SnO2 Core Research Articles

Impedance Spectroscopy Study of Charge Transfer in the Bulk and Across the Interface in Networked SnO2/Ga2O3 Core–Shell Nanobelts in Ambient Air

Metal oxide core–shell fibrous nanostructures are promising gas-sensitive materials for the detection of a wide variety of both reducing and oxidizing gases. In these structures, two dissimilar materials with different work functions are brought into contact to form a coaxial heterojunction. The influence of the shell material on the transportation of the electric charge carriers along these structures is still not very well understood. This is due to homo-, hetero- and metal/semiconductor junctions, which make it difficult to investigate the electric charge transfer using direct current methods. However, in order to improve the gas-sensing properties of these complex structures, it is necessary to first establish a good understanding of the electric charge transfer in ambient air. In this article, we present an impedance spectroscopy study of networked SnO2/Ga2O3 core–shell nanobelts in ambient air. Tin dioxide nanobelts were grown directly on interdigitated gold electrodes, using the thermal sublimation method, via the vapor–liquid–solid (VLS) mechanism. Two forms of a gallium oxide shell of varying thickness were prepared via halide vapor-phase epitaxy (HVPE), and the impedance spectra were measured at 189–768 °C. The bulk resistance of the core–shell nanobelts was found to be reduced due to the formation of an electron accumulation layer in the SnO2 core. At temperatures above 530 °C, the thermal reduction of SnO2 and the associated decrease in its work function caused electrons to flow from the accumulation layer into the Ga2O3 shell, which resulted in an increase in bulk resistance. The junction resistance of said core–shell nanostructures was comparable to that of SnO2 nanobelts, as both structures are likely connected through existing SnO2/SnO2 homojunctions comprising thin amorphous layers.

Optical simulation of triple-junction tandem solar cell based on SnO2 core nanowire array embedded in CZTSe, Cs2SnI6 and CuAlxIn1−xTe2 layers in bottom, middle and top cells, respectively

Optical simulation of triple-junction tandem solar cell based on SnO2 core nanowire array embedded in CZTSe, Cs2SnI6 and CuAlxIn1−xTe2 layers in bottom, middle and top cells, respectively

Electron Transfer Dynamics at Dye-Sensitized SnO2/TiO2 Core/Shell Electrodes in Aqueous/Nonaqueous Electrolyte Mixtures.

The dynamics of photoinduced electron transfer were measured at dye-sensitized photoanodes in aqueous (acetate buffer), nonaqueous (acetonitrile), and mixed solvent electrolytes by nanosecond transient absorption spectroscopy (TAS) and ultrafast optical-pump terahertz-probe spectroscopy (OPTP). Higher injection efficiencies were found in mixed solvent electrolytes for dye-sensitized SnO2/TiO2 core/shell electrodes, whereas the injection efficiency of dye-sensitized TiO2 electrodes decreased with the increasing acetonitrile concentration. The trend in injection efficiency for the TiO2 electrodes was consistent with the solvent-dependent trend in the semiconductor flat band potential. Photoinduced electron injection in core/shell electrodes has been understood as a two-step process involving ultrafast electron trapping in the TiO2 shell followed by slower electron transfer to the SnO2 core. The driving force for shell-to-core electron transfer increases as the flat band potential of TiO2 shifts negatively with increasing concentrations of acetonitrile. In acetonitrile-rich electrolytes, electron injection is suppressed due to the very negative flat band potential of the TiO2 shell. Interestingly, a net negative photoconductivity in the SnO2 core is observed in mixed solvent electrolytes by OPTP. We hypothesize that an electric field is formed across the TiO2 shell from the oxidized dye molecules after injection. Conduction band electrons in SnO2 are trapped at the core/shell interface by the electric field, resulting in a negative photoconductivity transient. The overall electron injection efficiency of the dye-sensitized SnO2/TiO2 core/shell photoanodes is optimized in mixed solvents. The ultrafast transient conductivity data illustrate the crucial role of the electrolyte in regulating the driving forces for electron injection and charge separation at dye-sensitized semiconductor interfaces.

Vacancy-Rich SnO2 Quantum Dot Stabilized by Polyoxomolybdate as Electrocatalyst for Selective NH3 Production.

The pronounced conductivity of tin dioxide (SnO2) nanoparticles makes it an ideal multifunctional electrode material, while the challenge is to stabilize the quantum dot (QD) SnO2 nanocore in water. An Anderson-type polyoxomolybdate, (NH4)6[Mo7O24], is employed as an inorganic ligand to stabilize a ca. 6 nm SnO2 QD (Mox@SnO2). X-ray scattering and diffraction studies confirm the tetragonal SnO2 nanocore in Mox@SnO2. Elemental analyses are in good agreement with the mass spectrometric detection of the [Mo7O24]6- cluster present in Mox@SnO2. The ionic POMs attached to the SnO2 surface through [Mo-O-Sn] covalent linkages have been established by surface zeta potential, shift of the [Mo = O]t Raman vibration, and extended X-ray absorption fine structure (EXAFS) analyses. The presence of the [Mo7O24]6- cluster in the Mox@SnO2 is responsible for the remarkable aqueous stability of Mox@SnO2 in the pH range of 3-9. Dominant oxygen vacancy in the SnO2 core, identified by EXAFS data and the anisotropic electron paramagnetic resonance (EPR) signals (g ∼ 2.4 and 1.9), results in facile electronic conduction in Mox@SnO2 while being deposited on the electrode surface. Mox@SnO2 acts as an active catalyst for the electrocatalytic nitrate reduction (eNOR) to ammonia with 94% faradaic efficiency (FE) at -0.2 V vs RHE and a yield rate of 28.9 mg h-1 cm-2. The stability of Mox@SnO2 in acidic pH provides scope to reuse the Mox@SnO2 electrode at least four times with notable NH3 selectivity and a superior production rate (239.06 mmol g-1(cat) h-1). This study demonstrates the essential role of POM in stabilizing SnO2 QD, harnessing its electrochemical activity toward electrocatalytic ammonia production.

Surface-Enhanced Raman Spectroscopy for Boosting Electrochemical CO2 Reduction on Amorphous-Surfaced Tin Oxide Supported by MXene.

Amorphous materials disrupt the intrinsic linear scalar dependence seen in their crystalline counterparts, typically exhibiting enhanced catalytic characteristics. Nevertheless, substantial obstacles remain in terms of boosting their stability, enhancing their conductivity, and elucidating distinct catalytic mechanisms. Herein, a core-shell catalyst, comprising a crystalline SnO2 core and an amorphous SnOx shell supported on MXene (denoted as SnO2@SnOx/MXene), was prepared utilizing hydrothermal and solution reduction methods. The SnO2@SnOx/MXene catalyst excels in the electrocatalytic conversion of CO2 to formate, yielding a Faradaic efficiency (FE) as high as 93% for formate production at -1.17 V vs RHE and demonstrating exceptional durability. Both density functional theory (DFT) calculations and experimental results indicate that the SnOx shell bolsters formate formation by fine-tuning the adsorption energy of the *OCHO intermediate. In SnO2@SnOx/MXene, MXene plays a vital role in enhancing the conductivity and stability of the amorphous shell and especially amplifying Raman signals of catalyst components. The ex/in situ surface-enhanced Raman scattering (SERS) application further confirms the formation of amorphous SnOx and further enables the direct detection of the formation of the intermediate species. This work provides the basis for the application of amorphous materials in practical electrocatalytic reduction of CO2 reduction.

Effect of electrospun bilayer titanium oxide–tin oxide nanofibers on the performance of dye-sensitized solar cells

The core–shell nanofibers, which contain titanium oxide (TiO2) and tin oxide (SnO2), are known as electrospun nanofibers that improve the performance of dye-sensitized solar cells by exploring the photoanode. The morphology and microstructure of the electrospun nanofibers are studied by scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X–ray diffraction (XRD). Based on the SEM micrographs, the fibers have a bilayer TiO2–SnO2 core–shell structure with a 70–120 nm diameter. The XRD analysis shows the dominant crystalline phase of the synthesized nanostructures after heat treatment. Finally, the synthesized nanofibers are used to prepare dye-sensitized solar cell photoanodes with thicknesses of 8, 11, 14, and 17 μm, which their performances are investigated. The current–voltage (I–V) curve of the solar cells under the Xenon lamp irradiation is measured and calculated. The optimal solar cell with a photoanode made electrophoretic at 30 V for 8 min shows the best performance. The optimal thickness of the TiO2–SnO2 nanocomposite for this photoanode is 14 μm. The short-circuit current density, open-circuit voltage, and optimal cell efficiency for this sample are 19.35 mA/cm2, 650 mV, and 9.27%, respectively.

Cu2O/SnO2 Heterostructures: Role of the Synthesis Procedure on PEC CO2 Conversion

Addressing the urgent need to mitigate increasing levels of CO2 in the atmosphere and combat global warming, the development of earth-abundant catalysts for selective photo-electrochemical CO2 conversion is a central and pressing challenge. Toward this purpose, two synthetic strategies for obtaining a Cu2O–SnO2 catalyst, namely co-precipitation and core–shell methods, were compared. The morphology and band gap energy of the synthesized materials were strongly different. The photoactivity of the core–shell catalyst was improved by 30% compared to the co-precipitation one, while its selectivity was shifted towards C1 products such as CO and formate. The stability of both catalysts was revealed by an easy and fast EIS analysis, indicating how the effective presence of a SnO2 shell could prevent the modification of the crystalline phase of the catalyst during PEC tests. Finally, directing the selectivity depending on the synthesis method used to produce the final Cu2O–SnO2 catalyst could possibly be implemented in syngas and formate transformation processes, such as hydroformylation or the Fischer–Tropsch process.

Construct Ni–SnO2 core coated amorphous Ni(BO2)2 shell boosts water splitting for hydrogen production

Through a simple redox reaction, the precursor of Ni (OH)2 mixed with SnO2 was in situ transformed into a core-shell structure with elemental Ni blend SnO2 as the core and nickel metaborate as the shell. The metaborate shell is an excellent adsorption site for water molecules, which paves the way for subsequent hydride adsorption. When a small amount of SnO2 is mixed with elemental Ni, the electronic structure is optimized, and the electron enrichment of Ni is realized, making the hydrogen adsorption performance better. This core-shell synergy promotes the Vomer step in HER, thereby enhancing HER performance. In addition, Ni–Sn@NiBO/NF possesses larger electrochemical surface area and smaller charge transfer resistance. Only an overpotential of 22 mV is needed to drive a current density of 10 mA cm−2, indicating the excellent HER performance of the Ni–Sn@NiBO/NF catalyst. At high current density of 50 mA cm−2, the overpotential is only 79 mV. When Ni–Sn@NiBO/NF is used as the bifunctional catalyst for coupling HER and OER, the voltage is only 1.595 V at 10 mA cm−2. It shows that the catalyst has great application potential in electrocatalytic water decomposition to produce hydrogen.

Electroabsorption as a Probe of Electrons Injected into Nanocrystalline SnO2/TiO2 Core/Shell Thin Films

Core/shell nanoparticles comprised of a SnO2 core and a TiO2 shell, SnO2/TiO2, present in a mesoporous thin film, are of practical interest for applications in dye-sensitized water splitting as they outperform sensitized materials based on SnO2 or TiO2 (anatase or rutile polymorphs) for the water oxidation half-reaction. Here we report electroabsorption studies designed to quantify the surface electric field and the ability of the shell to screen an electric field from a surface anchored dye. The metal-to-ligand charge transfer (MLCT) absorbance of [Ru(bpy)2(4,4′-(PO3H2)2-2,2′-bipyridine)](PF6)2, abbreviated RuP, was indeed sensitive to electron injection into the oxide support. When a fixed charge of 1 mC was injected, the electric field magnitude (in MV/cm) increased in the order 0.15 TiO2 (rutile) < 0.35 TiO2 (anatase) ≪ 1.4 SnO2 (rutile). This order tracks the reported bulk dielectric constants of the oxide materials. Comparative studies with SnO2/TiO2 core/shell materials, fabricated by atomic layer deposition (ALD) of a TiO2 shell on a mesoporous SnO2 thin film, diminished the field strength by about a factor of 4 to values less than or about equal to that measured for anatase TiO2. Heat treating some SnO2/TiO2 core/shell materials at 450 °C resulted in a crystalline rutile TiO2 shell that screened the field most effectively, more so even than rutile TiO2 alone. Taken together, the data indicate that injected electrons reside within the SnO2 core region.

Effect of tin dioxide sol on the peculiarities of electrodeposition and structure of copper and nickel coatings

Tin dioxide sol is proposed as the additive in weakly alkaline diphosphate copper and nickel plating electrolytes which provides the deposition on the carbon steel of fine-grained and close-packed coatings with the increased protective ability. It is revealed that nanoparticles of this sol have sizes of 2–5 nm, consist of the SnO2 core and SnO2–x(OH)2x shell, are stabilized to coagulation and dissolution in the electrolytes with the adsorbed copper or nickel diphosphate complex ions, and carry a charge of –(38–42) mV at the pH of the electrolytes within 8.2–8.6. They adsorb both on the initial substrate and on the surface of the growing coating, thus performing the function of nucleation centers in the process of copper and nickel electrodeposition. This happens under certain conditions, which include direct current density of 1.0 A/dm2 and tin dioxide concentration in the electrolyte of 0.5 g/dm3. In these conditions SnO2 sol does not affect the rate of deposition equal to 7−13 μm/h and current efficiency of 68−97%. Tin dioxide has not been detected inside copper and nickel coatings.

SnO2‐SiO2 1D Core‐Shell Nanowires Heterostructures for Selective Hydrogen Sensing

AbstractSnO2 is one of the most employed n‐type semiconducting metal oxide in chemo‐resistive gas‐sensing although it presents serious limitations due to a low selectivity. Herein, the authors introduce 1D SnO2‐SiO2 core‐shell nanowires (CSNWs). The amorphous SiO2‐shell layer with varying thicknesses (1.8–10.5 nm) is grown onto the SnO2 nanowires (NWs) by atomic layer deposition (ALD). SiO2‐coated SnO2 CSNWs show a dramatic improvement of the selectivity towards hydrogen. Moreover, the sensing‐response is strongly correlated to the thickness of the SiO2‐shell and the working temperature. The SnO2‐SiO2 CSNWs sensor with a 4.8‐nm SiO2 shell thickness exhibits the best selectivity and sensitivity, having ca. 7‐fold higher response toward hydrogen compared to bare‐SnO2 NWs. The selectivity and enhanced sensing‐response are related to the masking effect of the SiO2 shell and an increase in the width of the electron‐depletion‐layer due to a strong electronic coupling between the SnO2 core and SiO2 coating, respectively.

Controlled synthesis of electrospun hollow Pt-loaded SnO2 microbelts for acetone sensing

Challenges for ubiquitous diffusion of gas analytes into semiconducting metal oxides (SMOs) based sensing layers have necessitated the introduction of unprecedented synthesis techniques for thin, porous and high-performance gas sensing materials. In this work, electrospinning and calcination were employed to prepare unprecedented SiO2–SnO2 core–shell microbelts (hereinafter referred to as SiO2@SnO2 BLs) followed by etching away of SiO2 in NaOH solution (pH 12) to achieve hollow SnO2 BLs (hereinafter referred to as SnO2 HBLs) with mean crystal size of 14.01 nm, large BET surface area (143.5 m2‧g–1), high porosity (mean pore size of 5.7 nm), and shell thickness of 58.3 ± 11.4 nm. Sensitization of SnO2 HBLs with apoferritin-templated platinum nanoparticles (Pt NPs) enhanced their detection capability toward acetone. Response (defined as Ra/Rg, where Ra and Rg are sensor resistances in air and target gas, respectively) of Pt(0.12 %)_SnO2 HBLs toward 2 ppm acetone was up to 7.8 times higher compared to that of pristine SnO2 HBLs, and exhibited faster response (9.2 s). The Pt(0.12 %)_SnO2 HBLs based sensor indicated a promising long-term stability, and outstanding repeatability of response (Ra/Rg = 93.7 ± 0.89) toward 25 cycles of 2 ppm acetone exposure in a humid environment of 90 % relative humidity. This performance could be attributed to the unique morphology of HBLs, sensitization effects of catalytic Pt NPs, and enlargement of the electron-depleted layer resulting from a Schottky barrier between Pt NPs and SnO2 grains.

Synthesis of ZrO2-Shelled SnO2 Nanowires for NO2 Gas Sensing

Introduction NO2 gas, with its highly toxic nature, is mainly produced from automobile exhaust or the burning of fossil fuels [1]. This gas could lead to damage in the respiratory system when inhaled [2]. Moreover, when exposed to high concentration, could lead to cancer or related disease.One unique type of nanowires is core-shell (C-S) nanowires, where nanowires are covered by a thin shell. In this study, SnO2 nanowires covered by ZrO2 shell has been explored.The oxygen ions in ZrO2 are actively transported after it reaches 600°C limiting the application field. SnO2 has often been applied for gas sensing due to its physiochemical stability and high mobility of charge carriers. SnO2-ZrO2 C-S NWs are expected to show a prominent result in respect of sensor temperature and sensor response. This study has been published on Sensors and Actuators B: Chemical 319 (2020) 128309. Method SnO2 NWs were fabricated using the vapor-liquid-solid (VLS) method. Metallic Sn powders in alumina tube were placed into a furnace and were thermally evaporated at 900°C for 15 min. Evaporated Sn reacts with oxygen from the air, finally, SnO2 NWs are synthesized.ZrO2 was coated on SnO2 NWs by a thermal ALD system (Lucida D100, NCD Technology, Korea). The precursor and reactant for the ALD process were tris(dimethylamino) cyclopentadienyl zirconium (Cp-Zr) and ozone (O3), respectively. Cp-Zr was heated to 90°C in a canister, and Ar gas was used as a bubbler. The pressure and temperature of the ALD process were kept at 0.5 Torr and 300°C, respectively [3,4].A bi-layer electrode (200-nm thick Au and 50-nm thick Ti) was sputter-deposited on the samples for making of the gas sensors. The sensors were placed inside a gas chamber in a tubular furnace. The gas concentrations were controlled by mass flow controllers with air as a background gas. The total flow rate was fixed to 500 sccm during all measurements. Result and Conclusions Fig. 1(A,B), (C,D), (E,F) and (G,H) show TEM and high resolution TEM (HR-TEM) images of SnO2-ZrO2 C-S NWs with 50, 100, 150, 200 ALD cycles respectively. Owing to the very thin nature of the shell, the lattice fringes from the underlying SnO2 core were able to be observed.Fig. 2A and B show EDAX data of SnO2-ZrO2 C-S NWs after 50 cycles for core and shell parts, respectively. For evaluation of the presence of Zr in the core and shell regions, the ratio of Zr/(Zr+Sn) was used. The ratio of Zr/(Zr+Sn) in the core region was 0.08 and that of the shell region was 0.98. This demonstrates the successful deposition of Zr in the shell region. The same trend can be seen for other C-S NWs. Therefore, it can be concluded that ZrO2 is mainly concentrated in the outer regions, whereas the SnO2 is concentrated in the core region, regardless of ALD cycle time. The value of Zr/(Zr+Sn) in the core region becomes higher at higher ALD cycles, as the ZrO2 shell gets thicker, whereas the SnO2 core is constant.Fig. 3 depicts the response to 10 ppm NO2 gas versus temperature for pristine and C-S gas sensors. At low temperatures, the response is low and after reaching a peak at a particular temperature, the response decreases. The highest response for pristine SnO2 gas sensor occurred at 250°C, which was 20.9. For C-S NW gas sensors with a ZrO2 shell deposited at 50, 100, 150, and 200 cycles, the maximum responses were 14.9, 16.2, 24.7, and 14.2, respectively. The sensor with ZrO2 shell being deposited with 150 ALD cycles exhibited the highest gas response. All C-S gas sensors except that deposited with 100 ALD cycles showed their optimal sensing temperature at 150°C. However, for the sensor with ZrO2 shell deposited with 100 ALD cycles, the optimal sensing temperature was 100°C.The selectivity of SnO2-ZrO2 (150 cycles) C-S NW to 10 ppm of various gases at 150°C is presented in Fig. 4. The response to NO2 (24.7) was much higher than that of the other gases.To conclude, the optimal sensing temperature was varied from 100°C for the sensor with a ZrO2 shell deposited with 100 cycles to 250°C for pristine SnO2 gas sensor. Also, NO2 gas sensing results demonstrated a dependence of response to the thickness of the ZrO2 shell. The optimal sensor with a ZrO2 shell thickness of 24.1 nm (150 ALD cycles) revealed a high response to NO2 gas and also a good selectivity to NO2 gas.

Antimony doped SnO2 nanowire@C core–shell structure as a high-performance anode material for lithium-ion battery

SnO2 is considered as one of the high specific capacity anode materials for Lithium-ion batteries. However, the low electrical conductivity of SnO2 limits its applications. This manuscript reports a simple and efficient approach for the synthesis of Sb-doped SnO2 nanowires (NWs) core and carbon shell structure which effectively enhances the electrical conductivity and electrochemical performance of SnO2 nanostructures. Sb doping was performed during the vapor-liquid-solid synthesis of SnO2 NWs in a horizontal furnace. Subsequently, carbon nanolayer was coated on the NWs using the DC Plasma Enhanced Chemical Vapor Deposition approach. The carbon-coated shell improves the Solid-Electrolyte Interphase stability and alleviates the volume expansion of the anode electrode during charging and discharging. The Sb-doped SnO2 core carbon shell anode showed the superior specific capacity of 585 mAhg−1 after 100 cycles at the current density of 100 mA g−1, compared to the pure SnO2 NWs electrode. The cycle stability evaluation revealed that the discharge capacity of pure SnO2 NWs and Sb doped SnO2 NWs electrodes were dropped to 52 and 152 mAh g−1 after100th cycles. The process of Sb doping and carbon nano shielding of SnO2 nanostructures is proposed for noticeable improvement of the anode performance for SnO2 based materials.

Core-shell nanostructure α-Fe2O3/SnO2 binary oxides for the catalytic oxidation and adsorption of elemental mercury from flue gas

In this study, core-shell nanostructure α-Fe2O3/SnO2 binary oxides were prepared to for gaseous elemental mercury (Hg0) removal. The composites were characterized and the results showed that α-Fe2O3/SnO2 was created with the SnO2 core and α-Fe2O3 shell nanostructure. α-Fe2O3/SnO2 had both 76% of Hg0 removal efficiency and 80% of denitration efficiency during 120 min at 350 ℃, which was much higher than the Hg0 removal efficiency of α-Fe2O3 or SnO2 nanospheres. The O2 played an active role in the Hg0 removal over α-Fe2O3/SnO2 at high temperature, however, the SO2 and H2O vapor could reduce the Hg0 removal efficiency of α-Fe2O3/SnO2 to 35% and 40%, respectively. The HCl in flue gas can greatly promote the Hg0 removal efficiency to 95% interpreted as Deacon Reaction mechanism. When HCl is absent in flue gas, the mechanism of Hg0 removal is concluded to catalytic oxidation and adsorption. The gaseous Hg0 is oxidized by Fe3+ and surface-chemisorbed O2- to form HgO adsorbed on the surface and in the void of α-Fe2O3/SnO2. Meanwhile, the Fe2+ is re-oxidized by Sn4+ to form Fe3+ and Sn2+, and the Sn2+ is re-oxidized by O2 in the flue gas.

Studying Structural and Optical Properties of TiO2–SnO2 Core–Shell Synthesized by Sol–Gel Route

AbstractHerein, the TiO2–SnO2 core–shell structures with the core‐to‐shell molar ratios of 5:0.5, 5:0.67, and 5:1 are synthesized by the sol–gel route, and then the structural and optical properties of the synthesized samples are investigated. In order to characterize the samples, the XRD, Raman, FESEM, and TEM techniques are used for their structural verification, while the UV–visible and photoluminescence spectra are used for their optical characterization. The XRD results obtained showed that the annealed TiO2 sample has an anatase tetragonal structure and that the core–shell samples contain the diffraction peaks of both the core TiO2 and the shell SnO2. The XRD results obtained are supported by Raman spectroscopy. The TEM images obtained show evidence of the formation of the composite (core–shell) nanostructure in the samples. The optical investigation shows that the band gaps of the core–shell samples are indirect, like the TiO2 core itself, and increase with an increase in the core‐to‐shell molar ratio. These results also show that the synthesized core–shell samples are suitable candidates for use in optoelectronic devices.

Interface tailoring of SnO2–TiO2 photocatalysts modified with anionic/cationic surfactants

SnO2–TiO2 nanocomposites are prepared by growing TiO2 nanoparticles onto the preformed SnO2 nanoparticles. The SnO2 core nanoparticles ware obtained in the presence of two different surfactants, namely hexadecyltrimethyl ammonium bromide and polyethylene glycol 600 (PEG600), by chemical precipitation followed by a thermal treatment at 500 °C. The TiO2 was obtained directly on modified SnO2 nanoparticles by a sol–gel process. A sample without surfactants was prepared in the same conditions. The processes involved during annealing of precursors were revealed by TGA-FTIR. The crystalline and mesoporous structures of samples were evidenced by XRD, HRTEM and by N2 adsorption–desorption isotherms. XPS investigations highlighted the interface modifications due to the presence of cationic or anionic moieties resulted from the thermal decomposition of surfactants. Combined UPS and UV–Vis measurements allowed the determination of the oxidation energies, band gaps and energy bands alignment of nanocomposites. The photocatalytic activity based on reactive oxygen species (ROS) generation was studied toward degradation of RhB under visible-light irradiation and by the use of EPR coupled with spin-trapping technique. It was found that the generated ROS are only of ·OH type and, this specific process, is analyzed in terms of energy bands alignment.

Electron Localization and Transport in SnO2/TiO2 Mesoporous Thin Films: Evidence for a SnO2/SnxTi1-xO2/TiO2 Structure.

A study of SnO2/TiO2 core/shell films was undertaken to investigate the influences of shell thickness and post deposition sintering on electron localization and transport properties. Electrochemical reduction of the materials resulted in the appearance of a broad visible-near IR absorbance that provided insights into the electronic state(s) within the core/shell structures. As the shell thickness was increased from 0.5 to 5 nm, evidence for the presence of a SnxTi1-xO2 interfacial state emerged that was physically located between the core and the shell. The lifetime of photoinjected electrons increased with the shell thickness. Electron transport occurred through the SnO2 core; however, when materials with shell thicknesses ≥2 nm were annealed at 450 °C, a new electron transport pathway through the shell was evident. The data indicate that these materials are best described as SnO2/SnxTi1-xO2/TiO2 where electrons preferentially localize in a SnxTi1-xO2 interfacial state and transport through SnO2 and annealed TiO2 (if present). The implications of these results for applications in solar energy conversion are discussed.

Crystalline SnO2 @ amorphous TiO2 core-shell nanostructures for high-performance lithium ion batteries

Tin oxide (SnO2) is an attractive anode in lithium ion batteries (LIBs), but its applications have been significantly hampered by the huge volume change during the electrochemical cycling. In this work we demonstrate a rational design of crystalline SnO2 @ amorphous TiO2 core-shell nanostructures, where the crystalline SnO2 core was synthesized by a hydrothermal method and the amorphous TiO2 shell was deposited by atomic layer deposition. The SnO2@TiO2 nanostructures deliver excellent performances during the electrochemical process, having a high reversible capacity of 1259 mAh g−1 at cycling rate of 80 mA g−1, which is still up to 703 mAh g−1 after 50 cycles. The acceptable rate capacity is also revealed with 412 mAh g−1 at 400 mA g−1. The coulombic efficiency is stable at around 100% regardless of cycling rates and numbers. The electrochemical performances of the SnO2@TiO2 batteries are better than those of the SnO2 ones without TiO2 coating. In the SnO2@TiO2 nanostructures, the amorphous TiO2 shell layer can experience an isotropic stress, having the ability to evidently reduce the volume change, lattice stress and so the risk of fracture during the cycling process, which is responsible for their outstanding behaviors. The strategy provided in our study is expected to be a precious guideline for designing an ideal electrode for energy storage devices.

Facile synthesis of SnO2-Fe2O3 core-shell nanostructures and their 2-methoxyethanol gas sensing characteristics

Numerous health hazards arising from the exposure of 2-methoxyethanol (2-ME) and lack of best performing 2-ME sensors pushed us to develop a sensor that can sense 2-ME gas very efficiently. SnO2-Fe2O3 core-shell nanoparticles (CSNPs) were prepared using two step process, in first step core was prepared by co-precipitation method and in the second step the shell was developed by simple sol-gel method. Structural, morphological and compositional studies were carried out systematically and confirmed the perfect formation of core-shell structures with sizes around 18 nm. Further, it revealed that 4 nm Fe2O3 shell was uniformly coated on SnO2 core which demonstrated the formation of heterostructures. Gas sensing properties of fabricated sensors (pure SnO2, Fe2O3 nanoparticles (NPs) and SnO2-Fe2O3) were investigated at room temperature towards various toxic gases. SnO2-Fe2O3 gas sensor has shown tremendous response (∼2080) towards 100 ppm 2-ME gas at room temperature which was much higher than pure NPs based sensors. Response and recovery times of SnO2-Fe2O3 sensor also measured and found to be 43 s and 23 s respectively. Long term stability of the SnO2-Fe2O3 sensor during the first 30 days of its fabrication was tested. Enhanced sensing performance of SnO2-Fe2O3 sensor was attributed to the n-n heterostructures formed between SnO2 core and Fe2O3 shell and porous outer surface of the sensor. All the results suggested that the SnO2-Fe2O3 sensor has great potential for applications in designing practical 2-ME gas sensors.