Extracting Cu(II) from aqueous solutions with hydrophobic room-temperature ionic liquid in the presence of a pyridine-based ionophore to attempt Cu recovery: A laboratory study

Extraction of Cu(II) from neutral aqueous solutions with the hydrophobic room-temperature ionic liquid (IL) N-butyl-N-methylpyrrolidinium bis((trifluoromethyl)sulfonyl)imide (BMP-TFSI) in the presence of the pyridine-based ionophore N¹,N¹,N⁴,N⁴-tetrakis(2-(pyridin-2-yl)ethyl)butane-1,4-diamine (C₄N₂Py₄) is demonstrated in this study. Although the distribution coefficients, D_M, of Cu(II) extraction depend on the concentration of Cu(II) in aqueous solutions, all values were higher than 200, indicating extremely high extraction efficiency. Based on spectrophotometric, electrochemical, and X-ray crystallography studies, the coordination number of the C₄N₂Py₄-coordinated Cu(II) ions was determined as 2. The voltammetric behavior of Cu(I), Cu(II), and their C₄N₂Py₄ complex ions were also studied. The recovery of Cu from the IL was conducted by washing the IL phase containing the extracted Cu(II) complex with an acidic aqueous phase or by controlled-potential electrolysis. The IL containing C₄N₂Py₄ was employed for two complete rounds and a decrease in extraction efficiency was only observed when higher concentration of Cu(II) was used.     

Structure–property relations of ferroelectric BaTiO3 ceramics containing nano-sized Si3N4 particulates

Barium titanate/silicon nitride (BaTiO₃/xSi₃N₄) powder (when x = 0, 0.1, 0.5, 1 and 3 wt%) were prepared by solid-state mixed-oxide method and sintered at 1400 °C for 2 h. X-ray diffraction result suggested that tetragonality (c/a) of the BaTiO₃/xSi₃N₄ ceramics increased with increasing content of Si₃N₄. Density and grain size of BaTiO₃/xSi₃N₄ ceramic were found to increase for small addition (i.e. 0.1 and 0.5 wt%) of Si₃N₄ mainly due to the presence of liquid phase during sintering. BaTiO₃ ceramics containing such amount of Si₃N₄ also showed improved dielectric and ferroelectric properties.     

1H NMR study of temperature-induced phase transitions in aqueous solutions of poly(N-isopropylmethacrylamide)/poly(N-vinylcaprolactam) mixtures

¹H NMR spectroscopy was used to investigate the temperature-induced phase transitions in aqueous solutions of poly(N-isopropylmethacrylamide)/poly(N-vinylcaprolactam) (PIPMAm/PVCL) mixtures to find out if the phase transition of the given component (PIPMAm or PVCL) is affected by the presence of the second component. Our results that PVCL and PIPMAm transitions are in polymer mixtures shifted by ~2 K towards higher temperatures in comparison with neat polymers and depend on polymer concentration show that such effect exists. Spin–spin relaxation times of water (HDO) indicate that in solutions with c ≥ 1 wt% a portion of water is predominantly bound in PVCL mesoglobules even at temperatures above the LCST transition of PIPMAm component. Water is with time released from these mesoglobules without any induction period so indicating that it is mostly indirectly bound water. We assume that there is a direct connection between character of the bound water and the transition temperatures.     

Molecular structure of bituminous coal studied with pulse nuclear magnetic resonance

High-volatile bituminous coal and coal saturated with fully deuterated solvents, were studied using the ¹H n.m.r. pulse technique. Free-induction decay (FID) signals were separated into Gaussian and Lorentzian components and contents of immobile and mobile phases of coal matter were calculated. Spin-spin relaxation times, T₂, for both phases were determined. Some solvents caused a significant decrease in the content of the coal immobile phase. It is concluded that the immobile phase of coal consists of macromolecules and molecules. The latter are attached to macromolecules by electrondonor-acceptor interactions which can be destroyed by some solvents. The contents of macromolecules (60 wt%) and molecules (40 wt%) in the coal were determined.     

H NMR study of thermotropic phase transitions in D2O solutions of poly(N-isopropylmethacrylamide)/poly(vinyl methyl ether) mixtures

¹H NMR spectroscopy was used to investigate thermotropic phase transitions in D₂O solutions of poly(N-isopropylmethacrylamide) (PIPMAm)/poly(vinyl methyl ether) (PVME) mixtures. In all studied solutions (polymer concentrations c=0.1-10 wt%) two phase transitions were detected at temperatures roughly corresponding to different lower critical solution temperatures of PIPMAm and PVME. While the phase transition of PVME component (located at lower temperatures) is not affected by the presence of PIPMAm in the mixture, the phase transition temperatures of PIPMAm component (located at higher temperatures) are affected by the phase separation of the PVME component. Measurements of ¹H spin-spin relaxation of residual water (HDO) molecules revealed that above the phase transition, a certain portion of water molecules is bound to polymer globular structures. A major part of bound water is present in globular structures of predominating polymer component in the mixture.     

Effect of SiO2 content on the microstructure,mechanical and dielectric properties of Si3N4 ceramics

This study investigated the effect of SiO₂ content in the Y₂O₃–Al₂O₃ additive system on the microstructure, mechanical and dielectric properties of silicon nitride (Si₃N₄) ceramics. The total sintering additive content was fixed at 8 wt% and the amount of SiO₂ was varied from 0 to 7 wt%. The crystalline phases of the samples were determined by X-ray diffraction analysis. Complete α-to-β transformation of the Si₃N₄ occurred during sintering of all of the samples, which indicated that the phase transformation was unaffected by the SiO₂ content. However, the microstructures showed that the aspect ratio of the β-Si₃N₄ grains decreased and the residual porosity increased with increasing SiO₂ content. Additionally, the flexural strength and the dielectric constant decreased with increasing SiO₂ content because of the residual porosity and the formation of the Si₂N₂O phase via a reaction of SiO₂ with Si₃N₄.     

Isothermal crystallization study on aqueous solution of poly(vinyl methyl ether) by DSC method

A study on the isothermal crystallization of water in aqueous solutions of poly(vinyl methyl ether) (PVME) was carried out by the differential scanning calorimetry (DSC). The influence of PVME concentration (49.5, 44.5 and 39.5 v%) and the crystallization temperature (T_c) on crystallization rate G, crystallization enthalpy (ΔH_c) and melting enthalpy (ΔH_m) was investigated. Avrami equation cannot be used to describe the crystallization process of water in aqueous PVME solution. Within the measured temperature range, the crystallization rate G increases with the crystallization temperature T_c and with the decreasing PVME content. The crystallization enthalpy ΔH_c linearly increases with the degree of supercooling. The influence of T_c on the ΔH_c becomes more marked with increasing PVME concentration. For 49.5 and 44.5 v% PVME solutions, the amount of water arrested in solution during the isothermal crystallization and the final concentration of PVME-rich phase increase linearly with the T_c, whereas for 39.5 v% PVME solution, these two values almost do not change with T_c. The amount of frozen water in the subsequent cold crystallization is approximately proportional to the initial T_c. The approximately constant ΔH_m for a given concentration at the different initial isothermal crystallization temperatures suggests that the total amount of ice from the first isothermal crystallization and the second cold crystallization is same. The quantitative relation of the amount of frozen water in the cold crystallization and the initial T_c demonstrates that PVME/water complexes are thermodynamically unstable.     

Gelation behaviors of cellulose solution dissolved in aqueous NaOH/thiourea at low temperature

Cellulose was dissolved rapidly in 9.5 wt% NaOH/4.5 wt% thiourea aqueous solution pre-cooled to −5 °C, as a result of the formation of an inclusion complex (IC) associated with cellulose, NaOH and thiourea, which could bring cellulose to the aqueous system. To clarify the rheological behaviors of the system dissolved at low temperature, this cellulose solution was investigated by dynamic viscoelastic measurement. The shear storage modulus (G′) and loss modulus (G″) as a function of the angular frequency (ω), concentration (c), temperature (T) and weight-average molecular weight (M_w) were analyzed and discussed. The results revealed that gels could form in the cellulose solution at either high temperature or low temperature, or for longer time. Interestingly, 4 wt% cellulose solution having cellulose M_w of 12.0 × 10⁴ remained at liquid state for longer time (12 days) at the temperature ranging from 0 to 5 °C. The gels already formed at elevated temperature were irreversible, i.e., after cooling to lower temperature including the temperature of cellulose dissolution (−5 °C), they could not be dissolved to become liquid. The Arrhenius analysis of the temperature dependence of viscosity in the cellulose solution indicated that a high apparent activation energy (E_a) occurred at 0 to −5 °C, suggesting the relatively stable IC structure. However, the viscosity of the cellulose solution increased slowly with an increase in the temperature at 0-40 °C, leading to the negative E_a values. The results suggested that the cellulose solution in NaOH/thiourea system is complex to differ from normal polymer systems.     

Porous Si3N4 ceramics prepared by aqueous gelcasting using low–toxicity DMAA system: Regulatable microstructure and properties by monomer content

In this study, the low–toxicity monomer N, N–dimethylacrylamide (DMAA), serving as both gelling agent and pore–forming agent, was adopted to fabricate porous Si₃N₄ ceramics with a regulatable microstructure and property by aqueous gelcasting. Results indicate that monomer content played an important role in regulating and optimizing the properties of sintered bodies. With increasing monomer content (5.94–30.69?wt%), both slurry viscosity (maximum 0.14?Pa?s at 95.40 s^?1) and green body strength (11.35–49.23?MPa) exhibited monotonic increasing trends, demonstrating superior mechanical properties to those obtained using the neurovirulent acrylamide (AM) gelling system. The increased monomer content not only improved porosity, but also promoted α→β–Si₃N₄ transformation as well as β–Si₃N₄ grain growth through enhancing the connectivity of interlocking pores and accelerating the vapor phase transport during liquid–phase sintering. These variations in phase composition and microstructure derived from the varied monomer content further resulted in monotonic changes in porosity (40.32–51.50%), mean pore size (0.27–0.38?μm), flexural strength (202.77–132.15?MPa), fracture toughness (2.93–2.32?MPa?m^1/2), dielectric constant (3.48–2.78) and loss (3.52–3.09?×?10^?3) at 10?GHz for sintered bodies, displaying an excellent comprehensive properties. This study suggests a promising prospect for DMAA in preparation of high–performance porous Si₃N₄ ceramics by aqueous gelcasting.     

Isothermal and non-isothermal crystallization behavior of poly(l-lactic acid): Effects of stereocomplex as nucleating agent

The effects of incorporated poly(d-lactic acid) (PDLA) as poly(lactic acid) (PLA) stereocomplex crystallites on the isothermal and non-isothermal crystallization behavior of poly(l-lactic acid) (PLLA) from the melt were investigated for a wide PDLA contents from 0.1 to 10 wt%. In isothermal crystallization from the melt, the radius growth rate of PLLA spherulites (crystallization temperature (T_c)≥125 °C), the induction period for PLLA spherulite formation (t_i) (T_c≥125 °C), the growth mechanism of PLLA crystallites (90 °C≤T_c≤150 °C), and the mechanical properties of the PLLA films were not affected by the incorporation of PDLA or the presence of stereocomplex crystallites as a nucleating agent. In contrast, the presence of stereocomplex crystallites significantly increased the number of PLLA spherulites per unit area or volume. In isothermal crystallization from the melt, at PDLA content of 10 wt%, the starting, half, and ending times for overall PLLA crystallization (t_c(S), t_c(1/2), and t_c(E), respectively) were much shorter than those at PDLA content of 0 wt%, due to the increased number of PLLA spherulites. Reversely, at PDLA content of 0.1 wt%, the t_c(S), t_c(1/2), and t_c(E) were longer than or similar to those at PDLA content of 0 wt%, probably due to the long t_i and the decreased number of spherulites. This seems to have been caused by free PDLA chains, which did not form stereocomplex crystallites. On the other hand, at PDLA contents of 0.3-3 wt%, the t_c(S), t_c(1/2), and t_c(E) were shorter than or similar to those at PDLA content of 0 wt% for the T_c range below 95 °C and above 125 °C, whereas this inclination was reversed for the T_c range of 100-120 °C. In the non-isothermal crystallization of as-cast or amorphous-made PLLA films during cooling from the melt, the addition of PDLA above 1 wt% was effective to accelerate overall PLLA crystallization. The X-ray diffractometry could trace the formation of stereocomplex crystallites in the melt-quenched PLLA films at PDLA contents above 1 wt%. This study revealed that the addition of small amounts of PDLA is effective to accelerate overall PLLA crystallization when the PDLA content and crystallization conditions are scrupulously selected.     

Protein release behavior from carbonate apatite hydrogel

Incorporation of protein in poorly crystalline carbonate apatite hydrogel, the protein release behavior from the cake and the dissolution of the cake in aqueous solution were studied. Poorly crystalline apatite was prepared by precipitation of saturated solution of calcium and phosphate in air or under N₂ atmosphere. The carbonate content and particle size of obtained hydrogel depends on the maturation period and atmospheric condition. The mixture of apatite hydrogel and protein was dried for 4 days in air at 40% of relative humidity to yield cakes. The quantity of loaded cytochrome c in apatite hydrogel formed in air was 0.490 wt.%, while that in apatite hydrogel formed under N₂ atmosphere was 0.305 wt.%. But the quantity of loaded albumin in apatite hydrogel formed in air was less than that in apatite hydrogel formed under N₂ atmosphere. For the cakes containing protein immersed in aqueous solution, the protein release was less than the decrease in weight of apatite cake, which may be associated with apatite recrystallization and protein re-incorporation. The quantity of released protein may depend on the quantity of loaded protein in apatite hydrogel.     

Sphingomyelin from milk-characterization of liquid crystalline,liposome and emulsion properties

The properties of sphingomyelin obtained from bovine milk were investigated. In particular, the properties of liposomes and emulsions prepared from the spingomyelin, as well as the liquid crystalline behavior, were investigated and compared to those of related phosphatidylcholine systems. Like sphingomyelins from other sources, sphingomyelin from milk contains a large fraction of long and saturated acyl groups, which results in a high gel-to-liquid crystal transition temperature (T_c 35–82°C, depending on the lipid concentration). At high sphingomyelin concentrations, a lamellar phase forms above T_c, while a swollen gel phase is obtained below T_c. The gel phase swells to about 20 wt% water, whereas the swelling continues to about 40 wt% water above T_c. The limiting areas per molecule are 51 and 68 Ų below and above T_c, respectively. Sphingomyelin from milk forms liposomes readily in the presence of cholesterol. The liposomes formed have a diameter of about 100 nm and are stable, even at 0.1 M NaCl or HCl. Materials entrapped in the liposomes are released rather slowly (typically 40% over 5 h). A comparison shows that the sphingomyelin liposomes behave similarly to those formed by phosphatidylcholine systems. Furthermore, sphingomyelin from milk forms stable oil-in-water emulsions with soybean oil. The size of the emulsion droplets obtained was about 200 nm. Both the size of the emulsion droplets and its dependence on electrolyte addition correlate closely with those of emulsions formed by the corresponding phosphatidylcholine system. Therefore, it is possible to use sphingomyelin as an alternative for saturated phosphatidylcholines, which may be advantageous for oral and dermal pharmaceutical applications, as well as in cosmetics.     

Effect of Ionic Liquids on Surface and Aggregation Properties of Non-ionic Surfactant Triton™ X-100 in Aqueous Media

The effect of the hydrophilic ionic liquids (ILs) 1-butyl-2,3-dimethylimidazolium bromide [bdmim][Br] and 1-hexyl-2,3-dimethylimidazolium bromide [hdmim][Br] on the aggregation and surface active behaviour of the non-ionic surfactant Triton? X-100 (TX-100) was studied in aqueous media. Several aggregation properties of TX-100 + IL/water systems, such as critical micelle concentration (CMC), surface active parameters, aggregation number (N _agg) and aggregate size, were determined by surface tension, fluorescence and dynamic light scattering (DLS) techniques. It was found that the average micellar size and aggregation number decrease, whereas the CMC increases with increasing concentration of ILs. Interestingly, the CMC value of TX-100 is reduced slightly below 0.5 wt% of both the ILs in the medium. At higher wt% of IL in the system the CMC increases. It was demonstrated that ILs [bdmim][Br] and [hdmim][Br] can be judiciously used at different wt% for modifying the physico-chemical properties of TX-100.     

Thermal transitions of poly(N-isopropylmethacrylamide) in aqueous solutions

Thermal transitions of poly(N-isopropylmethacrylamide) (PIPMAm) in aqueous solutions were studied in a wide temperature range from −100 to 60 °C. The solutions of different polymer weight fractions (c=0.03-1) were investigated in cooling and heating scans of differential scanning calorimetry; four qualitatively different kinds of thermograms were identified in dependence of the fraction, c. The transitions are explained in a thermodynamic framework based on the phase diagram of the system. This diagram provides a complete understanding of thermal transitions in aqueous PIPMAm solutions as a function of c, in particular the existence of non-crystallizable water and the temperature induced phase transition that is due to the hydrophobic interaction in PIPMAm solutions.     

Effects of oxygen on the thermal stability of silicon nitride fibers

Two types of Si₃N₄ fibers with different oxygen contents were annealed in a nitrogen atmosphere at 1500 °C for 1 h. After annealing, the fiber (SN-L) containing 0.5 wt% oxygen crystallized to α-Si₃N₄ but lost its strength, whereas the fiber (SN-H) containing 4.2 wt% oxygen was amorphous and retained 63.6% of its strength. The phase transition in these fibers was mainly influenced by the oxygen level. The lower oxygen content in the SN-L favored the precipitation of an almost stoichiometric composition of α-Si₃N₄ initially at ~1450 °C with an activation energy (Ea) of 663.357 kJ/mol. Nanopores existing naturally in the fiber promoted crystallization via heterogeneous nucleation. SN-H precipitated as an amorphous SiN_xO_y metaphase preferentially at ~1400 °C with an Ea of 440.434 kJ/mol, owing to the higher oxygen content approaching that of Si₂N₂O. SiN_xO_y inhibited the crystallization of α-Si₃N₄, making SN-H more thermally stable than SN-L at temperatures above 1500 °C.     

Synthesis and properties of nanocomposites of WO3 and exfoliated g-C3N4

The nanocomposites of WO₃ nanoparticles and exfoliated graphitized C₃N₄ (g-C₃N₄) particles were prepared and their properties were studied. For this purpose, common methods used for characterization of solid samples were completed with dynamic light scattering (DLS) method and photocatalysis, which are suitable for study of aqueous dispersions.The WO₃ nanoparticles of monoclinic structures were prepared by a hydrothermal method from sodium tungstate and g-C₃N₄ particles were prepared by calcination of melamine forming bulk g-C₃N₄, which was further thermally exfoliated. Its specific surface area (SSA) was 115 m² g⁻¹.The nanocomposites were prepared by mixing of WO₃ nanoparticles and g-C₃N₄ structures in aqueous dispersions acidified by hydrochloric acid at pH = 2 followed by their separation and calcination at 450 °C. The real content of WO₃ was determined at 19 wt%, 52 wt% and 63 wt%. It was found by the DLS analysis that the g-C₃N₄ particles were covered by the WO₃ nanoparticles or their agglomerates creating the nanocomposites that were stable in aqueous dispersions even under intensive ultrasonic field. Using transmission electron microscopy (TEM) the average size of the pure WO₃ nanoparticles and those in the nanocomposites was 73 nm and 72 nm, respectively.The formation of heterojunction between both components was investigated by UV–Vis diffuse reflectance (DRS) and photoluminescence (PL) spectroscopy, high-resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS), photocatalysis and photocurrent measurements. The photocatalytic decomposition of phenol under the LED source of 416 nm identified the formation of Z-scheme heterojunction, which was confirmed by the photocurrents measurements. The photocatalytic activity of the nanocomposites decreased with the increasing content of WO₃, which was explained by shielding of the g-C₃N₄ surface by bigger WO₃ agglomerates. This study also demonstrates a unique combination of various characterization techniques working in solid and liquid phase.     

Toughening of silicon nitride ceramics by addition of multilayer graphene

Silicon nitride (Si₃N₄) ceramics have superior mechanical properties allowing their broad application in many technical fields. In this work, Si₃N₄-based composites with 1–5?wt% multilayer graphene (MLG) content were fabricated by spark plasma sintering at different temperatures and holding time in order to improve the fracture resistance of the Si₃N₄ ceramic. Our investigation focused on understanding the relationships between the microstructure and mechanical properties with special attention to the intergranular phases between Si₃N₄ matrix and MLG reinforcement.We have found that nanopores developed at the Si₃N₄-MLG interface due to a reaction between carbon and the oxygen available in the topmost layer of the Si₃N₄ particles. Interface porosity has an optimum for the toughening effect. In 1?wt% MLG/Si₃N₄ composites nanopores are local, but separated at the Si₃N₄-MLG interface, which promote the MLG pull-out mechanism imparting a significant toughening effect on the composite. Beyond the optimal 1?wt% MLG content, MLG platelets agglomerate and excessive porosity are developed at the Si₃N₄-MLG interfaces, leading to weaker matrix- graphene adhesion and thus lower fracture toughness.     

CO2‐Switchable Oil/Water Emulsion for Pipeline Transport of Heavy Oil

By mixing an aqueous solution of tertiary amine, N,N‐dimethylethanolamine (DMEA), with naphthenic acid (RCOOH) derived from heavy oil, a CO₂ switchable zwitterionic surfactant (RCOO^?DMEAH⁺) aqueous system was constructed. The CO₂ switchability of this zwitterionic surfactant was confirmed by visual inspection, pH measurements, and conductivity tests, i.e., the RCOO^?DMEAH⁺ decomposed into RCOOH, DMEAH⁺ and HCO₃^? after bubbling CO₂ through but switched back to its original state by subsequent bubbling N₂ through at 80 °C to remove the CO₂. The interfacial tension tests of heavy oil in DMEA aqueous solutions indicated that the solution containing 0.5 wt% of DMEA and 0.2 wt% of NaCl resulted in the lowest interfacial tension. The O/W emulsion formed when aqueous solutions of DMEA were used to emulsify heavy oil exhibited the best performance when the oil/water volume ratio, DMEA concentration, and NaCl concentration were 65:35, 0.5 and 0.2 wt%, respectively. The feasibility of pipeline transport of the O/W heavy oil emulsion was evaluated. The results illustrated that the demulsification of the O/W emulsion after transport could be easily realized by bubbling CO₂ through. Although demulsification efficiency still needs to be improved, the recycling of the aqueous phase after demulsification by removal of CO₂ looks promising.     

Stereolithographical fabrication of dense Si3N4 ceramics by slurry optimization and pressure sintering

Photocurable gray-colored Si₃N₄ ceramic slurry with high solid loading, suitable viscosity and high curing depth is critical to fabricate dense ceramic parts with complex shape and high surface precision by stereolithography technology. In the present study, Si₃N₄ ceramic slurry with suitable viscosity, high solid loading (45 vol %) and curing depth of 50 μm was prepared successfully when surface modifier KH560 (1 wt%) and dispersant Darvan (1 wt%) were used. The slurry exhibits the shear thinning behavior. Based on the Beer-Lambert formula, D_p (the attenuation length) and E_c (the critical energy dose) of Si₃N₄ ceramic slurry with solid loading of 45 vol % were derived as 0.032 mm and 0.177 mJ/mm², respectively. Si₃N₄ ceramic green parts with complex shape and high surface precision were successfully fabricated by stereolithography technology. After optimizing the debinding and sintering process for green parts, dense Si₃N₄ ceramics with 3.28 g/cm³ sintering density were fabricated. The microhardness and fracture toughness of as-sintered Si₃N₄ ceramics are ~14.63 GPa and ~5.82 MPa m^1/2, respectively, which are comparable to those of the samples by traditional dry-pressed and pressureless sintering technology. These results show that ceramic stereolithography technology could be promising to fabricate high performance ceramics, especially for gray-colored monolithic Si₃N₄ ceramics.     

Electrosynthesis in systems of two immiscible liquids and a phase transfer catalyst. V. The anodic chlorination of naphthalene

The anodic chlorination of naphthalene in a water/methylene chloride emulsion and using tetrabutylammonium ion as the phase transfer catalyst is demonstrated; in conditions where the aqueous phase is saturated NaCl, the organic yield of 1-chloronaphthalene is 56% and the current yield is 33% after the passage of 2.33 F mol^–1 of naphthalene. It is shown, however, that when the aqueous phase also contains zinc chloride so that the species transferred is [(C₄H₉)₄N⁺]₂ZnCl ₄ ^–– , the yields can be increased to 92% and 49% respectively. The mechanism of these chlorinations is discussed.