Radical Reactions Research Articles

Degradation pathways and product formation mechanisms of asphaltene in supercritical water

Asphaltene is the compound with the most complex structure and the most difficult degradation in oily sludge, which is the key to limit the efficiency of supercritical water oxidation treatment of oily sludge. In this paper, the supercritical water oxidation process of asphaltene was investigated in terms of free radical reaction, degradation pathway, and product generation mechanism using ReaxFF molecular dynamics simulation method. The results showed that increasing temperature, increasing O2, and increasing H2O have different effects on HO2·generation. Benzene rings undergo fusion and condensation through hydrogenation abstraction and oxygen addition reactions, subsequently breaking down into long-chain alkanes. Increasing O2 can effectively promote the ring-opening of nitrogen-containing heterocycles. -COOH is the most important intermediate fragment for CO and CO2 generation, and there is a reaction competition with -CHO3 and -CO3. When the number of oxygen molecules increases from 300 to 700, the reaction frequency of -CHO3 and -CO3 to generate CO and CO2 increases by 17.14 % and 12.77 %·H2O determines the production of H2 by controlling the number of H·radicals present. As the amount of H2O increases from 500 to 1500, the product ratio of H2 increases from 12.73 % to 21.31 %. Environmental implicationAsphaltene is the most structurally complex organic matter in oily sludge, and its presence makes it difficult for oily sludge to be completely degraded by conventional treatment methods such as pyrolysis and incineration. Polycyclic aromatic hydrocarbons (PAHs) represented by asphaltene increase the carcinogenicity and mutagenicity of oily sludge, and even irreversibly pollute soil and groundwater. Supercritical water oxidation, as an efficient organic waste treatment technology, can realize harmlessness in a green and efficient way. So the study on the mechanism of supercritical water oxidation of asphaltene is of great significance for environmental protection.

(Invited) Functional Fluorous Nanocarbons

Fluorination was one of the first hypothesized chemical reactions for a buckyball that could yield C60F60 with "superlubricant" properties. [1] This promise, however, has not come to fruition due to propensity of fluorofullerenes for hydrolysis. Research of fluorination of fullerenes has contributed to the basic understanding of chemical reactivity of nanocarbons, especially, in radical reactions. Overall, there are more fluorinated fullerenes than any other halogenated or hydrogenated fullerenes. Small size of F atom, its high reactivity, relative strength of C-F bond compared to C-Hal or C-H bonds, and relative thermal and environmental stability are among the major reasons of the existence of large libraries of well-characterized fluorinated fullerenes.[2] The latter include not only products of direct addition of F atoms to C(C60) atoms, i.e., C60F2n, but also numerous derivatives with fluorine-containing moieties, i.e., C60(RF)n.[3]Exploration of applications of various classes of fluorinated fullerene materials in organic optoelectronics and biomedical research that was carried out by the CSU group and collaborators in the past decade will be critically overviewed by the author.Partial support from NSF (CHE-2153922) is acknowledged.1. H.W. Kroto, J.R. Heath, S.C. O’Brien, R.F. Curl and R.E. Smalley, Nature 318 (1985) 162.2. O.V. Boltalina and S.H. Strauss (2014) Fluorofullerenes. In Dekker Encyclopedia of Nanosci. and Nanotech., CRC Press, Seven Volume Set, 1436.3. O. V. Boltalina, A. A. Popov, I. V. Kuvychko, N. B. Shustova, S. H. Strauss, Chem. Rev. (2015) 115, 1051.

Radical-Mediated Creation of Fluorescent Defects in Carbon Nanotubes

The fluorescent defects in carbon nanotubes have been demonstrated to give exceeding optical properties such as room temperature single photon emissions at telecom wavelengths. A handful of methods for creating these defects have been invented in the past 13 years and provides practical guidelines for obtaining desired functional groups. However, most reactions are performed in the aqueous solution, and the transfer of the single-wall carbon nanotubes (SWCNTs) from aqueous to organic solvents are usually challenging. This gives barriers for applications that require SWCNTs to be dissolved in an organic solvent. Here, we introduce controlled creations of three different fluorescent defects in carbon nanotube hosts in organic solvents using a single radical initiator. We achieved selective creations of benzyl, phenyl, and benzoyloxy defects by controlling the reaction conditions such as dissolved oxygen concentration, reaction temperature, solvents, and addition of radical scavengers. It is worth noting that the both radical initiator and solvent can provide functional groups at the defect sites through radical reaction. We believe that this method will serve as a practical platform for designing new fluorescent defects in the organic phase.

Direct ketone synthesis from primary alcohols and alkenes enabled by a dual photo/cobalt catalysis

Catalytic methods to couple alcohol and alkene feedstocks are highly valuable in synthetic chemistry. The direct oxidative coupling of primary alcohols and alkenes offers a streamlined approach to ketone synthesis. Currently, available methods are based on transition metal-catalyzed alkene hydroacylation, which involves the generation of an electrophilic aldehyde intermediate from primary alcohol dehydrogenation. These methods generally require high reaction temperatures and a high loading of precious metal catalysts and are predominantly effective for branch-selective reactions with electron-rich alkenes. Herein, we designed a dual photo/cobalt-catalytic method to manipulate the reactivity of nucleophilic ketyl radicals for the synthesis of ketones from primary alcohols and alkenes in complementary reactivity and selectivity. This protocol exhibits exceptional scope across both primary alcohols and alkenes with high chemo- and regio-selectivity under mild reaction conditions. Mechanism investigations reveal the essential role of cobalt catalysis in enabling efficient catalysis and broad substrate scope.

Modulation of the Intrinsic Radical Scavenging Properties of CeO2 Nanoparticles

Cerium dioxide (CeO2) has been extensively investigated as a scavenger of reactive oxygen radicals, particularly in the context of polymer electrolyte membrane fuel cells. This study focuses on elucidating the impact of exposed crystal facets of CeO2 nanoparticles on their radical scavenging activities. The manipulation of crystal shapes, including rod, cube, and octahedral forms, allows for controlled variation of the exposed crystal facets of CeO2 NPs. Characterization of the resulting CeO2 NPs is conducted using XRD, Raman spectroscopy, XPS, BET, and Fenton’s reaction. The research reveals that the intrinsic radical scavenging activity of CeO2 NPs can be effectively modulated by controlling their exposed crystal facets.

Functionalized Polysaccharides Improve Sensitivity of Tyramide/Peroxidase Proximity Labeling Assays through Electrostatic Interactions.

High-throughput assays that efficiently link genotype and phenotype with high fidelity are key to successful enzyme engineering campaigns. Among these assays, the tyramide/peroxidase proximity labeling method converts the product of an enzymatic reaction of a surface expressed enzyme to a highly reactive fluorescent radical, which labels the cell surface. In this context, maintaining the proximity of the readout reagents to the cell surface is crucial to prevent crosstalk and ensure that short-lived radical species react before diffusing away. Here, we investigated improvements in tyramide/peroxidase proximity labeling for enzyme screening. We modified chitosan (Cs) chains with horseradish peroxidase (HRP) and evaluated the effects of these conjugates on the efficiency of proximity labeling reactions on yeast cells displaying d-amino acid oxidase. By tethering HRP to chitosan through different chemical approaches, we localized the auxiliary enzyme close to the cell surface and enhanced the sensitivity of tyramide-peroxidase labeling reactions. We found that immobilizing HRP onto chitosan through a 5 kDa PEG linker improved labeling sensitivity by over 3.5-fold for substrates processed with a low turnover rate (e.g., d-lysine), while the sensitivity of the labeling for high activity substrates (e.g., d-alanine) was enhanced by over 0.6-fold. Such improvements in labeling efficiency broaden the range of enzymes and conditions that can be studied and screened by tyramide/peroxidase proximity labeling.

(Invited) Numerical Simulation of an Atmospheric Pressure Streamer Discharge and Induced Chemical Reactions

Streamer discharges are a type of non-thermal plasma produced by high-voltage electrical discharges, and have great potential as highly reactive chemical reaction fields. This is mainly due to the generation of high energy electrons that produce chemically active species. The applications of non-thermal plasma have attracted considerable interest in a wide range of industries. However, each radical has a different role in the plasma application and their reaction mechanism is also different. It's therefore important to understand exactly when, where and how much of these reactive species are produced in order to improve the treatment efficiency of atmospheric pressure plasma applications. Against this background, the aim of this study is to develop a simulation model capable of accurately predicting the chemical reactions of radicals. With a sufficiently validated simulation model, it would be possible to use such a model to design chemical reaction fields.The model consists of the first-order electrohydrodynamic model for electrons and positive and negative ions within the drift-diffusion approximation. Axis-symmetric coordinates were used to simulate the streamer discharge in air at atmospheric pressure. The electron transport and source parameters were calculated using two-term bltzmann equation and published electron impact cross-sections. The chemical reaction model used in this study includes electron impact collisions (excitation, ionisation, dissociation, recombination, attachment and detachment), ion recombination and the reactions of neutrals. In order to demonstrate the validity of the simulation, the light emission of the discharge is first compared between experiment and simulation. Then the spatial and temporal variations of each radical are simulated and compared with the simulation. In this talk, I will present the process of validation and verification (V&V) of the streamer discharge simulation and then the mechanism of radical production revealed by the simulation.

(Invited) Introducing Selectivity into Electrochemical Reactions: From Solution to Surfaces

Induction of asymmetry into electrosynthetic reactions has taken off in recent years for the electrochemical community. As of late most transformations have focused on either simple electrochemical oxidations or reductions, such as the reduction of various ketones to chiral alcohol feedstock molecules, or transition metal cross coupling reactions. At the same time, there has been little effort to introduce asymmetry into cyclization reactions that capitalize on highly reactive radical ion intermediates to accomplish umpolung-type transformations or to fully take advantage of electrode surfaces for manipulating the selectivity of synthetically more complex transformations like transition metal cross coupling reactions. In the case more complex electrochemical transformations, many of the reactions studied have led to either high ee and low yield or low ee and high yield. With this in mind, we are looking new approaches for introducing selectivity into electrochemical transformations by taking advantage of high yielding cathodic cyclization reactions and the Heck reaction. The influence of chiral electrolytes, chiral catalysts and mediators, and modified electrode surfaces on these transformations is being explored with a particular emphasis on both the induction of asymmetry into the reactions and the use of remote functionality in the molecules as a control element. This presentation to be given will detail our progress in these areas.

Chemical-Free Stable and Multifunctional Electro-Based System for Treatment of Pesticides from Aqueous Solution

The usage of pesticides has become a common practice in modern agricultural systems to meet the growing demand for food production. However, the uncontrolled use of such chemicals results in the deterioration of natural ecosystems and living beings. Thus, herein, a hybrid treatment system performing the combined functions of electro- and photo Fenton was designed to treat aqueous pesticide solution. The anode was comprised of metal oxide-based electrode (MOx), whereas the cathode was comprised of N-doped carbon electrode (N-C). Both the electrodes consist of light-responsive photocatalysts, which facilitates the removal of pollutants by generating reactive radical species such as OH• and O2 •-. The application of external anodic bias helps to improve the photocatalytic activity by preventing the recombination of electron-hole pairs. In addition, N-C on the cathode helps to catalyze the reduction of O2 to H2O2, which further reacts with Fe2+ in the system to initiate the Fenton reaction. The hybrid reactor was further optimized to study the underlying mechanisms by varying the experimental conditions such as pH, current density, electrolyte concentration, and external H2O2 concentration.Moreover, scavenging tests were performed using methanol and tertbutyl alcohol to identify the predominant radical species responsible for removing pollutants from the aqueous solution. Also, the reusability test showed that the prepared electrodes were stable for more than three successive cycles, thus offering sustainability. In general, the present study demonstrates the potential of hybrid treatment units for environmental applications and acts as a stepping stone for future endeavors in material synthesis and sustainable treatment solutions.

Et3Al/Light-Promoted Radical-Polar Crossover Reactions of α-Alkoxyacyl Tellurides.

Here, we report new radical-polar crossover reactions of α-alkoxy carbon radicals for constructing highly oxygenated molecules with contiguous stereocenters. The method employs a 370 nm UV light-emitting diode (LED) for the photoexcitation of α-alkoxyacyl telluride, and Et3Al as the radical initiator and terminator. First, Et3Al and UV LED promoted radical coupling between the α-alkoxyacyl telluride and cyclopentenone via C-Te bond homolysis, CO expulsion, and C-C bond formation. Second, Et3Al converted the radical species to the corresponding aluminum enolate. Third, the second C-C bond formation occurred via a polar mechanism: intermolecularly with aldehydes/ketones and intramolecularly with epoxide, producing aldol and SN2 adducts, respectively. The present coupling reactions increase the molecular complexity in a single step by stereoselective formation of the two hindered C-C bonds. The devised method is expected to be useful for the expeditious assembly of densely oxygenated natural products.

Vibrational relaxation of HOD by collisions with Ar atoms.

Vibrational relaxation of HOD(v12, v3) molecules by collisions with Ar was studied at 298K (v12 denotes coupled bending, v2, and OD stretching, v1, vibrational modes and v3 denotes OH stretching mode). The vibrationally excited HOD molecules were generated by exothermic abstraction reactions of OD radicals with 13 different RH reactants and observed by infrared emission from a fast-flow reactor as a function of Ar pressure and reaction time. State-specific relaxation rate constants were obtained by comparison of the time evolution of the experimental vibrational distributions with numerical kinetic calculations for vibrational populations. The relaxation mechanism was based on the relaxation scheme of H2O studied earlier with the addition of specific channels for HOD(v12, v3). Unlike H2O, energy in stretching and bending vibrations of HOD cannot be separated due to close ν1 and 2ν2 energies, which leads to fast collisional equilibration between these Fermi-resonant levels. For relaxation of the only pure bending state (10), a rate constant of (1.5 ± 0.3) × 10-13cm3molecule-1s-1 was obtained. The relaxation rate of higher v12 states linearly increases with quantum number and very likely includes transfer of population from OD stretch levels, v1, to a lower energy bend level. The average rate constants for the loss of population from (01), (02), and (03) stretching states are (1.1 ± 0.3) × 10-14, (3.2 ± 1.0) × 10-14, and (5.6 ± 1.2) × 10-14cm3molecule-1s-1, respectively.

Enter MnIV-NHC: A Dark Photooxidant with a Long-Lived Charge-Transfer Excited State.

Detailed photophysical investigation of a Mn(IV)-carbene complex has revealed that excitation into its lowest-energy absorption band (∼500 nm) results in the formation of an energetic ligand-to-metal charge-transfer (LMCT) state with a lifetime of 15 ns. To the best of our knowledge, this is the longest lifetime reported for charge-transfer states of first-row-based transition metal complexes in solution, barring those based on Cu, with a d10 configuration. A so-called superoxidant, Mn(IV)-carbene exhibits an excited state potential typically only harnessed via excited states of reactive organic radical species. Furthermore, the long-lived excited state in this case is found to be a dark doublet, with its transition to the quartet ground state being spin-forbidden, a contrast to most first-row literature examples, and a possible cause of the long lifetime. Showcasing excited state properties which in some cases exceed those of complexes based on precious metals, these findings not only advance the library of earth-abundant photosensitizers but also shed general insight into the photophysics of d3 and related Mn complexes.

Harnessing in vivo synthesis of bioactive multiarylmethanes in Escherichia coli via oxygen-mediated free radical reaction induced by simple phenols

BackgroundXanthenes and multi-aryl carbon core containing compounds represent different types of complex and condensed architectures that have impressive wide range of pharmacological, industrial and synthetic applications. Moreover, indoles as building blocks were only found in naturally occurring metabolites with di-aryl carbon cores and in chemically synthesized tri-aryl carbon core containing compounds. Up to date, rare xanthenes with indole bearing multicaryl carbon core have been reported in natural or synthetic products. The underlying mechanism of fluorescein-like arthrocolins with tetra-arylmethyl core were synthesized in an engineered Escherichia coli fed with toluquinol remained unclear.ResultsIn this study, the Keio collection of single gene knockout strains of 3901 mutants of E. coli BW25113, together with 14 distinct E. coli strains, was applied to explore the origins of endogenous building blocks and the biogenesis for arthrocolin assemblage. Deficiency in bacterial respiratory and aromatic compound degradation genes ubiX, cydB, sucA and ssuE inhibited the mutant growth fed with toluquinol. Metabolomics of the cultures of 3897 mutants revealed that only disruption of tnaA involving in transforming tryptophan to indole, resulted in absence of arthrocolins. Further media optimization, thermal cell killing and cell free analysis indicated that a non-enzyme reaction was involved in the arthrocolin biosynthesis in E. coli. Evaluation of redox potentials and free radicals suggested that an oxygen-mediated free radical reaction was responsible for arthrocolins formation in E. coli. Regulation of oxygen combined with distinct phenol derivatives as inducer, 31 arylmethyl core containing metabolites including 13 new and 8 biological active, were isolated and characterized. Among them, novel arthrocolins with p-hydroxylbenzene ring from tyrosine were achieved through large scale of aerobic fermentation and elucidated x-ray diffraction analysis. Moreover, most of the known compounds in this study were for the first time synthesized in a microbe instead of chemical synthesis. Through feeding the rat with toluquinol after colonizing the intestines of rat with E. coli, arthrocolins also appeared in the rat blood.ConclusionOur findings provide a mechanistic insight into in vivo synthesis of complex and condensed arthrocolins induced by simple phenols and exploits a quinol based method to generate endogenous aromatic building blocks, as well as a methylidene unit, for the bacteria-facilitated synthesis of multiarylmethanes.

Nature-Inspired Radical Pyridoxal-Mediated C-C Bond Formation.

Pyridoxal-5'-phosphate (PLP) and derivatives of this cofactor enable a plethora of reactions in both enzyme-mediated and free-in-solution transformations. With few exceptions in each category, such chemistry has predominantly involved two-electron processes. This sometimes poses a significant challenge for using PLP to build tetrasubstituted carbon centers, especially when the reaction is reversible. The ability to access radical pathways is paramount to broadening the scope of reactions catalyzed by this coenzyme. In this study, we demonstrate the ability to access a radical PLP-based intermediate and engage this radical intermediate in a number of C-C bond-forming reactions. By selection of an appropriate oxidant, single-electron oxidation of the quinonoid intermediate can be achieved, which can subsequently be applied to C-C bond-forming reactions. Through this radical reaction pathway, we synthesized a series of α-tertiary amino acids and esters to investigate the substrate scope and identify nonproductive reaction pathways. Beyond the amino acid model system, we demonstrate that other classes of amine substrates can be applied in this reaction and that a range of small molecule reagents can serve as coupling partners to the semiquinone radical. We anticipate that this versatile semiquinone radical species will be central to the development of a range of novel reactions.

Carbonaceous structures as electronic bridges to enhance charge migration and radical reactions in composite photocatalysts: An effective way to achieve efficient mineralization of pollutants

The intrinsic correlation between photo-induced extraction of hole and free radical reactions can facilitate the mineralization of contaminants via promoting the transfer of electrons from the semiconductor to the solution. TiO2/C/g-C3N4 composite photocatalysts are prepared using thermal polycondensation and sol-gel methods in this paper. The introduction of carbon at the interface between the two phases creates charge migration channels that facilitate electron transfer at the interface of semiconductor catalyst as well as collisions of dissolved oxygen to the catalytic sites, which are able to promote catalytic oxidation reactions. Considering Rh-B as target, the removal rate is 97.2±0.2 % within 90 min. The involvement of hydroxyl radicals and superoxide radicals is confirmed by carrying out radical quenching experiments and ESR characterization, suggesting that effective electron transfer synergistically promotes the production of hydroxyl radicals. Therefore, it emphasizes the importance of the indeterminate carbon bridged 2D/3D interface for constructing charge migration channels as well as promoting the efficiency of carrier separation in the process of photocatalytic efficient degradation of dyes.

A feasible strategy of Ag nanoparticles-sodium alginate-polyacrylamide-polyvinyl alcohol hydrogel coatings for preventing catheter-associated urinary tract infections

Catheter-associated urinary tract infections (CAUTIs) pose a significant clinical challenge, potentially resulting in complications such as bacteriuria and mortality. Developing coatings with antibacterial and antiadhesive properties for urinary catheters is essential to address these issues. In this study, a novel hydrogel coating composed of silver nanoparticles (Ag NPs), sodium alginate (SA), polyacrylamide (PAAm), and polyvinyl alcohol (PVA) was prepared on polydopamine (PDA)-modified latex urinary catheters using a simple dipping method. The Ag NPs were synthesized via an in-situ reduction of AgNO3 with SA, eliminating the need for additional chemical reductants. The Ag NPs-SA-PAAm-PVA hydrogel-coated urinary catheter demonstrated superior antibacterial and antiadhesive characteristics compared to the bare urinary catheter. The antiadhesive properties of the hydrogel-coated urinary catheter were attributed to its hydrophilicity and lubricity, while the antibacterial effects were linked to the penetration of Ag NPs and Ag+ ions into bacterial structures, disrupting bacterial metabolism through the generation of reactive oxygen species (ROS) and free radicals upon attachment of Ag+ ions to cell walls and membranes. Furthermore, the hydrogel coatings exhibited remarkable mechanical properties, along with good biocompatibility and hemocompatibility. The exceptional antibacterial and antiadhesive properties of the hydrogel-coated urinary catheter hold promise for reducing CAUTIs.

Unveiling the environmental significance of acetylperoxyl radical: Reactivity quantification and kinetic modeling.

Acetylperoxyl radical (CH3C(O)OO•) is among highly reactive organic radicals which are known to play crucial roles in atmospheric chemistry, aqueous chemistry and, most recently, peracetic acid (PAA)-based advanced oxidation processes. However, fundamental knowledge for its reactivity is scarce and severely hampers the understanding of relevant environmental processes. Herein, three independent experimental approaches were exploited for revelation and quantification of the reaction rates of acetylperoxyl radical. First, we developed and verified laser flash photolysis of biacetyl, ultraviolet (UV) photolysis of biacetyl, and pulse radiolysis of acetaldehyde, each as a clean source of CH3C(O)OO•. Then, using competition kinetics and selection of suitable probe and competitor compounds, the rate constants between CH3C(O)OO• and compounds of diverse structures were determined. The three experimental approaches complemented in reaction time scale and ease of operation, and provided cross-validation of the rate constants. Moreover, the formation of CH3C(O)OO• was verified by spin-trapped electron paramagnetic resonance, and potential influence of other reactive species in the systems was assessed. Overall, CH3C(O)OO• displays distinctively high reactivity and selectivity, reacting especially favorably with naphthyl and diene compounds (k ∼ 107-108 M-1 s-1) but sluggishly with N- and S-containing groups. Significantly, we demonstrated that incorporating acetylperoxyl radical-oxidation reactions significantly improved the accuracy in modeling the degradation of environmental micropollutants by UV/PAA treatment. This study is among the most comprehensive investigation for peroxyl radical reactivity to date, and establishes a robust methodology for investigating organic radical chemistry. The determined rate constants strengthen kinetic databases and improve modeling accuracy for natural and engineered systems.

Efficient Light-Based Bioprinting via Rutin Nanoparticle Photoinhibitor for Advanced Biomedical Applications.

Digital light processing (DLP) bioprinting, known for its high resolution and speed, enables the precise spatial arrangement of biomaterials and has become integral to advancing tissue engineering and regenerative medicine. Nevertheless, inherent light scattering presents significant challenges to the fidelity of the manufactured structures. Herein, we introduce a photoinhibition strategy based on Rutin nanoparticles (Rnps), attenuating the scattering effect through concurrent photoabsorption and free radical reaction. Compared to the widely utilized biocompatible photoabsorber tartrazine (Tar), Rnps-infused bioink enhanced printing speed (1.9×), interlayer homogeneity (58% less overexposure), resolution (38.3% improvement), and print tolerance (3× high-precision range) to minimize trial-and-error. The biocompatible and antioxidative Rnps significantly improved cytocompatibility and exhibited resistance to oxidative stress-induced damage in printed constructs, as demonstrated with human induced pluripotent stem cell-derived endothelial cells (hiPSC-ECs). The related properties of Rnps facilitate the facile fabrication of multimaterial, heterogeneous, and cell-laden biomimetic constructs with intricate structures. The developed photoinhibitor, with its profound adaptability, promises wide biomedical applications tailored to specific biological requirements.

Spectroscopic analysis of pulsed-mode plasma with argon addition for diamond growth

The advancement of high-speed growth technology for large-scale single-crystal diamonds is desired. In the widely used microwave plasma chemical vapor deposition method, the gas temperature in the plasma atmosphere significantly contributes to the generation of reactive radicals and enhancement of crystal growth. However, the impact of electron-dominated reactions in the plasma on the crystal growth remains unclear. In this study, we actively controlled the plasma environment by adding argon gas and adopting microwave pulse modulation to generate the plasma. We estimated the gas temperature and electron density of the plasma using optical emission spectroscopy. Our results implied that an increase in gas temperature alone hardly explained the enhancement of the growth rate by the argon addition or pulse modulation. In addition to the increase in the electron density due to the argon addition and pulse modulation, gas-phase chemical reaction calculations showed that the radical production enhancement became remarkable under an electron density higher than a threshold (1017 m−3). Therefore, the enhancement of the growth rate mentioned above may be attributed to electron-dominated reactions in the discharge region. These findings suggest that increasing the electron density can further improve the growth rate and potentially enable diamond synthesis at lower temperatures than traditional methods.

Catalytic Degradation of Bisphenol A with a Magnetically Recoverable Geopolymer Composite Using Coal Gangue.

The widespread presence and use of Bisphenol A (BPA) in aquatic environments has caused significant ecological damage. Coal gangue (CG), a byproduct of coal mining, poses a major environmental concern due to its vast land occupation and potential for pollution. A magnetic recyclable geopolymer (MnFe2O4-CGP) using coal gangue geopolymer (CGP) as the carrier was successfully synthesized and was evaluated for its ability to Fenton-like degrade BPA. The characterization techniques revealed the successful incorporation of spherical MnFe2O4 onto the CGP surface and that CGP serves as an excellent platform for the immobilization and dispersion of MnFe2O4. The degradation rate reached 100% within 60 min at pH = 5, 15 mmol/L H2O2, 0.6 g/L catalyst, and 50 mg/L BPA, significantly higher than MnFe2O4 and CGP alone. It was indicated that the degradation rate of BPA in MnFe2O4-CGP composites was 0.1121 min-1, which was consistent with the first-order kinetic model. The saturation magnetization of MnFe2O4-CGP was measured to be 10.96 emu/g, enabling convenient recovery. MnFe2O4-CGP exhibited excellent stability, as the degradation rate of BPA remained above 95% even after five reaction cycles. This efficiency may be due to the MnFe2O4-CGP induced generation of reactive radicals. Quenching and EPR radical trapping experiments unequivocally confirmed that the reactive radical was hydroxyl radical (•OH). These results indicate that MnFe2O4-CGP has potential application prospects as a magnetic recyclable geopolymer composite in Fenton-like catalysis.