Nanocomposites and nanomaterials 

Influence of doping with silver on photocatalytic properties of tin dioxide 
Samsonenko M.1*, Khalameida S.1, Sydorchuk V.1, Khyzhun O2.

1Institute for Sorption and Problems of Endoecology, NAS of Ukraine,
13 General Naumov Str., Kyiv 03164, bilychi@ukr.net
2I.M. Frantsevych Institute for Problems of Materials Science, NAS of Ukraine, 3 Krzhyzhanovsky St., Kyiv 03680

       Silver nanoparticles exhibit considerable UV and visible light absorption and, therefore, are potentially photocatalysts that utilize the full solar spectrum. It is also well known that silver species dispersed on oxide supports demonstrate higher photocatalytic activity due to charge separation of photogenerated electron-hole pairs. One of the options for such compositions using is the doping of wide-gap oxide semiconductors. We studied the tin dioxide doped with 1-5% of Ag which was synthesized by sonochemical and mechanochemical routes.
       No reflexes attributed to Ag-containing phases can be identified through XRD data. This indicates high dispersity of incorporated Ag-species as well as sufficiently uniform distribution of the dopant in SnO2 structure which is also confirmed by SEM and EDS investigations. XPS analysis shown that the silver exists in Ag+ and not in Ag0 state. The absence of surface plasmon resonance signal in UV-Vis spectra obtained for doped samples corroborates this assumption. UV-Vis spectra show considerable increase in absorption of visible light as well as red shift of absorption edge compared with pure tin dioxide. The latter reaches 476  nm which corresponds the band gap Eg=2.6 eV. Besides, introduction of dopant  on the stage of wet gel leads to formation of meso-macroporous structure of SnO2 which is accessible for molecules of substrates. 
        The combination of these physical-chemical characteristics causes higher photocatalytic activity of samples doped with different silver content compared to the initial sample in process of dyes (as pollutants) degradation under visible irradiation. It has been established that samples doped via sonochemical treatment are more active. Thus, SnO2 containing 1% silver exhibit maximum photocatalytic activity. The rate constant of rhodamine B degradation Kd increases nearly 200 times compared with initial sample. High activity of these samples in the photodegradation of safranin T, methyl orange and phenol are also observed. The Kd values achieves 10-3-10-4 s-1. The latter provides a degree of mineralization for tested dyes in the range of 65-80%.