Molybdenum Carbide Research Articles

Cobalt promoted molybdenum carbide supported on γ-alumina as an efficient catalyst for hydrodesulfurization of dibenzothiophene

The development of new hydrodesulfurization (HDS) catalysts with suitable electronic structure and metal-support interaction are critical for the efficient removal of sulfur from oil. In this work, cobalt-promoted molybdenum carbide supported on mesoporous alumina (CoxMo2C/MA) catalysts were prepared by a simple one-step hydrolysis method combined with a temperature programmed carbonization process, and the effects of Co on the physicochemical properties and HDS performance of the catalysts were systematically investigated. The results show that the appropriate Co addition can reduce the interaction between Mo species and alumina support, which is beneficial for the carbonization of Mo. Besides, the introduction of Co makes Mo species electron-rich, causing the C–S bond is vulnerable to attack. Taking dibenzothiophene (DBT) as a probe, Co0.3Mo2C/MA shows significant high sulfur removal efficiency (about 100%) and effective direct desulfurization selectivity. Furthermore, the density functional theory calculations further prove that the activation energy barrier of DBT HDS at the Co–Mo2C site is lower than that of Mo2C, confirming its reaction is easier to proceed. This work may provide a strategy for accessing new efficient modified molybdenum carbide catalysts for the HDS field.

Combining molybdenum carbide with ceria overlayers to boost Mo/CeO2 catalyzed ammonia synthesis

AbstractThe design of an efficient non‐noble metal catalyst is of burgeoning interest for ammonia synthesis. Herein, we report a Mo2C/CeO2 catalyst that is superior in ammonia synthesis activity. In this catalyst, molybdenum carbide coexisted with the ceria overlayers which is from the ceria support as the strong metal–support interaction. There is a high proportion of low‐valent Mo species, as well as high concentration of Ce3+ and surface oxygen species. The presence of Mo2C and CeO2 overlayers not only leads to enhancement of hydrogen and nitrogen adsorption, but also facilitates the desorption and exchange of adsorbed species with the gaseous reagents. Compared with the Mo/CeO2 catalyst prepared without carbonization, the Mo2C/CeO2 catalyst is more than sevenfold higher in ammonia synthesis rate. This work not only presents an explicit example of designing Mo‐based catalyst that is highly efficient for ammonia synthesis by tuning the adsorption and desorption properties of the reactant gases, but opens a perspective for other elements in ammonia synthesis.

Nanofibrous Cathode Catalysts with MoC Nanoparticles Embedded in N-Rich Carbon Shells for Low-Overpotential Li–CO2 Batteries

Li-CO2 batteries with high theoretical energy densities are recognized as next-generation energy storage devices for addressing the range anxiety and environmental issues encountered in the field of electric transportation. However, cathode catalysts with unsatisfactory activity toward CO2 absorption and reduction/evolution reactions hinder the development of Li-CO2 batteries with desired specific capacities and sufficient cycle numbers. In this work, a multifunctional nanofibrous cathode catalyst that integrates N-rich carbon shells embedded with molybdenum carbide nanoparticles and multiwalled carbon nanotube cores was designed and prepared. The N-rich carbon shell could strengthen the absorption capacity of CO2 and Li2CO3. The molybdenum carbide nanoparticles would improve the catalytic activity of both CO2 reduction and evolution reactions. The carbon nanotube cores would provide an efficient network for electron transportation. The synergistic effect of the cathode catalysts enhances the electrochemical performance of Li-CO2 batteries. A high cycling stability of more than 150 cycles at a current density of 250 mA g-1 with a cutoff capacity of 1000 mAh g-1 and a charge/discharge overpotential of less than 1.5 V is achieved. This work provides a feasible strategy for the design of a high-performance cathode catalyst for lithium-air batteries.

Enhancing electrochemical nitrogen fixation by mimicking π back-donation on laser-tuned Lewis acid sites in noble-metal-molybdenum carbide

Conventional electrocatalysts underperform with reaction kinetics, nitrogen dissociation, and activated hydrogen recombination, demanding effective strategies for improving electrochemical nitrogen fixation. The challenge lies in the rational design of electron back-donating centers for nitrogen activation and hydrogen migration path optimization. This study proposes an effective laser-tuning strategy to construct noble-metal Lewis acid sites on molybdenum carbide (M-Mo2C, M = Ru, Rh, Pd, Ir), yielding a more active material system by mimicking π back-donation behavior. Laser-tuned Lewis acid sites can effectively break N≡N bonds, lower thermodynamic energy barrier of the rate-determining hydrogenation step (*NN → *N-NH), and optimize hydrogen migration pathway. The Rh-Mo2C shows superior NRR activity with NH3 yield of ∼26.3 µg h−1 cm−2cat. and Faradaic efficiency of ∼15.4%, which are 5.1- and 3.6-fold higher than those of Mo2C, respectively. This work demonstrates a unique and universal strategy for designing high-performance electrocatalysts by accurately manipulating electronic structure of active sites.

Highly-dispersed Ni, N-doped Mo2C nanoparticles prepared from organic-derived polyoxomolybdates for efficient electrocatalytic hydrogen evolution

Molybdenum carbide is regarded as a noble metal-free and highly efficient electrocatalyst for hydrogen evolution reaction (HER) owing to its appropriate intermediate binding energy and Pt-like d orbital structure. It's an advanced method doping Ni, Zn, N, P and other atoms to further enhance the electrocatalytic performance of Mo2C, but the content of general doping elements is uncontrollable and cannot be accurately measured. In this work, we employ a unilateral Tris-functionalized Anderson polyoxomolybdate [H3NiMo6O21{(CH2O)3CNH3}]3- as a precursor for the first time to prepare Mo2C nanoparticles. The POMs were mixed with chitosan (CS) in aqueous solution and carbonized at high temperature to abtain highly dispersed N, Ni-doped Mo2C nanoparticles. The final electrocatalyst shows enhanced HER performance and good electrochemical stability. This article offers a feasible preparation of doped catalytic materials and extends the application of polyoxometalates.

Catalysts Based on Molybdenum Carbide Modified with Nickel and Alumina in Hydrogenation of Hydrocarbons and Hydrodesulfurization

Catalysts Based on Molybdenum Carbide Modified with Nickel and Alumina in Hydrogenation of Hydrocarbons and Hydrodesulfurization

Synthesis and in situ sulfidation of molybdenum carbide MXene using fluorine-free etchant for electrocatalytic hydrogen evolution reactions

Synthesizing MXenes from Mn+1AXn (MAX) phases using hazardous hydrogen fluoride is a common and effective method. However, fluorine termination on the basal planes and edges of the resulting MXenes is undesirable for the electrocatalytic hydrogen evolution reaction (HER), while oxygen (O), hydroxyl (OH), and sulfur (S) termination favors this reaction. Herein, we unveil a simple fluorine-free exfoliation and two-step vulcanization method for synthesizing molybdenum sulfide-modified molybdenum carbide (MoS2/Mo2CTx MXene, T = OH, O, S) for the HER in alkaline medium. Microwave-assisted hydrothermal treatment of the MAX phase (Mo3AlC2) with sodium hydroxide-sodium sulfide as an etching solution and thioacetamide as a source of sulfide ions enabled the selective dissolution of the aluminum (Al) layer and sulfidation of the surface Mo atoms to form amorphous MoS2. Thus, the vulcanization of Mo2CTx MXene resulted in the formation of MoS2/Mo2CTx MXene. The MoS2 formed on the surface of Mo2CTx provided enhanced stability by preventing oxidation. MoS2/Mo2CTx exhibited enhanced electrocatalytic activity toward the HER, mainly due to the O, OH, and amorphous MoS2 functionalities. The MoS2 sites on the surface exhibited an overpotential of 110 ± 7 mV at a current density of 10 mA cm−2 as a result of enhanced charge transfer and mass transfer. Thus, the sulfidation method demonstrated herein is capable of producing amorphous MoS2 structures on Mo2CTx MXene, which could be applied for the surface modification of other molybdenum-based nanomaterials or electrocatalysts to improve stability and enhance electrocatalytic activity.

Tailored architecture of molybdenum carbide/iron oxide micro flowers with graphitic carbon nitride: An electrochemical platform for nano-level detection of organophosphate pesticide in food samples

Herein we report the ternary hybrid nanocomposite of iron oxide @ molybdenum carbide micro flowers decorated graphitic-carbon nitride (Fe3O4@MoC MFs/g-CN), as a catalyst for the detection of organophosphorus pesticide, parathion (PAT), for the first time. The growth of hierarchical nanostructure from the core level will facilitate easy diffusion of analyte and interact more effectively with the reactive catalytic sites. Thus, Fe3O4 NFs architecture was hydrothermally grown over MoC flakes from the core level, which further hybridized with g-CN to ensure electrical conductivity and mechanical stability. Experimental results demonstrate that Fe3O4@MoC MFs/g-CN/GCE has superior catalytic efficacy for PAT reduction. At optimum conditions, the proposed sensor exhibits a low detection limit (7.8 nM), high sensitivity, and wide linear range (0.5–600 µM) toward PAT detection. The satisfactory test results of the food samples indicate that the Fe3O4@MoC MFs/g-CN/GCE sensor can be used as an excellent candidate for real-time PAT detection.

Deposition of molybdenum carbide thin films by dense plasma focus device

This work was motivated by the promising physiochemical properties and catalytic activity of molybdenum carbide. Thin films of molybdenum carbide were deposited on the mono-crystalline cubic Si (400) substrate by utilizing a 3.6 kJ dense plasma focus device (Mather-type) with multiple shots. The structure of the films was examined by X-ray diffraction (XRD). XRD results indicated the absence of crystalline film for 5 focus shots, while for increased numbers of focus shots, the emergence of Mo-C peaks in the orientations (120), (014) and (232) confirmed the formation of orthorhombic β-Mo2C polycrystalline films. Moreover, a small variation in the crystallite size was observed by increasing the number of focus shots. The presence of molybdenum and carbon was confirmed by energy-dispersive X-ray (EDX) analysis. Surface morphology was studied under scanning electron microscope (SEM). SEM micrographs revealed non-uniform films with some surface defects such as cracks and craters of micron size, and rough surface. Revealed by the ellipsometry technique, the film thickness increased by increasing the number of focus shots. The electric conductivity, measured by the four-point probe technique, was the highest for 10 focus shots. However, the films have some structural defects, low conductivity and impurities like silicon and silicon carbide, but it was the first ever successful attempt to deposit molybdenum-carbide (Mo2C) thin films using the dense plasma focus device.

Construction of frustrated Lewis pairs at N and Mo2C double sites boosts efficient electrocatalysts for Li-S batteries

The polysulfide shuttle effect and uncontrollable Li-dendrite growth on Li anode are the major reasons limiting the commercial development of Li-S batteries. Transition metal compounds on the carbon vector on the transition of polysulfides have been widely reported. However, there are few reports on the principle of simultaneous transformation and the effect of double active site spacing. Herein, we are based on the mechanism of the anchoring effect of doped elements on the carbon vector. Molybdenum carbide nanoparticles are mounted onto N-doped carbon nanosheets and coated on commercial separators (Mo2C-NCNS) for modification to satisfy the synchronization of S cathode and Li anode. The uniformly dispersed N element promotes the dispersion, homogenization and micro size regulation of Mo2C nanoparticles by anchoring Mo atoms. At the same time, the Mo2C site adjacent to N forms a spatially frustrated Lewis pairs with it. The reasonable spacing between them promotes the uniform deposition of lithium ions, the rapid transformation of polysulfides and the synchronous synergy between them. Characterization by XPS showed that using carbon as a bridge site further enhanced the strong metal-vector interaction between C3N4 and Mo2C, so as to improve the reaction kinetics. Thus, it has an initial specific capacity of 1186 mAh g−1 at 1C, and after 1000 cycles, 400 mAh g−1 remained, with a decay rate of only 0.06% per cycle. At a current density of 1 mA/cm2, the symmetric cell with Mo2C-NCNS modified separator exhibits steady cyclability over 1500 h, with a small overpotential of 76 mV.

Upgrading of benzofuran to hydrocarbons by hydrodeoxygenation over nickel–molybdenum carbide catalysts supported inside multi-wall carbon nanotubes

This work proposed a controllable synthesis of Ni-Mo catalyst supported inside multi-wall carbon nanotubes (CNTs). The results indicate that Ni improved the β-Mo2C formation and markedly promoted the benzofuran (BF) hydrogenation and hydrodeoxygenation activity of the catalysts. The synergistic interaction between Ni and Mo reached the maximum at a Ni/Mo molar ratio of 0.3, which could be favored by the proximity between the Ni and β-Mo2C particles inside the CNTs reaching a 99.5% of BF conversion to hydrogenated and deoxygenated products as 2,3-dihydrobenzofuran, octahydrobenzofuran, and ethylcyclohexane; in contrast, BF conversion on unsupported Ni-Mo2C-0.3 was only 0.7%. Deoxygenated products are favored under different conditions, such as the time, and mainly with the temperature achieving 93.8% of yield toward deoxygenated products with 100% of BF conversion at 320 °C. However, the catalyst activity is lost through reuse cycles, likely due to the deposition of high molecular weight compounds (coke) on the catalyst surface.

Coupling ceria with dual-phased molybdenum carbides for efficient and stable hydrogen evolution electrocatalysis at large-current-density in freshwater and seawater

In this study, we report a novel self-supported electrode consisting of ceria/molybdenum carbides composite microrods with adjustable crystalline phases and abundant heterostructures on carbon cloth (CeO2/MoxC/CC). The optimized CeO2/α-MoC/β-Mo2C MRs/CC electrode exhibits very low overpotentials of 22 and 29 mV at 10 mA cm−2 for hydrogen evolution reaction (HER) in alkaline freshwater and seawater, outperforming most of the reported molybdenum carbide-based electrocatalysts. Meanwhile, it could maintain long-term stability for over 100 h at a large current density of 1000 mA·cm−2. Theoretical study and experimental results reveal that the synergistic effects of α-MoC, β-Mo2C, and oxygen vacancy-rich CeO2 can effectively promote the dissociation of water molecules, tailor the d‐band electronic structure of MoxC with a thermoneutral hydrogen adsorption free energy, increase the numbers of active sites, and facilitate the vectorial electron transfer, thus achieving an enhanced HER performance. The CeO2/α-MoC/β-Mo2C MRs/CC electrode displays a potential large-scale application in hydrogen generation.

A Highly Stable Bimetallic Transition Metal Phosphide Catalyst for Selective Dehydrogenation of n‐Heptane

AbstractIn this work, we demonstrate RuP2‐MoP catalysts being highly stable and selective for the dehydrogenation of long‐chain alkanes like n‐heptane. Compared to a monometallic MoP catalyst, the bimetallic system substantially increases n‐heptene selectivity from 40 % towards 80 %. This effect can be traced back to a reduced surface acidity, suppressing the competitive hydrogenolysis reaction. The active transition metal phosphide is, furthermore, compared to its phosphorous‐free RuMo‐counterpart. As revealed by STEM‐EDX investigations, incorporation of phosphorous results in the formation of separated metal phosphide clusters instead of an intermetallic alloy. In the dehydrogenation of n‐heptane the phosphorous modification clearly avoids catalyst deactivation and maintains the high n‐heptene selectivity. X‐ray diffraction, elemental analysis and STEM‐EDX further reveal that catalyst coking and the formation of less active molybdenum carbide phases is effectively suppressed by phosphorous incorporation, making RuP2‐MoP an attractive system for selective dehydrogenation of long‐chain alkanes.

N, P-codoped molybdenum carbide nanoparticles loaded into N, P-codoped graphene for the enhanced electrocatalytic hydrogen evolution

Based on the ever-growing interest of heteroatoms (e.g., P, N, S, transition metals) doping into molybdenum carbide and graphene for electrochemical reactions, herein, a ternary phosphomolybdic acid-polyethyleneimine/graphene oxide nanocomposite as a suitable precursor was developed to not only uniformly hybridize molybdenum and carbon source to perform the controllable in situ growth of well-defined molybdenum carbide nanostructure on graphene by annealing, but also synchronously dope N and P atoms into molybdenum carbide crystal lattice and graphene. The as-prepared hybrid showed remarkable electrocatalytic activity and high stability for hydrogen evolution reaction in basic media, due to the following favorable features, i.e. a large accessible active sites afforded by the ultrafine molybdenum carbide, the heteroatoms doped, the regulated electronic structure, the balanced thermodynamics between hydrogen adsorption and desorption, the accelerated charge/mass transfer ability by the ultrathin and defective carbon layer, and the protection of molybdenum carbide by carbon layer. As a result, it only needed a small overpotential of 47 mV to drive 10 mA cm−2 and a low onset potential of 10 mV, as well as a small Tafel slope of 56.8 mV·dec−1, thus suggesting its promising potential for hydrogen evolution electrocatalyst.

Nickel-Molybdenum Carbide/Nitrogen-Doped Carbon Mott-Schottky Nanoarray for Water Spitting

Electrochemical water splitting, composed of two half reactions: the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER), is under intensive research to the development of H2 fuels to replace fossil fuels. Since both reactions are sluggish, catalysts are usually required to boost them. The state-of-the-art catalysts for both reactions are based on noble metals, such as Pt-based catalysts for HER and Ir or Ru-based catalysts for OER. Unfortunately, the high price and scarcity of these noble metals suppress the widespread application of water splitting. Hence, it is imperative to develop active, durable, low-cost and earth-abundant non-noble-metal electrocatalysts.[1]Among them, molybdenum carbide (Mo2C) has garnered tremendous attention as HER/OER catalysts owing to its Pt-like electronic structure and wide-pH-range catalytic performance. [2] Unfortunately, the catalytic activity of Mo2C towards HER or OER is still inferior to most advanced catalysts. One effective strategy to enhance electrocatalytic performance involves coupling and doping of Mo2C with late transition metals, e.g., Fe, Co, and Ni, which modifies electronic structure and adds active sites, metal-Mo2C interfaces. Unfortunately, similar to Mo2C, metal nanoparticles also tend to aggregate during preparation and operation. A semiconductive carbon catalyst support alleviating aggregation is usually the solution by not only conformally dispersing nanocatalysts but also providing heteroatom dopants and forming metal-semiconductor Mott-Schottky interface for further enhancing catalytic activity.[3] Besides the selection of catalysts with optimized structure and composition at the material level, the structure of electrodes derived from assembled catalysts at the device level also have a crucial influence on the water electrolyzer. Compared with powdery electrocatalysts with relatively large overpotential and easier peeling off from the electrode, self-supported hierarchical nanoarrayed electrodes are more promising for water electrolyzer because these electrodes facilitate transportation of charges and matter and thus reaction kinetics during HER/OER due to binder-free feature, catalysts-substrate seamless contact and highly exposed surface area.[4]We develop here the making of nickel-molybdenum carbide heterostructures embedded in large-area (100 cm2) hierarchically assembled nitrogen-enriched carbon, forming Mott-Schottky array on nickel foam (Ni-Mo2C/NC@NF).[5] The Ni-Mo2C/NC array is directly applied as the bifunctional catalyst with high activity and durability in alkaline electrolyte. Particularly, an extremely low overpotential of 40 mV is needed to generate hydrogen. Density functional theory calculation revealed that the formation of Ni-Mo2C Mott/NC Schottky interfaces enables favorable electronic structures for electrocatalytic water splitting. Besides, 3D hierarchical structure provides exposed active sites, facilitates mass and charge transfer, graphitic shells enhance stability. A symmetric electrolyzer using Ni-Mo2C/NC@NF generates 10 mA cm-2 at 1.59 V and operates steadily for 150 h, which even outperforms the noble metal couple, Pt/C//RuO2 for water electrolysis. The scalability, activity and durability renders Ni-Mo2C/NC@NF potential industrial application. Reference1. M. Walter, N. Lewis et al, Chem. Rev. 2010, 110, 11, 6446.2. M. Miao, B. Y. Xia, X. Wang et al, Chem. Eur. J. 2017, 23, 10947.3. F. Yu, Y. Li et al Nanoscale, 2018,10, 6080.4. H. Sun, F. Cheng., J. Chen et al. Adv. Mater. 2020, 32, 1806326.5. Z. Xu, S. Jin, M. H. Seo, X. Wang, Appl. Catal. B: Environ. 2021, 292, 120168

Mo2C as Pre-Catalyst for the C-H Allylic Oxygenation of Alkenes and Terpenoids in the Presence of H2O2

In this study, commercially available molybdenum carbide (Mo2C) was used, in the presence of H2O2, as an efficient pre-catalyst for the selective C-H allylic oxygenation of several unsaturated molecules into the corresponding allylic alcohols. Under these basic conditions, an air-stable, molybdenum-based polyoxometalate cluster (Mo-POM) was formed in situ, leading to the generation of singlet oxygen (1O2), which is responsible for the oxygenation reactions. X-ray diffraction, SEM/EDX and HRMS analyses support the formation mainly of the Mo6O192− cluster. Following the proposed procedure, a series of cycloalkenes, styrenes, terpenoids and methyl oleate were successfully transformed into hydroperoxides. After subsequent reduction, the corresponding allylic alcohols were produced with good yields and in lab-scale quantities. A mechanistic study excluded a hydrogen atom transfer pathway and supported the twix-selective oxygenation of cycloalkenes on the more sterically hindered side via the 1O2 generation.

Molybdenum carbide phase effects in heterogeneous catalytic ammonia synthesis

The design of an efficient catalyst utilizing non-precious metals is a top priority in ammonia synthesis, and Mo is found to be inferior in ammonia synthesis due to strong nitrogen adsorption. The carburization of Mo species might be an ideal strategy for optimizing nitrogen adsorption energy and ammonia synthesis activity. In this work, we prepare two molybdenum carbides with different crystal structures (α-MoC and β-Mo2C). The result shows that there is a larger number of Mo-C bonds and lower Mo/C ratio in α-MoC, leading to the strong adsorption of hydrogen and ammonia species on α-MoC. In contrast, the desorption energies of hydrogen and ammonia are lower for β-Mo2C, and the spillover and migration of hydrogen species are boosted. The facile desorption of hydrogen and ammonia species also limits the accumulation of H adatoms and ammonia on the surface of β-Mo2C, releasing of active sites available for the subsequent activation of hydrogen and nitrogen as well as ammonia synthesis reaction. As a result, the ammonia synthesis activity of β-Mo2C catalyst is 2.5-fold higher than that of α-MoC, and a small negative value of NH3 reaction order also would be obtained for β-Mo2C. This work not only reports the effect of molybdenum carbide phases on the adsorption–desorption properties of reactants and catalytic activities for ammonia synthesis, but also opens a perspective for the design and development of efficient metal based heterogeneous catalysts by tuning the adsorption and desorption properties of the reactant gases. Keywords: Molybdenum Carbide; Phase effect; Adsorption–desorption property; Mo catalyst; Ammonia synthesis

Edge‐Enriched Mo2TiC2Tx/MoS2 Heterostructure with Coupling Interface for Selective NO2 Monitoring

AbstractEndowed with rich terminal groups, good electrical conductivity, and controllable structure, transition metal carbides/nitrides (MXenes) have attracted extensive attention for potential application in gas sensor, but long‐standing challenges of the MXenes (titanium carbide as the representative) are their limited selectivity and sensitivity. Herein, a high‐active double transition‐metal titanium molybdenum carbide (Mo2TiC2Tx) with superstrong surface adsorption (−3.12 eV) for NO2 gas molecule is proposed, and it is further coupled with molybdenum disulfide (MoS2) by interface modulation to construct an edge‐enriched heterostructure. Due to the synergistic effect of strong adsorption, rich adsorption sites, and coupling interface of Mo2TiC2Tx/MoS2 composite, the as‐fabricated Mo2TiC2Tx/MoS2 gas sensor exhibits an outstanding response toward NO2 with high selectivity against various interference gases, which is well supported by density functional theory calculations. Meanwhile, the sensor exhibits a sensitivity of 7.36% ppm−1, detection limit of 2.5 ppb, and reversibility at room temperature. A portable, wireless NO2 monitoring system is demonstrated for gas leakage searching and dangerous warning based on Mo2TiC2Tx/MoS2 gas sensor. This work facilitates the gas sensing application of MXenes, and provides an avenue for the development of wireless sensing system in environmental monitoring and safety assurance.

Photocatalytic Decomposition of an Azo Dye Using Transition-Metal-Doped Tungsten and Molybdenum Carbides.

The preparation, characterization, and photocatalytic application of tungsten or molybdenum carbides (Ni-WC, 1, Co-WC, 2, Ni-MoC, 3, Co-MoC, 4, NiCo-WC, 5, NiCo-MoC, 6, NiFe-WC, 7, and NiFe-MoC, 8) doped with transition metals (Fe, Co, and Ni) are reported. These transition-metal carbide (TMC) particles show that the submicrometer globular particles agglomerated to form larger particles, with smaller crystallites present on the surface of the large particles. These crystallite sizes range between 4 and 34 nm (as calculated from X-ray diffraction data) depending on the metal dopant and type of carbide. Oxidation of the metal carbides is evident from the two sets of photoelectron lines present in the X-ray photoelectron spectroscopy (XPS) of the W 4f area. The Mo 3d spectra reveal four sets of photoelectron lines associated with oxidized MoO2 and MoO3 as well as Mo2+ and Mo3+ associated with MoC1–x. The XPS of the dopant metals Ni, Co, and Fe also show partial oxidation. The photocatalytic decomposition of Congo red (an azo dye) is used as a model reaction to determine the photocatalytic activities of the transition-metal carbides, which is related to the TMCs’ optical band gap energies.

Bio-electrocatalytic degradation of tetracycline by stainless-steel mesh based molybdenum carbide electrode.

In order to treat antibiotic wastewater with high efficiency and low energy consumption, this study proposed the coupling of electrocatalytic degradation and biodegradation, and explored a new modified electrocatalytic material in the coupling system. The stainless-steel mesh based molybdenum carbide (SS-Mo2C) was prepared by a low-cost impregnation method and showed superior electrocatalytic degradation ability for tetracycline (TC) when used as the anode in the electrocatalytic system. The degradation rate of TC with SS-Mo2C anode was 17 times higher than that of stainless-steel (SS) anode, and TC removal efficiency was 77% higher than that of SS anode. The electrocatalytic system prior to the biological reactor was proven to be the optimal coupling method. The external coupling system achieved a significantly higher TC removal (87.0%) than that of the internal coupling system (65.3%) and SS-Mo2C showed an excellent repeatable and stable performance. The fewer and smaller molecular weight intermediates products were observed in bio-electrocatalytic system, especially in the external coupling system. Alpha diversity analysis further confirmed that bio-electrocatalytic system increased the diversity of the microbial community. The stainless-steel mesh based molybdenum carbide (SS-Mo2C), which was prepared by a simple and low-cost impregnation method, significantly improved the electrocatalytic activity of anode, thus contributing to tetracycline removal in the bio-electrocatalytic system, especially in the external coupling system.