pH Value Of Aqueous Solution Research Articles

The Alkalescence Effect on the Acid-removal Rate of Imidazole and Its Derivatives: A DFT and Ab Initio Study

The molecular structure modeling of imidazole and its derivatives were calculated by ab initio method. The charge distribution of the optimal configuration was obtained. It showed that the optimal molecular structures of imidazole and its derivatives were reasonable. According to the calculations of the molecular charge distribution, the alkalescence order of imidazole and its derivatives is 2-methylimidazole > 4-methylimidazole > 2-ethylimidazole > imidazole > 1-methylimidazole. The pH value in aqueous solution and the deacidification capacity to high-acidic crude oil at certain conditions of the various substances were determined further through experiments. It was found that the aqueous solution pH and the acid-removal rate increased with the alkalescence of imidazole and its derivatives becoming stronger.

Determination of pH Value and Acid-base Property of Ionic Liquid Aqueous Solutions

The ionic liquids (ILs) and their aqueous solutions have been considered as a new generation of absorption working substances for applications in gas separation and absorption refrigeration processes. It is important to understand the physicochemical properties of ionic liquids in aqueous solutions, such as chemical potential and acid-base properties before any industry application. In this study, we focused on the acid-base properties of the IL aqueous solutions by testing the pH values of the aqueous solutions of two ionic liquids, 1-ethyl-3-methylimidazolium acetate ([EMIM]Ac) and 1-hexyl-3-methylimidazolium chloride ([HMIM]Cl). All the tests were carried out at 25 and in a well controlled dry air °C surrounding. There were 16 water mass fractions for each of [EMIM]Ac and [HMIM]Cl aqueous solutions tested in range of 0.04 to 0.95 and 0.01 to 0.96, respectively. There, two methods, the sophisticated pH paper and the pH meter, were applied for the tests and the differences between the two test methods were detected. The test data from the two test methods and their differences were then evaluated with an aggregation film model and the activity theory for the film and aqueous solution phases. The results show that the difference of the pH values tested by the two methods is significant. The pH data from the sophisticated pH paper test present the bulk acid-base property of the IL aqueous solutions, while the pH meter can only reflect the hydrogen ion concentration in the IL aggregation film which was formed on the surface of the electrode of the pH meter. With analysis of acid-base reaction in the IL aqueous solution, a calculation model for the pH value of the bulk solution region was developed, and the data of the sophisticated pH paper test were correlated and the solution acid-base values were obtained. Based on analysis of the water species equilibrium in the IL aggregation film and the bulk aqueous solution phases and its effect on the concentration of hydrogen ions in the aggregation film, a method for calculation of the difference of pH values between the aggregation film and the bulk solution was proposed and the data from the pH meter were then fitted with the proposed calculation method. The results provide experimental data and a quantitative method for analysis of the acid-base property of IL aqueous solution systems.

Ionic liquid-based optoelectronic sensor arrays for chemical detection

Development of ionic liquid (IL)-based colorimetric sensor arrays for detection and identification of chemicals in both the aqueous and vapor phases is reported. These facile and inexpensive optoelectronic sensors were fabricated by using ionic liquids (ILs) derived from readily available pH indicator dyes. A series of 12 different chemosensory ILs were synthesized by pairing anionic pH indicator dyes with trihexyl(tetradecyl)phosphonium ([P66614]) cation via an ion exchange reaction. The incorporation of the [P66614] cation imparted hydrophobic characteristics to these ILs, and this induced hydrophobicity led to their desired low solubility in aqueous solutions, as well as eliminated the need for a specialized hydrophobic matrix/substrate for immobilization. In this manuscript, four different matrices, i.e. glass microfiber filter papers, cotton threads, silica thin layer chromatography (TLC) plates, and alumina TLC plates, were employed for fabrication of sensor arrays. These sensor arrays were used to analyze pH values of aqueous solutions as well as for detection of acidic and basic vapors. To further prove the applicability of these IL sensor arrays as tools to sense closely related complex materials, the arrays were applied to successful discrimination of aqueous solutions of smoke from three commercially available cigarettes. The digital data generated from these sensor arrays were used in developing predictive models for accurately identifying various analytes. Two approaches were used for developing the models, and two methods were applied for assessing the predictive accuracy of the models. Use of cotton threads as a matrix led to development of a more flexible, low volume, and lightweight array to estimate pH and detect a variety of vapors. These wearable arrays may possibly be incorporated into bandages, sweatbands, diapers, and similar systems. Overall, these IL-based sensor arrays should provide a new research direction in the development of advanced colorimetric sensor arrays for detection and identification of a range of analytes relevant to many different applications.

Effect of solution pH value on thermoelectric performance of free-standing PEDOT:PSS films

Dependence of the thermoelectric (TE) performance of free-standing poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) composite films on the pH value in aqueous solution treated by acids and alkalis were systematically investigated. The TE performance can be enhanced by decreasing the pH value (acidic conditions), while it decreases rapidly with the increase in pH value (alkaline conditions). Carrier mobility and concentration, as well as morphology and structure characterizations of free-standing PEDOT:PSS films demonstrated that the pH value of the solution significantly affects their TE properties. With the maximum power factor of 1.35Wm−1K−2 and the highest Seebeck coefficient of 40.7μV/K, are promising organic thermoelectric materials.

Functionalized Pentamolybdodiphosphate-Based Inorganic–Organic Hybrids: Synthesis, Structure, and Properties

Three inorganic-organic hybrid compounds based on functionalized pentamolybdodiphosphonopropionate anion [(HO2CC2H4PO3)2Mo5O15](4-), [Co3(bipy)4(H2O)6{(HO2CC2H4PO3)2Mo5O15}2]·(H2bipy)2·18H2O (1), [Fe3(bipy)4(H2O)6{(HO2CC2H4PO3)2Mo5O15}2]·(H2bipy)2·18H2O (2), and [Cu(bipy)(H2O)2{(HO2CC2H4PO3)2Mo5O15}]·(H2bipy)·4H2O (3), where bipy = 4,4'-bipyridine, have been successfully synthesized at different pH values in aqueous solutions. In compound 1, [(HO2CC2H4PO3)2Mo5O15](4-) acts as a tridentate ligand and coordinates to the Co(2+) ions of trimeric complex cations [Co3(bipy)4(H2O)6](6+) forming a layer. In 3 [(HO2CC2H4PO3)2Mo5O15](4-) acts as a bidentate ligand and coordinates to the Cu(2+) ions of complex chains [Cu(bipy)(H2O)2]n(2n+), forming a different layer from that in 1. The three compounds were characterized by elemental analysis, IR spectra, and TGA. In addition, their fluorescent properties and magnetic properties have also been investigated.

Atmospheric Pressure Plasma Degradation of Azo Dyes in Water: pH and Structural Effects

The degradation of aqueous solutions containing azo dyes (ortho-, meta-, and para-methyl red) was carried out by means of atmospheric pressure plasma treatment. As evidenced by optical emission spectroscopy, the metastable argon in the discharge is responsible for initiating reactions in dye solutions. The bleaching of aqueous solutions is attributed to the destruction of dye molecules as observed in the UV–visible absorption spectra. We found that the degradation pathways of methyl red critically depend on the pH values in aqueous solutions as well as isomeric structures. The reaction pathways are entirely different in basic (pH = 11), near-neutral (pH = 6), and acidic conditions (pH = 2). Kinetic analysis shows that acidic condition gives the fastest degradation rates of methyl red isomers with removal rate: ortho > meta > para among all conditions. At basic condition, the degradation rates are equally slow for all methyl red isomers.

Efficient Removal of Cd<sup>2+</sup> by the Mesoporous Silica Functionalized by APTES

Amino-functionalized mesoporous silica (AFMS) with high amino loading, high surface area, and large pore size was synthesized using the anionic surfactant N-lauroylsarcosine sodium (Sar-Na) as template and 3-aminopropyltriethoxysilane (APTES) as co-structure directing agent (CSDA). The synthesized AFMS was characterized by N2adsorption-desorption, TEM and elemental analyzer. The results of the removal of Cd2+from aqueous solution showed that the pH value of aqueous solution affected the removal efficiency of Cd2+greatly, and that unary adsorption isotherm of Cd2+on the AFMS was well described by the Sips isotherm model, in which the adsorption capacity was 2.43 mmol/g for Cd2+, much higher than the literature data.

Crystalline and solution chemistry of tetrameric and dimeric molybdenum(VI) citrato complexes

Reaction of citrate with molybdenum(VI) salts under controlled conditions of reactant ratios and pH values in aqueous solutions affords a family of molybdenum citrates. It includes tetranuclear complexes K2(NH4)2[(MoO2)4O3(Hcit)2]·5H2O (1), (NH4)5[(MoO2)4O3(Hcit)(cit)]·3H2O (2) and K2(NH4)4[(MoO2)4O3(cit)2]·7H2O (3), dinuclear complexes K2[(MoO2)2O(H2cit)2]·4H2O (5), (NH4)3[(MoO2)2O(H2cit)(Hcit)] (6), (NH4)14{[(MoO2)2O(Hcit)2][(MoO2)2O(Hcit)(cit)]2}·14H2O (8) and (NH4)6[(MoO2)2O(cit)2]·3.5H2O (9), as well as a mononuclear complex (NH4)4[MoO3(cit)]·2H2O (10) (H4cit=citric acid), where 2, 5, 6, and 8 are new type of citrato complexes. X-ray single-crystal structural analyses reveal that the molybdenum atom in these complexes is hexa-coordinated in an approximately octahedral geometry. Each citrate ligand uses its α-alkoxy, α-carboxy and one β-carboxy groups to act as a tridentate ligand while the other β-carboxy group is left free. Also, structural analyses show that some of the complexes possess strong hydrogen bonds that lead to one and two dimensional polymeric associations. All of these complexes have been investigated by 13C and 1H NMR spectroscopy. The NMR spectra demonstrate that these complexes except 1 and 8 obviously undergo decomposition in solution. Furthermore, four series of solutions with the molar ratio Mo:cit=2:1, 1:1, 1:2, and 1:4 in the pH range 0.1–9.0 were investigated by 13C NMR spectroscopy. The solution NMR studies reveal that the state of equilibriums among different species [4,2]n−, [2,2]n−, [2,1]n−, [1,2]n− and/or [1,1]n− being established under each set of specified conditions.

Preparation and Fluorescence Properties of GdF3:Eu3+, NaGdF4:Eu3+ Materials

The GdF3:Eu3+and NaGdF4:Eu3+powders were synthesized by hydrothermal method as raw material of Gd2O3, Eu2O3, NaF, NH4HF2, EDTA and polyethylene glycol. The powders were characterized by means of X-ray powder diffraction, SEM microscopy and Molecular fluorescence photometer. It was discussed that the pH value of aqueous solution had affection on the phase composition of synthesized powders. The complex fluorides GdF3and NaGdF4were synthesized in aqueous solution at the pH values between 3 and 6. The synthesized powders were single hexagonal phase of NaGdF4 crystal at pH=8. It was also found that different fluorescence properties were exhibited by Eu3+doping powders synthesized at different pH values of aqueous solution. The synthesized powders of GdF3and NaGdF4were excellent fluorescence materials.

REMOVAL OF CATIONIC DYES FROM AQUEOUS SOLUTION USING CARBON-ENCAPSULATED SUPERPARAMAGNETIC COLLOIDAL NANOPARTICLES AS ADSORBENT

This paper demonstrates the application of negative charge-functionalized carbon-encapsulated superparamagnetic colloidal nanoparticles being as nanoadsorbents for the removal of cationic dyes from aqueous solutions. Adsorption characteristics of the magnetic nanoadsorbents were examined using methylene blue as adsorbates, exhibiting excellent ability to remove cationic dyes from aqueous solutions. In addition, the influences of uptake time, concentration of nanoadsorbents and pH values of aqueous solution on the removal of cationic dyes have been discussed. Results show that the removal efficiency can be up to 90% at a dye concentration of 100 mg L-1 when the uptake time is 1 min, which indicates rapidly removal ability of the magnetic nanoadsorbents. Furthermore, other cationic dyes including rhodamine B and methyl violet were used to examine the universality of nanoadsorbents.

Photochemical degradation of pyrazosulfuron-ethyl in aqueous solution

This report describes photochemical behaviors of pyrazosulfuron-ethyl in aqueous solution. The photodegradation of pyrazosulfuron-ethyl for the first time was investigated in aqueous solution at two different irradiation wavelengths and pH values ranging from 2.00 to 10.00. Results show that the rate of photodegradation was faster in acidic medium than that in basic medium, when pyrazosulfuron-ethyl was in neutral form. The half-lives of pyrazosulfuron-ethyl under ultra-violet light and simulated sunlight were found to be 27.17 and 153.33 min, respectively. The reactions followed first-order kinetics. The degradation pathways were proposed according to the identification results of photoproducts: carbon-sulfur and nitrogen-sulfur cleavages and photohydrolysis of the sulfonylurea bridge. It was concluded that photodegradation behaviors can occur within the sulfonylurea family, depending on the pH values of aqueous solution and the irradiation wavelengths.

Advantage of Fluorescence Correlation Spectroscopy for the Study of Polyelectrolytes

AbstractThe advantage of fluorescence correlation spectroscopy to study single chain behavior of polyelectrolytes has been demonstrated by checking the coil‐to‐globule transition of poly 2‐vinylpyridine with the change of pH value in aqueous solution. The ultra‐high sensitivity of FCS allows measurement at extreme dilution where the effect of electrostatic interaction between the chains is greatly suppressed. The results exposed first‐order conformation transition of P2VP as detected by FCS while inter‐chain aggregation occurred in the experiments of dynamic light scattering.

Rapid extraction of low concentration heavy metal ions by magnetic fluids in high gradient magnetic separator

A novel method for the extraction of low concentration heavy metal ions from aqueous solution by using magnetic fluids in the high gradient magnetic separator (HGMS) has been constructed. We dissolved the extractant tributyl phosphate (TBP) in the magnetic fluids, and selected the Au 3+ as the model of heavy metal ion to research the extraction efficiency of magnetic fluids containing TBP in this article. The magnetic fluids containing TBP, as stationary phase in the form of liquid-droplet, were immobilized on the surface of steel wires in the HGMS; the low concentration Au 3+, as mobile phase, flowed through the HGMS and was extracted from aqueous solution. The experiments investigated the dependence of the Au 3+ extraction efficiency of magnetic fluids on the pH value of aqueous solution, TBP concentration in magnetic fluids and flow rate of aqueous solution in magnetic separation column. Under the optimum conditions, the proposed method obtained a high extraction capacity and high treatment volume with a continuous extraction process. This method is especially suitable for the extraction of low concentration heavy metal ions solution that was very difficult to be recovered by use of traditional extraction technologies.

Spectral and fluorescent indication of the acid-base properties of biopolymer solutions

Methods of absorption and fluorescent spectroscopy and fluorescent chronoscopy are used to investigate aqueous fluorescein solutions with pH values increasing from 1.79 to 11.67. For each method, the calibration curves are drawn for the fraction of dianion fluorescein species, quantum fluorescence yield, and amplitude dianion contribution to the fluorescence intensity on the pH values of aqueous solutions. The calibration curves allow the pH values of aqueous fluorescein solutions with gelatin (pH = 6.4 ± 0.1, 6.6 ± 0.2, and 6.6 ± 0.1), starch (pH = 6.3 ± 0.1, 6.3 ± 0.2, and 6.4 ± 0.1), and acid-soluble chitosan additions (pH = 5.4 ± 0.1, 5.6 ± 02, and 5.8 ± 0.1) to be estimated by these three methods. The pH values of biopolymer solutions obtained by the potentiometer method for starch (6.51) and gelatin (6.69) and by the three spectral and fluorescent methods are close; they are significantly underestimated (3.85) for chitosan solutions.

Synthesis of polyacrylonitrile by single‐electron transfer‐living radical polymerization using Fe(0) as catalyst and its adsorption properties after modification

AbstractFe(0) was firstly used as single‐electron transfer‐living radical polymerization catalyst for acrylonitrile polymerization using carbon tetrachloride as initiator, hexamethylenetetramine as N‐ligand, and N,N‐dimethylformamide as the solvent at 65 °C. First‐order kinetic studies indicated that this polymerization proceeded in a “living”/controlled manner. The living nature of the polymerization was also confirmed by chain extension of methyl methacrylate with polyacrylonitrile (PAN) as macroinitiator. Furthermore, PAN was modified with NH2OH·HCl to generate amidoxime groups for extraction of heavy metal ions (Hg2+) from aqueous solutions. Fourier transformed infrared spectroscopy was performed to characterize chemical composition and structure. The adsorption property of Hg2+ was investigated at different pH values of aqueous solutions and distilled water. The maximal saturated adsorption capacity of Hg2+ was 4.8 mmol g−1. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011

Redispersible dried hydroxyapatite particles with grafted pH-sensitivity polymer brushes of poly(styrene-co-4-vinylpyridine)

Reversible aggregation–redispersion transition of colloidal particles is of considerable importance in colloidal science and various industrial fields. In the present study, stimuli-responsive hybrid hydroxyapatite (HA) particles were prepared with redispersible ability in aqueous solutions even after separation from the “as synthesized” state and subsequent dry heat treatment. We firstly modified HA particles with sodium oleate as chelating agent, then introduced bromoalkyl functional groups through an addition reaction of unsaturated oleate molecule with bromine, and finally grafted polymer brushes of polystyrene-co-4-vinylpyridine onto HA. It was the pH-sensitive polymer shell that had rendered HA particles the redispersible ability, which was attributed to the protonation of the pyridine blocks in acidic solutions. The reversible dispersion–aggregation transition of HA could be controlled by alternating the pH value of aqueous solution. Protonated pyridine blocks had provided enough electrostatic and steric repulsions for colloidal HA to avoid effective collision.

Novel multi-responsive P2VP-block-PNIPAAm block copolymers via nitroxide-mediated radical polymerization

Linear soluble multi-responsive block copolymers are able to form so called schizophrenic micelles in aqueous solution. Here, such polymers are prepared via nitroxide-mediated radical polymerization (NMRP). In a first step nitroxide-terminated poly(2-vinylpyridine) (P2VP) was prepared with different molecular weights and narrow molecular weight distributions. The best reaction conditions, optimized by kinetic studies, were bulk polymerization at 110 °C. Using P2VP as a macroinitiator, the synthesis of new soluble linear block copolymers of P2VP and poly(N-isopropylacrylamide) (PNIPAAm) (P2VP-block-PNIPAAm) was possible. The nitroxide terminated polymers were characterized by nuclear magnetic resonance (NMR) spectroscopy, size exclusion chromatography (SEC) and matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF MS). Thermal properties were investigated by the differential scanning calorimetry (DSC). Block copolymers showed pH- and temperature-responsive solubility in aqueous media. By increasing the P2VP content, the phase transition temperature shifted to lower temperatures (e.g. 26 °C for P2VP114-block-PNIPAAm180). Depending on the resulting block length, temperature and pH value of aqueous solution, the block copolymers form so called schizophrenic micelles. The hydrodynamic radius Rh of these micelles associated with pH values and temperature was analyzed by dynamic light scattering (DLS). Such kind of block copolymers has potential for many applications, such as controlled drug delivery systems.

A pH- and temperature-sensitive macrocyclic graft copolymer composed of PEO ring and multi-poly(2-(dimethylamino) ethyl methacrylate) lateral chains

A novel method for the synthesis of macrocyclic graft copolymers was developed through combination of anionic ring-opening polymerization (AROP) and atom transfer radical polymerization (ATRP). A linear α,ω-dihydroxyl poly(ethylene oxide) with pendant acetal protected hydroxyl groups (l-poly(EO-co-EEGE)) was prepared first by the anionic copolymerization of ethylene oxide (EO) and ethoxyethyl glycidyl ether (EEGE). Then l-poly(EO-co-EEGE) was cyclized. The crude cyclized product containing the linear byproduct was hydrolyzed and purified by being treated with α-CD. The pure cyclic copolymer [c-poly(EO-co-Gly)] was esterified by reaction with 2-bromoisobutyryl bromide, and then used as ATRP macroinitiators to initiate polymerization of 2-(dimethylamino) ethyl methacrylate (DMAEMA), and a series of pH- and temperature-sensitive macrocyclic graft copolymers composed of a hydrophilic PEO as the ring and PDMAEMA as side chains (c-PEO-g-PDMAEMA) were obtained. The behavior of pH- and temperature-sensitive macrocyclic copolymers was studied in aqueous solution by fluorescence and dynamic light scattering (DLS). The critical micellization pH values of macrocyclic graft copolymers and their corresponding linear graft copolymers (l-PEO-g-PDMAEMA) were measured. Under the same conditions, the cyclic graft copolymer with the shorter side chains gave the higher critical micellization pH value. The c-PEO-g-PDMAEMA showed the lower critical micellization pH value than the corresponding l-PEO-g-PDMAEMA. The average hydrodynamic diameters (D h) of the micelles were measured by DLS with the variation of the aqueous solution pH value and temperature.

Kinetics of styrene miniemulsion polymerization using poly[(stearyl methacrylate- co-( N, N-dimethylamino)ethyl methacrylate] as surfactant

Two comb-like amphiphilic copolymers have been prepared via conventional free-radical random copolymerization of stearyl methacrylate (SMA) and 2-( N, N-dimethylamino)ethyl methacrylate (DMAEMA) with different feed ratios. The resultant copolymers, poly(SMA- co-DMAEMA), were then characterized by 1H NMR and gel permeation chromatography (GPC) measurements. The surface activity of these copolymers in aqueous solution with different pH values was studied by surface tension measurements. Finally, these amphiphilic cationic copolymers were used as polymeric surfactants in the miniemulsion polymerization of styrene. The hydrophobic stearyl side chains of SMA could be strongly adsorbed onto the monomer droplets or propagating particles during the miniemulsion polymerization, while the hydrophilic and protonated PDMAEMA units at low pH media could stabilize the latexes. Moreover, the influences of the composition and amounts of the polymeric surfactants on the kinetics of the miniemulsion polymerization and colloidal stability have been investigated. The reaction rate of miniemulsion polymerization was found to increase with increasing amounts of polymeric surfactants and decrease with the increase of pH values of aqueous solution.

The development and in-vitro evaluation of novel mixed metal hydroxy-carbonate compounds as phosphate binders.

The currently available phosphate binders are relatively inefficient and suffer from clinical side-effects of increased absorption of calcium and aluminium and the diarrhoea-inducing effects of magnesium. A new class of compounds based on mixed metal hydroxides has been developed and evaluated for their potential as phosphate binders. The mixed metal hydroxides were prepared using a standard procedure for hydrotalcite (Al2Mg6(OH)16.CO3.4H2O) by substituting Fe3+ for Al3+, with Mg2+ or Ca2+ as the divalent metal ion. Phosphate precipitation (binding) was examined at different pH values in aqueous solution and in various food mixtures in comparison with hydrotalcite, Al(OH)3, CaCO3 and Mg(OH)2 on the same weight-to-weight basis. A series of compounds with differing ratios of metal ions (Fe:Mg/Ca 1:2 or 1:3) gave analytically similar ratios to those predicted from the initial amounts added. CTFeCa bound > 90% phosphate in aqueous solution compared with 65% binding with CTFeMg, 85% binding with Mg(OH)2, and less than 30% binding for CaCO3 and Al(OH)3. The mixed metal compounds also bound up to 80% phosphate in various food matrices, which was relatively independent of changes in pH, compared with Mg(OH)2, where binding decreased from 85% at pH 3.0 to 25% at pH 8.0. Al(OH)3 and CaCO3 were relatively ineffective phosphate binders under all the conditions tested. The mixed metal hydroxides compounds show considerable promise as phosphate binders over those currently available and warrant further patient-based in-vivo testing.