A novel catalyst functionalization method, based on protein-encapsulated metallic nanoparticles (NPs) and their self-assembly on polystyrene (PS) colloid templates, is used to form catalyst-loaded porous WO3 nanofibers (NFs). The metallic NPs, composed of Au, Pd, or Pt, are encapsulated within a protein cage, i.e., apoferritin, to form unagglomerated monodispersed particles with diameters of less than 5 nm. The catalytic NPs maintain their nanoscale size, even following high-temperature heat-treatment during synthesis, which is attributed to the discrete self-assembly of NPs on PS colloid templates. In addition, the PS templates generate open pores on the electrospun WO3 NFs, facilitating gas molecule transport into the sensing layers and promoting active surface reactions. As a result, the Au and Pd NP-loaded porous WO3 NFs show superior sensitivity toward hydrogen sulfide, as evidenced by responses (R(air)/R(gas)) of 11.1 and 43.5 at 350 °C, respectively. These responses represent 1.8- and 7.1-fold improvements compared to that of dense WO3 NFs (R(air)/R(gas) = 6.1). Moreover, Pt NP-loaded porous WO3 NFs exhibit high acetone sensitivity with response of 28.9. These results demonstrate a novel catalyst loading method, in which small NPs are well-dispersed within the pores of WO3 NFs, that is applicable to high sensitivity breath sensors.

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Microfiltration of emulsions of oil (dodecane) in water using electrospun membranes of poly(trimethyl hexamethylene terephthalamide) (PA6 (

Membrane-based separation is an important technique for removing emulsified oil from water. However, the mechanisms of fouling are complex because of the deformability and potential for coalescence and break-up of the oil droplets. Here, we report for the first time direct, three-dimensional (3D) visualization of oil droplets on electrospun fiber microfiltration membranes after a period of membrane-based separation of oil-in-water emulsions. High-resolution 3D images were acquired by a dual-channel confocal laser scanning microscopy (CLSM) technique in which both the fibers and the oil (dodecane) were fluorescently labeled. The morphology of dodecane as the foulant was observed for two different types of fibers, an oleophobic nylon (PA6(3)­T), and oleophilic polyvinylidene fluoride (PVDF). Through direct visualization, the rejected oil was found to form droplets of clam-shell shape on the PA6(3)­T fibers, whereas the oil tended to wet the PVDF fibers and spread across the membrane. The morphology was also analyzed as a function of separation time (i.e., “4D” imaging), as the oil accumulated within and upon the membranes. The observations are qualitatively consistent with a transition from blocking of individual pores in the membrane to coalescence of oil droplets into coherent liquid films with increasing filtration time. Analysis of permeate flux using blocking filtration models corroborate the transition of fouling modes indicated by the 3D images. This direct, 3D visualization CLSM technique is a powerful tool for characterizing the mechanisms of fouling in membranes used for liquid emulsion separations.

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