Green synthesis of a novel water-stable Sn(ii)-TMA metal–organic framework (MOF): an efficient adsorbent for fluoride in aqueous medium in a wide pH range

Abstract

An Sn(II) based MOF has been synthesized using benzene-1,3,5-tricarboxylic acid (TMA) as an organic linker via a solvothermal route. PXRD and FT-IR studies confirm the aqueous stability of the synthesized Sn(II)-TMA MOF. In a batch adsorption experiment, the equilibrium fluoride concentration was obtained at 1.6 mg L⁻¹ with an initial concentration of 12 mg L⁻¹, i.e., ∼84% removal efficiency achieved over a pH range of 3 to 10. The adsorption of fluoride on the Sn(II)-TMA MOF was best described by the Langmuir isotherm model, and the thermodynamic analysis confirmed the adsorption process to be endothermic, spontaneous, and thermodynamically feasible. The maximum fluoride adsorption capacity was calculated to be 30.86 mg g⁻¹ at 298 K. The experimental data were in good agreement with both the pseudo-first-order and pseudo-second-order kinetic model. The fluoride removal efficiency was unaffected by interfering ions such as Cl⁻, NO₃⁻, and SO₄²⁻ and the high ionic strength of the aqueous medium. This work would provide valuable insight into the eco-friendly synthesis of the Sn(II)-TMA MOF and its applicability as a promising adsorbent for efficient fluoride removal from aqueous solution.