Carboxylated Single-Walled Carbon Nanotube Sensors with Varying pH for the Detection of Ammonia and Carbon Dioxide Using an Artificial Neural Network

Abstract

Single-walled carbon nanotubes (SWCNTs) have long been advocated for the detection of various gases and vapors. Often, strategies to modify the nanotubes have been shown to be successful in eliciting a more sensitive response from the nanotubes when exposed to the target gas relative to the pristine material. Carboxylation of the SWCNTs is one such strategy commonly used in gas sensor construction. Interestingly, addition of acid or base to the carboxylation process can change the pH of the resulting material and yield inks with varying pH values that can be used in a sensor array. Here we show orthogonal responses to NH3 and CO2 from eight such materials with controlled pH values in the range of 1.9–12.1. The results and the approach will be applicable to sensing other acidic and basic gases and also can expand further to other sensor systems to maximize and obtain orthogonal sensor responses. A neural network architecture is used successfully to convert the measured resistance change into analyte concentration.

Atmospheric Pressure Plasma Printing of Nanomaterials for IoT Applications

“…In another channel of the sensor chip using carboxylic acid functionalized SWCNTs, the corresponding responses were higher at 2.5, 15 and 24%. The sensor response and detection limit obtained here are comparable to previous ammonia sensors on flexible and other substrates [39,40,42,43] confirming the suitability of the plasma printed samples for gas sensing applications. Additional variations in nanotubes can include doping, different functionalizations [42], metal loading etc.…”

“…SEM images of the SWCNT prints are shown in Figure 9 where the nanotubes were deposited on a PCB chip consisting of 16 sensors suitable for gas sensing. The resistance across all 16 channels of the PCB chip is in the range of 255 ohms to 2 Mohms, favorable for gas sensing applications [40]. In principle, multiple materials up to sixteen different candidates (CNTs, graphene, oxides etc.)…”

Composites of ion-in-conjugation polysquaraine and SWCNTs for the detection of H2S and NH3 at ppb concentrations

“…Accordingly, to fully exploit the advantageous sensing propeties of the reported composites, further exploration of sensing in analyte mixtures is needed, and should be combined with systematic data processing e.g. principal and multi-component analyses, pattern recognition and machine learning [71][72][73][74].…”

Explosive molecule sensing at lattice defect sites in metallic carbon nanotubes

“…Other chiralities might offer surface curvature or other properties with sensing advantages. With regards to data analysis, machine learning methods [84][85][86] merit close attention as a possible means to make more effective use of sensor array measurements.…”