Thermal treatment of H3PO4-impregnated hydrochar under controlled oxygen flows for producing materials with tunable properties and enhanced diclofenac adsorption

The chemical activation of biomass with phosphoric acid under an oxygenated atmosphere has been extensively studied in various papers. However, there is still uncertainty about how the oxygenated atmosphere affects the evolution of activated carbon properties, as the concentration of oxygen in the activation atmosphere has not been explored as an activation variable. Hence, this paper aims to fill the gap by exploring the effect of oxygen concentration on the activation process. The H3PO4-impregnated hydrochar was heated at 500 °C, under atmospheres containing various concentrations of oxygen. The evolution of activated carbons' properties was assessed by various techniques, including FTIR, SEM-EDS, N2-physisorption, CHNS/O elemental analysis, pHpzc, and Boehm titration. Additionally, the impact of oxygen concentration on the adsorption capacity was examined using diclofenac as a model pollutant. It was found that the activated carbons’ microporosity and surface functionality can be improved and controlled by changing the oxygen concentration in the activation atmosphere. This led to enhanced π-π and hydrogen bonding interactions between diclofenac molecules and activated carbons, resulting in increased adsorption capacities. This study emphasizes the importance of oxygen concentration as an activation variable, providing valuable insights for designing effective activated carbon adsorbents.