Yali Cheng

Controllable synthesis of Ho-doped In2O3 porous nanotubes by electrospinning and their application as an ethanol gas sensor

AbstractPure and Ho-doped In2O3 nanotubes (NTs) and porous nanotubes (PNTs) were successfully synthesized by conventional electrospinning process and the following calcination at different temperatures. X-ray diffractometry (XRD), thermogravimetric analysis (TGA), Raman spectrometer, energy-dispersive spectroscopy, scanning and transmission electron microscopy were carefully used to investigate the morphologies, structures and chemical compositions of these samples. Their sensing properties toward ethanol gas were studied. Compared with pure In2O3 NTs (response value is 17), pure In2O3 PNTs (response value is 20) demonstrated enhanced sensing characteristics. What’s more, the response of Ho-doped In2O3 PNTs sensors to 100xa0ppm ethanol was up to 60 at 240xa0°C, which increased three times more than that of the pure In2O3 PNTs. Additionally, the minimum concentration for ethanol was 200xa0ppb (response value is 2). The increased gas-sensing ability was attributed not only to the hollow and porous structure, but to the Ho dopant. Furthermore, Ho-doped In2O3 PNTs enable sensor to discriminate between ethanol and the other gas distinctly, particularly acetone that is usually indistinguishable from ethanol. Also, by analyzing XRD, TGA and Raman spectrometer, a possible formation mechanism of porous nanotubes and sensing mechanism were put forward.n

Synthesis of novel Ho 2 O 3 –Fe 2 O 3 porous nanotubes and their ultra-high acetone-sensing properties

The mono-disperse Ho2O3–Fe2O3 porous nanotubes were successfully synthesized via a facile electrospinning method. The morphologies, crystal structures and components of as-prepared samples were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), energy-dispersive X-ray spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS), Transmission electron microscope (TEM) and High Resolution Transmission Electron Microscopy (HRTEM), respectively. Then the samples were applied to construct gas sensor devices and their gas sensing properties were further investigated. The results showed that the Ho2O3–Fe2O3 porous nanotubes with the weight ratio of 3xa0wt% exhibit an ultra-high response to acetone (185/100xa0ppm) at the optimal operating temperature of 240xa0°C. Meanwhile, the detection limit of the sensor is estimated to be 500xa0ppb with a response of 2.4. The sensor also owned good linear characteristic (0–200xa0ppm) and selectivity, demonstrating the sensor based on Ho2O3–Fe2O3 porous nanotubes has a promising application for detecting acetone. Thus, further improvement of gas sensing properties in metal-oxide-semiconductors materials could be realized by forming porous nanocomposite.

Ultra-sensitive and selective acetone gas sensor with fast response at low temperature based on Cu-doped α-Fe2O3 porous nanotubes

In the present work, the acetone gas sensing material based on pure α-Fe2O3 nanotubes, pure and Cu-doped α-Fe2O3 porous nanotubes were fabricated by electrospinning and annealing processes. Different Cu dopant concentrations are introduced to investigate the dopant’s role in sensing performance. The structures and chemical compositions of the as-prepared products were examined using a series of material characterization methods including XRD, EDS, SEM and nitrogen adsorption–desorption analysis. And the acetone sensing results demonstrate that the gas sensitivity of porous nanotubes is better than nanotubes. Moreover, compared with pure samples, the sensor based on 3.0xa0wt% Cu-doped α-Fe2O3 porous nanotubes exhibits higher response (99.43/100xa0ppm) and excellent selectivity towards acetone at 164xa0°C. Meanwhile, the detection limit can extend down to ppb level (2.2/100xa0ppb). Additionally, the sensor also shows fast response and recovery time (5/18xa0s) and good repeatability to acetone. The enhancement of gas sensitivity is ascribed to not only the effective utility of hollow and porous structures, but also the high catalytic activity of the Cu additive.

A Comparison of Eu-Doped α-Fe2O3 Nanotubes and Nanowires for Acetone Sensing

Pure and Eu-doped (1.0, 3.0, 5.0wt.%) α-Fe2O3 (PFO and EFO) nanotubes and nanowires have been successfully synthesized through the combination of electrospinning and calcination techniques. The structures, morphologies and chemical compositions of the as-obtained products were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), thermogravimetric and differential scanning calorimetry (TG-DSC) and energy dispersive spectrum (EDS), respectively. To demonstrate the superior gas sensing performance of the doped nanotubes, a contrastive gas sensing study between PFO (EFO) nanotubes and nanowires was performed. It turned out that Eu doping could magnify the impact of morphology on gas sensitivity. Specifically, at the optimum operating temperature of 240∘C, the response value of PFO nanotubes to 100ppm acetone is slightly higher than that of nanowires (3.59/2.20). EFO (3.0wt.%) nanotubes have a response of 84.05, which is almost 2.7 times as high as that of nanowires (31.54). Moreover, ...

Fabrication, characterization and excellent formaldehyde gas sensing of Tb-doped In 2 O 3 beaded-porous nanotubes

The pure and Tb-doped In2O3 beaded-porous nanotubes (BPNTs) are fabricated by simple electrospinning method. The crystal phase, morphology and chemical composition of the obtained samples were analyzed by characteristic techniques (XRD, FE-SEM, TEM, EDS, XPS, etc.). The mechanism of forming BPNTs structure was studied, and phase separation plays a key role in the process of formation. A series of sensing tests toward formaldehyde gas showed that 6xa0mol% Tb-doped In2O3 BPNTs exhibited the best sensing performance: high response (75–50xa0ppm), shorter response and recovery times (2xa0s and 12xa0s), low limit of detection (LOD, 1.27–100xa0ppb), good selectivity and long-term stability, etc. The significantly improved gas sensing properties were mainly resulted from their high surface basicity, enriched defects (oxygen vacancies), small crystallite size and complex porous structures.

The comparison of gas sensing properties between hierarchical porous and nonporous SnO 2 microflowers

The hierarchical porous and nonporous SnO2 microflowers was successfully synthesized by a simple hydrothermal method and followed by calcination procedure. The microstructure and morphology of the product were characterized by X-ray diffraction, energy dispersive X-ray spectroscopy, and scanning electron microscopy (SEM). The SEM images display that the prepared SnO2 is a microflower composed of countless thin sheets, and each of the sheets covered in a series of porous by calcining at 500xa0°C. Nevertheless, there is no porous when it treated at 400xa0°C. The results of comparison show that the hierarchical porous SnO2 microflowers (HPSM) sensors possess a preferable gas-sensing property. The response of HPSM sensors to 100xa0ppm ethanol is 205.6 at the optimum operating temperature 240xa0°C. Which sensitivity is almost 3.9 higher than the hierarchical nonporous SnO2 microflowers (HNSM) (52.9). Meanwhile, the response and recovery times of HPSM (HNSM) are 3xa0s (3xa0s) and 45xa0s (145xa0s) to 100xa0ppm ethanol, respectively. What’s more, the minimum concentration of ethanol that we can detect is 0.1 (1.0)xa0ppm, and the response value is 1.9 (2.0). At last, both HPSM and HNSM own a good selectivity.

Highly sensitive and selective formaldehyde gas sensor based on CdO–In2O3 beaded porous nanotubes at low temperature

Pure In2O3 nanowires (PINW) and CdO–In2O3 composited beaded porous nanotubes (CIBPNT) were successfully prepared by conventional electrospinning method and followed by calcination. The peculiar surface morphological images of as-synthesized nanomaterials were observed via scanning electron microscope (SEM) and transmission electron microscopy (TEM) from which we could observe a series of irregular holes distributed on the surface of beaded nanotubes. The inner structure of the samples was investigated using X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The results reveal that the element composition of the samples are in conformity with the CdO–In2O3 materials. In addition, the average crystallite size of CIBPNT (17.5xa0nm) can be estimated from XRD which accords with the TEM images, and XPS analysis supports the oxygen vacancy principle by proving the oxygen vacancies concentration of CIBPNT is more than in PINW. The formaldehyde sensing performances of the samples were evaluated at different temperatures. The result shows that the sensor based on CIBPNT exhibits a excellent response (72–50xa0ppm formaldehyde) at a low operation temperature of 132xa0°C, and the value is eight times that of the response of PINW (9 to 50xa0ppm formaldehyde).The sensor based on CIBPNT could detect 0.1xa0ppm formaldehyde with a response of 2. In addition, good selectivity and a short response and recovery time (6xa0s, 12xa0s) are exhibited. The enhancement of gas sensitivity is attributed to not only the unique beaded shape of hollow and porous 1D nanostructures, but also the high catalytic activity of the CdO additive.