Gr/3D-ZnO Nanocomposites as Humidity Sensors with Enhanced Sensing Response.

Wang-De Lin,Murthy Chavali,You-Chen Lin,Ren-Jang Wu

doi:10.3390/polym13101623

Abstract

This work introduces a novel humidity sensor based on a nanocomposite material comprising graphene decorated with three-dimensional flower-like structures of zinc oxide (Gr/3D–ZnO) fabricated via a hydrothermal method with various weight percentages of graphene. The surface structure and morphology of the Gr/3D–ZnO nanocomposite were analyzed using XRD, EDS, SEM, TEM, and Raman spectroscopy. The influence of humidity on the electrical properties of the nanocomposite was also investigated. Experiment results revealed that the nanocomposite with 70 wt% of graphene provided high sensitivity (S = 446) with rapid response times (120 s) and recovery times (160 s). These results demonstrate the excellent potential of the proposed Gr/3D–ZnO nanocomposite in monitoring atmospheric humidity. A discussion on the mechanism underlying the effects of humidity on the Gr/3D–ZnO nanocomposite is also provided.

Highlights

Atmospheric levels of water vapor can profoundly affect electronic devices, meteorological phenomena, agriculture, manufacturing, and food storage [1]
Numerous types of humidity sensors have been developed using resistive [4,5] and capacitive devices [6,7], quartz crystal microbalances [8,9,10], optical devices [11,12], and even surface acoustic waves [13,14]. This very particular research has led to the development of materials and nanostructures that are highly sensitive to humidity, including TiO2 nanopowders [15] and nanotubes [16], Zinc oxide (ZnO) nanowires [17], WO3 nanosheets [18], Fe2O3 nanopowders [19], graphene layers [20], organic/inorganic polymers [21], ZrO2 nanorods [22], and NiO-SnO2 nanofibers [23]
Among the various metal oxides used for humidity sensing, n-type Zinc oxide (ZnO) semiconductors offer low cost, a high surface area ratio, high stability, and excellent chemical reactivity [24]

Summary

Introduction

Atmospheric levels of water vapor (i.e., humidity) can profoundly affect electronic devices, meteorological phenomena, agriculture, manufacturing, and food storage [1]. Numerous types of humidity sensors have been developed using resistive [4,5] and capacitive devices [6,7], quartz crystal microbalances [8,9,10], optical devices [11,12], and even surface acoustic waves [13,14] This very particular research has led to the development of materials and nanostructures that are highly sensitive to humidity, including TiO2 nanopowders [15] and nanotubes [16], ZnO nanowires [17], WO3 nanosheets [18], Fe2O3 nanopowders [19], graphene layers [20], organic/inorganic polymers [21], ZrO2 nanorods [22], and NiO-SnO2 nanofibers [23]. Tests were performed on nanocomposite sensing materials fabricated using graphene in various ratios (10, 20, 30, 50, 70, and 80 wt%)

Characterization

Sensor Fabrication and Humidity Testing

Characterization of the Nanocomposite Structure

Conclusions