Number Of Active Centers Research Articles

Engineering of nickel phosphate nanodots modified copper phosphate microflowers for highly efficient glucose monitoring

Transition metal phosphates have garnered significant interest as effective electrocatalysts due to their admirable chemical stability, unique physical features, low cost and exceptional electrocatalytic properties. Here, we design for the first time, a binary metal phosphate (BMP) heteroarchitecture based on nickel phosphate nanodots supported on copper phosphate microflowers (NDTs Ni3(PO4)2@Cu3(PO4)2 MFs). The surface characterizations reveal the interconnected cross-network of vertically oriented 3D nanosheets (NSs) which leads to the self-assembly of microflowers. In addition, the Ni3(PO4)2 nanodots, with an average diameter of 2.6 nm, are uniformly distributed throughout the structure, providing greater number of active centers on the surface of the designed catalyst. Thus, the customized structure has the potential to function as an excellent electrocatalyst by providing sufficient reaction space through the highly exposed edges of 3D nanosheets, and high density active site owe to the presence of NDTs. Typically, the Cu3(PO4)2 acts as an electron mediator by facilitating the Cu2+/Cu3+ redox couple, while the Ni3(PO4)2 enhances the electrocatalytic oxidation of glucose. Thus, owing to its unique physical and chemical aspects, the NDTs Ni3(PO4)2@Cu2(PO4)2 MFs demonstrate superior electrocatalytic efficacy for glucose sensing. Thanks to the novel NDTs Ni3(PO4)2@Cu2(PO4)2 MFs BMP for offering exceptional sensitivities (2197.119 and 206.111 μA mM–1 cm–2), a wide detection range (0.009–0.491 mM and 0.491–14.83 mM), a short response time (<1 s), and a low detection limit (0.06 μM, S/N = 3). Moreover, the designed sensor presents good reproducibility, admirable stability and excellent selectivity. Thus, the NDTs Ni3(PO4)2@Cu3(PO4)2 MFs are promising for the potential applications in glucose sensor, to monitor glucose in human serum and other body fluids.

Influence of Ligands on Physicochemical Characteristics of Magnetic Nanoparticles

Magnetic-bead separation or purification serves as a technique for effective isolation of biomolecules. In presented work we prepared and characterized core-shell magnetic nanoparticle samples consisted of Fe 3 O 4 core coated with SiO 2 shell. Samples were subsequently coated with ligands MPTMS (3-(mercaptopropyl)trimethoxysilane), CPTMS (3-(chloropropyl)trimethoxysilane) and MMSP (3-(trimethoxysilyl)propyl methacrylate) with aim to increase the number of active centers for specific binding with RNA. Such samples were further investigated for their magnetic properties, size, and morphology. Magnetic properties were studied in DC field up to 5 T in temperature range 5 – 300 K. Size and morphology were determined from SEM micrographs and elemental compositions of the samples were investigated using EDX analysis. Modification of nanoparticle surface with different ligands leads to modification of active centers on the SiO 2 surface on which the DNA and RNA molecules can be bounded. It also causes the change in magnetic and structural properties of nanoparticles.

Acid-Base and Photocatalytic Properties of the CeO2-Ag Nanocomposites

In this work, CeO2 nanoparticles, as well as CeO2 nanocomposites with plasmonic silver nanoparticles, were synthesized using a simple sol-gel process. The concentration of silver in the composites varied from 0.031-0.25 wt%. Cerium hydroxide dried gel was calcined at temperatures from 125 to 800 °C to obtain CeO2. It was shown that, at an annealing temperature of 650 °C, single-phase CeO2 nanopowders with an average particle size in the range of 10-20 nm can be obtained. The study of acid-base properties showed that with an increase in the calcination temperature from 500 to 650 °C, the concentration of active centers with pKa 9.4 and 6.4 sharply increases. An analysis of the acid-base properties of CeO2-Ag nanocomposites showed that with an increase in the silver concentration, the concentration of centers with pKa 4.1 decreases, and the number of active centers with pKa 7.4 increases. In a model experiment on dye photodegradation, it was shown that the resulting CeO2 and CeO2-Ag nanopowders have photocatalytic activity. CeO2-Ag nanocomposites, regardless of the silver concentration, demonstrated better photocatalytic activity than pure nanosized CeO2.

Adsorption Study of Methylene Blue from Aqueous Solutions onto Bituminous Coal Based Activated Carbon

Adsorption of methylene blue (MB) on activated carbon developed from bituminous coal (Barapukuria Coal) by physical activation has been investigated. The impacts of numerous variables, including absorbent concentration, contact time, initial dye concentration, and temperature, were explored. The equilibrium adsorption data analysis was performed using the Freundlich, Langmuir, and Temkin adsorption models. The Langmuir isotherm was considered to be the most appropriate. The Langmuir adsorption capacities (Qo) in 298, 303, 308, 313, 323, and 333K are 80.65, 84.75, 87.72, 90.09, 91.74, and 92.59 mg g-1, respectively. The dye removal percentages at 60 °C decline from 99.84% to 79.38% when dye concentrations are increased from 100 to 350 mgL-1. Increases in adsorbent concentration result in enhanced methylene blue adsorption because of increases in surface area and the number of active centers. From the thermodynamic studies, negative adsorption free energy (ΔG°) implies spontaneous adsorption, while positive enthalpy (ΔH°) reflects endothermic adsorption. Journal of Engineering Science 13(2), 2022, 91-100

Mixed MFI-MORD Zeolite Reactivation Study in Micro Structured Reactor in Methanol to Hydrocarbons Transformation Reaction

Restoring the activity of catalytic systems is an important scientific and technical problem. To date, a large number of catalyst regeneration methods have been developed, including: treatment with ultrasound, acids, alkalis, hydrogen, air, etc. However, to determine the necessary technological parameters, it is necessary to conduct experiments. Catalysts for the transformation of methanol into hydrocarbons are characterized by a significant tendency to lose their activity during operation. The main method for restoring their activity is oxidation in an air stream, however, it is possible to restore a different number of acid sites, both as a result of the retention of a certain amount of residual carbon, and as a result of thermal destruction of acid sites. In this connection, the determination of the optimal modes of zeolite thermal oxidation makes it possible to ensure the maximum residual activity of the regenerated catalyst. The article presents the results of studying the activity recovery of the MFI-MORD zeolite by the method of temperature-programmed oxidation at a sample heating rate of 5℃/min, 10℃/min, 20℃/min. Heating at 5℃/min leads to the recovery of the minimum number of acid sites, as well as the minimum value of the residual activity of the transformation of methanol into hydrocarbons of 0.121 kg(Hc)/(kg(Cat)×h). Increasing the heating rate to 10℃/min leads to the restoration of the maximum number of active centers and the achievement of a maximum residual activity of 0.21 kg(Hc)/(kg(Cat)×h). And an increase in the heating rate to 20℃/min leads to a decrease in the number of acid sites and a decrease in the residual catalytic activity of 0.142 kg(Hc)/(kg(Cat)×h). The decrease in the number of acid sites and residual activity at the highest heating rate of the sample may be due to the thermal destruction of active sites during rapid heating.

Diffusion controlled stereoregular polymerization in granule reactors - Reaction kinetic of Pr/Bt sequence polymerization with TiCl4/MgCl2 Ziegler-Natta catalyst

Diffusion controlled stereoregular polymerization was studied to understand the relations between fragmentation and growing of catalyst granules and its catalytic features for olefin polymerizations. In this work, propylene (Pr) polymerization kinetics and Pr/butene-1 (Bt) sequence polymerization kinetics with spherical TiCl4/MgCl2 Ziegler-Natta catalyst were investigated by monitoring catalytic activity (CA), the number of active centers ([C*]/[Ti]) and microstructure of polymers. It was found that the increase in Pr polymerization time benefiting to the catalyst granule fragmentation, had different influences on the [C*]/[Ti] and catalytic efficiency (CE) for Bt-stage polymerization in different stage. Anyway, the isotacticity and weight-average molecular weight (Mw) of isotactic polybutene-1 (iPB) fractions decreased gradually with the increase in Pr polymerization time. It was deduced that the easy solubility of polybutene-1 (PB) brought difficulties in further fragmentation of catalyst particles to expose more active centers, and Bt was more sensitive to the chemical and steric environment around the active species. This work provides further understanding of the catalytic characteristics of granule reactors in the initial polymerization stage, which will guide the novel polyolefin alloy production.

Increasing the number of active centers and matching acid micro-environment by the design of phosphorus immobilized for boosting catalytic activity

A series of MnMoP catalysts were prepared by ionic liquid assisted thermal synthesis method and characterized by Powder X-ray diffraction, Fourier Transform Infrared Spectrometer, Scanning Electron Microscope, X-ray Photoelectron Spectroscope and NH3-Temperature Programmed Desorption. The catalytic performance of MnMoP catalysts for the synthesis of cyclohexene oxide (CHO) was studied. The results showed that phosphorus was fixed via ionic liquid, which could improve the catalytic performance of the catalysts. Under the optimal conditions, MnMoP-80 catalyst showed the best catalytic performance with the cyclohexene conversion of 97.5% and CHO selectivity of 93.9%. Meanwhile, we have deduced that the reaction was mainly carried out according to the epoxidation pathway over MnMoP catalyst.

Synthesis and analysis of nanostructured graphene oxide

Work has been carried out to improve the method for obtaining and further oxidizing Graphene Oxide (GO) to obtain functionalized layers with a large number of active centres. We have determined that with an increase in the amount of H2O2 in the synthesis, it significantly increases the efficiency of the oxidation process and increases the number of functional groups, while the amount of NaNO3 and KMnO4 remains unchanged. Fourier-Transform Infrared Spectroscopy (FTIR), X-ray analysis, Scanning Electron Microscope (SEM) and Transmission Electron Microscope (TEM) analyses were carried out. Based on the FTIR result, all putative functional groups for a given material (GO) were determined, such as carbonyl, hydroxyl, ketone and epoxy groups which chemically bonded with graphene. SEM and TEM drawings were analysed, which gave a broad understanding of the morphology of GO nanostructures and, based on these drawings, it is fashionable to say that the material is semi-crystalline with the presence of such byproducts as amorphous carbon nanoparticles. Based on the EDX analysis, it was proved that this nano-structured material does not have third-party products.

Enhanced electricity generation and storage by nitrogen-doped hierarchically porous carbon modification of the capacitive bioanode in microbial fuel cells

Microbial fuel cells (MFCs) can potentially be utilized for power generation, but their low power density and low energy storage capabilities remain major bottlenecks for their large-scale development. In this research, a simplistic nitrogen-doped hierarchically porous carbon material (HPC-A) was developed through a one-step carbonization and activation process and was successfully hot-pressed on the carbon cloth (CC) substrate. This process fabricates capacitive bioanodes (HPC-A-CC) that can enhance electricity generation and storage in MFCs. The as-prepared HPC-A-CC anode delivered a power density of 2043.6 mW·m−2 and a cumulative total charge (Qm) of 426.4 ± 13.4C·m−2 at each cycle, which was 2.1 and 34.8 times higher than that of the plain CC anode, respectively. This was a result of the hierarchical and interconnected porous structure, improved hydrophilic surface, and increased number of active centers which host the bacteria for enhanced electron transfer. Electrochemical measurements indicated the superior electrochemical activity and capacitive behavior of the HPC-A-CC anode. Furthermore, biofilm analysis revealed that the HPC-A-CC biofilm exhibited higher cell viability and a more uniform spatial distribution. These findings not only demonstrate the potential of HPC-A-CC for power enhancement in MFCs but also provide a feasible solution to the problem of power generation and demand mismatch in MFC applications.

Functional mesoporous poly(ionic liquid)s-derived ultrafine MoP modified N, P-codoped carbon for stable hydrogen production in alkaline media

Molybdenum (Mo) based compounds have attracted growing attention in the electrochemical field due to their abundant reserves, high catalytic activity and stability. However, the efficient implementation of MoP for electrocatalytic hydrogen evolution reaction (HER) has been hindered by the limited number of active centers and the weakening electron transferring rate resulting from poor conductivity and easy accumulation during preparation. Herein, we innovate the use of porous poly(ionic liquid)s (MPILs)-loaded phosphomolybdic acid by ion exchange to achieve porous N, P-codoped carbon-encapsulated ultrafine MoP (MoP@NPC). The electronic structure of MoP can be modulated with the carbon matrix, while ultrafine average size of 3 nm nanoparticles afford highly exposed active sites, thus contributing to the boosted electrocatalytic performance of HER. Besides, N, P-codoped carbon coupling with porous structure could facilitate electron transport and shorten the ion transport distance during the electrochemical process. In alkaline media, the optimized MoP@NPC shows small overpotentials of 134 mV with Tafel slopes of 76 mV dec−1 for HER. In addition, excellent electrocatalysis stability has been acquired by MoP@NPC. The in-situ Raman and ex-situ XPS techniques are applied to confirm the superior electrocatalytic HER property of the obtained MoP@NPC. This work provides a new way to prepare a novel Mo-based electrocatalyst by exploiting a special catalyst precursor for hydrogen-energy-related applications.

A Framework for the Relationships between Stability and Functional Properties of Electrochemical Energy Materials

The path toward a renewable energy future relies on the development of materials for electrochemical energy technologies that are not only highly functional but also stable. In this Perspective, we will discuss a framework for the relationships between function and stability, starting by revisiting how we measure stability that should focus on changes to the nature and number of active centers (materials stability) together with monitoring how current/potential change over time during operation (reaction durability). By shifting our focus to materials properties, we then discuss how subtractive and additive processes such as dissolution, deposition, and (de)intercalation contribute to changes in the local surface composition, coordination environment, and phase restructuring that accompany the degradation of electrochemical materials. Ultimately, gaining insights into the processes responsible for changes to active centers during operation will help us better predict and control the durability of materials for clean energy.

Biocompatible Nanoparticle Heteroaggregates as Stabilizers of Pickering Emulsions for Vitamin D3 Efficient Delivery.

Vitamin D3 deficiency is a major public health problem worldwide, and standard cholecalciferol formulations provide poor absorbability of the vitamin. Several biphasic formulas have been proposed to overcome the disadvantages in which Pickering emulsions stand out in particular. This paper describes olive oil-in-water Pickering emulsions stabilized by pseudoboehmite (AlOOH), cellulose nanocrystals (CNC), and their heterocoagulates. Colloidal properties were assessed by laser Doppler microelectrophoresis, potentiometric titration, and rheology. It was shown that the heterocoagulation of CNC and AlOOH led to a drastic change in surface properties (ζ-potential, pKa, and number of active centers), which promoted the formation of more stable emulsions with the smallest size of droplets and the highest viscosity among the studied samples. Simulated digestion studies showed the targeted release in the small intestine medium where cholecalciferol should be delivered. High-performance liquid chromatography showed the efficient encapsulation of cholecalciferol in emulsions (86% of initial concentration). Oral administration to laboratory mice of initial nanoparticles and emulsions stabilized by them showed nontoxicity for all of the components, and they were estimated to be class V materials. The proposed emulsions have great potential as targeted delivery systems of lipophilic drugs.

Complex processing of wood debarking waste as a factor of environmental safety

In recent decades, the development of a modern industrial enterprise is impossible without considering the issue of complex processing or disposal of waste of the main production. This issue is very acute for the enterprises of the wood processing industry. The processing of wood waste should be considered not only as a factor of rational and environmentally safe use of forests, but also as a factor providing comprehensive processing of wood without increasing the amount of its harvesting and allowing production of new environmentally safe materials in constructing or other purposes. The paper presents the technological aspects of the production of innovative board composite materials made without binders based on debarking waste of coniferous wood raw materials and the studies` results of its operational properties. The produced composite is completely eco-friendly and biodegradable. The manufacturing technology consists of the mechanical activation of the tree bark in a hydrodynamic dispersant. Thanks to this treatment, the bark particles change their microstructure, acquire a large number of active centers and autocoherent properties, which make it possible to create slab materials based on it without introducing binding components and various types of additives into the composition.

Structural transformation of molybdenum carbide with extensive active centers for superior hydrogen evolution

Mo2C-based materials are expected to be extraordinary electrocatalysts for hydrogen evolution reaction (HER) due to their unique Pt-like electronic structures. However, the strong interaction between Mo and H as well as the scarce active centers impede their further applications. Herein, a facile and controllable route via Zn doping is proposed to weaken the H adsorption energy of Mo and create more active centers to boost the HER kinetics. A series of hierarchical branched MoC/Mo2C catalysts with promoted HER kinetics are constructed and well controlled by Zn-doping, where the structural transformation from Mo2C to MoC give rise to the optimized electronic structure and attenuate H adsorption energy. Besides, all Zn and Mo sites in Zn-MoC/Mo2C catalyst can be activated, and thereby dramatically increase the number of active centers as well as enhance the intrinsic catalytic activity. As expected, the Zn-MoC/Mo2C catalyst exhibits extremely low overpotential and Tafel slopes with excellent durability in both alkaline and acidic solutions. This work highlights a feasible strategy for enhancing hydrogen generation by dopant induced structural transformation and might provide an avenue for low-cost, efficient, and multifunctional electrocatalysts.

Improvement of catalytic activity for α‐diimine nickel complex with active sites stabilized by bulky boron counterions at elevated temperature

Three α‐diimine Ni (II) catalysts (Cat.1, Cat.2 and Cat.3) were synthesized and investigated for ethylene polymerization using alkyl aluminum and organoboron compounds as binary cocatalyst. The effects of different alkyl aluminum and boron complexes on ethylene polymerization catalyzed by Cat.1, Cat.2, and Cat.3 were studied. The sodium tetrakis[3,5‐bis (trifluoromethyl)phenyl]borate (NaBArF) was found to have best promotion for the catalytic activity of Cat.1, compared to negative effect of dimethylanilinium tetrakis (pentafluorophenyl)borate (TTB) and trityl tetrakis (pentafluorophenyl)borate (AB). All the three catalysts showed higher catalytic activity when NaBArF was introduced into the catalytic system, especially for Cat.3 (increased by 41.3% at 70°C). There was still minor increase of the catalytic activity for Cat.2 which have much better thermostability than Cat.3. The charging sequence of NaBArF and the [B]/[Ni] ratio have significant effects on the catalytic activity. The better catalytic performance of Cat.1/AlEt2Cl/NaBArF could be explained by its ability to raise the number of active centers. Namely, the molar percentage of active centers of Cat.1/AlEt2Cl/NaBArF was still above 30%, which was 1.7 times that of Cat.1/AlEt2Cl even if polymerization ran up to 30 min based on 2‐thiophenecarbonyl chloride (TPCC) quench‐labeling method. Lower [Al]/[Ni] ratio but more active centers and longer active centers lifetime of this binary cocatalyst is promising for improving the activity of ethylene polymerization industrially at elevated temperature.

Molybdenum carbide nanosheets decorated with Ni(OH)2 nanoparticles toward efficient hydrogen evolution reaction in alkaline media

Hydrogen Evolution Reaction (HER) in alkaline media occupies a significant position in industrial preparation. However, the HER reaction rate in alkaline media is much less than that in acidic media for most catalysts. Herein, the hybrid catalyst constituted by the Ni(OH)2 nanoparticles and favorable Mo2C nanosheets is applied to facilitate the HER catalytic activity in alkaline media. The decoration of Ni(OH)2 nanoparticles on Mo2C nanosheets with the textured surface not only increases the number of active centers but also promotes the transfer of electrons between Ni(OH)2 and Mo2C. The as-prepared activated Mo/Mo2C-Ni(OH)2 catalyst exhibits excellent catalytic performance for HER in alkaline media with a low overpotential and small tafel slope.

Isolated Single-Atom Ni-N5 Catalytic Site in Hollow Porous Carbon Capsules for Efficient Lithium-Sulfur Batteries.

Lithium-sulfur (Li-S) batteries suffer from multiple complex and often interwoven issues, such as the low electronic conductivity of sulfur and Li2S/Li2S2, shuttle effect, and sluggish electrochemical kinetics of lithium polysulfides (LiPSs). Guided by theoretical calculations, a multifunctional catalyst of isolated single-atom nickel in an optimal Ni-N5 active moiety incorporated in hollow nitrogen-doped porous carbon (Ni-N5/HNPC) is constructed and acts as an ideal host for a sulfur cathode. The host improved electrical conductivity, enhanced physical-chemical dual restricting capability toward LiPSs, and, more importantly, boosted the redox reaction kinetics by the Ni-N5 active moiety. Therefore, the Ni-N5/HNPC/S cathode exhibits superior rate performance, long-term cycling stability, and good areal capacity at high sulfur loading. This work highlights the important role of the coordination number of active centers in single-atom catalysts and provides a strategy to design a hollow nanoarchitecture with single-atom active sites for high-performance Li-S batteries.

Propylene polymerization over titanium–magnesium catalysts: The effect of internal and external stereoregulating donors on the number of active centers with different stereospecificity and their reactivity in propagation reaction

The combination of the method for measuring of the number of active centers by quenching of polymerization by radioactive carbon monoxide with fractionation of polymers obtained by TREF method (temperature rising elution fractionation) to the separate fractions with different isotacticity has been used for determination of the number of active centers with different isospecificity (CPi) responsible for the formation of Fi fractions as well as for calculation of propagation rate constants (kPi) for these centers.Data on the effect of catalyst composition on the CPi and kPi values have been obtained for the first time for polymerization with three types of titanium-magnesium catalysts with different internal stereoregulating donors (di-n-butyl phthalate – TMC-D, 2,3-di-iso-butyl-diethyl succinate – TMC-S, 9,9-bis(methoxymethyl)-fluorene – TMC-F) and for catalytic system TMC-D with external stereoregulating donor – cyclohexylmethyl(dimethoxy)silane.The possible structures of active centers with different isospecificity are discussed on the base of experimental data obtained on the CPi and kPi values.

Establishment of the Brazilian Registry of Hematopoietic Stem Cell Transplantation, using the database the Center for International Blood and Marrow Transplant Research

The number of hematopoietic stem cell transplantation (HSCT) in Brazil is growing rapidly. To better understand the outcomes of HSCT in Brazil, strategies have been developed with the Center for International Blood and Marrow Transplant Research (CIBMTR), using its standardized registry structure and data sharing application. The methods adopted to establish the registry were through efforts to increase the Brazilian centers that report to CIBMTR included training courses for HSCT data managers, the officialization of a multicenter HSCT study using the CIBMTR structure and the partnership between Brazilian Society of Bone Marrow Transplantation (SBTMO) and the CIBMTR. Here we describe the history for establishing the HSCT Brazilian database using the CIBMTR back to center data and present the aggregated results since 2016. We found a significant increase in the numbers of active centers reporting to CIBMTR from 11 in 2016 to 21 in 2020 corresponding to higher numbers of transplants reported to the CIBMTR from 574 to 921 in that period. The model used to generate this national database was effective as it leverages existing infrastructure to assess the activity and outcomes of HSCT in Brazil.&#x0D;

Regulation of alkoxysilane on stereoregular polymerization of Butene-1 catalyzed by TiCl4/MgCl2 Ziegler-Natta catalysts

External electron donors (ED) as one of the components in traditional Ziegler-Natta (Z-N) catalysts play important roles in determining the activity, stereoregularity of the active species for ɑ-olefin polymerization. Alkoxysilanes with different size and different electron-donating alkyl substituents were investigated to study the stereoregular polymerization of butene-1 catalyzed by TiCl4/MgCl2 Z-N catalysts. The obtained polybutene-1 (PB) was fractionated into three components including high isotactic PB (HiPB), medium isotactic PB (MiPB) and atactic PB (aPB) and the number of active centers ([C*]/[Ti]) of each component were measured accordingly. The mmmm sequence concentration, weight-average molecular weight (Mw), molecular weight distribution (MWD), and crystallizability of PB were studied by carbon-13 nuclear magnetic resonance spectrometry (13C-NMR), gel permeation chromatography (GPC) and differential scanning calorimetry (DSC). The addition of dimethyldimethoxysilane (D1) with 120.1 Å3 volume and 0.6802 a.u. electron density had little influence on the stereoregular polymerization of butene-1. The incorporation of diphenyldimethoxysilane (D3) with higher steric hindrance (231.2 Å3 volume), stronger electro-donating ability (0.6969 a.u. electron density) produced PB with higher HiPB component, higher mmmm sequence concentration, accompanying by the reduced catalytic activity and [C*]/[Ti]. The probably active center models absorbing different ED were proposed to explain the catalytic behaviors for butene-1 polymerization and formation of PB with different components.