Indium doping induced defect structure evolution and photocatalytic activity of hydrothermally grown small SnO2 nanoparticles

Well-crystalline SnO₂ nanoparticles of 4-5 nm size with different In contents were synthesized by hydrothermal process at relatively low temperature and characterized by transmission electron microscopy (TEM), microRaman spectroscopy and photoluminescence (PL) spectroscopy. Indium incorporation in SnO₂ lattice is seen to cause a lattice expansion, increasing the average size of the nanoparticles. The fundamental phonon vibration modes of SnO₂ lattice suffer a broadening, and surface modes associated to particle size shift gradually with the increase of In content. Incorporation of In drastically enhances the PL emission of SnO₂ nanoparticles associated to deep electronic defect levels. Although In incorporation reduces the band gap energy of SnO₂ crystallites only marginally, it affects drastically their dye degradation behaviors under UV illumination. While the UV degradation of methylene blue (MB) by undoped SnO2 nanoparticles occurs through the production of intermediate byproducts such as azure A, azure B, and azure C, direct mineralization of MB takes place for In-doped SnO₂ nanoparticles.