Catalyst Loaded WO3 Nanofibers using Metal-Organic Framework Templates for Exhaled Breath Analysis

Abstract

Increase in surface area and catalytic sensitization should be accompanied to achieve highly sensitive and selective exhaled breath sensors using semiconductor metal oxide (SMO)-based sensing materials. Among the numerous nanomaterials, metal-organic frameworks (MOFs) are strong candidates for breath sensing materials because they have fascinating features such as ultrahigh porosity and incredibly high surface area. In addition, noble metal nanoparticles (NPs) such as Pt and Pd can be encapsulated in the cavities of the MOFs. In this work, we propose Pd-functionalized ZnO loaded on WO3 nanofibers (Pd-ZnO-WO3 NFs) synthesized by using ZIF-8 templates. We loaded MOF templated catalytic Pd NP network on WO3 nanofibers (NFs) through electrospinning and subsequent calcination. As intermediates, MOFs containing Pd catalyst transform to metal oxide by calcination, and these metal oxide can act as a synergistic catalyst and delivery agent of NP catalyst network. Pd-ZnO-WO3 NFs exhibited a twenty-four times higher toluene response, which is a biomarker for lung cancer, (Rair/Rgas= 53.55 at 5 ppm) at 350 °C compared to that of pristine WO3 NFs. In addition, Pd-ZnO-WO3 NFs detected at 100 ppb of toluene with high response (Rair/Rgas= 4.37 at 350 °C). Moreover, Pd-ZnO-WO3 NFs improved other sensing characteristics, in terms of the response time and selectivity. These results demonstrates that the novel synthesis of catalyst-loaded SMO NFs by using MOF templates can be applicable for exhaled breath analysis.