Ultrathin manganese dioxide (MnO2) nanosheets with the thickness of 1-2 nm were synthesized by chemical oxidation of Mn2+ ions in the presence of tetramethylammonium cations in an aqueous solution. The composite material MnO2/PET (polyethylene terephthalate) was prepared by impregnating PET into MnO2 nanosheets colloid. The impregnation time has a great influence on HCHO adsorption and removal efficiency. When the PET was impregnated in nanosheets colloid for 1 h at room temperature, the concentration of HCHO decreased quickly within initial 10 min and finally reached about 81% removal efficiency with an initial HCHO concentration of similar to 200 ppm. Moreover, the used MnO2/PET can be simply regenerated by heating at 105 degrees C without any rinse treatment. Based on in-situ DRIFTS and TG-MS studies, the mechanism of formaldehyde removal and regeneration was proposed. All the results showed that as-synthesized MnO2/PET can be used as an effective, affordable, and recyclable materials to removal and oxide toxic HCHO in indoor air. (C) 2016 Elsevier B.V. All rights reserved.