Bimodally Porous WO 3 Microbelts Functionalized with Pt Catalysts for Selective H 2 S Sensors.

Bi-modally meso- (2-50 nm) and macro-porous (>50 nm) WO3 microbelts (MBs) functionalized with sub-3 nm Pt catalysts were fabricated via electrospinning technique followed by subsequent calcination. Importantly, apoferritin (Apo), tea saponin (TS) and polystyrene (PS)-colloid spheres (750 nm) dispersed in electrospinning solution acted as forming agents for producing meso- and macro-pores on WO3 MBs during calcination. Particularly, mesopores provide not only numerous reaction sites for effective chemical reactions, but also facilitate gas diffusion into interior of WO3 MBs, dominated by Knudsen diffusion. Macropores further accelerate gas permeability in the interior and on the exterior of WO3 MBs. In addition, Pt nanoparticles (NPs) with mean diameters of 2.27 nm were synthesized by using biological protein cages, i.e., Apo, to further enhance gas sensing performance. Bi-modally porous WO¬3 MBs functionalized by Pt catalysts showed remarkably high hydrogen sulfide (H2S) response (Rair/Rgas = 61 @ 1 ppm) and superior selectivity to H2S against other interfering gases, i.e., acetone (CH3COCH3), ethanol (C2H5OH), ammonia (NH3), and carbon monoxide (CO). These results demonstrate high potential for feasibility of catalyst-loaded meso- and macro-porous WO3 MBs as new sensing platforms for real-time diagnosis of halitosis.