Behaviour and mechanics of phenolic sorption by novel bio-based graphene derivatives as adsorbents

Phenolic compounds, notorious for their environmental and health hazards, demand efficient removal from wastewater. Our research leads in synthesizing bio-based graphene derivatives from biomass-derived lignin, such as graphene oxide (bGO) and reduced graphene oxide (brGO), and these materials show promise in effectively removing hydrophobic pollutants like phenol and tannic acid. Hence, this study investigated the mechanical and dynamical aspects of their sorptions by bGO and brGO. Both adsorbents demonstrated a comparable adsorption pattern, with enhanced efficiency observed at higher adsorbent dosage, prolonged contact time, neutralized pH solutions, and elevated temperatures. Of note, phenol is removed at a much greater rate (>94%) than tannic acid (>84%) by both adsorbents at a dosage of 180 mg L^-1, pH 6.5, 900 min, and 25 °C. The Freundlich model provided the best fit for the isotherm data of both phenol (R² = 0.99) and tannic acid (R² = 0.98), while the pseudo-second-order model effectively described the adsorption kinetics of phenol (R² = 0.99) and tannic acid (R² = 0.99). The determined activation energy exceeds 5.88 kJ mol^-1, affirming the prevalence of physisorption as the dominant mechanism in the adsorption process. Thermodynamic analysis confirmed that the adsorption process is endothermic (ΔH) and occurs spontaneously (ΔG), indicating a random (ΔS) nature. However, the percentage removal plunged considerably after five consecutive adsorption-desorption cycles, attributed to the alterations of active sites on bGO and brGO.