As mentioned above, these oxide NPs are harmful in part because both anatase and rutile forms are semiconductors and produce ROS. Particularly, P25 kind has band-gap energies estimated of 3.2 and 3.0 eV, equivalent to radiation wavelengths of approximately 388 and 414 nm, respectively. Irradiation at these wavelengths or below produces a separation of charge, resulting in a hole in the valence band and a free electron in the conduction band, due to the electron movement from the valence to conduction bands. These hole–electron pairs generate ROS when they interact with H₂O or O₂ [43,44]. It was described that they can cause an increase in ROS levels after exposure to UV-visible light [45]. The NBT assay in the studied samples showed that bare P25TiO₂NPs produce a large amount of ROS, which is drastically reduced by functionalization with vitamin B2 (Fig. 5). This vitamin, also known as riboflavin, was discovered in 1872 as a yellow fluorescent pigment, [46] but its function as an essential vitamin for humans was established more than sixty years later, and its antioxidant capacity was not studied until the end of the XX century [47,48]. This antioxidant role in cells is partially explained because the glutathione reductase enzyme (GR) requires it for good functionality. This enzyme is the one in charge of the conversion of oxidized glutathione to its reduced form which acts as a powerful inner antioxidant and can quench the ROS [49,50]. The cost of this action is that the glutathione is converted to the oxidized form and needs to be recovered by the GR. Consequently, the cells need more vitamin B2. Another glutathione action is the protection against hydroperoxide. This activity is also mediated by riboflavin. Therefore, local delivery of this vitamin seems to significantly help the cells in their fight to keep the oxidative balance, once they are exposed to high levels of ROS.

6.0-8.0

The FDA first approved the use of titanium dioxide in food in 1966, following its 1960 removal (along with the removal of other color additives) from the agency's original Generally Recognized as Safe list. In 1977, titanium dioxide joined the list of color additives that are exempt from certification, which means titanium dioxide doesn't have to be listed on the packaging of every product it's used in, Faber noted.

Appearance:

LITHOPONE

The morphology of vitaminB2@P25TiO₂NPs is coherent with the description of Degussa P25 typical population. Size distribution histograms were made from manual measures of the nanoparticles observed in SEM micrographs using ImageJ®. This data showed that more than 70% is anatase (between 20 and 60 nm) with a minor amount of rutile characteristic bars (between 80 and 100 nm) and a small amount of amorphous phase (<40 nm) [36]. Further analysis of the same sample areas with an EDS probe demonstrated the presence of organic material composed of C and O (Fig. 2). This material was found homogeneously distributed on the surface of the different shapes of P25TiO₂NP, not in the background, indicating a specific interaction that could be attributed to the functionalization of the P25TiO₂NPs with vitamin B2.

Porcelain White, 32 per cent sulphide, 68 per cent barium sulphate.