The effect of OH groups on the optical and structural properties of TiO 2 nanoparticles Sami Auvinen, Olga Miroshnichenko, Matti Alatalo, Lappeenranta.

The effect of OH groups on the optical and structural properties of

TiO2 nanoparticles

Sami Auvinen, Olga Miroshnichenko, Matti Alatalo,

Lappeenranta University of Technology

Motivation

Manufacturing methods are based on hydrolysis from different solutions

Many applications of titanium dioxide take place in aqueous environment

Source: Flickr

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Computational details

A B

• DFT, TDDFT

• Real space grid

• Non-periodic boundary conditions

• PBE

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Breaking or stretching Ti-Ti and Ti-O bonds =>

● Lower number of bonds in relaxed structures,● Increasing of average dimensions of clusters,

but the average length of bonds does not change much

Structural effects

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Electronic properties

DOS for bare A- (a) and B- (b) structures. HOMO and LUMO levels are plotted with vertical dashed lines.

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Electronic properties

DOS for bare B- (a) and B- with one OH (b) structures. HOMO and LUMO levels are plotted with vertical dashed lines. In (b) HOMO and LUMO levels are almost identical.

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Electronic properties

DOS for bare A- (a), A- with one OH (b), A- with 6 OH (c), and A- with 16 OH (d) structures. HOMO and LUMO levels are plotted with vertical dashed lines. In (b) and (d) HOMO and LUMO levels are almost identical. 8

Optical properties

Total photoabsorption spectra for bare A-structure, A-structure with one OH-group, with 6 OH-groups, and with 16 OH-groups.

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Optical properties

Total averaged refractive index function for bare A-structure, A-structure with one OH-group, with 6 OH-groups, and with 16 OH-groups.

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Conclusions

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• OH groups alter the structure of the particles, breaking and streching the near surface Ti-Ti and Ti-O bonds

• Adsorbed OH groups cause enhancement of the intensity of the DOS of particles at the lower part of the valence band and at the upper part of the conduction band

• The same trend with increasing absorption at low and higher energies can be seen in photoabsorption spectra and RIFs of the nanoparticles

=> The effects of the surrounding media have to be taken into consideration when considering the computationally modeled absorption properties of the small TiO2 nanoparticles