Property assessment of copper-doped SnO2 QDs and its use as ammonia sensor

Abstract

Development of ammonia sensors are very important as such technology will be needed to detect and monitor ammonia levels in various environments, contributing to safety, environmental protection, quality control, and regulatory compliance across a wide range of industries and applications. In this work, copper ions substituted SnO₂ quantum dots of different weight percentages were synthesized using the conventional co-precipitation method to test their ability for ammonia detection. The physical properties of all the prepared samples were investigated experimentally, and correlations were established between them. X-ray diffraction studies verified the formation of quantum dots, pure crystallographic phase, and complete dissolution of Cu ions in the host SnO₂ crystal structure. Sherrer's formula was utilized to evaluate the mean crystallite size of prepared quantum dots, which were found to be between 3.3 nm and 4.1 nm, respectively. Average particle sizes, obtained from HRTEM micrographs also supported the claim of quantum dots of prepared samples and were also found an excellent match with mean crystallite sizes. A red shift in absorption spectra was also observed with increasing Cu-content. Both the obtained XPS data and EDS spectra confirmed the presence of all elements in the synthesized quantum dots. A careful examination of the luminescence properties also supported the quantum size effects of the prepared samples. Weak ferromagnetic behavior was also noted in 6 % Cu-doped SnO₂ quantum dots at 300 K due to the p-d hybridization, which was further verified by the DFT study. Room temperature conductivity study revealed that the hopping of electrons was responsible for charge conduction. The incorporation of Cu ions made the SnO₂ quantum dots a lossy dielectric nanomaterial. Observed single semicircle in the Cole-Cole plot for all the samples confirmed that the grain boundaries contributed more efficiently in determining the dielectric properties of the systems. It was noted that 6 % of Cu-doped SnO₂ quantum dots detected ammonia at room temperature more efficiently and showed comparatively less response to other analytes. Therefore, these Cu-doped SnO₂ quantum dots have the potential to be used for ammonia sensing at room temperature.