Surface-mediated Reactions Research Articles

Practical Route for the Low-Temperature Growth of Large-Area Bilayer Graphene on Polycrystalline Nickel by Cold-Wall Chemical Vapor Deposition.

We report a practical chemical vapor deposition (CVD) route to produce bilayer graphene on a polycrystalline Ni film from liquid benzene (C6H6) source at a temperature as low as 400 °C in a vertical cold-wall reaction chamber. The low activation energy of C6H6 and the low solubility of carbon in Ni at such a low temperature play a key role in enabling the growth of large-area bilayer graphene in a controlled manner by a Ni surface-mediated reaction. All experiments performed using this method are reproducible with growth capabilities up to an 8 in. wafer-scale substrate. Raman spectra analysis, high-resolution transmission electron microscopy, and selective area electron diffraction studies confirm the growth of Bernal-stacked bilayer graphene with good uniformity over large areas. Electrical characterization studies indicate that the bilayer graphene behaves much like a semiconductor with predominant p-type doping. These findings provide important insights into the wafer-scale fabrication of low-temperature CVD bilayer graphene for next-generation nanoelectronics.

Reactivity of binary manganese oxide mixtures towards arsenite removal: Evidence of synergistic effects

The effects of manganese (Mn) mineral mixtures on arsenite (As(III)) removal (i.e., the sum of As(III) oxidation to As(V) and As species adsorption) were systematically quantified for the first time using varying ratios of hausmannite and manganite, common Mn(III)-containing oxides that often exist as mixtures in natural environments. Due to smaller particle sizes and a higher surface area, hausmannite alone exhibited a total As(III) removal of 8.86 μM m−2 at pH 5, almost double that of manganite, 4.63 μM m−2, with initially fast but then subsequently slower As(III) oxidation and Mn(II) production rates. Both minerals showed a substantial decrease in As(III) removal as pH increased. High resolution transmission electron microscopy (HRTEM) analysis showed mineral edge sites initially and preferably consumed for As(III) oxidation. Mixtures of hausmannite and manganite resulted in enhanced As(III) removal (9.62–11.2 μM m−2) relative to the single minerals at pH 5, increasing with increasing manganite quantities. The mineral mixtures also displayed two reaction phases, where As(III) oxidation and Mn(II) production were initially fast but then slowed after the first hour. Further, the mineral mixtures produced a Mn(II):As(V) ratio higher than the theoretical two, indicating enhanced mineral dissolution than that of a single Mn oxide. Enhanced reactivity was attributed to the aggregation structure of mixtures, as the presence of manganite effectively limited the aggregation of hausmannite particles, as observed in HRTEM, promoting the exposure of highly active edge sites for the surface-mediated reactions. Thus, mineral mixtures may serve as a better surrogate than a single mineral to examine the extent and magnitude of As(III) removal in natural environments, by more closely reflecting the heterogeneity and complexity in surface interactions and aggregation structures between the minerals.

Hydroxyl Radical-Involving p-Nitrophenol Oxidation during Its Reduction by Nanoscale Sulfidated Zerovalent Iron under Anaerobic Conditions.

Sulfidated zerovalent iron (S-ZVI) has been extensively used for reducing pollutants. In this study, the oxidation process in the reductive removal of p-nitrophenol (PNP) by S-ZVI was confirmed under anaerobic conditions. We revealed that a PNP oxidation process involving •OH resulted from the H2O2 activation by surface-bound Fe(II) in S-ZVI, in which H2O2 was generated via a surface-mediated reaction between water and FeS2. Only the PNP reduction process occurred for ZVI. Herein, efficient PNP degradation by S-ZVI resulted from two functions: reduction into p-aminophenol due to enhanced electron transfer and PNP oxidation into p-benzoquinone by •OH radicals from the interaction of surface-bound Fe(II) and in situ generated H2O2, the contributions of the oxidation and reduction processes to PNP degradation over S-ZVI were 10 and 90%, respectively. Sulfur in S-ZVI suppressed the pH increase in the reaction media and produced more surface-bound Fe(II) than ZVI for •OH generation via the heterogeneous Fenton reaction process. Since different degradation pathways could lead to different effects on the water environment, such as toxicity, our findings suggest that the oxidizing process induced by S-ZVI during groundwater decontamination should be considered.

Scholl reaction as a powerful tool for the synthesis of nanographenes: a systematic review.

Nanographenes, or extended polycyclic aromatic hydrocarbons, have been attracting increasing attention owing to their widespread applications in organic electronics. However, the atomically precise fabrication of nanographenes has thus far been achieved only through synthetic organic chemistry. Polycyclic aromatic hydrocarbons (PAHs) are popular research subjects due to their high stability, rigid planar structure, and characteristic optical spectra. The recent discovery of graphene, which can be regarded as giant PAH, has further stimulated research interest in this area. Chemists working with nanographene and heterocyclic analogs thereof have chosen it as their preferred tool for the assembly of large and complex architectures. The Scholl reaction has maintained significant relevance in contemporary organic synthesis with many advances in recent years and now ranks among the most useful C–C bond-forming processes for the generation of the π-conjugated frameworks of nanographene or their heterocyclic analogs. A broad range of oxidants and Lewis acids have found use in Scholl-type processes, including Cu(OTf)2/AlCl3, FeCl3, MoCl5, PIFA/BF3–Et2O, and DDQ, in combination with Brønsted or Lewis acids, and the surface-mediated reaction has found especially wide applications in PAH synthesis. Undoubtedly, the utility of the Scholl reaction is supreme in the construction of nanographene and their heterocyclic analogues. The detailed analysis of the progress achieved in this field reveals that many groups have contributed by pushing the boundary of structural possibilities, expanding into surface-assisted cyclodehydrogenation and developing new reagents. In this review, we highlight and discuss the recent modifications in the Scholl reaction for nanographene synthesis using numerous oxidant systems. In addition, the merits or demerits of each oxidative reagent is described herein.

Did a Complex Carbon Cycle Operate in the Inner Solar System?

Solids in the interstellar medium consist of an intimate mixture of silicate and carbonaceous grains. Because 99% of silicates in meteorites were reprocessed at high temperatures in the inner regions of the Solar Nebula, we propose that similar levels of heating of carbonaceous materials in the oxygen-rich Solar Nebula would have converted nearly all carbon in dust and grain coatings to CO. We discuss catalytic experiments on a variety of grain surfaces that not only produce gas phase species such as CH4, C2H6, C6H6, C6H5OH, or CH3CN, but also produce carbonaceous solids and fibers that would be much more readily incorporated into growing planetesimals. CH4 and other more volatile products of these surface-mediated reactions were likely transported outwards along with chondrule fragments and small Calcium Aluminum-rich Inclusions (CAIs) to enhance the organic content in the outer regions of the nebula where comets formed. Carbonaceous fibers formed on the surfaces of refractory oxides may have significantly improved the aggregation efficiency of chondrules and CAIs. Carbonaceous fibers incorporated into chondritic parent bodies might have served as the carbon source for the generation of more complex organic species during thermal or hydrous metamorphic processes on the evolving asteroid.

Comment to the article “Hydroxyl radical scavenging by solid mineral surfaces in oxidative treatment systems: Rate constants and implications” published by K. Rusevova Crincoli and S. G. Huling in Water Research 169, 2020, 115240

The fate of radicals in aqueous suspensions can be significantly affected by surfaces scavenging reactions. When short-lived radicals such as •OH are considered, mass-transfer limitation may come into play. Disregarding these limitations may lead to heavy overestimation of surface-mediated reactions. The present comment exposes a potential misinterpretation of experimental data in a recent study with implications for in-situ chemical oxidation (ISCO) techniques.

Pt deposition on Ni-based superalloy via a combination of galvanic displacement reaction and chemical reduction

We demonstrate the deposition of Pt film on a nickel-based superalloy (CMSX-4) via a combination of galvanic displacement reaction and chemical reduction. The aqueous plating bath contains an optimized mixture of Pt precursor (H2PtCl6), pH adjuster (NaOH), and reducing agent (HCHO). Both time-evolved UV–Vis and X-ray absorption spectra on the plating bath indicate a sequential chemical reduction of Pt4+ → Pt2+ → Pt. In addition, a parasitic galvanic displacement reaction occurs in which Ni, Al, and Co from the CMSX-4 suffer from corrosive dissolution whereas the Pt4+ ions from the plating bath are reduced directly. This surface-mediated galvanic displacement reaction produces numerous Pt nanoparticles serving as the nucleation sites for chemical reduction of Pt4+ from HCHO. Therefore, typical sensitization and activation steps for electroless plating are not necessary in our plating bath. From X-ray diffraction pattern, the Pt film adopts a fcc polycrystalline structure. Images from scanning electron microscope confirm the formation of a dense and continuous Pt film with 1 μm thickness.

Surface Potential and Interfacial Water Order at the Amorphous TiO2 Nanoparticle/Aqueous Interface.

Colloidal nanoparticles exhibit unique size-dependent properties differing from their bulk counterpart, which can be particularly relevant for catalytic applications. To optimize surface-mediated chemical reactions, the understanding of the microscopic structure of the nanoparticle–liquid interface is of paramount importance. Here we use polarimetric angle-resolved second harmonic scattering (AR-SHS) to determine surface potential values as well as interfacial water orientation of ∼100 nm diameter amorphous TiO2 nanoparticles dispersed in aqueous solutions, without any initial assumption on the distribution of interfacial charges. We find three regions of different behavior with increasing NaCl concentration. At very low ionic strengths (0–10 μM), the Na+ ions are preferentially adsorbed at the TiO2 surface as inner-sphere complexes. At low ionic strengths (10–100 μM), a distribution of counterions equivalent to a diffuse layer is observed, while at higher ionic strengths (>100 μM), an additional layer of hydrated condensed ions is formed. We find a similar behavior for TiO2 nanoparticles in solutions of different basic pH. Compared to identically sized SiO2 nanoparticles, the TiO2 interface has a higher affinity for Na+ ions, which we further confirm with molecular dynamics simulations. With its ability to monitor ion adsorption at the surface with micromolar sensitivity and changes in the surface potential, AR-SHS is a powerful tool to investigate interfacial properties in a variety of catalytic and photocatalytic applications.

Inhibition of Discharge Side Reactions by Promoting Solution-Mediated Oxygen Reduction Reaction with Stable Quinone in Li-O2 Batteries.

Aprotic lithium-oxygen (Li-O2) batteries with an ultrahigh theoretical energy density have great potential in rechargeable power supply, while their application still faces several challenges, especially poor cycle stability. To solve the problems, one of the effective strategies is to inhibit the generation of the LiO2 intermediate produced via a surface-mediated oxygen reduction reaction (ORR) pathway, which is an important species inducing byproduct generation and low cell cyclic stability. Herein, a series of quinones and solid materials serve as the solution-mediated and surface-mediated ORR catalysts, and it was found that the generation of LiO2 and byproducts from solid catalysts was inhibited by quinones. Among the studied quinones, benzo[1,2-b:4,5-b']dithiophene-4,8-dione, a quinone molecule with the advantage of a highly symmetrical planar and conjugated structure and without α-H, exhibits high redox potential, diffusion coefficient, and electrochemical stability, and consequently the best ORR activities and the capability to inhibit byproduct generation. It indicated that the increase of the solution-mediated ORR pathway plays an important role in restraining the discharging side reaction, substantially improving cell cycle stability and capacity. This study provides the theoretical and experimental basis for better understanding the ORR process of Li-O2 batteries.

Rational design of porous nitrogen-doped Ti3C2 MXene as a multifunctional electrocatalyst for Li–S chemistry

The detrimental shuttle effect and retarded sulfur reaction kinetics in lithium–sulfur (Li–S) chemistry mainly lead to inferior electrochemical performances, posing a fatal threat to the practical application of Li–S batteries. Herein, porous N-doped Ti3C2 MXene (P-NTC) has been realized by a scalable sacrificial templating route, resulting in the rational design of active electrocatalyst for Li–S chemistry. Benefiting from the superb electron conductivity, large surface area and strong interaction with lithium polysulfides (LiPSs), P-NTC can trigger the surface-mediated redox reaction of LiPSs. Moreover, the homogenous nitrogen doping on Ti3C2 gives rise to enhanced interfacial interaction with Li atom and lowered dissociation barrier for Li2S. Therefore, the template-derived P-NTC not only acts as an effective LiPS immobilizer but also serves as a multifunctional electrocatalyst to propel the nucleation and decomposition of Li2S in discharge and charge processes, respectively. As expected, thus-fabricated S/P-NTC cathode maintains a low capacity decay of only 0.033% per cycle at 2.0 C over 1200 cycles. In further contexts, our ability to tune the sulfur mass loadings enables fabricated cathodes to harvest a high areal capacity of 9.0 mAh cm−2, holding great promise in future practical applications.

Intensifying Diffusion-Limited Reactions by Using Static Mixer Electrodes in a Novel Electrochemical Flow Cell

Surface-mediated reactions require effective mixing for them to be intense and efficient. In electrochemistry where the reactants must contact electrode surfaces for a sufficient time to enable electron tunnelling to occur, exhaustive electrolysis in poorly stirred reactors can take many hours to complete. As a consequence, electrochemical processing in many industries is restricted to batch processing which is more costly and labour intensive than continuous processing and results in significant down time between batches. This is not ideal for bulk production or treatment. Here we describe CSIRO’s novel axial flow electrochemical cell which aims to address these mixing problems by using a bespoke static mixer electrode (SME), designed by computational fluid dynamics (CFD) and manufactured using additive manufacturing (AM) technology to retain the fidelity of the original design. This electrode was characterized by SEM-EDS and electrosorption measurements. The performance of the electrochemical flow cell was evaluated by probing the ferricyanide ([Fe(CN)6]3−) reduction reaction on a platinum-coated SME under controlled mass transport conditions using cyclic voltammetry (CV), linear sweep voltammetry (LSV) and chronoamperometric measurements. This reaction was chosen because it has fast electron transfer kinetics, so the rate of reaction in dilute solutions is limited only by mass transport of the reactant to the electrode surface. Under the highest flow rate used (400 ml min−1) the cell enhanced the rate of reduction of ([Fe(CN)6]3− in a 10−3 M solution by 45 times compared with the no flow result. The impact the cell has diminishes as the concentration increases where mass transport plays a diminishing role in controlling the reaction rate. The performance of the cell is compared with a rotating disk electrode and a tubular flow cell and mass transfer coefficients are also presented for different reactant concentrations and flow conditions.

How to Measure the Reaction Performance of Heterogeneous Catalytic Reactions Reliably

Ding Ma is a professor of Peking University. He is an advisory member for various journals, has been Associate Editor for the catalysis journal of RSC, Catalysis Science & Technology, since 2014, and was elected as a Fellow of the Royal Society of Chemistry in 2016. His research interests are heterogeneous catalysis, especially those related with energy issues, including C1 chemistry (methane, CO2, and syngas conversion), new reaction routes for sustainable chemistry, and the development of an in situ spectroscopic method that can be operated at working reaction conditions to study reaction mechanisms. Bingjun Xu is an Associate Professor in the Department of Chemical and Biomolecular Engineering at University of Delaware. He received his PhD in Physical Chemistry, advised by Prof. Friend, from Harvard University in 2011 and worked with Prof. Davis at Caltech as a postdoctoral researcher. The overarching goal of Xu research group is to develop innovative strategies to produce renewable electricity, fuels, and chemicals by the rational design of efficient thermo- and electro-catalytic processes. A special focus is placed on the mechanistic understanding of surface-mediated reactions by employing and developing state-of-the-art spectroscopic and kinetic techniques. Meng Wang is a Research Scientist in the College of Chemistry and Molecular Engineering at Peking University. He received his PhD in Chemistry from Technical University of Munich, advised by Prof. Lercher, in 2018 and worked in Pacific Northwest National Laboratory as a Research Associate from 2015 to 2019. Wang’s principal research task focuses on deciphering the kinetic and mechanistic pathways for catalytic reactions by combining reaction kinetics, isotopic experiments, and various in situ characterization methods. Mengtao Zhang is a PhD student in the College of Chemistry and Molecular Engineering at Peking University (Prof. Ding Ma). He received his BS (Chemistry) from Nanjing University in 2015. His research interests include water activation and hydrogen production, CO2 and other greenhouse gas conversion into desirable chemicals, design and development of new catalysts, and operando reaction mechanism and kinetics study.

Microcarrier-Assisted Inorganic Shelling of Lead Halide Perovskite Nanocrystals.

The conventional strategy of synthetic colloidal chemistry for bright and stable quantum dots has been the production of epitaxially matched core/shell heterostructures to mitigate the presence of deep trap states. This mindset has been shown to be incompatible with lead halide perovskite nanocrystals (LHP NCs) due to their dynamic surface and low melting point. Nevertheless, enhancements to their chemical stability are still in great demand for the deployment of LHP NCs in light-emitting devices. Rather than contend with their attributes, we propose a method in which we can utilize their dynamic, ionic lattice and uniquely defect-tolerant band structure to prepare non-epitaxial salt-shelled heterostructures that are able to stabilize these materials against their environment, while maintaining their excellent optical properties and increasing scattering to improve out-coupling efficiency. To do so, anchored LHP NCs are first synthesized through the heterogeneous nucleation of LHPs onto the surface of microcrystalline carriers, such as alkali halides. This first step stabilizes the LHP NCs against further merging, and this allows them to be coated with an additional inorganic shell through the surface-mediated reaction of amphiphilic Na and Br precursors in apolar media. These inorganically shelled NC@carrier composites offer significantly improved chemical stability toward polar organic solvents, such as γ-butyrolactone, acetonitrile, N-methylpyrrolidone, and trimethylamine, demonstrate high thermal stability with photoluminescence intensity reversibly dropping by no more than 40% at temperatures up to 120 °C, and improve compatibility with various UV-curable resins. This mindset for LHP NCs creates opportunities for their successful integration into next-generation light-emitting devices.

Reductive debromination of decabromodiphenyl ether by iron sulfide-coated nanoscale zerovalent iron: mechanistic insights from Fe(II) dissolution and solvent kinetic isotope effects

The mechanism that iron sulfide-coated nanoscale zero valent iron (S-nZVI) has better reduction activity towards organic pollutants than nanoscale zero-valent iron (nZVI) has long been debated. In this work, a systematic study was investigated to compare differences of main influences, BDE-209 degradation pathway, degradation kinetics and reduction mechanism of BDE-209 between nZVI and S-nZVI systems. The observed transformation rate of BDE-209 (kobs) by S-nZVI was 58.3 and 7.1 times greater than that by S2− and nZVI, respectively. The valence change of Fe and S on S-nZVI surface before and after BDE-209 degradation process based on XPS characterization confirmed that both Fe0 and iron sulfide were the reduction entity of the surface-mediated reaction. The presence of tetrahydrofuran (THF) promoted the surface contact of BDE-209 with S-nZVI, thus accelerating the BDE-209 degradation process. Compared with nZVI, the iron sulfide coated on the Fe0 core surface could not only greatly reduce unnecessary electron loss via Fe0 corrosion with water, but also accelerate the transmission of electrons from Fe0 core to organic pollutants according to Fe(II) dissolution and solvent kinetic isotope effects investigations. These findings help to clarify the synergistic degradation mechanism between Fe0 core and iron sulfide shell layer.

A field study of polychlorinated dibenzo-p-dioxins and dibenzofurans formation mechanism in a hazardous waste incinerator: Emission reduction strategies

To clarify the dominant formation mechanism of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) and reduce PCDD/F emissions in full-scale hazardous waste incinerators (HWIs), three tests were designed by adding different PCDD/F precursors in phenol-containing raw material. Flue gas from three stages of the incineration facility, as well as bottom ash and fly ash were collected to investigate formation pathways, emission characteristics and mass balance of PCDD/Fs. The results showed that in tests A and C, the PCDD/F emission levels were 0.02 and 0.83 ng I-TEQ Nm−3, with adding naphthalene and p-dichlorobenzene, respectively. Test B, the control group, only incinerated raw materials, resulting in 0.72 ng I-TEQ Nm−3 PCDD/F emissions. PCDD/F formation mechanism analysis suggested that high-temperature radical-molecule reaction was the dominate pathway in test A, while for test B, memory effect in the air pollution control devices (APCDs) led to high PCDD/F emissions. With the addition of p-dichlorobenzene in test C, PCDD/F levels at the quenching tower outlet were one order of magnitude higher than those observed at the inlet, indicating that the quenching tower failed to suppress the formation of PCDD/Fs. The PCDD/PCDF ratios indicate that with the abundance of PCDD/F precursors, surface-mediated precursor reaction is the dominant formation mechanism in low-temperature stages. These finding raise the following strategies for industry to control PCDD/F emissions: (1) strict regulation of the organochlorine content in feed material; (2) frequent and thorough cleaning the APCDs; (3) optimizing the injection rate of activated carbon.

Ni-Induced C-Al2O3-Framework (NiCAF) Supported Core-Multishell Catalysts for Efficient Catalytic Ozonation: A Structure-to-Performance Study.

During catalytic ozonation, Al2O3-supported catalysts usually have stable structures but relatively low surface activity, while carbon-supported catalysts are opposite. To encourage their synergisms, we designed a Ni-induced C-Al2O3-framework (NiCAF) and reinforced it with a Cu-Co bimetal to create an efficient catalyst (CuCo/NiCAF) with a core-multishell structure. The partial graphitization of carbon adjacent to Ni crystals formed a strong out-shell on the catalyst surface. The rate constant for total organic carbon removal of CuCo/NiCAF (0.172 ± 0.018 min-1) was 67% and 310% higher than that of Al2O3-supported catalysts and Al2O3 alone, respectively. The metals on CuCo/NiCAF contributed to surface-mediated reactions during catalytic ozonation, while the embedded carbon enhanced reactions within the solid-liquid boundary layer and in the bulk solution. Moreover, carbon embedment provided a 76% increase in ·OH-production efficiency and an 86% increase in organic-adsorption capacity compared to Al2O3-supported catalysts. During the long-term treatment of coal-gasification wastewater (∼5 m3 day-1), the pilot-scale demonstration of CuCo/NiCAF-catalyzed ozonation revealed a 120% increase in ozone-utilization efficiency (ΔCOD/ΔO3 = 2.12) compared to that of pure ozonation (0.96). These findings highlight catalysts supported on NiCAF as a facile and efficient approach to achieve both high catalytic activity and excellent structural stability, demonstrating that they are highly viable for practical applications.

Understanding Charge-Transfer and Kinetic Processes in Particulate Photoelectrode Morphologies for Solar Water Splitting

Z-scheme semiconductor particles, either as suspended solids in an aqueous solution1–3 with soluble redox shuttles, or as particulate sheets4,5 with solid-state electronic contacts, is a promising two-step approach to use solar energy to split water to produce hydrogen and oxygen. For Z-scheme particles to operate efficiently, it is important to realize efficient electron-transfer from the oxygen evolution particle to the hydrogen evolution particle, and to selectively drive the reactions of interest at the semiconductor-electrolyte interface. I will present on the development of a numerical modeling framework to evaluate the transport and kinetics of photogenerated charge-carriers inside a spherical semiconductor particle and across the semiconductor–electrolyte interface for Z-scheme systems with and without soluble redox shuttles. The boundary conditions applied at the electron-transfer interfaces are formulated to take into account all plausible particle surface-mediated redox reactions. The model is used to elucidate the impacts of particle size, recombination pathways, kinetic parameters and the electrochemical potential of the redox species on the performance of these particles. Results are further interpreted to identify strategies to boost the energy conversion efficiency and quantify the influence of the electrode morphologies on the overall rates of hydrogen production in Z-scheme solar water splitting systems. References Fabian, D. M. et al. Particle suspension reactors and materials for solar-driven water splitting. Energy Environ. Sci. 8, 2825–2850 (2015).Bala Chandran, R., Breen, S., Shao, Y., Ardo, S. & Weber, A. Z. Evaluating particle-suspension reactor designs for Z-scheme solar water splitting via transport and kinetic modeling. Energy Environ. Sci. 11, 115–135 (2018).Keene, S., Bala Chandran, R. & Ardo, S. Calculations of theoretical efficiencies for electrochemically-mediated tandem solar water splitting as a function of bandgap energies and redox shuttle potential. Energy Environ. Sci. (2019). doi:10.1039/C8EE01828FChen, S., Takata, T. & Domen, K. Particulate photocatalysts for overall water splitting. Nat. Rev. Mater. 2, 17050 (2017).Goto, Y. et al. A Particulate Photocatalyst Water-Splitting Panel for Large-Scale Solar Hydrogen Generation. Joule 0, (2018). Figure 1

The Effect of Surface Reconstruction on the Oxygen Reduction Reaction Properties of LaMnO3

Perovskites have been widely studied for electrocatalysis due to the exceptional activity they exhibit for surface-mediated redox reactions. To date, descriptors based on density functional theory ...

Bimetallic Fe/Al system: An all-in-one solid-phase Fenton reagent for generation of hydroxyl radicals under oxic conditions

In the classic Fenton reaction, both H2O2 and ferrous ion (Fe(II)) are required under a narrow low pH range to produce hydroxyl radicals (OH). The modified Fenton processes including heterogeneous Fenton-like reaction, photo-Fenton reaction and electro-Fenton reaction developed to overcome the drawbacks of the homogeneous Fenton reaction have recently received increasing attention. However, all the modifications of the classic Fenton reaction cannot be assembled into one system and require external supply of reagents or energy. We present here, bimetallic Fe/Al, a novel solid-phase Fenton reagent capable of in situ generation of H2O2 and Fe(II) to form OH under near neutral pH conditions without an external energy supply. Aluminum acts as an electron donor to maintain the electron supply and preserve the outer layer of iron at the zero-valence state with enhanced surface areas. The production of OH by bimetallic Fe/Al was quantified and further detected by an electron paramagnetic resonance (EPR) analysis under oxic conditions. Radical scavenging tests were performed by adding isopropanol or 1,4‑benzoquinone in the system to investigate the nature of the oxidants produced during the oxidative process. Bimetallic Fe/Al system for the Fenton reaction in water involves both surface-mediated and aqueous-phase reactions. A pilot scale test using a continuous-flow column packed with Fe/Al (9.8 kg) demonstrated the capability of bimetallic Fe/Al for COD removal of acidic dye solutions. The novelty of bimetallic Fe/Al is that it is an all-in-one solid-phase Fenton reagent that can be readily applied to a wide variety of environmental applications.

Promoting Surface-Mediated Oxygen Reduction Reaction of Solid Catalysts in Metal-O2 Batteries by Capturing Superoxide Species.

The oxygen reduction reaction (ORR) in aprotic electrolyte is the essential reaction in metal-oxygen batteries. Capturing and shifting the absorbed metal superoxide intermediates/products from a cathode surface is a long-standing challenge to clarify the ORR mechanism, accelerate the ORR, and improve the stability and energy density of metal-oxygen batteries. Herein, a bioinspired pathway in which cathode solid catalysts and soluble anthraquinone (AQ) molecules initiate an "enzyme-coenzyme" cooperative catalysis mechanism is developed to greatly boost the ORR activity of solid catalysts over 10-fold, in which AQ acts as a scavenger to capture and shift the absorbed superoxide species from the cathode surface to the aprotic electrolyte. Taking the lithium-oxygen (Li-O2) battery as a model system, the cell discharge ORR mechanism is well illustrated and capacities are significantly improved over 3 times in the presence of AQ molecules. This concept represents the first demonstration of stabilizing and solvating superoxide species to substantially accelerate ORR catalysis of solid catalysts and enhance the performance of metal-O2 batteries through biomimicking coenzyme-assisted reactions.