Showing papers on "Thermal decomposition published in 2017"

Thermal Decomposition Synthesis of Iron Oxide Nanoparticles with Diminished Magnetic Dead Layer by Controlled Addition of Oxygen

Abstract: Decades of research focused on size and shape control of iron oxide nanoparticles have led to methods of synthesis that afford excellent control over physical size and shape but comparatively poor control over magnetic properties. Popular synthesis methods based on thermal decomposition of organometallic precursors in the absence of oxygen have yielded particles with mixed iron oxide phases, crystal defects, and poorer than expected magnetic properties, including the existence of a thick “magnetically dead layer” experimentally evidenced by a magnetic diameter significantly smaller than the physical diameter. Here, we show how single-crystalline iron oxide nanoparticles with few defects and similar physical and magetic diameter distributions can be obtained by introducing molecular oxygen as one of the reactive species in the thermal decomposition synthesis. This is achieved without the need for any postsynthesis oxidation or thermal annealing. These results address a significant challenge in the synthesi...

CO2 hydrogenation to lower olefins on a high surface area K-promoted bulk Fe-catalyst

Abstract: A high surface area K-promoted iron-based catalyst is prepared by thermal decomposition of ammonium glycolate complexes, followed by impregnation with an aqueous solution of potassium carbonate, drying and calcination. It is found that the duration of the calcination has a dramatic effect on the textural and structural properties of the obtained material, as well as on the iron oxidation state. Fast calcinations allow to synthetize materials isostructural with Fe3O4/γ-Fe2O3 that, after a carburization treatment with CO/H2 mixtures, are highly active in the CO2 hydrogenation to lower (C2–C4) olefins at mild process conditions (300 °C and 5 barg). Interestingly, the decrease of the operating pressure leads to a shift from the “hydrocarbon synthesis” regime to reverse water gas shift regime. The selectivity to lower olefins is instead maximised at mild process conditions due to the moderate chain growth probability and the slow rate of olefin secondary hydrogenations, which dominate at higher pressure and temperatures, respectively. The former process is activated by type II catalytic sites (iron carbides), while the latter occurs on type III catalytic sites (Fe0). Type I catalytic sites also exist (Fe3O4) and are responsible for the RWGS activity of the catalyst. Collected data suggest that CO is the primary product of CO2 hydrogenation, while hydrocarbons are formed via CO hydrogenation, following a Fischer-Tropsch type mechanism. Eventually, the performances of the prepared catalyst are compared with those of K-promoted reference model samples based on commercial α-Fe2O3 and Fe3O4 powders. It is found that, due to a better carburization and the higher surface area, the catalyst prepared by fast decomposition of ammonium glycolate complexes is more active than the reference materials in terms of both CO2 conversion and C2–C4 olefins selectivity.

Conductive Carbon Nitride for Excellent Energy Storage.

Abstract: Conductive carbon nitride, as a hypothetical carbon material demonstrating high nitrogen doping, high electrical conductivity, and high surface area, has not been fabricated. A major challenge towards its fabrication is that high conductivity requires high temperature synthesis, but the high temperature eliminates nitrogen from carbon. Different from conventional methods, a facile preparation of conductive carbon nitride from novel thermal decomposition of nickel hydrogencyanamide in a confined space is reported. New developed nickel hydrogencyanamide is a unique precursor which provides self-grown fragments of ⋅NCN⋅ or NCCN and conductive carbon (C-sp2) catalyst of Ni metal during the decomposition. The final product is a tubular structure of rich mesoporous and microporous few-layer carbon with extraordinarily high N doping level (≈15 at%) and high extent of sp2 carbon (≈65%) favoring a high conductivity (>2 S cm−1); the ultrahigh contents of nongraphitic nitrogen, redox active pyridinic N (9 at%), and pyrrolic N (5 at%), are stabilized by forming NiN bonds. The conductive carbon nitride harvests a large capacitance of 372 F g−1 with >90% initial capacitance after 10 000 cycles as a supercapacitor electrode, far exceeding the activated carbon electrodes that have <250 F g−1.

Facile one-pot synthesis of iron nanoparticles immobilized into the porous hydrochar for catalytic decomposition of phenol

Abstract: Iron-based nanocatalysts were synthesized by a green and facile one-pot hydrothermal carbonization (HTC) process. Precursory iron salts with different concentrations were dissolved together with the lignocellulosic matrix (i.e., pinewood sawdust) in the solution, and the mixtures were heated to 200 °C for 1 h in a sealed autoclave. After hydrothermal treatment, carbon spheres were formed with the iron precursors tightly embedded in the microsphere/mesopheres of the amorphous carbon matrix. By contrast, the impregnation of the iron salts onto the hydrothermal carbons (hydrochars) derived from HTC of sawdust were conducted as a control method. The nanomaterials prepared by these two approaches were evaluated comparatively. Compared to the impregnation approach, a nanocatalyst with more uniformly dispersed Fe nanoparticles (NPs) immobilized on the hydrochars was produced by the one-pot synthesis. Furthermore, the particle size of the Fe NPs and surface area of the nanocatalysts via the one-pot synthesis can be manipulated. The catalytic abilities of the Fe-based nanomaterials prepared by the two approaches were then tested in a fixed bed tubular reactor for biomass tar using phenol as the model compound. The nanocatalysts prepared by the one-pot synthesis exhibited higher catalytic activity in the thermal decomposition of the phenol at mild temperatures and resistance to coke deposition. The present study showed that the simple and efficient one-pot synthesis assisted uniform dispersion of Fe NPs on the surface of hydrochar through a surface-mediated chemistry. In addition, such facile one-pot synthesis may be applied to synthesize other metal or metal oxide NPs embedded in the hydrochars with more complex structures and unique chemical/physical properties.

Photoregenerable, Bifunctional Granules of Carbon-Doped g-C3N4 as Adsorptive Photocatalyst for the Efficient Removal of Tetracycline Antibiotic

Abstract: Environmental remediation employing semiconducting materials offer a greener solution for pollution control. Herein, we report the development of high surface area porous architecture of C3N4 nanosheets by a simple aqueous spray drying process. g-C3N4 nanosheets obtained by the thermal decomposition of urea-thiourea mixture are spray granulated to microspheres using 2 wt% poly vinyl alcohol (PVA) as binder. The post granulation thermal oxidation treatment resulted in in situ doping of carbon leading to improved photophysical properties compared to pristine g-C3N4. The C3N4 granules with surface area values of 150 m2/g rendered repetitive adsorption of tetracycline antibiotic (∼75% in 60 min) and the extended absorption in the visible region facilitated complete photocatalytic degradation upon sunlight irradiation (>95% in 90 min). The delocalized π bonds generated after carbon doping and the macro-meso porous architecture created by the granulation process aided high adsorption capacity (70 mg/g). The pho...

Impact of Thermal Decomposition on Thermal Desorption Instruments: Advantage of Thermogram Analysis for Quantifying Volatility Distributions of Organic Species.

Abstract: We present results from a high-resolution chemical ionization time-of-flight mass spectrometer (HRToF-CIMS), operated with two different thermal desorption inlets, designed to characterize the gas and aerosol composition. Data from two field campaigns at forested sites are shown. Particle volatility distributions are estimated using three different methods: thermograms, elemental formulas, and measured partitioning. Thermogram-based results are consistent with those from an aerosol mass spectrometer (AMS) with a thermal denuder, implying that thermal desorption is reproducible across very different experimental setups. Estimated volatilities from the detected elemental formulas are much higher than from thermograms since many of the detected species are thermal decomposition products rather than actual SOA molecules. We show that up to 65% of citric acid decomposes substantially in the FIGAERO–CIMS, with ∼20% of its mass detected as gas-phase CO2, CO, and H2O. Once thermal decomposition effects on the det...

A comparison of graphitic carbon nitrides synthesized from different precursors through pyrolysis

Abstract: Two precursors, melamine and urea, were used to prepare graphitic carbon nitride through a thermal decomposition (pyrolysis) method. The pyrolysis was carried out at different temperatures in open air condition in a crucible with cover. The as-prepared samples were characterized by SEM, TEM, BET, XRD, XPS, FTIR and DRS. The characterization results revealed that the samples synthesized from different precursors had different physical and chemical properties. Specifically, it was found that the pyrolysis of urea yielded product with smaller crystalline domains but larger surface areas compared to that of melamine. To further qualify the as-prepared samples, the adsorption and photocatalytic activities were measured by using Rhodamine B (RhB) as target pollutant. It was found out that the precursors as well as pyrolysis temperatures had big influences on the adsorption and photocatalytic activities. Higher photocatalytic activities were achieved by samples synthesized from urea at higher temperatures. The mechanism of the degradation process was explored on the basis of the band structure and the roles of photo-generated radicals.

Thermal decomposition and recovery properties of ZnAl–CO3 layered double hydroxide for anionic dye adsorption: insight into the aggregative nucleation and growth mechanism of the LDH memory effect.

Abstract: The thermal decomposition of carbonate-intercalated layered double hydroxide (ZnAl–CO3-LDH) and recovery induced by water and dye solution addition were studied in situ by time-resolved wide angle X-ray scattering (WAXS) and time-resolved X-ray absorption spectroscopy (XAS), providing insights into the mechanisms of these structural transformations. LDH nanostructure recovery was driven by an aggregative nucleation and growth mechanism, which is limited by the steric hindrance caused by the adsorption of the Acid Blue 113 azo dye (AB) on the external surface of both the nanocrystalline tactoids and the exfoliated layers. The recovery behaviour in dye solution is consistent with the hypothesis of the LDH-recovery by a direct synthesis process, generating nanosized LDH particles with thickness about four times lower than those induced by water addition. These findings explain the higher AB adsorption capacity (1587 mg g−1) of calcined LDH, compared to pristine ZnAl–CO3-LDH (261.8 mg g−1) and also the efficient recycling of the spent adsorbent.

Sulfur Transformation during Microwave and Conventional Pyrolysis of Sewage Sludge

Abstract: The sulfur distributions and evolution of sulfur-containing compounds in the char, tar and gas fractions were investigated during the microwave and conventional pyrolysis of sewage sludge. Increased accumulation of sulfur in the char and less production of H2S were obtained from microwave pyrolysis at higher temperatures (500–800 °C). Three similar conversion pathways were identified for the formation of H2S during microwave and conventional pyrolysis. The cracking of unstable mercaptan structure in the sludge contributed to the release of H2S below 300 °C. The decomposition of aliphatic-S compounds in the tars led to the formation of H2S (300–500 °C). The thermal decomposition of aromatic-S compounds in the tars generated H2S from 500 to 800 °C. However, the secondary decomposition of thiophene-S compounds took place only in conventional pyrolysis above 700 °C. Comparing the H2S contributions from microwave and conventional pyrolysis, the significant increase of H2S yields in conventional pyrolysis was m...

Thermal Decomposition of the Solid Electrolyte Interphase (SEI) on Silicon Electrodes for Lithium Ion Batteries

Abstract: Thermal behavior of the solid electrolyte interphase (SEI) on a silicon electrode for lithium ion batteries has been investigated by TGA. In order to provide a better understanding of the thermal decomposition of the SEI on silicon, the thermal decomposition behavior of independently synthesized lithium ethylene dicarbonate (LEDC) was investigated as a model SEI. The model SEI (LEDC) has three stages of thermal decomposition. Over the temperature range of 50–300 °C, LEDC decomposes to evolve CO2 and C2H4 gases leaving lithium propionate (CH3CH2CO2Li) and Li2CO3 as solid residues. The lithium propionate decomposes over the temperature range of 300–600 °C to evolve pentanone leaving Li2CO3 as a residual solid. Finally, the Li2CO3 decomposes over 600 °C to evolve CO2 leaving Li2O as a residual solid. A very similar thermal decomposition process is observed for the SEI generated on cycled silicon electrodes. However, two additional thermal decomposition reactions were observed characteristic of LixPOyFz at 30...

Facile synthesis of g-C3N4 nanosheets loaded with WO3 nanoparticles with enhanced photocatalytic performance under visible light irradiation

Abstract: Graphitic carbon nitride (g-C3N4) nanosheets loaded with WO3 nanoparticles were prepared via heat treatment of g-C3N4 together with WOx-EDA nanobelts. The thermal treatment temperature and WOx-EDA precursor play the key role in enhancing the interaction between WO3 nanoparticles and g-C3N4 nanosheets, because the temperature of thermal decomposition of WOx-EDA (∼400 °C) is close to the thermal exfoliation temperature of g-C3N4. The structure evolution and promotion effect of the nanocomposites in photocatalytic performance were well studied. It is found that WO3 nanoparticles uniformly dispersed on the surface of the g-C3N4 nanosheets, and the close integration of WO3 and g-C3N4 lead to the high photocatalytic activity in the degradation of RhB under visible light irradiation. Meanwhile, a larger specific area and increase of visible light absorption are also of benefit to speed up the degradation of organic dye. Also, the mechanism of the photocatalytic reaction and its reutilization properties were investigated.

Temperature-Controlled Synthesis of Porous CuO Particles with Different Morphologies for Highly Sensitive Detection of Triethylamine

Abstract: Because porous metal oxides with controllable morphologies have been attracting much attention for their potential applications in the fields of adsorption/separation, sensing, energy storage, and conversion, it is highly desirable to prepare new morphology of metal oxides and investigate their performance. In this work, CuO particles with different shapes such as octahedron, sponge-like octahedron, and sphere have been synthesized through thermal decomposition of crystalline Cu(II)–organic frameworks (HKUST-1). The structure and morphology of as-prepared CuO particles have been fully characterized by the usage of XRD, XPS, SEM, and TEM. The gas-sensing behaviors of these CuO samples have been investigated and our results show that CuO-400 with spherical shape displays unprecedented high response (maximum value, 102) for triethylamine (TEA) at 100 ppm with a low detection limit of 5 ppm, a lower working temperature (230 °C), excellent reproducibility, and long-term stability. The highly sensing behavior o...

A study on the nature of the thermal decomposition of methylammonium lead iodide perovskite, CH3NH3PbI3: an attempt to rationalise contradictory experimental results

Abstract: The nature of the gas phase product released during the thermal decomposition of CH3NH3PbI3 (methylammonium lead iodide) to PbI2 (lead diiodide) under vacuum is discussed on the basis of thermodynamic predictions, recently published experimental results, and new experiments presented here. From the limited data currently available, the nature of the main decomposition path is not clear because, both, the process releasing HI(g) + CH3NH2(g) (1) and that leading to NH3(g) + CH3I(g) (2) were observed under different conditions. Our thermodynamic analysis showed that process (2) is largely favoured for all the CH3NH3PbX3 (X = Cl, Br, I) compounds. However, Knudsen effusion mass spectrometry experiments (temperature range 140–240 °C) showed that HI(g) and CH3NH2(g) were the predominant species in the vapor, with process (2) occurring to a much smaller extent than suggested by the thermodynamic driving force, thus being of minor importance under effusion conditions. We also found that this process was comparatively enhanced by high temperatures and low effusion rates (high impedance orifice). Our experimental evidence suggested that the thermodynamically favoured process (2) was affected by a significant kinetic hindrance. Overall, the prevailing decomposition path is likely to markedly depend on the actual operative conditions.

Monodisperse Iron Oxide Nanoparticles by Thermal Decomposition: Elucidating Particle Formation by Second-Resolved in Situ Small-Angle X-ray Scattering

Abstract: The synthesis of iron oxide nanoparticles (NPs) by thermal decomposition of iron precursors using oleic acid as surfactant has evolved to a state-of-the-art method to produce monodisperse, spherical NPs. The principles behind such monodisperse syntheses are well-known: the key is a separation between burst nucleation and growth phase, whereas the size of the population is set by the precursor-to-surfactant ratio. Here we follow the thermal decomposition of iron pentacarbonyl in the presence of oleic acid via in situ X-ray scattering. This method allows reaction kinetics and precursor states to be followed with high time resolution and statistical significance. Our investigation demonstrates that the final particle size is directly related to a phase of inorganic cluster formation that takes place between precursor decomposition and particle nucleation. The size and concentration of clusters were shown to be dependent on precursor-to-surfactant ratio and heating rate, which in turn led to differences in th...

Cobalt carbonate and cobalt oxide nanoparticles synthesis, characterization and supercapacitive evaluation

Abstract: Taguchi robust design methodology was used to optimize direct precipitation reaction conditions for simple and fast synthesis of cobalt carbonate nanoparticles. The effects of several parameters that influence on particle size of prepared cobalt carbonate were investigated. The significance of these parameters on the size of cobalt carbonate particles were quantitatively evaluated by using of analysis of variance (ANOVA). The results showed that flow rate and the concentrations of cobalt and carbonate solutions have significant effect on the size of cobalt carbonate nanoparticles. Also, optimum conditions for synthesis of cobalt carbonate nanoparticles via precipitation reaction were achieved. The ANOVA demonstrated that under optimum condition, cobalt carbonate nanoparticles will have of 39.6 ± 2.2 nm sizes. In addition, the solid state thermal decomposition reaction of precursor was used for preparation of Co3O4 nanoparticles. The results showed that the Co3O4 nanoparticles synthesized by thermal decomposition of cobalt carbonate nanoparticles have 53 nm sizes. Cyclic voltammetry, galvanostatic charge/discharge and electrochemical impedance spectroscopy were used to investigate the supercapacitive property of the Co3O4 electrode. The Co3O4 electrode shows high specific capacitance of 396 F g−1 at scan rate of 2 mV s−1 in 2.0 M H2SO4 electrolyte. Thus, the prepared electrode could be used for supercapacitor.

Pursuing reliable thermal analysis techniques for energetic materials: decomposition kinetics and thermal stability of dihydroxylammonium 5,5′-bistetrazole-1,1′-diolate (TKX-50)

Abstract: Thermal decomposition of a novel promising high-performance explosive dihydroxylammonium 5,5′-bistetrazole-1,1′-diolate (TKX-50) was studied using a number of thermal analysis techniques (thermogravimetry, differential scanning calorimetry, and accelerating rate calorimetry, ARC). To obtain more comprehensive insight into the kinetics and mechanism of TKX-50 decomposition, a variety of complementary thermoanalytical experiments were performed under various conditions. Non-isothermal and isothermal kinetics were obtained at both atmospheric and low (up to 0.3 Torr) pressures. The gas products of thermolysis were detected in situ using IR spectroscopy, and the structure of solid-state decomposition products was determined by X-ray diffraction and scanning electron microscopy. Diammonium 5,5′-bistetrazole-1,1′-diolate (ABTOX) was directly identified to be the most important intermediate of the decomposition process. The important role of bistetrazole diol (BTO) in the mechanism of TKX-50 decomposition was also rationalized by thermolysis experiments with mixtures of TKX-50 and BTO. Several widely used thermoanalytical data processing techniques (Kissinger, isoconversional, formal kinetic approaches, etc.) were independently benchmarked against the ARC data, which are more germane to the real storage and application conditions of energetic materials. Our study revealed that none of the Arrhenius parameters reported before can properly describe the complex two-stage decomposition process of TKX-50. In contrast, we showed the superior performance of the isoconversional methods combined with isothermal measurements, which yielded the most reliable kinetic parameters of TKX-50 thermolysis. In contrast with the existing reports, the thermal stability of TKX-50 was determined in the ARC experiments to be lower than that of hexogen, but close to that of hexanitrohexaazaisowurtzitane (CL-20).

Pd2Ga-Based Colloids as Highly Active Catalysts for the Hydrogenation of CO2 to Methanol

Abstract: Colloidal Pd2Ga-based catalysts are shown to catalyze efficiently the hydrogenation of CO2 to methanol. The catalysts are produced by the simple thermal decomposition of Pd(II) acetate in the presence of Ga(III) stearate, which leads to Pd0 nanoparticles (ca. 3 nm), and the subsequent Pd-mediated reduction of Ga(III) species at temperatures ranging from 210 to 290 °C. The resulting colloidal Pd2Ga-based catalysts are applied in the liquid-phase hydrogenation of carbon dioxide to methanol at high pressure (50 bar). The intrinsic activity is around 2-fold higher than that obtained for the commercial Cu-ZnO-Al2O3 (60.3 and 37.2 × 10–9 molMeOH m–2 s–1), respectively, and 4-fold higher on a Cu or Pd molar basis (3330 and 910 μmol mmolPd or Cu–1 h–1). Detailed characterization data (HR-TEM, STEM/EDX, XPS, and XRD) indicate that the catalyst contains Pd2Ga nanoparticles, of average diameters 5–6 nm, associated with a network of amorphous Ga2O3 species. The proportion of this Ga2O3 phase can be easily tuned by ad...

Alumina-graphene hybrid filled epoxy composite: Quantitative validation and enhanced thermal conductivity

Abstract: Alumina-graphene hybrid fillers (Gr-Al2O3) were synthesized and added to the epoxy matrix to improve thermal properties of the epoxy composite. The alumina particles were surface modified with silane coupling agents like 3-Aminopropyl triethoxysilane (A-Al2O3). 3-Glycidyloxypropyl trimethoxysilane (GPTMS) was used for the surface modification of the graphene (G-Graphene). These modifications on the filler surface help to develop the interface between the fillers and the epoxy matrix, which might help to form the effective 3D thermal conductive networks. The generation of these 3D networks facilitated in reducing the Kapitza resistance and increases the transportation of phonons in the matrix, Furthermore; it improved the integral procedure decomposition temperature (IPDT) and activation energy (Ea) of the composite. Alumina-graphene hybrid filled epoxy composite (hAG-Epoxy) with 50 vol% of hybrid filler (Gr-Al2O3) expressed the considerable improvement in in-plane thermal conductivity and IPDT by ∼8.4 and ∼3.1 folds in comparison with neat epoxy, respectively. The significant improvement in thermal conductivity was related to the generation of effective 3D thermal conductive pathways formed by 2D graphene and 1D alumina in the composite.

Thermal Decomposition Of The Amino Acids Glycine, Cysteine, Aspartic Acid, Asparagine, Glutamic Acid, Glutamine, Arginine And Histidine

Abstract: Calorimetry, thermogravimetry and mass spectrometry were used to follow the thermal decomposition of the eight amino acids G, C, D, N, E, Q, R and H between 185 °C and 280 °C. Endothermic heats of decomposition between 72 and 151 kJ/mol are needed to form 12 to 70 % volatile products. This process is neither melting nor sublimation. With exception of cysteine they emit mainly H2O, some NH3 and no CO2. Cysteine produces CO2 and little else. The reactions are described by polynomials, AA → a (NH3) + b (H2O) + c (CO2) + d (H2S) + e (residue), with integer or half integer coefficients. The solid monomolecular residues are rich in peptide bonds.

Design of Porous/Hollow Structured Ceria by Partial Thermal Decomposition of Ce-MOF and Selective Etching.

Abstract: Metal–organic frameworks (MOFs) have been widely used to prepare corresponding porous metal oxides via thermal treatment. However, high temperature treatment always leads to obtained metal oxides with a large crystallite size, thus decreasing their specific surface area. Different from the conventional complete thermal decomposition of MOFs, herein, using Ce-MOF as a demonstration, we choose partial thermal decomposition of MOF, followed by selective etching to prepare porous/hollow structured ceria because of the poor stability of Ce-MOF under acidic conditions. Compared with the ceria derived from complete thermal decomposition of Ce-MOF, the as-prepared ceria is demonstrated to be a good support for copper oxide species during the CO oxidation catalytic reaction. Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), and hydrogen temperature-programmed reduction (H2-TPR) analysis revealed that the as-prepared ceria is favorable for strengthening the interaction between the ceria and loaded copper ...