Subsequent Thermal Treatment Research Articles

DSC studies of the influence of gamma irradiation on the structural properties of the complexes formed with cetyl-trimethyl-ammonium bromide

The effect of irradiation carried out for potato starch on further transformations taking place in the starch-CTAB-water system (10:1:11) was studied using differential scanning calorimetry (DSC). Native solid starch and dense (25 wt%) starch gels were irradiated with 60Co gamma rays using doses in the range 1–30 kGy. DSC studies were carried out in heating-cooling-heating cycles (3 heating and 3 cooling cycles) with rates of 10 and 5 °C min-1. The differences were discovered between the amylose-lipid complex transition taking place in the case of the non-irradiated and the irradiated starch. The results are discussed in terms of modification the structural properties of the complex formed by the non-irradiated starch and the species irradiated using various doses. The structural changes were confirmed by FTIR spectroscopy and viscosity data. It can be concluded that the complexes formed using the irradiated starch have revealed decreased symmetry in comparison to the complex formed using the non-irradiated starch. In general, subsequent thermal treatment in the calorimeter induces further deterioration of the structure of the complex formed in the cases of the irradiated samples, while none or the opposite effect was noticed in the case of the non-irradiated starch. In the case of granular starch the changes of the complex structure were detected when the doses in the range 2–30 kGy were applied. Irradiation with a dose of 5 kGy causes easily noticeable modification of the complex.

ELECTROCHEMICAL SYNTHESIS OF DISPERSED BARIUM FERRITE USING ANODIC DISSOLUTION OF METAL

The process of anodic dissolution of iron (purity not less than 99%) in aqueous solutions of barium chloride, barium nitrate and binary electrolytes under galvanostatic conditions and by registration of potentiodynamic polarization curves was investigated. The influence of solution composition and concentration and the value of applied direct current on the intensity of anodic oxidation of iron was shown. It was revealed that the oxidation rate of metal in binary electrolytes containing barium chloride and barium nitrate is comparable with the intensity of anodic dissolution in a solution based on barium chloride. It was found that anodic polarization curve in solutions containing BaCl2 and Ba(NO3)2 has a complex form typical of passivated metals. There is a clear maximum of anodic oxidation current on this curve, as well as in barium nitrate solution, however the peak height is much higher (50-150 times). A method for the synthesis of dispersed barium ferrite, based on the anodic oxidation of iron in aqueous barium chloride and barium nitrate solutions with subsequent thermal treatment of the product of electrochemical dissolution was suggested. The phase and elemental composition and structural characteristics of obtained precursor and ferrite samples were examined using X-ray phase analysis. The influence of the heat treatment mode on the phase composition of the synthesized samples is shown. It is found that electrolysis with a soluble iron electrode using direct anode current in 0.05M BaCl2 + 0.5M Ba(NO3)2 solution and subsequent thermal treatment of the dissolution product at 1200 ° C provide the formation of dispersed system, whose phase composition is predominantly Ba0.87Fe11.08O17.15 (74%) and BaFe2O4 (17%).

Simple design of a Si–Sn–C ternary composite anode for Li-ion batteries

Previous research established that Si–Sn–C ternary composite electrodes composed of carbon nanofibers (CNFs) having robust double-hole structures filled with Si and SnOx nanoparticles displayed excellent electrochemical performance due to the thermodynamic contribution of Sn. This study reports simple and highly commercial ternary composite electrodes. By electrospinning and subsequent thermal treatment, Si and Sn nanoparticles were dispersed in solid CNFs to form Si–Sn–SC nanofibers, or they were incorporated into a core of hollow CNFs to form Si–Sn−HC nanofibers. The rate performances of these two ternary electrodes displayed quite good retention because of the ternary composition, but their rate performances differed at high current densities (5000 and 10,000mAg–1); the core/shell structure of the Si–Sn−HC nanofibers was more beneficial for rate performance retention than the Si–Sn–SC nanofibers having intimate electrical contact of Sn and Si with the carbon matrix. Improved cycling performances also resulted from the structure of the Si–Sn−HC nanofibers. The core/shell structured Si–Sn–C ternary composite anode thus has an advantageous structure for high-power Li-ion batteries having long-term stability.

Electrospun FeCo nanoparticles encapsulated in N-doped carbon nanofibers as self-supporting flexible anodes for lithium-ion batteries

This work reports a flexible, self-supporting anode, as a novel electrode material to improve the energy density of lithium-ion batteries (LIBs). In this work, FeCo nanoparticles uniformly encapsulated in one-dimensional N-doped carbon nanofibers (denoted as FeCo@NCNFs) were synthesized by electrospinning and subsequent thermal treatment. The as-prepared FeCo@NCNFs films with high electrical conductivity and good flexibility can be directly used as LIBs anodes without the addition of any conductive agents and binders. The lithium storage performance of FeCo@NCNFs is far superior to that of pure NCNFs. The impact of the carbonization temperature on the structure and electrochemical properties of FeCo@NCNFs was also investigated. Results show that FeCo@NCNFs obtained at 600 °C exhibits the optimal electrochemical performance with a relatively high reversible capacity, i.e., 566.5 mA h g−1 at 100 mA h g−1 after 100 cycles. The enhanced electrochemical properties can be mainly attributed to the synergy between 3D conductive NCNFs network and small FeCo nanoparticles, which can effectively improve the utilization rate of active materials, facilitate the transport of the electrons and lithium ions, and promote the charge-transport kinetics. Moreover, the homogeneous dispersion of FeCo nanoparticles in the NCNFs can also greatly buffer the volume change and improve the structural stability of the electrodes during the charge-discharge cycling.

Preparation and characterization of basic graphene-based catalysts and their application in biodiesel synthesis

A series of N-doped graphene-based materials was prepared from thermally reduced graphene oxide (TRGO) at elevated temperature (850 or 950 °C) under ammonia flow, and by impregnation of TRGO with melamine followed by subsequent thermal treatment. The performed analyses revealed efficient doping of TRGO with N functionalities of different types, the content of which was found to be between 3.4 wt% and 12.3 wt%, depending on the modification route and conditions. The functionalization of TRGO with NH3 was considerably less effective than that with melamine, however, the NH3-treated carbons were significantly more basic in nature (basicity up to 0.77 mmol g−1) due to the presence of quaternary N (NQ). It was also found that NQ was preferentially formed under more severe conditions, i.e., higher temperature and longer reaction time. The catalytic performance of the prepared samples was investigated in the transesterification of rapeseed oil with methanol under elevated pressure at 130 °C. The activity of carbons was strongly related to the content of NQ, and the highest yield of fatty acid methyl esters (of 65%) was obtained in the process performed with TRGO functionalized with ammonia at 950 °C for 8 h, which showed the highest number of quaternary nitrogen.

Single nozzle electrospinning promoted hierarchical shell wall structured zinc oxide hollow tubes for water remediation

HypothesisElectrospun metal oxide hollow tubes are of great interest owing to their unique structural advantages compared to solid nanofibers. Although intensive research on preparation of hollow tubes have been devoted, formation of hierarchical shells remains a significant challenge. ExperimentsHerein, we demonstrate the fabrication of highly uniform, reproducible and industrially feasible ZnO hollow tubes (ZHT) with two-level hierarchical shells via a simple and versatile single-nozzle electrospinning strategy coupled with subsequent controlled thermal treatment. FindingsThe morphological investigation reveals that the hollow tubes built from nanostructures which has unique surface structure on their wall. The mechanism by which the composite fibers transferred to hollow tubes is primarily based on the evaporation rate of the polymeric template. Notably, tuning the heating rate from 5 °C to 50 °C/min possess adverse effect on formation of hollow tubes, thus subsequently produced ZnO nanoplates (ZNP). The comparative photocatalytic analysis emphasized that ZHT shows higher photocatalytic activity than ZNP. This finding has made an evident that the inherent abundant defects in the electrospun derived nanostructures are not only sufficient for improving the photocatalytic activity. Studies on bacterial growth inhibition showcased a superior bactericidal effect against Staphylococcus aureus and Escherichia coli implying its potentiality for disinfecting the bacteria from water.

Co-presence of hydrophilic and hydrophobic sites in Ni/biochar catalyst for enhancing the hydrogenation activity

Hydrophilicity/hydrophobicity is one of the most important parameters in heterogenous catalysts, as it significantly impacts the adsorption and activation of the reaction substrate. In this study, we have demonstrated that the treatment of the biochar derived from the pyrolysis of rice husks with HNO3 oxidation and subsequent thermal treatment could remarkably increase the overall hydrophobicity of the Ni catalyst termed as Ni/biochar (treated). However, owing to the un-uniform surface of the biochar, some hydrophilic sites also exist. The co-presence of the hydrophobic and hydrophilic sites in the Ni/biochar (treated) facilitates the adsorption/activation of the CO functionality in vanillin and the aliphatic CC in eugenol. This renders the Ni/biochar (treated) catalyst with the much higher activity for hydrogenation of the unsaturated bonds than the Ni/biochar (un-treated) catalyst with mainly the hydrophilic sites. The reaction substrate like 1-chloro-2-nitrobenzene that could not form strong hydrogen bond with the biochar was less sensitive to the hydrophilicity/hydrophobicity of the catalyst. The results herein provide some reference information for optimizing catalytic performance via tailoring surface properties.

Enhanced performance of Ni catalysts supported on ZrO2 nanosheets for CO2 methanation: Effects of support morphology and chelating ligands

A series of Ni/ZrO2 catalysts was prepared by the impregnation method with modification of the morphology of ZrO2 support as well as the impregnation procedure and tested for CO2 methanation. The catalysts supported on the ZrO2 nanosheets displayed superior catalytic performance as compared with that on ZrO2 nanoparticles, which could be mainly attributed to the abundant oxygen vacancies promoting the adsorption and dissociation of CO2 molecules as well as the high dispersion of Ni species. With the introduction of ethylenediamine (En) in the impregnation procedure, the resulting Ni-15En/ZrO2-1.5 catalyst showed the optimal activity with CO2 conversion of 86% significantly higher than Ni/ZrO2-0 of 44% and Ni/ZrO2-1.5 of 79% at 0.5 MPa and 300 °C. The excellent performance was attributed to increased moderately basic sites for CO2 adsorption in ZrO2 nanosheets, as well as the enhanced dispersion of nickel caused by the complexation of Ni ions with En, which inhibited the aggregation of nickel particles in the subsequent thermal treatments. In conclusion, the synergistic effects of the morphology of ZrO2 nanosheets as well as the chelating behavior of En contributed to the enhanced performance of Ni-15En/ZrO2-1.5 in the CO2 methanation reaction. The strategy shows good prospects for controlling the size of active metals, especially those that were dispersed on the surface of the two-dimensional (2D) metal oxide materials.

Enhanced activity and selectivity of electrocatalytic denitrification by highly dispersed CuPd bimetals on reduced graphene oxide

Abstract Electrocatalytic denitrification is regarded as an environmentally friendly and effective technology for nitrate contaminated water. Enhanced activity of electrocatalysis and selectivity to benign N2 by tuning the properties of cathode materials are still desired. Herein, well-dispersed CuPd bimetals anchored on reduced graphene oxide (CuPd@rGO) are prepared via wet impregnation and subsequent thermal treatment. The synthesized materials possess relatively large surface areas (150–230 m2/g) and dispersive bimetal nanocrystals (8–25 nm, consisting of Cu, Pd, and Cu2.991Pd1.009 alloy). This catalyst achieves maximal nitrate conversion yield of 96.7% with the highest N2 selectivity of 85.5% (in the neutral electrolyte of 100 mg-N/L NaNO3), nitrate removal capacity of 5611 mg-N/mgCuPd (at 300 mg-N/L NaNO3), and superior stability after multiple cycles. The activity and stability of electrocatalyst are much higher than that of most of reported CuPd supported materials. Such outstanding performance owes to the synergistic cooperation of finely dispersive CuPd bimetals and high conductivity of rGO supports. Meanwhile, the effects of material property (e.g., metal loading) and various electrochemical conditions (e.g., potential, pH, concentration of nitrate, and concentration of electrolyte) on activity and selectivity of denitrification, as well as reaction kinetics, are systematically investigated. The cooperative denitrification mechanism of Cu, Pd and rGO is explored and creatively supported by cyclic voltammetry (CV), in-situ pH detection, inductively coupled plasma mass spectrometer (ICP-MS), and the comparison of reaction kinetics, interpreted as NO 3 - → NO 2 - → N 2 and NO 3 - → NO 2 - → NH 4 + → N 2 .

Low-Temperature Growth of Graphene on a Semiconductor

The industrial realization of graphene has so far been limited by challenges related to the quality, reproducibility, and high process temperatures required to manufacture graphene on suitable substrates. We demonstrate that epitaxial graphene can be grown on transition metal treated 6H-SiC(0001) surfaces, with an onset of graphitization starting around $450-500^\circ\text{C}$. From the chemical reaction between SiC and thin films of Fe or Ru, $\text{sp}^{3}$ carbon is liberated from the SiC crystal and converted to $\text{sp}^{2}$ carbon at the surface. The quality of the graphene is demonstrated using angle-resolved photoemission spectroscopy and low-energy electron diffraction. Furthermore, the orientation and placement of the graphene layers relative to the SiC substrate is verified using angle-resolved absorption spectroscopy and energy-dependent photoelectron spectroscopy, respectively. With subsequent thermal treatments to higher temperatures, a steerable diffusion of the metal layers into the bulk SiC is achieved. The result is graphene supported on magnetic silicide or optionally, directly on semiconductor, at temperatures ideal for further large-scale processing into graphene based device structures.

Insight into the mechanochemistry of the Maillard reaction: degradation of Schiff bases via 5-oxazolidinone intermediate

With the emergence of mechanochemistry as a fast and efficient synthetic methodology, we reported earlier that ball milling of glucose with histidine leads to the formation of reaction mixtures rich in Schiff bases. Upon subsequent thermal treatments, these mixtures exhibited enhanced reactivity generating more browning and pyrazine-rich volatiles, compared to non-milled samples. To rationalize these observations, we further investigated the mechanochemistry of the Maillard reaction using glycolaldehyde and histidine or phenylalanine as model systems. The conversion of Schiff bases into reactive 5-oxazolidinone in these model systems was proposed as the basis of the observed enhanced reactivity. Furthermore, the formation of 5-oxazolidinone in the ball-milled samples was verified through direct spectroscopic observation of its characteristic FTIR absorption band between 1780 cm−1 and 1810 cm−1 and through the identification of its specific degradation products. The important role of the carboxylic acid moiety in enabling the formation of reactive 5-oxazolidinone intermediate that facilitates its subsequent decarboxylation and formation of downstream degradation products such as dihydropyrazines and Strecker aldehydes were elucidated.

Physiological changes and stress responses of heat shock treated Salmonella enterica serovar Typhimurium

Mild heat treatment enhances the ability of microorganisms to endure subsequent heat treatment and other environmental stresses by initiating the heat shock response (HSR). This study was conducted to determine the thermal resistance of foodborne pathogens (Escherichia coli O157:H7, Salmonella enterica serovar Typhimurium, Listeria monocytogenes, Cronobacter sakazakii, and Staphylococcus aureus) after various heat shock treatments (HSTs) (50 °C for 30, 60, and 120 min) to subsequent thermal treatment at 60 °C and to investigate the mechanism for the HSR of S. Typhimurium by assessing cellular damage and morphological changes. Heat-shocked (HS) S. Typhimurium treated at 50 °C for 120 min showed the greatest resistance against subsequent heat treatment at 60 °C. Results revealed that HST caused less membrane damage and less heat-induced injury in the presence of metabolic inhibitors, compared with non-heat-shocked (non-HS) cells during thermal treatment. Furthermore, fluorescence microscopic images showed increased death, rather than sublethal injury, in non-HS cells, whereas HST induced mainly sublethal injury during thermal treatment. Analysis of electron micrographs showed that the cytoplasm was the main cellular component damaged by HST. Additionally, HST cross-protected S. Typhimurium against 15% ethanol and 25% NaCl, but not against pH 2.5, 0.01% H2O2, or -20 °C and it also enhanced thermal resistance in foods tested. Therefore, the ability of HS S. Typhimurium to tolerate subsequent thermal treatment and environmental stresses and its altered behavior should be considered when developing microbial control measures for food processing.

Dendrite-free lithium metal anode enabled by ion/electron-conductive N-doped 3D carbon fiber interlayer

Lithium metal is considered as the ultimate anode candidate for next-generation high-energy storage systems due to its ultrahigh specific capacity and low reduction potential. However, the practical application of lithium metal anode is severely impeded by uncontrollable lithium dendrite growth. In this work, a three-dimensional (3D) N-doped carbon fiber (NCF) network with ion/electron-conductivity has been fabricated by electrospinning the polyacrylonitrile solution and subsequent thermal treatment. The 3D NCF as an interlayer covering on the lithium anode is used to regulate the lithium plating/stripping behavior, accommodating partially deposited Li to realize lithium dendrite-free deposition on the lithium anode. Benefiting from these, the symmetrical cell of Li anode protected by NCF (Li@NCF) delivers long duration time (>1200 h) with a low initial nucleation overpotential (30 mV) at the current density of 1 mA cm−2. In addition, the full cell of Li@NCF||LiFePO4 exhibits excellent capacity retention of 114.6 mAh cm−2 over 360 cycles at the current density of 1 C. This strategy contributes a step forward for dendrite-free lithium metal batteries.

Achieving junction stability in heavily doped epitaxial Si:P

Junction stability and donor deactivation in silicon at high doping limit has been a long-standing issue in advanced semiconductor devices. Recently, heavily doped epitaxial Si:P layer with phosphorus concentrations as high as 3 × 1021 at./cm3 has been employed in nanowire field-effect transistor (FET) devices for sub-3 nm technology node as low resistance source-drain and channel stressor. In such highly doped Si:P, the actual dopant activation is much less than nominal phosphorus concentration due to inactive phosphorus atoms arising from dopant-vacancy defects (PnV) clustering phenomenon. Even with state-of-the-art high temperature millisecond annealing, this epitaxial film is thermally unstable upon subsequent thermal treatments. To overcome this limitation, we demonstrate a selective dopant activation scheme which results from the dipole moments of inactive PnV structures within the crystal lattice and their direct energy coupling with the external electric field. It's found that superior stability in dopant activation can be achieved through microwave annealing when a specific temperature and field conditions are met using a triple-parallel-susceptor setup in the microwave cavity. Based on experimental results and ab-initio calculation, we proposed a model, whereas the microwave-PnV interactions result in a specific distribution of dopant defect dominated by thermally stable P4V clusters through elimination of unstable low order PnV, leading to the suppression of donor deactivation and achieving thermally stable junction.

One-step in situ encapsulation of Ge nanoparticles into porous carbon network with enhanced electron/ion conductivity for lithium storage

Germanium (Ge) is considered to be one of the most promising anode materials due to the high theoretical capacity and excellent rate capability. However, its further development is hindered by the poor cycling stability caused by the severe volume change. Herein, we demonstrate a one-step in situ synthesis of Ge nanoparticles embedded into porous carbon framework (PC@Ge) using a facile sacrificial template method via the introduction of poly(methyl methacrylate) and subsequent thermal treatment. This unique nanoarchitecture not only enhances lithium-ion diffusivity and electron conductivity, but also effectively buffers the huge volume expansion and protects the Ge nanoparticles from cracking and aggregation during the cycling. Consequently, the as-prepared PC@Ge electrode exhibits superior capacity retention of 75% and 87% over 1000 cycles at 1.0 and 2.0 A·g−1, respectively.

Enhanced NO2 gas sensing properties based on Rb-doped hierarchical flower-like In2O3 microspheres at low temperature

In this work, Rb-doped hierarchical flower-like In2O3 microspheres were synthesized via a facile one-step solvothermal method along with the subsequent thermal treatment. The morphology and structure of the as-synthesized samples were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS). Gas sensors based on the pure and Rb-doped In2O3 were fabricated and their gas sensing properties were systematically investigated. The sensors based on 1 mol% Rb-doped In2O3 exhibited ultrahigh response (Rg/Ra = 1502) to 5 ppm NO2 at 75 °C, which was over 2 times higher than that of pure In2O3. Moreover, the sensors showed good response towards NO2 down to ppb level (Rg/Ra = 10.2–100 ppb), a very low theoretical detection limit of 3.5 ppb, high selectivity and reliable repeatability. The excellent and enhanced NO2 gas sensing properties were mainly owing to its high specific surface area, novel hierarchical structure and increased surface chemisorbed oxygen species induced by Rb doping.

Evolution of the Microstructure and Mechanical Properties of the Ultrafine-Grained VT8M-1 during Isothermal Die Forging and Thermal Treatment

The work addresses the microstructural evolution and mechanical properties of the ultrafine-grained (UFG) VT8M-1 subjected to isothermal die forging (IDF) and subsequent thermal treatment. An UFG microstructure with a mean size of secondary grains of about 0.3 μm was processed by a rotary swaging (RS) at Т=780°С. The ultimate tensile strength (UTS) of the alloy increased by 23% as compared to an initial state due to the formation of an UFG microstructure. It has been shown that isothermal die forging of the UFG alloy at Т=780°С leads to the growth of secondary phase grains by 0.7 μm. Subsequent heat treatment of the forged billets leads to hardening of 11%, which can be attributed both to the formation of additional interphase α/β boundaries at the precipitation of a tertiary α-phase and silicide dispersion.

Centrifugally spun SnSb nanoparticle/porous carbon fiber composite as high-performance lithium-ion battery anode

A SnSb alloy nanoparticle/porous carbon fiber (PCF) composite was prepared using a novel centrifugal spinning technology with subsequent thermal treatment. In SnSb/PCF composite, the SnSb nanoparticles are uniformly distributed in N-doped carbon fiber matrix due to the created porous structure. The centrifugal spinning can significantly increase the production rate of the fiber composites and the as-prepared SnSb/PCF composite demonstrated small particle size with uniform distribution, mesoporous structure which can facilitate the diffusion of electrolyte and N-doped carbon matrix that is beneficial to the acceleration of the electron transfer. Consequently, SnSb@CFs-20 exhibits a promising electrochemical performance in lithium storage.

Nanodesigned coatings obtained by plasma electrolytic oxidation of titanium implant and their cytotoxicity.

The titanium implant was treated with plasma electrolytic oxidation and subsequent ionic exchange and thermal treatment in order to obtain bioactive layer consisting of titanium oxide, calcium and sodium titanates and hydroxyapatite, as confirmed by X-ray diffraction (XRD). Scanning electron microscopy (SEM) revealed that the given method, besides corresponding phase composition, enables suitable nanotopology for cell attachment and proliferation. Cytotoxicity investigations by MTT, LDH and propidium iodide assays and light microscopy showed that these coatings were not toxic to L929 cells.

Catalysing the Combustion of Rice Husk and Rice Straw Towards an Energy Optimized Synthesis of Metal Modified Biogenic Silica

The classical approach for the synthesis of catalysts based on biogenic silica from rice husk or rice straw involves a high temperature (600 °C) calcination step to remove the organic matrix from the silica backbone. The remaining silica can then be impregnated with a variety of active components in the form of Mn-, Fe- and Ce-precursors, followed by subsequent thermal treatment to form the corresponding metal oxides. In this work, we introduce a novel energy optimized route for the preparation of biogenic silica supported metal oxides. The proposed synthesis procedure aims towards the reduction of pyrolysis steps by infiltrating metal salts into the biomass lignocellulosic matrix. The modified rice husk or rice straw can then be calcined to directly yield the desired metal oxide supported on biogenic silica. To evaluate the described method, as model system manganese oxide modified rice husk silica was compared to a set of materials synthesized via classical calcination-impregnation by means of textural (N2-Sorption, SEM/EDX), structural (XRD), thermal (TG/DTA) and elemental (ICP-OES; XRF) analysis. Results indicate that the introduction of transition metals into biomass powder promotes the combustion of the organic matrix in terms of temperature requirements for its complete removal. In addition, catalytic tests of the materials obtained by the novel synthesis route clearly show similar or even improved performance as compared to catalysts prepared via impregnation method.