Titanium and zirconium-based mixed oxides prepared by using pressurized and supercritical fluids: On novel preparation, microstructure and photocatalytic properties in the photocatalytic reduction of CO2

•Novel preparation of ZrxTi1-xOn mixed oxides by processing using pressurized hot water and supercritical methanol.•ZrxTi1-xOn mixed oxides investigated in the CO2 photocatalytic reduction.•TiO2 anatase-brookite mixture (67:33wt.%) resulted in the highest photoactivity.•Optimal Ti:Zr molar ratio of 0.9:0.1 in the ZrxTi1-xOn mixed oxide.•Small anatase and brookite crystallite-size allowed optimal optical and electronic properties.