First-Principles Study on the Enhancement of Formaldehyde Adsorption on Graphene-like ZnO via Doping Au and Vacancy Defects

Graphene-like 2D ZnO (g-ZnO), a wide-bandgap semiconductor, shows great potential for gas sensing, owing to its high surface area and carrier mobility. However, the practical use of it is hampered by its intrinsic chemical inertness. In this study, density functional theory was first used to study the effects of zinc vacancies (VZn), oxygen vacancies (VO), and Au doping on formaldehyde (CH2O) sensing. The results show that engineering of the defects and the Au doping both significantly improve the reactivity of the material. Specifically, the VZn system promotes dissociative chemisorption (Eads = −5.55 eV) of CH2O to CO and H atoms. Charge compensation effectively passivates the vacancy states and returns the direct bandgap semiconducting nature of the system. Furthermore, Au doping raises the conduction band and enlarges the bandgap, while the charge accumulation around Au atoms activates the surrounding sites, causing the adsorption mechanism to change from physisorption to chemisorption. Overall, the introduction of VZn and Au doping is an efficient way to overcome the surface inertness and improve sensing sensitivity, offering a theoretical framework for the design of high-performance 2D gas sensors.