Sub-micrometric β-CoMoO4 rods: optical and piezochromic properties

NiMoO4 nanorods photocatalytic activity comparison under UV and visible light

Waste water remediation is the ongoing hot research topic that can reduce the water scarcity all over the world. By reducing the pollutants in the waste water drawn from industries and other sources will be more useful for domestic purposes. To reduce the rate of pollutants in water may also help in improving the aquatic environment and decreases other side effects. Efficient and cost effective catalysts were in search for both dye degradation and water remediation treatment applications. NiMoO₄ nanorods were prepared by employing co-precipitation method with different stirrer time (2 h, 4 h and 6 h). The formation of NiMoO₄ was substantiated employing X-ray diffractometer analysis (XRD). Vibrational and rotational property of the samples was analyzed by FT-IR spectra and Raman spectra. The optical property was further confirmed by UV-vis spectral studies. Morphological analysis studies revealed growth of nanorods with 6 h stirrer time. The photocatalytic behavior of the obtained product was carried out under both UV light (364 nm) and visible light irradiation. The samples subjected to visible light environment showed better efficiency on degrading the methylene blue (MB) dye. The efficiency obtained under UV irradiation were 20%, 31%, 33%, 41% and efficiency obtained in visible light irradiation were 27%, 42%, 46%, 55% with respect to bare methylene blue (MB), MB with NiMoO₄ (2 h), MB with NiMoO₄ (4 h), MB with NiMoO₄ (6 h) catalyst added. NiMoO₄ sample with 6 h stirrer time and fine nanorods growth will be the good candidate for future use.

Insights into the Antimicrobial Activity of Hydrated Cobaltmolybdate Doped with Copper

Molybdates are biocidal materials that can be useful in coating surfaces that are susceptible to contamination and the spread of microorganisms. The aim of this work was to investigate the effects of copper doping of hydrated cobalt molybdate, synthesized by the co-precipitation method, on its antibacterial activity and to elucidate the structural and morphological changes caused by the dopant in the material. The synthesized materials were characterized by PXRD, Fourier Transformed Infrared (FTIR), thermogravimetric analysis/differential scanning calorimetry (TG/DSC), and SEM-Energy Dispersive Spectroscopy (SEM-EDS). The antibacterial response of the materials was verified using the Minimum Inhibitory Concentration (MIC) employing the broth microdilution method. The size of the CoMoO₄·1.03H₂O microparticles gradually increased as the percentage of copper increased, decreasing the energy that is needed to promote the transition from the hydrated to the beta phase and changing the color of material. CoMoO₄·1.03H₂O obtained better bactericidal performance against the tested strains of Staphylococcus aureus (gram-positive) than Escherichia coli (gram-negative). However, an interesting point was that the use of copper as a doping agent for hydrated cobalt molybdate caused an increase of MIC value in the presence of E. coli and S. aureus strains. The study demonstrates the need for caution in the use of copper as a doping material in biocidal matrices, such as cobalt molybdate.

A soft chemistry approach to preparing (de)sodiated transition-metal hydroxy molybdates

Polymorphic transformations were investigated for (de)sodiated Ni and Zn hydroxy molybdates prepared under mild hydrothermal conditions.

Probing Co- and Fe-doped LaMO3 (M = Ga, Al) perovskites as thermal sensors

The synthesis of a Co-doped or Fe-doped La(Ga,Al)O₃ perovskite via the Pechini process aimed to achieve a color change induced by temperature and associated with spin crossover (SCO). In Fe-doped samples, iron was shown to be in the high-spin state, whereas SCO from the low-spin to the high-spin configuration was detected in Co-doped compounds when the temperature increased. Fe-doped compounds clearly adopted the high-spin configuration even down to 4 K on the basis of Mössbauer spectroscopic analysis. The original SCO phenomenon in the Co-doped compounds LaGa_1-xCo_xO₃ (0 < x < 0.1) was evidenced and discussed on the basis of in situ X-ray diffraction analysis and UV-vis spectroscopy. This SCO is progressive as a function of temperature and occurs over a broad range of temperatures between roughly 300 °C and 600 °C. The determination of a crystal field strength of about 2 eV and a Racah parameter B of about 500 cm^-1 for Co³⁺ (3d⁶) ions show that these values allow the occurrence of SCO. Hence, this study shows the possibility of using LaGa_1-xCo_xO₃ compounds as thermal sensors at low Co contents (x = 0.02). The competition between steric and electronic effects in LaGaO₃ in which Co³⁺ is stabilized in the LS state shows that electronic effects with the creation of M-O covalent bonds are predominant and contribute to the stabilization of a high crystal field around Co³⁺ (LS) although its ionic radius is smaller in comparison with that of Ga³⁺.

Silver-, calcium-, and copper molybdate compounds: Preparation, antibacterial activity, and mechanisms

Developing novel compounds with antimicrobial properties can be an effective approach to decreasing the number of healthcare-associated infections, particularly in the context of medical devices and touch surfaces. A variety of molybdate powders (Ag₂MoO₄, CaMoO₄, CuMoO₄ and Cu₃Mo₂O₉) were synthesized and characterized, and Escherichia coli was used as a model gram-negative bacterium to demonstrate their antimicrobial properties. Optical density measurements, bacterial colony growth, and stained gel images for protein expression clearly showed that silver- and copper molybdates inhibit bacterial growth, whereas CaMoO₄ exhibited no bactericidal effect. All tests were performed in both daylight and darkness to assess the possible contribution of a photocatalytic effect on the activity observed. The main mechanism responsible for the antibacterial effect observed for Ag₂MoO₄ is related to Ag⁺ release in combination with medium acidification, whereas for compounds containing copper, leaching of Cu²⁺ ions is proposed. All these effects are known to cause damage at the cellular level. A photocatalytic contribution to the antibacterial activity was not clearly observable. Based on the pH and solubility measurements performed for powders in contact with various media (ultrapure water and bacterial growth medium), silver molybdate (Ag₂MoO₄) was identified as the best antibacterial candidate. This compound has great potential for further use in hybrid powder-polymer/varnish systems for touch surfaces in healthcare settings.

CoMoO4/CuMo0.9W0.1O4 mixture as an efficient piezochromic sensor to detect temperature/pressure shock parameters

A mixture of two piezochromic compounds can be used as a universal shock detector, i.e., to determine the shock pressure without knowing a priori the temperature at which the shock occurred. For this purpose, both piezochromic compounds must exhibit different temperature influences in their transition-pressure values. This demonstration uses two piezochromic compounds (CoMoO4 and CuMoO4-type oxides) that exhibit a first-order phase transition between their two allotropic forms associated with a drastic color change. The colorimetric coordinates of the mixture indicate the pressure and temperature of a shock.

Understanding the relationships between structural features and optical/magnetic properties when designing Fe(1-x)Mg(x)MoO4 as piezochromic compounds

Fe1-xMgxMoO4 compounds with x = 0, 0.25, 0.5, 0.75, and 1.0 were obtained after annealing under inert gas at T = 700 °C. All of the compounds exhibit a pressure-induced and/or temperature-induced phase transition between the two polymorphs adopted by AMoO4 compounds (A = Mn, Fe, Co, and Ni). For the FeMoO4 compound, for both the α and the β allotropic forms, the structural features have been correlated to the magnetic properties, the Mössbauer signals, and the optical absorption properties to gain a better understanding of the phenomena at the origin of the piezo(thermo)chromic behavior. The different contributions of the Mössbauer signals were attributed to the different Fe(2+) ions or Fe(3+) ions from the structural data (Wyckoff positions, bond distances and angles) and were quantified. Furthermore, the low Fe(3+) concentration (9 and 4 mol %, respectively, in the α and the β allotropic forms) was also quantified based on the magnetic susceptibility measurements. The net increase in the Fe(3+) quantity in the α-form in comparison to the β-form, which is associated with the occurrence of Fe-Mo charge transfer, is at the origin of the important divergence of coloration of the two forms. To design new piezo(thermo)chromic oxides and to control the pressure (temperature) of this first-order phase transition, FeMoO4-MgMoO4 solid solutions were synthesized. The optical contrast between the two allotropic forms was increased due to magnesium incorporation, and the phase transition (β → α) pressure increased steadily with the Mg content. A new generation of nontoxic and chemically stable piezochromic compounds that are sensible to various pressures was proposed.

Fabrication of ultrathin CoMoO4 nanosheets modified with chitosan and their improved performance in energy storage device

Ultrathin nanosheet-assembled cobalt molybdate (CoMoO₄) with a mesoporous morphology was synthesized by a urea-assisted solution combustion route at a temperature of 400 °C.