The Influence of the Temperature on the Optical Absorption Properties and Morphologies of WO<Subscript>3</Subscript> Nanorods Synthesized by the Hydrothermal Method

Crystalline WO₃ nanorods of less than 100 nm in diameter have been successfully synthesized at 240 °C for 48 h at pH 1.5 by the hydrothermal method with sodium tungstate as a tungsten source and potassium sulphate as a subsidiary salt. The morphologies and structures of WO₃ rods were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscope (TEM) and selected-area electron diffraction (SAED). SEM analysis confirms that the slenderness ratio of the WO₃ rods is enlarged with the increase of the reaction temperature at pH 1.5. SAED analysis shows that the synthesized WO₃ nanorods are crystalline. Ultraviolet–visible (UV-VIS) absorption spectroscopy shows that absorbent power of UV light for WO₃ nanorods enhances with an increase of the slenderness ratio.     

Shielding Behavior of Gamma-Irradiated MoO<Subscript>3</Subscript> or WO<Subscript>3</Subscript>-Doped Lead Phosphate Glasses Assessed by Optical and FT Infrared Absorption Spectral Measurements

Undoped and MoO₃- or WO₃- doped lead phosphate glasses were prepared by the melting-annealing technique. The glasses were characterized through UV-visible and infrared measurements which were repeated after gamma irradiation. Optical spectrum of binary lead phosphate glass shows distinct ultraviolet bands correlated with unavoidable trace iron impurities within the chemicals used for the preparation of the glasses. UV-visible absorption spectra of MoO₃- or WO₃- doped glasses exhibit additional UV-visible bands which are related to the presence of four oxidation states of the two transition metal (molybdenum or tungsten) ions (Mo³⁺, Mo⁴⁺, Mo⁵⁺, Mo⁶⁺, W³⁺, W⁴⁺, W⁵⁺, W⁶⁺). The extra UV band is related to hexavalent (5d⁰) state while the rest of the visible bands are related to (350–440 nm - trivalent state), (450, 550, 650 nm - tetravalent state) while the broad band centered at about 770 nm (pentavalent state). The intensities of the absorption bands are observed to change with the transition metal content and their valencies. Infrared absorption spectra reveal distinct vibrational bands which are assigned to phosphate groups with sharing of Pb-O vibrations within both the range 460–620 cm^-1 and the range 900–1100 cm^-1 revealing a compact network structure. Gamma irradiation causes a minor increase in intensity of one of the UV band due to suggested photo-oxidation of some trace ferrous ions to additional ferric ions but the remaining spectral curve remains unaffected which is obviously related to some shielding effects of heavy atomic weight of PbO. This heavy metal oxide (PbO) is assumed to retard or prohibit the free passage of free electrons or positive holes generated during the irradiation process.     

The Structural,Optical and Electrical Properties of Spin Coated WO<Subscript><Emphasis Type="Bold">3</Emphasis></Subscript> Thin Films Using Organic Acids

Tungsten trioxide (WO₃) thin films were prepared incorporating various organic acid additives by the sol-gel spin coating technique. They were characterized by X-ray diffraction (XRD), UV-Visible analysis, scanning electron microscopy (SEM) and dc electrical conductivity. From XRD, the crystal phase, average grain size and structural parameters of WO₃ thin films were found to vary owing to different water dissolved organic acid additives. The variation of optical conductivity and band gap energy was calculated from the UV-Visible analysis. The SEM studies revealed that the organic acids influenced the surface morphology of the microsized plates of tungsten oxides. The electrical conductivity at various temperatures correlated with the average grain size of the nanocrystallites of WO₃ thin films.     

Photoactive WO<Subscript>3</Subscript> and Se-WO<Subscript>3</Subscript> thin films for photoelectrochemical oxidation of organic compounds

Thin films of bare and Se-containing tungsten trioxide (WO₃) on AISI304-type stainless steel were prepared by electrochemical deposition using peroxy-tungstate solutions. The obtained films were characterized by X-ray diffraction, photoelectron spectroscopy, scanning electron microscopy, thermal and photovoltammetry analyses. The oxidation of methylene blue, phenol, and methanol was used to evaluate the photoelectrocatalytic activity of the prepared films. It has been established that the incident photon-to-current efficiency (IPCE) in 0.1-M K₂SO₄ decreases as the concentration of methylene blue and phenol increases. On the contrary, the IPCE values increase with the increase in initial concentration of methanol. The bulk electrolysis experiments revealed that the prepared films are stable and can be used for photoelectrochemical oxidation of methanol.     

Crystallographic,Structural and Band Gap Tailoring of Zn<Subscript>0.98</Subscript>Mn<Subscript>0.02</Subscript>S Quantum Dots Co-Doped with Cu by Co-Precipitation Method

Zn_0.98?xCu_xMn_0.02S (x = 0, 0.02, 0.04) quantum dots with different Cu concentrations have been successfully synthesized by co-precipitation method. Cubic phase exhibited in Zn_0.98Mn_0.02S turned to mixture of both cubic and hexagonal phases by Cu-doping which was confirmed by X-ray diffraction pattern. The shift of peak position along (111) plane and the diminishing of interplanar distance and lattice constant confirmed the proper substitution of Cu and Mn in ZnS. Cubic phase of ZnS was tuned towards hexagonal phase by Cu-doping i.e., morphology diminishes stability which was confirmed by microscopic images. Optical studies revealed the wide tuning of band gap between 3.3 and 3.93 eV by Mn-doping and Cu co-doping which is useful for opto-electronic device applications. Photoluminescence spectra illustrated two distinct emission bands, UV emission around 392–396 nm and defect related blue emission around 470–481 nm. The change in intensity and peak position of UV and blue emission was discussed based on crystallite size formation of defect states by Cu-doping.     

Infrared and raman characterization of V<Subscript>2</Subscript>O<Subscript>5</Subscript> on zirconia modified with WO<Subscript>3</Subscript> and activity for acid catalysis

Vanadium oxide supported on zirconia modified with WO₃ was prepared by adding Zr(OH)₄ powder into a mixed aqueous solution of ammonium metavanadate and ammonium metatungstate followed by drying and calcining at high temperatures. The characterization of prepared catalysts was performed by using FTIR, Raman, and XRD. In the case of calcination temperature at 773 K, for samples containing low loading V₂O₅ below 18 wt%, vanadium oxide was in a highly dispersed state, while for samples containing high loading V₂O₅ equal to or above 18 wt%, vanadium oxide was well crystallized due to the high V₂O₅ loading on the surface of ZrO₂. The ZrV₂O₇ compound was formed through the reaction of V₂O₅ and ZrO₂ at 873 K, and the compound decomposed into V₂O₅ and ZrO₂ at 1,073 K, these results were confirmed by FTIR and XRD. Catalytic tests for 2-propanol dehydration and cumene dealkylation have shown that the addition of WO₃ to V₂O₅/ZrO₂ enhanced both catalytic activity and acidity of V₂O₅-WO₃/ZrO₂ catalysts. The variations in catalytic activities for both reactions are roughly correlated with the changes of acidity.     

Hydrothermal synthesis of nanotubes based on (Mg,Fe,Co,Ni)<Subscript>3</Subscript>Si<Subscript>2</Subscript>O<Subscript>5</Subscript>(OH)<Subscript>4</Subscript> hydrosilicates

Hydrosilicate nanotubes of the variable composition (Mg,Fe,Co,Ni)₃Si₂O₅(OH)₄ with a chrysotile structure have been synthesized under hydrothermal conditions at temperatures of 250–450°C and pressures of 30–100 MPa in media of different compositions. The conditions and ranges of formation of nanotubular hydrosilicates of the compositions under investigation have been determined. It has been demonstrated that the type of cation of the octahedral layer in the chrysotile structure has a decisive effect on the physicochemical conditions, mechanism, and rate of formation of nanotubes, as well as on their structure, morphology, and sizes.     

Upgrading of pyrolysis bio-oil using WO<Subscript>3</Subscript>/ZrO<Subscript>2</Subscript> and Amberlyst catalysts: Evaluation of acid number and viscosity

Tungstated zirconia (WO₃/ZrO₂ with WO₃ loadings of 9.9 (WZ9.9), 15.5 (WZ15.5), and 15.7 wt% (WZ15.7)) and Amberlyst (15, 35, 36, 39 and 45) catalysts were employed to upgrade pyrolysis bio-oil of acacia sawdust through an esterification reaction using methanol at atmospheric pressure and room temperature or 80 °C. The upgrading efficiency was evaluated by measuring the total acid number (TAN) and viscosity. The viscosity and TAN of the resulting upgraded bio-oil were found to be dependent on the calcination temperature of the WO₃/ZrO₂ catalysts. At room temperature, the largest decrease in viscosity and TAN of the bio-oil and methanol mixture was obtained using WZ9.9 tungstated zirconia calcined at 900 °C. An increase in reaction temperature to 80 °C improved the flowability and TAN of the methanol-added bio-oil using WZ9.9 activated at 900 °C. The product distribution of the bio-oil upgraded using methanol revealed esterification to be the dominant reaction pathway under the reaction conditions of this study. When the ether extracted bio-oil was upgraded at 80 °C using methanol over catalysts, the Amberlyst catalysts were found more effective than tungstated zirconia catalysts in enhancing the esterification reaction and reducing TAN.     

Side-by-Side In(OH)<Subscript>3</Subscript> and In<Subscript>2</Subscript>O<Subscript>3</Subscript> Nanotubes: Synthesis and Optical Properties

A simple and mild wet-chemical approach was developed for the synthesis of one-dimensional (1D) In(OH)₃ nanostructures. By calcining the 1D In(OH)₃ nanocrystals in air at 250 °C, 1D In₂O₃ nanocrystals with the same morphology were obtained. TEM results show that both 1D In(OH)₃ and 1D In₂O₃ are composed of uniform nanotube bundles. SAED and XRD patterns indicate that 1D In(OH)₃ and 1D In₂O₃ nanostructures are single crystalline and possess the same bcc crystalline structure as the bulk In(OH)₃ and In₂O₃, respectively. TGA/DTA analyses of the precursor In(OH)₃ and the final product In₂O₃ confirm the existence of CTAB molecules, and its content is about 6%. The optical absorption band edge of 1D In₂O₃ exhibits an evident blueshift with respect to that of the commercial In₂O₃ powders, which is caused by the increasing energy gap resulted from decreasing the grain size. A relatively strong and broad purple-blue emission band centered at 440 nm was observed in the room temperature PL spectrum of 1D In₂O₃ nanotube bundles, which was mainly attributed to the existence of the oxygen vacancies.     

Synthesis of nanometer sized Bi<Subscript>2</Subscript>WO<Subscript>6</Subscript>s by a hydrothermal method and their conductivities

Nanometer-sized bismuth tungsten oxides, Bi₂WO₆s, were successfully synthesized by hydrothermal treatment at 200 °C for 24 hr, and their morphologies and crystallite sizes were influenced by adjusting the conditions to pH 4, 7, and 9. TEM images revealed that the particles were sheet-shaped and the crystallite sizes ranged from 7–120 nm. The samples absorbed in the visible range at about 380–400 nm. The lowest conductivity, 1.0×10⁶ ohm/square, was observed for Bi₂WO₆ prepared at pH 4 with a 150 nm film thickness. As the annealing temperature for Bi₂WO₆ prepared at pH 7 was increased, the conductivity decreased due of formation of larger particles by coagulation and sintering at high temperatures. Conductivity appears to improve with increasing film thickness up to 1,500 nm.     

Comparison of physically mixed and separated MgO and WO<Subscript>3</Subscript>/SiO<Subscript>2</Subscript> catalyst for propylene production via 1-butene metathesis

We examined the catalyst bed design of MgO and WO₃/SiO₂ for production of propylene via metathesis of 1-butene. WO₃/SiO₂ was used as a bi-functional catalyst for isomerization and metathesis reactions. Addition of MgO was proposed to help improve the isomerization activity and hence the propylene yield. Experimental studies were carried out to determine activity and reaction kinetics of 1-butene isomerization over MgO isomerization catalyst and 1-butene metathesis over WO₃/SiO₂ bi-functional catalyst for designing a suitable catalyst bed. Two types of catalyst bed arrangement—physically mixed bed and separated bed—were considered and compared by computer simulation. The simulations reveal that adding MgO in the separated bed by packing MgO before WO₃/SiO₂ offers superior propylene yield to the physically mixed bed. The appropriate %MgO loading in catalyst bed which offers a maximum propylene yield was found to vary (3 and 23%), depending on operating condition.     

Electrical conductivity of CuI-AsI<Subscript>3</Subscript>-As<Subscript>2</Subscript>Se<Subscript>3</Subscript> and CuI-SbI<Subscript>3</Subscript>-As<Subscript>2</Subscript>Se<Subscript>3</Subscript> chalcogenide films prepared by chemical deposition

The electrical conductivity of chalcogenide semiconductor films in the CuI-AsI₃-As₂Se₃ and CuI-SbI₃-As₂Se₃ systems, which have been prepared by chemical deposition from mono-n-butylamine, has been studied as a function of the temperature and film composition. It has been established that the electrical conductivity of the CuI-AsI₃-As₂Se₃ and CuI-SbI₃-As₂Se₃ films is predominantly determined by the copper iodide content. It has been demonstrated that the electrical properties of the chalcogenide glasses and the related films are characterized by the same values to within the experimental error, which is explained by the same model of dissolution of vitreous semiconductors in amines with the retention of the electrical properties of chalcogenide glasses after the deposition of films from their solutions.     

Electroconducting ceramics based on In<Subscript>2</Subscript>O<Subscript>3</Subscript>, CdO,and LaCrO<Subscript>3</Subscript>

The possibility of fabricating electroconducting (10¹–10⁴ S cm^–1) ceramics based on In₂O₃, CdO, and LaCrO₃ by liquid-phase synthesis methods has been demonstrated. The results of studies of the effect of temperature, dopants, and partial oxygen pressure on the specific electroconductivity of ceramic composites are presented.     

Effect of Laser Fluence on the Structural,Morphological and Optical Properties of 2H-PbI<Subscript>2</Subscript> Nanoparticles Prepared by Laser Ablation in Ethanol

The effect of laser fluence on the optical, structural and morphological properties of PbI₂ nanoparticles NPs synthesized by pulsed laser ablation in ethanol was studied. The direct optical energy gap of PbI₂ NPs prepared at various laser fluences was in the range of (3–3.3 eV) at room temperature. Three absorption peaks related to surface plasmon resonance at 337, 435 and 507 nm are observed. XRD results show that all the grown PbI₂ NPs are polycrystalline in nature and the formation of hexagonal structure 2H-polytype was observed at laser fluence of 3.6 J/cm². The surface morphology of PbI₂ NPs investigated by SEM revealed formation of hexagonal, platelet-like and spherical NPs morphologies. TEM images showed formation of spherical particles with size varied from 10 to 75 nm depending on the laser fluence. PL measurement shows emission of broad peak centered at 350 nm and increasing the laser fluence results in red shift. The Raman spectra of PbI₂ NPs revealed existence of five vibration modes situated at 74, 96,106, 169 and 213 per cm. FT-IR investigation showed a broad band at 3383 per cm indexed to symmetric stretching vibration of Pb–I clusters and band at 725 per cm related to bending mode of O–H.     

The role of V<Subscript>2</Subscript>O<Subscript>5</Subscript> on the Structural and Optical Properties of MgO-ZnO-CdO-P<Subscript>2</Subscript>O<Subscript>5</Subscript> Glasses and the Impact of Gamma Irradiation

The quaternary glasses of mixed divalent oxides including ZnO, MgO, CdO within a phosphate network former were prepared. Vanadium pentoxide was introduced as a dopant in the range from 0.5 to 3%. Optical and infrared absorption studies for all glass samples were carried out. The optical spectra reveal the presence of both V³⁺ and V⁴⁺ ions in the studied host mixed divalent oxides phosphate glass. Fourier transform infrared absorption spectral analysis indicates the appearance of distinct vibrational bands due to the presence of characteristic phosphate groups depending on the glass composition and the ratio of V₂O₅ content. The optical band gap and Urbach energy were calculated and discussed in relation to the effect of V₂O₅ content. Finally, the glasses were optically and structurally examined affter gamma irradiation with a dose of 80 KGy.     

Experimental and theoretical analysis of element mercury adsorption on Fe<Subscript>3</Subscript>O<Subscript>4</Subscript>/Ag composites

A novel magnetic nano-sorbent Fe₃O₄/Ag was synthesized and applied to capture the elemental mercury from the simulated flue gas. The morphology, components and crystal phase of the sorbents were characterized by transmission electron microscope (TEM), energy dispersive spectrometry (EDS) and X-ray diffraction (XRD), respectively. The mercury removal performance of the sorbents was investigated through the fixed-bed tests. The results indicated that silver was successfully loaded on the surface of Fe₃O₄ particles, which could significantly enhance the Hg⁰ removal performance of the sorbents. Flue gas components, including CO₂, SO₂, and NO, have little impact on the Hg⁰ removal performance of Fe₃O₄/Ag sorbents, while O₂ has a slightly positive effect. The Hg⁰ removal efficiency decreased with the increasing of temperature, Hg⁰ inlet concentration and gas hourly space velocity. Only one broad mercury desorption peak at approximately 210 °C could be observed during the temperature-programmed desorption (TPD) process, which indicated that mercury species existing on the surface of Fe₃O₄/Ag sorbents might be elemental mercury instead of oxidized mercury. Furthermore, the reusability tests showed that the Fe₃O₄/Ag sorbents could be efficiently regenerated and reused. Finally, the theoretical analysis based on the DFT method showed that a weak chemisorption of Hg⁰ on Fe₃O₄ sorbents changed to a strong chemisorption when silver was loaded. The results of theoretical analysis conformed to the experiments results well.