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 degrees 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.