Adsorption/Desorption and Recovery Studies for the Systems: Gallic Acid and Propyl Gallate Solutions/Activated Carbon

The present study investigates the adsorption, desorption, and recovery behavior of two phenolic antioxidants-gallic acid (GA) and propyl gallate (PG) onto microporous activated carbon. Adsorption equilibrium and kinetic experiments were conducted at 30 and 45°C under acidic conditions (pH = 2) to evaluate the influence of temperature on adsorption efficiency and to elucidate the underlying molecular interactions. Equilibrium data were modeled using the Generalized Langmuir isotherm, revealing enhanced adsorption at higher temperature and stronger affinity of PG toward the carbon surface, consistent with its greater hydrophobicity. Kinetic profiles demonstrated faster adsorption rates for PG, particularly at elevated temperature, confirming the contribution of diffusion activation and partial desolvation to mass transfer. Desorption studies using ethanol showed significantly reduced recovery efficiencies when GA and PG were previously adsorbed at higher temperature, indicating stronger adsorption. The thermogravimetry/derivative thermogravimetry/differential scanning calorimetry (TG/DTG/DSC) analyzer coupled with mass spectrometry (MS) technique to identify the gaseous products of thermal destruction was applied to confirm possible adsorption mechanism and thermal stability of the studied systems. Complementary thermal analyses (TG/DTG/DSC-MS) provided evidence of physical adsorption mechanisms and alterations in thermal stability resulting from the presence of phenolic molecules within the carbon structure.