Aqueous Systems Research Articles

Effect of annealing on the MnO2 cathodes for high-performance aqueous Zn-ion batteries

Zinc ion batteries (ZIBs) are increasingly prominent due to their cost-effectiveness, abundance, environmental safety, mature processing methods, high volumetric energy density, and compatibility with aqueous electrolytes. However, a significant challenge lies in finding a suitable cathode material with high capacity and structural stability. Manganese dioxide (MnO2) is a promising candidate for ZIB cathodes in aqueous systems, surpassing other metal oxides in potential. However, MnO2 cathodes encounter challenges, including rapid capacity degradation and limited cyclic stability. Enhancing the structural stability of host materials during intercalation presents a significant avenue for increasing cathode capacity. In this study, we employed a hydrothermal method to synthesize MnO2, followed by annealing in an argon atmosphere at 300 °C for 4 h for MnO2-300 and 400 °C for 2 h for MnO2-400 to bolster its structural integrity. The properties of annealed samples MnO2-300 and MnO2-400 are compared with pristine samples (MnO2-P). Initially, XRD analysis is conducted to compare their structures, followed by a comparison of electrochemical properties, including Cyclic Voltammetry (CV) and charge-discharge analysis. MnO2-400 exhibits a higher initial capacity (149.3 mAhg−1 at 0.1 Ag-1) than MnO2-300 (129.0 mAhg−1 at 0.1 Ag-1) and MnO2-P (107.9 mAhg−1 at 0.1 Ag-1). An extended cycling test of up to 500 cycles also indicates that annealing MnO2 in an Ar atmosphere enhances structural stability and capacity compared to the unannealed sample.

Robust ZIF-8 based superhydrophobic coating with anti-icing, anti-corrosion, and substrate universality

The design of superhydrophobic materials based on zeolite imidazolate frameworks (ZIF) has attracted considerable attention due to their exceptional chemical stability, high specific surface area, and environmental friendliness. However, research in the fields of anti-corrosion and anti-icing remains in its infancy, and the mechanical stability of reported ZIF-based superhydrophobic surfaces is generally poor. In this study, we synthesized ZIF-8@PDA materials in an aqueous system and followed with stearic acid (STA) modification to achieve low surface energy, resulting in ZIF-8@PDA@STA. Subsequently, we applied a spray-coating method to sequentially construct WPU and ZIF-8@PDA@STA layer on aluminum alloy substrates, achieving a ZIF-8@PDA@STA/WPU superhydrophobic coating with exceptional mechanical stability. This coating retained its superhydrophobicity even after 5600 cm of abrasion distance. Furthermore, results from surface wettability, electrochemical and anti-icing tests demonstrated that the coated aluminum alloy exhibited excellent interfacial non-wetting, self-cleaning, anti-fouling, and significantly enhanced corrosion resistance and delayed icing properties. Additionally, the facile preparation of this coating on various substrates facilitates the large-scale application of such materials. The construction of this multifunctional ZIF-8 based superhydrophobic coating is expected to greatly expand the application of ZIF materials across diverse fields.

Synthesis, Characterization, and Interaction Studies of Naphtho‐[2,3]‐furan‐Based Molecules with CTAB as Model Surfactant

AbstractThe synthesis of highly sensitive UV–visible active naphthofuran derivatives, namely naphtho‐[2,3]‐furan‐3‐yl acetate (NF), 9‐bromonaphtho‐[2,3]‐furan‐3‐yl acetate (BNF), 9‐nitronaphtho‐[2,3]‐furan‐3‐yl acetate (NNF), 9‐iodonaphtho‐[2,3]‐furan‐3‐yl acetate (INF), and naphtho‐[2,1‐b]‐furan‐4‐carboxylic acid (ONF) as solvatochromic molecules, was carried out through multistep synthetic approach. These molecules possess different substituents that tend to form micelles in cetyl trimethylammonium bromide (CTAB) aqueous system. During the micellization process, the absorption spectrum of the synthesized molecule exhibits sensitivity towards the polarity of the environment, which affects the critical micelle concentration (cmc) of CTAB. This study demonstrates that synthesized molecules can be used for estimating solvent polarity and cmc.

Highly enhanced fluoride removal from aqueous systems via solvent extraction utilizing trialkyl phosphine oxide as an efficient extractant

Solvent extraction (SX) has been recognized as an efficient approach for the large-scale removal of impurities, demonstrating considerable potential for fluoride extraction in industrial applications. However, existing fluoride extraction methods typically require the incorporation of additives to form complexes with fluoride for its removal. Due to the excessive additive requirements for efficient fluoride removal, these methods inevitably result in secondary contamination of feed solution, necessitating additional purification efforts to remove them. In this study, four extractants (trioctyl amine, tributyl phosphate, trioctyl phosphate, and trialkyl phosphine oxide (TRPO)) were investigated for fluoride removal via hydrogen bonding with hydrofluoric acid (HF). Various parameters, including the concentrations of extractants and stripping agents, pH values, extraction time, and temperature were initially optimized. It was found that TRPO exhibits the highest extraction efficiency for HF, with a single-stage extraction rate exceeding 70 %. Complete fluoride removal (> 99.9 %) was achieved through a consecutive four-stage extraction process. Further experiments, including maximum loading and slope analysis, combined with FT-IR and 19F NMR characterization, and DFT calculations elucidate the mechanism of the extraction. The transfer of HF into the organic phase is accomplished by the formation of a 1:1 hydrogen-bonded complex with TRPO. The loaded fluoride in the organic phase can be easily stripped by a base to get a fluoride salt. This study paves the way for the construction of novel SX systems to remove fluoride as HF.

Eggshell-Derived Fe-Mg Particles and Hydroxyapatite for Removal of Tetracycline and Metronidazole from Aqueous Systems

Eggshell-Derived Fe-Mg Particles and Hydroxyapatite for Removal of Tetracycline and Metronidazole from Aqueous Systems

Removal of Dyes from Waste Water Using Low‐Cost Adsorbents

AbstractThe principal objective of this article is a thorough analysis of the usage of inexpensive adsorbents to eliminate dyes from different aquatic environments. Dyes, commonly employed in industries—textiles, pharmaceuticals, and food, pose a significant environmental concern due to their persistence and potential toxicity. In response, researchers have explored the efficacy of low‐cost adsorbents (LCAs) as sustainable and economical alternatives for dye elimination. An overview of the environmental effects of dye contamination and the difficulties in using traditional dye removal techniques is given at the outset of the paper. It then delves into the diverse range of LCAs, including agricultural by‐products, waste materials, and natural substances, that have shown promise in adsorbing and eliminating dye contaminants. Examples of such adsorbents include activated carbon (AC) derived from agricultural residues, bio‐adsorbents from various plant materials, and industrial by‐products with inherent adsorption properties. Key mechanisms involved in the adsorption process, such as surface chemistry, pore structure, and electrostatic interactions, are elucidated to offer a fundamental understanding of the sorption capabilities of these materials. This comprehensive review consolidates the current knowledge on dye removal utilizing LCAs, offering insights into the challenges, advancements, and future directions in this environmentally significant field. The findings underscore the potential of harnessing readily available, sustainable materials as effective sorbents for mitigating the adverse impacts of dye pollutants in aqueous systems. The adsorption capacity is comparable to supplementary adsorbents suggested for the removal of dyes. The widely accessible adsorption properties of basic and acidic dyes do not significantly differ from one another.

Solid-liquid phase equilibria in the aqueous system containing the chlorides of potassium, ammonium, and calcium at 298.2, 323.2, and 348.2 K

In order to obtain the crystalline forms of the salts of the potassium, ammonium, calcium coexisting chloride system, the phase equilibria relationship of quaternary system K+, NH4+, Ca2+//Cl–-H2O at 298.2, 323.2, and 348.2 K was studied by isothermal dissolution equilibrium method. The solubility and density of equilibrium liquid phases of the system were experimentally determined; X-ray powder diffractometer was used to determine the compositions of the equilibrium solid phase at the quaternary invariant point. It is found that the quaternary system is a complex system at these three temperatures. The phase diagram at 298.2 K consists of three invariant points, seven univariate curves and five crystalline phase regions, forming the solid solutions (NH4Cl)x(KCl)1–x and (KCl)x(NH4Cl)1–x; while at 323.2 and 348.2 K the phase diagram consists of five invariant points, eleven univariate curves and seven crystalline phase regions, the double salts (KCl·CaCl2) and (2NH4Cl·CaCl2·3H2O), solid solutions (KCl)x(NH4Cl)1–x and (NH4Cl)x(KCl)1–x were formed. Among them, the crystalline phase region of solid solution (KCl)x(NH4Cl)1–x is the largest at three temperatures, indicating that it is the easiest to crystallize in this system. Comparing the phase diagrams of the quaternary system at 298.2, 323.2, and 348.2 K, it can be seen that the crystalline form of CaCl2 changes with the increase of temperature: CaCl2·6H2O at 298.2 K, CaCl2·2H2O at 323.2 and 348.2 K. From 323 to 348 K, the crystalline phase regions of (KCl·CaCl2) and (2NH4Cl·CaCl2·3H2O) increased gradually.

Chitosan-curcumin conjugate prepared by one-step free radical grafting: Characterization, and functional evaluation

Curcumin (Cur) is a naturally hydrophobic polyphenol, and it has a wide range of physiological functions. But the practical application of Cur is constrained by its low water solubility and poor stability. To improve these deficiencies of Cur, a novel Cur derivative (CS-Cur) was prepared by grafting chitosan (CS) with Cur through a one-step reaction of a free radical-mediated redox system. A series of characterizations provided evidence that the grafting of CS with Cur was successful. The obtained CS-Cur showed lower crystallinity and thermal properties than CS and Cur. After grafting, the water solubility of CS-Cur was found to be 9.76±2.45 g/L and greatly improved. Meanwhile, the CS-Cur showed good photothermal stability, antioxidant activity, and photodynamic antibacterial activity in an aqueous solution, and it had good in vitro biosafety. This provides an idea for the design and synthesis of novel highly water-soluble Cur derivatives and also improves the practical application of Cur in aqueous systems.

A novel deep eutectic solvent-based green extraction and purification of DPP-IV inhibitory peptides from tilapia (Oreochromis niloticus) viscera hydrolysate

The use of green and low-cost techniques to produce bioactive peptides with anti-diabetic properties from protein-rich fish waste is a sustainable way to manage agro-fishery and food industrial waste. This study investigated a novel ultrasound (UL) assisted deep eutectic solvent (DES) based extraction approach to recover bioactive protein-rich extracts from tilapia fish viscera waste under optimized conditions (52.52% ultrasound amplitude, 1:4 DES molar ratio, 25 min extraction time). The aqueous two-phase system (ATPS) method successfully concentrated the crude proteins in the top phase and back-extracted proteins to the bottom phase with a high recovery yield. Hydrolysis by Alcalase produced tilapia viscera protein hydrolysate (TVPH) with low molecular weight (MW) peptides and low dipeptidyl peptidase (DPP)-IV half-maximal inhibitory concentration (IC50) value of 1.57 ±0.16 mg/mL. Notably, TVPH-3 fraction and TVPH-3-2 sub-fraction exhibited appreciable DPP-IV IC50 values of 1.36 ±0.08 mg/mL and 0.42 ±0.01 mg/mL, respectively. Ultrafiltration combined with RP-HPLC enriched the DPP-IV inhibitory concentration of the individual protein fractions. TVPH-3-2 sub-fraction contained hydrophobic amino acids and peptide sequences with typical DPP-IV inhibitory peptide sequence motifs. The results presented in this study indicate that tilapia viscera biomass is a potential source for protein recovery aided with a green extraction approach, and tilapia viscera protein-derived hydrolysates have potential applications as a potent functional food ingredient for the management of metabolic diseases like type-2 diabetes.

Revealing protein aggregation behaviour and dispersion properties induced by molecular interactions between sucrose esters and myofibrillar protein in an aqueous phase system

The effects of sucrose esters (SE) with varying hydrophilic-lipophilic balance (HLB) values (SE 11, 13, 15) and different concentrations (0.01, 0.1, 1.0 mM) on the dispersion properties and structure of myofibrillar proteins (MPs) in the aqueous phase were investigated. The results demonstrated that the SE 11 and SE 13 reduced the particle size and enhanced the distribution uniformity of the MPs. All of the SE exhibited a slight reduction in the ζ-potential absolute values of the MPs. Meanwhile, the SE 11 significantly reduced the turbidity of the MPs, especially in the 0.1 mM group. Macroscopic and microscopic images showed that the optimum dispersion state was in the SE 11–0.1 group. Furthermore, the interactions between SE and MPs exerted a significant impact on the proteins structure. The SE 13 and SE 15 caused significant changes, which presented concentration correlation, in the tertiary and secondary spatial structures of the MPs. Nevertheless, slight structural changes were observed in MPs with different SE11 concentrations. The SE did not alter the molecular weight of the MPs, i.e. it did not induce irreversible aggregation, nor degradation of the proteins. These results were verified by the surface hydrophobicity, UV–Vis spectroscopy, intrinsic fluorescence, circular dichroism, and SDS-PAGE. Molecular docking simulation showed that hydrophobic interactions and hydrogen bonds were the main interaction force between SE 11 and MPs. Therefore, our findings provided meaningful insights into the dispersion state of the MPs aqueous containing SEs and contributed to the practical application of non-ionic surfactants in meat protein processing.

Simultaneous Production of 111In and 109Cd by Alpha Particle Irradiation of natAg Target and Synergistic Aqueous Biphasic Separation using Green Tea Polyphenols

Abstract111In and 109Cd radionuclides were produced by 31 MeV ‐particle irradiation of natAg target. To separate no‐carrier added (NCA) 111In and 109Cd from bulk Ag, Aqueous Biphasic System (ABS) was constructed using twelve salts and two polyethylene glycol (PEG) combinations. Out of all these combinations, only three salts e. g., Na2SO3, Na‐ malonate and Na‐Tartrate and PEG combinations showed significant separation between bulk Ag and NCA radioisotopes. Addition of catechins extracted from green tea to the above ABS systems increased the separation factors many folds. Highest separation factor (SIn/Ag=5.6×104) for 111In was obtained in Na2SO3‐PEG 4000 and 50 mg catechins system. 109Cd retained in NCA state in the Na‐malonate phase after the extraction of 111In and bulk Ag in the catechin‐PEG phase.

Hexafluoroisopropanol-based deep eutectic solvents for efficient aqueous two-phase extraction of flavonoids from Flos Sophorae Immaturus

Aqueous two-phase systems (ATPSs) based on deep eutectic solvents (DESs) are green extraction and separation media and have demonstrated remarkable potential for extracting bioactive substances from natural matrices. However, thus far, flavonoid extraction using DES-based ATPSs has rarely been reported. In this study, the state-of-the-art technique using DES-based ATPSs was employed for developing an effective method for extracting flavonoids from Flos Sophorae Immaturus (FSI). DESs prepared with hexafluoroisopropanol (HFIP) and five quaternary ammonium salts, N111xCl (x = 1, 4, 8, 12, and 16), were used as the hydrogen bond donor and hydrogen bond acceptors, respectively, for constructing ATPSs with K2HPO4 as a salting-out agent and utilized for extracting flavonoids from FSI. Fourier-transform infrared, 1H nuclear magnetic resonance, 1H–1H nuclear Overhauser effect spectroscopy analyses, and density functional theory calculations were implemented to demonstrate the successful preparation of DESs. The DES containing dodecyltrimethylammonium chloride and HFIP with a molar ratio of 1:2 was screened as the optimal DES, showing a higher extraction efficiency and yield of flavonoids compared to those of other DESs and the traditional solvent ethanol. Subsequently, various experimental parameters (amount of DES, salt concentration, liquid-to-solid ratio, extraction temperature, and ultrasonic time) for the extraction process were studied comprehensively and optimized using response surface methodology. The yield of flavonoids from FSI was 21.05 % under optimal extraction conditions (amount of DES = 2 g, salt concentration = 0.21 g/mL, liquid-to-solid ratio = 81 mL/g, and extraction temperature = 60 ℃), which is close to the predicted value of 20.82 %. Extraction mechanisms underlying the performance of DES-based ATPSs during the extraction of bioactive substances are yet to be fully understood. Therefore, molecular dynamics (MD) simulations were employed with rutin as the target compound to probe the extraction mechanism under DES-based ATPS conditions, and the results revealed that hydrogen-bonded frameworks are pivotal for the extraction process. Moreover, the existence of K2HPO4 was found to promote not only the increase in hydrogen bonding networks and π–π stacking interactions within rutin molecules but also the increase in solvent flexibility, facilitating the extraction process. The present work offers a promising approach for flavonoid extraction using DES-based ATPSs. Interpreting the extraction mechanism at the molecular level by adopting the MD simulation technique provides new insights that enable a deeper understanding and aid in the design of the extraction process for bioactive substances under DES-based ATPS circumstances.

A green extraction method based on aqueous two-phase system for trace-level enrichment of multi-residue pesticides in traditional Chinese medicine prior to HPLC-MS/MS quantitative analysis

A green extraction method based on aqueous two-phase system for trace-level enrichment of multi-residue pesticides in traditional Chinese medicine prior to HPLC-MS/MS quantitative analysis

Confinement induced alteration in interfacial energy in aqueous surfactant systems

When a liquid is confined between two parallel plates, the pressure field at its bulk alters, because of the concave meniscus at the air-water interface. For an aqueous surfactant solution in contact with an oil, like an oil-in-water emulsion, this effect can alter the surfactant concentration at the interface of the two phases thereby changing the interfacial energy. Alteration of interfacial energy is expected to affect morphology of a complex system consisting of three immiscible phases. To verify this hypothesis a drop of crosslinkable silicone liquid was placed on a glass slide and was immobilized by partial crosslinking. An aqueous solution of surfactant, with SiO2 microspheres dispersed in it, was dispensed on this drop to create a liquid pool. It was then confined between two parallel plates to create a meniscus. Consequently, the particles got embedded at the oil-water interface to different extent, depending on the degree of confinement. Force balance along tangents to different interfaces showed that the interfacial energy of silicone-water (aqCTAB 0.3 mM) interface increases from 33.3 ± 0.5 mJ/m2 for an unconfined system to 45.4 ± 2.2 mJ/m2 for the confined one. This effect then elucidates how confinement alters complex emulsion morphologies in multiphase systems.

A laboratory-based electrochemical NAP-XPS system for operando electrocatalysis studies

During electrocatalytic reactions, the electrode, adsorbates, electrolyte ions, and solvent molecules at the electrode-electrolyte interface each play an important role. Electrochemical X-ray photoelectron spectroscopy (XPS) holds great promise for deciphering these roles, providing the oxidation state or bonding environment of every element present at the interface. However, combining the vacuum required for XPS with the wet environment needed for electrochemistry constitutes a technical challenge, requiring purpose-built instrumentation and spectro-electrochemical cell design. Here, we present a laboratory-based electrochemical XPS instrument optimized for operando studies on nano-structured electrocatalysts. The core of the system is a 3D printed spectro-electrochemical cell containing a membrane-electrode-graphene assembly. We show that this design enables us to probe the electrode surface, interfacial water, and interfacial ions under well-defined potential control. Meanwhile, the introduction of a mesoporous membrane into the assembly enables the transport of any molecular or ionic reactant towards the working electrode, opening the way to study any aqueous phase electrocatalytic system using laboratory-based electrochemical XPS. We exemplify this for the oxygen reduction reaction.

Microscopic study on the memory effect of methane hydrate in the presence of silica nanoparticles: Ⅰ. Dissociation mechanism & guest supersaturated hypothesis

As a key issue emerged in the exploitation of combustible ice resources, the memory effect inducing hydrate reformation in sand-containing dissociated-water system is still ambiguous. Among them, methane hydrate dissociation kinetics and guest supersaturated hypothesis for methane hydrate reformation are the primary issues to be addressed. A molecular dynamics simulation system where methane hydrate interacts with surface-hydroxylated silica nanoparticles was established to simulate dissociation process, which is necessary to construct hydrate reformation systems for further microscopic study on hydrate memory effect. The transportation mechanism of methane during hydrate dissociation in sand-containing aqueous system was elucidated. Based on this, hydrate-dissociated systems with methane supersaturated were captured, and molecular dynamics simulations were carried out to further study hydrate reformation mechanism regarding the guest supersaturated hypothesis. By analyzing the distribution and transportation of methane, hydrate clusters, and silica nanoparticles, it can be concluded that the hydrate-like orderly arrangement of methane that are dissolved in the solution or on the surface of nanobubbles are necessary to trigger hydrate memory effect by inducing the reformation of hydrate clusters, while the silica nanoparticles can inhibit the reformation of hydrate clusters by disturbing the arrangement of methane molecules and water molecules. Thence, the microscopic analysis indicated that supersaturated guest molecules is vital to the occurrence of hydrate memory effect and its effect varies between the supersaturated states.

Mechanical force-switchable aqueous organocatalysis

Control over the catalytic activity of artificial catalytic systems in aqueous media is of high interest for biomimetic artificial catalysts. The activity of catalytic systems can be controlled via introducing stimuli-responsive feature in the structure of the catalytic systems. However, temperature, pH or light have been predominantly used as stimulus. Aqueous catalytic system whose activity can be turned ‘ON/OFF’ employing mechanical force has not been demonstrated. Here we show how catalytic activity of an aqueous catalytic system can be switched ‘ON/OFF’ via the application/ceasing ultrasound stimulus. We demonstrate that the accessibility of imidazole, a catalyst moiety, can be modulated via the presence/absence of the ultrasound stimulus, resulting temporal control over the rate of ester hydrolysis reactions in aqueous buffer solution. This generic approach enables using a large range of organocatalysts for the preparation of molecules and/or materials in aqueous media for their application to material science, and in biomedical field.

Effectiveness of magnetite nanoparticles for the removal of DNA of multidrug-resistant Escherichia coli from municipal wastewater.

Water is an important component of life and plays a vital role in human and animal lives, and because of these essential roles of water to life, access to quality water and in adequate quantity becomes imperative. Subsequently, water/wastewater systems have become established as reservoirs of antimicrobial resistance determinants in the environment. In this study, we carried out the synthesis and characterization of magnetite nanoparticles for use in the removal of genomic DNA of antibiotic resistant Escherichia coli isolate in aqueous system. The synthesis of this nanoparticle was achieved by using precipitation method and characterization of the material was conducted by using Fourier transform infrared spectroscopy (FTIR), scanning electron spectroscopy (SEM), electron diffraction spectroscopy (EDS), and vibrating sample magnetometry (VSM). The SEM analysis revealed that this material is spherical in shape, while the FTIR spectra revealed Fe-O vibrational band at ~ 450cm-1 confirming the success of the synthesis of this material. The magnetite nanomaterial showed efficiency for the removal of the bacterial DNA from water with a maximum removal capacity of 45.5ngg-1. The effect of pH (qe max = 55ngg-1 @ pH = 10), time (qt max @ 180min), DNA concentration (DNA concentration of 185ng/mL, qe max = 45.5ngg-1), and adsorbent weight (% adsorption max = 61.65% @ 0.025g) suggest that adsorption conditions influence the removal of DNA by this material. In addition, kinetic study shows that the removal of bacterial DNA obeyed pseudo 2nd order indicating that adsorption process was achieved by bimolecular interaction between magnetite and antibiotics resistant bacterial DNA. We conclude that magnetite nanoparticle appears to be a potential candidate for the removal of nucleic acids and antimicrobial resistance determinants in water/wastewater treatment.

Use of Chitosan-Iron Oxide Gels for the Removal of Cd2+ Ions from Aqueous Solutions.

High-quality water availability is substantial for sustaining life, so its contamination presents a serious problem that has been the focus of several studies. The presence of heavy metals, such as cadmium, is frequently studied due to the increase in the contamination levels caused by fast industrial expansion. Cadmium ions were removed from aqueous solutions at pH 7.0 by chitosan-magnetite (ChM) xerogel beads and chitosan-FeO (ChF) xerogel beads in batch systems. Kinetic studies were best modeled by the Elovich model. The adsorption isotherms obtained showed an inflection point suggesting the formation of a second layer, and the BET model adjusted to liquid-solid systems was adequate for the description of the experimental data. Maximum uptake capacities of 36.97 ± 0.77 and 28.60 ± 2.09 mg Cd/g xerogel were obtained for ChM and ChF, respectively. The studied composites are considered promising adsorbent materials for removing cadmium ions from aqueous systems.

Hydrodynamic Analysis of Polymer–Salt Aqueous Two-Phase Systems in a Millifluidic Channel

Hydrodynamic Analysis of Polymer–Salt Aqueous Two-Phase Systems in a Millifluidic Channel