C,N-doped TiO2 monoliths with hierarchical macro-/mesoporosity for water treatment under visible light

C,NTiO2 monoliths with homogeneous interconnected macro-/mesoporous hierarchical porosity, consisting in 83% anatase phase, exhibiting high visible light absorption were prepared in one pot synthesis. The hierarchical porosity was controlled by coupling a sol-gel method with a spinodal decomposition and the improved visible light absorption was obtained by self C,N-grafting during thermal treatment. Titanium isopropoxide, N-methylformamide, poly(ethylene oxide), and hydrochloric acid were used as reagents to form a sol, which was then treated at 40 and 60 °C, followed by a solvothermal treatment in autoclave at 200 °C in isopropanol. The monoliths were further heated at different temperatures from 250 to 500 °C under air. The best compromise between the structural and textural properties (TiO2 phase, surface, volume, pore diameter), the visible light absorbance and the mechanical properties was obtained for a calcination at 350 °C for 5 h. In batch mode, in glass containers, the monoliths demonstrated remarkable efficiency as photocatalysts under natural sunlight and artificial visible light with the total discoloration of the azo dye Orange G aqueous solution in 1 h compared to benchmark TiO2 P25 nanoparticles, which proved inefficient under these conditions. More interestingly, the monoliths used as reactors in flow mode in a recirculating system proved very efficient for the total discoloration of Orange G dye solution revealing the high potential of these TiO2 monoliths for continuous flow wastewater treatment under visible light. [Display omitted] •Easy C,N-codoping of TiO2 monoliths with hierarchical macro-/mesoporosity.•High decrease of band gap of TiO2 photocatalyst from 3.2 to 1.5 eV.•Higher activity under sunlight than TiO2 P25 benchmark photocatalyst and undoped TiO2 monoliths.•Fast elimination of dyes pollutants contained in water in batch and in flow modes.•A new family of photocatalysts highly efficient under visible light and easy to handle.