High-Performance Electrocatalytic Conversion of N2 to NH3 Using 1T-MoS2 Anchored on Ti3C2 MXene under Ambient Conditions

Cu-Bi Bimetallic Sulfides Loaded on Two-Dimensional Ti3C2Tx MXene for Efficient Electrocatalytic Nitrogen Reduction under Ambient Conditions

In this paper, Ti3C2Tx MXene/Cu-Bi bimetallic sulfide (Ti3C2Tx/BiCuS2.5) composites were prepared by a simple in situ deposition method for electrocatalytic nitrogen reduction reaction (eNRR). Compared to Ti3C2Tx/Bi2S3 and Ti3C2Tx/CuS, the eNRR performance of Ti3C2Tx/BiCuS2.5 is significantly improved. The results show that Ti3C2Tx/BiCuS2.5 exhibits a NH3 yield of 62.57 μg h-1 mg-1cat. in 0.1 M Na2SO4 at -0.6 V vs reversible hydrogen electrode, and the Faradaic efficiency (FE) reaches 67.69%, which is better than that of Ti3C2Tx/CuS (NH3 yield: 52.26 μg h-1 mg-1cat., FE: 34.15%) and Ti3C2Tx/Bi2S3 (NH3 yield: 54.04 μg h-1 mg-1cat., FE: 37.38%). According to density functional theory calculations, the eNRR at the Ti3C2Tx/BiCuS2.5 surface is the alternating pathway. The 1H NMR experiment of 15N proves that the N of NH3 generated in the experiment originates from N2 passed during the experiment.

A bulit-in self-calibration ratiometric self-powered photoelectrochemical sensor for high-precision and sensitive detection of microcystin-RR

A novel high-precision aptasensor of microcystin-RR (MC-RR) is developed based on a ratiometric self-powered photoelectrochemical platform. In detail, the defective MoS2/Ti3C2 nanocomposite with good photoelectric activity was designed to serve as the photoanode of the sensor for enhancing the signal and improving the detection sensitivity. In order to effectively eliminate external interferences, the key point of this ratiometric device is the introduction of the spatial-resolved technique, which includes the detection section and the reference section, generating reference signals and response signals, respectively. Moreover, output power was used as the detection signal, instead of the traditional photocurrent or photovoltage. Further, potassium persulfate was introduced as electron acceptor, which was beneficial for improving the electron transport efficiency, hindering electron-hole recombination, and significantly promoting the performance of the sensor. Finally, aptamer was adopted as recognition element to capture MC-RR molecules. The prepared sensor had a linear range from 10-12 to 10-6 M, and the detection limit was 5.6 × 10-13 M (S/N = 3). It has good precision, selectivity, and sensitivity, which shows great prospects in the on-site accurate analysis of samples with high energy output in the self-powered sensing field.

Synthesis and Electrocatalytic Applications of Layer-Structured Metal Chalcogenides Composites

Featured with the attractive properties such as large surface area, unique atomic layer thickness, excellent electronic conductivity, and superior catalytic activity, layered metal chalcogenides (LMCs) have received considerable research attention in electrocatalytic applications. In this review, the approaches developed to synthesize LMCs-based electrocatalysts are summarized. Recent progress in LMCs-based composites for electrochemical energy conversion applications including oxygen reduction reaction, carbon dioxide reduction reaction, oxygen evolution reaction, hydrogen evolution reaction, overall water splitting, and nitrogen reduction reaction is reviewed, and the potential opportunities and practical obstacles for the development of LMCs-based composites as high-performing active substances for electrocatalytic applications are also discussed. This review may provide an inspiring guidance for developing high-performance LMCs for electrochemical energy conversion applications.

Enhancing Nitrogen Reduction Reaction through Formation of 2D/2D Hybrid Heterostructures of MoS2@rGO

Given the challenging task of constructing an efficient nitrogen reduction reaction (NRR) electrocatalyst with enhanced ambient condition performance, properties such as high specific surface area, fast electron transfer, and design of the catalyst surface constitute a group of key factors to be taken into consideration to guarantee outstanding catalytic performance and durability. Thereof, this work investigates the contribution of the 2D/2D heterojunction interface between MoS2 and reduced graphene oxide (rGO) on the electrocatalytic synthesis of NH3 in an alkaline media. The results revealed remarkable NRR performance on the MoS2@rGO 2D/2D hybrid electrocatalyst, characterized by a high NRR sensitivity (faradaic efficiency) of 34.7% with an NH3 yield rate of 3.98 ± 0.19 mg h-1 cm-2 at an overpotential of -0.3 V vs RHE in 0.1 M KOH solution. The hybrid electrocatalysts also exhibited selectivity for NH3 synthesis against the production of the hydrazine (N2H4) byproduct, hindrance of the competitive hydrogen evolution reaction (HER), and good durability over an operation period of 8 h. In hindsight, the study presented a low-cost and highly efficient catalyst design for achieving enhanced ammonia synthesis in alkaline media via the formation of defect-rich ultrathin MoS2@rGO nanostructures, consisting predominantly of an HER-hindering hexagonal 2H-MoS2 phase.

Nitrogen activation and surface charge regulation for enhancing the visible-light-driven N2 fixation over MoS2/UiO-66(SH)2

A series of dehydrated MoS2/UiO-66(SH)2 (MS/UiS) composites has been prepared as photocatalysts for N2 fixation. Typically, 10% MS/UiS exhibits the best performance with an NH4+ yield rate of 54.08 μmol∙g-1∙h-1. 15N isotope test confirmed that the sample 10% MS/UiS was most effective for reducing N2 to ammonia. Such enhanced activity was due to the presence of abundant unsaturated Zr and Mo sites which would synergistically promote the adsorption and activation of N2. The photogenerated electrons would transfer to the unsaturated Zr-O clusters while part of photogenerated electrons at the interface migrate to MS via MoVI-O interactions between MS and UiS. These two electron transfer pathways effectively promote the separation of photogenerated carriers. The activated N2 is reduced to ammonia by the synergistic effect of protonated hydrogen and photogenerated electrons. Finally, a possible N2 fixation mechanism is proposed which emphasizes the significant roles of nitrogen activation and interface interaction in composites photocatalyst for improving photocatalytic performance.

A general strategy to stabilize 1T-MoS2 using MXene heterostructures and unlock its hydrogen evolution reaction capabilities

The two-dimensional (2D) metallic phase of MoS2, 1T-MoS2, has extraordinary electrical conductivity in contrast to the common 2D semiconducting phase, 2H-MoS2. However, the thermodynamic instabilities of 1T-MoS2 hinder its application. In this work, we investigate the possibilities of stabilizing 1T-MoS2 through heterostructure design using first-principles calculations. We found that MXene-based heterostructures could hamper phase transitions from 1T-MoS2 to 2H-MoS2 enabled by a larger phase transition kinetic energy barrier. Based on this finding, we propose a general and effective strategy for stabilizing 1T-MoS2, that is, building heterostructures using 1T-MoS2 and oxygen-functionalized MXenes. Besides, we have also observed that due to the occurrence of electron transfer in the heterostructure, 1T-MoS2 in the heterostructure exhibits improved hydrogen adsorption free energy and more active sites compared to the monolayer 1T-MoS2. These findings provide guidance for promoting and developing 1T-MoS2 for practical applications. In addition, the proposed heterostructure design strategy could inspire the study of phase transition behaviors and electrochemical properties of materials using interfaces.

Recent advances in the synthesis and electrocatalytic application of MXene materials

MXenes are a class of two-dimensional materials with a graphene-like structure, which have excellent optical, biological, thermodynamic, electrical and magnetic properties. Due to the diversity resulting from the combination of transition metals and C/N, the MXene family has expanded to more than 30 members and been applied in many fields with broad application prospects. Among their applications, electrocatalytic applications have achieved many breakthroughs. Therefore, in this review, we summarize the reports on the preparation of MXenes and their application in electrocatalysis published in the last five years and describe the two main methods for the preparation of MXenes, i.e., bottom-up and top to bottom synthesis. Different methods may change the structure or surface termination of MXenes, and accordingly affect their electrocatalytic performance. Furthermore, we highlight the application of MXenes in the electrocatalytic hydrogen evolution reaction (HER), oxygen evolution reaction (OER), oxygen reduction reaction (ORR), carbon dioxide reduction reaction (CO₂RR), nitrogen reduction reaction (NRR), and multi-functionalization. It can be concluded that the electrocatalytic properties of MXenes can be modified by changing the type of functional groups or doping. Also, MXenes can be compounded with other materials to produce electronic coupling and improve the catalytic activity and stability of the resulting composites. In addition, Mo₂C and Ti₃C₂ are two types of MXene materials that have been widely studied in the field of electrocatalysis. At present, research on the synthesis of MXenes is focused on carbides, whereas research on nitrides is rare, and there are no synthesis methods meeting the requirements of green, safety, high efficiency and industrialization simultaneously. Therefore, it is very important to explore environmentally friendly industrial production routes and devote more research efforts to the synthesis of MXene nitrides.

High efficient electrochemical biosensor based on exonuclease-Ⅲ-assisted dual-recycling amplification for ultrasensitive detection of kanamycin

A target-triggered and exonuclease-Ⅲ-assisted strand displacement, dual-recycling amplification reaction-based biosensor was developed for the rapid, ultrasensitive and accurate detection of kanamycin. The robust profiling platform was constructed using high conductive MXene/VS₂ for the electrode surface modification and high active CeCu₂O₄ bimetallic nanoparticles as nanozyme to improve the sensitivity as well as the catalytic signal amplification of the biosensor. Using the dual supplementary recycling of primer DNA and hairpin DNA, the electrochemical platform could accurately detect kanamycin to as low as 0.6 pM from the range of 5 pM to 5 μM. By profiling five other antibiotics, this platform exhibited high specificity, enhanced repeatability and reproducibility. Based on these intrinsic characteristics and by utilizing milk and water samples, the as-designed biosensor offers a remarkable strategy for antibiotic detection due to its favorable analytical accuracy and reliability, thereby demonstrating potential application prospect for various antibiotic biosensing in food quality control, water contamination detection and biological safety analysis.

A Rising 2D Star: Novel MBenes with Excellent Performance in Energy Conversion and Storage

As a flourishing member of the two-dimensional (2D) nanomaterial family, MXenes have shown great potential in various research areas. In recent years, the continued growth of interest in MXene derivatives, 2D transition metal borides (MBenes), has contributed to the emergence of this 2D material as a latecomer. Due to the excellent electrical conductivity, mechanical properties and electrical properties, thus MBenes attract more researchers' interest. Extensive experimental and theoretical studies have shown that they have exciting energy conversion and electrochemical storage potential. However, a comprehensive and systematic review of MBenes applications has not been available so far. For this reason, we present a comprehensive summary of recent advances in MBenes research. We started by summarizing the latest fabrication routes and excellent properties of MBenes. The focus will then turn to their exciting potential for energy storage and conversion. Finally, a brief summary of the challenges and opportunities for MBenes in future practical applications is presented.

1T-MoS2 Nanosheets Coupled with CoS2 Nanoparticles: Electronic Modulation for Efficient Electrochemical Nitrogen Fixation

Electrocatalytic nitrogen reduction reaction (eNRR), a substitute process for the conventional Haber-Bosch for NH₃ production, has drawn tremendous attention due to its merits in mild conditions, abundant reactant sources, low energy consumption, and environmental protection. However, electrocatalysts for eNRR are still subjected to low catalytic activity and selectivity. Herein, we constructed a CoS₂/1T-MoS₂ heterostructure with CoS₂ nanoparticles uniformly loaded on 1T-MoS₂ nanosheets and applied it as an eNRR electrocatalyst for the first time. Theoretical calculation suggests that electron transfer from CoS₂ to 1T-MoS₂ across their contact interface optimizes the local electronic structure of 1T-MoS₂, where the electron-depletion region near CoS₂ is in favor of accepting lone-pair electrons from N₂ to enable N₂ absorption, and the electron-accumulation region near 1T-MoS₂ is conductive to break inert N≡N triple bonds. Unlike pure 1T-MoS₂, the potential-determining step (PDS) demonstrates a significantly lower energy barrier. In addition, the weak interaction between CoS₂/1T-MoS₂ and hydrogen discourages competitive hydrogen evolution reaction. As a result, CoS₂/1T-MoS₂ exhibited noticeably improved eNRR activity and selectivity, with an NH₃ yield of 59.3 μg h^-1 mg^-1 and a high Faradaic efficiency of 26.6%.

Eu doped Ti3C2 quantum dots to form a ratiometric fluorescence platform for visual and quantitative point-of-care testing of tetracycline derivatives

Antibiotic residues have become a public health issues, the fast detection of tetracycline (Tc) in the environment is urgently required. In this work, Ti₃C₂ quantum dots (Ti₃C₂ QDs) and Europium ions jointly constructed a ratiometric fluorescence (FL) platform for the detection of Tc, based on synergistic impact of the Foster Resonance Energy Transfer (FRET) from Ti₃C₂ QDs to Eu³⁺ ions and the Antenna Effect (AE) between Tc and Eu³⁺ ions. And we proposed a ratiometric FL platform for detecting Tc with good linear response range (100-1000 uM) and low detection limit (48.79 nM). Meanwhile, we applied this platform to detect a serious of β-diketone ligands of Eu³⁺ ions, demonstrating the platform's versatility for this category of chemical. Furthermore, based on the color changes of QDs@Eu³⁺ from blue to red at 365 nm ultraviolet light, an intelligent detection smart device was built for the visual semi-quantitative detection of Tc in actual samples. We proved the applicability of the device in complicated samples and the potential for rapid, sensitive, intuitive and point-of-care detection in the field of environment, food, pharmaceutical and agriculture.

Sensitive electrochemical immunosensor for CYFRA21-1 detection based on AuNPs@MoS2@Ti3C2Tx composites

Cytokeratin fragment antigen 21-1 (CYFRA21-1) is a sensitive marker for detecting non-small cell lung cancer (NSCLC). Ti₃C₂T_x modified by gold nanoparticles (AuNPs) and molybdenum disulfide (MoS₂) were synthesized for the first time to obtain the AuNPs@MoS₂@Ti₃C₂T_x composites, which have large specific surface area and good electrocatalytic properties. A novel electrochemical immunoassay for sensitive detection of CYFRA21-1 was developed by loading a large quantity of secondary antibodies (Ab₂) and toluidine blue (TB) on the surface of the material as signal probe, and Nafion-AuNPs mixture as electrode material. When the electrochemical response value of CYFRA21-1 increased linearly within the concentration range of 0.5 pg mL^-1-50 ng mL^-1, the detection limit can reach as low as 0.03 pg mL^-1. In addition, the experimental results showed that the biosensor had the potential to rapidly detect CYFRA21-1 in the complex samples such as patient serum, and had a broad application prospect in the early diagnosis and monitoring of NSCLC.

2D WO3-x Nanosheet with Rich Oxygen Vacancies for Efficient Visible-Light-Driven Photocatalytic Nitrogen Fixation

Oxygen vacancy modulation holds great promise for enhancing the photocatalytic activity for efficient nitrogen fixation under mild conditions. In this work, the two-dimensional WO_3-x nanosheets with rich oxygen vacancies were prepared using solvothermal synthesis. The WO_3-x nanosheets (rich oxygen vacancies) display nice photocatalytic activity for N₂ reduction to ammonia with a high yield rate of 82.41 μmol·g_cat^-1·h^-1 under irradiation of visible light (420 nm), which is 3.59 times higher than that of the WO_3-x nanoparticles (poor oxygen vacancies). Electron spin resonance (ESR), N₂ adsorption-desorption isotherms, and transient photocurrent responses in the N₂ or Ar atmosphere experiments proved that the rich oxygen vacancies, which are induced by the nanosheet structure, could serve as active sites for the chemisorption of N₂ and facilitate the electron transfer from unsaturated sites to activated N₂. Moreover, based on the analysis of banding energy, the oxygen vacancies not only boosted the ability of visible light harvesting but also elevated the defect energy level to the Fermi level, further inhibiting the defect relaxation effect. The findings offer an insight into the design of the efficient photocatalysts via structure engineering and defect engineering for photocatalytic N₂ fixation.

Light induced ammonia synthesis by crystalline polyoxometalate-based hybrid frameworks coupled with the Sv-1T MoS2 cocatalyst

A series of crystalline polyoxometalate-based hybrid frameworks coupled with rich sulfur vacancy 1T MoS2 through the hydrothermal growth strategy are presented towards light induced ammonia synthesis.

Activation of MoS2 Monolayer Electrocatalysts via Reduction and Phase Control in Molten Sodium for Selective Hydrogenation of Nitrogen to Ammonia

Electrochemical nitrogen fixation under ambient conditions is promising for sustainable ammonia production but is hampered by high reaction barrier and strong competition from hydrogen evolution, leading to low specificity and faradaic efficiency with existing catalysts. Here we describe the activation of MoS₂ in molten sodium that leads to simultaneous formation of a sulfur vacancy-rich heterostructured 1T/2H-MoS_x monolayer via reduction and phase transformation. The resultant catalyst exhibits intrinsic activities for electrocatalytic N₂-to-NH₃ conversion, delivering a faradaic efficiency of 20.5% and an average NH₃ rate of 93.2 μg h⁻¹ mg_cat⁻¹. The interfacial heterojunctions with sulfur vacancies function synergistically to increase electron localization for locking up nitrogen and suppressing proton recombination. The 1T phase facilitates H–OH dissociation, with S serving as H-shuttling sites and to stabilize . The subsequently couple with nearby N₂ and NH_x intermediates bound at Mo sites, thus greatly promoting the activity of the catalyst. First-principles calculations revealed that the heterojunction with sulfur vacancies effectively lowered the energy barrier in the potential-determining step for nitrogen reduction, and, in combination with operando spectroscopic analysis, validated the associative electrochemical nitrogen reduction pathway. This work provides new insights on manipulating chalcogenide vacancies and phase junctions for preparing monolayered MoS₂ with unique catalytic properties.

We describe the activation of MoS₂ in molten sodium that leads to the simultaneous formation of a sulfur vacancy-rich heterostructured 1T/2H-MoS_x monolayer electrocatalyst via reduction and phase transformation.

MoS2 quantum dot-decorated MXene nanosheets as efficient hydrogen evolution electrocatalysts

2D MXene nanosheets are regarded as promising cathode catalysts towards the hydrogen evolution reaction (HER), while their overall electrocatalytic ability still needs to be optimized before the practical application. In...

Highly Efficient Electrocatalytic N2 Reduction to Ammonia over Metallic 1T Phase of MoS2 Enabled by Active Sites Separation Mechanism

The 1T phase of MoS2 has been widely reported to be highly active toward the hydrogen evolution reaction (HER), which is expected to restrict the competitive nitrogen reduction reaction (NRR). However, in this work, a prototype of active sites separation over 1T-MoS2 is proposed by DFT calculations that the Mo-edge and S atoms on the basal plane exhibit different catalytic NRR and HER selectivity, and a new role-playing synergistic mechanism is also well enabled for the multistep NRR, which is further experimentally confirmed. More importantly, a self-sacrificial strategy using g-C3 N4 as templates is proposed to synthesize 1T-MoS2 with an ultrahigh 1T content (75.44%, named as CNMS, representing the composition elements of C, N, Mo, and S), which yields excellent NRR performances with an ammonia formation rate of 71.07 µg h-1 mg-1 cat. at -0.5 V versus RHE and a Faradic efficiency of 21.01%. This work provides a promising new orientation of synchronizing the selectivity and activity for the multistep catalytic reactions.

Hierarchical CoS2/MoS2 flower-like heterostructured arrays derived from polyoxometalates for efficient electrocatalytic nitrogen reduction under ambient conditions

Electrochemical nitrogen reduction reaction (NRR) has been identified as a prospective alternative for sustainable ammonia production. Developing cost-effective and highly efficient electrocatalysts is critical for NRR under ambient conditions. Herein, the hierarchical cobalt-molybdenum bimetallic sulfide (CoS₂/MoS₂) flower-like heterostructure assembled from well-aligned nanosheets has been easily fabricated through a one-step strategy. The efficient synergy between different components and the formation of heterostructure in CoS₂/MoS₂ nanosheets with abundant active sites makes the non-noble metal catalyst CoS₂/MoS₂ highly effective in NRR, with a high NH₃ yield rate (38.61 μg h^-1 mg_cat.^-1), Faradaic efficiency (34.66%), high selectivity (no formation of hydrazine) and excellent long-term stability in 1.0 mol L^-1 K₂SO₄ electrolyte (pH = 3.5) at -0.25 V versus the reversible hydrogen electrode (vs. RHE) under ambient conditions, exceeding much recently reported cobalt- and molybdenum-based materials, even catch up with some noble-metal-based catalyst. Density functional theory (DFT) calculation indicates that the formation of N₂H* species on CoS₂(200)/MoS₂(002) is the rate-determining step via both the alternating and distal pathways with the maximum ΔG values (1.35 eV). These results open up opportunities for the development of efficient non-precious bimetal-based catalysts for NRR.

Fe Foam-Supported FeS2-MoS2 Electrocatalyst for N2 Reduction under Ambient Conditions

Highly efficient catalysts with enough selectivity and stability are essential for electrochemical nitrogen reduction reaction (e-NRR) that has been considered as a green and sustainable route for synthesis of NH₃. In this work, a series of three-dimensional (3D) porous iron foam (abbreviated as IF) self-supported FeS₂-MoS₂ bimetallic hybrid materials, denoted as FeS₂-MoS₂@IF_x, x = 100, 200, 300, and 400, were designed and synthesized and then directly used as the electrode for the NRR. Interestingly, the IF serving as a slow-releasing iron source together with polyoxomolybdates (NH₄)₆Mo₇O₂₄·4H₂O as a Mo source were sulfurized in the presence of thiourea to form self-supported FeS₂-MoS₂ on IF (abbreviated as FeS₂-MoS₂@IF₂₀₀) as an efficient electrocatalyst. Further material characterizations of FeS₂-MoS₂@IF₂₀₀ show that flower cluster-like FeS₂-MoS₂ grows on the 3D skeleton of IF, consisting of interconnected and staggered nanosheets with mesoporous structures. The unique 3D porous structure of FeS₂-MoS₂@IF together with synergy and interface interactions of bimetallic sulfides would make FeS₂-MoS₂@IF possess favorable electron transfer tunnels and expose abundant intrinsic active sites in the e-NRR. It is confirmed that synthesized FeS₂-MoS₂@IF₂₀₀ shows a remarkable NH₃ production rate of 7.1 ×10^-10 mol s^-1 cm^-2 at -0.5 V versus the reversible hydrogen electrode (vs RHE) and an optimal faradaic efficiency of 4.6% at -0.3 V (vs RHE) with outstanding electrochemical and structural stability.

NiWO4 Microflowers on Multi-Walled Carbon Nanotubes for High-Performance NH3 Detection

NiWO4 microflowers with a large surface area up to 79.77 m2·g-1 are synthesized in situ via a facile coprecipitation method. The NiWO4 microflowers are further decorated with multi-walled carbon nanotubes (MWCNTs) and assembled to form composites for NH3 detection. The as-fabricated composite exhibits an excellent NH3 sensing response/recovery time (53 s/177 s) at a temperature of 460 °C, which is a 10-fold enhancement compared to that of pristine NiWO4. It also demonstrates a low detection limit of 50 ppm; the improved sensing performance is attributed to the porous structure of the material, the large specific surface area, and the p-n heterojunction formed between the MWNTs and NiWO4. The gas sensitivity of the sensor based on daisy-like NiWO4/MWCNTs shows that the sensor based on 10 mol % (MWN10) has the best gas sensitivity, with a sensitivity of 13.07 to 50 ppm NH3 at room temperature and a detection lower limit of 20 ppm. NH3, CO2, NO2, SO2, CO, and CH4 are used as typical target gases to construct the NiWO4/MWCNTs gas-sensitive material and study the research method combining density functional theory calculations and experiments. By calculating the morphology and structure of the gas-sensitive material NiWO4(110), the MWCNT load samples, the vacancy defects, and the influence law and internal mechanism of gas sensitivity were described.

MoS2 -Based Catalysts for N2 Electroreduction to NH3 - An Overview of MoS2 Optimization Strategies

The nitrogen reduction reaction (NRR) has become an ideal alternative to the Haber-Bosch process, as NRR possesses, among others, the advantage of operating under ambient conditions and saving energy consumption. The key to efficient NRR is to find a suitable electrocatalyst, which helps to break the strong N≡N bond and improves the reaction selectivity. Molybdenum disulfide (MoS2 ) as an emerging layered two-dimensional material has attracted a mass of attention in various fields. In this minireview, we summarize the optimization strategies of MoS2 -based catalysts which have been developed to improve the weak NRR activity of primitive MoS2 . Some theoretical predictions have also been summarized, which can provide direction for optimizing NRR activity of future MoS2 -based materials. Finally, an outlook about the optimization of MoS2 -based catalysts used in electrochemical N2 fixation are given.

Oxygen and Titanium Vacancies in a BiOBr/MXene-Ti3C2 Composite for Boosting Photocatalytic N2 Fixation

Solar energy can be used as "green" energy by photocatalysis for the nitrogen fixation under the atmospheric conditions compared with the traditional energy-intensive industrial production of ammonia. However, the complex kinetics and high reaction barriers greatly hinder the development of the photocatalytic N₂ reduction reaction. Herein, a BiOBr/MXene-Ti₃C₂ composite catalyst is prepared by the simple electrostatic adsorption and self-assembly method. The as-prepared 10 wt % BiOBr/Ti₃C₂ exhibits the best performance for N₂ fixation to NH₃ by photocatalysis. The evolution rate of NH₃ is up to 234.6 μmol·g^-1·h^-1, which is approximately 48.8 times and 52.4 times higher than those of pure BiOBr and Ti₃C₂, respectively. It is found that the designed double vacancies of oxygen and titanium for BiOBr/Ti₃C₂ composites, with the availability of localized electrons, have the ability to adsorb and activate N₂, which can be efficiently reduced to NH₃ by the interfacial electrons transferred from the excited BiOBr/Ti₃C₂ composite. In addition, the results of in situ Fourier transform infrared show the generation of N_xH_y species by the continuous protonation processes. Moreover, titanium vacancy (V_Ti) induces a strong absorption energy for nitrogen atoms on the surface of BiOBr/Ti₃C₂ according to the density functional theory calculations. In particular, the P-electron feedback caused by V_Ti could effectively promote the weakening of the N≡N triple bond and elongate the N₂ bond length by ∼31.6%. This work might provide new insights into the synergistic effect of double defects and inspiration for the rational design of catalysts by defect engineering in the field of catalytic synthesis of ammonia.

Phosphorous-doped 1T-MoS2 decorated nitrogen-doped g-C3N4 nanosheets for enhanced photocatalytic nitrogen fixation

Herein, we report that the phosphorous-doped 1 T-MoS₂ as co-catalyst decorated nitrogen-doped g-C₃N₄ nanosheets (P-1 T-MoS₂@N-g-C₃N₄) are prepared by the hydrothermal and annealing process. The obtained P-1 T-MoS₂@N-g-C₃N₄ composite presents an enhanced photocatalytic N₂ reduction rate of 689.76 μmol L^-1 g^-1h^-1 in deionized water without sacrificial agent under simulated sunlight irradiation, which is higher than that of pure g-C₃N₄ (265.62 μmol L^-1 g^-1h^-1), 1 T-MoS₂@g-C₃N₄ (415.57 μmol L^-1 g^-1h^-1), 1 T-MoS₂@N doped g-C₃N₄ (469.84 μmol L^-1 g^-1h^-1), and P doped 1 T-MoS₂@g-C₃N₄ (531.24 μmol L^-1 g^-1h^-1). In addition, compared with pure g-C₃N₄ NSs (2.64 mmol L^-1 g^-1h^-1), 1 T-MoS₂@g-C₃N₄ (4.98 mmol L^-1 g^-1h^-1), 1 T-MoS₂@N doped g-C₃N₄ (6.21 mmol L^-1 g^-1h^-1), and P doped 1 T-MoS₂@g-C₃N₄ (9.78 mmol L^-1 g^-1h^-1), P-1 T-MoS₂@N-g-C₃N₄ (11.12 mmol L^-1 g^-1h^-1) composite also shows a significant improvement for photocatalytic N₂ fixation efficiency in the sacrificial agent (methanol). The improved photocatalytic activity of P-1 T-MoS₂@N-g-C₃N₄ composite is ascribed to the following advantages: 1) Compared to pure g-C₃N₄, P-1 T-MoS₂@N-g-C₃N₄ composite shows higher light absorption capacity, which can improve the utilization rate of the catalyst to light; 2) The P doping intercalation strategy can promote the conversion of 1 T phase MoS₂, which in turn in favor of photogenerated electron transfer and reduce the recombination rate of carriers; 3) A large number of active sites on the edge of 1 T-MoS₂ and the existence of N doping in g-C₃N₄ contribute to photocatalytic N₂ fixation.

Identifying the Dominant Role of Pyridinic-N-Mo Bonding in Synergistic Electrocatalysis for Ambient Nitrogen Reduction

For electrochemical nitrogen reduction reaction (NRR), hybridizing transition metal (TM) compounds with nitrogen-doped carbonaceous materials has been recognized as a promising strategy to improve the activity and stability of electrocatalysts due to the synergistic interaction from the TM-N-C active sites. Nevertheless, up to date, the fundamental mechanism of this so-called synergistic electrocatalysis for NRR is still unclear. Particularly, it remains ambiguous which configuration of N dopants, either pyridinic N or pyrrolic N, when coordinated with the TM, predominately contributes to this synergy. Herein, a self-assembled three-dimensional 1T-phase MoS₂ microsphere coupled with N-doped carbon was developed (termed MoS₂/NC), showing an impressive NRR performance in neutral medium. The hybridization of MoS₂ and N-doped carbon can synergistically enhance the NRR efficiency by optimizing the electron transfer of catalyst. Acidification/blocking/poisoning experiments reveal the decisive role of pyridinic-N-Mo bonding, rather than pyrrolic-N-Mo bonding, in synergistically enhancing NRR electrocatalysis. The electrochemical-based in situ Fourier transform infrared spectroscopy (in situ FTIR) technology provides deep insights into the substantial contribution of pyridinic-N-MoS₂ sites to NRR electrocatalysis and further uncover the underlying mechanism (associative pathway) at a molecular level.

Potential environmental applications of MXenes: A critical review

Various environmental pollutants (e.g., air, water and solid pollutants) are discharged into environments with the rapid development of industrializations, which is presently at the forefront of global attention. The high efficient removal of these environmental pollutants is of important concern due to their potential threat to human health and eco-diversity. Advanced nanomaterials may play an important role in the elimination of pollutants from environmental media. MXenes as the new intriguing class of graphene-like 2D transition metal carbides and/or carbonitrides have been widely used in energy storage, environmental remediation benefitting from exceptional structural properties such as highly active sites, high chemical stability, hydrophilicity, large interlayer spacing, huge specific surface area, superior sorption-reduction capacity. However, the comprehensive investigation concerning the removal of various environmental pollutants on MXenes is yet not available up to date. In this review, we summarized the synthesis and properties of MXenes to demonstrate the key roles in ameliorating their adsorption performance; then the recent advances and achievements in environmental application of MXenes on the removal of gases, organics, heavy metals and radionuclides were comprehensively reviewed in details; Finally, the formidable challenges and further perspectives regarding utilizing MXene in environmental remediation were proposed. Hopefully, this review can provide the useful information for environmental scientists and material engineers on designing versatile MXenes in actual environmental applications.

Molybdenum-Containing Metalloenzymes and Synthetic Catalysts for Conversion of Small Molecules

The energy deficiency and environmental problems have motivated researchers to develop energy conversion systems into a sustainable pathway, and the development of catalysts holds the center of the research endeavors. Natural catalysts such as metalloenzymes have maintained energy cycles on Earth, thus proving themselves the optimal catalysts. In the previous research results, the structural and functional analogs of enzymes and nano-sized electrocatalysts have shown promising activities in energy conversion reactions. Mo ion plays essential roles in natural and artificial catalysts, and the unique electrochemical properties render its versatile utilization as an electrocatalyst. In this review paper, we show the current understandings of the Mo-enzyme active sites and the recent advances in the synthesis of Mo-catalysts aiming for high-performing catalysts.

High electron transfer of TiO2 nanorod@carbon layer supported flower-like WS2 nanosheets for triiodide electrocatalytic reduction

1D–2D multidimensional nanostructured TNRs@C@WS₂ has been prepared and introduced as an effective catalyst for the triiodide reduction reaction.

A large scaled-up monocrystalline 3R MoS2 electrocatalyst for efficient nitrogen reduction reactions

Large-scale 3R MoS₂ was shown to be an efficient electrocatalyst for the NRR, and the NRR performance can be enhanced via improving the crystallinity of MoS₂ due to decreased resistance.

Superior light absorbing CdS/vanadium sulphide nanowalls@TiO2 nanorod ternary heterojunction photoanodes for solar water splitting

Vanadium sulphide is an emerging infrared active photocatalyst that has not been utilized to its maximum potential.

Amorphous MnCO3/C Double Layers Decorated on BiVO4 Photoelectrodes to Boost Nitrogen Reduction

NH₃ is mainly obtained by the Haber-Bosch method in the process of industrial production, which is not only accompanied by huge energy consumption but also environmental pollution. The reduction of N₂ to NH₃ under mild conditions is an important breakthrough to solve the current energy and environmental problems, so the preparation of catalysts that can effectively promote the reduction of N₂ is a crucial step. In this work, BiVO₄ decorated with amorphous MnCO₃/C double layers has been successfully synthesized by a one-step method for the first time. The C and MnCO₃ have been formed as ultrathin film, which enables the establishment of a uniform and tight interface with BiVO₄. The temperature-programmed desorption of N₂ (N₂-TPD) spectra confirmed that the MnCO₃/C could endow BiVO₄ with a drastic enhancement of the chemical absorption ability of a N₂ molecule compared with the pristine BiVO₄. Meanwhile, the method of isotope labeling proved that the catalyst exhibited excellent selectivity for the photocatalytic nitrogen reduction reaction (NRR). The production rate of NH₃ up to 2.426 mmol m^-2 h^-1 has been achieved over the BiVO₄/MnCO₃/C, which is almost 8 times that of pristine BiVO₄. The promoted production rate of NH₃ over BiVO₄/MnCO₃/C could be mainly attributed to the cooperative process between MnCO₃ and C amorphous layers. Therefore, this work could provide an alternative insight to understand the NRR process based on the model of a hierarchical amorphous structure.

Exploration and Investigation of Periodic Elements for Electrocatalytic Nitrogen Reduction

High demand for green ecosystems has urged the human community to reconsider and revamp the traditional way of synthesis of several compounds. Ammonia (NH₃ ) is one such compound whose applications have been extended from fertilizers to explosives and is still being synthesized using the high energy inhaling Haber-Bosch process. Carbon free electrocatalytic nitrogen reduction reaction (NRR) is considered as a potential replacement for the Haber-Bosch method. However, it has few limitations such as low N₂ adsorption, selectivity (competitive HER reactions), low yield rate etc. Since it is at the early stage, tremendous efforts have been devoted in understanding the reaction mechanism and screening of the electrocatalysts and electrolytes. In this review, the electrocatalysts are classified based on the periodic table with heat maps of Faraday efficiency and yield rate of NH₃ in NRR and their electrocatalytic properties toward NRR are discussed. Also, the activity of each element is discussed and short tables and concise graphs are provided to enable the researchers to understand recent progress on each element. At the end, a perspective is provided on countering the current challenges in NRR. This review may act as handbook for basic NRR understandings, recent progress in NRR, and the design and development of advanced electrocatalysts and systems.