Oriented growth of layered-MnO2 nanosheets over α-MnO2 nanotubes for enhanced room-temperature HCHO oxidation

- Oriented growth of layered-MnO2 nanosheets on α-MnO2 nanotubes is reported.
- Epitaxial relationship in the resulting α-MnO2@L-MnO2 heteroepitaxy is rationalized.
- Pt/α-MnO2@L-MnO2 show enhanced activity to room-temperature HCHO oxidation.
- The exposed α-MnO2 {100} surface facilitates adsorption and activation of O2.
- The exposed layered-MnO2 {001} surface is beneficial to desorption of resultant H2O.

Construction of heterostructures with well-defined size, dimension, surface and interface is an effective approach to develop enhanced and unprecedented functionality. Herein, oriented growth of layered-MnO2 nanosheets (L-MnO2) over α-MnO2 nanotubes backbones is demonstrated. The epitaxial relationship in the resulting α-MnO2@L-MnO2 heteroepitaxy is rationalized as (110)(α-MnO2)||(001)(layered-MnO2). With loading of 1 wt% Pt nanoparticles over the MnO2 samples, the resulting Pt/MnO2 samples show catalytic activity toward room-temperature HCHO oxidation via “HCHO + O2 = CO2 + H2O”. Upon 1 h treatment, 92.1% HCHO becomes mineralized over the Pt/α-MnO2@L-MnO2, higher than that of 81.3% and 75.9% for the Pt/α-MnO2 and Pt/L-MnO2. The oxidation of HCHO was well fitted with the second-order kinetic model, with the rate constant of the Pt/α-MnO2@L-MnO2 exceeding that of the Pt/α-MnO2 and the Pt/L-MnO2 by 2.27 and 5.92 times. Density-Functional-Theory (DFT) simulations show that α-MnO2 {100} surface facilitates adsorption/activation of O2, and layered-MnO2 {001} surface is beneficial to desorption of resultant H2O. The α-MnO2@L-MnO2 heteroepitaxy simultaneously integrates exposed facets of α-MnO2 {100} surface and layered-MnO2 {001} surface, in which the synergetic effect of the two surfaces leads to significantly enhanced room-temperature HCHO oxidation activity. The present study provides a rational design of manganese oxide-based catalysts for advanced environmental and energy applications.

Oriented growth of layered-MnO2 nanosheets over α-MnO2 nanotubes is demonstrated for construction of α-MnO2@L-MnO2 heteroepitaxy, which, with supported trace Pt nanoparticles, shows enhanced room-temperature HCHO oxidation.100