Hydrous TiO2@polypyrrole hybrid nanocomposite as an efficient selective scavenger for the defluoridation of drinking water

Abstract

An adsorptive process for the defluoridation of drinking water was performed using a hybrid nanocomposite of hydrous titanium oxide@polypyrrole (HTiO₂@PPy), as a scavenger. The adsorbent was successfully fabricated via facile in situ chemical oxidative polymerization of pyrrole monomer in aqueous media in which HTiO₂ nanoparticles were suspended. The developed adsorbent was characterized using various spectro-analytical techniques viz. BET, FTIR, FE-SEM, STEM, EDX, TGA and ZETA SIZER. Relatively high BET surface area (98.17 m² g⁻¹) and pH_pzc (∼8.4) values were obtained for HTiO₂@PPy. The synergistic effect of both the counterparts (PPy and HTiO₂) of the nanocomposite rapidly enhanced the F⁻ adsorption process. A noteworthy rapid fluoride uptake best described by the pseudo-second-order kinetic model was observed (equilibrium attainment within 5–30 min). The Langmuir model best described the isotherm data with a maximum adsorption capacity of 31.93 mg g⁻¹ at 25 °C and pH 6.5 (±0.2). Thermodynamic and activation parameters provided evidence of the spontaneous, endothermic and physical nature of the adsorption process. The selectivity of HTiO₂@PPy for F⁻ sorption was significant in the presence of Cl⁻, NO₃⁻, HCO₃⁻, SO₄²⁻ and PO₄³⁻ co-existing ions and noteworthy reusability for up to three regeneration cycles was achieved. Electrostatic interactions and ion-exchange were proposed to be the possible underlying mechanisms for the adsorption of F⁻ by HTiO₂@PPy nanocomposite. Thus, HTiO₂@PPy is anticipated to serve as an efficient scavenger for the defluoridation of drinking water.