Abstract

In this critical review, we mainly focus the novel outstanding categories of micro/nanoscale iron (Fe) oxide materials with or without various grain and grain boundary structures, which can be very potentially used for next-generation gas-sensor technology because Fe oxide materials show very good stability and durability for use in gas sensor devices for the detection and identification of toxic gases in air ambience. The important improvements and modifications of structures and properties of Fe oxidebased materials for their better sensitivity to gaseous species are briefly described. Beyond conventional zinc (Zn) and tin (Sn) based oxide materials for gas sensors, new micro/nanoscale materials systems with the utilization of novel α-Fe₂O₃ micro/nanoscale structures with grain and grain boundary configurations are briefly introduced for the development of next-generation sensor devices for practical applications in academia, government and industry. In this short review, we have presented the large-scale synthetic methods for metal and oxide particles by the most common wet chemical methods, which can be utilized as new key platform in gas sensors for the detection of pollutant and toxic gases. Currently, the high uniform Fe- or Pt-based particles with a wide diversity of exciting miro/nanoscale structures can be potentially used in the gas-sensing films of gas sensors for the detection of toxic gases in various public and industrial environments as well as indoor house pollution. Here, the very important roles of very tiny noble metal nanoparticles with uniform spherical or polyhedral shapes and morphologies, and very large nanoparticles with uniform spherical or polyhedral shapes and morphologies are discussed for the enhancement of gas-sensing ability and property of the gas-sensing oxide layers in gas sensors. Through the chemically or physically engineered micro/nanoscale particles, sensitivity, selectivity, and stability of various Fe oxide based gas sensors can be significantly improved. Additionally, the characteristics of new Fe oxide particles with micro/nanoscale structures, such as size, shape, surface, structure, and composition by heat treatment are discussed in detail in order to improve the gas-sensing property for new generation gas sensors. The best advantages of the new Fe oxides with the very specific micro/ nanoscale surfaces and structures for emerging next-generation gas sensors have indicated to be high capable of identifying different gaseous species at very low contents, especially very sensitive to various alcohols, typically such as ethanol with a high sensitivity of about 90%, especially for α-Fe₂O₃ oxide particles in a size range of about 10 μm. The potential applications of Fe₂O₃- and Fe₃O₄-based oxides nanomaterials increasingly become for gas sensor technology with low cost but high quality. Chemical/ physical metallurgy methods and technologies are also introduced for Fe oxides, and Fe alloys with or without rare earth for soft-, hard-, and soft/hard-phase magnetic materials as well as the modified SmCo- and NdFe-based alloys especially concerned with potential applications for next magnetic sensors. Finally, the important emphasis is on the practical applications of iron oxides and alloys for life, environment and energy.