Boundary engineering of porous zinc oxide nanosheets to enhance gas sensing performance

• Porous ZnO nanosheet boundaries are tailored by calcination temperature during hydrozincite-to-ZnO phase transformation. • Dense boundaries with oxygen vacancies enhance gas sensing by facilitating surface charge carrier transfer. • Gas sensing properties are influenced by the energy barrier for carrier transport and ionized oxygen species behavior. • Calcination-induced boundary engineering improves the gas sensing selectivity and sensitivity of porous ZnO nanosheets. • Oxygen vacancies in ZnO nanosheets reduce transport barriers, enhancing carrier mobility and gas sensing efficiency. Zinc oxide (ZnO) based gas sensors are noted for their high sensing response toward a wide range of gases, however, they often face challenges in achieving other required properties due to complex reaction dynamics under different operating conditions. Herein, we fabricated boundary-engineered porous ZnO nanosheets by controlling calcination temperature of hydrozincite. These materials were systematically evaluated their sensing performance towards oxidizing gases, reducing inorganic gases, and volatile organic compounds. Additionally, detailed sensing properties toward NO 2 , NH 3 , and acetone were examined to investigate the critical roles of the energy barrier for carrier transport ( E b ) and the nature of ionized oxygen species in the sensing materials. Characteristics of the materials, such as crystallite size, pore size, porosity, and surface area, were effectively tuned, which significantly influenced E b and sensing performance. The porous ZnO nanosheets calcined at 300 °C for 4 h, exhibiting a higher density of boundaries, demonstrated enhanced sensing performance with maximum response values of 10.59 for NO 2 , 0.38 for NH 3 , and 0.41 for acetone at personnel exposure level. This improvement is likely linked to the increased surface charge carrier concentration and the higher E b associated with greater boundary density, indicating an increase in available reaction active sites. Furthermore, our findings reveal that gas sensing behavior is strongly dependent on the type of ionized oxygen species present. The optimal sensing temperature for NO 2 is 250 °C, where the dominant ionized oxygen species is O − , while for NH 3 and acetone, the optimal temperature was 450 °C, where O 2− is the predominant species.