The size and shape of nanoparticles play a crucial role in determining their photochemical properties. These properties include absorption, emission, and scattering of light, as well as the generation of reactive species upon light irradiation. The size and shape of nanoparticles can influence their surface plasmon resonance SPR , quantum confinement effects, and surface-to-volume ratio, which in turn affect their photochemical properties.Experimental evidence supporting the influence of size and shape on the photochemical properties of nanoparticles can be found in several studies:1. Gold nanoparticles AuNPs : The size and shape of AuNPs have been shown to affect their SPR, which is responsible for their unique optical properties. A study by Haiss et al. 2004 demonstrated that the SPR peak of AuNPs shifts to longer wavelengths redshift as the particle size increases. This shift in SPR affects the absorption and scattering of light by the nanoparticles, which in turn influences their photochemical properties.2. Semiconductor quantum dots QDs : The size of QDs has a significant impact on their photochemical properties due to quantum confinement effects. As the size of the QDs decreases, the energy gap between the valence and conduction bands increases, leading to a blue shift in the absorption and emission spectra. A study by Peng et al. 1997 showed that the emission wavelength of CdSe QDs can be tuned from 480 nm to 640 nm by varying the particle size from 2.2 nm to 5.6 nm.3. TiO2 nanoparticles: The size and shape of TiO2 nanoparticles can affect their photocatalytic activity. A study by Zhang et al. 2008 demonstrated that anatase TiO2 nanoparticles with a smaller size 5 nm and a larger surface-to-volume ratio exhibited higher photocatalytic activity for the degradation of methylene blue compared to larger nanoparticles 25 nm .4. Silver nanoparticles AgNPs : The shape of AgNPs has been shown to influence their photochemical properties. A study by Jin et al. 2003 demonstrated that the SPR of AgNPs can be tuned by controlling their shape. Spherical AgNPs exhibited a single SPR peak, while triangular nanoplates showed two SPR peaks, one corresponding to the in-plane dipole mode and the other to the out-of-plane quadrupole mode. This shape-dependent SPR affects the absorption and scattering of light by the nanoparticles, which in turn influences their photochemical properties.In conclusion, the size and shape of nanoparticles have a significant impact on their photochemical properties, as evidenced by various experimental studies. By controlling the size and shape of nanoparticles, their photochemical properties can be tuned for specific applications, such as photocatalysis, photovoltaics, and sensing.