Annealing-free synthesis of CN co-doped TiO2 hierarchical spheres by using amine agents via microwave-assisted solvothermal method and their photocatalytic activities

• The synthesis method for CN co-doped TiO2 hierarchical spheres is proposed.
• Microwave-assisted solvothermal method is applied.
• C and N are doped into TiO2 via a direct chelating reaction of amine compounds.
• The photodegradation rate is eightfold higher than the commercial P25 powders.

The annealing-free synthesis of CN co-doped TiO2 hierarchical spheres is proposed in this study. C and N were doped into the TiO2 structure via a direct chelating process to the Ti-precursor by using different amine agents, including hexadecylamine (HDA), diethylamine (DEA), trimethylamine (TMA), and diethylenetriamine (DETA). CN co-doped TiO2 spheres (300 nm to 500 nm) composed of nanoparticles approximately 11 nm to 13 nm in size were obtained via an efficient microwave-assisted solvothermal reaction at 190 °C for 60 min. The effects of C and N doping by using different amine compounds on the bandgap energy and photocatalytic performance of TiO2 were investigated. Among the amine compounds, DETA provided the highest chelating efficiency because it provides two primary amine groups, which resulted in the highest C and N doping concentrations and the largest degree of bandgap narrowing (2.77 eV); nevertheless, the high chelating ratio of C and N restrained the crystallization of TiO2 and considerably decreased its photocatalytic activity. The use of TMA produced optimal C and N doping concentrations, which effectively reduced the bandgap of TiO2 to 2.85 eV without affecting its crystallization. Its photodecomposition activity to rhodamine B was eightfold of that of commercial Degussa P25 powders under visible light irradiation.

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