SnO2 Quantum Dots Research Articles

The role of SnO2quantum dots in improved CH4sensing at low temperature

The role of quantum dots (QDs) of SnO2 in detecting low concentrations of methane (CH4) at a relatively low temperature of ∼150 °C with high response (S ∼ 3.5%) and response time below 1 min is reported. A simple room temperature single step chemical process was adopted for the growth of SnO2 nanoparticles of a size around 2.4 nm. These nanoparticles were subsequently annealed at 800 °C to increase the grain size to 25 nm. The as-prepared SnO2 nanoparticles, being smaller than the corresponding Bohr radius (2.7 nm), showed a strong quantum confinement effect with a blue shift in the band gap energy from 3.6 eV for the bulk SnO2 to 4.37 eV for the QDs. These QDs exhibited a strong sensing response to CH4 in comparison to the annealed sample. A low activation energy of 90 meV, as estimated from the temperature dependent S plot for SnO2 QDs, was found to be the driving force for such unusual high sensitivity at a low operating temperature. X-ray diffraction, transmission electron microscopy, along with Raman spectroscopy measurements are used for the detailed structural studies. The critical role of the chemisorbed oxygen species present at different operating temperatures on the surface of the off-stoichiometric quantum sized SnO2 and bulk-like annealed samples are discussed in light of the adsorption kinetics.

Photogenerated Carriers Transfer in Dye–Graphene–SnO2 Composites for Highly Efficient Visible-Light Photocatalysis

The visible-light-driven photocatalytic activities of graphene-semiconductor catalysts have recently been demonstrated, however, the transfer pathway of photogenerated carriers especially where the role of graphene still remains controversial. Here we report graphene-SnO2 aerosol nanocomposites that exhibit more superior dye adsorption capacity and photocatalytic efficiency compared with pure SnO2 quantum dots, P25 TiO2, and pure graphene aerosol under the visible light. This study examines the origin of the visible-light-driven photocatalysis, which for the first time links to the synergistic effect of the cophotosensitization of the dye and graphene to SnO2. We hope this concept and corresponding mechanism of cophotosensitization could provide an original understanding for the photocatalytic reaction process at the level of carrier transfer pathway as well as a brand new approach to design novel and versatile graphene-based composites for solar energy conversion.

Size Distribution of SnO2 Quantum Dots Studied by UV–Visible, Transmission Electron Microscopy and X-Ray Diffraction

Measuring the size of the quantum dots (QDs) with accuracy is crucial considering its effect on the physical and chemical properties. Size determination of SnO2 QDs prepared by a soft chemical method using various techniques and their correlation is reported here. Direct method like high resolution transmission electron microscopy (HRTEM), and indirect method like X-ray diffraction and ultra violet-visible (UV-Vis) techniques used for size determination and then correlated. Effective crystallite size found from TEM morphological analysis is 2.4 ± 0.1 nm, which matches closely with the crystallite size of 2.3 ± 0.1 nm as calculated using Williamson-Hall plot. Particle size is also calculated from UV-Vis spectroscopy following quantum confinement effect in SnO2. The obtained slopes from the Tauc's plot provide a distri- bution of particle sizes which matches well with the result from TEM analysis.

Large scale synthesis of highly crystallized SnO2 quantum dots at room temperature and their high electrochemical performance

In this work, SnO2 quantum dots with high crystallinity were synthesized on a large scale under mild reaction conditions via an epoxide precipitation route. The SnO intermediate, which was produced in the reactions between epoxide and [Sn(H2O)6]2+, was converted to SnO2 quantum dots by the oxidation of H2O2. It is believed that the protonation and the following ring opening of epoxide promoted the hydrolysis and condensation of [Sn(H2O)6]2+ to form the intermediate. The obtained quantum dots had a maximum specific capacitance of 204.4 F g−1 at a scan rate of 5 mV s−1 in 1 mol l−1 KOH aqueous solution. The electrochemical measurements proved that this high specific capacitance of SnO2 resulted from the Faradaic reactions between SnO2 and the electrolyte. This demonstrates for the first time that SnO2 can be used as a pseudocapacitive electrode material.

Magnetic properties of a SnO2 quantum dot

By using first-principles calculations, the magnetic properties of a SnO2 quantum dot (QD) are investigated. It is found that dangling bonds (DBs) are equated with Co (Ni) dopants, which can induce magnetic moments in SnO2 QDs. Thus, the QD shows very abundant variation of the magnetic properties by combining dopants with DBs. The changes of magnetic moments can be explained well by a carrier modulation model.

Assembling Tin Dioxide Quantum Dots to Graphene Nanosheets by a Facile Ultrasonic Route

Nanocomposites have significant potential in the development of advanced materials for numerous applications. Tin dioxide (SnO2) is a functional material with wide-ranging prospects because of its high electronic mobility and wide band gap. Graphene as the basic plane of graphite is a single atomic layer two-dimensional sp(2) hybridized carbon material. Both have excellent physical and chemical properties. Here, SnO2 quantum dots/graphene composites have been successfully fabricated by a facile ultrasonic method. The experimental investigations indicated that the graphene was exfoliated and decorated with SnO2 quantum dots, which was dispersed uniformly on both sides of the graphene. The size distribution of SnO2 quantum dots was estimated to be ranging from 4 to 6 nm and their average size was calculated to be about 4.8 ± 0.2 nm. This facile ultrasonic route demonstrated that the loading of SnO2 quantum dots was an effective way to prevent graphene nanosheets from being restacked during the reduction. During the calcination process, the graphene nanosheets distributed between SnO2 nanoparticles have also prevented the agglomeration of SnO2 nanoparticles, which were beneficial to the formation of SnO2 quantum dots.

Visible light photocatalytic degradation of methylene blue by SnO2 quantum dots prepared via microwave-assisted method

SnO2 quantum dots (QDs) were successfully synthesized via a microwave-assisted reaction of a SnO2 precursor in an aqueous solution using a microwave system. The morphology, structure and photocatalytic performance in the degradation of methylene blue (MB) were characterized by scanning electron microscopy, transmission electron microscopy, energy dispersive X-ray spectroscopy, X-ray diffraction spectroscopy, UV-vis absorption/reflectance spectroscopy and electrochemical impedance spectroscopy, respectively. The results show that the SnO2 QDs synthesized at a pH value of 5 exhibit an optimal photocatalytic performance with a MB degradation rate of 90% at 240 min under visible light irradiation due to their easier adsorption of pollutants, higher visible light absorption and lower electron–hole pair recombination.

PEGME-bonded SnO2 quantum dots for excellent photocatalytic activity

The ultrafine SnO2 quantum dots (QDs) modified with poly(ethylene glycol methyl ether) (PEGME) (PEGME–SnO2 QDs) were synthesized via hydrothermal method. X-ray diffraction and high-resolution transmission electron microscopy were employed to illustrate that the PEGME–SnO2 QDs are uniform, monodispersed and about 4 nm in diameter. Then infrared spectrum and thermogravimetric analysis were used to prove that PEGME groups are bound tightly to SnO2 surfaces. The as-synthesized PEGME–SnO2 QDs excellently achieved photocatalytic degradation to Rhodamine B dye (RhB). The photon efficiency of the PEGME–SnO2 QDs catalyst and corresponding RhB dye degradation rate constant could reach 0.0058% and 9.98 × 10−2 min−1, respectively. This outstanding photocatalytic performance could be attributed to not only large surface-to-volume ratio and high crystallinity of the ultrafine and monodispersed QDs, but also good hydrophilicity and conductivity of the PEGME surface modifier. Remarkably, such PEGME–SnO2 QDs with outstanding photocatalytic efficiency and stable recyclability are promising to be applied to environmental purification.

Enhanced capability and cyclability of SnO2–graphene oxide hybrid anode by firmly anchored SnO2 quantum dots

A SnO2–graphene oxide (GO) hybrid composite was prepared by binding SnO2 nanocrystals smaller than 5 nm in GO using a facile hydrothermal method. Aided by hydrophilic radicals, such as hydroxyl and carboxyl, in in situ forming SnO2 quantum dots, the active material and the flexible support are highly coupled. When used as an anode material for lithium ion batteries (LIBs), the hybrid composite electrode delivers a high reversible capacity of nearly 800 mA h g−1 (based on the total weight of the composite, discharging at 100 mA g−1) with more than 90% retention for 200 cycles. Besides the excellent cycling performance at various rates, the composite also exhibits a superior rate performance at 10 A g−1 with recoverable initial reversible capacity and a long lifespan of 1000 cycles with 80% capacity retention, outperforming most previous SnO2–graphene hybrid electrodes.

Low threshold amplified spontaneous emission from tin oxide quantum dots: a instantiation of dipole transition silence semiconductors

Direct bandgap semiconductors, such as In2O3, Cu2O, and SnO2, have enormous applications in photochemistry, photovoltaics, and optoelectronics. Due to the same parity of conduction and valence bands, the dipole transition is silent in these direct bandgap semiconductors. The low band-to-band transition efficiency prevents them from high intensity light emission or absorption. Here, we report the fabrication of SnO2 quantum dots (QDs) with sizes less than the exciton Bohr radius by a facile "top-down" strategy based on laser fragmentation of SnO in water. The SnO2 QDs shows exciton emission at ∼300 nm with a high quantum yield of ~17%. Amplified spontaneous exciton emission is also achieved from a thin layer of SnO2 QDs dispersed in PEG400 on a quartz substrate. Therefore, we have shown that SnO2 QDs can be a potential luminescent material suitable for the realization of ultraviolet B lasing devices.

Self assembled surface adjoined mesoscopic spheres of SnO2 quantum dots and their optical properties

A simple one pot acidic solution single precursor synthesis method has lead to highly crystalline SnO2 quantum dots (QD) that self assemble to form mesoscopic spheres. The precursor solvent and pH conditions were changed to optimise the crystalline quality, particle size and luminescence properties of SnO2 QDS. X-ray diffraction and high resolution transmission electron microscopy clearly reveal the crystalline nature of SnO2 particles of size about 2.5nm with well defined lattice fringes and the surface adjoining to form mesoscopic spheres. Band gap enhancement due to quantum confinement effect has been observed. Blue luminescence and fast decay (1.2ns) indicate creation of exciton and recombination with an oxygen vacancy centre. The results suggest that the optical properties follow the quantum size effect whereas the mesoscopic spheres of self assembled QDs lower the surface energy and provide large surface area for applications such as photovoltaic and gas sensing.

Optical properties of SnO2 quantum dots synthesized by laser ablation in liquid

SnO2 quantum dots (QDs) were controllably synthesized by laser ablation in liquid (LAL). The HRTEM image shows that the diameters of the SnO2 nanoparticles fall into a small range of 1–5nm, with the majority being less than the exciton Bohr radius of SnO2 (∼2.7nm). The Selected Area Electron Diffraction (SAED) pattern of SnO2 QDs shows tetragonal crystalline structure. The photoluminescence (PL) spectrum of such SnO2 QDs exhibits blue and green emission peaks at 445nm and 540nm respectively. These QDs have potential future applications in optoelectronics, biosensor and other modern technologies.

SnO mesocrystals: additive-free synthesis, oxidation, and top-down fabrication of quantum dots

SnO mesocrystals were prepared via a hydrothermal method without any additives and were further oxidized to SnO2 mesocrystals. SnO and SnO2 quantum dots were successfully fabricated from these mesocrystals by an ultrasonic-assisted process. Sensors based on these quantum dots exhibited high selectivity in the detection of NO and NO2.

Influence of confinement regimes on magnetic property of pristine SnO2 quantum dots

We demonstrate a clear correlation between the quantum confinement effect and magnetization of pristine tin dioxide (SnO2) quantum dots (QDs). We have synthesized single crystalline QDs of SnO2 above and below the exciton Bohr radius (2.7 nm). Such fine control over the size of the QDs is a challenging task. The 2 nm QDs belong to strong confinement regimes and are found to be ferromagnetic in nature, whereas 3 nm QDs are diamagnetic like bulk SnO2. To the best of our knowledge, so far no experimental studies on the influence of confinement effect on the magnetic behaviour of SnO2 QDs have been reported. We propose two possible mechanisms based on the theory of localization of holes due to a strong confinement effect to explain room temperature ferromagnetism in 2 nm QDs. The localization of holes is confirmed from photoluminescence and UV visible spectroscopy.

Synthesis and nonlinear optical characterization of SnO2 quantum dots

The present paper demonstrates the preparation and characterization of SnO2 semiconductor quantum dots. Extremely small ∼1.1 and ∼1.4nm SnO2 samples were prepared by microwave assisted technique with a frequency of 2450MHz. Based on XRD analysis, the phase, crystal structure and purity of the SnO2 samples are determined. UV–vis measurements showed that, for the both size of SnO2 samples, excitonic peaks are obtained at ∼238 and ∼245nm corresponding to ∼1.1nm (sample 1) and ∼1.4nm (sample 2) sizes, respectively. STM analysis showed that, the quantum dots are spherical shaped and highly monodispersed. At first, the linear absorption coefficients for two different sizes of SnO2 quantum dots were measured by employing a CW He–Ne laser at 632.8nm and were obtained about 1.385 and 4.175cm−1, respectively. Furthermore, the nonlinear refractive index, n2, and nonlinear absorption coefficient, β, were measured using close and open aperture Z-scan respectively using the same laser. As quantum dots have strong absorption coefficient to obtain purely effective n2, we divided the closed aperture transmittance by the corresponding open aperture in the same incident beam intensity. The nonlinear refraction indices of these quantum dots were measured in order of 10−7(cm2/W) with negative sign and the nonlinear absorption coefficients were obtained for both in order of 10−3 (cm/W) with positive sign.

Sol–gel glass-ceramics comprising rare-earth doped SnO2 and LaF3 nanocrystals: an efficient simultaneous UV and IR to visible converter

We report a novel class of nanostructured glass-ceramics comprising two co-existing rare-earth doped nanocrystalline phases, SnO2 semiconductor nanocrystal (quantum dot), and LaF3, presenting sizes at around 4.6 and 9.8 nm, respectively, embedded into a silica glass matrix for an efficient simultaneous UV and IR to visible photon conversion. On one hand, the wide and strong UV absorption by SnO2 quantum dot and subsequent efficient energy transfer to Eu3+ and, on the other hand, the also very efficient IR to visible up-conversion with the pair Yb3+–Er3+ partitioned into low phonon LaF3 nanocrystalline environment, yield to visible emissions with application in improving the spectral response of photovoltaic solar cells. We report a novel class of nanostructured glass-ceramics comprising two co-existing rare-earth doped nanocrystalline phases, SnO2 semiconductor nanocrystal (quantum dot) and LaF3, presenting sizes at around 4.6 and 9.8 nm, respectively, embedded into a silica glass matrix for an efficient simultaneous UV and IR to visible photon conversion. On one hand, the wide and strong UV absorption by SnO2 quantum dot and subsequent efficient energy transfer to Eu3+ and, on the other hand, the also very efficient IR to visible up-conversion with the pair Yb3+–Er3+ partitioned into low phonon LaF3 nanocrystalline environment, yield to visible emissions with application in improving the spectral response of photovoltaic solar cells.

Morphological Evolution from SnO2 Quantum Dots to Quantum Chains inside Channels of Mesoporous Spheres

Morphological evolution from SnO2 quantum dots (QDs) to quantum chains (QCs) confined in channels of mesoporous silica (MS) has been studied systematically in this work by varying the nuclei quantity deposited on the channels’ inner surface under hydrothermal conditions. Decreasing the MS amounts could influence the nuclei quantity and the subsequent crystal growth as well as the assembly process to form QCs by oriented attachment inside the channels. It is interesting to find that the evolution of SnO2 QDs→QCs systems would induce the variation of strain type tolerated, simultaneously, from tensile to compressive strain, and also exhibit morphology-dependent photoluminescence properties.

Carrier Transport in Volatile Memory Device with SnO2 Quantum Dots Embedded in a Polyimide Layer

Carrier transport in a volatile memory device utilizing self-assembled tin dioxide quantum dots (SnO2 QDs) embedded in a polyimide (PI) layer was investigated. Current–voltage (I–V) curves showed that the Ag/PI/SnO2 QDs/PI/indium–tin-oxide (ITO) device memory device had the ability to write, read, and refresh the electric states under various bias voltages. The capacitance–voltage (C–V) curve for Ag/PI/SnO2 QDs/PI/p-Si capacitor exhibited a counterclockwise hysteresis, indicative of the existence of sites occupied by carriers. The origin of the volatile memory effect was attributed to holes trapping in the shallow traps formed between QD and PI matrix, which determines the carrier transport characteristics in the hybrid memory device.

Synthesis of novel SnO2 quantum cubes and their selfassembly

Nano-structured cubic SnO2 crystalines were successfully synthesized through solvothermal route. The obtained products were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM) and high resolution TEM (HRTEM). The study showed that, the SnO2 particles were rutile structured and almost uniformly cube shaped crystals in quantum size (3–8 nm). Self-assembly behavior of the cubic SnO2 quantum dots was also observed. The synthesis process can be defined as an nonhydrolysis (NH) hydroxylation reaction provided by the amide elimination of carboxylated precursors. The formation of cubic morphology of SnO2 can be ascribed to the mild reaction featured by high nucleation rate and low growth rate, surface energy difference of the crystallographic facets of SnO2 and the passivation effect of the starting material-dodecylamine which drastically reduced the dipole interation. The selfassembly of the cubic SnO2 quantum dots was driven by van der Waals force and capillary force.

Quantum Confinement Effects and Electronic Properties of SnO2 Quantum Wires and Dots

On the basis of the density functional theory (DFT) within local density approximations (LDA) approach, we calculate the band gaps for different size SnO2 quantum wires (QWs) and quantum dots (QDs). A model is proposed to passivate the surface atoms of SnO2 QWs and QDs. We find that the band gap increases between QWs and bulk evolve as ΔEgwire = 1.74/d1.20 as the effective diameter d decreases, while being ΔEgdot = 2.84/d1.26 for the QDs. Though the ∼d1.2 scale is significantly different from ∼d2 of the effective mass result, the ratio of band gap increases between SnO2 QWs and QDs is 0.609, very close to the effective mass prediction. We also confirm, although the LDA calculations underestimate the band gap, that they give the trend of band gap shift as much as that obtained by the hybrid functional (PBE0) with a rational mixing of 25% Fock exchange and 75% of the conventional Perdew−Burke−Ernzerhof (PBE) exchange functional for the SnO2 QWs and QDs. The relative deviation of the LDA calculated band gap ...