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A traditional semiconductor (WO3) was synthesized from different precursors via hydrothermal crystallization targeting the achievement of three different crystal shapes (nanoplates, nanorods and nanostars). The obtained WO3 microcrystals were analyzed by the means of X-ray diffraction (XRD), scanning electron microscopy (SEM) and diffuse reflectanc...
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... partial hydrate. Interestingly, WO3-HW and WO3-HW5 semiconductors contained both of the previously mentioned crystal phases in different amounts ( Figure 6, Table 1). The crystal size values determined from the XRD patterns were well- correlated with the observations made in the previous section of the paper (except for the WO3-COM, which was not shown separately; the determined crystal size was 20 nm). ...
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... 3 -COM and WO 3 -AMT contained only the monoclinic crystal phase, while WO 3 -NWH contained exclusively WO 3 ¨ 0.33H 2 O hexagonal partial hydrate. Interestingly, WO 3 -HW and WO 3 -HW5 semiconductors contained both of the previously mentioned crystal phases in different amounts ( Figure 6, Table 1). The crystal size values determined from the XRD patterns were well-correlated with the observations made in the previous section of the paper (except for the WO 3 -COM, which was not shown separately; the determined crystal size was 20 nm). ...
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... a partial hydrate, such as WO 3 ¨ 0.33H 2 O, is desired, then a high ionic strength medium is required, where the ionic strength is determined by a joint cation and foreign anion (e.g., Na + /Cí Na 2 WO 4 -precursor/NaCl ionic strength modifier). These strategies were proven to be efficient, as it was shown in Figure 6 and Table 1. However, to modify the ratio of these two crystal phases, a more elaborate method is required, such as the intermediate peroxo-complex approach, which yields a different ratio of the two crystal phases depending on the H 2 O 2 content, and it was also proven to be successful. ...
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... a partial hydrate, such as WO3•0.33H2O, is desired, then a high ionic strength medium is required, where the ionic strength is determined by a joint cation and foreign anion (e.g., Na + /Cl − Na2WO4-precursor/NaCl ionic strength modifier). These strategies were proven to be efficient, as it was shown in Figure 6 and Table 1. However, to modify the ratio of these two crystal phases, a more elaborate method is required, such as the intermediate peroxo-complex approach, which yields a different ratio of the two crystal phases depending on the H2O2 content, and it was also proven to be successful. ...
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... to modify the ratio of these two crystal phases, a more elaborate method is required, such as the intermediate peroxo-complex approach, which yields a different ratio of the two crystal phases depending on the H2O2 content, and it was also proven to be successful. Therefore, the next step is to verify if this crystal phase/morphology changes are related 20 Figure 6. XRD patterns of the obtained WO 3 . ...
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... Our as-prepared WO 3 QDs displayed maximum peaks at various positions, accompanied by peak broadening, as shown in Figure 4d. Specifically, while bulk WO 3 has been reported to exhibit a peak at 480 nm [22], the observed peaks for our WO 3 QDs were situated differently. The blueemitting WO 3 QDs displayed peaks at around~275 nm and~300 nm, the green-emitting WO 3 QDs showed a peak at around~280 nm with broadening extending from 320 nm to 380 nm, and the red-emitting WO 3 QDs exhibited broadened peaks spanning from 300 nm to 480 nm, respectively. ...
With a rising interest in smart windows and optical displays, the utilization of metal oxides (MOs) has garnered significant attention owing to their high active sites, flexibility, and tunable electronic and optical properties. Despite these advantages, achieving precise tuning of optical properties in MOs-based quantum dots and their mass production remains a challenge. In this study, we present an easily scalable approach to generate WO3 quantum dots with diverse sizes through sequential insertion/exfoliation processes in solvents with suitable surface tension. Additionally, we utilized the prepared WO3 quantum dots in the fabrication of luminescent transparent wood via an impregnation process. These quantum dots manifested three distinct emitting colors: red, green, and blue. Through characterizations of the structural and optical properties of the WO3 quantum dots, we verified that quantum dots with sizes around 30 nm, 50 nm, and 70 nm showcase a monoclinic crystal structure with oxygen-related defect sites. Notably, as the size of the WO3 quantum dots decreased, the maximum emitting peak underwent a blue shift, with peaks observed at 407 nm (blue), 493 nm (green), and 676 nm (red) under excitation by a He-Cd laser (310 nm), respectively. Transparent woods infused with various WO3 quantum dots exhibited luminescence in blue/white emitting colors. These results suggest substantial potential in diverse applications, such as building materials and optoelectronics.
... [30] and monoclinic WO 3 (γ-WO 3 ; JCPDS card no. . The crystal phase composition was 90.6% WO 3 ·0.33H 2 O partial hydrate and 9.3% monoclinic [31]. The corresponding diffractions for the first one were identified at 2θ: 28 Depending on the synthesis of Au deposition, changes in the crystal structure may occur, as the deposition is influenced by the metal oxides' morphology [33][34][35]. ...
... The crystal phase composition was 90.6% WO3•0.33H2O partial hydrate and 9.3% monoclinic [31]. The corresponding diffractions for the first one were identified at 2θ: 28.2°, 33.58°, 36.6°, and 37.75°, while for the latter, at 2θ: 23.02°, and 49.98° [32]. ...
... posites [31]. ...
Developing highly efficient Au/TiO2/WO3 heterostructures with applications in heterogeneous photocatalysis (photocatalytic degradation) and surface-enhanced Raman spectroscopy (dye detection) is currently of paramount significance. Au/TiO2/WO3 heterostructures were obtained via heat or time-assisted synthesis routes developed by slightly modifying the Turkevich–Frens synthesis methods and were investigated by TEM, SEM, XRD, Raman spectroscopy, XPS, photoluminescence, and UV–vis DRS techniques. Structural features, such as WO3 crystalline phases, TiO2 surface defects, as well as the WO3 (220) to TiO2-A (101) ratio, were the key parameters needed to obtain heterostructures with enhanced photocatalytic activity for removing oxalic acid, phenol, methyl orange, and aspirin. Photodegradation efficiencies of 95.9 and 96.9% for oxalic acid; above 96% (except one composite) for phenol; 90.1 and 97.9% for methyl orange; and 81.6 and 82.1% for aspirin were obtained. By employing the SERS technique, the detection limit of crystal violet dye, depending on the heterostructure, was found to be between 10−7–10−8 M. The most promising composite was Au/TiO2/WO3-HW-TA it yielded conversion rates of 82.1, 95.9 and 96.8% for aspirin, oxalic acid, and phenol, respectively, and its detection limit for crystal violet was 10−8 M. Au/TiO2/WO3-NWH-HA achieved 90.1, 96.6 and 99.0% degradation efficiency for methyl orange, oxalic acid, and phenol, respectively, whereas its limit of detection was 10−7 M. The Au/TiO2/WO3 heterojunctions exhibited excellent stability as SERS substrates, yielding strong-intensity Raman signals of the pollutant molecules even after a long period of time.
... [1][2][3] With these unique advantages, this material has been employed in various applications including photocatalysis, photoelectrocatalysis, gas sensors, water splitting, electrochromic devices, and degradation of organic molecules. [4][5][6][7][8][9][10][11] However, low surface area, limited utilization of the solar spectrum, and the high extent of electron-hole recombination restrict their photocatalytic performances in practical applications. 6,12,13 Therefore, to overcome these limitations, many approaches such as fabrication of WO 3 with different nanosized morphologies, the combination with noble metals or other materials, and the creation of oxygen vacancy defects have been proposed. ...
Oxygen vacancy in tungsten trioxide (WO3) nanostructures (WO3-x) dominates the major characteristics of the material and determines their activity in various applications including photocatalysis and surface-enhanced Raman spectroscopy (SERS). Despite...
... Differently shaped metal oxide nanoparticles have received increased attention, due to their potential applicability in the field of advanced oxidation processes [1][2][3][4][5], especially in the field of photocatalysis. Besides the well-known TiO 2 , the list of efficient photocatalysts is continuously extending and further investigations have been carried out regarding their crystalline structure to understand and enhance the catalytic process. ...
Orthorhombic molybdenum oxide (α-MoO3) samples were prepared via calcination. During this process, the ratio of the (040)/(110) or (040)/(021) crystallographic planes was fine-tuned by applying different calcination temperatures. Textural characterization of the samples was carried out to comprehend their differences in photocatalytic and adsorption applications. Except for methyl orange, all the tested dyes (methylene blue, crystal violet, malachite green, and rhodamine B) presented adsorption affinity towards α-MoO3. It was revealed that the presence of α-MoO3 significantly decreased the photocatalytic performance of TiO2 under UV light irradiation. With the growth of the (040) facet of α-MoO3, the photocatalytic activity increased while the adsorption affinity decreased for cationic dyes. It was found that the solubility of α-MoO3 depends on the proportional presence of the (040) facet, which determines both the adsorption and photocatalytic behaviors of the oxide. The solubility of α-MoO3 is reflected by the decreasing rate of solution pH, hence the adsorption can be measured accurately, but it varies according to the cationic dye structure. Using cationic dyes to assess the photocatalytic activity of α-MoO3 requires meticulous investigations since adsorption can be mistaken with photocatalytic activity: the adsorption rate depends on both adsorptive and adsorbent structures.
... The answer lies mainly in the previously mentioned energetic criteria. Coupling of WO 3 with TiO 2 -in a well-determined ratio, using the corresponding method of preparationeither physical mixing [18] or pH adjustment corresponding to the surface charge of the components of the composite [19] is considered as an efficient way to prepare composites with great sensorial and photocatalytic efficiency (in certain cases, such as phenol, methyl-orange) [20][21]. According to Lee and coworkers, the excitation of TiO 2 /WO 3 composites triggers the following steps [22]: (i) the excitation of semiconductors and the formation of charge carriers, (ii) charge-transfer (WO 3 (h + , e -) / TiO 2 (h + , e -) → WO 3 (e -) / TiO 2 (h + )), (iii) re-oxidation of W 5+ to W 6+ due to the involvement of molecular O 2 . ...
... The joint key component of the previously described biohybrid (RCsbased) and inorganic systems (TiO 2 -based) is WO 3 because of its high affinity towards electrons (expressed by the terms of positive reduction potential) [23] and efficient charge separation capacity [18]. Tungsten trioxide has four well-known crystal phases: monoclinic, tetragonal, triclinic, and orthorhombic [20]. While the most common obtained crystal phase is monoclinic, the formation of thermodynamically unfavored crystal phases can be facilitated via shaping agents (e.g., NaCl [24], K 2 SO 4 [25]). ...
... It was followed by a washing step (centrifugal washing at 5000 rpm, 10 min), which facilitated the removal of undesired compounds. The obtained product was dried at 40 • C for 24 h [20]. 0.768 g (NH 4 ) 6 H 2 W 12 O 40 ·xH 2 O was dissolved in 12.5 mL 5 M HCl solution under continuous stirring for 15 min. ...
In this work, reaction centers (RCs) isolated from Rhodobacter sphaeroides purple bacteria was coupled with WO3(∙0.33H2O) via physical adsorption, where vectorial electron transfer (from RCs towards the inorganic carrier) was demonstrated using flash kinetics and photoluminescence measurements. The efficiency of the interaction between RCs and WO3(∙0.33H2O) was correlated to the components’ surface charge at the working pH and the structural/morphological and surface properties of the inorganic carrier (e.g., anchoring capacity assured by H-O, W=O bonds). The role of WO3(∙0.33H2O) as final electron trap and charge separator was proven not only in RCs/WO3(∙0.33H2O) biohybrid systems but also in TiO2/WO3(∙0.33H2O) composites. The charge transfer in the inorganic composites was evaluated by monitoring the reverse process of the color reaction (W⁵⁺ → W⁶⁺) via diffuse reflectance spectroscopy (DRS) after a previous UV-A (320-400 nm) exposure. The efficiency of the charge transfer process in inorganic systems was correlated to the initial W⁵⁺ content of WO3(∙0.33H2O), followed by the photocatalytic efficiency evaluation of these inorganic composites under UV-A irradiation.
... Tungsten trioxide (WO3) is an extensively studied n-type semiconductor (SC) that has a broad application spectrum, including pigment in paints [1], gas sensors [2,3], and humidity sensors [4], or is an essential component in (photo) electrochromic devices [5][6][7][8]. It can also be employed as a photocatalyst on its own or in composites with other metal oxides [9][10][11][12][13][14], or with carbon-based materials [15]. Its band gap value is ≈2.6 eV, meaning a light absorption maximum at 480 nm. ...
... The optimum ratio seems to be around 87.5:12.5 (HPH to MC), which is very close to the 89:11 anatase rutile ratio in TiO2. In our previous work [13], a similar phenomenon was observed. We obtained WO3 from tungstic acid, which lead to a semiconductor with a 90.6:9.3 (HPH to MC) crystal phase ratio. ...
The design of a semiconductor or a composite semiconductor system—with applications in materials science—is complex because its morphology and structure depend on several parameters. These parameters are the precursor type, solvent, pH of the solution, synthesis approach, or shaping agents. This study gives meaningful insight regarding the synthesis design of such WO3 materials. By systematically alternating the precursor (sodium tungstate dihydrate—NWH, or ammonium tungstate hydrate—AMT), subsequently shaping the agents (halide salts—NaX, KX, or hydrohalic acids—HX; X = F−, Cl−, Br−, I−), we have obtained WO3 semiconductors by hydrothermal treatment, which in composite systems can enhance the commercial TiO2 photocatalytic activity. We investigated three sample series: WO3-NWH-NaX/WO3-NWH-KX and, subsequently, WO3-AMT-HX. The presence of W+5 centers was evidenced by Raman and X-ray photoelectron spectroscopy. W+5 and W+6 species affected the band gap values of the NaX and KX series; a higher percentage of W+5 and, subsequently, W+6 caused a redshift, while, regarding the HX series, it led to a blue shift. Increased electronegativity of the halide anions has an unfavorable effect on the composites’ photoactivity. In contrast, in the case of hydrohalic acids, it had a positive impact.
... Tungsten trioxide possesses a small band energy gap of 2.4-2.8 eV and responds to both ultraviolet and visible light irradiation [28,29]. However, prior to photocatalysis, we require efficient adsorbance as it enhances the effectivity of the adsorbate's photocatalytic activity; i.e., the larger the amount of dye molecules adsorbed on the catalyst's surface, the higher the reaction probability between photo-excited holes and adsorbed dyes [10] using the right amount of catalyst makes sense not only from an economic standpoint, but also from an environmental perspective. ...
Transition metal oxides have been applied to degrade organic dyes found in water bodies via photocatalysis. To do it, however, is essential that the dye molecules adsorb onto the metal oxide surface. Thus, optimizing the adsorption capacity of the adsorbent increases the probability of reaction between oxidation radicals and organic dye molecules and maximizes the effectiveness per gram of photocatalyst. With this in mind, we studied the adsorption behavior of Methylene Blue (MB) and Acid Orange 7 (AO7), two commonly found pollutants, as a function of dilution's pH, WO3 load, and initial dye concentration. We found out that WO3 adsorbs up to 80% of MB at pH=6, and 13% of AO7 at pH=2, although it is unable to adsorb AO7 at the natural pH of the dye dilution. Assuming a pseudo-second order kinetics model for the analysis of the MB adsorption amount, we determined a rate constant k2 = 6 × 10-2(g · mg-1)/min for the adsorption process. We put forward a molecular model for adsorption, driven by concentration gradients and electrostatic interactions. Finally, from a statistical analysis, we determined that pH is the most significant factor for the adsorption of MB and AO7 on WO3, reinforcing the notion that electrostatic interactions are the main mechanism driving the adsorption process. The Box-Behnken design optimization also evinces the key playing role of WO3 load in the adsorption percentage of AO7 and let us establish the optimal load required to maximize adsorption.
... It is classified as an n-type semiconductor, wherein electrons are the major carriers. Due to its narrow band gap, WO3 absorbs light radiation in the visible range, and it has been used in a wide range of applications such as fuel production and combating water pollution [16,17]. This semiconductor exists in different polymorphs, which include monoclinic, triclinic, tetragonal and orthorhombic. ...
Tungsten trioxide (WO3) is a photocatalyst that has gained interest amongst researchers because of its non-toxicity, narrow band gap and superior charge transport. Due to its fast charge recombination, modification is vital to counteract this limitation. In this paper, we report on the fabrication of Mn-doped WO3/SnS2 nanoparticles, which were synthesised with the aim of minimising the recombination rates of the photogenerated species. The nanomaterials were characterised using spectroscopic techniques (UV-Vis-diffuse reflectance spectroscopy (DRS), Raman, XRD, photoluminescence (PL) and electrochemical impedance spectroscopy (EIS)) together with microscopic techniques (FESEM-EDS and high resolution transmission electron microscopy selected area electron diffraction (HRTEM-SAED)) to confirm the successful formation of Mn-WO3/SnS2 nanoparticles. The Mn-doped WO3/SnS2 composite was a mixture of monoclinic and hexagonal phases, confirmed by XRD and Raman analysis. The Mn-WO3/SnS2 heterojunction showed enhanced optical properties compared to those of the un-doped WO3/SnS2 nanoparticles, which confirms the successful charge separation. The Brunauer-Emmett-Teller (BET) analysis indicated that the nanoparticles were mesoporous as they exhibited a Type IV isotherm. These nanomaterials appeared as a mixture of rectangular rods and sheet-like shapes with an increased surface area (77.14 m 2 /g) and pore volume (0.0641 cm 3 /g). The electrochemical measurements indicated a high current density (0.030 mA/cm 2) and low charge transfer resistance (157.16 Ω) of the Mn-WO3/SnS2 heterojunction, which infers a high charge separation, also complemented by photoluminescence with low emission peak intensity. The Mott-Schottky (M-S) plot indicated a positive slope characteristic of an n-n heterojunction semiconductor, indicating that electrons are the major charge carriers. Thus, the efficiency of Mn-WO3/SnS2 heterojunction photocatalyst was monitored for the degradation of chlorpyrifos. The effects of pH (3-9), catalyst loading (0.1-2 g) and initial chlorpyrifos concentration (100 ppb-20 ppm) were studied. It was observed that the degradation was purely due to photocatalysis, as no loss of chlorpyrifos was observed within 30 min in the dark. Chlorpyrifos removal using Mn-WO3/SnS2 was performed at the optimum conditions of pH = 7, catalyst loading = 1 g and chlorpyrifos concentration = 1000 ppb in 90 min. The complete degradation of chlorpyrifos and its major degradation by-product 3,5,6-trichloropyridin-2-ol (TCP) was achieved. Kinetic studies deduced a second order reaction at 209 × 10 −3 M −1 s −1 .
... Most commonly WO 3 is employed as sensor (gas [26,27], humidity [28], moisture sensor [29]), paint pigment [30], or as an important component in photovoltaic [31] and electrochromic devices [32], and as photocatalyst [33,34]. The photocatalytic activity under UV/Vis light irradiation of hydrothermally synthesized pristine WO 3 materials is very limited towards specific organic pollutants (phenol and oxalic acid), according to our previous research [35]. The photoactivity of WO 3 particles can be enhanced by diverse composite preparation methods, like deposition of noble metal nanoparticles on the surface of WO 3 [36,37], mechanical mixing of WO 3 and TiO 2 powders [38] or by the semiconductors' surface charge adjustment [39]. ...
... In our previous work, the morphology of the obtained WO 3 ·0.33H 2 O and WO 3 had been investigated, and it was observed that WO 3 ·0.33H 2 O samples showed plate and sheet-like microcrystals, while microstars where the dominant morphology of the sample containing pure WO 3 (the samples' morphology is presented in Fig. 1) [35]. ...
... The DRS spectra of the three main components provided us information about their optical properties from which it can be determined the band gap values of these semiconductors applying the Kubelka-Munk approach. In the case of TiO 2 3.11 eV, for WO 3 ·0.33H 2 O 2.75 eV, and for WO 3 2.25 eV [35] were the band gap energy values. ...
... This material is used as photocatalyst for the photocatalytic splitting of water molecules into hydrogen and oxygen. Purely WO 3 has higher recombination rate of electrons and holes pair due to formation the superoxide radicals [14,15]. These properties of the pure WO 3 nanoparticle have been tuned by the help of dopant contents that can reduce the recombination rate, particle size and energy band gap. ...
Modified composite of the pure monoclinic tungstun oxide with 2.0% of activated carbon photocatalyst with BiVO4 as coupling content is synthezed via facile hydrothermal route. The composite is fabricated with coupling ratio of 0.5%,1.0%,1.5% and 2.0% dopant BiVO4. These composite were characterized by the XRD, SEM, UV–Vis, PL and BET to investigate the various properties (particle size, structural, morphological, purity and optical) and the energy band of the photocatalytic material. It is commonly examined that the C-WO3 showed the extraneous results for the evolution of the hydrogen energy by increasing the coupling contents upto 1.5% of BiVO4 and gave extraordinary photocatalytic activity towards the hydrogen energy production. The formation of the orthorhombic phases from the monoclinic and hexagonal at 2.0% of doping content indicated the increase of size of the particles and energy band gap. The average grain size of the composite is ranging from 30 to 50 nm. The increment of the BiVO4 content in the C-WO3 composite causes the reduction of photocatalytic activity because of the increase in the grain size and the forbidden gap of the photocatalytic composite.
