Mesoporous zirconium pyrophosphate for the adsorption of fluoride from dilute aqueous solutions

[Display omitted] •Quaternary ammonium salts enabled pore structure in zirconium pyrophosphate adsorbents.•Specific surface area played a major role on fluoride adsorption density.•Fluoride adsorption on zirconium pyrophosphate adsorbents was specific chemical reaction.•Octadecyltrimethylammonium was the best Quats for zirconium pyrophosphate synthesis.•Optimal zirconium molar fraction, with respect to Octadecyltrimethylammonium, was 0.57. Mesoporous zirconium pyrophosphate(ZPP) adsorbents were synthesized, with six quaternary ammonium salts (Quats), namely, Octyltrimethylammonium (OTMA, C8), Decyltrimethylammonium (DCTMA, C10), Dodecyltrimethylammonium (DDTMA, C12), Tetradecyltrimethylammonium (TDTMA, C14), Hexadecyltrimethylammoium (HDTMA, C16), and Octadecyltrimethylammonium (ODTMA, C18), as template for studying fluoride adsorption. Quats of long carbon chain length significantly affected the specific surface area of mesoporous ZPP adsorbents. C18-ZPP exhibited the largest specific surface area and fluoride adsorption density. Fluoride adsorption density remained constant at pH 10–11. Langmuir adsorption isotherm described fluoride adsorption characteristics well. Results showed that mesoporous ZPP synthesized with C18 at Zr to C18 molar ratio of 0.57:1 exhibited the best fluoride adsorption capacity (32 mmol/g) among all ZPP adsorbents prepared at various Zr to C18 molar ratios. C18-ZPP exhibited two-fold increase in fluoride removal capacity compared to plain ZPP. The reusability of C18-ZPP was assessed by running fluoride removal at least five cycles. Mesoporous ZPP is a promising adsorbent for fluoride removal from water with much enhanced adsorption capacity, regenerability, and reusability.