Amorphous MoO3 Research Articles

SERS Detection of Trace Carcinogenic Aromatic Amines Based on Amorphous MoO3 Monolayers.

Aromatic amines are important commercial chemicals, but their carcinogenicity poses a threat to humans and other organisms, making their rapid quantitative detection increasingly urgent. Here, amorphous MoO3 (a-MoO3) monolayers with localized surface plasmon resonance (LSPR) effect in the visible region are designed for the trace detection of carcinogenic aromatic amine molecules. The hot-electron fast decay component of a-MoO3 decreases from 301 fs to 150 fs after absorption with methyl orange (MO) molecules, indicating the plasmon-induced hot-electron transfer (PIHET) process from a-MoO3 to MO. Therefore, a-MoO3 monolayers present high SERS performance due to the synergistic effect of electromagnetic enhancement (EM) and PIHET, proposing the EM-PIHET synergistic mechanism in a-MoO3. In addition, a-MoO3 possesses higher electron delocalization and electronic state density than crystal MoO3 (c-MoO3), which is conducive to the PIHET. The limit of detection (LOD) for o-aminoazotoluene (o-AAT) is 10-9 M with good uniformity, acid resistance, and thermal stability. In this work, trace detection and identification of various carcinogenic aromatic amines based on a-MoO3 monolayers is realized, which is of great significance for reducing cancer infection rates.

SERS Detection of Trace Carcinogenic Aromatic Amines Based on Amorphous MoO3 Monolayers

AbstractAromatic amines are important commercial chemicals, but their carcinogenicity poses a threat to humans and other organisms, making their rapid quantitative detection increasingly urgent. Here, amorphous MoO3 (a‐MoO3) monolayers with localized surface plasmon resonance (LSPR) effect in the visible region are designed for the trace detection of carcinogenic aromatic amine molecules. The hot‐electron fast decay component of a‐MoO3 decreases from 301 fs to 150 fs after absorption with methyl orange (MO) molecules, indicating the plasmon‐induced hot‐electron transfer (PIHET) process from a‐MoO3 to MO. Therefore, a‐MoO3 monolayers present high SERS performance due to the synergistic effect of electromagnetic enhancement (EM) and PIHET, proposing the EM‐PIHET synergistic mechanism in a‐MoO3. In addition, a‐MoO3 possesses higher electron delocalization and electronic state density than crystal MoO3 (c‐MoO3), which is conducive to the PIHET. The limit of detection (LOD) for o‐aminoazotoluene (o‐AAT) is 10−9 M with good uniformity, acid resistance, and thermal stability. In this work, trace detection and identification of various carcinogenic aromatic amines based on a‐MoO3 monolayers is realized, which is of great significance for reducing cancer infection rates.

Detailed work function and structural investigations of layered MoO3 onto SiO2 and MoS2 in air

MoS2, its oxides and heterostructures are increasingly utilized in nanoscale opto-electronics and catalysis, where electrical properties such as work function (WF) affect their performance. Herein, a detailed study of the thickness-dependent work function in the case of thermally produced layered Mo oxides onto SiO2 and MoS2 substrates in air is presented. First, the effects of typical contaminants on the mechanically exfoliated MoS2 substrates are investigated. Then, high resolution structural characterization by atomic force microscopy supported by X-ray photoelectron spectroscopy shows that thermal MoS2 oxidation in humid air produces layered amorphous MoO3 with nano-crystallites. Kelvin-probe force microscopy analysis shows that the first MoO3 layer on both substrates is negatively charged and that the MoO3 work function depends on the oxide thickness. The thickness-dependent WF is explained by presence of screened electric field at the MoO3/substrate interface. The negative doping to MoO3 by the studied substrates is confirmed through density functional theory simulations. Moreover, an electrical device from amorphous MoO3 monolayer onto MoS2 is built and shows rectification behavior due to p-type doping of the MoS2 by the oxide layer. Overall, this study provides an insight to understand and manipulate electrical properties of MoO3 and MoO3/MoS2 heterostructures in various devices.

Transformation from MoO3 into MoS2: Experimental study on phase transition and energy band modulation

The transformation of MoO3 into MoS2 is investigated by sulfurizing MoO3 on sapphire at various temperatures. The amorphous MoO3 are crystallized at 500 ℃ and then sulfurized from 500 ℃ to 900 ℃. The phase transition occurs as the temperature increases, from MoO3 to S- doped MoO3 at 500 ℃, mixture of MoO3 and MoS2 at 600 ℃, O- doped MoS2 at 700 ℃, ideal stoichiometric ratio of MoS2 at 800 ℃, and S- deficient MoS2 at 900 ℃, respectively. Correspondingly, the work function is significantly modulated from 4.68 eV for MoO3 to 3.90 eV for MoS2, and the band gap energy decreases from 3.08 eV to 1.00 eV gradually, which are fairly consistent with the theoretical predictions. The contacts between titanium and S- doped MoO3, or the mixture of MoO3 and MoS2, are ohmic- like contacts with specific contact resistivities of 2.68 × 10-3 Ω•cm2 and 3.14 × 10-3 Ω•cm2. While the contacts between Ti and O- doped MoS2, ideal stoichiometric ratio of MoS2, or S- deficient MoS2 are Schottky contacts with barrier heights of 0.22 eV, 0.43 eV and 0.45 eV, respectively. Those results demonstrate that temperature plays pivotal role in determining the phase of sulfurized MoO3 and their properties.

Highly stable, self-powered UV-Vis-NIR broadband isotype photodetector based on Ti-doped amorphous MoO3

Ti-doped MoO3 thin film was sputtered onto a n-Si substrate and the MoO3:Ti/n-Si heterojunction photodetector fabricated. The elemental composition and the morphological analyses of the MoO3 film have been carried out by EDX and SEM studies, respectively. The band gap of sputtered MoO3:Ti film was found to be 3.26 eV from UV-Vis spectra. The optical performance of the constructed device under visible light between 10 and 150 mW, under 365 nm and 395 nm UV light and 850 nm NIR light was examined in detail with the help of current-voltage (I-V) characteristics. From the analysis of the experimental I-V characteristics of the MoO3:Ti/n-Si heterojunction photodetector, the largest responsivity values were determined as 0.41 A/W in visible light of 10 mW/cm2, 2.03 A/W under UV light of 365 nm and 0.67 A/W for 850 nm NIR light, respectively. Furthermore, the largest specific detectivity values were calculated as 3.21×109 Jones in visible light (10 mW/cm2), 1.61×1010 Jones, under UV light of 365 nm, and 3.21×109 Jones, respectively. Repeated measurements after 30 days showed that the device was quite stable both in the dark and in a broadband.

Heterogeneous CNF/MoO3 nanofluidic membranes with tunable surface plasmon resonances for solar-osmotic energy conversion.

Two-dimensional (2D) nanofluidic membranes are competitive candidates for osmotic energy harvesting and have been greatly developed. However, the use of diverse inherent characteristics of 2D nanosheets, such as electronic or optoelectronic properties, to achieve intelligent ion transport, still lacks sufficient exploration. Here, a cellulose nanofiber/molybdenum oxide (CNF/MoO3) heterogeneous nanofluidic membrane with high performance solar-osmotic energy conversion is reported, and how surface plasmon resonances (SPR) regulate selective cation transport is revealed. The SPR of amorphous MoO3 endows the heterogeneous nanofluidic membranes with tunable surface charge and good photothermal conversion. Through DFT calculations and finite element modeling, the regulation of electronic and optoelectronic properties on the surface of materials by SPR and the influence of surface charge density and temperature gradient on ion transport in nanofluidic membranes are demonstrated. By mixing 0.01/0.5 M NaCl solutions using SPR and photothermal effects, the power density can achieve a remarkable value of ≈13.24 W m-2, outperforming state-of-the-art 2D-based nanofluidic membranes. This work first reveals the regulation and mechanism of SPR on ion transport in nanofluidic membranes and systematically studies photon-electron-ion interactions in nanofluidic membranes, which could also provide a new viewpoint for promoting osmotic energy conversion.

Electrochemical reduction of nitrite to ammonia on amorphous MoO3 nanosheets.

Electrocatalytic NO2- reduction to NH3 (NO2RR) is an appealing approach for mitigating NO2- pollution and for the synthesis of valuable NH3, and so the exploration for high-performance NO2RR catalysts is pivotal yet remains challenging. Herein, amorphous MoO3 nanosheets (am-MoO3) were designed as a high-performance NO2RR electrocatalyst, delivering a maximum NO2--to-NH3 faradaic efficiency of 94.8% and NH3 yield rate of 480.4 μmol h-1 cm-2 at -0.6 V vs. RHE. Theoretical computations revealed that the largely enhanced NO2RR activity of am-MoO3 originated from the amorphization-induced O-vacancies, which could enhance the NO2--to-NH3 reaction energetics and hamper the competitive hydrogen evolution.

Exploring the Surface Oxidation and Environmental Instability of 2H-/1T'-MoTe2 Using Field Emission-Based Scanning Probe Lithography.

An unconventional approach for the resistless nanopatterning 2H- and 1T'-MoTe2 by means of scanning probe lithography is presented. A Fowler-Nordheim tunneling current of low energetic electrons (E = 30-60eV) emitted from the tip of an atomic force microscopy (AFM) cantilever is utilized to induce a nanoscale oxidation on a MoTe2 nanosheet surface under ambient conditions. Due to the water solubility of the generated oxide, a direct pattern transfer into the MoTe2 surface can be achieved by a simple immersion of the sample in deionized water. The tip-grown oxide is characterized using Auger electron and Raman spectroscopy, revealing it consists of amorphous MoO3 /MoOx as well as TeO2 /TeOx . With the presented technology in combination with subsequent AFM imaging it is possible to demonstrate a strong anisotropic sensitivity of 1T'-/(Td )-MoTe2 to aqueous environments. Finally the discussed approach is used to structure a nanoribbon field effect transistor out of a few-layer 2H-MoTe2 nanosheet.

Electrodepositing a Mo layer and composite siliconized coating on Nb-based alloy for high temperature protection

In order to protect Nb-based alloy from oxidation attack, a Mo layer was first electrodeposited under different current densities and then its siliconized coating was obtained via halide activated pack cementation (HAPC) process. Microstructure, chemical composition, hardness and adhesive strength of the Mo pre-layer on the Nb-based alloy were analyzed and oxidation behavior of the siliconized coating exposed at 1200 °C and 1300 °C was investigated. The results showed that the electrodeposited Mo layer was composed of amorphous Mo phase and MoO3. The oxygen content in the Mo layer was low as 38.2 at% when the current density during electrodeposition was 400 mA/cm2 with the microhardness as 238 ± 18 HV. The HAPC siliconized coating exhibited a multilayer structure of MoSi2/(Mo, Nb)5Si3/NbSi2, which showed an increase in the cohesive/adhesive strength compared to the Mo layer. Mainly Nb2O5 and SiO2 were formed on the exposed siliconized coating. An accelerated mass gain and a thicker oxidation layer were found as the exposure temperature increased with a thinning of NbSi2 inner layer. The siliconized coating provided an effective oxidation resistance for the Nb-based alloy and the increased exposure temperature made the protection of the coating deteriorate.

Sunlight Driven Reversible and Tunable Plasmon Resonance in 2D Amorphous Molybdenum Oxide

AbstractTwo‐dimensional molybdenum oxide (2D MoO3), as a non‐noble metal semiconductor material, is of particular significance for exploring the localized surface plasmon resonance (LSPR). However, the high excitation energy and the irreversible LSPR performance significantly restrict its practical application. To resolve these challenges, the hydrogen intercalated 2D amorphous MoO3 is investigated, and it can be observed that tunable plasmon resonances in the visible and near‐infrared regions occur. More importantly, the LSPR effect can be triggered by visible light and monochromatic light. For the first time, it is found out that the hydrogen intercalated 2D amorphous MoO3 presents a light‐modulated reversible LSPR effect, and its color can transfer from dark blue under illumination to transparent in light‐off. Additionally, solar energy can be effectively stored in bulk‐amorphous MoO3 materials. Therefore, these findings may provide a new platform to utilize sun power.

Fabrication of self-rolled Ni catalyst using water-soluble ceramics for NaBH4 dehydrogenation

This study explores the use of roll-up nickel films as catalysts for the dehydrogenation of sodium borohydride (NaBH4). The proposed structure, consisting of a 345-nm-thick Ni film and a 100-nm-thick sacrificial layer, is naturally rolled-up due to thermal stress induced by physical vapor deposition or additional heating. The catalytic performance was evaluated using the water displacement method, and it was found that a three-layer stacked structure using amorphous MoO3 as the sacrificial layer showed maximum efficiency. The stability of the structure was maintained even after repeated use, and surface analysis by X-ray photoelectron spectroscopy revealed the presence of Mo component that accelerates the rate of hydrolysis. Zeta potential and Kelvin probe force microscopy analysis further revealed that the amount of surface electrons of the Ni catalyst can be changed according to the sacrificial layer used. Based on these findings, MoO3/Ni/MoO3 and layered structures were found to have excellent catalytic performance. Importantly, the wafer can be reused, and the catalytic efficiency is maintained even with a low-thickness nickel catalyst, suggesting the economic advantage. This study offers insights into the development of cost-effective and high-performance catalysts for hydrogen generation.

Atomic-Scale Mechanisms of MoS2 Oxidation for Kinetic Control of MoS2/MoO3 Interfaces.

Oxidation of transition metal dichalcogenides (TMDs) occurs readily under a variety of conditions. Therefore, understanding the oxidation processes is necessary for successful TMD handling and device fabrication. Here, we investigate atomic-scale oxidation mechanisms of the most widely studied TMD, MoS2. We find that thermal oxidation results in α-phase crystalline MoO3 with sharp interfaces, voids, and crystallographic alignment with the underlying MoS2. Experiments with remote substrates prove that thermal oxidation proceeds via vapor-phase mass transport and redeposition, a challenge to forming thin, conformal films. Oxygen plasma accelerates the kinetics of oxidation relative to the kinetics of mass transport, forming smooth and conformal oxides. The resulting amorphous MoO3 can be grown with subnanometer to several-nanometer thickness, and we calibrate the oxidation rate for different instruments and process parameters. Our results provide quantitative guidance for managing both the atomic scale structure and thin-film morphology of oxides in the design and processing of TMD devices.

Flower-Like Amorphous MoO3- x Stabilized Ru Single Atoms for Efficient Overall Water/Seawater Splitting.

Benefitting from the maximum atom utilization efficiency, special size quantum effects and tailored active sites, single-atom catalysts (SACs) have been promising candidates for bifunctional catalysts toward water splitting. Besides, due to the unique structure and properties, some amorphous materials have been found to possess better performance than their crystalline counterparts in electrocatalytic water splitting. Herein, by combining the advantages of ruthenium (Ru) single atoms and amorphous substrates, amorphous molybdenum-based oxide stabilized single-atomic-site Ru (Ru SAs-MoO3- x /NF) catalysts are conceived as a self-supported electrode. By virtue of the large surface area, enhanced intrinsic activity and fast reaction kinetics, the as-prepared Ru SAs-MoO3- x /NF electrode effectively drives both oxygen evolution reaction (209mV @ 10mA cm-2 ) and hydrogen evolution reaction (36mV @ 10mA cm-2 ) in alkaline media. Impressively, the assembled electrolyzer merely requires an ultralow cell voltage of 1.487V to deliver the current density of 10mA cm-2 . Furthermore, such an electrode also exhibits a great application potential in alkaline seawater electrolysis, achieving a current density of 100mA cm-2 at a low cell voltage of 1.759V. In addition, Ru SAs-MoO3- x /NF only has very small current density decay in the long-term constant current water splitting test.

Etching of molybdenum via a combination of low-temperature ozone oxidation and wet-chemical oxide dissolution

Etching of molybdenum was demonstrated in two steps. Mo was first oxidized in an ozone gas ambient to form molybdenum oxide. It is shown that comparable oxide thicknesses can be obtained in ozone and oxygen but at lower temperatures for the former. Initial oxide growth is fast but then considerably slows down due to its diffusion-limited character. The metal-oxide thickness can be controlled by temperature and defines the amount of metal etch per cycle (EPC). XPS analysis showed that the thermally grown oxide is MoO3. In the second, wet-chemical step, MoO3 was dissolved selectively toward the Mo metal using an aqueous solution. The dissolution rate of amorphous MoO3 formed in O3 at temperatures below ∼230 °C is fast, but the dissolution of MoO3 formed at Tox > 230 °C was shown to be incomplete. Cross-section TEM showed a matrix of amorphous oxide with crystallized MoO3 islands, the latter more difficult to dissolve. However, the crystalline phase could be completely and selectively removed using a more concentrated NH4OH solution at an elevated temperature (70 °C). The EPC was determined for temperatures between 150 and 290 °C. The etch rates increased with temperature from 1–2 nm/cycle at 150 °C to 5–6 nm/cycle at 290 °C. This hybrid thermal-wet etching sequence is well suited for vertical and lateral recess etching as it shows a controlled and isotropic dissolution of polycrystalline Mo at the nanoscale. Furthermore, the process shows a progressive surface smoothening upon increasing the number of etching cycles.

P-Block Antimony Single-Atom Catalysts for Nitric Oxide Electroreduction to Ammonia

Electrocatalytic NO reduction to NH3 (NORR) offers a prospective approach to attain both harmful NO removal and efficient NH3 electrosynthesis. Main-group p-block metals are promising NORR candidates but still lack adequate exploration. Herein, p-block Sb single atoms confined in amorphous MoO3 (Sb1/a-MoO3) are designed as an efficient NORR catalyst, exhibiting the highest NH3 yield rate of 273.5 μmol h–1 cm–2 and a NO-to-NH3 Faradaic efficiency of 91.7% at −0.6 V vs RHE. In situ spectroscopic characterizations and theoretical computations reason that the outstanding NORR performance of Sb1/a-MoO3 arises from the isolated Sb1 sites, which can optimize the adsorption of *NO/*NHO to lower the reaction energy barriers and simultaneously exhibit a higher affinity to NO than to H2O/H species. Moreover, our strategy can be extended to prepare Bi1/a-MoO3, showing a high NORR property, demonstrating the immense potential of p-block metal single-atom catalysts toward the high-performing NORR electrocatalysis.

Main-group indium single-atom catalysts for electrocatalytic NO reduction to NH3

In single atoms confined in amorphous MoO3(In1/a-MoO3) are reported to be an efficient catalyst for NO electroreduction to NH3, attributed to the ability of single-site In to inhibit hydrogen evolution and optimize NO-to-NH3hydrogenation energetics.

Nanomechanical, Structural and Electrochemical Investigation of Amorphous and Crystalline MoO3 Thin-Film Cathodes in Rechargeable Li-Ion Batteries

In this work, a comprehensive investigation of amorphous and crystalline modification of identical electrode active material as a thin-film electrode for a future all-solid-state Li-ion battery application is presented and discussed. Using the proposed micro-battery system, we aim to unravel the effect of the crystallinity of the positive electrode material on the intrinsic durability of all-solid-state thin-film Li-ion batteries during prolonged electrochemical cycling. We demonstrate the preparation, structural-, nanomechanical and electrochemical characteristics of molybdenum (VI) oxide (MoO3) thin-film cathodes based on their different crystallinity. The nanomechanical properties of the electrode layers were determined using nanoindentation along with acoustic emission studies. Based on the electrochemical test results, as-prepared thin films that did not go under any heat treatment showed the best performance and stability throughout cycling around 50 μAh initial capacity when cycled at C/2. This suits well their nanomechanical properties, which showed the highest hardness but also the highest flexibility in comparison with the heat-treated layers with lower hardness, high brittleness, and numerous cracks upon mechanical loads. According to our results, we state that amorphous-type electrode materials are more durable against electro-chemo-mechanical-aging related battery performance loss in all-solid-state Li-ion batteries compared to their crystalline counterparts.

Metallic Interface Induced Ionic Redistribution within Amorphous MoO3 Films

AbstractThe phase evolution and ionic redistribution in amorphous MoO3 films, deposited on metallic aluminium (Al) and copper (Cu) substrates and subjected to distinct thermal treatments, are systematically investigated in this work. It is shown that the metallic interface significantly modifies the formation and dynamics of oxygen vacancies within the resulted structure, reducing the oxygen content of the MoO3 up to x < 2.94. The concentration of the oxygen vacancies can also be extended to the bulk via thermal treatment up to 400 °C. It is demonstrated that the MoO3 structure on metallic substrates is affected either by the diffusion of the metallic atoms inserted from the interface, which results in a formation of the meta‐stable alloy phases in case of Cu, or by the introduction of the oxygen vacancies into the crystalline matrix in case of Al. The oxygen vacancy density in the MoO3 films with a metallic interface can be tuned via optimal choice of the metal and treatment parameters such as temperature and oxygen partial pressure. Furthermore, the intrinsic defects present in the amorphous structure enhance the ionic mobility and diffusion of the metallic ions inside the crystalline structure.

Boosting K-ion kinetics by interfacial polarization induced by amorphous MoO3- for MoSe2/MoO3-@rGO composites

Ø The K-ion storage of MoSe 2 @rGO is enhanced by incorporating amorphous MoO 3- x with oxygen vacancies. Ø A built-in electric field benefits for electron-transfer and K-ion migration across the hetero-junction interface. Ø Larger dielectric polarization induced by MoO 3- x reduces charge transfer resistance and enhance K-ion migration across electric double-layer. Promoting interfacial reaction kinetics is highly desirable for achieving high-performances of anode material in alkali-ion batteries. Herein, flower-like MoSe 2 /MoO 3- x @rGO composites are fabricated by a facile solvothermal method involving a thermal-treatment at 800°C. When evaluated as an anode material for potassium ion batteries, MoSe 2 /MoO 3- x @rGO delivers 248.2 mA h g −1 after 50 cycles at 0.2 A g −1 with a capacity retention of 84.6% and 182.9 mA h g −1 after 150 cycles at 1.0 A g −1 with a capacity retention of almost 61.2%, superior to those of bare MoSe 2 or MoSe 2 @rGO composites. Analysis from electrochemical measurements, the amorphous MoO 3- x containing oxygen vacancies could not only effectively buffer the self-aggregation of MoSe 2 nanosheets but also provides lots of accessible active sites for potassium ion storage. Additionally, the open channels in the amorphous MoO 3- x phase lead to easier ion hopping and smaller diffusion barriers. Furthermore, the built-in electric field at the interface would be beneficial for electron transfer and K-ion migration across the hetero-junction interface. Moreover, larger dielectric polarization induced by the high relative permittivity of amorphous MoO 3- x would reduce charge transfer resistance and enhance K-ion migration across electric double-layer. Our work provides new insight into the enhanced performance of anode material coated by an amorphous layer with large relative permittivity.

Mesoporous Molybdenum Sulfide-Oxide Composite Thin-Film Electrodes Prepared by a Soft Templating Method for the Hydrogen Evolution Reaction

Electrode designs involving binder-free nanoparticles integrated within interconnected pore networks are critical in scaling up electrolyzers. MoS2 is the most promising electrocatalyst candidate that can show hydrogen evolution reaction (HER) activity comparable to platinum (Pt). Herein, a facile one-step soft templating method was developed to synthesize mesoporous molybdenum sulfide-oxide composite thin-film electrocatalysts directly on any substrate without using a binder or a template. Fabricated electrocatalysts contain amorphous MoS3 and small crystallite-sized MoS2 embedded into amorphous MoO3 with a large surface area (around 182 m2/g). The electrocatalyst layer undergoes in situ electrochemical activation in which amorphous MoS3 is reduced to MoS2 during the HER in acidic media. The electrocatalyst layer on the carbon fiber exhibits a low overpotential (∼189 mV at 10 mA/cm2) and Tafel slope (53 mV/dec) toward the HER after electrochemical activation.