Because of its electrically
conducting properties combined with
excellent thermal stability and transparency throughout the visible
spectrum, tin oxide (SnO
2
) is extremely attractive as a
transparent conducting material for applications in low-emission window
coatings and solar cells, as well as in lithium-ion batteries and
gas sensors. It is also an important catalyst and catalyst support
for oxidation reactions. Here, we describe a novel nonaqueous sol–gel
synthesis approach to produce tin oxide nanoparticles (NPs) with a
low NP size dispersion. The success of this method lies in the nonhydrolytic
pathway that involves the reaction between tin chloride and an oxygen
donor, 1-hexanol, without the need for a surfactant or subsequent
thermal treatment. This one-pot procedure is carried out at relatively
low temperatures in the 160–260 °C range, compatible with
coating processes on flexible plastic supports. The NP size distribution,
shape, and dislocation density were studied by powder X-ray powder
diffraction analyzed using the method of whole powder pattern modeling,
as well as high-resolution transmission electron microscopy. The SnO
2
NPs were determined to have particle sizes between 3.4 and
7.7 nm. The reaction products were characterized using liquid-state
13
C and
1
H nuclear magnetic resonance (NMR) that
confirmed the formation of dihexyl ether and 1-chlorohexane. The NPs
were studied by a combination of
13
C,
1
H, and
119
Sn solid-state NMR as well as Fourier transform infrared
(FTIR) and Raman spectroscopy. The
13
C SSNMR, FTIR, and
Raman data showed the presence of organic species derived from the
1-hexanol reactant remaining within the samples. The optical absorption,
studied using UV–visible spectroscopy, indicated that the band
gap (
E
g
) shifted systematically to lower
energy with decreasing NP sizes. This unusual result could be due
to mechanical strains present within the smallest NPs perhaps associated
with the organic ligands decorating the NP surface. As the size increased,
we observed a correlation with an increased density of screw dislocations
present within the NPs that could indicate relaxation of the stress.
We suggest that this could provide a useful method for band gap control
within SnO
2
NPs in the absence of chemical dopants.