Alessandro Resmini

Au and Pt Nanoparticles Effects on the Optical and Electrical Gas Sensing Properties of Sol–Gel-Based ZnO Thin-Film Sensors

The optical and conductometric responses of sol-gel-based ZnO thin films with embedded 5% mol. Au or Pt nanoparticles (NPs) have been compared at different operating temperatures, to assess the effect of noble metal additions on to H2, CO and NO2 gases sensors response. The scanning electron microscopy and X-ray diffraction techniques have been utilized for morphological characterization of the crystal structures of the films after annealing at 400°C for 30 min and the effect of Au and Pt NPs additions on crystallite growth is discussed. Au NPs additions is effective to enhance the optical response to H2 and CO at 390 nm and in the 500-700-nm wavelength range at 300- °C temperature. No optical response to NO2 gas, even at low concentrations has been measured in the optical mode. The catalytic action of Pt NPs additions powerfully improves both the optical to H2 and CO at 390 nm, and the conductometric gas responses. Detection limits as low as 20-ppb NO2 and 50-ppm H2, in line with the best performances reported to the best of our knowledge in literature for ZnO-based sensors, have been measured in the conduction mode. Response times have been also compared, highlighting the positive effects played by Pt additions.

Optimization of 3D ZnO brush-like nanorods for dye-sensitized solar cells

In a dye-sensitized solar cell (DSSC) the amount of adsorbed dye on the photoanode surface is a key factor that must be maximized in order to obtain enhanced DSSC performance. In this study 3D ZnO nanostructures, named brush-like, are demonstrated as alternative photoanodes. In these structures, long ZnO nanorods are covered with a metal–organic precursor, known as a layered-hydroxide zinc salt (LHZS), which is subsequently converted to crystalline ZnO using two-step annealing. The LHZS is able to easily grow on any surface, such as the ZnO nanorod surface, without needing the assistance of a seed-layer. Brush-like structures synthesized using different citrate concentrations in the growth solutions and different annealing conditions are characterized and tested as DSSC photoanodes. The best-performing structure reported in this study was obtained using the highest citrate concentration (1.808 mM) and the lowest temperature annealing condition in an oxidative environment. Conversion efficiency as high as 1.95% was obtained when these brush-like structures were employed as DSSC photoanodes. These results are extremely promising for the implementation of these innovative structures in enhanced DSSCs, as well as in other applications that require the maximization of surface area exposed by ZnO or similar semiconductors, such as gas- or bio-sensing or photocatalysis.