SnO2 highly sensitive CO gas sensor based on quasi-molecular-imprinting mechanism design

Template Imprinting Versus Porogen Imprinting of Small Molecules: A Review of Molecularly Imprinted Polymers in Gas Sensing

The selective sensing of gaseous target molecules is a challenge to analytical chemistry. Selectivity may be achieved in liquids by several different methods, but many of these are not suitable for gas-phase analysis. In this review, we will focus on molecular imprinting and its application in selective binding of volatile organic compounds and atmospheric pollutants in the gas phase. The vast majority of indexed publications describing molecularly imprinted polymers for gas sensors and vapour monitors have been analysed and categorised. Specific attention was then given to sensitivity, selectivity, and the challenges of imprinting these small volatile compounds. A distinction was made between porogen (solvent) imprinting and template imprinting for the discussion of different synthetic techniques, and the suitability of each to different applications. We conclude that porogen imprinting, synthesis in an excess of template, has great potential in gas capture technology and possibly in tandem with more typical template imprinting, but that the latter generally remains preferable for selective and sensitive detection of gaseous molecules. More generally, it is concluded that gas-phase applications of MIPs are an established science, capable of great selectivity and parts-per-trillion sensitivity. Improvements in the fields are likely to emerge by deviating from standards developed for MIP in liquids, but original methodologies generating exceptional results are already present in the literature.

Additive Manufacturing of a Flexible Carbon Monoxide Sensor Based on a SnO2-Graphene Nanoink

Carbon monoxide (CO) gas is an odorless toxic combustion product that rapidly accumulates inside ordinary places, causing serious risks to human health. Hence, the quick detection of CO generation is of great interest. To meet this need, high-performance sensing units have been developed and are commercially available, with the vast majority making use of semiconductor transduction media. In this paper, we demonstrate for the first time a fabrication protocol for arrays of printed flexible CO sensors based on a printable semiconductor catalyst-decorated reduced graphene oxide sensor media. These sensors operate at room temperature with a fast response and are deposited using high-throughput printing and coating methods on thin flexible substrates. With the use of a modified solvothermal aerogel process, reduced graphene oxide (rGO) sheets were decorated with tin dioxide (SnO2) nanoscale deposits. X-ray diffraction data were used to show the composition of the material, and high-resolution X-ray photoelectron spectroscopy (XPS) characterization showed the bonding status of the sensing material. Moreover, a very uniform distribution of particles was observed in scanning (SEM) and transmission electron microscopy (TEM) images. For the fabrication of the sensors, silver (Ag) interdigitated electrodes were inkjet-printed from nanoparticle inks on plastic substrates with 100 µm linewidths and then coated with the SnO2-rGO nanocomposite by inkjet or slot-die coating, followed by a thermal treatment to further reduce the rGO. The detection of 50 ppm of CO in nitrogen was demonstrated for the devices with a slot-die coated active layer. A response of 15%, response time of 4.5 s, and recovery time of 12 s were recorded for these printed sensors, which is superior to other previously reported sensors operating at room temperature.

Identification and Statistical Analysis of Impulse-Like Patterns of Carbon Monoxide Variation in Deep Underground Mines Associated with the Blasting Procedure

The quality of the air in underground mines is a challenging issue due to many factors, such as technological processes related to the work of miners (blasting, air conditioning, and ventilation), gas release by the rock mass and geometry of mine corridors. However, to allow miners to start their work, it is crucial to determine the quality of the air. One of the most critical parameters of the air quality is the carbon monoxide (CO) concentration. Thus, in this paper, we analyze the time series describing CO concentration. Firstly, the signal segmentation is proposed, then segmented data (daily patterns) is visualized and statistically analyzed. The method for blasting moment localization, with no prior knowledge, has been presented. It has been found that daily patterns differ and CO concentration values reach a safe level at a different time after blasting. The waiting time to achieve the safe level after blasting moment (with a certain probability) has been calculated based on the historical data. The knowledge about the nature of the CO variability and sources of a high CO concentration can be helpful in creating forecasting models, as well as while planning mining activities.

PdO/SnO2 heterostructure for low-temperature detection of CO with fast response and recovery

In this paper, we developed a simple two-step route to prepare a PdO/SnO₂ heterostructure with the diameter of the SnO₂ and PdO nanoparticles at about 15 nm and 3 nm, respectively.

A Three-Step Resolution-Reconfigurable Hazardous Multi-Gas Sensor Interface for Wireless Air-Quality Monitoring Applications

This paper presents a resolution-reconfigurable wide-range resistive sensor readout interface for wireless multi-gas monitoring applications that displays results on a smartphone. Three types of sensing resolutions were selected to minimize processing power consumption, and a dual-mode front-end structure was proposed to support the detection of a variety of hazardous gases with wide range of characteristic resistance. The readout integrated circuit (ROIC) was fabricated in a 0.18 μm CMOS process to provide three reconfigurable data conversions that correspond to a low-power resistance-to-digital converter (RDC), a 12-bit successive approximation register (SAR) analog-to-digital converter (ADC), and a 16-bit delta-sigma modulator. For functional feasibility, a wireless sensor system prototype that included in-house microelectromechanical (MEMS) sensing devices and commercial device products was manufactured and experimentally verified to detect a variety of hazardous gases.

Gas Sensors Based on Molecular Imprinting Technology

Molecular imprinting technology (MIT); often described as a method of designing a material to remember a target molecular structure (template); is a technique for the creation of molecularly imprinted polymers (MIPs) with custom-made binding sites complementary to the target molecules in shape; size and functional groups. MIT has been successfully applied to analyze; separate and detect macromolecular organic compounds. Furthermore; it has been increasingly applied in assays of biological macromolecules. Owing to its unique features of structure specificity; predictability; recognition and universal application; there has been exploration of the possible application of MIPs in the field of highly selective gas sensors. In this present study; we outline the recent advances in gas sensors based on MIT; classify and introduce the existing molecularly imprinted gas sensors; summarize their advantages and disadvantages; and analyze further research directions.

Aerosol assisted chemical vapour deposition of gas sensitive SnO2 and Au-functionalised SnO2 nanorods via a non-catalysed vapour solid (VS) mechanism

Tin oxide nanorods (NRs) are vapour synthesised at relatively lower temperatures than previously reported and without the need for substrate pre-treatment, via a vapour-solid mechanism enabled using an aerosol-assisted chemical vapour deposition method. Results demonstrate that the growth of SnO2 NRs is promoted by a compression of the nucleation rate parallel to the substrate and a decrease of the energy barrier for growth perpendicular to the substrate, which are controlled via the deposition conditions. This method provides both single-step formation of the SnO2 NRs and their integration with silicon micromachined platforms, but also allows for in-situ functionalization of the NRs with gold nanoparticles via co-deposition with a gold precursor. The functional properties are demonstrated for gas sensing, with microsensors using functionalised NRs demonstrating enhanced sensing properties towards H2 compared to those based on non-functionalised NRs.

Enhanced CO gas sensing properties of Cu doped SnO2 nanostructures prepared by a facile wet chemical method

Cu doped SnO₂ nanosheets and nanodiscs exhibit highly enhanced CO gas sensing properties and excellent selectivity for CO gas.