Zn2+-Doped TiO2:WO3 Films Prepared by Electrospinning and Sintering: Microstructural Characterization and Electrical Signature to Moisture Sensing

Georgenes M G Silva,Pedro M Faia,Victor N S Leão,Michel F G Pereira,Evando S Araújo

doi:10.3390/ceramics4040041

Abstract

In this work, Zn2+-doped TiO2:WO3 nanostructured films, with different doping levels, were produced by electrospinning followed by sintering, and tested as potential materials for relative humidity (RH) detection. The materials microstructure was investigated by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), Fourier-transform infrared spectroscopy (FTIR), Raman spectroscopy, and X-ray diffraction (XRD). The electrical characterization was performed by electrical impedance spectroscopy in the range of 400 HZ–40 MHZ, at 20 °C. The sensors’ sensitivity to moisture was evaluated from the impedance variations in response to changes in RH (10–100%). The analyses confirmed the interaction of water molecules with the oxides surface, and showed that zinc atoms were incorporated into the titanium vacancies in the crystal lattice. All the studied sensors showed a p- to n-type conduction transition taking place at around 40% RH. The nanocomposite with 2 wt% of dopant presented the best sensitivity to moisture, with an impedance variation of about 1 order of magnitude. The results are discussed in relation to the microstructure and fabrication route.

Highlights

Relative humidity (RH) is one of the most important environmental parameters for prevention and monitoring of a wide variety of processes in medical, food and industrial sectors [1].Moisture sensors are the most commonly used instruments in monitoring this parameter
The surface morphology analysis returned regular diameter composite fibers with no apparent structural defects, indicating that the electrospinning process parameters were adequate for preparation of these materials
The present results showed that doping is a highly valuable path that can be used to improve metal oxide heterogeneous nanostructures (MOHN) moisture electrical response

Summary

Introduction

Relative humidity (RH) is one of the most important environmental parameters for prevention and monitoring of a wide variety of processes in medical, food and industrial sectors [1].Moisture sensors are the most commonly used instruments in monitoring this parameter. Titanium (IV) oxide (TiO2 )-based metal oxide heterogeneous nanostructures (MOHN) have been receiving increasing interest, and have been studied as potential materials for the development of high sensitivity and low cost moisture sensing devices [7] In this configuration, the interaction at the atomic and surface level between TiO2 and the other oxide constituents enables the improvement of the electrical and structural properties of the resulting material (when compared to the use of pure TiO2 ) and, the moisture sensing [7]. The choice of selective oxides, dopant ions and fabrication route are other factors that directly influence the obtention of sensors with high surface area/volume ratio, and higher sensitivity to RH [8] In this sense, Zanetti et al [9] showed that the addition of tungsten (VI) oxide (WO3 ) to TiO2 by sintering improves the stability of the TiO2 anatase phase and the sensitivity to relative humidity, due to the occurrence of surface heterojunction between the oxides. The results still revealed decreasing pore size and smaller variance in particle size distribution, which improves the chemisorption of water molecules on the semiconductors surface

Methods

Results

Conclusion