SnO2 Shell Research Articles

ZnSe/SnO2 Heterostructure-Based Sensor for Ultralow Concentration of NO2 Detection

Introduction Nitrogen dioxide is a hazardous gas species, which commonly causes the air pollution, acid rain, photochemical smog and is known to be harmful to human health.[1,2] According to World Health Organization (WHO) reports, approximately two million premature deaths of humans per year around the world are due to the influence of NO2 contaminants in the atmosphere.[3] Therefore, it is imperative to develop a reliable sensor with high sensitivity and selectivity for NO2 detection. In this aspect, ZnSe-core/SnO2-shell hybrid microspheres based sensor has been synthesized for ppb-level NO2 detection. The as-fabricated sensor exhibits a response of 1.21 to ultralow concentration of NO2 detection (75 ppb) at 160 °C. It has been demonstrated that the sensor presents an excellent reproducibility, long-term stability and selectivity. Experiment ZnSe microspheres were synthesized through the hydrothermal reaction. In a typical procedure, 4.5 mmol ZnCl2 and 3 mmol SeO2 were added to a mixed solution of triethylenetetramine (TETA, C6H18N4) and deionized water (DIW). The mixture was transferred into a 50 ml Teflon-lined autoclave and heated at 180 °C for 10 h. The as-prepared ZnSe microspheres were dispersed in an aqueous solution of tin chloride, and control the Zn source to Sn source in different mole ratios. The mixture was then maintained at 130 °C for 4 h. The obtained precipitates were washed by deionized water and absolute alcohol until the absence of chloride ion. Results and conclusions Figure 1a-d show the low-magnification SEM images of as-fabricated samples. The insets at the left-top corners are the enlarged images of the corresponding selected areas. Obviously, the pristine ZnSe sample exhibits a microspherical morphology with a particle size in the range of 4 μm ~ 6 μm. As the amount of SnO2 coated on the ZnSe surface increases, the spherical surface of the sample became rougher and coarser. However, with further increasing the content of SnO2 to Zn/Sn-0.5, the surface of the sample instead became smoother. Figure 1e shows the HRTEM of the Zn/Sn-1 sample. The fringe interval of 0.33 nm can be attributed to the (111) crystal planes of ZnSe, whereas the fringe intervals of 0.34 nm and 0.27 nm are consistent with the (110) and (101) crystal planes of SnO2. Figure 1f reveals the selected area electron diffraction pattern of the Zn/Sn-1 sample. The ring-shape patterns are assigned to the (110), (101), (200) and (211) crystal planes of SnO2. Two spots represent the (111) and (220) crystal planes of ZnSe, which confirms that both ZnSe and SnO2 are present in the hybrid Zn/Sn-1 sample. The elemental distributions on the surface of the Zn/Sn-1 sample are recorded in Figure 1h-l. It can be observed that Zn, Se, Sn and O elements are uniformly and continuously distributed along the shape of the core-shell microsphere structure, indicating the homogeneous distribution of ZnSe and SnO2 in the sphere-shape matrix. Figure 2a shows a comparison of the responses of the mesoporous ZnSe/SnO2 heterostructure based sensors with different concentrations of SnO2 shells to 2.4 ppm NO2 at different operating temperatures from 140 °C to 180 °C. Among these samples, the Zn/Sn-1 heterostructure based sensor achieves the highest response approximately 6.94 at the optimum operating temperature of 160 °C, which is higher than that of Zn/Sn-0.5 (~4.55) and SnO2 (~2.86) based sensors. Figure 2b reveals the selectivity of the Zn/Sn-1 based sensor for several possible interferents with a concentration of 100 ppm such as SO2, CO2, CO, methanol, ethanol, acetone, benzene, methylbenzene, xylene, ammonia and formaldehyde, respectively. The sensor represents the highest response to 2.4 ppm NO2 than others, which indicates an excellent selectivity.

Achievement of self-heated sensing of hazardous gases by WS2 (core)–SnO2 (shell) nanosheets

With the recent rapid development of portable smart electronic devices, there is a great demand for gas sensors having high performance, high flexibility, and low energy consumption. We explored the effects of SnO2 shell thickness and operating voltage on the sensing behavior of WS2 nanosheets (NSs) deposited over a flexible substrate in self-heating mode. Commercial WS2 nanowires (NWs) were used as the core and SnO2 shells with various thicknesses were deposited on the core by an advanced physical technique, namely atomic layer deposition (ALD). With regard to CO sensing, a shell thickness of 15 nm operating at 3.4 V, was optimal. Alternatively, for NO2 sensing, the optimal shell thickness was 30 nm. Therefore, using engineering design principles to determine the shell material and shell thickness, it is possible to selectively detect reducing gases such as CO, while the response to oxidizing gases is weak. We have also discussed the details of this sensing mechanism. We believe that our results can lead to further study of C–S NSs for sensing studies from different points of views.

A SnO2 shell for high environmental stability of Ag nanowires applied for thermal management.

Since silver nanowires (AgNWs) show high infrared reflectance many studies present their applicability as thermal management products for various wearable textiles. However, their use for practical purposes is only partially evaluated, without focusing on improving their low atmospheric and liquid stability. This report describes a new approach for the topic and proposes a facile method of Ag nanowire passivation with a SnO2 layer for high environmental stability and retention of high infrared reflectance. The one-step passivation process of AgNWs was carried out in the presence of sodium stannate in an aqueous solution at 100 °C, and resulted in the formation of core/shell Ag/SnO2 nanowires. This study presents the morphological, chemical, and structural properties of Ag/SnO2NWs formed with a 14 nm thick SnO2 shell, consisting of 7 nm rutile-type crystals, covering the silver metallic core. The optical properties of the AgNWs changed significantly after shell formation, and the longitudinal and transverse modes in the surface plasmon resonance spectrum were red shifted as a result of the surrounding media dielectric constant changes. The passivation process protected the AgNWs from decomposition in air for over 4 months, and from dissolution in a KCN solution at concentrations up to 0.1 wt%. Moreover, the report shows the microwave irradiation effect on the shell synthesis and previously synthesised Ag/SnO2NWs. The post-synthesis irradiation, as well as the SnO2 shell obtained by microwave assistance, did not allow long-term stability to be achieved. The microwave-assisted synthesis process was also not fast enough to inhibit the formation of prismatic silver structures from the nanowires. The Ag/SnO2NWs with a shell obtained by a simple hydrolysis process, apart from showing high infra-red reflectance on the para-aramid fabric, are highly environmentally stable. The presented SnO2 shell preparation method can protect the AgNW's surface from dissolution or decomposition and facilitate the designing of durable smart wearable thermal materials for various conditions.

Type-II Heterojunctions in SnO2-Coated TiO2 Core-Shell Nanoparticles

Titanium dioxide (TiO2) and tin oxide (SnO2) are two popular wide band-gap semiconductors for photocatalytic and electronic applications such as solar cells, optoelectronic devices, and lithium-ion batteries. Nanosized TiO2 structures have strong absorption in the UV region while SnO2 is a powerful transparent conducting oxide. Composites of TiO2 and SnO2 are especially attractive since they form a type-II heterojunction extending the lifetime of charge carriers and enhancing photoconversion efficiency. In this study, the synthesis of TiO2 nanoparticles as well as their uniform and controlled coating with SnO2 shells are described, providing the first utilization of sodium stannate to grow SnO2 shells on a metal-oxide core. The step-growth method utilized here shows the ability to vary the shell thickness between 5-40 nm while maintaining uniformity of the shell. As such, the complete synthesis route involves facile and reproducible surfactant-free solution-based methods at moderate temperatures. The nanoparticles were characterized using scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), energy-dispersive X-ray spectroscopy (EDX), and X-ray diffraction (XRD). Overall, this paper represents reliable nanoscale fabrication techniques offering key advancements in photovoltaic and optoelectronic applications. Keywords: TiO2, SnO2, Heterojunction, Core-shell, Nanoparticles, Wide Band-gap Semiconductor

Experimental Investigation for Some Properties of PMMA Denture Base Strengthened by Different Nanoadditives

In dental and medical applications, poly-methyl methacrylate (PMMA) has been widely accepted due to the excellent biocompatibility and easy fabrication. Yet, some of the physical and mechanical characteristics of this compound are considered inferior. Seven groups of PMMA nano-composite samples were reported to be fabricated at laboratory temperature . These samples could be used in manufacturing the complete or partial maxillary denture base. The aim of this research is to prepare nano-composite materials which consist of PMMA as a matrix material and two different types of powder (prepared nanoparticles of SnO2 and natural egg shell powder (ESP)) as strengthening materials. The selected additives were used in many cases as pure or hybrid composites, specifically with weight percentage ratios of 1 and 2 wt%. Several analytical tests, namely AFM, FTIR, XRD and SEM, were used on the prepared nanoparticles. In addition, several tests were applied to assess the mechanical behavior before and after the reinforcement, including thermal conductivity, Vickers micro-Hardness, and water absorption. The results showed that the maximum amount of energy absorption in the composites was 1% at different types of additives, while a significant increase in thermal conductivity was recorded as the SnO2NPs percentage was increased. For surface micro-hardness, an obvious trend of increase was observed with the increase in additive percentage. The highest measured values of micro-hardness (19.59VHS and 13.30VHS) were recorded for the pure composites of 2% ESP and 2% SnO2, respectively. The results of water absorption test showed that higher percentages of ESP and SnO2, separately, within the pure composite resulted in higher water absorption capacity and an increased value of diffusion coefficient (D).

A facile strategy towards high capacity and stable Sn anodes for Li-ion battery: Dual-confinement via Sn@SnO2 core-shell nanoparticles embedded in 3D graphitized porous carbon network

A scalable and facile one-pot spray pyrolysis method combined with reduction process during hydrogen atmosphere at a low temperature of 400 °C is developed for the formation of Sn@SnO2-3DGHPC materials, in which Sn@SnO2 core-shell nanoparticles are uniformly anchored on a 3D graphitized hierarchical porous carbon network. In this constructed architecture, the SnO2 shell composed of single crystals could effectively not only facilitate the Li+/electrons transport but also alleviate mechanical stress caused by the large volume variation of internal Sn nanoparticles, while the 3D graphitized hierarchical porous carbon network with high electrical conductivity and mechanical stability can tightly capture the Sn@SnO2 nanoparticles and avoid direct contaction between them, thus leading to the internal integrity and structural stability of overall electrode materials. Consequently, this novel Sn@SnO2-3DGHPC anode exhibits high reversible capacity, outstanding cycling stability and rate capability.

Sulfur dioxide gas sensing at room temperature based on tin selenium/tin dioxide hybrid prepared via hydrothermal and surface oxidation treatment

In this paper, a novel SnSe/SnO2 nanoparticles (NPs) composite has been successfully fabricated through hydrothermal method and surface oxidation treatment. The as-prepared sample was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM). A series of morphological and structural characteristics confirm that the SnSe/SnO2 NPs composite shows a core–shell structure with a SnO2 shell with thickness of 6 nm. The prepared SnO2 NPs and SnSe/SnO2 NPs composite were applied as gas-sensing materials, and their gas-sensing properties were investigated at room temperature systematically. Experimental results show that the response value of the SnSe/SnO2 composite sensor toward 100 × 10–6 SO2 is 15.15%, which is 1.32 times higher than that of pristine SnSe (11.43%). And the SnSe/SnO2 composite sensor also has a detection limit as low as 74 × 10–9 and an ultra-fast response speed. The enhanced gas-sensing performance is attributed to the formation of p–n heterojunction between SnSe and SnO2 and the appropriate SnO2 shell thickness.

Palladium Nanoparticles Embedded in Yolk–Shell N-Doped Carbon Nanosphere@Void@SnO2 Composite Nanoparticles for the Photocatalytic Reduction of 4-Nitrophenol

Herein, a novel visible-light-driven yolk–shell nanoreactor has been fabricated, called as Pd/N–Cs@SnO2, which is consisted of movable nitrogen-doped carbon sphere (N–Cs) yolk, interlayer void, mesoporous tin oxide (SnO2) shell, and encapsulated palladium nanoparticles (Pd NPs). The obtained yolk–shell Pd/N–Cs@SnO2 nanoreactor can serve as an excellent catalyst in the visible-light-driven photocatalytic reduction of 4-nitrophenol (4-NP). More importantly, Pd/N–Cs@SnO2 exhibits a remarkable superior activity and higher reusability than core–shell Pd@SnO2 and yolk–shell Pd/N–Cs@mSiO2 nanoreactors. The fabulous character of Pd/N–Cs@SnO2 nanoreactor is attributed to (I) the mesostructured SnO2 shell provides a large surface area for the collection of light as well as the anchoring of Pd to avoid aggregating or leaching; (II) the interlayer void space improves the light absorption by multiple scattering, as well as favors the contact of active sites with reactants in the photocatalytic reactions; (III) the N–Cs allow more permeable visible-light absorption, and accelerate the photoexcited electrons transportation from SnO2 semiconductor to Pd NPs to suppress the electron–hole recombination. This enriches the electron density of Pd NPs surface and then facilitates the photocatalytic reduction of 4-NP. Both the structural advantages and enhanced synergy of Pd/N–Cs@SnO2 nanoreactor make it to be an efficient and stable photocatalyst, which can open an avenue for designing photocatalysts in a board range of organic reactions.

Highly sensitive ultraviolet photodetectors based on ZnO/SnO2 core-shell nanorod arrays

ZnO/SnO2 core-shell nanorod arrays (CSNAs) were synthesized by a facile preparation method. Compared with bare ZnO nanorod arrays (NAs), the near-band-edge photoluminescence (PL) emission was significantly enhanced by coating with SnO2 shell layer. The photoresponse performance of the ultraviolet (UV) photodetector (PD) based on ZnO/SnO2 CSNAs was further investigated. The responsivity and specific detectivity were estimated to be 28.5 (±0.6) A∙W−1 and 2.9 (±0.1) × 1014 cm∙Hz1/2∙W−1, which were much better than those of the PD based on bare ZnO NAs. Moreover, the ZnO/SnO2 heterojunction PD also exhibited improved response and recovery times. The localized states introduced by nanocrystalline SnO2 shell layer could effectively prevent the excitons from being trapped by defect states, resulting in the enhancement of the UV emission and photoresponse performance.

A study on Gas sensing Properties and Reaction Mechanism of Au@SnO2 Core-shell Structure Nanoparticles to H2S Gas

The H2S is a toxic and malodorous gas produced from coal mine, natural gas manufacturing processes, and wastewater treatment plants. Due to increased environmental concern, there is an increasing demand for semiconductor gas sensors that are selective and responsive towards H2S gas.SnO2 has been known as a representative semiconductor gas sensing material because of chemical stability and high electron mobility. However SnO2 has a problem that H2S gas doesn’t detached after adsorbing on the surface on SnO2. To solve this problem, the use of noble metal catalysts has been suggested. Au nanoparticles (NPs) are reported to be a good catalyst for the H2S oxidation reaction. To investigate the effects of Au NPs on H2S adsorption and desorption, Au@SnO2 core-shell NPs were applied as a sensing material.In this study, Au@SnO2 core-shell NPs has been synthesized by microwave-assisted hydrothermal method. Au@SnO2 core-shell NPs were calcined at various temperatures (350°C ~ 550°C) to control the surface morphology and crystallinity of SnO2 shell, and their gas sensing property were investigated towards H2S gas (2 ppm to 100 ppm). Based on the results of the sensing test of Au@SnO2 core-shell NPs, we examined the effect of Au NPs on H2S adsorption and desorption.The Au@SnO2 core-shell structure NPs were successfully synthesized by microwave-assisted hydrothermal method, and the particle size was 26-30 nm and the shell thickness of SnO2 shell layer was 14-18 nm. The highest sensing responses of pure SnO2 and Au@SnO2 core-shell NPs showed at the working temperature of 200°C, the responses value to 100 ppm H2S gas were 4,748 and 517, respectively. The optimum working temperature for Au@SnO2 core-shell NPs for detecting H2S gas was at 300°C because the gas sensing response showed relatively high as compared to pure SnO2 and the recovery rate was the highest value. Moreover, the selectivity of H2S toward CO, CH4, C2H5OH gases appeared at this working temperature. The reason why Au@SnO2 core-shell NPs selectively reacted with H2S gas at 300°C was due to the catalytic activity of Au core for H2S oxidation reaction.Keywords: Au@SnO2, nanoparticle, semiconductor gas sensor, H2S gas, adsorption

Investigation on the impact of different stabilizing agents on structural, optical properties of Ag@SnO2 core - shell nanoparticles and its biological applications

Abstract This manuscript details the impact of stabilizing agents on the structural, optical properties of Ag@SnO2 core – shell nanoparticles and its biological applications. Three different stabilizing agent viz. Poly Vinyl Pyrrolidone (PVP), zeroth generation triazolyl glycodendrimer and zeroth generation triazolyl chalcone dendrimer were used as stabilizers in the synthesis of Ag@SnO2 nanoparticles. The results were compared to study their effect on the structural and optical properties of the synthesized samples. The structural parameters of the samples were investigated by XRD analysis, FESEM and HRTEM images. The presence of SnO2 shell on the Ag core was also corroborated by XPS results. The XRD data was used for refining and characterizing the elements present in the sample by Reitveld method. The average crystallite size, dislocation density, lattice parameters (a, c), lattice strain of the samples were calculated using XRD measurements. Williamson – Hall (W-H) method and Size – Strain Plot (SSP) method were used to calculate the lattice strain of the synthesized sample. The concentric rings of the SAED pattern and the lattice fringe images exhibited the interplanar d-spacing values and the results were compared with XRD measurements. The optical properties of the samples were investigated using UV–Vis spectra and the band gap energy were calculated using Tauc plot. The Photoluminescence (PL) studies of the Ag@SnO2 core – shell nanoparticles with the three stabilizing agents are also discussed in this work. The antibacterial and antifungal activities of the chalcone dendrimer stabilized Ag@SnO2 core – shell nanoparticles were tested against the pathogens Bacillus subtilis, Proteus mirabilis, Candida albicans and Aspergillus niger.

Precise preparation of WO3@SnO2 core shell nanosheets for efficient NH3 gas sensing

Development of high-performance ammonia (NH3) sensor is imperative for monitoring NH3 in the living environment. In this work, to obtain a high performance NH3 gas sensor, structurally well-defined WO3@SnO2 core shell nanosheets with a controllable thickness of SnO2 shell layer have been employed as sensing materials. The prepared core shell nanosheets were used to obtain a miniaturized gas sensor based on micro-electro-mechanical system (MEMS). By tuning the thickness of SnO2 layer via atomic layer deposition, a series of WO3@SnO2 core-shell nanosheets with tunable sensing properties were realized. Particularly, the sensor base on the fabricated WO3@SnO2 nanosheets with 20-nm SnO2 shell layer demonstrated superior gas sensing performance with the highest response (1.55) and selectivity toward 15 ppm NH3 at 200 °C. This remarkable enhancement of NH3 sensing ability could be ascribed to the formation of unique WO3-SnO2 core-shell heterojunction structure. The detailed mechanism was elucidated by the heterojunction-depletion model with the help of specific band alignment.

Localized inside-out Ostwald ripening of hybrid double-shelled cages into SnO2 triple-shelled hollow cubes for improved toluene detection.

Unique SnO2 triple-shelled hollow cages with a well-defined cubic shape have been successfully prepared via additional deposition of polycrystalline SnO2 on hybrid Zn2SnO4/SnO2 double-shelled nanotemplates followed by removal of Zn2SnO4. Structural characterization demonstrates that SnO2 triple-shelled hollow cubes (THCs) are hierarchically composed of numerous primary nanoparticles with a size of about several nanometers. The synthetic step-dependent multilayered evolution mechanism can be addressed in terms of different hollowing strategies. Based on the unique less-agglomerated multilayered and porous configuration, the gas sensing performances of SnO2 THCs exhibit an obvious improvement of response and shortened response-recovery characteristics at their optimal working temperature, compared with those of referenced single- and double-shelled SnO2 nanostructures.

Self-sacrificing template strategy to facilely prepare well-defined SnO2@C quasi-hollow nanocubes for lithium-ion battery anode

With many attracted physicochemical properties, hollow nanostructures have gained extensive attention in field of anode materials for lithium-ion batteries. The template-assisted method is a common and simple method to prepare hollow nanomaterials. However, the geometry of 0D resultant hollow nanomaterials from template-assisted methods is mostly spherical due to the difficulties ranging from forming uniform coating around high curvature surfaces to the deficiency of nonspherical templates available. Herein, we successfully demonstrate a self-sacrificing template strategy for facile preparation of a well-defined nonspherical SnO2@C quasi-hollow nanocubes composite (SnO2@C q-HNCs) for the first time. More importantly, thus cubic geometry offers the SnO2@C q-HNCs several architectural advantages in lithium storage: (i) the external carbon coating and internal hollow space can availably mitigate a large volume expansion, and thus guarantee the improved structural stability; (ii) the thin SnO2 shell can dramatically lower the diffusion distances of electrons and ions, therefore accelerates ions and electrons transport; (iii) the carbon can enhance the conductivity of whole composite, and accordingly enhances the rate property; and (iv) the well-defined cubic geometry with the accessible exposed active planes can offer more lithium storage sites and enlarge the contact area between SnO2@C q-HNCs and electrolytes, hence promote the diffusion efficiency. Consequently, the SnO2@C q-HNCs electrodes reveal superior electrochemical performance, delivering 732 mAh g−1 after 350 cycles at 200 mA g−1 as well as 545 mAh g−1 at even 3000 mA g−1. Broadly, this strategy may be extended to preparation of other nonspherical metal oxides/carbon nanocomposites for applications in various fields such as energy storage and conversion, environmental analysis, catalysis, drug delivery, and sensor.

Core@shell structured Au@SnO2 nanoparticles with improved N2 adsorption/activation and electrical conductivity for efficient N2 fixation

The design of electrocatalysts with enhanced adsorption and activation of nitrogen (N2) is critical for boosting the electrochemical N2 reduction (ENR). Herein, we developed an efficient strategy to facilitate N2 adsorption and activation for N2 electroreduction into ammonia (NH3) by vacancy engineering of core@shell structured Au@SnO2 nanoparticles (NPs). We found that the ultrathin amorphous SnO2 shell with enriched oxygen vacancies was conducive to adsorb N2 as well as promoted the N2 activation, meanwhile the metallic Au core ensured the good electrical conductivity for accelerating electrons transport during the electrochemical N2 reduction reaction, synergistically boosting the N2 electroreduction catalysis. As confirmed by the 15N-labeling and controlled experiments, the core@shell Au@amorphous SnO2 NPs with abundant oxygen vacancies show the best performance for N2 electroreduction with the NH3 yield rate of 21.9 μg h−1 mg−1cat and faradaic efficiency of 15.2% at −0.2 VRHE, which surpass the Au@crystalline SnO2 NPs, individual Au NPs and all reported Au-based catalysts for ENR.

Core–Shell ZnO@SnO2 Nanoparticles for Efficient Inorganic Perovskite Solar Cells

The ideal charge transport materials should exhibit a proper energy level, high carrier mobility, sufficient conductivity, and excellent charge extraction ability. Here, a novel electron transport material was designed and synthesized by using a simple and facile solvothermal method, which is composed of the core-shell ZnO@SnO2 nanoparticles. Thanks to the good match between the energy level of the SnO2 shell and the high electron mobility of the core ZnO nanoparticles, the PCE of inorganic perovskite solar cells has reached 14.35% (JSC: 16.45 mA cm-2, VOC: 1.11 V, FF: 79%), acting core-shell ZnO@SnO2 nanoparticles as the electron transfer layer. The core-shell ZnO@SnO2 nanoparticles size is 8.1 nm with the SnO2 shell thickness of 3.4 nm, and the electron mobility is seven times more than SnO2 nanoparticles. Meanwhile, the uniform core-shell ZnO@SnO2 nanoparticles is extremely favorable to the growth of inorganic perovskite films. These preliminary results strongly suggest the great potential of this novel electron transfer material in high-efficiency perovskite solar cells.

Shell isolated nanoparticle enhanced Raman spectroscopy (SHINERS) studies of steel surface corrosion

Electrochemical shell isolated nanoparticle enhanced Raman spectroscopy (SHINERS) in alkaline environments using Au@SnO2 core-shell particles is reported. Au nanoparticles covered by an approximately 4 nm thick SnO2 shell are shown to be pinhole free and provide strong surface enhanced Raman scattering of a pyridine derivative adsorbed on smooth gold surfaces. The Au@SnO2 core-shell particles are used to demonstrate the first electrochemical SHINERS spectra of corrosion products on 304 stainless steel and carbon steel. Unlike Au@SiO2 particles, the SnO2 shells are not degraded by the local high pH created by electrolysis reactions. The SHINERS spectra for 304 stainless steel are indicative of amorphous or microcrystalline Fe(OH)2 with a small contribution from Cr(VI) oxide at high overpotentials. In the presence of KCl, a band attributed to γ-FeOOH is found in the spectra. For carbon steel the SHINERS spectra did not show any evidence of Fe oxides, hydroxides or oxyhydroxides but rather the formation of the Fe-water complex, [Fe(H2O)6]n+ (n = 2,3) at the electrode surface. SHINERS data for carbon steel in the presence of an organic inhibitor, benzotriazole (BTA), indicate that BTA inhibits the formation of Fe-water complexes at the surface of the electrode that form in its absence.

Variation of shell thickness in ZnO-SnO2 core-shell nanowires for optimizing sensing behaviors to CO, C6H6, and C7H8 gases

ZnO-SnO2 core-shell nanowires (C-S NWs) with different shell thicknesses (0–120 nm) were prepared and their sensing behavior was systematically studied. ZnO-SnO2 C-S NWs were prepared using a two-step synthesis procedure, where core ZnO NWs were synthesized by a vapor-liquid-solid growth technique, and subsequently these cores were coated with SnO2 shell layers by using an advanced atomic layer deposition technique. The sensors were exposed to 10-ppm CO, C6H6, and C7H8 gases at an optimal working temperature. The shell thickness was optimized to be 40 nm, for which the sensor revealed the highest sensitivity and fastest dynamics to the above-mentioned gases. The sensing mechanism was discussed in detail and the dominant mechanism was related to the radial modulation effect as well as the volume fraction of the shell to the total volume of C-S NWs.

ZIF-67-derived CoO (tetrahedral Co2+)@nitrogen-doped porous carbon protected by oxygen vacancies-enriched SnO2 as highly active catalyst for oxygen reduction and Pt co-catalyst for methanol oxidation

Fabrication of efficient catalyst/co-catalyst for enhancing methanol oxidation and oxygen reduction reactions (MOR/ORR) is the key to make direct methanol fuel cells more economical. Here, hierarchical CoO@nitrogen-doped porous carbon@SnO2 (CoO@NPC@SnO2) polyhedrons are prepared as active catalysts for ORR and Pt supports/co-catalysts for MOR using zeolitic imidazolate frameworks-67 (ZIF-67). For ORR, CoO@NPC@SnO2-1 (Co@NPC-to-SnCl2·2H2O mass ratio of 1: 1) exhibits a more positive peak potential (0.82 V vs. RHE) than that of commercial Pt/C (10 wt.%). Outer SnO2 shells can prevent CoO cores (active tetrahedral Co2+) from corrosion during ORR. For MOR, Pt-CoO@NPC@SnO2-1 (5 wt.%) shows a much higher mass activity (1518 mA mgPt−1) than that of Pt/C (496.8 mA mgPt−1). High CO tolerance of Pt-CoO@NPC@SnO2-1 is attributed to strong metal (Pt)-metal oxides (SnO2) interactions, which facilitate adsorption of OH− on SnO2 to remove COads. Therefore, this study provides a strategy to enhance ORR/MOR performance by using hierarchically-structured catalysts/co-catalysts from ZIF templates.

Outstanding Room-Temperature Hydrogen Gas Detection by Plasma-Assisted and Graphene-Functionalized Core-Shell Assembly of SnO2 Nanoburflower.

Here, we have reported the synthesis of three-dimensional, mesoporous, nano-SnO2 cores encapsulated in nonstoichiometric SnO2 shells grown by chemical as well as physical synthesis procedures such as plasma-enhanced chemical vapor deposition, followed by functionalization with reduced graphene oxide (rGO) on the surface. The main motif to fabricate such morphology, i.e., core–shell assembly of burflower-like SnO2 nanobid is to distinguish gases quantitatively at reduced operating temperatures. Electrochemical results reveal that rGO anchored on SnO2 surface offers excellent gas detection performances at room temperature. It exhibits outstanding H2 selectivity through a wide range, from ∼10 ppm to 1 vol %, with very little cross-sensitivity against other similar types of reducing gases. Good recovery as well as prompt responses also added flair in its quality due to the highly mesoporous architecture. Without using any expensive dopant/catalyst/filler or any special class of surfactants, these unique SnO2 mesoporous nanostructures have exhibited exceptional gas sensing performances at room temperature and are thus helpful to fabricate sensing devices in most cost-effective and eco-friendly manner.