Template-free synthesis and gas sensing properties of well-controlled porous tin oxide nanospheres

High yield of tin dioxide (SnO2) nanospheres with various degrees porosity have been successfully synthesized without any physical template via an economical, easily scalable hydrothermal process. The porosity or the specific surface area of SnO2 nanospheres can effectively be tuned via precursor concentration, temperature and the removal of additive urea. Higher reaction temperature, low precursor concentration and elimination of urea additive favorably increase the porosity of the nanospheres. The gas sensing properties of the nanospheres show that the operating temperature has a strong influence on the response of the sensor whereby a higher operating temperature leads to greater change in conductance and hence, greater response. Other than the specific surface area, pore diameter of the nanospheres has shown to have an effect on the sensing behaviour. The response time is dependent on the operating temperature, 90% of resistance change (Rair–Rgas) was achieved within the first 1.3–3.0 min.