Removal of the AO7 dye by adsorption on activated carbon based on grape marc: equilibrium, regeneration, and FTIR spectroscopy

Activated carbon was prepared from grape marc after activation with H3PO4. It was used to adsorb an azo dye (AO7) from aqueous solutions. The adsorption process was spontaneous (Delta G (<) 0) and endothermic as indicated by the thermodynamic parameters (Delta H = 12.28 kJ /mol and Delta S = 0.041 kJ/mol K). The adsorption capacity was found to increase with increasing temperature (from 140.5 mg/ g at 25 degrees C to 174.6 mg/g at 55 degrees C). The nonlinear regression adsorption equilibrium modeling revealed that the adsorption of AO7 by the activated carbon was best represented by the Freundlich model (R-2 > 0.975). The desorption of the dye and the regeneration of the activated carbon are crucial steps to consider in evaluating the efficacy of contaminant elimination from aqueous solutions. Among six solvents used, ethanol had the greatest capacity of dye desorption from the activated carbon (48%). The FTIR investigation revealed that ethanol was partially bound to the activated carbon which adversely decreases the adsorption capacity in each adsorption-desorption cycle. The investigation carried out revealed that the grape marc adsorbent was effective in removing dyes from waste water.