W.Q. Li

Bio: W.Q. Li is an academic researcher from Northwest Normal University. The author has contributed to research in topics: Electrospinning & Scanning electron microscope. The author has an hindex of 19, co-authored 46 publications receiving 1145 citations.

Synthesis of SnO2–ZnO heterostructured nanofibers for enhanced ethanol gas-sensing performance

Abstract: SnO 2 –ZnO hetero-nanofibers were fabricated by a facile electrospinning method and calcination in this study. The SnO 2 –ZnO nanofibers were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), Brunauer–Emmett–Teller (BET) and X-ray diffraction (XRD). The gas sensor prepared by the SnO 2 –ZnO hetero-nanofibers revealed better ethanol sensing performance than pure ZnO and pure SnO 2 nanofibers, good stability and excellent selectivity at the optimum temperature of 300 °C. The response and recovery time to 100 ppm ethanol were about 25 s and 9 s, respectively. The growth mechanism of the hetero-nanofibers was discussed, as well as the ethanol adsorption–desorption mechanism.

Highly sensitive acetone sensors based on Y-doped SnO2 prismatic hollow nanofibers synthesized by electrospinning

Abstract: Pure and Y-doped SnO 2 hollow nanofibers with porous structures were fabricated via electrospinning technique and calcination procedure. The porous SnO 2 hollow nanofibers were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), Brunauer–Emmett–Teller (BET) and X-ray photoelectron spectroscopy (XPS). Acetone sensing properties of the hollow nanofibers were also investigated. The surface morphology of pure SnO 2 and Y-doped SnO 2 possessed a hollow nanostructure with rough porous surface after being annealed at 600 °C, and the diameters of the nanofibers were in the range of 154–200 nm. The BET surface area measurement further indicated that the surface textural was mesoporous, and the pore size was calculated above 24 nm by Barret–Joyner–Halenda (BJH). Gas sensing properties revealed that Y-doped SnO 2 hollow nanofibers exhibited a much higher response to acetone vapor than pure SnO 2 hollow nanofibers at 300 °C. Y-doped SnO 2 hollow nanofibers exhibited good stability and excellent selectivity, which were ascribed to the 1D hollow nanostructure and the effect of Y doping. The formation mechanism and the acetone sensing mechanism of SnO 2 hollow nanofibers were also discussed.

Excellent acetone sensor of La-doped ZnO nanofibers with unique bead-like structures

Abstract: In this work, Lanthanum (La) doped ZnO nanofibers with bead-like structures were facilely produced by electrospinning technique. The obtained La-doped ZnO products were investigated by scanning electron microscopy (SEM), X-ray diffraction (XRD), Brunauer–Emmett–Teller method, transmission electron microscopy and X-ray photoelectron spectroscopy (XPS). The results show that La doping changes the structures of ZnO nanofibers markedly. La-doped ZnO nanofibers have unique bead-like nanostructures, in which two phases of hexagonal La2O3 and wurtzite ZnO coexist along with partially incorporation of La into ZnO lattice. The gas sensing performances of the La-doped ZnO nanostructures to acetone were investigated via static gas sensor testing system. The sensing test results indicate that an appropriate amount of La doping greatly improves the gas sensing properties of ZnO nanofibers. The 1.0 wt% La-doped ZnO sensor has the highest selectivity and response (64, to 200 ppm acetone at 340 °C), in addition to its short response time and recovery time. The unique bead-like structure and the gas sensing mechanism of La-doped ZnO nanofibers are discussed. The La-doped ZnO nanostructures we have produced can be used as a promising material for acetone sensors.

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

Abstract: The hierarchical pure and Cu-doped SnO2 nanoflowers were synthesized by a low-cost and simple hydrothermal method at 160 °C for 20 h. 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 18 nm. 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, 2.5 wt% 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 2.5 wt% Cu-doped SnO2 to 500 ppm acetone was 221.6 at 260 °C, which was about 11.5 times higher than that of ammonia (about 19.3). In addition, the response and recovery time of 2.5 wt% Cu-doped SnO2 were 9 and 6 s, 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.

Hydrothermal synthesis of monodisperse porous cube, cake and spheroid-like α-Fe2O3 particles and their high gas-sensing properties

Abstract: The monodisperse porous cube, cake and spheroid-like α-Fe 2 O 3 microparticles were successfully synthesized via a facile hydrothermal approach. The as-synthesized α-Fe 2 O 3 microparticles were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), Brunauer–Emmett–Teller (BET) and gas-sensing measurement device, and the results showed that the diameters of all these microparticles were around 2–3 μm. Meanwhile, the gas-sensing properties revealed that both reaction time of hydrothermal and Cu doping could remarkably enhance the performances of gas sensors. The response value of 1.0 wt% Cu-doped α-Fe 2 O 3 microcakes to 500 ppm acetone was 205.3 at 270 °C when the reaction time was 15 h, which was about 11.9 times higher than that of ammonia (about 17.3). In addition, both of the response and recovery time were within 10 s, demonstrating the sensor based on 1.0 wt% Cu-doped α-Fe 2 O 3 microcakes has a potential application for acetone detection at the reaction time of 15 h. Finally, the possible formation mechanism and gas-sensing mechanism of α-Fe 2 O 3 microstructures were proposed, too.

A review of ZnO nanoparticles as solar photocatalysts: Synthesis, mechanisms and applications

Abstract: Persistent organic pollutants (POPs) are carbon-based chemical substances that are resistant to environmental degradation and may not be completely removed through treatment processes. Their persistence can contribute to adverse health impacts on wild-life and human beings. Thus, the solar photocatalysis process has received increasing attention due to its great potential as a green and eco-friendly process for the elimination of POPs to increase the security of clean water. In this context, ZnO nanostructures have been shown to be prominent photocatalyst candidates to be used in photodegradation owing to the facts that they are low-cost, non-toxic and more efficient in the absorption across a large fraction of the solar spectrum compared to TiO 2 . There are several aspects, however, need to be taken into consideration for further development. The purpose of this paper is to review the photo-degradation mechanisms of POPs and the recent progress in ZnO nanostructured fabrication methods including doping, heterojunction and modification techniques as well as improvements of ZnO as a photocatalyst. The second objective of this review is to evaluate the immobilization of photocatalyst and suspension systems while looking into their future challenges and prospects.

Supramolecular Luminescent Sensors

Abstract: There is great need for stand-alone luminescence-based chemosensors that exemplify selectivity, sensitivity, and applicability and that overcome the challenges that arise from complex, real-world media. Discussed herein are recent developments toward these goals in the field of supramolecular luminescent chemosensors, including macrocycles, polymers, and nanomaterials. Specific focus is placed on the development of new macrocycle hosts since 2010, coupled with considerations of the underlying principles of supramolecular chemistry as well as analytes of interest and common luminophores. State-of-the-art developments in the fields of polymer and nanomaterial sensors are also examined, and some remaining unsolved challenges in the area of chemosensors are discussed.

Role of Oxygen Vacancies in Nanostructured Metal-Oxide Gas Sensors: A Review

Abstract: Investigations into the mechanisms governing the behavior of metal oxide gas sensors continue to be of great interest. Oxygen vacancies are a ubiquitous defect in this class of materials and their characteristics can be affected by synthesis, processing and operating parameters. The primary role of oxygen vacancies in modifying sensing performance cited in the gas sensing literature is based on a modulation of the amount of surface adsorbed oxygen or alternatively, the baseline resistance. Unfortunately, this generalized description does not provide a complete representation of the role of oxygen vacancies that would aid in more a fundamental understanding of their role in gas sensing. To this end, an attempt is made to distinguish between the role of surface and bulk oxygen vacancies where emphasis on proper characterization is first highlighted. The influence of surface oxygen vacancies on factors affecting adsorption, such as surface structure, are examined to gain understanding on improved sensing performance. The effect of bulk oxygen vacancy concentration and distribution on sensing are also discussed. Finally, the importance of these concepts within the context of doped and heterostructured gas sensors are then briefly discussed.