Preparation and characterization of carbon-encapsulated iron nanoparticles and their catalytic activity in the hydrogenation of levulinic acid

This study describes the synthesis of carbon-encapsulated iron nanoparticles using an ultrasonic method and also investigates their catalytic activity. These nanoparticles have been prepared using ultrasonic irradiation followed by annealing at various temperatures. As the annealing temperature of as-prepared α-Fe₂O₃ nanoparticles increased, the sample transformed into γ-Fe₂O₃, Fe₃O₄, and Fe nanoparticles via the reduction process without requiring any additional reducing agents such as H₂ gas, thus, creating a carbon shell surrounding the nanoparticles. By controlling the experimental conditions, Fe nanoparticles of various sizes can be formed with diameters in the range 100–800 nm; these nanoparticles are tightly encapsulated by 20-nm-thick carbon shells. Because of their high saturation magnetization 212 emu g^?1, the carbon-encapsulated Fe nanoparticles can be used for magnetic resonance imaging with a dramatically enhanced efficiency compared to commercially available T ₂ contrast agents. Moreover, the carbon-encapsulated Fe nanoparticles showed its superior catalytic activity and reusability for the hydrogenation of biomass-derived levulinic acid to GVL (99.6 %) in liquid phase.     

快速热解法制备炭包覆纳米金属磁性颗粒(英文)

以简单金属前躯体为原料通过快速热解法制备炭包覆纳米金属磁性颗粒,通过透射电镜、X-射线衍射、热重-示差扫描同步热分析及振动样品磁强计等对产物形貌、结构、成分与磁性能进行表征。结果表明:采用该方法制备的炭包覆纳米金属磁性颗粒形状为近球形颗粒,粒径均一,其中炭包覆镍纳米磁性颗粒的粒径集中在10nm～30nm范围,炭包覆铁纳米磁性颗粒粒径则在50nm～60nm范围;所制炭包覆纳米金属磁性颗粒在室温下具有顺磁性,其磁性能随金属颗粒含量的变化而改变。该方法有望发展成一种工艺简单,可进行连续工业化生产炭包覆纳米金属磁性颗粒的方法。     

Nano iron oxide (Fe2O3)/carbon black electrodes as electrode material for electrochemical capacitors: Effect of the nanoparticles dispersion quality

In the present study, nano Fe₂O₃/carbon black electrodes are proposed for electrochemical capacitors and the effect of nanoparticles dispersion quality on the surface morphology, nature and electrochemical properties of the electrodes are investigated. Mechanical pressing is accompanied by different mixing (mechanical and sonication) processes to prepare the electrode. Electrochemical properties of the produced nanocomposites are studied using cyclic voltammetry and electrochemical impedance spectroscopy tests in 2 M KCl electrolyte. Scanning electron microscopy is used to characterize the microstructure and the nature of the nanoparticles on the nanocomposites produced. Results obtained show that the sonicated and unsonicated 10:80:10 (CB:Fe₂O₃:PTFE) electrodes have specific capacitance of 22.02 and 22.35 F g⁻¹ respectively, at scan rate of 10 mV s⁻¹. Sonication process breaks the agglomerated particles and disperses them on the electrode surface, uniformly. This increases the specific surface area and the electrical resistance of the electrodes. The sonicated electrodes show a higher charge separation capability at electrolyte/electrode interfaces, lower ratio of outer to total charge (q_O*/q_T*) of 0.13 and lower current response at end potentials. Energy density was increased after the sonication process from 0.686 to 1.498 (Wh kg⁻¹). Charge/discharge cycling results confirmed that the uniform dispersion of active material on the electrode surface postpones the electrolyte decomposition and improves the electrical conductivity during cycling.     

Electrochemistry of Cu(I) doped CdS nanoparticles hosted by DNA–CTMA in aqueous electrolyte

The electrochemical redox behaviors of Cu(I) doped CdS nanoparticles in DNA–CTMA films are investigated in aqueous electrolyte. Both oxidation and reduction processes are electrochemically irreversible. The degradation of nanoparticles and the coupled chemical reactions in the electrochemical measurements can be avoided by fast potential scan as 1.5 V s⁻¹. It is hardly found the residual O₂ effect on the redox behavior of nanoparticles in DNA–CTMA film. The role of DNA–CTMA matrix in the charge transfer process between nanoparticles and the electrode is discussed.     

The preparation of carbon-encapsulated Fe/Co nanoparticles and their novel applications as bifunctional catalysts to promote the redox reaction for <Emphasis Type="Italic">p</Emphasis>-nitrophenol

As a common organic pollutant in industrial and agricultural wastewater, p-Nitrophenol (p-NP) is difficult to be degraded naturally. Though, various methods have been developed for degradation of p-NP, the utilization of catalysts to electrochemically degrade p-NP became a novel effective way. In this article, two magnetic nanoparticles (carbon-encapsulated iron, Fe/C; carbon-encapsulated cobalt, Co/C) were prepared. Through a series of physical phase characterization, we found that the average dimension of the prepared magnetic nanoparticles arrived at 60 nm for Fe/C and 80 nm for Co/C, and within such small dimensions, the prepared nanoparticles might have some remarkable catalytic characters in electrochemical degradation of p-NP. Therefore, two novel types of Fe/C and Co/C modified glassy carbon electrodes were fabricated to investigate their catalytic activity for p-NP degradation. In our results, both of the two modified electrodes showed favorable stability and excellent electro-catalytic activity for p-NP degradation. In addition, two modified electrodes also exhibited favorable electro-catalytic reductive ability for p-NP. The electrochemical reactions on the surface of the two modified electrodes were all diffusion controlled processes. Therefore, Fe/C and Co/C were excellent bifunctional catalysts which could be considered as a practical way to be applied in industrial hydrogenation and oxidative degradation of organic compounds.     

Sponge-like β-Ni(OH)<Subscript>2</Subscript> nanoparticles: synthesis,characterization and electrochemical properties

The present investigation describes the synthesis of uniform sponge-like Ni(OH)₂ nanoparticles on stainless steel substrates by a two-step successive ionic layer adsorption and reaction method; the study also explores electrochemical properties. The formation of the β-phase Ni(OH)₂ and it’s nanocrystallinity are confirmed by X-ray diffraction and X-ray photoelectron spectroscopy studies. Scanning electron microscopy revealed the formation and random distributions of porous and sponge-like nanoparticles with high Brunauer–Emmett–Teller surface area of 56.4 m² g⁻¹. The maximum specific capacitance of 428 F g⁻¹ was obtained at 5 mV s⁻¹ in a 2 M KOH electrolyte, indicating promising supercapacitor applications with remarkable rate capability. These results suggest the importance of rational design and synthesis of thin nanomaterials for high-performance energy applications.     

生物质基碳包覆纳米磁性颗粒的研究进展

碳包覆纳米磁性颗粒(CEMNPs)是一种具有核/壳结构的新型纳米复合材料,独特的理化性质使其在众多技术领域显示出巨大的应用潜力。随着全球化石能源的日渐枯竭,利用廉价、易获取、环境友好的生物质原料作为替代碳源已成为近年来CEMNPs材料的研究热点。综述了生物质基CEMNPs的制备方法、反应机理以及在电化学、催化、吸附等领域中的应用,最后展望了其发展方向和趋势。     

Electrochemical Activation Applied to Perovskite Titanate Fibers to Yield Supported Alloy Nanoparticles for Electrocatalytic Application

Active bi-metallic nanoparticles are of key importance in catalysis and renewable energy. Here, the in situ formation of bi-metallic nanoparticles is investigated by exsolution on 200 nm diameter perovskite fibers. The B-site co-doped perovskite fibers display a high degree of exsolution, decorated with NiCo or Ni₃Fe bi-metallic nanoparticles with average diameter about 29 and 35 nm, respectively. The perovskite fibers are utilized as cathode materials in pure CO₂ electrolysis cells due to their redox stability in the CO/CO₂ atmosphere. After in situ electrochemical switching, the nanoparticles exsolved from the perovskite fiber demonstrate an enhanced performance in pure CO₂ electrolysis. At 900 °C, the current density of solid oxide electrolysis cell (SOEC) with 200 µm YSZ electrolyte supported NiFe doped perovskite fiber anode reaches 0.75 Acm⁻² at 1.6 V superior to the NiCo doped perovskite fiber anode (about 1.5 times) in pure CO₂. According to DFT calculations (PBE-D3 level) the superior CO₂ conversion on NiFe compared to NiCo bi-metallic species is related to an enhanced driving force for C-O cleavage under formation of CO chemisorbed on the nanoparticle and a reduced binding energy of CO required to release this product.     

Regulated Surface Electronic States of CuNi Nanoparticles through Metal-Support Interaction for Enhanced Electrocatalytic CO2 Reduction to Ethanol

Developing stable catalysts with higher selectivity and activity within a wide potential range is critical for efficiently converting CO₂ to ethanol. Here, the carbon-encapsulated CuNi nanoparticles anchored on nitrogen-doped nanoporous graphene (CuNi@C/N-npG) composite are designedly prepared and display the excellent CO₂ reduction performance with the higher ethanol Faradaic effiency (FE_ethanol ≥ 60%) in a wide potential window (600 mV). The optimal cathodic energy efficiency (47.6%), Faradaic efficiency (84%), and selectivity (96.6%) are also obtained at −0.78 V versus reversible hydrogen electrode (RHE). Combining with the density functional theory (DFT) calculations, it is demonstrated that the stronger metal-support interaction (Ni-N-C) can regulate the surface electronic structure effectively, boosting the electron transfer and stabilizing the active sites (Cu⁰-Cu^δ+) on the surface of CuNi@C/N-npG, finally realizing the controllable transition of reaction intermediates. This work may guide the designs of electrocatalysts with highly catalytic performance for CO₂ reduction to C₂₊ products.     

Capacitive behavior studies on electrical double layer capacitor using poly (vinyl alcohol)–lithium perchlorate based polymer electrolyte incorporated with TiO2

Electric double layer capacitors (EDLCs) based on activated carbon electrodes and poly (vinyl alcohol)–lithium perchlorate (PVA–LiClO₄)-nanosized titania (TiO₂) doped polymer electrolyte have been fabricated. Incorporation of TiO₂ into PVA–LiClO₄ system increases the ionic conductivity. The highest ionic conductivity of 1.3 × 10⁻⁴ S cm⁻¹ is achieved at ambient temperature upon inclusion of 8 wt.% of TiO₂. Differential scanning calorimetry (DSC) analyses reveal that addition of TiO₂ into polymer system increases the flexibility of polymer chain and favors the ion migration. Scanning electron microscopy (SEM) analyses display the surface morphology of the nanocomposite polymer electrolytes. The electrochemical stability window of composite polymer electrolyte is in the range of −2.3 V to 2.3 V as shown in cyclic voltammetry (CV) studies. The performance of EDLC is evaluated by electrochemical impedance spectroscopy (EIS), CV and galvanostatic charge–discharge technique. CV test discloses a nearly rectangular shape, which signifies the capacitive behavior of an ELDC. The EDLC containing composite polymer electrolyte gives higher specific capacitance value of 12.5 F g⁻¹ compared to non-composite polymer electrolyte with capacitance value of 3.0 F g⁻¹ in charge–discharge technique. The obtained specific capacitance of EDLC is in good agreement with each method used in this present work. Inclusion of filler into the polymer electrolyte enhances the electrochemical stability of EDLC.     

Efficient purification of His-tagged protein by superparamagnetic Fe3O4/Au–ANTA–Co2 + nanoparticles

Superparamagnetic Fe₃O₄/Au nanoparticles were synthesized and surface modified with mercaptopropionic acid (MPA), followed by conjugating Nα,Nα-Bis(carboxymethyl)-l-lysine hydrate (ANTA) and subsequently chelating Co^2 +. The resulting Fe₃O₄/Au–ANTA–Co^2 + nanoparticles have an average size of 210 nm in aqueous solution, and a magnetization of 36 emu/g, endowing the magnetic nanoparticles with excellent magnetic responsivity and dispersity. The Co^2 + ions in the magnetic nanoparticle shell provide docking site for histidine, and the Fe₃O₄/Au–ANTA–Co^2 + nanoparticles exhibit excellent performance in binding of a His-tagged protein with a binding capacity of 74 μg/mg. The magnetic nanoparticles show highly selective purification of the His-tagged protein from Escherichia coli lysate. Therefore, the obtained Fe₃O₄/Au–ANTA–Co^2 + nanoparticles exhibited excellent performance in the direct separation of His-tagged protein from cell lysate.     

Effect of doping cobalt on the micro-morphology and electrochemical properties of birnessite MnO2

Birnessite-type MnO₂ nanoparticles are synthesized by mixing KMnO₄ solution directly with ethylene glycol under ambient conditions. When cobalt exists in the solution, the micro-morphology of the products transforms from conglomeration to dispersive state. The result of transmission electron microscopy (TEM) and field emission scanning electron microscopy (FE-SEM) shows that the product is constructed with nanosphere in sizes of ca. 40 nm. These nanospheres are twisted by nanorods clusters. X-ray diffraction (XRD) pattern shows that the products are birnessite-type. The electrochemical properties of the prepared materials are studied using cyclic voltammetry (CV) and galvanostatic charge–discharge test in aqueous electrolyte. The product shows a very high specific capacity of 326.4 F g⁻¹. These results indicate that cobalt has great effects on the micro-morphology and electrochemical properties of manganese dioxide.     

Enhancing the efficiency of AuCl4 ion removal from aqueous solution using activated carbon and carbon nanomaterials

The removal of AuCl₄⁻ ion from acidic aqueous solutions is studied using a series of non-oxidized and surface oxidized carbon materials (activated carbon, carbon nanotubes, carbon-encapsulated iron nanoparticles and carbon black). The studied sorbents differ in crystallinity, porosity and morphology. In the case of non-oxidized carbon materials the maximum removal efficiency (74%) is found for activated carbon, whilst graphitized nanomaterials (i.e. carbon nanotubes and carbon-encapsulated iron nanoparticles) are able to remove 42–45% of gold ion from the solution. The oxidation in nitric acid significantly improves the removal efficiencies. The uptake of Au(III) increases two times (to 91–92%) for oxidized carbon nanotubes and carbon-encapsulated iron nanoparticles. The same oxidation procedure applied to activated carbon and carbon black moderately enhances the uptake efficiency to 88% and 55%, respectively. The observed substantially distinct uptakes are discussed in the frames of textural properties, morphology, surface chemistry characteristics and crystallinity of the studied carbon materials. Moreover, the possibility of a galvanic exchange reaction between AuCl₄⁻ and metallic Fe in the carbon encapsulate core is also evaluated.     

Synthesis and study of magnetic properties of NiFe<Subscript>2</Subscript>O<Subscript>4</Subscript> nanoparticles by PVA assisted auto-combustion method

NiFe₂O₄ nanoparticles are prepared by a simple and cost-effective method using via polyvinyl alcohol assisted sol–gel auto-combustion method. The X-ray diffraction result indicated that the synthesized nanoparticles have only the inverse spinel structure without the presence of any other phase impurities. HR-SEM and TEM images showed that the particles are spherical shape with particle size in the range ~11 nm. The magnetic property of these nanoparticles is studied for the enlightening ferrimagnetic behaviour at room temperature. The value of the magnetic saturation (M_s) is 44.3 emug⁻¹, remanent magnetization (M_r) is 19.8 emug⁻¹ and coercive force (H_c) is 672.02 Oe.     

Physical Properties of Pyridinium Fluorohydrogenate, [pyridine · H+][H2F3]−

Ionic liquids (ILs), also referred to as molten salts, have found application as electrolytes for batteries and super-capacitors, in electroplating baths, as designer solvents, and as reaction media. A few of the desired properties of a super-capacitor electrolyte are nonflammability, thermal stability, and electrochemical stability. ILs containing aromatic cations have been shown to have low viscosity which results in a high electrochemical conductivity. There is a delicate balance between increasing the thermal stability, or decreasing the melting point, and increasing the electrochemical conductivity of the IL. This study focuses on pyridinium fluorohydrogenate, [pyridine · H⁺][H₂F₃]⁻. Pyridinium fluorohydrogenate has been synthesized by the reaction of pyridine and anhydrous hydrofluoric acid. This IL has a relatively high electrical conductivity (~98 mS · cm⁻¹ at 23 °C), a wide electrochemical window, and a boiling point of 186 °C. A stable gel can also be formed by combining [pyridine · H⁺][H₂F₃]⁻ and a super absorbent polymer such as polyacrylic acid. The gel adds mechanical stability to the matrix while not greatly affecting the conductivity of the IL.     

Solvent Induced Activation Reaction of MoS2 Nanosheets within Nitrogen/Sulfur-Codoped Carbon Network Boosting Sodium Ion Storage

MoS₂, as a classical 2D material, becomes a capable anode candidate for sodium-ion batteries. However, MoS₂ presents a disparate electrochemical performance in the ether-based and ester-based electrolyte with unclear mechanism. Herein, tiny MoS₂ nanosheets embedded in nitrogen/sulfur-codoped carbon (MoS₂@NSC) networks are designed and fabricated through an uncomplicated solvothermal method. Thanks to the ether-based electrolyte, the MoS₂@NSC shows a unique capacity growth in the original stage of cycling. But in the ester-based electrolyte, MoS₂@NSC shows a usual capacity decay. The increasing capacity puts down to the gradual transformation from MoS₂ to MoS₃ with the structure reconstruction. Based on the above mechanism, MoS₂@NSC demonstrates an excellent recyclability and the specific capacity keeps around 286 mAh g⁻¹ at 5 A g⁻¹ after 5000 cycles with an ultralow capacity fading rate of only 0.0034% per cycle. In addition, a MoS₂@NSC‖Na₃V₂(PO₄)₃ full cell with ether-based electrolyte is assembled and demonstrates a capacity of 71 mAh g⁻¹, suggesting the potential application of MoS₂@NSC. Here the electrochemical conversion mechanism of MoS₂ is revealed in the ether-based electrolyte and significance of the electrolyte design on the promoting Na ion storage behavior is highlighted.     

Characterization of carbon nanotubes decorated with NiFe2O4 magnetic nanoparticles as a novel electrochemical sensor: Application for highly selective determination of sotalol using voltammetry

A magnetic nano‐composite of multiwall carbon nanotube, decorated with NiFe₂O₄ nanoparticles, was synthesized with citrate sol–gel method. The multiwall carbon nanotubes decorated with NiFe₂O₄ nanoparticles (NiFe₂O₄–MWCNTs) were characterized with different methods such as Fourier transform infrared spectroscopy (FT‐IR), transmission electron microscopy (TEM), atomic force microscopy (AFM), vibrating sample magnetometer (VSM), cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS). The new nano-composite acts as a suitable electrocatalyst for the oxidation of sotalol at a potential of 500 mV at the surface of the modified electrode. Linear sweep voltammetry exhibited two wide linear dynamic ranges of 0.5–1000 μmol L^? 1 sotalol with a detection limit of 0.09 μmol L^? 1. The modified electrode was used as a novel electrochemical sensor for the determination of sotalol in real samples such as pharmaceutical, patient and safe human urine.     

Low-cost quasi-solid-state dye-sensitized solar cells based on a metal-free organic dye and a carbon aerogel counter electrode

Low-cost quasi-solid-state dye-sensitized solar cells (DSSCs) are designed and fabricated by using a metal-free organic dye and a mesoporous carbon aerogel instead of expensive ruthenium-based sensitizers and Pt electrode. The electrospun TiO₂ nanorods are added into a polyvinylidene fluoride (PVDF) solution to form a 3D network nanocomposite gel electrolyte. The presence of TiO₂ nanorods in the gel electrolyte obviously increases the ionic conductivity and decreases charge-transfer resistance of the DSSC. The effects of the gel electrolyte and the carbon aerogel counter electrode on electrochemical and photovoltaic properties have been investigated in detail. Particularly, an optimized DSSC with a nanocomposite gel electrolyte and a carbon aerogel counter electrode affords a power conversion efficiency (PCE) of 6.20% at a light intensity of 100 mW cm⁻².     

Self-activated ‘green’ carbon nanoparticles for symmetric solid-state supercapacitors

Tuning of porosity and surface properties of nanoparticles especially on carbon-based nanomaterials, adopting a ‘greener’ or self-activation synthesis technique for electrical charge storage, is progressing. Herein, we report the self-activation of Teak wood sawdust in a nitrogen atmosphere at different activation temperatures to synthesize carbon nanoparticles. The activated carbon nanoparticles synthesized at 900 °C exhibits a maximum?~?360 m² g^?1 surface area with?~?2 nm average pore size diameter. Five electrolytes viz. KOH, KCl, Na₂SO₄, NaCl, and H₃PO₄ are used for studying the supercapacitance nature of the activated carbon nanoparticles in a 3-electrode configuration. A maximum specific capacitance of?~?208 F g^?1 @ 0.25 A g^?1 is obtained in 1 M KOH as the electrolyte. Two symmetric supercapacitors, aqueous (1 M KOH) and solid-state (PVA/KOH), are fabricated, and their performance difference is compiled. The solid-state symmetric supercapacitor performs in a wider voltage window (1.7 V) with a superior energy density of 27.1 Wh kg^?1 at a power density of 178 W kg^?1.

Graphical abstract

     

Synthesis and characterizations of manganese ferrites for hyperthermia applications

In the last few years, magnetic nanoparticles have turned out to offer great potential in biomedical applications. This study was focused on Mn_xFe_1−xFe₂O₄ ferrite particles series with x ranging between 0 and 1. Manganese ferrites nanoparticles were prepared by co-precipitation method that allows a good control of their shape and size. The X-ray analysis indicated a crystallite size of the particles in the nanometers domain increasing with the Mn cation substitution level. Average grain size of the nanoparticles calculated from transmission electron microscopy images of the samples was ranging between 10.5 and 19.0 nm suggesting that the majority of the nanoparticles are monodomain. The hydrodynamic diameter of the water dispersed nanoparticles measured by dynamic light scattering was ranging between 60 and 105 nm proving the tendency of agglomeration. Vibrating sample magnetometer measurement confirmed the superparamagnetic behavior of the powders. The magnetic properties were analyzed considering the proposed cation distribution and Yafet–Kittel angles, while the specific absorption rate (SAR) measurement at 1.95 MHz frequency confirmed the influence of substitution level on magnetic properties and thermal transfer rate. From our results the highest value for specific absorption rate was 148.4 W g⁻¹ for Mn₂Fe₂O₄ at an AC field of 4500 A m⁻¹.