High-performance gas sensors prepared using p-type oxide semiconductors such as NiO, CuO, Cr2O3, Co3O4, and Mn3O4 were reviewed. The ionized adsorption of oxygen on p-type oxide semiconductors leads to the formation of hole-accumulation layers (HALs), and conduction occurs mainly along the near-surface HAL. Thus, the chemoresistive variations of undoped p-type oxide semiconductors are lower than those induced at the electron-depletion layers of n-type oxide semiconductors. However, highly sensitive and selective p-type oxide-semiconductor-based gas sensors can be designed either by controlling the carrier concentration through aliovalent doping or by promoting the sensing reaction of a specific gas through doping/loading the sensor material with oxide or noble metal catalysts. The junction between p- and n-type oxide semiconductors fabricated with different contact configurations can provide new strategies for designing gas sensors. p-Type oxide semiconductors with distinctive surface reactivity and oxygen adsorption are also advantageous for enhancing gas selectivity, decreasing the humidity dependence of sensor signals to negligible levels, and improving recovery speed. Accordingly, p-type oxide semiconductors are excellent materials not only for fabricating highly sensitive and selective gas sensors but also valuable additives that provide new functionality in gas sensors, which will enable the development of high-performance gas sensors.

Highly sensitive and selective gas sensors using p-type oxide semiconductors: Overview

The analysis of various parameters of metal oxides and the search of criteria, which could be used during material selection for solid-state gas sensor applications, were the main objectives of this review. For these purposes the correlation between electro-physical (band gap, electroconductivity, type of conductivity, oxygen diffusion), thermodynamic, surface, electronic, structural properties, catalytic activity and gas-sensing characteristics of metal oxides designed for solid-state sensors was established. It has been discussed the role of metal oxide manufacturability, chemical activity, and parameter's stability in sensing material choice as well.

Metal oxides for solid-state gas sensors: What determines our choice?

Hierarchical and hollow oxide nanostructures are very promising gas sensor materials due to their high surface area and well-aligned nanoporous structures with a less agglomerated configurations. Various synthetic strategies to prepare such hierarchical and hollow structures for gas sensor applications are reviewed and the principle parameters and mechanisms to enhance the gas sensing characteristics are investigated. The literature data clearly show that hierarchical and hollow nanostructures increase both the gas response and response speed simultaneously and substantially. This can be explained by the rapid and effective gas diffusion toward the entire sensing surfaces via the porous structures. Finally, the impact of highly sensitive and fast responding gas sensors using hierarchical and hollow nanostructures on future research directions is discussed.

Gas sensors using hierarchical and hollow oxide nanostructures: Overview

Sensor technology has an important effect on many aspects in our society, and has gained much progress, propelled by the development of nanoscience and nanotechnology. Current research efforts are directed toward developing high-performance gas sensors with low operating temperature at low fabrication costs. A gas sensor working at room temperature is very appealing as it provides very low power consumption and does not require a heater for high-temperature operation, and hence simplifies the fabrication of sensor devices and reduces the operating cost. Nanostructured materials are at the core of the development of any room-temperature sensing platform. The most important advances with regard to fundamental research, sensing mechanisms, and application of nanostructured materials for room-temperature conductometric sensor devices are reviewed here. Particular emphasis is given to the relation between the nanostructure and sensor properties in an attempt to address structure-property correlations. Finally, some future research perspectives and new challenges that the field of room-temperature sensors will have to address are also discussed.

Nanostructured Materials for Room-Temperature Gas Sensors

Over the last decade, significant effort has been devoted to the applications of hierarchically structured porous materials owing to their outstanding properties such as high surface area, excellent accessibility to active sites, and enhanced mass transport and diffusion. The hierarchy of porosity, structural, morphological and component levels in these materials is key for their high performance in all kinds of applications. The introduction of hierarchical porosity into materials has led to a significant improvement in the performance of materials. Herein, recent progress in the applications of hierarchically structured porous materials from energy conversion and storage, catalysis, photocatalysis, adsorption, separation, and sensing to biomedicine is reviewed. Their potential future applications are also highlighted. We particularly dwell on the relationship between hierarchically porous structures and properties, with examples of each type of hierarchically structured porous material according to its chemical composition and physical characteristics. The present review aims to open up a new avenue to guide the readers to quickly obtain in-depth knowledge of applications of hierarchically porous materials and to have a good idea about selecting and designing suitable hierarchically porous materials for a specific application. In addition to focusing on the applications of hierarchically porous materials, this comprehensive review could stimulate researchers to synthesize new advanced hierarchically porous solids.

Applications of hierarchically structured porous materials from energy storage and conversion, catalysis, photocatalysis, adsorption, separation, and sensing to biomedicine

Copper is an essential trace metal element that significantly affects human physiology and pathology by regulating various important biological processes, including mitochondrial oxidative phosphorylation, connective tissue crosslinking, and antioxidant defense. Copper level has been proved to be closely related to the morbidity and mortality of cardiovascular diseases such as atherosclerosis, heart failure, and diabetic cardiomyopathy (DCM). Copper deficiency can induce cardiac hypertrophy and aggravate cardiomyopathy, while copper excess can mediate various types of cell death, such as autophagy, apoptosis, cuproptosis, pyroptosis, and cardiac hypertrophy and fibrosis. Both copper excess and copper deficiency lead to redox imbalance, activate inflammatory response, and aggravate diabetic cardiomyopathy. This defective copper metabolism suggests a specific metabolic pattern of copper in diabetes and a specific role in the pathogenesis and progression of DCM. This review is aimed at providing a timely summary of the effects of defective copper homeostasis on DCM and discussing potential underlying molecular mechanisms.

https://downloads.hindawi.com/journals/omcl/2022/5418376.pdf

The Molecular Mechanisms of Defective Copper Metabolism in Diabetic Cardiomyopathy

The composite powders composed of red mud (RM) and NH4H2PO4 (NH4H2PO4/RM) were successfully prepared by the anti-solvent method. The composition and structure of the NH4H2PO4/RM composite powders were characterized by the techniques of X-ray diffraction (XRD), SEM, N2 adsorption-desorption and Thermogravimetry-Differential scanning calorimetry (TG-DSC). The analysis results indicate that the as-prepared samples are composed with uniform nanoparticles and possess the porous structure. The methane explosion suppression characteristics of the NH4H2PO4/RM composite powders were tested by a 20 L spherical explosion system and a 5 L pipe test system. The results show that the NH4H2PO4/RM composite powders possess considerable suppression properties on methane explosion. When the loading content of NH4H2PO4 reached 30%, the maximum pressure and the maximum pressure rise rate of methane explosion were decreased by 35.1% and 95.8%, respectively. When comparing with no powder addition, the time to reach the pressure peak was extended from 0.07 s to 0.50 s. The NH4H2PO4/RM composite powders presented a synergistic suppression effect between NH4H2PO4 and RM, which made it exhibit considerable suppression property than that of pure NH4H2PO4 or red mud powders.

The Suppression Characteristics of NH4H2PO4/Red Mud Composite Powders on Methane Explosion

In this study, pristine palygorskite powders were used as the inhibition materials to suppress the explosion of methane-air premixed gas for the first time. The composition, porosity and pyrolysis characteristics of the powders were tested by X-ray diffraction (XRD), energy dispersive spectrometry (EDS), N2 adsorption-desorption and Thermogravimetry-differential scanning calorimetry (TG-DSC) techniques. The effects of pristine palygorskite powders concentration on the explosion pressure and the average velocity of flame propagation of the 9.5% methane-air premixed gas were tested by a 20 L spherical explosion system and a 5 L pipeline explosion system. The results indicated the pristine palygorskite powders possess a considerable suppression property on methane explosion. When the mass concentration of pristine palygorskite powders was 0.20 g·L−1, the max-pressure of methane explosion was decreased by 23.9%. The methane explosion flame propagation velocity was inhibited obviously. Owing to the excellent inhibitory performance and the advantage of low-cost and environmental harmlessness, pristine palygorskite powders are potential new materials for the application on gas explosion suppression.

Effect of Pristine Palygorskite Powders on Explosion Characteristics of Methane-Air Premixed Gas

In order to investigate the change law of the explosion characteristic parameters of hybrid mixture of coal dust and gas, and then establish an effective prediction method of these parameters, the maximum explosion pressure, explosion index, and lower explosion limit of coal dust and gas mixtures were measured in a standard 20 L spherical explosion system. Four different kinds of hybrid mixture were selected in this study and they are composed of coal dust with different components and gas respectively. According to the measured results, the change law of the explosion characteristic parameters of hybrid mixture of coal dust and gas was analyzed, and the prediction method of these parameters was discussed. The results show that the addition of gas to a coal dust cloud can obviously increase its maximum explosion pressure and explosion index and notably reduce its minimum explosion concentration. On increasing the gas equivalent ratio, the maximum explosion pressure of coal dust and gas mixture increases linearly and the explosion index increases quadratically, while the decrease curve of the lower explosion limit is nonlinear. Based on these change laws, the methods for predicting the maximum explosion pressure and the explosion index of hybrid mixture of coal dust and gas were established respectively. The applicability of the existing methods for predicting the lower explosion limit of hybrid mixture to coal dust and gas mixture was demonstrated.

Variation and Prediction Methods of the Explosion Characteristic Parameters of Coal Dust/Gas Mixtures

In this paper, montmorillonite inhibitors modified with polyhydroxy functional groups by gluconic acid (GA) were successfully prepared. The particle size distribution, composition, surface functional groups, and pyrolysis characteristics of the pure montmorillonite powders (Mt) and the gluconic acid modified powders (G-Mt) were analyzed by using a laser particle analyzer, X-ray diffraction (XRD), Fourier transform infrared (FTIR) and thermogravimetry–differential scanning calorimetry (TG-DSC), respectively. The suppression effect of Mt and G-Mt on the 9.5% methane–air premixed gas was tested in a 20 L spherical explosion device and a 5 L pipeline experimental system. The results show that G-Mt displays a much better suppression property than that of Mt. The optimal explosion suppression effect concentration of Mt or G-Mt powders is about 0.25 g·L−1. In this concentration, for G-Mt, the maximum explosion pressure declined by 26.7%, the maximum rate of pressure rise declined by 74.63%, and the time for the flame front to reach the top of the pipe was delayed by 242.5%. On the basis of the experimental data, the better suppression effect of G-Mt than Mt might be attributed to the presence of more hydroxyl groups on the surface.

Yan Wang

Papers

The Molecular Mechanisms of Defective Copper Metabolism in Diabetic Cardiomyopathy

The Suppression Characteristics of NH4H2PO4/Red Mud Composite Powders on Methane Explosion

Effect of Pristine Palygorskite Powders on Explosion Characteristics of Methane-Air Premixed Gas

Variation and Prediction Methods of the Explosion Characteristic Parameters of Coal Dust/Gas Mixtures

Suppression Effects of Hydroxy Acid Modified Montmorillonite Powders on Methane Explosions