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Metal-organic frameworks (MOFs) are increasingly being investigated as electrocatalysts for the oxygen evolution reaction (OER) due to their unique modular structures that present a hybrid between molecular and heterogeneous catalysts, featuring well-defined active sites. However, many fundamental questions remain open regarding the electrochemical stability of MOFs, structural reconstruction of coordination sites, and the role of in situ-formed species. Here, we report the structural transformation of a surface-grown MOF containing cobalt nodes and 1,1'-ferrocenedicarboxylic acid linkers (denoted as CoFc-MOF) during the OER in alkaline electrolyte. Ex situ and in situ investigations of CoFc-MOF film suggest that the MOF acts as a precatalyst and undergoes a two-step restructuring process under operating conditions to generate a metal oxyhydroxide phase. The MOF-derived metal oxyhydroxide catalyst, supported on nickel foam electrodes, displays high activity toward the OER with an overpotential of 190 mV at a current density of 10 mA cm-2. While this study demonstrates the necessity of investigating structural evolution of MOFs during electrocatalysis, it also shows the potential of using MOFs as precursors in catalyst design.
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The degradation and aging of carbon felt electrodes is a main reason for the performance loss of Vanadium Redox Flow Batteries over extended operation time. In this study, the chemical mechanisms for carbon electrode degradation are investigated and distinct differences in the degradation mechanisms on positive and negative electrodes have been revealed. A combination of surface analysis techniques such as X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, and Electrochemical Impedance Spectroscopy (EIS) was applied for this purpose. In addition to understanding the chemical and physical alterations of the aged electrodes, a thermal method for reactivating aged electrodes was developed. The reactivation process was successfully applied on artificially aged electrodes as well as on electrodes from a real-world industrial vanadium redox flow battery system. The aforementioned analysis methods provided insight and understanding into the chemical mechanisms of the reactivation procedure. By applying the reactivation method, the lifetime of vanadium redox flow batteries can be significantly extended.
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Carbon-based electrodes are used in flow batteries to provide active centers for vanadium redox reactions. However, strong controversy exists about the exact origin of these centers. This study systematically explores the influence of structural and functional groups on the vanadium redox reactions at carbon surfaces. Pyridine, phenol and butyl containing groups are attached to carbon felt electrodes. To establish a unique comparison between the model and real-world behavior, both non-activated and commercially used thermally activated felts serve as a substrate. Results reveal enhanced half-cell performance in non-activated felt with introduced hydrophilic functionalities. However, this cannot be transferred to the thermally activated felt. Beyond a decrease in electrochemical activity, a reduced long-term stability can be observed. This work indicates that thermal treatment generates active sites that surpass the effect of functional groups and are even impeded by their introduction.
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The controlled cation substitution is an effective strategy for optimizing the density of states and enhancing the electrocatalytic activity of transition metal oxide catalysts for water splitting. However, achieving tailored mesoporosity while maintaining elemental homogeneity and phase purity remains a significant challenge, especially when aiming for complex multi-metal oxides. In this study, we utilized a one-step impregnation nanocasting method for synthesizing mesoporous Mn-, Fe-, and Ni-substituted cobalt spinel oxide (Mn0.1Fe0.1Ni0.3Co2.5O4, MFNCO) and demonstrate the benefits of low-temperature calcination within a semi-sealed container at 150-200 °C. The comprehensive discussion of calcination temperature effects on porosity, particle size, surface chemistry and catalytic performance for the alkaline oxygen evolution reaction (OER) highlights the importance of humidity, which was modulated by a pre-drying step. The catalyst calcined at 170 °C exhibited the lowest overpotential (335 mV at 10 mA cm-2), highest current density (433 mA cm-2 at 1.7 V vs. RHE, reversible hydrogen electrode) and further displayed excellent stability over 22 h (at 10 mA cm-2). Furthermore, we successfully adapted this method to utilize cheap, commercially available silica gel as a hard template, yielding comparable OER performance. Our results represent a significant progress in the cost-efficient large-scale preparation of complex multi-metal oxides for catalytic applications.
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In this paper, the experimental characterization of the viscoelastic properties of thermoplastic polyurethane (TPU) samples through creep experiments is presented. Experiments were conducted at different constant temperature levels (15, 25, and 35 ∘C), for three different tensile stress levels (0.3, 0.5, and 0.7 MPa), and at different physisorbed water contents, providing access to: (i) the temperature dependency of creep parameters and (ii) the assessment, if behavior is indeed viscoelastic. The physisorbed water content was achieved by exposing virgin samples to environments with relative humidity ranging from 0 to 80 percent until mass stability was reached. Creep tests were conducted immediately afterwards with this particular humidity level. The main results of this study are as follows. The temperature dependency of the obtained creep parameters is well described in Arrhenius plots. With regard to water content, two prototype material responses were observed in the experimental program and accurately modeled using the following fractional-type models: (i) Scott Blair-type (i.e., power-law-type) only behavior, pronounced for the combination of low water content/low temperature; (ii) combined Scott Blair plus Lomnitz (i.e., log-type) behavior for high water content/high temperature. This change in behavior associated with certain thresholds for the specified environmental conditions (temperature and relative humidity) may indicate the initiation of hydrogen bond breakage and rearrangement (carbamate H-bonds and physisorbed water H-bonds). Regarding the short-term or quasi-instantaneous behavior, the Scott Blair element seems highly appropriate and may be better suited than the standard elastic model: the Hookean spring. We associated Scott Blair behavior with the load-induced, quasi-instantaneous re-arrangement of polymer network chains. The secondary viscoelastic mechanism associated with the Lomnitz element, hydrogen bond breakage and rearrangement, comes into play for higher temperatures and/or higher physisorbed water contents. In this case, the contribution of the two constitutive elements is well separated due to the large number of the characteristic time of the Lomnitz element, much larger than the respective value for the Scott Blair element.
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Plastic upcycling through catalytic transformations is an attractive concept to valorize waste, but the clean and energy-efficient production of high-value products from plastics remains challenging. Here, we introduce chemoenzymatic photoreforming as a process coupling enzymatic pretreatment and solar-driven reforming of polyester plastics under mild temperatures and pH to produce clean H2 and value-added chemicals. Chemoenzymatic photoreforming demonstrates versatility in upcycling polyester films and nanoplastics to produce H2 at high yields reaching â¼103-104 µmol gsub-1 and activities at >500 µmol gcat-1 h-1. Enzyme-treated plastics were also used as electron donors for photocatalytic CO2-to-syngas conversion with a phosphonated cobalt bis(terpyridine) catalyst immobilized on TiO2 nanoparticles (TiO2|CotpyP). Finally, techno-economic analyses reveal that the chemoenzymatic photoreforming approach has the potential to drastically reduce H2 production costs to levels comparable to market prices of H2 produced from fossil fuels while maintaining low CO2-equivalent emissions.
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In this paper, an experimental campaign, as regards the thermo-mechanical properties (heat capacity, thermal conductivity, Young's modulus, and tensile (bending) strength) of talcum-based steatite ceramics with artificially introduced porosity, is presented. The latter has been created by adding various amounts of an organic pore-forming agent, almond shell granulate, prior to compaction and sintering of the green bodies. The so-obtained porosity-dependent material parameters have been represented by homogenization schemes from effective medium/effective field theory. As regards the latter, thermal conductivity and elastic properties are well described by the self-consistent estimate, with effective material properties scaling in a linear manner with porosity, with the latter in the range of 1.5 vol-%, representing the intrinsic porosity of the ceramic material, to 30 vol-% in this study. On the other hand, strength properties are, due to the localization of the failure mechanism in the quasi-brittle material, characterized by a higher-order power-law dependency on porosity.
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A molecular cobalt phthalocyanine (CoPc) catalyst has been integrated in an ethylene-bridged periodic mesoporous organosilica (PMO) to fabricate a hybrid material, CoPc-PMO, that catalyses CO2 reduction to CO in a photocatalytic system using [Ru(bpy)3]2+ (bpy = 2,2'-bipyridine) as a photosensitizer and 1,3-dimethyl-2-phenyl-2,3-dihydro-1H-benzo[d]imidazole (BIH) as an electron donor. CoPc-PMO displays a Co-based turnover number (TONCO) of >6000 for CO evolution with >70% CO-selectivity after 4 h irradiation with UV-filtered simulated solar light, and a quantum yield of 1.95% at 467 nm towards CO. This system demonstrates a benchmark TONCO for immobilised CoPc-based catalysts towards visible light-driven CO2 reduction.
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Ethylene is an important feedstock in the chemical industry, but currently requires production from fossil resources. The electrocatalytic oxidative decarboxylation of succinic acid offers in principle an environmentally friendly route to generate ethylene. Here, a detailed investigation of the role of different carbon electrode materials and characteristics revealed that a flat electrode surface and high ordering of the carbon material are conducive for the reaction. A range of electrochemical and spectroscopic approaches such as Koutecky-Levich analysis, rotating ring-disk electrode (RRDE) studies, and Tafel analysis as well as quantum chemical calculations, electron paramagnetic resonance (EPR), and in situ infrared (IR) spectroscopy generated further insights into the mechanism of the overall process. A distinct reaction intermediate was detected, and the decarboxylation onset potential was determined to be 2.2-2.3 V versus the reversible hydrogen electrode (RHE). Following the mechanistic studies and electrode optimization, a two-step bio-electrochemical process was established for ethylene production using succinic acid sourced from food waste. The initial step of this integrated process involves microbial hydrolysis/fermentation of food waste into aqueous solutions containing succinic acid (0.3 M; 3.75 mmol per g bakery waste). The second step is the electro-oxidation of the obtained intermediate succinic acid to ethylene using a flow setup at room temperature, with a productivity of 0.4-1 µmol ethylene cmelectrode -2 h-1. This approach provides an alternative strategy to produce ethylene from food waste under ambient conditions using renewable energy.
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Pollution from microplastics and anthropogenic fibres threatens lakes, but we know little about what factors predict its accumulation. Lakes may be especially contaminated because of long water retention times and proximity to pollution sources. Here, we surveyed anthropogenic microparticles, i.e., microplastics and anthropogenic fibres, in surface waters of 67 European lakes spanning 30° of latitude and large environmental gradients. By collating data from >2,100 published net tows, we found that microparticle concentrations in our field survey were higher than previously reported in lakes and comparable to rivers and oceans. We then related microparticle concentrations in our field survey to surrounding land use, water chemistry, and plastic emissions to sites estimated from local hydrology, population density, and waste production. Microparticle concentrations in European lakes quadrupled as both estimated mismanaged waste inputs and wastewater treatment loads increased in catchments. Concentrations decreased by 2 and 5 times over the range of surrounding forest cover and potential in-lake biodegradation, respectively. As anthropogenic debris continues to pollute the environment, our data will help contextualise future work, and our models can inform control and remediation efforts.
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Lagos , Microplásticos , Material Particulado , Poluentes da Água/análise , Ecossistema , Europa (Continente) , Água Doce/química , Hidrologia , Plásticos , Águas ResiduáriasRESUMO
The chemical inertness of polyethylene makes chemical recycling challenging and motivates the development of new catalytic innovations to mitigate polymer waste. Current chemical recycling methods yield a complex mixture of liquid products, which is challenging to utilize in subsequent processes. Here, we present an oxidative depolymerization step utilizing diluted nitric acid to convert polyethylene into organic acids (40% organic acid yield), which can be coupled to a photo- or electrocatalytic decarboxylation reaction to produce hydrocarbons (individual hydrocarbon yields of 3 and 20%, respectively) with H2 and CO2 as gaseous byproducts. The integrated tandem process allows for the direct conversion of polyethylene into gaseous hydrocarbon products with an overall hydrocarbon yield of 1.0% for the oxidative/photocatalytic route and 7.6% for the oxidative/electrolytic route. The product selectivity is tunable with photocatalysis using TiO2 or carbon nitride, yielding alkanes (ethane and propane), whereas electrocatalysis on carbon electrodes produces alkenes (ethylene and propylene). This two-step recycling process of plastics can use sunlight or renewable electricity to convert polyethylene into valuable, easily separable, gaseous platform chemicals.
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Solar-driven reforming uses sunlight and a photocatalyst to generate H2 fuel from waste at ambient temperature and pressure. However, it faces practical scaling challenges such as photocatalyst dispersion and recyclability, competing light absorption by the waste solution, slow reaction rates and low conversion yields. Here, the immobilisation of a noble-metal-free carbon nitride/nickel phosphide (CNx |Ni2 P) photocatalyst on textured glass is shown to overcome several of these limitations. The 1â cm2 CNx |Ni2 P panels photoreform plastic, biomass, food and mixed waste into H2 and organic molecules with rates comparable to those of photocatalyst slurries. Furthermore, the panels enable facile photocatalyst recycling and novel photoreactor configurations that prevent parasitic light absorption, thereby promoting H2 production from turbid waste solutions. Scalability is further verified by preparing 25â cm2 CNx |Ni2 P panels for use in a custom-designed flow reactor to generate up to 21â µmolH 2 m-2 h-1 under "real-world" (seawater, low sunlight) conditions. The application of inexpensive and readily scalable CNx |Ni2 P panels to photoreforming of a variety of real waste streams provides a crucial step towards the practical deployment of this technology.
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Metal salt hydrate (MSH) solutions allow for the complete solubilisation of biomass and we demonstrate its use as a reaction medium for the photocatalytic reforming of lignocellulose. Different types of photocatalysts such as TiO2 and carbon nitride can be employed in MSH to produce H2 and organic products under more benign conditions than the commonly required extreme pH aqueous solutions.
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Several ZrO2 -supported ruthenium catalysts were prepared and utilized in the oxidation of 5-hydroxymethylfurfural (HMF) to 2,5-furandicarboxylic acid (FDCA) under base-free conditions. Full conversion of HMF and almost perfect selectivity towards FDCA (97 %) were achieved after 16â h by using pure O2 as an oxidant and water as a solvent. The catalytic tests show that the size of the Ru particles is crucial for the catalytic performance and that the utilization of high-surface-area ZrO2 leads to formation of very small Ru particles. Superior activity was obtained for catalysts based on ZrO2 that had been synthesized by a surface-casting method and has high surface areas up to 256â m2 g-1 . In addition to good activity and selectivity, these catalysts show also high stability and constant activity upon recycling, confirming the suitability of Ru/ZrO2 in the base-free oxidation of HMF.
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About 15â years ago, the Ryoo group described the synthesis of CMK-5, a material consisting of a hexagonal arrangement of carbon nanotubes. Extension of the surface casting synthesis to oxide compositions, however, was not possible so far, in spite of many attempts. Here it is demonstrated, that crystalline mesoporous hollow zirconia materials with very high surface areas up to 400â m2 g-1 , and in selected cases in the form of CMK-5-like, are indeed accessible via such a surface casting process. The key for the successful synthesis is an increased interaction between the silica hard template surface and the zirconia precursor species by using silanol group-rich mesoporous silica as a hard template. The surface areas of the obtained zirconias exceed those of conventionally hard-templated ones by a factor of two to three. The surface casting process seems to be applicable also to other oxide materials.
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The characterization of the target proteins of drug molecules has become an important goal in understanding its mode of action and origin of side effects due to off-target binding. This is especially important for covalently binding drugs usually containing electrophilic moieties, which potentially can react with nucleophilic residues found in many proteins. This review gives a comprehensive overview of the use of activity-based protein profiling (ABPP) as an efficient tool for the target identification of covalently binding drugs.
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Descoberta de Drogas/métodos , Terapia de Alvo Molecular/métodos , Preparações Farmacêuticas/química , Preparações Farmacêuticas/metabolismo , Proteínas/química , Proteínas/metabolismo , Animais , Humanos , Ligação ProteicaRESUMO
The urgency of producing new environmentally-friendly polyesters strongly enhanced the development of bio-based poly(ethylene furanoate) (PEF) as an alternative to plastics like poly(ethylene terephthalate) (PET) for applications that include food packaging, personal and home care containers and thermoforming equipment. In this study, PEF powders of various molecular weights (6, 10 and 40kDa) were synthetized and their susceptibility to enzymatic hydrolysis was investigated for the first time. According to LC/TOF-MS analysis, cutinase 1 from Thermobifida cellulosilytica liberated both 2,5-furandicarboxylic acid and oligomers of up to DP4. The enzyme preferentially hydrolyzed PEF with higher molecular weights but was active on all tested substrates. Mild enzymatic hydrolysis of PEF has a potential both for surface functionalization and monomers recycling.
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Hidrolases de Éster Carboxílico/metabolismo , Furanos , Polietilenos , Actinobacteria/enzimologia , Proteínas de Bactérias/metabolismo , Ácidos Dicarboxílicos/química , Ácidos Dicarboxílicos/metabolismo , Furanos/química , Furanos/metabolismo , Hidrólise , Polietilenos/química , Polietilenos/metabolismoRESUMO
PURPOSE: Over the preceeding decades, after periods of dramatic decline and extinction in many parts of Europe, the White-tailed Sea Eagle (Haliaeetus albicilla) has re-colonized traditional breeding areas. However, this large apex predator remains threatened, not only by the bioaccumulation of environmental pollutants, but also by targeted poisoning and poaching. In connection with a forensic case, a novel PCR assay was developed for the sensitive and specific detection of sea eagle DNA traces in questioned samples of unknown origin. METHODS: The assay amplifies a fragment of the popular phylogenetic marker gene cytochrome b. Primers were designed to bind sites with relatively high variability between homologous sequences from H. albicilla and other related European birds of prey. RESULTS: Assay sensitivity was sufficient for single cell analysis. Specificity was tested in vitro and the primers did not cross-detect DNA from humans, chicken and the following raptors: Common Buzzard (Buteo buteo), Northern Goshawk (Accipiter gentilis), Red Kite (Milvus milvus) and Black Kite (Milvus migrans). Applicability for the analysis of poor quality samples was demonstrated with extracts from field-collected small molted down feathers that did not contain detectable amounts of sea eagle nuclear DNA. Amplicons of the expected size were generated, purified and sequenced. Sequence data were subjected to Basic Local Alignment Search Tool analysis and affiliated with cytochrome b from H. albicilla. CONCLUSIONS: The novel PCR primers allowed for the correct assignment of traces from H. albicilla, even in mixed samples and in cases with limited and degraded biological material.