Figure 5 - available via license: Creative Commons Attribution 4.0 International
Content may be subject to copyright.
Source publication
Molybdenum blue dispersions were synthesized by reducing an acidic molybdate solution with glucose, hydroquinone and ascorbic acid. The influence of the H/Mo molar ratio on the rate of formation of molybdenum particles was established. For each reducing agent, were determined the rate constant and the order of the particle formation and were establ...
Contexts in source publication
Context 1
... and FTIR spectroscopy is used to characterize molybdenum blue particles and its structure [21]. Figure 5 shows the UV/Vis spectra of molybdenum blue nanoparticles synthesized using various reducing agents. The particles were preliminarily isolated from dispersion by electrolyte coagulation (KCl), then the resulting precipitate was washed with water and ethanol to remove traces of organic substances (reducing agents and their oxidation products). ...
Similar publications
Aqueous zinc‐ion batteries (ZIBs) have recently attracted people's extensive attention in their application in energy storage systems resulting from their exclusive characteristics of low cost and environmental compatibility. However, finding suitable cathode materials continues to be the major challenge. Polyoxovanadates (POVs), as an important br...
Citations
... The presence of an absorption band with a maximum at 937 nm indicates that the reduction process occurs under the action of light quanta and not chemical reagents. 30,31 The appearance of absorption bands in the ranges of 770-1000 and 900-1300 nm are responsible for two types of charge transfer between Mo 6+ and Mo 5+ by different types of molybdenum-oxygen bonds in the MoO 6 octahedron. 32 The tungsten oxide sols are characterized by the presence of three poorly resolved bands with maxima at 640, 790, and 960 nm ( Figure 4B). ...
Novel photochromic composites based on biopolymers (polyvinyl alcohol, starch) and Mo 4 O 11 and W 18 O 49 as the fillers were obtained and characterized. To improve the photochromic properties, molybdenum and tungsten oxide sols were treated by an underwater diaphragm discharge to obtain binary structures of the MoO x /WO x and WO x /MoO x (2 < x < 3) types. The formation of such oxides was confirmed by TEM, EDX, XRD analysis, and Raman spectroscopy data. Plasma treatment is increased the color intensity and reversibility. The modified sols were incorporated into polymer matrices. Spectral studies have shown that the color of photo‐colored composites depends on the chemical structure of the polymer matrix. Mechanical tests have shown the possibility of obtaining hardened or plastic composites depending on the concentration and nature of the filler.
Highlights
Photochromic polymer composites with W 18 O 49 and Mo 4 O 11 as fillers were obtained.
Diaphragm discharge used as a tool for sol modification.
WO x /MoO x and MoO x /WO x structures have improved photochromic properties.
Color of irradiated polymer composites depends on chemical structure of polymer.
Mechanical properties are determined by the polymer filler concentration.
... The versatile nature of polyoxometalate compounds in terms of structure, size, redox behavior, photochemistry, and charge distribution, among other aspects, has made it one of the fastest-growing inorganic chemistry fields with many applications (Bijelic et al., 2019;Cherevan et al., 2020, Gavrilova et al., 2020Liu and Wang, 2020;Myachina et al., 2021). All systems known as "molybdenum blue" are polyoxometalates. ...
ABSTRACT
Context: The actual experimental conditions of molybdenum blue spectrophotometric method, used for antioxidant activity estimation, promote degradation of flavonoids, with potential interferences in the above determination.
Objectives: To evaluate the effects of physicochemical factors on the formation of the complex for optimizing the Total Antioxidant Activity method, for a better estimation of the antioxidant activity of natural products.
Methods: A 3^4-1 fractional experimental design was applied. Independent variables were temperature, color development time, type of acid and acidity, and dependent variable was the absorbance of the complex. The concentration of ammonium molybdate tetrahydrate and sodium hydrogen phosphate remained constant throughout the study. The effects of the reducing agent and its concentration were studied independently. The effect of acidity in a wide range of values, the color development time considering temperature, the influence of co-solvents and the antioxidant activity of various natural metabolites were also evaluated.
Results: Acid concentration and temperature greatly influenced on the complex formation, being type of acid and incubation time less significant. Ascorbic acid showed a shorter color development time than reference metabolites. Ethanol negatively influenced the amount of complex formed. The proposed conditions for developing this method were: type of acid, HCl or H2SO4; acid concentration, 0.01 N; incubation temperature, 65 °C; and incubation time, 40 min. Under these experimental conditions, the ranking order of antioxidant activity was pyrogallol>quercetin> ascorbic acid>gallic acid>rutin.
Conclusions: The new experimental conditions for the molybdenum complex assay give a more reliable determination of the antioxidant activity for natural products.
... Likewise, the presence of Mo in the FTIR spectra of the CDC samples after adsorption can be observed in Figure 8. The peaks at 597 and 898 cm −1 were reported in the literature to correspond to the stretching vibrations of Mo-O and Mo=O, respectively [41,42]. The Mo peaks in the FTIR spectra confirm the adsorption of Mo onto CDC. ...
In the present work, the removal of Mo from aqueous solutions and real groundwater by using the novel high-surface-area adsorbent carbide-derived carbon (CDC) was performed. The adsorbent was characterized using X-ray photoelectron spectroscopy (XPS), X-ray powder diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDS), Brunauer, Emmett, and Teller (BET) surface area analysis, and Fourier-transform infrared spectroscopy (FTIR). The effect of the operational parameters (contact time, CDC loading, Mo concentration, and pH) on the adsorptive performance of the sorbent in the batch adsorption mode was studied. The experimental work revealed that the adsorption of Mo onto CDC is a very fast process and provides 99% Mo removal in less than 30 min. The adsorption process was pH-dependent, achieving the maximum adsorptive removal at a pH range of 3–5. The highest adsorption capacity corresponded to 16.24 mg/g at a Mo concentration of 10 ppm, adsorbent loading of 0.6 g/L, and pH 3. Four models were used to analyze the adsorption isotherms of Mo onto CDC, which were Freundlich, Langmuir, Temkin, and Sips. The obtained adsorption results were also processed using four adsorption kinetic models: intra-particle diffusion, Elovich, second-order, and pseudo-first-order. The adsorption of Mo onto CDC was found to fit the Freundlich isotherm model, as confirmed by the highest R2 values (0.9118) and lowest SSE (0.4777), indicating the heterogeneous multilayer adsorption of Mo onto CDC. Likewise, the experimental adsorption data were found to be more consistent with the pseudo-second-order model. The main adsorption mechanisms contributing to Mo adsorption were found to be electrostatic interactions and ligand–ligand exchange, in addition to surface complexation or ion exchange between Mo ions and oxygen-containing groups on the CDC’s surface. Moreover, the removal efficiency under acidic conditions (pH: 3) was found to be stable and high (>99%), regardless of the Mo concentration (0.5–10 ppm) due to the characteristic PZC corresponding to CDC (pH 9.9). A performance test of the CDC using both real groundwater and GW spiked with 570 µg/L Mo showed an almost complete removal of Mo from GW. The regeneration tests confirmed that adsorbed Mo can be recovered from CDC by pH adjustment and the regenerated CDC can be reused.
... The broad absorption band in the range of 2700-3620 cm −1 refers to the valency vibrations of the water molecule. Absorption bands were in the range of 1500-1790 cm −1 to deformation vibrations of the water molecule [42]. The absorption bands 795 and 1049 cm −1 , characteristic of silicon oxide, are also observed on the SiO2 (RH) sample, indicating the presence of a Si-O and Si-O-Si bond [43]. ...
The article presents the results of comparative research on the physicochemical characteristics and catalytic activity of copper oxide supported on synthetic SiO2 and SiO2 (RH) from rice husk. SiO2 (RH) is more hydrophobic compared to SiO2, which leads to the concentration of copper oxide on its surface in the form of a “crust”, which is very important in the synthesis of low-percentage catalysts. According to SEM, XRD, and TPR-H2, the use of SiO2 (RH) as a carrier leads to an increase in the dispersion of copper oxide particles, which is the active center of ethanol dehydrogenation.
This study investigated UV-induced photodegradation of cyhalothrin (Cy) and elucidated the photocatalytic effect of molybdenum(VI) oxide (MoO3). Cyhalothrin was exposed to MoO3 (in the dark): [Cy. + MoO3-dark], to ultraviolet (UV) irradiation: [Cy + UV-irrad.], and UV irradiation in the presence of MoO3: [Cy. + MoO3 + UV-irrad.]. The intensity and nature of the absorption bands were monitored by time-dependent UV–vis-NIR wavelength scan spectroscopic measurements (190–1100 nm) and used to characterize photodegradation and photocatalytic activities. The kinetic analysis of the experiments: [Cy. + UV-irrad.] and [Cy. + MoO3 + UV-irrad.] showed that the average pseudo-first-order photodegradation rate constants (kav.) increased by a factor of between 2.27 and 2.56 in the presence of MoO3, hence indicating photocatalytic activity. The control experiment [Cy. + MoO3-dark], with no UV irradiation, showed no change in the absorbance of Cy molecules over the same period. The results showed that MoO3 exhibits optimal photocatalytic activity at typical operating conditions of UV = 254 nm, 766–775 mmHg, 273–275 K; and 1:2 molar ratio [MoO3]:[Cy]. The photodegradation kinetic data best fitted the Boltzmann equations (R2 = 099). Time-dependent near-infrared (NIR) wavelength scans characterized the formation of reactive intermediates, Mo-complexes, and by-products in the photodegradation catalytic cycles during the [Cy. + MoO3 + UV-irrad.] experiment. These results show that MoO3 can be used to enhance the UV photodegradation of Cy residues for environmental remediation purposes.
This study investigates the effects of gas atmosphere and synthesis temperature on the thermal decomposition of (NH4)6Mo7O24.4H2O. Samples were synthesized in a CVD furnace at temperatures of 450, 550, and 650 °C, using different gases: H2, O2, and Ar, individually. The resulting samples were characterized by powder X-ray diffraction (XRD), scanning electron microscopy (SEM), Raman spectroscopy, Fourier transform infrared spectroscopy (FTIR), vibrating sample magnetometry (VSM), and optical absorbance. XRD results revealed the formation of MoO3 in all samples produced in an O2 atmosphere. However, in samples synthesized in an inert atmosphere (Ar), a mixture of MoO3 and Mo4O11 phases was detected. The same phase mixture was observed in samples produced at 450 and 550 °C in an H2 atmosphere. However, in samples synthesized in H2 at 650 °C, MoO2 mixed with Mo4O11 was formed. Raman and FTIR spectroscopy confirmed the results obtained by XRD, and these two techniques were also used to compare samples synthesized at 550 °C in different environments. The VSM results indicate a paramagnetic response in the analyzed samples, and there is also an increase in magnetization as the percentage of the Mo4O11 phase increases. Absorbance measurements were also performed and further confirm expected changes in sample composition.
Energy storage via electrochemical supercapacitors (ECSC) is critical for regulating and implementing
intermittent renewable resources and enhancing the development of electric vehicles. In this paper,
novel adenine/sulfanilamide functionalized molybdenum oxide (FMO) nanoflakes are synthesized by
anodizing exfoliation followed by a simple hydrothermal method. The structural and optical properties of
the FMO nanoflakes are elucidated by X-ray diffraction (XRD), Fourier transforms infrared (FT-IR), field
emission scanning electron microscopy (FESEM), Raman spectroscopy, thermogravimetric analysis (TGA),
UVevis spectroscopy, X-ray photoelectron spectroscopy (XPS), and transmission electron microscopy
(TEM). The electrochemical behavior of the synthesized materials has been evaluated in 1 M Li2SO4 using
cyclic voltammetry (CV), galvanostatic charge/discharge, and electrochemical impedance spectroscopy
(EIS). The FMO electrodes display a high specific capacitance of 1261.9 F/g at 1 A/g with an outstanding
cycle life of 99.8 after 1000 cycles and 94.9% after 3000 cycles at 10 A/g. The fabricated FMO-based
symmetric supercapacitor device delivers superior energy and power densities of 87.1 Wh/kg and
2116W/kg, respectively, at 2 A/g. The superior supercapacitive performance of FMO is correlated to the
improved wettability, unstacking of the MoOx nanoflakes, and enrichment with oxygen vacancies. These
results indicate the significant potential of FMO as an electrode material for highly capacitive ECSC.
