Rational design of mesoporous semiconducting metal oxide nanostructures for sensitive and selective gas sensing applications

Abstract

The novel use of synthetic methods is an effective way to engineer the morphology of semiconducting metal oxide (SMO) based gas-sensing materials to overcome their shortcomings such as low sensitivity and poor intrinsic selectivity to target gases. Although the single-nozzle electrospraying and single-nozzle electrospinning are generally considered versatile techniques in the synthesis of spherical and fibrous SMO nanostructures, respectively, the sole dependence of porosity on the decomposition of the organic and polymeric matters during the calcination stage limits the introduction of ubiquitous porosity for diffusion of gases through these materials, resulting in low surface areas. This is because during a typical high temperature calcination, crystal sizes grow larger, accompanied with a consequent sintering of grain necks. In this dissertation, unprecedented templating techniques are introduced to synthesize highly porous hollow spheres, nanotubes, and core-shell/fiber-in-tube fibrous nanostructures by employing electrospraying etching, electrospinning etching, and electrospinning impregnation methods, respectively. The obtained SMO-based nanostructures afford meso/macroporous morphologies with short diffusion length, small crystallites, and large Brunauer Emmett Teller surface area. Accordingly, the synthesized materials exhibit outstanding sensitivity and selectivity properties toward gaseous disease biomarkers in human exhaled breath.