A room temperature operated ammonia gas sensor based on Ag-decorated TiO₂ quantum dot clusters

In this research, nanometer size aggregates (clusters) of titanium dioxide (TiO₂) quantum dot clusters (QDs) have been successfully prepared via a convenient hydrolysis method at a low temperature (80 °C). Then different amounts (0-5%) of Ag were further decorated on the TiO₂ QDs via dipping and annealing under a nitrogen atmosphere. After Ag decoration, the TiO₂ QD sensing materials were synthesized, and characterization and NH₃ gas sensing performance studies were carried out. Analysis via XRD and EDS was conducted, and the results showed that Ag⁺ ions were successfully reduced to Ag and decorated on the surface of the anatase TiO₂ QDs. Noble metal Ag acted as the sites for adsorbates, catalysts, or promoters during the surface reactions, and as the element improving the thermal stability of the nanostructure. Therefore, the Ag-decorated gas sensor possessed better gas sensing performance than an undecorated gas sensor, and 3% Ag dopant proved to be the optimal amount of addition. The fabricated 3% Ag-decorated TiO₂ QDs gas sensor, compared with the undecorated TiO₂ QDs sensor, displayed a 6-times-higher sensing response at room temperature and demonstrated excellent gas sensing properties toward 10-100 ppm NH₃ gas, good selectivity, gas sensitivity and stability, rapid response/recovery time, and a linear relationship between the response and the target gas concentration. In particular, the excellent performance of the Ag decorated-TiO₂ QDs gas sensor was achieved at room temperature, which suggests the great possibility of a prompt gas sensing response, with the use of paper as a substrate, that requires a low operation temperature.