A. М. H. Hussein

Nanoparticles are not only hard. Nanoparticles can be made of "soft matter": dye micelles, surfactant micelles with adsorption in the ultraviolet range, protein globules (micelles) .... They decompose under the action of ultraviolet radiation (photodegradation).

Photodegradation of nanoparticles refers to the light-driven chemical decomposition or structural modification of nanoscale materials when exposed to light, particularly UV or visible radiation, in the presence of reactive species like oxygen or water. This process involves the absorption of photons by nanoparticles, generating electron-hole pairs that react with surrounding molecules to produce reactive oxygen species (ROS) such as hydroxyl radicals (•OH) and superoxide anions (•O₂⁻), which subsequently attack and degrade the nanoparticle's surface and structure. The rate and extent of photodegradation depend on multiple factors including the nanoparticle's material composition (e.g., metal oxides like TiO₂ or quantum dots like CdSe), light exposure conditions (wavelength, intensity, duration), and environmental factors (oxygen levels, pH, humidity). Photodegradation can lead to beneficial applications such as photocatalytic pollutant breakdown but also poses challenges like stability loss in optoelectronic devices or toxicity from released metal ions. To mitigate unwanted degradation, strategies like protective coating with silica or polymers, operating in oxygen-free environments, or developing doped/composite nanomaterials are employed. The characterization of photodegradation typically involves analytical techniques such as TEM for structural changes, XRD for crystallinity analysis, and UV-Vis spectroscopy for tracking optical property alterations. Understanding and controlling photodegradation is crucial for both harnessing its advantages in environmental applications and ensuring nanoparticle stability in technological and biomedical uses.