UV-assisted, template-free synthesis of ultrathin nanosheet-assembled hollow indium oxide microstructures for effective gaseous formaldehyde detection

Hollow micro-/nanostructures, especially those with well-defined nanoscale subunits, have been widely used in a variety of areas including catalysis, sensing, energy storage, drug delivery, etc. Herein, we report a novel, UV-assisted, template-free synthesis of hollow indium oxide microstructures that are composed of ultrathin nanosheets (∼2.5 nm). The two key steps for the synthesis of the materials being successful are: (i) the UV-induced conversion of a photoactive solid indium alkoxide precursor into hollow indium hydroxide microspheres composed of ultrathin nanosheets, and (ii) the thermal treatment of the resulting hollow hydroxide microspheres into the hollow In2O3 material with a morphological preservation. Moreover, we show that the as-obtained hollow nanomaterials exhibit excellent sensing performance (e.g., high response value, good stability, as well as fast response speed) for the detection of ppm-level gaseous formaldehyde. The efficient sensing performance of the material is attributed to their overall conducive structural features, including their hollow architecture and ultrathin nanoscale building blocks. These structural features can offer a large amount of active sites on the surface, facilitate the diffusion and adsorption of the target gas, and thus enhance the material's sensing performance.