Changes In Chemical Structure Research Articles

Composite flat-sheet membrane adsorbent of Li2TiO3-Ethylene-co-vinyl alcohol (LTO-EVAL) for lithium extraction

Composite bead adsorbents have been prevalent for the extraction of Li+ from brines. However, adsorbent beads generally demonstrate declining adsorption capacity and require extended equilibrium time when used repeatedly in absorption/desorption cycles. To overcome this challenge, a novel composite flat-sheet membrane adsorbent based on ethylene-co-vinyl alcohol (EVAL) and Li2TiO3 (LTO) is reported herein for highly efficient Li+ extraction from a geothermal brine. At an optimal LTO loading and membrane thickness, the resulting LTO-EVAL membrane was characterized by a large open macrovoid structure for fast ion transport, a fast adsorption rate that reached equilibrium in 0.5 h, and a high capacity of 96 % of that of the powder. The new membrane adsorbent showed adsorption behavior consistent with the Langmuir model and pseudo-second-order kinetic model. For a geothermal brine with a low lithium concentration, the LTO-EVAL membrane showed stable performance in 13 rapid adsorption/desorption cycles, with adsorption capacity at an average adsorption capacity of 7.3 mg/g and a 70 % adsorption efficiency. The average dissolution rate of Ti4+ was below 0.6 % in each cycle. The structure of the adsorbent material showed no discernable changes in chemical structure as confirmed by XRD and SEM results. With the improved extraction efficiency, the reusable membrane adsorbents would be economically viable in the long run and could potentially serve as the next generation of scalable Li+ adsorption material for brines. Further utilization of membrane adsorbent would lead to new design of adsorption modules and systems with reduced footprint. We need to further optimize the stability of the membrane adsorbents so that loss of Li2TiO3 remain at low level to reduce the lost for lithium extraction from the geothermal brine.

Structural evolution and reaction kinetics of lignin-carbohydrate complex oxidized by chlorine dioxide

Lignin-carbohydrate complexes (LCC) present a significant barrier to pulp purification, and their oxidation mechanisms remain unclear. In this study, chlorine dioxide (ClO2), a common oxidant in the paper industry, was used to treat LCCs from various plant sources. The chemical composition, structural changes, and reaction kinetics of LCC were analyzed. After ClO2 oxidation, the LC bonds connected to syringyl (S)-type lignin structural unit and FA/pCA structures in LCC were effectively degraded, whereas those connected to guaiacyl (G) and p-hydroxyphenyl propane (H)-type units remained stable. Kinetic studies revealed that under conventional oxidation conditions, the degradation rates of LCCs from bagasse, bamboo, and eucalyptus were 0.40, 1.12, and 1.75, respectively, with consumption amounts of 6.23 mg, 10.92 mg, and 15.48 mg. The differences in the degree of LCC oxidative degradation were determined by the composition of lignin structural units. The findings provide theoretical support for the action mechanism of ClO2 on LCCs during the pulp purification process, and offer important guidance for optimizing the pulp purification process.

Glucomannan is a promising isoniazid’s enhancer that inducing macrophage phagocytosis

Isoniazid (INH) is a frontline antituberculosis agent effective against Mycobacterium tuberculosis (Mtb), but the increasing challenge of avoiding multidrug-resistant tuberculosis, including INH resistance, necessitates innovative approaches. This study focused on enhancing macrophage phagocytosis to overcome INH resistance. Glucomannan, an immunomodulatory polysaccharide, emerged as a potential macrophage activator. Our objective was to characterize the glucomannan-INH mixture and assess its impact on INH efficacy and macrophage activity. Detailed examination of the glucomannan from Amorphophallus muelleri (0.05%–0.2%) was performed in several methods. INH sensitivity tests were carried out with the Mtb strain H37RV on Löwenstein–Jensen medium. Murine macrophage (RAW264.7) viability and activity were evaluated through MTT and latex bead phagocytosis assays. Ultraviolet-wavelength spectrophotometry was used to analyze chemical structure changes. Glucomannan (0.05%–0.2%) significantly enhanced murine macrophage viability and activity. When glucomannan was combined with INH, the IC50 value was greater compared to INH only. Phagocytosis assays revealed heightened macrophage activity in the presence of 0.05% and 0.1% glucomannan. Importantly, glucomannan did not compromise INH efficacy or alter its chemical structure. This study underscores the potential of glucomannan, particularly with a lower molecular weight, as a promising enhancer of INH, boosting macrophage phagocytosis against INH-resistant Mtb. These findings challenge the assumptions about the impact of glucomannan on drug absorption and prompt potential reevaluation. While specific receptors for glucomannan in macrophage phagocytosis require further exploration, the complement receptors are proposed to be potential mediators.

On application of molecular dynamics simulation for studying the effect of temperature and heating rate on HTL of biomass

Abstract Hydrothermal liquefaction (HTL) of biomass has garnered increasing attention as a promising pathway for converting solid biomass to liquid biofuels and valuable chemical products. HTL involves processing of biomass in water at high-temperature and high-pressure conditions. The heating rate during this process plays a critical role in determining the yield and composition of the liquefied products. To probe the impact of heating rate, we develop a detailed atomistic model biomass by using cellulose as model compound and place it in a simulated HTL reactor. Our Reactive molecular dynamics simulations are capable of capturing the dynamic chemical reactions and structural changes during HTL. The effect of reaction temperature and heating rates on reaction pathways, product distributions, and reaction kinetics is rigorously analyzed. Our findings reveal that the reaction temperature and heating rate significantly influences the extent of cellulose degradation and the composition of bio-oil product.

Low reaction threshold of ambient temperature oxidation of coal: Perspective from oxygen concentration and airflow rate

Coal spontaneous combustion remains a significant hazard in mining operations. In this study, the temperature rise characteristics of sub-bituminous coal were investigated using an air stream of varying concentration and airflow rate. The chemical structure changes under various oxygen contents were analyzed using the FTIR technique. The findings demonstrate that ambient temperature oxidation can occur even under low oxygen and airflow rate conditions, emphasizing the need for vigilance. Although oxygen enrichment in the atmosphere promotes the coal-oxygen complex and increases the total temperature rise (TTR), TTR can still reach 0.31 °C with 6 vol% oxygen. There exists an optimum ventilation rate to maximize the TTR. TTR at the flow rate of 25 mL/min is 47 %, 36 %, 165 % and 308 % higher than at the 10, 50, 75 and 100 mL/min. Moreover, FTIR experiments indicated the difference of active groups under different oxygen concentrations is slight. The low reaction threshold for ambient temperature oxidation complicates the prevention of coal spontaneous combustion during latency periods.

What Phenomena Happen During Pyrolysis of Plastic? FTIR AND GC-MS Analysis of Pyrolyzed Low Linear Density Polyethylene (LLDPE) Polymer Particles Completed with Bibliometric Research Trend and Pyrolysis Chemical Reaction Mechanism

This research aims to determine the compounds produced from the pyrolyzed Low Linear Density Polyethylene (LLDPE) using Fourier Transform Infrared (FTIR) and Gas Chromatography-Mass Spectroscopy (GC MS). We used pyrolysis of 985 g of 2-mm diameter LLDPE plastic ore at a temperature between 192-194°C for 135 min using a batch reactor (length x width x height = 35 cm x 24 cm x 44 cm) equipped with an outlet connected to two condensers (24°C). To ensure the chemical results, the reactor was connected in series to condensers 1 and 2. The results obtained in condenser 1 were 3 mL of 2-phase liquid with a strong odor. The upper fluid is yellow, and the lower fluid is brown. In condenser 2 (connected directly to condenser 1), 4 mL of yellow single-phase liquid was produced with a strong odor. The liquid obtained from the pyrolysis process was then analyzed by FTIR and GC-MS. FTIR results on both samples showed that the samples contained the functional groups O-H, CH₂, and C=O. The GC-MS results on condenser sample 2 showed that the pyrolysis product contained acetone compounds. This confirmed that pyrolysis caused chemical structural changes in LLDPE due to LLDPE chain bond-breaking reactions, producing many smaller chemical compounds. Additionally, some oxidation happens, which is due to the oxygen content in the reactor. This study provides new insights into the LLDPE pyrolysis mechanism and the physical and chemical properties of the liquid resulting from the pyrolysis process.

Type of pectin affects the functionality of potato protein-pectin conjugates in emulsions

This study investigated the effect of the molecular structure of pectin on conjugate formation and its functionality in plant protein-based emulsions. For this purpose, high-methoxylated, low-methoxylated, amidated citrus pectin and their mixtures with potato protein were vacuum-dried at defined process conditions. The change in free amino groups, colour and molecular weight distribution assessed conjugation. The side reaction, such as pectin degradation, was monitored by the degree of methoxylation, galacturonic acid content and intrinsic viscosity. In addition, FT-IR and hydrophobicity measurements were performed to determine the changes in chemical structure due to the occurring reactions. The ζ-potential, solubility and oil droplet size reflected the functionality of the conjugated samples.The results confirm that, apart from the conjugation of protein and pectin, where the most significant decrease in free amino groups was obtained with an increasing degree of methoxylation or presence of amide groups, undesirable degradation of pectin occurring, resulting in a broad molecular weight distribution of the conjugate samples. The conjugate formation was the highest with amidated pectin. The FT-IR measurements confirmed the formation of Maillard conjugates. The FT-IR spectra showed a decrease in the intensity signals of amide I and amide II and the formation of new C–N bond maxima. In addition, the conjugation caused the shift of the protein's isoelectric point to the acidic environment, resulting in higher solubility and improved emulsion stability at the isoelectric point of the protein.Regarding emulsion stability, the conjugates with amidated pectin performed best and achieved the narrowest oil droplet size distribution over a wider pH range. Emulsion-stabilising properties of conjugates with high- and low-methoxylated pectin differed only slightly. To better understand the underlying mechanisms for emulsion stabilisation, future research will focus on the interfacial properties of the conjugates as determined by interfacial shear rheology and pendant drop analysis.

Aging effects on asphalt adhesive properties: molecular dynamics simulation of chemical composition and structural changes

ABSTRACT Asphalt aging is a natural process that causes changes in the properties of asphalt, particularly in asphalt adhesion. Previous studies show that the effect of aging on asphalt adhesion performance is not uniform and depends on the asphalt source and aging conditions. To investigate the effects of different SARA (saturates, aromatics, resins, and asphaltenes) ratios and structural changes on the adhesive properties of asphalt after aging, this study employs molecular dynamics simulation to calculate asphalt properties such as density, viscosity, and work of adhesion. The above properties were computed for 12 categories of asphalt molecules, individual SARA components, and asphalt models characterised by diverse SARA ratios, followed by a correlation analysis. The study reveals that asphalt aging increases density, viscosity, and adhesion to silica. The increase in polar functional groups, namely ketone and sulfoxide, is responsible for the enhanced adhesion of asphalt to silica due to the resulting increase in electrostatic potential energy. Different SARA ratios lead to different asphalt properties, with the RA/SA index ((asphaltene%+resin%)/(saturate% + aromatic%)) showing a better correlation with the properties. Positive correlations were observed among density, viscosity, and work of adhesion. This study advances our understanding of chemical and structural effects on aged asphalt properties.

Phase Transition Control in Molecular Solids via Complementarity of Hydrogen-Bond Strength.

Phase transitions in molecular solids involve synergistic changes in chemical and electronic structures, leading to diversification in physical and chemical properties. Despite the pivotal role of hydrogen bonds (H-bonds) in many phase-transition materials, it is rare and challenging to chemically regulate the dynamics and to elucidate the structure-property relationship. Here, four high-spin CoIIcom-pounds were isolated and systematically investigated by modifying the ligand terminal groups (X = S, Se) and substituents (Y = Cl, Br).S-ClandSe-Brundergo a reversible structural phase transition near room temperature, triggering the rotation of 15-crown-5 guests and the swing between syn- and anti-conformation of NCX-ligands, accompanied by switchable magnetism. Conversely,S-BrandSe-Clretain stability in ordered and disordered phases, respectively. H-bonds geometric analysis andab initiocalculations reveal that the electronegativity of X and Y affects the strength of NY-ap-H···X interactions. Entropy-driven structural phase transitions occur when the H-bond strength is appropriate; otherwise, the phase stays unchanged if it is too strong or weak. This work highlights a phase transition driven by H-bond strength complementarity - pairing strong acceptor with weak donor andvice versa, which offers a straightforward and effective approach for designing phase-transition molecular solids from a chemical perspective.

Biomimetic papilla texture by femtosecond laser for high-strength CFRTP/A6061-T6 FSSW hybrid structures

The lightweight design concept in structural applications has generated interest in hybrid structures of carbon-fiber-reinforced thermoplastics (CFRTP) and metals as attractive structure components. However, these hybrid structures face challenges due to the significant differences in physical and chemical properties between CFRTP and metals, resulting in limited strength and rendering them unsuitable for advanced transportation. To address these limitations, the current research focuses on creating a biomimetic texture on A6061-T6 (6061) surfaces using femtosecond laser to manufacture high-strength hybrid structures, inspired by organismal body surfaces. The CFRTP and 6061 were joined by friction stir spot welding (FSSW). The femtosecond laser treatment produces double-scale roughness on 6061 surfaces and causes carbon to absorb into alumina. These changes in physical and chemical structures enhance the compatibility between 6061 and CFRTP. The biomimetic rough aluminum surface creates effective mechanical interlock at the interface with CFRTP, preventing the initiation and propagation of fracture cracks. The presence of absorbed carbon enhances the Al-O covalency, which influences the bonding behavior at CFRTP/6061 interfaces. The improved compatibility, mechanical interlock, and enhanced bonding behavior synergistically strengthen the joint strength of CFRTP/6061 hybrid structure modified by the biomimetic papilla structure. Current biomimetic design strategy inherits the remarkable natural wisdom and is expected to provide valuable insights for the development and application of CFRTP/metal hybrid structures.

Identification of plastic-degrading bacteria in the human gut

Environmental pollution caused by the excessive use of plastics has resulted in the inflow of microplastics into the human body. However, the effects of microplastics on the human gut microbiota still need to be better understood. To determine whether plastic-degrading bacteria exist in the human gut, we collected the feces of six human individuals, did enrichment cultures and screened for bacterial species with a low-density polyethylene (LDPE) or polypropylene (PP)-degrading activity using a micro-spray method. We successfully isolated four bacterial species with an LDPE-degrading activity and three with a PP-degrading activity. Notably, all bacterial species identified with an LDPE or PP-degrading activity were opportunistic pathogens. We analyzed the microbial degradation of the LDPE or PP surface using scanning electron microscopy and confirmed that each bacterial species caused the physical changes. Chemical structural changes were further investigated using X-ray photoelectron spectroscopy and Fourier-transform-infrared spectroscopy, confirming the oxidation of the LDPE or PP surface with the formation of carbonyl groups (C=O), ester groups (CO), and hydroxyl groups (-OH) by each bacterial species. Finally, high temperature gel permeation chromatography (HT-GPC) analysis showed that these bacterial species performed to a limited extent depolymerization. These results indicate that, as a single species, these opportunistic pathogens in the human gut have a complete set of enzymes and other components required to initiate the oxidation of the carbon chains of LDPE or PP and to degrade them. Furthermore, these findings suggest that these bacterial species can potentially biodegrade and metabolize microplastics in the human gut.

Continuous straw returning enhances the carbon sequestration potential of soil aggregates by altering the quality and stability of organic carbon

Soil structure plays an important role in organic carbon (OC) sequestration, thereby influencing soil fertility and changes in global climate. However, aggregate OC chemical structure changes due to long-term return of straw in oasis farmland of arid northwest China remains unclear. This study conducted 0-, 5-, 10-, 15-, and 20-year straw returning experiments during which three soil components where measured: (1) the functional carbon (C) pool and macroaggregates; (2) microaggregates and silt + clay; (3) the chemical structure of soil OC (SOC). The results demonstrated that in comparison with the control, straw return increased SOC, particulate OC (POC), and mineral-associated OC (MAOC) by 21.90%–63.51%, 5.00%–31.00%, and 46.00%–226.00%, respectively. With increasing duration of straw return, microaggregates transitioned to macroaggregates, and percentages of soil macroaggregates under 10-year straw return increased by 20.26%, 3.39%, 4.40%, and 11.12% compared with that under 0-, 5-, 15- and 20-year straw return, respectively. Soil geometric mean diameter (GMD) and mean weight diameter (MWD) first increased and then decreased, with maximum values after 10-year straw return at 1.20 mm and 1.63 mm, respectively. Solid state 13C NMR (Nuclear Magnetic Resonance) indicated O-alkyl C to be the dominant chemical component of soil OC over different years of straw return. There were increases in aromatic C, aromaticity, and hydrophobicity up to 10-year straw return, after which they decreased. A mantel test confirmed positive correlations of the distributions of macroaggregates, microaggregates, OC of macroaggregates, and silt + clay with MWD and GMD, whereas the OC content of aggregates was positively correlated with O-OA and hydrophobicity. Long-term straw returns improved soil structure and stabilized soil OC, thereby facilitating soil sequestration of OC.

Characterization of recycled nitrile butadiene rubber industrial scraps

The amount of rubber scraps derived from rubber goods production consists of about 20–30% of the processed material, so it is necessary to enhance this material by developing new recycling techniques as well as a new market for recycled rubber products. In the present research, nitrile-butadiene rubber (NBR) scraps are reprocessed via a calendering process acting with a mechanical devulcanization. Compounds were prepared with 20%, 80%, and 100% recycled rubber content and characterized. The experimental results highlighted that the compound prepared with 20% recycled rubber content via calendering and compression molding processes shows comparable mechanical properties to that of virgin NBR. The tensile properties are the most penalized by the increasing content of recycled material (100% recycled shows − 25% and − 50% stress and strain at break, respectively). Other properties remain comparable to the standard material up to 80% recycled material: 60 ± 5 Shore A, compression elastic modulus 8 MPa, compression set 20%. FTIR analysis revealed no changes in chemical structure from the recycling process. The results demonstrate that simple mechanical devulcanization can effectively reprocess industrial rubber waste while largely maintaining useful properties. This provides a potential pathway to enhance sustainability in rubber production through the valorization of process scraps.Graphical

Salicylic and tartaric ions co-doped polypyrrole to enhance the corrosion protection of polypyrrole/zinc bilayer coating on ZK60 magnesium alloy in Hank's solution

To enhance the corrosion protection of the polypyrrole/zinc (PPy/Zn) bilayer coating on biodegradable ZK60 magnesium alloy in Hank's solution at 37 °C, sodium salicylate (NaSA) in different concentrations (CNaSA, 0.5–4.0 mM) is selected as a co-doping reagent of tartrate anions (TA−), and an electropolymerization method that combines potentiostatic and galvanostatic synthesis is developed to prepare PPy(TA + SA)/Zn bilayer coatings. The co-doping of SA− suppresses the growth of PPy and notably increases its synthesis potential (Epoly) with increasing CNaSA. The co-doped PPy(TA + SA) films have a surface morphology and thickness similar to the PPy(TA) film. However, their chemical composition, structure, and adhesion strength change notably due to their varying growth conditions. In the long-term immersion test of PPy(TA + SA)/Zn/ZK60 samples, the PPy(TA + SA)/Zn coatings exhibit high stability, and the coating prepared with CNaSA = 1.0 mM has the most prolonged protection time (54 ± 1.5 d). As CNaSA increases, the co-doped PPy(TA + SA) film becomes heavily over-oxidized to produce more defects on PPy chains due to the high Epoly, ultimately decreasing the protection time to 40 ± 1.0 d. The corresponding mechanism involved is thoroughly discussed.

Optical characterization and dispersion analyses of plasma polymerized methyl acrylate thin films

This work reports the structural characteristics, surface morphology, linear and nonlinear optical properties of 110 to 225 nm thick plasma polymerized methyl acrylate (PPMA) thin films. X-ray diffraction analyses confirm the amorphous nature of the films. Field emission scanning electron micrographs of the films display cluster-based surface morphology. Attenuated total reflectance Fourier transform infrared spectroscopy confirms the chemical structural changes in the films. The optical properties were studied based on the absorbance, transmittance, and reflectance spectra measured by an ultraviolet–visible spectrophotometer within the wavelength ranges from 200 to 800 nm. The direct optical band gap and Urbach values are increased from 3.66 to 3.83 eV and 0.28 to 0.45 eV, respectively with increasing film thickness. The extinction coefficient and refractive index were evaluated, and discussed a correlation between the refractive index and the optical bandgap. The real and imaginary dielectric constants, volume/surface energy loss functions and skin depth were deduced. The oscillator energies and parameters were analyzed using the concept of Wemple-DiDomenico and Sellmeier models, respectively for a single oscillator. Static linear refractive index for the studied films exhibits normal dispersion behavior with film thicknesses and satisfied Moss, Ravindra-Gupta, and Herve-Vandamme rules. The linear susceptibility, third-order nonlinear susceptibility and the non-linear refractive index are considerably reduced from 0.20, 29.5 × 10−14 esu, and 5.89 × 10−12 esu with increasing optical band gap energies. The outcomes from the analyses of PPMA demonstrated their potential for usage in electronic, optoelectronic, and non-linear device applications.

Hydrophobic Modification of Bi2O3-Doped Si-Ti Composite Film on a Wood Surface

In order to improve the hydrophobicity of the composite film on the wood surface, the wettability of the wood surface and its morphology, chemical structure, roughness and free energy changes were investigated in this paper after modification treatments with different volume fractions of octadecyltrichlorosilane (OTS) and polydimethylsiloxane (PDMS). It can be found that the water contact angle and surface roughness of the hydrophobically modified wood increased with the increase in volume fraction, but the overall effect of OTS hydrophobic modification was better than that of PDMS, and a maximum water contact angle of up to 140.8° could be obtained at a volume fraction of 2% of OTS. In addition, the intensity of the stretching vibration peak of -OH was weakened after the modification, while the intensity of the stretching vibration peak of -CH2- was enhanced, resulting in an increase in hydrophobicity. At the same time, it can be found that the surface free energy of the modified wood specimens was reduced, which shows that OTS and PDMS improve the surface hydrophobicity of the wood by increasing the surface roughness and decreasing the surface free energy together. Finally, the hydrophobically modified Bi2O3-doped silica–titanium composite film still possessed high photocatalytic degradation activity for rhodamine B and gas formaldehyde, and the degradation rate could reach more than 90%.

Isobornyl and Isocamphyl Photostabilizers in Poly(lactic acid)-Based Electrospun Fibers.

In this work, electrospun polylactide fibers with new photostabilizing additives, 4-methyl-2,6-diisobornylphenol (DIBP) and N-isocamphylaniline (NICA), have been tested under the influence of UV-C radiation (254 nm). The changes in the polymers' chemical structure under UV-C radiation were revealed through the increase in absorption in the 3600-3100 cm-1 region in regard to the FTIR spectra. In the samples that were irradiated for 1 h, the stabilizing effect of the photoprotectors became most noticeable as the difference in the content of the hydroxyl groups in stabilized and the pure PLA reached a maximum. The TG-DSC method revealed that the most sensitive indicator of the irradiation effect was the glass transition temperature (Tg), which persisted after 2 h of irradiation when using photostabilizers and their combinations. The PLA/DIBP(1) and PLA/NICA(1) samples showed the best results in protecting PLA from UV-C radiation based on the Tg values; although, the mixture of DIBP and NICA was not as effective. The chemical structure of the photostabilized PLA samples was studied using NMR, GPC, and Py-GC/MS analysis. The electrospun polylactide fibers were mechanically tested and the effects of the electrospun samples on cell viability were studied.

CO2 and Lignin‐Based Sustainable Polymers with Closed‐Loop Chemical Recycling

AbstractThis work highlights the conversion method of chaining up greenhouse gas CO2 with biomass lignin to develop new sustainable, recyclable polymers from abundant and non‐food based renewable resources. A cyclic carbonate monomer has synthesized using a cost‐effective, non‐phosgene‐based, and greener approach under atmospheric pressure and room temperature. The fully programable ring‐opening polymerization is accomplished by varying the catalyst (DBU and TBD), catalyst loading (0.5–5.0%) and reaction time (2–40 min). The best polymer is obtained in 1% TBD with a 30‐min reaction. The precise characterization of the synthesized cyclic carbonate monomer and polymers' structure are established using spectroscopic analyses including 1H, 13C, and 2D HSQC NMR, FT‐IR, and GPC. The new polymers exhibit high molecular weights (Mn: 120.34–154.58 kDa) and adequate thermal stabilities (Td5%: 244–277 °C from TGA and Tg: 33–52 °C from DSC), rendering them advantageous for practical applications. Significantly, the CO2 and lignin‐based polymers have successfully recycled to the monomer for a circular plastic economy by heating at 90 °C for 12 h in the presence of DBU. This process yields original monomers for another polymerization without unwanted changes in chemical structures, presenting an ultimate sustainable solution.

Modification and characterization of tricalcium silicate bio-ceramic powders synthesized by sol-gel process for potential application in dental treatment

Tricalcium silicate powders (Ca3SiO5 or C3S) were fabricated by sol-gel process from the initial materials of Ca(NO3)2·4 H2O and Si(OC2H5)4 (TEOS) in acid medium. Effects of stoichiometry of reagent and catalyst, and temperature on physical-chemical, mechanical, and biological properties of C3S powders were examined systematically. The radiopacity, setting time, compressive strength, and bioactivity were investigated according to ISO recommendations. The radiopacity was compared and evaluated using dopants. The setting time and compressive strength were determined using water solvent. Analysis of bioactivity, antibacterial activity, and biocompatibility of Ca3SiO5 powders was performed and evaluated using simulated body fluid (SBF), and Tetrazolium (WST-1) reagent assay on Escherichia coli bacterium (E. coli), respectively. The milled-C3S powders showed a fine radiopacity with ZrO2 dopant, a shorter setting time, a higher density and a feasible compressive strength. The high purity of the milled-C3S powders with presence of Ca and Si compositions was confirmed by SEM-EDS analysis. Also, hydroxyapatite (HAp) was induced to form on the surface of milled-C3S powders when immersed in SBF. The surface compositional, morphological and chemical structural changes of the milled-C3S powders before and after immersing were analyzed by X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), and scanning electron microscopy (SEM). The results showed that a dense HAp layer was formed after 7 days of immersing. It indicated that C3S powders were bioactive and might be used for preparation of dental biomaterials. The milled-C3S powders also showed a potential antibacterial activity on the E.Coli cells and a high biocompatibility for cell viability. The good physical and excellent mechanical properties, bioactivity, and antibacterial activity confirmed the milled-Ca3SiO5 powders as a promising dental filling material.

Temperature-induced structure evolution in CoxBy liquids studied by ab initio molecular dynamics simulation

The relationship between the local structures and the thermodynamic properties of metallic liquids has been a fundamental issue, which significantly impacts the comprehensive performances of metallic materials. The temperature-induced structure evolution in CoxBy alloy liquids, involving CoB, Co2B, Co3B, and Co23B6, was investigated using ab initio molecular dynamics simulations. The results show that the clusters of icosahedral-like polyhedrons are found predominantly in all alloys at low temperature, while the heating induces the decrease in ideal icosahedral and the increase in defected icosahedral. At high temperature, the polyhedron clusters decrease significantly and the ideal icosahedra transforms into smaller short-range polyhedrons, signifying the temperature-induced chemical structure change from long-range to short-range ordering. The aggregation of B atoms at high temperature is confirmed by atomic configuration, charge density, and B-centered Voronoi polyhedrons, and the α-Co single phase is observed below 1600 K. This study is helpful for understanding the local structure variability in eutectic Co-B alloys and guiding solidification path in theory.