Composite WO3/CdS/W Photocatalyst

The meaning of compound semiconductor firstly lies in that the semiconductor particles with different energy band structure brings the possibility of narrow band-gap semiconductor sensitizing wide band-gap semiconductor nano-particles; secondly, in the quadratic element compound semiconductor, the energy difference between the two semiconductors making the photo-generated carriers injected into a energy level of the semiconductor particle from the another, thus to ensure the charge separation being effective and long-term; in addition, the excess charges which generated by  coordination of different metal ions and different charge properties also help the increasing of the semiconductors capture proton or electronic, and thus to enhance the photocatalytic activity.
 
WO3/CdS/W composite photocatalyst is a complex phase of semiconductors, after the researchers continued to explore the photocatalytic reaction mechanism, and discussed the relationship between the composition of the composite catalyst, use level, pH of test solution, illumination time and the removal rates of COD, color. Experimental results have shown that, when in the conditions of the mass ratio of the WO3/CdS/W composite photocatalyst that m (WO3) / m (CdS) / m (W) equals to 60: 39: 1, the pH value of test solution is 6.5, the shinning time of 10h, the removal rate of COD, color of printing and dyeing wastewater reaches the highest point.

WO3 and CdS
 
There are two forms of crystal of cadmium sulfide (CdS): α- formula presents in the form of lemon yellow powder; β- formula presents in the form of orange powder. High purity of CdS is a semiconductor with excellent property, which has a strong visible light photoelectric effect, and can be applied in the production like photoelectric cells, solar battery, light-sensitive resistors, photocatalyst ect.. Studies have shown that adding an appropriate amount of CdS into WO3 can improve the catalytic activity of the photocatalyst. That is because WO3 has the larger band gap of Eq = 2.8eV, and the CdS has the smaller band gap of is Eq = 2.12eV, the composite use of WO3 and CdS will substantially increasing the absorption rate of visible light.
 
At the same time, the use level of the reagent, pH value of test solution and illumination time also affect WO3/CdS/W the efficiency of photocatalyst:
1. With the increasing using level of reagent, the removing rate of COD, color increased; however, when it higher than a certain amount, the increase of the removal rate becomes very slow;
2. Under the premise of controlling the other variables being stable, the removal rate of COD, color increased with the increasing of pH value; however, when the pH value is higher than 6.5, the removal rate began to decline, and when the pH value equals to 6.5, its COD, color removal reaches the maximum, that we can see 6.5 is the optimal pH value;
3. Fix the amount of photocatalyst with the composition of m (WO3): m (CdS): m (W) equals to 60: 39: 1, the test solution pH value of 6.5, and just change the illumination time, then we can see that with the longer of the photocatalytic reaction time, the removal rate of COD, color increased gradually; but, when the reaction time is more than eight hours, the increasing rate of COD, color removal rate is becoming very slow; and when the reaction time reaches 10 hours, its COD, color removal rate reaches the highest value;
relationship between time and COD-color removal
Wherein the abscissa represents the reaction time (h); the ordinate represents the removal rate (%); a, b, c and d are respectively on behalf of color removal efficiency of photocatalytic reaction, COD removal efficiency of photocatalytic reaction; COD removal efficiency of the dark reaction; COD removal efficiency of the blank experiment.
 
4. Furthermore, through the contrast of the dark reaction (the same amount of photocatalyst, but stirring reaction in the absence of light), the blank experiment (without catalyst, and stirring reaction under the light) and the photocatalytic reaction, we can draw that, photocatalytic oxidation reaction will not be occurred in the situations of simply adding the photocatalyst (only add photocatalyst, but the light is absence) and illumination condition (only light, but no photocatalyst), then it can be concluded that the photocatalytic reaction occurs only under condition of exist simultaneously of photocatalyst and light.

 

As-Reduced Ammonium Tungsten Bronze Nanoparticles Preparation

Tungsten bronze compounds are an important class of inorganic compounds, such compounds of tungsten ions W6 +, W5 + and W4 + and other mixed valence state so that the overall charge balance compound. Rich crystal structure, the structure of the tunnel and this particular valence state to have excellent properties, such as electronic and ionic conductivity, superconductivity, optical properties, which in the secondary battery, electrical system color, and near-infrared absorption application of chemical sensors and other aspects of widespread research interest.
 
Currently, the synthesis of compounds of tungsten bronze Lei depends on the wet chemical method, a thermal reduction and thermal decomposition. Wet chemical synthesis of ammonium tungsten bronze is mainly starting material under reflux for several days in a reducing solvent, obtained by this method sample size is too large, usually between a few to tens of microns, and the preparation process for a long time , energy consumption. Thermal reduction sucked tungsten oxide, a tungsten metal powder and metal tungstates uniformly mixed in proper proportions, then heated in a vacuum or under an inert atmosphere, the reaction temperature is usually about 1000 ° C, to remove unreacted after completion of the reaction impurities. Since the thermal stability of ammonium tungsten bronze difference, decomposition temperature (300 ° C) below the synthesis temperature, the thermal reduction can not be used to synthesize ammonium tungsten bronze. Pyrolysis synthesis of ammoniumtungsten bronze is ammonium paratungstate in a reducing atmosphere (H2 or H2 and N2, a mixed gas of Ar, etc.) under thermal decomposition, in addition to the resulting sample size is too large, but this method also can not be ammonium tungstate completely pure phase bronze, ammonium content of the sample is too low and easy to excessive oxidative decomposition of the crane and other shortcomings.
 
As the current study can not directly produce ammonium tungsten bronze Nanopowders pure phase, it is often the large micron-sized particles obtained by milling the way broken into small particles, but such compounds during the milling process is easy It is oxidized and inactivated and easy to break down, but also accompanied by a crystallization performance degradation and other shortcomings, and therefore has no way to step directly nano ammonium tungsten bronze powder.
 
Restore preparing ammonium tungsten bronze nanoparticles, wherein the method steps are as follows: 0.01 ~ 1g organic tungsten source was dissolved in 20 ~ 40ml organic acid solution, and stirred to obtain a homogeneous solution, then adding 4 ~ 30ml organic amines, mixed until homogeneous, to move the reaction vessel, 150 ~ 350 ° C crystallization for 0.5 to 48 hours, the reaction was powder samples were centrifuged, washed, at 40 to 250℃ vacuum drying 1 ~ 12 hours i.e. get the reduced form ammonium tungsten bronze nanoparticles.
 
The present invention under solvothermal conditions, the long-chain organic acid is a high boiling point reaction media, organic tungsten source and a high-boiling organic amines as raw materials in a non-aqueous environment next ammonium tungsten bronze controlled synthesis of nanoparticles. A significant advantage of this method is that the synthesis of simple steps can yield, to thereby obtain a uniform particle morphology, crystallinity is good, narrow particle size distribution, size is adjustable within a certain range, the chemical valence of reduced state, without the need for prolonged process and subsequent milling process, direct access to nano-powders.
 
The present invention is a sample preparation hexagonal tungsten bronze ammonium nanocrystals size between 80 ~ 500nm can be regulated, uniform shape, a narrow particle size distribution, the valence state and W6 +, W5 + mixed, rich in free electrons. Further, the samples of the present invention is prepared having strong near-infrared absorbing ability, a film containing nanoparticles can effectively shield the near infrared rays of 780 ~ 2500nm and maintaining high visible light transmittance.

Chemical Sensors
 
Example 1: The 0.4g tungsten chloride is dissolved in 20ml of oleic acid, stir until completely dissolved, then add 20ml oil amine and mixed until uniform, moved to supercritical autoclave, 350 ° C crystallization reaction 1 hour, the reaction after the powder body samples were centrifuged, washed, and dried in vacuo at 60 V for 6 hours to obtain a blue powder ammonium tungsten bronze, which is a square block of ammonium tungsten bronze particles, the average diameter of 250nm.
 
Example 2: 100ml of water after the hydrothermal reaction vessel was added 36ml of oleic acid and 0.4 g WCl4 powder was mixed at room temperature with stirring; until completely dissolved, then add 4 ml of oleyl amine, and then sealed reactor, in an oven at 200 ° C Crystal was allowed to stand of 24 h. After cooling to room temperature, centrifuged, and washed three times successively alternately with 30 mL deionized water and 30 mL of absolute ethanol, and dried under vacuum to give ammonium tungsten bronze blue powder, which is a square block of ammonium tungsten bronze particles, the average diameter of 200nm.

electrochromism films

Tungsten Trioxide Denitration Catalyst Applies High Temperature Flue Gas Denitration

90% of the NOx in the flue gas exists in the form of NO. The denitration and desulfurization technologies of coke oven flue gas are namely four, which shows as bellows: integration process of sodium carbonate semidry desulfurization + low temperature denitration; coke oven flue gas heating + high temperature catalytic reduction denitration process; SICS Catalytic Oxidation (Organic Catalysis Method) desulfurization and denitrification process; activated carbon desulfurization and denitrification process. Wherein the principle of coke oven flue gas heating + high temperature catalytic reduction denitration process is under the present of tungsten trioxide de-NOx catalyst, the NOx in the flue gas reacts with the injected ammonia to occur the reduction reaction, and finally generate N2 and H2O, to achieve the goal of NOx removal. Generally, the reaction temperature is controlled at among 290~420 ℃.

dust denitrification project
 
The process that tungsten trioxide denitration catalyst plays a role in coke oven flue gas is as follows:
1. Use the Master original flue exhaust fan from the coke oven flue always leads through the GGH heat exchanger or furnace heated to 320 ℃ (The heating furnace is heated with the coke oven gas.);
2. The heated flue gas enters the SCR reactor, under the effect of tungsten trioxide denitration catalyst the gas will have a selective reduction reaction with the added denitration agent - liquid ammonia, to achieve purpose of efficient denitration;
3. The clean flue gas after denitration enters the GGH (flue gas - flue gas reheater), the clean flue gas comes out from GGH will go through the waste heat boiler for heating cold water to achieve the effect of heat recovery, and finally exhaust to the atmosphere through the chimney.
 
Generally, in the process of high temperature denitrification of tungsten trioxide denitration catalyst, the optimum reaction temperature is 350°C, the efficiency can reach to 70%, which meets emission standards of 150mg/m3; in addition, its denitration efficiency is quite stable, and has more stable removal ability for low NOx emissions; moreover, the setting up of GGH makes the energy exchange between the cleaned high temperature (350°C) flue gas outlet from the purification SCR and relatively low temperature (180°C) of oven raw tobacco gas coming true, to enhance the original coke oven flue gas temperature, reducing fuel consumption and greatly reduce system power consumption.

 

Tungsten Carbide Roll Ring

Compared with the roll ring by other materials, tungsten carbide roll ring has many advantages, such as high hardness, high flexural or compressive strength, with low affinity of steel, low coefficient of expansion and excellent wear resistance and so on. What’s more, it can also effectively accelerate the rolling process, remarkably decrease stopping times and maintain high-speed rolling, which improves the overall efficiency; roll ring does not occur substantially scratches, it burns the melt and stick onto steel, and the shorter the time required for grinding; the rolled products have high dimensional accuracy, good surface quality, overall performance has improved significantly. According to differences of materials, tungsten carbide roll ring can be specifically divided into WC-Co based carbide, TiC based carbide and steel bonded carbide. In addition, in order to meet the special requirement of wear resistance and corrosion resistance, it can correspondly add some Ni, Cr elements. Generally, the content of WC of tungsten carbide is between 70%-97%, decrease the binder Co or the grain size of WC will all improve the hardness of roll ring.

The monolithic cemented carbide roll ring, for the user, a one-time investment costs are relatively high, which is also a barrier of development of carbide roll ring. So consider on the properties and the cost, researchers develop new tungsten carbide composite roll ring, which can greatly save the carbide consumption and decrease the production cost. It is composed of tungsten carbide outer ring and ductile iron inner ring. Tungsten carbide outer ring can ensure the roll ring has no deformation by high-speed friction under high temperature and high pressure, so the quality and dimensional accuracy of products will not be affected; ductile iron inner ring has high strength, good strength and ductility, which play an important role in rolling force delivering and can effectively reduce the failure rate of roll ring under impacting. Furthermore, it can also be processed by ductile iron and keyway with the keyway by a plurality of taper roller ring (up to 4) mounted on the roller body, compared to the overall carbide roller ring with the roll change a lot of convenience.

tungsten carbide roll ring

 

TTB Structures Lead-Free Ferroelectrics

Tetragonal tungsten bronze (TTB) structures offer some promise as lead-free ferroelectrics and have an advantage of great flexibility in terms of accessible composition ranges due to the number of crystallographic sites available for chemical substitution. The ferroic properties of interest are coupled with strain, which will be important in the context of stability, switching dynamics and thin film properties. Coupling of strain with the ferroelectric order parameter gives rise to changes in elastic properties, and these have been investigated for a ceramic sample of Ba6GaNb9O30 (BGNO) by resonant ultrasound spectroscopy. Room temperature values of the shear and bulk moduli for BGNO are rather higher than for TTBs with related composition which are orthorhombic at room temperature, consistent with suppression of the ferroelectric transition. Instead, a broad, rounded minimum in the shear modulus measured at ~1 MHz is accompanied by a broad rounded maximum in acoustic loss near 115 K and signifies relaxor freezing behaviour. Elastic softening with falling temperature from room temperature, ahead of the freezing interval, is attributed to the development of dynamical polar nanoregions (PNRs), whilst the nonlinear stiffening below ~115 K is consistent with a spectrum of relaxation times for freezing of the PNR microstructure.
 
Recently, the tetragonal tungsten bronze (TTB) class of materials—a structure closely related to perovskites, has gathered the attention of the research community. The TTB structure: (A1)2(A2)4(C)4(B1)2(B2)8O30, due to the presence of crystallographically nonequivalent A- and B-sites and an extra C-site, provides supplementary degrees of freedom for manipulation of the structure, huge compositional flexibility allowing the insertion of various metals into the five different TTB sites, nevertheless offering the possibility of fine-tuning both electrical and magnetic behaviour. The TTB structure consists of a network of corner sharing BO6 octahedra formed around the perovskitic A1 site that creates further two types of channels: pentagonal A2 channels (which can be occupied by alkali, alkaline earth and rare earth cations) and smaller triangular C channels (mostly vacant, they can be filled/ just partially filled by small low-charged cations like Li+ —e.g., K6Li4Nb10O30). These materials, known to exhibit diverse properties as a result of compositional flexibility and by a higher probability for cation ordering, may offer better ways of attaining room-temperature ferro-electricity and (anti)ferromagnetism, multiferroic behaviour and eventually magnetoelectric coupling. Whilst ferroelectric TTBs (including Ba2NaNb5 O 15and (Ba,Sr)Nb2O6) were widely investigated during the 1960s and 1970s, our understanding of manipulating this structure type is still poor, with the research surprisingly limited compared to that in perovskites. Early attempts focused on tungsten bronzes of nominal composition A6B10O30(mainly compositions where the C-sites are vacant). A particular interest was developed regarding the Nb-based TTBs due to their enhanced ferroelectric properties over other analogues such as Ta. In the search for novel multiferroic and magnetoelectric materials, the effect of the A-site size in a family of unfilled ferroelectric TTBs Ba4RE0.67Nb10O30(RE = La, Nd, Sm, Gd, Dy, Y) and of the A-site strain on dipole stability in fully filled TTBs family A6GaNb9O30(A = Ba, Sr, Ca) was studied. In addition to their ferroelectric and/or magnetic behaviour, the majority of TTBs reported in the literature exhibit relaxor properties. Most TTBs that have been investigated to date are also lead-free materials.
 
In recent years, the research dedicated to novel TTB ferroelectric and ferroelectric-related (i.e., relaxors) materials has undergone a revival, with Ba6FeNb9O30(BFNO) as a starting point; many related compositions or solid solutions, usually containing lanthanides, were studied. Arnold and Morrison, and subsequently Liu et al. showed that these compounds display relaxor-type behaviour, with the peak maxima in the dielectric permittivity occurring in the temperature range 130–150 K. Earlier data indicated that BFNO is not electrically homogeneous, with oxygen vacancy gradients due to the variable oxidation state of Fe (Fe3+/Fe2+), as both low-temperature dielectric spectroscopy (DS) and high-temperature impedance spectroscopy (IS) data revealed a higher number of electroactive regions than expected. In order to avoid these additional complications whilst studying such materials, the replacement of Fe3+ with Ga3+ (similar in size) and other trivalent species like Sc3+ and In 3+ was proposed. In previous research, temperature-dependent powder neutron diffraction (TDPND) and microstructural characterisation by scanning electron microscopy (SEM) confirmed the nature of the phases formed and contributed to their crystallographic identification. Moreover, the origin of the polar response and the nature of the relaxor behaviour were established by combining the results of the structural investigations with the dielectric properties inspected by immittance spectroscopy (IS), whilst the dynamics of dielectric relaxation of dipoles was understood by fitting the dielectric data (permittivity and loss) with the Vogel–Fulcher (VF) and the universal dielectric response (UDR) models.

perovskite

Tetragonal tungsten bronze

 

 

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