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.
•Both substitutional doped and interstitial N-doped TiO2 is prepared by a simple annealing method.•The photocatalytic activity toward decomposing benzene of N-TiO2 is higher than that of ...NAM-TiO2.•The surface hydroxyl group and different location of nitrogen in the lattice is responsible for the distinct photocatalytic activity.•The presence of oxygen favors the formation of interstitial nitrogen dopant during synthesis.•The deep Ni-energy level in bandgap tends to form the recombination center.
Nitrogen-doped TiO2 nanomaterial attracts enormous attention due to its excellent visible photocatalytic activity. A simple annealing method assisted by adjusting gas composition to control the positions of nitrogen dopants in TiO2 lattice is presented. The nitrogen doping sites are confirmed by XPS. The photo-degradation results of gaseous benzene under visible light illumination reveal that photocatalytic activity in as-prepared samples containing the substitutional nitrogen species is higher than that in samples containing interstitial nitrogen species. The improvement of photocatalytic performance is ascribed to the increased amounts of surface hydroxyl group in N-TiO2 samples. The efficient separation of electron-hole pairs was also responsible for the enhanced photocatalytic activity. In addition, an important conclusion is pointed out: the presence of oxygen during annealing process has an important effect on the formation of interstitial nitrogen dopants. The present work is believed to have guiding significance for preparing nitrogen-doped TiO2 with high photocatalytic activity.
The fabrication and applications of VO2 film continue to be of considerable interest due to their good thermochromic performance for smart windows. However, low visible transmittance (Tlum) and solar ...modulation efficiency (∆Tsol) impede the application of VO2 film, and they are difficult to improve simultaneously. Here, a facile zinc solution process was employed to control the surface structure of dense VO2 film and the processed VO2 film showed enhanced visible transmittance and solar modulation efficiency, which were increased by 7.5% and 9.5%, respectively, compared with unprocessed VO2 film. This process facilitated the growth of layered basic zinc acetate (LBZA) nanosheets to form mesh morphology on the surface of VO2 film, where LBZA nanosheets enhance the visible transmittance as an anti-reflection film. The mesh morphology also strengthened the solar modulation efficiency with small caves between nanosheets by multiplying the times of reflection. By increasing the zinc concentration from 0.05 mol/L to 0.20 mol/L, there were more LBZA nanosheets on the surface of the VO2 film, leading to an increase in the solar/near-infrared modulation efficiency. Therefore, this work revealed the relationship between the solution process, surface structure, and optical properties, and thus can provide a new method to prepare VO2 composite film with desirable performance for applications in smart windows.
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/WO₃/TiO₂ heterojunctional-electrical layered (HEL) system is proposed to realize this attempt. The HEL system consists of interdigital electrode, WO₃ layer and TiO₂ 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 TiO₂ and WO₃, and enrich the TiO₂ surface layer with photogenerated holes to degrade the gaseous pollutants. In comparison with the pure TiO₂ 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 WO₃ layer or the low external bias was absent.
Efficient chemical warfare agents (CWAs) detection is required to protect people from the CWAs in war and terrorism. In this work, a Pd-doped SnO
2
nanoparticles-based gas sensor was developed to ...detect a nerve agent simulant named methyl salicylate. The sensing measurements of methyl salicylate under different Pd doping amounts found that the 0.5 at.% Pd-doped SnO
2
exhibited a significant improvement in the detection of methyl salicylate at the ppb (1 ppb = 10
−9
) level, and the response value to 160 ppb methyl salicylate is 0.72 at 250 °C. Compared with the pure SnO
2
, the response value is increased by 4.5 times, which could be attributed to the influence of the noble metal Pd on the oxygen state and its catalytic effect. In addition, the 0.5 at.% Pd-doped SnO
2
sensor still has an obvious response to 16 ppb methyl salicylate with a response value of 0.13, indicating the lower detection limit of the sensor.
As inspired by a novel materials-sensor integration fabrication strategy, nanowire-like network (NWN) structured ZnO, Co3O4, In2O3 and SnO2 films are synthesized directly onto an alumina substrate by ...the screen printing combined with micro-injecting and calcination (SPMIC) to fabricate a flat-type coplanar gas sensor array based on these four sensors. The gas-sensing properties of the sensor array are investigated at different operating temperatures (150–350°C), and the best selectivity is interestingly found among the four indoor pollution gases including toluene (C7H8), formaldehyde (HCHO), acetone (CH3COCH3) and ammonia (NH3) at 300°C. This is also confirmed by the principal component analysis (PCA) result that the four gases can be discriminated and recognized by the sensor array. The enhancement in the selectivity is attributed to the combination of special nanostructures with large surface area and sensor array based on the four different metal oxides. Furthermore, the SPMIC method is demonstrated to be an effective route not only to synthesize NWN structured metal oxides directly onto an alumina substrate without being destroyed, but also to fabricate coplanar sensor array based on various NWN structured metal oxide films.
Aluminium–lithium alloy (Al–Li alloy) powder has excellent ignition and combustion performance. The combustion product of Al–Li alloy powder combined with ammonium perchlorate is gaseous at the ...working temperature of solid rocket motors, which greatly reduces the loss of two-phase flow. Experimental investigations were thoroughly conducted to determine the effect of the Al–2.5Li (2.5 wt% lithium) content on propellant combustion and agglomeration based on thermogravimetry-differential scanning calorimetry, heat combustion, laser ignition, combustion diagnosis, a simulated 75 mm solid rocket motor and a condensed combustion products (CCPs) collection device. The results show that the exothermic heat and weight gain upon the thermal oxidation of Al–Li alloy is obviously higher than those of Al powder. Compared with the reference propellant’s formulation, Al–2.5Li leads to an increase in the burning rate and a decrease in the size of the condensed combustion products of the propellants. As the Al–2.5Li alloy content gradually increases from 0 wt% to 19 wt%, the burning rate increases from 5.391 ± 0.021 mm/s to 7.244 ± 0.052 mm/s at 7 MPa of pressure; meanwhile, the pressure exponent of the burning rate law is changed from 0.326 ± 0.047 to 0.483 ± 0.045, and the d43 of the combustion residue is reduced from 165.31 ± 36.18 μm to 12.95 ± 4.00 μm. Compared to the reference propellant’s formulation, the combustion efficiency of the HTPB propellant is increased by about 4.4% when the Al–2.5Li alloy content is increased from 0 to 19%. Therefore, Al–2.5Li alloy powder is a promising fuel for solid propellants.
The testing chamber humidity and the storage circumstance humidity effects on the tetrapod-shaped ZnO nanopowder (named as T-ZnO) thick film sensors were investigated by measuring the resistance and ...sensitivity. The resistance increases gradually with increasing relative humidity (RH) in a range of 32%–75% RH in testing chamber, while in a range of 75%–96% RH, decreases gradually with the increase of RH. The sensitivity to ethanol 100
ppm in testing chambers with different humidity is in the order of 50% RH
>
of 75% RH
>
of 32% RH
>
of 96% RH. The sensitivity change in the storage circumstance with different RH is similar to the change in testing chamber with different RH. The stability of T-ZnO sensor is influenced evidently by the storage circumstance humidity. The water vapour in the tetrapod-shaped ZnO nanopowders was investigated by thermogravimetric analysis (TGA). The testing gas and the reactant adsorbed in the sensitive film were characterized by infrared spectrum (IR). The explanation of the observed effects was given and the mechanism of interaction of the ZnO sensing layer with H
2O was proposed.
•La, Gd, and Lu doped SnO2 with their sensing properties toward CO2 were compared.•The microstructures of SnO2-based nanoparticles were elaborately characterized.•La-SnO2 thick film shows superior ...response toward trace ppm CO2.•Our sensing material can be recommended to employ in oxygen-free environment.
SnO2 thick films doped with atomic ratios ranging from 0 up to 8at.% La, 8at.% Gd, 8at.% Lu were fabricated, respectively, via hydrothermal and impregnation methods. The crystal phase, morphology, and chemical composition of the SnO2-based nanoparticles were characterized by XRD, FE-SEM, EDX, HRTEM and XPS. Sensing properties of La-SnO2, Gd-SnO2, Lu-SnO2 films, as well as the pure SnO2 film, were analyzed toward CO2 in the absence of O2. It was found that the optimal doping element was La and the best doping ratio was 4at.%. The maximum response appeared at an operating temperature of 250°C, on which condition the 4at.% La-SnO2 exhibited a remarkable improvement of response from 5.12 to 29.8 when increasing CO2 concentration from 50 to 500ppm. Furthermore, the working mechanism underlying such enhancement in CO2-sensing functions by La additive in the absence of O2 was proposed and discussed.
Two-dimensional (2D) transition metal oxides (TMOs) have attracted much attention for various applications, owing to the abundance of active sites, rapid ion transmission speed, and short carrier ...migration distance. However, the current preparation strategies are usually limited to producing intrinsically layered compounds or sacrificing template. Here, we report a universal strategy for preparing ultrathin porous 2D TMO nanosheets by chemical topological transformation of the corresponding transition metal selenides. We observed that the as-prepared 2D TMO nanosheets not only perfectly inherit the transition metal selenides’ 2D topological structure, but also possess numerous pore structures formed as a way to release the structural stress associated with lattice growth. As a proof of concept, ultrathin porous WO
3
, MoO
3
, and Co
3
O
4
nanosheets were successfully prepared based on the
in-situ
oxidation of the corresponding ultrathin WSe
2
, MoSe
2
, and Co
0.85
Se, respectively. The outstanding sensing properties and photodetector performance displayed by the as-prepared porous 2D WO
3
nanosheets further indicate the promising prospects of topology transformation for the preparation of porous 2D TMO nanosheets.
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