Size and morphology dependent gas-sensing selectivity towards acetone vapor based on controlled hematite nano/microstructure (0D to 3D)

Solvent induced phase transformations of ZIF-L to ZIF-8 and their derivatives’ gas sensing properties

Detailed study of topological phase transition is essential in guiding the controlled synthesis of materials. Herein, a series of zeolitic-imidazolate frameworks (ZIFs) and derived metal oxide with tailored morphologies and...

Structure, Defects, and Magnetism of Electrospun Hematite Nanofibers Silica-Coated by Atomic Layer Deposition

In the last years, hematite has been utilized in a plethora of applications. High aspect-ratio nanohematite and hematite/silica core-shell nanostructures are arousing growing interest for applications exploiting their magnetic properties. Atomic layer deposition (ALD) is utilized here to produce SiO₂-coated α-Fe₂O₃ nanofibers (NFs) through two synthetic routes, viz. electrospinning/calcination/ALD or electrospinning/ALD/calcination. The number of ALD cycles (10-100) modulates the coating thickness, while the chosen route controls the final nanostructure. Porous and partially hollow NFs are produced. Their hierarchical structure and the nature and density of the lattice defects and strain are characterized by combining electron microscopy, diffraction, and spectroscopy techniques. The uncoated hematite NFs mostly have surface-related strain, which is attributed to oxygen vacancies/Fe²⁺ sites. ALD coating causes microstrain release and decrease of surface states. NFs calcined after ALD have extensive bulk strain, which is ascribed to the presence of dislocations throughout the volume of the NF grains. Bulk strain determines the remanent magnetization, whereas both surface and bulk strain influence the coercive field and the thermal behavior across the Morin temperature, including the magnetic memory effect. To the best of the authors' knowledge, the correlation between lattice defects/strain and magnetic properties of SiO₂-coated α-Fe₂O₃ NFs has never been reported before.

Ultrafast Detection of Low Acetone Concentration Displayed by Au-Loaded LaFeO3 Nanobelts owing to Synergetic Effects of Porous 1D Morphology and Catalytic Activity of Au Nanoparticles

Herein, we report on one-dimensional porous Au-modified LaFeO₃ nanobelts (NBs) with high surface area, which were synthesized through the electrospinning method. The incorporation and coverage of Au nanoparticles (NPs) on the surface of the LaFeO₃ NBs was achieved by adjusting the HAuCl amount in the precursor solution. Successful incorporation of Au NPs was examined by X-ray diffraction, high-resolution transmission electron microscopy, and X-ray photoelectron spectroscopy. The gas-sensing performance of both the pure and Au/LaFeO₃ NB-based sensors was tested toward 2.5-40 ppm of acetone at working temperatures in the range from room temperature to 180 °C. The gas-sensing findings revealed that Au/LaFeO₃ NB-based sensor with the Au concentration of 0.3 wt % displayed improved response of 125-40 ppm of acetone and rapid response and recovery times of 26 and 20 s, respectively, at an optimal working temperature of 100 °C. Furthermore, all sensors demonstrated an excellent response toward acetone and remarkable selectivity against NO₂, NH₃, CH₄, and CO. Hence, the Au/LaFeO₃-NB-based sensor is a promising candidate for sensitive, ultrafast, and selective acetone detections at low concentrations. The gas-sensing mechanism of the Au/LaFeO₃ sensors is explained in consideration of the catalytic activity of the Au NPs, which served as direct adsorption sites for oxygen and acetone.