Self-Assembled 3D ZnO Porous Structures with Exposed Reactive {0001} Facets and Their Enhanced Gas Sensitivity

Jin Chang,Wojtek Wlodarski,Eric Waclawik,Muhammad Ahmad

doi:10.3390/s130708445

Jin Chang, Wojtek Wlodarski + Show 2 more

Open Access

https://doi.org/10.3390/s130708445

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Abstract

Complex three-dimensional structures comprised of porous ZnO plates were synthesized in a controlled fashion by hydrothermal methods. Through subtle changes to reaction conditions, the ZnO structures could be self-assembled from 20 nm thick nanosheets into grass-like and flower-like structures which led to the exposure of high proportions of ZnO {0001} crystal facets for both these materials. The measured surface area of the flower-like and the grass, or platelet-like ZnO samples were 72.8 and 52.4 m2·g−1, respectively. Gas sensing results demonstrated that the porous, flower-like ZnO structures exhibited enhanced sensing performance towards NO2 gas compared with either grass-like ZnO or commercially sourced ZnO nanoparticle samples. The porous, flower-like ZnO structures provided a high surface area which enhanced the ZnO gas sensor response. X-ray photoelectron spectroscopy characterization revealed that flower-like ZnO samples possessed a higher percentage of oxygen vacancies than the other ZnO sample-types, which also contributed to their excellent gas sensing performance.

Highlights

IntroductionSemiconductor gas sensors (SGS) based on metal oxides (e.g., SnO2, ZnO, In2O3, WO3, TiO2)
Semiconductor gas sensors (SGS) based on metal oxides (e.g., SnO2, ZnO, In2O3, WO3, TiO2)continue to draw attention due to increased demands for environmental monitoring and protection in both industrial or domestic gas detection settings [1,2,3,4,5]
It should be noted that the morphology of F4 became less uniform than the samples prepared at lower concentration, which is probably due to faster crystal growth kinetics at high reactant concentration

Summary

Introduction

Semiconductor gas sensors (SGS) based on metal oxides (e.g., SnO2, ZnO, In2O3, WO3, TiO2). The strong dependence of electrical resistance on interfacial effects, grain boundaries and inter-particle contacts in these devices means performance of SGS may be significantly influenced by the size, morphology and surface atomic structures of the gas sensing materials [8,10,11,12,13]. For this reason, a particular recent focus of the SGS field has been the synthesis of metal oxides with different morphologies and crystal structures [14,15]. SGS response could be attributed to the high porosity of the material, combined with what is effectively an active site concentration-effect arising through reactivity of the ZnO {0001} facets toward the target gas

Synthesis of 3D ZnO Porous Structures

Characterization

Sensor Fabrication and Gas Sensing Test

Results and Discussion

Conclusions