The Effect of Removal of External Proteins PsbO, PsbP and PsbQ on Flash-Induced Molecular Oxygen Evolution and Its Biphasicity in Tobacco PSII.

The oxygen evolution within photosystem II (PSII) is one of the most enigmatic processes occurring in nature. It is suggested that external proteins surrounding the oxygen-evolving complex (OEC) not only stabilize it and provide an appropriate ionic environment but also create water channels, which could be involved in triggering the ingress of water and the removal of O2 and protons outside the system. To investigate the influence of these proteins on the rate of oxygen release and the efficiency of OEC function, we developed a measurement protocol for the direct measurement of the kinetics of oxygen release from PSII using a Joliot-type electrode. PSII-enriched tobacco thylakoids were used in the experiments. The results revealed the existence of slow and fast modes of oxygen evolution. This observation is model-independent and requires no specific assumptions about the initial distribution of the OEC states. The gradual removal of exogenous proteins resulted in a slowdown of the rapid phase (~ms) of O2 release and its gradual disappearance while the slow phase (~tens of ms) accelerated. The role of external proteins in regulating the biphasicity and efficiency of oxygen release is discussed based on observed phenomena and current knowledge.

High-Entropy Fluorite Oxide-Modified CaO-Based Sorbent Pellets for Enhanced High-Temperature CO2 Capture.

The calcium looping technology employing CaO-based sorbents is pivotal for capturing CO2 from flue gas. However, the intrinsic low thermodynamic stability of CaO-based sorbents and the requisite molding step induce severe sintering issues, diminishing their cyclic stability. Herein, a high-entropy fluorite oxide (HEFO) inert stabilizer premised on entropy stabilization and synergistic effect strategies is introduced. HEFO-modified, CaO-based sorbent pellets are synthesized via a rapid cigarette butt-assisted combustion process (15 min) combined with the graphite molding method. Post-multiple cycles, their CO2 capture capacity reaches 0.373 g g-1, which is 2.6-fold superior to that of pure CaO, demonstrating markedly enhanced anti-sintering properties. First, the subtle morphological and crystallographic modifications suggest that the inherent entropy stability of HEFO imparts robust thermal resistance. Concurrently, the disordered structure of single-phase HEFO exhibits a high affinity for CaO, resulting in an interface binding energy of -1.83 eV, in sharp contrast to the -0.112 eV of pure CaO, thereby restricting CaO migration. Additionally, the multi-element synergistic effect of HEFO reduces the energy barrier by 0.15 eV, leading to a 40% and 140% increase in carbonation and calcination rates, respectively. This work presents highly efficient and rapidly synthesized CaO-based sorbent pellets, showcasing promising potential for industrial application.

Biodiesel production from eggshells derived bio-nano CaO catalyst-Microemulsion fuel blends for up-gradation of biodiesel.

The utilization of bio-oil derived from biomass presents a promising alternative to fossil fuels, though it faces challenges when directly applied in diesel engines. Microemulsification has emerged as a viable strategy to enhance bio-oil properties, facilitating its use in hybrid fuels. This study explores the microemulsification of Jatropha bio-oil with ethanol, aided by a surfactant, to formulate a hybrid liquid fuel. Additionally, a bio-nano CaO heterogeneous catalyst synthesized from eggshells is employed to catalyse the production of Jatropha biodiesel from the microemulsified fuel using microwave irradiation. The catalyst is characterized through UV-Vis, XRD, and SEM analysis. The investigation reveals a significant reduction in CO, CO2, and NOX emissions with the utilization of microemulsion-based biodiesel blends. Various blends of conventional diesel, Jatropha biodiesel, and ethanol are prepared with different ethanol concentrations (5, 10, and 20 wt%). Engine performance parameters, including fuel consumption, NOX emission, and brake specific fuel consumption, are analyzed. Results indicate that the conventional diesel/Jatropha biodiesel/ethanol (10 wt%) blend exhibits superior performance compared to conventional diesel, Jatropha biodiesel, and other blends. The fuel consumption of the conventional diesel/Jatropha biodiesel/ethanol (10 wt%) blend is measured at 554.6 g/h, surpassing that of conventional diesel and other biodiesel blends. The presence of water (0.14 %) in the blend reduces the heating value, consequently increasing the energy requirement. CO and CO2 emissions for the conventional diesel/Jatropha biodiesel/ethanol (10 wt%) blend are notably lower compared to conventional C-18 hydrocarbons and various biodiesel blends. These findings accentuate the efficacy of the microemulsion process in enhancing fuel characteristics and reducing emissions. Further investigations could explore optimizing the emulsifying agents and their impact on engine performance and emission characteristics, contributing to the advancement of sustainable fuel technologies.

Bio-fabrication of calcium oxide nanoparticles from Coccinia grandis as a potential photocatalyst for dye degradation with antimicrobial activity.

In the current study, Coccinia grandis fruit extract was used to synthesize calcium oxide nanoparticles (CaO NPs) in an economical and environmentally friendly manner. UV-Vis spectroscopy and Fourier transform infrared spectroscopy revealed that the phytoconstituents found in Coccinia grandis fruit extract facilitated the production of CaO NPs by acting as better stabilizing, biodegradable, and reducing agents. The synthesized CG-CaO NPs were also tested for photocatalytic activity in the breakdown of selective dyes such as methyl red, methyl orange, and methylene blue in the presence of sunlight. The degradation percentage was determined by analyzing the color removal rates for all dye components. After 6 h of reaction, the IC50 values for methyl red, methyl orange, as well as methylene blue dyes were 73, 107, and 133, respectively. The CG-CaO NPs were further evaluated for their antimicrobial activity against specific bacteria and fungi using the agar-well diffusion method. 200 µg/mL CG-CaO NPs inhibited Aspergillus niger, Escherichia coli, Salmonella typhi, Streptococcus mutans, and Staphylococcus aureus at zones of 13, 14, 16, 14, and 15 mM, respectively. Further checkerboard assay confirmed the antagonism effect with gentamicin. Also, Artemia salina toxicity assay showed that the LD50 value of CaO NPs was 400 µg/mL of CaO NPs. The findings confirm that Coccinia grandis-mediated CG-CaO NPs can be used effectively in antimicrobial and environmental settings.

Biodiesel Production by Methanolysis of Rapeseed Oil-Influence of SiO2/Al2O3 Ratio in BEA Zeolite Structure on Physicochemical and Catalytic Properties of Zeolite Systems with Alkaline Earth Oxides (MgO, CaO, SrO).

Alkaline earth metal oxide (MgO, CaO, SrO) catalysts supported on BEA zeolite were prepared by a wet impregnation method and tested in the transesterification reaction of rapeseed oil with methanol towards the formation of biodiesel (FAMEs-fatty acid methyl esters). To assess the influence of the SiO2/Al2O3 ratio on the catalytic activity in the tested reaction, a BEA zeolite carrier material with different Si/Al ratios was used. The prepared catalysts were tested in the transesterification reaction at temperatures of 180 °C and 220 °C using a molar ratio of methanol/oil reagents of 9:1. The transesterification process was carried out for 2 h with the catalyst mass of 0.5 g. The oil conversion value and efficiency towards FAME formation were determined using the HPLC technique. The physicochemical properties of the catalysts were determined using the following research techniques: CO2-TPD, XRD, BET, FTIR, and SEM-EDS. The results of the catalytic activity showed that higher activity in the tested process was confirmed for the catalysts supported on the BEA zeolite characterized by the highest silica/alumina ratio for the reaction carried out at a temperature of 220 °C. The most active zeolite catalyst was the 10% CaO/BEA system (Si/Al = 300), which showed the highest triglyceride (TG) conversion of 90.5% and the second highest FAME yield of 94.6% in the transesterification reaction carried out at 220 °C. The high activity of this system is associated with its alkalinity, high value of the specific surface area, the size of the active phase crystallites, and its characteristic sorption properties in relation to methanol.

Green preparation of CaO-based CO2 adsorbent by calcium-induced hydrogenation of shell wastes at room/moderate temperature.

Capturing CO2 using clamshell/eggshell-derived CaO adsorbent can not only reduce carbon emissions but also alleviate the impact of trash on the environment. However, organic acid was usually used, high-temperature calcination was often performed, and CO2 was inevitably released during preparing CaO adsorbents from shell wastes. In this work, CaO-based CO2 adsorbent was greenly prepared by calcium-induced hydrogenation of clamshell and eggshell wastes in one pot at room/moderate temperature. CO2 adsorption experiments were performed in a thermogravimetric analyzer (TGA). The adsorption performance of the adsorbents obtained from the mechanochemical reaction (BM-C/E-CaO) was superior to that of the adsorbents obtained from the thermochemical reaction (Cal-C/E-CaO). The CO2 adsorption capacity of BM-C-CaO at 650 °C is up to 36.82 wt%, but the adsorption decay rate of the sample after 20 carbonation/calcination cycles is only 30.17%. This study offers an alternative energy-saving method for greenly preparing CaO-based adsorbent from shell wastes.

Recovery of Li from waste Li-containing Al electrolytes with high F and Na contents by using a CaO roasting-water leaching process.

With the increasing demand for Li, the recovery of Li from solid waste, such as Li-containing Al electrolytes, is receiving growing attention. However, Li-containing Al electrolytes often contain large amounts of F, leading to environmental pollution. Herein, a new method for preparing water-soluble Li salt from waste Li-containing Al electrolytes with high F and Na contents is proposed based on CaO roasting and water leaching. The effects of different roasting and leaching conditions on the Li leaching efficiency and reaction pathway were systematically investigated. Under the optimum processing conditions, the Li leaching efficiency reached 98%, while those of Na and F were 98.41% and 0.24%, respectively. Phase evolution analysis showed that the addition of CaO promoted the conversion of LiF and Na2LiAlF6 to Li2O, whereas F entered the slag phase as CaF2, which could be reused as a raw material for steel refinement. Overall, this study proposes an efficient and environmentally friendly method for the treatment and resource utilization of waste Al electrolytes with high F and Na contents.

The Degradation of Aqueous Oxytetracycline by an O3/CaO2 System in the Presence of HCO3-: Performance, Mechanism, Degradation Pathways, and Toxicity Evaluation.

This research constructed a novel O3/CaO2/HCO3- system to degrade antibiotic oxytetracycline (OTC) in water. The results indicated that CaO2 and HCO3- addition could promote OTC degradation in an O3 system. There is an optimal dosage of CaO2 (0.05 g/L) and HCO3- (2.25 mmol/L) that promotes OTC degradation. After 30 min of treatment, approximately 91.5% of the OTC molecules were eliminated in the O3/CaO2/HCO3- system. A higher O3 concentration, alkaline condition, and lower OTC concentration were conducive to OTC decomposition. Active substances including ·OH, 1O2, ·O2-, and ·HCO3- play certain roles in OTC degradation. The production of ·OH followed the order: O3/CaO2/HCO3- > O3/CaO2 > O3. Compared to the sole O3 system, TOC and COD were easier to remove in the O3/CaO2/HCO3- system. Based on DFT and LC-MS, active species dominant in the degradation pathways of OTC were proposed. Then, an evaluation of the toxic changes in intermediates during OTC degradation was carried out. The feasibility of O3/CaO2/HCO3- for the treatment of other substances, such as bisphenol A, tetracycline, and actual wastewater, was investigated. Finally, the energy efficiency of the O3/CaO2/HCO3- system was calculated and compared with other mainstream processes of OTC degradation. The O3/CaO2/HCO3- system may be considered as an efficient and economical approach for antibiotic destruction.

Calcium oxide enhances the anaerobic co-digestion of excess sludge and plant waste: performance and mechanism.

The study investigates the effect of the oxidant calcium oxide (CaO) on the codigestion of excess sludge (ES) and plant waste (PW) under mesophilic anaerobic conditions to enhance methane production. The findings indicate that CaO significantly elevated methane yield in the codigestion system, with an optimum CaO addition of 6% resulting in a maximum methane production of 461 mL/g volatile solids, which is approximately 1.3 times that of the control group. Mechanistic exploration revealed that CaO facilitated the disintegration of organic matter, enhanced the release of soluble chemical oxygen demand, and increased the concentrations of soluble proteins and polysaccharides within the codigestion substrate. The presence of CaO was conducive to the generation and biological transformation of volatile fatty acids, with a notable accumulation of acetic acid, a smaller carboxylic acid within the VFAs. The proportion of acetate in the CaO-amended group increased to 32.6-36.9%. Enzymatic analysis disclosed that CaO enhanced the activity of hydrolytic and acidogenic enzymes associated with the ES and PW codigestion process but suppressed the activity of coenzyme F420. Moreover, CaO augmented the nutrient load in the fermentation liquid. The study provides an alternative scheme for the efficient resource utilization of ES and PW.

Identification of Intermediates in the Reaction Pathway of SO2 on the CaO Surface: From Physisorption to Sulfite to Sulfate.

The interaction of CaO and Ca(OH)2 with solvated or gaseous SO2 plays a crucial role in the corrosion of urban infrastructure by acid rain or in the removal of SO2 from flue gas. We carried out a combined spectroscopic and theoretical investigation on the interaction of SO2 with a CaO(001) single crystal. First, the surface chemistry of SO2 was investigated at different temperatures using polarization-resolved IR reflection absorption spectroscopy. Three species were identified, and an in-depth density functional theory study was carried out, which allowed deriving a consistent picture. Unexpectedly, low temperature exposure to SO2 solely yields a physisorbed species. Only above 100 K, the transformation of this weakly bound adsorbate first to a chemisorbed sulfite and then to a sulfate occurs, effectively passivatating the surface. Our results provide the basis for more efficient strategies in corrosion protection of urban infrastructure and in lime-based desulfurization of flue gas.

CaO2nanomedicines: a review of their emerging roles in cancer therapy.

Metal peroxide-based nanomedicines have emerged as promising theranostic agents for cancer due to their multifunctional properties, including the generation of bioactive small molecules such as metal ions, H2O2, O2, and OH-. Among these metal peroxides, calcium peroxide (CaO2) nanomedicines have attracted significant attention due to their facile synthesis and good biocompatibility. CaO2nanoparticles have been explored for cancer treatment through three main mechanisms: (1) the release of O2, which helps alleviate tumor hypoxia and enhances oxygen-dependent therapies such as chemotherapy, photodynamic therapy, and immunotherapy; (2) the generation of H2O2, a precursor for ·OH generation, which enables cancer chemodynamic therapy; and (3) the release of Ca2+ions, which induce calcium overload and promote cell apoptosis (called ion-interference therapy). This review provides a comprehensive summary of recent examples of CaO2nanoparticle-based cancer therapeutic strategies, as well as discusses the challenges and future directions in the development of CaO2nanomedicines for cancer treatment.

Comparative environmental assessment of low and high CaO fly ash in mass concrete mixtures for enhanced sustainability: Impact of fly ash type and transportation.

The effect of fly ash type on the sustainability of concrete mixtures has yet to be quantified. This study aims to assess the environmental impacts of low calcium oxide (CaO) and high CaO fly ash in mass concrete mixtures from Thailand. The study analyzed 27 concrete mixtures with varying percentages of fly ash as a cement replacement (0%, 25%, and 50%) for 30 MPa, 35 MPa, and 40 MPa compressive strengths at specified design ages of 28 and 56 days. Sources of fly ash have been located between 190 km and 600 km away from batching plants. The environmental impacts were assessed using SimaPro 9.3 software. The global warming potential of concrete is reduced by 22-30.6% and 44-51.4% when fly ash, regardless of type, is used at 25% and 50%, respectively, in comparison with pure cement concrete. High CaO fly ash has more environmental benefits than low CaO fly ash when utilized as a cement substitute. The reduction in environmental burden was most significant for the midpoint categories of mineral resource scarcity (10.2%), global warming potential (8.8%), and water consumption (8.2%) for the 40 MPa, 56-day design with 50% fly ash replacement. The longer design age (56 days) for fly ash concrete showed better environmental performance. However, long-distance transport significantly affects ionizing radiation and ecotoxicity indicators for terrestrial, marine, and freshwater environments. Furthermore, the results show that a high cement replacement level (50%) may not always have a reduced environmental impact on mass concrete when considering long-distance transportation. The critical distance calculated based on ecotoxicity indicators was shorter than those calculated using global warming potential. The results of this study can provide insights for developing policies to increase concrete sustainability using different types of fly ash.

Impacts of calcium peroxide on phosphorus and tungsten releases from sediments.

In this study, CaO2 was used as a capping material to control the release of Phosphate (P) and tungsten (W) from the sediment due to its oxygen-releasing and oxidative properties. The results revealed significant decreases in SRP and soluble W concentrations after the addition of CaO2. The mechanisms of P and W adsorption by CaO2 were mainly chemisorption and ligand exchange mechanisms. In addition, the results showed significant increases in HCl-P and amorphous and poorly crystalline(oxyhydr)oxides bound W after the addition of CaO2. The highest reduction rates of sediment SRP and soluble W release were 37 and 43%, respectively. Furthermore, CaO2 can promote the redox of iron (Fe) and manganese (Mn). On the other hand, a significant positive correlation was observed between SRP/soluble W and soluble Fe (II) and between SRP/soluble W and soluble Mn, indicating that the effects of CaO2 on Fe and Mn redox play a crucial role in controlling P and W releases from sediments. However, the redox of Fe plays a key role in controlling sediment P and W release. Therefore, CaO2 addition can simultaneously inhibit sediment internal P and W release.

Synthesis and characterization of barium doped CaO heterogeneous nanocatalyst for the production of biodiesel from Catharanthus roseus seeds: Kinetics, optimization and performance evaluation.

The exploitation of petroleum derivatives to meet the energy demands of the cutting edge is thought of as impractical because of asset shortage. The current necessitates that the world community improves future energy sources by developing sustainable, ecofriendly alternatives. In this work, biodiesel is produced through the transesterification of Catharanthus roseus seed oil with a barium-doped CaO heterogeneous nanocatalyst. The catalyst characterization is assessed using FTIR, GC-FID, EDAX, XRD, and SEM. The optimum conditions of time (70 min), temperature (58 °C), the molar ratio of methanol: oil is 15:1, and catalyst load (4% w/w) resulted in a conversion of the maximum biodiesel yield of 91.83%. Finally, by using Catharanthus roseus as a feedstock, the low optimal reaction conditions contribute to the development of the economic impact of biodiesel synthesis. Biodiesel blend (B20) containing barium-doped CaO nanoparticles showed better combustion engine performance and lower emissions than fossil fuels.

Mint leaves (Mentha arvensis) mediated CaO nanoparticles in dye degradation and their role in anti-inflammatory, anti-cancer properties.

In ancient times, herbal plants were considered one of the greatest gifts from nature that human beings could receive, and about 80% of these plants have medicinal uses. In traditional medicine, Mentha arvensis, commonly known as mint, has many applications, and in the present study, the mint leaf extract has been used to synthesis nanoparticles using the mint leaf extract as a biosource for the extraction of nanoparticles. In addition to having a wide range of applications in various fields, calcium oxide (CaO) nanoparticles are also considered to be safe for human use. In order to assess the characteristics of the abstracted CaO nanoparticles, UV-visible absorption spectrophotometers, Fourier Transform Infrared spectrophotometers (FTIR), Scanning Electron Microscopes (SEMs), Dynamic Light Scattering (DLS), and X-ray Diffraction Spectrophotometers (XRDs) were used. By conducting a protein denaturation assay and nitric oxide scavenging assay, mint leaf mediated CaO nanoparticles were evaluated for their therapeutic applications. MTT assays were used to prove that the CaO nanoparticles mediated by mint leaf had anti-cancer properties. By examining the ability of mint leaf mediated CaO nanoparticles to degrade various dyes such as methyl red, methyl orange, and methylene blue, which are the most used azo dyes in textile industries resulting in water contamination, the ability of these nanoparticles to act as a photocatalytic agent was examined.

Stimulation the immune response through ξ potential on core-shell 'calcium oxide/magnetite iron oxides' nanoparticles.

This study investigated the role of ξ Potential on Monometallic (MM) and Bimetallic (BM) Calcium Oxide/Magnetite Iron Oxides nanoparticles to stimulate the immune response. Metallic nanoparticles (MNPs) were biosynthesis using Pseudomonas fluorescens S48. MNPs characterization was carried out by UV-Vis spectra, XRD analysis, Zeta potential and Particles size, SEM-EDS, and TEM, and the concentrations were calculated by ICP-AES. The immune system activity was measured by estimation of lymphocytes transformation, phagocytic activity. The end point was in evaluating the toxicity of Metallic NPs by comet assay. SEM-EDS and TEM micrographs showed that MM CaO and Fe3O4 represent a perfect example of zero-dimensional (0-D) NPs with cubic and spherical particles in shape, while BM CaO/Fe3O4 NPs appeared in the form of Core-shell structure. The variations effect of novelty MM, BM CaO/Fe3O4 NPs in enhancing immune activity were based on the ξ Potential whereas negatively and positively charged. These findings demonstrate that the cationic CaO/Fe3O4 NPs are inefficient in stimulating the immune system which causes a high cytotoxic effect. But the anionic CaO/Fe3O4 NPs have advantages in targeting the immune system because of enhanced delivery to the cells through adsorptive endocytosis as well as the half-life clearance from the blood.

Investigations on the polymorphism of K4CaSi6O15 at elevated temperatures.

In the present study, single crystals and polycrystalline material of K4CaSi6O15 were prepared from solid-state reactions between stoichiometric mixtures of the corresponding oxides/carbonates. Heat capacity (C p) measurements above room temperature using a differential scanning calorimeter indicated that two thermal effects occurred at approximately T 1 = 462 K and T 2 = 667 K, indicating the presence of structural phase transitions. The standard third-law entropy of K4CaSi6O15 was determined from low-temperature C p's measured by relaxation calorimetry using a Physical Properties Measurement System and amounts to S°(298K) = 524.3 ± 3.7 J·mol-1·K-1. For the 1st transition, the enthalpy change ΔH tr1 = 1.48 kJ·mol and the entropy change ΔS tr1 = 3.25 J·mol-1·K-1, whereas ΔH tr2 = 3.33 kJ·mol-1 and ΔS tr2 = 5.23 J·mol-1·K-1 were determined for the 2nd transition. The compound was further characterized by in-situ single-crystal X-ray diffraction between ambient temperature and 1063 K. At 773 K, the high-temperature phase stable above T 2 has the following basic crystallographic data: monoclinic symmetry, space group P21/c, a = 6.9469(4) Å, b = 9.2340(5) Å, c = 12.2954(6) Å, ß = 93.639(3)°, V = 787.13(7) Å3, Z = 2. It belongs to the group of interrupted framework silicates and is based on tertiary (Q3-type) [SiO4]-tetrahedra. Together with the octahedrally coordinated Ca-cations, a three-dimensional mixed polyhedral network structure is formed, in which the remaining K-ions provide charge balance by occupying voids within the net. The intermediate temperature modification stable between T 1 and T 2 shows a (3+2)-dimensional incommensurately modulated structure that is characterized by the following q-vectors: q1 = (0.057, 0.172, 0.379), q2 = (-0.057, 0.172, -0.379). The crystal structures of the high- and the previously studied ambient temperature polymorph (space group Pc) are topologically equivalent and show a group-subgroup relationship. The index of the low- in the high-symmetry group is six and involves both, losses in translation as well as point group symmetry. The distortion is based on shifts of the different atom species and tilts of the 4- and 6-fold coordination polyhedra. Actually, for some of the oxygen atoms, the displacements exceed 0.5 Å. A more detailed analysis of the distortions relating to both structures has been performed using mode analysis, which revealed that the primary distortion mode transforms according to the Λ1 irreducible representation of P21/c. However, other modes with smaller distortion amplitudes are also involved.

Co-vitrification of hazardous waste incineration fly ash and hazardous waste sludge based on CaO-SiO2-Al2O3 system.

Based on the CaO-SiO2-Al2O3 system, the feasibility of co-vitrification of hazardous waste incineration fly ash (FA) and hazardous waste sludge (HWS) was verified. In the CaO-SiO2-Al2O3 ternary system diagram, the melting point of the system gradually decreases with an appropriate increase in SiO2 content when the CaO/Al2O3 ratio is determined to be approximately 1. The TG-DSC results revealed that the liquid phase generation temperature in the FA and HWS mixture system was significantly lower than those of FA and HWS individually owing to the different CaO, SiO2, and Al2O3 contents; this is consistent with the results of the theoretical melting characteristics analysis, which show that the melting characteristic temperatures can be reduced by controlling the CaO-SiO2-Al2O3 ratio in the system. The co-vitrification experimental results confirmed that a vitreous content above 92%, a loss ratio on acid dissolution less than 1.74%, and leaching toxicity of heavy metals lower than 0.15 mg/L could be obtained by adjusting the CaO, SiO2, and Al2O3 contents in the FA and HWS system to 20 wt%-32.5 wt%, 35 wt%-61 wt% and 14 wt%-32.5 wt%, respectively, and under a melting temperature of 1350 °C.

Study on the Influence of CaO on the Electrochemical Reduction of Fe2O3 in NaCl-CaCl2 Molten Salt.

The presence of calcium-containing molten salts in the electrolysis of oxides for metal production can lead to the formation of CaO and, subsequently, the generation of intermediate products, affecting the reduction of metals. To investigate the impact of CaO on the reduction process, experiments were conducted using a Fe2O3-CaO cathode and a graphite anode in a NaCl-CaCl2 molten salt electrolyte at 800 °C. The electrochemical reduction kinetics of the intermediate product Ca2Fe2O5 were studied using cyclic voltammetry and I-t curve analysis. The phase composition and morphology of the electrolysis products were analyzed using XRD, SEM-EDS, and XPS. The experimental results demonstrate that upon addition of CaO to the Fe2O3 cathode, Ca2Fe2O5 is formed instantly in the molten salt upon the application of an electrical current. Research conducted at different voltages, combined with electrochemical analysis, indicates that the reduction steps of Ca2Fe2O5 in the NaCl-CaCl2 molten salt are as follows: Ca2Fe2O5 ⟶ Fe3O4 ⟶ FeO ⟶ Fe. The presence of CaO accelerates the electrochemical reduction rate, promoting the formation of Fe. At 0.6 V and after 600 min of electrolysis, all of the Ca2Fe2O5 is converted into Fe, coexisting with CaCO3. With an increase in the electrolysis voltage, the electrolysis product Fe particles visibly grow larger, exhibiting pronounced agglomeration effects. Under the conditions of a 1 V voltage, a study was conducted to investigate the influence of time on the reduction process of Ca2Fe2O5. Gradually, it resulted in the formation of CaFe3O5, CaFe5O7, FeO, and metallic Fe. With an increased driving force, one gram of Fe2O3-CaO mixed oxide can completely turn into metal Fe by electrolysis for 300 min.

The Adsorption Behaviors of CO and H2 to FeO onto CaO Surfaces: A Density Functional Theory Study.

The adsorption behaviors of CO and H2 to FeO onto CaO surfaces have been studied using the density functional theory (DFT) to determine the reactions of FeO by CO and H2. The adsorption mechanisms of FeO clusters on the CaO(100) and CaO(110) surfaces were calculated first. The structure of the Ca(110) surface renders it highly chemically reactive compared with the Ca(100) surface because of low coordination. After gas adsorption, CO bonds to the O atom of FeO, forming CO2 compounds in both configurations through the C atom. H2 favors the O atom of FeO, forming H2O compounds and breaking the Fe-O bond. Comparing the adsorption behavior of two reducing gases to FeO on the Ca surface, the reaction of the CO molecule being adsorbed to generate CO2 compounds is exothermic. The reaction of H2 molecule adsorption to generate H2O compounds is endothermic. This property is essential for the inertial-collision stage of the reduction. However, the dissociation of the CO2 compound from the reaction interface will overcome a high energy barrier and slow down the reduction. The H2O compound dissociates from the surface more easily, which can accelerate the reduction.