SnO2 Nanoflowers Research Articles

Fabrication and gas-sensing performance of nanorod-assembled SnO2 nanostructures

The manner how nano building blocks assemble into hierarchical architectures exerts a tremendous influence on gas-sensing property of the metal oxides. Herein, we focus on tuning the 1D SnO2 rectangular nanorods into 3D hierarchical nanoflowers by manipulating the concentration of surfactant (citric acid) as well as the period of hydrothermal process, and then investigate their gas-sensing performance. Nanostructures assembled by short, unordered and well-ordered rectangular nanorods were successfully fabricated, corresponding to infant, abnormal and blooming SnO2 nanoflowers, respectively. In comparison, sensor based on blooming SnO2 nanoflowers exhibited significantly enhanced gas response to ethanol than the other two, not only in terms of the sensitivity but also the response/recovery time, which may be mainly attributed to the sufficient diffusion channel and exposed surface provided by finely dispersed nanorods in the blooming nanoflowers.

Nanosheet-assembled hierarchical SnO2 nanostructures for efficient gas-sensing applications

The manner how nano building blocks assemble into hierarchical architectures exerts a tremendous influence on gas-sensing performance of the metal oxides. Here, we focus on tuning the 2D SnO2 nanosheets into 3D hierarchical nanoflowers by manipulating the presence of NaOH, and investigate their gas-sensing functionalities. We find that the blooming SnO2 nanoflowers assembled by ultrathin nanosheets (∼50nm) are shrunk into semi-blooming state, and that the semi-blooming nanoflowers based sensor shows enhanced gas-sensing performance towards the ethanol, which is attributed mainly to the confined effect due to numerous nano or micro reaction rooms by keeping oxygen and ethanol molecules to complete gas-sensing reactions. While the semi-blooming nanoflowers turn into ordered mesoporous via thermally removing the periodically arranged polyvinyl pyrrolidone micelles, their gas-sensing performance is found to be improved dramatically, indicating that sufficient amount of gas diffusion is crucial to gas-sensing properties rather than the fast gas diffusion speed. As a final verification, we fabricate the sensors using the mesoporous semi-blooming SnO2 nanoflowers and successfully monitor the existence of beer by a simple integrated device, making it a promising candidate in detecting drunk driving.

Facile surfactant- and template-free synthesis and electrochemical properties of SnO2/graphene composites

In this work, we demonstrate a facile and green hydrothermal process without using any surfactant or template to synthesize SnO2 nanoflowers (NFs)/graphene nanosheets (GNSs) composites as a high-performance electrode material for electric double layer capacitors (EDLCs). The crystal structure and morphology of the products were characterized by X-ray diffraction, scanning electron microscopy, and transition electron microscopy. The electrochemical properties were investigated by galvanostatic charge/discharge cycling and cycling voltammetry in a voltage range of −0.2–0.8 V. The results exhibit that the addition of GNSs did not change the tetragonal crystal structure of SnO2, and the GNSs were successfully coated on the flower-like surface of SnO2. The grain morphology of SnO2@GNSs composites has a flower-like appearance suggesting excellent electrochemical properties which were confirmed by electrochemical techniques. Compared with the GNSs, the SnO2@GNSs composites exhibit a high specific discharge capacitance of 126 F g−1 at 0.2 A g−1 and remains 98.2% after 2000 charge–discharge cycles. The combination of GNSs and SnO2 could significantly improve the electrical conductivity, enhance the interactions between GNSs and SnO2 NFs and provide more reaction sites, thereby resulting in improved electrochemical properties for the SnO2@GNSs composites in contrast with the pristine GNSs sample. The high specific capacity and long stability make the SnO2@GNSs nanocomposite as a electrode material for high-performance supercapacitors.

A novel low temperature gas sensor based on Pt-decorated hierarchical 3D SnO2 nanocomposites

A novel gas sensor composed of Pt nanoparticles-decorated hierarchical SnO2 nanostructures (Pt–SnO2) was synthesized via a facile dipping-precipitation strategy. Pt nanoparticles with small sizes (avg. 4nm) were successfully dispersed onto our pre-synthesized 3D hierarchical SnO2 nanoflowers supports by using lysine as both capping and linking agents. The morphology, structure and composition of the as-prepared samples were characterized by means of field-emission scanning electron microscopy (FESEM), X-ray diffraction (XRD), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). Comparisons of the gas sensing performance between pure SnO2 and Pt–SnO2 nanocomposites revealed that after supporting Pt nanoparticles, the decorated sensor not only got an optimal working temperature of as low as 100°C, but also exhibited faster response and recovery speeds and higher response than the pristine one at such low temperature. Moreover, good selectivity and excellent stability were also shown for the hybrid sensor. Sensing mechanisms were illustrated to help explain the strong spillover effect of the Pt nanoparticles and the Schottky barriers at the interface of metal and semiconductor, both of which facilitated the low temperature sensing performance. The Pt–SnO2 sensors are considered to be a promising candidate for trace environmental gas detections in practical use.

Surface Superoxide Complex Defects-Boosted Ultrasensitive ppb-Level NO2 Gas Sensors.

Sn(4+) -O2 (-•) centers are intentionally created in SnO2 nanoflowers by a thermodynamically instable synthetic process. The resulting SnO2 nanoflower-based sensor is confirmed to be the most sensitive ppb-level chemiresistor NO2 sensor to date. The Sn(4+) -O2 (-•) centers with strong gas-adsorbing and high eletron-donating capability towards NO2 molecules decisively determine the sensor sensitivity.

Urchin-like SnO2 nanoflowers via hydrothermal synthesis and their gas sensing properties

Novel urchin-like SnO2 nanostructures were prepared by a facile hydrothermal process. The well-defined nanostructures were composed of numerous one-dimensional nanowires with a diameter of ∼8–10nm. Based on comparative studies, a possible formation mechanism was proposed in detail. It was believed that the nucleation was initiated by formation of ZnSn(OH)6. Furthermore, gas-sensing measurement indicated that the urchin-like SnO2 nanoflowers showed excellent gas-sensing properties.

Hydrothermal self-assembly of novel porous flower-like SnO2 architecture and its application in ethanol sensor

Different morphologies of tin dioxide (SnO2) architectures were prepared by increasing reaction time (12, 18, 24 and 48h) under a facile hydrothermal process and followed by calcination. The crystal structures and morphologies of the hierarchical architecture were characterized in detail by means of powder X-ray diffraction (XRD), energy dispersive X-ray detector (EDX), scanning electron microscope (SEM) and transmission electron microscope (TEM). The results showed that the porous flower-like SnO2 architecture was obtained by 24h hydrotherm treatment. Most importantly, the sensors based on porous flower-like SnO2 architecture exhibited perfect sensing performance toward ethanol with excellent selectivity, high response and fast response-recovery capability compared with other SnO2 nanoflowers for the same ethanol concentration at 300°C. The response value was about 208 and the response-recovery time was around 8 and 7s for 500ppm ethanol, respectively. The enhancement in gas sensing properties was attributed to the unique structures, including the flower-like structure and porous feature, which provided more gas active center and diffusion pathways. The results indicated that porous flower-like SnO2 architecture was a potential candidate for fabricating effective ethanol sensor. Furthermore, the possible growth mechanism and the ethanol sensing mechanism of the architecture were discussed, too.

Synthesis of hierarchical SnO2 nanoflowers with enhanced acetic acid gas sensing properties

Different morphologies hierarchical flower-like tin dioxide (SnO2) nanostructures were fabricated by changing the volume ratio of glycol and de-ionized water (Vg:Vw=0, 1:2, 1:1 and 2:1) under a template-free and low-cost hydrothermal method and subsequent calcinations. The architectures, morphologies and gas sensing performances of the products were characterized by X-ray diffraction patterns (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Brunauer–Emmett–Teller (BET) and gas-sensing measurement device. It can be observed that all the nanoflowers were composed of two-dimensional (2D) nanosheets, and the thickness of nanosheets is only about 9nm when Vg:Vw=1:1. The sensor based on the product of Vg:Vw=1:1 exhibited excellent gas sensing performance toward 500ppm acetic acid at 260°C, and the response value of this sensor was about 153.6, which was above 7.5 times higher than that of ammonia (about 20.3). In addition, the 3D flower-like SnO2 nanostructures exhibited not only high response and selectivity to ppm level acetone, but also fast response and recovery time within 10s, demonstrating it can be used as a potential candidate for detecting acetic acid. Finally, the possible formation mechanism was proposed, too.

Surfactant assisted hydrothermal synthesis of porous 3-D hierarchical SnO2 nanoflowers for photocatalytic degradation of Rose Bengal

Novel visible-light-activated tin dioxide (SnO2) nanoflowers possessing high surface area (~44m2/g) is fabricated through a facile hydrothermal technique using Sodium dodecyl sulfate (SDS) as structure directing agent which assisted in generating the porosity and induces beautiful flower like morphology. The highly porous SnO2 exhibits excellent response towards degradation of Rose Bengal (RB) dye under visible light (λ>400nm) irradiation wherein the ~96% degradation of RB was achieved within 90min.

One-step synthesis and highly gas-sensing properties of hierarchical Cu-doped SnO2 nanoflowers

The hierarchical pure and Cu-doped SnO2 nanoflowers were synthesized by a low-cost and simple hydrothermal method at 160°C for 20h. These uniform SnO2 nanoflowers were composed of nanosheets. The morphology, structure and gas-sensing performance of the as-synthesized products were characterized by X-ray diffraction pattern (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and gas-sensing measurement device. The results revealed that the average thickness of the nanosheets is around 18nm. The XRD of the doped products were similar with the undoped, but had a shift slightly toward right, which indicated that Cu ions had entered into the crystal lattice of SnO2 without deteriorating the original crystal structure. The obtained samples were found that the gas sensors based on this structure had a low optimum operating temperature of 260°C. Moreover, 2.5wt% Cu-doped SnO2 displayed the maximum response and excellent selectivity to acetone at operating temperature of 260°C among all these sensors, and the response value of 2.5wt% Cu-doped SnO2 to 500ppm acetone was 221.6at 260°C, which was about 11.5 times higher than that of ammonia (about 19.3). In addition, the response and recovery time of 2.5wt% Cu-doped SnO2 were 9 and 6s, respectively. It indicated that our sample showed high sensitivity, short response-recovery time and good selectivity to acetone. Finally, the possible formation mechanism of SnO2 nanoflowers and the gas-sensing mechanism of sensors were proposed, too.

Synthesis of hierarchical SnO2 nanoflowers and their high gas-sensing properties

The hierarchical SnO2 flower-like nanostructure was successfully synthesized by a low-cost and simple hydrothermal method at 160°C for 22h. These uniform SnO2 nanoflowers were composed of nanosheets. The polyvinyl pyrrolidone (PVP), sodium citrate (Na3C6H5O7·2H2O) and ammonia (NH3·H2O) played a pivotal role in the growth of nanoflowers, and the possible formation mechanism was also proposed according to the results. Moreover, the gas sensor based on this structure showed a response about 160 and a response time around 12s to 200ppm acetone at the optimum operating temperature of 260°C. It indicated that our sample has high response, fast response time and good selectivity to acetone. Thus, the peculiar structure of our sample endowed acetone detection with widely application prospects.

Synthesis and enhanced acetone sensing properties of 3D porous flower-like SnO2 nanostructures

The three-dimensional (3D) hierarchical SnO2 nanoflowers constructed by two-dimensional (2D) porous nanosheets were successfully fabricated by a one-step hydrothermal method and calcination procedure. The nanostructure and morphology of the hierarchical flower-like SnO2 were characterized by X-ray diffraction (XRD), energy dispersive X-ray detector (EDX), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS) techniques. A possible formation process and growth mechanism for such fabricated 3D hierarchical SnO2 nanostructures have been proposed based on the experimental results. It is found that the flower-like SnO2 architectures were composed of many 2D porous nanosheets with the thickness about 20nm. In addition, the gas sensor based on this 3D hierarchical structure has an optimum operating temperature of 280°C, high sensitivity, quick response/recovery time and good selectivity for acetone.

Performance of 3D SnO2 microstructure with porous nanosheets for acetic acid sensing

The porous flower-like SnO2 was successfully synthesized by a simple hydrothermal strategy and followed by calcination. The well-defined nanoflower was composed of thin nanosheets, which has many pores on its surface. The sensor based on these porous SnO2 nanoflowers showed excellent selectivity, fast response–recovery capability and high response to acetic acid at 340°C. The response and recovery time were about 11s and 6s, respectively. The enhancement in gas sensing properties was attributed to their unique structures, including the 3D hierarchical structure and porous feature. The present study could be applied to the acetic acid detection.

High-quality SnO2@SnS2 core–shell heterojunctions: Designed construction, mechanism and photovoltaic applications

High-quality SnO2@SnS2 core–shell heterojunctions have been constructed through sulfurization of SnO2 nanoflowers self-sacrificial templates with H2S gas at relatively low temperature in this paper. The unreacted SnO2 core and the in-situ synthesized SnS2 shell are in good crystallinity with a low lattice mismatch interface. The formation mechanism of the core–shell heterostructures have been examined by experiments and theoretic computation from the perspectives of both adsorption and diffusion. When used as photoanode in all-solid-state semiconductor-sensitized solar cells, the SnO2@SnS2 core–shell heterojunctions based hybrid solar cell shows a promising conversion efficiency of 1.45% under 1 sun illumination, which is over 5 times than that of SnS2 quantum dot sensitized SnO2 electrode made by the common chemistry bath deposition method. The enhanced photovoltaic performance is contributed to the unique structure of SnO2@SnS2 core–shell heterojunctions which provide highly covered sensitizers and favored interface for suppressing the charge recombination from SnO2 to electrolyte. This strategy and understanding can be extended to other nanostructure core–shell architecture and fields.

Hierarchical growth of SnO2 nanostructured films on FTO substrates: structural defects induced by Sn(II) self-doping and their effects on optical and photoelectrochemical properties.

Direct hydrothermal growth of Sn(II)-doped SnO2 films on fluorine-doped tin oxide (FTO) substrates results in the formation of upstanding SnO2 nanosheet arrays covered by hierarchical SnO2 nanoflowers. The n-type semiconductor films show extended photoresponse in the visible spectrum arising from the coexistence of Sn(II) dopant ions and oxygen vacancies in these hierarchical SnO2 nanostructures, which leads to a narrowed bandgap. Photoluminescence spectroscopy revealed that the emission in the UV, blue and red spectral ranges is related to the evolution of Sn(II) dopants and oxygen vacancies with annealing temperature, whereas oxygen vacancies are mostly responsible for visible emission. The Sn(II)-doped SnO2 films show higher photocurrent when sensitized with narrow bandgap CdS nanoparticles, serving as efficient electron acceptors.

Controlled synthesis of SnO2 nanostructures with different morphologies and the influence on photocatalysis properties

SnO2 nanoparticles, nanoflowers, and nanorods of highly crystalline were synthesized via a simple hydrothermal method. The size and morphology of the SnO2 nanostructures could be controlled by varying the NaOH concentration of the precursor solutions. The SnO2 structures appeared to be sphere-like nanoparticles with diameters in the range of 5–10 nm in lower NaOH concentrations. In higher NaOH concentrations, the nanostructures showed orientation growth behavior and were flower-like or rod-like in morphology. The sphere-like shape demonstrated that Ostwald ripening took effect only at lower NaOH concentration while the preferential growth behavior at higher NaOH concentration testified “oriented attachment” was more suitable under this condition. Photocatalysis experiments were carried out to study the influence of the morphology, size, and surface on photocatalytic activities of SnO2. The nanoparticles synthesized with the MNaOH:MSnCl4 = 4:1 showed the highest photolytic activities owing to their tiny size, large surface area, and abundant defect-related energy states.

A SnO2 and ZnO Nanocomposite Photoanodes in Dye-Sensitized Solar Cells

2.02% conversion efficiency Dye-sensitized solar cell (DSSC) is achieved based on an additional insulating layer of Li doped ZnO nanoparticles (LZN) onto SnO2 nanocomposite photoanode. The morphology, incident photon to current conversion efficiency (IPCE), AC impedance and photovoltaic performance were investigated of nanocomposited, nanoflower and nanoparticle photoanodes based DSSCs. Suppression recombination rate in nanocomposite DSSC, has achieved a high filling factor of 68.9% with 80.6% of IPCE. SnO2 nanoparticles improved the interconnections between SnO2 nanoflowers with FTO substrate and LZN. Fully covered SnO2 nanocomposite by an insulating layer of LZN nanoparticles improved the conversion efficiency of SnO2 DSSC. © 2013 The Electrochemical Society. [DOI: 10.1149/2.013311ssl] All rights reserved.

Synthesis and Characterization of NiO Doped SnO<sub>2</sub> Nano-Flowers

In this present work, a new method for preparing NiO doped SnO2 nanoflowers by hydrothermal route is suggested. The composition and microstructure of samples were characterized by field emission scanning electron microscopy (FE-SEM), X-ray diffraction (XRD) and Fourier transform infrared spectrum (FTIR). Moreover, a possible formation mechanism was discussed.

Synthesis of SnO2 nanoflowers and electrochemical properties of Ni/SnO2 nanoflowers in supercapacitor

3D SnO2 nanoflowers on Ti foil have been synthesized by a simple hydrothermal method without using any surfactant or catalyst. The synthesized 3D SnO2 nanostructures are characterized by X-ray diffraction, field emission scanning electron microscopy and X-ray photoelectron spectroscopy. The FESEM results showed that the nanoflower consists of multiple nanopetals of width ∼5nm and each SnO2 nanoflower is ∼3μm in diameter. The time-dependent morphology evolution of SnO2 nanoflowers was studied in detail, and a possible growth mechanism was proposed. In addition, high dispersed Ni nanoparticles was loaded on SnO2 nanoflowers applied in supercapacitor. The electrochemical properties of the 3D Ni/SnO2 nanoflowers were investigated by a series of electrochemical tests.

Synthesis of hierarchical SnO2 nanostructures assembled with nanosheets and their improved gas sensing properties

Well-defined three-dimensional (3D) hierarchical tin dioxide (SnO2) nanoflowers (NFs) constructed by two-dimensional (2D) nanosheets (NSs) are successfully fabricated by a simple one-pot low-temperature (90°C) hydrothermal strategy. The influence of the experiment parameters on the morphology of the products is investigated in detail. Field-emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM) and X-ray diffraction (XRD) demonstrate that the size and shape of the 3D hierarchical SnO2 NFs can be tailored by modulating the molar ratio of OH− to Sn2+, reaction time and reaction temperature in the process of hydrothermal synthesis. A possible formation process and growth mechanism for such fabricated 3D hierarchical SnO2 nanostructures has been proposed based on the experimental results. The gas sensing tests of the SnO2 NF sensor for several reducing volatile organic compounds (VOCs) including ethanol, n-butanol, acetone, methanol, chloroform and benzene have been performed at the relatively low operating temperature of 240°C. The excellent gas sensing performances of the unique 3D hierarchical SnO2 NFs at low operating temperature of 240°C indicate their potential application as gas sensors. The unique 3D hierarchical SnO2 NFs with high accessible surface area and commodious inter space can also be expected to use as catalyst, dye-sensitive solar cell and Li ion battery materials.