Changsheng Xie

The thermal physical formation of ZnO nanoparticles and their morphology

The present study examines the structural development of ZnO nanoparticles. The coarse pure Zn powder material was melted and evaporated in an oxygen-filled chamber by renovated hybrid induction and laser heating (HILH) to produce ZnO needle-shaped nanoparticles. Simultaneously, Zn nanoparticles were also produced by HILH in an argon-filled chamber. The Zn nanoparticles were annealed in the atmosphere at temperatures of 300°C, 400°C, 420°C and 500°C, respectively, to investigate the corresponding thermal oxidation behavior. By annealing above 400°C, Zn structural transformation took place, and the morphology of the nanoparticles changed to needle and/or tetrapod shape. No sintered necks between ZnO nanoparticles were found. The growth of the nanoparticles is considered to be controlled by evaporation.

A full-sunlight-driven photocatalyst with super long-persistent energy storage ability

A major drawback of traditional photocatalysts like TiO2 is that they can only work under illumination, and the light has to be UV. As a solution for this limitation, visible-light-driven energy storage photocatalysts have been developed in recent years. However, energy storage photocatalysts that are full-sunlight-driven (UV-visible-NIR) and possess long-lasting energy storage ability are lacking. Here we report, a Pt-loaded and hydrogen-treated WO3 that exhibits a strong absorption at full-sunlight spectrum (300–1,000 nm), and with a super-long energy storage time of more than 300 h to have formaldehyde degraded in dark. In this new material system, the hydrogen treated WO3 functions as the light harvesting material and energy storage material simultaneously, while Pt mainly acts as the cocatalyst to have the energy storage effect displayed. The extraordinary full-spectrum absorption effect and long persistent energy storage ability make the material a potential solar-energy storage and an effective photocatalyst in practice.

Selectively enhanced UV and NIR photoluminescence from a degenerate ZnO nanorod array film

Energy band engineering is a promising method to tune the photoelectric properties of semiconductors. In this paper, we report an un-element-doped ZnO nanorod array film with a degenerate energy band via annealing in a hydrogen atmosphere. Due to the energy band modification, the photogenerated carrier transitions in the degenerate energy band, involving the valance band, the defect bands and the degenerate conduction band, cause unique photoelectric properties in the degenerate ZnO film. The degenerate ZnO film performs with outstanding conductivity and exhibits an obvious optical absorption in the visible region. Its photoluminescence and photoresponse properties are investigated to understand the fundamentals of photogenerated carrier excitation and recombination in the degenerate ZnO film. Interestingly, the degenerate ZnO film performs with poor photoresponse and has poor photocurrent efficiencies for ultraviolet, blue, and green illuminations, but the photoresponse for near-infrared illumination is attractive. Our results also demonstrate the selectively enhanced down-conversion photoluminescence both at the UV band and at the near-infrared band from the degenerate ZnO film after being excited by an ultraviolet laser source.

A low temperature gas sensor based on Pd-functionalized mesoporous SnO2 fibers for detecting trace formaldehyde

The permissible limitation of formaldehyde (HCHO) is 80 ppb in an indoor environment. Hence, the rapid real-time monitoring of trace HCHO is urgent and faced as a great challenge by gas sensors based on semiconducting metal oxides. To enhance the HCHO sensing performance of gas sensors, mesoporous SnO2 fibers are used to fabricate a bare SnO2 sensor and then the sensor is functionalized with Pd nanodots by a facile dipping–annealing process. The obtained Pd-functionalized SnO2 sensor exhibits a very high response to HCHO, ultralow detection limit (50 ppb), excellent sensor selectivity over other reducing gases, and short response and recovery time to 100 ppb HCHO (53 s and 103 s, respectively) at a low working temperature of 190 °C. Herein, the Pd nanodots loaded onto SnO2 fibers serve as sensitizers or promoters, increasing the amount of adsorbates as well as molecule–ion conversion rate and simultaneously providing a new catalytic oxidization pathway of HCHO (HCHO → [CH2O]n (POM) → HCOOH → CO2 + H2O) accompanied with a promotion in the electron transfer rate, and thus improving HCHO sensing performance. The combination of the SnO2 mesoporous structure and catalytic activity of the Pd nanodots loaded could give us a very attractive sensing behavior for applications as real-time monitoring gas sensors with rapid response speed.

Processing–structure–property relationships of Bi2WO6 nanostructures as visible-light-driven photocatalyst

QDS modified Bi(2)WO(6) (BWO) nanostructures were processed by calcination at different temperatures. A strong correlation was found among the processing, structure and properties of the samples. With increasing calcination temperature from 200°C to 500°C, the crystallinity increased and the BWO QDS gradually disappeared from the nanostructures. Both surface area and band gap of the samples decreased. The light absorption of the samples became lower for the long-wavelength range, accompanied by a red shift of the absorption edge. The photocatalytic activity of the samples decreased after calcination at higher temperature. The competitive relations between crystallinity and surface area in affecting photocatalytic activity were discussed. The role of BWO QDS that played in enhancement of photocatalytic activity was also revealed by studying structure and property evolution of the calcined samples.

Improvement of gaseous pollutant photocatalysis with WO3/TiO2 heterojunctional-electrical layered system.

Since the photogenerated holes play a much more important role than electrons in gas-phase photocatalysis, it is better to enrich the holes in the surface of a material system. Here, a novel [interdigital electrode/WO(3)/TiO(2)] heterojunctional-electrical layered (HEL) system is proposed to realize this attempt. The HEL system consists of interdigital electrode, WO(3) layer and TiO(2) layer, and they are orderly printed onto the alumina substrate from bottom to top using the technology of screen printing. It is surprise that the synergistic effect of layered heterojunction and external low bias can strengthen the separation of electron-hole pairs in both TiO(2) and WO(3), and enrich the TiO(2) surface layer with photogenerated holes to degrade the gaseous pollutants. In comparison with the pure TiO(2) film, a 6-fold enhancement in photocatalytic activity was observed using the HEL system by applying a very low bias of 0.2V. Furthermore, the results also showed that the remarkable improvement could not be obtained when either the WO(3) layer or the low external bias was absent.

Mechanistic Insights into Formation of SnO2 Nanotubes: Asynchronous Decomposition of Poly(vinylpyrrolidone) in Electrospun Fibers during Calcining Process

The formation mechanism of SnO2 nanotubes (NTs) fabricated by generic electrospinning and calcining was revealed by systematically investigating the structural evolution of calcined fibers, product composition, and released volatile byproducts. The structural evolution of the fibers proceeded sequentially from dense fiber to wire-in-tube to nanotube. This remarkable structural evolution indicated a disparate thermal decomposition of poly(vinylpyrrolidone) (PVP) in the interior and the surface of the fibers. PVP on the surface of the outer fibers decomposed completely at a lower temperature (<340 °C), due to exposure to oxygen, and SnO2 crystallized and formed a shell on the fiber. Interior PVP of the fiber was prone to loss of side substituents due to the oxygen-deficient decomposition, leaving only the carbon main chain. The rest of the Sn crystallized when the pores formed resulting from the aggregation of SnO2 nanocrystals in the shell. The residual carbon chain did not decompose completely at temperatures less than 550 °C. We proposed a PVP-assisted Ostwald ripening mechanism for the formation of SnO2 NTs. This work directs the fabrication of diverse nanostructure metal oxide by generic electrospinning method.

Synthesis of TiO2/WO3/MnO2 Composites and High-Throughput Screening for Their Photoelectrical Properties

On the basis of the idea of equilateral ingredient triangle, a material library of the TiO(2)/WO(3)/MnO(2) composite material system was designed, which consisted of 66 ingredient points. Each point in the library corresponded with a device. To fabricate the device, the technology of screen printing was used. The pastes which were suitable for this technology were prepared by ball milling. After we printed the pastes onto the alumina substrate which had been preprinted with Au interdigital electrodes, these printed samples were sintered at 550 degrees C for 2 h in air. The photocurrent of each device under different light sources was measured respectively using a high-throughput screening system. The largest photocurrent was observed when the mole ratio of TiO(2)/WO(3) was 2/8 in the composite system. X-ray diffraction (XRD) was used to investigate the phase structure of the powder which had excellent photoelectric response.

Characterization of Photoelectric Properties and Composition Effect of TiO2/ZnO/Fe2O3 Composite by Combinatorial Methodology

On the basis of combinatorial methodology and the idea of an equilateral ingredient triangle, the TiO(2)/ZnO/Fe(2)O(3) composite system including 66 ingredient points was designed. The photocurrents under different light sources and bias voltages were measured, and the photocurrent amplitude at 300 s was chosen as a parameter to evaluate the photoelectric response of the composite. To appraise the composition effect of the composite compared with pure materials, the quantitative formula of the composition effect has been provided for the first time in this paper. We found that not all the ingredient points demonstrated the enhanced composition effect in the as-designed ingredient triangle material library. The reasons of different composition effect for different ingredient points have been discussed in detail. X-ray diffraction (XRD) and field emission scanning electron microscopy (FE-SEM) were used to investigate the phase structure and the grain morphology of the composite.

Detection and discrimination of low concentration explosives using MOS nanoparticle sensors

In the present study, four explosives of NH(4)NO(3), mineral explosives (ME), picric acid (PA) and 2,6-dinitrotoluene (2,6-DNT) have been investigated by using ZnO-doped nanoparticle sensors with additives of Sb(2)O(3), TiO(2), V(2)O(5) and WO(3). Firstly, eighteen ZnO-doped nanoparticle sensors were optimized and selected six best sensors to compose a new optimized array. Then, the detection capability of the sensor array was studied by using static sampling method. The results showed that with the increase in concentration of samples, the sensitivities of the sensors also increased, and the lowest detection limit of the four samples were low to 3.34 microg/L. At last, for the sake of approaching closer practical application, these four explosives were also studied with full dynamic sampling method and the results demonstrated that all the samples could be well identified completely at the concentration of 15.4 microg/L when maximum values of slope were extracted as the feature parameters to DFA analysis.