Magnetic rod-based metal-organic framework metal composite as multifunctional nanostirrer with adsorptive,peroxidase-like and catalytic properties

Although magnetic stirring is frequently used to enhance the kinetics for adsorption, chemical and biochemical reactions, the introduction of stirrers inevitably leads to the adsorption of analytes and thus interferes with the efficiency of the chemical process or reaction. In this work, magnetic Fe₃O₄ nanorods with tunable length-to-diameter ratio were synthesized via a hydrothermal method and used as templates for the in-situ depositing of MIL-100(Fe) and gold nanoparticles. Such nanorod-based material can not only function as an adsorbent, nanozyme, and a heterogeneous catalyst for corresponding applications but also serve as a magnetic nanostirrer to enhance kinetics. As a proof-of-concept, the capture of bacteria pathogen, mimic-peroxidase-based colorimetric detection of hydrogen peroxide, and the catalytic reduction of selected organic pollutants were conducted using the as-synthesized Fe₃O₄@MIL-100(Fe)-Au nanostirrer with and without magnetic field. The results show that the rates of bacteria capture, mimetic enzyme reaction and catalysis were tremendously expedited. We believe this magnetic field-assisted approach holds great promise for future applications, because, not only does it eliminate the use of external magnetic stirrers and thereby decrease the risk of foreign pollution but also, is adaptable for nanoscale reaction systems where conventional stirring is not applicable due to size limitations.     

Electrooxidation mechanisms and discharge characteristics of borohydride on different catalytic metal surfaces

The electrooxidation behavior of BH4(-) on electrocatalytic Pt, hydrolytically active Ni, and noncatalytic Au electrodes were comparatively reexamined and a more generalized reaction mechanism was proposed to explain the very different anodic properties of BH4(-) on the different metal electrodes. In this mechanism, the anodic reaction behavior of BH4(-) are determined by a pair of conjugated reactions: electrochemical oxidation and chemical hydrolysis of BH4(-), the relative rates of which depend on the anodic materials, applied potentials, and chemical states of the anodic surfaces. At Pt surface, the electron number of BH4(-) oxidation increases with the increased potential polarization, while the actual electron number of BH4(-) oxidation on Ni electrode is 4 at most due to the poor electrocatalytic activity of the oxidized Ni surface and the strong catalytic activity of metallic Ni for chemical recombination of the adsorbed H intermediate. On the hydrolytic-inactive Au surface, the anodic reaction of BH4(-) can proceed predominately through direct electrochemical oxidation, delivering a near 8e discharge capacity.     

Influence of thermal and hydrothermal activation on the adsorptive, acidic and catalytic properties of high-silica zeolites

Influence of HS-zeolite calcination up to 1023 K in air and steam on its adsorptive, acidic and catalytic properties in n-hexane cracking has been studied.

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- 1023 , -.

     

Protection of lithium metal surfaces using chlorosilanes

In this paper, we present a new approach for protecting metallic lithium surfaces based on a reaction between the thin native layer of lithium hydroxide present on the surface and various chlorosilane derivatives. The chemical composition of the resulting layer and the chemistry involved in layer formation were analyzed by polarization modulated infrared reflection absorption spectroscopy (PM-IRRAS), X-ray photoelectron spectroscopy (XPS), and energy dispersive X-ray analysis (EDX). Spectroscopy shows the disappearance of surface hydroxide groups and the appearance of silicon and chloride on the lithium surface. Differential scanning calorimetry (DSC) and electrochemical impedance spectroscopy (EIS) show that this surface treatment protects the lithium from certain gas-phase reactions and is ionically conductive.     

Acid/Base-treated activated carbons: characterization of functional groups and metal adsorptive properties

Surface modification of activated carbons by various physicochemical methods directs an attractive approach for improvement of heavy metal uptake from aqueous solutions. Activated carbons were modified with HCl and HNO3 optionally followed by NaOH. The effects of surface modifications on the properties of the carbons were studied by the specific surface area, carbon pH, and total acidity capacity as well as by scanning electron microscopy, X-ray photoelectron spectroscopy, and Fourier transform infrared spectroscopy. The modifications bring about substantial variation in the chemical properties whereas the physical properties remain nearly unchanged. NaOH causes an increase in the content of hydroxyl groups, while the HCl treatment results in an increase in the amount of single-bonded oxygen functional groups such as phenols, ethers, and lactones. The HNO3 modification generates a large number of surface functional groups such as carbonyl, carboxyl, and nitrate groups. The HNO3 modification significantly increases the copper adsorption, while the HCl treatment slightly reduces the copper uptake. Most of the copper ions are adsorbed rapidly in the first 2 h; the adsorption equilibrium is established in around 8 h. An intraparticle diffusion model successfully describes the kinetics of copper adsorption onto the carbons.     

Structure and catalytic properties of chromium complexes on cation-exchange resin surfaces

The type of bonding of Cr(III) on the surface of cation-exchange resins has been studied. The complexes of Cr(III) with ethylenediamine were obtained by direct synthesis on the surface. Coordination to nitrogen bases increases the catalytic activity of Cr(III) ions in hydrogen peroxide decomposition.

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Cr(III) . Cr(III) . Cr(III) .

     

Recent developments in the adsorptive removal of heavy metal ions using metal-organic frameworks and graphene-based adsorbents

Clean and potable water is a growing concern around the globe. Among the different water pollutants, heavy metal ions pose a serious health concern to all living beings. The quest for new adsorbents to remove heavy metal ions received a boost with the development in the field of metal-organic framework (MOF). The advancement in synthetic strategies and designing of MOF enabled the researchers to tune the adsorption characteristics and tailor the material specific to a heavy metal ion. Similar to MOF, graphene-based two-dimensional and three-dimensional materials are also promising due to the diverse functionalization possibilities and cost-effectiveness. There had been growing interest in applying MOF and graphene-based materials for the removal of heavy metal ions in the past decade. This review summarizes these developments in detail.     

Chromium speciation study in polluted waters using catalytic adsorptive stripping voltammetry and tangential flow filtration

The catalytic adsorptive stripping voltammetry (CAdSV) has been applied to physico-chemical chromium speciation study in the upper Dunajec catchment, severely polluted by the tannery wastewater. The method is based on the adsorptive preconcentration of the Cr(III)-diethylenetriammine-N,N,N′,N″,N″-pentaacetic acid (DTPA) complex and the utilization of the catalytic reaction in the presence of nitrate. Under optimized conditions the CAdSV enables the oxidation state speciation study of Cr content by direct determination of Cr(VI) in the presence of the predominant Cr(III) concentration with the detection limit for chromium(VI) of 0.08 nM and the linearity range from 0.1 to 80 nM obtained for 20 s of accumulation, as well as the determination of total Cr after UV oxidation of Cr(III) to Cr(VI). Due to the difference in the chemical properties of different chromium species the CAdSV method makes possible a speciation study of Cr(III) and Cr(VI) oxidation state. The RSD of the determination of Cr(VI) and Cr(III) varies from 0.5 to 5%. It has been proved that in natural water in which strong complexants of Cr(III) such a humid acids are presented, Cr(VI) can be determined accurately in the presence of high excess of Cr(III). Fractionation of selected water samples with tangential flow filtration (TFF, cut-off 10 and/or 1 kDa) provides insight into physical Cr speciation, i.e. partitioning of the Cr(VI) and Cr(III) between the colloidal and the dissolved fractions. It has been shown that the content of the Cr species in the Dunajec river depends on the season, and is significantly higher in autumn and winter during the most intensive tanneries production processes. The concentration of total Cr exceeds occasionally the legally admissible level. A large fraction of total Cr(III) concentration is associated with the colloidal material, while Cr(VI) occurs solely in the truly dissolved form.     

Influence of the various forms of molybdena on the adsorptive and catalytic (dehydrogenation and hydrogenolysis) properties of molybdena-alumina catalysts

The contents of three forms of molybdenum oxide compounds in molybdena-alumina catalysts have been determined by their solubility in water and ammonia. The form which is readily soluble in water and reducible to Mo(IV) at 400°C and P_H2=10⁵ Pa is active in cyclohexane dehydration, and the forms soluble in water and ammonia are active in thiophene hydrogenolysis.

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. , 400°C P_{H 2}=I Mo(IV); — .

     

Influence of chemical composition of carbon catalysts on their adsorptive properties in catalytic oxidation of o-xylene

It has been established that o-xylene chemisorption on coals requires the presence of nucleophylic surface sites. Selectivity in o-xylene oxidation over carbon catalysts depends not only on their structure, but also on their surface functional groups.

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, - . - , .

     

Method to affect catalytic properties of low-temperature transition metal oxides

A method to affect the catalytic properties of low-temperature oxide catalysts by their synthesis through hydroxide compounds of the required composition and structure is suggested.

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.

     

Polyamide-bound metal complex catalysts: Synthesis,characterization and catalytic properties

A series of polyamides having different numbers of methylene groups in their repeating units have been synthesized by interfacial polycondensation of terephthaloyl chloride with piperazine and aliphatic diamines H₂N(CH₂)_nNH₂ (n = 2, 6, 10). These materials, which have high thermal stability, were used for immobilization of rhodium and platinum complexes. Chloroplatinic acid and the compounds PtCl₂(CH₃CN)₂ and [RhCl(CO)₂]₂ were used as precursors of the supported catalysts. Low molecular weight analogues of the polyamides were prepared for a study of the coordination mode between the metal ion and the polymer by IR spectroscopy. The results suggest that the carbonyl oxygen of the polyamide is the site of coordination to both rhodium and platinum. The bound catalysts exhibited high activity in hydrosilylation of hexene-1. The activities of the rhodium complexes were found to be dependent on the structure of the polyamide support, decreasing with increasing distance between the amide groups, and closely paralled the changes in the degree of crystallinity of the polymers. Repeated use of the polymers bearing rhodium complexes showed that the bond between the metal and polyamide is fairly stable.     

Determination of traces molybdenum by catalytic adsorptive stripping voltammetry

A reliable and very sensitive procedure for the determination of ultra trace of molybdenum is proposed. Molybdenum was determined by cathodic stripping differential pulse voltammetry based on the adsorption collection of the Mo(VI)-Tiron complex on a hanging mercury drop electrode (HMDE). The variation of peak current with pH, concentration of Tiron and chlorate, plus several instrumental parameters such as accumulation time, accumulation potential and scan rate, were optimized. Under optimized condition, the relationship between the peak current and molybdenum concentration is linear in the range of 0.010-21.0 ng ml⁻¹. The limit of detection was found to be 0.006 ng ml⁻¹. The relative standard deviation for 10 replicates determination of 0.6 and 10 ng ml⁻¹ Mo(VI) is equal to 1.3 and 0.9%, respectively. The method was applied to the determination of molybdenum in river water, tap water, well water, plant foodstuff samples such as cucumber, tomato, carrot, and certified steel reference materials.     

Chromatographic and adsorptive properties of mercury sulfide

Summary The behaviour of mercury sulfide (metacinnabarite) as an adsorbent in gas-solid chromatography was investigated. Adsorption of some aliphatic, alicyclic, chlorimated and aromatic hydrocarbons and acetone is discussed in the light of adsorbate-adsorbent interactions. For the organic compounds used, thermodynamic parameters were determined and discussed in terms of the specific reactions that may take place on the adsorbent surface. Experimental data obtained show that mercury sulfide can be successfully employed as an adsorbent in analytical gas-solid chromatography.     

不对称席夫碱过渡金属配合物的合成和催化性能

用乙二胺、乙酰丙酮与水杨醛反应合成了一种不对称四齿席夫碱配体(H2L)及其铜、钴、镍、锌配合物,通过元素分析、摩尔电导、红外光谱、紫外光谱、X-射线光电子能谱等手段对配体及其配合物进行了表征,并推测所有配合物均为烯醇式四配位结构,确定新配合物的组成为MC14H16N2O2(M=Cu,Co,N i,Zn)。并研究了配合物对双氧水的催化分解性能。     

Functional microporous materials of metal carboxylate: Gas-occlusion properties and catalytic activities

Copper(II) terephthalate is the first transition metal complex found capable of adsorbing gases. This complex has opened the new field of adsorbent complex chemistry. It is recognized as the lead complex in the construction of microporous complexes. This specific system has been expanded to a systematic series of derivatives of other isomorphous transition metals, molybdenum(II), ruthenium(II, III), and rhodium(II). These complexes with open frameworks are widely recognized as very useful materials for applications to catalysis, separation at molecular level, and gas storage.     

Physicochemical properties and catalytic activity of metal tetraphenyl porphins in the oxidation of alkylaromatic hydrocarbons

We consider the effect of complexing metal in a tetraphenylporphin molecule on its catalytic activity in oxidizing alkylaromatic hydrocarbons by molecular oxygen. The catalytic activity of metal porphyrins (Co, Cu, Zn, Mn, and In TPP) is found to depend on their oxidation potentials and the distribution of electron density in the molecule. The electron-donating compound imidazole is shown to affect the oxidation rate.