SnO2 Quantum Dots Research Articles

Dopant incorporation in ultrasmall quantum dots: a case study on the effect of dopant concentration on lattice and properties of SnO2 QDs

Although impurity doping of nanocrystals is essential in controlling their properties for various applications, but the doping mechanism of ultrasmall semiconductor QDs is not yet understood. In this study, the effect of concentration of Ni2+ ions on the lattice and properties of 1.4 nm SnO2 QDs, prepared via chemical-precipitation route has been studied in detail. The quantum dot lattice contracted at maximum Ni concentration of 10% due to the incorporation of Ni ions at the substitutional sites on the surface of SnO2 lattice, while it began to expand gradually as the Ni concentration was further decreased from 10 to 1%, due in part to the Ni ions located in the core of the host lattice, occupying interstitial sites between Sn and O atoms leading to the expansion of the lattice with the decrease in the amount of strain and dislocation density. High resolution transmission electron microscopy confirms the presence of such dislocations in pure and doped SnO2 QDs. Optical investigation shows that the Ni doping in SnO2 lattice leads to a blue shift in the absorption wavelength. The concentration quenching effect of the PL emission with Ni doping is explained in detail. An enhancement in the photocatalytic activity has been achieved with optimum Ni incorporation in SnO2. The work also successfully correlates photoluminescence quenching and enhanced photocatalytic activity with the defect production happened in SnO2 system on Ni doping.

A facile room temperature solution synthesis of SnO2quantum dots for perovskite solar cells

We introduce a facile route to synthesize SnO2quantum dots colloidal solution at room temperature and superior homogeneous ETL is obtained by spin coating of the QDs colloidal solution with post-deposition annealing.

Nanorod Array of SnO2 Quantum Dot Interspersed Multiphase TiO2 Heterojunctions with Highly Photocatalytic Water Splitting and Self-Rechargeable Battery-Like Applications.

The ever-growing demand for sustainable and renewable power sources has led to the development of novel materials for photocatalytic water splitting, but enhancing the photocatalytic efficiency remains a core problem. Herein, we report a conceptual effective and experimental confirmed strategy for SnO2 quantum dot (QD) interspersed multiphase (rutile, anatase) TiO2 nanorod arrays (SnO2/RA@TiO2 NRs) to immensely enhance the carrier separation for highly efficient water splitting by merging simultaneously the QD, multiphase, and heterojunction approaches. Under this synergistic effect, a doping ratio of 25% SnO2 QD interspersed into multiphase TiO2 NRs exhibited a superior optical adsorption and excellent photocurrent density (2.45 mA/cm2 at 1.0 V), giving rise to a largely enhanced incident light to current efficiency in the UV region (45-50%). More importantly, this material-based device can act as power supply with a voltage of ∼2.8 V after illumination, which can automatically self-recharge by reacting with oxygen vacancy and water molecule to realize reuse. The current study provides a new paradigm about heightening the carrier separation extent of QD interspersed multiphase heterojunctions, fabricating a new solar-energy-converting material/device, and achieving a highly photocatalytic water splitting/self-charging battery-like application.

Novel in-situ synthesis of Au/SnO2 quantum dots for enhanced visible-light-driven photocatalytic applications

In recent years, visible-light-driven metal–semiconductor nanocomposites have emerged as a suitable material for the decomposition of various water and air pollutants. In this work, a novel plasmonic Au nanoparticle (NP)/SnO2 quantum dot (SQD) nanocomposite photocatalysts were prepared via a one-step solvothermal technique. The as-prepared plasmonic photocatalysts were characterized by various techniques, and the results established the formation of Au/SQD nanocomposites. The photocatalytic activity of the as-prepared plasmonic Au/SQD nanocomposites was examined by the degradation of Rhodamine B (RhB) at room temperature under visible light, and the Au/SQD photocatalyst, prepared using 1.0 g of tin chloride, exhibited a higher rate constant of RhB degradation than pristine SQDs. This exceptional improvement in catalytic performance under visible light is ascribed to a shift of the band gap from the ultraviolet to the visible region. The surface plasmon resonance effect of Au NPs and the synergistic coupling of the metal and the semiconductor QDs also played a vital role in enhancing the catalytic performance. The process of the photocatalytic degradation of RhB by the Au/SQD nanocomposites under visible light is described.

Synthesis of SnO2 quantum dots by chemical precipitation assisted by ultrasound

SnO2 quantum dots were successfully prepared via chemical precipitation assisted by ultrasound. X-ray diffraction analysis confirmed the rutile tetragonal structure of SnO2 QDs with a crystallite size of 1.4 nm. The SEM micrographs of the obtained powder exhibited that the SnO2 QDs are agglomerated particles of around 10 nm, while TEM images confirmed that the crystallite size are similar to the measured from XRD. The band-gap energy of the SnO2 QDs measured from the UV–Vis reflectance spectrum of the SnO2 QDs was 4.3 eV, displaying a significantly blue-shifting attributed to quantum confinement.

SnO2 quantum dots @ 3D sulfur-doped reduced graphene oxides as active and durable anode for lithium ion batteries

SnO2 has attracted growing attention as a promising anode material for next generation of Lithium ion batteries because of its high theoretical capacity (1494 mAh g−1) and low working potential. However, the severe volume change during cycling remains one of the great challenges for its practical application. To overcome the obstacle, we propose to utilize the SnO2 quantum dots loaded on the sulfur-doped reduced graphene oxides by one-pot synthesis. The SnO2 quantum dots are uniformly dispersed on the sulfur-doped reduced graphene oxides and retain their tiny sizes during the electrochemical reaction, thus alleviate the volume expansion. Meanwhile, the sulfur-doped reduced graphene oxides introduces many defects and can benefit charge transfer and lithium ion diffusion in the electrode. With the synergetic effect between SnO2 quantum dots and sulfur-doped reduced graphene oxides, the composite anode material can deliver a specific capacity of 897 mA h g−1 at 100 mA g−1 and maintain 88% of original capacity after over 500 cycles at 500 mA g−1, featuring large lithium ion storage capacity and high stability.

Simultaneous Ligand Exchange Fabrication of Flexible Perovskite Solar Cells using Newly Synthesized Uniform Tin Oxide Quantum Dots.

Halide perovskite solar cells (HPSCs) have a significant potential for future photovoltaic systems because of a high power conversion efficiency (PCE) exceeding 23% using solution processing methods. A low-temperature processed oxide layer is a challenging issue for large-scale manufacture of flexible and low-cost HPSCs. Here, we propose a simple reverse micelle-water injection method for highly dispersed ligand-capped ultrafine SnO2 quantum dots (QD). Interestingly, we observed that the ligands, which help in the formation of a uniform SnO2 QD thin film, spontaneously exchange for halide through a perovskite solution, and finally we form a suitable SnO2 QD-halide junction for high-performance HPSCs. The flexible HPSC with the SnO2 QD-halide junction formed via the ligand exchange exhibits a high PCE of 17.7% using a flexible substrate. It also shows an excellent flexibility, where the initial PCE is maintained within 92% after 1000 bending cycles with a bending radius of 18 mm.

Simple Fabrication of SnO2 Quantum-dot-modified TiO2 Nanorod Arrays with High Photoelectrocatalytic Activity for Overall Water Splitting.

Photoelectrochemical (PEC) water splitting has been demonstrated as a promising way to acquire clean hydrogen energy. However, the efficiency has been limited by the high recombination rate of photogenerated electron-hole pairs. Herein, we provided a simple approach to construct a novel SnO2 quantum dots (QDs) modified TiO2 nanorod arrays (NAs) by the calcination of SnCl2 -adsorbed TiO2 NAs. The photocurrent density of SnO2 QDs/TiO2 NAs exhibits about 5 times higher than that of parent TiO2 NAs at a bias of 0.4 V vs. Ag/AgCl. SnO2 QDs/TiO2 NAs also show a high photoelectrocatalytic activity for overall water splitting with an actual yield of H2 and O2 to be 27.85 and 11.87 μmol cm-2 h-1 , respectively. The excellent performance of photoanode for PEC water splitting could be attributed to its Z-scheme heterostructure for good separation efficiency and transport rate of photogenerated charge carries.

All-fiber-based quasi-solid-state lithium-ion battery towards wearable electronic devices with outstanding flexibility and self-healing ability

In recent years, high-performance flexible power sources require not only the improvement for high energy density and power density, but also the reliability and flexibility for practical application. However, the energy storage devices often fail to work and even cause safety problems under deformation, so the effective protection is particularly important. Here, we present a flexible and self-healable all-fiber-based quasi-solid-state lithium-ion battery (LIB). The anode is made up of porous reduced graphene oxide (rGO) fiber with SnO2 quantum dots and the cathode consists of spring-shaped rGO fiber with LiCoO2. The adjustable length of the spring-shaped cathode makes it easy to match the capacity with anode. The fibrous anode and cathode with diameters of 750 µm and 250 µm, respectively, are thick enough to reconnect by visual observation. The LIB can be assembled by the as-prepared cathode, anode and gel polymer together with the self-healing protective shell. The flexible and self-healable LIB has a capacity of 82.6 mAh g−1 under a series of deformation and retains 50.1 mAh g−1 after the 5th healing process at a current density of 0.1 A g−1. This work gives an essential strategy to design LIB for wearable devices.

Enhancing lithium-ion batteries performance via electron-beam irradiation strategies: A case study of graphene aerogels loaded with SnO2 quantum dots

Exploring versatile strategies for microstructural evolution and surface modification are of fundamental importance in the development of advanced electrode materials. In this work, we report that electron-beam irradiation is a facile approach to perform surface modification for the ultrathin cross-stacked graphene aerogels loaded with SnO2 quantum dots, resulting in a remarkable modulation on the lithium storage performance. It is found that the as-synthesized SnO2/graphene aerogels composites irradiated at 280 kGy exhibit excellent high reversible lithium storage capacity, good rate capability and cycling stability, which retains a discharge capacity of 703 mAh g−1 after 50 cycles at 0.1 C rate. Microstructure analysis indicates that the enhanced electrochemical properties are mainly attributed to the exfoliation of graphene nanosheets, the increase of amorphization, disorder, defects and the removal of partial oxygen-containing functional groups on the surface of graphene nanosheets. The strategy presented here demonstrates that the electron-beam irradiation is a potential strategy to improve the electrochemical performance of graphene-based metal oxides.

Functionalized Nano-adsorbent for Affinity Separation of Proteins

Thiol-functionalized silica nanospheres (SiO2-SH NSs) with an average diameter of 460 nm were synthesized through a hydrothermal route. Subsequently, the prepared SiO2-SH NSs were modified by SnO2 quantum dots to afford SnO2/SiO2 composite NSs possessing obvious fluorescence, which could be used to trace the target protein. The SnO2/SiO2 NSs were further modified by reduced glutathione (GSH) to obtain SnO2/SiO2-GSH NSs, which can specifically separate glutathione S-transferase-tagged (GST-tagged) protein. Moreover, the peroxidase activity of glutathione peroxidase 3 (GPX3) separated from SnO2/SiO2-GSH NSs in vitro was evaluated. Results show that the prepared SnO2/SiO2-GSH NSs exhibit negligible nonspecific adsorption, high concentration of protein binding (7.4 mg/g), and good reused properties. In the meantime, the GST-tagged GPX3 separated by these NSs can retain its redox state and peroxidase activity. Therefore, the prepared SnO2/SiO2-GSH NSs might find promising application in the rapid separation and purification of GST-tagged proteins.

Enhanced catalytic activity of SnO2 quantum dot films employing atomic ligand-exchange strategy for fast response H2S gas sensors

Colloidal quantum dots (CQDs) are considered as one of the ideal materials candidates for next-generation electronics and optoelectronics. Their large surface-to-volume ratio with exchangeable surface ligands offers a versatile freedom for the regulation of the semiconductor gas sensors. Here we demonstrated an atomic-ligand exchange strategy to construct highly sensitive and selective SnO2 quantum dot gas sensors. Both the cations and anions of the atomic ligands were engineered to enhance the gas adsorption and carrier transport via a film-level atomic ligand exchange treatment, among which the CuCl2-treated SnO2 CQD gas sensors exhibiting highest response of 1755 toward 50 ppm H2S with a fast response and recovery time (48 s/35 s) at 70 °C. The Fourier transform infrared (FTIR), X-ray photoelectron spectroscopy (XPS) and UV–vis absorption spectra suggest that the long-chain organic ligands capping on the SnO2 CQDs were successfully exchanged by the atomic ligands and the quantum confinement of the CQDs were well conserved, which is favorable to preserve the catalytic activities of QD materials in real gas-sensing devices. Simultaneously, the copper (II) introduced on the surface of SnO2 CQD films can also act as a catalytic promoter by forming p-CuO/n-SnO2 heterojunctions, thereby enhancing the H2S-sensing performance at relatively low temperatures.

Significance of in-plane oxygen vacancy rich non-stoichiometric layer towards unusual high dielectric constant in nano-structured SnO2

Influence of non stoichiometric layer to the possible contribution towards the unusually high dielectric constant of n-type SnO2 is discussed. Oxygen deficient and oxygen rich environments during the growth of SnO2 nanoparticles synthesized from the as prepared SnO2 quantum dots (QDs) of ∼2.4 nm have enabled creation of various defects states; however, it results to similar dimension of NPs. Defects states bring in strong changes in dielectric property including other electrical properties. Oxygen vacancies related defects have been spectroscopically elucidated using Raman spectroscopy and photoluminescence measurements. The study offers a plausible correlation between oxygen vacancies and unusually high dielectric constant of SnO2. In-plane oxygen vacancy is found to be responsible for enhanced dielectic value. The understanding of phenomena involved in the colossal permittivity can be utilized for tuning and the engineering of the macroscopic device applications.

Green synthesis of SnO2 quantum dots using Parkia speciosa Hassk pods extract for the evaluation of anti-oxidant and photocatalytic properties

In the present study, microwave heating method was established for the biosynthesis of SnO2 Quantum dots (QDs) using Parkia speciosa Hassk pods extract. The as-synthesized quantum dots have been characterized by various techniques such as UV, XRD, EDX, TEM, HRTEM, SAED and FTIR spectroscopy. The biosynthesized SnO2 QDs was employed for the first time as an efficient photocatalyst for the degradation of a food dye, acid yellow 23 dye from aqueous phase under the UV254 light. Various parameters, such as the effect of catalyst dose, the initial concentration of acid yellow 23 dye (AY23), pH of the solution and irradiation time on the photodegradation process are also studied for efficient and better use of the synthesized SnO2 QDs as a catalyst. The biosynthesized SnO2 QDs exhibited excellent photocatalytic performances with degradation efficiency 98% on the degradation of an aqueous solution of AY23 of concentration 5 mg/L with a catalyst dose of 20 mg under UV254 light within 24 min. The synthesized SnO2 QDs can be reused up to 5 cycles of photodegradation experiment without losing its stability and efficiency. The biosynthesized SnO2 QDs also shows a fair activity in the scavenging of 2,2-diphenyl-1-picrylhydrazyl free radical with the IC50 value of 312.6 ± 0.025 μg/mL.

Green Synthesis and Photogenerated Charge Carriers Transfer in SnO2 QDs Decorated rGO Nanosheets for Highly Efficient Visible Light Photocatalysis

In recent years, SnO2/carbon nanostructures based composites have got attracted in solar–physical energy conversion as well as energy storage applications. We had conducted a green-SILAR (successive ionic layer absorption and reduction) methodology to produce the SnO2 QDs decorated reduced graphene oxide (rGO) sheets. The obtained materials were studied for their structural, morphological, optical, and sun light photocatalytic applications. The SnO2 QDs grown on the rGO sheets have exhibited the average crystalline size of 3.6 nm and the particles size of 3–7 nm. The UV–Vis absorption spectrum authenticate the existence of strong quantum confinement in the SnO2 QDs grown on the rGO sheets. The photocatalytic reaction conducted under sunlight exposure have showed several times enhanced efficiency for rGO/SnO2 QDs over the commercial Degussa P25 TiO2 nanoparticles. This study also acquaintances to the synergistic effect of co-photosensitization of dye molecules and graphene to SnO2.

Bandgap tuning and XPS study of SnO2 quantum dots

In this study, we investigated the influence of annealing temperature on ultra-small SnO2 quantum dots (SQDs) prepared by a simple chemical reduction process. The structural and optical properties of annealed SQDs were systematically studied by different techniques. Our results show that the crystallinity and average crystallite size of annealed SQDs increased gradually with annealing temperature. The average crystallite size was maintained below 10 nm even for high annealing temperatures. XPS peak fitting analysis yielded information on the presence of mixed ionic states of Sn2+ and Sn4+ in SQDs and further revealed that the number of Sn2+ ions decreased at high temperature. Band-edge shifts were estimated from XPS data. It was possible to shift the bandgap of annealed SQDs from UV to the visible wavelength region, which is likely to have a beneficial impact on many applications of optoelectronic devices.

SnO2 quantum dots with rapid butane detection at lower ppm-level

SnO2 quantum dots (QDs) were successfully synthesized by a facile approach employing benzyl alcohol and ammonium hydroxide at lower temperature of 130 °C. It is revealed that the SnO2 QDs is about 3 nm in size to form clusters. The gas sensor based on SnO2 QDs shows a high potential for detecting low-ppm-level butane at 400 °C, exhibiting a high sensitivity, short response and rapid recovery time, and effective selectivity. The sensing mechanism is understood in terms of adsorbed oxygen species. Significantly, the excellent sensing performance is attributed to the smaller size of SnO2 and larger surface area (204.85 m2/g).

Effective Carrier-Concentration Tuning of SnO2 Quantum Dot Electron-Selective Layers for High-Performance Planar Perovskite Solar Cells.

The carrier concentration of the electron-selective layer (ESL) and hole-selective layer can significantly affect the performance of organic-inorganic lead halide perovskite solar cells (PSCs). Herein, a facile yet effective two-step method, i.e., room-temperature colloidal synthesis and low-temperature removal of additive (thiourea), to control the carrier concentration of SnO2 quantum dot (QD) ESLs to achieve high-performance PSCs is developed. By optimizing the electron density of SnO2 QD ESLs, a champion stabilized power output of 20.32% for the planar PSCs using triple cation perovskite absorber and 19.73% for those using CH3 NH3 PbI3 absorber is achieved. The superior uniformity of low-temperature processed SnO2 QD ESLs also enables the fabrication of ≈19% efficiency PSCs with an aperture area of 1.0 cm2 and 16.97% efficiency flexible device. The results demonstrate the promise of carrier-concentration-controlled SnO2 QD ESLs for fabricating stable, efficient, reproducible, large-scale, and flexible planar PSCs.

Synergistically enhanced lithium storage performance based on titanium carbide nanosheets (MXene) backbone and SnO2 quantum dots

Titanium carbide MXene (Ti3C2Tx) possesses a metallic conductivity and an opened nanostructure, being an ideal host for transition metal oxide (TMO) to construct advanced lithium-ion battery anodes. However, Ti3C2Tx is prone to be oxidized under hydrothermal treatment, which limits the growth of TMO/MXene composites through a wet-chemistry approach. Here, we take advantage of the strong electrostatic interaction between SnO2 quantum dots (QDs) and delaminated Ti3C2Tx to protect the latter from oxidation under the hydrothermal condition. The in-situ heterogeneously nucleated SnO2 QDs are tightly anchored on the Ti3C2Tx nanosheets, while the Ti3C2Tx nanosheets effectively limit the growth/aggregation of SnO2. Further freeze-drying of the colloidal mixture results in the SnO2 QDs@Ti3C2Tx composite with conductive Ti3C2Tx nanosheets as backbone, which displays a high specific surface area and abundant voids. The unique architecture design renders SnO2 QDs@Ti3C2Tx a high capacity (1021 mAh g−1 at 100 mA g−1 in the 2.6 mg cm−2 electrode) and long lifetime performance, which maintains 810 mAh g−1 after 200 cycles (100 mA g−1), 697 mAh g−1 after 520 cycles (200 mA g−1) and 500 mAh g−1 after 700 cycles (at 500 mA g−1). More importantly, this wet-chemistry/freeze-drying approach is general, and can be extended to other TMOs and MXenes to fabricate corresponding TMO QDs/MXene composites for various applications.

An insight into the origin of room-temperature ferromagnetism in SnO2 and Mn-doped SnO2 quantum dots: an experimental and DFT approach.

SnO2 and Mn-doped SnO2 single-phase tetragonal crystal structure quantum dots (QDs) of uniform size with control over dopant composition and microstructure were synthesized using the high pressure microwave synthesis technique. On a broader vision, we systematically investigated the influence of dilute Mn ions in SnO2 under the strong quantum confinement regime through various experimental techniques and density functional theoretical (DFT) calculations to disclose the physical mechanism governing the observed ferromagnetism. DFT calculations revealed that the formation of the stable (001) surface was much more energetically favorable than that of the (100) surface, and the formation energy of the oxygen vacancies in the stable (001) surface was comparatively higher in the undoped SnO2 QDs. X-ray photoelectron spectroscopy (XPS) and first-principles modeling of doped QDs revealed that the lower doping concentration of Mn favored the formation of MnO-like (Mn2+) structures in defect-rich areas and the higher doping concentration of Mn led to the formation of multiple configurations of Mn (Mn2+ and Mn3+) in the stable surfaces of SnO2 QDs. Electronic absorption spectra indicated the characteristic spin allowed ligand field transitions of Mn2+ and Mn3+ and the red shift in the band gap. DFT calculations clearly indicated that only the substitutional dopant antiferromagnetic configurations were more energetically favorable. The gradual increase of magnetization at a low level of Mn-doping could be explained by the prevalence of antiferromagnetic manganese-vacancy pairs. Higher concentrations of Mn led to the appearance of ferromagnetic interactions between manganese and oxygen vacancies. The increase in the concentration of metallic dopants caused not just an increase in the total magnetic moment of the system but also changed the magnetic interactions between the magnetic moments on the metal ions and oxygen. The present study provides new insight into the fundamental understanding of the origin of ferromagnetism in transition metal-doped QDs.