Enhanced room temperature gas sensing of aligned Mn₃O₄ nanorod assemblies functionalized by aluminum anodic membranes

The study includes a conductometric chemical sensor design using aligned Mn₃O₄ nanorods. Nanostructuring is an emerging field of prominence due to its capacity to introduce unprecedented properties in materials with potential applications. A hydrothermally prepared in situ Mn₃O₄ sample appears with an urchin rod-like morphology, which changes to a spherical shape upon annealing. An aluminum anodic membrane/template (AAO) is used for the growth of the nanorods and also as a medium to support the sensor. The aligned Mn₃O₄ nanorods are formed in the pores of the AAO by vacuum infiltration approach, which is later on annealed. The gold electrical contacts are deposited on the top or bottom ends of the Mn₃O₄-embedded AAO to ensure conductometric sensing along the length of the Mn₃O₄ nanorods. In comparison to the Mn₃O₄ film-based sensor, the Mn₃O₄ nanorods in the AAO template have enhanced sensitivity for detecting ethanol and acetone vapor at room temperature. The novel property observed is a result of the large surface area and number of oxygen vacancies of the uniformly aligned and parallel assemblies of the nanorods. The sensor exhibits the lowest response time at 4 s for ethanol and 2 s for acetone at room temperature with a concentration of 50 ppm. The response time is 7 and 5 s, respectively, for 25 ppm. The maximum sensitivities of the sensor at room temperature for ethanol and acetone gases are 67% and 68%, respectively, for 50 ppm concentration. The growth mechanism of the aligned nanorods formed in the AAO template is well established through FESEM analysis. The XPS and HRTEM study give additional evidence for the presence of oxidation states and structure of the prepared nanostructures, respectively.