Control over the morphology and structure of manganese oxide by tuning reaction conditions and catalytic performance for formaldehyde oxidation

Flower-like manganese oxide nanospheres as assembled by layered MnO2 sheets have been successfully fabricated via a facile route using a hydrothermal treatment at 120 °C for 12 h. XRD, FE-SEM, TEM and BET were used to investigate the crystalline structure, morphology, specific surface area, and porosity of the products. The products have a BET surface area of ca. 94.6 m2/g. Effects of preparation conditions including hydrothermal temperature, reaction time, pH value and kinds of anion were investigated on the morphology, structure and crystalline phase. It was found that control over the morphology and structure of product can be achieved by tuning reaction conditions. On the basis of experimental results, the formation mechanism of the products was investigated and discussed. The manganese oxide nanomaterials showed high catalytic activities for oxidative decomposition of formaldehyde. The crystallographic structure of the products had great influence on the catalytic performance in formaldehyde oxidation. Thereinto, the catalytic activity of the cryptomelane-type MnO2 was higher than other crystalline manganese oxides below 120 °C.

Graphical abstractThe crystallographic structure of the products had great influence on the catalytic performance in formaldehyde oxidation. Thereinto, the catalytic activity of the cryptomelane-type MnO2 was higher than other crystalline manganese oxides below 120 °C.Figure optionsDownload full-size imageDownload as PowerPoint slideHighlights► A facile hydrothermal route was used to fabricate flower-like MnO2 nanospheres as assembled by layered MnO2 nanosheets. ► Control over the morphology, structure and crystalline phase of manganese oxide nanomaterials can be achieved by tuning reaction conditions. ► Birnessite-type, cryptomelane-type and ramsdellite MnO2 nanostructures were successfully fabricated. ► On the basis of experimental results, the formation mechanism of the products was investigated and discussed. ► The crystallographic structure had great influence on the catalytic performance in formaldehyde oxidation.