Ammonia removal from aqueous solution using novel biosorbent developed from TEMPO oxidized flax fibres

Ammonia is a significant environmental pollutant, and this study explores the use of flax fibres, a sustainable agricultural waste, for its removal. Fibres underwent chemical treatment to eliminate non-cellulosic matter and increase exposure of functional groups and were subsequently oxidized using TEMPO-mediated oxidation. Surface characterization methods, including scanning electron microscopy, x-ray photon spectroscopy, and Fourier transform infrared spectroscopy, indicated successful treatment, showing the removal of surface extractives and the presence of new functional groups. Batch adsorption tests showed adsorption capacity improved from 0.912 mg/g using unmodified fibres to 3.373 mg/g following chemical modification, indicating approximately 270 % increase, with optimal ammonia uptake at pH 6–7. Both the Langmuir (R 2 = 0.981, RMSE = 0.064) and Freundlich (R 2 = 0.980, RMSE = 0.066) models described the experimental data well, and chemisorption was suggested as the removal mechanism based on the pseudo-second order kinetic model (R 2 = 0.998). Thermodynamic analysis indicated the removal process as being endothermic and non-spontaneous under the conditions tested. Regeneration tests demonstrated 87 % retention in adsorption capacity when using a 10 % NaCl regenerant solution over three cycles. This study demonstrates the potential of flax fibres as an eco-friendly, cost-effective material for ammonia removal, highlighting its potential applicability in sustainable wastewater treatment technologies. • A biosorbent derived from TEMPO-oxidized flax fibers demonstrated effective ammonia removal. • TEMPO-oxidized flax fibres showed a 270% increase in ammonia uptake capacity compared to non-treated fibres. • Kinetic and thermodynamic analyses revealed insights into the adsorption mechanism, suggesting removal via chemisorption. • Surface characterization showed effective oxidation and removal of non-cellulosic extractives, enhancing surface properties.