Aqueous Solution Phase Research Articles

A Nanofiltration Membrane Preparation Process Based on Polyethyleneimine Diffusion Modulation and Surface Modification

ABSTRACTNanofiltration (NF) membranes play a huge role in industrial manufacturing with their unique selective permeability. Membrane material and structure are the main factors affecting the effectiveness of NF separation. Typically, NF membranes are produced by interfacial polymerization (IP). Therefore, control of the IP process is particularly important. This work provides a NF membrane preparation process by combining internal modulation of the separation layer and surface modification. The diffusion of polyethyleneimine (PEI) molecules is accelerated by the introduction of ethanol and cetyltrimethylammonium bromide into the PEI aqueous phase solution, resulting in the formation of a loose interior. In addition, the high selectivity is maintained by high molecular weight PEI modifying. After optimizing the process, the NF membrane permeate flux and selectivity can be increased compared to the blank group (MgCl2 desalination from 90% to 97%, permeate flux from 17 to 35 L m−2 h−1). The resulting PEI/TMC NF membranes also show excellent separation properties in mixed salt applications for magnesium‐lithium separation.

Constructing positively charged hollow fiber nanofiltration membranes with high performance for the treatment of wastewater containing heavy metal ions

The presence of heavy metal ions in wastewater has been identified as a significant environmental and human health concern. Positively charged hollow fiber (HF) Nanofiltration (NF) membranes show great promise and excellent potential for the removal of heavy metal ions due to Donnan exclusion effect. Nevertheless, the current limitations of positively charged HF NF membranes, including complex preparation process, low flux and poor selectivity, continue to impede their broader implementation. In this work, a high flux HF NF membrane with positively charged surface was fabricated via doping piperazine in the aqueous-phase solution of polyethyleneimine to modulate the interfacial polymerization and to adjust the structure of the subsequent polyamide skin layer. Subsequently, the surface of this nascent skin layer was modified with diethylenetriamine/ethanol solution to increase its positive charge density, and thus to improve the rejection of multivalent cations. The optimal HF NF membrane shows a pure water permeability of 160 LMH/MPa and a MgCl2 rejection of higher than 97 %. In addition, it shows a rejection of higher than 95 % for heavy metal salts such as CoCl2, MnCl2, NiCl2, CuCl2 and Cr2(SO4)3, and a rejection of more than 98 % for antibiotics such as tetracycline hydrochloride, oxytetracycline and levofloxacin. It also possesses good resistance to acid and contamination. In addition, the optimal HF NF membrane has been successfully scaled up to a module of 20 filaments and still shows excellent separation performance, suggesting its vast potential for industrial application.

Antisolvent crystallization of rare earth sulfate hydrates: Thermodynamics, kinetics and impact of iron

The thermodynamics and kinetics of ethanol antisolvent crystallization of rare earths from sulfate solutions has been explored, with a view towards separating the rare earths as part of a NdFeB magnet recycling process. The solubility of single and binary metal (Nd, Pr, Fe) phases in aqueous ethanol solutions has been determined. The impact of Fe and Pr on the crystallization of Nd is evaluated, the oxidation kinetics of Fe(II) to Fe(III) quantified, and the influence of Fe oxidation state on the thermodynamics and kinetics of crystallization investigated. Oxidation to Fe(III) is slow, with a half life of approx. 600 h. For pure Nd, the solubility of the obtained, stable sulphate octahydrate decreases exponentially with increased molar organic:aqueous (O/A) ratio, and is well described by the OLI model until O/A=0.2. Pr crystallizes as an isostructural octahydrate with similar solubility. Fe(II) precipitates as a mixed solid phase, with a solubility approximately 40 times higher than the rare earths at O/A=0.2. Fe(III) solutions exhibit liquid–liquid phase separation without precipitation at all evaluated concentrations. Nd and Pr coprecipitate together in proportion to their relative concentrations, with Pr precipitating at concentrations well below its pure component solubility. Fe(II) does not precipitate with Nd at O/A≤0.2 even at high concentration, with significant precipitation as separate particles at higher O/A for all concentrations. The crystallization kinetics and the morphology of the Nd phase is affected by the Fe oxidation state. The work highlights the potential of antisolvent crystallization for selective and efficient separation of REE from Fe.

Interfacial polymerization modulated by COFs interlayer to fabricate efficient mono/divalent ions separation nanofiltration membrane

Thin-film composite (TFC) membranes have been recently applied in the mono/divalent ions separation, which is essential for resource recycle, wastewater treatment, and lithium resource extraction. However, the TFC membranes fabricated between the polyethyleneimine (PEI) and trimesoyl chloride (TMC) usually show a low water permeance. Herein, piperazine (PIP) is added in the PEI aqueous phase solution to fabricate a polyamide (PA) layer for the enhancement of water permeance. Meanwhile, the diffusion rate of PIP to the two-phase interface is reduced by the hydrogen bond effect between PIP and MPDTp COFs interlayer, which can weaken the reaction of PIP and TMC and maintain a high ion rejection. Pure water permeance of the obtained PA-PIP/Fe-COF/PES membrane is 16.1 L m−2 h−1 bar−1, and the Li+/Mg2+ separation factor is 73.0, which is almost two times higher than the PA-PIP/PES under Li+/Mg2+ mass ratio of 1:20. Besides, the membrane also keeps satisfactory performance in Na+/Mg2+, Cl−/SO42−, Na+/Ca2+ separation, and ten days of long-term testing. Therefore, this work raises a new strategy to prepare a high-efficiency mono/divalent ions separation nanofiltration membrane.

Interpenetrating Polymer Network Capturing FRET-Sensitive Polymers Available for an Enzyme Assay.

Fluorogenic glycomonomers have been used for biological evaluations, and water-soluble and Förster resonance energy transfer (FRET)-sensitive glycopolymers have also been reported. A FRET-sensitive polymer was conveniently prepared from a fluorogenic donor monomer and a fluorogenic acceptor monomer by means of simple radical polymerization in high yield. Continuous fluorospectroscopic monitoring of the polymer in the presence of an enzyme was performed, and the results showed the possible application of the FRET-sensitive glycopolymer for practical use. In addition to the use of aqueous solution phase, the water-soluble and FRET-sensitive glycopolymer was completely captured into an interpenetrating polymer network (IPN) by means of radical polymerization with a combination of acrylamide and bis-acrylamide as used for the cross-linking reagent system. The IPN including the FRET-sensitive glycopolymer was allowed to react with amylases in an aqueous buffer solution at 37 °C, and the enzymatic reaction was continuously and conveniently monitored by means of fluorometric spectroscopy.

Quantification and analyses of seven tyrosine kinase inhibitors targeting hepatocellular carcinoma in human plasma by QuEChERS and UPLC-MS/MS

Tyrosine kinase inhibitors (TKIs) are commonly used to treat various cancers. Literature suggests that the blood concentration of TKIs strongly correlates with their efficacy and adverse effects. Therefore, establishing a Therapeutic Drug Monitoring (TDM) methodology for TKI drugs is crucial to improving their clinical efficacy and minimizing the treatment-related adverse effects. However, quantifying their concentrations in the plasma using existing methods to avoid potential toxicity is challenging. Herein, seven TKIs, namely sorafenib tosylate, axitinib, erlotinib, cediranib, brivanib, linifanib, and golvatinib, were successfully analyzed in human plasma by following a quick, easy, cheap, effective, rugged, and safe (QuEChERS) pretreatment method combined with ultra-high performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS). Briefly, biological samples were extracted using 1 mL of methanol, followed by the sequential addition of 250 mg of anhydrous magnesium sulfate and 25 mg of N-propylethylenediamine (PSA) for salinization and purification by adsorption, respectively. In this study, dovitinib was used as the internal standard. The seven TKIs were detected by the gradient elution method for 4 min in the positive ion electrospray mode. The mobile phase comprised methanol (phase A) and 0.1 % aqueous formic acid solution (phase B) on the Agilent Zorbax RRHD Stablebond Aq, (2.1 × 50 mm; 1.8 μm). Brivanib, linifanib, axitinib, sorafenib tosylate, and golvatinib exhibited good linearity in the range of 5–500 ng/mL, and erlotinib and cediranib exhibited good linearity in the range of 10–1000 ng/mL, with linear correlation coefficients (R2) ≥ 0.99. The limits of detection and quantification were 0.60–0.18 ng/mL and 5–10 ng/mL, respectively. The intraday and interday accuracy values ranged from −6.12 % to 7.31 %, with a precision (RSD) of ≤ 10.57 %. The method was rapid, accurate, specific, simple, reproducible, and suitable for the quantitative determination of the seven TKIs in human plasma.

Simultaneous Determination of 17 Phenolic Compounds in Surface Water and Wastewater Matrices Using an HPLC-DAD Method

A high-performance liquid chromatography with diode array detector (HPLC-DAD) analytical method was developed for the simultaneous detection of 17 phenolic compounds, including phenols, chlorophenols, alkylphenols, and nitrophenols, in two types of water matrices: wastewater and surface water. Prior to HPLC-DAD determination, a solid-phase extraction (SPE) procedure was optimized. The proposed method uses multiwavelength analysis, with the optimum detection wavelengths selected as 268 nm, 280 nm, 386 nm, 304 nm, and 316 nm. The highest resolution was achieved using a chromatographic column, Eclipse XDB-C18 (150 × 4.6 mm, 5 μm), which was kept at 20 °C. The mobile phase consisted of a gradient elution program, with mobile phase A being a 0.1% H3PO4 aqueous solution and mobile phase B being acetonitrile. The flow rate was set at 0.6 mL/min. The 17 target phenolic compounds were fully separated in less than 27 min. All compounds showed good linear regression, with correlation coefficients higher than 0.999. The method’s quantitation limits ranged from 4.38 to 89.7 ng/L for surface water and 7.83 to 167 ng/L for wastewater. The recovery rates were in the range of 86.2–95.1% for surface water and 79.1–86.3% for wastewater. The SPE-HPLC-DAD method was proven to be fast, sensitive, accurate, and reproducible. The developed method was successfully applied for the analysis of the 17 phenolic compounds in real surface water and wastewater samples, with phenol, 2,4-DNP, and 2,4-DNP being determined at levels greater than the method’s limits of quantitation (LOQs). The proposed analytical method represents an original technical resource for the simultaneous determination of 17 phenolic compounds in environmental water matrices.

The electronic, structural and nonlinear optical properties of licochalcone L in the aqueous solution and gaseous phase: A DFT study

In the present article, various conformers of licochalcone L, a chalcone derivative extracted from the G. inflata root, have been analyzed in the aqueous solution and gaseous phase using calculation based on density functional theory (DFT). Nonlinear optical parameters such as dipole moment (μ), mean polarizability (α), polarizability anisotropy (Δα) and the first order hyperpolarizability (β) have been estimated to examine the NLO properties of the title molecule. These parameters were found to be significantly higher than those of standard molecules, indicating the potential NLO applications of licochalcone L. The analysis of natural bond orbitals (NBO) has been carried out to characterize various intramolecular interactions. The nucleus-independent chemical shift (NICS) technique has been used to investigate the aromaticity. Further, the pKa values have been computed for each hydroxyl group, revealing that the neutral form predominates at physiological pH, while the monoanionic form becomes predominant at pH greater than 9. The impact of solvation on the molecular electrostatic potentials and frontier molecular orbitals has been investigated for the neutral as well as monoanionic form of licochalcone L. A variety of global chemical reactivity descriptors have been calculated to highlight the structure-activity relationship.

In-situ construction of covalent organic frameworks membrane via interfacial polymerization and crosslinking modification using trimesoyl chloride for organic solvent nanofiltration

Organic solvent nanofiltration (OSN) is a modern technology for separating and purifying organic solvents. It has the advantages of both low energy consumption and low environmental pollution. In this work, we utilized an oligomer triggered interfacial polymerization (OT-IP) method and followed by a post-IP modification using trimesoyl chloride (TMC) to synthesize a kind of covalent organic frameworks (COFs)/TMC membrane. This process involves pre-mixing both COFs monomers in a same organic solvent to form oligomers, followed by conducting an IP reaction at the interface between the organic solvent phase and an aqueous phase solution containing acetic acid as a catalyst. Subsequently, a surface modification is conducted using TMC n-hexane solution, which effectively manipulates the surface hydrophilicity, average size, solute rejection, solvent permeance and solvent resistance of the membrane. Afterward, crosslinking and solvent activation are performed to improve its solvent resistance and separation permeance. The optimized OSN membrane exhibits an ethanol permeance of 72.5 L m−2 h−1 MPa−1 with an RDB rejection of 98.4 %. Its surface roughness is as low as 3.4 nm. Furthermore, it has high permeance for both polar solvents (MeOH permeance of 176.7 L m−2 h−1 MPa−1) and weakly polar solvents (EtOAc permeance of 183.0 L m−2 h−1 MPa−1). Moreover, the optimized OSN membrane demonstrates excellent solvent resistance and excellent catalyst recovery performance. Therefore, this work presents a promising avenue for the application of COFs in OSN membranes.

Prediction of the univariant two-phase coexistence line of the tetrahydrofuran hydrate from computer simulation.

In this work, the univariant two-phase coexistence line of the tetrahydrofuran (THF) hydrate is determined from 100 to 1000bar by molecular dynamics simulations. This study is carried out by putting in contact a THF hydrate phase with a stoichiometric aqueous solution phase. Following the direct coexistence technique, the pressure is fixed, and the coexistence line is determined by analyzing if the hydrate phase grows or melts at different values of temperature. Water is described using the well-known TIP4P/Ice model. We have used two different models of THF based on the transferable parameters for phase equilibria-united atom approach (TraPPE-UA), the original (flexible) TraPPe-UA model and a rigid and planar version of it. Overall, at high pressures, small differences are observed in the results obtained by both models. However, large differences are observed in the computational efforts required by the simulations performed using both models, being the rigid and planar version much faster than the original one. The effect of the unlike dispersive interactions between the water and THF molecules is also analyzed at 250bar using the rigid and planar THF model. In particular, we modify the Berthelot combining rule via a parameter ξO-THF that controls the unlike water-THF dispersive interactions. We analyze the effect on the dissociation temperature of the hydrate when ξO-THF is modified from 1.0 (original Berthelot combining rule) to 1.4 (modified Berthelot combining rule). We use the optimized value ξO-THF = 1.4 and the rigid THF model in a transferable way to predict the dissociation temperatures at other pressures. We find excellent agreement between computer simulation predictions and experimental data taken from the literature.

Tannic acid etched ZIF-8 incorporated thin-film nanocomposite nanofiltration membrane with enhanced performance

Incorporating functionalized nanomaterials in the selective layer of conventional polyamide nanofiltration (NF) membrane is a promising strategy for overcoming the trade-off between permeability and selectivity. Highly hydrodispersible TA/ZIF-8 composite nanomaterials were prepared by etching ZIF-8 with tannic acid, and the thin-film nanocomposite (TFN) NF membranes were prepared by introducing TA/ZIF-8 into the interfacial polymerization aqueous phase solution. The nanomaterials and NF membranes' structure, chemical composition, and hydrophilicity were comprehensively characterized. The influence and mechanism of introducing TA/ZIF-8 into the polyamide layer on the separation performance of the TFN membranes were discussed by separating typical mono- and divalent salts. The optimal TFN membrane had a water flux of 26.59 LMH-bar−1 (increased by 86.6% than that of the TFC-blank membrane) with 94.95% rejection of Na2SO4 while having good antifouling performance and stability. Furthermore, the inverse size exclusion phenomenon of chlorine-contained salts was explored through relevant control experiments. This work is valuable for expanding the application of 3D nanomaterials in membrane separation technology and preparing high-performance TFN nanofiltration membranes.

Acid-responsive polydiacetylene-Na+ assemblies with unique red-to-blue color transition

Polydiacetylenes (PDAs), conjugated and stimuli-responsive polymers, are of interest for colorimetric sensing technologies. Commercially available PDAs with carboxylic headgroup do not show any colorimetric response to acid. To achieve acid-responsive property, the headgroups of PDAs are often modified with some functional moieties, involving complicated synthetic processes. This contribution presents a facile approach to develop acid-responsive materials via co-assembly of PDA and excess sodium hydroxide (NaOH). After low-temperature incubation and photopolymerization, the mixtures of 10,12-tricosadiynoic acid (TCDA) and NaOH develop into red-phase poly (TCDA-Na+) assemblies. A unique red-to-blue color transition occurs when the poly (TCDA-Na+) assemblies are exposed to hydrogen chloride (HCl) acid both in aqueous solution and gas phase. Increasing the concentrations of NaOH and TCDA monomer during the self-assembly process affects the molecular organization and morphologies of the resultant poly (TCDA-Na+) assemblies, which in turn govern the sensitivity to acid. The results of this study offer a simple and inexpensive method for developing acid-responsive PDAs, extending their colorimetric sensing applications.

Isothermal compressibility, internal pressure studies of aqueous rare earth nitrate solutions at 298.15 K: An attempt to estimate ionic radii and understand inner– and outer–sphere exchange water structural interactions

In this communication, we report our analysis and results concerning the determination of ionic radii in aqueous solution phase for Lanthanum (La+3), Neodymium (Nd+3), Erbium (Er+3) and Ytterbium (Yb+3) ions in presence of nitrate (NO3-) anion at 298.15 K. The literature data for density, adiabatic compressibility, and specific heat capacity of solutions at constant pressure have been used to compute isothermal compressibility, internal pressure of solutions in limiting concentration range. The apparent molar isothermal compressibility of electrolytes and hydration numbers have been obtained. The electrostriction for rare earth cations and intrinsic volumes have been calculated using thermodynamic equations. The ionic radii of cations have been obtained using the ionic partial molar volume data of NO3- ions and the results are compared with those obtained for rare earth chlorides. The two series affect is also observed for ionic radii and internal pressure. The results have been explained on the basis of water structural effects due to electrostatic field and water dipole interaction between the inner– and outer–sphere water exchange reaction.

Development of a dispersive liquid-liquid microextraction method for the determination of plastic additives in seawater.

A method using dispersive liquid-liquid microextraction (DLLME) prior to high performance liquid chromatography-diode array detection (HPLC-DAD) was developed to determine seven additives from the plastics industry (butylated hydroxytoluene, diisodecyl phthalate, irgafos 168, lawsone, quercetin, triclosan and vitamin E) in seawater samples. These compounds can reach seawater due to direct discharge from wastewater treatment plants and leaching from plastics and microplastics. The extraction was performed using 25 mL of seawater, 500 μL of 1-octanol (extraction solvent) and a stirring step instead of dispersive solvent. Additive concentrations were determined by LC-DAD on a C18 column with a mobile phase of acetonitrile and phosphoric acid aqueous solution (pH 3.5) by gradient elution. The analytical recoveries ranged from 82 to 93% for all compounds, except for lawsone (60%). Repeatability and intermediate precision were adequate with RSD < calculated values following the Horwitz equation at the concentration levels evaluated (0.06 and 0.24 mg L-1). All additives exhibited linear matrix calibration curves (R2 > 0.99). Detection limits ranged from 0.009 to 0.028 mg L-1 and quantification limits ranged from 0.027 to 0.084 mg L-1. Finally, the application of the method to real samples verified the method as accurate and applicable to seawater.

Greener synthesis of thin-film nanocomposite membranes with varied nanofillers for enhanced organic micropollutant removal

Nowadays, the green process in membrane science is essential for industrial applications. The nanofiltration (NF) membrane developed by a green approach with effective separation of micropollutant from aqueous media makes it possible. Here, we designed a series of thin-film nanocomposite membranes prepared with structurally and morphologically different nanofillers, such as graphene oxide (GO)–NH2, arginine (Arg)-MMT and cloisite (C) MMT-NH2. The vapour-phase interfacial polymerisation (VP-IP) process is used to prepare highly selective and permeable thin-film nanocomposite (TFN) membranes. The polymerization reaction was done on the surface of the polysulfone (PSf) support membrane between an aqueous phase solution of 3,5-diaminobenzoic acid (DABA) and vapours of trimesoyl chloride (TMC). The nanomaterials' and prepared membranes' chemical and physical properties were determined using different characterization techniques. The TFN membranes (TFN-1, TFN-2 and TFN-3) prepared using three different nanomaterials (GO-NH2, Arg-MMT, CMMT-NH2) were compared for their separation against pharmaceutical compounds sulfamethoxazole (SMZ), triclosan (TRI), diclofenac (DIC) and cephalexin (CEP). The membranes demonstrated good hydrophilicity and antibacterial activity, resulting in a reasonable permeate flux rate. The fabricated membranes showed excellent selectivity for pharmaceutical compounds. Still, the TFN-3 membrane embedded with CMMT-NH2 nanomaterial recorded the highest rejection rate (> 99%) compared to the TFN-2 (Arg-MMT) and TFN-1 (GO-NH2) membranes. In contrast, the permeate flux rates for the individual TFN membranes showed slight variation. The developed TFN membranes via green and sustainable vapour-phase interfacial polymerization process demonstrated the possibility of being utilized for removing organic micropollutants from water to prevent the terrible devastation of our environment and aquatic systems.

Advanced ion separation in polyamide nanofiltration membranes via interfacial polymerization regulated by dynamic polyphenol-metal coordination

Developing advanced nanofiltration membranes (NFMs) for inorganic salt ions separation remains a significant challenge in the value-added process of water treatment. Herein, we engineered a highly permeable-selective TA/Fe/Ca/PA-p NFM through a novel strategy for the interfacial polymerization (IP) regulated by the dynamic polyphenol-metal coordination. Interestingly, the dynamic coordination occurred after the substrate surface was first modified with tannic acid (TA) and Fe3+ and then coated with an aqueous phase solution containing piperazine (PIP) and Ca2+. In this process, the coordination competition between Fe3+ and Ca2+ for TA and the conversion of TA/Fe3+ bis-complex into tris-complex were conducive to forming more uniform TA/Fe/Ca complex on the substrate surface. Meanwhile, TA can also perform Michael addition with PIP to control the diffusion of PIP to the organic phase. Following the IP reaction, the nascent TA/Fe/Ca/PA NFM underwent post-treatment in a sodium citrate (SC) solution to dissociate the TA/Fe/Ca complex by further applying the dynamic coordination, resulting in a crumpled and thinner separation layer with desirable surface properties. The optimized TA/Fe2/Ca/PA-p NFM exhibited a pure water permeability of 36.1 L m−2 h−1⋅bar−1, nearly 2.4 times higher than that of the original PA NFM. Correspondingly, the Na2SO4 rejection reached 99.4 % and its Cl−/SO42− separation factor was 118.3. This outstanding permselectivity was mainly attributed to the decreased mass transfer resistance, the expanded effective permeability area, and the increased negative charge on the membrane surface. Additionally, the TA/Fe2/Ca/PA-p NFM was endowed with good operational stability, pressure resistance, and antifouling performance. This eco-friendly and cost-effective approach paves the way for fabricating high-performance NFMs and demonstrates the great potential of dynamic polyphenol-metal coordination in water treatment.

Tailoring Properties of Hyaluronate-Based Core-Shell Nanocapsules with Encapsulation of Mixtures of Edible Oils.

Dispersions of core-shell nanocapsules (nanoemulsion) composed of liquid oil cores and polysaccharide-based shells were fabricated with emulsification using various mixtures of edible oils and amphiphilic hyaluronate derivatized with 12-carbon alkyl chains forming the shells. Such nanocapsules, with typical diameters in the 100-500 nm range, have been previously shown as promising carriers of lipophilic bioactive compounds. Here, the influence of some properties of the oil cores on the size and stability of the capsules were systematically investigated using oil binary mixtures. The results indicated that, in general, the lower the density, viscosity, and interfacial tension (IFT) between the oil and aqueous polymer solution phases, the smaller the size of the capsules. Importantly, an unexpected synergistic reduction of IFT of mixed oils was observed leading to the values below the measured for individual oils. Such a behavior may be used to tailor size but also other properties of the nanocapsules (e.g., stability, solubility of encapsulated compounds) that could not be achieved applying just a single oil. It is in high demand for applications in pharmaceutical or food industries and opens opportunities of using more complex combinations of oils with more components to achieve an even further reduction of IFT leading to even smaller nanocapsules.

Construction of highly permeable organic solvent nanofiltration membrane via β-cyclodextrin assisted interfacial polymerization

As the key of organic solvent nanofiltration (OSN) technology, OSN membranes could effectively retain small molecules with molecular weight between 200 and 1000 Dalton (Da), but they still face some problems such as low solvent permeance. In this work, we fabricated a poly(amide-ester) selective layer on polyimide substrate surface by introducing β-cyclodextrin (β-CD) into the aqueous phase solution to assist the interfacial polymerization reaction between m-phenylenediamine (MPD) and trimesoyl chloride (TMC), followed by cross-linking and solvent activation treatment. Thus, we successfully fabricated a kind of thin film composite (TFC) membrane with high selective permeability for OSN. We emphasized that extra-low contents were employed for both MPD and β-CD, which were 0.05 wt% and 50 mg L−1, respectively. The effect of β-CD content on the pore size, surface shape, surface hydrophilicity, surface chemistry, filtration performance, as well as durability performance of the OSN membrane was studied in depth. β-CD endows the selective layer with better hydrophilicity and larger pore size. The optimized OSN membrane possesses a Rhodamine B (RDB, 479 Da) rejection of 99.2 % and an ethanol permeance of 70.6 L m−2 h−1 MPa−1. Furthermore, the optimized OSN membrane remains above 99 % RDB rejection after being immersed in DMF at 25 °C for 1000 h, which demonstrates its superb solvent resistance. Additionally, the optimized OSN membrane exhibits outstanding long-time performance and possesses a rejection of 98 % for Jacobsen catalyst during more than 106 h semi-continuous filtration using Jacobsen catalyst/ethyl acetate solution as feed, indicating its vast potential in the recovery of catalyst.

Investigation of pH-switchability of hydrophobic deep eutectic solvents for the extraction and preconcentration of triazine herbicides in water samples

An environmental friendly, fast, easy, inexpensive and dispersive-solvent-free liquid–liquid microextraction (LLME) based on pH-switchable hydrophobic deep eutectic solvent (HDES) procedure was developed and combined with high performance liquid chromatography–ultraviolet (HPLC − UV) detection for the extraction and analysis of triazine herbicides in water samples. In this method, 10 different DESs were prepared and then their pH-switchability was investigated. DESs that could be switched with pH were employed for separation and preconcentration of triazine herbicides in water samples. In this method, dispersing the extractant phase in the aqueous solution and subsequent phase separation is done only by changing the pH. Important parameters affecting extraction, such as type of DES and its volume, concentration of KOH, volume of HCL, effect of salt and extraction time were investigated and optimum conditions were obtained. In optimized conditions, the values of relative standard deviations (RSDs) for intra-day and inter-day of the procedure based on seven replicate analysis of 100 μg L–1 of triazines in water samples were 1.9–4.4 and 2.7–6.2%, respectively. The calibration graphs were linear ranging from 0.5 to 350 μg L–1 with correlation coefficients (r2) better than 0.990. The limit of detections (LODs) and limit of quantifications (LOQs) were 0.2–0.5 and 0.5–1.5 μg L–1, respectively. The relative recoveries (RRs) of real water samples which have been spiked with different levels of triazines were 91–107.8%.

Complexes of 1,10-phenanthroline-mono-N-oxides with copper(II) and nickel(II) in aqueous solution and solid phase

Thorough equilibrium and spectroscopic studies are reported on the complexes formed between copper(II) or nickel(II) and derivatives of phenanthroline-mono-N-oxides (1,10-phenanthroline-1-N-oxide (phenO), 2,9-dimethyl-1,10-phenanthroline-1-N-oxide (DMPO) and 3,4,7,8-tetramethyl-1,10-phenanthroline-1-N-oxide (TMPO)). PhenO exhibits excellent metal binding ability, both copper(II) and nickel(II) form bis complexes in which the ligands coordinate to the metal ions via the (N,O) donor set. In the case of copper(II), a square-pyramidal complex forms, where the phenO-s coordinate at the corners of the square and the remaining site is occupied by the water molecule. The bis complex formed between nickel(II) and phenO possesses square-planar geometry in solution, however, the Ni(II) ion exhibits a distorted octahedral geometry in solid phase. DMPO forms relatively stable complexes with copper(II), but the coordination of this ligand to nickel(II) could not be confirmed. Because of precipitate formation in the entire studied pH range (pH = 2.0 – 11.0), well defined complexes could not be identified in the copper(II) – TMPO system. In contrast, this ligand forms stable water soluble nickel(II) complexes. The noted selectivity of these ligands in complex formation reactions is explained by considering the plasticity of copper(II), the rigid, square-planar geometry of nickel(II) and the enhanced steric repulsion of the methyl substituents of DMPO.