Weak Basic Aqueous Solutions Research Articles

Modulating depth of 1,2-propanediol oxidation over La(III) doped MCM-41 supported binary Pd and Bi nanoparticles for selective production of C3 carbonyl compounds

Selective oxidation of bio-based 1,2-propanediol (PDO) to value-added C3 carbonyl compounds has been received great attention. An alternative mesoporous lanthanum doped MCM-41 (LaM) supported bimetallic PdxBiynanoparticles has been constructed for the selective PDO oxidation. The La doping endows thecatalysts with new basic sites, and synergy between Pd and Bi species enhances the catalytic oxidation capacity. Pure MCM-41 supported PdxBiy/M favors catalyzing the deep oxidation of PDO topyruvic acid, whereas La doped PdxBiy/LaM facilitates theoxidative dehydrogenation of PDO to hydroxyacetone in weak basic aqueous solution (pH < 10). Raising the pH value to 13 efficiently promotes thePDOoxidation to lactic acid over PdxBiy/LaM. Kinetics study and DFT calculation suggeststrong interaction between La species and PDO molecule contributes to the enhanced oxidative dehydrogenation of PDO for PdxBiy/LaM. This work highlights a flexible strategy to produce value-added C3 carbonyl compounds via selective PDO oxidation.

Two-Step Elution Recovery of Cyanide Platinum Using Functional Metal Organic Resin.

A novel functional ion-exchange/adsorption metal organic resin (MOR), TEBAC-HKUST-1, was prepared and characterized. Ethanedithiol was used as the grafting agent to introduce thiol groups onto HKUST-1, and 4-vinylbenzyl chloride was then grafted onto SH-HKUST-1 using thiol groups. Finally, the quaternary ammonium functional group was immobilized onto the carrier by performing a quaternization reaction. The structure and property of TEBAC-HKUST-1 MOR were characterized by TGA, N2 adsorption–desorption, FTIR, SEM, and XRD. TEBAC-HKUST-1 MOR was used to remove metal cyanide complexes from wastewater. The adsorption was rapid, and the metal cyanide complexes including Pt(CN)42−, Co(CN)63−, Cu(CN)32−, and Fe(CN)63− were removed in 30 min. TEBAC-HKUST-1 MOR exhibited a high stability in neutral and weak basic aqueous solutions. Furthermore, Pt(II) could be efficiently recovered through two-step elution. The recovery rate of Pt(II) for five cycles were over 92.0% in the mixture solution containing Pt(CN)42−, Co(CN)63−, Cu(CN)32−, and Fe(CN)63−. The kinetic data were best fitted with the pseudo second-order model. Moreover, the isothermal data were best fitted with the Langmuir model. The thermodynamic results show that the adsorption is a spontaneous and exothermic process. TEBAC-HKUST-1 MOR not only exhibited excellent ability for the rapid removal of metal cyanide complexes, but also provided a new idea for the extraction of noble metals from cyanide-contaminated water.

Homochiral MOF as Circular Dichroism Sensor for Enantioselective Recognition on Nature and Chirality of Unmodified Amino Acids.

Self-assembly of zinc salt with rationally designed chiral ligand, (1R,2R)-2-(pyridine-4-ylcarbamoyl) cyclohexanecarboxylic acid (RR-PCCHC) generated 2D homochiral metal-organic framework [Zn(RR-PCCHC)2] (HMOF-1) that is composed of DNA-like right-handed double-helix structure. HMOF-1 shows high solvent and thermal stability and is also stable in neutral, weak acidic and weak basic aqueous solution. Emulsified HMOF-1 shows strong inherent circular dichroism (CD) signal in aqueous solution, which can show regular intensity change by induction of amino acids. On the basis of the measuring of CD signal intensity, a chemosensor for unmodified amino acids is fabricated, which differ from reported those in which CD signal is amplified by a complicated chemical reaction of originally CD-silent molecule with probed amino acids. This chemosensor can be used for rapid, convenient and sensitive detection of micro amount of amino acids. Most remarkably, 3 × 10-8 mol of l-aspartic acid and 4 × 10-8 mol of d-aspartic acid in aqueous solution can completely quench CD signal of emulsified HMOF-1 in H2O. It is found that the difference of recognition ability between d- and l-proline is the largest in all probed amino acids. The LOD (limit of detection) of the proposed sensor for the determination of aspartic acid is 13.31 ppm. The recognition efficiency η = [Formula: see text] × 100% for l-aspartic acid is as high as 92.1%. The interacting mechanism of DNA-like HMOF-1 with probed amino acids is similar to that of groove binding of targeting drug with DNA.

Synthesis, spectroscopy, and binding constants of ketocatechol-containing iminodiacetic acid and its Fe(iii), Cu(ii), and Zn(ii) complexes and reaction of Cu(ii) complex with H2O2 in aqueous solution

A new neuromelanin-like ketocatechol-containing iminodiacetic acid ligand, (N-(3,4-dihydroxyl)phenacylimino)diacetic acid (H4L), which is also quite similar to compounds found in insect cuticle, has been synthesized and characterized. The X-ray crystal structure of H4L has been successfully determined. Proton binding and coordination with Fe(III), Cu(II), and Zn(II) have been studied by potentiometric titrations and UV-vis spectrophotometry in aqueous solution. UV spectra of H4L in the absence and presence of different metal ions indicate complexes formed with the catechol moiety of H4L in aqueous solution. Visible spectra and NMR reveal that H4L with Fe(III), Cu(II), and Zn(II) can all give stable mono-(ML) and dinuclear complexes [M(ML)]. Fe(III) can also form {Fe(FeL)2} and {Fe(FeL)3} species with sufficient base. The process is accompanied by a drastic color change from light blue to deep-blue to wine-red. The Fe(III)-Cu(II) heteronuclear complex also exists in aqueous solution whose spectra are similar to the homonuclear Fe(III) complex. However, the spectra of {Fe(CuL)} shifted to a longer wavelength and {Fe(CuL)2} and {Fe(CuL)3} shifted to a shorter wavelength. Keto-enol tautomerism was observed in weak basic aqueous solution as indicated by (1)H NMR spectra. The reaction products of Cu(II) complex with H2O2 depend on the H2O2 concentration and pH value. Low concentrations of H2O2 oxidize H4L to a series of semiquinone and quinone compounds with absorption maxima at 314-400 nm, while a high concentration of H2O2 oxidizes H4L to colorless muconic acid derivatives. NaIO4 gives different oxidase products, but no 2,4,5-trihydroxyphenylalanine quinone (TPQ)-like hydroxyquinone can be found.

Hydrothermal synthesis and selective photocatalytic properties of tetragonal star-like ZrO2 nanostructures

Tetragonal star-like ZrO2 nanostructures were prepared using ZrOCl2·8H2O and CH3COONa as raw materials via a hydrothermal process. The zirconia nanostructures were investigated in detail by X-ray diffraction (XRD), transmission electron microscopy (TEM), high-resolution TEM (HR-TEM), infrared (IR) spectrum, thermal-gravimetry (TG) and other techniques, and possible formation mechanism was proposed. In the formation of the tetragonal star-like zirconia nanostructures, acetate played an important role due to the adsorption on certain of the crystal's facets. Tetragonal star-like zirconia showed excellent selective photocatalytic activity for the photodegradation of anionic dyes (methyl orange, congo red and rhodamine B) in acidic, neutral and weak basic aqueous solutions.

Low temperature fabrication of ZnO–whey protein isolate nanocomposite

Nanocrystalline zinc oxide (ZnO) particles coated with whey protein isolate (WPI) were fabricated in the weak basic aqueous solution condition at near room temperature. The X-ray diffraction and transmission electron microscopy measurements confirmed the nanoscaled composite structure of ZnO–WPI. The average composite granules size was about 300 nm and the embedded ZnO nanoparticles were uniform and monodisperse with an average diameter of 65 nm.

Cation alkyl polyglycoside for preparation of mesoporous silica and direct synthesis of mesoporous carbon

Using industrial grade cation alkyl polyglycoside as structure-directing agent, a new low-cost route has been developed to prepare ordered mesoporous silica through inorganic–organic self-assembling in weak basic aqueous solution. The XRD patterns, TEM images and the corresponding BET analysis show that it has a worm-like mesostructure with narrow pore size distribution centered at 3.6 nm. Moreover, alkyl polyglucoside can be used as carbon precursor, and the direct pyrolysis of silica/cation alkyl polyglucoside composite with trace amount H 2SO 4 as catalyst can lead to the formation of mesoporous carbon material, which shows the excellent performance in adsorbing fuchsine from aqueous solution.

The electrocatalytic reactions of adenine, guanine, H2O, H2O2, N2H4, and l-cysteine catalyzed by poly(Ni(4-TMPyP)) film-modified electrodes

Electrochemical preparation of poly(nickel tetrakis(N-methyl-4-pyridyl)porphyrin) tetratosylate (poly-Ni(4-TMPyP)) produces stable and electrochemically active films in strong and weak basic aqueous solutions. These films were produced on glassy carbon and gold electrodes. The electrochemical quartz crystal microbalance and cyclic voltammetry were used to study the in situ growth of poly(Ni(4-TMPyP)) films. The electrochemical properties of poly(Ni(4-TMPyP)) films indicate that the redox process was confined in to the immobilized film. The electrochemical quartz crystal microbalance results showed an ion exchange reaction for the redox couple. The polymer films showed one new redox couple when transferred to strong and weak basic aqueous solutions and the formal potential was found to be pH dependent. The electrocatalytic oxidation of H2O by a nickel tetrakis(N-methyl-4-pyridyl)porphyrin film-modified electrode was also performed. The mechanism of oxygen evolution was determined by cyclic voltammetry, chronoamperometry and rotating ring disc electrode methods. The oxygen evolution was determined by a bicatalyst system using hemoglobin, and iron tetrakis (N-methyl-2-pyridyl)porphyrin as catalyst to detect the oxygen by electrocatalytic reduction. The electrocatalytic oxidations of adenine, guanine, H2O2, N2H4, NH2OH, and l-cysteine by the film-modified electrode obtained from water-soluble nickel porphyrin were also investigated.

Stability Improvement of Electrospun Chitosan Nanofibrous Membranes in Neutral or Weak Basic Aqueous Solutions

Further utilization of chitosan nanofibrous membranes that are electrospun from chitosan solutions in trifluoroacetic acid (TFA) with or without dichloromethane (DCM) as the modifying cosolvent is limited by the loss of the fibrous structure as soon as the membranes are in contact with neutral or weak basic aqueous solutions due to complete dissolution of the membranes. Dissolution occurs as a result of the high solubility in these aqueous media of -NH(3)(+)CF(3)COO(-) salt residues that are formed when chitosan is dissolved in TFA. Traditional neutralization with a NaOH aqueous solution only maintained partial fibrous structure. Much improvement in the neutralization method was achieved with the saturated Na(2)CO(3) aqueous solution with an excess amount of Na(2)CO(3)(s) in the solution. We showed that electrospun chitosan nanofibrous membranes, after neutralization in the Na(2)CO(3) aqueous solution, could maintain its fibrous structure even after continuous submersion in phosphate buffer saline (pH = 7.4) or distilled water for 12 weeks.

Comparison of the direct electrochemistry of myoglobin and hemoglobin films and their bioelectrocatalytic properties

The electrocatalytic properties of two related proteins, myoglobin (Mb) and hemoglobin (Hb), immobilized in a surfactant film (didodecyldimethylammonium bromide, DDAB) on an electrode were investigated. The direct electrochemistry of the myoglobin/DDAB and hemoglobin/DDAB films was compared and showed one redox couple, two redox couples, and three redox couples, when transferred to strong acidic, weak acidic and basic, and pH 13 aqueous solutions, respectively. The redox couples and their formal potentials are pH dependent. An electrochemical quartz crystal microbalance (EQCM) and cyclic voltammetry were used to study the in situ growth of both DDAB deposition on gold disk electrodes and myoglobin deposition on DDAB film-modified electrodes. The electrocatalytic properties were investigated and showed that the myoglobin/DDAB and hemoglobin/DDAB film modified electrodes are both electrocatalytically active for oxygen reduction, and more H 2O 2 was produced during electrocatalytic reduction using a myoglobin/DDAB film than when using a hemoglobin/DDAB film. The electrocatalysis that was active for l-cystine, N 2O, and 2,2′-dithiosalicylic acid reductions showed an electrocatalytic current developed from the cathodic peak of the redox couple at about −0.9 V (Fe(II)/Fe(I) redox couple) in neutral and weak basic aqueous solutions. The electrocatalysis that was active for l-cysteine oxidation, showed an electrocatalytic current developed from the cathodic peak of the redox couple at about +0.2 V (Fe(III)/Fe(IV) redox couple). Mb/DDAB and Hb/DDAB film modified electrodes are electrocatalytically active for trichloroacetic acid reduction in weak acidic and basic buffered aqueous solutions through the Fe(II)/Fe(I) redox couple. However, the electrocatalytic current developed from the cathodic peak of the redox couple at a potential of about −0.1 V (from the Fe(III)/Fe(II) redox couple) in strong acidic aqueous solutions occurs only with higher concentrations of reactant.

The characterization and bioelectrocatalytic properties of hemoglobin by direct electrochemistry of DDAB film modified electrodes

Direct electrochemistry of hemoglobin can be performed in acidic and basic aqueous solutions in the pH range 1–13, using stable, electrochemically active films deposited on a didodecyldimethylammonium bromide (DDAB) modified glassy carbon electrode. Films can also be produced on gold, platinum, and transparent semiconductor tin oxide electrodes. Hemoglobin/DDAB films exhibit one, two, and three redox couples when transferred to strong acidic, weak acidic and weak basic, and strong basic aqueous solutions, respectively. These redox couples, and their formal potentials, were found to be pH dependent. An electrochemical quartz crystal microbalance and cyclic voltammetry were used to study the in situ deposition of DDAB on gold disc electrodes and hemoglobin deposition on DDAB film modified electrodes. A hemoglobin/DDAB/GC modified electrode is electrocatalytically reduction active for oxygen and H 2O 2, and electrocatalytically oxidation active for S 2O 4 2− through the Fe(III)/Fe(II) redox couple. In the electrocatalytic reduction of S 4O 6 2−, S 2O 4 2−, and SO 3 2−, and the dithio compounds of 2,2′-dithiosalicylic acid and 1,2-dithiolane-3-pentanoic acid, the electrocatalytic current develops from the cathodic peak of the redox couple at a potential of about −0.9 V (from the Fe(II)/Fe(I) redox couple) in neutral and weakly basic aqueous solutions. Hemoglobin/DDAB/GC modified electrodes are electrocatalytically reduction active for trichloroacetic acid in strong acidic buffered aqueous solutions through the Fe(III)/Fe(II) redox couple. However, the electrocatalytic current developed from the cathodic peak of the redox couple at a potential of about −0.9 V (from the Fe(II)/Fe(I) redox couple) in weak acidic and basic aqueous solutions. The electrocatalytic properties were investigated using the rotating ring-disk electrode method.

The electropolymerization and electrocatalytic properties of polymerized new fuchsin film modified electrodes

Electropolymerization of new fuchsin produces two types of stable and electrochemically active films in strong and weak acidic aqueous solutions. These films can be produced on glassy carbon, platinum, gold, and transparent semiconductor tin oxide electrodes. An electrochemical quartz crystal microbalance and cyclic voltammetry were used to study the in situ growth of poly (new fuchsin) films. New fuchsin is a molecule that has three branched monomers, and its polymerization forms a dendrimer. The polymer films showed redox couples, and when transferred to various acidic to weak basic aqueous solutions, the formal potential versus pH plot had a slope of −60 mV pH −1. The electrocatalytic reduction of HNO 2 by poly (neutral red) in a strong acidic aqueous solution showed obvious electrocatalytic reduction activity. A modified electrode containing a hybrid of two organic films was also prepared from poly (new fuchsin) and poly (neutral red) films. The two films, with a formal potential difference of about 0.6 V, were both electrocatalytically active for IO 3 − oxidation, but produced different products in strongly acidic aqueous solution. The electrocatalytic reduction of BrO 3 − was achieved only by poly (neutral red) in a strongly acidic aqueous solution. The polymer films also reduced SO 5 2−, IO 4 − and Cr 2O 7 2− electrocatalytically, and oxidized ascorbic acid electrocatalytically in aqueous solution.

The electrocatalytic transformation of HS −, S 2O 32−, S 4O 62− and SO 32− to SO 42− by water-soluble iron porphyrins

The electrocatalytic transformation of S 4O 6 2−, S 2O 3 2−, SO 3 2− and HS − to SO 4 2− by water-soluble iron porphyrins was investigated. The electrocatalytic oxidation of S 2O 3 2− to SO 4 2− can be performed by Fe( n-TMPyP) ( n=2,3, and 4). S 4O 6 2− is reduced to S 2O 3 2− by iron(I) species at weak basic aqueous solution, then S 2O 3 2− is oxidized to SO 4 2− through iron(IV) porphyrin species. S 4O 6 2− can be transformed to S 2O 3 2− by a chemical processes first and then the electrocatalytic oxidation of S 2O 3 2− to SO 4 2− is performed through iron(IV) species in a strong basic aqueous solution. HS − can be oxidized to S 2O 3 2− in a solution containing O 2 by chemical process, and then S 2O 3 2− is oxidized by iron porphyrin using electrocatalytic process. At a weak basic solution, S 4O 6 2− as the minor product can be reduced back to S 2O 3 2− by electrocatalytic method and the cyclic process of oxidation and reduction repeated. The electrocatalytic oxidation of S 4O 6 2− to SO 4 2− can be performed directly by Fe( n-TMPyP) ( n=2, 3, 4) in a strong basic aqueous solution. The electrocatalytic oxidation of SO 3 2− by Fe( n-TMPyP) through Fe(IV) was investigated at room temperature in aqueous solution. Fe III( n-TMPyP) ( n=2,3,4) can be oxidized to iron(IV) species by electrochemical method in the range of basic aqueous solution, then Fe(IV)( n-TMPyP) oxidizes SO 3 2− to SO 4 2−. The electrocatalytic oxidation activity is pH dependent in a wide pH range from 2.0 to 13.0, (O)Fe IVP has more catalytic activity than (OH)(O)Fe IVP.