As we know, TiO2 has its own bandgap > 3.0 eV and the aim of the preparation of nano-structure is to increase the surface area of the catalyst. However, does the preparation for nano-structure such as nanobelts, nanofiber, nanotubes, nanoparticles can influence the bandgap of bulk TiO2? and why? because I found some article that mentioned the preparation of TiO2 nanobelt caused the bandgap to be narrowed by 2.95 eV, which mean it can be conducted under visible light irradiation.
http://www.arpnjournals.com/jeas/research_papers/rp_2013/jeas_1013_966.pdf
http://www.arpnjournals.com/jeas/research_papers/rp_2013/jeas_1013_966.pdf
Yes, in general, the bandgap of a material increases with decreasing size (typically less than a few 10s of nanometers). This is due to quantum confinement effects.
Apart from the particle size, the shape of the nanoparticles can also have important effects.
Article Size and shape effects on the band gap of semiconductor comp...
If the size of the particles are in the nano-size regime, the bandgap of the material will become discrete. As a general rule, the band gap energy should increase with a decrease in particle size. Further, not only the size and shape but defects present in the sample may also influence the band gap energy.
Yes, The band gap increases with the decrease in the size of a material, this is due to the confinement of electrons on the nanometric scale, called "quantum size effect" or effective mass approximation "EMA".
Please refer to the following link for more details:
https://www.sciencedirect.com/topics/engineering/effective-mass-approximation
http://www.arpnjournals.com/jeas/research_papers/rp_2013/jeas_1013_966.pdf
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