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. 2017 Mar 24;17(4):675.
doi: 10.3390/s17040675.

A Formaldehyde Sensor Based on Molecularly-Imprinted Polymer on a TiO₂ Nanotube Array

Xiaohui Tang  1 , Jean-Pierre Raskin  2 , Driss Lahem  3 , Arnaud Krumpmann  4 , André Decroly  5 , Marc Debliquy  6
Affiliations

A Formaldehyde Sensor Based on Molecularly-Imprinted Polymer on a TiO₂ Nanotube Array

Xiaohui Tang et al. Sensors (Basel). .

Abstract

Today, significant attention has been brought to the development of sensitive, specific, cheap, and reliable sensors for real-time monitoring. Molecular imprinting technology is a versatile and promising technology for practical applications in many areas, particularly chemical sensors. Here, we present a chemical sensor for detecting formaldehyde, a toxic common indoor pollutant gas. Polypyrrole-based molecularly-imprinted polymer (PPy-based MIP) is employed as the sensing recognition layer and synthesized on a titanium dioxide nanotube array (TiO₂-NTA) for increasing its surface-to-volume ratio, thereby improving the sensor performance. Our sensor selectively detects formaldehyde in the parts per million (ppm) range at room temperature. It also shows a long-term stability and small fluctuation to humidity variations. These are attributed to the thin fishnet-like structure of the PPy-based MIP on the highly-ordered and vertically-aligned TiO₂-NTA.

Keywords: formaldehyde sensor; humidity influence; molecularly-imprinted polypyrrole; titanium dioxide nanotube array.

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Conflict of interest statement

The authors declare no conflict of interest. The founding sponsors had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript, and in the decision to publish the results.

Figures

Figure 1
Figure 1
(a) Schematic cross-section of the polypyrrole-based MIP/TiO2-NTA sensor, showing the molecularly-imprinted polypyrrole synthesized on TiO2 nanotube array; (b) schematic illustration of the electropolymerization system; (c) chemical scheme illustrations ((i) polymerization mechanism of polypyrrole, (ii) structure of pyrrole-carboxylic, and (iii) specific bond of pyrrole-carboxylic with formaldehyde); (d) quartz crystal wafers with circular gold electrodes and with the polypyrrole-based MIP layer; and (e) image of the gas sensing setup.
Figure 2
Figure 2
Scanning electron microscope images of (a) top view of TiO2 nanotube array, (b) cross-section view of TiO2 nanotube array, (c) thin layer of molecularly-imprinted polypyrrole synthesized on a TiO2 nanotube array, (d) zoom of (c); and (e) thick polypyrrole film on the flat substrate.
Figure 3
Figure 3
FTIR spectra of (a) molecularly-imprinted polypyrrole films synthesized without the HCHO template, with HCHO template, and after removing the HCHO template; and (b) zoom on the insert circle in (a).
Figure 4
Figure 4
Energy dispersive X-ray spectroscopy spectra of (a) molecularly-imprinted polypyrrole; (b) TiO2 nanotube array; and (c) Ti sheet substrate.
Figure 5
Figure 5
Mass changes for molecularly-imprinted polypyrrole films synthesized on quartz crystal wafers (a) with and (b) without HCHO template, showing uptake during 33 ppm HCHO injections at 22 °C in 50% RH air.
Figure 6
Figure 6
Mass changes for molecularly imprinted polypyrrole films synthesized on quartz crystal wafers, uptake during (a) 30 ppm C2H4O; (b) 35 ppm C2H4O2; and (c) 40 ppm C2H6O at 22 °C in 50% RH air.
Figure 7
Figure 7
Conductance behaviors of (a) polypyrrole-based MIP/TiO2-NTA sensor for detecting 1 ppm HCHO; (b) TiO2 nanotube array for detecting 50 ppm HCHO; (c) dependence between conductance responses and HCHO concentrations for the polypyrrole-based MIP/TiO2-NTA sensor; and (d) conductance responses after the polypyrrole-based MIP/TiO2-NTA sensor exposed to five cycles of 5 ppm HCHO.
Figure 8
Figure 8
Polypyrrole-based MIP/TiO2-NTs sensor for detecting (a) acetone-saturated vapor (‎C3H6O, 23.7%) and (b) 5 ppm ethanol (C2H6O).
Figure 9
Figure 9
Conductance behavior of the polypyrrole-based MIP/TiO2-NTA sensor for the humidity range from 35% to 95% at 22 °C.
Figure 10
Figure 10
Chemical scheme illustration for the cavities on the polypyrrole-based MIP layer to detect formaldehyde.
See this image and copyright information in PMC

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