Lasers Research Articles

Incorporating Si into NiO support to facilitate oxygen activation for CH4 combustion

In this study, high-performance Pd/NiO-Si catalysts for lean methane oxidation were synthesized using the solution combustion and impregnation method. The incorporation of silicon in NiO promoted the generation of Ni2+ and strengthened the metal-support interaction. This enhanced interaction promoted the generation and movement of active oxygen species on surface, which are essential for maintaining Pd species in an active oxidized state, thereby ensuring the effective activation of CH4. The Pd/NiO-Si catalyst with an optimal amount of Si exhibited an excellent catalytic performance, achieving a T90 of 440 °C for methane oxidation under wet conditions. The elemental doping strategy in this study, which significantly enhances the production of highly active oxygen species with strong mobility, plays a crucial role in the effective utilization of precious metals such as Pd.

Enhanced removal of phenolic pollutants over MnO2 initiated by peracetic acid: In situ generation of a heterogeneous Mn(III)-hydroperoxo complex

Widely distributed manganese oxides are among the strongest oxidants in nature and effectively enhance the water decontamination by peracetic acid (PAA) activation. However, the precise mechanism requires further investigation. In this work, the intrinsic mechanism of PAA activation by MnO2 was systematically studied. Through in situ diffuse-reflectance UV–vis spectra and resonance Raman spectra, the active species was identified as a non-radical heterogenous Mn(III)-hydroperoxo complex. During the process, PAA drastically converted Mn(IV) in MnO2 into homogeneous Mn(II), which subsequently generated the active Mn(III) species in the aid of PAA on the surface of MnO2. By interacting with pollutants, the peroxide bond in Mn(III)-hydroperoxo broke, accompanied by the regeneration of Mn(IV). Eight phenolic compounds having para-substituent of –CH3, −H, −Cl, –COCH3, –CHO, –COOH, –COOCH3, and –NO2 were selected for degradation. Due to the electrophilic character of Mn(III)-hydroperoxo, the removal rates were 100 %, 100 %, 98.8 %, 69.8 %, 49.6 %, 30.2 %, 28.1 %, and 3.0 % respectively at the 45 min of experiment. The MnO2/PAA system was also readily coupled with a filtration membrane for continuous treatment of phenol in nearly 100 % removal efficiency. This study not only offered an efficient non-radical PAA activation protocol for water decontamination, but also elucidated the catalytic mechanism and redox cycle of MnO2 in PAA solution in the selective oxidation process.

Cobalt doped MoS2: A photoactivated nanomaterial for removal of methylene blue and phenol

This research work reports the study about synthesis, characterizations and Photocatalytic applications of hydrothermally produced MoS2 and Cobalt doped MoS2 nanomaterials to overcome the environmental pollution caused by wastewater. MB dye and Phenol were used as model pollutants for evaluation of photocatalytic proficiency of MoS2 and Cobalt doped MoS2 nanostructures. The well matched ionic radius of Cobalt with host Mo atom increases their probability regarding alteration of nanomaterial’s optical, structural and catalytic properties. The Cobalt incorporation provided the synergistic effect attributed to efficient degradation up to 96 % and 80 % for MB dye and phenol respectively. Additionally, the prepared samples were characterized to elucidate their optical, electronic and structural properties. Scavenger analysis and reusability test had performed to check the role of active species and stability of optimized sample. This study predicts that the fabrication of Cobalt doped MoS2 can be used as potential and promising photocatalyst for industrial applications for wastewater treatment.

Synergistic Surface Engineering of BiVO4 Photoanodes for Improved Photoelectrochemical Water Oxidation.

Surface engineering of BiVO4 photoanodes is effective and feasible for photoelectrochemical (PEC) water splitting. To achieve superior PEC performance, however, more than one surface engineering method is usually indispensable, for which a positive synergistic effect is vital and thus highly desired. Herein, it is reported that the incorporation of borate moieties into ultrathin p-type NiOx catalysts can induce the reconfiguration of surface catalytic sites to form new highly active species, in addition to enhanced fast charge separation and transfer. The photocurrent density of BiVO4 photoanodes is enhanced from 1.49 to 5.76 mA cm-2 at 1.23 V versus reversible hydrogen electrode (RHE) under AM 1.5G illumination, which is achieved by successive modifications of NiOx and borate moieties. It is found that BO3 groups anchored to Ni atoms by replacing the surface hydroxyl sites of NiOx catalysts not only increase the relative ratio of Ni3+ species to facilitate charge transfer but also provide efficient active sites for H2O molecule adsorption and oxidation reactions. This work demonstrates the positive synergistic effect of these two surface engineering methods and provides an effective pathway to construct highly efficient and stable photoanodes for PEC water splitting.

Co-pyrolyzed biochar derived from microplastics and microalgae as peroxymonosulfate activator: Influence of microplastic types and analysis of systemic causes

This work investigated the catalytic activity of co-pyrolyzed biochar (MP-SBC) from microplastic (MP) and Spirulina biomass and its activation mechanism for peroxymonosulfate (PMS). Given that different types of MPs had varied effects on the properties of biochar, polypropylene (PP), polyvinyl chloride (PVC), polystyrene (PS), and polylactic acid (PLA) were chosen as MP feedstocks. The results showed that the four kinds of MP-SBCs activated PMS more efficiently than the pristine algal-based biochar (SBC), with 100 % of the acetaminophen (ACT) degraded within 20 min. Based on the reaction mechanism analysis, the main pathways for the degradation of ACT by SBC and MP-SBC activated PMS were both non-radical pathways, and ACT was also efficiently degraded by the synergistic effect of 1O2 and electron transport pathway (ETP). Moreover, it was found that the microplastic modification could significantly enhance the efficacy of SBCs in triggering the non-radical pathway. Establishing the correlation between the structural features of BC and the degradation mechanism (active species contribution) revealed that the persistent free radicals (PFRs), defective structures, CO, and graphite N are all potential active sites. Thereinto, PFRs are the active sites for radicals, defects are the active sites for 1O2 production, and CO, defects, and graphitic N are the active sites for ETP. Overall, this work provides an innovative approach for designing efficient biochar-based catalysts for environmental remediation.

Tunable and selective transformation of aromatic thioether enabled by regulating active species under visible light irradiation

Through effective regulation of active species in photocatalytic process, the oxidation or C(sp3)‐S bond cleavage upgrading of widespread aryl alkyl sulfides under mild conditions was successfully achieved by using a pyridinium photocatalyst. Benefiting from the excellent redox ability of the photocatalyst, the electron transfer between the pyridinium molecule and the substrate, molecular oxygen, or counter‐anion effectively promotes the conversion and upgrading of the substrate thioether. Among them, the efficient generation of reactive oxygen species (ROS) enables the highly selective oxidation of sulfides to sulfoxides under visible light and air atmosphere. More importantly, the chlorine radical (Cl•) generated by electron transfer, reported for the first time, contributes to the cleavage of C(sp3)‐S bonds, achieving the transformation of aryl alkyl sulfides to disulfides. By harnessing the superior photocatalytic ability of pyridinium molecules, this work not only achieves the highly selective conversion of thioether by taming the active species in the photocatalytic process, but also sheds light on the untapped potential of chlorine radicals in the field of C(sp3)‐S bond activation and cleavage.

Modulation of the Microstructure and Enhancement of the Photocatalytic Performance of g-C3N4 by Thermal Exfoliation

This work explores the impact of reaction temperature during thermal exfoliation treatment of bulk-g-C3N4 in the air atmosphere on the structure and performance of the resulting CN photocatalyst. The analysis conducted using XRD, FT-IR, XPS, SEM, and elements mapping tests, illustrated an increase in nitrogen-vacancy and oxygen content on the surface of the CN photocatalyst, resulting in a porous and sparse structure, changes in crystal size, and improved visible light absorption performance. The photocatalytic reduction experiments of hexavalent chromium (Cr(VI)) showed that the CN-540 showed the highest reduction rate of 96.9%, with a reaction rate constant 6.21 times that of bulk-g-C3N4. After 100 min of illumination, the photocatalytic degradation rates of CN-540 for TC-HCl and RhB were 66.7% and 60.6%, respectively. The TOC test results indicated mineralization rates of 51.5% for TC-HCl and 46.6% for RhB. Room temperature fluorescence spectroscopy (PL), transient photocurrent response (TPC), and electrochemical impedance spectroscopy (EIS) measurements confirmed the excellent photogenerated charge carrier separation and transport efficiency of CN-540. The photocatalytic mechanism for reducing Cr(VI) by CN-540 was elucidated based on the active species •OH and •O2– and Mott-Schottky (M-S) tests. This study provides experimental data for optimizing the photocatalytic performance of g-C3N4 and paves a new way for developing efficient photocatalysts. Copyright © 2024 by Authors, Published by BCREC Publishing Group. This is an open access article under the CC BY-SA License (https://creativecommons.org/licenses/by-sa/4.0).

Shuttle HAT for mild alkene transfer hydrofunctionalization.

Hydrogen atom transfer (HAT) from a metal-hydride is a reliable and powerful method for functionalizing unsaturated C-C bonds in organic synthesis. Cobalt hydrides (Co-H) have garnered significant attention in this field, where the weak Co-H bonds are most commonly generated in a catalytic fashion through a mixture of stoichiometric amounts of peroxide oxidant and silane reductant. Here we show that the reverse process of HAT to an alkene, i.e. hydrogen atom abstraction of a C-H adjacent to a radical, can be leveraged to generate catalytically active Co-H species in an application of shuttle catalysis coined shuttle HAT. This method obviates the need for stoichiometric reductant/oxidant mixtures thereby greatly simplifying the generation of Co-H. To demonstrate the generality of this shuttle HAT platform, five different reaction manifolds are shown, and the reaction can easily be scaled up to 100 mmol.

Catalytic performances of Ag/SiC catalysts for styrene epoxidation in O2 atmosphere

SiC supported Ag catalysts were prepared by an impregnation-reduction method for styrene epoxidation in O2 atmosphere. Under the condition of 100 °C, 0.5 MPa O2 and 4 h, 5 wt% Ag/SiC catalyst achieved styrene conversion of 98.5 % and styrene oxide selectivity of 69.7 %. Further studies show that O2 was activated on the Ag surface and then formed reactive oxygen species, 1O2 and •O2-. Based on the O2 adsorption results, the atomic ratio of O/Ag larger than 0.5 indicated that more oxygen species had spilled over to the SiC surface. In-situ diffuse reflectance Fourier transform infrared spectroscopy and Density Functional Theory calculation results showed that styrene was adsorbed on the SiC surface. The active oxygen species generated on the Ag surface could spill over to the SiC surface, reacting with the adsorbed styrene to produce styrene oxide or benzaldehyde. In addition, the catalyst exhibits good stability.

Front Cover: A Cytochrome P450 TxtE Model System with Mechanistic and Theoretical Evidence for a Heme Peroxynitrite Active Species

Front Cover: A Cytochrome P450 TxtE Model System with Mechanistic and Theoretical Evidence for a Heme Peroxynitrite Active Species

Reduction Polymerization of CO2 with Phenylene Silanes Catalyzed by Single Component B(C6F5)3.

CO2 is an abundant C1 resource but a green-house gas and chemically inert. Thus, its utilization has been a promising but challenging project. Herein, we report the unprecedented polymerization of CO2 and C6H4(SiMe2H)2 using B(C6F5)3 alone under mild conditions to give poly(silphenylene siloxane) accompanied by releasing CH4. The copolymerization can be extended to comonomers of phenylene silanes bearing functional groups. Moreover, it combines with Piers-Rubinsztajn reaction to establish a tandem polymerization system to achieve super thermal resistant poly(siloxane-co-silphenylene siloxane)s. Density functional theory reveals that B(C6F5)3 is activated by silanes to form free HB(C6F5)2, which is the true active species for CO2 reducing to borylformate, the rate controlling step of the polymerization procedure. The subsequent multiple reductions of borylformate to CH4 and the step-growth to poly(silphenylene siloxane)s can be fulfilled by both B(C6F5)3 and HB(C6F5)2, and the former shows a slightly higher activity. This work opens a new avenue of utilizing CO2 to fabricate polysiloxanes that is unable to access using current manners.

Cobalt/iron bimetallic oxide coated with graphitized nitrogen-doped carbon (Fe2O3-CoO@NC) derived from cobalt/iron solid complex as peroxymonosulfate (PMS) activator for efficient bensulfuron-methyl degradation

Cobalt/iron bimetallic oxide coated with graphitized nitrogen-doped carbon (Fe2O3-CoO@NC) was synthesized by convenient solid phase coordination combined with calcination method to activate PMS for the degradation of BSM. A series of Co/Fe bimetallic oxides with different metal ratios were designed and prepared to select the most efficient catalyst and Fe2O3-CoO@NC(Co:Fe = 1:1) demonstrated the highest catalytic activity and the lowest ions leaching. The reasons for high catalytic activity of Fe2O3-CoO@NC(Co:Fe = 1:1) were evaluated by a range of characterization techniques and the results showed it stemmed from higher mental content and larger current density. Complete (100%) degradation of 10 g L−1 BSM was achieved within 10 min under the conditions of 0.05 g L−1 catalyst and 0.3 mmol/L PMS dosage at 25 °C. Moreover, Fe2O3-CoO@NC(Co:Fe = 1:1) showed more excellent catalytic activity and lower ions leaching than Fe2O3, CoO and Fe2O3-CoO, indicating superior bimetallic synergy and carbon encapsulation effect. Furtherly, radical experiments and XPS analysis revealed the main active species and catalytic mechanism of the Fe2O3-CoO@NC/PMS system, respectively. Finally, the degradation pathway of BSM by Fe2O3-CoO@NC/PMS system was deduced by LC-TOF-MS. This paper is aimed to provide a new insight into the convenient preparation method for the construction of catalysts which could reach efficient removal of complex organic pollutants.

Natural Vanadium–Titanium Magnetite Activated Peroxydisulfate and Peroxymonosulfate for Acid Orange II Degradation: Different Activation Mechanisms and Influencing Factors

Persulfate-based advanced oxidation processes have emerged as a promising approach for the degradation of organic pollutants in aqueous environments due to their ability to generate sulfate radicals (SO4−·) within catalytic systems. In this study, peroxydisulfate (PDS) and peroxymonosulfate (PMS) were investigated with the natural vanadium–titanium magnetite (VTM) as the activator for the degradation of acid orange II. The degradation efficiency increased with higher dosages of VTM or persulfate (both PDS and PMS) at lower concentrations (below 10 mM). However, excessive PMS (higher than 10 mM) in the PMS/VTM system led to the self-consumption of free radicals, significantly inhibiting the degradation of acid orange II. The VTM-activated PDS or PMS maintained an effective degradation of acid orange II in a wide pH range (3~11), suggesting remarkable pH stability. The SO4−· was the main active species in the PDS/VTM system, while hydroxyl radical (·OH) also contributed significantly to the PMS/VTM system. In addition, PMS exhibited better thermal stability during VTM activation. Coexisting ions in an aqueous environment such as bicarbonate (HCO3–), carbonate (CO32–), and hydrogen phosphate (HPO42–) had obvious effects on persulfate activation. Our study systematically investigated the different activation processes and influencing factors associated with PDS and PMS when the natural VTM was used as a catalyst, thereby providing new insights into the persulfate-mediated degradation of organic pollutants in aqueous environments.

Front Cover: A Cytochrome P450 TxtE Model System with Mechanistic and Theoretical Evidence for a Heme Peroxynitrite Active Species

Front Cover: A Cytochrome P450 TxtE Model System with Mechanistic and Theoretical Evidence for a Heme Peroxynitrite Active Species

Levofloxacin degradation in electro-Fenton system with FeMn@GF composite electrode

In this work, a one-step solvent-thermal approach was used to synthesize an Mn-doped Fe3O4 modified graphite felt (GF) composite electrode material (FeMn@GF), which was then used as the cathode in an Electro-Fenton (EF) system. The levofloxacin (LEV) in wastewater can be successfully removed by the EF system, which can produce and activate H2O2 in situ. The successful fabrication of the FeMn@GF composite electrode was confirmed by employing the characterization techniques of Scanning Electron Microscope, X-ray Diffraction, and X-ray Photoelectron Spectroscopy. Additionally, the electrochemical performance test was conducted. The FeMn@GF composite electrode demonstrated a greater electrochemical activity and a more robust electronic transmission ability. The LEV degradation experiment demonstrated reached 98.9 % that under ambient temperature conditions, within 120 minutes, given initial LEV concentration of 20 mg·L −1, Na2SO4 concentration of 50 mM, applied voltage of 3.0 V, initial pH value of 3, and aeration rate of 3.0 L·min −1.The highest leaching quantities of Fe and Mn were 1.294 mg·L−1 and 0.675 mg·L−1, respectively, while the removal effectiveness of LEV remained at 85.2 % after five cycles. Experiments using radical quenching revealed that the main active species were ·OH. The reaction mechanism of the EF system with FeMn@GF as the cathode (FeMn@GF-EF) and the degradation pathway of LEV were investigated.

A Cytochrome P450 TxtE Model System with Mechanistic and Theoretical Evidence for a Heme Peroxynitrite Active Species

AbstractThe cytochrome P450 homolog, TxtE, efficiently catalyzes the direct and regioselective aromatic nitration of the indolyl moiety of L‐tryptophan to 4‐nitro‐L‐tryptophan, using nitric oxide (NO) and dioxygen (O2) as co‐substrates. Pathways for such direct and selective nitration of heteroaromatic motifs present platforms for engineering new nitration biocatalysts for pharmacologically beneficial targets, among a medley of other pivotal industrial applications. Precise mechanistic details concerning this pathway are only weakly understood, albeit a heme iron(III)‐peroxynitrite active species has been postulated. To shed light on this unique reaction landscape, we investigated the indole nitration pathway of a series of biomimetic ferric heme superoxide mimics, [(Por)FeIII(O2−⋅)], in the presence of NO. Therein, our model systems gave rise to three distinct nitroindole products, including 4‐nitroindole, the product analogous to that obtained with TxtE. Moreover, 15N and 18O isotope labeling studies, along with meticulously designed control experiments lend credence to a heme peroxynitrite active nitrating agent, drawing close similarities to the tryptophan nitration mechanism of TxtE. All organic and inorganic reaction components have been fully characterized using spectroscopic methods. Theoretical investigation into several mechanistic possibilities deem a unique indolyl radical based reaction pathway as the most energetically favorable, products of which, are in excellent agreement with experimental findings.

Reduction Polymerization of CO2 with Phenylene Silanes Catalyzed by Single Component B(C6F5)3

AbstractCO2 is an abundant C1 resource but a green‐house gas and chemically inert. Thus, its utilization has been a promising but challenging project. Herein, we report the unprecedented polymerization of CO2 and C6H4(SiMe2H)2 using B(C6F5)3 alone under mild conditions to give poly(silphenylene siloxane) accompanied by releasing CH4. The copolymerization can be extended to comonomers of phenylene silanes bearing functional groups. Moreover, it combines with Piers‐Rubinsztajn reaction to establish a tandem polymerization system to achieve super thermal resistant poly(siloxane‐co‐silphenylene siloxane)s. Density functional theory reveals that B(C6F5)3 is activated by silanes to form free HB(C6F5)2, which is the true active species for CO2 reducing to borylformate, the rate controlling step of the polymerization procedure. The subsequent multiple reductions of borylformate to CH4 and the step‐growth to poly(silphenylene siloxane)s can be fulfilled by both B(C6F5)3 and HB(C6F5)2, and the former shows a slightly higher activity. This work opens a new avenue of utilizing CO2 to fabricate polysiloxanes that is unable to access using current manners.

A convection-enhanced flow field with height-changing ribs for redox flow batteries

Serpentine flow fields with flat ribs can effectively improve the performance of redox flow batteries. However, the marginal pressure difference between adjacent channels near the end side of ribs in conventional designs leads to weak convection in the regions, increasing the local concentration overpotential. This problem will be exacerbated in scaled-up redox flow battery stacks due to enlarged under-rib regions near the end side of ribs. In this work, two modified serpentine flow fields with height-changing ribs are proposed to adjust the electrode compression ratio at the under-rib region, thereby enhancing the convection in the electrode near the end side of ribs. Therefore, the active species are distributed more uniformly, resulting in an improved battery performance. Specifically, the uniformity of V2+, the energy efficiency and the system efficiency of the vanadium redox flow batteries with the ramp ribs are improved by 21 %, 2.7 %, and 2.7 % respectively compared with that of the conventional flat ribs, at the current density of 200 mA cm−2, the flow rate of 3.4 mL min−1 cm−2, and the active area of 117 cm2.

Dark Population Transfer Mechanism for Sterile Neutrino Dark Matter

We present a mechanism for producing a cosmologically significant relic density of one or more sterile neutrinos. This scheme invokes two steps: First, a population of “heavy” sterile neutrinos is created by scattering-induced decoherence of active neutrinos. Second, this population is transferred, via sterile neutrino self-interaction-mediated scatterings and decays, to one or more lighter mass (∼10 keV to ∼1 GeV) sterile neutrinos that are far more weakly (or not at all) mixed with active species and could constitute dark matter. Dark matter produced this way can evade current electromagnetic and structure-based bounds, but may nevertheless be probed by future observations. Published by the American Physical Society 2024

Electrochemical Formation of C2+ Products Steered by Bridge-Bonded *CO Confined by *OH Domains.

During the electrochemical CO2 reduction reaction (eCO2RR) on copper catalysts, linear-bonded CO (*COL) is commonly regarded as the key intermediate for the CO-CO coupling step, which leads to the formation of multicarbon products. In this work, we unveil the significant role of bridge-bonded *CO (*COB) as an active species. By combining in situ Raman spectroscopy, gas and liquid chromatography, and density functional theory (DFT) simulations, we show that adsorbed *OH domains displace *COL to *COB. The electroreduction of a 12CO+13CO2 cofeed demonstrates that *COB distinctly favors the production of acetate and 1-propanol, while *COL favors ethylene and ethanol formation. This work enhances our understanding of the mechanistic intricacies of eCO(2)RR and suggests new directions for designing operational conditions by modifying the competitive adsorption of surface species, thereby steering the reaction toward specific multicarbon products.