Chemical Oxidation Research Articles

Isostructural Series of a Cyclometalated Iron Complex in Three Oxidation States.

An isostructural series of FeII, FeIII, and FeIV complexes [Fe(ImP)2]0/+/2+ utilizing the ImP 1,1'-(1,3-phenylene)bis(3-methyl-1-imidazol-2-ylidene) ligand, combining N-heterocyclic carbenes and cyclometalating functions, is presented. The strong donor motif stabilizes the high-valent FeIV oxidation state yet keeps the FeII oxidation state accessible from the parent FeIII compound. Chemical oxidation of [Fe(ImP)2]+ yields stable [FeIV(ImP)2]2+. In contrast, [FeII(ImP)2]0, obtained by reduction, is highly sensitive toward oxygen. Exhaustive ground state characterization by single-crystal X-ray diffraction, 1H NMR, Mössbauer spectroscopy, temperature-dependent magnetic measurements, a combination of X-ray absorption near edge structure and valence-to-core, as well as core-to-core X-ray emission spectroscopy, complemented by detailed density functional theory (DFT) analysis, reveals that the three complexes [Fe(ImP)2]0/+/2+ can be unequivocally attributed to low-spin d6, d5, and d4 complexes. The excited state landscape of the FeII and FeIV complexes is characterized by short-lived 3MLCT and 3LMCT states, with lifetimes of 5.1 and 1.4 ps, respectively. In the FeII-compound, an energetically low-lying MC state leads to fast deactivation of the MLCT state. The distorted square-pyramidal state, where one carbene is dissociated, can not only relax into the ground state, but also into a singlet dissociated state. Its formation was investigated with time-dependent optical spectroscopy, while insights into its structure were gained by NMR spectroscopy.

Chemoenzymatic Oxidation of Labdane and Formal Synthesis of Nimbolide.

In nature, basic terpene skeletons are produced and subsequently undergo enzymatic or nonenzymatic oxidative transformations, leading to diverse structural variations. To date, thousands of natural products featuring a variety of oxidation patterns have been isolated solely from the labdane family. This work describes a strategy for the comprehensive introduction of oxidation states into the labdane core by employing a combination of enzyme library screening, directed evolution, and sequential chemical oxidation processes. Furthermore, we showcase the functional viability of our chemoenzymatic approach by accomplishing a formal synthesis of nimbolide, highlighting its potential for streamlining the synthesis of complex natural products.

Mapping the heterogeneous removal landscape of wastewater virome in effluents of different advanced wastewater treatment systems of swine farm

In advanced wastewater treatment plants on pig farms, meticulous design aims to eliminate intrinsic pollutants such as organic matter, heavy metals, and biological contaminants. In our field survey across Southern China, a notable disparity in wastewater treatment procedures among various farming facilities lies in the utilization of terminal chemical oxidation post-sedimentation tank. However, recent focus in wastewater surveillance has predominantly centered on antibiotic resistance genes, leaving the efficacy of virus removal in different effluent systems largely unexplored. To profile virus composition at the effluent, assess the virus elimination efficiency of chemical oxidation at the effluent end, and the potential environmental driver of virus abundance, we deployed a meta-transcriptomics approach to first determine the total virome in effluent specimens of terminal clean water tank system (CWT) and terminal chemical oxidation system (TCO) in Southern China pig farms, respectively. From these data, 172 viruses were identified, with a median reads per million (RPM) of 27,789 in CWT and 19,982 in TCO. Through the integration of analyses encompassing the co-occurrence patterns within viral communities, the ecology of viral diversity, and a comparative assessment of average variation degrees, we have empirically demonstrated that the procedure of TCO may perturb viral communities and diminish their abundance, particularly impacting RNA viral communities. However, despite the diminished abundance, pathogenic viruses such as PEDV and PRRSV persisted in the effluent following chemical deoxidation at a moderate RPM value, indicating a substantial in situ presence at effluent. Our environmental driver modeling, employing GLM and mantel tests, substantiated the intricate nature of virus community variation within the effluent, influenced heterogeneously by diverse factors. Notably, pond temperature emerged as the foremost determinant, while fishing farming exhibited a positive correlation with virus diversity (p < 0.05). This revelation of the cryptic persistence of virus communities in wastewater effluent expands our understanding of the varied responses of different virus categories to oxidation. Such insights transcend mere virus characterization, offering valuable implications for enhancing biosafety measures in farming practices and informing wastewater-based epidemiological surveillance.

MOF-derived metal oxides with hollow porous nanocube structure realize ultra-wideband, lightweight, and anticorrosion microwave absorber

High density, skin effect, and environmental instability are significant limitations that restrict the application of metal-based microwave absorbers in achieving lightweight, high performance, and long service life. This study broke from traditional methods for preparing a microwave absorber Mn2O3-Fe3O4@PPy (polypyrrole) by employing an innovative annealing process to convert metal into metal oxide by the introduction of metal organic framework (MOF), which effectively achieving a more lightweight absorber material with hollow porous nanocube structure. Subsequently, PPy was coated onto the metal oxide surface to form a core-shell structure by a situ chemical oxidation synthesis method. The combination of metal oxide of the hollow porous nanocube structure and the core-shell structure formed by highly conductive PPy shell significantly enhanced heterogeneous interfaces and electromagnetic (EM) wave reflection. Excellent dielectric loss and impedance matching contributed evidently to the ultra-wideband EM wave absorption performance. It was demonstrated that, with a filling amount of only 20 wt%, the prepared Mn2O3-Fe3O4@PPy achieved an effective bandwidth (EAB) of 10.0 GHz at a thickness of 3.08 mm, with EABmax reaching 13 GHz. At a filling amount of only 10 wt%, the reflection loss (RL) was −62.13 dB, achieving an EAB of 7.4 GHz at 2.98 mm thickness, with EABmax reaching 11.4 GHz. Furthermore, the proposed strategy incorporating metal oxide and PPy enhanced corrosion resistance with higher charge transfer resistance.

Entrapment of Cyanase from Thermomyces lanuginosus Using Biomimetic Silica and Its Application for Cyanate Bioremediation.

Cyanate, a toxic product from the chemical oxidation treatment of highly toxic cyanide, can be converted to harmless ammonia and carbon dioxide by cyanase (EC 4.2.1.104). Cyanase from Thermomyces lanuginosus was entrapped in biomimetic silica to improve stability and reusability. After entrapment, the enzyme's activity increased by two-fold, and the residual activity after 30-min of incubation at 60 °C also increased by two-fold, compared to the free enzyme. After being stored at room temperature for 28 days, the entrapped cyanase retained 79% of the initial activity, while the free form retained 61%. The immobilized cyanase was successfully applied to cyanate detoxification; the co-entrapment of carbonic anhydrase from Sulfurihydrogenibium azorense decreased the amount of bicarbonate necessary for cyanate detoxification by 50%. The cyanate degradation retained 53% of the initial value after the co-entrapped cyanate and carbonic anhydrase were reused five times.

Photochemical Decarboxylative Radical Alkylation/Cyclization Reaction to Fused Nitrogen Heterocycles by LiI/PPh3 Catalysis

Comprehensive SummaryA visible‐light‐induced decarboxylative radical cascade cyclization reaction between N‐(2‐cyanoaryl)‐acrylamides and alkyl N‐(acyloxy)phthalimide (NHPI esters) for the construction of phenanthridine derivatives has been developed. This approach utilizes lithium iodide (LiI) and triphenylphosphine (PPh3) as the redox catalysts and the alkyl radical is produced through the photoactivation of the electron donor‐acceptor (EDA) complex. A series of primary, secondary, and tertiary alkyl‐substituted phenanthridines are prepared in up to 82% yield without transition‐metal catalysts, chemical oxidants, or metal‐/organic dye‐based photocatalysts.

Efficient H2O2 Synthesis through a Two-Electron Oxygen Reduction Reaction by Electrocatalysts.

The two-electron oxygen reduction reaction (2e-ORR) for the sustainable synthesis of hydrogen peroxide (H2O2) has demonstrated considerable potential for local production of this environmentally friendly chemical oxidant on small, medium, and large scales. This method offers a promising alternative to the energy-intensive anthraquinone approach, placing a primary emphasis on the development of efficient electrocatalysts. Improving the efficiency of electrocatalysts and uncovering their catalytic mechanisms are essential steps in achieving high 2e-ORR activity, selectivity, and stability. This comprehensive review summarizes recent advancements in electrocatalysts for in-situ H2O2 production, providing a detailed overview of the field. In particular, the review delves into the design, fabrication, and investigation of catalytic active sites contributing to H2O2 selectivity. Additionally, it highlights a range of electrocatalysts including pure metals and alloys, transition metal compounds, single-atom catalysts, and carbon-based catalysts for the 2e-ORR pathway. Finally, the review addresses significant challenges and opportunities for efficient H2O2 electrosynthesis, as well as potential future research directions.

An efficient chemiluminescent probe based on Ni-doped CsPbBr3 perovskite nanocrystals embedded in mesoporous SiO2 for sensitive assay of L–cysteine

This study presents an efficient chemiluminescence (CL) probe based on perovskite nanocrystals (NCs) for detection of L–cysteine (L–Cys). It consists of nickel–doped CsPbBr3 NCs embedded in the mesoporous SiO2 matrix as CL reagent and cerium (IV) as an oxidant in aqueous environment. The probe was designed for the highly selective determination of L–Cys based on its remarkable enhancing effect on the CL intensity. The colloidal nanocomposite of nickel–doped CsPbBr3 NCs@SiO2 with photoluminescence quantum yield of 58% was fabricated by ligand–assisted re–precipitation method and characterized by using UV–Vis absorption, FT–IR, X–ray diffraction, and transmission electron microscopy. The sensor was utilized to determine L–Cys in the linear concentration range of 20–300 nM with a detection limit of 12.8 nM. Direct chemical oxidation of Ni–doped CsPbBr3 NCs@SiO2 by Ce(IV) was the single cause of the formation of the excited-state NCs and subsequent production of CL. The developed probe provides outstanding selectivity towards L–Cys over structurally related compounds. Accurate determination of L–Cys in human serum samples was achieved without interference, and the results were confirmed by HPLC method.

Investigation of the effect of electrodeposited Cu from graphite wrapped in polypyrrole film formed by chemical oxidation

The metallization of graphite substrates is currently confronted by negative issues including insufficient adhesion and inherent instability. In an effort to surmount these challenges, a layer of conductive polypyrrole (PPy) film on a graphite surface is formed through simple polymerization, followed by an electroplating copper layer. The graphite enveloped by the PPy film, subjected to cyclic voltammetry (CV) and linear sweep voltammetry (LSV) analyses, demonstrates enhanced electrochemical activity and thus renders the more efficient electrodeposition of copper. Further investigation was conducted through orthogonal experiments to explore the optimal formulation of electroplating solutions containing popular additives including 3, 3′-dithiobis-1-propanesulfonic acid disodium salt (SPS), Janus Green B (JGB), and polyethylene glycol 8000 (PEG8000)., According to the optimal additive formulation, a dense copper layer with superior adhesion was electroplated on the graphite substrate employing PPy as an intermediate layer.

Oxidation of NOBINs Toward α-Spiropyrrolidones.

While the oxidation of phenols and BINOLs is well documented to lead to a broad range of useful organic scaffolds, that of NOBINs is far less explored. We investigate herein their oxidation with a number of standard chemical oxidants, leading upon skeletal rearrangement to the corresponding α-spiropyrrolidones, which represent a rare and highly valuable heterocyclic core.

Electrochemical Trioxygenation of Allylarenes

AbstractTrioxygenation is a highly effective method for rapidly increasing molecular complexity by incorporating three C–O bonds from simple, readily available raw materials. In this study, we present an electrochemical trioxygenation protocol for allylarenes, which enables the synthesis of a diverse array of triacetoxylation products without external chemical oxidants. These products, which are difficult to obtain through conventional methods, highlight the potential of electrochemistry in promoting sustainable synthesis.

Chemical Oxidation-Induced Degradation in Gas Diffusion Layers for PEFC: Mechanisms and Performance Implications

Gas Diffusion Layers (GDLs) are integral in polymer electrolyte fuel cells, facilitating gas and water transport while providing structural support. However, their susceptibility to chemical degradation significantly impacts their functionality over extensive periods of time. This study investigates the mechanisms of GDL degradation, focusing on chemical oxidation. Accelerated stress testing, which involves immersing GDL in Fenton’s reagent for 24 h, is used. Ex-situ analysis reveals changes in surface properties, including a 3% reduction in contact angle, from 15% to only 9% remaining fluorine on the surface, and OH group presence in GDLs exposed to Fenton’s reagent. In-situ methods are used to study the impact of GDL degradation on fuel cell performance. Polarization curve reveals a 17% performance enhancement in aged GDLs, with a corresponding 19% decrease in voltage loss due to oxygen transport resistance at a high current observed via transient limiting current analysis. Electrochemical impedance spectroscopy reveals a 51% reduction in mass transport resistance, providing insights into structural alterations, such as pore widening and increased hydrophilicity. Despite these improvements, aged GDL demonstrates substantial degradation under high humidity, leading to water management challenges and voltage instability. This is attributed to the loss of fluorine, as indicated by the ex situ analysis.

Surface plasmon-induced various characteristics of Gold@Copper oxide nanostructures

The combined effect of metal incorporated semiconductor nanostructures (NSs) provides hybrid, proficient and more functional properties that are difficult to be provided by single component NSs in modern applications and industry. A facile seed growth method is adapted for the synthesis of gold coated by cuprous oxide (Au@Cu2O) core@shell NSs that are functionalized in their shell thickness and surface states. As synthesized Au@Cu2O core@shell cubic NSs contain single cubic Au as a core material with varying Cu2O shell thickness, confirmed by their microscopic analysis. Various spectroscopic analyses are is accomplished to confirm the chemical structure, crystallinity, oxidation state and binding energy of the concerned material over the core's surface. Optical absorption properties of core@shell NSs are greatly affected causing a shift in the surface plasmon resonance (SPR) peaks intensities with increase of the shell size. Photoluminescence (PL) spectra explain influence of Cu2O shell morphology over the emission characteristics that an increasing shell thickness caused an enhancement in PL emission peak along with red-shift of the peak. The elemental quantifying is done by XPS technique to provide a detailed surface reaction chemistry about oxidation states of copper. The charge-transfer at the metal-semiconductor interface results in highly intense and selective enhanced SERS signals via PL quenching, using Rhodamine-6G as the probe. The results provide useful information for preparation of various Au@Cu2O NSs for applications involving charge-transfer and SPR based interaction.

Chromium speciation from tannery wastewater using spectroscopic techniques

The toxicity and reactivity of chromium (Cr) depend on its chemical form or oxidation state which directs the significance of chromium speciation. Cr(VI) is a ‘Class A’ carcinogen whereas Cr(III)) is considered as essential for metabolism. In this work, concentrations of Cr species in different sampling sites of a tannery effluent have been spectroscopically determined. Cr(VI) was determined by UV-visible spectrophotometer through azo dye formation. Total Cr was determined by FAAS while Cr(III) was through subtraction. The Cr(IV) concentration before and after treatment was found in close proximity since the wastewater treatment process was evidently not effective at reducing the level of Cr(IV) in the waste stream (i.e., 3.34 mg/ L versus 3.15 mg/L). The Cr(VI) concentration after treatment (3.15 mg/L) is more than 31 times higher than the permissible limit of WHO (0.1 mg/L). Furthermore, the concentration of Cr(VI) in the downstream of the receiving river (0.59 mg/L) is more than 12 times higher than the upstream (0.046 mg/L) while Cr(III) in the downstream (25.73 mg/L) is more than 50 times higher than the upstream concentration (0.51 mg/L), confirming that the pollution of the river is from the tannery effluent.

Optimisation of Catalytic Oxidation Conditions for the 2‐Keto‐L‐Gulonic Acid Production Using Response Surface Methodology

AbstractL‐Ascorbic acid, also known as vitamin C, is a very important antioxidant ingredient situated many usage areas in different industries. 2‐keto‐L‐gulonic acid (2‐KLG) is the main precursor component of L‐ascorbic acid production and it can be produced from L‐sorbose via microbial fermentation or chemical (catalytic) oxidation. While some special strains are used in microbial fermentation, it is benefitted from some catalysts in chemical oxidation. Herein, it was aimed to determine the optimum reaction temperature, pH, and time conditions to produce maximum 2‐KLG compound with the catalytic oxidation of L‐sorbose in the presence of Pt/Al2O3 catalyst with response surface methodology approach. For this aim, the reaction temperature, pH, and time used as variable factors. The limit values of variable factors were applied as 40–60 °C for the temperature, 7.00–9.00 for the pH value, and 3–9 h for the time. The analyses results demonstrated that the increasing temperature and time negatively effected the conversion of L‐sorbose into the 2‐KLG. The optimum conditions of variable factors were determined as 41.30 °C for the temperature, 8.23 for the pH, and 3.25 h for the reaction time by the central composite design. Under these optimum conditions, L‐sorbose was converted into 2‐KLG with an average yield of 43.70 %.

Synthesis of PPy-MnO2 Nanocomposite for Utilization in Supercapacitor Applications

Polypyrrole (PPy) nanocomposites were prepared using chemical oxidation and were combined with manganese oxide (MnO2) nanoparticles. The PPY-MnO2 nanocomposite was synthesized by integrating PPy nanofibers with varying volume ratio percentages of MnO2 dopant (10, 30, and 50% vol. ratio). The structural features of the PPy and PPy-MnO2 nanocomposite were investigated using X-ray diffraction (XRD). Fourier transfor infrared (FTIR) spectroscopy was used to demonstrate the molecular structures of primary materials and the final product of PPy, MnO2, and PPy- MnO2 nanocomposites. Field Emission Scanning Electron Microscopy (FESEM) showed that the morphology of PPy consisted of a network of nanofibers. Increasing the volume ratios of manganese oxide added to the PPY nanofiber led to the increase of manganese oxide nanoparticles on the surface of the PPY nanofiber network. This resulted in a noticeable alteration in the structure of the nanocomposite. It has been observed that the nanocomposites demonstrate a significant level of pseudocapacitive activity. The highest capacitance of 236 F/g was observed when pure PPy was doped with 30% MnO2 compared to 125 F/g of the pure PPy.

Chemical oxygen demand oxidation via sustained-release persulfate balls: a rate-compatibility study of flow velocity, releasing, and oxidation

Chemical oxygen demand oxidation via sustained-release persulfate balls: a rate-compatibility study of flow velocity, releasing, and oxidation

Anomalous Temperature Dependence of the Triplet-Triplet Energy Transfer in Cereibacter sphaeroides I(L177)H Mutant Reaction Centers.

In photosynthetic reaction centers, quenching of the primary donor triplet state by energy transfer to the carotenoid molecule provides efficient suppression of generation of singlet-excited oxygen, potent chemical oxidant. This process in the Cereibacter sphaeroides reaction centers is thermoactivated, and discontinues at temperatures below 40K. In these reaction centers, substitution of amino acid residue isoleucine at the 177position of the L-subunit with histidine results in the sharp decrease of activation energy, so that the carotenoid triplets are populated even at 10K. Activation energy of the T-T energy transfer was estimated as 7.5cm-1, which is more than 10-fold lower than activation energy in the wild type reaction centers. At certain temperatures, the energy transfer in the mutant is decelerated, which is related to the increase of effective distance of the triplet-triplet transfer. To the best of our knowledge, the described mutation presents the first reaction center modification leading to the significant decrease in activation energy of the T-T energy transfer to carotenoid molecule. TheI(L177)H mutant reaction centers present a considerable interest for further studies of the triplet state quenching mechanisms, and of other photophysical and photochemical processes in the reaction centers of bacterial photosynthesis.

Carbon coating engineering enhances the stability of graphite anode in potassium ion batteries

Graphite forms reversible potassium-graphite intercalation compounds electrochemically. Graphite anode possesses a high reversible specific capacity (279 mAh g−1) and an optimal low potential platform, rendering it an ideal anode material for potassium-ion batteries. However, the intercalation of K+ ions in graphite causes a bulk volume expansion of up to 61%, resulting in irreversible damage to the structure of graphite, which leads to inferior cycling stability. In this paper, surface-oxidized graphite (OG) with reduced particle size and increased defect densities was obtained by mechanical ball milling and chemical oxidation. Composites of soft carbon-coated OG (OG@PC) were prepared by soft carbon coating. The soft carbon coating can alleviate the bulk expansion caused by K+ intercalation/deintercalation in OG, thus slowing down the destruction of the crystalline structure of graphite after multiple charging/discharging cycles. OG@PC exhibits increased reversible specific capacity from 267 mAh g−1 to 314 mAh g−1 compared with pristine graphite at a current density of 0.05 A g−1. Moreover, at a high current density of 0.5 A g−1, a reversible specific capacity of 213 mAh g−1 was achieved after 200 cycles. This work investigates simple surface carbon coating strategies to improve the cycling stability of a graphite anode of potassium-ion batteries.

Synthesis and Characterization of Polyaniline / [BMIM][BF4] Polyionic Liquid by Interfacial Polymerization

Polyaniline (PANI) was prepared by polymerization via the chemical oxidation of aniline monomer with ammonium persulfate as the initiator. The interfacial polymerization method was used to prepare PANI/1-butyl-3-methylimidazolium tetrafluoroborate [BMIM][BF4] polyionic liquid (PIL). The obtained PANI/ [BMIM][BF4] PIL was investigated by the XRD, EDX, SEM, FTIR, and UV-Visible characterizations. X-ray diffractogram of PANI showed five prominent characteristic peaks at 27.1°, 24o, 21.8°, 19.8°, and 18.2°. This demonstrates the semi-crystalline character of the polyaniline produced through the interfacial polymerization process. Incorporation of [BMIM][BF4] into PANI reduced the crystalline phase and enhanced amorphicity. From the EDX pattern, several elements appeared in this test; oxygen had of the highest weight percentage of 54.2%. The SEM image showed a clear hierarchal porous structure with nano-sticks particles and forms a cross-linked framework between PANI and [BMIM][BF4]. From FTIR spectra of PIL, a prominent absorption peak at 3163.26 cm-1 was noted because of the N-H stretching vibrations present in the polymer. The UV-Vis spectra for PANI/[BMIM][BF4] polyionic liquid showed three peaks between 200 and 1060 nm. These bands result from π → π* and n → π* transitions, which are related to the excitement absorption of benzenoid and quinoid groups.