Preparation of SnO2 nanoparticles using a helical tube reactor via continuous hydrothermal route

• We present a continuous hydrothermal route using helical tube reactor.
• Tetragonal SnO2 nanoparticles were successfully prepared without calcination.
• Mean size of SnO2 increased from 4 to 7 nm as hydrothermal temperature increased.
• The prepared SnO2 nanoparticles demonstrated the red-shifted property.
• The obtained SnO2 nanoparticles showed good degradation ability for MB solution.

SnO2 nanoparticles were prepared by a continuous hydrothermal process carried out in a helical tube reactor (HTR). The products prepared at different hydrothermal temperatures (from 160 °C to 300 °C) were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), energy dispersive spectroscopy (EDS), selected area electron diffraction (SAED) and UV–Visible spectroscopy (UV–Vis). The obtained SnO2 nanoparticles had a tetragonal structure and mean size of about 4–7 nm. It was found that the mean size of SnO2 nanoparticles increased with the increase of the hydrothermal temperature. The analysis of UV–Visible spectroscopy showed that with an increasing hydrothermal temperature from 160 °C to 300 °C the optical absorption edge shifted from about 320 nm to 350 nm, responding to the optical band gap value variation from 3.78 eV to 3.50 eV and indicating the red-shifted property of the prepared SnO2 nanoparticles. In addition, when employed as a photocatalyst, the as-obtained SnO2 nanoparticles demonstrated good degradation ability for methylene blue solution.