A Novel Mesoporous CaO‐Loaded In2O3 Material for CO2 Sensing

A mesoporous CaO-loaded In 2 O 3 material (with Ca/In 2 O 3 ratios ranging from 2.5 to 8.5 at %) has been synthesized and used as resistive gas sensor for the detection of CO2. A nanostructured In 2 O 3 matrix has been obtained by hard template route from the SBA-15 silica template. Additive presence does not distort the lattice of In 2 O 3 , which crystallizes in the Ia3 cubic space group. It has been proved by XRD, HRTEM, Raman and XPS measurements that samples contain not only CaO but also CaCO 3 in calcite phase as a consequence of CaO carbonation. Pure In 2 O 3 based sensors are low sensitive to CO2, whereas those containing the additive show an important response in the 300-5000 ppm range of gas concentrations. As seen by DRIFTS, the electrical response arises from the interaction between CO 3 2- and CO2, yielding bicarbonates products. The reaction is water-assisted, so that hydration of the sensing material ensures sensor reliability whilst its dehydration would inhibit sensor response. The use of CaCO 3 instead of CaO does not cause significant differences in electrical and DRIFTS data, which corroborates the important role played by carbonate species in the sensing mechanism.

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