Investigation of halloysite nanotubes with deposited silver nanoparticles by methods of optical spectroscopy

Halloysite nanotube composites covered by silver nanoparticles with the average diameters of 5 nm and 9 nm have been studied by methods of optical spectroscopy of reflectance/transmittance and Raman spectroscopy. It has been established that silver significantly increases the light absorption by nanocomposites in the range of 300 to 700 nm with a maximum near 400 nm, especially for the samples with the nanoparticle size of 9 nm, which is explained by plasmonic effects. The optical absorption increases also in the long-wavelength spectral range, which seems to be due to the localized electronic states in an alumosilicate halloysite matrix after deposition of nanoparticles. Raman spectra of nanocomposites reveal intense scattering peaks at the local phonons, whose intensities are maxima for the samples with the silver nanoparticle sizes of 9 nm, which can be caused by plasmonic enhancement of the light scattering efficiency. The results show the ability to use halloysite nanotube nanocomposites in photonics and biomedicine.