pH Value Of Aqueous Solution Research Articles

Fabrication of Amino-Functionalized Magnetic Graphene Oxide Nanocomposites for Adsorption of Ag(I) from Aqueous Solution

In this study, amino-functionalized magnetic graphene oxide (Fe3O4/GO-NH2) nanocomposites were fabricated by one-pot solvothermal method. As-prepared Fe3O4/GO-NH2 nanocomposites were characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS), nitrogen adsorption/desorption isotherm, elemental analysis, and vibrating sample magnetometer (VSM). Adsorption behaviors of Fe3O4/GO-NH2 nanocomposites for Ag(I) in aqueous solution were investigated. Detailed adsorption studies demonstrate that Ag(I) was reduced to silver in the process of the adsorption by Fe3O4/GO-NH2 nanocomposites. The pH value of aqueous solution had a major impact on Ag(I) adsorption. The maximum adsorption capacity of Fe3O4/GO-NH2 nanocomposites for Ag(I) was 114.90 mg/g. The adsorption process of Fe3O4/GO-NH2 nanocomposites for Ag(I) was well described by the pseudo-second-order kinetics model and the Langmuir isotherm model.

Sodium lactate loaded chitosan-polyvinyl alcohol/montmorillonite composite film towards active food packaging

Abstract A sodium lactate loaded chitosan-polyvinyl alcohol/montmorillonite (NaL-CS/PVA/MMT) barrier film with antibacterial activity was developed by coating method and the effectiveness and diffusion behavior were investigated. An intercalated structure was achieved for CS/PVA/MMT film and the interfacial interactions among CS, PVA and MMT were intermolecular hydrogen bonds. An appropriate increase of MMT contents (15 wt% and below) could achieve a remarkable enhancement in tensile strength and Young's modulus, meanwhile, the water vapor, oxygen and carbon dioxide barrier properties of the films were also significantly improved. The NaL-CS/PVA/MMT film exhibited good antibacterial activity against E. coli and well controlled release of NaL. Moreover, the diffusions of NaL from films were dependent on the pH value of aqueous solution and ionic strength, and the initial diffusions ( M t / M ∞

Synthesis of a novel silica-based macroporous HNA/SiO2-P adsorbent and its adsorption behavior for uranium from aqueous solutions

In order to separate and pre-concentrate uranium from aqueous phase, a novel silica-based adsorbent was prepared by impregnating nalidixic acid (HNA) into a macroreticular silica/polymer composite support (SiO2-P) with a mean diameter of 60 μm. Adsorption behavior of uranium from aqueous solution onto the adsorbent was studied. Experimental results indicated that HNA/SiO2-P showed strong adsorption for uranium in a wide range of pH from 3.5 to 10.0, and the maximum adsorption capacity was 35.4 mg g−1. In addition, HNA/SiO2-P exhibited good selectivity for U(VI) and showed weak or bare adsorption affinity to foreign ions. Kinetic and isotherm of uranium adsorption were in accordance with the pseudo-second-order kinetic model and Langmuir isotherm adsorption model, respectively. Moreover, U(VI) sorption was found to be an endothermic reaction and spontaneous under experimental state. The synthesized adsorbent showed an admirable stability at lower pH values in aqueous solution.

The influence of surface modification, coating agents and pH value of aqueous solutions on physical properties of magnetite nanoparticles investigated by ESR method

The article presents the results of electron spin resonance (ESR) studies for aqueous solutions of functionalized superparamagnetic iron(II,III) oxide nanoparticles. The samples studied differed in type of organic ligands at the magnetite surface, type of coating agent and pH value of aqueous solutions. The ESR spectra of the samples were obtained at room temperature and at 230K. The field cooling (FC) experiment was performed for selected samples, and the effective anisotropy field (HK2) and the first order magnetocrystalline anisotropy constant (K1) was calculated. The process of the nanoparticles diffusion in different environments (human blood, human serum) forced by an inhomogeneous magnetic field was monitored and their interactions with different solvents have been discussed. It has been shown that ESR method is useful to observe the impact of organic ligands at the magnetite surface, type of coating agent and pH value of aqueous solutions on the properties of iron(II,III) oxide nanoparticles.

Temperature- and pH-dependent aggregation behavior of hydrophilic dual-sensitive poly(2-oxazoline)s block copolymers as latent amphiphilic macromolecules

A variety of hydrophilic diblock and triblock copolymers of AB and ABA type with temperature-sensitive poly(2-isopropyl-2-oxazoline) blocks und pH-sensitive poly(2-carboxyethyl-2-oxazoline) blocks have been synthesized. The temperature- and pH-induced reversible phase transition renders the block copolymers as amphiphilic macromolecules and allows for defined aggregation through self-assembly following the packing parameter of amphiphilic macromolecules. Size, structure and arrangement of the individual block copolymer segments define the temperature and pH values of the transitions as well as the nature of the formed aggregates. DLS measurements were used to determine the transition temperatures at selected pH values in aqueous solution whereas AFM was used to visualize and characterize the formed aggregates adsorbed on Si wafer surfaces. In the case of vesicles formed by the diblock and triblock copolymers, double and monolayer membranes could be verified. The tendency of different states of organization of poly(2-isopropyl-2-oxazoline) blocks from crystalline to amorphous is assumed to be the cause for the different box-like structures determined on Si wafer surfaces.

Kinetic and equilibrium studies of Pb(II) and Cd(II) adsorption on African wild mango (Irvingia gabonensis) shell

The adsorption behavior of NaOH-activated African wild mango ( Irvingia gabonensis ) shell with respect to Pb 2+ and Cd 2+ has been studied in order to consider its application to purify metal finishing waste water. The optimum conditions of adsorption were determined by investigating the initial metal ions concentration, contact time, adsorbent dose, pH value of aqueous solution and temperature. The extent of adsorption of metal ions was investigated by batch method using metal concentrations in solution ranging from 5-200 mg/L. The adsorption efficiencies were found to be pH dependent, with maximum metals uptake recorded at pH of 5. The equilibrium adsorption capacity for lead and cadmium ions were obtained from Freundlich, Langmuir, Temkin and DRK isotherms and the experimental data were found to fit best the Langmuir isotherm with values of 21.28 and 40.00 mg/g for Cd(II) and Pb(II) ions, respectively. The Pseudo-second order kinetics model had the best fitting for lead and cadmium adsorption kinetic data. The thermodynamic investigation showed that the adsorption processes of both metals are exothermic. An optimum concentration of 0.05 M HCl was found to be adequate for the regeneration of the spent adsorbent with recovery values of 78% and 71% for Pb 2+ and Cd 2+ respectively from the spent adsorbent. The results revealed that lead and cadmium are considerably adsorbed on the adsorbent and could be an economic method for the removal of these metals from aqueous solutions. KEY WORDS : Adsorption, Lead, Cadmium, Aqueous solution, African wild mango shell, Langmuir isotherm Bull. Chem. Soc. Ethiop. 2016 , 30(2), 185-198. DOI: http://dx.doi.org/10.4314/bcse.v30i2.3

Reversible pH Stimulus-Response Material Based on Amphiphilic Block Polymer Self-Assembly and Its Electrochemical Application.

Stimulus-responsive microporous solid thin films were successfully fabricated by simple molecular self-assembly via an amphiphilic block polymer, polystryene–b–polyacrylic acid (PS–b–PAA). The solid thin films exhibit different surface morphologies in response to external stimuli, such as environments with different pH values in aqueous solutions. The experiments have successfully applied atomic force microscope (AFM) technology to observe in-situ surface morphological changes. There is a reversible evolution of the microstructures in buffer solutions over a pH range of 2.4–9.2. These observations have been explained by positing that there is no conventional PAA swelling but that the PAA chains in the micropores stretch and contract with changes in the pH of the solution environment. The hydrophobicity of the solid thin film surface was transformed into super-hydrophilicity, as captured by optical contact angle measurements. The stimulus-responsive dynamics of pore sizes was described by a two-stage mechanism. A promising electrochemical application of this film is suggested via combination with an electrochemical impedance technique. This study is aimed at strategies for the functionalization of stimulus-responsive microporous solid thin films with reversible tunable surface morphologies, and exploring new smart materials with switch-on/switch-off behavior.

Raman spectral characterization of NH4H2PO4 single crystals: Effect of pH on microstructure

Single crystals of ammonium dihydrogen phosphate (NH4H2PO4, ADP) were grown from aqueous solutions using “point seeds” method. The Raman spectra of the NH4H2PO4 single crystals were recorded as a function of pH. The band intensities and frequencies were monitored to determine the diagnostic bands for the crystals grown from the solutions of different pH values of aqueous solution. In the Raman spectra of ADP crystal samples at different pH, the position and intensity of the peaks in the range 300–900cm−1 did not change; the peaks in the range 1400–1700cm−1 shifted their position, although they had the same intensity. This indicates that the structure of (PO4)3− did not change with pH, whereas the structure of NH4+ changed with pH. In the Raman study in the range 1700–4000cm−1, the primary discrimination occurred for the intensity of the peaks at 3050cm−1 and 3147cm−1, which is attributed to the vibration of O–H⋯O hydrogen bond, it can be inferred that pH slightly affected the O–H⋯O hydrogen bonding. This Raman spectral characterization may help to better understand the microstructural change under different conditions and optimize the growth and property of this type of material.

The metal-organic framework MIL-101(Cr) as efficient adsorbent in a vortex-assisted dispersive solid-phase extraction of imatinib mesylate in rat plasma coupled with ultra-performance liquid chromatography/mass spectrometry: Application to a pharmacokinetic study

Metal-organic framework MIL-101(Cr) was successfully used as an efficient sorbent in a vortex-assisted dispersive solid-phase extraction (VA-DSPE) and applied for the determination and the pharmacokinetic of imatinib mesylate in rat plasma by UPLC–MS/MS. In the enrichment of imatinib from rat plasma, the analyte was efficiently adsorbed on MIL-101(Cr) and simply recovered by using initial mobile phase (0.1% formic acid-methanol (6:4 v/v)) as elution solvent. Meanwhile, the protein in the plasma samples was excluded from the porous structure of MIL-101(Cr), leading to direct extraction of drug molecule from protein-rich biological samples without any other pretreatment procedure. After being removed, the supernatant was filtered and directly injected into the UPLC–MS/MS for the analysis of the target. The experimental parameters, including nature of MOFs, amount of MIL-101(Cr), pH value of aqueous solution, extraction time, type and volume of elution solvent, were systematically optimized. After VA-DSPE, chromatographic separation was performed on an ACQUITY UPLC® BEH C18 column (2.1mm×100mm, 1.7μm) with a 3min gradient elution using 0.1% formic acid and methanol as mobile phase at a flow rate of 0.3mL/min. The detection was accomplished on a tandem mass spectrometer via an electrospray ionization (ESI) source by multiple reaction monitoring (MRM) in the positive ionization mode. The lower limit of quantification of 1ng/mL was achieved and the mean recovery of the analyte was higher than 81.2%. Moreover, computational simulation was primarily applied to predict the adsorption behavior and revealed the molecular interactions and free binding energies between MIL-101(Cr) and imatinib with the molecular modeling method, providing certain explanation of the adsorption mechanism. The originally established pretreatment and detection method has some merits, such as less solvent consumption, easy operation, higher sensitivity and lower matrix effect. And the MIL-101(Cr) exhibited a potential as an efficient sorbent in the enrichment of the analyte from complex biosamples.

EDTA-modified DR/SiO2 adsorbent: Preparation, characterization, and application in heavy metal adsorption

ABSTRACTA hybrid material of diazoresin (DR) and ethylenediaminetetraacetic acid disodium salt (EDTA-2Na) coated onto silica particles were synthesized and applied as adsorbents. The study of UV-vis spectrum revealed that DR and EDTA could be successfully modified onto silica. The effect of initial pH value of aqueous solution and dosage of the adsorbents on the adsorption capability for heavy metal Cu(II) ion were investigated and discussed.

Silica Encapsulation of SrAl<sub>2</sub>O<sub>4</sub>:Eu<sup>2+</sup>, Dy<sup>3+</sup> Phosphors by Sol-Gel Method

SrAl2O4:Eu2+,Dy3+ phosphors were synthesized under different temperature by high temperature solid phase method. Encapsulation modification of SrAl2O4:Eu2+,Dy3+ by using SiO2glycol were made over chemically unstable against water. Photoluminescence measurement result shows that when the sintering temperature is 1300 °C, the initial afterglow brightness of SrAl2O4:Eu2+,Dy3+ is up to the highest, 12101 mcd/m2. FTIR results showed that new IR peaks at 1085 cm−1 due to the vibration of Si-O-Si and at 931cm−1 due to the vibration of Si-O-Al appeared after silica encapsulation. This verified that the silica encapsulation is not only a physical absorption process but also involving chemical bonding process. Both phosphors before and after encapsulation have same emission peak at 510 nm. A dense layer of silica formed on phosphor surface has the highest water-resistance after being encapsulated for 2h under the condition of pH 4 and encapsulation amount 10:1. The pH value of aqueous solution contained phosphor was steadily 8, and the initial afterglow brightness decreased only by 9%, that is, from 12101 to 11011 mcd/m2.

Separation of chromium (VI) from its liquid solution using new montmorillonite supported with amine based solvent

The present work deals with the study of Cr (VI) adsorption onto montmorillonite (MM) and modified montmorillonite (MMT). The modification is done by using an amine based solvent, trioctylamine (TOA). Equilibrium and kinetic experiments are carried out to determine the effect of adsorbent dose (w, 0.05g to 0.3g for MM, 0.01g to 0.06g for MMT), initial Cr (VI) concentration (C0, 25mgL−1 to 125mgL−1), pH (1 to 9), and contact time (t, 10min to 100min) on the capacity of both the adsorbents. With an increase in the adsorbent dosage, the uptake capacity of MM and MMT for Cr (VI) is found to decrease but with an enhancement in the recovery efficiency. The optimum dosage of MM and MMT is proposed to be 0.2g and 0.02g, respectively. A better adsorption of Cr (VI) is observed at low pH values of aqueous solution, and is decreased with an increase in the value of pH. In the kinetic experiments, the percentage removal of Cr (VI) reaches to a constant value of 70.68% with MM (0.2g) and 33.92% with MMT (0.02g) after 80min. Equilibrium data are analysed by using Langmuir and Freundlich isotherm models. Kinetic models such as pseudo-first order (PFO) and pseudo-second order (PSO) are used to predict the kinetics of the adsorption process by MM and MMT for the Cr (VI) removal.

Kinetics of 2-chlorobiphenyl Reductive Dechlorination by Pd-fe0Nanoparticles

Kinetics of 2-chlorobiphenyl (2-Cl BP) catalytic reductive dechlorination by Pd-Fe 0 nanoparticles were investigated. Experimental results showed that ultrafine bimetallic Pd-Fe 0 e nanoparticles were synthesized in the presence of 40 kHz ultrasound in order to enhance disparity and avoid agglomeration. The application of ultrasonic irradiation during the synthesis of Pd-Fe 0 nanoparticles further accelerated the dechlorinated removal ratio of 2-Cl BP. Up to 95.0% of 2-Cl BP was removed after 300 min reaction with the following experimental conditions: initial 2-Cl BP concentration 10 mg L -1 , Pd content 0.8 wt. %, bimetallic Pd-Fe 0 nanoparticles prepared in the presence of ultrasound available dosage 7g L -1 , initial pH value in aqueous solution 3.0, and reaction temperature 25°C. The catalytic reductive dechlorination of 2-Cl BP followed pseudo-first-order kinetics and the apparent pseudo-first-order kinetics constant was 0.0143 min -1 .

An environmentally friendly electrochemical method for synthesis of pyrazole derivatives

Abstract Electrochemical oxidation of catechol and some of 3-substituted catechols (1a–c ) has been studied in the presence of 3-methyl-1-phenyl-1H-pyrazol-5(4H)-one ( 3 ) as the nucleophile at various pH values in aqueous solution using cyclic voltammetric and controlled-potential coulometric methods. The results revealed that the products derived from catechols ( 1a–c ) participate in Michael addition reactions with 3-methyl-1-phenyl-1H-pyrazol-5(4H)-one ( 3 ) via an ECEC mechanism, converts it to form the corresponding pyrazole derivatives ( 8a–c ). The electrosynthesis of these products was carried out at the surface of carbon electrode in an undivided cell under controlled-potential conditions which is an environmentally friendly method.

Adsorptive Separation of Cu2+ from an Aqueous Solution Using Trioctylamine Supported Montmorillonite

Montmorillonite (Mt) was used to remove copper (Cu2+) ion from wastewater stream generated from industrial effluents. This clay was modified (Mt-TOA) by using an amine-based solvent, trioctylamine (TOA). Equilibrium and kinetic experiments were carried out to determine the effect of adsorbent amount (w, 0.05 g to 0.3 g for Mt, 0.001 to 0.006 g for Mt-TOA), initial Cu2+ ion concentration (C0, 8 mg·L–1 to 16 mg·L–1), pH (2 to 10), and contact time (t, 10 to 90 min) on the capacity of both adsorbents. With an increase in the adsorbent amount, the uptake capacity of Mt and Mt-TOA for Cu2+ ion was found to decrease but with an enhancement in the removal efficiency. The optimum amount of Mt and Mt-TOA was found to be 0.1 and 0.001 g, respectively. A better adsorption of Cu2+ ion was observed at low pH value of aqueous solution, and was found to decrease with an increase in the value of pH. In the kinetic experiments, the amount removal of Cu2+ ion reached to a constant value of 75.62 % with Mt (0.1 g) and 80.12...

Photocatalytic Degradation of the Azo Dye Acid Red 14 in Nanosized TiO2 Suspension under Simulated Solar Light

The degradation and mineralization of azo dye acid red 14 by Titanium dioxide (TiO2) photocatalysis under simulated solar light was studied at lab scale. The characteristics (such as phase features, specific surface area, bandgap energy, etc.) of nanosized TiO2 were investigated in detail. The color removal rate, decrease rate of total organic carbon, and production rate of sulfate ions in aqueous solution were determined. Acid red 14 could be decolorized and mineralized efficiently with nanosized TiO2 under simulated solar light. Acidic or neutral conditions were beneficial to the decolorization of acid red 14 aqueous solutions. Acid red 14 was nearly 100% mineralized after 60 min irradiation by simulated solar light under certain experimental conditions. The photocatalytic degradation efficiency increased with increasing the irradiation intensity of solar simulated light. TiO2 dosage, pH value of aqueous solution, and initial concentration of acid red 14, had significant influences on the decolorization efficiency. It is feasible to use photocatalysis with nanosized TiO2 under simulated solar light to efficiently degrade and mineralize acid red 14. The high photocatalytic efficiency of TiO2 under simulated solar light might be related to its lower bandgap energy and the relatively higher fraction of anatase phase.

Synthesis of temperature and pH/CO2 responsive homopolymer bearing oligo(ethylene glycol) unit and N,N-diethylamino ethyl group and its solution property

A homopolymer strategy was developed to synthesize temperature and pH/CO2 stimulus-responsive homopolymers. A new class of acrylamide monomers bearing oligo(ethylene glycol) unit and N,N-diethylaminoethyl group were designed and prepared through Aza-Michael addition reaction followed by amidation with acryloyl chloride using amino group as a linkage to connect oligo(ethylene glycol), N,N-diethylaminoethyl, and polymerizable double bond groups together. Subsequently, the corresponding homopolymers containing oligo(ethylene glycol) unit and N,N-diethylaminoethyl group in each repeated unit were prepared via RAFT polymerization with controlled molecular weights and relatively narrow molecular weight distributions. The lower critical solution temperature (LCST) of homopolymer was examined to be influenced by molecular weight, salt concentration, and pH value of aqueous solution. The LCSTs of homopolymers could be tuned in a wide temperature window by changing pH value of aqueous solution and it increased with the decrease of pH value. Particularly, CO2 gas as a unique pH stimulus can also reversibly adjust the solubility of homopolymer without the addition of acids or bases.

PH-switchable self-assembled materials.

Self-assembled materials, which are able to respond to external stimuli, have been extensively studied over the last decades. A particularly exciting stimulus for a wide range of biomedical applications is the pH value of aqueous solutions, since deprotonation-protonation events are crucial for structural and functional properties of biopolymers. In living cells and tissues, intra- and extracellular pH values are stringently regulated, but can deviate from pH neutral as observed for example in tumorous, inflammatory sites, in endocytic pathways, and specific cellular compartments. By using a pH-switch as a stimulus, it is thereby possible to address specific targets in order to cause a programmed response of the supramolecular material. This strategy has not only been successfully applied in fundamental research but also in clinical studies. In this feature article, current strategies that have been used in order to design materials with pH-responsive properties are illustrated. This discussion only addresses selected examples from the last four years, the self-assembly of polymer-based building blocks, assemblies emerging from small molecules including surfactants or derived from biological macromolecules, and finally the controlled self-assembly of oligopeptides.

Thermodynamic and kinetic studies of biosorption of iron and manganese from aqueous medium using rice husk ash

The adsorption behavior of rice husk ash with respect to manganese and iron has been studied by batch methods to consider its application for water and waste water treatment. The optimum conditions of adsorption were determined by investigating the effect of initial metal ion concentration, contact time, adsorbent dose, pH value of aqueous solution and temperature. Adsorption equilibrium time was observed at 120 min. The adsorption efficiencies were found to be pH dependent. The equilibrium adsorption experimental data were found to fit the Langmuir, Freundlich and Temkin isotherms for iron, but fitted only Langmuir isotherm for manganese. The pseudo-second order kinetic model was found to describe the manganese and iron kinetics more effectively. The thermodynamic experiment revealed that the adsorption processes involving both metals were exothermic. The adsorbent was finally applied to typical raw water with initial manganese and iron concentrations of 3.38 mg/l for Fe and 6.28 mg/l, respectively, and the removal efficiency was 100 % for Mn and 70 % for Fe. The metal ions were desorbed from the adsorbent using 0.01 M HCl, it was found to quantitatively remove 67 and 86 % of Mn and Fe, respectively, within 2 h. The results revealed that manganese and iron are considerably adsorbed on the adsorbent and could be an economic method for the removal of these metals from aqueous solutions.

Thermoresponsive Homopolymer Tunable by pH and CO2.

A new acrylamide monomer bearing isopropylamide and N,N-diethylamino ethyl groups in the side chain, i.e., N-(2-(diethylamino)ethyl)-N-(3-(isopropylamino)-3-oxopropyl)acrylamide (DEAE-NIPAM-AM), was synthesized through Aza-Michael addition reaction followed by amidation with acryloyl chloride. The homopolymers, poly(N-(2-(diethylamino)ethyl)-N-(3-(isopropylamino)-3-oxopropyl)acrylamide)s [poly(DEAE-NIPAM-AM)], with controlled molecular weights and relatively narrow molecular weight distributions were then prepared via RAFT polymerization. The lower critical solution temperature (LCST) of the homopolymer was examined to be influenced by molecular weight, salt concentration, and pH value of aqueous solution. The LCST of the homopolymer could be tuned in a wide temperature window by changing the pH value of aqueous solution, and it increased with the decrease of pH value. Particularly, CO2 gas as a unique pH stimulus can also reversibly adjust the solubility of homopolymer without the addition of acids or bases.