As typical titanium nanomaterials, TiO2 and titanate nanotubes (TNTs) are extensively used. Although the toxicity of nano-TiO2 under solar light has been investigated, it is not enough to evaluate its environmental toxicity because the dark environment is also important in the natural environment. In addition, little is known about the environmental toxicity and mechanism of the emerging TNTs. In this study, we investigated the toxicity of nano-TiO2 and TNTs based on the inactivation performance on Escherichia coli cells under simulated solar light and in a dark chamber, and their toxicity mechanisms were explored on a subcellular level. The inactivation performance was: nano-TiO2-solar (100.0%) > TNTs-solar (62.7%) > TNTs-dark (36.6%) > TiO2-dark (0.5%). The excellent inactivation performance of nano-TiO2 under solar light is caused by the large amount of active free radicals attacking cell organelles until peroxidation and death, which is due to the strong photocatalytic properties. The lower inactivation ability of nano-TiO2 in the dark was due to the absence of radicals and its accessible physical morphology. For TNTs, the inactivation ability under solar light is derived from a combination of its weak photocatalytic performance and morphological effects, and TNTs in a dark environment can only attack cells via physical piercing.
Titanate nanotubes (TNTs), derived from TiO2 nanoparticles through hydrothermal treatment, have been attracting intensive research interests in recent years. Unlike the precursor TiO2 nanoparticles that have high photocatalytic activity under ultraviolet light, TNTs exhibit multi-layered and tubular structures. In addition, TNTs are composed of corrugated ribbons of edge-sharing [TiO6] octahedrons as the skeleton and H+/Na+ are located in the interlayers. Thus, TNTs usually have uniform tubular microstructures, large specific surface area, abundant functional groups (–ONa/–OH), good ion-exchange properties, high solution stability and high photoelectric quantum conversion effects. The specific physicochemical properties of TNTs indicate their great application potential in water and wastewater treatment. This chapter provides an overview of the latest research on the environmental applications and implications of TNTs. Conventional methods for the synthesis and characterization of TNTs are also summarized. TNTs and modified TNTs used as adsorbents, photocatalysts and catalysts for peroxymonosulfate/peroxydisulfate activation are systematically discussed. The environmental behaviors of aggregation and sedimentation of TNTs in water are also described.