Precipitation In Aqueous Solution Research Articles

Optimization study for cement-based grout mixture ratio of shield tunnel considering spatiotemporal evolution of grout buoyancy

The grout buoyancy for segments during shield tunnel construction can cause significant floating displacement or even cracking of the segments, and the grout buoyancy is directly related to the grout buoyancy volumetric weight (GBVW). This study proposes an optimization process for the mixture ratio of cement-based grout based on the actual engineering environment. Based on a self-designed GBVW test instrument considering the interaction between grout and strata, this study reveals the evolution law of GBVW and the 3D spatial distribution law of grout buoyancy under different mixture ratios in different strata. Then, this study calculates the segment displacement under slurry buoyancy by the multi-factor coupled numerical calculation model. Research shows that the GBVW in different strata exhibits an evolutionary characteristic of sharp fluctuation-rapid decrease-slow decrease-complete disappearance. The upward precipitation of aqueous solutions in grout in different strata occurs during the stage of GBVW sharp fluctuations, and the decrease in GBVW is mainly accompanied by the seepage of aqueous solutions into the lower strata. The average GBVW and the duration of GBVW in muddy soil are larger than those in silty soil and coarse sand, respectively. An increase in the water binder ratio will reduce the GBVW and accelerate the dissipation of GBVW, while an increase in the bentonite water ratio will promote the growth of GBVW. The lower the strata permeability, the more easily the average GBVW is affected by the water cement ratio. The peak GBVW is more easily affected by the water binder ratio, and the duration of GBVW is more easily affected by the water cement ratio.

Influence of surface interaction between Ag/Mn3O4 on zinc-ion storage performance

Manganese-based compounds, as the most widely used among aqueous zinc-ion batteries cathode materials, have the advantages of high theoretical specific capacity and high voltage. However, their low electrical conductivity and poor cycling stability make them unsuitable for practical applications. Surface modification with metal ions is the most effective and convenient method for improving the situation. Composites deposited with Ag on the surface of Mn3O4 (referred to as AMO) are prepared by the aqueous solution precipitation method. The specific capacity of the AMO-0.5 composite is 423.1 mAh/g at a current density of 0.1 A g−1, and the capacity retention is 87.7% after 1000 cycles at 1.5 A g−1. The surface interaction of AMO improves the intrinsic defects of the material, enhances the electrical conductivity, stabilizes the crystalline structure of the material, and hinders the Jahn-Teller effect. Ag nanoparticles can also inhibit the gas bubbles generated by water decomposition during the cycling process and prevent the dissolution of Mn2+, thus improving the cycling stability. The study on the synergistic mechanism of surface-modified metal nanoparticles can provide inspirations for the development of other similar new materials.

Green synthesis of Co-Ce ZIF derivatives for enhanced O3/PMS degradation of levofloxacin

Antibiotics that permeate aquatic environments present significant risks to both ecosystems and human health. In this study, we employed the techniques of room temperature aqueous solution precipitation to fabricate ZIF-67 derivatives, and established a Co3O4/CeO2/O3/PMS (Co-Ce/OP) system. Furthermore, a 10 mg/L Levofloxacin (LEF) solution could reach rapid degradation (97.2%) and effective mineralization (40.4%) under specific conditions. Subsequent investigations identified the primary active substances, intermediates, and reaction mechanism in the Co-Ce/OP system. Evidence from Electron Paramagnetic Resonance (EPR) and quenching experiments indicates that SO4·-, OH·, O2·- and 1O2 contribute to the degradation process. Applying High Performance Liquid Chromatography-Mass Spectrometry (HPLC-MS), we discovered that the principal degradation mechanisms for LEF encompass the cleavage and subsequent loss of the piperazine, quinolone, and morpholine rings, in addition to decarboxylation and defluorination reactions. Besides, we studied the acute toxicity, bioconcentration factor, developmental toxicity, and mutagenicity of LEF and its intermediate products. Our findings reveal a notable reduction in the toxicity of the intermediate products relative to LEF. Later experiment demonstrates that the degradation rate of LEF sustains above 90% after five cycles of reactions, indicative that the catalyst has excellent recyclability and stability. Furthermore, this study employed experiments across four different natural water matrices, demonstrating the system's considerable potential for effective application within authentic aquatic settings.

Synthesis of magnesium-containing calcium phosphates by methods of chemical precipitation in aqueous solutions and solid-state interaction

The peculiarities of the partial isovalent substitution of calcium atoms by magnesium in the structure of -Са3(РО4)2 within the compositions of Ca10.5–хMgx(PO4)7 (х=0.4, 0.8, 1.0 and 1.5) were investigated by methods of chemical precipitation in aqueous solutions and solid-state interaction. In the first case, the biphasic calcium phosphates (based on Са10(РО4)6(ОН)2 and -Са3(РО4)2) doped with magnesium cations as well as monophasic Ca9.5Mg(PO4)7 and Ca9Mg1.5(PO4)7 (whitlockite-related, trigonal system, space group R-3c) were prepared as a result of mixing aqueous solutions at molar ratios Ca2+:Mg2+:PO43–=(10.5–x):x:7 (where x=0.4, 0.8, 1.0 and 1.5), with further evaporation of water and heating of the solid residue at a temperature of 6000С (for 2 hours). The biphasic calcium phosphates were also obtained by the solid-state interaction of initial components at the temperature range of 500–7000С (for 6 hours) and the same molar ratios Ca2+:Mg2+:PО43–=(10.5–х):х:7 (х=0.4, 0.8, 1.0 and 1.5). It was found that only the apatite-type phase (Са10(РО4)6(ОН)2) contains magnesium, and the content of this phase in the biphasic composites increases with the growing of magnesium amount in the initial mixtures. The established conditions of the formation of single phasic whitlockite-related magnesium-containing calcium phosphates as well as biphasic composites of modified calcium phosphates can be used in the future to obtain bioactive materials for medical purposes.

Effect of manganese addition to Ni-Cu oxides on properties and activity in the oxidation of volatile organic compounds

Transition metal oxides are suitable for the total oxidation of harmful volatile organic compounds. The effect of Mn addition to Ni-Cu oxides was investigated to determine the optimum cation composition for achieving high catalytic performance in the total oxidation of ethanol and toluene, which were chosen as model volatile organic compounds. Single component (Ni, Cu, Mn), binary Ni-Cu, and ternary (Ni-Cu-Mn) oxide catalysts with various Ni:Cu and Ni:Cu:Mn molar ratios were prepared by precipitation of aqueous nitrate solutions followed by calcination at 500 °C in air. The catalysts were characterized by AAS, powder XRD, Raman spectroscopy, N2 adsorption, H2-TPR, and XPS spectroscopy. The addition of Mn to Ni-Cu oxides led to the formation of Ni-Cu-Mn mixed oxides with spinel structure and Ni-Mn mixed oxides (Ni6MnO8, NiMnO3). On the other hand, the Ni-Cu catalysts contained a mixture of NiO and CuO. In the H2-TPR experiments, the Ni-Cu-Mn oxides were reduced at lower temperatures compared to the binary Ni-Cu catalysts. The catalytic performance of Ni-Cu-Mn oxide catalysts was higher than that of the Ni-Cu catalysts. As the Mn concentration increased, the concentration of metal-bound oxygen raised, while the concentration of oxygen vacancies slightly decreased. A linear correlation was revealed between the surface concentrations of oxygen vacancies determined by XPS and specific reaction rates in ethanol and toluene oxidation over the Ni-Cu and Ni-Cu-Mn catalysts. For the Ni-Cu-Mn mixed oxides and the mixture of Ni and Cu oxides, a synergistic effect was found in the oxidation of both model compounds.

Medicinal Plant-Derived Copper Nanoparticles Effectively Manage Early Blight Disease in Tomato: An In vitro Study

Aims: Early blight of tomato (Solanum lycopersicum L.) incited by Alternaria solani is an economically important disease. This paper analyses the efficacy of copper nanoparticles (Cu-NPs) as an alternative to its existing management practices that predominantly rely on toxic fungicides which are potentially harmful to humans and the environment.
 Study Design: The experiment was conducted in a completely randomized block design with 7 treatments viz. T1:Cu-NPs from tulsi leaves, T2:Cu-NPs from neem leaves, T3:Cu-NPs from bael leaves, T4: Cu-NPs from chemical A (prepared from 0.2 M of Cu(NO3)2.3H2O + 0.2 M Ascorbic acid), T5: Cu-NPs from chemical B (0.2 M Cu(NO3)2.3H2O + 0.2 M CuCl2 + 0.4 N NH4OH), T6: Carbendazim 50 WP as check and T7: Control. Each treatment was tested at two levels of in vitro concentrations (i.e. 300 and 500 ppm) and the treatments were replicated thrice.
 Place and Duration of Study: Considering the importance of the disease and for developing an effective management strategy, the present study was carried out in the Department of Plant Pathology, College of Agriculture, Odisha University of Agriculture and Technology, Bhubaneswar during 2020-21.
 Methodology: Stable Cu-NPs were synthesized through three green synthesis methods by using bael (Agel marmelos L.), tulsi (Ocimum sanctum L.), and neem (Azadirachta indica L.) leaves and two chemical synthesis methods (i.e. chemical A and B).
 Results: The size (diameter) of the Cu-NPs from Agel marmelos, Ocimum sanctum, and Azadirachta indica were 427.4, 1,019, and 246.5 nm, and that from the aqueous solution reduction method and precipitation method were 1,537 and 867.8 nm, respectively. The synthesized Cu-NPs were evaluated against Alternaria solani at 300 and 500 ppm while Carbendazim 50 WP served as the standard check. The Azadirachta indica leaf-derived Cu-NPs at 300 and 500 ppm in the in vitro potato dextrose ager (PDA) medium exhibited the maximum mycelial growth inhibition of 60.24% and 75.9%, respectively. The size of Cu-NPs showed an inverse relation with the antifungal efficacy that indicated greater cellular penetration of smaller nanoparticles whereas much lower inhibition of mycelial growth in Carbendazim 50 WP as a check showed the lowest growth inhibition of 39.75% (300 ppm) and 59.03% (500 ppm).
 Conclusion: The results thus indicated higher efficacy of nanoformulations at lower concentrations that can be effectively used for the development of new nano-based plant protection agents against the early blight of tomatoes.

Synthesis and crystal structure of layered molybdate NH4Co2OH(MoO4)2⋅H2O

A new compound NH4Co2OH(MoO4)2⋅H2O was prepared by precipitation of aqueous solutions of cobalt nitrate and ammonium heptamolybdate at pH = 7.5. The crystal structure was identified by X-ray powder diffraction (XRPD) and Rietveld refinement as a known polymorph of layered molybdates (Φy) with general formula AT2OH(MoO4)2⋅H2O (A = NH4+, Na+, K+ and T = Zn2+, Co2+, Cu2+, Ni2+) and refined from a model based on that structure. The lattice parameters were refined with R-3 space group (148) a = 6.1014(2) Å, b = 6.1014(2) Å, c = 21.826(1) Å, α = 90°, β = 90°, and γ = 120°.

Nanoscale Y3AlFe4O12 garnets: Looking into subtle features of crystalline structure and properties formation

Nanoscale Al-doped yttrium-iron garnets attract enhanced scientific and practical interest in the development of microwave devices due to their remarkable physical-chemical properties, which depend essentially on the method and conditions of synthesis. This work highlights the advantages of a specific two-stage synthesis of Y3AlFe4O12 garnet ferrite nanoparticles by the precipitation in aqueous solutions and deals with the detailed examinations of the precipitates obtained during this process. The results of the complex studies using high resolution transmission microscopy, dynamic light scattering and magnetic measurements have allowed assessing the features of the formation of crystalline structure. It is demonstrated that the sequence of the precipitation of components during the synthesis strongly affects the physical-chemical properties of the formed precipitate (filtration coefficient value, surface charge, micelle’s structure) as well as the physical properties of nanoparticles obtained after their heat treatment at 800 °C (saturation magnetization, coercive force). Simultaneous precipitation of Fe(OH)3 and Al(OH)3 metal hydroxides, which form one of three crystallographic sub-lattices of the garnet structure, at the first stage of the synthesis of ferrite-garnets is revealed to provide higher values of filtration coefficient of the formed precipitate and better technological and physical-chemical parameters of the fabricated garnet nanoparticles that makes this method highly advantageous for industrial application.

Transformation of Cu(OH)2 to mesostructural copper-silicate in alkaline silicate solution

Mesoporous materials with high surface area, tunable pore size, and large pore volume have applications in catalysis, adsorption, and optical devices. While the templating method has been used widely to synthesize these materials, removing the organic template leads to energy and chemical waste, and the emission of CO2 greenhouse gas. Here, a new non-organic templating method, based on structural transformation, is proposed to prepare mesostructural copper silicate with a high surface area (425 m2g-1) and large pore volume. This mesostructural transformation is already achieved by hydrothermally treating the Cu(OH)2 crystalline precipitate in an alkaline silicate aqueous solution. The copper silicate platelets obtained from a 5-day hydrothermal treatment in silicate solution have mesopores of about 3.5 nm. For the applications in absorption and catalyst application, the copper silicate has a high absorption efficiency (∼67%) and a fast removal rate toward PH3 gas at 600 ppb and a high-performance catalyst (yield of phenol derivatives about 86%) for the C–O coupling reaction. The mesostructural copper silicate platelets offer a cost-effective and environmentally friendly production method due to their flexible and straightforward preparation process. The synthetic route provides a promising approach to preparing different mesoporous metal silicates.

Laboratory synthesis, spectroscopic characteristics, and conversion relationships of five calcium sulfate double salts relevant to Mars

Calcium sulfate veins have been found in Gale crater and Endeavour crater as indicators of Martian fluid events. The presence of mixed-cation sulfates has been suggested because a wide variety of sulfates containing different cation elements have been detected in in-situ exploration targets (e.g., soils, drilled materials, calcium sulfate veins, and sandstones). In order to establish a spectroscopic library of mixed-cation sulfates, five calcium sulfate double salts (CSDS) were successfully synthesized using high-temperature solid phase reaction and aqueous solution precipitation methods. The phase and homogeneity of these samples were confirmed by X-ray diffraction (XRD). Raman, mid-infrared (MIR), visible and near-infrared (VNIR), and Laser-induced breakdown spectrometry (LIBS) spectra were also collected to study vibrational features and elemental emission properties. All these spectral data are valuable for the mixed-cation sulfate detections by those payloads with similar spectroscopic technologies empolyed on Mars. We also studied the conversion relationships among five CSDS, providing constraints for their origins in sedimentary (e.g., calcium sulfate veins) and volcanic environments on Mars.

Synthesis of stoichiometric hydroxyapatite nanoparticles via aqueous solution-precipitation at 37 °C

Synthesis of stoichiometric hydroxyapatite nanoparticles via aqueous solution-precipitation at 37 °C

Reaction of stoichiometric hydroxyapatite with different crystallinity in Mg<sup>2+</sup> aqueous solution

The reaction of stoichiometric hydroxyapatite (HAp) with different crystallinity in Mg2+ aqueous solution was investigated using X-ray absorption near edge structure (XANES). Crystallinity is one of important factors for the properties of HAp. Therefore, this study aimed to clarify the effect of crystallinity on the behavior of HAp in aqueous solutions. Stoichiometric HAp samples with different crystallinities were prepared using an aqueous solution precipitation method and subsequent calcination. The Mg-K XANES spectra of the HAp pellets after immersing in Mg(NO3)2 aqueous solution were classified into two groups: those of Mg-doped HAp and Mg(OH)2. This difference is caused by the solubility of the HAp pellets in water, owing to their crystallinity. This result provides insights into the reaction mechanism of HAp in the human body and facilitates selection of suitable biomaterials.

Characteristics of nano-sized composites based on rare earth orthoferrites and hematite

Photocatalysts based on orthoferrites of rare earth elements are used to neutralize a number of harmful substances and organic dyes under the influence of visible light, which makes them to promise the introduction of resource-saving water purification technologies. The thermal-gravimetric analysis, X-ray phase analysis, scanning electron microscopy, and energy-dispersive spectroscopy was used to study nanoscale samples of orthoferrites of rare earth elements and hematite obtained by the chemical precipitation of aqueous solutions of inorganic salts of ferrum with lanthanides (La, Er, Sm, Dy, Nd, Yb ) and Y in a weakly alkaline environment and subsequent heat treatment of sediments at 800 and 1100 °C. It was found that during the simultaneous precipitation of hydroxide phases of ferrum and REE, their transformation under the influence of temperature is spatially separated due to the differences in the temperatures of phase transformations and the hydrogen index of the precipitation of precursor phases. It is shown that, depending on the chemical composition of the initial solutions, goethite is formed in the temperature range of 190-250 °C, and the formation of hematite takes place at 425-450 °C. Dehydroxylation of lanthanum hydroxide is observed at 300-330 °С, and the formation of lanthanum oxides continues in the range from 390 to 900 °С. The perovskite phase crystallizes at 960 °C. Using the X-ray phase analysis method, it was established that hematite and a mixture of REE oxygen phases are present in the sediments heat-treated at 800 °C. At 1100 °C, the structure of perovskite and hematite with particle sizes from 25 to 40 nm was identified in the composition of the powders. It was determined that the removal of auxiliary substances takes place at temperatures of 650-770 °C and no impurities of K, Na, S, Cl, or C in the powders fired at 1100 °C. Hematite and perovskite particles are well crystallized and form fragile aggregates, the specific surface area of the samples is several m2/h.

Design and validation of recombinant protein standards for quantitative Western blot analysis of cannabinoid CB1 receptor density in cell membranes: an alternative to radioligand binding methods

BackgroundReplacement of radioligand binding assays with antibody-antigen interaction-based approaches for quantitative analysis of G protein-coupled receptor (GPCR) levels requires the use of purified protein standards containing the antigen. GPCRs in general and cannabinoid CB1 receptor in particular show a progressive tendency to aggregate and precipitate in aqueous solution outside of their biological context due to the low solubility that the hydrophobic nature imprinted by their seven transmembrane domains. This renders full-length recombinant GPCRs useless for analytical purposes, a problem that can be overcome by engineering soluble recombinant fragments of the receptor containing the antigen.ResultsHere we generated highly soluble and stable recombinant protein constructs GST-CB1414–472 and GST-CB1414-442 containing much of the human CB1 receptor C-terminal tail for use as standard and negative control, respectively, in quantitative Western blot analysis of CB1 receptor expression on crude synaptosomes of the adult rat brain cortex. To this end we used three different antibodies, all raised against a peptide comprising the C-terminal residues 443–473 of the mouse CB1 receptor that corresponds to residues 442–472 in the human homolog. Estimated values of CB1 receptor density obtained by quantitative Western blot were of the same order of magnitude but slightly higher than values obtained by the radioligand saturation binding assay.ConclusionsCollectively, here we provide a suitable Western blot-based design as a simple, cost-effective and radioactivity-free alternative for the quantitative analysis of CB1 receptor expression, and potentially of any GPCR, in a variety of biological samples. The discrepancies between the results obtained by quantitative Western blot and radioligand saturation binding techniques are discussed in the context of their particular theoretical bases and methodological constraints.

Modeling of a Continuous Carbonation Reactor for CaCO3 Precipitation

To stop global warming well below 2°C, a rapid decarbonization of our economy, including the industrial sector is required—reaching net-zero GHG emissions in 2050. CO2 mineralization processes, capturing CO2 from industrial point sources and trapping it as carbonate minerals, have the potential to store climate-relevant amounts of CO2. To get there, the potential processes have to be designed and developed, with the help of a process model that can support the process scale-up and optimization. In this work, a process model describing a gas-liquid-solid continuous cristallizer for CO2 absorption into an aqueous ammonium nitrate solution and CaCO3 precipitation has been developed. It consists of the relevant material balances, of a speciation model, and a population balance equation. While several of the model parameters can be obtained from the literature, a few have been estimated by fitting a comprehensive set of experimental data presented earlier. In particular, the process quantities used for parameter estimation are the CO2 mass transfer rate, the calcium carbonate crystallization rate, and the average particle size of the CaCO3 product crystals. The accuracy of the model, particularly in reproducing mass transfer rates and average particle sizes, has been assessed. Interestingly, it has been shown that the dominating mechanism for crystal formation is primary rather than secondary nucleation. The validated model has been used to explore the effect of the different operating conditions on various key performance indicators so as to gain a deeper insight into the process performance and potential. It has been shown that the CO2 absorption efficiency is mainly affected by the feed stoichiometry and the gas feed rate, whereas the CO2 capture and precipitation efficiency are controlled by the liquid phase composition and the residence time; increasing the calcium concentration in the feed is obviously one way to improve the efficiency. Moreover, we could show that the particle size tends to increase with calcium concentration and to decrease with liquid feed rate and supersaturation of the solution.

Effect of stabilizers on Mn ZnSe quantum dots synthesized by using green method

Abstract Herein, the effect of three types of capping polymers, mercaptopropionic acid (MPA), polyethylene glycol (PEG), and starch on the photoluminescence of Mn(2+)-doped ZnSe (ZnSe:Mn) nanoparticles, has been investigated. ZnSe:Mn nanoparticles were successfully prepared with a green method of precipitation in aqueous solutions containing MPA, PEG, or starch as stabilizers. The X-ray photoelectron spectroscopy and Fourier-transform infrared spectroscopy had proved the formation of ZnSe:Mn particles and the interaction between them and the capping agents. The resultant nanoparticles with different capping polymers were identical in optical property; however, photoluminescence quantum yields (PLQY) as well as the photoluminescence lifetime varied by capping agents. Starch-capped ZnSe:Mn nanoparticles had the biggest size compared to others, which was confirmed using transmission electron microscopy, dynamic light scattering, UV-Vis absorbance and Raman spectroscopy. Also, the PL intensity was significantly enhanced with starch-capped ZnSe:Mn nanoparticles. The PLQYs of starch archived 26%, which was 1.23 or 1.8 times lower than that of ZnSe:Mn nanoparticles capping with MPA or PEG, respectively. Furthermore, the highest decline of PL intensity was detected in PEG, which completely diminished in the 19th week, while both MPA and starch endowed ZnSe:Mn nanoparticles with outstanding PL lifetimes diminished over seven weeks.

SYNTHESIS AND INVESTIGATION OF SILVER DOPED ZINC SELENIUM NANOPARTICLES USING MERCAPTOPROPIONIC ACID AS A SURFACTANT FOR MEDICAL APPLICATIONS

The synthesis of silver doped zinc selenium nanoparticles (ZnSe:Ag NPs) in aqueous medium using mercaptopropionic acid (MPA) as a surface stabilizer was carried out with the aim of having potential applications in luminescence and medicine. The optimal percentage of Ag dopant was found to be 1 %. The luminescence properties of the ZnSe:Ag particles was initially evaluated by using UV light. The UV spectrum was used to investigate the absorption of ZnSe:Ag Nanoparticles, and the interaction of ZnSe:Ag/MPA quantum dots with amino acid was investigated to determine the biocompatibility of the particles for applying to potential applications. The results showed that the fluorescence intensity of the particles was effectively improved. The photoluminescence (PL) of quantum dots (QDs) increased significantly as the amino acid concentration increased (Poly-L-Lysine). Moreover, ZnSe:Ag nanoparticles were successfully prepared with a green method of precipitation in aqueous solutions and using MPA as a stabilizer. The X-ray photoelectron spectroscopy and fourier-transform infrared spectroscopy had proved the formation of ZnSe:Ag particles and the interaction between them and the MPA stabilizer. TEM image was used to measure the size of the ZnSe:Ag (1 %) luminescent nanoparticles synthesized by green method. Besides, the XPS spectrum shows elements present in the ZnSe:Ag nanoparticle crystals.

Recovery of Model Pharmaceutical Compounds from Water and Organic Solutions with Alginate-Based Composite Membranes.

In this work, we combined the non-solvent induced phase separation (NIPS) and further cross-linking by cations towards the preparation of nanofiltration membranes based on sodium alginate, a biodegradable, natural polymer. Acetone, ethanol, toluene, and hexane were used as non-solvents, and cations of calcium, silver, and aluminum—for polymer cross-linking, respectively. Results showed the precipitation strength of non-solvent played a noticeable role in the membrane’s performance; for instance, the toluene permeability changed by four orders of magnitude with the decrease of precipitation strength of the non-solvent: acetone (Ptoluene = 0.1 kg∙m−2∙h−1∙bar−1) < ethanol (3 kg∙m−2∙h−1∙bar−1) < hexane (41 kg∙m−2∙h−1∙bar−1) < toluene (415 kg∙m−2∙h−1∙bar−1). It was shown that simultaneous precipitation and crosslinking in aqueous solutions AlCl3 or AgNO3 must be used in the preparation of alginate membranes for the highly selective recovery of pharmaceutical compounds from organic media. These membranes show rejection R = 90–93% of substances with MW = 626 g/mol and ethanol permeability PEtOH = 1.5–2.5 kg∙m−2∙h−1∙bar−1. For the highly selective recovery of pharmaceutical compounds from water, the method of obtaining membranes must be changed. Precipitation in toluene and then crosslinking in aqueous solutions of AlCl3 or AgNO3 must be used sequentially instead of simultaneous precipitation and crosslinking in aqueous solutions of the same inorganic salts. The permeability of such membranes varied from 0.44 to 7.8 kg∙m−2∙h−1∙bar−1 depending on the crosslinking cation in the alginate. The rejection of model substances with MW 350 and 626 g/mol were on the level of 99%. Alginate membranes can be used to solve separation problems in the pharmaceutical field, for example, to isolate antibiotics from their extractants and remove the same antibiotics from aqueous pharmaceutical waste to prevent their accumulation in the environment and the emergence of resistant genes and bacteria.

Thermodynamic and Kinetic Studies on the Conversion of Solvent-Shared to Contact Ion Pairs in Sparingly Soluble MF2 (M = Mg2+ and Ca2+) Aqueous Solutions: Implications for Understanding Supersaturated Behavior and Association Constant Determination.

The thermodynamic and kinetic behaviors of Mg2+-F- ion pairing in aqueous solution are investigated theoretically and experimentally and are contrasted to those of Ca2+-F-. Thermodynamically, similar to CaFx(H2O)142-x (x = 1 and 2), MgF(H2O)y+ (y = 14-20) contact ion pairs (CIPs) are more stable than their solvent-shared ion pairs (SSIPs), whereas the CIPs and SSIPs of MF2(H2O)y are almost isoenergetic. However, in kinetics, the conversion of SSIPs to CIPs for M2+-F- (M = Mg2+ and Ca2+) ion pairing must overcome a high energy barrier due to the strong hydration of Mg2+ and F-. The kinetics dominate after the thermodynamics and kinetics are balanced, which hinders the formation of M2+-F- CIPs in practical MF2 aqueous solutions (less than or equal to saturated concentrations). This result is also supported by the 19F nuclear magnetic resonance spectra of saturated MF2 solutions. Although the interaction between Mg2+ and F- is slightly stronger than that between Ca2+ and F- due to the smaller radius of Mg2+, the formation of Mg2+-F- CIPs needs to go through two rate-limiting steps, the dehydration and entrance of F- (i.e., via exchange mode) with a higher energy barrier, due to the ability of strongly bound water molecules and rigorous octahedral coordinated configuration of Mg2+, while the formation of Ca2+-F- CIPs only goes through a single rate-limiting step, the entrance of F- (i.e., via swinging mode) with a lower energy barrier, due to the flexible coordination configuration of Ca2+. This is responsible for precipitation in MgF2 aqueous solution requiring a larger supersaturation degree and a lower precipitation rate than in CaF2. These kinetic factors lead to the association constants previously reported for MF+ determined by a fluoride ion-selective electrode (ISE) combined with the titration method, where the MF2 solutions were always unsaturated at the titration end point, which actually corresponds to those of the ligand process going from completely free M2+ and F- to their SSIPs. A possible strategy to accurately determine the association constants of MF+ and MF2(aq) CIPs by fluoride ISEs is proposed. The present results suggest that judging the formation of M2+-F- CIPs in practical solutions from a theoretical calculation perspective requires significant consideration of the kinetic factors, except for the thermodynamic factors.

Brevundimonas diminuta isolated from mines polluted soil immobilized cadmium (Cd2+) and zinc (Zn2+) through calcium carbonate precipitation: Microscopic and spectroscopic investigations

The toxic metal(loid)s TMs resistant bacterium Brevundimonas diminuta was isolated for the first time from mines polluted soil in Fengxian, China, and assessed for its potential for Cd and Zn precipitation in Cd and Zn co-contaminated aqueous solution at various Cd and Zn levels (20, 40, 80, 160, and 200 mg L−1), pH values (5, 6, 7, 8, and 9), and temperatures (20, 25, 30, and 35 °C). B. diminuta showed a high resistance to both Cd and Zn and was able to precipitate up to 99.2 and 99.7% of dissolved Cd and Zn respectively, at a pH of 7 and temperature of 30 °C. B. diminuta reduced the dissolved concentrations of Cd and Zn below the threshold levels in water. The 3D-EEM analysis revealed the presence of extracellular polymeric substances (EPS) such as tryptophan indicating bacterial growth under Cd/Zn stress. FTIR showed polysaccharides, CO32−, CaCO3, PO43−, and proteins, which may enhance bacterial growth and metal precipitation. SEM-EDS confirmed the leaf-like and granular shape of the biological precipitation and reduction in the percent weight of TMs, which promoted the adhesion/adsorption of Cd2+, Zn2+, and Ca2+. Moreover, XRD analysis confirmed the precipitation of Cd, Zn, and Ca in the form of CdCO3/Cd3(PO4)2, ZnCO3/ZnHPO4/Zn2(OH)PO4/Zn3(PO4)2, and CaCO3/Ca5(PO3)4OH, respectively. These findings indicate that Brevundimonas diminuta can be used for the bioremediation of TMs-contaminated aquatic environments.