CO2-assisted synthesis of mesoporous carbon/C-doped ZnO composites for enhanced photocatalytic performance under visible light.

Visible-light-responsive mesoporous carbon/C-doped ZnO (mC/C-ZnO) composites were fabricated using a facile, fast, one-step process in CO2-expanded ethanol solution. It is a green and sustainable process that does not need tedious pretreatment, surfactants or precipitants. CO2 played triple roles in the synthesis of mC/C-ZnO composites; the first was to provide a simple physical expansion to evenly dope the carbon in the ZnO; the second was to offer some chemical groups such as CO3(2-) and HCO3(-), facilitating the uniform and complete deposition through the coordination of a metallic cation with these anions; and the third was to offer CO3(2-) acting as a template for the formation of mesoporosity in the carbon. When used as a photocatalyst for the photodegradation of RhB and the organic pollutant phenol, the mC/C-ZnO composites with glucose content at 22 wt% (mC/C-ZnO-CE-2) synthesized in CO2-expanded ethanol exhibited better recycling stability and photodegradation rate than the corresponding sample synthesized in pure ethanol. Such improved photocatalytic performance was attributed to the well-mixing of the mesoporous carbon and the small sized C-doped ZnO particles in the mC/C-ZnO-CE-2 composites. The facile and fast synthesis method could be extended to other mesoporous carbon/C-doped metal oxide composites, which are expected to be good photocatalyst candidates, or in other application fields.