Mesoporous polycrystalline SnO2 framework synthesized by direct soft templating method for highly selective detection of NO2

Characterization and enhanced carbon dioxide sensing performance of spin-coated Na- and Li-doped and Co-doped cobalt oxide thin films

Recognizing the substantial effects of carbon dioxide on human health and the environment, monitoring CO2 levels has become increasingly vital. Owing to energy constraints and the widespread application of CO2 gas sensors, it is important to design cost-effective, more efficient, and faster response CO2 gas sensors that operate at room temperature and involve a low-cost technique. This study aims to develop a cost-effective and efficient CO2 gas detector that functions at room temperature and uses less power than traditional high-temperature CO2 sensors. In this study, we achieved this by employing innovative Co3O4 thin films with optimized spinel-structured p-type semiconductors through spin-coating, facilitated by Li and Na doping as well as Li/Na codoping. Doping with 3% Li/Na reduced the crystallite size from 92.4 to 8.03 nm and increased the band gap from 3.31 to 3.69 eV. At room temperature (30 °C), the sensor response improved significantly, increasing from 50% to 345.01% for 3% Li-Co3O4 upon the addition of 3% Na at a concentration of 9990 ppm. This performance surpasses that of most metal-oxide-based CO2 sensors reported in the literature. Additionally, this optimized sensor demonstrated a very short response time of 18.8 s and a recovery time of 16.4 s at a CO2 concentration of 9990 ppm diluted with air. It outperformed other films in terms of sensitivity, stability, response and recovery times, and performance across a wide range of relative humidity levels (43-90%). The sensor exhibited superior selectivity for CO2 than for N2, H2, and NH3. Overall, the 3% Li, Na-Co3O4 sensor is well-suited for climate change mitigation and industrial applications.

Synergistic Effect of Electron Scattering and Space Charge Transfer Enabled Unprecedented Room Temperature NO2 Sensing Response of SnO2

Metal oxide gas sensors have long faced the challenge of low response and poor selectivity, especially at room temperature (RT). Herein, a synergistic effect of electron scattering and space charge transfer is proposed to comprehensively improve gas sensing performance of n-type metal oxides toward oxidizing NO2 (electron acceptor) at RT. To this end, the porous SnO2 nanoparticles (NPs) assembled from grains of about 4 nm with rich oxygen vacancies are developed through an acetylacetone-assisted solvent evaporation approach combined with precise N2 and air calcinations. The results show that the as-fabricated porous SnO2 NPs sensor exhibits an unprecedented NO2 -sensing performance, including outstanding response (Rg /Ra  = 772.33 @ 5 ppm), fast recovery (<2 s), an extremely low detection limit (10 ppb), and exceptional selectivity (response ratio >30) at RT. Theoretical calculation and experimental tests confirm that the excellent NO2 sensing performance is mainly attributed to the unique synergistic effect of electron scattering and space charge transfer. This work proposes a useful strategy for developing high-performance RT NO2 sensors using metal oxides, and provides an in-depth understanding for the basic characteristics of the synergistic effect on gas sensing, paving the way for efficient and low power consumption gas detection at RT.

Low-Dimensional Nanostructures Based on Cobalt Oxide (Co3O4) in Chemical-Gas Sensing

Highly sensitive, stable, low production costs, together with easy maintenance and portability, sensors are ever most demanded nowadays for monitoring and quantification of hazardous chemicals/gases in the environment. The utilization of one dimensional (1D) metal oxide nano structured chemical/gas sensors for environmental monitoring is vastly investigated because of their superior surface to volume ratio, stability, and low production costs, to provide information on the presence of chemical species. Several outstanding attempts have been pursued investigating 1D nano structures of Co3O4 over the past decades as an active material for chemical analytes detection owing to its superior catalytic effect together with its excellent stability. This article reviews the state-of-the-art of growth and characterization of Co3O4 1D nano structures and their functional characterization as chemical/gas sensors. Moreover, fundamental concepts and characteristic features, that enhance the key performances of chemical/gas sensors, are discussed. Finally, challenges and prospective for growth and fabrication of 1D Co3O4 chemical/gas sensors are discussed.

Ordered mesoporous metal oxides for electrochemical applications: correlation between structure, electrical properties and device performance

Ordered mesoporous metal oxides with a high specific surface area, tailored porosity and engineered interfaces are promising materials for electrochemical applications. In particular, the method of evaporation-induced self-assembly allows the formation of nanocrystalline films of controlled thickness on polar substrates. In general, mesoporous materials have the advantage of benefiting from a unique combination of structural, chemical and physical properties. This Perspective article addresses the structural characteristics and the electrical (charge-transport) properties of mesoporous metal oxides and how these affect their application in energy storage, catalysis and gas sensing.