Dawen Zeng

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 (300–1,000u2005nm), and with a super-long energy storage time of more than 300u2005h 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.

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.

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.

High Sensitivity and Selectivity of C-Doped

High sensitivity and selectivity of C-doped WO3 gas sensors are reported in this paper. C-doped WO3 is synthesized by a facile infiltration and calcination process using the cotton fibers as templates. The response of C-doped WO3 sensor toward toluene (50 ppm) and xylene (50 ppm) reach 91 and 199, respectively. By comparing the response of C-doped WO3 sensor toward various indoor noxious gases (toluene, formaldehyde, ethanol, methane, benzene, and xylene), distinctive selectivity toward toluene and xylene is found. In addition, C-doped WO3 exhibits relative hygro-stability, differing from traditional gas sensor material. The results indicate that C-doped WO3 has good potential in practical applications, due to its remarkable performance and facile synthesized methods.

{\rm WO}_{3}

The desorption part of MOXs response curves to gases represents the dynamic information of gas desorption and oxide recovery on the sensitive layer. It contains abundance information and lacks to be well investigated. This paper proposes a feature extraction method from the desorption part of response curves in phase-space. The method extracts only one feature, min(dS t/dt)/max(S t), which is found to be able to represent the recovery profile. This feature could be extracted in the front part of the recovery process. Besides, it is also found that this feature does not change with the reacting time (of the reaction between a sensor and a sample) changing. A dataset was used in the paper, which was consisted of 189 measurements of 9 VOCs by 5 TGS gas sensors at three concentrations. A common feature extraction method that extracted integral in phase-space was used as a comparison in sort classification with the proposed method. The correct recognition rates of Fisher Discriminant Analysis (FDA) with the proposed method and the phase-space integral extracting method were 91.5% and 79.9%, respectively. The results show that the proposed method is an efficient feature extraction method of the recovery profile of response curves.

Gas Sensors Toward Toluene and Xylene

A combinatorial high-throughput temperature-programmed method to obtain the optimal operating temperature (OOT) of gas sensor materials is demonstrated here for the first time. A material library consisting of SnO2, ZnO, WO3, and In2O3 sensor films was fabricated by screen printing. Temperature-dependent conductivity curves were obtained by scanning this gas sensor library from 300 to 700 K in different atmospheres (dry air, formaldehyde, carbon monoxide, nitrogen dioxide, toluene and ammonia), giving the OOT of each sensor formulation as a function of the carrier and analyte gases. A comparative study of the temperature-programmed method and a conventional method showed good agreement in measured OOT.

A Method of Feature Extraction From the Desorption Part of MOX's Response Curves to Gases

In the fast recognition applications of electronic nose, not only the recognition time is important, another parameter response-recovery time also needs to be considered. The response-recovery time could be defined as the time from the beginning of measuring one sample to the state of being ready for new sample measurement. An electronic nose with nine metal oxide (MOX) gas sensors and a method of feature extraction on sensor recovery curves were presented in this paper. The electronic nose was designed to reduce the recognition time and the response-recovery time synchronously. In the sampling module of the electronic nose, there were two pumps, which could let the sensor quickly recovered. The feature extraction method could rapidly extract features from sensor recovery curves with robust information. Nine volatile organic compounds (VOCs) gas samples were measured with the electronic nose. The correct recognition ratios under 10 and 15 s recognition time are 91.0% and 95.8%, respectively. The mean response-recovery time of these sensors in the measurements was 33.5 s, which was about 42.7% of the response-recovery time in typical traditional gas sample measurements. The results show that the proposed feature extraction method could extract robust information with short recognition time and response-recovery time.