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Heterogeneous photocatalytic (PC) degradation of organic dyes in aqueous solution with semiconductor oxides has been very effective in relation to conventional methods for the wastewater treatment. In this paper, MgWO4 powder was synthesized by the complex polymerization method and heat-treated at 900 °C for 2 h. Their structure, morphology and opt...
Citations
... To describe the photocatalysis in general, the rate of the dye degradation [51][52][53][54][55] was investigated and the reaction rate was studied following the pseudo first order kinetics of the Langmuir Hinshelwood model. First order kinetics of the reaction rate was used to label the interactions occurring between the solid and liquid interface, and is denoted as follows: ...
We have synthesized lead tungstate (PbWO4), nickel doped PbWO4 (Ni- PbWO4) and poly ethylene glycol assisted Ni doped PbWO4 (Ni-PEG-PbWO4) by the co-precipitation method. XRD results indicate that the prepared PbWO4 based nanoparticles have a tetragonal structure. FTIR results indicated that the characterized functional groups in PEG combined well with the surface of Ni- doped PbWO4. The PEG molecules in the adsorbed state are controlled by the field of the solid-state surface due to its uniformly ordered chain structure and its hydrogen-bonding nature.The optical properties of the prepared nanoparticles are confirmed by UV–visible and photoluminescence spectrum. The BET surface area of PbWO4, Ni-PbWO4 and Ni-PEG-PbWO4 nanoparticles are found to be 1.616, 4.027 and 4.409 m² /g respectively. The SEM analysis confirmed the presence of dendrites and polyhedrons. The presence of expected elements and its oxidation states are confirmed from EDX and XPS measurements, respectively. PbWO4, Ni-PbWO4 and Ni-PEG-PbWO4 nanoparticles showed good photo-catalytic activity against a hazardous dye, methyl orange (MO) and showed improved activity by Ni-PEG-PbWO4 because of its smaller particle size and higher surface area. It has been discovered that the influence of a number of important experimental factors such as pH, concentration of dye as well as concentration of catalyst on the photodegradation process. Thus, these materials have great potential for oxidizing hazardous dye pollutants from wastewater and their application in realistic environmental cleanup needs additional attempt.
... In addition, it has a wolframitetype monoclinic structure, belongs to the space group (P2/c), symmetry point group (C 2h 4 )and has two molecular formula units per unit cell [19,20]. Of late, Gouveia et al. [21] reported that MgWO 4 crystals proved to be a promising semiconductor for the degradation of the organic bromocresol green dye. However, the low charge transfers and separation efficiency, besides the narrow light absorption range, limit its application in the catalysis field [21,22]. ...
... Of late, Gouveia et al. [21] reported that MgWO 4 crystals proved to be a promising semiconductor for the degradation of the organic bromocresol green dye. However, the low charge transfers and separation efficiency, besides the narrow light absorption range, limit its application in the catalysis field [21,22]. In this context, some alternative strategies can be adopted to compensate for these existing deficiencies, such as a combination with different semiconductors (composite), such as coating, embedding, or doping of catalyst oxides with a metal or a non-metal, ZnWO 4 /MgWO 4 n-n heterojunctions, and surface modification with metal nanoparticles [23][24][25]. ...
... For the synthesis of pure MgWO 4 crystals was employed the polymeric precursor method (PPM) [21]. A tungsten citrate (Cit-W) was initially prepared at pH = 7 using deionized water [ The polymerized solution was heated until water evaporation and formation of a polymer resin, which was then placed in a muffle furnace (W-One, EDG equipment) at 350 • C for 10 h with a heating rate of 10 • C. min − 1 . ...
... Environmental pollution includes air, water and plants, causing many problems for all living things [5][6][7]. Water pollution is one of the main problems that scientists are working on it to find an effective and inexpensive solution [8][9][10]. The colored organic dyes compounds are one of the main contaminants which discharge into water resources from industrial activities [11,12]. ...
Advance the photo-activity of the nano-sized ZnO photocatalyst is an essential factor in remediation of environmental pollution caused by industrial-organic dyes. Blends of transition elements including Mn, Fe and Co ions were employed to modify the energy gap and the visible absorption state tail of ZnO as well as inhibit the charge carriers recombination by their flexible oxidation states. Five nanocatalysts composed of ZnO, Zn0.97Mn0.015Fe0.015O, Zn0.97Mn0.015Co0.015O, Zn0.97Fe0.015Co0.015O and Zn0.97Mn0.01Fe0.01Co0.01O were simply synthesized. All the prepared compositions have a single phase of ZnO wurtzite structure. Both compositions of Zn0.97Fe0.015Co0.015O and Zn0.97Mn0.01Fe0.01Co0.01O have high sensitive responses to visible light spectrum owing to band gap reduction and formation of absorption state tails. The SEM images demonstrated that the kind of the transition metal blends added to ZnO powder have a significant effect on its morphology. Remarkably, the addition of (Fe, Co) mixture to ZnO powder leads to formation of homogenous rods structure besides very fine spherical particles. All modified ZnO samples revealed enhanced photocatalytic activity but Zn0.97Fe0.015Co0.015O powder possesses the greatest efficiency (98%) for 25 ppm Reactive Yellow 145 dye in 75 min of solar illumination with acceptable stability. In addition, Zn0.97Fe0.015Co0.015O catalyst revealed high photo-removal activity for 25 ppm Rhodamine B and malachite green with measured efficiencies of 94 and 91% in 75 min, respectively. The suitable catalyst dose was identified to be 0.04 g (100 mL solution) and the main effective radicals are the hydroxyl (·OH) species.
... Recently, some synthesis methods were employed for obtention of metal tungstate-based photoanode films as hydrothermal method [40], template-assisted synthesis method [52], co-precipitation [20], spray pyrolysis [53] and electrochemical deposition [54]. The polymeric precursor's method (PPM) has been very effective about conventional methods principally for wastewater treatment [55]. The main advantages of PPM have been seen allowing the control of the composition, the grain size, and the homogeneity of powders [56]. ...
... This is a modified sol-gel method that is based on the complexation of metal alkoxides, and the esterification/polymerization reaction [58]. Recently, this synthesis method has been successfully used to obtain crystalline ceramic powders when calcined at temperatures between 500 and 700 °C [55,59,60]. For first time here was used to obtain metal tungstate thin films. ...
This paper discusses about a facile transition metal tungstate thin films preparation method and their remarkable photoelectrochemical properties. The films of AWO4 (A²⁺ = Fe, Co, Ni, Cu) were deposited onto conductive fluorine-doped tin oxide (FTO) glass substrate. The results of X-ray diffraction analysis indicated the presence of crystalline films. Field emission scanning electron microscopy images revealed nanostructured materials. X-ray photoelectron studies were employed to analyze elemental and chemical composition. Optical behavior indicated indirect transitions for all AWO4 films. Photoelectrochemical studies displayed that AWO4 films were successfully used as photoanodes in a photoelectrochemical cell under polychromatic irradiation. From electrochemical measurement, it was possible to estimate the flat band potential and so prevising suitable application of photoelectrodes. This work reports for the first time a comparative and comprehensive photoelectrochemical study with AWO4 films prepared in a simple way. The results indicate that the films can be used as photoanodes in water splitting reactions and other photoelectrocatalytic applications.
Graphical Abstract
... MgWO 4 is an n-type semiconductor with wolframite type structure. It was widely studied as microwave dielectric ceramic, scintillation, luminescence material, burning catalyst and photocatalyst [38][39][40]. However, its sonocatalytic performance was rarely reported. ...
A novel ZnWO4/MgWO4 n-n heterojunction (0.9% ZnWO4/MgWO4) was fabricated successfully and characterized by different techniques. The methylene blue (MB) was removed to confirm the sonocatalytic activity by the 0.9% ZnWO4/MgWO4 composite. The sonocatalytic removal ratio of MB usingMgWO4 was 40.04±4.34(%). It was significantly increased to 93.82±3.44(%) in the presence of 0.9% ZnWO4/MgWO4 composite. The significantly improved sonocatalytic performance was due to the form of n-n heterojunction, which could hinder the recombination of electron and hole (e⁻-h⁺) pairs effectively. The mechanism showed that hydroxyl radical (•OH) and h⁺ had important roles for the elimination of MB. Moreover, the 0.9% ZnWO4/MgWO4 composite had remarkable stability during the process of MB removal under the ultrasonic irradiation. The results suggested that the fabrication of heterojunction is a valid method to promote the sonocatalytic performance of catalyst. The results of this paper would provide valuable references for the development of new sonocatalysts used in environmental remediation.
... The generation of surface O 2 •was favored by the presence of more oxygen vacancies in FeMoO 4 (Zhang et al., 2011). MgWO 4 (Bhuyan et al., 2017), like in the WW photocatalysts, had more active photocatalytic or Lewis acid sites, and the effect of O 2 •on the photocatalytic dye removal was noted (Gouveia et al., 2020). Also, •OH was found to be the most reactive species generated when WO 3 was irradiated (Nisar et al., 2020). ...
The use of antiviral drugs has surged as a result of the COVID-19 pandemic, resulting in higher concentrations of these pharmaceuticals in wastewater. The degradation efficiency of antiviral drugs in wastewater treatment plants has been reported to be too low due to their hydrophilic nature, and an additional procedure is usually necessary to degrade them completely. Photocatalysis is regarded as one of the most effective processes to degrade antiviral drugs. The present study aims at synthesizing multiphase photocatalysts by a simple calcination of industrial waste from ammonium molybdate production (WU photocatalysts) and its combination with WO3 (WW photocatalysts). The X-ray diffraction (XRD) results confirm that the presence of multiple crystalline phases in the synthesized photocatalysts. UV-Vis diffuse reflectance spectra reveal that the synthesized multiphase photocatalysts absorb visible light up to 620 nm. Effects of calcination temperature of industrial waste (550-950C) and WO3 content (0-100%) on photocatalytic activity of multiphase photocatalysts (WU and WW) for efficient removal of SARS-CoV-2 antiviral drugs (lopinavir and ritonavir) in model and real wastewaters are studied. The highest k1 value is observed for the photocatalytic removal of ritonavir from model wastewater using WW4 (35.64×10–2 min–1). The multiphase photocatalysts exhibit 95% efficiency in the photocatalytic removal of ritonavir within 15 of visible light irradiation. In contrast, 60 min of visible light irradiation is necessary to achieve 95% efficiency in the photocatalytic removal of lopinavir. The ecotoxicity test using zebrafish (Danio rerio) embryos shows no toxicity for photocatalytically treated ritonavir-containing wastewater, and the contrary trend is observed for photocatalytically treated lopinavir-containing wastewater. The synthesized multiphase photocatalysts can be tested and applied for efficient degradation of other SARS-CoV-2 antiviral drugs in wastewater in the future.
... In particular, tungsten powders with a surface of 41 m 2 g -1 were obtained by reduction of tungstate MgWO 4 with magnesium vapor [12]. This compound [13]. It was assumed that if we choose a precursor with a similar structure in which magnesium is replaced by chromium, then, upon its reduction, we can expect to obtain a mixture of W-Cr powders also with a large specific surface area. ...
The process of producing W-Cr powders by the reduction of trirutile Cr 2 WO 6 with magnesium vapor in the temperature range 700–850 °C at residual pressure of 5-20 kPa was studied. W-Cr powders with a specific surface area at the level of 43-47 m ² ⋅g ⁻¹ were obtained. The resulting W-Cr powders are characterized by a mesoporous structure.
... The tunning of electronic and structural properties can be observed not only for nanotubes, but also for several other morphologies such as nanocube 28 , nanocone 29 , nanopillar 30 , nanoplate 31 , nanopyramid 32 , nanorod 33,34 , nanosheet 35 , nanosphere 36,37 and nanowire 38,39 . He et al. 33 studied leadfree (K,Na)NbO 3 nanorods arrays and observed that both, the charge density map and deformation charge density map exhibit asymmetric charge distribution along the [110] orientation, which should be due to the displacement of Nb atom from the center position toward the [110] direction. ...
We demonstrate here for the first time an original and facile approach to preparing titanium oxide (TiO2) tubes using hydrogen peroxide (H2O2) and titanyl (IV) oxysulfate (TiOSO4) as sacrificial templates. The method involves dissolving TiOSO4 powder in H2O2 solution and subsequently applying thermal treatment on the resulting amorphous precipitate. Prepared samples were characterized by X-ray diffraction, scanning electron microscopy (SEM) images, thermogravimetric (TG) analysis, and UV-vis analysis. Experimental results indicated that the samples exhibit tube-like structures with lengths of approximately 1.9 mm in diameter and 11.5 mm in length. Anatase and rutile phases were formed after annealing at different temperatures in air. The crystallite size estimated by Rietveld refinement showed an increase from 34.69 to 354.28 nm with an increase in the annealing temperature from 600 to 1000 °C. At the same time, the band gap values decreased from 3.14 to 2.97 eV. The electron density maps were calculated, and the electronic density was observed to increase from 497.56 e- Å-2 (600 °C) to 533.10e- Å-2 (740 °C) and decrease with the annealing temperature of samples. A possible mechanism for the formation of TiO2 tubes was proposed.
Nickel tungstate (NiWO4) thin films of different thicknesses were synthesized using binder free successive ionic layer adsorption and reaction (SILAR) method at ambient temperature and succeeded by calcination at temperature of 727 K. The physico‐chemical characterizations of NiWO4 thin films were carried out using different techniques. The electrochemical performances of NiWO4 films were evaluated in 2 M KOH electrolyte using standard three electrode system. The specific capacitance of 1536 F g‐1 at the current density of 2 A g‐1 was obtained for NiWO4 film. The film exhibited excellent electrochemical stability of 87% after 5000 galvanostatic charge discharge (GCD) cycles at the current density of 3 A g‐1. This study highlights use of SILAR deposited NiWO4 thin films as a cathode in aqueous asymmetric supercapacitors (ASC). Asymmetric supercapacitor device NiWO4/KOH/Fe2O3 exhibited a specific capacitance of 115 F g‐1 at 2 A g‐1, and specific energy of 23Wh kg‐1 at specific power of 1.2 kW kg‐1. The device showed remarkable electrochemical cycling stability (78% capacitance retention after 5000 GCD cycles). The SILAR deposited NiWO4 thin films are expected to emerge as a potential candidate for supercapacitors. This article is protected by copyright. All rights reserved.
