The crystal facet-dependent gas sensing properties of ZnO nanosheets: Experimental and computational study

• Published in: Sensors and actuators. B, Chemical Vol. 242; pp. 148 - 157
• Main Authors: Xu, Jiaqiang, Xue, Zhenggang, Qin, Nan, Cheng, Zhixuan, Xiang, Qun
• Format: Journal Article
• Language: English
• Published: Lausanne Elsevier B.V 01-04-2017; Elsevier Science Ltd
• Subjects: Biosensors; Chemisorption; Crystal defects; Crystal facet; Crystal structure; Density functional theory; Detection; Exposure; Gas sensing mechanism; Gas sensor; Gas sensors; Nanosheets; Organic chemistry; Pore size; Porosity; Porous materials; Sensitivity analysis; Sensitivity enhancement; Zinc oxide; Zinc oxides; ZnO nanosheet; Density functional theory; Crystal facet; Gas sensor; ZnO nanosheet; Gas sensing mechanism
• ISSN: 0925-4005; 1873-3077
• DOI: 10.1016/j.snb.2016.09.193

•To clarify the fundamental question of how (0001) facet of ZnO exhibits a better gas sensing performance than (10 0) facet, we calculated the chemisorption energy of an oxygen molecule (O2) on different facets of ZnO by density functional theory.•Our calculations show that the reduced energy is 1.0665eV when the O2 molecule is chemically absorbed on the (0001) facet while 0.5233eV on the (10 0) facet.•The higher the reduced energy is, the stronger the chemisorption of oxygen will be.•It is easier for the reactive (0001) facet to chemically absorb O2 molecules than it is for the (10 0) facet under the same conditions.•It can well explain why ZnO nanostructure with more (0001) facets shows a superior gas sensing performance.
Herein, we focused on the effects of exposed crystal planes on the gas sensing property of ZnO. For this purpose, we designed and synthesized two porous ZnO nanosheets with different exposed crystal facets (0001) and (101¯0) by a facile hydrothermal routes. The characterization results show that both the porous nanosheets have a near specific surface area about 7.5m2/g, thickness about 100nm, diameter about 5μm and pore size of tens of nanometers. However, their dominating exposed crystal facets are (0001) and (101¯0), respectively. When employed them as sensing materials in gas sensors, porous ZnO nanosheets with dominating exposed (0001) facet exhibit a superior sensitivity than the (101¯0) one. The enhanced gas response is attributed to a large amount of oxygen vacancy defects and unsaturated dangling bonds existing in the ZnO nanosheets with exposed crystal facet (0001), which is favorable for the adsorption of gas molecular on the sensor surface and result in improvement of the gas response. Finally, the calculation of the chemisorption energy of oxygen on ZnO crystal facets also proves the reactive-facet-enhanced gas sensitivity.