Nano-twinned structure and photocatalytic properties under visible light for undoped nano-titania synthesised by hydrothermal reaction in water–ethanol mixture

Nano-TiO2 crystals showing visible light driven photocatalytic activity were synthesized by hydrothermal reaction in an ethanol–water mixture. The experiments were conducted to optimise the synthesis conditions for nano titania, in the range of temperature from 200 to 400 °C. X-ray diffraction depicted that the products obtained were anatase at 250 °C and above. For the products obtained at 250 °C, detailed analysis was conducted since it depicted high crystallinity with smallest particle sizes. Shape of the crystal was rounded rectangular with the size of 4 ± 1 nm to 7 ± 1 nm. The high-resolution transmission electron microscopy (HRTEM) revealed the existence of novel nano-twin structure in anatase grains and surface defects around the nanocrystals. Photocatalytic property was investigated for these undoped titania samples under UV and visible light. The nano twin structure, surface defects, and nano-meter size of the synthesized titania are believed to play a crucial role for the high catalytic activity.

HRTEM micrograph of the synthesised titania nanoparticles depicting the anatase nano-twin, and selected area electron diffraction (SAED) pattern of the same. The presence of nano-twins combined with other forms of defects could be the possible reasons for the superior photocatalytic properties of these undoped titania samples.Figure optionsDownload as PowerPoint slideHighlights
► Nano-TiO2 crystals showing photo-catalytic activity in visible light, size was in the range from 3 to 8 nm.
► HRTEM revealed the existence of interestingly novel nano-twin structure in anatase grains which has a structural similarity to rutile and brookite.
► The nano-meter particle size and the presence of surface modulations are also contributing to the reasons for the superior photocatalytic properties of titania.