Academic literature on the topic 'Silver molybdates'

AbstractStandard molar quantities of molybdate ion entropy, $S_{\rm{m}}^0,$ enthalpy of formation, ${\Delta _{\rm{f}}}H_m^{\rm{o}},$ and Gibbs energy of formation, ${\Delta _{\rm{f}}}G_{\rm{m}}^{\rm{o}},$ are key data for the thermodynamic properties of molybdenum compounds and complexes, which are at present investigated by an OECD NEA review project. The most reliable method to determine ${\Delta _{\rm{f}}}H_{\rm{m}}^{\rm{o}}$ of molybdate ion and alkali molybdates directly consists in measuring calorimetrically the enthalpy of dissolution of crystallized molybdenum trioxide and anhydrous alkali molybdates in corresponding aqueous alkali metal hydroxide solutions. Solubility equilibria of sparingly soluble alkaline earth molybdates and silver molybdate lead to trustworthy data for ${\Delta _{\rm{f}}}G_{\rm{m}}^{\rm{o}}$ of molybdate ion. Thereby the Gibbs energies of the metal molybdates and the corresponding metal ions are combined with the Gibbs energies of dissolution. As reliable values are available for ${\Delta _{\rm{f}}}G_{\rm{m}}^{\rm{o}}$ of the relevant metal ions the problem reduces to select the best values of solubility constants and ${\Delta _{\rm{f}}}G_{\rm{m}}^{\rm{o}}$ of alkaline earth molybdates and silver molybdate. There are two independent possibilities to achieve the latter task. (1) ${\Delta _{\rm{f}}}H_{\rm{m}}^{\rm{o}}$ for alkaline earth molybdates and silver molybdate have been determined by solution calorimetry. Entropy data of molybdenum have been compiled and evaluated recently. CODATA key values are available for $S_{\rm{m}}^{\rm{o}}$ of the other elements involved. Whereas $S_{\rm{m}}^{\rm{o}}({\rm{CaMo}}{{\rm{O}}_4},{\rm{ cr}})$ is well known since decades, low-temperature heat capacity measurements had to be performed recently, but now reliable values for $S_{\rm{m}}^{\rm{o}}$ of Ag2MoO4(cr), BaMoO4(cr) and SrMoO4(cr) are available. (2) ${\Delta _{\rm{f}}}H_{\rm{m}}^{\rm{o}}({\rm{BaMo}}{{\rm{O}}_4},{\rm{ cr}}),$ for example, can be obtained from high temperature equilibria also, but the result is less accurate than that of the first method. Once Gibbs energy of formation, ${\Delta _{\rm{f}}}G_{\rm{m}}^{\rm{o}},$ and enthalpy of formation, ${\Delta _{\rm{f}}}H_{\rm{m}}^{\rm{o}},$ of molybdate ion are known its standard entropy, $S_{\rm{m}}^{\rm{o}},$ can be calculated.

The Ag2MoO4–Cs2MoO4 system was studied by powder X-ray diffraction, the formation of a new double molybdate CsAg3(MoO4)2 was established, its single crystals were obtained, and its structure was determined. CsAg3(MoO4)2 (sp. gr. P3¯, Z = 1, a = 5.9718(5), c = 7.6451(3) Å, R = 0.0149) was found to have the structure type of Ag2BaMn(VO4)2. The structure is based on glaserite-like layers of alternating MoO4 tetrahedra and Ag1O6 octahedra linked by oxygen vertices, which are connected into a whole 3D framework by Ag2O4 tetrahedra. An unusual feature of the Ag2 atom environment is its location almost in the centre of an oxygen face of the Ag2O4 tetrahedron. Caesium atoms are in cuboctahedral coordination (CN = 12).We determined the structures of the double molybdate of rubidium and silver obtained by us previously and a crystal from the solid solution based on the hexagonal modification of Tl2MoO4, which both are isostructural to glaserite K3Na(SO4)2 (sp. gr. P3¯m1). According to X-ray structural analysis data, both crystals have nonstoichiometric compositions Rb2.81Ag1.19(MoO4)2 (a = 6.1541(2), c = 7.9267(5) Å, R = 0.0263) and Tl3.14Ag0.86(MoO4)2 (a = 6.0977(3), c = 7.8600(7) Å, R = 0.0174). In the case of the rubidium compound, the splitting of the Rb/Ag position was revealed for the first time am ong molybdates. Both structures are based on layers of alternating MoO4 tetrahedra and AgO6 or (Ag, Tl)O6 octahedra linked by oxygen vertices. The coordination numbers of rubidium and thallium are 12 and 10

The coating system MoN-Ag is an interesting candidate for industrial applications as a low friction coating at elevated temperatures, due to the formation of lubricous molybdenum oxides and silver molybdates. Film deposition was performed by high-power impulse magnetron sputtering and direct current magnetron sputtering. To facilitate a future transfer to industry Mo-Ag composite targets have been sputtered in Ar/N2 atmosphere. The chemical composition of the deposited MoN-Ag films has been investigated by wavelength dispersive X-ray spectroscopy. Morphology and crystallographic phases of the films were studied by scanning electron microscopy and X-ray diffraction. To obtain film hardness in relation to Ag content and bias voltage, the instrumented indentation test was applied. Pin-on-disc tribological tests have been performed at room temperature and at high temperature (HT, 450 °C). Samples from HT tests have been analyzed by Raman measurements to identify possible molybdenum oxide and/or silver molybdate phases. At low Ag contents (≤7 at.%), coatings with a hardness of 18–31 GPa could be deposited. Friction coefficients at HT decreased with increasing Ag content. After these tests, Raman measurements revealed the MoO3 phase on all samples and the Ag2Mo4O13 phase for the highest Ag contents (~23–26 at.%).

The features of the formation of compounds based on silver antimonate obtained in the AgNO3–Sb2O3–MoO3 system by the solid-phase reaction were investigated. For a synthesis temperature of 1023 K, a homogeneous concentration region of the Ag2−xSb2−xMoxO6 solid solution with a structure of the defective pyrochlore type in the range of 0.0 ≤ x ≤ 2.0 was detected. The Rietveld method, within the constraints of the Fd-3m space group, was used to refinement of X-ray diffraction data, specify the structural parameters of powders, and the correlation of structural disorder with their electrically conductive properties. Relative density and average particle size for ceramic samples sintered at 1223 K were determined using scanning electron microscopy.

Submitted by JÚLIO HEBER SILVA (julioheber@yahoo.com.br) on 2017-05-03T20:30:01Z No. of bitstreams: 2 Dissertação - Douglas Carlos de Sousa Silva - 2017.pdf: 3036182 bytes, checksum: c02aa9da97c239bf3b1954923b5ee8a0 (MD5) license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5)
Approved for entry into archive by Luciana Ferreira (lucgeral@gmail.com) on 2017-05-04T11:06:57Z (GMT) No. of bitstreams: 2 Dissertação - Douglas Carlos de Sousa Silva - 2017.pdf: 3036182 bytes, checksum: c02aa9da97c239bf3b1954923b5ee8a0 (MD5) license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5)
Made available in DSpace on 2017-05-04T11:06:57Z (GMT). No. of bitstreams: 2 Dissertação - Douglas Carlos de Sousa Silva - 2017.pdf: 3036182 bytes, checksum: c02aa9da97c239bf3b1954923b5ee8a0 (MD5) license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) Previous issue date: 2017-04-07
Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPES
Nanostructured materials, such as: Ag2MoO4 and ZnO are of great importance because they have unique characteristics and properties, and can be applied in sensors, catalysis, photoluminescence, among other applications. In this work, the Ag2MoO4 and ZnO powders were synthesized separately and in the form of heterostructures, by two different routes, coprecipitation (CP), at room temperature and coprecipitation with subsequent microwave assisted hydrothermal treatment (CPMAHT), at 130 ° C for 30 min, with a heating rate of 10 ° C / min. The heterostructures composed of both materials, Ag2MoO4 and ZnO present in molar proportions ranging from 0.25-2.00%, were synthesized by coprecipitation with subsequent sonochemical processing (CPSP). The Ag2MoO4 samples were obtained with pure cubic phase of spinel type with crystallite size of 143 nm for the sample obtained by CP and 90 nm for the sample obtained by CPTHAM. For the ZnO the hexagonal phase of the wurtzite type, with crystallite sizes of 19 and 49 nm, was obtained for the samples obtained by CP and CPTHAM, respectively. The phases of both Ag2MoO4 and ZnO were observed for the heterostructures obtained by CPSP. The structural and morphological characterization of the obtained materials was performed using X-ray diffraction (XRD) techniques and scanning electron microscopy (SEM). The diffusion reflectance UV-Vis spectroscopy (DRS) was performed to determine the band gap values of the materials. The photoluminescent property was investigated by means of the photoluminescence spectroscopy (PHS) technique, with an improvement in the photoluminescent property of broadband for all the obtained heterostructures. It was also observed that the synergism of the Ag2MoO4 and ZnO materials in the heterostructures resulted in an improvement in the photocatalytic property, leading to a 90% discoloration of the rhodamine B dye in 90 min for the photocatalysis using the Ag2MoO4: 2 ZnO heterostructure.
Materiais nanoestruturados, tais como: o Ag2MoO4 e o ZnO são de grande importância por apresentarem características e propriedades únicas, podendo ser aplicados em sensores, catálise, fotoluminescência, dentre outras aplicações. Neste trabalho, os pós de Ag2MoO4 e ZnO foram sintetizados na sua forma pura por duas rotas diferentes, coprecipitação (CP) a temperatura ambiente e coprecipitação com posterior tratamento hidrotérmico assistido por microondas (CPTHAM), a 130 °C durante 30 min, com taxa de aquecimento de 10 °C/min. Heteroestruturas compostas por ambos os materiais, Ag2MoO4 e ZnO foram obtidas com proporções de 0,25; 0,50; 1 e 2 mols de ZnO para 1 mol de Ag2MoO4. Estas heteroestruturas foram sintetizadas por coprecipitação com posterior processamento sonoquímico (CPPS). As amostras de Ag2MoO4 foram obtidas com fase cúbica pura do tipo espinélio com tamanho de cristalito de 143 nm para a amostra obtida por CP e 90 nm para a amostra obtida por CPTHAM. Para o ZnO foi obtida a fase hexagonal do tipo wurtzita, com tamanhos de cristalito de 19 e 49 nm, para as amostras obtidas por CP e CPTHAM, respectivamente. Foram observadas ambas as fases, tanto do Ag2MoO4 quanto do ZnO para as heteroestruturas obtidas por CPPS. A caracterização estrutural e morfológica dos materiais obtidos foi realizada utilizando das técnicas de difração de raios X (DRX) e microscopia eletrônica de varredura (MEV). A espectroscopia de UV-Vis por reflectância difusa (ERD) foi realizada para determinação dos valores de “band gap” dos materiais. A propriedade fotoluminescente foi investigada por meio da técnica de espectroscopia de fotoluminescência (EFL), sendo observado uma melhora na propriedade fotoluminescente de banda larga para todas as heteroestruturas obtidas. Foi observado também que a sinergia dos materiais Ag2MoO4 e ZnO nas heteroestruturas resultou em uma melhora na propriedade fotocatalítica, levando a uma descoloração do corante rodamina B de 90 % em 90 min para a fotocatálise usando a heteroestrutura Ag2MoO4: 2 ZnO.

碩士
國立臺北科技大學
化學工程研究所
104
We have fabricated different composite modified electrdoes for application to electrochemical sensors, biosensors and photocatalysis. For instance, in the fisrt part we describe the use of a nanocomposite consisting of graphene and β-cyclodextrin (β-CD) which was used to modify a glassy carbon electrode (GCE) to serve as a matrix for immobilization of hemoglobin (Hb). The composite was characterized by scanning electron microscopy (SEM), Ultraviolet-visible spectroscopy (UV-vis) and Fourier-transform infrared (FTIR) spectroscopy. The modified electrode displays an enhanced and well-defined reversible peaks for the heme protein at a formal potential of -0.284 V (vs. Ag/AgCl). The direct electrochemistry of Hb is strongly enhanced at this modified electrode compared to electrodes not modified with graphene or β-CD. The heterogeneous electron transfer rate constant (Ks) is 3.18 ± 0.7 s‾¹ which indicates fast electron transfer. The biosensor exhibits excellent electrocatalytic activity towards the reduction of bromate, with a linear amperometric response in the 0.1 to 177 μM concentration range at a working voltage of -0.33 V. The sensitivity is 3.39 µA µM‾¹ cm‾², and the detection limit (LOD) is 33 nM. The biosensor is fast, selective, well repeatable and reproducible, and therefore represents a viable platform for sensing bromate in aqueous samples. The part II deals with the fabrication of novel and sensitive amperometric sensor for chlorpromazine (CPZ) based on the reduced graphene oxide (RGO) and polydopamine (PDA) composite modified glassy carbon electrode (GCE). The RGO@PDA composite was prepared by the electrochemical reduction of graphene oxide (GO) and PDA composite. The resulting composite was further characterized by SEM, Raman and FTIR spectroscopy. The RGO@PDA composite modified electrode shows an excellent electro-oxidation behaviour to CPZ when compared with other modified electrodes such as GO, RGO and GO@PDA. An amperometric i-t method was used for the determination of CPZ and shows that the RGO@PDA composite could detect the CPZ in the linear ranging from 0.03 to 967.6 µM. The sensor exhibits a low LOD of 0.0018 µM with the analytical sensitivity of 3.74 µA µM–1 cm–2. The RGO@PDA composite shows its high selectivity in the presence of other potentially interfering drugs such as metronidazole, phenobarbital, chlorpheniramine maleate, pyridoxine and riboflavin. The fabricated sensor has also showed an appropriate recovery towards CPZ in the pharmaceutical tablets. In the final part (Part III) we have investigated the phtocatalytic activity of as-synthesized silver molybdate (Ag2MoO4) modified electrode. The potato-like Ag2MoO4 microstructure was synthesized through simple hydrothermal treatment with the assistance of urea. The successful formation of Ag2MoO4 was confirmed by various analytical and spectroscopic techniques such as X-ray diffraction, FTIR, Raman, SEM, Energy dispersive x-ray and X-ray photoelectron spectroscopies. Furthermore, the as-prepared Ag2MoO4 was used as a photocatalyst for the degradation of ciprofloxacin (CIP) as well as an electrochemical sensor for the detection of H2O2, for the first time. The obtained UV-vis spectroscopy results demonstrate that, Ag2MoO4 had excellent reusable photocatalytic activity for the degradation CIP under Ultraviolet-light illumination possess great degradation rate of above 98% after 40 min. Moreover, the cyclic voltammetry and amperometry results revealed that Ag2MoO4 modified GCE showed good electrocatalytic performance for the detection of H2O2 with good linear range and LOD are 0.04 to 240 µM, and 0.03 µM, respectively. It also exhibit high selectivity of H2O2 in the presence of range of biological interferences such as catechol, fructose, lactose, sucrose, glucose, hydroquinone, ascorbic acid, uric acid, dopamine, and epinephrine. Hence, the potato-like Ag2MoO4 microstructure has great practical applicability for use as wastewater treatment and electrochemical detection of H2O2 in real samples.