Radical Reactions Research Articles

The synthesis of an efficient titanium-based flame retardant with high dispersibility in polyamide 66

The preparation of high-performance flame retardants specialized for melt-spinning polyamide 66 (PA66) fibers remains a big challenge nowadays. This study has synthesized a highly dispersed, phosphorus-containing titanocene complex, namely Cp2Ti(DBA). The synthesized flame retardant possesses high dispersibility and compatibility in PA66. Flammability tests show that Cp2Ti(DBA) exhibits efficient flame retardancy in PA66. With the addition of 15 wt % of Cp2Ti(DBA) in PA66, a LOI value of 29.9 % is achieved, and the peak heat release rate (PHRR) and total heat release (THR) are reduced by 36 % and 26 %, respectively, as compared to pure PA66. Based on the py-GC MS study and char analysis, Cp2Ti(DBA) shows a dual-phase flame-retardant mechanism. In the gas phase, Cp2Ti(DBA) releases the phosphorus-containing free radicals, which capture the highly reactive free radicals. While in the condensed phase, titanium promotes the phosphaphenanthrene fragments to degrade and retains phosphorus in the form of titanium phosphates, which reinforce the barrier effect and stability of the char layer. This work may provide an efficient flame retardant with promising applications in PA66, especially for the melt-spinning of fibers.

Synergistic degradation and ecotoxicology assessment of tetracycline by II-scheme Cu3BiS3/Bi2Fe4O9 photocatalytic activation of peroxymonosulfate

The increasing reliance on antibiotics in recent years has led to the growing overuse of antibiotics, and tetracycline (TC) is a widely used antibiotic. In this study, a hierarchical configuration system was constructed by combining Cu3BiS3 and Bi2Fe4O9 for the study of photocatalytic activation of persulfate degradation of TC, and its photocatalytic performance on TC was fully evaluated. Results found that Bi2Fe4O9 and Cu3BiS3 formed a type-II heterojunction, which inhibited the complexation of photogenerated carriers and synergized with peroxymonosulfate (PMS) to promote the generation of reactive radicals and thus enhance the photocatalytic effect. Also, in the photocatalytic activation of persulfate systemCu3BiS3/Bi2Fe4O9/PMS/ visible (Vis), the best catalytic performance of 12.5 %Cu3BiS3/Bi2Fe4O9 was achieved when the catalyst injection was 0.3 g/L, the concentration of TC was 20 mg/L, the concentration of PMS was 1 mmol/L, and the pH=6.5, which degraded 97.9 % of TC within 60 min. The 12.5 % Cu3BiS3/Bi2Fe4O9/PMS/ Vis system has a contribution of active substances of SO4•−>O2•−>h+>O12>•OH. Further, the degradation mechanism and pathways of TC by the Cu3BiS3/Bi2Fe4O9/PMS/Vis system was proposed, and it was proved that the system could realize the safe conversion of TC according to the toxicity estimation using software Toxicity Estimation Software Tool (TEST).

Predictive Models for Ligand Effects on a Reactive Al-Containing Radical Intermediate from Multivariate Linear Regression Analysis

Predictive Models for Ligand Effects on a Reactive Al-Containing Radical Intermediate from Multivariate Linear Regression Analysis

Aryl Radicals Generated from Aryl Pinacol Boronates Modify Peptides and Proteins

We report here a distinct reaction, which generates aryl radicals from aryl pinacol boronates under mild aqueous conditions and can be used for peptide and protein modifications. The strategy leverages the versatile reactivity of aryl pinacol boronates to form aryl radicals in presence of ammonium persulfate (APS). The formed aryl radicals insert readily into peptide disulfide bonds while tolerating other functionalities. On the protein level, the reactivity extends beyond the disulfide bonds. The methodology benefits from the accessibility of starting aryl pinacol boronates, as well as biocompatible conditions. In contrast to conventional methods used for aryl radical generation, the strategy is metal‐free, does not require photoinduction and can be readily performed under aqueous conditions. The mechanism of the reactions was investigated by radical‐trapping experiments, spectroscopic analysis and oxygen scavenging. The presented approach broadens the application of aryl pinacol boronate esters in radical reactions.

Copper-Catalyzed Radical Sulfonylation: Divergent Construction of C(sp3)-Sulfonyl Bonds with Sulfonylhydrazones.

Sulfonylhydrazones have been proven to be versatile synthetic intermediates in a panel of transformations. However, radical sulfonylation with sulfonylhydrazone as sulfonyl radical source is relatively rare. Here, we found that sulfonylhydrazone can serve as a new sulfonyl radical precursor to couple various partners such as arylacetic acids, ene-yne-ketones, and para-quinone methides under copper catalysis and microwave irradiation. The reactions of sulfonyl radicals have been successively developed to enable the divergent synthesis of C(sp3)-sulfonyl bonds. In addition, when alkynes and alkenes are used as radical receptors, this method can also promote the formation of C(sp2)-sulfonyl bonds. This finding suggests that sulfonylhydrazone could be regarded as a potentially useful sulfonyl radical in sulfone synthesis.

Inhibiting Mitochondrial Damage for Efficient Treatment of Cerebral Ischemia-Reperfusion Injury Through Sequential Targeting Nanomedicine of Neuronal Mitochondria in Affected Brain Tissue.

Oxidative stress, predominantly from neuronal mitochondrial damage and the resultant cytokine storm, is central to cerebral ischemia-reperfusion injury (CIRI). However, delivering drugs to neuronal mitochondria remains challenging due to the blood-brain barrier (BBB), which impedes drug entry into affected brain tissues. This study introduces an innovative tannic acid (TA) and melanin-modified heteropolyacid nanomedicine (MHT), which highly specifically eliminates the neuronal mitochondrial reactive oxygen radicals burst to efficiently reduce neuronal mitochondrial damage through a strategically designed sequential targeting strategy from affected brain tissue to neuronal mitochondria. TA endows MHT with sequential targeting ability by binding to matrix proteins exposed to the damaged BBB and mitochondrial outer membrane proteins of neurons, while melanin significantly enhances the antioxidant capacity of MHT. Consequently, MHT effectively inhibits neuronal apoptosis by protecting mitochondria and reversing the inflammatory immune environment through the deactivation of the cyclic GMP-AMP synthase-stimulator of interferon genes (cGAS-STING) pathway. MHT demonstrated a strong therapeutic effect on CIRI, with an ultralow dose (2 mgkg-1) proving effective in reversing the condition. This work not only introduces a new avenue to significantly reduce CIRI through sequential targeting therapy but also offers a new paradigm for treating other ischemia-reperfusion injury diseases.

Impact of UV-B Photoaging on Chlorpyrifos Adsorption by PET Microplastics: Insights from Experimental and DFT Analysis.

Microplastics (MPs) in the environment pose a persistent concern, as these plastic particles can adversely impact both aquatic ecosystems and human health. MPs are subject to natural weathering and aging processes, such as photodegradation, which significantly alter their surface morphology and physicochemical properties, thereby influencing their fate, transport, and sorption behavior. To better understand how aging affects these properties and to elucidate the mechanisms behind the interactions with the chlorpyrifos pesticide, poly(ethylene terephthalate) (PET) microplastics (<100 μm) were subjected to accelerated photoaging in a UV-B chamber for varying exposure times. Several characterization techniques were employed, including scanning electron microscopy (SEM), energy dispersive X-ray spectrometry (EDS), X-ray diffraction (XRD), infrared spectroscopy (IR), point of zero charge (pHPZC), and thermogravimetric analysis (TGA). Additionally, the percentage of crystallinity and carbonyl index (CI) were calculated. The results demonstrated a decrease in pHPZC following photodegradation, likely due to an increase in δ- (-C=O) groups, consistent with the CI findings. SEM revealed surface deterioration caused by aging, while TGA indicated an early thermal degradation stage associated with water volatilization, suggesting enhanced hydrophilicity. Density functional theory (DFT) calculations showed that the PET monomer absorbs slightly in the UV-B region, leading to excitation and subsequent radical reactions that form Norrish type I products. The adsorption capacity of aged PET increased compared to the pristine material, likely due to the molecular geometry becoming more planar, facilitating interactions between the aged MPs and chlorpyrifos, as confirmed by noncovalent interaction (NCI) analysis. These findings highlight the significant potential of aged microplastics to adsorb micropollutants and act as vectors in aquatic environments.

Key process of ethanol hydrogen donor promoting the conversion of organic matter in sludge to bio-oil

To develop clean energy utilization of sewage sludge, this study investigated the conversion behavior of organics and energy in supercritical sludge-ethanol system. The influence of liquefied parameters on products distribution, hydrogen supply process of ethanol for sludge liquefaction, migration of organics, and energy transformation were investigated. Results indicated that ethanol acted as both a solvent and a hydrogen donor. It providing H⋅ to promote organics dissociation for bio-oil production through radical reactions. Formation of new products in bio-oil such as C20H38O2 and C20H38O2 may be caused by H⋅ generated from OH and CH in ethanol. The increase in dodecanes and hexadecanes in bio-oil may be formed by recombination of smaller radicals such as HO·, H·, CH3⋅, CH3CH2⋅ from dissociation of ethanol and organics. Additionally, energy migration process indicated that higher temperatures increased carbon content in bio-oil from 40.88 to 48.92 %, decreased oxygen content from 48.6 to 39.56 %, and raised the calorific value of bio-oil from 29.63 to 30.11 MJ/kg. Besides, approximately 74.14 % of sludge energy transferred to bio-oil, while about 71.94 % of oxygen moved to bio-char, reducing the calorific value of bio-char to 0.03 MJ/kg. Notably, about 240.5 kg of bio-oil can be produced from 1t of sludge, reducing net carbon emissions by 43.583 kg, and presenting a sustainable alternative to fossil fuels. This study innovatively investigated the dual role of ethanol for sludge liquefaction, providing an efficient and sustainable method for energy recovery from sludge.

Possible formation of long-lived photo-oxidants by photolysis of organic matter phenols in sunlit waters

AbstractPhotodegradation in sunlit waters is a major process of contaminant abatement, yet underlying chemical processes in the presence of dissolved organic matter are poorly known. Long-lived photo-oxidants are reactive species formed when the chromophoric dissolved organic matter absorbs sunlight, and they are involved in the degradation of contaminants. Previous works identified long-lived photo-oxidants with phenoxy radicals, which could be formed upon oxidation of natural phenols by the excited triplet states of chromophoric dissolved organic matter. Here, we generated reactive phenoxy radicals by direct ultraviolet-A photolysis of 2-nitrophenol and 4-nitrophenol. We measured the second-order rate constants for reaction of these phenoxy radicals with 2,4,6-trimethylphenol, a model electron-rich phenol. Results show rate constants of 9.39 × 108(M−1s−1) for the 2-nitrophenoxyl radical, and 1.56 × 108(M−1s−1) for the 4-nitrophenoxyl radical. These values are slightly lower than the typical rate constant of the reaction between 2,4,6-trimethylphenol and the excited triplet states of chromophoric dissolved organic matter, of 3 × 109(M−1s−1). This means that 2,4,6-trimethylphenol would not be degraded to comparable extents by the excited triplet states of chromophoric dissolved organic matter and by long-lived photo-oxidants, if long-lived photo-oxidants were generated solely by the triplet states of chromophoric dissolved organic matter. Overall, findings suggest the occurrence of new pathway involving the direct photolysis of organic matter phenols that generates long-lived photo-oxidants.

Synergistic effect of curcumin and Piperine loaded Niosomal nanoparticles on acute pulmonary toxicity induced by Paraquat in mice.

Paraquat (PQ), a widely used non-selective herbicide, induces severe lung toxicity by promoting cell death and tissue necrosis through the generation of reactive oxygen species (ROS) and free radicals. This study aimed to develop and evaluate novel niosomal nanoparticles (NPs) encapsulating curcumin and piperine to mitigate PQ-induced acute pulmonary toxicity in Balb/c mice. The NPs were prepared using non-ionic surfactants and cholesterol via the thin film hydration method. Characterization revealed high encapsulation efficiency (>85%), proper particle sizes (264-286nm), narrow polydispersity index (PDI) (0.19±0.04 to 0.23±0.02), and good stability over 90days. Thermal analysis confirmed successful encapsulation of curcumin and piperine within the niosomal NPs. In vivo studies showed that PQ exposure significantly elevated ROS, lipid peroxidation (LPO), and protein carbonylation (PC) levels, while reducing glutathione (GSH) levels and impairing mitochondrial function (P<0.001). However, co-treatment with curcumin- and piperine-loaded niosomal NPs effectively reversed these effects (P<0.001), improving mitochondrial function. The combined formulation of curcumin and piperine in niosomal NPs offers a promising therapeutic strategy for treating PQ-induced pulmonary toxicity, likely due to enhanced bioavailability and potent antioxidant activity.

Dication Disulfuranes as Photoactivatable Sources of Radical Organocatalysts.

The recent development of photoredox and energy transfer catalysis has led to a significant expansion of visible light-driven chemical transformations. These methods have demonstrated exceptional efficiency in converting a wide range of substrates into radical intermediates and generating open-shell catalytic species. However, the simplification of catalytic systems and the direct generation of highly reactive radical organocatalysts through direct visible light irradiation from stable precatalysts remains largely an unrealized goal. This challenge is mainly due to the limited availability of precatalysts that are responsive to visible light. Herein, we introduce a new class of bench-stable dicationic disulfuranes, which release highly reactive thiyl radicals upon blue light excitation. Spectroscopic and computational studies reveal that this reactivity arises from a combination of structural features and intermolecular interactions. This family of molecules has been employed to catalyze radical cascades previously incompatible with photoredox conditions, enabling the efficient formation of 1,2-dioxolanes and 1,3-hydroxyketones in excellent yields and short reaction times.

Dication Disulfuranes as Photoactivatable Sources of Radical Organocatalysts

The recent development of photoredox and energy transfer catalysis has led to a significant expansion of visible light‐driven chemical transformations. These methods have demonstrated exceptional efficiency in converting a wide range of substrates into radical intermediates and generating open‐shell catalytic species. However, the simplification of catalytic systems and the direct generation of highly reactive radical organocatalysts through direct visible light irradiation from stable precatalysts remains largely an unrealized goal. This challenge is mainly due to the limited availability of precatalysts that are responsive to visible light. Herein, we introduce a new class of bench‐stable dicationic disulfuranes, which release highly reactive thiyl radicals upon blue light excitation. Spectroscopic and computational studies reveal that this reactivity arises from a combination of structural features and intermolecular interactions. This family of molecules has been employed to catalyze radical cascades previously incompatible with photoredox conditions, enabling the efficient formation of 1,2‐dioxolanes and 1,3‐hydroxyketones in excellent yields and short reaction times.

Uncovering Metal-Decorated TiO2 Photocatalysts for Ciprofloxacin Degradation-A Combined Experimental and DFT Study.

Optimization of the efficiency of the photocatalytic degradation of organic and pharmaceutical pollutants represents a matter of fundamental and practical interest. The present experimental and DFT study deals with evaluation of OH radical binding energy as a simple computational descriptor of the catalytic activity of d-metal-decorated TiO2 photocatalysts for the photodegradation of the widely used antibiotic ciprofloxacin. Five d-metals commonly used in catalytic materials (Zr, Pt, Pd, Fe, and Cu) were deposited on the TiO2 surface, and the obtained photocatalysts were characterized experimentally (XRPD, ICP-OES, and SEM) and theoretically (DFT). Attention was also paid to the mechanistic insights and degradation byproducts (based on UV-Vis spectrometry and LC/MS analysis) in order to obtain systematic insight into their structure/performance relationships and confirm the proposed model of the degradation process based on OH radical reactivity.

Abatement of volatile organic compounds (VOCs) and fluorine gases by a microwave plasma torch (MPT)

The use of microwave plasma torch (MPT) in the abatement of potent greenhouse and fluorinated (F-gases) gases is crucial due to their high global warming potential. The purpose of this study was the abatement of volatile organic compounds (VOCs) and carbon tetrafluoride (CF4) using specifically designed reverse vortex flow reactor (RVR) and pillar of fire reactor (POF). The RVR has properties that are crucial for their synergistic effects with the MPT, and the POF configurations showed high-efficiency combustion due to plasma radicals and a large contact area with the MPT. The study used Aspen Plus and COMSOL software to analyse the mass balance involved in the thermal decomposition of isopropyl alcohol (C₃H₈O) and CF4 and to design the RVR and POF reactors. Using MPT without hydrocarbon fuel, low-concentration C₃H₈O and CF4 were successfully destroyed in high-flow streams. The experiment on C₃H₈O showed that using a plasma power of 2 kW and 1 cubic meter per minute (CMM) of bulk gas, a destruction removal efficiency (DRE) of 95 % was achieved for a polluted C₃H₈O of 410 ppm. In a second experiment, a DRE of 94 % was achieved for a polluted C₃H₈O of 370 ppm. The first CF4 experiment achieved a DRE of 93.3 % with a 7 kW plasma power and 1 CMM bulk gas polluted at 285 ppm. In the second experiment, the presence of highly reactive hydroxyl radicals (OH*) in steam plasma improved the DRE to 99.8 % at 7 kW plasma power and 100 LPM bulk polluted at 180 ppm.

A new strategy toward synthesis of novel bifunctional N- and S-bearing sorbent for platinum(IV) removal from aqueous solutions and acidic leaching residue of Pt/Al2O3 catalyst

Strong incentive politics have been elaborated for promoting the recovery of precious metals from secondary resources. Solid leaching generates acidic effluents that can be pre-treated using precipitation steps for partial separation before applying sorption for metal recovery from mild acidic solutions. For this purpose, a new sorbent was designed bearing numerous N- and S-bearing reactive groups with good affinity for platinum (as chloroanionic species). Thiazole precursors were first reacted before being grafted (by free radical reaction) with triallyl cyanurate (to form CTTR sorbent). The material was characterized by a series of analytical tools (SEM, BET, FTIR, XPS, TGA, elemental analysis, and titration). The effect of pH combined with FTIR and XPS spectroscopy analyses allowed identifying the mechanisms involved in metal binding: (a) electrostatic attraction of chloroplatinate anions with protonated amine groups (especially in acidic conditions), (b) while at moderate acidic pH metal sorption proceeds through ligand exchange and chelation onto N-based and S-based groups. Optimum sorption was found at pH close to 4 (near pHpzc value). Under selected experimental conditions, the equilibrium was reached in 25–35 min. The pseudo-first order rate equation fitted well experimental profile (though the resistance to intraparticle diffusion contributes to the kinetic control). The maximum sorption capacity at room temperature reached up to 1.58 mmol Pt g−1 (at pH 4). The sorption isotherm was successfully fitted by the Temkin equation. The sorption is spontaneous and exothermic (with reduction in maximum sorption capacity reaching up to 25 %, when temperature increases to 50 °C). Optimum platinum desorption was obtained with 0.3 M HCl solution (with solid/liquid ratio 1.67 g L−1) for complete desorption and enrichment factor close to 4.6. Complete desorption was maintained over 5 cycles, while the sorption efficiency decreased by less than 3.5 % at the fifth cycle. The sorbent showed remarkable stability for PGMs (Pd(II) in addition to Pt(IV)) against alkali-earth elements or base metals (from equimolar synthetic solutions); the selectivity is driven by the preference of the reactive groups (soft base and intermediary base) for soft PGM metals against hard and borderline metal ions; this selectivity is also affected by metal speciation (formation of chloro-anionic species). The valorization of platinum from non-compliant Pt/Al2O3 catalyst was investigated after leaching with aqua regia. Platinum was precipitated from the leachate with ammonium chloride. In a second step, aluminum was removed by precipitation at pH 5. The residual solution was then treated by adsorption on CTTR: optimum separation between Pt and Al was achieved at pH ≈ 3.

A highly-efficient peroxymonosulfate activator using a sewage sludge derived biochar supported cobalt oxide: Mechanism and characteristics

The application of biochar derived from sewage sludge (BS) in Fenton-like reactions for contaminant removal has attracted considerable attention. Herein, a BS-supported Co3O4 (BS-Co3O4) catalyst was synthesized using a simple two-step hydrothermal-calcination process to achieve highly efficient activation of peroxymonosulfate (PMS). The introduction of biochar effectively inhibited the aggregation of Co3O4 and reduced cobalt leaching. Compared to Co3O4, the mesoporous BS-Co3O4 exhibited an 8-fold increase in specific surface area (SSA) to 111.92 m2∙g−1, and a 46 %-66.4 % reduction in crystal plane size. The interaction between biochar and cobalt oxide resulted in several notable enhancements in the BS-Co3O4 composite. Specifically, there was an increase in sp2 carbon content, a 42.69 % rise in capacitance, and a 79.99 % reduction in charge transfer resistance. These improvements contributed to enhanced PMS activation performance. The BS-Co3O4 also contained a higher content of Co(II), sp2 carbon, and oxygen vacancies (OV). Co(II) played a crucial role in the redox reaction, accelerating the formation of SO4•− and 1O2 during the PMS activation process. Additionally, OV acted as electron capture centers, further promoting the generation of 1O2. Evidence from reactive species investigations and electron paramagnetic resonance (EPR) tests indicated that SO4•− and 1O2 were the main reactive radicals for eliminating tetracycline (TC). Based on the identification of TC intermediates, two potential degradation pathways were proposed, and a reduction in intermediate toxicity was observed. Experiments involving interference and repetition demonstrated that the BS-Co3O4 catalyst was stable and reusable. This work provides a solution with low metal leaching, high recycling performance, and safety for antibiotic wastewater treatment.

Cu-NC single-atom nanozymes with peroxidase-like activity for colorimetric detection of d-penicillamine

Most conventional nanozymes have poor specificity and low activity, and designing high-performance nanozymes remains a challenge. In contrast, single-atom nanozymes have high atom utilization and high reactivity. Here, we prepared Cu single-atom nanozymes (Cu-NC) with excellent peroxidase-like activity by high-temperature pyrolysis using Cu as a transition metal source. The introduction of Cu formed the Cu-Nx active site, which accelerated charge transfer between the reactants and the active site and was the key for improving the activity. With Cu-NC as a catalyst, H2O2 rapidly oxidized 3,3′,5,5′-tetramethylbenzidine (TMB) to oxTMB, and the solution turned blue with strong absorption at 652 nm. Because d-penicillamine (D-PA) can reduce oxTMB or react with reactive oxygen species radicals to inhibit the color reaction, we built a colorimetric sensing platform around Cu-NC for the determination of D-PA and successfully used it for the determination of D-PA in urine samples. This work provides new ideas for the design of high-performance nanozymes and the detection of D-PA in real environments.

Co-doped Zr-UiO-66-NH2@carboxylated cellulose nanocrystals/PAN membrane for oil/water separation with photocatalysis-PMS synergistic self-cleaning and antibacterial activity

The development of superwetting membranes is a promising approach for separating emulsified oily wastewater. However, challenges such as low flux without external pressure and membrane fouling have hindered membrane performance. Herein, we fabricated a novel nanofibrous membrane by grafting Co-doped Zr-UiO-66-NH2 (UiO(Zr/Co)) nanoparticles onto carboxylated cellulose nanocrystals (CCNC)-polyacrylonitrile (PAN) mixed matrix electrospinning membrane via chemical bonds through EDC/NHS reaction. CCNC served a dual purpose by enhancing membrane hydrophilicity and providing connection points for UiO(Zr/Co). The as-prepared UiO(Zr/Co)@CCNC/PAN exhibited superhydrophilic/underwater superoleophobic and anti-fouling properties. The membrane demonstrated excellent demulsification and gravity-driven separation capabilities for various oil-in-water emulsions, with superior permeation flux (1588–2557 L m−2 h−1) and separation efficiency (above 99 %). Furthermore, UiO (Zr/Co)@CCNC/PAN could activate peroxomonosulfate (PMS) under visible light to remove both high viscous crude oil-fouling and bio-fouling, exhibiting impressive photocatalytic self-cleaning and antibacterial activity. The generation of reactive radicals (O2−, OH and SO4−) and non-radical (1O2) species in UiO(Zr/Co)@CCNC/PAN+PMS system through multiple pathways was confirmed. Additionally, the band structure of UiO(Zr/Co) and synergistic photocatalytic-PMS activation mechanism were investigated. This work provides new insights into the design and fabrication of MOF modified superwetting nanofibrous membrane with inherent bonding, high permeation flux, anti-fouling and self-cleaning properties.

Application of a Film Model to Mass Transfer and Chemical Reaction at a Plasma-Liquid Interface

Plasma electrodes provide novel ways of conducting electrochemical processes in liquids, in particular because of the ability to generate unique reactive radical species. However, the radicals injected into the liquid and their ensuing reactions are often confined to a narrow region near the interface of the plasma and the liquid. Thus, mass transfer has been found to play an important role in the observed kinetics and a modeling framework that includes both transport and kinetics is required to interpret experimental data. Here, we apply the idea of a film model for interphase mass transfer to plasma-liquid electrochemical processes, whereby transport is described by a stagnant film that is inherently linked to the concentration boundary layer and the mass transfer coefficient. Equations that govern the transport and reaction of radicals and substrates within the film are solved assuming a quasi-steady state approximation. The model is applied to specific case studies from the literature to estimate important parameters that are difficult to measure experimentally, such as the mass transfer coefficient. Our study shows that a film model can elucidate the effect of mass transfer on observed conversion rates and allow the intrinsic kinetics to be unraveled.

Surface Fluorination Mediated Electro-Oxidative Degradation of HFPO-DA on Boron-Doped Diamond Electrode

Heptafluoropropylene oxide dimer acid (HFPO-DA), as an alternative to perfluorooctanoic acid (PFOA), has been shown to pose similar environmental and health risks as other perfluorinated compounds. The electrochemical-based advanced oxidation processes are promising techniques for the treatment of perfluorinated compounds, and the boron-doped diamond (BDD) anode could degrade HFPO-DA under mild conditions. However, the roles of radicals in the degradation and how to overcome the steric hindrance of the –CF3 branch on the carboxyl group were not yet clear. In this study, we investigated the degradation mechanism of HFPO-DA on the BDD anode. Instead of other non-active anodes (PbO2 and SnO2 electrodes), HFPO-DA can be degradable on the BDD electrode with a rate constant logarithmic correlation to the applied current density. The hydroxyl radical (•OH) was one of the key factors in the degradation of HFPO-DA, accounting for almost 89% of the significant effect, and the direct electron transfer was the rate-limiting step in the degradation reaction. Physicochemical characterization including field emission scanning electron microscope (FE-SEM), X-ray photo-electron spectroscopy (XPS), water contact angle, and electrochemical property indicated that the BDD electrode was fluorinated after electrolysis, the electrode surface became more hydrophobic due to the bonding of –CxFy, leading to a decrease in the electrochemically active area. Moreover, degradation products (pentafluoropropionic acid, trifluoroacetic acid, and fluorine ion) were detected and the mass balance of carbon and fluorine was calculated during the degradation. Therefore, a degradation mechanism for HFPO-DA was proposed, which involved direct electron transfer, decarboxylation, radical reaction, decarboxylation, and decarboxylation. The de–CF3 step initiated the fluorination of the BDD electrode, which was initiated by the defluorination process. This study contributes to the understanding of the electro-oxidative degradation of perfluoroalkyl ether carboxylic acids and provides guidance for the application of electrochemical advanced oxidation processes.