Tingting Zhou

Hybrid Co3O4/SnO2 Core–Shell Nanospheres as Real-Time Rapid-Response Sensors for Ammonia Gas

Novel hybrid Co3O4/SnO2 core-shell nanospheres have been effectively realized by a one-step hydrothermal, template-free preparation method. Our strategy involves a simple fabrication scheme that entails the coating of natural cross-link agents followed by electrostatic interaction between the positive charges of Sn and Co ions and the negative charge of glutamic acid. The core-shell architecture enables novel flexibility of gas sensor surfaces compared to commonly used bulk materials. The highly efficient charge transfer and unique structure are key to ensuring the availability of high response and rapid-response speed. It demonstrates how hybrid core-shell nanospheres can be used as an advance function material to fabricate electrical sensing devices that may be useful as gas sensors.

Hollow ZnSnO3 Cubes with Controllable Shells Enabling Highly Efficient Chemical Sensing Detection of Formaldehyde Vapors

In structural hierarchy, inherently hollow nanostructured materials preferentially possessing high surface area demand attention due to their alluring sensing performances. However, the activity of hollow and structural hierarchy nanomaterials generally remains suboptimal due to their hollow space structure and large lateral size, which greatly hamper and limit the availability of inner space active sites. Here, hollow ZnSnO3 cubes with a controllable interior structure were successfully prepared through a simple and low-cost coprecipitation approach followed with a calcination process. The solid-, single-, double-, and multishelled ZnSnO3 hollow cubes could be selectively tailored by repeated addition of alkaline solution. The multishelled architecture displayed outstanding sensing properties for formaldehyde vapors due to large specific surface area, less agglomerations, abundant interfaces, thin shells, and high proportion porous structure, which act synergistically to facilitate charge transfer and promote target gas adsorption.

Fast and real-time acetone gas sensor using hybrid ZnFe2O4/ZnO hollow spheres

Special hollow ZnFe2O4/ZnO hybrid spheres were successfully designed and synthesized via a facile hydrothermal procedure. Carbon spheres were used as the core template, which were removed during the calcination process in an air-rich atmosphere, thus leading to interior voids and an outer shell structure due to the contraction and combustion of the carbon spheres. The hybrid ZnFe2O4/ZnO hollow spheres not only possess a hollow structure, but also have a porous shell with a thickness of approximately 30 nm. Inspired by this special structure and design composition, a gas sensor based on the hybrid ZnFe2O4/ZnO hollow spheres showed a high response and fast response/recovery speed compared with nanoparticles. A short response time usually enables a gas sensor to accurately detect and real-time monitor a certain target gas. This study may give insight for the rational fabrication of high performance sensing materials.

The synthesis and fast ethanol sensing properties of core–shell SnO2@ZnO composite nanospheres using carbon spheres as templates

Core–shell SnO2@ZnO composite nanospheres were successfully prepared by using carbon spheres as sacrificial templates via a facile three-step procedure including a hydrothermal method. In contrast, pristine SnO2 nanospheres and ZnO nanoparticles were obtained through a similar method with different steps, respectively. The composition and structures of the as-synthesized samples were confirmed by a series of characterization procedures. The obtained composite materials exhibited the special core-in-hollow-shell structure at the nanometer level. And as potential sensing materials, the obtained core–shell SnO2@ZnO composite nanomaterials demonstrated better gas sensing properties to ethanol including higher response, better selectivity, faster response and favorable repeatability, which may be related to the special core-in-hollow-shell structure with a porous surface and the hetero-contact between two different metal oxide semiconductors.

Metal–Organic Frameworks-Derived Hierarchical Co3O4 Structures as Efficient Sensing Materials for Acetone Detection

Highly sensitive and stable gas sensors have attracted much attention because they are the key to innovations in the fields of environment, health, energy savings and security, etc. Sensing materials, which influence the practical sensing performance, are the crucial parts for gas sensors. Metal-organic frameworks (MOFs) are considered as alluring sensing materials for gas sensors because of the possession of high specific surface area, unique morphology, abundant metal sites, and functional linkers. Herein, four kinds of porous hierarchical Co3O4 structures have been selectively controlled by optimizing the thermal decomposition (temperature, rate, and atmosphere) using ZIF-67 as precursor that was obtained from coprecipitation method with the co-assistance of cobalt salt and 2-methylimidazole in the solution of methanol. These hierarchical Co3O4 structures, with controllable cross-linked channels, meso-/micropores, and adjustable surface area, are efficient catalytic materials for gas sensing. Benefits from structural advantages, core-shell, and porous core-shell Co3O4 exhibit enhanced sensing performance compared to those of porous popcorn and nanoparticle Co3O4 to acetone gas. These novel MOF-templated Co3O4 hierarchical structures are so fantastic that they can be expected to be efficient sensing materials for development of low-temperature operating gas sensors.

Carbon materials-functionalized tin dioxide nanoparticles toward robust, high-performance nitrogen dioxide gas sensor

Carbon (C) materials, which process excellent electrical conductivity and high carrier mobility, are promising sensing materials as active units for gas sensors. However, structural agglomeration caused by chemical processes results in a small resistance change and low sensing response. To address the above issues, structure-derived carbon-coated tin dioxide (SnO2) nanoparticles having distinct core-shell morphology with a 3D net-like structure and highly uniform size are prepared by careful synthesis and fine structural design. The optimum carbon-coated SnO2 nanoparticles (SnO2/C)-based gas sensor exhibits a low working temperature, excellent selectivity and fast response-recovery properties. In addition, the SnO2/C-based gas sensor can maintain a sensitivity to nitrogen dioxide (NO2) of 3 after being cycled 4 times at 140 °C for, suggesting its good long-term stability. The structural integrity, good synergistic properties, and high gas-sensing performance of SnO2/C render it a promising sensing material for advanced gas sensors.

Controllable construction of multishelled p-type cuprous oxide with enhanced formaldehyde sensing

Hollow metal oxide semiconductor (MOS) materials with controllable shells have attracted increasing attention because of their interesting properties and potential applications in sensors, catalysis, biology, etc. Cuprous oxide (Cu2O), which is a typical p-type semiconductor material, has four kinds of nanostructures (i.e., single-, double-, triple-, and quadruple-shelled spheres) and was successfully synthesized by the simple regulation of hexadecyl trimethyl ammonium bromide (CTAB) concentration. All as-obtained samples were at the nanometer level, and the hollow layers were also located between the two shells of the Cu2O nanostructures. The structural evolution and formation mechanism of the core-in-hollow multishelled nanostructure were also studied in this work. Moreover, the gas sensing performance of four kinds of materials was measured. The performance of the quadruple-shelled Cu2O-based formaldehyde (HCHO) sensor was greater than that of other sensors. The results indicated that the well-defined multishelled structure may significantly enhance HCHO detection by facilitating the gas adsorption quantity and transport rate.

Robust cobalt perforated with multi-walled carbon nanotubes as an effective sensing material for acetone detection

Herein, we report the development of a facile hydrothermal method to fabricate plum and octahedron-like cobalt tetroxide (Co3O4) particles decorated with multi-walled carbon nanotube (MWCNT) one-dimensional (1D) hybrid structures. The morphology of Co3O4 particles on MWCNTs was controlled by changing the volume ratios of a mixed solvent of ethylene glycol and water. The Co3O4 particles grew on and across MWCNTs, resulting in structures with necklace-like morphology. The assembled MWCNTs/Co3O4 composites were used to detect acetone vapors and showed enhanced sensing performances than a pure MWCNT-based sensor. This enhanced gas sensing performance could be due to the structural integrity of the hybrid nanostructure as well as the surface defects and catalytic Co cations on the surfaces of MWCNT and Co3O4 octahedra, respectively.

NiO/NiCo2O4 Truncated Nanocages with PdO Catalyst Functionalization as Sensing Layers for Acetone Detection

Achieving a novel structural construction and adopting appropriate catalyst materials are key to overcoming inherent limitations of gas sensors in terms of designing sensing layers. This work introduces NiO/NiCo2O4 truncated nanocages functionalized with PdO nanoparticles, which were proved to possess the ability of effective acetone detection. The device realized an enhanced acetone-sensing sensitivity, together with excellent selectivity and long-term stability. The sensing performance is far better than sensors based on NiO/NiCo2O4 solid nanocubes and NiO/NiCo2O4 truncated nanocages without PdO decorating, which is related to cooperative effects of the high specific surface area and efficient catalytic activity. The results provide promising metal-organic frameworks (MOFs)-derived material with the optimization of catalytic performance, demonstrating the remarkable potential for acetone sensors.