Low-concentration Aqueous Solutions Research Articles

A novel electroactive PPy/HKUST-1 composite film-coated electrode for the selective recovery of lithium ions with low concentrations in aqueous solutions

A novel electroactive polypyrrole (PPy)-threaded HKUST-1 metal-organic framework (MOF) composite film was constructed on an electrode. This was achieved by the in situ conversion of CuO in a PPy/CuO composite film to HKUST-1 MOF by a unipolar pulse electro-erosion (UPEE) and in situ coordination method for the recovery of lithium ions (Li+) with low concentrations in aqueous solutions. The obtained films were characterized by scanning electron microscopy, Fourier transform infrared spectroscopy, X-ray diffraction (XRD), and thermogravimetric analysis. A PPy/HKUST-1 composite film with HKUST-1 anchored in the PPy nanorod networks was successfully formed on the electrode. Extraction of various metal ions, Li+, K+, Na+, Mg2+, and Cu2+ with this film was investigated using the electrochemically switched ion exchange technique. The PPy/HKUST-1 composite film exhibited a high selective extraction ability for Li+ present in low concentrations. The Li+ adsorption capacity reached 37.55 mg/g with an adsorption equilibrium time of less than 25 min owing to the sieving function of the voids and excellent affinity of this film for the Li+ ions. It is expected that such an electroactive film can be applied to the separation and recovery of dilute Li resources from various aqueous solutions.

Supramolecular Self-Assembly and Phase Transformations in Aqueous Systems Based on Chitosan and Sulfonated Metallophthalocyanines

The supramolecular self-assembly in mixed low-concentrated aqueous solutions of chitosan and sulfonated metallophthalocyanines was examined by spectroscopic and dynamic light scattering techniques. The research subjects were Cu(II) and Co(II) tetrasulfophthalocyaninates, as well as Cu(II) phthalocyaninate containing sulfonate groups and a vinylsulfonic substituent. The resulting supramolecular complexes were characterized by a reproducible stoichiometric composition, as well as by the ability to move slowly into a colloidal-dispersed state. Phase separation was preceded by a metastable state with unchanging spectral characteristics, for which the size and ζ-potential of the primary supramolecular particles were determined.

Optimization of As (III) and As (V) removal by Saccharomyces cerevisiae biomass for biosorption of critical levels in the food and water resources

In this study bioremoval ability of Saccharomyces cerevisiae for arsenic ions at very low concentrations in aqueous solution was evaluated. Three significant variables: solution pH, arsenic ion concentration and inoculum size were studied by using response surface methodology to maximize biosorption of arsenic ions by central composite design via of twenty test treatment combination. Results of arsenic ions biosorption were validated based on analytical quality assurance before performing instrumental measurements. The adjusted conditions in the best treatment combination were 5.0, 95.0 μg/L and 32.5 × 107 colony forming units for pH, and inoculum size, respectively. Results show that arsenic ions biosorption in aqueous solution is affected by all the three factors. An optimum arsenic (III) and arsenic (V) biosorption rate of 66.2% and 15.8% were found at initial of 132.4 and 132.8 μg/L, and Inoculum size of 48.5 and 47.5 × 107 CFU, respectively. The present study show that in the optimized conditions, S. cerevisiae has suitable ability to remove very low amounts of arsenic (III) ions from aquatic solutions. as a safe and eco-friendly strategy for decontamination arsenic (III), which is the most toxic form of arsenic.

Feasibility Study on Rapid Analysis of Doxycycline Hydrochloride Aqueous Solution by Terahertz Time-Domain Spectroscopy

Abstract. Antibiotics have been extensively applied in the treatment of infections in food-producing animals. However, the residues of these agents create a potential risk to human health. Among the methods available for rapid detection of antibiotics, terahertz time-domain spectroscopy (THz-TDS) has emerged as a technique with unique advantages over other methods. In this study, we demonstrate that rapid analysis of doxycycline hydrochloride (DCH) aqueous solutions could be achieved with THz-TDS through transmission, attenuated total reflection (ATR), and reflection with minimum detectable concentrations of 5000, 10, and 80 mg L-1, respectively, indicating that the ATR and reflection methods are superior to the transmission method for low-concentration aqueous solutions. This study is an effort to promote the development of rapid analysis of antibiotic residues in an aqueous matrix using THz spectroscopy. Keywords: Attenuated total reflection, Doxycycline hydrochloride solution, Reflection, Terahertz, Transmission.

Study of the influence of surfactants on the paper properties and degradation

Surfactants are one of the materials recommended for the cleaning of movable cultural properties. These substances are widespread in other fields – medicine, cosmetics, household appliance industry, etc. Quaternary ammonium compounds are particularly prevalent due to their cleansing and disinfectant properties. Initial studies have shown that surfactants, including quaternary ammonium compounds, have a positive effect on preserved/ restored cultural properties. Using relatively low concentrations of aqueous solutions of these substances, it is possible to obtain sufficiently good results to wash out from the restoration of the document or textiles dirt, acidification of the object and colour changes that cause aging and decomposition processes – hydrolysis and oxidation.

Computational chemistry study of zirconium monomers in low acid concentration aqueous solutions

Zirconium and hafnium have to be separated prior to their use in nuclear energy reactors. Therefore, a lot of research has been done on the solvent extraction of zirconium. However, most of this research involved screening studies that focused on finding suitable solvent extraction processes, rather than attempting to gain insights into the extraction mechanisms. An important part of understanding extraction mechanisms is knowing which zirconium species are present in aqueous solutions since these are the species with which extractants react. In this study, we used density functional theory based molecular dynamics calculations to model zirconium monomers in low acid concentration solutions. Specifically, we modelled aqua and hydroxo zirconium complexes using an explicit solvent approach. By calculating radial distribution functions for each of these zirconium complexes, using either 10, 20, 30, 40 or 50 explicit solvent water molecules, we were able to determine that at least about 30 solvent water molecules are needed to model the first two solvation spheres of a zirconium ion during an explicit solvent approach. We anticipate that this work will be useful for further explicit solvent based computational chemistry studies on the solvent extraction mechanisms of zirconium and hafnium.

Dielectric measurement of low-concentration aqueous solutions: assessment of uncertainty and ion-specific responses

Excessive amounts of chemicals and ions flowing into water sources cause serious environmental and human-health related concerns. The lack of affordable and real-time monitoring systems for these contaminants limits effective conservation and management strategies. To establish a basis for developing an effective, fast, real-time, and affordable sensing system, a dielectric spectroscopy method has been employed to characterize aqueous solutions of sodium chloride (NaCl), sodium nitrate (NaNO3), and sodium sulphate (Na2SO4) at environmentally-relevant (low) concentrations. Dielectric spectra were measured over a frequency range of 200 MHz to 20 GHz, at a temperature of 25.00 °C ± 0.01 °C and for concentrations 0–20 mmol l−1. The measured spectra were fitted with a Debye model using a non-linear, weighted, least-squares analysis. A method of judiciously exploiting the resulting fitting parameters is proposed, that allows the concentration and type of ions to be uniquely determined. Uncertainties due to random and systematic errors that contribute to the measured dielectric spectra and become critical in the context of low concentration aqueous solutions have been assessed. Furthermore, two methods of calculating associated uncertainties of the indicator parameters, viz. covariance matrix and Monte Carlo methods have been performed. The results show the numerical approach taken by a Monte Carlo method, while yielding the same estimates, reduces the tediousness accompanied by the analytical covariance matrix method.

Plasma Polishing of Stainless Steels – The Electrolyte Concentration Vs. Gloss Level

Abstract The technology of plasma polishing in electrolyte is considered as environmental friendly alternative to the common electrochemical polishing process. The solutions of the electrolyte use no acids or toxicants, but the environmental safe, low concentrated aqueous solutions of various inorganic salts are used instead. The dependence of the gloss level of the treated surface upon the electrolyte concentration as well as upon the voltage is examined in this paper. The specimens of stainless steel were used for plasma polishing in ammonium sulphate based electrolyte. The influence of the voltage on the overall properties of the process is discussed, as well.

The solvent sublation of bromocresol green from waters solutions

The object of research is wastewaters contaminated with dyes. The available methods for treating wastewater from dyes are often imperfect, ineffective or absent. This calls for the development and implementation of efficient and inexpensive to use and operate dye removal technologies. When treating wastewater, the biggest problem is removing the dyes from dilute low-concentration solutions. For the purification of such effluents, solvent sublation is suggested. This method is based on a combination of flotation and extraction techniques, and on the transmission of gas bubbles through the aqueous phase and removal of the pollutant (sublate) into the organic phase. During the study, imitates of contaminated wastewater with an anionic dye bromocresol green are used in the concentration range of 2–20 mg/dm 3 . The influence of some parameters on the dye removal degree is studied: the pH of the initial solution, the molar ratio surfactant: dye, the size of the air bubbles, the initial concentration of the dye, and the solvent sublation duration. The rational conditions for removing the dye are established: pH 3–3.5, molar ratio bromocresol green-hexadecylpyridinium chloride=1:1. Effective removal of the dye is ensured by using a Schott filter with a pore diameter of 100 μm, an air flow rate of 110–120 cm 3 /min, duration –10 min. Under these conditions, the dye removal degree is 88–99 %. The obtained results confirm the prospects of the proposed method for the effective removal of dyes from low-concentration aqueous solutions. The method has several advantages: possibility to work with large volumes of water bodies; active substance is carried out by gas bubbles and enters the hydrophobic liquid layer without mixing the phases; process is not equilibrium and is not limited by the distribution constant; impossibility of formation of emulsions; multiple concentration of ions in small volumes of organic solvent; requires a small amount of extractant compared to liquid extraction.

Degradation of ofloxacin by UVA-LED/TiO2 nanotube arrays photocatalytic fuel cells

The degradation of ofloxacin (OFX) at low concentration in aqueous solution by UVA-LED/TiO2 nanotube arrays photocatalytic fuel cells (UVA-LED/TiO2 NTs PFCs) was investigated. TiO2 nanotube arrays (TiO2 NTs) photoanode prepared by anodization-constituted anatase–rutile bicrystalline framework. The results indicated that the degradation efficiency of OFX by UVA-LED/TiO2 NTs PFC was significantly enhanced by 14.3% compared with UVA-LED/TiO2 NTs photocatalysis. The pH affected the degradation efficiency markedly; the highest degradation efficiency (95.0%) and the pseudo-first-order reaction rate constant k value (0.049 min−1) were achieved in neutral condition (pH 7.0). The degradation efficiency increased with the increasing concentration of dissolved oxygen (DO) in the UVA-LED/TiO2 NTs PFC. The main reactive species of OFX degradation are positive holes (h+) and superoxide ion radicals (O 2 ·− ) in a DO sufficient condition. Furthermore, the possible pathways of OFX degradation were proposed.

Effective Removal of Chromium(III) from Low Concentration Aqueous Solution Using a Novel Diazene/Methoxy-Laced Coordination Polymer.

In this study, a novel coordination polymer [CdL2(H2O)0.5]n (1), [HL = 4-(2-(4-((pyridin-3-yl)methoxy)phenyl)diazenyl)benzoic acid] was fabricated via an in situ ligand transformation reaction under solvothermal conditions. The as-prepared polymer exhibited a selectivity and efficiency for Cr(III) removal with a high uptake capacity of 106.13 mg·g−1. Interestingly, even in the low concentration (0.02–0.20 ppm), it still performs a relatively high efficiency (≥ 92.5%) towards the removal of Cr(III) in aqueous solution. Remarkably, it also presents good selectivity and high efficiency (93.3%) for Cr(III) removal in the presences of interfering metal ions. The good removal performance for Cr(III) was demonstrated to be a structure-dependent chemical process between polymer and Cr(III) involving the diazene and methoxy groups in polymer 1, which happened not only on the surfaces of the adsorbent but also in the pores of polymer, giving rise to a strong affinity toward Cr(III) adsorption. The possible adsorption mechanism of Cr(III) was proposed and systematically verified by FT-IR, scanning electron microscope (SEM), atomic force microscope (AFM) and energy dispersive spectrometer (EDS) measurements.

Sharp rise in resistance of ion exchange membranes in low concentration NaCl solution

Abstract Using a modified impedance measurement technique, ohmic resistance of commercial ion exchange membranes (Selemion CMV and AMV as well as Neosepta CMX and AMX) was measured in low concentration aqueous NaCl solutions. The ohmic resistance increased by an order of magnitude as the NaCl concentration was reduced from 0.5 M to 0.017 M Resistance of cation exchange membranes increased more than the anion exchange membranes. Resistance increased monotonically with a decrease in the NaCl concentration and the variation of resistance could be explained very well using a model based on the Kohlrausch law of conductivity. The model also provided value of the tortuosity for the membranes. Tortuosity of the membranes was between 3.4 and 4.5.

Mechanism of gelation in low-concentration aqueous solutions of silver nitrate with l-cysteine and its derivatives.

We discuss the results of experimental studies of the processes of gelation in aqueous solutions of silver nitrate with l-cysteine and its derivatives. We focus on understanding what determines if these small molecules will self-assemble in water at their extremely low concentration to form a gel. A mechanism of gel formation in a cysteine-silver solution (CSS) is proposed. The analysis of the results indicates that filamentary aggregates of a gel network are formed via interaction of NH3+ and C(O)O- groups that belong to neighboring silver mercaptide (SM) aggregates. In turn, formation of sulphur-silver bonds between silver mercaptide molecules is responsible for self-assembling these molecules into SM aggregates which can be considered as supramonomers. Free polar groups located on the surfaces of the aggregates can form hydrogen bonds with water molecules, which explains the unique ability of CSS hydrogels to trap water at low concentrations of low-molecular-weight hydrogelators.

Preparation of Amidoxime-Based Nylon-66 Fibers for Removing Uranium from Low-Concentration Aqueous Solutions and Simulated Nuclear Industry Effluents

Amidoximated nylon-66 fiber containing double amidoxime groups per repeating unit (coded as PA66-g-PGMA-IDPAO) for the purpose of removing low uranium concentrations (1–25 mg/L) from aqueous solutions and application in simulated nuclear industry effluents was prepared by a simultaneous radiation-induced emulsion graft polymerization method. It was characterized by Fourier transform infrared spectroscopy, scanning electron microscopy, thermogravimetric analysis, and single fiber tensile strength tester. Batch adsorption experiments were conducted to investigate the effect of initial pH, sorption isotherm, adsorption kinetics, and thermodynamics. It was found that the optimum initial pH is 5.0. The sorption isotherm followed the Langmuir isotherm. The adsorption kinetics fit the pseudo-second-order model. The thermodynamics parameters revealed that the adsorption process was spontaneous and endothermic. The sorption test performed in a simulated nuclear industry effluent demonstrated a high adsorption effi...

ROBUST SPECTRAL MODEL FOR LOW METAL CONCENTRATION MEASUREMENT IN AQUEOUS SOLUTION REVEALS THE IMPORTANCE OF WATER ABSORBANCE BANDS

In this study, we focused on detection of metal ions at low concentration in aqueous solution by using NIRS. New “aquaphotomics” concept (Tsenkova, 2007) has become a powerful strategy to understand the spectral changes related to small concentration of solutes in aqueous solution. To improve the model accuracy it is important to understand why it is possible to detect the object of interest using NIRS. Although detectable, metals have no absorption in NIR region (Sakudo,et,al, 2007). However it is perhaps due to their vibrational modes that are modulated by forming complexes with organic molecules containing C-H, N-H and O-H bonds. Therefore, alteration of the vibrational mode of water matrix caused by metal can be detected by NIRS. In this study, we present NIR spectroscopy link to aquaphotomics as a tool to predict low concentration (0-10.mg L-1) of Mg(II), Zn(II), Mn(II) and Cd(II).Key words : NIR spectroscopy, spectral changes, absorbance

Ethanol Recovery from Low-Concentration Aqueous Solutions Using Membrane Contactors with Ionic Liquids

Abstract Recovery of alcohols from diluted aqueous solutions is highly energy-intensive. In order to reduce the costs of concentration of alcohols, membrane processes (including membrane extraction) are used. This paper reports the results of ethanol concentration from diluted aqueous solutions using a hollow fiber membrane contactor with ionic liquid. The studies were performed using a contactor with microporous hollow fiber membranes. The membrane creates a barrier between the feed and extracting solvent, also providing a large mass transfer area. In the process, selected ionic liquid presenting different selectivity towards ethanol was used as extractant. The experiments were performed with feed concentrations of ethanol ranging from 1 to 5 wt.% and various feed flow rates ranging from 1 to 8 dm3/h.

Accurate and absolute diffusion measurements of Rhodamine 6G in low-concentration aqueous solutions by the PGSE-WATERGATE sequence.

A pulsed field gradient spin-echo nuclear magnetic resonance (NMR) sequence with solvent suppression (PGSE-WATERGATE) was applied to accurately measure the diffusion coefficients of Rhodamine 6G (Rh6G) in low-concentration aqueous solutions. Three samples with Rh6G concentrations of CRh6G = 1, 4.5, and 25 μM were investigated. The precise determination of the diffusion coefficients in this low-concentration range was made possible by using a cryogenically cooled NMR probe and by the effective solvent suppression of the PGSE-WATERGATE sequence. The present results bridge the gap between diffusion data measured by fluorescence correlation spectroscopy in the single molecule limit and diffusivities obtained by pulsed field gradient NMR (PFG-NMR) without solvent suppression at higher concentrations. To further extend the concentration range, the diffusion coefficient of Rh6G was also measured on a sample with CRh6G = 410 μM by PFG-NMR. The overall concentration dependence of the Rh6G diffusion at 25 °C is discussed in terms of dimerization of the Rh6G molecules. The concentration-dependent monomer/dimer proportion is deduced from the diffusion data.

Power consumption and mixing time in rheologically complex fluids by a two-bladed impeller

This study investigates the power consumption and mixing time of a two-bladed stirrer during the mixing of viscoelastic fluids in the laminar region of flow. For the rheological part, we use a polymer with low-concentration aqueous solutions that present viscoelastic behavior. The rheological study performed on polyacrylamide solutions shows the viscoelastic behavior of the generalized “Kelvin-Voigt” model. The power consumption for the viscoelastic fluids is greater than that needed to mix Newtonian fluids at the same Reynolds number. The mixing time is found to depend strongly on the viscoelasticity of the solutions.

A robust microporous metal-organic framework as a highly selective and sensitive, instantaneous and colorimetric sensor for Eu³⁺ ions.

An extremely thermostable magnesium metal-organic framework (Mg-MOF) is reported for use as a highly selective and sensitive, instantaneous and colorimetric sensor for Eu(3+) ions. There has been extensive interest in the recognition and sensing of ions because of their important roles in biological and environmental systems. However, only a few of these systems have been explored for specific rare earth ion detection. A robust microporous Mg-MOF for the recognition and sensing of Eu(3+) ions with high selectivity at low concentrations in aqueous solutions has been synthesized. This stable metal-organic framework (MOF) contains nanoscale holes and non-coordinating nitrogen atoms inside the walls of the holes, which makes it a potential host for foreign metal ions. Based on the energy level matching and efficient energy transfer between the host and the guest, the Mg-MOF sensor is both highly selective and sensitive as well as instantaneous; thus, it is a promising approach for the development of luminescent probing materials with unprecedented applications and its use as an Eu(3+) ion sensor.

Preparation and pervaporation characteristics of novel ethanol permselective polyelectrolyte–surfactant complex membranes

Recovery of ethanol from a low concentration aqueous solution is a critical step for biofuel production.