Solid-state Thermal Reaction Research Articles

Magnesiothermic reduction SiO coated with vertical carbon layer as high-performance anode for lithium-ion batteries

Silicon monoxide (SiO), as one of the most competitive anode materials for lithium-ion batteries (LIBs), has received considerable attention. Nevertheless, poor initial Coulombic efficiency (ICE) and larger volume change are the main obstacles to the application of SiO. Here, we suggest a controllable route for the modification of micro-sized SiO via magnesiothermic reduction. To prevent the excessive growth of Si grains caused by the overheating reaction, the solid-state thermal reaction between Mg and SiO is achieved by mixing a certain proportion of NaCl at a suitable temperature, resulting in a loose surface and porous structure of SiO particles, which is conducive to the transportation of lithium ions and electrons. Combined with chemical vapor deposition (CVD), the carbon-coated SiOx composites (M-SiOx@C-R, where R is the molar ratio for Mg and SiO) exhibit unique morphology structure and remarkable electrochemical characteristics. As expected, the vertical carbon network improves the conductivity and alleviates the volume expansion of SiOx. Notably, the M-SiOx@C-0.75 electrode offers a large initial specific capacity of 2283.17 mAh g−1 with a higher ICE of 86.03 % at 100 mA g−1. Furthermore, the full cells using M-SiOx@C-0.75 composite as the negative electrode and LiNi0.8Co0.1Mn0.1O2 (NCM811) as the positive electrode were assembled. After 150 cycles, the full cell still delivers a high specific capacity of 72.22 mAh g−1 (with a retention rate of 47 %). This work provides a feasible route for the fabrication of applicable SiO-based anode materials.

Modulation of Solid-state Thermal Reaction of Iron(III)Citrate by a Co-precursor Studied using Thermogravimetry: Evaluation of Kinetic and Thermodynamic Parameters and Nucleation Rate

Background: Solid state reaction of iron(III)citrate leads to a range of ironbased oxides by varying the reaction conditions, e.g., the presence of co-precursor. The influence of reaction conditions on the kinetics of the solid-state reaction of iron(III)citrate needs to be investigated. Objective: Kinetic analysis of the solid-state reaction of iron(III)citrate in the presence of a co-precursor has been explored to realize the influences of the co-precursor on the reaction process as well as decomposed material. Method:: Non-isothermal thermogravimetry profiles are deconvoluted to individual reaction steps. The model-free kinetic methodology is utilized to estimate step-wise activation energy and, hence, the reaction mechanism along with the reaction rate. Conversiondependent thermodynamic parameters and nucleation rate are estimated. XRD analysis has been used to characterize the decomposed material. Results: Thermogravimetry profiles obtained for an iron(III)citrate and malonic acid mixture are deconvoluted into six steps. The decomposed nanomaterial is identified as magnetite (size 10 nm). The observed reaction mechanisms associated with each step are different, where the activation/reaction rate is conversion-dependent. A good fit between the experimental and reverse-constructed conversion profiles is obtained. The nucleation rate at higher temperatures is affected by both the extent of conversion and the heating rate. A possible reaction pathway is proposed. The study elucidates the role of malonic acid as a co-precursor in modifying the thermal reaction of iron(III)citrate and product formation. Conclusion: This investigation proposes the applicability of suitable co-precursors as a potential controlling factor for preparing iron oxides from iron-based compounds.

Highly efficient (V2O5)0.91Zn0.09 powdered catalyst for water organic pollutant elimination

(V2O5)1-x Znx powdered samples with different light doping levels (x = 0.03–0.09) were prepared by a solid-state thermal reaction and studied by X-ray diffraction (XRD), field emission scanning electron microscope (FE-SEM), energy dispersive analysis (EDAX), and optical diffuse reflectance spectroscopies. The prepared samples has been revealed that the increments in Zn-doping levels accompanied by vacuum heat treatment lead to the appearance of an additional V12O26 phase beside the pure V2O5 oxide, resulting not only in more donor vanadium atom liberation but also in multi-heterojunction component formation. Besides, Eg values decrease from 2.38 to 2.2 eV as Zn doping increases from x = 0 to x = 0.09. All previous observations improve the process of purifying water from pollutants by increasing the number of free carriers of V2O5 powder by adding Zn atoms and making vacuum heat treatments. The photocatalytic examination has been carried out using constants of 0.5 g and 0.01 g/L (10 ppm) of the catalyst quantity and MB-dye concentration, respectively, under Vis – irradiations. The acidic solution medium with a pH of 2 strongly motivated the degradation activity. The highest catalytic efficiency of 99.78% was attained by the (V2O5)0.91 Zn 0.09 compound within a time of 70 min and continued invariably for 5 hours in the dark. These catalytic results have proved the possibility of their reusability.

High entropy alloy nanoparticles encapsulated in graphitised hollow carbon tubes for oxygen reduction electrocatalysis.

High entropy alloys (HEAs) with a tunable alloy composition and fascinating synergetic effects between various metals have attracted significant attention in the field of electrocatalysis, but their potential is limited by inefficient and unscalable fabrication methodologies. This work proposes a novel solid-state thermal reaction method to synthesise HEA nanoparticles encapsulated in an N-doped graphitised hollow carbon tube. This facile method is simple and efficient and involves no use of organic solvents during the fabrication process. The synthesized HEA nanoparticles are confined by the graphitised hollow carbon tube, which is possibly beneficial for preventing the aggregation of alloy particles during the oxygen reduction reaction (ORR). In a 0.1 M KOH solution, the HEA catalyst FeCoNiMnCu-1000(1 : 1) exhibits an onset and half-wave potential of 0.92 V and 0.78 V (vs. RHE), respectively. We assembled a Zn-Air battery with FeCoNiMnCu-1000 as a catalyst for the air electrode, and a power density of 81 mW cm-2 and a long-term durability of >200 h were achieved, which is comparable to the performance of the state-of-the-art catalyst Pt/C-RuO2. This work herein offers a scalable and green method for synthesising multinary transition metal-based HEAs and highlights the potential of HEA nanoparticles as electrocatalysts for energy storage and conversion.

Insights into a co-precursor driven solid-state thermal reaction of ferrocene carboxaldehyde leading to hematite nanomaterial: a reaction kinetic study.

Thermal decomposition of a mixture of ferrocene carboxaldehyde and oxalic acid dihydrate in O2 atmosphere produced rod-like hematite nanomaterial. The decomposition reaction was complex as evident from the overlapped multistep reaction steps in the non-isothermal thermogravimetry (TG) profiles obtained in the 300-700 K range. A peak deconvolution method was applied to separate the overlapped reaction steps. The multistep TG profiles were successfully deconvoluted, which showed that the decomposition occurs in six individual steps. However, it was found that only the last three reaction steps were responsible for the production of hematite. To estimate the activation energy values for these thermal reactions, six model-free integral isoconversional methods were used. The activation energy value significantly depends on the extent of conversion in each step; however, the nature of its dependence significantly different for each step. The most probable stepwise reaction mechanism functions for the solid-state reactions were obtained using the master plot method. The reaction mechanism was found to be different for different steps. Utilizing the activation energy and reaction mechanism function, the reaction rates of decomposition for each step were determined. To substantiate the validity of the assumed kinetic models, the experimental conversion curves were compared with the constructed ones, and the agreement was quite reasonable. The conversion-dependent thermodynamic parameters were obtained utilising the estimated kinetic parameters. Role of the co-precursor in the thermal reaction of the precursor was plausibly revealed. The present study describes how the use of a co-precursor significantly enhances the thermal decomposition of the precursor, how hematite nanomaterials can be synthesized from a co-precursor driven solid state reaction at low temperatures, and how the kinetic calculations facilitate the understanding of the solid-state reaction process. This study proposes the use of a suitable combination of precursor and co-precursor for solid-state thermal synthesis of iron-based nanoparticles using organo-iron compounds as precursor and also illustrates the effective application of the thermal analysis technique to understand the decomposition reaction.

A Green Chemistry Approach toward the Stereospecific Synthesis of Densely Functionalized Cyclopropanes via the Solid-State Photodenitrogenation of Crystalline 1-Pyrazolines.

The cyclopropane ring features prominently in active pharmaceuticals, and this has spurred the development of synthetic methodologies that effectively incorporate this highly strained motif into such molecules. As such, elegant solutions to prepare densely functionalized cyclopropanes, particularly ones embedded within the core of complex structures, have become increasingly sought-after. Here we report the stereospecific synthesis of a set of cyclopropanes with vicinal quaternary stereocenters via the solvent-free solid-state photodenitrogenation of crystalline 1-pyrazolines. Density functional theory calculations at the M062X/6-31+G(d,p) level of theory were used to determine the origin of regioselectivity for the synthesis of the 1-pyrazolines; favorable in-phase frontier molecular orbital interactions are responsible for the observation of a single pyrazoline regioisomer. It was also shown that the loss of N2 may take place via a highly selective solid-state thermal reaction. Scalability of the solid-state photoreaction is enabled through aqueous nanocrystalline suspensions, making this method a "greener" alternative to effectively facilitate the construction of cyclopropane-containing molecular scaffolds.

The kinetic analysis of lignite and waste biomass during co-combustion process by general distributed activation energy model

In this work, the new general distributed activation energy model (G-DAEM) was employed to obtained kinetic parameters during co-combustion process. Four pseudo-components for both lignite and waste biomass were optimized and the simulation results demonstrated excellent match. The results suggested that the G-DAEM is an effective and comprehensive kinetic model for complex solid-state thermal reaction. Assume the pre-frequency factor A is not a fixed number, the real kinetic mechanism may be obtained by the G-DAEM method.

The structure and photoluminescence properties of a novel yellow-green emission phosphor Ba3Sc2B4O12: Ce3+ excited by NUV light

A kind of borate mineral (Ba3Sc2B4O12) based Ce3+ doped phosphor is prepared by high thermal solid state reaction successfully. Its crystal and energy band is studied in detail by TEM, XRD and First Principle calculation. Ba3Sc2B4O12 crystallizes by trigonal system and P-3m1(164) space group. Series of Ce3+ doped Ba3Sc2B4O12 phosphors are researched. The energy band, electron cloud density and luminescent properties of Ba3Sc2B4O12: Ce3+ are investigated in great detail by density functional theory calculations, emission-excitation spectra, decay times and thermal dependent spectra. Ba3Sc2B4O12: Ce3+ can yield blue-green-yellow broad light at ~539 nm with FWHM 190 nm upon 370 nm light stimulation and the quantum efficiency is 22.7%. According to electron cloud density and photoluminescence (PL) property analysis, Ce3+ can occupy two kinds luminescent centers. White-LED is also fabricated combining with NUV chip covered by this phosphor and (Ca, Sr)AlSiN3: Eu2+ mixture driven by 3 V and 25 mA. It can generate warm-white light with 4180 K correlated color temperature. It demonstrates that Ba3Sc2B4O12: Ce3+ is a kind of RGB phosphor to get warm white light combining with NUV LED chip.

Solid state and phase transformation mechanism of kaolin sintered with limestone for alumina extraction

The present work aims to investigate the effects of the solid-state thermal reactions at different sintering temperatures on the phase transformation mechanisms and the microstructural changes, the self-disintegration mechanism as well as the efficiency of alumina percent recovery during alumina extraction from kaolin by the lime-sinter process. The sinters were produced at different temperatures within the range 800 °C - 1400 °C then subjected to leaching process (at the optimum dissociation of 1:5 solid : liquid ratio) by using sodium carbonate solutions (120 g/L) which finally were given to the alumina-pregnant solution. Thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) were used for characterizing the transformational changes resulted during the thermal reactions between the sintered mineral components in the raw kaolin and limestone samples (i.e., kaolinite and calcite). Microstructural and textural changes of the obtained sinters and sludges were characterized by means of X-ray diffractometry (XRD/XRF), scanning electron microscopy (SEM/EDX) and particle size granulometry. The results indicated that the sintering temperature at 1360 °C was the optimum for inducing of the solid-state reaction between the clay and carbonate components with enhancement of alumina productivity by the highest recovery (80.49%). At this superlative sintering condition, the kaolinite was dehydroxylated and transformed into metakaolinite while the calcite was decomposed into calcium oxide, then they reacted together forming to the calcium aluminates that are considered as the highly effective and generative precursor phases in the alumina extraction. Moreover, the obtained sludges were obviously exhibited morphological changes with size enlargements during the leaching process due to the formation of calcium carbonate particles that agglomerated at the surfaces of the insoluble sludge particles.

Solventless synthesis and characterization of α-Fe, γ-Fe, magnetite and hematite using iron(III)citrate

The paper presents a method to synthesize α-Fe, γ-Fe, magnetite and hematite through solventless thermal decomposition technique using an organo-metallic compound iron(III)citrate in two different atmospheres (N2 and O2) at different temperatures and the characteristics of these products. The solid state thermal reaction has been monitored by non-isothermal thermogravimetry. The FT-IR spectra and powder XRD pattern of the decomposed products reveal the type of materials formed and the SQUID measurements confirm those. Mössbauer spectroscopic study confirms the nature of magnetic structure of the synthesized materials. The SEM and TEM studies are used to study the shape and size of the particles formed. EDX technique has been employed to know the elemental composition. The solid state reaction processes involved in the synthesis have been proposed. The present study indicates that different types of iron/iron oxide particles in the range of nano-scale can be synthesized on thermal decomposition of iron(III)citrate depending on the decomposition temperature as well as the reaction atmosphere.

Effect of Co-precursor Maliec Anhydride on the Thermal Decomposition of Acetyl Ferrocene: A Reaction Kinetic Analysis

Background: Thermal decomposition of iron-bearing organometallic complex acetyl ferrocene, (C5H4COCH3)Fe(C5H5), leads to hematite (α-Fe2O3) nanoparticles. Presence of maliec anhydride, C4H2O3 as co-precursor during thermal decomposition modifies the size of the particles as well as the quantity of the reaction product significantly. Objective: Kinetic analysis of the solid-state thermal reaction of acetyl ferrocene in the presence of varying amount of co-precursor maliec anhydride under inert reaction atmosphere has been studied in order to understand the reaction mechanism involved behind the formation of hematite and the role of co-precursor in the reaction process. For this purpose, reaction kinetic analysis of three mixtures of acetyl ferrocene and maliec anhydride has been carried out. Methods: Thermogravimetry under non-isothermal protocol with multiple heating rates has been employed. The data are analyzed using model-free iso-conversional kinetic techniques to estimate the activation energy of reaction and reaction rate. The most-probable reaction mechanism has been identified by master plot method. The kinetic triplets (activation energy, reaction rate, most probable reaction mechanism function) have been employed to estimate the thermodynamic triplets (ΔS, ΔH and ΔG). Observations: Acetyl Ferrocene (AFc) undergoes thermal decomposition in a four-step process leaving certain residual mass whereas maliec anhydride (MA) undergoes complete mass loss owing to melting followed by evaporation. In contrast, the (AFc1-x-MAx) mixtures undergo thermal decomposition through a two-step process, and the decompositions are completed at much lower temperatures than that in AFc. The estimated activation energy and reaction rate values are found strongly dependent on the extent of conversion as well as on the extent of mixing. Introduction of MA in the solid reaction atmosphere of AFc in one hand reduces the activation energy required by AFc to undergo thermal decomposition and the reaction rate, while on the other hand varies the nature of reaction mechanism involved. Results: The range of reaction rate values estimated for the mixtures indicate that the activated complexes during Step-I of thermal decomposition may be treated as ‘loose’ complex whereas ‘tight’ complex for the Step-II. From the estimated entropy values, thermal process of (AFc1-x-MAx) mixture for Steps I and II may be interpreted as ‘‘slow’’ stage. Conclusion: Variation of Gibb’s free energy with the fraction of maliec anhydride in the mixtures for Step-I and II indicate that the thermal processes of changing the corresponding activated complexes are non-spontaneous at room temperature.

Molybdenum doped CuWO4 nanoflake array films as an efficient photoanode for solar water splitting

We developed a two-step method to prepare Mo-doped CuWO4 NF array films, which involved a hydrothermal process to grow Mo-doped WO3 NF arrays and a follow-up thermal solid-state reaction to convert WO3 to CuWO4. The obtained Mo-doped CuWO4 NF array films retained the network structure of crosslinked CuWO4 NFs when the Mo-to-W atomic ratio in precursor solution is lower than 2 : 3. Mo doping not only narrowed the bandgap of CuWO4 but also significantly improved its electron density, both benefiting the photoelectrochemial (PEC) performance for oxygen evolution reaction (OER). The Mo-doped CuWO4 NF array films exhibited a high catalytic activity toward PEC OER, and the activity varied as a function of the Mo doping concentration. The highest activity was obtained on 32 at.% Mo-doped samples, with photocurrent densities of 0.62 mA cm−2 and 1.23 mA cm−2 at 1.23 V and 1.60 V vs RHE, respectively, which are the highest values among those reported in literature. Moreover, even at high OER overpotentials, the Mo-doped CuWO4 NF array films showed an excellent stability in weak alkaline solution. This work indicates that cation doping is an effective strategy to prepare highly efficient CuWO4-based photoanodes for PEC OER.

Kinetics Study of the Solid State Reaction of Iron(III)Citrate Leading to Hematite Nanoparticles

Background: Thermal decomposition of iron-bearing organic complexes is a useful way to prepare iron oxides. Iron(III)citrate, FeC6H5O7, is a precursor for hematite (α-Fe2O3) synthesis by thermal decomposition technique. However, there is no information available on the nature of the mechanism of the reaction. Objective: Kinetic analysis of the solid-state thermal reaction of Iron(III)citrate, which decomposes to hematite under oxidative reaction atmosphere, has been studied in order to understand the reaction process. Method: Non-isothermal thermogravimetry under multiple heating rates has been employed. The obtained data are analyzed using model-free iso-conversional kinetic techniques in order to estimate the activation energy of reaction and reaction rate. Master plot method has been employed to determine the most-probable reaction mechanism. Reaction rate has been used to estimate the thermodynamic parameters (ΔS*, ΔH* and ΔG*). Decomposed material has been studied by XRD and TEM. Observations: Thermal decomposition of Iron(III)citrate is a three-step process and is completed by ~600 K. The decomposed product obtained is hematite nanomaterial. The estimated activation energy and reaction rate values are strongly dependent on the extent of conversion. The initial two steps of thermal decomposition reaction may involve ‘threedimensional diffusion’ and ‘random nucleation’, whereas the third step may be assigned again to ‘three-dimensional diffusion’. Simulated conversion curves justify the estimated kinetic parameters. A reaction pathway has also been predicted. Keywords: Iron(III)citrate, iso-conversional method, kinetics, thermal decomposition, thermogravimetry, thermal energy.

Thermal kinetic analysis of a complex process from a solid-state reaction by deconvolution procedure from a new calculation method and related thermodynamic functions of Mn0.90Co0.05Mg0.05HPO4·3H2O

Abstract Three individual peaks of thermal solid-state reaction processes of the synthesized Mn0.90Co0.05Mg0.05HPO4·3H2O were observed corresponding to dehydration I, dehydration II and polycondensation processes. An alternative method for the calculation of the extent of conversion was proposed from the peak area of the individual DTG peak after applying the best fitting deconvolution function (Frazer-Suzuki function). An iterative integral isoconversional equation was used to compute the values of the apparent activation energy Eα and they were found to be 65.87, 78.16 and 119.32 kJ/mol for three peaks, respectively. Each individual peak was guaranteed to be a single-step kinetic system with its unique kinetic parameters. The reaction mechanism functions were selected by the comparison between experimental and model plots. The results show that the first, second and final individual peaks were two-dimensional diffusion of spherical symmetry (D2), three-dimensional diffusion of spherical symmetry (D3) and contracting cylinder (cylindrical symmetry, R2) mechanisms. Pre-exponential factor values of 3.91×106, 1.35×107 and 2.15×107 s−1 were calculated from the Eα values and reaction mechanisms. The corresponded standard thermodynamic functions of the transition-state (activated) complexes were determined and found to agree well with the experimental data.

One-Pot Fabrication of Perforated Graphitic Carbon Nitride Nanosheets Decorated with Copper Oxide by Controlled Ammonia and Sulfur Trioxide Release for Enhanced Catalytic Activity.

In this article, we have judiciously interfaced copper oxides with graphitic carbon nitride (g-C3N4) from thermal reaction of melamine and copper sulfate in a one-pot protocol and manipulated the perforated sheet morphology thereafter. The CCN-X (X = 30, 40, 50, 60, and 70, depending on the wt % of CuSO4·5H2O) nanocomposites were prepared by homogenously mixing different percentages of CuSO4·5H2O with melamine from a solid-state thermal reaction in a furnace in air. Drastic lowering of CuSO4 decomposition temperature due to Cu(II)–amine complex formation and subsequent reduction of Cu(II) species by in situ produced ammonia (NH3) resulted in the production of CuO and catalytic amount of Cu2O, homogeneously dispersed within the perforated g-C3N4 nanosheet. How perforated sheet morphology evolved by combined effect of NH3, released from thermal condensation of melamine ensuring two-dimensional (2D) growth, and sulfur trioxide (SO3), expelled from CuSO4·5H2O facilitating the perforation, yielding better catalytic performance, has been elucidated. Excess NH3 from added NH4Cl removed perforation and ensued a marked decrease in efficacy. However, a high proportion of CuSO4·5H2O ruptured the framework of 2D sheets because of excess SO3 evolution. Among the different nanocomposites synthesized, CCN-40 (CuO–Cu2O/g-C3N4) showed the highest catalytic activity for 4-nitrophenol reduction. Thus, enhanced efficiency of the copper oxide catalyst by interfacing it with an otherwise inactive g-C3N4 platform was achieved.

Tribological and electrical behavior of Cu-based composites with addition of Ti-doped NbSe2 nanoplatelets

PurposeThis paper aims to clarify the size and morphology of transition metal dichalcogenides has an impact on lubrication performance of Cu-based composites. This study is intended to show that Cu-based electrical contact materials containing Nb0.91Ti0.09Se2 have better electrical and tribological properties than those containing NbSe2. The tribological properties of Cu-based with different Ti-dopped NbSe2 content were also discussed.Design/methodology/approachThe NbSe2 and Nb0.91Ti0.09Se2 particles were fabricated by thermal solid state reaction method. The powder metallurgy technique was used to fabricate composites with varying Nb0.91Ti0.09Se2 mass fraction. The phase composition of Cu-based composites was identified by X-ray diffraction, and the morphology of NbSe2/Nb0.91Ti0.09Se2 and the worn surface of composites were characterized by scanning electron microscopy and transmission electron microscopy. In addition, the tribological properties of composites were appraised using a ball-on-disk multi-functional tribometer. The data of friction coefficient and resistivity were analyzed and the corresponding conclusion was drawn.FindingsIn comparison with the pure copper, Cu-based composites containing Nb0.91Ti0.09Se2/NbSe2 had a lower friction coefficient, illustrating the Nb0.91Ti0.09Se2 with nano-size particles prepared in this work is a perfect choice for the fabrication of excellent electrical contact composites. Compared to composites with NbSe2, composites containing Nb0.91Ti0.09Se2 have better tribological and electrical properties.Research limitations/implicationsBecause of the use of thermal solid state reaction method, the size of NbSe2 and Nb0.91Ti0.09Se2 is relatively large. Therefore, the fabrication of finer particles of Nb0.91Ti0.09Se2 is encouraged.Originality/valueIn this paper, the authors discuss the tribological and electrical properties of Cu-based composites, and the value of optimum obtained as Nb0.91Ti0.09Se2 content is 15 Wt.%.

Electronic and thermal properties of stoichiometric Pt3Si films grown by co-evaporation

A stoichiometric Pt3Si thin-film phase has been stabilized by electron beam (e-beam) co-evaporation of controlled Pt and Si fluxes onto several different substrates. This Pt3Si phase has high electrical conductivity (≥ 106 S/m) and is inaccessible via the more conventional solid-state thermal reaction of a Pt film/Si substrate diffusion couple, a method that is ubiquitous for forming Pt-silicide films (PtSi and Pt2Si) in the semiconductor industry. The Pt3Si films exhibit finely grained columnar morphologies when grown at ambient temperature but develop a larger granular morphology at deposition temperatures exceeding 200 °C and have an electrical conductivity of ~ 1 × 106 S/m independent of substrate type and film thickness. For films deposited above 400 °C, film agglomeration and grain boundary grooving during fabrication leads to a decrease in overall film conductivity. Pt3Si films are less conductive than Pt2Si films, yet have a higher DOS population near the Fermi level as measured by valence band photoemission spectra in agreement with DOS calculations, which suggests a lower electron mobility in the Pt3Si phase. In situ high-temperature X-ray diffraction (XRD) studies indicate that a polymorphic phase transition between a monoclinic-Pt3Si and an orthorhombic-Pt3Si phase occurs ca. 225 °C. Also, the melting temperature of Pt3Si films was measured by in situ XRD to be ca. 920 °C; after cooling from melt, a small subset of Pt3Si grains resolidify with a crystallographic texture strongly oriented in the direction of the film normal.

"The Easier the Better" Preparation of Efficient Photocatalysts-Metastable Poly(heptazine imide) Salts.

Cost-efficient, visible-light-driven hydrogen production from water is an attractive potential source of clean, sustainable fuel. Here, it is shown that thermal solid state reactions of traditional carbon nitride precursors (cyanamide, melamine) with NaCl, KCl, or CsCl are a cheap and straightforward way to prepare poly(heptazine imide) alkali metal salts, whose thermodynamic stability decreases upon the increase of the metal atom size. The chemical structure of the prepared salts is confirmed by the results of X-ray photoelectron and infrared spectroscopies, powder X-ray diffraction and electron microscopy studies, and, in the case of sodium poly(heptazine imide), additionally by atomic pair distribution function analysis and 2D powder X-ray diffraction pattern simulations. In contrast, reactions with LiCl yield thermodynamically stable poly(triazine imides). Owing to the metastability and high structural order, the obtained heptazine imide salts are found to be highly active photocatalysts in Rhodamine B and 4-chlorophenol degradation, and Pt-assisted sacrificial water reduction reactions under visible light irradiation. The measured hydrogen evolution rates are up to four times higher than those provided by a benchmark photocatalyst, mesoporous graphitic carbon nitride. Moreover, the products are able to photocatalytically reduce water with considerable reaction rates, even when glycerol is used as a sacrificial hole scavenger.

Double function method for the confirmation of the reaction mechanism of LiCoPO4 nanoparticle formation, reliable activation energy, and related thermodynamic functions

In this study, dehydration I and II, polycondensation, and decarbonization processes of the thermal solid-state reaction between CoHPO4⋅3H2O and Li2CO3 were observed and the LiCoPO4 nanoparticles were obtained. For the sample characterization, the TG/DTG/DTA, FTIR, and AAS/AES techniques were applied. Structures and morphologies were investigated by the XRD and SEM techniques, respectively. To calculate the variable activation energy (\(E_{\alpha }\)) value, various isoconversional equations were used. In addition, the iterative isoconversional equations were also used to obtain the more reliable \(E_{\alpha }\) values of 64.04 ± 3.20, 78.54 ± 3.23, 100.41 ± 6.00, and 140.07 ± 5.02 kJ mol−1 for the first (regions I and II), second, and final steps, respectively. The first (regions I and II) as well as the second and final steps were confirmed to be a single-step kinetic process with the unique kinetic parameters. The double function \(y(\alpha )\) and \(z(\alpha )\) method was used to confirm the reaction mechanisms and found to be \(R_{2}\), \(R_{3}\), \(A_{3}\), and \(P_{3}\) corresponding to contracting cylinder, contracting sphere, assumed random nucleation (and its subsequent growth), and nucleation processes, respectively. The studied processes lead to the formation of the final nanoparticle product LiCoPO4. The four pre-exponential factors calculated using \(E_{\alpha }\) and mechanism functions were found to be 1.01 (±0.016) × 107, 7.80 (±0.009) × 107, 4.52 (±0.010) × 105, and 1.03 (±0.003) × 106 s−1, respectively. The related standard thermodynamic functions of the transition-state complexes were evaluated by using the calculated kinetic parameters.

Solid-State Thermal Reaction of a Molecular Material and Solventless Synthesis of Iron Oxide

Solid-state thermal decomposition reaction of a molecular material $$\{\hbox {As}(\hbox {C}_{6}\hbox {H}_{5})_{4}[\hbox {Fe}^{\mathrm{II}}\hbox {Fe}^{\mathrm{III}} (\hbox {C}_{2}\hbox {O}_{4})_{3}]\}_{\mathrm{n}}$$ has been studied using non-isothermal thermogravimetry (TG) in an inert atmosphere. By analyzing the TG data collected at multiple heating rates in 300 K–1300 K range, the kinetic parameters (activation energy, most probable reaction mechanism function and frequency factor) are determined using different multi-heating rate analysis programs. Activation energy and the frequency factor are found to be strongly dependent on the extent of decomposition. The decomposed material has been characterized to be hematite using physical techniques (FT-IR and powder XRD). Particle morphology has been checked by TEM. A solid-state reaction pathway leading the molecular precursor to hematite has been proposed illustrating an example of solventless synthesis of iron oxides utilizing thermal decomposition as a technique using innocuous materials.