Weak Alkaline Medium Research Articles

Improvement of the Oxidative Desulfurization Performance Using MoO3/CuO‐Modified Hierarchical HY Zeolite

AbstractThe presence of sulfur compounds in the chemical industry poses significant environmental and economic problems, including endangering human and animal lives and damaging equipment. For this purpose, hierarchical HY zeolite (Hie‐Y) with a SiO2/Al2O3 molar ratio 10 was successfully synthesized through sequential desilication‐dealumination using NH4OH treatment. A weak alkaline media with surfactant cetyltrimethylammonium bromide (CTAB) facilitates mesoporosity formation and preserves the zeolite structure. Metal oxide (CuO, MoO3) ‐ hierarchical HY zeolite nanocomposites have been prepared by one or a combination of 3 methods: 1) ion exchange, 2) precipitation, and 3) calcination. The obtained catalysts were characterized using XRD, FT‐IR, FESEM, UV‐Vis, EDS, and BET techniques. The formation of a hierarchical structure is associated with structure preservation, but partial destruction occurs based on the entering Cu in the zeolite pores. These catalysts have been studied in the oxidative desulfurization (ODS) reaction. Several parameters, including temperature, catalyst amount, DBT concentration, and reaction time, were evaluated in ODS using the Taguchi Design of Experiments. Catalytic activity order was obtained as Y<Hie‐Y<Hie‐Y/CuO<Hie‐Y/MoO3<Hie‐Y/MoO3/CuO. Results indicate an activity increase for the Hie‐Y/MoO3/CuO hierarchical structure owing to synergistic effects of secondary mesoporosity and metal oxides. The catalyst was recoverable and reused for five consecutive runs with preservation of catalytic activity.

Surfactant effects on structural, optical and morphological characteristics of microwave irradiated CdO nanostructures

Surfactant based microwave irradiated and alkaline medium involving wet chemical method was adopted to prepare CdO nanostructures. The phase evaluation of prepared and annealed CdO nanostrucutures has been analyzed by XRD and FTIR. The average size of the crystallite was estimated to be 54 nm for the NH4OH reagent and 60 nm for the NaOH reagent in the assisted synthesis. Specific surface area, lattice parameter, X-ray density, dislocation density, microstrain, texture coefficient and Williamson Hall have been calculated from the XRD profile. UV transmittance and the K-M plot of DRS and PL spectra were used to examine the optical properties of CdO nanostructures. The spherical and rod-like structures of CdO prepared with strong and weak alkaline medium have been recorded through SEM and TEM micrographs. The four-step process of hydration, intermediate formation, metal hydroxide formation, and metal oxide formation confirms that the experiment in the presence of 0.1 M sodium hydroxide results in rod-shaped nanostructures.

Enhanced Photocatalytic Removal of Cyanotoxins by Al-Doped ZnO Nanoparticles with Visible-LED Irradiation.

The ZnO-based visible-LED photocatalytic degradation and mineralization of two typical cyanotoxins, microcystin-LR (MC-LR), and anatoxin-A were examined. Al-doped ZnO nanoparticle photocatalysts, in Al:Zn ratios between 0 and 5 at.%, were prepared via sol-gel method and exhaustively characterized by X-ray diffraction, transmission electron microscopy, UV-vis diffuse reflectance spectroscopy, photoluminescence spectroscopy, and nitrogen adsorption-desorption isotherms. With both cyanotoxins, increasing the Al content enhances the degradation kinetics, hence the use of nanoparticles with 5 at.% Al content (A5ZO). The dosage affected both cyanotoxins similarly, and the photocatalytic degradation kinetics improved with photocatalyst concentrations between 0.5 and 1.0 g L−1. Nevertheless, the pH study revealed that the chemical state of a species decisively facilitates the mutual interaction of cyanotoxin and photocatalysts. A5ZO nanoparticles achieved better outcomes than other photocatalysts to date, and after 180 min, the mineralization of anatoxin-A was virtually complete in weak alkaline medium, whereas only 45% of MC-LR was in neutral conditions. Moreover, photocatalyst reusability is clear for anatoxin-A, but it is adversely affected for MC-LR.

Electrochemical conversion pathways and existing morphology of arsenic(III) in anode-cathode separated electrolytic cells

Abstract To explore the electrochemical conversion of arsenic at different voltages and pH, an open separated electrolytic cell with a platinum anode and a graphite cathode was selected for this paper. The form and concentration of arsenic in the anodic cell and cathodic cell were detected. Experimental results proved that at 40.0 V, As(III) in an acid electrolyte in the cathodic cell was firstly mainly reduced to AsH3 with trace As(0) as intermediate. As the electrolysis time arrived at 27 min, pH in the cathodic cell jumped suddenly from acidity to alkalinity, accompanied by the majority of the remaining As(III) converting to As(V) for an instant. As time went on, As(III) and As(V) remained almost unchanged at the ratio of 1:3, and the reduction of As(III) became extremely weak in the alkaline environment. When pH in the cathodic tank was adjusted to keep it acid, As(III) was eventually converted to AsH3. Compared with high voltage, at a low voltage of 1.0 V the cathode failed to achieve the potential of As(III) reduction and As(III) was eventually oxidized to As(V) in the acid catholyte. Electrochemical oxidation of As(III) in the open cathodic cell was likely caused by in-situ generation of peroxide from electrochemical reduction of O2. Theoretical support for electrochemical oxidation of As(III) on a carbon cathode in neutral and weak alkaline media is provided in this study.

A new composite based on graphene oxide-poly 3-aminophenol for solid-phase microextraction of four triazole fungicides in water and fruit juices prior to high-performance liquid chromatography analysis

An environmentally friendly method which is based on preparation and use of a new composite consisting of poly 3-aminophenol and graphene oxide for solid-phase microextraction of triazole fungicides from natural water and juices is introduced. The composite was synthesized by in-situ polymerization of 3-aminophenol and graphene oxide in weak alkaline media. By using the obtained results from the characterization, a suitable mechanism for polymerization and a proper structure for the polymer were proposed. Under optimal conditions, there are linear relationships between concentration of triazoles and their HPLC peak areas in the range of 0.5–100 µg L−1. The recovery percentages, pre-concentration factors and LOQ for all triazoles were 95.2–98.0%, about 200 and 0.2–0.4 µg L−1, respectively. The offered method was applied for extraction and determination of triazoles from natural water, some juices and it represents a promising alternative method for analysis of triazoles.

Co(II, III) Hydroxides Supported on Zeolite Acting as an Efficient and Robust Catalyst for Catalytic Water Oxidation with Ru(bpy)33+

A novel highly efficient and stable for many cycles catalyst (1% Со-ZSM-5(17)) for water oxidation was developed using the method of polycondensation for stabilization of oxo/hydroxo complexes of cobalt (II, III) and nanosize Co3O4 in zeolite channels. In a weak-alkaline medium (pH 8.0, 9.2, 10.0) in the presence of a one-electron oxidant (Ru(bpy)33+), the catalyst provided the yield of oxygen as high as 56, 73 и 78% of the stoichiometric quantity, respectively. Catalysts based on ZSM-5 zeolite exhibited higher catalytic activity as compared to the catalysts based on the MOR, BEA, Y. Inspection of the electron states of cobalt in the Co-containing zeolite-based catalysts using TPR-H2 and UV–Vis DR techniques revealed that α-Co(OH)2-like polynuclear clusters and hydrocomplexes stabilized in the zeolite channels were most active to catalytic oxidation of water, while their transformation to Co3O4-like clusters/nanoparticles and Co2+ oxocomplexes, respectively, during thermal treatment led to some decrease in the catalyst efficiency. Coarsening of Co3O4-like clusters/nanoparticles caused the further decrease in the system efficiency. The minimal activity was observed with the catalysts containing predominantly isolated Co2 +Oh ions. The result obtained indicates a kind of at least polynuclear structure of the catalytically active center ConOx, where n > 2.

A pH-sensitive microemulsion-filled gellan gum hydrogel encapsulated apigenin: Characterization and in vitro release kinetics.

In this work, the incorporation of O/W microemulsion in gellan gum hydrogels was performed to prepare the composite hydrogel as the carrier of apigenin. In vitro release studies resulted that the composite hydrogels could control the drug release under acidic (pH 1.2) and weak alkaline conditions (pH 7.4). This was due to the increase of crosslinking degree under acidic medium and degradation under weak alkaline medium, observed by SEM technique. The FT-IR analysis further confirmed that the hydrogen ions (H+) under acidic conditions could diminish the electrostatic repulsion between the gellan gum molecules by offsetting the negative charge of carboxyl groups, promoting the formation of double helices. The in vitro release kinetics resulted that the release under acidic conditions was a Fickian diffusion-controlled mechanism. While the in vitro release under weak alkaline condition was erosion-controlled mechanism. In addition, the components of microemulsion have also an influence on the release behavior, which was related to the diameter distributions of microemulsion droplets and the hydrogen bond degrees between surfactants and polymers. As a result, the microemulsion-filled hydrogels could be a promising pH-controlled release system for oral delivery of hydrophobic drug.

Injectable and self-healing polysaccharide-based hydrogel for pH-responsive drug release

Injectable hydrogels with self-healing and pH-responsive property are appealing for biomedical applications. Herein, we developed a facile and green method to prepare a multifunctional polysaccharide-based hydrogel as a new carrier of drug. The hydrogels were prepared by forming reversible chemical bond between carboxyethyl-modified chitosan (CEC) and aldehyde modified hyaluronic acid (A-HA). The morphology and rheological property of the hydrogels with different solid content were systematically characterized. Owing to the dynamic equilibrium of the Schiff base bonds between amine groups on CEC and aldehyde groups on A-HA, the rapid self-healing performance of hydrogels was confirmed through qualitative and quantitative methods without any external stimulus. The pH-responsive behaviour was demonstrated by equilibrium swelling and in vitro Doxorubicin (Dox) release in PBS medium with various pH. In acidic condition, Dox can be release more rapidly compared with weak alkaline medium. Furthermore, the kill effect of Dox released from hydrogels for cancer cells was investigated. In vitro degradation and cytotoxicity examinations showed that the hydrogel is biodegradable and biocompatible. Therefore, such polysaccharide-based injectable self-healing and pH-responsive hydrogel is a promising candidate as drug delivery carrier.

STUDY OF SOME MINERAL WATER OF UVS NURSKOY AYMAK OF MONGOLIA

The article presents the results of studies on the current state, properties and chemical composition of some mineral waters of the Uvs Aimak, located in the west of Mongolia. The article presents the results of studying the mineral waters in different sums of Uvs aimak in Mongolia, such as Malchin Sagil, Tsagaanhayrhan, Umnugobi, Turgun, Tarialan, Zuungobi, Ulaangom and others. For each sample, 37 standard indicators were obtained using a conventional in hydro-chemical practice traditional chemical methods (weight and volume) and the highly sensitive method of spectrometric study of mineral waters. The results showed that the composition of 11 mineral sources referred to sodium and potassium groups of bicarbonate and the sulphate classes with weak alkaline conditions. According to research history of Uvs province, for the first time, in 1960, chemists O. Namnandorj, E.M Murzaev, and Sh. Tsegmed undertook research on Chandmani spring, Khar тermes spring and Givantin spring, respectively. But the chemists determined only contents of macro elements in their research. There are few research data of studying micro elements, dissolved gas and bioactive elements. The sources had a high content of sulphate ions. As compared with the results obtained in 1960, the mineralization of the most mineral sources tends to increase. The mineral waters studied differ insignificantly between each other in the relations of physical properties and chemical composition. We found that most of the studied waters belong to the first type of calcium group of the hydrocarbonate class, to waters with a weak alkaline medium (pH = 6.94-8.74), with a large mineralization (197.67-1577.25 mg/L) according to the mineral water classification system. The mineralization of these waters has a strong correlation depending on the content of cations Mg2+, Na+ + K+, etc., as well as anions SO42- and HCO3-.Forcitation:Ulziikhishig I., Sukhbaatar I., Battumur T. Study of some mineral water of Uvs nurskoy aymak of Mongolia. Izv. Vyssh. Uchebn. Zaved. Khim. Khim. Tekhnol. 2018. V. 61. N 4-5. P. 126-132

Synthesis and spectral properties of symmetrical and asymmetrical 3-cyano-1,5-diarylformazan dyestuffs for dyeing polyester fabrics

In this study, we report on a general synthetic approach to both symmetrical and asymmetrical 3-cyano-1,5-diarylformazan dyes. The reaction of enaminonitrile with aromatic diazonium salts in slightly acidic medium affords arylhydrazonals as stable intermediate that are readily converted into asymmetrical formazans via second azo-coupling in a weak alkaline medium. Symmetrical formazan dyestuffs are synthesized directly via double azo-coupling of the key intermediate 3-piperidinylacrylonitrile with the corresponding diazonium salts in weak alkaline medium using sodium acetate as a weak base. The structures of the prepared dyestuffs and intermediates are demonstrated by elemental analysis (C, H, N), 1H and 13C NMR, FTIR and GC-MS spectroscopic techniques. The prepared formazan disperse colorants are applied to dye polyester fabric to give satisfactory fastness properties to wash, perspiration, rubbing and light.

Selective colorimetric analysis of spermine based on the cross-linking aggregation of gold nanoparticles chain assembly

A selective colorimetric assay for spermine was proposed in this work. In a weak alkaline medium, the conformational structure of double-stranded calf thymus DNA (ctDNA) was loosened to install gold nanoparticles (AuNPs) into chains. While, the chain assembly of AuNPs could form cross-linking aggregates when spermine was present, which was attributed to the electrostatic interaction between the positive change of spermine and negative change both of AuNPs and ctDNA, as well as the groove binding between ctDNA and spermine. Under the optimum conditions, the aggregation degree of AuNPs was proportional to the concentration of spermine in the range of 0.1–2.0μM with a limit of detection of 11.6nM. More interestingly, AuNPs changed from red to purple and even to blue depending on the concentration of spermine, which could be developed as the colorimetric analysis of spermine. ctDNA-AuNPs assembly was demonstrated as a novel visual probe for the specific sensing of spermine with high specificity and sensitivity.

Fe (III)-Based Ammonia-Free Bath for Electrodeposition of Fe-W Alloys

Electrodeposited Fe-W alloys are the subject of extensive studies to be applied in versatile engineering applications, and many solutions based on Fe(II) complexes are described for their deposition. However, in aqueous solutions containing dissolved oxygen, Fe(II) compounds are unstable thermodynamically and tend to oxidize to Fe(III) state that decreases the sustainability of the baths. The aim of the present study was to develop an environment-friendly and thermodynamically stable Fe(III)-based electrolyte for electrodeposition of Fe-W alloys with tunable composition. It was found that: (i) concurrent use of two complexing agents as citric and glycolic acids stabilizes Fe(III)-based bath in neutral and weak alkaline medium (no precipitates are formed); (ii) the current efficiency of the process can reach up to 60–70%, which has never been reported before for Fe-W alloys electrodeposition; (iii) nanocrystalline Fe-W coatings containing 11–24 at.% of W can be obtained from Fe(III)-based glycolate-citrate bath at temperature range 20–65°C. The increase in tungsten content in the alloy resulted in decreased grain size up to < 5 nm; (iv) smooth, free of cracks and having deposition rates up to 0.18 μm/cm1 alloys are successfully electrodeposited at elevated temperatures from elaborated glycolate-citrate electrolyte.

Rhenium(VII) solvent extraction with mixtures of tertiary amine and oxygen-containing extractants from sulphate media

The extraction of rhenium(VII) from sulfate media by mixtures of tri-iso-octylamine (TIOA) and oxygen-containing reagents (2-octanol, 2-octanone, phenetole) has been examined. The synergistic effect for mixtures of TIOA and electron-donor reagents (ketone, ether) was established. The maximal synergistic enhancement factor (3.1) was observed for the “TIOA-2-octanone” mixture. Rhenium(VII) was extracted by this mixture as (R3NH)ReO4∙0.2B. The maximal rhenium(VII) extraction was found at weak acid concentrations in aqueous phase (pH~2–3), whereas the “TIOA-ketone” mixture could extract rhenium(VII) from weak alkaline media (pH~7–9) in contrast to the “TIOA-alcohol” mixture.Effective stripping from the loaded “TIOA-2-octanone” mixture was achieved with a 3mol/L NH4OH in 2–3 stages.

The effect of quorum sensing on anaerobic granular sludge in different pH conditions

The effects of several signal molecules on anaerobic granular sludge at different pHs were investigated. The results showed that pH affected the synthesis and maintaining of the signal molecules. In an alkaline medium (pH 9), sludge bacteria secreted less acyl-homoserine lactone (AHLs), which had an opposite variation with the synthesis of extracellular polymeric substances (EPS), and its effect did not present. Additionally, the synthesis of EPS (mainly loosely bound layer) was majorly promoted by auto-inducers-2 (AI-2), but a lower negative role of diffusible signal factor (DSF). In neutral and weak alkaline media, the combining regulation of increasing AI-2 content and decreasing DSF content enhanced relative hydrophobicity (RH) and granular strength in granular sludge, which made granules to have a greater diameter and a more glossy granular shape. Whereas, in acid medium, the decreasing AI-2 content and increasing DSF content made a decrease in RH and granular strength, resulting in the degeneration of anaerobic granular sludge.

Selective Tumor Cell Inhibition Effect of Ni-Ti Layered Double Hydroxides Thin Films Driven by the Reversed pH Gradients of Tumor Cells.

Nitinol is widely fabricated as stents for the palliation treatment of many kinds of cancers. It is of great importance to develop nitinol stents with selective tumor cell inhibition effects. In this work, a series of pH sensitive films composed of Ni(OH)2 and Ni-Ti layered double hydroxide (Ni-Ti LDH) with different Ni/Ti ratios were prepared on the surface of nitinol via hydrothermal treatment. The films with specific Ni/Ti ratios would release a large amount of nickel ions under acidic environments but were relatively stable in neutral or weak alkaline medium. Cell viability tests showed that the films can effectively inhibit the growth of cancer cells but have little adverse effects to normal cells. Besides, extraordinarily high intracellular nickel content and reactive oxygen species (ROS) level were found in cancer cells, indicating the death of cancer cells may be induced by the excessive intake of nickel ions. Such selective cancer cell inhibition effect of the films is supposed to relate with the reversed pH gradients of tumor cells.

Synthesis of Multiwalled TiO&lt;SUB&gt;2&lt;/SUB&gt; Nanotubes Under Weak Alkaline Conditions for Dye-Sensitized Solar Cells

Mesoporous Tubular TiO2 nanostructures were synthesised under hydrothermal condition in weak alkaline medium using high surface area mesoporous anatase TiO2 nanoparticles as seeds. These anatase TiO2 nanoparticles react with weak NaOH under hydrothermal conditions to form sheet like structures. By treating these sheets with dilute HCl multilayered nanotubes were obtained. X-ray diffraction, Scanning Electron Microscopy, Transmission Electron Microscopy, N2 sorption analysis were used for the physical characterization of the material. These nanotubes were applied as anode material for Dye-sensitized solar cell and an increase of 7.86% in current density is observed as compared to the commercial paste (Solaronix Ti-Nanoxide T/SC).

Development of the kinetic-spectrophotometric method for quantitative determination of zopiclone in tablets by the perhydrolysis reaction

A simple and express method for the quantitative determination of zopiclone in model solutions of the substance and in “Zopiclone” tablets, 7.5 mg, by the kinetic-spectrophotometric method according to 3,3’,5,5’-tetramethylbenzidine oxidation has been developed. It is based on the system of two coupled reaction: 4-methyl-1-piperazineperoxycarboxylic acid generated in zopiclone perhydrolysis reacts with the excess of hydrogen peroxide in the weak alkaline medium with formation of coloured 3,3’,5,5’-tetramethyldiphenylquinone diimine (λmax = 420 nm, рН = 8.4). The reaction is performed spectrophotometrically by measuring the rate of change of the absorbance at 420 nm. The method was used for constructing the calibration graph. The initial rate of the reaction was obtained from the linear site of the slope of the initial tangent to the absorbance-time curve. In the pH range of 8.2-8.5 the rate of the coloured product formation becomes maximum. The calibration graph for zopiclone has a linear dependence in the range of 6-36 mg/l with the limit of detection (LOD) and quantitation (LOQ) of 1.81 and 6.04 mg/l, respectively. For five determinations of 18, 24 and 30 mg/l of zopiclone RSD is 1.81, 1.46 and 1.69%, respectively. The analytical performance of the method was validated statistically with respect to LOD, LOQ, accuracy, precision and linearity for zopiclone estimation in a pure substance and the results were satisfactory. “Zopiclone” tablets compared to the reference method contain 99.83±1.19% of C17H17ClN6O3 (RSD = 0.96% , δ = -0.17%). The assay of zopiclone in the presence of its hydrolysis products without preliminary separation is an important advantage of the method.

Catalysts based on NaY zeolite for oxidative destruction of organic azo dyes in wastewater

Samples of catalysts containing Ag+ and Co+2 cations were prepared on the basis of NaY granulated synthetic zeolite without binders by the ion-exchange method with the subsequent thermal treatment at 350–500°C. It was found that CoNaY samples are most catalytically active in the process of carmoisine oxidation by hydrogen peroxide in a weak alkaline medium (pH 8.5).

Influence of Organic Alkali on the Preparation of Lignin-Based Anionic Adsorbents and their Performance in the Removal of Nitrate

Lignin-based anionic exchange resin was synthesized by modified alkali lignin after reaction with epichlorohydrin and triethylamine in the weak alkaline medium provided by pyridine in the organic medium of N,N-dimethylformamide (DMF). The influence of pyridine on synthesis process and yield of products were discussed. The product was characterized by FTIR spectroscopy analysis and the adsorbent capabilities for N from aqueous solution were also exploited. The factors that might influent the adsorption performance were investigated. An adsorbent dosage of 0.2g, adsorption time of 100min, pH of 4 and the initial concentration of nitrate concentration was 10mg/l were selected as optimum conditions.

Oxidation of arsenite in aqueous solutions by redox copolymer with N-bromosulfonamide functional groups

Macromolecular oxidant [P]-SO2NBrNa (a macroporous styrene/divinylbenzene copolymer containing N-bromosulfonamide functional groups in the sodium form) was synthesized and used to oxidize arsenites to arsenates in dilute aqueous solutions. The oxidant, containing active bromine (1.65mmol/g) in its functional groups, was obtained through the transformation of Amberlyst 15 (Rohm and Haas) commercial cation exchanger’s sulfonic functional groups. The batchwise method and the column method and NaAsO2 solutions (375, 93 and 10mg As(III)/dm3) in water alone and in 0.01M NaOH were used in the investigations. Special potentiometric, reductometric measurements showed that the investigated oxidation reaction was favoured by a weak acidic to weak alkaline medium. The determined redox potential of the resin was 440mV at pH=6.3 and 130mV at pH=11.01. In the column process experiments, conducted using NaAsO2 solutions with a concentration of 10mg As(III)/dm3 at a flow rate of 6BV/h, a breakthrough (defined as the exceedance of 0.01mg As(III)/dm3 in the effluent) would occur after the solutions amounting to about 1700 bed volumes were passed though the column.