The increasing demand for a whiter smile has resulted in an increased popularity for tooth whitening procedures. The most classic hydrogen peroxide-based whitening agents are effective, but can lead to enamel demineralization, gingival irritation, or cytotoxicity. Furthermore, these techniques are excessively time-consuming. Here, we report a nondestructive, harmless and convenient tooth whitening strategy based on a piezo-catalysis effect realized by replacement of abrasives traditionally used in toothpaste with piezoelectric particles. Degradation of organic dyes via piezo-catalysis of BaTiO₃ (BTO) nanoparticles was performed under ultrasonic vibration to simulate daily tooth brushing. Teeth stained with black tea, blueberry juice, wine or a combination thereof can be notably whitened by the poled BTO turbid liquid after vibration for 3 h. A similar treatment using unpoled or cubic BTO show negligible tooth whitening effect. Furthermore, the BTO nanoparticle-based piezo-catalysis tooth whitening procedure exhibits remarkably less damage to both enamel and biological cells.

Photocatalytic hydrogen evolution, as an environmental-friendly, energy-saving and simple process, has been widely reported. However, there are some important factors that prohibit practical application of photocatalytic hydrogen production, including the low efficiency of solar energy utilization, and the lack of response in the dark. Temperature fluctuation is a very common phenomenon in our daily life, which is rarely reported for use for hydrogen production. Here we demonstrate direct hydrogen evolution through the harvesting of cold–hot 298–323 K (25–50 °C) alternation energy by using pyroelectric nanomaterial Ba_0.7Sr_0.3TiO₃ (BST). The yield of hydrogen achieved was 46.89 μmol per gram of catalyst after 36 thermal cycles and the rate of hydrogen generation was up to 1.30 μmol g⁻¹ per thermal cycle. The minimum of the conduction band of BST is more negative than the conduction band level of H⁺/H₂, enabling the reduction of water to form hydrogen. This efficient and eco-friendly pyro-catalytic method provides a promising future for hydrogen evolution utilizing natural cold–hot temperature fluctuation energy.

A strong pyro-catalytic dye degradation with an ultrahigh degradation efficiency (>99%) in hydrothermally synthesized pyroelectric BiFeO₃ nanoparticles was achieved under a room-temperature cold–hot alternating excitation (between 27 °C to 38 °C). The pyro-catalysis originated from a combination of the pyroelectric effect and the electrochemical oxidation–reduction reaction. The intermediate products (hydroxyl radicals and superoxide radicals) of pyro-electro-catalysis were observed. Pyro-catalysis provides a highly efficient and reusable dye wastewater decomposition technology through utilizing environmental day–night temperature variation.