International Journal of Chemical Kinetics最新文献

Owing to the significant physical and chemical properties and the usage in numerous fields, nanoparticles/microparticles synthesis is becoming important in the present scenario. L-Serine, a non-essential amino acid, plays an effective role in regulating insulin sensitivity, is used for the treatment of skin inflammation, and is an important ingredient of beauty products specifically for skin and hair. Polyvinylpyrrolidone (PVP) is widely used in food, medicine, and cosmetics, showing pharmaceutical and biomedical applications. PVP served as the polymeric matrix for the synthesis of microparticles containing L-serine and provides structural integrity and modulate release kinetics through diffusion and polymer relaxation mechanisms. With this view, in the present studies, PVP microparticles containing l-serine have been synthesized and characterized by FTIR, XRD, and EDS SEM data. Release data of L-serine from PVP microparticles were fitted using a zero-order, Higuchi and Korsmeyer–Peppas model and kinetic constants for each model were calculated. The theoretical zero-order rate constant is found to be 0.305 mg/min, which matches with its graphical value of 0.311 mg/min. Release kinetics of L-serine from PVP microparticles does not follow normal Higuchi's criteria for drug release up to 60% but with a polynomial of order 2 trend-line is obtained. For Korsmeyer–Peppas model, the value of K and n is found to be 1 and 0.9, respectively, with regression coefficient of 0.99. Result indicates that the system follows zero-order kinetics as well as Korsmeyer–Peppas model with n values of about 0.9 indicating the super-case II transport mechanism suggesting that the release is not controlled by diffusion alone; instead, polymer relaxation dominates the release process which often results in constant release rate over time. Such release profile is considered ideal for sustained release formulations, reducing side effects, and improving patient compliance. It was observed that release of l-serine from PVP microparticles exhibit 65% release within 120 min, which is substantial in release kinetics. On the basis of FTIR analysis, an attempt was made to propose the structure highlighting the interaction of L-serine encapsulated in PVP microparticles using free online Avogadro's software.

Poly(chitosan)/hydroxyapatite (CS/HA) and carboxymethyl poly(chitosan)/hydroxyapatite (CMCS/HA) composite coatings were successfully fabricated via biomimetic mineralization, with their structural characteristics and properties systematically analyzed. As the CS concentration increased during fabrication, the growth morphology of CS/HA coating transitioned from clustered to sheet-like structures, forming dense and uniform composite coating with strong substrate adhesion and excellent biocompatibility. The CMCS/HA coatings exhibited a coral-like structure comprising spherical particles, which ensured higher substrate coverage and demonstrated superior corrosion resistance. At 20 g/L, coatings prepared by mixing pre-calcified solution A with CMCS and then adding biomimetic mineralization solution A (defined as YOCS), or by mixing pre-calcified solution A with a mixture of biomimetic mineralization solution A and CMCS (defined as FOCS), both show optimum structure. Coatings incorporating 30 g/L CS or 20 g/L CMCS in the biomimetic mineralization solution exhibited optimum corrosion resistance, antibacterial activity, and biocompatibility.

Owing to the significant physical and chemical properties and the usage in numerous fields, nanoparticles/microparticles synthesis is becoming important in the present scenario. L-Serine, a non-essential amino acid, plays an effective role in regulating insulin sensitivity, is used for the treatment of skin inflammation, and is an important ingredient of beauty products specifically for skin and hair. Polyvinylpyrrolidone (PVP) is widely used in food, medicine, and cosmetics, showing pharmaceutical and biomedical applications. PVP served as the polymeric matrix for the synthesis of microparticles containing L-serine and provides structural integrity and modulate release kinetics through diffusion and polymer relaxation mechanisms. With this view, in the present studies, PVP microparticles containing l-serine have been synthesized and characterized by FTIR, XRD, and EDS SEM data. Release data of L-serine from PVP microparticles were fitted using a zero-order, Higuchi and Korsmeyer–Peppas model and kinetic constants for each model were calculated. The theoretical zero-order rate constant is found to be 0.305 mg/min, which matches with its graphical value of 0.311 mg/min. Release kinetics of L-serine from PVP microparticles does not follow normal Higuchi's criteria for drug release up to 60% but with a polynomial of order 2 trend-line is obtained. For Korsmeyer–Peppas model, the value of K and n is found to be 1 and 0.9, respectively, with regression coefficient of 0.99. Result indicates that the system follows zero-order kinetics as well as Korsmeyer–Peppas model with n values of about 0.9 indicating the super-case II transport mechanism suggesting that the release is not controlled by diffusion alone; instead, polymer relaxation dominates the release process which often results in constant release rate over time. Such release profile is considered ideal for sustained release formulations, reducing side effects, and improving patient compliance. It was observed that release of l-serine from PVP microparticles exhibit 65% release within 120 min, which is substantial in release kinetics. On the basis of FTIR analysis, an attempt was made to propose the structure highlighting the interaction of L-serine encapsulated in PVP microparticles using free online Avogadro's software.

Poly(chitosan)/hydroxyapatite (CS/HA) and carboxymethyl poly(chitosan)/hydroxyapatite (CMCS/HA) composite coatings were successfully fabricated via biomimetic mineralization, with their structural characteristics and properties systematically analyzed. As the CS concentration increased during fabrication, the growth morphology of CS/HA coating transitioned from clustered to sheet-like structures, forming dense and uniform composite coating with strong substrate adhesion and excellent biocompatibility. The CMCS/HA coatings exhibited a coral-like structure comprising spherical particles, which ensured higher substrate coverage and demonstrated superior corrosion resistance. At 20 g/L, coatings prepared by mixing pre-calcified solution A with CMCS and then adding biomimetic mineralization solution A (defined as YOCS), or by mixing pre-calcified solution A with a mixture of biomimetic mineralization solution A and CMCS (defined as FOCS), both show optimum structure. Coatings incorporating 30 g/L CS or 20 g/L CMCS in the biomimetic mineralization solution exhibited optimum corrosion resistance, antibacterial activity, and biocompatibility.

In this work, binary composites of graphitic carbon nitride (g-C₃N₄) with iron oxide (Fe₂O₃) and zinc oxide (ZnO), namely GF4 and GZ4, were synthesized via cost-effective and environmentally friendly methods. The composites showed enhanced specific surface area and improved charge carrier separation compared to the bare g-C₃N₄, Fe₂O₃, and ZnO. The photocatalytic activity of the binary composites was evaluated based on the degradation of model organic pollutants, methyl orange (MO) and caffeine, under UV and visible light irradiation. Under 120 min UV light irradiation, the most efficient GZ4 and GF4 composites achieved 97% degradation of MO. Meanwhile, under similar condition, the GF4 and GZ4 composites showed a much lower degradation efficiency toward caffeine, 47% and 64%, respectively. Interestingly, the binary composites exhibited a 26-fold increase in MO degradation under visible light compared to bare g-C₃N₄ due to a synergistic effect. Total organic carbon (TOC) analysis revealed 58% mineralization of caffeine under UV light, indicating the potential of these materials for effective wastewater treatment. The obtained photocatalysts displayed excellent stability and reusability, suggesting their practical use for the remediation of our environment.

Coal spontaneous combustion (CSC) process releases a large number of combustible gases, which bring threat to the combustion and explosion of mine methane (CH₄). Under the action of CSC, the combustion characteristics of CH₄ will undergo significant changes. In the current work, the laminar burning velocity (LBV) of CH₄/CSC gases mixed flame was obtained in a constant volume chamber (CVC) under an initial pressure of 0.1 MPa and an initial temperature of 300 K over a wide equivalence ratio range of 0.7–1.3 with three kinds of CSC gases mixing ratios. The effects of CSC gases addition on the LBV of CH₄ were analyzed first. And then, four kinds of mixing laws were used to predict the LBV of CH₄/CSC gases mixed flame. In addition, six kinds of detailed reaction mechanisms were used to calculate the LBV of CH₄/CSC gases mixed flame. Results show that the mixing of all kinds of CSC gases increases the LBV of CH₄, and T mixing law is more suitable for predicting the LBV of CH₄ mixed with CSC gases in the second stage, while the modified and simplified USC 2.0 mechanism can predict the LBV of CH₄ mixed with CSC gases well in all three stages.

Coal spontaneous combustion (CSC) process releases a large number of combustible gases, which bring threat to the combustion and explosion of mine methane (CH₄). Under the action of CSC, the combustion characteristics of CH₄ will undergo significant changes. In the current work, the laminar burning velocity (LBV) of CH₄/CSC gases mixed flame was obtained in a constant volume chamber (CVC) under an initial pressure of 0.1 MPa and an initial temperature of 300 K over a wide equivalence ratio range of 0.7–1.3 with three kinds of CSC gases mixing ratios. The effects of CSC gases addition on the LBV of CH₄ were analyzed first. And then, four kinds of mixing laws were used to predict the LBV of CH₄/CSC gases mixed flame. In addition, six kinds of detailed reaction mechanisms were used to calculate the LBV of CH₄/CSC gases mixed flame. Results show that the mixing of all kinds of CSC gases increases the LBV of CH₄, and T mixing law is more suitable for predicting the LBV of CH₄ mixed with CSC gases in the second stage, while the modified and simplified USC 2.0 mechanism can predict the LBV of CH₄ mixed with CSC gases well in all three stages.

The complex effect of L-ascorbic acid on the oscillatory course of the Orbán–Epstein system, in which the Cu²⁺-catalyzed oxidation of thiocyanate ions with hydrogen peroxide occurs, was investigated. Our studies involved both the original and EDTA-perturbed system, analyzed in previous works. Potentiometric and spectrophotometric measurements were supported by numerical modeling of the proposed schemes of interaction of L-ascorbic acid with the components of the system. In this way the kinetic mechanism of the effect of EDTA on the Orbán–Epstein system, based on the idea of excess production of $�{\mathrm{HO}}_2^{•}$ radicals, enhancing the negative feedback loop in the oscillation cycle, was confirmed. The eventual involvement of other radicals, as, for example, OS(O)CN^• is possible, but kinetically indistinguishable from that of $�{\mathrm{HO}}_2^{•}$ species. The novel observation of the slowdown of oscillatory dynamics upon increasing concentrations of L-ascorbic was explained in terms of removal of HO₂Cu(OH)₂⁻ intermediate from reaction medium, presumably by the reduction of the central copper ion to elemental copper.

The kinetics of oxidation of pectin by acidic permanganate was studied at higher concentrations of pectin, previously. Consequently, the pseudo-first order plots of (ln (Abs. vs. time) were deviated from linearity. The results were interpreted in terms of two-stage reactions. Therefore, the results and postulated reaction mechanism were faced some debates which means that the redox reaction needs a further investigation. We expected that deviation may be attributed to the use of pectin of high concentration which leads to the creation of some complicated intermediates. These formed complexes may tend to retard the reaction rates and, hence, the noticed deviation from linearity. Therefore, in the present work pectin substrate of low concentrations was applied to check the linearity of pseudo first-order plots. Fortunately, all curves obtained from all plots were found to be fairly linear. This result was considered as evidence to support our expectation. Again, the experimental observations revealed second order rate constants in [H⁺] on contrary to that reported previously. Such diversity and contrariety observed may indicate the complexity and non-complementary nature of the present redox system. The activation parameters calculated by the least-squares method from the temperature dependency of the second-order rate constants were found to be ∆H^≠ = 52.67 kJ/mole, ∆S^≠ = –65.54 J/mole K, ∆G^≠ = 71.90 kJ/mole and E^≠ = 55.36 (±0.2–2.0 kJ/mole), respectively. However, the results obtained agreed with both inner and outer-sphere mechanism, a simultaneous two-electron change in one step of inner-sphere nature was suggested to be the more preferable pathway route for the electron-transfer. Speculated reaction mechanisms based on the experimental observations and the evaluated kinetic parameters were postulated and a pertinent discussion is presented.