Low-concentration Aqueous Solutions Research Articles

Luminescent Silicon Nanocrystals as Metal Ion Sensors.

At relatively low concentrations in aqueous solution, Fe3+, Fe2+, Cu2+, and Ni2+ quench the photoluminescence (PL) of the undecenoic acid-capped silicon (Si) nanocrystals. The PL could be restored by adding a chelating agent, such as ethylenediaminetetraacetic acid (EDTA), to remove the ions. Fe3+ and Cu2+ also significantly increase the PL lifetime. Other metal ions, including Cd2+, Mn2+, Pb2+, Zn2+, In3+, K+, and Ca2+, had no effect on the Si nanocrystal PL. The limits of detection (LODs) for Fe3+ and Cu2+ of 370 and 150 nM, respectively, are low enough for metal ion sensing applications.

A New Bioactive Thiazolidinone-based Azo Dye for Naked-eye Colorimetric Detection of Cyanide Ions

Abstract: A new bioactive azo dye embedding a thiazolidinone heterocyclic core was designed and synthesized for antibacterial application and colorimetric sensing of cyanide ion (CNˉ) in organic solutions. The structure of the prepared dye was elucidated from its 1H NMR, FT-IR and UV-Vis spectral data. It proved to be a fast and sensitive colorogenic sensor for detection of CNˉ. Spectroscopic studies were carried out to investigate the effect of different CNˉ concentrations on the detection efficiency. Moreover, the studies revealed no significant competition or influence of other anions on the sensitivity of CNˉ detection by the synthesized dye. A Job's plot indicated a 1:1 stoichiometry of the dye and CNˉ in their colorful complex. Further development of the method for naked-eye detection of CNˉ in low-concentration aqueous solutions was achieved by using the cellulose papers painted with the dye. The as-prepared testing paper allowed CNˉ sensing in concentrations as low as 2 μM. Evaluation of the dye for antibacterial activities using the well diffusion technique displayed that its inhibitory activity is at least as good as and in some cases superior to ampicillin against the bacterial strains employed in the zone assay. In response to CN¯, the dye changes color from yellow to reddish brown which accounts for its significant interactions with CNˉ and affords a naked-eye sensing method without resorting to any spectroscopic instrumentation.

The effect of thiol ligands on the adsorption behavior of silver ions on functionalized nanomagnetic graphene oxides

The magnetic graphene oxides (MGO) were modified with l-cysteine (Cys), glutathione (GSH), and thioglycolic acid (TGA) as the thiol ligands. using field emission scanning electron microscopy, X-ray diffraction, Fourier transform infrared spectroscopy, vibrating sample magnetometry, and Brunauer Emmett Teller (BET) surface area analysis, the structural and magnetic properties of the as-prepared samples have been studied. The results affirmed the successful synthesis of functionalized adsorbents. The adsorbents presented here have been reported for the first time to remove Ag ions from dilute aqueous solutions. The influence of the adsorption conditions (pH, contact time, and initial concentration) was investigated. The experimental data were consistent with both the pseudo-second-order kinetic model and the Langmuir isotherm model indicating chemisorption monolayer adsorption with the fast kinetics. The maximum adsorption capacity for MGO-TGA, MGO-Cys, and MGO-GSH based on the Langmuir isotherm model was found to be qm = 67.16, 53.42, and 43.73 mg/g, respectively. The calculated separation factors (0 < RL < 1) revealed that the adsorption process was favorable for three adsorbents. The large surface area of the adsorbents (57.244, 37.006, and 15.676 m2/g, for MGO-TGA, MGO-Cys, and MGO-GSH, respectively), along with the presence of thiol ligands on them, significantly affects the adsorption behavior. Therefore, these adsorbents offer an effective and rapid process for adsorbing silver ions from low concentration aqueous solutions.

Preparation of magnetic oil-based gel microspheres containing di(2-ethylhexyl)phosphoric acid for extraction of scandium ions at low concentrations in aqueous solutions

Extraction of low-concentration rare earths is one of the important paths for the sustainability of the rare earth industry. The research and development of materials suitable for the extraction of rare earth ions at low concentrations is of great significance. Currently, the application of solvent extraction in the rare earth production industry is highly mature. However, it is not economical to use it for the extraction of low concentration rare earths with problems of phase separation and organic phase loss. This work innovatively proposes to encapsulate the extractant and diluent in magnetic oleogel microspheres, which are obtained by solubilizing magnetic poly (phenyl divinylbenzene)(PS-DVB) microspheres with the extractant and diluent.. The magnetic PS-DVB microspheres of 3 ∼ 16 μm were prepared by suspension polymerisation, followed by encapsulation of di(2-ethylhexyl)phosphoric acid (D2EHPA) and dichloroethane in magnetic PS-DVB microspheres using emulsion swelling, and then magnetic oil-based gel microspheres containing D2EHPA with a particle size of 10 ∼ 32 μm were obtained. The magnetic oil-based gel microspheres containing D2EHPA consist of about 96 wt% liquid phase and about 4 wt% solid phase, with D2EHPA accounting for more than 4.19 wt%. The magnetic oil-based gel microspheres are very close to small oil droplets and are superparamagnetic. The magnetic oil-based gel microspheres containing D2EHPA could completely extract 60 ppm of scandium ions(Sc3+) under the conditions of O:A = 1:50,1:60,1:70, and the extraction equilibrium times were 6, 9 and 12 min, respectively. This extractant encapsulation scheme inherits the selectivity of traditional extractants while simultaneously preserving the advantages of rapid extraction by solvent extraction.

Tentative Approaches for Extraction of Lanthanides from Wastewater with Low Metal Concentration

Lanthanides are critical elements, and their recovery from wastewater increases the availability of these elements and reduces their impacts on the environment. In this study, tentative approaches to extract lanthanides from low-concentration aqueous solutions were investigated. PVDF membranes soaked with different active compounds or synthesized chitosan-based membranes containing these active compounds were used. The membranes were immersed in 10-4 M of aqueous solutions of selected lanthanides, and their extraction efficiency was assessed using ICP-MS. The PVDF membranes showed quite poor results, with only the membrane with oxamate ionic liquid giving some positive results (0.75 mg of Yb, 3 mg of lanthanides per gram of membrane). However, the chitosan-based membranes led to very interesting results, with the maximum concentration factor for the final solution relative to the initial solution being 13 times higher for Yb, which was obtained with the chitosan-sucrose-citric acid membrane. Several of the chitosan membranes, namely the one with 1-Butyl-3-methylimidazolium-di-(2-ethylhexyl)-oxamate, could extract around 10 mg of lanthanides per gram of membrane, with the better one being the membrane with sucrose/citric acid that achieved more than 18 mg/g of membrane. The use of chitosan for this purpose is a novelty. Since these membranes are easily prepared and have a very low cost, practical applications can be envisaged after further studies to better understand the underlying mechanism.

A rapid colorimetric method for the determination of lead (II) at low concentrations in aqueous solution

A rapid colorimetric method for the determination of lead (II) at low concentrations in aqueous solution

Naphthyl-Poly(S-((2-carboxyethyl)thio)-l-cysteine) Peptide Amphiphiles with Different Degrees of Polymerization: Synthesis, Self-Assembly, pH/Reduction-Triggered Drug Release, and Cytotoxicity.

Four peptide amphiphiles (PA1-4) with different degrees of polymerization (DP = 40, 15, 10, and 6) were synthesized by Fuchs-Farthing and ring-opening polymerization followed by post-polymerization modification, as fully characterized by 1H NMR, FT-IR, gel permeation chromatography, and circular dichroism (CD) spectroscopy. It was found that PAs could self-assemble to form regular spherical micelles in low-concentration (about 1 mg/mL) aqueous solution, which had different contents of secondary structures and mainly adopted random coil conformations. The water solubility of PAs increases with the increase of DP, the polypeptide chain stretches randomly in water, the β-sheets decrease, and the random coil conformations dominate. When the pH of PA solution decreases or increases, intramolecular hydrogen bonds break, and molecular chains stretch, leading to a decrease of α-helix, turn conformations, and an increase of β-sheets. Meanwhile, the particle size of micelles increases. At around 0.4 mg/mL, the hemolysis ability of PA2 is negligible at pH 7.4 and 6.5 and about 33% at pH 5.5. Cisplatin (CDDP) was linked to micelles by coordination bonds to explore their potential as drug carriers, exhibiting controlled pH and reduction in dual drug release effects. MTT assay showed that the HeLa cell viability was 78% when cultured in the 13.5 μg/mL PA2 blank micelles for 2 days, while the cell viability was 60% in the CDDP-loaded micelles. Furthermore, a high concentration of PA2 (about 100 mg/mL) could self-assemble into a fibrous hydrogel at pH 5.5, which self-healed 2 h after incision and self-degraded 71% within 14 days. The CDDP-loaded fiber hydrogel exhibited a sustained release effect similar to the CDDP-loaded micelles. The cytotoxicity of CDDP-loaded fibers at 48 h was detected to be the same as that of the same amount of CDDP, and the cell viability was 7%. Therefore, we provide a new strategy for the synthesis of amphiphilic peptides with potential applications in nano-drug carriers and cancer therapy.

Guest-induced breathing mediated selective alcohol recovery from water by MIL-88A(Fe)

Guest-induced breathing mediated selective alcohol adsorption.

Model for Aqueous Polymer Solutions with Damping Term: Solvability and Vanishing Relaxation Limit.

The main aim of this paper is to investigate the solvability of the steady-state flow model for low-concentrated aqueous polymer solutions with a damping term in a bounded domain under the no-slip boundary condition. Mathematically, the model under consideration is a boundary value problem for the system of strongly nonlinear partial differential equations of third order with the zero Dirichlet boundary condition. We propose the concept of a full weak solution (velocity–pressure pair) in the distributions sense. Using the method of introduction of auxiliary viscosity, the acute angle theorem for generalized monotone nonlinear operators, and the Krasnoselskii theorem on the continuity of the superposition operator in Lebesgue spaces, we obtain sufficient conditions for the existence of a full weak solution satisfying some energy inequality. Moreover, it is shown that the obtained solutions of the original problem converge to a solution of the steady-state damped Navier–Stokes system as the relaxation viscosity tends to zero.

An aqueous magnesium-ion hybrid supercapacitor operated at −50 °C

The recent advances in aqueous magnesium-ion hybrid supercapacitor (MHSC) have attracted great attention as it brings together the benefits of high energy density, high power density, and synchronously addresses cost and safety issues. However, the freeze of aqueous electrolytes discourages aqueous MHSC from operating at low-temperature conditions. Here, a low-concentration aqueous solution of 4 mol L−1 Mg(ClO4)2 is devised for its low freezing point (−67 °C) and ultra-high ionic conductivity (3.37 mS cm−1 at −50 °C). Both physical characterizations and computational simulations revealed that the Mg(ClO4)2 can effectively disrupt the original hydrogen bond network among water molecules via transmuting the electrolyte structure, thus yielding a low freezing point. Thus, the Mg(ClO4)2 electrolytes endue aqueous MHSC with a wider temperature operation range (−50 °C–25 °C) and a higher energy density of 103.9 Wh kg−1 at 3.68 kW kg−1 over commonly used magnesium salts (i.e., MgSO4 and Mg(NO3)2) electrolytes. Furthermore, a quasi-solid-state MHSC based on polyacrylamide-based hydrogel electrolyte holds superior low-temperature performance, excellent flexibility, and high safety. This work pioneers a convenient, cheap, and eco-friendly tactic to procure low-temperature aqueous magnesium-ion energy storage device.

Optimization of an rGO-based biosensor for the sensitive detection of bovine serum albumin: Effect of electric field on detection capability.

Despite significant progress in the field of biosensing, the impact of electric field on biosensor detection capability and the feasibility of the biosensor application in wastewater has yet to be investigated. The objective of this study was to develop a low-cost, highly sensitive, and selective reduced graphene oxide (rGO)-based biosensor. The constructed biosensor consists of an in-house prepared GO and a four-terminal Kelvin sensing. Spin-coating was chosen as the deposition technique and results revealed an optimal GO number of layers and concentration of 7 and 2mg/mL, respectively. Experiments to determine the effects of electric field on the performance of the biosensor showed significant changes in the biosensor surface, also presenting a direct impact on the biosensor functionality, such that the biosensor showed an increase in limit of detection (LOD) from 1 to 106fg/mL when the applied voltage was increased from 0.0008 to 0.2V. Furthermore, this study successfully explores a pilot scale setup, mimicking wastewater flow through sewage pipelines. The demonstrated improvements in the detection capability and sensitivity of this biosensor at optimized testing conditions make it a promising candidate for further development and deployment for the detection of protein analytes present at very low concentrations in aqueous solutions. In addition, the application of this biosensor could be extended to the detection of protein analytes of interest (such as the spike protein of SARS-CoV-2) in much more complex solutions, like wastewater.

Highly selective PDMS membranes embedded with ILs-decorated halloysite nanotubes for ethyl acetate pervaporation separation

The development of high-performance polydimethylsiloxane (PDMS)-based mixed matrix membranes (MMMs) for the recovery of ethyl acetate (EtAc) from low-concentration aqueous solutions remains a challenge in the pervaporation field. In this study, ionic-liquids-decorated halloysite nanotubes (ILs@HNTs) composites, which were precisely designed and prepared using a tandem modification strategy, were embedded into PDMS matrix to fabricate MMMs for the permselective pervaporation of EtAc. The results revealed that the ILs incorporated within the lumens and onto the external surfaces of HNTs not only exhibited excellent compatibility with PDMS, but also created permselective diffusion channels for EtAc. Benefit from the synergistic effect of highly permeable HNTs lumens and highly selective ILs, the resultant MMM loaded with 15 wt% ILs@HNTs presented a remarkable separation factor (341) and high flux (925 g m−2 h−1) for the separation of 1 wt% EtAc aqueous solutions at 30 °C. These values were 2.10 and 1.45 times higher, respectively, than those of pristine PDMS membranes. Furthermore, the molecular simulations conducted to analyze the permeation behavior of guest molecules in the HNTs lumens provided theoretical support for the pervaporation experimental results. Moreover, the effects of ILs grafting degree, filler loading, feed temperature, and feed concentration on the pervaporation performance of the fabricated MMMs were systematically investigated. The unique modification method developed in this study can be expanded to other tubular materials and provide valuable guidelines for designing high-performance membrane structures.

Potentiometric and spectroscopic studies of the complex formation in the 6-methyl-2-thiouracil and copper(ii) ion system

New complexes of 6-methyl-2-thiouracil (L) with copper(ii) ions were investigated. The studies were performed in relatively low concentrations in aqueous solutions that allowed the formation of solubility complexes. Hydroxo complexes were detected and characterized for the first time, as well as the influence of the metal ion:ligand concentration ratio on the distribution of forms and the fluorescent properties was demonstrated. Analysis was performed using a potentiometric method with computer analysis of the data and electron paramagnetic resonance, Vis, and fluorescence spectroscopy. The overall stability constants of the complexes were calculated. Analysis of the equilibrium constants as well as spectroscopic data and theoretical calculations allowed us to determine the type of coordination in the complexes found in the studied system.

Determination of the influence of basic parameters on the solvent sublation of anionic dye

The object of research is wastewater contaminated with anionic dyes. Traditional methods of wastewater treatment from dyes are imperfect and inefficient or non-existent. Therefore, the need to develop and implement effective and inexpensive to use and operate dye removal technologies is important. The biggest problem in dye removal is when large volumes of low concentration wastewater have to be treated. To purify just such effluents, a combined method, solvent sublation, has been proposed. It combines flotation and extraction methods and has the benefits of both. The essence of the method is the passage of gas bubbles through the aqueous phase and the transport of a hydrophobic complex (sublate) formed by a dye and a surfactant into the organic phase. The study used imitates of wastewater contaminated with an anionic dye, active bright blue in the concentration range of 5–50 mg/dm3. The influence of the main parameters on the degree of dye removal was studied: the pH of the initial solution, the molar ratio of surfactant: dye, the size of air bubbles, the gas flow rate, the initial concentration of the dye, the duration of solvent sublation. Rational parameters of the process have been established, which are advisable to use in solvent sublation: – purification process must be carried out in the presence of a cationic collector hexadecyltrimethylammonium bromide; – extractant – isoamyl alcohol; – molar ratio Dye: surfactant=1:1.5; – pH 5.5; – generation of gas bubbles by a Schott filter with a porosity of 40 µm; – gas flow rate – 127 cm3/min. Under such conditions, the removal efficiency of active bright blue is 97 % at a process time of 10–25 min. The results obtained confirm the promise of the proposed method for the effective removal of dyes from low-concentration aqueous solutions. The method has a number of advantages: it requires a small amount of extractant compared to liquid extraction; ions are concentrated in small volumes of an organic solvent; the process proceeds without phase mixing, so no emulsions are formed.

Structure of corn bran hemicelluloses isolated with aqueous ethanol solutions and their potential to produce furfural

The alkali-soluble hemicelluloses extracted with 10% KOH solution from corn bran were further isolated with different concentrations of aqueous ethanol solutions. Herein 92.2% of the original hemicelluloses can be obtained and the cellulase enzymatic hydrolysis rate of the alkali treated corn bran can reach to 97.2%. The corn bran hemicelluloses were mainly glucuronoarabinoxylan, in which xylose (48.4–53.8%) and arabinose (27.8–33.2%) were the main components. More linear hemicelluloses with high molecular weight tended to be precipitated in low concentration aqueous ethanol solutions. Furthermore, the relationship between the structural features of these alkali-soluble corn bran hemicelluloses and their furfural yield was investigated in MIBK (methyl isobutyl ketone)/H2O biphasic system. Results showed that the hemicelluloses with high xylose content are benefit to the furfural production, and the highest furfural yield of 67.7% was obtained.

Characterization of particles of the dispersed system based on low-concentrated aqueous solutions of L-cysteine and silver acetate

The authors of this work conducting a study of the precursor of reference materials of the zeta potential of particles in dispersed systems. The precursor is based on supramolecular solution of L-cysteine and silver acetate (CSSac). Particles and aggregates of CSSac were studied by dynamic light scattering (DLS), phase analysis of scattered radiation (PALS), inductively coupled plasma mass spectrometry (ICP-MS) and high-resolution transmission electron microscopy (HR-TEM). It was established that the diameter of the potential-determining aggregates of the CSSac is in the range from 20 nm to 100 nm. These aggregates consist of nanoparticles up to 10 nm in diameter.

Aluminum-copper alloy anode materials for high-energy aqueous aluminum batteries

Aqueous aluminum batteries are promising post-lithium battery technologies for large-scale energy storage applications because of the raw materials abundance, low costs, safety and high theoretical capacity. However, their development is hindered by the unsatisfactory electrochemical behaviour of the Al metal electrode due to the presence of an oxide layer and hydrogen side reaction. To circumvent these issues, we report aluminum-copper alloy lamellar heterostructures as anode active materials. These alloys improve the Al-ion electrochemical reversibility (e.g., achieving dendrite-free Al deposition during stripping/plating cycles) by using periodic galvanic couplings of alternating anodic α-aluminum and cathodic intermetallic Al2Cu nanometric lamellas. In symmetric cell configuration with a low oxygen concentration (i.e., 0.13 mg L−1) aqueous electrolyte solution, the lamella-nanostructured eutectic Al82Cu18 alloy electrode allows Al stripping/plating for 2000 h with an overpotential lower than ±53 mV. When the Al82Cu18 anode is tested in combination with an AlxMnO2 cathode material, the aqueous full cell delivers specific energy of ~670 Wh kg−1 at 100 mA g−1 and an initial discharge capacity of ~400 mAh g−1 at 500 mA g−1 with a capacity retention of 83% after 400 cycles.

Catalytic Upgrading of Xylose to Furfuryl Alcohol over Zr-SBA-15

Direct conversion of xylose to furfuryl alcohol was investigated over Zr-SBA-15 mesoporous catalysts. A low-concentration aqueous xylose solution was used as feedstock to fit the conditions that the monosaccharide is released during waste biomass pretreatment for 2G ethanol production. A coupled dehydration-transfer hydrogenation approach was adopted in this study, using 2-propanol as the hydrogen donor in the liquid phase. It was shown that addition of Zr into the SiO2 framework created active surface acid sites for converting xylose to furfuryl alcohol, rendering selectivity of around 45%, and furfural and xylulose as the main coproducts. Activity and product distribution were significantly affected by the proportion of water and 2-propanol in the liquid phase. Both xylose conversion and selectivity to furfuryl alcohol dropped progressively by decreasing the volumetric amount of 2-propanol.

Bamboo-Based Biofoam Adsorbents for the Adsorption of Cationic Pollutants in Wastewater: Methylene Blue and Cu(II).

Human health is being threatened by cationic pollutants in wastewater, for example, methylene blue (MB) and Cu(II). Our research team successfully fabricated biofoam adsorbents from recycled bamboo waste that removed cationic pollutants via introducing bamboo fiber sources, i.e., bamboo fiber, bamboo α-cellulose fiber, and bamboo nanocellulose fiber, into a polyurethane (PU) foam matrix. The biofoam adsorbent with 1 g of nanocellulose (PUN1) presented high removal efficiencies for MB (95.52%) and Cu(II) (100%) in low cationic pollutant concentration aqueous solutions. The biofoam adsorbent with 1 g of bamboo fiber (PUB1) also displayed excellent removal efficiency for MB (98.61%) at pH 11. Meanwhile, 100% removal of Cu(II) was obtained by PUB1 at pH 7 (initial content = 15 mg/L). Furthermore, the PUN1 sample had excellent reusability, evidenced by 61.25% removal of MB after five adsorption–desorption cycles, suggesting that PUN1 is a promising renewable adsorbent for cationic pollutants. In addition, PUB1 is a low-cost adsorbent with good adsorption efficiencies for MB in weak alkaline solutions and Cu(II) in neutral aqueous solutions.

Optimal Boundary Control of the Boussinesq Approximation for Polymeric Fluids

We consider an optimal control problem for non-isothermal steady flows of low-concentrated aqueous polymer solutions in a bounded 3D domain. In this problem, the state functions are the flow velocity and the temperature, while the control function is the heat flux through a given part of the boundary of the flow domain. We obtain sufficient conditions for the existence of weak solutions that minimize a cost functional under a given bounded set of admissible controls. It is shown that the marginal function of the considered control system is lower semi-continuous and the optimal states operator generates a continuous branch in a suitable function space.