SnO2: A comprehensive review on structures and gas sensors

The controlled synthesis of nanohybrids composed of noble metals (Au, Ag, Pt and Pd, as well as AuAg alloy) and metal oxides (ZnO, TiO2, Cu2O and CeO2) have received considerable attention for applications in photocatalysis, solar cells, drug delivery, surface enhanced Raman spectroscopy and many other important areas. The overall architecture of nanocomposites is one of the most important factors dictating the physical properties of nanohybrids. Noble metals can be coupled to metal oxides to yield diversified nanostructures, including noble metal decorated-metal oxide nanoparticles (NPs), nanoarrays, noble metal/metal oxide core/shell, noble metal/metal oxide yolk/shell and Janus noble metal–metal oxide nanostructures. In this review, we focus on the significant advances in tailored nanostructures of noble metal–metal oxide nanohybrids. The improvement in performance in the representative solar energy conversion applications including photocatalytic degradation of organic pollutants, photocatalytic hydrogen generation, photocatalytic CO2 reduction, dye-sensitized solar cells (DSSCs) and perovskite solar cells (PSCs) are discussed. Finally, we conclude with a perspective on the future direction and prospects of these controllable nanohybrid materials.

Noble metal–metal oxide nanohybrids with tailored nanostructures for efficient solar energy conversion, photocatalysis and environmental remediation

Sensing of gas molecules is critical to environmental monitoring, control of chemical processes, agricultural, and medical applications In particular, the detection of industrial toxic gases such as CO, NO x , and NH 3 is very important for many industries Metal oxides have been widely studied for the sensitivity of their properties to gases even though they do have some limitations Recently, graphene has been considered as a promising material for gas sensing since its electronic properties are strongly affected by the adsorption of foreign molecules Intrinsic graphene has high sensitivity at low gas concentrations; but the sensor selectivity is poor which limits its use in many practical applications Hence, hybrid architectures formed by blending of nanoparticles of metal–oxides with graphene or its derivatives have been explored by several researchers which showed improved gas sensing ability, especially the sensitivity and selectivity at room temperature Here we review the state of the art of gas sensors based on graphene and metal oxide hybrid nanostructures for detection of various common toxic gases

Graphene–metal oxide nanohybrids for toxic gas sensor: A review

Great progress has been made in the preparation and application of multi-shelled hollow micro-/nanostructures during the past decade. However, the synthetic methodologies and potential applications of these novel and interesting materials have not been reviewed comprehensively in the literature. In the current review we first describe different synthetic methodologies for multi-shelled hollow micro-/nanostructures as well as their compositional and geometric manipulation and then review their applications in energy conversion and storage, sensors, photocatalysis, and drug delivery. The correlation between the geometric properties of multi-shelled hollow micro-/nanostructures and their specific performance in relevant applications are highlighted. These results demonstrate that the geometry has a direct impact on the properties and potential applications of such materials. Finally, the emerging challenges and future development of multi-shelled hollow micro-/nanostructures are further discussed.

Multi-shelled hollow micro-/nanostructures

Metal oxides possess exceptional potential as base materials in emerging technologies. In recent times, significant amount of research works is carried out on these materials to assess new areas of applications, including optical, electronic, optoelectronic and biological domains. In such applications, the response and performance of the devices depend crucially, among other factors, on the size, shape and surface of the active oxide materials. For instance, the electronic and optical properties of oxides depend strongly on the spatial dimensions and composition [1] . The large number of atoms on the surface, and the effective van der Waals, Coulombic and interatomic coupling significantly modify the physical and chemical properties of the low dimensional oxide materials vis-a-vis its bulk counterparts. As a result, low dimensional oxide materials, such as nanoparticles, nanospheres, nanorods, nanowires, nanoribbon/nanobelts, nanotubes, nanodisks, nanosheets evoke vast and diverse interests. Thermal and physical deposition, hydro/solvothermal process, spray-pyrolysis, assisted self-assembly, oil-in-water microemulsion and template-assisted synthesis are regularly employed to synthesis one-, two- and three-dimensional nanostructures, which have become the focus of intensive research in mesoscopic physics and nanoscale devices. It not only provides good scopes to study the optical, electrical and thermal properties in quantum-confinement, but also offers important insights for understanding the functional units in fabricating electronic, optoelectronic, and magnetic devices of nanoscale dimension. Tin oxide (SnO 2 ) is one such very important n-type oxide and wide band gap (3.6 eV) semiconductor. Its good quality electrical, optical, and electrochemical properties are exploited in solar cells, as catalytic support materials, as solid-state chemical sensors and as high-capacity lithium-storage. Previously, Chopra et al. [2] reviewed different aspects of transparent conducting SnO 2 thin films. Wang et al. [3] discussed device applications of nanowires and nanobelts of semiconductor oxides, including SnO 2 . Batzill et al. [4] discussed about the surface of single crystalline bulk SnO 2 . However, it is understood that neither there is any comprehensive review on various crystallographic phases, polymorphs, bulk modulus, lattice parameters and electronic states of SnO 2 , nor there is any updated compilation on the recent progress and scope on SnO 2 nanostructures. Therefore, the proposed review covers the past and recent progress on the said topics and is summarized in the following manner. The available theoretical and experimental works on crystal structures, bulk modulus, lattice parameters are reviewed in details. The electronic states and the band structures of these phases are discussed next. Active crystal surfaces of SnO 2 play vital roles in its many interesting properties, including sensing and catalytic applications. So, a short review is written on its different surfaces, its electronic structures and density of states. The discussion on the importance of morphological variations on the properties of SnO 2 is followed by a review on different methods for obtaining such structures. A detail survey on the existing literature on techniques and mechanisms for the growth of nanostructures are included. SnO 2 is efficiently employed in gas sensing applications. A review on such applications is compiled based on the role of morphology and performance. The future course of SnO 2 as an important material in the contemporary research is also discussed.

SnO2: A Comprehensive Review on Structures and Gas Sensors

New Au@SnO2 yolk–shell nanospheres have been successfully synthesized by using Au@SiO2 nanospheres as sacrificial templates. This process is environmentally friendly and is based on hydrothermal shell-by-shell deposition of polycrystalline SnO2 on spheriform Au@SiO2 nanotemplates. Au nanoparticles can be impregnated into the SnO2 nanospheres and the nanospheres show outer diameters of 110 nm and thicknesses of 15 nm. The possible growth model of the nanospheres is proposed. The gas sensing properties of the Au@SnO2 yolk–shell nanospheres were researched and compared with that of the hollow SnO2 nanospheres. The former shows lower operating temperature (210 °C), lower detection limit (5 ppm), faster response (0.3 s) and better selectivity. These improved sensing properties were attributed to the catalytic effect of Au, and enhanced electron depletion at the surface of the Au@SnO2 yolk–shell nanospheres.

Encapsuled nanoreactors (Au@SnO2): a new sensing material for chemical sensors

Recently, developing matchable cathode materials of Zn ion hybrid capacitor still remains difficult owing to insufficient understanding of the charge storage behavior. However, most previous efforts are devoted to explain the effect of oxygen‐containing groups without paying attention to graphitic structure. Herein, the charge storage capability and electrochemical kinetics of reduce graphene oxide (rGO) nanosheets are optimized as a function of their surface properties. Beyond the contribution of oxygen‐containing groups, an extra contribution from the reversible adsorption/desorption of H+ on carbon atom of rGO sheets is confirmed. Electrochemical analysis and density functional theory calculations reveal that H+ induces disruption of π cloud in aromatic domain, accompanied by C sp2‐sp3 re‐hybridization and the distortion/restoration of graphitic structure. The optimal electrochemical performance with a specific capacitance of 245 F g‐1 at 0.5 A g‐1 with 53% retention at 20 A g‐1 is achieved for rGO thermally treated at 200 °C. As a proof‐of‐concept application, the 3D printed rGO electrode delivers a high areal capacitance of 1011 mF cm‐2 and an energy density of 266 μWh cm‐2. The study is believed to broaden the horizons of proton adsorption chemistry and shed light on the design of novel electrode materials.

Revisiting Charge Storage Mechanism of Reduced Graphene Oxide in Zinc Ion Hybrid Capacitor beyond the Contribution of Oxygen‐Containing Groups

In2O3 micro/nanotubes (MNTs) with different diameters are successfully synthesized by an effective and template-free coaxial electrospinning method. The diameters of the MNTs can be simply tailored by controlling the ratio of reactants. The HCHO sensing tests of as-prepared MNTs reveal that the samples possess high response value, fast response and recovery rate, and favorable selectivity. Moreover, compared with the large diameter (∼1 μm or ∼500 nm) In2O3 MNTs, the small diameter (∼100 nm) In2O3 MNTs exhibit highly enhanced sensing properties. The gas sensing mechanism of In2O3 MNTs has been discussed in detail. The promising HCHO-sensing properties enable In2O3 MNTs to be a competitive candidate for detecting poisonous HCHO in practice. The experiment also indicates that the coaxial electrospinning is an environmental friendly and easy method for constructing tubular structure of metal oxides with different diameters for various applications.

Controllable synthesis and HCHO-sensing properties of In2O3 micro/nanotubes with different diameters

Hollow ZnO microspheres with tunable interior architecture are successfully synthesized by a simple green chemistry routes at low temperature. This process is environmentally friendly processing, which based on without using solvents, employing carbon microspheres as template and reaction at low temperature. The layer-control of hollow ZnO microspheres can be easily adjusted by varying the concentration of the zinc precursor added. To demonstrate the usage of such hollow ZnO microspheres, gas sensors have been fabricated from the as-synthesized hollow ZnO microspheres with different shelled and investigated for formaldehyde (HCHO) detection. Interestingly, the response of hollow ZnO microspheres increased with increasing the number of shell structures. These results indicate that three-shelled ZnO sensor displays about 1.5 and 3–4 fold enhancement in response compared to double and single-shelled one, respectively. The mechanism of enhanced sensor performances is also proposed.

Controllable and enhanced HCHO sensing performances of different-shelled ZnO hollow microspheres

https://www.nature.com/articles/s41467-021-27755-x.pdf

Zinc ion thermal charging cell for low-grade heat conversion and energy storage

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