Activation Energy Of Decomposition Research Articles

Isothermal and non-isothermal decomposition mechanisms of bastnaesite during the hydrogen-based mineral phase transformation

The hydrogen-based mineral phase transformation-flotation process can realize the efficient development of iron-bearing rare earth ores. The isothermal and non-isothermal decomposition mechanisms of bastnasite in the hydrogen atmosphere were studied to optimize the hydrogen-based mineral phase transformation process. The thermal decomposition of bastnasite first produced REOF, which would react with oxygen to produce rare earth oxides and fluorides during the analysis process. The thermal decomposition was an endothermic reaction, and the generated gas were mainly CO2 and trace CO, with a mass loss of about 20%. Increasing the temperature can greatly promote the thermal decomposition. After thermal decomposition, the particles showed a layered structure, and many parallel slits run through the particles. The porosity and specific surface area of the particles were significantly improved. The apparent activation energy of isothermal decomposition was 71.80 ± 5.40 kJ/mol, and the kinetic mechanism was random nucleation and growth model (n = 2). The apparent activation energy of non-isothermal decomposition was 201.96 kJ/mol, and the kinetic mechanism was phase-boundary controlled reaction mechanism (n ≈ 2).

Surface modification of nitrocellulose by interfacial self-assembly of metal-phenolic network for enhanced thermal stability and eco-friendly propulsion energy

Metal-phenolic networks (MPNs) have received widespread interest owing to their ability to incorporate metal ions and phenolic ligands in a modular manner. However, the effect of MPNs on nitrocellulose (NC), an energetic material for propulsion, has not been extensively investigated. Herein, we fabricated MPN-coated NC fibers (NC@MPN) and confirmed the successful coating and homogeneous distribution of MPN on the surface of NC through Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), UV–visible spectroscopy, scanning electron microscopy (SEM) and Energy Dispersive spectroscopy (EDS). The thermal stability of NC was enhanced as evidenced by differential scanning calorimetry (DSC), accelerating rate calorimetry (ARC) and the ignition point test. The thermal decomposition activation energy of NC@MPN can reach 200.73 kJ•mol−1, 7.50 % higher than that of NC primitive fiber (186.72 kJ•mol−1). The ARC tests demonstrate that the implementation of MPN coating prolonged the time of entering the adiabatic section by 5.4 °C and the forecast temperatures for TD8 and TD24 have increased by 4.6 and 4.8 °C, respectively. Additionally, the ignition point was also raised by 2 °C. The aforementioned three experimental results provide evidence for the enhanced thermal stability conferred by MPNs. Besides, thermogravimetric analysis (TGA) results demonstrate a reduction in the residue from thermal decomposition. The present study presents a simple and robust coating strategy for the modular surface engineering of energetic materials, which significantly improves thermal stability and reduces the residues of thermal decomposition.

NO Dissociation on Platinum and Platinum-Rhodium Alloy: A Theoretical Investigation

In this computational study, the preferential adsorption and co-adsorption sites of various chemical species (N, O, and NO) on the Pt (111) and Rh3Pt (111) surfaces were identified. The preferential adsorption site for NO and co-adsorption sites for N and O on the Pt (111) surface are the hollow (fcc) sites; and these on the Rh3Pt (111) surface are the hollow (fcc1) site and hollow N(hcp2)-O(fcc1) sites, respectively. The activation energies of the NO dissociation reaction on the Pt (111) and Rh3Pt (111) catalytic surfaces are 2.35 and 2.02 eV, respectively. The lower activation energy of the NO decomposition on the Rh3Pt (111) surface is explained by the stronger back-donation from the 4d orbital of the Rh atoms to the 2π* anti-bonding orbital of the NO molecule. The activation energies of the N and O recombination reaction on the Pt (111) and Rh3Pt (111) catalytic surfaces are 1.51 and 2.30 eV, respectively. The study indicates that the Rh3Pt (111) surface not only facilitates the NO decomposition but also better prevents N and O from recombination. Copyright © 2024 by Authors, Published by BCREC Group. This is an open access article under the CC BY-SA License (https://creativecommons.org/licenses/by-sa/4.0).

Experimental and theoretical study on the thermal stability and pyrolysis mechanism of octamethyltrisiloxane (MDM) with lubricating oil

In actual organic Rankine cycle systems (ORCs), the inclusion of lubricating oil in the working fluid is nearly unavoidable. Under the condition of high-temperature operation, the presence of lubricating oil can potentially exacerbate the thermal stability of the working fluid. The impact of polyol ester (POE) and mineral lubricant on the thermal stability of octadethyltrisiloxane (MDM) is studied. Results indicate that both POE and mineral lubricant contribute to the decomposition of MDM to a certain extent. Specifically, at a 5.0% mass fraction of POE and mineral lubricant, MDM remains its stable at 230 °C and 210 ℃, respectively. However, as the mass fraction of lubricant increases, the decomposition of MDM intensifies, with mineral lubricant exhibiting a more pronounced effect compared to POE lubricant. Regarding pyrolysis products, the presence of lubricants leads to an increase in CH4, C2H6 and C2H4 gases. Furthermore, the addition of lubricant promotes the formation of siloxane oligomers, particularly MD5M to MD9M, and enhances the production of unidentified products. Compared to MDM, both POE and mineral lubricant molecules exhibit lower bond dissociation Gibbs free energies. The free radicals generated from lubricant decomposition are prone to hydrogen abstraction reactions with MDM to promote MDM decomposition. Moreover, ReaxFF simulation results demonstrate that lubricant molecules also enhanced the activation of MDM and increased its susceptibility to Si-C bond cleavage. Following the removal of the methyl group, the Si-O bonds in the radicals are more likely to break, leading to the formation of additional siloxane oligomers through Si-O bond recombination. Kinetic analysis reveals that the apparent activation energy of MDM decomposition drops from 134.4 kJ∙mol−1 to 110.8 kJ∙mol−1 as the mass fraction of n-hexadecane (model compounds for mineral lubricant) rises from 0% to 10.30%.

Cotton stalk decomposition with DBD low-temperature plasma: Characteristics and kinetics

DBD low-temperature plasma (DLTP) is recognized as one of the most efficient technologies for treating cotton stalks. This study investigates the impact of various conditions on the gas production characteristics of cotton stalks (CS) and delves into the DLTP decomposition kinetics of CS and CSC in oxygen-enriched (30 % O2/Ar) and CO2 atmospheres. The decomposition rates of CS followed the order CO2 > N2 > Ar. The decomposition behavior of CSC in oxygen-enriched DLTP (30 % O2/Ar) aligned well with the chemical reaction model. The activation energies for CSC decomposition at 900 °C and 1000 °C were determined to be 23.8 kJ/mol and 33.8 kJ/mol, respectively. Moreover, the reaction rate decreased at higher carbonization temperatures, which proved to be detrimental to the decomposition of CSC. The DLTP decomposition of CSC in CO2 exhibited consistency with the fitting results of the unreacted shrinking core model, revealing an observed activation energy of 19.4 kJ/mol.

Effects of graphene organic iron nanocomplex on the pyrolysis and laser ignition performance of TKX-50

Novel graphene iron tannate and graphene iron gallate nanocomplex (G-D-Fe and G-M-Fe) were designed, prepared and characterized by SEM, EDS, FTIR, RAMAN and XPS equipment. The catalytic property of the G-D-Fe and G-M-Fe for energetic TKX-50 was explored by DSC, kinetic calculation and laser ignition. The synthesized G-D-Fe and G-M-Fe present a positive impact on pyrolysis and ignition combustion of TKX-50, resulting in the significantly reduced decomposition temperature, activation energy (Ea) and ignition delay time. After adding G-D-Fe (G-M-Fe), the first and second decomposition peak temperatures (TFDP and TSDP) of TKX-50 were decreased by 42.3 °C (43.9 °C) and 45.0 °C (49.6 °C), respectively. At the conversion degree of 0.2–0.8, the nonlinear kinetic data showed that after adding G-D-Fe and G-M-Fe, the Ea of TKX-50 decreased from 163.5 to 141.3 and 145.4 kJ·mol−1 respectively. Additionally, after adding G-D-Ni and G-M-Ni, the laser ignition delay time of TKX-50 was reduced from 58 ms to 26 ms and 28 ms, respectively. The possible catalytic mechanism of preferred combustion catalyst G-D-Fe was disclosed by in-situ FTIR and gas-phase MS-FTIR analysis. The results are helpful to broaden the catalysts for pyrolysis and ignition combustion of TKX-50 and to disclose the catalytic mechanism.

Effect of internal phase particle size on properties of site mixed emulsion explosive at plateau environment

To study the effect of internal particle size on the microstructure properties and thermal decomposition characteristics of site mixed emulsion explosive at different altitudes. Site mixed emulsion explosive was prepared with different shear rate. The particle size, viscosity, sensitized bubbles, detonation velocity and peak pressure of the emulsion explosive were tested after stored at different simulated altitudes. The thermal decomposition characteristics of emulsion matrix prepared at three different rotational speeds were measured by thermogravimetric analyzer and kinetic analysis was performed by non-isothermal model Kissinger–Akah–Sunose (KAS) method. The results show that with the increase in altitude, the internal phase size showed a trend of first increasing and then decreasing, and the number of sensitized bubbles within the emulsion explosive decreases. At an altitude of 0 m, the detonation velocity and peak overpressure of the emulsion explosive prepared by 1600 r min−1 increased 4.78% and 29.09%, respectively compared with 1200 r min−1, and at an altitude of 4500 m, the detonation velocity increased 11.87%, the peak overpressure increased 43.98%. The thermal decomposition activation energy of the emulsion matrix at 1600 r min−1 increased 13.14% compared to 1200 r min−1. It shows that in the production of site mixed emulsion explosive at high altitude, reducing the particle size of the internal phase of emulsion explosives in a certain range can effectively improve the performance of emulsion explosives.

Thermal decomposition behavior of Mountain Pass rare earth concentrate in air/CO2 atmosphere

The Mountain Pass mine is recognized as one of the world’s primary sources of rare earth minerals. These rare earth minerals mainly consist of bastnaesite and a small amount of monazite phosphate, which cannot be decomposed and recovered through conventional oxidative roasting and hydrochloric acid leaching process. An efficient, clean, and economical process called the "combined method" was proposed for the utilization of the Mountain Pass mine to extract rare earths from Mountain Pass rare earth concentrate (MPREC). The main steps of this process include weak oxidation atmosphere roasting, step leaching of hydrochloric acid, solid-liquid separation, the monazite slag with sulfuric acid roasting water leaching, etc. In this paper, the roasting process of MPREC under a weak oxidation atmosphere was investigated. The study examines the thermal decomposition kinetics, phase transition process, and leaching behavior of MPREC in air/CO2 atmosphere. Results show that, the activation energy (Ea) for MPREC thermal decomposition in air and CO2 atmosphere are 146 and 320 kJ/mol, respectively. At temperature above 500 °C in air or above 700 °C in CO2 atmosphere, REOF are generated from bastnaesite through an in-situ reaction with CaO, which is decomposed from CaCO3, to form CaF2 and rare earth oxide (REO). Thus, F is regulated into solid phase. In an oxidizing atmosphere, the thermal decomposition of bastnaesite is accompanied by the rapid oxidation of Ce(Ⅲ). In contrast, the oxidation of Ce(Ⅲ) in a CO2 atmosphere is significantly inhibited. At 700 °C, the oxidation rate of Ce in air is 74.09%, while in a CO2 atmosphere, it is only 33.83%. The hydrochloric acid leaching experiment shows that, the leaching rate of rare earth after roasting at 600 °C under an air atmosphere reaches to 82.9%, and it reaches 87% after roasting at 800 °C under a CO2 atmosphere. The reduction of Ce oxidation in a weak oxidizing atmosphere significantly improves the leaching rate of Ce.

Isoconversional kinetic analysis of thermal decomposition of Bidirectionally stabilized amorphous formulation loading Vitamin D3 (Cholecalciferol) and Calcium Carbonate

Cholecalciferol, generally known as vitamin D3 (VD), and calcium (Ca2+) are very common dietary co-supplements in the pharmaceutical formulations, as they are symbiotically and pharmacologically dependent. Development of the VD/Ca2+ formulation is highly challenging due to stability and solubility issues, mainly for VD instability toward temperature, light, oxygen and pH. In this study, VD was loaded into carrier which consisted of amorphous calcium carbonate (ACC) and hydroxypropyl methylcellulose acetate succinate (HPMCAS), yielding amorphous VD/ACC/HPMCAS formulation with various composition ratios. The structural and thermal stability study of the formulations was conducted to find that VD was a promising molecule for the stabilization of ACC even with the trace amount (0.6 %). On the other hand, ACC stabilized the amorphous state of VD; thus, they had a bidirectional stabilizing effect. The amount of VD played a significant role in thermal stabilization of the VD/ACC/HPMCAS formulations, for which kinetic analysis was performed. Using isoconversional expanded Friedman's model (FRM) activation energies of decomposition of the organic part were determined as 190, 133, and 114 kJ mol−1 for VD/ACC/HPMCAS = 0.6/64.0/35.4, 2.3/56.8/40.9, and 4.9/52.6/42.5 formulations, respectively, revealing that the formulation with the highest amount of VD (4.9 %) was the least stable. The dissolution advantage for VD by amorphization was also demonstrated.

The structure of deposited coke on hydrocracking and reforming catalysts: Coke deactivation and kinetics

AbstractThis comprehensive study investigates the structural deposition of coke, particularly its association with sulphides, in spent hydrocracking and reforming catalysts, leveraging advanced kinetic modelling and characterization techniques. Its objective is to elucidate coke removal kinetics, offering insights into optimizing catalyst regeneration. Utilizing thermogravimetric analysis, spectroscopic methods, and modelling, the research outlines the characteristics and kinetic behaviour of coke during regeneration. The novelty aspect of this study is the use of a reaction‐based model for accurate kinetic analysis and identifying optimal conditions for coke removal. The study recognized both hydrogen‐deficient and hydrogen‐rich amorphous coke, alongside graphitic coke spent catalysts. Thermogravimetric analysis revealed that coke constitutes ~23.8% and 4.6% of the total weight in hydrocracking and reforming catalysts, respectively. The traditional model‐free method for deactivation was found inadequate in predicting coke in the spent reforming catalyst, likely due to the presence of low‐temperature hydrocarbons of soft coke within the catalyst pores. In contrast, a reaction model‐based deactivation approach yielded more consistent evaluations for soft and hard coke of spent catalyst. For the spent hydrocracking catalyst, the estimated activation energies for coke decomposition were 41.56 and 128.97 kJ/mol for soft and hard coke, respectively, during regeneration. Although the coke in the spent reforming catalyst displayed similar temperature trends for decomposition, the average activation energies were 52.61 and 128.62 kJ/mol for soft and hard coke, respectively. The theoretical results from the multi‐reaction model for coke decomposition are consistent with the experimental results for both catalysts.

Green, solventless debromination of C70Br10 to C70 with CsI

A smooth, solventless and solid state debromination of C70Br10 can be achieved in a CsI matrix with the restoration of the pristine C70 in quantitative yields. Such debromination reaction was studied with FT-IR spectroscopy and its kinetics was fitted by a pseudofirst order law, with a rate constant in the range of 3.6-5.2 x 10−5 s−1. The thermal properties of the compound C70Br10 were studied with TGA and DSC analysis focusing on the thermal decomposition processes. From the DSC data both the activation energy for the thermal decomposition of C70Br10 as well as its enthalpy of formation were determined. Some considerations on the relative weakness of C-Br bonds in brominated fullerenes compounds were made. Accordingly, the debromination mechanism is discussed in terms of unimolecular elimination reaction (E1) in a concerted mechanism which leads to the restoration of the pristine C70 fullerene.

Green, solventless debromination of C70Br10 To C70 with CsI

A smooth, solventless and solid state debromination of C70Br10 can be achieved in a CsI matrix with quantitative restoration of the pristine C70 in quantitative yields. The debromination kinetics was studied with FT-IR spectroscopy and according to the pseudofirst order kinetics law, the rate constant was found in the range 3.6–5.2 × 10−5 s−1. The compound C70Br10 was studied with TGA and its thermal decomposition by DSC analysis. From the DSC data both the activation energy for the thermal decomposition of C70Br10 was determined as well as its enthalpy of formation, which has led to some considerations on the relative weakness of C–Br bonds in brominated fullerenes compounds. The debromination mechanism is discussed in terms of unimolecular elimination reaction (E1) in a concerted mechanism which leads to the restoration of the pristine C70 fullerene.

Nano-clay treatment of jute fiber for reinforcement in polymer composites: Mechanical, morphological, and thermo-kinetic analysis

Natural fibers have demonstrated exceptional properties that can be utilized as a viable and environmentally reliable material for reinforcement in polymer composites replacing their synthetic counterparts creating numerous environmental problems. Jute fiber is a prominent natural fiber that has been successfully applied for manufacturing noble natural fiber-based composites. This article describes the advantages and comparison between two surface treatment techniques that is alkali treatment and nano-clay treatment of jute fiber to enhance the properties for producing improved composite material. FTIR, SEM, AFM, and TGA have been utilized to compare and study how different surface treatment methods affect jute fiber. Isoconversional methods FWO and KAS are applied for the thermos-kinetic analysis and evaluation of activation energy of thermal decomposition. More than 30% increase in peak activation energy has been observed (120 KJ/mole to 160 KJ/mol). Alkali–nano-clay treated jute fiber exhibits nearly 32% improvement (405 MPa to 535 MPa) in tensile strength, 24% increment (11.85 GPa to 14.69 GPa) in tensile modulus, and 15% improvement (1.4 gm/cm3 to 1.61 gm/cm3) in fiber density as compared to that of untreated jute fiber. This study validates that nano-clay treatment has shown promising results and can improve the overall properties of natural fibers significantly.

Synthesis, self-assembly and surface-active properties of alkyl halide mediated imidazolium monomeric surfactants

Two imidazolium monomeric surfactants, that is, 1-tetradecyl-1H-imidazole [14IM] and 1-hexadecyl-1H-imidazole [16IM] has been synthesized and characterized by 1H NMR,13C NMR, FTIR, HRMS spectroscopies and thermogravimetric analysis (TGA) for number and types of protons and carbon, functional groups, estimation of molecular weight and thermal stability of these compounds. The conductivity was measured in double distilled water at four different temperatures, 288, 293, 298, and 303 K. The results showed that these surfactants behave as weak electrolytes. The density and viscosity data have shown the existence of strong interactions between imidazolium surfactants and solvent (water) molecules. The results obtained from Root’s equation indicate that surfactant–solvent interactions are important than surfactant–surfactant interactions in dilute solutions, that is, below critical micellar concentration. The values of constants obtained from Einstein and Moulik equations have revealed that there was stronger and significant interaction between imidazolium surfactants and water molecules below critical micellar region. The surface tension parameters have indicated that these surfactants are good contenders to lower the surface tension of air/water interface. The results obtained from surface tension data have shown that standard change in free energy of micellization (ΔG°mic) and adsorption (ΔG°ads) were negative, indicating that these surfactants molecules have spontaneous tendencies to form micelles in solution at higher concentration and to get adsorb at the air/water interface at lower concentration. The TGA has indicated good thermally stability and activation energy for thermal decomposition was found in the range of 37.26.26–98.20.20 kJ/mol.

Study on controlling factors and developing a quantitative assessment model for spontaneous combustion hazard of coal gangue

Developing a quantitative hazard assessment model for spontaneous coal gangue combustion is imperative to ensuring the safety of coal mining operations. In this study, eight types of coal gangue from different coalfields were used to determine the controlling factors for spontaneous combustion. A variety of physical and chemical characterization methods were employed to investigate the physical and chemical characteristics of the samples. Based on the experimental results, six key parameters were identified, namely the aliphatic C–H components, pyrite sulfur content, physical oxygen absorption capacity, ash content, ignition point temperature, and activation energy for thermal decomposition. The results show that the spontaneous combustion hazard of coal gangue is positively correlated with the first three of these and is negatively correlated with the rest. Using the entropy-weight method combined with the analytic hierarchy process, appropriate weighting factors for each parameter were obtained and used to establish a quantitative assessment model for the spontaneous combustion hazard of coal gangue. This model is expected to enhance the current industrial best practices for the prevention and control of spontaneous coal gangue combustion.

Micromodulation of dual-shell CL-20/desensitizer interface based on in-situ assembly of tea polyphenols

Although the research on CL-20 crystals has reached a high level, the property of the explosive-desensitizer interface is a key concern for composite explosive applications. Herein, inspired by super adhesion performance on cup, the in-situ assembly ability of tea polyphenol (TP) was utilized to enhance the surface performance and desensitize CL-20. The five kinds of core-dual-shell composites were fabricated by the “one-pot” water suspension method under the influence of ionic charge, -OH bonding, and the structure like suction cup of ivy. They were characterized by SEM, XPS, TG-DSC, XRD, and mechanical sensitivity device. The morphology and surface analysis results indicated that TP and desensitizer were evenly coated on the surface of CL-20, forming a core-dual-shell structure. This provided a great structural contribution to its security. The thermal analysis results suggested that TP/microcrystalline wax (MW) was endowed with thermal decomposition activation energy (Ea) of CL-20 from 190.92 kJ/mol up to 200.99 kJ/mol. While, the Ea of CL-20/TP, CL-20/TP/GO, CL-20/TP/TPU, and CL-20/TP/TPU-PDA were only 189.33 kJ/mol, 190.61 kJ/mol, 199.77 kJ/mol, and 184.75 kJ/mol, respectively. Meanwhile, the TP/GO film reduced Tp0 of CL-20 from 218.15 ℃ to 208.21 ℃ and Tb from 220.27 ℃ to 210.14 ℃, respectively. Besides, the XRD results confirmed that the five films had not caused a transformation of the ε-CL-20 crystal phase, which afforded process safety support for the further application of these composite particles. Due to the properties of MW and the advantages of dual-shell composite structural, the TP/MW film brought mechanical sensitivity of CL-20 from 60 N and 3.5 J to 336 N and 8.97 J, closing to the level of PBXs with 95% LLM-105% and 5% ternary composite (11 J). These safety parameters indicate materiel of moderate sensitivity that possibly can be handled in accordance with standard procedures. Moreover, the particle coated with TP/TPU-PDA possessed better free-running property. These findings can provide reference for the large-scale application of CL-20.

Non-isothermal curing kinetics of soybean oil-based resins: Effect of initiator and reactive diluent

Soybean oil has been utilized as a raw material to develop biobased polymer to replace petroleum-based counterparts due to its abundance, renewability, and molecular designability. Acrylated epoxidized soybean oil (AESO) is a commercially available product and has been used in coatings, plasticizers, and composites. The curing of AESO resins normally refers to the free-radical polymerization of CC bonds, which is closely related to the types of initiators and reactive diluents (RDs). In this work, the processing parameters and curing kinetic mechanism of AESO resins were investigated based on the extrapolation method, Kissinger, Crane, and Friedman equations, and the influences of initiators and RDs on the curing of the resins were explored. Results indicated that the types of initiators significantly affected the processability and curing kinetics of AESO resins, and the curing temperatures and reaction activation energy of the resins were strongly associated with the decomposition temperature and activation energy of the initiators. The number of CC bonds and molecular structure of RDs considerably influence the curing characteristics of the resins. The addition of RDs endowed the reaction more complexity, and the activation energy significantly depended on the level of CC conversion.

Thermal decomposition and combustion performance of the organic-inorganic hybrid crystal structure oxidant DAN-2

In this paper, we investigated the potential use of a new organic-inorganic hybrid crystal structure based on KNO3 in ignition compositions. H2dabco[K(NO3)3] (DAN-2) with organic-inorganic hybrid crystal structure is synthesized through intermolecular assembly technology. Scanning electron microscopy (SEM), X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FT-IR) were used to detect the crystal morphology, structure and molecular structure of DAN-2, which has a regular cubic structure. Experimental data were obtained using thermogravimetric/differential scanning calorimetry (TG-DSC), closed bomb test and high-speed photography, which were then used to study and analyze the thermal decomposition properties and combustion properties of DAN-2. The initial thermal decomposition temperature of DAN-2 was low (194 °C) and the activation energy of the thermal decomposition was 154 kJ/mol. Possible thermal decomposition mechanisms are further discussed and proposed. This research pushed forward the application of organic-inorganic hybrid crystal structure oxidant DAN-2 in ignition system.

Regulating electronic structure of Fe single-atom site by S/N dual-coordination for efficient Fenton-like catalysis

The activity of single-atom catalysts in peroxymonosulfate activation process is bound up with the local electronic state of metal center. However, the large electronegativity of N atoms in Metal-N4 restricts the electron transfer between center metal atom and peroxymonosulfate. Herein, we constructed Fe-SN-C catalyst by incorporating S atom in the first coordination sphere of Fe single-atom site (Fe-S1N3) for Fenton-like catalysis. The Fe-SN-C with a low valent Fe is found to exhibit excellent catalytic activity for bisphenol A degradation, and the corresponding rate constant reaches 0.405 min−1, 11.9-fold higher than the original Fe-N-C. Besides, the Fe-SN-C/PMS system exhibits ideal catalytic stability under the effect of wide pH range and background substrates by the fast generation of high-valent Fe species. Experimental results and theoretical calculations reveal that the dual coordination of S and N atoms notably increases the local electron density of Fe atoms and electron filling in eg orbital, causing a d band center shifting close to the fermi level and thereby optimizes the activation energy for peroxymonosulfate decomposition via Fe 3d-O 2p orbital interaction. This work provides further development of promising SACs for the efficient activation of peroxymonosulfate based on direct regulation of the coordination environment of active center metal atoms.

The influence of B doping on phase formation and microstructural evolution in NHL during solid-state reactions

Natural Hydraulic Lime (NHL), was synthesized by doping B2O3 into calcium carbonate and silica aerogel. By introducing varying levels of B3+ ion doping (0/1/5/10/15/20/25 mol%), a range of NHL compositions were successfully prepared, thereby enabling regulation of the NHL phase composition. Furthermore, through the doping of 25 mol% B3+ ions, in-depth investigations employing XRD, SEM, and FT-IR were conducted to explore phase transitions and ion migration during NHL calcination at different temperatures. Thermal analysis kinetics studies further revealed the variation of activation energies for CaCO3 decomposition and C2S crystallization with changing levels of B3+ ion doping. The introduction of B ions was observed to stabilize the α’ phase of dicalcium silicate (C2S) and moderately enhance the reactivity of calcium oxide (CaO). B3+ ions significantly influenced the crystallization mechanism of C2S, shifting it from a diffusion-controlled process to a heterogeneous nucleation process. The application of the Kissinger and Flynn-Wall-Ozawa (FWO) methods assisted in elucidating the underlying reasons for these differences. Both approaches demonstrated a substantial decrease in activation energy, signifying the pronounced influence of B doping on the sintering regime and phase transition mechanism of NHL. In summary, the precise modulation of NHL phase composition and sintering regime was achieved through B doping. These findings not only deepen our understanding of the mechanistic role of B3+ ions in NHL preparation and application but also offer robust guidance for the production process of NHL.