NaOH Aqueous Solution Research Articles

UV-Induced Thiol-Ene "Click" Surface Grafting Polymerization on BOPP Substrate and Its Postmodifying for Hydrophilic and Antibacterial Applications.

This paper proposed a novel and versatile surface modification route by integrating UV light-mediated thiol-ene "click" surface grafting polymerization and postmodification via the reactions of the surface thiol groups. At first, poly(thiol ether) layers with tunable thiol group density, up to 8.2 × 102 ea/nm3 for cross-linked grafting layers, were grafted from biaxially oriented polypropylene (BOPP) film. Then, the surface -SH groups reacted with epoxy compounds to introduce quaternary ammonium salt. With the immobilized quaternary ammonium salt and coordinated Zn2+ ions, the modified film demonstrated 99.98% antibacterial rate against Staphylococcus aureusafter soaking in DI water for 21 days and in a highly alkaline environment (0.1 M NaOH aqueous solution) for 3 days, and the surface water contact angle decreased to 39°. At last, the polymethacrylate chains were also successfully grafted from the surface thiol groups of the cross-linked poly(thiol ether) under visible light irradiation. With 2-(dimethyldodecylammonium) ethyl methacrylate as the grafting monomer, the modified BOPP film had shown a 99.99% antibacterial rate against both Escherichia coliand S. aureus. Meanwhile, with 2-methacryloxyethyl phosphoryl choline as grafting monomer, the modified surface showed an excellent antibioadhesion of living S. aureus, and the surface water contact angle was as low as 48°.

A novel method for producing benzene polycarboxylic acids by electrochemical oxidation of Zhaotong lignite in aqueous NaCl solution

The development of a coal-based synthetic route to produce benzene polycarboxylic acids (BPCAs) is of great importance for the highly efficient utilization of lignites. In this paper, aqueous NaCl electrolytic system was used to oxidize Zhaotong lignite to prepare BPCAs. The electrochemical oxidation of lignite in aqueous NaCl solution could produce more BPCAs than that in aqueous NaOH solution. The aqueous NaCl electrolytic system could in-suit produce a stable OCl−, which was synthesized by the combination reaction between Cl2 and OH− generated in the anode or cathode, respectively. The in-suit produced OCl− would degrade the organic structures of the lignite dispersing in the electrolyte to generate BPCAs. The formation of BPCAs could be greatly affected by current density, electrolysis time and the addition amount of NaCl in the electrolytic system, which resulted from that the factors played an important role in the generation of OCl−. The coal related model compounds including anthracene and phenanthrene were used to investigate the electrochemical oxidation mechanism of the lignite. The results indicated that the aromatic ring structures in the lignite were attacked by O2− from the OCl− to afford BPCAs.

Effect of electric field on the wetting behavior of GaInSnBiZn high-entropy alloy in NaOH aqueous solution

The GaInSnBiZn low-melting-point high-entropy alloy exhibits promising prospects for utilization in the realm of flexible electronic devices, offering a promising alternative to common binary or ternary room-temperature liquid metals. By utilizing the sessile drop method, the wetting behavior of GaInSnBiZn/SiO2 was investigated, focusing on the effects of applied voltage and NaOH solution concentration. It was revealed that the alloy's electro-wetting is primarily influenced by the generation and dissolution of the surface oxide layer, as well as the interaction of the electric double-layer effect. The optimal response voltages for achieving the fastest wetting rate were found to be 16 V, 10 V, 18 V, and 8 V in 0.5 mol/L, 1.0 mol/L, 1.5 mol/L, and 2.0 mol/L concentrations, respectively, with 18 V at 1.5 mol/L concentration identified as the optimal process selection. The spreading behavior of the alloy in low-concentration NaOH solutions followed Tanner's Law, while in the 2.0 mol/L concentration, significant repellence and wetting angle saturation were observed. The wetting process of the alloy at various stages was described using the power-law equation R = atc, while the wetting mechanism of the alloy was elucidated through the application of the Lippmann equation and the electric double-layer effect equation.

Biodegradability of bacterial cellulose polymer below the soil and its effects on soil bacteria diversity

The increasing demand for sustainable materials has led to a surge in research on biodegradable polymers. This study evaluated the weight and visual changes of bacterial cellulose (BC) polymers and nylon membranes during an eight-week biodegradation study below soil. Scanning electron microscope (SEM) images were taken to investigate morphological changes from decomposition. Changes in soil microbial communities and the relationship between microbial abundance and BC biodegradation were investigated. BC was produced from the fermentation of coffee kombucha using 15 % d-dextrose C6H12O6 (DE) as the nutrient carbohydrate substrate. BCs were purified with 0.5 mol/L aqueous NaOH solution and 1.5 % (v/v) aqueous NaOCl and then freeze-dried. The biodegradation study was conducted using seedling pots and nylon membrane filters inside a greenhouse over eight weeks, with sample points taken at various intervals. Soil characteristics such as pH, nutrient content, texture, organic matter, and soil moisture were analyzed. Results showed that BC polymers underwent significant weight losses and visual decomposition, while nylon membranes did not show any weight or visual losses. Approximately 75 % of the BC polymers were decomposed by the end of the study. Fatty acid methyl ester (FAMEs) analysis showed increased microbial absolute abundance (nmol/g) for BC treatments over biodegradation time. FAMEs principal component analysis (PCA) ordination plots showed the relative abundance of fungi increased in BC microbial communities suggesting fungi's attraction to cellulose. Soil bacterial DNA analysis revealed the dominance of Proteobacteria for all treatments. PCA plots and Faith-pd index Alpha Diversity results showed significant bacterial community variations for week 2 of the biodegradation study compared to the other weeks. Adonis microbial community Beta Diversity analysis showed significant differences between treatments (p = 0.001). PCA plots also showed a slight differentiation of the bacterial communities with BC compared to bacterial communities with nylon and soil (control). This study confirms that BC is easily decomposed in soil and that its biodegradability is likely driven by fungal communities.

Enhanced thermoelectric and compressive performance of MnO2 coated carbon fiber/cement composites by microwave electrodeposition/microwave alkali treatment

The microwave electrodeposition/microwave NaOH aqueous solution treatment was developed for the first time to prepare MnO2 modified carbon fiber/cement composite (MCFC). The effects of the MnO2 modified carbon fiber (MCF) content and alkali treatment temperatures on the thermoelectric properties of the cement composites were investigated. The results show that the composite with the MCF content of 3.75 wt% has the optimal thermoelectric performance. After microwave alkali treatment at 333K, this composite has a Seebeck coefficient of −2308.9 μV/K, electrical and thermal conductivities of 2.72 S/m and 0.632 W/mK, and as a result, the ZT value of 7.73 × 10−3 could be achieved, which is the best value among the reported carbon fiber cement composites. Moreover, the composite has a compressive strength and strain of 38.6 MPa and 2.8%, respectively, which are 15.2% and 75% higher than those of the original cement, and shows good toughness.

Amphoteric dissolution of two-dimensional polytriazine imide carbon nitrides in water.

Crystalline two-dimensional carbon nitrides with polytriazine imide (PTI) structure are shown to act amphoterically, buffering both HCl and NaOH aqueous solutions, resulting in charged PTI layers that dissolve spontaneously in their aqueous media, particularly for the alkaline solutions. This provides a low energy, green route to their scalable solution processing. Protonation in acid is shown to occur at pyridinic nitrogens, stabilized by adjacent triazines, whereas deprotonation in base occurs primarily at basal plane NH bridges, although NH2 edge deprotonation is competitive. We conclude that mildly acidic or basic pHs are necessary to provide sufficient net charge on the nanosheets to promote dissolution, while avoiding high ion concentrations which screen the repulsion of like-charged PTI sheets in solution. This article is part of the theme issue 'Exploring the length scales, timescales and chemistry of challenging materials (Part 2)'.

Effective Removal of Cu2+ Ions from Aqueous Media Using Poly(acrylamide-co-itaconic acid) Hydrogels in a Semi-Continuous Process.

Adsorption is one of the most crucial processes in water treatment today. It offers a low-cost solution that does not require specialized equipment or state-of-the-art technology while efficiently removing dissolved contaminants, including heavy metals. This process allows for the utilization of natural or artificial adsorbents or a combination of both. In this context, polymeric materials play a fundamental role, as they enable the development of adsorbent materials using biopolymers and synthetic polymers. The latter can be used multiple times and can absorb large amounts of water per gram of polymer. This paper focuses on utilizing adsorption through hydrogels composed of poly(acrylamide-co-itaconic acid) for removing Cu2+ ions dissolved in aqueous media in a semi-continuous process. The synthesized hydrogels were first immersed in 0.1 M NaOH aqueous solutions, enabling OH- ions to enter the gel matrix and incorporate into the polymer surface. Consequently, the copper ions were recovered as Cu(OH)2 on the surface of the hydrogel rather than within it, allowing the solid precipitates to be easily separated by decantation. Remarkably, the hydrogels demonstrated an impressive 98% removal efficiency of the ions from the solution in unstirred conditions at 30 °C within 48 h. A subsequent study involved a serial process, demonstrating the hydrogels' reusability for up to eight cycles while maintaining their Cu2+ ion recovery capacity above 80%. Additionally, these hydrogels showcased their capability to remove Cu2+ ions even from media with ion concentrations below 100 ppm.

Experimental investigation of hydrogen production performance of various salts with a chlor-alkali method

In this experimental study, the hydrogen production performance of aqueous solutions of NaCl, KCl, and CaCl2 salts via an electrochemical method through a chlor-alkali reactor is investigated. For this purpose, a laboratory-scale reactor consisting of anode and cathode compartments is built. The compartments of the reactor are separated by a cation exchange membrane which prevents the mixing of anolyte and catholyte solutions and also allows positive ions (Na+, K+, and Ca2+) and some water to pass through. Electrodes made of 316 stainless steel are used in the compartments of the reactor due to their economic efficiency. While the anode compartment of the reactor is fed with the aqueous solutions of NaCl, KCl, and CaCl2 salts one by one, the cathode compartment is fed with one of the diluted aqueous solutions of NaOH, KOH, and Ca(OH)2 bases depending on the type of salt used. Experiments are carried out at three different cell voltages (3, 4, and 5 V) and three different cell temperatures (30, 50, and 70 °C), and five different electrolyte flows (0.4, 0.6, 0.8, 1.0, and 1.2 g/s). Since the reactor dimensions are very small, experiments are also carried out with small changes in the electrolyte mass flow rate. It is observed that active chlorine gas causes serious contamination in the anode compartment and erosion on the electrode in this compartment. Therefore, the expected chlorine gas output from the anode compartment of the reactor is not observed. Luckily, a significant amount of hydrogen gas output is observed from the cathode compartment of the reactor. The minimum hydrogen production rate is 37.23 mL/h when the aqueous solution of CaCl2 is used with a mass flow rate of 0.4 g/s and cell voltage of 3 V at the cell temperature of 30 °C. The maximum hydrogen production rate is 437.72 mL/h when KCl salt solution is used with a mass flow rate of 1.2 g/s and cell voltage of 5 V at the cell temperature of 70 °C.

Investigation of the electrical sensing properties of cementitious composites produced with multi-wall carbon nanotubes dispersed in NaOH

The use of nanomaterials, such as carbon nanotubes, in cement-based composites has been a topic of considerable attention in recent years due to their potential to monitor civil structures and infrastructures. One of the main challenges is the adequate and efficient dispersion of the carbon nanotubes due to their nanoparticle size and the high adhesion forces developing among them. The most common strategy to tackle this challenge is to use sonic treatments that are unfeasible for field-scale implementations. Alternatively, specific chemicals (i.e. surfactants) facilitating nanotube mixing are used, but this often results in poor mechanical properties, reduced electrical conductivity and high environmental impact of the composites. This works has as the main aim to analyze the self-sensing properties of the cementitious composites developed with NaOH as the dispersing agent. For this purpose, the work investigates electrical and sensing properties of cement-based nanocomposites with different contents of multi-wall carbon nanotubes (MWCNT), namely 1%, 1.5%, and 2% with respect to cement weight, previously dispersed in NaOH aqueous solution. The composites' fresh and electrical properties are evaluated, and a microstructural analysis is carried out. The major findings of the work reveal that cement paste samples with different contents of MWCNT presented increasing sensing properties up to 2%, and that the dispersing strategy was promising despite its simplicity.

Spherical silica particles coated with lamellar nanocomposites based on a hydrophobic functionalized phyllosilicate

The surface of spherical silica particles (monodisperse, 2.6 µm) was modified with inorganic–organic lamellar ordered hybrids for applications as hydrophobic dye supports in cosmetics. The inorganic–organic multilayers comprised a 2:1 phyllosilicate (two sheets of linked SiO4 tetrahedra with one sheet of M2–3(OH)6 octahedra, where M is either magnesium or aluminum), consisting of octyl chains directly bonded to the inorganic sheets via Si–C covalent bonds. Octyltriethoxysilane was allowed to react at room temperature with spherical silica and aluminum acetylacetonate in a mixed aqueous solution of NaOH and NaCl at pH 10. The formation of a 2:1 phyllosilicate grafted with an octyl chain was confirmed by X-Ray powder diffraction, where a lamellar structure with the d001 value of 2.4 nm was displayed. The lamellar structure included the isomorphic substitution of Si by Al and the formation of C–Si–O–Aloct bonds, as shown in 29Si–and 27Al–magic angle spinning (MAS)–nuclear magnetic resonance (NMR) spectra. Further, the 23Na–MAS NMR spectrum indicated the incorporation of Na aquo complex cations into the organophyllosilicate. The hydrated Na ions were exchanged with a cationic dye (methylene blue) to be adsorbed. An anionic dye (Phloxine B), which has frequently been used as cosmetic pigments, was adsorbed onto the resulting hybrid particles when Al3+ was present in the dye solution. The hydrophobic dye supports can be used instead of plastic beads to reduce marine pollution.

Novel glass-based membranes for Cu adsorption: From alkali activation to sintering

A porous membrane was developed through alkali activation of pharmaceutical boro-alumino-silicate glass powders suspended in diluted NaOH and KOH aqueous solutions (2.5 M). A consolidated porous structure was obtained by the binding of unreacted particles mediated by a surface gel, developed upon drying of the suspensions and their curing at 40 °C for 14 days. The binding phase was sufficiently stable to resist immersion in boiling water and in acidic solutions. Copper adsorption tests were carried out under acidic pH, immersing the membranes in a Cu(NO3)2 solution for different periods of time. To determine the effect of surface washing on capture of copper ions, adsorption experiments with washed and unwashed membranes were also carried out, at varying pH. It was determined that the adsorption kinetics follow the pseudo-second-order kinetic model. The main adsorption mechanism observed is the electrostatic interaction between the negative surface charge of the washed membrane and the Cu2+ ions present in solution. An adsorption higher than 60% was observed at pH = 5, while at pH = 2 the efficiency decreased due to the presence of H3O+ ions. To ensure immobilization of copper, the membranes were densified by viscous flow sintering at a moderate temperature (700 °C). Leaching tests on membranes demonstrated the efficiency of the process in terms of copper ions immobilization.

Bulk Al-Al9Co2 alloys: Microstructure, corrosion behavior and hydrogen evolution kinetics

Two Al alloys with 1 and 3 at% Co were prepared by arc-melting of Al and Co in argon. The corrosion behavior of the as-cast alloys was studied in a NaOH aqueous solution (0.01 M). Furthermore, a hydrogen evolution was investigated by volumetric measurements. The results were compared with pure Al. The alloy with 1% Co was the least corrosion resistant and evolved most hydrogen. The presence of Al9Co2 in the eutectic facilitated hydrogen evolution and contributed to corrosion activation. The results can be used for the design of Al-Co alloys for hydrogen generation.

A New Neodymium Complex on Boehmite Nanoparticles with 1,3‐Bis(pyridine‐3‐ylmethyl)thiourea as a Practical and Reusable Nanocatalyst for the Chemoselective Synthesis of Tetrazoles

AbstractIn first part, boehmite nanoparticles were synthesized using aqueous solutions of NaOH and Al(NO3)3 ⋅ 9H2O. Then, it surface was modified by 3‐choloropropyltrimtoxysilane, and further 1,3‐bis(pyridin‐3‐ylmethyl)thiourea was anchored on the modified boehmite nanoparticles. In the final step, a neodymium complex was stabilized on its surface (Nd‐bis(PYT)@boehmite NPs). The obtained nanoparticles were characterized by TGA, BET, ICP, EDS, WDX, SEM, and XRD techniques. In the second part, Nd‐bis(PYT)@boehmite NPs were employed as an efficient, recoverable, and organic‐inorganic hybrid nanocatalyst in the homo‐selective synthesis of tetrazole compounds. The chemoselectivity of Nd‐bis(PYT)@boehmite NPs was studied in the [3+2] cycloaddition of phthalonitrile and sodium azide (NaN3). This catalyst is stable and has heterogeneous nature therefore it can be recovered and used again for several consecutively run without any re‐activation

Photoresponsive Magnetic Relaxation Behavior of a Highly Stable π···π Interaction-Stacked Framework Based on a DyIII Single-Ion Magnet

Endowing lanthanide single-ion magnets (Ln-SIMs) with high stability and stimulus responsiveness is of significance for the practical applications of these novel magnetic materials, but still of challenge at present. Herein, we report on a highly stable and photoresponsive Ln-SIM system achieved by designing and synthesizing a π···π interaction-stacked framework based on DyIII-SIM (πOF-1). Its molecular formula is [Dy(thqa)] (H3thqa = tris[(8-hydroxyquinoline-2-yl)methylene]amino). Each of its C3-symmetric molecules consists of a thqa3– ligand and a DyIII ion, and it is linked to three neighbors by intermolecular π···π interactions, forming a supermolecular two-dimensional (2D) honeycombed topology. Such unique structure endows πOF-1 with not only air and thermal stability but also excellent chemical stability in different solvents, even in alkali solutions, including a 20 M NaOH aqueous solution. Dual magnetic relaxation behavior was observed in πOF-1. Magnetic dilution revealed that it is related to π···π-mediated intermolecular magnetic interactions. More significantly, both the static magnetic susceptibility and the dual-relaxation behavior of πOF-1 show response to photoirradiation, which could be ascribed to the photo-triggered intermolecular π → π* charge transfer (CT). So far as we know, πOF-1 could be the first Ln-SIM system possessing both a high stability and photoresponsiveness, and also the first photoresponsive Ln-SIM supermolecular system that does not rely on the single-crystal to single-crystal (SCSC) structural transformation. Its successful design and synthesis suggests that the introduction of π···π interactions can be a new strategy to fabricate stable and/or photoresponsive Ln-SIMs.

Visible-Light-driven Photocatalytic Properties of Copper(I) Oxide (Cu2O) and Its Graphene-based Nanocomposites

In this study, an improved process was proposed for the synthesis of structure-controlled Cu2O nanoparticles, using a simplified wet chemical method at room temperature. A chemical solution route was established to synthesize Cu2O crystals with various sizes and morphologies. The structure, morphology, and optical properties of Cu2O nanoparticles were analyzed by X-ray diffraction, SEM (scanning electron microscope), and UV-Vis spectroscopy. By adjusting the aqueous mixture solutions of NaOH and NH2OH•HCl, the synthesis of Cu2O crystals with different morphology and size could be realized. Strangely, it was found that the change in the ratio of de-ionized water and NaOH aqueous solution led to the synthesis of Cu2O crystals of different sizes, while the morphology of Cu2O crystals was not affected. The synthesized Cu2O crystal samples were used as photocatalysts for methyl orange (MO) dye decomposition, as a model molecule, to evaluate the photocatalytic activities. However, under 200 watts of a visible light source, there are four samples with and without graphene-based nanocomposite of Cu2O NPs. The results showed that, compared with roughly spherical, irregular but thick plates, brick and small granule spheres shaped Cu2O nanoparticles provided better activity. The Cu2O sample with irregular but thick platelet-like shapes, having an average particle size of 0.53 µm, exhibited excellent photocatalytic activity (99.08% degradation). In addition, by reducing the size of Cu2O particles and preparing their graphene composition, one can fabricate a sample (Cu2-Cu2Gr) with the highest efficiency which has significantly better photocatalytic activity in comparison to the others. This work represents an innovative strategy for pre-the-case production of nanomaterials with shapes and sizes, that is, Cu2O crystals, with excellent photocatalytic activity through compositing with graphene

Experimental Investigation and Modelling by Machine Learning Techniques for Hydrogen Generation by Reacting Aluminium with Aqueous NaOH Solution

Hydrogen gas is projected as the future fuel for energy generation due to high energy density, and almost zero COx and NOx emissions during combustion. Production of H2 gas by the chemical reaction of aluminium and aqueous NaOH solution appears to be a simple and cost effective technique. Accurate forecasting of the reaction kinetics based on multi-variable interactions is necessary for large scale in-situ production and control of hydrogen gas. In the present study, the kinetics of the reaction between Al and aq. NaOH to produce H2 at different temperatures and concentrations of NaOH is investigated. Data obtained from these investigations are used to predict the reaction rate and correlate the simulated and experimental results using Machine Learning Techniques, viz, Artificial Neural Network (ANN) and Multiple Linear Regression (MLR). The simulation model obtained by the MLR technique is found to be less accurate in terms coefficient of correlation than the ANN model while comparing with the experimental results. The coefficient of correlations (Rcc) and average absolute relative error % are found to be 0.998 and 1.377% respectively during simulation by ANN. During the ANN simulation, 97.8 % of data points lie within a 95 % level of confidence indicating very good simulation capability. The results of the investigation reveal the application of Machine learning technique for the accurate prediction of hydrogen gas generation by a chemical reaction.

A novel strategy for fabrication, activation and cleaning of fully 3D printed flexible planar electrochemical platforms

AbstractIn recent years, 3D printing of carbon‐based conductive filaments has received growing attention for assembling electrodes to be used in a wide variety of electroanalytical devices and applications. Despite the large amount of work present in literature concerning the development of three‐dimensional (3D) conductive structures, its potential as dry deposition method for assembling two‐dimensional (2D) electrodes to be used in planar configuration is still largely unexplored. In fact, the possibility to rapidly change the geometry of the electrochemical circuits, associated with the reduction of waste and the absence of solvents, which are instead important components of ink and paste formulations, makes this strategy a valid green and efficient alternative to other deposition approaches such as screen‐printing technology. We report here a rapid and solvent‐free method for assembling fully 3D printed flexible planar electroanalytical platforms (3DEPs) to be used with microliters of liquid. At the same time, a novel protocol for the surface pre‐treatment of 3D printed electrodes based on ultrasonication in aqueous NaOH solution followed by electrochemical activation using the same medium, is presented. In addition, the same procedure has proved to be efficient for cleaning the electrode surface after electrochemical passivation, thus confirming the validity of both time‐efficient and environmentally‐friendly assembling and activation/cleaning procedures developed which allow efficient and reusable electrodes to be produced. Finally, 3DEPs were tested by a proof‐of‐concept quantification of a commonly used food dye (Brilliant Blue, E‐133) in commercial solutions used for homemade food coloring.

Wet spinning and 3D printing of supramolecular hydrogels in acid-base and dynamic conditions

N-alkyl-D-galactonamides give biocompatible hydrogels that are very delicate and not injectable. To circumvent their mechanical fragility and the injectability issue, we have developed a method of injection based on solvent-water exchange. A solution of the gelator in a good solvent is injected vertically in a bath of water. The diffusion of water inside the solvent jet triggers the fast self-assembly of the N-alkyl-D-galactonamides into supramolecular fibers. It leads to the formation of well-defined gel filaments. We first used dimethylsulfoxide (DMSO) as the good solvent of N-alkyl-D-galactonamides. Then, we considered to get rid of this organic solvent by implementing an “all-aqueous method”, paving the way to green chemistry methods. Despite the fact that these molecules do not have conventional acid-base functions in water, N-alkyl-D-galactonamides can be deprotonated and solubilized in highly concentrated NaOH aqueous solutions. As with DMSO, the basic solution is denser than the solution in the bath. Thus, a well-defined vertical jet falls down when the solution is injected in an acidic aqueous solution. The neutralization of the base at the acid-base interface triggers the gelation and leads to the formation of well-defined gel filaments as well. The acid-base reaction at the interface has been visualized by colored pH indicators. With phenol red (pKa = 7.9), a pink-to-yellow V-shaped “flame” transition is clearly observed. A similar transition from colorless-to-pink is observed with the pH indicator acid fuchsin, which pKa = 13 is close to the N-heptyl-D-galactonamide pKa. The distance from the nozzle of this transition zone is directly related to the injection rate, which is well-described by a model. We also applied this method to 3D printing, by a liquid-in-liquid direct writing. It gives well-resolved patterns. The opportunity to get noodles or 3D printed patterns made of single small molecules by acid-base exchange opens new perspectives. Notably, the supramolecular fibers could be used to support and direct the formation of inorganic materials with original microstructures.

PH stable thin film composite poly(amine-urea) nanofiltration membranes with excellent rejection performance

pH stable nanofiltration membranes are highly desirable in treating acidic and alkali effluents and recovering the valuable byproducts. Efforts have been devoted to preparing nanofiltration membranes with good acid/alkali resistance but the separation performance is still to be improved. Poly(amine-urea) nanofiltration membranes with excellent rejection performances were prepared by the interfacial polymerization between polyethyleneimine with the mixed organic monomer of cyanuric chloride and 1, 4-phenylene diisocyanate. In comparison with pure polyamine and polyurea membranes, the optimal poly(amine-urea) membranes exhibit simultaneously improved membrane permeability and salt rejection, > 99% for MgSO4. The membrane morphology, pore structure and chemical properties of the membranes were thoroughly characterized, demonstrating that the poly(amine-urea) selective layer is thinner and denser compared with the polyamine/polyurea prepared with a single organic monomer. The underlying mechanisms for the synergistic effect between cyanuric chloride and 1, 4-phenylene diisocyanate were revealed. In addition, the poly(amine-urea) nanofiltration membranes maintain a high rejection for MgSO4, >96%, after exposure to 20 wt% HCl and 20 wt% NaOH aqueous solutions for 150 days, demonstrating excellent acid/alkali stability.

CHEMOSORPTION COMPOSITIONS BASED ON PHLOGOPITE FOR LOW-TEMPERATURE AIR PURIFICATION FROM SULFUR DIOXIDE

It is known that a large amount of sulfur dioxide is released into the atmosphere during the production of sulfuric acid, the combustion of metal sulfides at non-ferrous metallurgy enterprises, during the burning of coal containing sulfur, at thermal power plants, and in many other industries. In the air of industrial companies, its concentrations often significantly exceed the maximum allowable concentration (10 mg/m3 for the working area), despite the use of equipment for the sanitary treatment of exhaust gases. Therefore, there is a need to develop highly effective personal protection equipment of workers’ respiratory organs against sulfur dioxide in the form of respirators or gas masks. For their production, it is necessary to create cheap, affordable and reliable sorbents. A large number of methods for cleaning air and exhaust gases from sulfur dioxide are known. Among them, a special place is occupied by methods based on the use of nitrogen-containing bases, for example, urea, mono-, di- and triethanolamines, hydrazine, hydroxylamine, and hexamethylene tetramine (HMTA). Therefore, the use of aqueous solutions of nitrogen-containing bases as active components of sulfur dioxide chemosorbents is quite promising. However, their use in respiratory personal protection equipment, which would work according to the principle of using the absorption process, is quite difficult. Therefore, we made an attempt to impregnate a porous medium, as natural flagopite, with aqueous solutions of HMTA and NaOH. It was determined using X-ray phase analysis, that natural phlogopite, in addition to the main phlogopite phase, contains various impurities, such as diopside, vermiculite, clinochlore, and cordierite. To establish the type of adsorption, the adsorption and desorption of sulfur dioxide by natural phlogopite was studied. It has been proven that sulfur dioxide is weakly bound to the surface of natural phlogopite, that is, its physical adsorption mainly occurs. The perspective of using natural and chemically modified phlogopite for chemisorption neutralization of sulfur dioxide, provided its low concentration (150 mg/m3) in the air, is shown. It was established that monocomponent compositions based on NaOH and HMTA fixed on natural phlogopite absorb sulfur dioxide, but under the condition of their combined action at a certain ratio of components, a synergistic effect is observed, which is manifested in an increase in the time of the protective effect and adsorption capacity of the compositions.