Graphene-assisted photothermal effect on promoting catalytic activity of layered MnO2 for gaseous formaldehyde oxidation

It is an ideal approach to utilize solar energy instead of heat to drive catalytic reactions. Graphene exhibits a significant photothermal effect and is among the prominent candidates for the utilization of solar energy, especially that of near infrared radiation (NIR). Herein, a kind of graphene (disordered graphene nanoplatelet)based MnO2 nanohybrid (MnO2-G) was prepared and investigated under irradiation of a xenon lamp for catalytic oxidation of gaseous formaldehyde. Compared to using only MnO2, the MnO2-G hybrid exhibited much higher activity, and the transformation rate of HCHO into CO2 increased to 80%. The excellent activity of the MnO2-G hybrid can be attributed to the synergistic photothermal effect between MnO2 and graphene, which enhances the use of light, especially in the infrared region. Because of the high heat conducting ability of graphene, heat was rapidly transferred from the graphene nanoplatelet to MnO2. Thus, the surface temperature of MnO2 was even higher than that of solo graphene, and this in turn facilitated the activation of surface lattice oxygen. In addition, the chargeability of Mn atom increased because of the hybridization between MnO2 and grapheme at interface. As a result, increased electron density on MnO2-G surface facilitated the activation of oxygen molecules and the formation of superoxide radicals. This result demonstrates a novel approach for efficient use of inexhaustible solar energy, and the assistance of graphene photothermal effect in a traditional catalytic process is a promising strategy for improving catalytic efficiency of traditional thermo-catalysts.