Sustainable hierarchically porous carbons from bio-oil to remove emerging contaminants

Abstract

This work reports the sustainable production of high-value-added products from biomass residues. Hierarchically porous carbons (HPCs) (micro/meso/macroporous) were obtained using the template-free route from bio-oil (biomass) pyrolysis and activation with zinc chloride in a single step. The materials obtained were characterized and applied to remove the following emerging contaminants 17α-ethinylestradiol, amoxicillin, ibuprofen, caffeine, and paracetamol from water. The hierarchically porous carbons presented high carbon contents (>80%), specific surface areas between 764 and 919 m² g⁻¹, and a multimodal pore size distribution (1 and 3.3 nm). The HPCs showed high thermal stability (>400 °C) and presence of nitrogen and oxygen groups on the surface such as ketones, phenols, ethers, pyrrolic-N and pyridinic-N. Preliminary adsorption contact tests showed removal rates above 70% for all contaminants studied. Adsorption isotherm studies demonstrated that most materials obtained q_max values of 188 mg g⁻¹ and 310 mg g⁻¹ for caffeine and paracetamol, respectively. Paracetamol exhibited a higher adsorption capacity when compared to caffeine. In addition, it was shown that the adsorption capacity of the material remained at 96% for caffeine and 85% for paracetamol until the tenth cycle. The increase in synthesis temperature has a direct influence on the textural parameters as well as surface chemistry, and can either alter or not the adsorption capacities, depending on the adsorption mechanisms involved. With this approach, we demonstrated the sustainable production of hierarchically porous carbons from biomass residues that have added value and can be used as adsorbents for emerging contaminants in water resources.