Efficient detection/monitoring of low-concentration C1–C3 aliphatic hydrocarbons (e.g., methane) is a challenging task, mainly due to their intrinsically low chemical reactivity and thereby weak sensing response. Herein we report the template-free synthesis of porous nanoparticle-assembled In2O3 microspheres that can serve as a highly sensitive material for C1–C3 detection. In particular, porous In2O3 microspheres with a BET surface area of 57 m2 g−1 are prepared through simple thermal treatment of an indium glycerolate precursor. The gas-sensing properties of the porous In2O3 material are evaluated by a series of C1–C3 hydrocarbons including methane (CH4), ethane (C2H6), propane (C3H8), ethylene (C2H4) and acetylene (C2H2). The porous In2O3 material has the ability to detect these gases with a rapid response (<10 s) in a wide concentration range from 200 ppm to 50000 ppm (the lower explosion limit of methane). In the testing range, the logarithm of response shows a good linear dependency on the logarithm of gas concentration, demonstrating that the porous In2O3 material may be used for quantitative detection of C1–C3 hydrocarbons. Given the rapid response and high sensitivity below the explosion limit, this porous In2O3 material is promising to provide earlier warning against the explosion risk of hydrocarbon compounds.

High-quality single-crystalline hollow α-Fe2O3 nanospheres were prepared, using the ZnS–CHA (CHA = cyclohexylamine) nanohybrid as an additive through a solvothermal reaction, which avoids tedious steps and a high temperature calcination process. The formation process of these hollow nanospheres can be divided into two stages: (i) formation of solid Fe2O3 nanospheres and (ii) preferential inside-out dissolution of the solid nanoparticles to form hollow nanospheres. Due to the unique single-crystalline hollow structure, the as-obtained α-Fe2O3 nanomaterial exhibits enhanced gas sensing properties.

Based on the theory of sol–gel science, perovskite SrHfO3 hollow cuboidal particles with tunable sizes were rationally synthesized by templateless hydrothermal reactions in KOH solutions. The concentrated KOH solution not only elevated the supersaturation of the reactants to promote the grain growth of SrHfO3 but also controlled the aggregated particle sizes by compressing the electrical double layers of the primary particulates. The following Ostwald ripening process produced hollow particles with sizes ranging from submicrometer to hundred nanometre. The HRTEM image and SAED pattern revealed the single crystal nature of each hollow cuboidal nanoshell. The KOH concentration and reaction time related experiments confirmed that the formation of SrHfO3 hollow cuboidal nanoshell was driven by the Ostwald ripening process and followed our assumption. The particles experienced solid, core-shell and hollow morphologies as the reaction proceeded. Also, the formation of SrHfO3 hollow cuboidal nanoshells favored high reaction temperature which initiated and accelerated the ripening process. The as-prepared hollow cuboidal nanoshells displayed blue light emission under UV laser excitation at room temperature. After calcination, the photoluminescence intensity declined due to the improvement of crystallinity.

Perovskite-type SrZrO3 hollow cuboidal nanoshells have been successfully prepared via a simple hydrothermal route from concentrated KOH solutions without any organic or inorganic templates. The products experienced morphology variations of solid microparticles, core–shell particles and hollow nanoshells by alternatively adjusting the base concentration, the reaction temperature and the reaction duration. The hollow cuboidal nanoshells were size tunable by simply adjusting the base concentration. Investigations of the synthetic parameters revealed that the formation of SrZrO3 hollow cuboidal nanoshells was driven by the Ostwald ripening process. Also, the hollow cuboidal nanoshells exhibited defect-induced blue light emission that centered at 468 nm when the samples were exposed to a 324 nm laser.

Based on the theory of sol–gel science, perovskite SrHfO3 hollow cuboidal particles with tunable sizes were rationally synthesized by templateless hydrothermal reactions in KOH solutions. The concentrated KOH solution not only elevated the supersaturation of the reactants to promote the grain growth of SrHfO3 but also controlled the aggregated particle sizes by compressing the electrical double layers of the primary particulates. The following Ostwald ripening process produced hollow particles with sizes ranging from submicrometer to hundred nanometre. The HRTEM image and SAED pattern revealed the single crystal nature of each hollow cuboidal nanoshell. The KOH concentration and reaction time related experiments confirmed that the formation of SrHfO3 hollow cuboidal nanoshell was driven by the Ostwald ripening process and followed our assumption. The particles experienced solid, core-shell and hollow morphologies as the reaction proceeded. Also, the formation of SrHfO3 hollow cuboidal nanoshells favored high reaction temperature which initiated and accelerated the ripening process. The as-prepared hollow cuboidal nanoshells displayed blue light emission under UV laser excitation at room temperature. After calcination, the photoluminescence intensity declined due to the improvement of crystallinity.