Kilogram-Scale Synthesis of Pd-Loaded Quintuple-Shelled Co₃O₄ Microreactors and Their Application to Ultrasensitive and Ultraselective Detection of Methylbenzenes

Abstract

We report the kilogram-scale, simple, and cost-effective synthesis of Pd-loaded quintuple-shelled Co3O4 microreactors by spray drying of aqueous droplets containing cobalt nitrate, palladium nitrate, citric acid, and ethylene glycol and subsequent heat treatment. Highly viscous gel spheres containing Co and Pd salts were successfully converted into multi thin-shelled Co3O4 reactors uniformly loaded with Pd catalysts by the sequential combustion of carbon and decomposition of the metal salts from the outer to the inner regions during one-step heat treatment. The responses (resistance ratio) of the Pd-loaded quintuple-shelled Co3O4 microreactors to 5 ppm toluene and p-xylene were 30.8 and 64.2, respectively, and the selectivity values to toluene and p-xylene against ethanol interference (response ratio) were 14.5 and 30.1, respectively. The unprecedented high response and selectivity were attributed to the effective dissociation of less reactive methylbenzenes into more active smaller species assisted both by catalytic Co3O4 and Pd during the prolonged retention within the microreactors. Kilogram-scale preparation of noble metal-loaded multishelled microreactors and their unique gas-sensing characteristics based on a novel microreactor concept can pave a new way to design of high-performance gas sensors for practical applications.

Monolayer Co3O4 Inverse Opals as Multifunctional Sensors for Volatile Organic Compounds

“…The response of the monolayer Co 3 O 4 IO thin film to 0.25–5 ppm ethanol was measured at 200 °C and compared to those observed for undoped Co 3 O 4 ‐based gas sensors in the literature (Figure a) . The response of the monolayer Co 3 O 4 IO thin film to 5 ppm ethanol at 200 °C is as high as 112.9, which is among the highest values published to date.…”

“…The size, shape, and assembled configuration of nanoparticles are key morphological factors in determining the gas response of oxide semiconductors. [1,2,13] To date, various Co 3 O 4 nanostructures, such as nanorods, [12,14] nanofibers, [15,16] nanosheets, [14] nanocubes, [11,14] yolk-shell spheres, [17] hierarchical spheres, [18,19] and hollow spheres, [10,19] have been explored for use in gas sensors, butt he gas responses of thesem aterials need further enhancement to detect trace concentrations of analyte gases in ar eliable and reproducible manner.R ecently, monolayer inverse opal (IO) structures of the n-type oxides SnO 2 [20] and Fe 2 O 3 [21] have been suggested as excellent nanostructures for gas-sensor applications, owing to their periodic arrays of macropores with high gas accessibility and unique connecting configurations of nanoscale walls. However,t he gas-sensing capabilities of monolayer IO thin films of p-type Co 3 O 4 have not yet been investigated.…”

Intricate Hollow Structures: Controlled Synthesis and Applications in Energy Storage and Conversion

“…The esterification reaction between the citric acid and the ethylene glycol during the spray‐drying plays a significant role in producing dense, spherical, and non‐aggregated precursor particles with low hygroscopicity, which is essential for the subsequent formation of well‐defined multishelled Co 3 O 4 hollow spheres. With the introduction of palladium nitrate into the precursor solution, Pd‐loaded quintuple‐shelled Co 3 O 4 hollow spheres can be successfully obtained …”

“…Due to the high operating temperature, an additional thermal‐decomposition process may occur after drying of the droplets in spray pyrolysis. Second, the production efficiency of the spray‐pyrolysis process is tens of times lower than that of similar‐scale spray‐drying …”

Sequential Templating Approach: A Groundbreaking Strategy to Create Hollow Multishelled Structures

“…Owing to their unique physical/chemical properties, HoMSs have been widely functionalized and applied to broad applications, such as lithium ion batteries, solar cells, photocatalysis, sensors, supercapacitors, and drug delivery . Well understanding of geometric effects on properties may promote the rapid development of HoMSs in practical applications.…”