NaOH Aqueous Solution Research Articles

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.

Detection of limited-energy α particles using CR-39 in laser-induced p −11B reaction

Due to the harsh radiation environment produced by strong laser plasma, most of the detectors based on semiconductors cannot perform well. So, it is important to develop new detecting techniques with higher detection thresholds and highly charged particle resolution for investigating nuclear fusion reactions in laser-plasma environments. The Columbia Resin No. 39 (CR-39) detector is mainly sensitive to ions and insensitive to the backgrounds, such as electrons and photons. The detector has been widely used to detect charged particles in laser-plasma environments. In this work, we used a potassium–ethanol–water (PEW) etching solution to reduce the proton sensitivity of CR-39, by raising the detection threshold for the research of laser-induced 11B(p, α)2α reaction. We calibrated the 3–5 MeV α particles in an etching condition of 60°C PEW-25 solution (17% KOH + 25%C2H5OH + 58%H2O) and compared them with the manufacturer’s recommended etching conditions of 6.25 N NaOH aqueous solution at 98°C in our laser-induced nuclear reaction experiment. The results indicate, with the PEW-25 solution, that CR-39 is more suitable to distinguish α tracks from the proton background in our experiment. We also present a method to estimate the minimum detection range of α energy on specific etching conditions in our experiment.

Manual applied polyurethane-urea: High performance coating based on CO2-based polyol and polyaspartic ester

Brushable polyurea based on slow reactive process was prepared by simple, mild and solvent-free method. Firstly, polyurethane prepolymer was synthesized from poly (propylene carbonate) diol (PPCD, copolymer of propylene oxide/CO2) and 4,4′-dicylocyhexylmethane diisocyanate (HMDI). Polyurethane-urea (PPCD–PUU) was then obtained by the chain extension of prepolymer with polyaspartic ester (PAE). The mechanical properties of PPCD–PUU were optimized by adjusting the content of –NCO in the prepolymer and the ratio of prepolymer to PAE. The mechanical strength, thermal resistance, solvent resistance and hydrolysis resistance of PPCD–PUU were compared with those of PUUs derived from polypropylene glycol and poly-caprolactone diol. The results showed that the comprehensive mechanical properties of PPCD–PUU were balanced when the R value was 1.15 and the content of –NCO was 8 %. The tensile strength was 20.5 MPa, the elongation at break was 352 %, and the Young's modulus was 168.2 MPa. Especially, after soaking in 10 % H2SO4 aqueous solution, 10 % NaOH aqueous solution and 10 % NaCl aqueous solution for 24 h, the tensile properties were basically unchanged. Manual applied polyurethane-urea based on commercial PPCD has broad application prospects because it avoids the use of expensive spraying equipment.

Preparation of an asymmetric membrane via vapor induced phase separation for membrane distillation

Lately, membrane with asymmetric properties of its two sides has shown promising potential in direct contact membrane distillation (DCMD) application, based on the fact that the hydrophilic side of the asymmetric membrane can effectively mitigate wetting and fouling, while the hydrophobic layer facilitate transportation of water vapor to realize separation. We here report an asymmetric membrane prepared via a facile method of vapor induced phase separation (VIPS). Namely, hydrophobic polymer of poly(styrene-block-butadiene-block-styrene) (SBS) and hydrophilic cellulose acetate (CA) were co-dissolved in tetrahydrofuran, and then cast in an ethanol vapor atmosphere to evaporate solvent. After solvent evaporation (within 10 min), the obtained membrane was observed with scanning electron microscope (SEM) to indicate even microstructure of porous network matrix with nodular morphology, and its top surface consisted of SBS only, while microspheres of CA were found to be evenly embedded in the SBS matrix at the bottom side layer. The membrane was further treated with NaOH aqueous solution for CA deacetylation, which was confirmed by attenuated total reflection Fourier transform infrared spectroscopy, SEM and water contact angle (WCA) analyses. The deacetylated CA exposes OH groups to decrease the WCA of the bottom surface greatly. As a result, an asymmetric membrane with large difference in WCA between the top surface and the bottom surface has been obtained. The asymmetric membrane was employed for DCMD to separate an oily saline emulsion containing n-hexadecane, surfactant of Tween 80, and NaCl. The stable flux and high salt rejection of the asymmetric membrane indicate excellent resistance to wetting and fouling, which is attributed to the hydration layer formed by the OH groups of the deacetylated CA at the bottom surface of the membrane. The facile strategy reported in this work implies possible large scale production of the asymmetric membrane that is suitable for membrane distillation application.

Improved Catalytic Performances of the NaOH-Treated ZSM-22 Zeolite in the 1-Butene Skeletal Isomerization Reaction: Effect of External Acid Sites.

In this paper, a series of alkaline-treated ZSM-22 zeolite samples were prepared by treating the parent ZSM-22 zeolite using NaOH aqueous solution with different concentrations. By investigating the effects of alkaline treatment on the parent ZSM-22 zeolite, we discovered that the alkaline treatment contributed to the reduction of Brønsted acid sites due to the coverage of extra-framework Al on its external surface. In addition, it was found that the alkaline-treated samples were favorable to the improvement of the isobutene yield and selectivity, while these features appeared to be low for the subsequent acid-washed counterparts in the skeletal isomerization reaction of 1-butene. These results indicate that the catalytic performance of ZSM-22 zeolite is related to reduced amounts of Brønsted acid sites in it. To further reveal the reasons for the promoted catalytic performances of the alkaline-treated ZSM-22 series zeolites, we studied the properties of coke deposited on the two series of samples using Raman spectroscopy and thermogravimetric analysis and mass spectrometry (TG/MS-TPO). It was shown that the carbon deposited on the alkaline-treated series samples was mainly distributed at the outer surface, while the coke was distributed to a relatively lesser extent at the exterior surface for the acid-washed series samples. Moreover, by partially passivating outer acid sites of the parent zeolite, the selected alkaline-treated zeolite, and acid-washed zeolite, their isobutene selectivities were all improved with the decrease in outer acid sites. These phenomena confirmed that the improved catalytic performances of the alkaline-treated samples are related to their decreased external Brønsted acid site density, which further demonstrated that the high isobutene yield and selectivity in the skeletal isomerization reaction of 1-butene is realized via the monomolecular reaction pathway of 1-butene.

Implementation of endurable superhydrophobic surfaces through dilution rate control of the PDMS coating on micro-nano surface structures

Modifying the wettability of engineering surfaces has been widely practiced for several years because changing the surface properties of materials can induce useful functional properties. Superhydrophobic surfaces with maximized hydrophobicity prevent contamination, freezing, and corrosion, and are usually categorized based on the coating solution used. Among the various coating solutions, polydimethylsiloxane (PDMS) has attracted wide attention because it yields fluorine-free superhydrophobic coatings. Herein, fluorine-free superhydrophobic coatings were fabricated by varying the ratio of PDMS and toluene with respect to their viscosity. The roughness, wettability, and durability of the coatings were measured and described in detail. A simple chemical etching and oxidizing process was used to fabricate micro-nanostructures on the hydrophilic surface before hydrophobic coating. The variance in the morphological structure and surface roughness of the yielded micro-nanostructures in accordance with the viscosity control was analyzed using SEM images and surface roughness values, respectively. To measure the contact angle of the water droplet, coating conditions were derived to realize a superhydrophobic surface with a contact angle of over 150°. Furthermore, these superhydrophobic specimens were tested for durability in saline, acidic, and alkaline solutions. The superhydrophobic specimens showed no sign of degradation in brine for 72 h, and some surfaces showed degradation in HCl and NaOH aqueous solutions.

Thermal behaviour, microstructural changes and mechanical properties of alkali-activated volcanic scoria-fired waste clay brick blends

The present work aims at producing volcanic scoria (Zg) based geopolymer containing high volume of waste fired clay brick (WB). The objective was producing Zg-based geopolymer incorporating WB powders up to 50 wt% and then investigated a potential thermal stability. All formulated samples were prepared with sodium silicate made from rice husk ash and 6 M of an aqueous NaOH solution. The first series of consolidated geopolymer samples were cured at 25 °C, while the second ones were exposed to high temperatures of 400, 600 and 800 °C. The specimens were subjected to mechanical performance, physicochemical and microstructural properties evaluation. The results indicated that incorporating the WB positively influenced the physicochemical performances of geopolymers. Sample prepared with 10 wt% of WB gave highest mechanical property (33 MPa) at 600 °C. The use of WB favoured the densification and strength development of end products in the range of 25–600 °C.

Effective and Efficient Porous CeO2 Adsorbent for Acid Orange 7 Adsorption.

A porous CeO2 was synthesized following the addition of guanidine carbonate to a Ce3+ aqueous solution, the subsequent addition of hydrogen peroxide and a final hydrothermal treatment. The optimal experimental parameters for the synthesis of porous CeO2, including the amounts of guanidine carbonate and hydrogen peroxide and the hydrothermal conditions, were determined by taking the adsorption efficiency of acid orange 7 (AO7) dye as the evaluation. A template-free hydrothermal strategy could avoid the use of soft or hard templates and the subsequent tedious procedures of eliminating templates, which aligned with the goals of energy conservation and emission reduction. Moreover, both the guanidine carbonate and hydrogen peroxide used in this work were accessible and eco-friendly raw materials. The porous CeO2 possessed rapid adsorption capacities for AO7 dye. When the initial concentration of AO7 was less than 130 mg/L, removal efficiencies greater than 90.0% were obtained, achieving a maximum value of 97.5% at [AO7] = 100 mg/L and [CeO2] = 2.0 g/L in the first 10 min of contact. Moreover, the adsorption-desorption equilibrium between the porous CeO2 adsorbent and the AO7 molecule was basically established within the first 30 min. The saturated adsorption amount of AO7 dye was 90.3 mg/g based on a Langmuir linear fitting of the experimental data. Moreover, the porous CeO2 could be recycled using a NaOH aqueous solution, and the adsorption efficiency of AO7 dye still remained above 92.5% after five cycles. This study provided an alternative porous adsorbent for the purification of dye wastewater, and a template-free hydrothermal strategy was developed to enable the design of CeO2-based catalysts or catalyst carriers.

Effects of Wall Thickness Variation on Hydrogen Embrittlement Susceptibility of Additively Manufactured 316L Stainless Steel with Lattice Auxetic Structures

In the present study, the hydrogen embrittlement (HE) susceptibility of an additively manufactured (AM) 316L stainless steel (SS) was investigated. The materials were fabricated in the form of a lattice auxetic structure with three different strut thicknesses, 0.6, 1, and 1.4 mm, by the laser powder bed fusion technique at a volumetric energy of 70 J·mm-3. The effect of H charging on the strength and ductility of the lattice structures was evaluated by conducting tensile testing of the H-charged specimens at a slow strain rate of 4 × 10-5 s-1. Hydrogen was introduced to the specimens via electrochemical charging in an NaOH aqueous solution for 24 h at 80 °C before the tensile testing. The microstructure evolution of the H-charged materials was studied using the electron backscattered diffraction (EBSD) technique. The study revealed that the auxetic structures of the AM 316L-SS exhibited a slight reduction in mechanical properties after H charging. The tensile strength was slightly decreased regardless of the thickness. However, the ductility was significantly reduced with increasing thickness. For instance, the strength and uniform elongation of the auxetic structure of the 0.6 mm thick strut were 340 MPa and 17.4% before H charging, and 320 MPa and 16.7% after H charging, respectively. The corresponding values of the counterpart's 1.4 mm thick strut were 550 MPa and 29% before H charging, and 523 MPa and 23.9% after H charging, respectively. The fractography of the fracture surfaces showed the impact of H charging, as cleavage fracture was a striking feature in H-charged materials. Furthermore, the mechanical twins were enhanced during tensile straining of the H-charged high-thickness material.

Electrochemistry and Stability of 1,1'-Ferrocene-Bisphosphonates.

Here, we investigate the electrochemical properties and stability of 1,1'-ferrocene-bisphosphonates in aqueous solutions. 31P NMR spectroscopy enables to track decomposition at extreme pH conditions revealing partial disintegration of the ferrocene core in air and under an argon atmosphere. ESI-MS indicates the decomposition pathways to be different in aqueous H3PO4, phosphate buffer, or NaOH solutions. Cyclovoltammetry exhibits completely reversible redox chemistry of the evaluated bisphosphonates, sodium 1,1'-ferrocene-bis(phosphonate) (3) and sodium 1,1'-ferrocene-bis(methylphosphonate) (8), from pH 1.2 to pH 13. Both the compounds feature freely diffusing species as determined using the Randles-Sevcik analysis. The activation barriers determined by rotating disk electrode measurements revealed asymmetry for oxidation and reduction. The compounds are tested in a hybrid flow battery using anthraquinone-2-sulfonate as the counterside, yielding only moderate performance.

Solubility and thermodynamic properties of sodium theophylline salt in aqueous sodium hydroxide solution at different temperatures

The solubility data of sodium theophylline salt in the water and aqueous sodium hydroxide systems with molarities of 0.00, 0.01, 0.10, 0.20, 0.49, and 0.96 mol kg−1 at temperatures ranging from 283.15 to 368.15 K are determined via the equilibrium method. The experimental results show that the solubility of sodium theophylline increases on increasing the temperature at the same concentration of NaOH solution and decreases with an increase in the NaOH concentration at the same temperature. These results correlate well with the polynomial empirical equation, the modified Apelblat equation, and the λh equation. At the same time, it is found that the modified Apelblat equation gives better correlation results than the polynomial empirical and the λh equations. The results show that the three models correlate well with the solubility data of sodium theophylline. The modified Van’t Hoff equation is used to estimate the thermodynamic properties including the dissolution enthalpy, the dissolution entropy, and the Gibbs free energy change of sodium theophylline when dissolved in aqueous NaOH solution at different concentrations. The solubility data and correlation results obtained from the experiments can provide basic data for the cooling crystallization, separation, and purification of sodium theophylline and are expected to be of great significance for the research and development of sodium theophylline and for caffeine production.

One-step synthesis of non-equilibrium Pd-Ru alloys from Al-Pd-Ru quasicrystals and approximants

Non-equilibrium Pd–Ru alloys were synthesized by leaching quasicrystal (icosahedral quasicrystal, IQC: Al71Pd19Ru10) and approximants (3/2 approximant, P40: Al72Pd16.4Ru11.6, 1/1 approximant, C1: Al70.4Pd14.7Ru14.9) of Al–Pd–Ru alloys with 20 wt% NaOH aqueous solution. The Pd-Ru alloys were investigated using XRD and HAADF-STEM, which showed that Pd and Ru were mixed and formed a non-equilibrium state (atomic ratio: 0.9 < Pd/Ru < 2). The Pd–Ru alloy obtained by leaching of P40 phase was found to exhibit high catalytic performance toward CO oxidation than Pd and Ru catalysts obtained by leaching of Al3Pd (decagonal quasicrystal) and Al13Ru4 (decagonal approximant), respectively (i.e., the alloying effect). Consequently, Al-Pd-Ru quasicrystals and approximant alloys are found to be useful precursors to obtain the non-equilibrium Pd-Ru alloys.

Fabrication of metal-based superhydrophilic and underwater superoleophobic surfaces by laser ablation and magnetron sputtering

Fabricating underwater superoleophobic surfaces is an advanced technique for controlling undesirable oil and wax adhesion on engineering structures and household appliances. This article presented a facile method based on the combination of laser ablation of stainless steel substrates followed by magnetron sputtering of a metallic tungsten target to fabricate superhydrophilic and underwater superoleophobic surfaces. The results showed that the laser-ablated stainless steel substrate without coatings exhibited hydrophilicity and underwater oleophobicity. However, its transition to superhydrophilicity and underwater superoleophobicity with a 0° water contact angle and higher than 156° underwater oil contact angles occurred after the deposition of a thin tungsten film followed by annealing at 300 °C. The prepared surface maintained its wetting behavior for more than 4 weeks, even in corrosive aqueous HCl and NaOH solutions. According to the data from SEM and XPS, this distinguished wetting behavior resulted from the presence of the regular microscale texture patterns, abundant hydroxyl content, and low carbon content on the tungsten layer after annealing at 300 °C. Thus, laser ablation combined with magnetron sputtering of tungsten demonstrated effective results in fabricating superhydrophilic and underwater superoleophobic surfaces that are independent of the initial wetting of the substrates.

PHBV-based polymers as food packaging: Physical-chemical and structural stability under reuse conditions

Until recently, reuse models for food packaging plastics were generally considered burdensome. Today, reuse is placed second in the waste management hierarchy of the plastics circular economy. This work addresses, for the first time, the reuse of biobased and biodegradable materials such as PHBV and PHBV-quercetin. The safety and structural integrity of the materials were evaluated in two scenarios: (i) within a full reuse cycle including: food contact/detergentwashing/food contact; and (ii) successive washing operations in water, detergent and NaOH aqueous solutions. PHBV material that underwent the full reuse cycle using aqueous (10% ethanol) and acidic (3% acetic acid) food simulants showed an overall migration close to zero with a maintenance of its physical-chemical properties. It was also able to withstand up to 20 cycles of washing in water and detergent with slight changes in its intrinsic properties. Its washing with a 1 wt% aqueous NaOH solution, for one cycle, led to the removal of its external surface without altering its physical-chemical properties. The use of quercetin as additive had no consequence in the first scenario (the full reuse cycle). Even the migration of a part of it (2 wt% from the initial amount in the polymer) in the first contact with the food was far below the admissible daily intake. However, the release of quercetin during detergent washing steps and the production of acidic oxidation products during NaOH washing contributed to accelerate material degradation, questioning the use of such additives for PHAs.

Hydrothermal alkaline defluorination rate of perfluorocarboxylic acids (PFCAs)

AbstractBACKGROUNDAlthough perfluoroalkyl and polyfluoroalkyl substances (PFASs), including perfluorocarboxylic acids (PFCAs), are used for various industrial and consumer products, they can cause serious damage to human health. Various defluorination/destruction methods have been investigated on the decomposition/removal of PFASs under low‐concentration conditions. These methods are not suitable for treating large amounts of contaminants or waste liquids with a high PFAS concentration. The hydrothermal alkaline defluorination (HAD) method has advantages, such as a relatively high reaction rate and a high recovery of halide ions in the aqueous phase. However, a few studies on the HAD method have been reported and they did not recover all the fluorine atoms/fluoride ions. Also, the reaction kinetics over a wide range of experimental conditions have not been studied.RESULTSPerfluorooctanoic acid (PFOA) and PFCAs having 4 to 12 carbon atoms to 12 were subjected to aqueous NaOH solution under hydrothermal conditions, and the defluorination rates were found to be expressed by the second‐order reaction kinetics with respect to each concentration of OH− and fluorinated compound. The defluorination rate constants of both 4 to 12 carbon atom PFCAs at 553 K and PFOA at 513–573 K fall along a straight line in logarithmic plot. This suggests that the mass transfer of PFCAs or PFOA between the vapor and liquid phases can strongly affect the defluorination reactions.CONCLUSIONThe HAD rates of PFCAs were determined and suggested to be significantly affected by mass transfer of PFCAs between vapor and liquid phases. © 2023 Society of Chemical Industry (SCI).

Variation of the Bulk Etch Rate of Nuclear Track Detector CR-39 With the Chemical Etchant Solution Normality

The variation of the bulk etch rate (VB) of nuclear track detector CR-39 with the normality of the chemical etchant were studied. The removal thickness measurement method is used to determine the bulk etch rate. the detectors were etched by an aqueous solution of NaOH with normalities (4, 5, 6, 7) N at temperature (70±1) oC. It was found that the bulk etch rate is exponentially increasing with the normality of the solution and its values are (0.687, 1.421, 0.954, 2.082) µm/h at normalities (4, 5, 6, 7) N respectively. the relation between the bulk etch rate and the etchant normality was an exponential relation and the results showed good agreement with the results of the others used other normalities and another measurement method. &#x0D;

Electrodialysis with Bipolar Membranes for the Sustainable Production of Chemicals from Seawater Brines at Pilot Plant Scale.

Environmental concerns regarding the disposal of seawater reverse osmosis brines require the development of new valorization strategies. Electrodialysis with bipolar membrane (EDBM) technology enables the production of acid and base from a salty waste stream. In this study, an EDBM pilot plant with a membrane area of 19.2 m2 was tested. This total membrane area results much larger (i.e., more than 16 times larger) than those reported in the literature so far for the production of HCl and NaOH aqueous solutions, starting from NaCl brines. The pilot unit was tested both in continuous and discontinuous operation modes, at different current densities (200-500 A m-2). Particularly, three different process configurations were evaluated, namely, closed-loop, feed and bleed, and fed-batch. At lower applied current density (200 A m-2), the closed-loop had a lower specific energy consumption (SEC) (1.4 kWh kg-1) and a higher current efficiency (CE) (80%). When the current density was increased (300-500 A m-2), the feed and bleed mode was more appropriate due to its low values of SEC (1.9-2.6 kWh kg-1) as well as high values of specific production (SP) (0.82-1.3 ton year-1 m-2) and current efficiency (63-67%). These results showed the effect of various process configurations on the performance of the EDBM, thereby guiding the selection of the most suitable process configuration when varying the operating conditions and representing a first important step toward the implementation of this technology at industrial scale.

Fluoride ion adsorption isotherms, kinetics, and thermodynamics on iron(III) oxyhydroxide powders containing cellulose nanofibrils

The adsorption isotherms, kinetics, and thermodynamics of fluoride ions (F−) on FeOOH powders in water were investigated to obtain fundamental information on FeOOH powders, which are used as F− adsorbents in drinking and industrial water, and industrial wastewater. FeOOH powders were prepared as precipitates by mixing aqueous FeCl3 and NaOH solutions (1:3 mol/mol) in the presence of 2,2,6,6,-tetramethylpiperidine-1-oxyl radical (TEMPO)-oxidized cellulose nanofibrils (TOCNs), carboxymethylcellulose (CMC), or TEMPO-oxidized cellulose (TOC) fibers (without nanofibrillation), and subsequent drying and pulverizing. The FeOOH:TOCN, FeOOH:CMC, and FeOOH:TOC dry mass ratios were controlled at 87:13. The amount of F− adsorbed by the FeOOH/TOCN powder per FeOOH mass was higher than those adsorbed by FeOOH, FeOOH/CMC, or FeOOH/TOC. The F− adsorption isotherms on the FeOOH-containing powders showed higher correlation coefficients with the Langmuir model than with the Freundlich model. This indicates that F− adsorbed on FeOOH initially formed a monolayer, predominantly via physical adsorption. Pseudo-second-order kinetics fitted well to the time-dependent F− adsorption behaviors on the FeOOH-containing powders. Thermodynamic analysis of F− adsorption on the FeOOH-containing powders showed that the ΔG values were negative, which indicates that F− adsorption on the FeOOH-containing powders proceeded spontaneously in water. The negative ΔG value for FeOOH/TOCN was higher than those for FeOOH, FeOOH/CMC, and FeOOH/TOC at the same temperature. This shows that the FeOOH/TOCN powder can be used as an excellent and efficient F− adsorbent in water.Graphical abstract