Getting nanometric MoO3 through chemical synthesis and high energy milling

Santos-Beltrán, M.; Paraguay‐Delgado, F.; Santos-Beltrán, A.; Fuentes, L.

doi:10.1016/j.jallcom.2015.06.176

Cited by 14 publications

(12 citation statements)

References 27 publications

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“…3(d). Unlike all other phases of MoO 3 , the β phase possesses a direct band gap of 2.8 eV at the high-symmetry Γ k point, which is very much in line with the reported experimental value [47,48]. Arguably, the "directness" of its electronic band gap is somewhat controversial-the VBM and the CBM are almost undistinguishable at both the Γ and B k points, with very small energy differences of 0.02 and 0.01 eV, respectively.…”

Section: B Electronic Structure Of Moo 3 Polymorphssupporting

confidence: 89%

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Aligning the Band Structures of Polymorphic Molybdenum Oxides and Organic Emitters in Light-Emitting Diodes

et al. 2017

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Heavy transition-metal oxides are widely studied for key applications in electronics and energy technologies. In cutting-edge organic-light-emitting-diode (OLED) devices, there remain scientific challenges to achieve an efficient transfer of charges between electrodes and the organic layer. Recently, polymorphic MoO 3 has been actively investigated to exploit its unique high work-function values, especially for its use in the electrode buffer layer to effectively transfer the charges in OLED devices. However, no systematic fundamental studies of its electronic structure are available. Thus, in this study, we use first-principles density-functional theory to investigate both the crystal structure and the electronic structure of the MoO 3 polymorphs, and we conclude with a simple perspective to screen the best candidate for OLED applications via a hole transport-barrier descriptor.

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Section: B Electronic Structure Of Moo 3 Polymorphssupporting

confidence: 89%

“…To date, several experimentally measured E g 's of h-MoO 3 have been reported [19,[45][46][47], ranging from 2.6 to 3.0 eV. However, to the best of our knowledge, the theoretical E g of h-MoO 3 has not been reported.…”

Section: B Electronic Structure Of Moo 3 Polymorphsmentioning

confidence: 90%

Aligning the Band Structures of Polymorphic Molybdenum Oxides and Organic Emitters in Light-Emitting Diodes

et al. 2017

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“…M. Santos-Beltrán 1 , F. Paraguay-Delgado 1 , R. García-Alamilla 2 , A. Santos-Beltrán 3 , V. Gallegos-Orozco 3,4 1. Centro de Investigación en Materiales Avanzados (CIMAV), Chihuahua, Chih., México.…”

Section: In Situ Xrd Study Of Moo3 Particles During Heat Treatment Anunclassified

“…Employing high energy mechanical milling technique was possible to get nanoparticles with size below 40 nm at 30 min milling time from HW sample with previous calcination process (HWCM sample) [1]. The milling nanoparticles showed greater removal of Methylene blue (MB) compared to the microparticles [2].…”

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confidence: 99%

In Situ XRD Study of MoO3 Particles During Heat Treatment and Their Capacity of Removing the MB

et al. 2018

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The effects of heat treatment (HT) at different temperatures from 25 to 600 ° C were studied in their morphology and crystal structure for particles of MoO3 with orthorhombic (OW sample) and hexagonal (HW sample) phases. Employing high energy mechanical milling technique was possible to get nanoparticles with size below 40 nm at 30 min milling time from HW sample with previous calcination process (HWCM sample) [1]. The milling nanoparticles showed greater removal of Methylene blue (MB) compared to the microparticles [2].The morphology and microstructure were determined using electron microscopy techniques and X-ray diffraction. Figures 1a and 1b show the X-ray diffraction patterns evolution during HT of the OW and HW samples, respectively. In general, at all temperatures the diffraction patterns correspond to the orthorhombic phase (see Fig. 1a) and practically remains stable as temperature increase, however there is a slight decrease in width at 600 ºC, indicating that exist an increase in crystallite size due to atomic diffusion during HT. Figure 1b, shows the X-ray diffraction patterns evolution during HT of the HW sample, above 440°C, hexagonal phase changes into orthorhombic phase, and an apparent broadening of the diffraction peaks is observed, this phenomenon corresponds to a delamination of the hexagonal phase [3]. The secondary electrons SEM image on OW sample before HT shows elongated, thin and smooth surface ribbon-like structures (see fig. 2a). For the 440 ° C temperature some particles were maintained with tape-shaped morphology but with larger dimensions (see fig, 2b). Figure 2c shows the SEM image of secondary electrons obtained before the HT of the HW sample, the particles show hexagonal prism shape morphology. Fig. 2d shows different agglomerates particles showing a micro-lamella type morphology corresponding to the orthorhombic phase of the HWC (before the MM process) sample submitted at 440 ° C. On the other hand an irregular morphology of agglomerated nanoparticles was observed when the particles were subjected to mechanical milling (samples named HWCM) as is shown in the TEM image (see Fig.3a). These particles were also analyzed through SAED diffraction patterns annexed. The nanometric particles produced allowed an increase in surface area, improving noticeable the adsorption activity of MB in a time of 50 min for the calcined milled HWCM sample. The nanometric particles powder increased the speed discoloration, without using photonic irradiation.

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“…In a microwave-assisted synthesis, process there is an inverse temperature profile compared to conventional methods: heating occurs by conversion rather than by energy transfer, so the temperature distribution in the synthesis is uniform and highly controlled, which allows rapid synthesis, efficient and with better results than traditional heating [1]. This discovery has allowed the synthesis of new materials in more controlled morphologies [1][2][3], additionally a phase transformation can be achieve by thermal treatment [3], and the morphological changes are due to the crystalline structures obtained.Molybdenum oxide (MoO3) materials were synthesized according to previously method reported by Paraguay-Delgado et al [3], for which an aqueous solution of ammonium heptamolybdate ((NH46Mo7O24 · 4H2O) at concentration of 0.3 M and controlling the pH was treated in microwave assisted hydrothermal method at 200°C for 20 minutes, achieving pressures around 41 bar. The microwave-assisted hydrothermal method allows the synthesis two samples of MoO3 with hexagonal bar morphology structures as showed by scanning electron microscopy (SEM) in image 1 and hexagonal MoO3 phase according to X ray diffraction technique (XRD) in figure 2 whit a clear difference in (100) and (210) patterns intensity directions.…”

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confidence: 99%

Molybdenum Oxide Structures Synthetized by Microwave Technique and Its Phase Transformation by Thermal Treatment

Ornelas¹,

Paraguay‐Delgado²,

Lara‐Romero

2017

Microsc Microanal

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The use of microwave radiation for the materials synthesis presents great benefits: energy saving, short processing times, increased performance, economical and environmentally friendly procedures, etc. In a microwave-assisted synthesis, process there is an inverse temperature profile compared to conventional methods: heating occurs by conversion rather than by energy transfer, so the temperature distribution in the synthesis is uniform and highly controlled, which allows rapid synthesis, efficient and with better results than traditional heating [1]. This discovery has allowed the synthesis of new materials in more controlled morphologies [1][2][3], additionally a phase transformation can be achieve by thermal treatment [3], and the morphological changes are due to the crystalline structures obtained.Molybdenum oxide (MoO3) materials were synthesized according to previously method reported by Paraguay-Delgado et al [3], for which an aqueous solution of ammonium heptamolybdate ((NH46Mo7O24 · 4H2O) at concentration of 0.3 M and controlling the pH was treated in microwave assisted hydrothermal method at 200°C for 20 minutes, achieving pressures around 41 bar. The microwave-assisted hydrothermal method allows the synthesis two samples of MoO3 with hexagonal bar morphology structures as showed by scanning electron microscopy (SEM) in image 1 and hexagonal MoO3 phase according to X ray diffraction technique (XRD) in figure 2 whit a clear difference in (100) and (210) patterns intensity directions. A complete statistical study made to both samples with pressure variation during the synthesis show DCLML2 MoO3 sample with hexagonal bars 8% shorter and 7% thinner than DCLM1 MoO3 sample. The pressure was for DCLM1 and DCLM2 41 and 38.5 bar respectively.In order to made a phase transformation the MoO3 samples were treated in a muffle at 450°C for 45 min in static atmosphere, the materials after treatment are characterized by SEM, the results are shown in figure 3 and the XRD results are show in figure 2. X ray diffraction show a complete phase transformation in both materials to orthorhombic MoO3 structures and by SEM and high resolution transmission electron microscopy (HRTEM) the morphological changes in the hexagonal bar structures are studied. Deformation in the morphology hexagonal bars structures of MoO3 samples are observed and transformation in the sheets type within the bars was observed, these sheets are observed both horizontal and vertical with respect to the original bar, the transformation process is studied by means of HRTEM and its morphological changes is due to crystalline phase transformation process.References:[1] J.

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Getting nanometric MoO3 through chemical synthesis and high energy milling

Cited by 14 publications

References 27 publications

Aligning the Band Structures of Polymorphic Molybdenum Oxides and Organic Emitters in Light-Emitting Diodes

Aligning the Band Structures of Polymorphic Molybdenum Oxides and Organic Emitters in Light-Emitting Diodes

In Situ XRD Study of MoO3 Particles During Heat Treatment and Their Capacity of Removing the MB

Molybdenum Oxide Structures Synthetized by Microwave Technique and Its Phase Transformation by Thermal Treatment

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