Mechanism Of Oxidative Degradation Research Articles

Oxygen concentration regulated the efficient liquefaction of vulcanized natural rubber

Oxidative liquefaction represents a promising avenue for the homogeneous and high-value utilization of waste tire rubber. Given that truck tires predominantly comprise natural rubber (NR), this study investigated the efficient liquefaction of vulcanized NR regulated by oxygen concentration. Remarkably, the liquefaction of vulcanized NR was realized with an oxygen concentration of 75% at 200°C within 3 min. FTIR spectroscopy showed that carbonyl, ether and sulphoxide groups were produced during the liquification of NR vulcanizates. Oxygen concentration significantly affected the oxidative efficiency of both the main chains and crosslinks, with a more pronounced effect observed on the main chains. Nevertheless, the similar molecular weights and polydispersity indices across various degraded products suggested a selective oxidative cleavage of the NR backbone. Furthermore, online ATR-FTIR was used to monitor the dynamic changes of NR's molecular structure to elucidate the oxidative degradation mechanism. The oxidative cleavage of NR main chain primarily occurred at the C-C bonds connected with allyl groups, producing oxidized products enriched with conjugated carbonyl groups. Alternatively, the main chain scission may also occur due to the electronic rearrangement effect of the C=C bond and produce saturated carbonyl groups. Oxygen concentration modulated the degradation efficiency of vulcanized NR, which provided an efficient strategy for the upcycling of NR-based waste tires.

Efficient degradation of vulcanized natural rubber into liquid rubber by catalytic oxidation

Waste tire rubber based on natural rubber (NR) represents an abundant feedstock for the production of valuable products. This study investigated an efficient approach to convert NR vulcanizates into liquid rubber with the number-average molar masses of 1.3 × 104 g/mol. Compared to the anaerobic liquefaction at 300 °C for 3 min, NR vulcanizates were liquefied efficiently at 210 °C for 3 min by thermo-oxidative degradation catalyzed by manganese (II) stearate. The apparent activation energy of the NR degradation reaction decreased from 470.8 kJ/mol to 208.2 kJ/mol with catalysis, which was attributed to the formation of a coordination complex between catalysts and peroxides via the single-electron transfer redox reaction, leading to the catalytic oxidative degradation of NR vulcanizates. The main chain scission and crosslink scission occurred simultaneously during the degradation process, and the main chain scission was the primary catalytic oxidation reaction according to the Horikx theory. In addition, the obtained liquid rubber contained carbonyls, ether linkages, and sulfoxide groups, as proved by FTIR and 13CNMR . The catalytic oxidative degradation mechanism of NR vulcanizates was proposed based on the chemical structure of products and simulation results. The efficient method was proposed to highly facilitate the recycling and valorization of NR-based waste tire rubber.

An assessment of the role of nanosilica in thermal/thermo‐oxidative degradation mechanism of poly(lactic acid)/polybutylene adipate terephthalate blend nanocomposites

AbstractAs a packaging materials candidate, based on a polylactic acid/ polybutylene adipate terephthalate (PLA/PBAT) blends (90/10 and 75/25 wt/wt) containing 1, 3, and 5 phr hydrophilic (HPL) and hydrophobic (HPB) nanosilica (NS) particles in the presence of a multifunctional epoxide compatibilizer were prepared by melt mixing, in a twin‐screw extruder. Scanning electron microscopic studies confirmed a matrix‐droplet morphology with finer dispersed domains at higher NS content. Energy dispersive spectroscopy mapping also indicated uniform dispersion of NS in blends, with some agglomerates at higher content of nanoparticles. Moreover, transmission electron microscope was applied to study the impact of nanofillers' localization on the systems' morphology. It was observed that NS particles localized at the PLA‐PBAT interface. In addition, thermogravimetric analysis (TGA) was used to investigate thermal stability and thermal degradation kinetics. Data indicates that hydrophobic NS improved thermal stability. The activation energy of degradation was calculated using several techniques of data modeling, including Friedman, Flynn‐Ozawa‐Wall, and Kissinger‐Akahira‐Sunose models. Among blend nanocomposites, 75/25 blend containing 5 phr HPB NS had the maximum degradation activation energy, suggesting that this sample had the most resistance to heat degradation. The intensity of the TGA/FTIR peaks of the evolved products was found to be correlated with the activation energy. The Criado's technique was also used to investigate the changes in the thermal degradation mechanism.

Atomic insights into the oxidative degradation mechanisms of sulfide solid electrolytes

Atomic insights into the oxidative degradation mechanisms of sulfide solid electrolytes

Modulating interface internal electric field for efficient charge separation in Co3O4/M-TiO2 p-n junction

The practical application of photocatalysis in water purification is restricted by the high electron-hole recombination efficiency. Herein, a Co3O4/M-TiO2 p-n composite catalyst with internal electric field (IEF) modulation was constructed. Because of the large number of oxygen vacancies (OVs) within Co3O4/M-TiO2, which could redistribute extra electrons to adjacent Co sites through the strong electron absorption effect of Co. Consequently, the charge distribution at the interface of Co3O4/M-TiO2 have been changed, forming positive and negative charge regions on M-TiO2 and Co3O4, respectively. Compared with Co3O4/P25, the amount of OVs in Co3O4/M-TiO2 is significantly increased, making the charge distribution at the interface more uneven and resulting in a significantly increased IEF intensity of Co3O4/M-TiO2 by 1.9 times. A series of photoelectric chemical experiments showed that driven by powerful IEF, the photogenerated electron-hole separation efficiency of Co3O4/M-TiO2 is significantly improved. In the photocatalysis-peroxymonosulfate (PMS) oxidation coupling system, Co3O4/M-TiO2 achieved high efficiency degradation of tetracycline hydrochloride (93.6 %) within 30 min, and a synergistic degradation mechanism of photocatalysis and PMS oxidation was proposed. This study provides a novel perspective on the construction of heterojunctions possessing strong internal electric fields.

High-temperature oxidation degradation mechanism of novel Zr-containing SiC fibers

The application of ceramics matrix composites (CMCs) in extreme environments is often dictated by the oxidation resistance of SiC fibers, which are frequently utilized as the reinforcement of CMCs. Introducing heterogeneous elements into SiC fibers is one effective way to enhance their oxidation resistance. In this work, the chemical composition, microstructural evolution, phase evolutions, and tensile strength of the newly developed Zr-containing Zeralon 200™ SiC fiber oxidation-treated at elevated temperatures in an air atmosphere for 5 h was investigated in depth, using transmission electron microscope (TEM), X-ray diffractometer (XRD), X-ray photoelectron spectroscopy (XPS), energy dispersive spectroscope (EDS), field emission scanning electron microscopy (FESEM), thermogravimetric analysis (TGA), and Raman spectroscopy (Raman). Results indicate that the Zeralon 200™ SiC fiber has a significantly better oxidation resistance than some typical non-heterogeneous element SiC fibers. ZrSiO4 was found to generate in the fiber after oxidation treatment at 1100 °C for 5 h. The specific generation mechanism of ZrSiO4 and its oxidation resistance mechanism in the Zeralon 200™ SiC fiber were revealed. Meanwhile, the degradation mechanism of the tensile strength of Zeralon 200™ SiC fiber was discussed in detail. In short, the decline in the tensile strength of Zeralon 200™ SiC fiber can be ascribed to the decomposition of the amorphous phase SiCxOy, the enlargement of defects within the fiber bulk, and the decrease in the effective load-bearing cross-sectional area of the fiber caused by extensive oxidation, sequentially occurring at various elevated temperatures.

The mechanism of room‐temperature oxidation of a HF‐etched Ti3C2TxMXene determined via environmental transmission electron microscopy and molecular dynamics

AbstractThe oxidation chemistry of two‐dimensional transition metal carbide MXenes has brought new research significance to their protection and application. However, the oxidation behavior and degradation mechanism of MXenes, in particular with time under oxygen conditions at room temperature, remain largely unexplored. Here, several experimental and theoretical techniques are used to determine a very early stage of the oxidation mechanism of HF‐etched Ti3C2Tx (a major member of MXenes and Tx = surface functional groups) in an oxygen environment at room temperature. Aberration‐corrected environmental transmission electron microscopy coupled with reactive molecular dynamics simulations show that the crystal plane‐dependent oxidation rate of Ti3C2Tx and oxide expansion are attributed to differences in the coordination and charge of superficial Ti atoms, and the existence of the channels between neighboring MXene layers on the different crystal planes. The complementary x‐ray photoelectron spectroscopy and Raman spectroscopy analyses indicate that the anatase and a tiny fraction of brookite TiO2 successively precipitate from the amorphous region of oxidized Ti3C2Tx, grow irregularly and transform to rutile TiO2. Our study reveals the early‐stage structural evolution of MXenes in the presence of oxygen and facilitates further tailoring of the MXene performance employing oxidation strategy.

Effective Treatment Methodology for Environmental Safeguard Catalytic Degradation of Fluconazole by Permanganate Ions in Different Acidic Environments: Kinetics, Mechanistics, RSM, and DFT Modeling.

In this paper, the degradation of fluconazole drug (Flz) was explored kinetically utilizing permanganate ion [MnO4-] as an oxidant in different acidic environments, namely sulfuric and perchloric acids at various temperatures. Stoichiometry of the reactions between Flz and [MnO4-] in both acidic environments was attained to be 1.2 ± 0.07 mol. The kinetics of the degradation reactions in both cases were the same, being unit order regarding [MnO4-], fewer than unit orders in [Flz], and fractional second orders in acid concentrations. The rate of oxidative degradation of fluconazole in H2SO4 was higher than that in HClO4 at the same investigational circumstances. The addition of small amounts of Mg2+ and Zn2+ enhanced the degradation rates. The activation quantities were evaluated and debated. The gained oxidation products were characterized using spot tests. A mechanistic approach for the fluconazole degradation was suggested. Finally, the rate law expressions were derived which were agreed with the acquired outcomes. The rates of degradation for various [Flz] were mathematically modeled using the response surface methodology (RSM). The RSM model's conclusions and the experimental findings are in agreement. The oxidative degradation mechanism of Flz using density functional theory (DFT) was performed. The fluconazole drug degrades in acidic settings, protecting both the environment and human health, according to a method that is easy to use, powerful, inexpensive, practical, affordable, and safe.

Selective oxidation of organic pollutants over a new Co-based MOF via peroxymonosulfate activation under UV light: Performance and mechanism

The oxidation processes dominated by nonradical singlet oxygen (1O2) could accomplish highly selective oxidation, which attracted increasing attentions in recent years. However, the 1O2 generation path still remains ambiguous. In this study, a new 3D Co-based metal–organic framework (MOF) namely BUC-100 was solvothermally synthesized from CoCl2·6H2O, 1,3,5-tris(1-imidazolyl) benzene (TIB) and terephthalic acid (H2BDC). The as-prepared BUC-100 was used to selectively degrade various organic contaminants including both electron-donating and electron-withdrawing contaminants. The results revealed that the organic contaminants with electron-donating functional groups like –OH, –NH2 and alkyl groups rather than electron-withdrawing functional groups like –NO2 were easier to be degraded without significant interference of co-existing anions. Furthermore, Rhodamine B (RhB) was adopted as a pollutant model to optimize the reaction conditions and explore the possible oxidative degradation mechanism. The RhB degradation efficiency was up to 100% within 40 min in the presence of 0.3 g/L BUC-100, 0.4 mM peroxymonosulfate (PMS) and LED UV light irradiation. According to the results of trapping experiments, electron spin resonance (ESR) characterization, and quantitative/qualitative experiments, it was found that 1O2 played the dominant role in organic pollutants decontamination, in which the self-reaction of SO5•− was the main source of 1O2.

Tribological behavior of ultra-high molecular weight polyethylene (UHMWPE) for acetabular replacement under frictional heat based on molecular dynamics

Abstract Hip prostheses generate higher frictional heat than natural joints at the joint head-socket interface during in vivo service, resulting in higher temperatures of the contact surfaces and surrounding synovial fluid, which affects the frictional properties of the prosthetic material. In order to clarify the influence mechanism of frictional heat on the tribological behavior of ultra-high molecular weight polyethylene (UHMWPE) for acetabular replacement, the tribological tests of three contact pairs were carried out under different synovial fluid temperatures in this research. Furthermore, the movement processes of the molecular chain structure of UHMWPE during friction were simulated by Materials Studio (MS), and the mechanism of oxidative degradation was discussed. The results show that the temperature of synovial fluid has a significant effect on the friction and wear resistance of UHMWPE and the lubrication characteristics of synovial fluid. At the same time, the action mechanism of the proteins in the synovial fluid that gradually precipitate with the temperature rise to participate in the friction process is related to the friction pair material and contact mode. The synergistic effect of temperature rise and friction will accelerate the oxidative degradation reaction of UHMWPE and form ketone and alcohol oxides on its surface, thus reducing its wear resistance.

Mechanistic elucidation of the degradation and transformation of hydroxy-α-sanshool and its conformers as the pungent dietary components in Sichuan pepper: A DFT study

To better understand the structural changes of sanshool pungent dietary components during the process and preservation of Sichuan pepper and pungent foods, the mechanistic insights into the intrinsic degradation and transformation of 16 hydroxy-α-sanshool conformers have been explored computationally. Our results have revealed that increasing the cis-CC bond numbers in the most stable all-trans hydroxy-β-sanshool structure causes the maximum 34.21 kJ/mol conformational energetic difference, and the existent probability of C2nnn would be lower than that of C1nnn (n = 1,2). The isomerization between the conformers could be much easier when they are excited by light radiation, as the strength of the CC bonds and their connected CC bonds becomes significantly close, and the relative energies among conformers are largely reduced. Besides, the different combination of cis/trans-CC bonds changes the delocalization degree of molecular Frontier orbitals, which consequently causes the different photochemical stability. Finally, the possible molecular oxidation degradation mechanism is proposed.

Oxidative pyrolysis of ion exchange resin in the presence of manganese dioxide: Product analysis, conversion and simplification mechanism

The development of nuclear energy has brought a great challenge of the efficient treatment of spent radioactive ion exchange resin, and oxidative pyrolysis is a potential method of solving this issue. This study aims to investigate the oxidative degradation and conversion mechanism of tar and off-gas, byproducts produced in the pyrolysis process, in the presence of a catalyst, manganese dioxide. The results show that it presents three processes including liquefaction, gasification and direct gasification in pyrolysis, in which manganese dioxide could reduce the dominant temperature of gasification by 200 ℃. Tar and off-gas undergo secondary pyrolysis, and the yield of tar decreased by approximately 50%. Simultaneously, manganese dioxide could promote the conversion of tar into off-gas, making both of them simplified, for which long-chain hydrocarbons are transformed into short-chain hydrocarbons, CO2, H2O, H2, etc. The catalytic oxidation effect of manganese dioxide is attributed to the adsorption and catalysis of oxygen vacancy, which significantly simplifies the composition of tar and off-gas.

New insights into the degradation mechanism and risk assessment of HFPO-DA by advanced oxidation processes based on activated persulfate in aqueous solutions

Hexafluoropropylene oxide dimer acid (HFPO-DA) is widely used as a substitute for perfluorooctanoic acid (PFOA). HFPO-DA exhibits high water solubility and low adsorption potential, conferring significant fluidity in aquatic environments. Given that the toxicity of HFPO-DA is similar to PFOA, it is necessary to control its content in aquatic environments. Electrochemical and thermally-activated persulfates have been successfully used to degrade HFPO-DA, but UV-activated persulfates cannot degrade the compound. Given that research on degradation mechanisms is still incomplete and lacks kinetic research, the mechanism and kinetic calculations of oxidative degradation were studied in detail using DFT calculations. And the toxicity of HFPO-DA degradation intermediates and products was evaluated to reveal the feasibility of using advanced oxidation process (AOP) technology based on persulfate to degrade HFPO-DA in wastewater. The results showed that the committed step of HFPO-DA degradation was initiated by the electron transfer reaction of SO4•- radicals. This reaction is not spontaneous at room temperature and requires sufficient electrical or thermal energy to be absorbed from the external environment. The perfluoroalcohol produced during this reaction can subsequently undergo four possible reactions: H atom abstraction from alcohol groups by an OH radical; H atom abstraction by SO4•-; direct HF removal; and HF removal with water as the catalyst. The final degradation products of HFPO-DA mainly include CO2, CF3CF2COOH, CF3COOH, FCOOH and HF, which has been identified through previous experimental analysis. Ecotoxicity assessment indicates that degradation does not produce highly toxic intermediates, and that the final products are non-toxic, supporting the feasibility of persulfate-based AOP technologies.

Enhanced degradation of tetracycline hydrochloride with in situ prepared ferrate supernatant based on calcium hypochlorite: Compare with purified and commercial ferrate

Ferrate (Fe(VI)) salts are commonly regarded as green and high efficient oxidants to eliminate organic contaminants. Current studies mainly focused on develop homogeneous activation technology or heterogeneous catalysts to promote Fe(VI) performances in contaminants degradation. Interestingly, this study disclosed that the degradation performance of tetracycline hydrochloride (TC) was enhanced by using in situ prepared ferrate supernatant (Fe(VI)s), and the oxidation performance and degradation mechanism were systematically explored by comparing with the ferrate precipitation (Fe(VI)p) and the commercial ferrate (Fe(VI)c). Results showed that the degradation rate of TC by Fe(VI)s reached to 98.5 % within 5 min, while the degradation rate of Fe(VI)p and Fe(VI)c were obtained less than 20 % in 30 min. Although degradation process of TC in these three system were all conformed to the pseudo-first-order reaction kinetic, the rate of degradation (Kobs) obtained in Fe(VI)s was 5.30 and 37.2 times higher than that in Fe(VI)c and Fe(VI)p, respectively. Electron paramagnetic resonance (EPR), radical quenching and PMSO probe experiments proved that Fe(IV)/Fe(V) were the main active species for TC degradation with Fe(VI)s, while ∙OH and ⋅O2− were the main active substance of Fe(VI)c. On the basis of the intermediates detected by LC-MS/MS analysis, a pathway for TC degradation was proposed. In addition, the toxicity of TC and its degradation products was evaluated by using the toxicity evaluation software tool. This study demonstrated efficient organic contaminant oxidation with in situ prepared ferrate solution (Fe(VI)s) and provided a comprehensive understanding of degradation process for pollutants removal.

Development of (Fe-Co-Ni)-Si-B metallic glass catalyst for promoting degradation of acid orange II azo-dye

Fe-based metallic glass (MG) catalyst, also called amorphous zero-valent iron (AZVI), is a functional material that has recently been in the spotlight due to its high reactivity compared to conventional catalysts for wastewater purification. In this study, novel Fe-based MG with excellent degradation rate and reusability was developed through systematic investigation by tailoring the contents of Co and Ni and structural design to form (Fe, Co, Ni)-rich clusters. We found that the process of dye degradation by a Fenton-like oxidative reaction with H2O2 can have low activation energy, assisted by a reductive reaction with nickel hydride formation. Consequently, the reductive and oxidative complex dye degradation mechanism can be effectively implemented to improve degradation rate and reusability, significantly superior to that of the commercial zero-valent iron(Fe0, ZVI) powder. Our findings revealed the compositional and structural key principles of Fe-based MG design, and are expected to provide new opportunities for industrial applications of advanced Fe-based MG.

Oxidation behavior and microstructural evolution of Cr coatings prepared by multi-arc ion plating on Zry-4 in steam environments up to 1400 °C

This study aimed to investigate the effectiveness of the multi-arc ion plating method in depositing Cr coatings on Zry-4 substrate and to study the oxidation behavior and microstructural evolution of the Cr coatings in steam environments up to 1400 ℃. The results showed that the Cr-coated sample exhibited excellent high-temperature resistance at 1100-1200 ℃, but accelerated oxidation occurred at 1300 ℃, leading to the formation of bubbles and voids in the Cr2O3 layer and the development of a new Cr-Zr-O layer between the residual Cr layer and the ZrCr2 layer. At 1400 ℃, the coating failed completely. These findings provide valuable insights into the oxidation behavior and degradation mechanism of Cr-coated zirconium alloys under accident conditions. The novelty of this study lies in the investigation of the microstructural evolution and failure mechanism of Cr coatings on Zry-4 using multi-arc ion plating method in high-temperature steam environments, which has not been extensively explored in previous research.

Complete oxidative degradation of diclofenac via coupling free radicals and oxygenases of a micro/nanostructured biogenic Mn oxide composite from engineered Pseudomonas sp. MB04R-2

Oxidative degradation can effectively degrade aromatic emerging contaminants (ECs). However, the degradability of lone inorganic/biogenic oxides or oxidases is typically limited when treating polycyclic ECs. Herein, we report a dual-dynamic oxidative system comprising engineered Pseudomonas and biogenic Mn oxides (BMO), which completely degrades diclofenac (DCF), a representative halogen-containing polycyclic EC. Correspondingly, recombinant Pseudomonas sp. MB04R-2 was constructed via gene deletion and chromosomal insertion of a heterologous multicopper oxidase cotA, allowing for enhanced Mn(II)-oxidizing activity and rapid formation of the BMO aggregate complex. Additionally, we characterized it as a micro/nanostructured ramsdellite (MnO2) composite using multiple-phase composition and fine structure analyses. Furthermore, using real-time quantitative polymerase chain reaction, gene knockout, and expression complementation of oxygenase genes, we demonstrated the central and associative roles of intracellular oxygenases and cytogenic/BMO-derived free radicals (FRs) in degrading DCF and determined the effects of FR excitation and quenching on the DCF degradation efficiency. Finally, after identifying the degraded intermediates of 2H-labeled DCF, we constructed the DCF metabolic pathway. In addition, we evaluated the degradation and detoxification effects of the BMO composite on DCF-containing urban lake water and on biotoxicity in zebrafish embryos. Based on our findings, we proposed a mechanism for oxidative degradation of DCF by associative oxygenases and FRs.

Insights into the Oxidative Degradation Mechanism of Solid Amine Sorbents for CO2 Capture from Air: Roles of Atmospheric Water

AbstractDirect air capture (DAC) processes for extraction of CO2 from ambient air are unique among chemical processes in that they operate outdoors with minimal feed pretreatments. Here, the impact of humidity on the oxidative degradation of a prototypical solid supported amine sorbent, poly(ethylenimine) (PEI) supported on Al2O3, is explored in detail. By combining CO2 adsorption measurements, oxidative degradation rates, elemental analyses, solid‐state NMR and in situ IR spectroscopic analysis in conjunction with 18O labeling of water, a comprehensive picture of sorbent oxidation is achieved under accelerated conditions. We demonstrated that the presence of water vapor can play an important role in accelerating the degradation reactions. From the study we inferred the identity and kinetics of formation of the major oxidative products, and the role(s) of humidity. Our data are consistent with a radical mediated autooxidative degradation mechanism.

Insights into the Oxidative Degradation Mechanism of Solid Amine Sorbents for CO2 Capture from Air: Roles of Atmospheric Water.

Direct air capture (DAC) processes for extraction of CO2 from ambient air are unique among chemical processes in that they operate outdoors conditions with minimal feed pretreatments. Here, the impact of humidity on the oxidative degradation of a prototypical solid supported amine sorbent, poly(ethylenimine) (PEI) supported on Al2O3, is explored in detail. By combining CO2 adsorption measurements, oxidative degradation rates, elemental analyses, solid-state NMR and in situ IR spectroscopic analysis in conjunction with 18O labeling of water, a comprehensive picture of sorbent oxidation is achieved under accelerated conditions. We demonstrated that the presence of water vapor can play an important role in accelerating the degradation reactions. From the study we inferred the identity and kinetics of formation of the major oxidative products, and the role(s) of humidity. Our data are consistent with a radical mediated autooxidative degradation mechanism.

Oxidative Degradation Mechanism and Antidegradation Strategy of Paper-Based Relics with Transition Metal Pigments: From the Cellobiose Model to Cellulose Paper

Oxidative Degradation Mechanism and Antidegradation Strategy of Paper-Based Relics with Transition Metal Pigments: From the Cellobiose Model to Cellulose Paper