N3-dye-induced visible laser anatase-to-rutile phase transition on mesoporous TiO2 films

Visualization and Quantification of the Laser-Induced ART of TiO2 by Photoexcitation of Adsorbed Dyes

Dye-pretreated anatase TiO₂ films, commonly used as photoanodes in dye-sensitized solar cells, were utilized as a model system to investigate the laser-induced anatase to rutile phase transformation (ART), using N719 dye, N749 dye, D149 dye, and MC540 dye as photosensitizers. The visible lasers (532 and 785 nm) used for Raman spectroscopy were able to transform pure anatase into rutile at the laser spot when excitation of the dye sensitizer caused an electron injection from the excited state of the dye molecule into the conduction band of TiO₂. The three dyes with carboxylic acid anchor groups (N719, N749, and D149 dyes) experienced ART upon dye excitation; diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) and Raman spectra validated that these dyes were chemisorbed to the semiconductor surface. The MC540 dye with a sulfonic acid anchor group did not experience ART, and the DRIFTS and Raman spectra were inconclusive about the chemisorption of this dye to TiO₂. A TiO₂ calibration curve and percent rutile contour plots developed for this project are able to quantify the amount of rutile created at the surface of the samples. These improved chemical images which map rutile concentration help to visualize how ART propagates from the center of the laser spot to the surroundings. Factors such as visible-light absorption and anchor groups that covalently bind to the semiconductor play a key role in effective laser-induced ART.

Laser-flash-photolysis-spectroscopy: a nondestructive method?

Herein, we report the effect of the laser illumination during the diffuse-reflectance laser-flash-photolysis measurements on the morphological and optical properties of TiO₂ powders. A grey-blue coloration of the TiO₂ nanoparticles has been observed after intense laser illumination. This is explained by the formation of nonreactive trapped electrons accompanied by the release of oxygen atoms from the TiO₂ matrix as detected by means of UV-vis and EPR spectroscopy. Moreover, in the case of the pure anatase sample a phase transition of some TiO₂ nanoparticles located in the inner region from anatase to rutile occurred. It is suggested that these structural changes in TiO₂ are caused by an energy and charge transfer to the TiO₂ lattice.

Photocatalytically induced hydrophilicity influences bone remodelling at longer healing periods: a rabbit study

OBJECTIVES

Previously, we have reported that photocatalytically active hydrophilicity of the anatase titanium dioxide (TiO₂) nanoparticles coated onto commercially pure titanium discs presented significantly improved hydrophilicity after ultraviolet irradiation. As hydrophilicity has shown enhancement of osseointegration, the in vivo responses were of great interest. The aim of this study was to evaluate whether or not the photo-activated hydrophilicity generated at the time of implant placement has an effect on the longer healing periods for osseointegration.

MATERIALS AND METHODS

Photocatatytically active nanostructured TiO₂ powder (Degussa P-25), which consists of approximately 80% anatase and 20% rutile, was spin-coated onto commercially pure titanium discs and was heat-treated thereafter. These P25-coated discs were irradiated with ultraviolet (UV) light for the test (+UV) group, and non-irradiated discs were prepared for the control (-UV) group. Both groups of discs were placed in the rabbits' tibiae. After 12 weeks of healing period, histological analysis and gene expression analysis using real-time RT-PCR were performed.

RESULTS

From the histological analyses, there were no specific differences between -UV and +UV groups. However, from the gene expression analysis, ALP, RUNX-2 and IL-10 were significantly upregulated for the +UV group compared with the -UV group.

CONCLUSIONS

The biologically enhancing effect to photocatalytically activated surfaces remained even after 12 weeks of healing time in terms of genetic responses.

In vitro characterization and osteoblast responses to nanostructured photocatalytic TiO2 coated surfaces

The aims of the study were to characterize a nanostructured photoactive titanium dioxide (TiO(2)) coating and to compare the cellular response of human osteoblasts before and after ultraviolet (UV) irradiation of the coating. A specific nanostructured TiO(2) powder (Degussa P-25), which consists of approximately 80% anatase and 20% rutile, was spin-coated onto commercially pure titanium discs, and was heat-treated thereafter. After topographical, chemical and photocatalytic property characterizations, human osteoblasts were cultured on the coated discs before and after UV irradiation. Cell morphology was evaluated by scanning electron microscopy (SEM), and cell viability was analysed by 3-(4,5-dimethylthiazol)-2,5-diphenyltetrazolium bromide (MTT) assay. From the contact angle analysis, the wettability significantly improved after UV irradiation. The cultured cells were flattened with numerous elongated lammellipodia; however, no morphological differences were indicated between -UV and +UV surfaces. The MTT assay analysis showed that -UV surface presented significantly higher viability compared to the +UV surface except for one cell population group at 3h where there were no differences. The nanostructured photoactive TiO(2) surface improved its hydrophilicity by UV irradiation, however no enhancing effect in cell response was confirmed at the time tested compared to the non-irradiated surface.