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A Novel Mesoporous CaO-Loaded In2O3 Material for CO2 Sensing

Authors


  • The authors thank the Serveis Cientificotècnics (University of Barcelona) for the use of their equipment. The authors gratefully acknowledge Dr. Núria Ferrer and Anna Vila of the FTIR unit for their help, advice and patience and Enric Menéndez and Teresa Andreu for their assistance. EME group is with CeRMAE (Centre de Referència en Materials Avançats per a L'Energia) and it also belongs to IN2UB (Institut de Nanociència i Nanotecnologia de la UB). This work has been financially supported by the MAT 2004-06859-C02-01 project. A.P. is indebted to the Spanish Ministry of Education (MEC) for the FPI grant. Supporting Information is available online from Wiley InterScience or from the authors.

Abstract

A mesoporous CaO-loaded In2O3 material (with Ca/In2O3 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 In2O3 matrix has been obtained by hard template route from the SBA-15 silica template. Additive presence does not distort the lattice of In2O3, 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 CaCO3 in calcite phase as a consequence of CaO carbonation. Pure In2O3 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 CO32– 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 CaCO3 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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