Chemiresistor gas sensors based on photoconductivity changes in phthalocyanine thin films: enhancement of response toward ammonia by photoelectrochemical deposition with metal modifiers

Abstract

Determination of NH3 in flowing N2 or air Is demonstrated by monitoring changes in the photoconductivity of chlorolndlum phthalocyanine (InPc-CI) and chlorogalllum phthalocyanine (GaPc-CI) thin films vacuum deposited on platinum silicide Interdlgltated array microcircuits. Photoconductivity changes were measured, as opposed to the more commonly measured dark conductivity changes, yielding reasonable sensitivity to the adsorption of submonolayer amounts of gas analytes such as NH3. Photoelectrochemical modification of Pc-coated microcircuits was carried out in order to obtain submonolayer coverages of a variety of different metals (Ag, Au, Cu, Pt, and Hg) on the Pc film. This modification apparently provides new chemisorption sites for NH3, thus improving the performance of these microcircuit assemblies as NH3 sensors In N2 and In air. The Hg-modlfied microcircuits demonstrated a superior performance compared to the microcircuits modified with other metals, by showing a linear photocurrent response as a function of NH3 concentration In N2 at room temperature over the range from ca. 1.5 to 5.4 ppm, and a logarithmic relationship above that level (up to ca. 84 ppm). Photoconductivity measurements in NH3-air mixtures were carried out on microcircuit assemblies "as-prepared" and after photoelectrochemical modification. The presence of the metal modifier on the InPc-CI film markedly Improves the assembly performance In air, providing a detection limit for NH3 in air of ca. 1.0 part per thousand (ppt). The effect on the photoconductivity of 02 and other impurities present in GaPc-CI and InPc-CI Is discussed, and a mechanism Is proposed to explain the variations observed In the photocurrent response to NH3 in these assemblies before and after modification.

Rapid, Trace‐Level Ammonia Gas Sensor Based on Surface‐Engineered Ag Nanoclusters@Polyaniline/Multiwalled Carbon Nanotubes and Insights into Their Mechanistic Pathways

“…Apart from this, un‐oxidized Ag + complexed with PANI also could be present at inner layers which could facilitate the net charge transfer in the AgNC@PANI/MWCNT nanocomposite as represented in scheme 1(b). Complexation of Ag + with benzenoid imine (‐NH‐) groups of PANI makes these –N–H groups to be electron deficient at these sites . This in‐turn enhances the interaction of NH 3 with PANI.…”

“…proved the enhancement in the NH 3 gas sensing behavior of MWCNT by doping Ag NCs, which act as a dominant active adsorption site with the help of Density Functional Theory (DFT) analysis . In other case, metal doping in PANI generally results in the hybridization of metal and polymer thereby creates a new class of material which enrich the property library and broaden their application . Specifically, in Ag/PANI nanocomposites, the introduction of Ag the most conductive metal in to the PANI has been studied widely for various applications and many efforts have been devoted on the synthesis of Ag‐PANI and composites, using various procedures and being analyzed by different characterization techniques for gas sensing and other applications .…”

Study of the sensor response of spun metal phthalocyanine films to volatile organic vapors using surface plasmon resonance

“…The study of the photoconductivity changes of ClGaPc and ClInPc films has been employed in improving the detection of NH 3 and NO 2 [26,27]. Note that in all cited work thermal evaporation was used as a conventional method for the deposition of thin films of unsubstituted metal phthalocyanines.…”

Effect of post‐deposition annealing on surface morphology and gas sensing properties of palladium phthalocyanine thin films

“…Particular interests have been shown in phthalocyanine thin films, primarily for NO 2 and NH 3 . In our laboratory, extensive studies were carried out on using PdPc nanostructure thin films as active layers to fabricate gas sensors.…”