Mesoporous and P-doped Kraft Lignin-derived biocarbon for PFAS removal

Per- and polyfluoroalkyl substances (PFAS) are persistent microcontaminants originating from sources such as firefighting foams, non-stick cookware, and industrial applications. Due to their high chemical stability, PFAS are environmentally pervasive and have been associated with severe adverse health effects, including carcinogenicity.

This study investigates the remediation of PFAS from groundwater using sustainable, biomass-derived carbon materials synthesized from kraft lignin. They were synthesized under systematically varied conditions, including carbonization temperature, acid concentration, and treatment duration, to optimize their surface characteristics in order to enhance the adsorption properties. Two representative PFAS: long-chain Perfluorononanoic acid (PFNA) and Perfluorooctane sulfonate (PFOS), were selected to evaluate adsorption efficiency and material selectivity. Based on screening experiments, two optimized carbons (denoted P1 and P2) were identified for detailed removal studies. Comprehensive material characterization was performed using BET surface area analysis, SEM, XRD, XPS and FTIR to elucidate porosity, surface morphology, crystallinity and functional group chemistry. Adsorption experiments demonstrated high removal efficiencies. For P1, PFNA removal reached 97.5% at 25 ppm and 96.7% at 50 ppm, while PFOS removal was 89% and 85.7% at the respective concentrations. P2 exhibited superior performance, achieving 96% (25 ppm) and 98% (50 ppm) removal for PFNA, and 98% (25 ppm) and 98.8% (50 ppm) for PFOS. Overall, removal efficiencies exceeding 90% were achieved for both long-chain PFAS, with enhanced performance of P2 attributed to its higher phosphorus doping. Adsorption isotherm analysis showed that the Langmuir-Freundlich model provided the best fit, indicating heterogeneous surface adsorption and multilayer uptake. Kinetic studies revealed rapid adsorption within the first 60–90 minutes, indicating fast adsorption kinetics and efficient uptake of contaminant molecules onto the adsorbent surfaces. Subsequently, the synthesized carbons were investigated under dynamic adsorption conditions through continuous-flow column studies to evaluate their performance for the treatment of PFAS contaminated groundwater. In conclusion, lignin-derived, heteroatom-doped carbons demonstrate excellent potential for the efficient removal of long-chain PFAS from groundwater. The use of a renewable biomass precursor enhances the sustainability of the process, while the high removal efficiencies and favourable kinetics highlight its potential for application at contaminated sites.

Acknowledgments. This work was supported by the Wallenberg Initiative Materials Science for Sustainability (WISE), funded by the Knut and Alice Wallenberg Foundation. Oleg Tkachenko gratefully acknowledges support from the Olle Engkvist Foundation for the scholarship (235-0413).