Urea-modified activated carbon for enhanced α-tocopherol adsorption via tailored mesoporosity

The selective recovery of α-tocopherol from vegetable oils is of growing interest due to its high nutritional and commercial value. Here, activated carbon was modified via a facile hydrothermal treatment with urea to investigate the effects of surface chemistry and morphology on α-tocopherol adsorption. Structural and surface analyses (XRD, FTIR, Raman spectroscopy, UV-Vis-DRS, and N2 physisorption) revealed that urea treatment increased the proportion of disordered carbon, which resulted in enlarged mesopores and a higher specific surface area. Adsorption experiments demonstrated that the improved performance of the urea-modified carbon (maximum capacity ∼85 mg/g at 0.7 M urea) was strongly correlated with mesopore development (R2 = 0.9969) rather than with changes in surface functional groups. Fitting the data to the Langmuir isotherm indicated comparable maximum adsorption capacities (ca. 93–101 mg/g) for pristine and urea-modified carbons with a three-fold higher affinity constant for the urea-treated sample, reflecting improved adsorbate accessibility. Kinetic analysis using the pore volume and surface diffusion model (PVSDM) confirmed that intraparticle diffusion governed uptake, with surface diffusion dominating in the mesopore-enriched sample. These results demonstrate that pore engineering is the primary driver of α-tocopherol adsorption on activated carbons. Therefore, the simple urea hydrothermal treatment offers a cost-effective strategy to enhance pore size, accelerate adsorption kinetics, and broaden the applicability of activated carbons for purifying bioactive molecules.