Triple Play of Band Gap, Interband, and Plasmonic Excitations for Enhanced Catalytic Activity in Pd/HxMoO3 Nanoparticles in the Visible Region

Plasmonic photocatalysis has been limited by the high cost and scalability of plasmonic materials, such as Ag and Au. By focusing on earth-abundant photocatalyst/plasmonic materials (HxMoO3) and Pd as a catalyst, we addressed these challenges by developing a solventless mechanochemical synthesis of Pd/HxMoO3 and optimizing photocatalytic activities in the visible range. We investigated the effect of HxMoO3 band gap excitation (at 427 nm), Pd interband transitions (at 427 nm), and HxMoO3 localized surface plasmon resonance (LSPR) excitation (at 640 nm) over photocatalytic activities toward the hydrogen evolution and phenylacetylene hydrogenation as model reactions. Although both excitation wavelengths led to comparable photoenhancements, a 110% increase was achieved under dual excitation conditions (427 + 640 nm). This was assigned to a synergistic effect of optical excitations that optimized the generation of energetic electrons at the catalytic sites. These results are important for the development of visible-light photocatalysts based on earth-abundant components.

Highly Sensitive NO2 Gas Sensors Based on MoS2@MoO3 Magnetic Heterostructure

Recently, two-dimensional (2D) materials and their heterostructures have attracted considerable attention in gas sensing applications. In this work, we synthesized 2D MoS₂@MoO₃ heterostructures through post-sulfurization of α-MoO₃ nanoribbons grown via vapor phase transport (VPT) and demonstrated highly sensitive NO₂ gas sensors based on the hybrid heterostructures. The morphological, structural, and compositional properties of the MoS₂@MoO₃ hybrids were studied by a combination of advanced characterization techniques revealing a core-shell structure with the coexistence of 2H-MoS₂ multilayers and intermediate molybdenum oxysulfides on the surface of α-MoO₃. The MoS₂@MoO₃ hybrids also exhibit room-temperature ferromagnetism, revealed by vibrating sample magnetometry (VSM), as a result of the sulfurization process. The MoS₂@MoO₃ gas sensors display a p-type-like response towards NO₂ with a detection limit of 0.15 ppm at a working temperature of 125 °C, as well as superb selectivity and reversibility. This p-type-like sensing behavior is attributed to the heterointerface of MoS₂-MoO₃ where interfacial charge transfer leads to a p-type inversion layer in MoS₂, and is enhanced by magnetic dipole interactions between the paramagnetic NO₂ and the ferromagnetic sensing layer. Our study demonstrates the promising application of 2D molybdenum hybrid compounds in gas sensing applications with a unique combination of electronic and magnetic properties.

Highly enhanced dye adsorption of MoO3 nanoplates fabricated by hydrothermal-calcination approach in presence of chitosan and thiourea

Water pollution by organic dyes poses great challenge to the environment and living organism. Hence effective removal of organic dyes by cost effective methods have received significant attention in recent years. Herein, we report the complete removal of organic dyes (rhodamine B), methylene blue) and eosin yellow) from water via effective adsorption by MoO₃ catalyst. Hydrothermally synthesised MoO₂ (1) and amorphous MoS_x (2) using ammonium molybdate without and with thiourea exhibited low dye adsorption. In contrast, crystalline micro/nanoplates of MoO₃ (3 and 4) obtained from calcination of 1 and 2 showed highly enhanced dye adsorption. Particularly 4 showed higher dye adsorption compared to 3. UV-Visible absorption studies confirmed complete removal of organic dyes upon stirring with MoO₃ catalyst. Dye removal studies further revealed that cationic dyes are adsorbed faster than anionic dye that could be attributed to the surface charge of MoO₃. Interestingly, the adsorbed dyes were not released from MoO₃ for more than 50 days. The exhausted MoO₃ catalyst can be recovered by annealing at 400 °C. MoO₃ catalyst has also been used as packing materials in dropper column and demonstrated effective removal of dyes by passing through dyes separately as well as mixture.

An Investigation on the Synthesis of Molybdenum Oxide and Its Silica Nanoparticle Composites for Dye Degradation

The molybdenum oxide (MoO₃) and MoO₃@SiO₂ nanoparticles were successfully prepared using the chemical bath deposition (CBD) method. The photocatalytic activities of molybdenum oxide (MoO₃), SiO₂, and MoO₃@SiO₂ nanoparticles composite have shown a synergistic photocatalytic effect of SiO₂ combined with MoO₃. The first-order degradation rate constants for MoO₃, SiO₂, and MoO₃@SiO₂ nanocomposite were 10.3 × 10⁻³ min⁻¹, 15.1 × 10⁻³ min⁻¹, and 16.3 × 10⁻³ min⁻¹, respectively. The MoO₃@SiO₂ composite showed degradation efficiencies in the methylene blue solution close to 100% after 60 min of UV irradiation. The X-ray diffraction (XRD) showed that the MoO₃ powder has a hexagonal crystal structure and the silica is the tridymite type of SiO₂. The crystallite size was about 94 nm, 32 nm, and 125 nm for MoO₃, silica, and MoO₃@SiO₂, respectively, as calculated by the Scherrer equation. The scanning electron microscopy (SEM) images revealed that the MoO₃ powder consisted of a uniform hexagonal structure; the silica showed a rod-like micro-flake morphology and the MoO₃@SiO₂ composite had the appearance of coral-like structures.

Layered α-MoO3 nanoplates for gas sensing applications

A versatile chemical route to produce rectangular layered α-MoO₃ nanoplates with enhanced NO₂ gas sensing response.

Multi-amine-assisted crystal growth of large-sized α-MoO3 elongated nano-plates

Large-sized α-MoO₃ elongated nano-plates were synthesized by the introduction of multi-amines such as ethylene di-amine and diethylene tri-amine (DETA) in the conventional hydrothermal reaction. DETA made large hexagonal rods with an h-MoO₃ intermediate phase containing H₂O, NH₄OH, and DETA ions. During the hydrothermal reaction, the hexagonal rods were transformed to elongated α-MoO₃ nano-plates by the re-dissolution of h-MoO₃ and re-growth to α-MoO₃ because DETA retarded the preferred growth reaction of the MoO₆ octahedra to the [001] direction and helped the MoO₆ octahedra to grow in the [100] direction. In addition, DETA promoted α-MoO₃ nano-belts to be assembled into elongated nano-plates by oriented attachment because the multi-ammonium groups in the DETA backbone could adhere to the α-MoO₃ nano-belts due to attractive Coulomb interactions.

Amorphous MoO3-x nanosheets prepared by the reduction of crystalline MoO3 by Mo metal for LSPR and photothermal conversion

Amorphous MoO3-x with enhanced LSPR has been fabricated successfully by introducing Mo atoms into the interlayers of MoO3 nanosheets via a hydrothermal method. The inserted Mo atom could bond with inherent Mo atoms and further form a distorted atomic configuration structure. Thus, the amorphous MoO3-x possesses a relatively excellent photothermal conversion efficiency of 61.79%.

Nanostructured Fe,Co-Codoped MoO₃ Thin Films

Molybdenum oxide (MoO₃) and Fe,Co-codoped MoO₃ thin films obtained by spray pyrolysis have been in-depth investigated to understand the effect of Co and Fe codoping on MoO₃ thin films. The effect of Fe and Co on the structural, morphological and optical properties of MoO₃ thin films have been studied using X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and energy-dispersive X-ray analysis (EDAX), optical and photoluminescence (PL) spectroscopy, and electropyroelectric methods. The XRD patterns demonstrated the formation of orthorhombic α-MoO₃ by spray pyrolysis. SEM characterization has shown an increase in roughness of MoO₃ thin films by Fe and Co doping. Optical reflectance and transmittance measurements have shown an increase in optical band gap with the increase in Fe and Co contents. Thermal conductivity and thermal diffusivity of Fe,Co-doped MoO₃ were 24.10–25.86 Wm⁻¹K⁻¹ and 3.80 × 10⁻⁶–5.15 × 10⁻⁶ m²s⁻¹, respectively. MoO₃ thin films have shown PL emission. Doping MoO₃ with Fe and Co increases emission in the visible range due to an increase number of chemisorbed oxygen atoms. The photodegradation of an aqueous solution of methylene blue (MB) depended on the content of the codoping elements (Fe,Co). The results showed that a degradation efficiency of 90% was observed after 60 min for MoO₃: Fe 2%-Co 1%, while the degradation efficiency was about 35% for the undoped MoO₃ thin film.

Methylene Blue-Fortified Molybdenum Trioxide Nanoparticles: Harnessing Radical Scavenging Property

A hybrid nanosystem with impeccable cellular imaging and antioxidant functionality is demonstrated. The microwave irradiation-derived molybdenum trioxide nanoparticles (MoO₃ NPs) were surface-functionalized with the cationic dye molecule, methylene blue (MB), which enables superior UV-visible absorbance and fluorescence emission wavelengths potential for bioimaging. The radical scavenging property of the pristine MoO₃ NPs and MoO₃-MB NPs were studied in vivo using Caenorhabditis elegans as the model system. Heat shock-induced oxidative stress in C. elegans was significantly resolved by the MoO₃-MB NPs, in agreement with the in vitro radical scavenging study by electron paramagnetic resonance spectroscopy. Hybrid nanostructures of MoO₃-MB demonstrate synergistic benefits in intracellular imaging with intrinsic biocompatibility and antioxidant behavior, which can facilitate application as advanced healthcare materials toward bioimaging and clinical therapeutics.

Self-expansion, self-exfoliation and self-dispersion: insights into colloidal formation of atomically thin two-dimensional MoO2.5(OH)0.5

Schematic of the formation mechanism of highly self-dispersible colloidal solutions of monolayered MoO_2.5(OH)_0.5 nanosheets by self-expansion and self-exfoliation process.

Effects of MoO3 crystalline structure of MoO3–SnO2 catalysts on selective oxidation of glycol dimethyl ether to 1,2-propandiol

Hexagonal, monoclinic and orthorhombic MoO₃ crystalline phases were prepared to explore rational design requirements of the MoO₃–SnO₂ structure that are beneficial for the reaction of glycol dimethyl ether to 1,2-propandiol.

Effects of tetrahedral molybdenum oxide species and MoOx domains on the selective oxidation of dimethyl ether under mild conditions

A new preparation method for MoO₃–SnO₂ catalysts precipitated by HNO₃ was developed to selectively synthesize industrially useful chemicals formaldehyde and methyl formate via oxidation of dimethyl ether.

Constructing a High-Efficiency MoO3/Polyimide Hybrid Photocatalyst Based on Strong Interfacial Interaction

A novel two-dimensional hybrid polymer photocatalyst black-MoO3/polyimide was synthesized by one-pot thermopolymerization of monomers, ammonium molybdate, and thiourea at mild temperatures. Thiourea and ammonium molybdate as fluxing agents promote the formation of black molybdenum oxide (BMO) on polyimide (PI) and enhance the crystallinity of PI. It is confirmed by X-ray photoelectron spectroscopy, electron paramagnetic resonance, and Fourier transform infrared that the strong interaction between BMO and PI leads to the formation of a Mo-N coordination bond through the coordination of N atoms of heptazine units to the unsaturated Mo atoms of BMO and results in a large number of Mo5+ cations in BMO/PI. UV-vis and photoluminescence reveal that the visible light absorption of BMO/PI was increased and the separation efficiency of photogenerated electron/hole obviously was significantly enhanced, which facilitates the improvement of the photocatalytic activity of BMO/PI. This work provides a new approach to synthesizing efficient inorganic-organic hybrid semiconductor photocatalysts.

Highly monodisperse Cu3Mo2O9 micropompons with excellent performance in photocatalysis, photocurrent response and lithium storage

The as-obtained highly monodisperse Cu₃Mo₂O₉ micropompons present excellent performance in photocatalysis, photocurrent response and lithium storage.

Highly selective and efficient adsorption dyes self-assembled by 3D hierarchical architecture of molybdenum oxide

A novel hierarchical architecture of MoO₃ exhibits a fast and selective adsorption to the organic pollutants.

Construction of Cu3Mo2O9 nanoplates with excellent lithium storage properties based on a pH-dependent dimensional change

1D, 2D and 3D nanostructures of CMOHs were successfully constructed through a pH-dependent dimensional transformation of ACM.

Alteration of architecture of MoO₃ nanostructures on arbitrary substrates: growth kinetics, spectroscopic and gas sensing properties

MoO3 nanostructures have been grown in thin film form on five different substrates by RF magnetron sputtering and subsequent annealing; non-aligned nanorods, aligned nanorods, bundled nanowires, vertical nanorods and nanoslabs are formed respectively on the glass, quartz, wafer, alumina and sapphire substrates. The nanostructures formed on these substrates are characterized by AFM, SEM, GIXRD, XPS, micro-Raman, diffuse reflectance and photoluminescence spectroscopy. A detailed growth model for morphology alteration with respect to substrates has been discussed by considering various aspects such as surface roughness, lattice parameters and the thermal expansion coefficient, of both substrates and MoO3. The present study developed a strategy for the choice of substrates to materialize different types MoO3 nanostructures for future thin film applications. The gas sensing tests point towards using these MoO3 nanostructures as principal detection elements in gas sensors.

Leveling effects of ammonium salts on thermal stabilities of polyethylene glycols

In this work, the thermal stabilities of a series of polyethylene glycols (PEG 4000, 6000 and 10000) were investigated after compositing with different kinds of inorganic salts, such as ammonium molybdate tetrahydrate (AMT), NH4VO3, (NH4)2SO4, NH4NO3, Na2SO4, Na2MoO4. It was first observed that all the ammonium salts exerted leveling effects for the thermal stabilities of the PEGs. In other words, the presence of the ammonium salts caused the occurrence of the maximum decomposition rates of the PEGs with the same repeat sequence but different chain lengths at almost the same temperatures. Leveling effects were defined by three parameters: leveling spans, leveling degrees and dispersion degrees of leveling. Further experiments revealed that leveling effects also occur in similar types of polymers: polypropylene glycols (PPG 2000, 3000 and 4000). A series of independent experiments including Fourier transformation infrared spectroscopy, Raman spectroscopy, differential scanning calorimetry, time-of-flight mass spectrometry, conductivity and field-emission scanning electron microscopy were performed to explore the origin of leveling effects. We consider that the interaction between inorganic ions and polymer molecules and the Hofmeister effect of ions in solution are two important factors affecting the stability of salt–polymer composites, because they can contribute to decrease the interaction between the polymer chains, leading to changes in the conformation and pyrolysis mode of polymers. We believe that the finding of leveling effects would be significant for both basic and applied research of soft matter.

The Synthesis of α-MoO₃ by Ethylene Glycol

This study investigated the use of ethylene glycol to form α-MoO₃ (molybdenum trioxide) from ammonium molybdate tetrahydrate at various sintering temperatures for 1 h. During the sintering process, the morphologies of the constituents were observed using scanning electron microscopy (SEM), and Fourier transform infrared (FTIR) spectroscopy was used to explain the reaction process. In this work, the results obtained using X-ray photoelectron spectroscopy (XRD) demonstrated that, when the molybdenum trioxide powder was treated thermally at 300 °C, the material exhibited crystallinity. The peaks were indexed to correspond with the (110), (040), (021), (111), and (060) crystallographic planes, and the lattice parameters of a, b, and c were about 3.961, 13.876, and 3.969 Å. Using these observations, we confirmed that orthorhombic α-MoO₃ was formed for sintering temperatures from 300 to 700 °C. Pattern images were obtained by the selected area electron diffraction pattern (SAED) technique, and the d distance of the high resolution transmission electron microscopy (HRTEM) images were almost 0.39 and 0.36 nm, and the Mo 3d_5/2, Mo 3d_3/2, and O 1s of X-ray photoelectron spectroscopy (XPS) were located at 233.76, 237.03, and 532.19 eV, which also demonstrated that α-MoO₃ powder had been synthesized.