Metal oxide gas sensors are predominant solid-state gas detecting devices for domestic, commercial and industrial applications, which have many advantages such as low cost, easy production, and compact size. However, the performance of such sensors is significantly influenced by the morphology and structure of sensing materials, resulting in a great obstacle for gas sensors based on bulk materials or dense films to achieve highly-sensitive properties. Lots of metal oxide nanostructures have been developed to improve the gas sensing properties such as sensitivity, selectivity, response speed, and so on. Here, we provide a brief overview of metal oxide nanostructures and their gas sensing properties from the aspects of particle size, morphology and doping. When the particle size of metal oxide is close to or less than double thickness of the space-charge layer, the sensitivity of the sensor will increase remarkably, which would be called “small size effect”, yet small size of metal oxide nanoparticles will be compactly sintered together during the film coating process which is disadvantage for gas diffusion in them. In view of those reasons, nanostructures with many kinds of shapes such as porous nanotubes, porous nanospheres and so on have been investigated, that not only possessed large surface area and relatively mass reactive sites, but also formed relatively loose film structures which is an advantage for gas diffusion. Besides, doping is also an effective method to decrease particle size and improve gas sensing properties. Therefore, the gas sensing properties of metal oxide nanostructures assembled by nanoparticles are reviewed in this article. The effect of doping is also summarized and finally the perspectives of metal oxide gas sensor are given.

It is of great significance for dynamic monitoring of foods in storage or during the transportation process through on-line detecting trimethylamine (TMA). Here, TMA were sensitively detected by Au-modified hierarchical porous single-crystalline ZnO nanosheets (HPSCZNs)-based sensors. The HPSCZNs were synthesized through a one-pot wet-chemical method followed by an annealing treatment. Polyethyleneimine (PEI) was used to modify the surface of the HPSCZNs, and then the PEI-modified samples were mixed with Au nanoparticles (NPs) sol solution. Electrostatic interactions drive Au nanoparticles loading onto the surface of the HPSCZNs. The Au-modified HPSCZNs were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and energy dispersive spectrum (EDS), respectively. The results show that Au-modified HPSCZNs-based sensors exhibit a high response to TMA. The linear range is from 10 to 300 ppb; while the detection limit is 10 ppb, which is the lowest value to our knowledge.

Room temperature sensor is a research hot for metal–oxide gas sensors. However, electron activation is a bottleneck to improve sensitivity for room temperature sensors. Here, an ultraviolet (UV)‐activated gas sensor based on a single‐sheet porous single‐crystalline (PSC) zinc oxide (ZnO) sheet has been fabricated instead of heating activation, which works at room temperature. The PSC ZnO nanosheets were first prepared by a one‐pot wet‐chemical method. Then, the precursors were annealed for 2 h in air to obtain the PSC ZnO nanosheets. They were characterised by scanning electron microscopy, high‐resolution transmission electron microscopy and UV–visible spectrum. Finally, the single‐sheet ZnO gas sensors were fabricated by focused ion beam technology, which exhibited good responses to 1–300 ppm of ethanol. The single‐sheet ZnO UV‐activated sensing mechanism was also put forward to explain the excellent sensing property.

SnO₂@reduced graphene oxide (SnO₂@rGO) nanocomposites are prepared using a freeze-drying method followed by heat treatment. The structure and morphology of the nanocomposites are characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, Raman spectra, and X-ray photoelectron spectroscopy. A large number of small uniform SnO₂ nanorods are successfully anchored on the surface of the rGO nanosheet, and a p–n junction is formed at their interface. In addition, the gas-sensing properties of SnO₂@rGO are tested using different concentrations of H₂ at a low operating temperature of 80 °C. The SnO₂@rGO sensor exhibits outstanding gas-sensing properties towards H₂, such as fast response and recovery, high sensitivity, selectivity, and stability. The sensor response to 1% H₂ at 80 °C was approximately 1.58, and the response and recover times were 15 s and 61 s, respectively. The satisfactory gas-sensing performance can be attributed to the large specific surface area, high electrical conductivity and width of the electron depletion layer. A possible gas-sensing mechanism is also proposed.

This article discusses the microstructure and mechanical properties of an Al-3.0Ce-0.9Ca-1.9Mn-1.2Zr alloy produced by selective laser melting (SLM) technology. The new alloy leverages the excellent heat resistance of Al-Ce alloys, incorporating Ca to lower both the cost and density, while the addition of Mn and Zr enhances formability and provides additional precipitation strengthening. Through the optimization of heat-treatment parameters, the optimal conditions were determined, with an annealing temperature of 375 °C and a holding time of 8 h. After annealing, the alloy’s tensile strength increased from 333 MPa to 412 MPa, yield strength rose from 246 MPa to 359 MPa, and elongation decreased from 24.4% to 16.4%. Compared to the as-built state, tensile strength and yield strength increased by 23.6% and 46.1%, respectively, while elongation decreased by 32.7%. The alloy demonstrates excellent heat resistance, with yield strengths at test temperatures of 200 °C, 250 °C, 300 °C, and 350 °C at 167 ± 17 MPa, 144 ± 8 MPa, 84 ± 4 MPa, and 57 ± 5 MPa, respectively. Notably, alloying imparts a degree of superplasticity, likely due to the synergistic effects of the Ca, Mn, and Zr elements.