Effect of Doping on Optical and Photocatalytic Properties of TiO₂-Ti₃C₂T_x Hybrid

The light absorption of TiO₂ can be extended from ultraviolet to visible region via structure disorder, chemical and physical doping, but with the trade-off of photocatalyst deactivation due to the short lifetime of photoexcited charge carriers. In this study, we report the simultaneous reduction and carbon doping of TiO₂ through refluxing with titanium carbide MXene (Ti₃C₂T_x) in the presence of a reducing agent (ethanol or hydrazine) to shift TiO₂ absorption to the visible region and allow visible light activity without compromising the lifetime of charge carriers. Carbon doping and defects (oxygen vacancies and Ti³⁺ ions) in TiO₂ enable visible light absorption by allowing sub-band transition while MXene hinders the consumption of charge carrier and promotes the formation of active radicals on TiO₂-Ti₃C₂T_xby accepting the photoexcited electrons. UV-Visible spectroscopic measurement reveals absorption of TiO₂-Ti₃C₂T_x in the visible region with an indirect band gap of ~2.85 eV. The effective charge carrier separation and subsequent formation of active radicals in TiO₂-Ti₃C₂T_x are confirmed by photoluminescence and electron paramagnetic resonance spectroscopy. Multiple spectroscopic techniques are used to investigate the chemical interaction between TiO₂ and Ti₃C₂T_xin the hybrid structure and evaluate carbon doping in TiO₂, as well as correlate the density of defects in TiO₂-Ti₃C₂T_x with photocatalytic activity.