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1. What is titanium dioxide?

If you want to avoid titanium dioxide, read labels carefully and stick to minimally processed whole foods.

The ingredient in question? Titanium dioxide.

Titanium dioxide goes into many industrial and consumer products. It makes paper white and bright, it keeps plastics and rubber soft and flexible, and helps remove harmful emissions from car exhaust, among many other uses. In the drug industry, it's a key ingredient in pill capsules and tablet coatings to keep the medicine inside from being affected by sunlight. 

Lithopone was developed in the 1870s as a substitute for lead carbonate (lead white), to overcome its drawbacks of toxicity and poor weathering resistance. Within a few years, titanium dioxide displaced lithopone to become the white pigment (PW6) par excellence in the industry and the world’s best-selling inorganic pigment. However, titanium is a product whose price is subject to large price variations due to product availability. These price increases affect the competitiveness of finished products, and so the search for an alternative to titanium dioxide has generated a variety of possibilities to optimise its use. 

With the rise of nanotechnology, research in recent years has also shown the dangers of titanium dioxide (TiO2) nanoparticles, and their genotoxicity, which refers to a chemical agent’s ability to harm or damage DNA in cells, thus potentially causing cancer. 

The basic scenario of resistive switching in TiO₂ (Jameson et al., 2007) assumes the formation and electromigration of oxygen vacancies between the electrodes (Baiatu et al., 1990), so that the distribution of concomitant n-type conductivity (Janotti et al., 2010) across the volume can eventually be controlled by an external electric bias, as schematically shown in Figure 1B. Direct observations with transmission electron microscopy (TEM) revealed more complex electroforming processes in TiO₂ thin films. In one of the studies, a continuous Pt filament between the electrodes was observed in a planar Pt/TiO₂/Pt memristor (Jang et al., 2016). As illustrated in Figure 1C, the corresponding switching mechanism was suggested as the formation of a conductive nanofilament with a high concentration of ionized oxygen vacancies and correspondingly reduced Ti³⁺ ions. These ions induce detachment and migration of Pt atoms from the electrode via strong metal–support interactions (Tauster, 1987). Another TEM investigation of a conductive TiO₂ nanofilament revealed it to be a Magnéli phase Ti_nO_2n−1 (Kwon et al., 2010). Supposedly, its formation results from an increase in the concentrations of oxygen vacancies within a local nanoregion above their thermodynamically stable limit. This scenario is schematically shown in Figure 1D. Other hypothesized point defect mechanisms involve a contribution of cation and anion interstitials, although their behavior has been studied more in tantalum oxide (Wedig et al., 2015; Kumar et al., 2016). The plausible origins and mechanisms of memristive switching have been comprehensively reviewed in topical publications devoted to metal oxide memristors (Yang et al., 2008; Waser et al., 2009; Ielmini, 2016) as well as TiO₂ (Jeong et al., 2011; Szot et al., 2011; Acharyya et al., 2014). The resistive switching mechanisms in memristive materials are regularly revisited and updated in the themed review publications (Sun et al., 2019; Wang et al., 2020).

The so-called “barrier effect” makes it possible to achieve good anti-corrosion protection in primers.

Why Did Europe Ban Titanium Dioxide?

Titanium dioxide comes in the form of a white powder and is sometimes used in cosmetics to adjust a color to a lighter shade. This is also why it can produce a white cast.