Abstract
Halloysite-polypyrrole-silver nanocomposite has been prepared via in situ photopolymerizations of pyrrole in the presence of silanized halloysite and silver nitrate as a photoinitiator. The halloysite nanoclay (HNT) was modified using the hydrogen donor silane coupling agent (DMA) in order to provide anchoring sites for the polypyrrole/silver composite (PPy@Ag). The mass loadings for both PPy and Ag have been estimated to be 21 and 26 wt%, respectively. The anchored Ag particles were found in the metallic state. The resulting PPy@Ag-modified silanized HNT has been evaluated for the potential application for impedance humidity sensors. HNT-DMA-PPy@Ag nanocomposite with different weight % of PPy@Ag (0.25 wt%, 0.5 wt%, and 1 wt%) was deposited on the pre-patterned interdigital Indium Tin Oxide (ITO) electrodes by spin coating technique. The addition of Ag nanoparticles within the nanocomposite enhances the hydrophilicity of the sensing film, which improves the sensitivity of the humidity sensors. The HNT-DMA-PPy@Ag (0.5 wt%) nanocomposite-based impedance sensors showed good sensitivity and lowered hysteresis as compared to the other ratios of the composite. The maximum calculated hysteresis loss of the HNT-DMA-PPy@Ag (0.5 wt%)-based humidity sensor is around 4.5% at 80% RH (relative humidity), and the minimum hysteresis loss estimated to be 0.05% at 20% RH levels. The response and recovery time of HNT-DMA-PPy@Ag (0.5 wt%) nanocomposite-based impedance sensors were found to be 30 and 35 s, respectively. The interesting humidity-dependent impedance properties of this novel composite make it promising in humidity sensing.
Highlights
Humidity sensors are widely used in environmental monitoring, in the human comfort zones and industrial manufacturing processes [1]
The contemporary need for high-performance humidity sensors has led to rigorous research and development (R&D) in this area during the last decade
Previous studies showed that ceramic materials doped with silver nanoparticles, as proven to have a positive effect on the efficiency of humidity sensors, with the addition of an optimized concentration of silver was proven to improve the sensitivity of the sensors and reduce the response time compared to pristine [11,20]
Summary
Humidity sensors are widely used in environmental monitoring, in the human comfort zones and industrial manufacturing processes [1]. We reasoned modifying the HNT surface with hydrogen donor silane in a similar way to silica and other reported materials [19], this will induce the formation of PPy rich surface with the presence of silver nanoparticles in metallic state, as previously reported in our group, on silica and bentonite clay [11,19]. In this way, we aimed to design new hybrid functional materials (relevant to humidity sensing) by valorizing HNT natural nanoclay. HNT nanocomposite, doped with silver nanoparticles as well as PPy, are expected to present superior humidity sensing properties due to their ability to improve electrical properties of HNT, as well as their high water vapor molecules adsorption capabilities, through the pore openings present in PPy surface
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