Chemiresistive gas sensors have been widely applied to monitor analytes of environmental, food and health importance. Among the plethora of materials that can be used for designing chemiresistive sensors, ZnO is one of the most explored for gas sensing, as this material has a low-cost, is non-toxic and can be easily obtained through standard chemical synthesis. Adding to this, ZnO can form heterostructures capable to improve sensor performance regarding sensitivity, selectivity and stability. Moreover, ZnO heterostructures also contribute to lower operating temperature of gas sensors, since the synergistic effects contribute to amplify the sensor signal. In this review, we survey recent advances on different types of chemiresistive ZnO-based gas sensors, focusing on how the morphology and structure of these materials influence on the sensor response. Challenges and future perspectives for ZnO chemiresistive sensors are also discussed. 

A Review on Chemiresistive ZnO Gas Sensors

This paper provides an overview of recent developments in the field of volatile organic compound (VOC) sensors, which are finding uses in healthcare, safety, environmental monitoring, food and agriculture, oil industry, and other fields. It starts by briefly explaining the basics of VOC sensing and reviewing the currently available and quickly progressing VOC sensing approaches. It then discusses the main trends in materials' design with special attention to nanostructuring and nanohybridization. Emerging sensing materials and strategies are highlighted and their involvement in the different types of sensing technologies is discussed, including optical, electrical, and gravimetric sensors. The review also provides detailed discussions about the main limitations of the field and offers potential solutions. The status of the field and suggestions of promising directions for future development are summarized.

Sensors for Volatile Organic Compounds.

Edge-enriched MoS2 nanosheets modified porous nanosheet-assembled hierarchical In2O3 microflowers for room temperature detection of NO2 with ultrahigh sensitivity and selectivity.

Semiconducting metal oxide based gas sensors are a highly attractive option for use in a widespread array of applications as they can be miniaturized, are highly robust and inexpensive. This review focuses on SnO2, In2O3 and WO3, three commonly used metal oxides that are known to show a diversity in sensing behavior. In order to optimize the sensing behavior, it is imperative that the mechanism is understood. It is unanimously agreed upon that adsorption of oxygen and the resulting charge layer play a central role in the sensor response. Surface oxygen had proven to be illusive experimentally. Recent insights gained from operando methods, sophisticated surface science analysis tool and theoretical calculations are discussed. Additionally, these studies have revealed that the surface reactions are far more complicated than initially assumed. It is found that other adsorbates beyond oxygen can influence the sensor response. Depending on the site, the formation of adsorbates can have different effects on the sensor depending on the reaction site, e.g. hydroxyl group formation from humidity can result in the removal of negative charge or be electroneutral. The importance of understanding the effect of adsorbates becomes particularly evident when examining the chemically complicated volatile organic compounds, e.g. ethanol and acetone. In this review simplified schematics based on insights from theoretical and experimental studies are developed, so that the surface chemistry can be presented in an understandable manner despite its complexity. 

Current state of knowledge on the metal oxide based gas sensing mechanism

Since the third scientific and technological revolution, electronic information technology has developed rapidly, and piezoelectric materials that can convert mechanical energy into electrical energy have become a research hotspot. Among them, piezoelectric polymers are widely used in various fields such as water treatment, biomedicine, and flexible sensors due to their good flexibility and weak toxicity. However, compared with ceramic piezoelectric materials, the piezoelectric properties of polymers are poor, so it is very important to improve the piezoelectric properties of polymers. Electrospinning technology can improve the piezoelectric properties of piezoelectric polymers by adjusting electrospinning parameters to control the piezoelectrically active phase transition of polymers. In addition, the prepared nanofibrous membrane is also a good substrate for supporting piezoelectric functional particles, which can also effectively improve the piezoelectric properties of polymers by doping particles. This paper reviews the piezoelectric properties of various electrospun piezoelectric polymer membranes, especially polyvinylidene fluoride (PVDF)-based electrospun nanofibrous membranes (NFs). Additionally, this paper introduces the various methods for increasing piezoelectric properties from the perspective of structure and species. Finally, the applications of NFs in the fields of biology, energy, and photocatalysis are discussed, and the future research directions and development are prospected.

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Processes of Electrospun Polyvinylidene Fluoride-Based Nanofibers, Their Piezoelectric Properties, and Several Fantastic Applications

1D Metal Oxide Semiconductor Materials for Chemiresistive Gas Sensors: A Review

Determination of eight neonicotinoid insecticides in Chinese cabbage using a modified QuEChERS method combined with ultra performance liquid chromatography-tandem mass spectrometry.

Piezo-photocatalytic flexible PAN/TiO2 composite nanofibers for environmental remediation.

A simple, fast and reliable analytical method was developed for 20 free amino acids (FAAs) determination in honey samples through a dilute-and-shoot strategy and hydrophilic interaction liquid chromatography tandem mass spectrometry. Compared with previous reports, direct dilution by water has significantly reduced the matrix effect and facilitated full extraction of FAAs. Further, a 5 min determination method was established with an acetonitrile–water mobile phase system with 0.1% formic acid addition. The established method was validated and demonstrated several advantages including short detection time, wide linear range over 3–4 orders of magnitude, high sensitivity down to 0.1 ng/mL and negligible matrix effect. Twenty FAAs were determined in 10 honey samples from different botanical origins by this method, and 19 FAAs were found. This general applicable method was also promising for fast determination of FAAs in other practical samples.

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Development of a Simple, Underivatized Method for Rapid Determination of Free Amino Acids in Honey Using Dilute-and-Shoot Strategy and Liquid Chromatography-Tandem Mass Spectrometry

Bingxin Yang

Papers

1D Metal Oxide Semiconductor Materials for Chemiresistive Gas Sensors: A Review

Determination of eight neonicotinoid insecticides in Chinese cabbage using a modified QuEChERS method combined with ultra performance liquid chromatography-tandem mass spectrometry.

Piezo-photocatalytic flexible PAN/TiO2 composite nanofibers for environmental remediation.

Development of a Simple, Underivatized Method for Rapid Determination of Free Amino Acids in Honey Using Dilute-and-Shoot Strategy and Liquid Chromatography-Tandem Mass Spectrometry

Impurity identification in thiamethoxam by high resolution mass spectrometry and computer assisted elucidation