OH Production Research Articles

On-Site Electrochemical Oxygen Reduction to Hydroxide and Hydrogen Peroxide for Sulfuryl Fluoride Solution Hydrolysis

Sulfuryl fluoride (SO2F2) has been largely used as a postharvest fumigant replacing methyl bromide (widely recognized among ozone-depleting substances). Sulfuryl fluoride, however, is a potent greenhouse gas with a Global Warming Potential (GWP) of ~ 5000 for a 100-year time zone far higher than that of carbon dioxide and methane. Ongoing pilot work showed that SO2F2 fumes vented from fumigation chambers can be captured and hydrolyzed by hydroxide (OH-) and hydrogen peroxide (H2O2) solution at pH ~12 in a scrubber with a complete conversion into SO4 2- and F- as waste salts. The purchase, shipment, storage, and handling of concentrated stocks of H2O2 and NaOH for use in SO2F2 hydrolysis involve cost and safety concerns. Herein, we present an on-site, facile, and cost-effective pathway for the electrochemical production of OH- and H2O2 in large enough concentrations to fully degrade ~ 95% of SO2F2 captured. In that, we employed a commercial carbon catalyst that produced 250 mM H2O2 at pH 12.6 within 4 h with a Faradaic efficiency of 98.8% for O2 reduction to H2O2. We also propose a facile approach via surface oxidation of abundant carbon materials to significantly enhance both activity and selectivity for OH- and H2O2 production under electrochemical oxygen reduction reaction. These findings provide new insights in the on-site production of industrial chemicals by means of clean, facile, and environmentally friendly electrochemical pathway. Moreover, the capability of recycling the hazardous SO2F2 fumes and using the SO4 2- and F- waste products as free sources of electrolyte can’t be overemphasized.

Defect engineering in seaweed-like TiO2@carbon nitride strengthening hydroxyl production for thorough elimination of antibiotics

The highly selective production of ·OH to strengthen the mineralization of antibiotics remains a significant scientific challenge. In this work, the seaweed-like fibrous membrane containing oxygen-vacancies in TiO2 ultrafine nanocrystals and nitrogen-vacancies in g-C3N4 nanosheets, was rationally designed through a HCl-mediated polycondensation strategy. The photocatalytic test confirmed that the dual-defects membrane containing dual defects exhibited highly efficient capacities in removing a variety of antibiotics under visible light and natural light irradiation, which was much stronger than that of single- or none-defective samples. The mechanism analysis displayed that the dual defects were beneficial to migration of photogenerated charges, expansion of Fermi level gap, and capture of oxygen. The strengthened ·OH production was derived from the decomposition of H2O2, bypassing the high barrier of direct oxidation of H2O. This work focuses the key roles of defects in photocatalytic reaction and attempts to present a promising stride towards advancing defect engineering.

Acidic biofilm microenvironment-responsive ROS generation via a protein nanoassembly with hypoxia-relieving and GSH-depleting capabilities for efficient elimination of biofilm bacteria

Reactive oxygen species (ROS) are widely considered to the effective therapeutics for fighting bacterial infections especially those associated with biofilm. However, biofilm microenvironments including hypoxia, limited H2O2, and high glutathione (GSH) level seriously limit the therapeutic efficacy of ROS-based strategies. Herein, we have developed an acidic biofilm microenvironment-responsive antibacterial nanoplatform consisting of copper-dopped bovine serum albumin (CBSA) loaded with copper peroxide (CuO2) synthesized in situ and indocyanine green (ICG). The three-in-one nanotherapeutics (CuO2/ICG@CBSA) are capable of releasing Cu2+ and H2O2 in a slightly acidic environment, where Cu2+ catalyzes the conversion of H2O2 into hydroxyl radical (•OH) and consumes the highly expressed GSH to disrupt the redox homeostasis. With the assistance of an 808 nm laser, the loaded ICG not only triggers the production of singlet oxygen (1O2) by a photodynamic process, but also provides photonic hyperpyrexia that further promotes the Fenton-like reaction for enhancing •OH production and induces thermal decomposition of CuO2 for the O2-self-supplying 1O2 generation. The CuO2/ICG@CBSA with laser irradiation demonstrates photothermal-augmented multi-mode synergistic bactericidal effect and is capable of inhibiting biofilm formation and eradicating the biofilm bacteria. Further in vivo experiments suggest that the CuO2/ICG@CBSA can effectively eliminate wound infections and accelerate wound healing. The proposed three-in-one nanotherapeutics with O2/H2O2-self-supplied ROS generating capability show great potential in treating biofilm-associated bacterial infections. Statement of significanceHere, we have developed an acidic biofilm microenvironment-responsive nanoplatform consisting of copper-dopped bovine serum albumin (CBSA) loaded with copper peroxide (CuO2) synthesized in situ and indocyanine green (ICG). The nanotherapeutics (CuO2/ICG@CBSA) are capable of releasing Cu2+ and H2O2 in an acidic environment, where Cu2+ catalyzes the conversion of H2O2 into •OH and consumes the overexpressed GSH to improve oxidative stress. With the aid of an 808 nm laser, ICG provides photonic hyperpyrexia for enhancing •OH production, and triggers O2-self-supplying 1O2 generation. CuO2/ICG@CBSA with laser irradiation displays photothermal-augmented multi-mode antibacterial and antibiofilm effect. Further in vivo experiments prove that CuO2/ICG@CBSA effectively eliminates wound infection and promotes wound healing. The proposed three-in-one nanotherapeutics show great potential in treating biofilm-associated bacterial infections.

An evaluation of pyrite as a component of respirable coal dust

Over the past two decades, the rise in coal worker’s pneumoconiosis has prompted research into the effects of respirable coal dust components. This study explores how coal-pyrites produce hydroxyl radicals (•OH), a reactive oxygen species closely associated with particle toxicity, and assesses the ability of safe chemical additives to reduce •OH production at various pH levels. Promising candidates were evaluated in various solutions, including tap and process waters and simulated lung fluid. We employed electrokinetic measurements, infrared and X-ray photoelectron spectroscopies, and ab initio atomistic simulations to analyze particle surfaces. The study also looked at how surface aging affects •OH production. Our results show that •OH generation of the pyrite varies and is catalyzed by elements like silicon, aluminum, and iron in pyrite. Carboxymethyl cellulose was effective in reducing •OH production by targeting surface sulfide and silicon sites and affecting surface hydration and charge. Atmospheric aging was found to increase •OH production, especially in the pyrite with high iron and silicon and low calcium contents, relative to other samples. This highlights the role of the pyrite surface properties and chemical composition, and the solution pH and composition in •OH generation by coal-pyrites.

Photonic crystal-assisted sub-bandgap photocatalysis via triplet-triplet annihilation upconversion for the degradation of environmental organic pollutants

This study explores novel approaches to enhance photocatalysis efficiency by introducing a photonic crystal (PC)-enhanced, multi-layered sub-bandgap photocatalytic reactor. The design aims to effectively utilize sub-bandgap photons that might otherwise go unused. The device consists of three types of layers: (1) two polymeric triplet-triplet annihilation upconversion (TTA-UC) layers converting low-energy green photons (λEx = 532 nm, 2.33 eV) to high-energy blue photons (λEm = 425 nm, 2.92 eV), (2) a platinum-decorated WO3 layer (Eg = 2.8 eV) serving as a visible-light photocatalyst, and (3) a PC layer optimizing both TTA-UC and photocatalysis. The integration of the PC layer resulted in a 1.9-fold increase in UC emission and a 7.9-fold enhancement in hydroxyl radical (•OH) generation, achieved under low-intensity sub-bandgap irradiation (17.6 mW cm–2). Consequently, the combined layered structure of TTA/Pt-WO3/TTA/PC achieved a remarkable 38.8-fold improvement in •OH production, leading to outstanding degradation capability for various organic pollutants (e.g., 4-chlorophenol, bisphenol A, and methylene blue). This multi-layered sub-bandgap photocatalytic structure, which uniquely combines TTA-UC and PC layers, offers valuable insights into designing efficient photocatalytic systems for future solar-driven environmental remediation.

Sustainable nitrogen fixation by bubble discharge plasma: Performance optimization and mechanism

Sustainable nitrogen fixation driven by renewable energy sources under mild conditions has been widely sought to replace the industrial Haber-Bosch process. The fixation of nitrogen in the form of NOx− and NH4+ into aqueous solutions using electricity-driven gas–liquid discharge plasma is considered a promising prescription. In this paper, a scalable bubble discharge excited by nanosecond pulse power is employed for nitrogen fixation in the liquid phase. The nitrogen fixation performance and the mechanisms are analyzed by varying the power supply parameters, working gas flow rate and composition. The results show that an increase in voltage and frequency can result in an enhanced NO3− yield. Increases in the gas flow rate can result in inadequate activation of the working gas, which together with more inefficient mass transfer efficiencies can reduce the yield. The addition of O2 effectively elevates NO3− production while simultaneously inhibiting NH4+ production. The addition of H2O vapor increases the production of OH and H, thereby promoting the generation of reactive nitrogen and enhancing the yield of nitrogen fixation. However, the excessive addition of O2 and H2O vapor results in negative effect on the yield of nitrogen fixation, due to the significant weakening of the discharge intensity. The optimal nitrogen fixation yield was up to 16.5 μmol/min, while the optimal energy consumption was approximately 21.3 MJ/mol in this study. Finally, the mechanism related to nitrogen fixation is discussed through the optical emission spectral (OES) information in conjunction with the simulation of energy loss paths in the plasma by BOLSIG + . The work advances knowledge of the effect of parameter variations on nitrogen fixation by gas–liquid discharge for higher yield and energy production.

Long-term Application of Agricultural Amendments Regulate Hydroxyl Radicals Production during Oxygenation of Paddy Soils.

Hydroxyl radicals (•OH) play a significant role in contaminant transformation and element cycling during redox fluctuations in paddy soil. However, these important processes might be affected by widely used agricultural amendments, such as urea, pig manure, and biochar, which have rarely been explored, especially regarding their impact on soil aggregates and associated biogeochemical processes. Herein, based on five years of fertilization experiments in the field, we found that agricultural amendments, especially coapplication of fertilizers and biochar, significantly increased soil organic carbon contents and the abundances of iron (Fe)-reducing bacteria. They also substantially altered the fraction of soil aggregates, which consequently enhanced the electron-donating capacity and the formation of active Fe(II) species (i.e., 0.5 M HCl-Fe(II)) in soil aggregates (0-2 mm), especially in small aggregates (0-3 μm). The highest contents of active Fe(II) species in small aggregates were mainly responsible for the highest •OH production (increased by 1.7-2.4-fold) and naphthalene attenuation in paddy soil with coapplication of fertilizers and biochar. Overall, this study offers new insights into the effects of agricultural amendments on regulating •OH formation in paddy soil and proposes feasible strategies for soil remediation in agricultural fields, especially in soils with frequent occurrences of redox fluctuations.

Infrared signature of the hydroperoxyalkyl intermediate (·QOOH) in cyclohexane oxidation: An isomer-resolved spectroscopic study.

Infrared (IR) action spectroscopy is utilized to characterize carbon-centered hydroperoxy-cyclohexyl radicals (·QOOH) transiently formed in cyclohexane oxidation. The oxidation pathway leads to three nearly degenerate ·QOOH isomers, β-, γ-, and δ-QOOH, which are generated in the laboratory by H-atom abstraction from the corresponding ring sites of the cyclohexyl hydroperoxide (CHHP) precursor. The IR spectral features of jet-cooled and stabilized ·QOOH radicals are observed from 3590 to 7010cm-1 (∼10-20kcal mol-1) at energies in the vicinity of the transition state (TS) barrier leading to OH radicals that are detected by ultraviolet laser-induced fluorescence. The experimental approach affords selective detection of β-QOOH, arising from its significantly lower TS barrier to OH products compared to γ and δ isomers, which results in rapid unimolecular decay and near unity branching to OH products. The observed IR spectrum of β-QOOH includes fundamental and overtone OH stretch transitions, overtone CH stretch transitions, and combination bands involving OH or CH stretch with lower frequency modes. The assignment of β-QOOH spectral features is guided by anharmonic frequencies and intensities computed using second-order vibrational perturbation theory. The overtone OH stretch (2νOH) of β-QOOH is shifted only a few wavenumbers from that observed for the CHHP precursor, yet they are readily distinguished by their prompt vs slow dissociation rates to OH products.

Microscopic insights into the ammonia-methanol blended combustion at high temperatures

Ammonia and methanol have a broad application prospect in the future as green renewable liquid fuels. Methanol has high reactivity and good solubility with ammonia, which is conducive to solving the dilemma of ammonia combustion. However, there are few studies on ammonia-methanol blended combustion, and the effect of blended combustion on the reaction pathways needs to be further investigated. Therefore, this study used the reaction molecular dynamics simulations to reveal the role of methanol on the ammonia combustion and emission process at the microscopic level, focusing on the effects of different fuel blending ratios and oxygen concentration in the air under stoichiometric conditions. The variation of oxidation pathways from ammonia to NO and methanol to CO under different conditions was analyzed in detail. It was found that the methanol accelerated ammonia combustion mainly through enhancing OH production, but methanol and its intermediates inhibited the initial oxidation of ammonia. When the fuel blending ratio was 0.75, the system had lower fuel-type NO production alongside a higher ammonia consumption rate under stoichiometric conditions. The crucial role of NH in the HNO formation at high-temperature ammonia oxidation conditions was revealed. The pathway of HNO + OH → NO + H2O dominated the conversion of HNO to NO in this study. Increasing the methanol content promoted the conversion of NH to HNO and the pyrolysis of HNO while inhibiting the reaction between HNO and O2. In addition, the finding indicated that the high O2 level in air can enhance the reactions between ammonia and OH radicals but inhibit the pyrolysis of CH2OH/CH3O significantly.

Degradation of bromothymol blue and methyl green from aqueous media by Photo-Fenton: comparison between UV-lamp and sun irradiation

Abstract The degradation of two textile dye molecules was studied using photochemical processes, both in the absence and presence of light. Various methods were employed, including photolysis/UV, combined H2O2/UV photolysis, Fe2+/UV treatment, Photo-Fenton/UV at 350 nm and Photo-Fenton with solar irradiation. The decolorization efficiency of dyes in aqueous solution was evaluated for two specific dyes: Bromothymol Blue (BTB) and Methyl Green (MG). These experiments were carried out in batch mode. The results demonstrated a synergy between light irradiation and the presence of Fenton’s reagents, such as hydrogen peroxide and divalent iron. In addition, it was demonstrated that direct solar irradiation can be used without specific devices to achieve high efficiency at low cost. In the first part, we checked the impact of the various operating parameters. Reaction efficiencies were compared for the same system in the dark and under the assistance of an artificial or solar light source. In the second part, we studied the parameters of the Photo-Fenton process, such as the initial pH of the solution, the initial concentrations of oxidant, iron catalyst, and dye under irradiation from either light source. Whereas the mere photolysis without Fenton’s reagents allowed decolorization yields below 26 %, addition of the oxidant (H2O2) or the catalyst (Fe(II) species amplified the treatment efficiency. However, the presence of both H2O2 and Fe(II) under light irradiation was shown synergetic with yields ranging from 72 to 85 % depending on the dye worked and the light source: because of its broader spectrum in the UV domain, solar irradiation led to the highest decolorization yields. The above results were obtained for well-defined proportions of dye and reagents: for a 20 mg/l dye solution, Fe(II) catalyst concentration equal to 10−3 M, peroxide concentration of 5.10−2 M and a pH of 3. These conditions allowed optimal production of OH· radicals, allowing high efficiency in systems using solar irradiation.

Gold Nanodots-Anchored Cobalt Ferrite Nanoflowers as Versatile Tumor Microenvironment Modulators for Reinforced Redox Dyshomeostasis.

Given that tumor microenvironment (TME) exerts adverse impact on the therapeutic response and clinical outcome, robust TME modulators may significantly improve the curative effect and increase survival benefits of cancer patients. Here, Au nanodots-anchored CoFe2O4 nanoflowers with PEGylation (CFAP) are developed to respond to TME cues, aiming to exacerbate redox dyshomeostasis for efficacious antineoplastic therapy under ultrasound (US) irradiation. After uptake by tumor cells, CFAP with glucose oxidase (GOx)-like activity can facilitate glucose depletion and promote the production of H2O2. Multivalent elements of Co(II)/Co(III) and Fe(II)/Fe(III) in CFAP display strong Fenton-like activity for·OH production from H2O2. On the other hand, energy band structure CFAP is superior for US-actuated 1O2 generation, relying on the enhanced separation and retarded recombination of e-/h+ pairs. In addition, catalase-mimic CFAP can react with cytosolic H2O2 to generate molecular oxygen, which may increase the product yields from O2-consuming reactions, such as glucose oxidation and sonosensitization processes. Besides the massive production of reactive oxygen species, CFAP is also capable of exhausting glutathione to devastate intracellular redox balance. Severe immunogenic cell death and effective inhibition of solid tumor by CFAP demonstrates the clinical potency of such heterogeneous structure and may inspire more relevant designs for disease therapy.

Development of efficient nonthermal atmospheric-pressure Ar-plasma jet through simultaneous spectroscopic characterization and radical quantification

The work investigates the correlation between the plasma characteristics and reactive chemical species generation in an Ar-nonthermal atmospheric pressure plasma-jet (Ar-NTAPPJ) under various operating conditions such as gas flow rate, excitation voltage, and electrode gap and demonstrates the application of such understanding in developing efficient nonthermal plasma systems. The critical plasma parameters such as electron temperature (T e) and electron density (n e) under the various operating conditions were estimated using optical emission spectroscopy coupled with the collision radiative model and Stark broadening methods. At optimal setting of 5 LPM gas flow rate, 4 kV excitation voltage, and 6 mm electrode gap resulted in maximum T e (0.6 eV), enhancing •OH production (0.056 mM) in the liquid phase and OH(A-X) emission in the gas phase, highlighting the significance of operating conditions on building energy efficient plasma systems. The enhanced performance of the optimized Ar-NTAPPJ is demonstrated by taking atrazine as a model herbicide. The degradation performance data was correlated and validated with results obtained from spectroscopic diagnostics. By adequately tuning the operating parameters, four times enhancement in energy yield (∼150 mg kWh−1) was obtained without perturbing the nonthermal plasma mode. In nonthermal mode, to best of the authors knowledge, it is the highest reported energy yield for atrazine degradation. The scalability aspect of the present plasma jet was also investigated by Intensified Charge-Coupled Device camera-based imaging technique. The study establishes the importance of adequate diagnostics in developing efficient next-generation plasma reactors.

Critical roles of low-molecular-weight organic acid in enhancing hydroxyl radical production by ferrous oxidation on γ-Al2O3 mineral surface

Recognizing the pervasive presence of alumina minerals and low-molecular-weight organic acids (LMWOAs) in the environment, this study addressed the gap in the interaction mechanisms within the ternary system involving these two components and Fe(II). Specifically, the impacts of LMWOAs on hydroxyl radicals (•OH) production and iron species transformation during Fe(II) oxidation on γ-Al2O3 mineral surface were examined. Results demonstrated that adding 0.5 mM oxalate (OA) or citrate (CA) to the γ-Al2O3/Fe(II) system (28.1 μM) significantly enhanced •OH production by 1.9-fold (51.9 μM) and 1.3-fold (36.2 μM), respectively, whereas succinate (SA) exhibited limited effect (30.7 μM). Raising OA concentration to 5 mM further promoted •OH yield to 125.0 μM after 24 h. Deeper analysis revealed that CA facilitated the dissolution of adsorbed Fe(II) and its subsequent oxygenation by O2 through both one- and two-electron transfer mechanisms, whereas OA enhanced the adsorption of dissolved Fe(II) and more efficient two-electron transfer for H2O2 production. Additionally, LMWOAs presence favored the formation of iron minerals with poor crystallinity like ferrihydrite and lepidocrocite rather than well-crystallized forms such as goethite. The distinct impacts of various LMWOAs on Fe(II) oxidation and •OH generation underscore their unique roles in the redox processes at mineral surface, consequently modulating the environmental fate of prototypical pollutants like phenol.

Mechanistic and kinetic insights of the formation of allene and propyne from the C3H3 reaction with water.

Allene (H2C = C = CH2) and propyne (CH3-C≡CH) are important compounds in the combustion chemistry. They can be created from the reaction of proparyl radicals with water. In this study, therefore, a computational study into the C3H3 + H2O potential energy landscape has been carefully conducted. The computed results indicate that the reaction paths forming the products (allene: CH2CCH2 + •OH) and (propyne: HCCCH3 + •OH) prevail under the 300-2000K temperature range, where the latter is much more predominant compared to the former. However, these two products are not easily formed under ambient conditions due to the high energy barriers. In the 300 - 2000K temperature range, the branching ratio for the propyne + •OH product declines from 100 to 86%, whereas the allene + •OH product shows an increase, reaching 14% at 2000K. The overall bimolecular rate constant of the title reaction can be presented by the modified Arrhenius expression of ktotal = 1.94 × 10-12 T0.14 exp[(-30.55kcal.mol-1)/RT] cm3 molecule-1s-1. The total rate constant at the ambient conditions in this work, 2.37 × 10-34 cm3 molecule-1s-1, was found to be over five orders of magnitude lower than the total rate constant of the C3H3 + NH3 reaction, 7.98 × 10-29 cm3 molecule-1s-1, calculated by Hue et al. (Int. J. Chem. Kinet. 2020, 4(2), 84-91). The results in this study contribute to elucidating the mechanism of allene and propylene formation from the C3H3 + H2O reaction, and they can be used for modeling C3H3-related systems under atmospheric and combustion conditions. All the geometric structures of the C3H3 + H2O system were optimized by the B3LYP method in conjunction with the 6-311 + + G(3df,2p) basis set. Single-point energies of these species were calculated at the CCSD(T)/6-311 + + G(3df,2p) level of theory. The CCSD(T)/CBS level has also been used to compute single-point energies for the two major reaction channels (C3H3 + H2O → allene + •OH and C3H3 + H2O → propyne + •OH). Rate constants and branching ratios of the key reaction channels were calculated in the 300-2000K temperature interval using the Chemrate software based on the transition state theory (TST) with Eckart tunneling corrections.

Exposure to O3 and NO2 on the interfacial chemistry of the pulmonary surfactant and the mechanism of lung oxidative damage

Exposure to ozone (O3) and nitrogen dioxide (NO2) are related to pulmonary dysfunctions and various lung diseases, but the underlying biochemical mechanisms remain uncertain. Herein, the effect of inhalable oxidizing gas pollutants on the pulmonary surfactant (PS, extracted from porcine lungs), a mixture of active lipids and proteins that plays an important role in maintaining normal respiratory mechanics, is investigated in terms of the interfacial chemistry using in-vitro experiments; and the oxidative stress induced by oxidizing gases in the simulated lung fluid (SLF) supplemented with the PS is explored. The results showed that O3 and NO2 individually increased the surface tension of the PS and reduced its foaming ability; this was accompanied by the surface pressure-area isotherms of the PS monolayers shifting toward lower molecular areas, with O3 exhibiting more severe effects than NO2. Moreover, both O3 and NO2 produced reactive oxygen species (ROS) resulting in lipid peroxidation and protein damage to the PS. The formation of superoxide radicals (O2•–) was correlated with the decomposition of O3 and the reactions of O3 and NO2 with antioxidants in the SLF. These radicals, in the presence of antioxidants, led to the formation of hydrogen peroxide and hydroxyl radicals (•OH). Additionally, the direct oxidation of unsaturated lipids by O3 and NO2 further caused an increase in the ROS content. This change in the ROS chemistry and increased •OH production tentatively explain how inhalable oxidizing gases lead to oxidative stress and adverse health effects. In summary, our results indicated that inhaled O3 and NO2 exposure can significantly alter the interfacial properties of the PS, oxidize its active ingredients, and induce ROS formation in the SLF. The results of this study provide a basis for the elucidation of the potential hazards of inhaled oxidizing gas pollutants in the human respiratory system.

Bird’s nest-like Nb2O5: preparation, characterization and multifunctional photocatalytic application

ABSTRACT A bird’s nest-like structure of Nb2O5 (Nb2O5/PVP) was produced using a hydrothermal method that involved the introduction of PVP. This unique structure provides a micro-reactor for the photocatalytic reaction, which improves the reaction efficiency. The test results demonstrated that the surface properties of Nb2O5 were altered by the introduction of PVP. This change caused an enhancement of the water adsorption capacity and ∙OH production yield. Another aspect, the energy band structure was altered by the introduction of PVP. Thus, the photogenerated charge recombination rate was reduced, the photogenerated charge mobility was improved, the reduction of photogenerated electrons was enhanced, and the ∙O2- production yield was increased. The PVP introduction broadened the light absorption range of Nb2O5 from the UV to the visible light region, increasing the light utilization efficiency. The degradation experiments demonstrated that Nb2O5/PVP had significantly better catalytic activity than pristine Nb2O5. Meanwhile, the photocatalytic degradation efficiency of TC using Nb2O5/PVP reached 90.4% in 25 min.

Photothermal catalysis enhances cellulose oxidation kinetics to promote the hydrogen evolution in alkaline solution over Pt/ZnIn2S4

The slow oxidation kinetics of cellulose severely limits photocatalytic cellulose reforming for hydrogen production. Herein, ZIS photocatalysts with different morphologies were prepared and Pt nanoparticles were deposited on their surfaces. The cellulose oxidation kinetics were enhanced through the strategy of photothermal catalysis and pH optimization, which led to efficient hydrogen generation. The ultrathin nanosheet structure endows 1 % Pt/ZIS-300 with a stronger photogenerated carrier separation ability than 1 % Pt/ZIS-0 (nanoflower) and facilitates ·OH generation. Heat can induce the production of ·OH from 1 % Pt/ZIS-300 and enhance the adsorption of 1 % Pt/ZIS-300 to cellulose by changing the surface potential of 1 % Pt/ZIS-300, which promotes the oxidation kinetics of cellulose. As a result, the hydrogen yield of 1 % Pt/ZIS-300 under photothermal catalytic condition (80 ℃) reached 1218 μmol/gcat after 4 h of reaction. Appropriate NaOH concentration contributes to cellulose solubilization and ·OH production, but too high OH− concentration causes a negative shift of the potential on the 1 % Pt/ZIS-300 and cellulose surface, which hinders the mass transfer process and reduces the oxidation kinetics of cellulose.

Spatially Separated Electron Donor‐Acceptor Dual Single‐Atom Sites Coordinating Selective Generation of Hydroxyl Radicals via Fenton‐Like Catalysis

AbstractHeterogeneous Fenton catalysis offers a promising alternative to traditional Fenton oxidation for water treatment as its wider operating pH range and high cyclic performance. However, designing catalysts that can activate H2O2 both actively and selectively to mineralize refractory pollutants remains challenging. Here, a state‐of‐the‐art design principle of constructing spatially separated Fe‐M (M denotes an oxophilic first‐row transition metal) dual single‐atom sites is developed for Fenton‐like catalysis. This strategy enables accelerated redox cycles between the dual metal centers, leading to precise manipulation of Fe···O‐O···M intermediate in H2O2 activation. This, in turn, aids the homolytic decomposition of H2O2 toward selective and efficient •OH generation. Taking Fe‐Cu pairs as an example, the constructed dual sites outperform the individual Fe or Cu sites, demonstrating a higher activation selectivity (94%) for •OH production. Further benefitting from the electronic communications between Fe (electron acceptor) and Cu (electron donor), the SA‐Fe‐Cu‐CN catalyst exhibited an effective H2O2 decomposition with 0.94 mm of •OH yielded within 50 min. Compared to the typical homogeneous system, the SA‐Fe‐Cu‐CN/H2O2 system has higher mineralization capacities toward refractory pollutants and greater pH tolerance. The work provides a new strategy for the design of robust catalysts by creating spatially separated dual single‐atom sites toward multi‐reactant systems.

High-efficiently utilizing micro-nano ozone bubbles to enhance electro-peroxone process for rapid removal of trace pharmaceutical contaminants from hospital wastewater

The electro-peroxone (EP) process encounters two inherent challenges in wastewater treatment: sluggish O2/O3 transfer and substantial ozone waste. To overcome these limitations, we introduced micro-nano bubbles (MNBs) aeration to enhance O2/O3 dissolution and diffusion, ultimately aiming to improve the removal of trace pharmaceutical contaminants from hospital wastewater. In the MNBs aeration system, the ozone transfer coefficient ranging from 0.536 to 0.265 min−1, significantly surpassing that of conventional aeration (0.220 to 0.090 min−1) by approximately 2 to 4.5 times. Consequently, the EP process under MNBs aeration significantly enhanced ozone-resistant ibuprofen (IBU) removal, achieving a removal rate of 98.4 ± 1.5 %, far exceeding the 47.3 ± 4.7 % observed with conventional aeration. This significant improvement was attributed to the heightened production of hydroxyl radicals (•OH), reaching 0.97 × 10−9 M s, compared to only 0.28 × 10−9 M s in conventional aeration. The mechanism behind the enhanced •OH production in the MNBs-EP process relied primarily on two factors: improved O2/O3 dissolution due to high internal pressure/large surface and enhanced O3/H2O2 activation from high collapse energy. These factors together contributed to the robust oxidation capability of the MNBs-EP system. As a result, over 97 % removal efficiency was achieved for five representative pharmaceutical pollutants (sulfamethoxazole, ribavirin, norfloxacin, tetracycline and ampicillin) in just 1 min. Furthermore, when applied to real hospital wastewater, the MNBs-O3-E treatment system reduced all 15 detected trace pharmaceutical compounds to below 10 ng L−1 and achieved 14 types of pollutants with removal rates of over 85 % within 15 min, resulting in an ultrahigh total removal rate of 98.6 %, from an initial total concentration of 2108 ng L−1 to less than 30 ng L−1. Thus, micro-nano aeration endowed the EP process as a promising advanced oxidation system for rapid and highly-effective removal of trace pharmaceutical contaminants from hospital wastewater.

Plasma-assisted NH3/air flame: Simultaneous LIF measurements of O and OH

In the emerging field of plasma-assisted ammonia (NH3) combustion, the evolution of key intermediate species has rarely been reported. This work establishes a simultaneous measurement system of laser-induced fluorescence (LIF) for hydroxyl (OH) and quantitative two-photon-absorption LIF for atomic oxygen (O), to explore the OH and O dynamics in an NH3/air flame affected by a nanosecond (ns) pulsed plasma discharge. Firstly, with the plasma on, the molar fraction of O is quantified to reach 8.7 × 10–3 in the burnt zone, about two orders of magnitude higher than that without plasma. In addition, the OH LIF signal intensity is four times higher, indicating a significant kinetic enhancement. Then, the spatial characteristics of OH and O are discussed and compared, showing remarkable discrepancy. The discrepancy between them indicates that O production is dominated by plasma kinetics, however, the OH production, primarily stemming from reactions between O and NH3/H2O, still depends on parameters associated with combustion kinetics. We further study the temporal dynamics of O and OH. It is concluded that O and OH peaks at 1.75 μs are mainly attributed to the pathway of quenching of the excited species. After that, O and OH start to decay but show significant differences between unburnt and burnt zones, which are characterized by a single-exponential decay and a bi-exponential decay, respectively. In the unburnt zone, the OH decay is much slower than the O decay due to the diverse pathways for OH production. In the burnt zone, the bi-exponential decay of O and OH can essentially be regarded as a process in which the NH3/air reactive system reaches chemical equilibrium. At this stage, the impacts of the excited species from the plasma gradually diminish and combustion kinetics dominates alone.