Radical intermediates in photoinduced reactions on TiO2 (an EPR spin trapping study)

Plasma catalysis. A study of the influence of oxysulfur, SOx• species through the degradation of sulfonated dyes by non-thermal plasma

This work studied the degradation reaction of sulfonated dyes, indigo carmine, phenol red, and their mixtures by non-thermal plasma (NTP). Interestingly, the degradation rate constant showed a faster process and lower activation energy (Ea) for the dye mixtures than for the degradation reaction of the individual dyes. This unexpected result opened up new opportunities for understanding plasma chemistry and the interaction between reactive species formed by the plasma and the target molecule. As no catalyst or chemical additive was added to the reactor, the decrease in Ea came from a self-synergistic effect (SSE), through the dye molecules fragmentation, which resulted in plasma catalysis. The hypothesis proposed in this work is that oxysulfur (SOx) species are formed by the desulfonation reaction of dyes. The sulfonic groups (SO3) present in the chemical structures of dyes can function as precursors for forming several SOx•- species. Studies based on oxygenated sulfonated species such as SO3•-, SO4•- and SO5•- have been widely applied in advanced oxidative and reductive processes due to their satisfactory efficiency and low cost. Among them, SO4•- is the key reactive species with the best performance in the degradation of pollutants due to its high oxidation potential (E° = 2.60 V). In addition, it is an alternative source of HO• in aqueous media, improving the oxidation reaction. In order to elucidate the SSE, the kinetic process was followed by UV-Vis analysis, and the reactive species, such as alkyl, hydroxyl, and oxy-sulfur radicals were identified by Electron Paramagnetic Resonance. The by-products of the NTP degradation reaction were analyzed by ultrafast liquid chromatography coupled with a mass spectrometer, and a fragmentation route was proposed.

The Effect of Nitriding Temperature of AISI 316L Steel on Sub-Zero Corrosion Resistance in C2H5OH

In this paper, glow nitriding processes at cathode potential are used at various temperatures to investigate how they affect the corrosion resistance of 316L steel in ethanol at temperatures of 22 °C and -30 °C. Lowering the test temperature reduces the corrosion rate of the nitrided layers. Conversely, glow nitriding at 450 °C improves the corrosion resistance of the tested steel. Increasing the nitriding temperature to 520 °C increases the corrosion rate. It should be noted that the ethyl alcohol solution, due to the lack of aggressive ions, does not cause significant changes in the corrosion rate of the steel. The value of the corrosion current varies in the range of 10-2-10-3 µA/cm2. Nitrided layers increase the contact angle measured for water and are entirely wettable for ethanol. The objective of this study is to evaluate the effect of the nitriding temperature of AISI 316L steel on its corrosion resistance in an ethanol solution at room temperature and at -30 °C.

Development of a novel LED-IoT photoreactor for enhanced removal of carbamazepine waste driven by solar energy

This study introduces an innovative LED-IoT photoreactor, representing a significant advancement in response to the demand for sustainable water purification. The integration of LED-IoT installations addresses the challenge of intermittent sunlight availability, employing LEDs with a spectrum mimicking natural sunlight. Passive Infra-Red (PIR) sensors and Internet of things (IoT) technology ensure consistent radiation intensity, with the LED deactivating in ample sunlight and activating in its absence. Utilizing a visible light-absorbing photocatalyst developed through sol-gel synthesis and mild-temperature calcination, this research demonstrates a remarkable carbamazepine removal efficiency exceeding 95% under LED-IoT system illumination, compared to less than 90% efficiency with sunlight alone, within a 6-h exposure period. Moreover, the designed photocatalytic system achieves over 60% mineralization of carbamazepine after 12 h. Notably, the photocatalyst demonstrated excellent stability with no performance loss during five further cycles. Furthermore, integration with renewable energy sources facilitated continuous operation beyond daylight hours, enhancing the system's applicability in real-world water treatment scenarios. A notable application of the LED-IoT system at an operating sewage treatment plant showed nearly 80% efficiency in carbamazepine removal from sewage in the secondary settling tank after 6 h of irradiation, coupled with nearly 40% mineralization efficiency. Additionally, physicochemical analyses such as XPS and STA-FTIR confirm that the carbamazepine photooxidation process does not affect the surface of the photocatalyst, showing no adsorption for degradation products.

Atomically isolated Sb(CN)3 on sp2-c-COFs with balanced hydrophilic and oleophilic sites for photocatalytic C-H activation

Activation of carbon-hydrogen (C-H) bonds is of utmost importance for the synthesis of vital molecules. Toward achieving efficient photocatalytic C-H activation, our investigation revealed that incorporating hydrophilic C≡N-Sb(CN)3 sites into hydrophobic sp2 carbon-conjugated covalent organic frameworks (sp2-c-COFs) had a dual effect: It simultaneously enhanced charge separation and improved generation of polar reactive oxygen species. Detailed spectroscopy measurements and simulations showed that C≡N-Sb(CN)3 primarily functioned as water capture sites, which were not directly involved in photocatalysis. However, the potent interaction between water molecules and the Sb(CN)3-modified framework notably enhanced charge dynamics in hydrophobic sp2-c-COFs. The reactive species ·O2- and ·OH (ad) subsequently combined with benzyl radical, leading to the formation of benzaldehyde, benzyl alcohol, and lastly benzyl benzoate. Notably, the Sb(CN)3-modified sp2-c-COFs exhibited a 54-fold improvement in reaction rate as compared to pristine sp2-c-COFs, which achieved a remarkable 68% conversion rate for toluene and an 80% selectivity for benzyl benzoate.

New visible-light-driven Bi2MoO6/Cs3Sb2Br9 heterostructure for selective photocatalytic oxidation of toluene to benzaldehyde

Herein, new Bi2MoO6/Cs3Sb2Br9 heterostructure (BiMo/CSB) was investigated for the first time as a visible-light-driven photocatalyst for C(sp3)-H bond activation using molecular oxygen as a green oxidant and toluene as a model substrate. The optimized BiMo/CSB photocatalyst exhibited enhanced toluene oxidation activity (2,346 μmol g-1h-1), which was almost two- and five-fold that of pristine CSB (1,165 μmol g-1h-1) and BiMo (482 μmol g-1h-1), respectively. The improved photocatalytic performance was essentially attributed to the formation of staggered band energy lineup in the BiMo/CSB hybrid, which promoted S-scheme charge transfer across the BiMo/CSB heterointerface as supported by ultraviolet photoelectron spectroscopy (UPS), density functional theoretical (DFT), time-resolve photoluminescence (TRPL), and photoelectrochemical studies. Spin-trapping electron paramagnetic resonance (EPR) and radical scavenging studies revealed that photoinduced hole, molecular oxygen, and superoxide radical are key active species in this photocatalytic system. The developed BiMo/CSB catalyst provided good selectivity toward benzaldehyde product (94-98 %), presumably due to the inhibiting effect of benzyl alcohol on benzaldehyde oxidation. No significant change in structure and morphology was observed for the spent catalyst, however small negative shift of Sb 3d and Bi 4f binding energy was found suggesting partial reduction of Sb3+ and Bi3+. This work not only provides a new visible-light-driven photocatalyst for C(sp3)-H bond activation but also opens the doors for exploitation of the conversion and functionalization of this inert bond toward the production of high value-added organic chemicals.

Spiky Artificial Peroxidases with V-O-Fe Pair Sites for Combating Antibiotic-Resistant Pathogens

With the sharp rise of antibiotic-resistant pathogens worldwide, it is of enormous importance to create new strategies for combating pathogenic bacteria. Here, we create an iron oxide-based spiky artificial peroxidase (POD) with V-O-Fe pair sites (V-Fe2 O3 ) for combating methicillin-resistant Staphylococcus aureus (MRSA). The experimental studies and theoretical calculations demonstrate that the V-Fe2 O3 can achieve the localized "capture and killing" bifunction from the spiky morphology and massive reactive oxygen species (ROS) production. The V-Fe2 O3 can reach nearly 100 % bacterial inhibition over a long period by efficiently oxidizing the lipid membrane. Our wound disinfection results identify that the V-Fe2 O3 can not only efficiently eliminate MRSA and their biofilm but also accelerate wound recovery without causing noticeable inflammation and toxicity. This work offers essential insights into the critical roles of V-O-Fe pair sites and localized "capture and killing" in biocatalytic disinfection and provides a promising pathway for the de novo design of efficient artificial peroxidases.

Eggshell-Derived Copper Calcium Hydroxy Double Salts and Their Activity for Treatment of Highly Polluted Wastewater

By using methyl orange (MO) removal as a model reaction, the best temperatures for processing eggshells are 750 °C and above to obtain biobased CaO materials, a raw material for producing CuCa hydroxy double salt (HDS) materials with high efficiency in treatments of highly polluted wastewater (the initial concentration of MO is 500 ppm). Characterization techniques employed in this study include power X-ray diffraction, scanning electron microscopy, thermogravimetric analysis, nitrogen adsorption-desorption analysis, and the colorimetric method, as well as energy-dispersive X-ray, infrared-, and electron spin resonance spectroscopies. Complete MO removal and high chemical oxygen demand (COD) efficiencies (>90%) can be achieved after 3 min treatments of the aqueous MO with the calcined eggshell-derived CuCa HDS materials. The spent, deactivated HDS materials can be regenerated by an acid wash method. The activity of CuCa HDS materials in MO removal is unaffected by eggshell sources, implying that sorting steps may be unnecessary when eggshell food waste (duck, quail, and hen eggshells) is collected to produce biobased CaO. The findings of this study demonstrated that eggshells can be used in place of limestone and could be a more sustainable, renewable, and cost-effective source for material development and other applications.

Single-Atoms on Crystalline Carbon Nitrides for Selective C─H Photooxidation: A Bridge to Achieve Homogeneous Pathways in Heterogeneous Materials

Single-atom catalysis is a field of paramount importance in contemporary science due to its exceptional ability to combine the domains of homogeneous and heterogeneous catalysis. Iron and manganese metalloenzymes are known to be effective in C─H oxidation reactions in nature, inspiring scientists to mimic their active sites in artificial catalytic systems. Herein, a simple and versatile cation exchange method is successfully employed to stabilize low-cost iron and manganese single-atoms in poly(heptazine imides) (PHI). The resulting materials are employed as photocatalysts for toluene oxidation, demonstrating remarkable selectivity toward benzaldehyde. The protocol is then extended to the selective oxidation of different substrates, including (substituted) alkylaromatics, benzyl alcohols, and sulfides. Detailed mechanistic investigations revealed that iron- and manganese-containing photocatalysts work through a similar mechanism via the formation of high-valent M═O species. Operando X-ray absorption spectroscopy (XAS) is employed to confirm the formation of high-valent iron- and manganese-oxo species, typically found in metalloenzymes involved in highly selective C─H oxidations.

TiO2 Phase Ratio's Contribution to the Photocatalytic Activity

Photocatalysis is one of the approaches for solving environmental issues derived from extremely harmful pollution caused by industrial dyes, medicine, and heavy metals. Titanium dioxide is among the most promising photocatalytic semiconductors; thus, in this work, TiO2 powders were prepared by a hydrothermal synthesis using titanium tetrachloride TiCl4 as a Ti source. The effect of the hydrochloric acid (HCl) concentration on TiO2 formation was analyzed, in which a thorough morpho-structural analysis was performed employing different analysis methods like XRD, Raman spectroscopy, SEM/TEM, and N2 physisorption. EPR spectroscopy was employed to characterize the paramagnetic defect centers and the photogeneration of reactive oxygen species. Photocatalytic properties were tested by photocatalytic degradation of the rhodamine B (RhB) dye under UV light irradiation and using a solar simulator. The pH value directly influenced the formation of the TiO2 phases; for less acidic conditions, the anatase phase of TiO2 crystallized, with a crystallite size of ≈9 nm. Promising results were observed for TiO2, which contained 76% rutile, showing a 96% degradation of RhB under the solar simulator and 91% under UV light after 90 min irradiation, and the best result showed that the sample with 67% of the anatase phase after 60 min irradiation under the solar simulator had a 99% degradation efficiency.

Dioxygen concentration-dependent selective hydroxysulfonylation of olefins by rose bengal-sensitized photocatalysis

The synthesis of β-hydroxysulfones selectively in preference to β-ketosulfones by dye-sensitized photocatalysis is demonstrated by employing inexpensive and readily available olefins and sulfonyl hydrazides/N-hydroxy sulfonamides in the presence of oxygen. The facile hydroxysulfonylation reaction, which involves the use of rose bengal (RB) as a photocatalyst and dioxygen as an oxidant, permits access selectively to secondary and tertiary β-hydroxysulfones in good to excellent isolated yields at rt and is compatible with aryl, heteroaryl and alkyl sulfonyl hydrazides. Mechanistically, sulfonyl radicals are generated by a cascade of redox reactions, set off by the photocatalyst RB, between sulfonyl hydrazide and dioxygen. Attack of the sulfonyl radicals on olefins followed by oxygenation of the radical intermediates leads to hydroxysulfonylation products selectively without the requirement of a metal catalyst/additive/reductant/base, conforming to the tenets of sustainable chemistry. It is shown that the formations of β-hydroxysulfones and β-ketosulfones proceed concurrently through two different routes and that the outcome is crucially dependent on oxygen concentration with the former being formed predominantly under an oxygen atmosphere, a feature that is heretofore unprecedented to the best of our knowledge.

Revealing the intrinsic peroxidase-like catalytic mechanism of O-doped CoS2 nanoparticles

CoS2 nanoparticles (NPs) have shown promise as potential peroxidase (POD)-like catalysts, but the catalytic molecular mechanisms are largely unknown. Moreover, no study has adequately explored the influence of O-doping induced by the inevitable oxidation of CoS2 on their POD-like activity. Here, O-doped CoS2 NPs were prepared by a one-step method, and their intrinsic POD-like catalytic mechanism was investigated with a combined experimental and theoretical approach. The hydroxyl radical (˙OH) and the superoxide radical (O2˙-) have been found to play significant roles in the POD-like activity, and ˙OH is the major radical. The O-doping could reduce the transition-state energy barrier of H2O2 dissociation, thus promoting the decomposition of H2O2 to ˙OH and inducing the formation of O2˙-. Therefore, O-doping is an effective method for enhancing the catalytic activity of CoS2 NPs. Furthermore, due to the excellent oxidation property of ˙OH and O2˙-, this nanozyme exhibited efficient catalytic activity towards the degradation of organic dyes with H2O2. This manuscript provides a new inspiration for designing more promising anion-defective transition-metal sulfide nanozymes for different applications.

Resolving the Mechanism for H2O2 Decomposition over Zr(IV)-Substituted Lindqvist Tungstate: Evidence of Singlet Oxygen Intermediacy

The decomposition of hydrogen peroxide (H2O2) is the main undesired side reaction in catalytic oxidation processes of industrial interest that make use of H2O2 as a terminal oxidant, such as the epoxidation of alkenes. However, the mechanism responsible for this reaction is still poorly understood, thus hindering the development of design rules to maximize the efficiency of catalytic oxidations in terms of product selectivity and oxidant utilization efficiency. Here, we thoroughly investigated the H2O2 decomposition mechanism using a Zr-monosubstituted dimeric Lindqvist tungstate, (Bu4N)6[{W5O18Zr(μ-OH)}2] ({ZrW5}2), which revealed high activity for this reaction in acetonitrile. The mechanism of the {ZrW5}2-catalyzed H2O2 degradation in the absence of an organic substrate was investigated using kinetic, spectroscopic, and computational tools. The reaction is first order in the Zr catalyst and shows saturation behavior with increasing H2O2 concentration. The apparent activation energy is 11.5 kcal·mol-1, which is significantly lower than the values previously found for Ti- and Nb-substituted Lindqvist tungstates (14.6 and 16.7 kcal·mol-1, respectively). EPR spectroscopic studies indicated the formation of superoxide radicals, while EPR with a specific singlet oxygen trap, 2,2,6,6-tetramethylpiperidone (4-oxo-TEMP), revealed the generation of 1O2. The interaction of test substrates, α-terpinene and tetramethylethylene, with H2O2 in the presence of {ZrW5}2 corroborated the formation of products typical of the oxidation processes that engage 1O2 (endoperoxide ascaridole and 2,3-dimethyl-3-butene-2-hydroperoxide, respectively). While radical scavengers tBuOH and p-benzoquinone produced no effect on the peroxide product yield, the addition of 4-oxo-TEMP significantly reduced it. After optimization of the reaction conditions, a 90% yield of ascaridole was attained. DFT calculations provided an atomistic description of the H2O2 decomposition mechanism by Zr-substituted Lindqvist tungstate catalysts. Calculations showed that the reaction proceeds through a Zr-trioxidane [Zr-η2-OO(OH)] key intermediate, whose formation is the rate-determining step. The Zr-substituted POM activates heterolytically a first H2O2 molecule to generate a Zr-peroxo species, which attacks nucleophilically to a second H2O2, causing its heterolytic O-O cleavage to yield the Zr-trioxidane complex. In agreement with spectroscopic and kinetic studies, the lowest-energy pathway involves dimeric Zr species and an inner-sphere mechanism. Still, we also found monomeric inner- and outer-sphere pathways that are close in energy and could coexist with the dimeric one. The highly reactive Zr-trioxidane intermediate can evolve heterolytically to release singlet oxygen and also decompose homolytically, producing superoxide as the predominant radical species. For H2O2 decomposition by Ti- and Nb-substituted POMs, we also propose the formation of the TM-trioxidane key intermediate, finding good agreement with the observed trends in apparent activation energies.

Achieving High Selectivity in Photocatalytic Oxidation of Toluene on Amorphous BiOCl Nanosheets Coupled with TiO2

The inert C(sp³)-H bond and easy overoxidation of toluene make the selective oxidation of toluene to benzaldehyde a great challenge. Herein, we present that a photocatalyst, constructed with a small amount (1 mol %) of amorphous BiOCl nanosheets assembled on TiO₂ (denoted as 0.01BOC/TiO₂), shows excellent performance in toluene oxidation to benzaldehyde, with 85% selectivity at 10% conversion, and the benzaldehyde formation rate is up to 1.7 mmol g^-1 h^-1, which is 5.6 and 3.7 times that of bare TiO₂ and BOC, respectively. In addition to the charge separation function of the BOC/TiO₂ heterojunction, we found that the amorphous structure of BOC endows its abundant surface oxygen vacancies (Ov), which can further promote the charge separation. Most importantly, the surface Ov of amorphous BOC can efficiently adsorb and activate O₂, and amorphous BOC makes the product, benzaldehyde, easily desorb from the catalyst surface, which alleviates the further oxidation of benzaldehyde, and results in the high selectivity. This work highlights the importance of the microstructure based on heterojunctions, which is conducive to the rational design of photocatalysts with high performance in organic synthesis.

Viral inactivation using microwave-enhanced membrane filtration

Pathogenic viruses (e.g., Enteroviruses, Noroviruses, Rotaviruses, and Adenovirus) present in wastewater, even at low concentrations, can cause serious waterborne diseases. Improving water treatment to enhance viral removal is of paramount significance, especially given the COVID-19 pandemic. This study incorporated microwave-enabled catalysis into membrane filtration and evaluated viral removal using a model bacteriophage (MS2) as a surrogate. Microwave irradiation effectively penetrated the PTFE membrane module and enabled surface oxidation reactions on the membrane-coated catalysts (i.e., BiFeO₃), which thus elicited strong germicidal effects via local heating and radical formation as reported previously. A log removal of 2.6 was achieved for MS2 within a contact time as low as 20 s using 125-W microwave irradiation with the initial MS2 concentration of 10⁵ PFU∙mL^-1. By contrast, almost no inactivation could be achieved without microwave irradiation. COMSOL simulation indicates that the catalyst surface could be heated up to 305 ^oC with 125-W microwave irradiation for 20 s and also analyzed microwave penetration into catalyst or water film layers. This research provides new insights to the antiviral mechanisms of this microwave-enabled catalytic membrane filtration.

Photocatalytic removal of 2-chlorophenol from water by using waste eggshell-derived calcium ferrite

A new approach to recycling low-value eggshell food waste was to produce a CaFe₂O₄ semiconductor with a narrow band gap (E_g = 2.81 eV) via hydrothermal treatments of powdered eggshell suspended in aqueous ferric salt (Fe³⁺) solutions at varying Fe loadings. It was possible to obtain a single phase of CaFe₂O₄ without any Ca(OH)₂ and CaO impurities using an optimal Fe loading (30 wt% of Fe³⁺ by eggshell weight). The CaFe₂O₄ material was used as a photocatalyst for the breakdown of 2-chlorophenol (2-CP, a herbicide model chemical) as a pollutant in water. The CaFe₂O₄ with a Fe loading of 7.1 wt% exhibited a high 2-CP removal efficiency of 86.1% after 180 min of UV-visible light irradiation. Additionally, the eggshell-derived CaFe₂O₄ photocatalyst can be effectively reused, giving a high removal efficiency of 70.5% after the third cycle, without the requirement of regeneration processes (washing or re-calcination). Although radical trapping experiments confirmed that hydroxyl radicals were generated in the photocatalytic reactions, photogenerated holes play a significant role in the high 2-CP degradation efficiencies. The performance of the bioderived CaFe₂O₄ photocatalysts in the removal of pesticides from water demonstrated the benefits of resource recycling in the area of materials science and in environmental remediation and protection.

Targeting Pathogenic Formate-Dependent Bacteria with a Bioinspired Metallo-Nitroreductase Complex

Nitroreductases (NTRs) constitute an important class of oxidoreductase enzymes that have evolved to metabolize nitro-containing compounds. Their unique characteristics have spurred an array of potential uses in medicinal chemistry, chemical biology, and bioengineering toward harnessing nitro caging groups and constructing NTR variants for niche applications. Inspired by how they carry out enzymatic reduction via a cascade of hydride transfer reactions, we sought to develop a synthetic small-molecule NTR system based on transfer hydrogenation mediated by transition metal complexes harnessing native cofactors. We report the first water-stable Ru-arene complex capable of selectively and fully reducing nitroaromatics into anilines in a biocompatible buffered aqueous environment using formate as the hydride source. We further demonstrated its application to activate nitro-caged sulfanilamide prodrug in formate-abundant bacteria, specifically pathogenic methicillin-resistant Staphylococcus aureus. This proof of concept paves the way for a new targeted antibacterial chemotherapeutic approach leveraging on redox-active metal complexes for prodrug activation via bioinspired nitroreduction.

Photoinduced Dynamics at the Water/TiO_{2}(101) Interface

We present a femtosecond time-resolved optical pump-soft x-ray probe photoemission study in which we follow the dynamics of charge transfer at the interface of water and anatase TiO_{2}(101). By combining our observation of transient oxygen O 1s core level peak shifts at submonolayer water coverages with Ehrenfest molecular dynamics simulations we find that ultrafast interfacial hole transfer from TiO_{2} to molecularly adsorbed water is completed within the 285 fs time resolution of the experiment. This is facilitated by the formation of a new hydrogen bond between an O_{2c} site at the surface and a physisorbed water molecule. The calculations fully corroborate our experimental observations and further suggest that this process is preceded by the efficient trapping of the hole at the surface of TiO_{2} by hydroxyl species (-OH), that form following the dissociative adsorption of water. At a water coverage exceeding a monolayer, interfacial charge transfer is suppressed. Our findings are directly applicable to a wide range of photocatalytic systems in which water plays a critical role.

Extrinsic Point Defects in TiO2-Acetylacetone Charge-Transfer Complex and Their Effects on Optical and Photochemical Properties

TiO₂-based visible-light-sensitive nanomaterials are widely studied for photocatalytic applications under UV-Vis radiation. Among the mechanisms of visible-light sensitization, extrinsic oxygen vacancies have been introduced into TiO₂ and charge-transfer complexes (CTCs) have been formed between chelating ligands, such as acetylacetone, and nanocrystalline TiO₂ (TiO₂-ACAC). However, the influence of extrinsic oxygen vacancies on the photocatalytic performance of TiO₂-based CTCs is unknown. In this work, surface/bulk extrinsic oxygen vacancies were introduced into TiO₂-ACAC through calcination at 270 °C under static air, argon, and hydrogen atmospheres. TiO₂-ACAC CTCs were characterized by X-ray powder diffraction, thermogravimetric analysis, diffuse-reflectance spectroscopy, photoluminescence, electron paramagnetic resonance (EPR), and X-ray photoelectron spectroscopy techniques. The correlation between EPR-spin trapping and tetracycline (TC) photodegradation, using scavengers, highlighted the key role of the superoxide radical in TC degradation by TiO₂-ACAC CTCs under low-power visible-light radiation. The increased extrinsic oxygen vacancies concentration was not beneficial for the photocatalytic performance of TiO₂ CTCs, since bulk extrinsic oxygen vacancies additionally act as recombination centers. In fact, the TiO₂-ACAC CTC with the lowest extrinsic oxygen vacancies concentration exhibited the highest photocatalytic performance for TC degradation due to an adequate distribution of extrinsic bulk oxygen vacancies, which led to the trapped electrons undergoing repeated hopping, reducing the recombination rates and improving the efficiency in superoxide radicals production. Our findings indicated that TiO₂-ACAC CTCs are able to degrade pollutants via interactions with electronic holes and principally superoxide radicals and also, provided fundamental information about the influence of surface/bulk extrinsic oxygen vacancies on the photocatalytic performance, lattice parameters, and optical and photochemical properties of TiO₂-based CTCs.

Characterization of a Novel Amphiphilic Cationic Chlorin Photosensitizer for Photodynamic Applications

A novel amphiphilic cationic chlorin e₆ derivative was investigated as a promising photosensitizer for photodynamic therapy. Two cationic -N(CH₃)₃⁺ groups on the periphery of the macrocycle provide additional hydrophilization of the molecule and ensure its electrostatic binding to the mitochondrial membranes and bacterial cell walls. The presence of a hydrophobic phytol residue in the same molecule results in its increased affinity towards the phospholipid membranes while decreasing its stability towards aggregation in aqueous media. In organic media, this chlorin e₆ derivative is characterized by a singlet oxygen quantum yield of 55%. Solubilization studies in different polymer- and surfactant-based supramolecular systems revealed the effective stabilization of this compound in a photoactive monomolecular form in micellar nonionic surfactant solutions, including Tween-80 and Cremophor EL. A novel cationic chlorin e₆ derivative also demonstrates effective binding towards serum albumin, which enhances its bioavailability and promotes effective accumulation within the target tissues. Laser confocal scanning microscopy demonstrates the rapid intracellular accumulation and distribution of this compound throughout the cells. Together with low dark toxicity and a rather good photostability, this compound demonstrates significant phototoxicity against HeLa cells causing cellular damage most likely through reactive oxygen species generation. These results demonstrate a high potential of this derivative for application in photodynamic therapy.

Luminescence, Paramagnetic, and Electrochemical Properties of Copper Oxides-Decorated TiO2/Graphene Oxide Nanocomposites

The properties of newly synthesized Cu₂O/CuO-decorated TiO₂/graphene oxide (GO) nanocomposites (NC) were analyzed aiming to obtain insight into their photocatalytic behavior and their various applications, including water remediation, self-cleaning surfaces, antibacterial materials, and electrochemical sensors. The physico-chemical methods of research were photoluminescence (PL), electron paramagnetic resonance (EPR) spectroscopy, cyclic voltammetry (CV), and differential pulse voltammetry (DPV). The solid samples evidenced an EPR signal that can be attributed to the oxygen-vacancy defects and copper ions in correlation with PL results. Free radicals generated before and after UV-Vis irradiation of powders and aqueous dispersions of Cu₂O/CuO-decorated TiO₂/GO nanocomposites were studied by EPR spectroscopy using two spin traps, DMPO (5,5-dimethyl-1-pyrroline-N-oxide) and CPH (1-hydroxy-3-carboxy-2,2,5,5-tetramethylpyrrolidine), to highlight the formation of hydroxyl and superoxide reactive oxygen species, respectively. The electrochemical characterization of the NC modified carbon-paste electrodes (CPE) was carried out by CV and DPV. As such, modified carbon-paste electrodes were prepared by mixing carbon paste with copper oxides-decorated TiO₂/GO nanocomposites. We have shown that GO reduces the recombination process in TiO₂ by immediate electron transfer from excited TiO₂ to GO sheets. The results suggest that differences in the PL, respectively, EPR data and electrochemical behavior, are due to the different copper oxides and GO content, presenting new perspectives of materials functionalization.

Detection of radicals produced during electro-oxidation of atrazine using commercial DSA®-Cl2 in methanol media: Keys to understand the process

This work reports the radicals detected and identified during the degradation of atrazine in methanol medium in the presence and absence of different proportions of water (0%, 5%, and 10%). The determination of these radicals is an important step to understand the electrolysis processes in methanol medium and contribute to clarify the degradation mechanism. Furthermore, the parameters for the successful removal of the contaminant were optimized and the results showed that the application of the technique led to the removal of nearly 99.8% of atrazine after 1 h of electrolysis. The oxidation kinetics was found to be very fast and most of the atrazine molecule in the medium was degraded in the first hour of electrolysis. The results obtained from a thorough analysis conducted with a view to evaluating the effects of different current densities and initial pH values on atrazine degradation showed that the application of higher current densities resulted in lower energy consumption, as this led to faster removal of atrazine. Additionally, the initial pH of the solution was found to favor the formation of different species of active chlorine. The radicals formed during the electro-oxidation process were detected by electron paramagnetic resonance spectroscopy and include hydroxyl, methoxy and hydroxymethyl. The use of methanol for the degradation of pollutants is a highly promising technique and this work shows that the identification of the different radicals formed in the process can be the key to understanding the degradation mechanism.

Photocatalytic co-production of hydrogen gas and N-benzylidenebenzylamine over high-quality 2D layered In4/3P2Se6 nanosheets

The concurrent photocatalytic synthesis of hydrogen gas and high-valued chemicals over two-dimensional semiconductors is extremely attractive to alleviate global energy and environmental concerns through directly using sunlight. Herein, a novel layered In_4/3P₂Se₆ nanosheet is synthesized by a space confined chemical vapor conversion method, and it acts as a dual-functional photocatalyst to deliver the co-production of hydrogen gas and N-benzylidenebenzylamine from water reduction and selective benzylamine oxidation. The simultaneous yield of hydrogen gas and N-benzylidenebenzylamine is 895 μmol g^-1 and 681 μmol g^-1, respectively, within 16-hour continuous reaction involving a small amount of water in acetonitrile solvent. Moreover, 97.4% N-benzylidenebenzylamine selectivity from benzylamine oxidation can be achieved with continuous 10 hour-reaction only in acetonitrile solvent under ambient conditions. Further in situ electron paramagnetic resonance measurements and reaction optimization tests reveal that the reaction mechanism strongly relies on the conditions over the In_4/3P₂Se₆ nanosheet photocatalyst.

Role of persistent free radicals and lewis acid sites in visible-light-driven wet peroxide activation by solid acid biochar catalysts - A mechanistic study

We report the synthesis of H₂SO₄-modified biochars (SBCs) as solid-acid catalysts to activate H₂O₂ at circumneutral pH under visible light radiation. Spent coffee grinds were pyrolyzed with TiO₂ at 300, 500 and 600 °C followed by steeping in 5 M H₂SO₄ and were used for the Fenton-like degradation of methyl orange (MO). The catalytic activity of SBC depended on the pyrolysis temperature and correlated well with the surface acidity and persistent free radical (PFR) concentration. Results showed that a complete MO removal and a TOC reduction of 70.2% can be achieved with SBC500 under photo-Fenton conditions. However, poisoning of the Lewis acid sites on SBC by PO₄^3- led to a dramatic decrease in the removal of MO with inhibition effects more pronounced than with radical scavengers, suggesting the key role played by acid-sites on the activation of H₂O₂. Finally, electron paramagnetic resonance (EPR) studies identified •OH as the key transient in the degradation followed by •O₂^- and ¹O₂. These findings suggest that H₂O₂ was likely adsorbed on the surface oxygenated functional groups before being decomposed by accepting electrons from the PFRs on the SBC surface.

Photocatalytic Biocidal Coatings Featuring Zr6Ti4-Based Metal-Organic Frameworks

The world is currently suffering socially, economically, and politically from the recent pandemic outbreak due to the coronavirus disease 2019 (COVID-19), and those in hospitals, schools, and elderly nursing homes face enhanced threats. Healthcare textiles, such as masks and medical staff gowns, are susceptible to contamination of various pathogenic microorganisms, including bacteria and viruses. Metal-organic frameworks (MOFs) can potentially address these challenges due to their tunable reactivity and ability to be incorporated as porous coatings on textile materials. Here, we report how incorporating titanium into the zirconium-pyrene-based MOF NU-1000, denoted as NU-1012, generates a highly reactive biocidal photocatalyst. This MOF features a rare ligand migration phenomenon, and both the Ti/Zr center and the pyrene linker act synergistically as dual active centers and widen the absorption band for this material, which results in enhanced reactive oxygen species generation upon visible light irradiation. Additionally, we found that the ligand migration process is generally applicable to other csq topology Zr-MOFs. Importantly, NU-1012 can be easily incorporated onto cotton textile cloths as a coating, and the resulting composite material demonstrates fast and potent biocidal activity against Gram-negative bacteria (Escherichia coli), Gram-positive bacteria (Staphylococcus epidermidis), and T7 bacteriophage virus with up to a 7-log(99.99999%) reduction within 1 h under simulated daylight.

Magnetic visible-light activated photocatalyst ZnFe2O4/BiVO4/g-C3N4 for decomposition of antibiotic lomefloxacin: Photocatalytic mechanism, degradation pathway, and toxicity assessment

Magnetic ZnFe₂O₄/BiVO₄/g-C₃N₄ (ZBC) composites were prepared via a facile hydrothermal and calcination method for the degradation of a representative antibiotics lomefloxacin (LFX) under visible light irradiation. The optimal photocatalyst ZBC-10 with a ZnFe₂O₄:BiVO₄:g-C₃N₄ mass ratio of 1:8:10 performed 96.1% removal of LFX after 105 min of illumination. The excellent performance is ascribed to the effective construction of heterojunctions and its capacity to form a double Z-scheme charge transmission pathway among the hosts in ZBC-10. The composite enhanced the separation and migration of photoexcited charge carriers and the effective generation of multiple active radicals including ·OH, ·O₂^-, and ¹O₂. The LFX degradation process, identified based on an integrated HPLC-Q-TOF-MS analysis and density functional theory computation of the Fukui indices, comprised of three pathways initiated by the opening of the piperazinyl ring, separation of piperazinyl and quinoline moieties, and cleavage of the pyridine ring on the quinoline moieties. Ecotoxicological evaluation confirmed the reduced toxicity of transformation intermediates over photocatalysis. Convenient magnetic recovery, high performance, and high recyclability made ZBC-10 a promising visible-light-activated photocatalyst for practical implementation in eliminating antibiotics from wastewater.

Photoreduction of carbon dioxide and photodegradation of organic pollutants using alkali cobalt oxides MCoO2 (M = Li or Na) as catalysts

The recycling of lithium batteries should be prioritized, and the use of discarded alkali metal battery electrode materials as photocatalysts merits research attention. This study synthesized alkali metal cobalt oxide (MCoO₂, M = Li or Na) as a photocatalyst for the photoreduction of CO₂ and degradation of toxic organic substances. The optimized NaCoO₂ and LiCoO₂ photocatalysts increased the photocatalytic CO₂-CH₄ conversion rate to 21.0 and 13.4 μmol g^-1 h^-1 under ultraviolet light irradiation and to 16.2 and 5.3 μmol g^-1 h^-1 under visible light irradiation, which is 17 times higher than that achieved by TiO₂ P25. The rate constants of the optimized reactions of crystal violet (CV) with LiCoO₂ and NaCoO₂ were 2.29 × 10^-2 and 4.35 × 10^-2 h^-1, respectively. The quenching effect of the scavengers and electron paramagnetic resonance in CV degradation indicated that active O₂^•-, ¹O₂, and h⁺ play the main role, whereas ^•OH plays a minor role for LiCoO₂. The hyperfine splitting of the DMPO-^•OH and DMPO-^•CH₃ adducts was a_N = 1.508 mT, a_Hβ = 1.478 mT and a_N = 1.558 mT, a_Hβ = 2.267 mT, respectively, whereas the hyperfine splitting of DMPO^+• was a_N = 1.475 mT. The quenching effect also indicated that active O₂^•- and h⁺ play the main role and that ^•OH and ¹O₂ play a minor role for NaCoO₂. The hyperfine splitting of the DMPO-^•OH and DMPO^+• adducts was a_N = 1.517 mT, a_Hβ = 1.489 mT and a_N = 1.496 mT, respectively. Discarded alkali metal battery electrode materials can be reused as photocatalysts to address environmental pollution.

Elucidation of Structure-Activity Relationships in Indolobenzazepine-Derived Ligands and Their Copper(II) Complexes: the Role of Key Structural Components and Insight into the Mechanism of Action

Indolo[3,2-d][1]benzazepines (paullones), indolo[3,2-d][2]benzazepines, and indolo[2,3-d][2]benzazepines (latonduines) are isomeric scaffolds of current medicinal interest. Herein, we prepared a small library of novel indolo[3,2-d][2]benzazepine-derived ligands HL¹-HL⁴ and copper(II) complexes 1-4. All compounds were characterized by spectroscopic methods (¹H and ¹³C NMR, UV-vis, IR) and electrospray ionization (ESI) mass spectrometry, while complexes 2 and 3, in addition, by X-ray crystallography. Their purity was confirmed by HPLC coupled with high-resolution ESI mass spectrometry and/or elemental analysis. The stability of compounds in aqueous solutions in the presence of DMSO was confirmed by ¹H NMR and UV-vis spectroscopy measurements. The compounds revealed high antiproliferative activity in vitro in the breast cancer cell line MDA-MB-231 and hepatocellular carcinoma cell line LM3 in the low micromolar to nanomolar concentration range. Important structure-activity relationships were deduced from the comparison of anticancer activities of HL¹-HL⁴ and 1-4 with those of structurally similar paullone-derived (HL⁵-HL⁷ and 5-7) and latonduine-derived scaffolds (HL⁸-HL¹¹ and 8-11). The high anticancer activity of the lead drug candidate 4 was linked to reactive oxygen species and endoplasmic reticulum stress induction, which were confirmed by fluorescent microscopy and Western blot analysis.

Hydroxyl radicals in anodic oxidation systems: generation, identification and quantification

Anodic oxidation has emerged as a promising treatment technology for the removal of a broad range of organic pollutants from wastewaters. Hydroxyl radicals are the primary species generated in anodic oxidation systems to oxidize organics. In this review, the methods of identifying hydroxyl radicals and the existing debates and misunderstandings regarding the validity of experimental results are discussed. Consideration is given to the methods of quantification of hydroxyl radicals in anodic oxidation systems with particular attention to approaches used to compare the electrochemical performance of different anodes. In addition, we describe recent progress in understanding the mechanisms of hydroxyl radical generation at the surface of most commonly used anodes and the utilization of hydroxyl radical in typical electrochemical reactors. This review shows that the key challenges facing anodic oxidation technology are related to i) the elimination of mistakes in identifying hydroxyl radicals, ii) the establishment of an effective hydroxyl radical quantification method, iii) the development of cost effective anode materials with high corrosion resistance and high electrochemical activity and iv) the optimization of electrochemical reactor design to maximise the utilization efficiency of hydroxyl radicals.

Self-redox reaction driven in situ formation of Cu2O/Ti3C2Tx nanosheets boost the photocatalytic eradication of multi-drug resistant bacteria from infected wound

BACKGROUND

MXenes with interesting optical and electrical properties have been attractive in biomedical applications such as antibacterial and anticancer agents, but their low photogeneration efficiency of reactive oxygen species (ROS) and poor stability are major concerns against microbial resistance.

METHODS

Water-dispersible single layer Ti₃C₂T_x-based MXene through etching tightly stacked MAX phase precursor using a minimally intensive layer delamination method. After addition of Cu(II) ions, the adsorbed Cu(II) ions underwent self-redox reactions with the surface oxygenated moieties of MXene, leading to in situ formation of Cu₂O species to yield Cu₂O/Ti₃C₂T_x nanosheets (heterostructures).

RESULTS

Under NIR irradiation, the Cu₂O enhanced generation of electron-hole pairs, which boosted the photocatalytic production of superoxide and subsequent transformation into hydrogen peroxide. Broad-spectrum antimicrobial performance of Cu₂O/Ti₃C₂T_x nanosheets with sharp edges is attributed to the direct contact-induced membrane disruption, localized photothermal therapy, and in situ generated cytotoxic free radicals. The minimum inhibitory concentration of Cu₂O/Ti₃C₂T_x nanosheets reduced at least tenfold upon NIR laser irradiation compared to pristine Cu₂O/Ti₃C₂T_x nanosheets. The Cu₂O/Ti₃C₂T_x nanosheets were topically administrated on the methicillin-resistant Staphylococcus aureus (MRSA) infected wounds on diabetic mice.

CONCLUSION

Upon NIR illumination, Cu₂O/Ti₃C₂T_x nanosheets eradicated MRSA and their associated biofilm to promote wound healing. The Cu₂O/Ti₃C₂T_x nanosheets with superior catalytic and photothermal properties have a great scope as an effective antimicrobial modality for the treatment of infected wounds.

Modulating Electron Transfer in Vanadium-Based Artificial Enzymes for Enhanced ROS-Catalysis and Disinfection

Nanomaterials-based artificial enzymes (AEs) have flourished for more than a decade. However, it is still challenging to further enhance their biocatalytic performances due to the limited strategies to tune the electronic structures of active centers. Here, a new path is reported for the de novo design of the d electrons of active centers by modulating the electron transfer in vanadium-based AEs (VO_x -AE) via a unique Zn-O-V bridge for efficient reactive oxygen species (ROS)-catalysis. Benefiting from the electron transfer from Zn to V, the V site in VO_x -AE exhibits a lower valence state than that in V₂ O₅ , which results in charge-filled V-d_yz orbital near the Fermi level to interfere with the formation of sigma bonds between the V- d z 2 and O-p_z orbitals in H₂ O₂ . The VO_x -AE exhibits a twofold V_max and threefold turnover number than V₂ O₅ when catalyzing H₂ O₂ . Meanwhile, the VO_x -AE shows enhanced catalytic eradication of drug-resistant bacteria and achieves comparable wound-treatment indexes to vancomycin. This modulating charge-filling of d electrons provides a new direction for the de novo design of nanomaterials-based AEs and deepens the understanding of ROS-catalysis.

Fabrication of TiO2/NiO p-n Nanocomposite for Enhancement Dye Photodegradation under Solar Radiation

A p-n nanocomposite based on TiO₂ nanotubes (NTs) and NiO nanoparticles (NPs) was designed and optimized in this study to improve the photocatalytic performance of methylene blue (MB). The hydrothermal technique has been used to produce TiO₂/NiO nanocomposites with different NiO NPs weight ratios; 1TiO₂:1NiO, 1TiO₂:2NiO, and 1TiO₂:3NiO. The crystal phase, chemical composition, optical properties, and morphology of TiO₂/NiO were explored by various techniques. TiO₂ NTs have a monoclinic structure, while NiO NPs have a cubic structure, according to the structural study. The bandgap of TiO₂ NTs was reduced from 3.54 eV to 2.69 eV after controlling the NiO NPs weight ratio. The TiO₂/2NiO nanocomposite showed the best photodegradation efficiency. Within 45 min of solar light irradiation, the efficiency of MB dye degradation using TiO₂/2NiO hits 99.5% versus 73% using pure TiO₂ NTs. Furthermore, the catalytic photodegradation efficiency did not deteriorate significantly even after five reusability cycles, intimating the high stability of the TiO₂/2NiO nanocomposite. This suggests that the loading of NiO NPs into TiO₂ NTs lowers the recombination of photo-produced electron/hole pairs and enlarged solar spectral response range, which results in improved photocatalytic activity. The mechanism of charge transfer in the TiO₂/NiO and kinetic models were discussed for the photodegradation of MB.

Insights into the mechanism of low-temperature H2S oxidation over Zn-Cu/Al2O3 catalyst

Odor pollution caused by toxic chemicals with low human olfactory thresholds, such as hydrogen sulfide (H₂S), has become a major cause of environmental grievance world-wide. Although the low-temperature (<180 °C) catalytic oxidation of H₂S using metal oxides has received widespread attention, desulfurization performance is not ideal. Herein, a series of Zn-Cu/Al₂O₃ catalysts were developed using an impregnation method based on the Al₂O₃ hydrophilicity and the effects of zinc loading on the catalyst physicochemical properties and performance were systematically studied. The catalysts were characterized using inductively coupled plasma-optical emission spectrometry (ICP-OES), N₂ adsorption-desorption isotherms, scanning electron microscopy with energy dispersive spectrometry (SEM-EDS), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Fourier-transform infrared spectroscopy (FTIR) and electron paramagnetic resonance (EPR). It was found that optimization of zinc doping could improve the hydrophilicity of the catalyst, and hence its activity. Catalytic activity was also dependent on operational parameters such as temperature, humidity and space velocity. The Zn₃Cu₃ catalyst exhibited the highest breakthrough capacity of 353.91 mg/g at 50 °C and at a relative humidity of 50%. The excellent desulfurization performance was attributed to oxygen vacancies contributed by CuO, Cu₂O and ZnO, which facilitated the conversion of H₂O into hydroxyl radicals. Consequently, a hydroxyl radical-induced desulfurization mechanism over Zn-Cu/Al₂O₃ is proposed. This work provides a potential green and efficient catalyst for the selective oxidation of H₂S.

Detection of singlet oxygen by EPR: The instability of the nitroxyl radicals

The use of spin traps and redox probes coupled with electron paramagnetic resonance (EPR) is a method frequently applied in the evaluation of the efficiency of photosensitizers and photocatalysts in phototherapeutic and photocatalytic processes that involve reactive oxygen species. In this way, the method helps to clarify the mechanism behind photo-induced reactions. Hydroxy-TEMP is a very specific redox probe for selectively identifying and quantifying singlet oxygen (¹O₂). In this work, the kinetics of radical generated by the oxidation products of the Hydroxy-TEMP redox probe was analyzed from EPR spectra in aqueous solutions of several water-soluble porphyrins ([H₂T4MPyP](OTs)₄, Na₄[H₂T4SPP], [H₂T2MPyP](OTs)₄, [ZnT4MyPyP](OTs)₄, [MnT4MyPyP](OTs)₅, H₂T4CPP, and [H₂T4TriMAPP](OTs)4) under white light illumination. Different factors such as the concentration of the redox probe, pH of the medium, and photostability of the porphyrins were evaluated. A systematic study was carried out to reveal the factors associated with stable radical degradation (TEMPOL) by illumination in the visible spectral region in systems containing photosensitizer (porphyrin) and redox probe (Hydroxy-TEMP). With the aid of EPR and gas chromatography coupled with mass spectroscopy (GC-MS) techniques, the mechanism of the radical degradation and the photobleaching of porphyrins were investigated. After successive interactions with the porphyrin in its excited state, in alkaline aqueous solution (pH > 10), the free radical TEMPOL is transformed into TEMPONE until the final diamagnetic product Phorone. A protocol was elaborated to identify and quantify the generation of ¹O₂ by Hydroxy-TEMP reliably, to avoid possible errors in the interpretation of efficiency of photosensitizers.

Cu2-x Sx Capped AuCu Nanostars for Efficient Plasmonic Photothermal Tumor Treatment in the Second Near-Infrared Window

Plasmonic nanohybrids are promising photo energy conversion materials in photoelectronics and biomedicine, due to their unique surface plasmon resonance (SPR). Au and Cu_2-x S_x nanostructures with strong SPR in the near-infrared (NIR) spectral region are classic plasmonic systems used to convert NIR photons into heat for photothermal therapy (PTT). The rational design of the Au/Cu_2-x S_x nanohybrids is expected to induce better photothermal conversion; however, the construction of such hybrids via wet-chemistry methods with a well-controlled interfacial structure is still challenging. Here, the synthesis of an AuCu Star/Cu_2-x S_x nanohybrid is reported, where the Cu_2-x S_x components are selectively grown on the AuCu nanostar tips to form "caps". The spatial formation of the Cu_2-x S_x caps on star tips is mainly governed by surfactant concentration, tip curvature, and experimental manipulation. The nanohybrids show low cytotoxicity and superior photothermal conversion efficiency, enabling robust PTT to kill cancer cells in the second NIR window. Numerical simulation reveals that the coupling of Cu_2-x S_x on nanostar tips generates strong interfacial electric field, improving photothermal conversion. Moreover, the spatial separation structure favors the continuous flow of hot charge carriers to produce active radicals, further promoting the tumor treatment effect.

Fabrication of Hydrotalcite-like Copper Hydroxyl Salts as a Photocatalyst and Adsorbent for Hexavalent Chromium Removal

Cu-HyS-urea and Cu-HyS-NaOH, which are hydrotalcite-like copper hydroxyl salts, were prepared by two different methods, urea hydrolysis and precipitation, respectively. Both synthesis methods provided the successful formation of a copper hydroxyl salt, Cu2(OH)3NO3. From XRD and UV-DRS results, the product from the urea hydrolysis methods (Cu-HyS-urea) displayed higher crystallinity, small bandgap energy (Eg), and high light absorption ability because of some intercalated carbonate anions. For the Cr(VI) removal test, the Cu-HyS-NaOH showed superior adsorption of Cr(VI) than Cu-HyS-urea due to a higher specific surface area, confirmed by BET analysis. However, the Cu-HyS-urea presented higher photocatalytic Cr(VI) reduction under light irradiation than Cu-HyS-NaOH, owing to narrow Eg, less recombination, and a high transfer of the photogenerated charge carriers, proven by the results from photoluminescence, photocurrent density, and electrochemical impedance spectroscopy. Thus, this work provides a new function of the hydrotalcite-like copper hydroxyl salts (Cu-HyS-urea and Cu-HyS-NaOH) that can be utilized not only for adsorption of Cr(VI) but also as photocatalysts for Cr(VI) reduction under light irradiation.

Design of a Polyoxometalate-Based Metal-Organic Framework for Photocatalytic C(sp3)-H Oxidation of Toluene

A powerful and promising route for developing novel photocatalysts for light-driven toluene oxidation in water under mild conditions is presented. Herein, a novel polyoxometalate-based metal-organic framework (POMOF), {Co₄W₂₂-DPNDI}, is prepared by incorporating the unusual Co₄-sandwiched POM anion [Co₄(μ-OH)₂(SiW₁₁O₃₉)₂]^10- ({Co₄W₂₂}) and the photoactive organic bridging link N,N'-bis(4-pyridylmethyl)naphthalene diimide (DPNDI) into a framework. {Co₄W₂₂} is a good candidate for photocatalytic water oxidation. DPNDI is easily excited to form the radical species DPNDI* in the presence of an electron donor, which is beneficial for activation of the inert O₂. Anion···π interactions and covalent bonds between {Co₄W₂₂} and DPNDI facilitate electron-hole separation and electron transfer. {Co₄W₂₂-DPNDI} displays high catalytic activity for the activation of the C(sp³)-H bond of toluene using light as a driving force and inexpensive water as an oxygen source under mild conditions. In particular, the yield and selectivity are improved by replacing oxygen with water, which may be ascribed to the release of protons during the water oxidation process that facilitate the generation of ^•OH.

Selective Photocatalytic Activation of Ethanol C-H and O-H Bonds over Multi-Au@SiO2/TiO2: Role of Catalyst Surface Structure and Reaction Kinetics

The chemical bond diversity and flexible reactivity of biomass-derived ethanol make it a vital feedstock for the production of value-added chemicals but result in low conversion selectivity. Herein, composite catalysts comprising SiO₂-coated single- or multiparticle Au cores hybridized with TiO₂ nanoparticles (mono- or multi-Au@SiO₂/TiO₂, respectively) were fabricated via electrostatic self-assembly. The C-H and O-H bonds of ethanol were selectively activated (by SiO₂ and TiO₂, respectively) under irradiation to form CH₃CH^•(OH) or CH₃CH₂O^• radicals, respectively. The formation and depletion kinetics of these radicals was analyzed by electron spin resonance to reveal marked differences between mono- and multi-Au@SiO₂/TiO₂. Consequently, the selectivity of these catalysts for 1,1-diethoxyethane after 6 h irradiation was determined as 81 and 99%, respectively, which was attributed to the more pronounced effect of localized surface plasmon resonance for multi-Au@SiO₂/TiO₂. Notably, only acetaldehyde was formed on a Au/TiO₂ catalyst without a SiO₂ shell. Fourier transform infrared (FTIR) spectroscopy indicated that the C-H adsorption of ethanol was enhanced in the case of multi-Au@SiO₂/TiO₂, while NH₃ temperature-programmed desorption and pyridine adsorption FTIR spectroscopy revealed that multi-Au@SiO₂/TiO₂ exhibited enhanced surface acidity. Collectively, the results of experimental and theoretical analyses indicated that the adsorption of acetaldehyde on multi-Au@SiO₂/TiO₂ was stronger than that on Au/TiO₂, which resulted in the oxidative coupling of ethanol to afford 1,1-diethoxyethane on the former and the dehydrogenation of ethanol to acetaldehyde on the latter.

Electron paramagnetic resonance and spin trapping to detect free radicals from allergenic hydroperoxides in contact with the skin: from the molecule to the tissue

A major research topic consists of revealing the contribution of radical-mediated reactions in dermatological diseases related to xenobiotic-induced stress, to succeed risk assessment procedures protecting producers and consumers. Allergic contact dermatitis is the clinically relevant consequence of skin sensitization, one of the most critical occupational and environmental health issues related to xenobiotics exposure. The first key event identified for the skin sensitization process to a chemical is its aptitude to react with epidermal proteins and form antigenic structures that will further trigger the immune response. Many chemical sensitizers are suspected to react through mechanisms involving radical intermediates. This review focuses on recent progress we have accomplished over the last few years studying radical intermediates derived from skin sensitizing chemicals by electron paramagnetic resonance in combination with the spin trapping technique. Our work is carried out "from the molecule", performing studies in solution, "to the tissue", by the development of a methodology on a reconstructed human epidermis model, very close in terms of histology and metabolic/enzymatic activity to real human epidermis, that can be used as suitable biological tissue model. The benefits are to test chemicals under conditions close to human use and real-life sensitization exposures and benefit from the 3D microenvironment. This article is protected by copyright. All rights reserved.

An organophotocatalytic late-stage N–CH3 oxidation of trialkylamines to N-formamides with O2 in continuous flow

We report an organophotocatalytic, N–CH₃-selective oxidation of trialkylamines in continuous flow. Based on the 9,10-dicyanoanthracene (DCA) core, a new catalyst (DCAS) was designed with solubilizing groups for flow processing. This allowed O₂ to be harnessed as a sustainable oxidant for late-stage photocatalytic N–CH₃ oxidations of complex natural products and active pharmaceutical ingredients bearing functional groups not tolerated by previous methods. The organophotocatalytic gas–liquid flow process affords cleaner reactions than in batch mode, in short residence times of 13.5 min and productivities of up to 0.65 g per day. Spectroscopic and computational mechanistic studies showed that catalyst derivatization not only enhanced solubility of the new catalyst compared to poorly-soluble DCA, but profoundly diverted the photocatalytic mechanism from singlet electron transfer (SET) reductive quenching with amines toward energy transfer (E_nT) with O₂.

An N–CH₃-selective trialkylamine oxidation to N-formamides is reported in continuous flow using gaseous O₂. A novel, enhanced-solubility dicyanoanthracene organophotocatalyst switched the photochemical mechanism from electron to energy transfer.

Contrasting Photochemical Activity of Two Sub-layers for Natural 2D Nanoclay with an Asymmetric Layer Structure

The two-dimensional (2D) materials with asymmetric sub-layers have recently attracted tremendous interest in many fields, and investigating the structure-performance relationship of different sub-layers is critical but challenging. Herein, we report that natural kaolinite (Kaol) nanosheets with an asymmetric layer structure possess a contrasting photocatalytic activity on its Al-O and Si-O sub-layers. The experimental and theoretical results reveal that the ion isovalent structure of Fe³⁺ and Al³⁺ not only results in a high iron doping concentration in the Al-O sub-layer but also causes superb intrinsic photochemical activity of the Al-O sub-layer compared with the Si-O sub-layer. Thus, the Al-O sub-layers of Kaol NSs have more excellent photogenerated charge generation and separation efficiency than Si-O sub-layers, resulting in about 1-2 orders of magnitude higher photocatalytic performance. This study not only unravels the structure-performance relationship of different sub-layers of 2D nanoclay but also sheds new light on the design of 2D materials with the asymmetric sub-layer.

Application of EPR Spectroscopy in TiO2 and Nb2O5 Photocatalysis

The interaction of light with semiconducting materials becomes the center of a wide range of technologies, such as photocatalysis. This technology has recently attracted increasing attention due to its prospective uses in green energy and environmental remediation. The characterization of the electronic structure of the semiconductors is essential to a deep understanding of the photocatalytic process since they influence and govern the photocatalytic activity by the formation of reactive radical species. Electron paramagnetic resonance (EPR) spectroscopy is a unique analytical tool that can be employed to monitor the photoinduced phenomena occurring in the solid and liquid phases and provides precise insights into the dynamic and reactivity of the photocatalyst under different experimental conditions. This review focus on the application of EPR in the observation of paramagnetic centers formed upon irradiation of titanium dioxide and niobium oxide photocatalysts. TiO2 and Nb2O5 are very well-known semiconductors that have been widely used for photocatalytic applications. A large number of experimental results on both materials offer a reliable platform to illustrate the contribution of the EPR studies on heterogeneous photocatalysis, particularly in monitoring the photogenerated charge carriers, trap states, and surface charge transfer steps. A detailed overview of EPR-spin trapping techniques in mechanistic studies to follow the nature of the photogenerated species in suspension during the photocatalytic process is presented. The role of the electron donors or the electron acceptors and their effect on the photocatalytic process in the solid or the liquid phase are highlighted.

Targeted Antibacterial Strategy Based on Reactive Oxygen Species Generated from Dioxygen Reduction Using an Organoruthenium Complex

Pathogenic microorganisms pose a serious threat to global public health due to their persistent adaptation and growing resistance to antibiotics. Alternative therapeutic strategies are required to address this growing threat. Bactericidal antibiotics that are routinely prescribed to treat infections rely on hydroxyl radical formation for their therapeutic efficacies. We developed a redox approach to target bacteria using organotransition metal complexes to mediate the reduction of cellular O₂ to H₂O₂, as a precursor for hydroxyl radicals via Fenton reaction. We prepared a library of 480 unique organoruthenium Schiff-base complexes using a coordination-driven three-component assembly strategy and identified the lead organoruthenium complex Ru1 capable of selectively invoking oxidative stress in Gram-positive bacteria, in particular methicillin-resistant Staphylococcus aureus, via transfer hydrogenation reaction and/or single electron transfer on O₂. This strategy paves the way for a targeted antimicrobial approach leveraging on the redox chemistry of organotransition metal complexes to combat drug resistance.