Hierarchical Assembly of Interleaved n-ZnO Network and p-CuO for Improved Chemo-Resistive CO2 Gas Sensing Performance

3D hierarchical hollow ZnO microspheres were impregnated with CuO microleaves to form p-n heterojunctions. The synthesized p-type CuO/n-type ZnO composite was characterized for its composition and morphology. X-ray diffractograms confirmed formation of phase pure ZnO along with CuO in equimole ratio by a solution precipitation technique. FE-SEM micrographs revealed 3D ZnO hollow microspheres in the size range 3-8 mu m formed of interleaved sheets, 10-20 nm thick as the primary building blocks. The results indicated an improved sensor response (S) of 44% at 320 degrees C for a CO2 gas concentration of 10,000 ppm for the developed CuO/ZnO mixed metal oxide based sensor. The improved sensor response observed here, when compared with commercial ZnO powder decorated with CuO microleaves was attributed to the specific role of CuO in the sensing mechanism, formation of p-CuO/nZnO heterojunction and nanostructured sensitive layer, thus presenting CuO/ZnO composite as a candidate material for CO2 gas sensing.