Low temperature synthesis of NbC/C nano-composites as visible light photoactive catalyst

Superconducting NbC nanoparticles synthesized by laser ablation in a liquid

Niobium carbide (NbC) is a high-field type II superconductor with a critical temperature (TC) of 11.1 K, slightly exceeding that of pure Nb (TC = 9 K). The reduction of NbC to the nanoparticle scale leads to significant changes in its critical field and/or the superconducting temperature. This study presents findings on superconducting NbC nanoparticles with TC ≃ 10 K produced through laser ablation in acetone, where different conditions of laser fluence and centrifugation were studied. Analysis by X-ray diffraction confirmed the cubic NbC phase, while electron microscopy images displayed approximately 8 nm spherical particles, showing no noticeable size variation with laser fluence. Additionally, magnetization curves exhibited both magnetic and superconducting loops for all investigated samples. A decrease in laser fluence resulted in the suppression of diamagnetic behavior below TC. Furthermore, all samples exhibited a weak electron spin resonance (ESR) Curie-like signal at g ≃ 2.0, probably linked to localized defects on the particle's surface. The simultaneous existence of superconductivity and magnetism in nanoparticles has recently garnered significant research attention. This intricate scenario and unique properties arise from the significant enhancement of the surface-to-volume ratio in these superconducting NbC nanoparticles, emphasizing the need for further investigation to unveil novel material properties and shed new light on our comprehension of the superconducting phenomenon in this particular morphology.

NbC Nanoparticles Decorated Carbon Nanofibers as Highly Active and Robust Heterostructural Electrocatalysts for Ammonia Synthesis

Transition-metal carbides with metallic properties have been extensively used as electrocatalysts due to their excellent conductivity and unique electronic structures. Herein, NbC nanoparticles decorated carbon nanofibers (NbC@CNFs) are proposed as an efficient and robust catalyst for electrochemical synthesis of ammonia from nitrate/nitrite reduction, which achieves a high Faradaic efficiency (FE) of 94.4 % and a large ammonia yield of 30.9 mg h-1 mg-1 cat.. In situ electrochemical tests reveal the nitrite reduction at the catalyst surface follows the *NO pathway and theoretical calculations reveal the formation of NbC@CNFs heterostructure significantly broadens density of states nearby the Fermi energy. Finite element simulations unveil that the current and electric field converge on the NbC nanoparticles along the fiber, suggesting the dispersed carbides are highly active for nitrite reduction.

Solid-State Synthesis of Niobium Carbide Electrocatalyst in the Presence of Vanadium as Suppressor of Energy Input and Greenhouse Gas Emission

Solid-state reaction (SSR) is a widely adopted method for functional inorganic material syntheses. Unlike intricate systems emerging from chemically unstable precursor usage, the SSR can proceed from stable precursor couples using simple apparatuses. However, this reaction is associated with high temperatures that overcome solid-state diffusion. Moreover, solid-state syntheses of technologically crucial carbides lead to greenhouse gas emissions. Therefore, exploring an extrinsic component to suppress these challenges is vital to confronting global energy and environmental issues. This study reports that the presence of an ordinary element, vanadium (V), changes the routes of the SSR of niobium carbide (NbC), producing NbC efficiently and cleanly. 1000 °C is far below the temperature required to obtain NbC from a precursor couple of Nb2O5 and C, i.e., approximately 1500 °C is required. However, a carbon substitute, vanadium carbide, completely consumed Nb2O5 before reaching 1000 °C and consummated NbC crystallization for 10 h. Furthermore, NbC crystallites were observed using X-ray diffraction from 770 °C, and their formation was primarily accompanied by VNbO4, rather than being routed through NbO2 produced for the Nb2O5-C combination. The obtained NbC contained V as a dopant in the 15-50% range (NbC:V), and the relative abundance was correlated with the preparation temperature. Mass analyses revealed that the formation of NbC/V is barely associated with greenhouse gas emissions because of the sizable thermodynamic driving force for primarily forming vanadium oxide byproducts. Device performance using NbC/V was also assessed for a standard electrochemical hydrogen evolution reaction.

Superior functionality of niobium pentoxide nano-rod/tripod photocatalyst synthesized using polyethyleneimine as a soft template for the abatement of methylene blue under UV and visible irradiation

Polyethyleneimine (PEI) capping agent-cum-template-mediated synthesis of niobium oxide nanoparticles is reported to explore its impact on the resultant morphology, porosity, crystallinity, phase complexation, and thus on the photocatalytic activity. The resultant niobium oxides calcined at 800°C and 1000°C crystallized into highly ordered nano-rod/tripod nanostructure with inter-rod angle <120° having orthorhombic phase and heavily agglomerated rod-like nanostructures having monoclinic crystal phase, respectively. Contrary to the expectations, the nano-rod/tripods showed superior photocatalytic degradation kinetics and high adsorption of methylene blue dye in the hydrocolloid than formerly reported monoclinic nanoparticles. The best adsorption capability and photocatalytic activity are observed for the sample calcined at 800°C, resulting in a combined degradation efficiency of 98.8% of methylene blue dye. The adsorption characteristics, stability of the hydrocolloid system, the existence of oxygen vacancies, and the distinct morphology of the photocatalytic nano-rod/tripods are mainly responsible for this behavior. The process and the performance of unique nanostructure over others presents a superior alternative.

Understanding the charge carriers dynamics in the La0.55Ca0.45Mn0.8Nb0.2O3 perovskite: scaling of electrical conductivity spectra

The present work proposes the best realistic theoretical approaches to examine the experimental conductivity data taken for La0.55Ca0.45Mn0.8Nb0.2O3. For this purpose, we comprehensively discussed the structural, microstructural, and electrical properties of the La0.55Ca0.45Mn0.8Nb0.2O3 perovskite. Both X-ray diffraction and Rietveld analysis show the orthorhombic structure of the ceramic. Scanning electron microscope showed the existence of well-defined irregularly shaped particles with a grain-size distribution of 0.843 μm. The X-ray photoemission spectroscopy reveals the existence of Mn3+ and Mn4+ states. The complicated behavior of the lanthanum states is demonstrated using the La3d line. AC-conductivity responses are related to the correlated barrier hopping contribution. At high temperatures, the compound's semiconductor behavior is attributed to the activation of the polaronic transport. At low temperatures, the occurrence of semiconductor behavior in the La0.55Ca0.45Mn0.8Nb0.2O3 ceramic is attributed to the effect of the variable range hopping conduction process. The application of the time-temperature-superposition-principle and the Summerfield scaling formalisms leads to the superposition of the isotherms. Using the Ghosh formalism, the superposition of the spectra confirms that the number density and the hopping distance are temperature-dependent. The superposition of the spectra suggested the temperature-independent relaxation and polaronic processes. In addition, it confirms that the relaxation mechanism is independent of the microstructure response.

Synthesis of niobium(iv) carbide nanoparticles via an alkali-molten-method at a spatially-limited surface of mesoporous carbon

One-pot synthesis of niobium carbabide (NbC) nanoparticles with ca. 30-50 nm was achieved via a rationally designed novel alkali-molten salt method using niobium oxide (Nb2O5), potassium carbonate (K2CO3), and mesoporous carbon (MPC). In this reaction, potassium niobate (KNbO3) was produced as an intermediate and carbonization of KNbO3 proceeds at a spatially limited external surface encompassed by the mesopores of MPC due to the repulsive characteristics of ionic KNbO3 toward hydrophobic MPC, which affords the size-controlled NbC nanoparticles with a narrow particle distribution. The particle sizes tended to become smaller as the pore sizes of MPCs or the temperature on the calcination under the nitrogen stream decreased. Elemental reactions along the one-pot synthesis of NbC nanoparticles were clarified by X-ray spectroscopic, thermogravimetric, and mass spectrometric measurements.

Nanoengineered lanthanum niobate nanocaviar anchored carbon nanofibers for trace level detection of menadione in environmental samples

An innovative sensor is prepared by electrode modification through a nano-ranged electrode modifier composed of LaNbO₄ nano caviars decorated on the enmeshed carbon nanofibers to identify excess vitamins in animal feed. Menadione (Vitamins K3) is a micronutrient fundamentally required in precise quantities for animal health upkeep. Still, its exploitation has recently resulted in water reservoir contamination through waste generated from animal husbandry. Sustainable prevention of water contamination makes menadione detection highly imperative and flickered the attention of researchers. Considering these aspects, a novel menadione sensing platform is designed by interdisciplinary incorporation of nanoscience and electrochemical engineering. The structural and crystallographic features and the electrode modifier's morphological insights were keenly investigated. The hierarchal arrangement of individual constituents in nanocomposite is benefited through hybrid heterojunction and quantum confinement that synchronously activate the menadione detection with a LOD of 68.5 nM and 67.49 nM for oxidation and reduction, respectively. The as-prepared sensor has a wide linear range (0.1-173.6 μM), high sensitivity, good selectivity, and stability. The application of this sensor is extended to a water sample to monitor the consistency of the proposed sensor.

Influence of Phase Composition and Pretreatment on the Conversion of Iron Oxides into Iron Carbides in Syngas Atmospheres

CO2 Fischer–Tropsch synthesis (CO2–FTS) is a promising technology enabling conversion of CO2 into valuable chemical feedstocks via hydrogenation. Iron–based CO2–FTS catalysts are known for their high activities and selectivities towards the formation of higher hydrocarbons. Importantly, iron carbides are the presumed active phase strongly associated with the formation of higher hydrocarbons. Yet, many factors such as reaction temperature, atmosphere, and pressure can lead to complex transformations between different oxide and/or carbide phases, which, in turn, alter selectivity. Thus, understanding the mechanism and kinetics of carbide formation remains challenging. We propose model–type iron oxide films of controlled nanostructure and phase composition as model materials to study carbide formation in syngas atmospheres. In the present work, different iron oxide precursor films with controlled phase composition (hematite, ferrihydrite, maghemite, maghemite/magnetite) and ordered mesoporosity are synthesized using the evaporation–induced self–assembly (EISA) approach. The model materials are then exposed to a controlled atmosphere of CO/H2 at 300 °C. Physicochemical analysis of the treated materials indicates that all oxides convert into carbides with a core–shell structure. The structure appears to consist of crystalline carbide cores surrounded by a partially oxidized carbide shell of low crystallinity. Larger crystallites in the original iron oxide result in larger carbide cores. The presented simple route for the synthesis and analysis of soft–templated iron carbide films will enable the elucidation of the dynamics of the oxide to carbide transformation in future work.

Synthesizing environmentally friendly non-silicone oxygen bleaching stabilizer for linen yarn using oligomeric acrylic acid

Using potassium peroxodisulfate as an initiator and acrylic acid as a monomer, an acrylic acid oligomer was synthesized and then compounded with magnesium salt to form a non-silicone oxygen bleaching stabilizer. By investigating the effects of reaction temperature, reaction time, initiator concentration, monomer concentration, and magnesium salt dosage on product performance, the effect of stabilizers on linen yarn bleaching was analyzed. The synthetic conditions of oxygen bleaching stabilizer were determined by orthogonal test method, namely, acrylic acid monomer concentration 25%, initiator dosage 5%, oligomeric acrylic acid and magnesium salt compound ratio 5:1, reaction temperature 65 °C, reaction time 4 h. At this time, the chelated iron value of the product was as high as 239.314 mg/g, and the chelated calcium value also reached 145.000 mg/g. The dosage of the synthesized stabilizer were determined to be 4 g/L through indicators such as the decomposition rate of hydrogen peroxide and whiteness. The results showed that the environmentally friendly non-silicone oxygen bleaching stabilizer not only had a good ability to inhibit the decomposition of hydrogen peroxide, but also provided bleached linen yarn with a superior degree of whiteness and less metal ion residue, which can effectively solve the "silicon scale" problem and improve the quality of the pre-treatmented products.

Synergistic Effects of Carbon Dots and Palladium Nanoparticles Enhance the Sonocatalytic Performance for Rhodamine B Degradation in the Absence of Light

Carbon dot (CD) and palladium nanoparticle (Pd NP) composites are semiconducting materials having tremendous applications in catalysis with suitable band gaps. However, their combination with a suitable polymer matrix in sonophotocatalysis has not been explored. Herein, we have synthesized and characterized a new nanohybrid catalyst from a polyamide cross-linked CD-polymer and subsequent deposition of Pd NPs. A sonocatalytic activity of 99% rhodamine B dye degradation was achieved in mere 5 min in the dark. A model catalyst replacing CDs with benzene and other control studies revealed that the synergistic effects of CDs and Pd NPs enhance the sonocatalytic activity of the nanohybrid catalyst. Interestingly, visible light did not influence the activity significantly. Mechanistic investigations suggest that generation of reactive oxygen species on the surface of the CD-polymer initiated by ultrasound, which is further facilitated by Pd NPs, is the key for remarkable catalytic activity (a rate constant of 0.99 min-1). Recyclable heterogeneous catalysts under ambient conditions are promising for exploring sono-assisted dark catalysis for several avenues.

A novel L-Histidine (C, N) codoped-TiO2-CdS nanocomposite for efficient visible photo-degradation of recalcitrant compounds from wastewater

The aim of current study is to synthesis novel visible driven photocatalysts (L-Histidine (C, N) codoped-TiO₂-CdS) with different loadings of L-Hisitdine (1, 2, and 3 wt.%) and CdS (1:9, 7:1, and 1:5 mass ratios of CdS to TiO₂). Then, their application for photo-degradation of methyl orange (MO) and biologically treated palm oil mill effluent (POME) were studied. The structure, optical properties, and morphology of the prepared nanocomposites were also characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), Fourier transform infrared (FT-IR), photoluminescence spectroscopy (PL), and diffuse reflectance spectra (DRS). DRS results indicated that all the modified samples with different L-Hisitdine and CdS loadings showed a red shift to visible region. The results of photo-degradation experiments showed that L-Hisitdine with a weight fraction of 2% and mass ratio of TiO₂ to CdS of 7:1 were the optimum amount of the modifiers in the photocatalyst network. The PL intensity of the photocatalyst decreased with addition of L-Hisitdine and CdS nanoparticles due to a decrease in e^-/h⁺ recombination. The effects of organic pollutant concentration, initial pH, catalyst concentration, and irradiation time on the photo-degradation process of MO and POME were studied using full faced centered central composite design (CCFD) under response surface methodology (RSM). The obtained results showed that MO was completely removed at initial concentration of 10 mg/L, acidic pH, and catalyst loading of 1.5 g/L after 120 min. The complete degradation of biologically treated POME was achieved at original pH, 300 mg/L of chemical oxygen demand (COD) concentration, catalyst loading of 2 g/L, and irradiation time of 2 h.