Template-Free Construction of Tin Oxide Porous Hollow Microspheres for Room-Temperature Gas Sensors

Abstract

Porous hollow microsphere (PHM) materials represent ideal building blocks for realizing diverse functional applications such as catalysis, energy storage, drug delivery, and chemical sensing. This has stimulated intense efforts to construct metal oxide PHMs for achieving highly sensitive and low-power-consumption semiconductor gas sensors. Conventional methods for constructing PHMs rely on delicate reprogramming of templates and may suffer from the structural collapse issue during the removal of templates. Here, we propose a template-free method for the construction of tin oxide (SnO 2 ) PHMs via the competition between the solvent evaporation rate and the phase separation dynamics of colloidal SnO 2 quantum wires. The SnO 2 PHMs (typically 3 ± 0.5 μm diameter and approximately 200 nm shell thickness) exhibit desirable structural stability with desirable processing compatibility with various substrates. This enables the realization of NO 2 gas sensors having a superior response and recovery process at room temperature. The superior NO 2 -sensing characteristic is attributed to the effective gas adsorption competition on solid surfaces benefiting from efficient diffusion channels, enhancing the interaction of metal oxide solids with gas molecules in terms of the receptor function, transducer function, and utility factor. In addition, the one-step deposition of SnO 2 PHMs directly onto device substrates simplifies the fabrication conditions for semiconductor gas sensors. The desirable structural stability of PHMs combined with the functional diversity of metal oxides may open new opportunities for the design of functional materials and devices.

Room-Temperature Semiconductor Gas Sensors: Challenges and Opportunities

“…Compared to the relatively thick and dense membranes obtained through drip or vacuum filtration, this 3D structure can provide highly interconnected porous structures that allow easy entry and diffusion of gas molecules, further enhancing the utility. SnO 2 porous hollow microspheres (PHMs) have been constructed via a template free electrostatic spray of 1D SnO 2 nanowires . The superior RT NO 2 -sensing characteristic is attributed to the effective gas adsorption competition on solid surfaces benefiting from efficient diffusion channels.…”

“…SnO 2 porous hollow microspheres (PHMs) have been constructed via a template free electrostatic spray of 1D SnO 2 nanowires. 194 The superior RT NO 2 -sensing characteristic is attributed to the effective gas adsorption competition on solid surfaces benefiting from efficient diffusion channels. Kim et al 195 employed MOF templates to synthesize few-layered WS 2 nanoplates confined in Co, N-doped hollow carbon nanocages (Figure 2h).…”

Critical Review on Synthetic Routes and Catalytic Applications of Hollow Nanomaterials

“…PMMA core removed with the help of acetone washing. [75] Zeng et al used porous polystyrene-divinylbenzene (PS-DVB) as template for the generation of multishelled titania hollow spheres. [76] Multishelled and sphere-in-sphere hollow structures of titania results after different heat treatment for the seeded polymerization of polystyrene-divinylbenzene and infiltration process of titania sol within polymer beads.…”

Oxidation-enabled SnS conversion to two-dimensional porous SnO2 flakes towards NO2 gas sensing

“…Taking into account the sensing theory of an electron depletion layer (EDL) between an n-type semiconductor and an oxidizing gas, 6–9 many efforts were made to boost the performance of NO 2 sensors by modulating the gas/semiconductor surface interactions and interparticle electric contacts from the perspectives of chemistry and materials science. Reducing the size of crystalline grains, 9,10 building specific morphologies and structures, 9–15 locating nanosized noble metal catalysts or other metal oxides to form electronic heterojunctions 10,15–18 and doping with impurities or oxygen vacancies, 19–22 among others ( e.g. , UV illumination and humidity modulation) 11,12,23,24 are representative means.…”