Homogeneous Aqueous Solution Research Articles

Degradation of Cellulose to Organic Acids in its Homogeneous Alkaline Aqueous Solution

Conversion of cellulose to chemicals or fuels is the key point for the utilization of biomass to substitute for fossil resources. Here, a simple method has been developed to degrade the cellulose chains in its homogeneous solution in free of any noble or transition metal catalysts. The homogeneous alkaline aqueous solution of cellulose was prepared at first, and then it was hydrothermally degraded at 160–300 °C . Malonic acid (MA), lactic acid (LA), formic acid (FA), and acetic acid (AA) are the major valuable products, among them MA and LA are the top valuable platform molecules for synthesis of bulk chemicals and fuels. The maximum yield of MA is 39.7%, and the maximum total yield of the four kinds of organic acid is 81.2%. In addition, it is the first report that cellulose can be directly degraded to MA in a simple chemical route.

Photocatalytic reactions of a nickel(ii) annulene complex incorporated in polymeric structures

A study of the structural and chemical processes of a new polymeric photocatalyst containing a Ni(ii) macrocyclic complex and its application to the solar reduction of CO2 in aqueous homogeneous solution.

Discovery of a new crystalline phase: BiGeO2(OH)2(NO3)

A new crystalline phase, BiGeO2(OH)2(NO3), has been synthesized from a homogeneous aqueous solution. This new phase is found to possess a layered structure consisting of BiO6polyhedra, GeO5trigonal bipyramids and nitrate ions.

Analysis of ion-association equilibrium of precipitable dipicrylaminate ion in aqueous solution by capillary zone electrophoresis.

The ion-association equilibrium of the dipicrylaminate ion (DPA(-)) was investigated in an aqueous solution with alkali metal ions and with its 18-crown-6 ether complexes as pairing cations by capillary zone electrophoresis (CZE). Although DPA(-) is precipitable with the pairing cations of K(+) and Cs(+) in a homogenous aqueous solution, a low concentration of DPA(-) below its solubility suppressed the formation of the precipitates, and DPA(-) was detected as a usual CZE signal. Changes in the electrophoretic mobility of DPA(-) was analyzed for its ion-association equilibrium. The ion association constants determined were almost comparable among alkali metal ions, while the ion association constants were meaningfully large with a hydrophobic 18-crown-6 ether complex of K(+). The CZE separation was also proved to be useful for the equilibrium analysis under precipitating conditions. It was suggested that the precipitable property of DPA(-) with K(+) and Cs(+) could not be attributed to the ion-association process in an aqueous solution, but to the condensation process concerning the intermolecular CH···O bond in the precipitate crystals, as reported.

Preparation and properties of an eco-friendly superabsorbent based on flax yarn waste for sanitary napkin applications

Recently, cellulose-based superabsorbent has attracted attention as a promising material in many fields because of its rich sources and outstanding properties of biodegradability and biocompatibility. This study examines the potential application of a novel flax yarn waste-g-poly(acrylic acid-co-acrylamide) (FYW/PAA) superabsorbent in the absorbent core layer of sanitary napkins. Acrylic acid (AA) and acrylamide (AM) were grafted onto the pretreated flax yarn waste (PFYW) by free-radical graft copolymerization in homogeneous aqueous solution. The synthesis conditions of the FYW/PAA superabsorbent and its application performance for sanitary napkin were investigated. The results showed that, under the optimal synthesis conditions, the water absorbency of the prepared FYW/PAA reached 787.6 g/g in deionized water, 109.5 g/g in 0.9 wt% NaCl solution and 206.5 g/g in artificial blood solution. The composited absorbent core layer containing the FYW/PAA achieved the similar artificial blood solution absorbency of 192.6 g/g and retention of 83.9 wt% to those of the marketed sanitary napkin products. Meanwhile, a weight residue of 53.6 wt% was attained for the FYW/PAA after being buried in soil for 90 d.

Tube radial distribution phenomenon observed in an aqueous micellar solution of non-ionic surfactant fed into a microspace and an attempt of capillary chromatographic application

A new type of tube radial distribution phenomenon was observed in an aqueous micellar solution of non-ionic surfactant that was fed into a microspace. A homogeneous aqueous solution containing 2 wt % Triton X-100 and 2.0 M sodium chloride was fed into a microchannel (40 μm in depth and 200 μm in width) in a microchip at a flow rate of 4.0 μL/min, where the microchip was maintained at a temperature of 34°C. The homogeneous aqueous solution changed to a heterogeneous solution with two phases in the microchannel; the surfactant-rich phase was generated around the middle of the channel, while the aqueous phase containing little surfactant was formed near the wall. The radial distribution of the surfactant was observed through Rhodamine B dissolved in the aqueous micellar solution with a bright-field microscope — CCD camera system. An open-tubular capillary chromatographic system was also tried to develop using the fusedsilica capillary tube (75 μm inner diameter and 120 cm length) as a separation column and the aqueous micellar solution as a carrier.

Hydrogenation and Redox Isomerization of Allylic Alcohols Catalyzed by a New Water-Soluble Pd–tetrahydrosalen Complex

For applications in aqueous media, sulfonated tetrahydrosalen (sulfosalan, HSS) was synthesized by sulfonation of tetrahydrosalen in fuming sulfuric acid. The Pd(II) complex of this ligand, [Pd(HSS)], showed outstanding activity in hydrogenation and redox isomerization of allylic alcohols in homogeneous aqueous solutions or in aqueous–organic biphasic systems (for oct-1-en-3-ol TOF(hydrogenation) = 1580 h–1, TOF(redox isomerization) = 400 h–1). DFT calculations revealed that H2 is activated heterolytically, resulting in a Pd(II)–hydride complex, [Pd(H)(HSS-Hphen)], in which one of the phenolate oxygens is protonated. Both hydrogenation and redox isomerization take place via concerted transfer of a proton and a hydride from the hydrogenated catalyst to the allylic alcohol.

Effect of interaction with micelles on the excited-state optical properties of zinc porphyrins and J-aggregates formation

This work reports on the photophysical properties of zinc porphyrins meso-tetrakis methylpyridiniumyl (Zn2+TMPyP) and meso-tetrakis sulfonatophenyl (Zn2+TPPS) in homogeneous aqueous solutions and in the presence of sodium dodecyl sulfate (SDS) and cetyltrimethyl ammonium bromide (CTAB) micelles. The excited-state dynamic was investigated with the Z-scan technique, UV–Vis absorption, and fluorescence spectroscopy. Photophysical parameters were obtained by analyzing the experimental data with a conventional five-energy-level diagram. The interaction of the charged side porphyrin groups with oppositely charged surfactants can reduce the electrostatic repulsion between porphyrin molecules leading to aggregation, which affected the porphyrin characteristics such as absorption cross-sections, lifetimes and quantum yields. The interaction between anionic ZnTPPS with cationic CTAB micelles induced the formation of porphyrin J-aggregates, while this effect was not observed in the interaction of ZnTMPyP with SDS micelles. This difference is, probably, due to the difference in electrostatic repulsion between the porphyrin molecules. The insights obtained by these results are important for the understanding of the photophysical behavior of porphyrins, regarding potential applications in pharmacokinetics as encapsulation of photosensitizer for drug delivery systems and in its interaction with cellular membrane.

Removal of toxic dyes from aqueous medium using adenine based bicomponent hydrogel

By utilizing hydrogen bonding and π–π stacking interactions, we have demonstrated the construction of three dimensional adenine based gel networks due to the self assembly with complementary tricarboxylic acid derivatives which were designed and unambiguously characterized with the help of NMR, HRMS, and FTIR. Upon cooling the homogeneous aqueous solution of adenine and tricarboxylic acid, it formed hydrogels which were thermoreversible in nature and characterized by various instrumental techniques such as OM, FESEM, TEM, AFM, FL, XRD, FT-IR, rheology etc. Networks of belts in the hydrogel were clearly observed and the dimension of belt depended on the tricarboxylic acid used. The intermolecular hydrogen bonds which were considered to be the driving force for the formation of stable gel were confirmed by FT-IR studies. In spite of the absence of symmetry either in bpca or adenine, these two moieties surprisingly produced gels and it was due to the symmetrical position of complementary interaction sites between adenine and tricarboxylic acids. The mechanical strength of the hydrogel network as revealed by rheological study depended on the tricarboxylic acid used in the two-component systems and also on the composition of fixed pair. These kind of hydrogels have potential to be utilized as inexpensive materials for the treatment of waste water containing organic dyes (methylene blue, rhodamine 6G and crystal violet) that are widely used in textile as well as dye industries.

Water oxidation catalysis via immobilization of the dimanganese complex [Mn2(μ-O)2Cl(μ-O2CCH3)(bpy)2(H2O)](NO3)2 onto silica

Adsorption of a dinuclear μ-oxo bridged Mn complex onto mesoporous silica was observed when SBA15 was treated with an acetonitrile solution of [Mn2(μ-O)2Cl(μ-O2CCH3)(H2O)(bpy)2](NO3)2 (1). This complex was immobilized via the displacement of NO3(-) into solution, and characterization by spectroscopic (DRIFTS and DRUV-vis) and magnetic data indicates that the intact dication is electrostatically bound to the silica surface. Loadings of up to 4.1% by weight of [Mn2(μ-O)2Cl(μ-O2CCH3)(H2O)(bpy)2](2+) were achieved. TEM images of the grafted material revealed retention of the mesoporous structure of SBA15, and no clusters of manganese greater than ca. 10 nm were observed. The SBA15-supported dimanganese complex functions as a catalyst for the oxidation of H2O with (NH4)2Ce(NO3)6 as stoichiometric oxidant. In contrast, homogenous aqueous solutions of 1 do not evolve oxygen upon treatment with (NH4)2Ce(NO3)6. Labeling studies with H2(18)O confirm that the oxygen formed in this catalysis is derived from water. Monitoring the O2 evolution allowed determination of an initial rate for the catalysis (TOFi = 1.1 × 10(-3) s(-1)). These studies also reveal a first order dependence on manganese surface concentration, and a zero order rate dependence for (NH4)Ce(NO3)6. Spectroscopic investigations were employed to investigate the difference in activities between dissolved and supported dimanganese complexes.

Novel Preparation and Characterization of Calcium-Strontium Hydroxyapatite

Calcium-strontium hydroxyapatite [Ca5-xSrx(PO4)3OH, Ca-SrHA] were prepared by a novel coprecipitation process. The homogeneous aqueous solution of calcium nitrate, strontium nitrate and phosphoric acid was used as starting material, and ammonia was used as precipitator. A series of Ca-SrHA samples had been synthesized by adding ammonia into the precursor solution to pH10 and following aging at 60°C for 18h. The samples were characterized by X-ray diffraction, Fourier transformed infrared spectroscopy and scanning electron microscopy. The results show that so-prepared samples present essential characteristics of Ca-SrHA. All samples have a short rod-like morphology. The cell parameters of Ca5-xSrx(PO4)3OH are linear to the value of x, and the infrared absorption bands of PO43- groups shift to lower wave numbers with the increase of x.

Zinc(II) 2,9,16,23-tetrakis[4-(N-methylpyridyloxy)]-phthalocyanine anchored on an electrospun polysulfone polymer fiber: Application for photosensitized conversion of methyl orange

In this work, a comparative study of photodegradation of methyl orange, an azo dye, in homogeneous aqueous solution of a quarternized cationic zinc phthalocyanine and a heterogeneous catalytic system based on the same phthalocyanine anchored on polysulfone polymer fiber is presented. In both cases, conversion involved the azo bond of the dye with no detectable opening up of the aromatic benzene rings. The reaction kinetics in both cases were consistent with first order with the conversion occurring in the homogeneous system being faster than when the functionalized polymer fiber was used. The reaction products consisted of a coupling product as well as a series of oligopolymeric products.

In Situ STM Investigation of Aromatic Poly(azomethine) Arrays Constructed by “On-Site” Equilibrium Polymerization

Two-dimensional (2D) arrays of π-conjugated aromatic polymers produced by surface-selective Schiff base coupling reactions between an aromatic diamine and an aromatic dialdehyde were investigated in detail using in situ scanning tunneling microscopy. Surface-selective coupling was achieved for almost all diamine/dialdehyde combinations attempted, although several combinations did not proceed even in homogeneous aqueous alkaline solution. Most of the combinations of an aromatic diamine and a dialdehyde, except the combinations of 4,4'-azodianiline with mono/bithiophenedicarboxaldehyde, formed highly ordered π-conjugated polymer arrays on an iodine-modified Au(111) surface in aqueous solution at a suitable pH. The simplest polymer of the various combinations tested, obtained from the combination of 1,4-diaminobenzene with terephthaldicarboxaldehyde, gave a 2D array consisting of linearly connected benzene units. Poly(azomethine) adlayers caused a positive shift in the electrochemical potential of the butterfly shaped oxidative adsorption and reductive desorption of iodine. The acceleration of the reductive desorption of iodine suggests the existence of a weak interaction between the polymer layer and iodine. Not only the first polymer adlayers but also partially adsorbed secondary adlayers with "on-top" epitaxial behavior were frequently observed for all polymer systems. The alignment of the polymer chains in the adlayers possessed a certain regularity in terms of a regular interval between polymer chains because of repulsive interpolymer interactions.

Kinetics of the photosensitized degradation of benzyl 4-hydroxybenzoate in homogeneous aqueous solution under visible-light irradiation

The photosensitized oxidation of benzyl 4-hydroxybenzoate (benzylparaben, BeP), the endocrine disrupting compound, in homogenous aqueous solution of 4,4′,4″,4‴-(porphine-5,10,15,20-tetrayl)tetrakis(benzenesulphonic acid) (TPPS4) as photosensitizer was examined. A xenon lamp simulating solar radiation was used as a light source. The influence of pH of the reaction mixture, oxygen content and initial concentrations of photosensitizer and BeP on the reaction rate was studied. The major role of singlet oxygen in BeP degradation was proved by the experiments performed in the presence of hydroxyl radicals scavengers and singlet oxygen quenchers. The rate constants of singlet oxygen quenching by BeP in D2O buffer (pD 7, 9 and 10.8) were determined. Based on the kinetic model, the rate constants of singlet oxygen quenching and reaction with BeP as well as the rate constant of excited photosensitizer quenching by BeP were determined.

Synthesis and urea sustained-release behavior of an eco-friendly superabsorbent based on flax yarn wastes

In order to develop an eco-friendly superabsorbent composite, flax yarn waste (FYW) was used as raw material to synthesize a novel flax yarn waste-g-poly(acrylic acid-co-acrylamide) (FYW/PAA) superabsorbent composite. Acrylic acid (AA) and acrylamide (AM) were grafted onto the pretreated flax yarn waste (PFYW) by free-radical graft copolymerization in homogeneous aqueous solution. The properties and synthesis conditions of the FYW/PAA superabsorbent composite were investigated. As a result, the prepared FYW/PAA attained the best water absorbency of 875g/g in distilled water, 490g/g in rainwater and 90g/g in 0.9wt% NaCl solution. The urea loading percentage of FYW/PAA could be modulated by the concentration of urea. The release of urea from FYW/PAA in water showed a typical three-stages sustained release behavior. Meanwhile, a weight residue of 53.6wt% was attained after being buried in soil for 90d.

Aqueous RAFT Polymerization ofN‐Acryloylmorpholine, Synthesis of an ABA Triblock Glycopolymer and Study of its Self‐Association Behavior

AbstractThe RAFT polymerization ofN‐acryloylmorpholine with a symmetric trithiocarbonate was investigated in homogeneous aqueous solution. The effects of temperature and of a high magnetic field were examined and RAFT experiments were compared with the corresponding conventional radical polymerizations. For all temperatures tested, the molar mass of the polymer increased linearly with conversion and closely matched the theoretical value. Molar mass dispersities were in the range 1.05–1.16 and the presence of a magnetic field had little effect on the rate of RAFT polymerizations, although the latter were systematically slower than the corresponding conventional processes. A uniform ABA triblock glycopolymer was prepared, which formed unilamellar polymersomes with a diameter of 380 nm in 91% (v/v) THF/water mixture.

Depolymerization of poly(trimethylene terephthalate) in hot compressed water at 240–320 °C

Poly(trimethylene terephthalate) (PTT) was depolymerized in hot compressed water (HCW) using a fused-silica capillary reactor (FSCR) and a batch-type autoclave reactor. The phase behavior of PTT in water during the heating, reaction, and cooling processes was observed in an FSCR with a microscope and recorded by a digital camera. It was found that PTT can dissolve in water in a temperature range of 240–320 °C and form a homogeneous aqueous solution. The effects of the reaction temperature (240–320 °C) and reaction time (5–60 min) were evaluated in a batch-type autoclave reactor. The main depolymerization products of PTT were terephthalic acid (TPA) and 1,3-propanediol (1,3-PDO), which were identified by liquid chromatography mass spectrometry, Fourier-transform infrared spectroscopy, gas chromatography mass spectrometry, Raman spectroscopy, and quantified by high-performance liquid chromatography as well as gas chromatography. Additionally, it was found that 1,3-PDO was converted to 1,5-dioxocane partly in the presence of TPA. Under optimal reaction conditions, i.e. 300 °C, 15 min, with a water/PTT ratio of 8:1 (w/w), complete depolymerization was achieved, and the yields of TPA and 1,3-PDO reached 90.5% and 69.03%, respectively. Based on the results, a reaction mechanism for PTT depolymerization in HCW was proposed.

Photo oxidative degradation of azure-B by sono-photo-Fenton and photo-Fenton reagents

A model for the decomposition of azure-B by photo-Fenton reagent in the presence of ultrasound in homogeneous aqueous solution has been described. The photochemical decomposition rate of azure-B is markedly increased in the presence of ultrasound. It is a rather inexpensive reagent for wastewater treatment. The effect of different variables like the concentration of ferric ion, concentration of dye, hydrogen peroxide, pH, light intensity etc. on the reaction rate has been observed. The progress of the sono-photochemical degradation was monitored spectrophotometrically. The optimum sono-photochemical degradation conditions were experimentally determined. The results showed that the dye was completely oxidized and degraded into CO2 and H2O. A suitable tentative mechanism for sono-photochemical bleaching of azure-B by sono-photo-Fenton’s reaction has been proposed.

Synthesis of supported fibrous nanoceramics via electrospinning

Stable homogeneous aqueous spinning solutions have been experimented under electro-hydrodynamic conditions in order to synthesize fibrous ZnO, TiO2 and Al2O3. A favourable combination of optimal solution, electrospinning, thermal post-processing and calcination parameters have provided the preparation of dense webs of fibres with a mean diameter in the nanosized range. The samples have been characterized by electron imaging under SEM and HRTEM. Conventional WAXRD and SAED have been applied to determine the phase composition. Simple mechanical and gas flow tests give a first evidence for building of fibre-to-fibre and web-to-substrate cohesive forces. The fibre immobilization has been found very important for the development of various functional ceramic materials.

Optimization study and neutronic design calculations of LEU fuelled homogeneous aqueous solution nuclear reactors for the production of short lived fission product isotopes

Low enriched uranium (LEU) based solution reactors possess the potential to meet increasing demand of 99Mo and other short lived fission product radioisotopes being used in medical field. In the current study, optimization and neutronic design calculations have been carried out for an LEU homogeneous aqueous solution reactor with uranyl nitrate as a solution fuel. Lattice calculations and core modeling was performed employing available standard nuclear reactor codes WIMSD and CITATION. Calculation procedure was verified using experimental published data and simulated criticality results were compared with the published data. After verification of the calculation methodology, optimization and design calculations were performed for four different uranium enrichments (5%, 10%, 15%, and 19.99%) of the uranyl nitrate solution. Keeping in view the restraints on peak power density of solution reactors, annular geometry is suited as compared to the cylindrical geometry. Among the four considered enrichments in the analysis, 19.99% enriched uranyl nitrate solution with annular geometry presents optimum design parameters for the homogeneous aqueous solution reactor.