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

Abstract

The study includes a conductometric chemical sensor design using aligned MnO 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 MnO 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 MnO 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 MnO-embedded AAO to ensure conductometric sensing along the length of the MnO nanorods. In comparison to the MnO film-based sensor, the MnO 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.

Hydrogen Gas Sensing Performances of p-Type Mn3O4 Nanosystems: The Role of Built-in Mn3O4/Ag and Mn3O4/SnO2 Junctions

“…X-ray diffraction (XRD) patterns were recorded at room temperature using a Bruker (Billerica, MA, USA) D8 Advance X-ray diffractometer with a Cu Kα X-ray source (λ = 1.54 Å) operated at 40 kV and 40 mA, employing an incidence angle of 1.0 • . The average crystallite dimensions were calculated by means of the Scherrer equation [29,33,36,55].…”

“…To account for the performance increase yielded by composite systems, it is necessary to consider the mechanism of hydrogen detection by the target p-type materials, which can be described as follows. Upon air exposure prior to contact with the target analyte, oxygen molecules undergo chemisorption processes, yielding the formation of various species [6,9,29,36,43,55], among which O − is the prevailing one in the present working temperature interval [14,17,30,33]:…”

“…Among p-type systems, Mn 3 O 4 has received significant attention due to its low cost, large natural abundance, environmentally friendly character and versatile chemico-physical properties, including the coexistence of mixed valence states [36,37]. Over the last decade, different studies have reported on Mn 3 O 4 -containing gas sensors for various analytes, including CH 3 CH 2 OH, CH 3 COCH 3 , NH 3 and chemical warfare agent simulants [31,[35][36][37][38][39][40][41].…”

“…Among p-type systems, Mn 3 O 4 has received significant attention due to its low cost, large natural abundance, environmentally friendly character and versatile chemico-physical properties, including the coexistence of mixed valence states [36,37]. Over the last decade, different studies have reported on Mn 3 O 4 -containing gas sensors for various analytes, including CH 3 CH 2 OH, CH 3 COCH 3 , NH 3 and chemical warfare agent simulants [31,[35][36][37][38][39][40][41]. Nonetheless, only two works on Mn 3 O 4 -based gas sensors for molecular hydrogen detection are available in the literature so far [35,42], and the implementation of H 2 sensors endowed with improved sensitivity and selectivity undoubtedly requires additional research efforts [29,35,37,38].…”

Top-down synthesis of sponge-like Mn3O4at low temperature

“…9,10 It is also a starting material for manufacturing manganese zinc ferrite used as so magnetic materials and lithium manganese oxides used as electrode materials due to its low cost and great environmental compatibility. Considerable interest has been paid to synthesizing Mn 3 O 4 nanostructures, 11,12 for instance, nanoparticles, [13][14][15][16] nanorods, 17,18 nanowires or nanobers, 19,20 nanoplates, 21 superlattices 22 and hierarchical nanostructures. [23][24][25][26][27][28] Among these, hierarchical Mn 3 O 4 nanostructures take advantage of both nanometer-sized building blocks and micro-sized assemblies.…”