Nanocomposites and nanomaterials

Nanosized materials CeO2/SnO2 and CeO2/ SnO2-Sb2O5 for adsorption semiconductor sensors to detect hydrogen in air
Matushko I. P., Arinarkhova H. O., Oleksenko L. P., Maksymovych N. P., Fedorenko G. V.
Chemical Department, Taras Shevchenko National University of Kyiv, 
12 Lva Tolstogo Str., Kyiv, 01033, Ukraine.
E-mail: Anna.arinarkhova@gmail.com.
Nowadays H2 is regarded as the most ecologically clean fuel. But formation of leakage of hydrogen during its production, usage, storage and transportation can result in explosive situations. Adsorption semiconductor sensors are widely used as detectors of gas analysis devices to control microconcentrations of H2 in air. Tin dioxide remains the most promising as the sensor gas sensitive layer material due to its chemical stability. Antimony additives are added to SnO2 to achieve an optimum value of an electrical resistance of the sensors in air. Nanomaterials are characterized by a high ratio of their specific surfaces to volumes. This can improve the sensor properties such as the sensor response, detection limit, response and recovery time. Catalytic active additives are introduced in the gas sensitive sensor layer to increase the sensor response. The aim of this work is to study the parameters of the sensors based on CeO2/SnO2 and CeO2/SnO2-Sb2O5 nanomaterials since cerium (IV) oxide has shown great catalytic activity in H2 oxidation.
Nanosized SnO2 and SnO2-Sb2O5 materials were prepared by a sol–gel method using ethylene glycol as a solvent. It was shown by TEM method that SnO2 particle size ranged from 6 to 25 nm (an average particle size was 15 nm); particle sizes of SnO2-Sb2O5 materials were ranged from 5 to 23 nm, an average particle size was 12 nm. Study by XRD method revealed that the structures of the obtained nanomaterials were corresponded to a cassiterite type. The adsorption semiconductor sensors with different CeO2 contents were created on the base of the nanosized SnO2 and SnO2-Sb2O5 materials using CeCl3 solutions of different concentrations (0.4×10-2 - 2×10-2 M). A ratio of the sensor electrical resistance in air (R0) to its electrical resistance in a hydrogen-air mixture with 40 ppm H2 (Rg) was chosen as a measure of the sensor response (γ = R0/Rg). 
It was found that addition of cerium leads to significant increasing of the value of γ for all sensor operating temperatures and increasing the catalytic activities of the corresponded sensor nanomaterials in H2 oxidation reaction. The highest sensor responses to H2 were achieved at 325 0С and 350 0С that connected with features of running of the oxidation reaction on the studied samples.