Optical properties of Codium tomentosum seaweed like Bi2O3 nanostructure and its gas-sensing activity

Codium tomentosum seaweed structured Bi2O3 was prepared by anodization technique using thermally evaporated bismuth films. The present study concerns the development of an efficient CO2 sensor at room temperature by controlling the crystallinity, morphology, carrier concentration, and bang gap. Crystal structure variation was achieved by sequential annealing from 200 to 600 degrees C. During anodization, truncated polyhedral aggregates of bismuth particles get reformed into Codium tomentosum seaweed like nanostructures of Bi2O3. The nature of Bi2O3 semiconductor with carrier concentration has been identified from the Mott-Schottky plot. Lattice defects such as oxygen vacancies, Bi interstitials, recombination effect, and band gap values were analyzed through optical studies. The sensor study was performed at room temperature for the detection of CO2 gas in the concentration 10-100 ppm. Bi2O3 nanostructure annealed at 400 degrees C having amorphous nature offered the maximum response magnitude. The underlying, sensing mechanism was correlated with the experimental findings on the basis of optical properties and surface morphology.