Calcination Conditions Research Articles

Structure, and Phase Transformations of HPM-3: A Layered Precursor of the Neutral Aluminophosphate with JSN Topology.

The structure of HPM-3, a layered aluminophosphate prepared using 1,2,3-trimethylimidazolium (123TMI) as an organic structure-directing agent by the fluoride route, has been solved by continuous rotation electron diffraction (cRED), and Rietveld refined against synchrotron powder X-ray diffraction data. Charge balance of the occluded cation is achieved through F- anions and dangling Al(OP)3OH groups. Half of the Al is pentacoordinated in negatively charged Al(OP)4-F-Al(OP)4 pairs. The layers in HPM-3, denoted as jsn, are observed in the fully connected metalloaluminophosphate molecular sieves with JSN topology. Thus, HPM-3 can be a precursor to a JSN metal-free aluminophosphate if a topotactic condensation can be reached, which proved to be difficult but feasible. Treatments under different conditions resulted in a number of known (PST-27 and AlPO4-5 by a disruptive transformation) or new phases (through mild thermal treatments). Among the latter, a layered phase with a shorter interlayer space, denoted as HPM-3S, contains half the amount of organic as HPM-3. This is afforded by the capability of 123TMI compounds to sublimate at relatively low temperatures. HPM-3S still contains the same jsn layers. Therefore, the transformation of HPM-3 into HPM-3S is topotactic but without reaching condensation. Among the phases appearing under calcination conditions at relatively low temperature (<350 °C), we observed solids compatible with the JSN topology, but with poor crystallinity. This is attributed to a wrong alignment in HPM-3 of the dangling Al(OP)3OH and P(OAl)3═O that should connect adjacent layers in a topotactic condensation, which favors 1-dimensional stacking disorder by random shifts of layers during the thermal treatments. However, detemplation at a much lower temperature (175 °C) using O3 finally afforded an aluminophosphate molecular sieve with JSN topology with only moderate stacking disorder. This is just the third reported 2D-to-3D topotactic condensations in aluminophosphates.

Optimizing calcination for low-grade calcined kaolinite clay: Reactivity and energy consumption

The cement industry is actively seeking sustainable strategies to enhance efficiency and reduce its environmental influences. Calcined kaolinite clay (CC) has emerged as a promising supplementary cementitious material (SCM) that offers significant cost and carbon emission reduction emissions compared to traditional materials. However, the variability in calcination conditions due to differing procedures and clay properties often leads to sub-optimal outcomes, diminishing pozzolanic reactivity and strengths. To address this, we developed an empirical model that accurately predicts energy consumption in relation to the metakaolin (MK) transformation ratio, enabling more efficient and sustainable production processes. Our study investigates the effects of different calcination conditions on low-grade CC by analyzing its physical and chemical characteristics, thermal decomposition, reactivity, and thermodynamics. We identified optimal calcination conditions at 800°C for 180 minutes using an electric furnace, achieving the highest pozzolanic reactivity and mechanical strength while enhancing the slump value by up to 40 %. The proposed model demonstrates a robust correlation coefficient of approximately 0.97, providing reliable energy consumption predictions across various calcination scenarios. This research provides valuable insights into balancing energy efficiency with material performance in low-grade CC calcination processes to augment sustainable development initiatives of the cement industry.

Promoting Sustainability in the Cement Industry: Evaluating the Potential of Portuguese Calcined Clays as Clinker Substitutes for Sustainable Cement Production

The cement industry significantly contributes to global CO2 emissions, posing several challenges for a future low-carbon economy. In order to achieve the target established by the European Sustainable Development Goals of reaching carbon neutrality by 2050, the European Cement Association (Cembureau) has devised a comprehensive roadmap based on five key approaches, referred to as the 5C strategies. Portland clinker is one of the crucial concerns, since its production emits over 60% of the cement manufacturing emissions. Therefore, supplementary cementitious materials (SCMs) to partially replace clinker content in cement have gained significant attention in providing alternatives to traditional clinker in cement production. This paper evaluates the potential of Portuguese calcined clays (CCs) as viable substitutes for clinker to enhance sustainability in cement manufacturing. More than 50 clays were characterised through chemical and mineralogical analyses to assess their reactivity and suitability for calcination using the strength activity index (SAI), along with XRD, XRF, and TGA techniques. This study investigated the calcination conditions that provide the best clay reactivity, which were subsequently used for calcination. This investigation is part of a project to evaluate the behaviour of calcined clays through mechanical, hydration, and durability properties. The findings indicate that Portuguese calcined clays exhibit promising pozzolanic activity. Furthermore, these clays could significantly reduce CO2 emissions and raw material consumption in cement production. This research underscores the potential of local calcined clays as a sustainable clinker substitute, promoting eco-friendly practices in the construction industry.

N-alkylation of amines with alcohols over hydrothermally prepared Nb-W mixed oxides

Hydrothermally synthesized Nb-W mixed oxides (Nb-W-O) have been employed as a cost-effective and recyclable alternative to noble metals and homogeneous catalysts for the N-alkylation of amines with alcohols, with the model reaction of aniline and benzyl alcohol. The synergistic roles of Nb and W and the influence of calcination conditions were explored. Nb-W-O exhibited a linear packing of corner-sharing octahedra, analogous to the hexagonal tungsten bronze (HTB) structure, but without the long-range order of the HTB in the ab plane, characteristic of pseudo-crystalline materials. Calcination at 773 K in an N2 flow preserved the pseudo-crystalline phase and generated additional Brønsted acid sites, associated with reduced tungsten oxide species stabilized by Nb. The primary reaction pathway involved the activation of the benzyl alcohol by Brønsted acid sites, followed by a nucleophilic attack of the formed carbocation by the aniline. Nb-W-O demonstrated superior activity to other solid acids including metal oxides, silica-alumina, and zeolites in the N-alkylation reaction.

Promoting role of residual organic structure directing agent in skeletal butene isomerization over ferrierite

This work examines how acid site concentration (FT-IR) and strength (NH3-TPD) as well as pore mouth accessibility modulate the activity of the microporous zeolite ferrierite (H-FER) during the skeletal isomerization of 1-butene to iso-butene. Restricting the accessibility of catalyst pores and strong acid sites is achieved by selective oxidation of residual organic structure directing agent (OSDA) through precise control of calcination conditions. Because this reaction is mediated by catalytically active carbonaceous deposits, residual OSDA affects their formation. This work demonstrates that small amounts of residual OSDA (∼ 0.2 wt%) are beneficial to the reaction under industrially relevant reaction conditions in three ways. Selective poisoning of strong BAS with OSDA nearly halves the amount of dimerization and cracking byproducts and improves catalyst lifetime. Simultaneously, carbonaceous fragments of the OSDA act as coke precursors and help shorten the startup time. Hence, catalyst lifetime may be significantly improved through both optimal pretreatment conditions and by designing catalysts with an increased number of accessible pore mouths.

Densely populated single‐atom catalysts for boosting hydrogen generation from formic acid

AbstractThe single‐atom M‐N‐C (M typically being Co or Fe) is a prominent material with exceptional reactivity in areas of catalysis for sustainable energy. However, the formation of metal nanoparticles in M‐N‐C materials is coupled with high‐temperature calcination conditions, limiting the density of M‐Nx active sites and thus restricting the catalytic performance of such catalysts. Herein, we describe an effective decoupling strategy to construct high‐density M‐Nx active sites by generating polyfurfuryl alcohol in the MOF precursor, effectively preventing the formation of metal nanoparticles even with up to 6.377% cobalt loading. This catalyst showed a high H2 production rate of 778 mL gCat−1 h−1 when used in the dehydrogenation reaction of formic acid. In addition to the high density of the active site, a curved carbon surface in the structure is also thought to be the reason for the high performance of the catalyst.

Hydrothermal synthesis of three-dimensional snowflake-like MgCO3@MnCO3@Mn3N2 composite materials and their application in aqueous zinc-ion battery cathodes

Aqueous zinc-ion batteries have attracted considerable interest in the energy storage sector due to their distinctive advantages. The use of water as an electrolyte enhances their environmental friendliness, and the abundant and low-cost nature of zinc resources confers a significant economic edge. Manganese-based materials, utilized as cathode materials in these batteries, offer favorable electrical conductivity, high theoretical capacity, and superior stability. The paper describes the hydrothermal synthesis of magnesium- and manganese-based composite material MgCO3@MnCO3@Mn3N2, through the optimization of the amounts of magnesium nitrate and urea, as well as the hydrothermal and calcination conditions. Under the optimal synthesis conditions, the composite material achieved a high capacity of 457.8 mAh/g at the current density of 50 mA/g, with capacity of 391.5 mAh/g at the current density of 100 mA/g. Notably, even at the current density of 200 mA/g, the capacity remained above 300 mAh/g. The SEM tests reveal that the MgCO3@MnCO3@Mn3N2 composite material exhibits three-dimensional snowflake-like morphology at the microscopic level. The EDS tests indicate a very uniform distribution of manganese and magnesium elements. Both infrared and Raman spectroscopy tests detected characteristic peaks of carbonate groups. The XPS tests show that the oxidation states of Mn and Mg elements are consistent with those of MgCO3 and MnCO3. In the XRD test, data fitting analysis indicates that the predominant components of the composite material are MgCO3 and MnCO3, with a ratio approximating 5:4. The presence of a small quantity of Mn3N2 is also identified within the composite material. The composite material synthesized under this composition exhibits superior electrochemical performance.

Precisely designed 3-stage calcination strategy for lithium-rich manganese-based cathodes with improved cycling performance

The poor cycling performance of Li-rich manganese-based (LMR) cathodes is one of the challenges that need to be urgently overcome. Enhancing the stability of the layered structure responsible for lithium-ion diffusion is an effective way to improve the cycling performance. Layered structures are mainly formed during the high-temperature solid-phase reaction, whereas the prolonged and constant-high-temperature calcination conditions in conventional calcination procedure may pose a threat to the layered structural stability. Thus, in order to optimize the formation environment of layered structures under high-temperature solid-phase reaction, we have designed suitable temperature-controlled strategies for each stage of layered structure formation, gradual maturation, and post-treatment, respectively, referred to as the 3-stage calcination strategy. This calcination strategy contributes to the formation of a more ordered and stable layered structure, which significantly improves the cycling performance of LMR cathodes (capacity retention rate of 85.2 % after 200 cycles at 1C). The shortening of the constant high temperature calcination time helps to further reduce the production cost of the batteries. The design concept of this work is to regulate the formation process of layered structures in stages, which provides inspiration for the efficient and controllable synthesis of electrode materials with excellent structural stability at low production cost.

Advanced Synthesis of Hierarchically Porous Zeolite Catalysts Utilizing Biomass Templates for the Catalytic Pyrolysis of Stearic Acid into Short-Chain Olefins.

In this study, hierarchically porous ZSM-5 catalysts were fabricated by one-pot assembling ZSM-5 particles onto diverse biomass templates (e.g., rice husk, tea seed husk, tung shell, and coconut shell), wherein the biomass template was transformed into bio-SiO2 or biochar depending on the calcination conditions. The biotemplated ZSM-5 variants, including ZSM-5(RH), ZSM-5(TSH), ZSM-5(TS), and ZSM-5(CS), exhibited significantly improved deoxygenation performance, achieving ∼100.0% deoxygenation efficiency as compared to the untemplated ZSM-5 catalyst (85.3%). Among them, the ZSM-5(TSH) catalyst exhibited the best performance, accompanied by 100% conversion, 99.6% deoxygenation rate, and 82.3% olefin selectivity. Interestingly, the product distribution over biotemplated ZSM-5 was dominant C4=-C8= (selectivity of ∼100% in total olefins), while long-chain olefins (C9=-C17=) was the major product (selectivity of 57.3%) over the untemplated ZSM-5. Moreover, molecular dynamics (MD) simulations revealed that biotemplated ZSM-5 exhibited superior diffusion coefficients of stearic acid (reaction substrate) and anthracene (coke precursor) compared to the untemplated ZSM-5, indicating higher self-diffusion rates and consequently superior activity and stability in the catalytic pyrolysis reactions. Furthermore, in situ DRIFTS results showed stearic acid over ZSM-5(TSH) primarily was converted to the C17H36 intermediate mainly via the decarboxylation route, followed by dehydrogenation pyrolysis and C-C breaking reactions into C4=-C8= products. Overall, this work developed an effective strategy for manufacturing hierarchically porous zeolite catalysts using biomass-derived bio-SiO2 or biochar as the platform.

A way to macroporous and alveolar geopolymer foams elaboration: Influence of operating parameters on porosity characteristics

Alveolar cellular foams are widely used in a wide range of applications, from aeronautics and filtration systems to chemical and transformation processes. Their porous characteristics make them a prime candidate for reactions, radiative transfer and flow. Geopolymeric foams, which have their origins in civil engineering, are materials with promising potential in terms of mechanical, thermal and acoustic resistance. As they are mainly used in civil engineering, the structures currently being developed are mainly closed-pore matrices. However, if they are to invert the field of photocatalytic oxidation processes, solar collectors or concentrated solar power plants, the supports need to develop a high exchange surface area. Metal alveolar foams have been identified as ideal but very costly supports. Geopolymeric foams could meet these requirements, but their surface areas are currently too limited for photoreactors. In this study, it is proposed to develop and optimize the operating conditions for geopolymer foam synthesis in order to impart macroporous properties and an interconnected alveolar structure. Based on two well-established synthesis methods (direct foaming and replication), operating conditions such as foaming agent and surfactant content, and drying and calcination conditions, are studied. Geopolymer foams are produced with different macroporous characteristics. We aim to define the synthesis conditions required to produce interconnected macroporous alveolar foams with milimetric pores. In civil engineering, these materials have the advantage of being easy to design, use and shape according to the application.

Beyond dopant selection: The critical grain size window as a key performance dictator for Co-free, Ni-rich cathode materials

Despite the immense potential of cobalt-free, nickel-rich cathode materials to replace their cobalt-containing counterparts in lithium-ion batteries (LIBs), their widespread adoption remains hindered by performance limitations. While extensive research has explored various doping strategies to address this challenge, the reported benefits vary significantly, suggesting an incomplete understanding of dopant influence and thus hindering the full potential of these additives. Our investigation into the effect of various dopants on Li(Ni0.95Mn0.05)O2 performance yielded a surprising discovery: the LIB performance of transition metal-doped Li(Ni0.95Mn0.05)O2 becomes remarkably consistent across different dopant types, provided the calcination conditions are optimized. Regardless of dopant type, a critical grain size window is identified as a key factor influencing the performance of the doped Li(Ni0.95Mn0.05)O2. Calcination within a specific temperature range is paramount to control this previously overlooked performance determinant, which significantly impacts grain growth, primary particle morphology, and lattice structure. This novel insight allows us to demonstrate that cost-effective dopants such as Ti can achieve performance in stabilizing Li(Ni0.95Mn0.05)O2 comparable to that of more expensive, higher-valence alternatives (e.g., Nb, Ta, W, and Mo). This discovery paves the way for developing practical material design processes that meet the stringent requirements of the LIB industry.

Effective electromagnetic wave absorption strategy: Unlocking the potential of NiCo2O4 as an absorber

This study addresses a scientific challenge by elucidating the influence of calcination temperature on the properties and electromagnetic wave absorption capabilities of NiCo2O4, a material whose performance is inherently tied to its preparation process. Specifically, we systematically investigate how varying calcination temperatures not only diversify the material’s composition and morphology but also enhance its electromagnetic wave absorption properties. By controlling the calcination temperature, we not only achieve the successful synthesis of NiCo2O4 but also unravel intricate correlations among calcination conditions, material composition, and wave absorption performance. Notably, NiCo2O4 sample calcined at 400 °C exhibits remarkable electromagnetic wave absorption, marked by an exceptional maximum reflection loss of −53.93 dB and a broad absorption bandwidth spanning 6.24 GHz. These insights contribute to advancing the frontiers of NiCo2O4 utilization, particularly in the realm of electromagnetic wave absorption and beyond, underscoring the novelty and impact of our research.

Ag-TiO2 Photovoltaic Synergistic Field-catalyzed Degradation Performance of Tetracycline

Background: Tetracycline (TC), a commonly used antibiotic, is extensively utilized in the medical sector, leading to a significant annual discharge of tetracycline effluent into the water system, which harms both human health and the environment. Objective: A novel technique was developed to address the issues of photogenerated carrier complexation and photocatalyst immobilization. Compared to traditional photocatalytic photoelectrodes, the suspended catalyst used in the photovoltaic synergy field is more stable and increases the solidliquid contact area between the catalyst and the pollutant. Methods: This paper uses sol-gel-prepared Ag-TiO2 materials for the photoelectric synergistic fieldcatalyzed degradation of TC. The study examined how the Ag doping ratio, calcination conditions, catalyst injection, pH, electrolytes, and electrolyte injection affected photoelectric synergistic fieldcatalyzed degradation. The experiments were performed in a photocomposite field with a constant 50 mA current and a 357 nm UV lamp for 60 minutes. The composites underwent characterization using XRD, TEM, and XPS techniques. Results: Ag-TiO2 photoelectric synergistic field-catalyzed reaction with 357 nm ultraviolet lamp irradiation for 60 min and a constant current of 50 mA degraded 5 mg/LTC under preparation conditions of molar doping ratio of Ti: Ag=100:0.5, roasting temperature of 500 °C, and roasting time of 2 h. The photoelectric synergistic field-catalyzed degradation process achieved a degradation rate of 90.49% for 5 mg/L TC, surpassing the combined degradation rates of electrocatalysis and photocatalysis. The quenching experiments demonstrated that the degradation rate of TC decreased from 90.49% in the absence of a quencher to 53.23%, 42.58%, and 74.52%. The presence of •OH had a more significant impact than h+ and •O2 -. Conclusion: The findings suggest that Ag-TiO2 significantly enhanced the efficacy of photoelectric synergistic field-catalyzed degradation and can be employed to treat high-saline and lowconcentration TC. This establishes a benchmark for using photoelectrocatalytic materials based on titanium in treating organic wastewater.

Enhanced catalytic transfer hydrogenation of biomass-based furfural into furfuryl alcohol over Co3O4-based mixed oxide catalysts from hydrotalcite

Catalytic furfural (FF) into high value-added furfuryl alcohol (FOL) is a very important biomass improvement process and remains a challenging task. Herein, a series of Co-based composite oxide (CoMgAl-LDO) catalysts with highly dispersed Co3O4-based spinel oxide nanoparticles were synthesized by the topological transformation of Co-based ternary layered hydroxides (CoMgAl-LDH) under calcination conditions and tested for catalytic transfer hydrogenation of FF to FOL using isopropanol (2-PrOH) as hydrogen donor. The CoMgAl-LDO, especially Co1.5Mg1.5Al1-LDO calcinated at 500 °C (Co1.5Mg1.5Al1-LDO-500) offered the outstanding catalytic performance for the catalytic transfer hydrogenation of FF to FOL (99.7 % FF conversion and 95.9 % FOL selectivity), which was attributed to effectively dispersed active sites, abundant acid-base sites and mesoporous structure. Additionally, the Co1.5Mg1.5Al1-LDO-500 catalyst manifested good stability with wider universality to other carbonyl compounds, making the catalytic system extremely economical and practical in various biomass hydrogenation processes.

High-temperature dolomite decomposition: An integrated experimental and computational fluid dynamics analysis for calcium looping and industrial applications

The thermal decomposition of dolomite was investigated as a potential low-cost and high-performance precursor to CaO in the calcium looping process, which shows great promise when integrated with carbon capture and storage and thermochemical energy storage technologies. Experimental thermogravimetric analysis (TGA) and computational fluid dynamics (CFD) modelling were used to study the isothermal calcination process of dolomite considering industrially relevant conditions, focusing on high temperatures (800–1200 °C), sample sizes (12–18 mm), different calcination atmospheres (air and CO2) and gas velocities (0.2–3 m·s−1). Based on experimental findings, optimal calcination conditions for industrial applications require a minimum temperature of 1000 °C to achieve complete conversion within 25 min and smaller particles for faster conversion rates. Calcination atmosphere is flexible as CO2 concentration shows minimal impact on conversion rates. Laminar flow gas velocity is not a limiting factor and its value should be considered based on other aspects (i.e., costs). Higher particle initial porosity is seen to increase reactivity and thermal efficiency. The CFD model was validated with experimental data, resulting in determination coefficients (R2) higher than 0.9 for all simulated cases. Model predictions revealed insights into particle level phenomena during calcination, such as increased rates at higher temperatures with proportional self-cooling effects, wake formation enhancing fluid mixing and the presence of a thermal boundary layer reducing heat transfer. The findings presented in this paper can be used in future work to determine reaction mechanisms and optimize kinetic parameters for decomposition, as well as further optimize other aspects of the process at industrially relevant operating conditions.

Role of the Microstructure in the Li-Storage Performance of Spinel-Structured High-Entropy (Mn,Fe,Co,Ni,Zn) Oxide Nanofibers

High-entropy oxides with spinel structure (SHEOs) are promising anode materials for next-generation lithium-ion batteries (LIBs). In this work, electrospun (Mn,Fe,Co,Ni,Zn) SHEO nanofibers produced under different conditions are evaluated as anode materials in LIBs and thoroughly characterised by a combination of analytical techniques. The variation of metal load (19.23 or 38.46 wt% relative to the polymer) in the precursor solution and of calcination conditions (700 °C/0.5 h, or 700 °C/2 h followed by 900 °C/2 h) affects the morphology, microstructure, crystalline phase, and surface composition of the pristine SHEO nanofibers and the resulting electrochemical performance, whereas mechanism of Li+ storage does not substantially change. Causes of long-term (≥650 cycles) capacity fading are elucidated via ex situ synchrotron X-ray absorption spectroscopy. The results evidence that the larger amounts of Fe, Co, and Ni cations irreversibly reduced to the metallic form during cycling are responsible for faster capacity fading in nanofibers calcined under milder conditions. The microstructure of the active material plays a key role. Nanofibers composed by larger and better-crystallized grains, where a stable solid/electrolyte interphase forms, exhibit superior long-term stability (453 mAh g−1 after 550 cycles at 0.5 A g−1) and rate-capability (210 mAh g−1 at 2 A g−1).

Effect of dopant loading and calcination conditions on structural and optical properties of ZrO2 nanopowders doped with copper and yttrium

Undoped, Cu and/or Y doped ZrO2 nanopowders were synthesized with Zr, Y, and Cu nitrates using a co-precipitation approach. Their structural and optical properties were examined regarding dopant content (0.1–8.0 mol.% of CuO and 3–15 mol.% of Y2O3) and calcination conditions (400 °C–1000 °C and, 1,2 or 5 h) through Raman scattering, XRD, TEM, EDS, AES, EPR, UV–vis and FTIR diffused reflectance methods. The results showed that both Cu and Y dopants promoted the appearance of additional oxygen vacancies in ZrO2 host, while the formation of tetragonal and cubic ZrO2 phases was primarily influenced by the Y content, regardless of Cu loading. The bandgap of most of the powders was observed within the 5.45–5.65 eV spectral range, while for those with high Y content it exceeded 5.8 eV. The (Cu,Y)-ZrO2 powders with 0.2 mol.% CuO and 3 mol.% Y2O3 calcined at 600 °C for 2 h demonstrated nanoscaled tetragonal grains (8–12 nm) and a significant surface area covered with dispersed CuxO species. For higher calcination temperatures, the formation of CuZr 2+ EPR centers, accompanied by tetragonal-to-monoclinic phase transformation, was found. For fitting of experimental FTIR reflection spectra, theoretical models with one, five, and seven oscillators were constructed for cubic, tetragonal, and monoclinic ZrO2 phases, respectively. Comparing experimental and theoretical spectra, the parameters of various phonons were determined. It was found that the distinct position of the high-frequency FTIR reflection minimum is a unique feature for each crystalline phase. It was centered at 700–720 cm−1, 790–800 cm−1, and 820–840 cm−1 for cubic, tetragonal, and monoclinic phases, respectively, showing minimal dependence on phonon damping coefficients. Based on the complementary nature of results obtained from structural and optical methods, an approach for monitoring powder properties and predicting catalytic activity can be proposed for ZrO2–based nanopowders.

Predictive Synthesis of Transition Metal Carbide via Thermochemical Oxocarbon Equilibrium.

Fabricating nanoscale metal carbides is a great challenge due to them having higher Gibbs free energy of formation (ΔG°) values than other metal compounds; additionally, these carbides have harsh calcination conditions, in which metal oxidation is preferred in the atmosphere. Herein, we report oxocarbon-mediated calcination for the predictive synthesis of nanoscale metal carbides. The thermochemical oxocarbon equilibrium of CO-CO2 reactions was utilized to control the selective redox reactions in multiatomic systems of Mo-C-O, contributing to the phase-forming and structuring of Mo compounds. By harnessing the thermodynamically predicted processing window, we controlled a wide range of Mo phases (MoO2, α-MoC1-x, and β-Mo2C) and nanostructures (nanoparticle, spike, stain, and core/shell) in the Mo compounds/C nanofibers. By inducing simultaneous reactions of C-O (selective C combustion) and Mo-C (Mo carbide formation) in the nanofibers, Mo diffusion was controlled in C nanofibers, acting as a template for the nucleation and growth of Mo carbides and resulting in precise control of the phases and structures of Mo compounds. The formation mechanism of nanostructured Mo carbides was elucidated according to the CO fractions of CO-CO2 calcination. Moreover, tungsten (W) and niobium (Nb) carbides/C nanofibers have been successfully synthesized by CO-CO2 calcination. We constructed the thermodynamic map for the predictive synthesis of transition metal carbides to provide universal guideline via thermochemical oxocarbon equilibrium. We revealed that our thermochemical oxocarbon-mediated gas-solid reaction enabled the structure and phase control of nanoscale transition metal compounds to optimize the material-property relationship accordingly.

Investigation of the thermal decomposition of Pu(IV) oxalate: a transmission electron microscopy study

The degradation of the internal structure of plutonium (IV) oxalate during calcination was investigated with Transmission Electron Microscopy (TEM), electron diffraction, Electron Energy-Loss Spectroscopy (EELS), and 4D Scanning TEM (STEM). TEM lift-outs were prepared from samples that had been calcined at 300°C, 450°C, 650°C and 950°C. The resulting phase at all calcination temperatures was identified as PuO2 with electron diffraction. The grain size range was obtained with high-resolution TEM. In addition, 4D STEM images were analyzed to provide grain size distributions. In the 300°C calcined sample, the grains were &amp;lt;10 nm in diameter, at 650°C, the grains ranged from 10 to 20 nm, and by 950°C, the grains were 95–175 nm across. Using the Kolmogorov-Smirnov (K-S) two sample test, it was shown that morphological measurements obtained from 4D-STEM provided statistically significant distributions to distinguish samples at the different calcination conditions. Using STEM-EELS, carbon was shown to be present in the low temperature calcined samples associated with oxalate but had formed carbon (possibly graphite) deposits in the 950°C calcined sample. This work highlights the new methods of STEM-EELS and 4D-STEM for studying the internal structure of special nuclear materials (SNM).

Preparation of DyVO4 by Sol-Gel Method and Research of Its Photocatalytic Activity

Using dysprosium oxide (Dy2O3), ammonium metavanadate (NH4VO3), nitric acid (HNO3) and citric acid (C6H8O7·H2O) as main raw materials, DyVO4 was successfully prepared by sol-gel method. DyVO4 samples were characterized by thermogravimetry differential scanning calorimetry (TG-DSC), X-ray diffraction (XRD), scanning electron microscope (SEM), diffuse reflectance spectrum (DRS) and Fourier transform infrared spectroscopy (FT-IR). Under condition of ultraviolet light, taking 10 mg/L methyl orange solution as simulated sewage, the effects of synthesis temperature and illumination time on the photocatalytic activity of DyVO4 were studied. The results show that pure tetragonal zircon DyVO4 samples can be obtained under calcination conditions of 600 °C to 900 °C. The average grain size is about 2 μm and the breadth of band gap is about 3.52 eV. The sample prepared at 800 °C has the best photocatalytic activity. Under ultraviolet light illumination for 150 min, the degradation rate of 10 mg/L methyl orange can reach nearly 100% in presence DyVO4. DyVO4 prepared by sol-gel method is a photocatalyst which has broad application prospect.