) and fish waste (FW) treated with urea and ZnCl 2 for the adsorption of toxic metals and dyes. The adsorbent was also explored in the treatment of acid brown 14 (AB14) and acid orange 7 (AO7) dye molecules and hexavalent chromium (Cr 6+ ) ions. The pH controls the sorption of individual contaminants, with an observed superlative % of individual contaminants removed at pH 1.5. Removal at pH was credited to the electrostatic interaction (EI) between the anion dyes and Cr 6+ species at this pH and the protonated sites accessible on the AC5-600 adsorbent surface. Based on the error values obtained from the non-linear modelling (NLM) of the kinetic and isotherm models, the Elovich (ELM-AB14 and Cr 6+ ), pseudo-first- (PFOM-AB14) and second-order models (PSOM-AB14, AO7 and Cr 6+ ) and the Freundlich (FRHM) model were found to ideally define the sorption of the various contaminants. The determined maximum sorption capacity ( Q m ) based on the NLM was 1114, 1929 and 318 mg.g -1 for AB14 dye, AO7 dye and Cr 6+ ions, respectively. Based on the computational adsorption calculations, the sorption energies for the AO7 and AB14 dyes were -4.492 and -8.090 eV and 2.563, 1.789, 1.226 and 1.928 eV for Cr 2 , CrO 3 , CrO 4 , and CrO 4 H species. AB14 and AO7 dyes and Cr 6+ ions adsorption to synthesised AC5-600 was predicted employing the response surface methodology (RSM) and artificial neural network (ANN) models. The ANN model was more effective in predicting AB14 and AO7 dyes and Cr 6+ ions adsorption than the RSM, and it was highly applicable in the sorption process.