Enhanced purification of supercritical fluid extracts of palm kernel cake phenolics using modified graphene-based adsorbents

This study evaluated the effectiveness of graphene-based adsorbents in purifying phenolic compounds extracted from palm kernel cake (PKC) by supercritical fluid extraction (SFE) at 80 °C, 300 bar, and 42 minutes. Four adsorbents—graphite, graphene oxide (GO), nitrogen-reduced GO (N-rGO), and three-dimensional nitrogen-doped reduced graphene oxide (3D-N-rGO)—were tested under fixed adsorption conditions (30 °C, 1 g adsorbent, 60 min, 300 rpm). Among these, 3D-N-rGO exhibited the highest adsorption capacity (15.47 mg/g), nearly double that of graphite (7.76 mg/g), and achieved the highest desorption ratio (75.58%). It also reduced the total phenolic content from 0.6162 to 0.1927 mg GAE/g bio-oil, representing a reduction of 68.7% . FTIR analysis confirmed the presence of nitrogen-related functional groups (N–H, C=N at ~1550–1650 cm⁻¹) and a reduction in oxygen-containing groups (C=O at ~1720 cm⁻¹, C–O at ~1050–1250 cm⁻¹), indicating successful nitrogen doping and deoxygenation. These structural features enhanced hydrophobicity and selectivity toward phenolic compounds. The findings suggest that 3D-N-rGO shows promise for applications in phytochemical purification, wastewater treatment, and bio-refinery processes. However, challenges such as adsorbent regeneration, material cost, and scalability must be addressed before industrial implementation.