The ISO 18473-4-2022 standard specifies requirements and test methods for nano-scale titanium dioxide (TiO2) for photocatalytic applications. These nano-scale TiO2 particles have excellent catalytic performance and are widely used in areas such as green synthesis, degradation of organic pollutants, purification of air and water. The standard covers the properties of these nanoparticles including their size, surface preparation and doping to ensure their effectiveness in photocatalytic applications. The standard helps to regulate the production and application of nano-TiO2, promoting its use in environmentally friendly technologies.