Insights about CO Gas-Sensing Mechanism with NiO-Based Gas Sensors—The Influence of Humidity

Recent Progress on Potentiometric Sensor Applications Based on Nanoscale Metal Oxides: A Comprehensive Review

Electrochemical sensors have been the subject of much research and development as of late, with several publications detailing new designs boasting enhanced performance metrics. That is, without a doubt, because such sensors stand out from other analytical tools thanks to their excellent analytical characteristics, low cost, and ease of use. Their progress has shown a trend toward seeking out novel useful nano structure materials. A variety of nanostructure metal oxides have been utilized in the creation of potentiometric sensors, which are the subject of this article. For screen-printed pH sensors, metal oxides have been utilized as sensing layers due to their mixed ion-electron conductivity and as paste-ion-selective electrode components and in solid-contact electrodes. Further significant uses include solid-contact layers. All the metal oxide uses mentioned are within the purview of this article. Nanoscale metal oxides have several potential uses in the potentiometry method, and this paper summarizes such uses, including hybrid materials and single-component layers. Potentiometric sensors with outstanding analytical properties can be manufactured entirely from metal oxides. These novel sensors outperform the more traditional, conventional electrodes in terms of useful characteristics. In this review, we looked at the potentiometric analytical properties of different building solutions with various nanoscale metal oxides.

Road Map of Semiconductor Metal-Oxide-Based Sensors: A Review

Identifying disease biomarkers and detecting hazardous, explosive, flammable, and polluting gases and chemicals with extremely sensitive and selective sensor devices remains a challenging and time-consuming research challenge. Due to their exceptional characteristics, semiconducting metal oxides (SMOxs) have received a lot of attention in terms of the development of various types of sensors in recent years. The key performance indicators of SMOx-based sensors are their sensitivity, selectivity, recovery time, and steady response over time. SMOx-based sensors are discussed in this review based on their different properties. Surface properties of the functional material, such as its (nano)structure, morphology, and crystallinity, greatly influence sensor performance. A few examples of the complicated and poorly understood processes involved in SMOx sensing systems are adsorption and chemisorption, charge transfers, and oxygen migration. The future prospects of SMOx-based gas sensors, chemical sensors, and biological sensors are also discussed.

High sensitivity carbon monoxide detector using iron tetraphenyl porphyrin functionalized reduced graphene oxide

The detection of pollutant and toxic gases has attracted extensive attention due to the growing environmental issues. In the present investigation, free-based tetraphenyl porphyrin (TPP) and iron tetraphenyl porphyrin (FeTPP) are used to functionalize thermally reduced graphene oxide (rGO) and further used for the detection of carbon monoxide (CO). TPP and FeTPP functionalized rGO (FeTPP@rGO) sensors are fabricated on a glass substrate with thermally coated copper electrodes. The materials are characterized with X-ray diffraction (XRD), Fourier transforms infrared (FTIR) spectroscopy, Raman spectroscopy, UV-visible spectroscopy, atomic force microscopy, scanning electron microscopy, and energy dispersive spectroscopy. The current-voltage (I-V) characteristics have also been studied to demonstrate the operation of the device. In addition, the FeTPP@rGO device shows high sensitivity toward the detection of CO. By testing in the chemiresistive sensing modality, the as-fabricated device shows good response and recovery of 60 s and 120 s, respectively, with a low detection limit of 2.5 ppm.

Effects of Calcination Temperature on CO-Sensing Mechanism for NiO-Based Gas Sensors

NiO-sensitive materials have been synthesized via the hydrothermal synthesis route and calcined in air at 400 °C and, alternatively, at 500 °C. Structural, morphological, and spectroscopic investigations were involved. As such, the XRD patterns showed a higher crystallinity degree for the NiO calcined at 500 °C. Such an aspect is in line with the XPS data indicating a lower surface hydroxylation relative to NiO calcined at 400 °C. An HRTEM microstructural investigation revealed that the two samples differ essentially at the morphological level, having different sizes of the crystalline nanoparticles, different density of the surface defects, and preferential faceting according to the main crystallographic planes. In order to identify their specific gas-sensing mechanism towards CO exposure under the in-field atmosphere, the simultaneous evaluation of the electrical resistance and contact potential difference was carried out. The results allowed the decoupling of the water physisorption from the chemisorption of the ambient oxygen species. Thus, the specific CO interaction mechanism induced by the calcination temperature of NiO has been highlighted.