  A set of experiments was conducted to synthesize doped and undoped sodium
tantalates with carbon and sulfur in energy efficient single-step hydrothermal
process. Undoped sodium tantalate nanocubes were synthesized at 140$^\circ$C
and doped one at 180$^\circ$C for 12 hours in rich alkaline atmosphere. The
sizes of undoped, carbon-doped, and sulfur-doped sodium tantalate nanocubes
were 38 nm, 45 nm, and 40 nm, respectively. The morphological, elemental,
compositional, structural, thermal, and photophysical properties of
as-synthesized doped and undoped sodium tantalate (NaTaO$_3$) were
characterized using scanning electron microscope (SEM), energy dispersive x-ray
spectroscope (EDS), Raman spectroscopy, X-ray powder diffraction (XRD), thermal
gravimetric analysis (TGA), Fourier transform infrared spectrophotometer
(FTIR), and UV-vis spectrophotometer. The sulfur doped NaTaO$_3$ shows a higher
photocatalytic activity in degradation of methylene blue than carbon doped and
the undoped NaTaO$_3$. The band gaps of undoped NaTaO$_3$, carbon doped
c-NaTaO$_3$, and sulfur doped s-NaTaO$_3$ were calculated to be 3.94 eV, 3.8
eV, and 3.52 eV, respectively using Tauc plot.
