Trimodally porous SnO2 nanospheres with three-dimensional interconnectivity and size tunability: a one-pot synthetic route and potential application as an extremely sensitive ethanol detector

The rapid and effective transfer of chemical reactants to solid surfaces through porous structures is essential for enhancing the performance of nanomaterials for various energy and environmental applications. In this paper, we report a facile one-pot spray pyrolysis method for preparing highly reactant-accessible and porous SnO2 spheres, which have three-dimensionally interconnected and size-tunable trimodal (microscale, mesoscale and macroscale) pores. For this synthetic method, macroscale polystyrene spheres and mesoscale-diameter, long carbon nanotubes were used as sacrificial templates. The promising potential of the SnO2 spheres with trimodal pores (sizes ≈3, 20 and 100 nm) was demonstrated by the unprecedentedly high response to several p.p.b. levels of ethanol. Such an ultrahigh response to ethanol is explained with respect to the hierarchical porosity and pore-size-dependent gas diffusion mechanism. Spray pyrolysis has been used to prepare tin dioxide nanospheres that contain size-tunable ‘trimodal’ pores. To enhance the performance of porous nanostructures in various energy and environmental applications involving reactions at surfaces and interfaces, it is desirable to gain precise control of multimodal pores in nanostructures. Jong-Heun Lee at Korea University and co-workers have used a simple ‘one-pot’ spray pyrolysis method to produce tin dioxide nanospheres with three levels of pore sizes. Aqueous droplets containing a metal salt, macroscale polystyrene spheres and mesoscale-diameter carbon nanotubes were subjected to pyrolysis, which decomposed the metal salt and polystyrene. Heat treatment then decomposed the carbon nanotubes. The potential of this method was demonstrated by using tin dioxide spheres containing pores with sizes of 3, 20 and 100 nanometres to detect ethanol at levels of several parts per billion. Trimodally porous SnO2 nanospheres with pore sizes of 3, 20 and 100 nm were prepared with facile one-pot spray pyrolysis and their potential for extremely sensitive ethanol detector was demonstrated. The precise control over, as well as the tuning of, multimodal pores in metal oxide nanostructures provides a new and general strategy for enhancing the performance of nanomaterials for various energy and environmental applications.