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Defluoridation of water through adsorption using biosorbents is currently attracting attention. A thermo-chemically developed biosorbent derived from Ficus glomerata bark was used in the present study. The adsorption data were analysed using Langmuir, Freundlich, Temkin and Dubinin–Radushkevich isotherm models at varying initial adsorbate concentrations (2–25 mg/l). It was found that the adsorption of fluoride onto F. glomerata biosorbent followed the Langmuir isotherm and the Langmuir isotherm constants a and b obtained were 2·27 mg/g and 0·651 l/mg, respectively, at an adsorbent dose of 5 g/l and temperature of 26 ± 1°C. The mean free sorption energy was found to be 8·770 kJ/mol, indicating that the adsorption of fluoride onto F. glomerata bark adsorbent was by a chemisorption mechanism. The kinetic study also supported chemisorption, with the adsorption data fitting well with pseudo-second-order kinetic model. The thermodynamic study indicated the spontaneous and endothermic nature (ΔH° = 15 430·78 J/mol) of fluoride adsorption onto F. glomerata adsorbent. Field scanning electron microscopy and energy dispersive spectroscopy, Brunauer–Emmett–Teller analysis and Fourier transform infrared spectroscopy were used to analyse the surface morphology of the adsorbent before and after the fluoride adsorption process. Practical application of F. glomerata Roxb. biosorbent to a fluoride-contaminated groundwater sample showed encouraging results.

Present research focuses on optimization of process parameters for defluoridation on novel Ficus benghalensis leaf biosorbent using Taguchi design tool. The maximum fluoride removal is obtained at pH 7, initial concentration 5 mg/L, contact time 120 min, adsorbent dose 10 g/L, and temperature 30°C, and its percentage contribution is found using ANOVA in the following order: pH 50.76% > initial concentration of adsorbate 44.76% > contact time 2.54% > adsorbent dose 1.17% > temperature 0.76%. It follows Langmuir isotherm with constants “a” and “b” obtained as 2.183 mg/g and 0.667 L/mg and fitting well with pseudo‐second‐order kinetic model. The thermodynamic study indicated the spontaneous and endothermic nature (ΔH = 15,530.55 J/mol). Advanced Analyses, viz., BET, FESEM‐EDS, and FTIR are done to know the characteristics of Ficus benghalensis leaf biosorbent. Experiment on defluoridation of contaminated groundwater indicated over 90% removal efficacy, and the concentration of treated water satisfies drinking water standards for fluoride. Practitioner points A fundamental research leading towards development of a novel biosorbent from Ficus benghalensis leaves waste for defluoridation. Necessary adsorption equilibrium, kinetic and thermodynamic studies to arrive at optimum operating parameters using Taguchi method and constants useful for designing defluoridation unit and advanced analysis mainly BET, FESM‐EDS and FTIR to have better insight. Validation on real field samples to prove its technical feasibility of defluoridation using the novel biosorbent developed.

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