Effects of Cu, Ag, Au, & Pd Nanocluster Loading on Acetone & Ethanol Sensing Performance of ZnO: A DFT Study

Abstract

Gas sensors find widespread applications from healthcare to industrial safety. The detection of volatile organic compounds like acetone and ethanol in their gaseous state is very important, especially in the biomedical field. SMO-based gas sensors, which have simple architecture and several favorable features, require additional treatments like noble metal loading onto the SMOs like ZnO surface for superior performance. Experimental trial-and-error approach to performance improvement has been the prevalent practice due to the lack of knowledge of the electronic and chemical properties of such systems. Computational studies can play significant roles as predictive tools in this field. In this work, by using DFT study, we explore how Cu, Ag, Au, or Pd nanocluster loading onto ZnO cluster affects acetone vs. ethanol sensing performance of ZnO semiconductor. DFT simulations have been used obtain the chemical and electronic properties of various nanoclusters systems, which have been associated with sensor performances. First, we have studied the binding of acetone and ethanol to pristine (ZnO)2 cluster which explains how ZnO show better sensor response to acetone than ethanol. Next, we have explored the metal nanocluster M6 (where M = Cu, Ag, Au, and Pd) loading onto ZnO. Since the actual working motifs in the nanostructured sensor materials could be a small cluster of few atoms, we have taken M6 nanocluster as a model for the metal nanoparticle. Finally, we have investigated acetone vs. ethanol sensing performance of the metal nanocluster loaded ZnO systems. For each system, we have calculated various parameters like the binding energy, HOMO-LUMO energy and bandgap, Mulliken charge distributions, bond distance, etc. The study shows that the electronic structure effects of M6/ZnO nanoclusters can be used to understand the molecular level mechanism of sensor activation by metal nanoclusters and explain their acetone vs. ethanol sensing performance. A better understanding of the roles of various components of the sensor materials will help in better selection of sensor materials and develop efficient, low cost and portable sensors.