Showing papers on "Substrate (chemistry) published in 2017"

A review on the factors affecting the photocatalytic degradation of hazardous materials

Abstract: The oxidation rates and efficiency of the photocatalytic system are highly dependent on a number of operational parameters that govern the photodegradation of the organic molecule Several study have been reported the significance of operational parameter The photodegradation depends on the some basic parameters which are concentration of substrate amount of photocatalyst pH of the solution temperature of reaction medium time of irradiation of light the intensity of light surface area of photocatalyst dissolve oxygen in the reaction medium nature of the photocatalyst nature of the substrate doping of metal ions and non metal and structure of photocatalyst and substrate The photodegradation of organic compound have been studied by the several scientists and conclude the optimum conditions for the photodegradation of organic compound The photodegradation of organic compounds was found maximum at low concentration of organic substrate with optimum amount of photocatalyst The pH of the solution is also affect the photodegradation of organic substrate The Titania show the maximum adsorption at low pH hence the photodegradation also found maximum at low pH The surface area is the crucial factor for the photodegradation of organic substrate If we are increasing the surface area of photocatalyst the photodegradation of organic substrate increase This is because that the number of active site increased with increasing the surface area The amount of photocatalyst is the primary requirement of any photocatalysis process The amount of photocatalyst should be optimum if we take the high amount of photocatalyst the photodegradation is decreased if we take the low amount of photocatalyst the photodegradation also decreased The doping of metal ions and non metal ions affect the photodegradation of organic substrate Therefore we have to use the metal ions which increased the positive charge on the surface of photocatalyst The temperature and irradiation of light also affect the photodegradation of organic substrate For the maximum photodegradation the photocatalytic reaction should perform at room temperature not greater than deg C The light of irradiation should be used which exit the electron easily from valence band to conduction band or equal to band gap energy

One-step synthesis of uniform nanoparticles of porphyrin functionalized ceria with promising peroxidase mimetics for H2O2 and glucose colorimetric detection

Abstract: Hydrogen peroxide (H 2 O 2 ) is a key molecule in biology. As a byproduct of many enzymatic reactions, H 2 O 2 is also a popular biosensor target. We report the first use of uniform nanoparticles of porphyrin functionalized ceria (Por-Ceria) prepared by a one-step method, as a colorimetric probe in detection for H 2 O 2 . Por-ceria nanoparticles exhibited strong intrinsic peroxidase activity toward a classical peroxidase substrate, 3,3′,5,5′-tetramethylbenzidine (TMB), in the presence of H 2 O 2 . Enhanced peroxidase-like activity of Por-ceria originated from synergistic effect of porphyrin and ceria, thereby explaining the high performance of Por-Ceria as an artificial enzyme mimicking peroxidase. When coupled with glucose oxidase, glucose is detected. A detection limit of 1.9 × 10 −2 mM glucose with a linear range up to 0.15 mM.

MoS2 gas sensor functionalized by Pd for the detection of hydrogen

Abstract: A facile, scalable and low-cost strategy for fabricating hydrogen sensors with few-layered Pd-functionalized MoS2 according to a simple solution process is reported. The sensors were prepared by drop-casting a MoS2-containing solution onto a SiO2 substrate and functionalizing the surface of the MoS2 with Pd using evaporation. Patterned deposition of Cr/Au on top of the MoS2-coated SiO2 substrate was then performed using evaporation through a shadow mask to place the micro electrodes on the substrate. The fabricated Pd-MoS2 sensors successfully detected hydrogen gas diluted by air at room temperature. With exposure to hydrogen gas, the Pd was converted to palladium hydride, which has a lower work function than MoS2, resulting in the transfer of electrons from palladium hydride to MoS2, thereby decreasing the resistance of the sensor. The functionalized MoS2 showed a 35.3% resistance change when exposed to a 1% hydrogen-containing gas, while the pristine MoS2 showed no reaction. The lower limit of detection of the resulting functionalized MoS2 sensor was 50 ppm.

Immobilization on Metal-Organic Framework Engenders High Sensitivity for Enzymatic Electrochemical Detection.

Abstract: The protection effect of metal–organic framework (MOF) provides high stability for immobilized enzyme. The small cavities of MOFs, however, usually result in decreased apparent substrate affinity and enzymatic activity of immobilized enzyme, compared to native enzyme. We synthesized zeolitic imidazolate framework-8 (ZIF-8) with a combination of mesoporous and microporous channels for cytochrome c (Cyt c) immobilization. Compared with native Cyt c, the immobilized Cyt c displayed increased apparent substrate affinity (Michaelis constant Km reduced by ∼50%), ∼128% increased enzymatic activity, and 1.4-fold increased sensitivity in the enzymatic electrochemical detection of H2O2. The immobilized Cyt c-coated screen-printed electrode was applied for the fast detection of residual H2O2 in microliter food samples such as milk and beer, making it promising for the development of efficient biosensors.

Half Layer By Half Layer Growth of a Blue Phosphorene Monolayer on a GaN(001) Substrate.

Abstract: First-principles calculations suggest a new kinetic pathway for growing either black or blue phosphorene monolayers on metallic and semiconducting substrates.

Air‐Stable Manganese(I)‐Catalyzed C−H Activation for Decarboxylative C−H/C−O Cleavages in Water

Abstract: The decarboxylative C−H/C−O functionalization was accomplished by air- and water-tolerant manganese(I) catalysis. The versatile C−H allylation occurred by facile organometallic C−H metalation on indoles, arenes, amino acids and synthetically meaningful aryl ketimines with ample substrate scope and high levels of chemo-, site- and regio-selectivity.

High intrinsic catalytic activity of two-dimensional boron monolayers for the hydrogen evolution reaction

Abstract: Two-dimensional (2D) boron monolayers have been successfully synthesized on a silver substrate very recently. Their potential application is thus of great significance. In this work, we explore the possibility of boron monolayers (BMs) as electrocatalysts for the hydrogen evolution reaction (HER) by first-principles methods. Our calculations show that BMs are active catalysts for HER with nearly zero free energy of hydrogen adsorption, metallic conductivity and plenty of active sites in the basal plane. The effect of the substrate on HER activity is further assessed. It is found that the substrate has a positive effect on the HER performance caused by the competitive effect of mismatch strain and charge transfer. The in-depth understanding of the structure dependent HER activity is also provided.

Single-molecule study of oxidative enzymatic deconstruction of cellulose.

Abstract: LPMO (lytic polysaccharide monooxygenase) represents a unique paradigm of cellulosic biomass degradation by an oxidative mechanism. Understanding the role of LPMO in deconstructing crystalline cellulose is fundamental to the enzyme’s biological function and will help to specify the use of LPMO in biorefinery applications. Here we show with real-time atomic force microscopy that C1 and C4 oxidizing types of LPMO from Neurospora crassa (NcLPMO9F, NcLPMO9C) bind to nanocrystalline cellulose with high preference for the very same substrate surfaces that are also used by a processive cellulase (Trichoderma reesei CBH I) to move along during hydrolytic cellulose degradation. The bound LPMOs, however, are immobile during their adsorbed residence time ( ~ 1.0 min for NcLPMO9F) on cellulose. Treatment with LPMO resulted in fibrillation of crystalline cellulose and strongly ( ≥ 2-fold) enhanced the cellulase adsorption. It also increased enzyme turnover on the cellulose surface, thus boosting the hydrolytic conversion. Understanding the role of enzymes in biomass depolymerization is essential for the development of more efficient biorefineries. Here, the authors show by atomic force microscopy the real-time mechanism of cellulose deconstruction by lytic polysaccharide monooxygenases.

Highly flexible, high-performance perovskite solar cells with adhesion promoted AuCl3-doped graphene electrodes

Abstract: Super flexible TCO-free FAPbI3−xBrx planar type inverted perovskite solar cells with a 179% power conversion efficiency under 1 sun conditions were demonstrated by introducing an APTES (3-aminopropyl triethoxysilane) adhesion promoter between a PET flexible substrate and a AuCl3-doped single-layer graphene transparent electrode (TCE) Due to the formation of covalent bonds by the APTES inter-layer, the AuCl3-GR/APTES/PET substrate had excellent flexibility, whereas the AuCl3-GR/PET substrate and the ITO/PET substrate had significant degradation of the sheet resistance after a bending test due to the break-off or delamination of AuCl3-GR from the PET substrate and the cracking of ITO Accordingly, the perovskite solar cells constructed on the AuCl3-GR/APTES/PET TCE substrate exhibited excellent bending stability and they maintained their PCE at over 90% of the initial value after 100 bending cycles at R ≥ 4 mm

An Inverse Michaelis–Menten Approach for Interfacial Enzyme Kinetics

Abstract: Interfacial enzyme reactions are ubiquitous both in vivo and in technical applications, but analysis of their kinetics remains controversial. In particular, it is unclear whether conventional Michaelis–Menten theory, which requires a large excess of substrate, can be applied. Here, an extensive experimental study of the enzymatic hydrolysis of insoluble cellulose indeed showed that the conventional approach had a limited applicability. Instead we argue that, unlike bulk reactions, interfacial enzyme catalysis may reach a steady-state condition in the opposite experimental limit, where the concentration of enzyme far exceeded the molar concentration of accessible surface sites. Under this condition, an “inverse Michaelis–Menten equation”, where the roles of enzyme and substrate had been swapped, proved to be readily applicable. We suggest that this inverted approach provides a general tool for kinetic analyses of interfacial enzyme reactions and that its analogy to established theory provides a bridge to t...

Sensitive and specific detection of explosives in solution and vapour by surface-enhanced Raman spectroscopy on silver nanocubes

Abstract: Surface-enhanced Raman spectroscopy (SERS) has been widely utilised as a sensitive analytical technique for the detection of trace levels of organic molecules. The detection of organic compounds in the gas phase is particularly challenging due to the low concentration of adsorbed molecules on the surface of the SERS substrate. This is particularly the case for explosive materials, which typically have very low vapour pressures, limiting the use of SERS for their identification. In this work, silver nanocubes (AgNCs) were developed as a highly sensitive SERS substrate with very low limit-of-detection (LOD) for explosive materials down to the femtomolar (10−15 M) range. Unlike typical gold-based nanostructures, the AgNCs were found suitable for the detection of both aromatic and aliphatic explosives, enabling detection with high specificity at low concentration. SERS studies were first carried out using a model analyte, Rhodamine-6G (Rh-6G), as a probe molecule. The SERS enhancement factor was estimated as 8.71 × 1010 in this case. Further studies involved femtomolar concentrations of 2,4-dinitrotoluene (DNT) and nanomolar concentrations of 1,3,5-trinitroperhydro-1,3,5-triazine (RDX), as well as vapour phase detection of DNT.

Impact of substrate diffusion and enzyme distribution in 3D-porous electrodes: a combined electrochemical and modelling study of a thermostable H2/O2 enzymatic fuel cell

Abstract: Using redox enzymes as biocatalysts in fuel cells is an attractive strategy for sustainable energy production. Once hydrogenase for H2 oxidation and bilirubin oxidase (BOD) for O2 reduction have been wired on electrodes, the enzymatic fuel cell (EFC) thus built is expected to provide sufficient energy to power small electronic devices, while overcoming the issues associated with scarcity, price and inhibition of platinum based catalysts. Despite recent improvements, these biodevices suffer from moderate power output and low stability. In this work, we demonstrate how substrate diffusion and enzyme distribution in the bioelectrodes control EFC performance. A new EFC was built by immobilizing two thermostable enzymes in hierarchical carbon felt modified by carbon nanotubes. This device displayed very high power and stability, producing 15.8 mW h of energy after 17 h of continuous operation. Despite the large available electrode porosity, mass transfer was shown to limit the performance. To determine the optimal geometry of the EFC, a numerical model was established, based on a finite element method (FEM). This model allowed an optimal electrode thickness of less than 100 μm to be determined, with a porosity of 60%. Thanks to very efficient enzyme wiring and high enzyme loading, non-catalytic signals for both enzymes were detected and quantified, enabling the electroactive enzyme distribution in the porous electrode to be fully determined for the first time. High total turnover numbers, approaching 107 for BOD and 108 for hydrogenase, were found, as was an impressive massic activity of 1 A mg−1 with respect to the mass of the electroactive enzyme molecules. This strategy, relying on stable enzymes and mesoporous materials, and the model set up may constitute the basis for a larger panel of bioelectrodes and EFCs.

Reliable molecular trace-detection based on flexible SERS substrate of graphene/Ag-nanoflowers/PMMA

Abstract: Flexible substrate consisted of PMMA-supported monolayer graphene with sandwiched Ag-nanoflowers (G/AgNFs/PMMA) for ultrasensitive, reproducible, and stable surface-enhanced Raman scattering (SERS) detection is reported. Graphene templated micro-current-assisted chemical reduction method was employed to support AgNFs growth, and uniform-distribution AgNFs with all directions nanotips can generate tremendous enhancement factor and intensive hotspots. The minimum detectable concentration (i.e., detection limit) for rhodamine 6G (R6G) in-situ detection by covering this as-synthesized G/AgNFs/PMMA flexible substrate can be as low as 10−14M. Moreover, graphene can effectively stabilize the SERS signals and protect AgNFs from oxidation, endowing this flexible substrate a long-term stability with maximum intensity deviation lower than 10%, for the quantitative measurements from spot-to-spot or substrate-to-substrate. In order to trial its practical applications with various real-world surfaces, the in-situ SERS detection of phenylalanine@apple, adenosine aqueous solution and methylene-blue@fish was performed by covering this G/AgNFs/PMMA flexible substrate. Clear Raman peaks can be obtained for all the selected samples with concentration of 10−10M and, importantly, good linear relationship between Raman intensity and molecular concentration indicates the potential application of the G/AgNFs/PMMA flexible substrate in quantitative determination. Thus, this high-efficiency and low-cost flexible SERS substrate may provide a new way for the molecular trace-detection in food security and environmental protection.

meta-C−H Arylation and Alkylation of Benzylsulfonamide Enabled by a Palladium(II)/Isoquinoline Catalyst

Abstract: Palladium(II)-catalyzed meta-C-H arylation and alkylation of benzylsulfonamide using 2-carbomethoxynorbornene (NBE-CO2 Me) as a transient mediator are realized by using a newly developed electron-deficient directing group and isoquinoline as a ligand This protocol features broad substrate scope and excellent functional-group tolerance The meta-substituted benyzlsulfonamides can be readily transformed into sodium sulfonates, sulfonate esters, and sulfonamides, as well as styrenes by Julia-type olefination The unique impact of the isoquinoline ligand underscores the importance of subtle matching between ligands and the directing groups

Tuning the selectivity of the catalytic CO2 hydrogenation reaction by strong metal-support interaction

Abstract: A one-step ligand-free method based on absorption-precipitation process is developed to fabricate Ir/CeO2 nano-catalysts. It is observed that Ir species have strong metal-support interaction (SMSI) with the cerium oxide substrate. Depends on the loading of Ir, the chemical state of iridium could be finely tuned. In CO2 hydrogenation reaction, it was shown that the chemical state of iridium species, induced by SMSI, has a major impact on the reaction selectivity. Ir/Ce catalyst (20% Ir) with relatively large particle size and almost pure metallic iridium species shows high selectivity towards methane. And Ir/Ce catalysts with lower iridium loading (5% and less), with the chemical state of iridium strongly modulated and partially decorated with oxygen, have almost 100% selectivity towards CO. This study shows the potential of tuning the surface chemistry of metal catalyst by substrate and thus to control the selectivity of a catalytic reaction towards designated direction.

Substrates and oxygen dependent citric acid production by Yarrowia lipolytica: insights through transcriptome and fluxome analyses.

Abstract: Unlike the well-studied backer yeast where catabolite repression represents a burden for mixed substrate fermentation, Yarrowia lipolytica, an oleaginous yeast, is recognized for its potential to produce single cell oils and citric acid from different feedstocks. These versatilities of Y. lipolytica with regards to substrate utilization make it an attractive host for biorefinery application. However, to develop a commercial process for the production of citric acid by Y. lipolytica, it is necessary to better understand the primary metabolism and its regulation, especially for growth on mixed substrate. Controlling the dissolved oxygen concentration (pO2) in Y. lipolytica cultures enhanced citric acid production significantly in cultures grown on glucose in mono- or dual substrate fermentations, whereas with glycerol as mono-substrate no significant effect of pO2 was found on citrate production. Growth on mixed substrate with glucose and glycerol revealed a relative preference of glycerol utilization by Y. lipolytica. Under optimized conditions with pO2 control, the citric acid titer on glucose in mono- or in dual substrate cultures was 55 and 50 g/L (with productivity of 0.6 g/L*h in both cultures), respectively, compared to a maximum of 18 g/L (0.2 g/L*h) with glycerol in monosubstrate culture. Additionally, in dual substrate fermentation, glycerol limitation was found to trigger citrate consumption despite the presence of enough glucose in pO2-limited culture. The metabolic behavior of this yeast on different substrates was investigated at transcriptomic and 13C-based fluxomics levels. Upregulation of most of the genes of the pentose phosphate pathway was found in cultures with highest citrate production with glucose in mono- or in dual substrate fermentation with pO2 control. The activation of the glyoxylate cycle in the oxygen limited cultures and the imbalance caused by glycerol limitation might be the reason for the re-consumption of citrate in dual substrate fermentations. This study provides interesting targets for metabolic engineering of this industrial yeast.

COx-free hydrogen production via decomposition of ammonia over Cu–Zn-based heterogeneous catalysts and their activity/stability

Abstract: Cu–Zn mixed metal oxides were synthesized with a modified citrate method, supported on an Al2O3 substrate, and tested for ammonia decomposition process to attain a high-purity hydrogen generation for fuel cells. Alumina-supported catalytic materials prepared by wet impregnation technique exhibited the highest surface copper species dispersion along with an increase in distributed acidic and basic sites. TPD studies using NH3 and CO2 revealed the presence of the Lewis and Bronsted acidity and basicity. SEM demonstrated a uniform particle distribution and morphology, regardless of Cu/Zn ratio. Cu/ZnO/Al2O3 exhibited a superior conversion activity when compared to neat Cu–Zn, which may be due to an improved Cu–Zn synergistic effect, a smaller average bimetallic nanoparticle size, and moderate acid–base characteristics. TEM micrographs confirmed the round-shaped metallic particles, ranging up to 7 nm in diameter and comprising both active copper oxide phases (Cu1+ and Cu2+), further investigated by EELS spectroscopy, as well as by XPS analysis. With reactions resulting in an effective first-order turnover (rate-determining step limitation), the apparent activation energies of (50–80) ± 5 kJ mol−1 were estimated in between 450 and 600 °C which is in agreement with other commercial catalysts. All fabricated bi-functional catalysts exhibited a high long-term stability and hydrogen productivity; nonetheless, comprised no critical scarce raw resources (e.g. platinum-group metals), which is appealing for emerging chemically-bonded H2 storage and release be it in relation to production only (electrolysis) or with consumption (regenerative fuel cells).

Catalytic Site-Selective Acylation of Carbohydrates Directed by Cation–n Interaction

Abstract: Site-selective functionalization of hydroxyl groups in carbohydrates is one of the long-standing challenges in chemistry. Using a pair of chiral catalysts, we now can differentiate the most prevalent trans-1,2-diols in pyranoses systematically and predictably. Density functional theory (DFT) calculations indicate that the key determining factor for the selectivity is the presence or absence of a cation–n interaction between the cation in the acylated catalyst and an appropriate lone pair in the substrate. DFT calculations also provided a predictive model for site-selectivity and this model is validated by various substrates.

CVD Mo DEPOSITION BY USING MoOCl4

Abstract: A method of forming a molybdenum-containing material on a substrate is described, in which the substrate is contacted with molybdenum oxytetrachloride (MoOCl4) vapor under vapor deposition conditions, to deposit the molybdenum-containing material on the substrate. In various implementations, a diborane contact of the substrate may be employed to establish favorable nucleation conditions for the subsequent bulk deposition of molybdenum, e.g., by chemical vapor deposition (CVD) techniques such as pulsed CVD.