Preparation of MnO2-Al2O3 adsorbent with large specific surface area for fluoride removal

Abstract MnO 2 –Al 2 O 3 (MOAO) binary nanocomposite with a 1:3 MnO 2 to Al 2 O 3 molar ratio was synthesized by impregnation technique using mesoporous alumina (MA) precursor. The MOAO product consisted of MA and amorphous MnO 2 . The manganese valence in MOAO was +4, indicative of MnO 2 being coated on the surface of MA during the impregnation process. MOAO had a large specific surface area (385.266 m 2 /g) and wormhole-like mesoporous structure. The average pore size, which could be precisely controlled over the range of 3.4–4.1 nm. The optimum removal of fluoride was obtained when the initial pH was in the range of 4–10. The defluorination efficiency of MOAO was far superior to that of MA when the initial fluoride concentration exceeded 40 mg/L. The large surface area and bimodal porous structure of MOAO after coating MnO 2 may be responsible for the high removal efficiency in the defluorination process.