Solar-Enhanced Plasma-Catalytic Oxidation of Toluene over a Bifunctional Graphene Fin Foam Decorated with Nanofin-like MnO.

In this work, we propose a hybrid and unique process combining solar irradiation and post-plasma catalysis (PPC) for the effective oxidation of toluene over a highly active and stable MnO/GFF (bifunctional graphene fin foam) catalyst. The bifunctional GFF, serving as both the catalyst support and light absorber, is decorated with MnO nanofins, forming a hierarchical fin-on-fin structure. The results show that the MnO/GFF catalyst can effectively capture and convert renewable solar energy into heat (absorption of >95%), leading to a temperature rise (55.6 °C) of the catalyst bed under solar irradiation (1 sun, light intensity 1000 W m). The catalyst weight (9.8 mg) used in this work was significantly lower (10-100 times lower) than that used in previous studies (usually 100-1000 mg). Introducing solar energy into the typical PPC process via solar thermal conversion significantly enhances the conversion of toluene and CO selectivity by 36-63%, reaching ∼93% for toluene conversion and ∼83% for CO selectivity at a specific input energy of ∼350 J L, thus remarkably reducing the energy consumption of the plasma-catalytic gas cleaning process. The energy efficiency for toluene conversion in the solar-enhanced post-plasma catalytic (SEPPC) process reaches up to 12.7 g kWh, ∼57% higher than that using the PPC process without solar irradiation (8.1 g kWh), whereas the energy consumption of the SEPPC process is reduced by 35-52%. Moreover, the MnO/GFF catalyst exhibits an excellent self-cleaning capability induced by solar irradiation, demonstrating a superior long-term catalytic stability of 72 h at 1 sun, significantly better than that reported in previous works. The prominent synergistic effect of solar irradiation and PPC with a synergistic capacity of ∼42% can be mainly attributed to the solar-induced thermal effect on the catalyst bed, boosting ozone decomposition (an almost triple enhancement from ∼0.18 g g h for PPC to ∼0.52 g g h for SEPPC) to generate more oxidative species (e.g., O radicals) and enhancing the catalytic oxidation on the catalyst surfaces, as well as the self-cleaning capacity of the catalyst at elevated temperatures driven by solar irradiation. This work opens a rational route to use abundant, renewable solar power to achieve high-performance and energy-efficient removal of volatile organic compounds.