Water Aqueous Solutions Research Articles

Determination of chromium traces by atomic ionization spectroscopy in aqueous standard solutions and in gallium arsenide using the «rod – flame» atomization system

The results of the determination of trace amounts of chromium in aqueous standard solutions of chromium and in high purity gallium arsenide using atomic ionization spectroscopy are presented. Single — and two-step schemes of chromium atom excitation from the ground state 3d54s 7S3 to septet states 3d54p 7P2,3,4, 3d44s4p 7P2,3,4 were studied using a «rod – flame» atomizer. A mechanism of forming atomic-ionization signal for two-step excitation schemes is revealed. The most effective two step excitation schemes for chromium atoms were determined and experimentally studied at different wavelengths λ1 = 425.4 nm, λ2 = 451.4 nm; λ1 = 425.4 nm, λ2 = 426.1 nm. The low limit of chromium detection in aqueous water solutions was 50 pg/ml. The analytical potentiality of the «rod – flame» system for determining traces of chromium in gallium arsenide solutions has been demonstrated. The possibility of determining traces of chromium in gallium arsenide using a flame – rod atomizer at a level of 5 × 10–7 % is demonstrated. Two methods are proposed to increase the selectivity and sensitivity of atomic-ionization determination of chromium: optimization of the temperature program of the flame – rod atomizer and the use of two-stage excitation of chromium atoms. It is shown that the main interfering factor is the background attributed to the matrix ionization. Methods are proposed to reduce or eliminate the matrix impact, which ensure direct determination of elements in samples.

Application of South African heulandite (HEU) zeolite for the adsorption and removal of Pb2+ and Cd2+ ions from aqueous water solution: Experimental and computational study

The capacity of South African Heulandite (HEU) zeolite to remove Pb2+ and Cd2+ ions from aqueous solution was investigated using batch experiments and molecular simulations studies. The effect of different factors on the adsorption of these ions onto the zeolite was investigated; contact time, initial metal ion concentration and the amount of HEU adsorbent. Molecular simulations was done using Monte Carlo and density functional theory. Experimental results obtained indicate that the maximum adsorption for the two ions occur at pH 5 and after 240 min of contact time. The percent removal based on contact time of Pb2+ and Cd2+ ions from water by the heulandite zeolite were 99.7 and 76.7 %, respectively. The adsorption of two metal ions onto the HEU zeolite follows the Langmuir adsorption isotherm. From the molecular simulation findings, the adsorption of Pb2+ ions onto the HEU window is equidistant from the two adjacent oxygen atoms within the HEU structure while the Cd2+ ion is adsorbed in the upper left side of the 8-ring HEU window. It was observed that the performance of the zeolite can significantly be improved by doping with germanium, aluminum, thallium indium, and sodium cations. These results indicate that the application of HEU zeolite as an adsorbent holds a great promise in heavy metal removal from aqueous solutions.

Ionic Competition between Na+ and H+ in Aqueous Sodium-Ion Battery Electrolytes.

Aqueous electrolytes have become a research hotspot because of their high safety and low cost, while the inevitable ionization phenomenon of water in aqueous solution leads to the existence of competitive ions (H+) except the active ions. In this article, we take aqueous Na base electrolyte as an example to clear the ion competition behavior by modeling, simulating together with experimental verification. First, the reaction tendency of the two ions (Na+ and H+) is obtained by calculating the Gibbs energy change of the reaction. Furthermore, the properties of electrolytes with different concentrations including transportation are obtained by modeling. After that, relevant experiments are also proceeded to verify the simulation results. Then, the ion competition behavior is analyzed by in situ observation by controlling the constant concentration of Na+: the high concentration of Na+ can reduce the proportion of H+ and reduce the competitiveness of H+; a high concentration of Na+ causes the increased viscosity and reduces the ion diffusion. Based on this, the correlation between ion competitiveness and ion ratio is also confirmed by keeping the concentration of Na+ unchanged and adjusting the concentration of H+ (adjusting pH). The influence of the ion competition phenomenon (Na+ and H+) is the reaction characteristics of the substance itself and the ratio of ion concentration. Finally, the electrochemical performance is further verified in 3,4,9,10-perylene tetracarboxylic dianhydride (PTCDI) symmetric cells and in full-cells with vanadium phosphate sodium (NVP) as the cathode and PTCDI as the anode.

A novel strategy to construct hydrogels with anti-swelling and water-retention abilities by covalent surface modification.

Hydrogels have been widely used in various fields due to their diverse properties and flexible preparation methods. However, limited by the open network structure, hydrogels inevitably lose water in air or absorb water in aqueous solution, resulting in the loss of intrinsic functions, which severely hinders their practical applications. To address this issue, a general strategy was developed by subsequently modifying the surface of hydrogels with branched polyethyleneimine (PEI) and (3-(methacryloxy)propyl)trimethoxysilane (MPS) to covalently construct a dense cross-linked siloxane layer on the hydrogel surface. As a proof of concept, poly(2-(dimethylamino)ethyl methacrylate)/sodium alginate (PDMAEMA/SA) hydrogels were chosen as the model hydrogels to verify the feasibility of this strategy. The hydrogels adsorbed PEI to form amino-rich surfaces through hydrogen bonding, followed by covalently grafting MPS through rapid and catalyst-free mutual chemical reactions between acrylates and amine groups, as well as the hydrolysis of MPS. After modification, robust hydrophobic surfaces were successfully fabricated on the hydrophilic hydrogels. The modified hydrogels exhibited extraordinary anti-swelling and water-retention abilities. As the most typical intrinsic properties of hydrogels, the conductivity and sensing performance were well preserved. The strategy reported here provides a new insight into the construction of hydrogels with anti-swelling and water-retention abilities.

Improved emulsifying properties of water-soluble myofibrillar proteins at acidic pH conditions: Emphasizing pH-regulated electrostatic interactions with chitosan

Water-soluble muscle protein with enhanced functionalities has attracted great interest for low-salt food design. Electrostatic interactions of chitosan (CS) with myofibrillar proteins (MP) in water-aqueous solution at acidic pHs (4.0–6.5) were investigated, and how pH regulated complex formation, microstructures, conformation changes, and emulsifying capacity was systematically explored. At pH 4.0–4.5, MP and CS were positively charged and displayed a co-soluble system, exhibiting small particles and high solubility. When the pH increased to near the isoelectric point (pI) of MP (pH 5.0–6.0), electrostatic interactions largely inhibited the aggregation of MP by forming smaller particle complexes. The flexible structures and improved amphiphilic properties promoted protein absorption at the oil-water interface, further improving the emulsion stability. When the pH increased to 6.5, large aggregates were formed causing poor functionalities. This study could provide great insights to further exploit meat-protein-based low-salt functional foods in novel food design.

Impact of Water Content on the Superlubricity of Ethylene Glycol Solutions

Aqueous solutions of water and ethylene glycol (EG) are prevalently employed in braking, heat transfer, and lubrication systems. However, the precise mechanism through which water content affects the lubricative attributes of EG solutions remains elusive. This research systematically examines the tribological characteristics of EG solutions at varying concentrations using a ceramic–TiAlN friction-pair system. As the concentration of EG increases, the sequential transformation of the associated molecular complex structure in the lubricating medium can be described as follows: [H2O]m·EG → [H2O]m·[EG]n → H2O·[EG]n. Among them, the stoichiometric coefficients “m” and “n” are the simplest mole ratio of H2O and EG in the molecular complex structure, respectively. The most favorable EG concentration was determined to be 50 wt.%. At this concentration, a flexible molecular complex adsorption structure ([H2O]m·[EG]n) with a significant bearing capacity (due to intense hydrogen bonding) forms on the surface of the friction pair, which results in a reduction in the running-in duration and facilitates the achievement of superlubricity, and the coefficient of friction (COF) is about 0.0047. Solutions containing 50 wt.% EG enhance the load-bearing ability and hydrophilicity of the lubricating medium. Moreover, they minimize the roughness of the worn region and curtail the adhesive forces and shear stress at the frictional interface, enabling the realization of superlubricity. Consequently, this research offers valuable insights into the optimal water-to-EG ratio, revealing the mechanism of a superlubricity system that possesses exceptional tribological attributes and holds significant potential for practical applications.

Single-detector double-beam modulation for high-sensitivity infrared spectroscopy

Balanced detection based on double beams is widely used to reduce common-mode noises, such as laser intensity fluctuation and irregular wavelength scanning, in absorption spectroscopy. However, employing an additional detector can increase the total system noise due to added non-negligible thermal noise of the detector, particularly with mid-infrared (IR) detectors. Herein, we demonstrate a new optical method based on double-beam modulation (DBM) that uses a single-element detector but keeps the advantage of double-beam balanced detection. The sample and reference path beams were modulated out-of-phase with each other at a high frequency, and their average and difference signals were measured by two lock-in amplifiers and converted into absorbance. DBM was coupled with our previously reported solvent absorption compensation (SAC) method to eliminate the IR absorption contribution of water in aqueous solutions. The DBM-SAC method enabled us to acquire IR absorption spectra of bovine serum albumin solutions down to 0.02 mg/mL. We investigated the noise characteristics of DBM measurements when the wavelength was either fixed or scanned. The results demonstrate that DBM can lower the limit of detection by ten times compared to the non-modulation method.

Thermodynamic Model of the H2O–H2SO4–UO2SO4 System Incorporating Novel Experimental Data on Water Activity

Activity of water in aqueous solutions containing sulfuric acid and uranyl sulfate has been determined at 298.15, 310.65, and 323.15 K by means of the apparatus AQUALAB 4TE. The data obtained, along with literature information about activity of water and solid–liquid equilibria in the H2O–UO2SO4 and H2O–H2SO4–UO2SO4 systems, were used to develop a thermodynamic model of the ternary system mentioned. The resulting model, employing Pitzer–Simonson–Clegg (PSC) equations to represent the properties of a liquid phase, is valid within a wide range of temperatures and concentrations. Apart from introducing novel experimental data and a thermodynamic model, the reported study discusses advantages and disadvantages of the PSC-based thermodynamic descriptions of the H2O–H2SO4 subsystem presented in the literature.

Preparation of Functionalized Palm Kernel Shell Bio-adsorbent for the treatment of heavy metal-contaminated water

Human beings and living creatures are at great risk because of heavy metal contamination in water resulting from industrialization. On the other hand, millions of tons of palm kernel shells (PKS) and other oil palm wastes are produced every year from oil palm downstream industries. In this study, we attempt to consolidate both problems, where the PKS was oxidized with sulfuric acid for the formation of PKS-Sulfo, where the oxygenated and sulfonated functional groups are attached to the activated carbon. The resulting PKS-Sulfo bio-adsorbent was characterized in detail and was used for the treatment of heavy metal-contaminated water. Different adsorption parameters; pH, concentrations of metal ions, contact time, and adsorbent dosage were optimized. It was found that the PKS-Sulfo bio-adsorbent is highly efficient in adsorbing heavy metal ions; Cr6+, Pb2+, Cd2+, and Zn2+ from their aqueous water solutions. The adsorption process was found to follow the pseudo-second-order model and the Langmuir isotherm was better fitted compared to the Freundlich adsorption isotherm for the adsorption process of the heavy metal ions. Furthermore, the adsorption capacities were also determined for all the metal ions were found to be 99% for Cr6+ and Pb2+ and Cd2+ and Zn2+ was found to be 80 % and 70% respectively. This study opens up a new horizon for the preparation of functionalized bio-adsorbents with the potential for numerous applications, especially for water remediation.

Experimental and modeling on hydrate phase equilibrium conditions for hydrogen-containing gas mixtures in pure water and brines

Hydrate-based technology is considered as one of potential ways for hydrogen separation and storage. Additionally, it has been reported that injecting CO2/H2 mixture is an effective approach to the enhancement of natural gas hydrate exploitation. Hence the determination of hydrate formation conditions of hydrogen containing gas mixtures is of fundamental significance. A series of hydrate formation conditions of hydrogen-containing gas mixtures were then measured under 273.8 to 285.5 K and 2.61 to 10.52 MPa, including 3 binary (CH4 + H2) gas mixtures and 5 ternary (CH4 + CO2 + H2) gas mixtures in pure water, as well as 8 ternary (CH4 + CO2 + H2) gas mixtures in aqueous solutions of NaCl and Na2SO4. Meanwhile, a thermodynamic model for predicting hydrate formation conditions of hydrogen-containing systems were developed, in which Chen–Guo hydrate model was used to calculate the fugacities of guest species in hydrate phase and Patel–Teja equation of state was used to calculate the fugacities of guest components in gas phase and those of water in aqueous solutions. Two mixing rules, van der Waals mixing rule and Wang-Sandler mixing rule, were applied in parallel to determine the values of parameters of Patel–Teja equation of state. The overall average absolute deviation on formation pressure for 273 data points is 4.61 % when using Wang-Sandler mixing rule while it is 5.70 % when using van der Waals mixing rule. The experimental data and prediction method presented might be of significance for both exploitation of natural gas hydrate via injecting CO2/H2 mixture as well as the purification of hydrogen via forming hydrate.

Crystallinity Dependence of PLLA Hydrophilic Modification during Alkali Hydrolysis.

Poly(L-lactic acid) (PLLA) has been extensively used in tissue engineering, in which its surface hydrophilicity plays an important role. In this work, an efficient and green strategy has been developed to tailor surface hydrophilicity via alkali hydrolysis. On one hand, the ester bond in PLLA has been cleaved and generates carboxyl and hydroxyl groups, both of which are beneficial to the improvement of hydrophilicity. On the other hand, the degradation of PLLA increases the roughness on the film surface. The resultant surface wettability of PLLA exhibits crucial dependence on its crystallinity. In the specimen with high crystallinity, the local enrichment of terminal carboxyl and hydroxyl groups in amorphous regions accelerates the degradation of ester group, producing more hydrophilic groups and slit valleys on film surface. The enhanced contact between PLLA and water in aqueous solution (i.e., the Wenzel state) contributes to the synergistic effect between generated hydrophilic groups and surface roughness, facilitating further degradation. Consequently, the hydrophilicity has been improved significantly in the high crystalline case. On the contrary, the competition effect between them leads to the failure of this strategy in the case of low crystallinity.

Ion-pairing equilibria and kinetics of dimethyl phosphate: A model for counter-ion binding to the phosphate backbone of nucleic acids

Dimethyl phosphate (DMP–) is the simplest model ion to assess ion-pairing phenomena between metal ions and the phosphate backbone of nucleic acids. Yet, the equilibria and dynamics of ion binding to DMP– have not been fully uncovered. Here, we study the interaction of DMP– with different cations and water in aqueous solutions of NaDMP using dielectric relaxation and nuclear magnetic resonance spectroscopies. We find DMP– to be weakly hydrated and weakly associated with Na+ in the absence of added salt. Upon addition of NaCl, MgCl2, or CaCl2 to solutions of NaDMP, we detect the formation of solvent-shared (NaDMP0) and contact (MgDMP+, CaDMP+) ion-pairs; the degree of ion association is 20–27 % at 2:1 salt:DMP molar ratio for the bivalent ions. Comparison to literature results suggests the formation constant of MgDMP+ to be a good estimate for the binding of Mg2+ to RNA. From the concentration dependence of the rotational relaxation time of the ion-pairs, we find ion-pair dissociation rates to follow the order Mg2+≪Ca2+<Na+. Strikingly, our data suggest that the overall ion-pair dissociation dynamics are governed by an ion-pair metathesis reaction, which provides a different pathway for the binding of ions by DMP–.

Chemometrics: An Excavator in Temperature-Dependent Near-Infrared Spectroscopy.

Temperature-dependent near-infrared (NIR) spectroscopy has been developed and taken as a powerful technique for analyzing the structure of water and the interactions in aqueous systems. Due to the overlapping of the peaks in NIR spectra, it is difficult to obtain the spectral features showing the structures and interactions. Chemometrics, therefore, is adopted to improve the spectral resolution and extract spectral information from the temperature-dependent NIR spectra for structural and quantitative analysis. In this review, works on chemometric studies for analyzing temperature-dependent NIR spectra were summarized. The temperature-induced spectral features of water structures can be extracted from the spectra with the help of chemometrics. Using the spectral variation of water with the temperature, the structural changes of small molecules, proteins, thermo-responsive polymers, and their interactions with water in aqueous solutions can be demonstrated. Furthermore, quantitative models between the spectra and the temperature or concentration can be established using the spectral variations of water and applied to determine the compositions in aqueous mixtures.

Quantum chemical investigation of the effect of alkali metal ions on the dynamic structure of water in aqueous solutions.

We report quantum chemical molecular dynamics (MD) simulations based on the density-functional tight-binding (DFTB) method to investigate the effect of K+, Na+, and Mg2+ ions in aqueous solutions on the static and dynamic structure of bulk water at room temperature and with various concentrations. The DFTB/MD simulations were validated for the description of ion solvation in aqueous ionic solutions by comparing static pair distribution functions (PDFs) as well as the cation solvation shell between experimental and available ab initio DFT data. The effect of the cations on the water structure, as well as relative differences between K+, Na+, and Mg2+ cations, were analyzed in terms of atomically resolved PDFs as well as time-dependent Van Hove correlation functions (VHFs). The investigation of the VHFs reveals that salt ions generally slow down the dynamic decay of the pair correlations in the water solvation sphere, irrespective of the cation size or charge. The analysis of partial metal–oxygen VHFs indicates that there are long-lived correlations between water and Na+ over long distances, in contrast to K+ and Mg2+.

Non-monotonic composition dependence of the breakdown of Stokes-Einstein relation for water in aqueous solutions of ethanol and 1-propanol: explanation using translational jump-diffusion approach.

A series of experimental and simulation studies examined the validity of the Stokes-Einstein relationship (SER) of water in binary water/alcohol mixtures of different mixture compositions. These studies revealed a strong non-monotonic composition dependence of the SER with maxima at the specific alcohol mole fraction where the non-idealities of the thermodynamic and transport properties are observed. The translational jump-diffusion (TJD) approach elucidated the breakdown of the SER in pure supercooled water as caused by the jump translation of molecules. The breakdown of SER in the supercooled water/methanol binary mixture was successfully explained using the same TJD approach. To further generalize the picture, here we focus on the non-monotonic composition dependence of SER breakdown of water in two water/alcohol mixtures (water/ethanol and water/propanol) for a broad temperature range. In agreement with previous studies, maximum breakdown of SER is observed for the mixture with alcohol mole fraction x = 0.2. Diffusion of the water molecules at the maximum SER breakdown point is largely contributed by jump-diffusion. The residual-diffusion, obtained by subtracting the jump-diffusion from the total diffusion, approximately follows the SER for different compositions and temperatures. We also performed hydrogen (H-)bond dynamics and observed that the contribution of jump-diffusion is proportional to the total free energy of activation of breaking all H-bonds that exist around a molecule. This study, therefore, suggests that the more a molecule is trapped by H-bonding, the more likely it is to diffuse through the jump-diffusion mechanism, eventually leading to an increasing degree of SER breakdown.

Facile synthesis of Ni-based layered double hydroxides with superior photocatalytic performance for tetracycline antibiotic degradation

The purpose of this study was to investigate the photocatalytic performance of Ni-based layered double hydroxides (LDHs) in degradation of tetracycline (TC) as a model antibiotic pollutant. Two kinds of Ni-based LDHs (NiFe-LDH and NiCr-LDH) with chloride and carbonate ions in the interlayer region were facile fabricated by chemical co-precipitation method at room temperature and characterized using Fourier transform infrared (FT-IR), thermogravimetric analysis (TGA), powder X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), energy disperse spectroscopy (EDS), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and Brunauer-Emmett-Teller (BET) techniques. The results showed that the as-prepared LDHs materials performed superior photocatalytic efficiency to eliminate TC from aqueous water solution under UV–vis light irradiation. The photocatalytic efficiency depends on the catalyst dosage and TC concentration. Furthermore, the plausible photocatalytic degradation mechanism was proposed by means of radical trapping and electron spin resonance (ESR) tests. It is found that the photocatalytic degradation of TC by Ni-based LDHs follows an oxygen-induced pathway, and the superoxide radical (•O2−) and hydroxyl radical (•OH) play a major role in the photocatalytic degradation process. The study provided a valuable insight into fabricating high-performance and environmentally friendly LDHs for removal of antibiotics in waste water.

Dicationic-Type Quaternary Ammonium Salts as Candidates of Desiccants for an Air-Conditioning System

Liquid desiccant air conditioners contribute to sustainable living by reducing the electricity consumption. They can be driven with continuous ventilation and thus can prevent airborne transmission of infectious diseases like COVID-19. In order to develop efficient desiccant materials for liquid desiccant air conditioners, we have investigated the dehumidification capability of 21 types of ammonium salts, many of them being ionic liquids. The hygroscopicity of dicationic quaternary ammonium bis(dimethyl or diethylphosphate) is found to increase with the carbon chain length of the spacer group -(CH2)n- that bridges the two terminal cationic moieties of the dication, that is, (CH2)2 < (CH2)3 < (CH2)6. This trend remains unchanged when methyl substituents on the cation and the phosphate anion are replaced by ethyl groups. A high dehumidification capability is obtained for N1,N1,N1,N6,N6,N6-hexamethylhexane-1,6-diaminium bis(dimethylphosphate) ([HMC6][DMPO4]2) and 1,6-diethyl-1,1,6,6-tetramethylhexane-1,6-diaminium bis(diethylphosphate) ([DETMC6][DEPO4]2);their capability per gram reaches almost twice that of CaCl2, and their dehumidification rate is superior to popular solid desiccants. A favorable equilibrium water vapor pressure for the liquid desiccant air-conditioning system is attained for an 80% (w/w) aqueous solution of [HMC6][DMPO4]2. In addition, the 80% aqueous solution of [HMC6][DMPO4]2 affords no corrosive effect on steel, aluminum, and stainless steel and a very weak effect on copper. Dicationic quaternary ammonium bis(dimethyl or diethylphosphate)s are stable compounds;their aqueous solutions produce no odor after storing for over 1 year under ambient conditions. Molecular dynamics simulations are performed to gain insights into the solvation structure, energetics, and transport behavior of water in aqueous solutions of [HMC6][DMPO4]2 and related salts. ©

Tuning the selectivity of biomass oxidation over oxygen evolution on NiO–OH electrodes

Small cation size along with removal of trace iron from the electrolyte solution enables the practical use of earth-abundant nickel oxide electrodes for selective oxidation of organic molecules over water in aqueous solutions.

Are There Indeed Spliced Peptides in the Immunopeptidome?

The claims that a large fraction of the immunopeptidome is composed of spliced major histocompatibility complex (MHC) peptides have stirred significant excitement and raised controversy. Here, I suggest that there are likely no spliced peptides in the immunopeptidome, and if they exist at all, they are extremely rare. I base this claim on both biochemical and bioinformatics considerations. First, as a reactant in normal proteolytic reactions, water will compete with transpeptidation, which has been suggested as the mechanism of peptide splicing. The high mobility and abundance of water in aqueous solutions renders transpeptidation very inefficient and therefore unlikely to occur. Second, new studies have refuted the bioinformatics assignments to spliced peptides of most of the immunopeptidome MS data, suggesting that the correct assignments are likely other canonical, noncanonical, and post-translationally modified peptides. Therefore, I call for rigorous experimental methodology using heavy stable isotope peptides spiking into the immunoaffinity-purified mixtures of natural MHC peptides and analysis by the highly reliable targeted MS, to claim that MHC peptides are indeed spliced.

Knowledge-based genetic algorithm for resolving the near-infrared spectrum and understanding the water structures in aqueous solution

The structure of water has been an interesting subject in various research fields due to its complexity and flexibility. Near-infrared (NIR) spectroscopy has been proven to be a powerful tool for analyzing the structure of water in aqueous solutions. However, low resolution of the spectrum and overlapping of the peaks make it difficult to obtain the spectral components for understanding the structure of water. In this work, a knowledge-based genetic algorithm was developed for Gaussian fitting of the NIR spectra of water measured at different temperatures. The number of the water structures was determined from the result of molecular dynamics simulation, and the spectral peak of the structures was simulated by a Gaussian function. Continuous wavelet transform was adopted to enhance the resolution and remove the background variation of the spectra. Through the variation of the water structures with temperature, the dissociation of the larger clusters into smaller ones was observed. Furthermore, an enhancement of the ordered (tetrahedral) water structures is indicated by the relative content in the glucose solutions of different concentrations, providing a proof for glucose making the water structure more ordered to explain the protective effect of glucose on the bio-molecules in bio-aqueous solution.