Nanofiltration in non-aqueous solutions by porous silica–zirconia membranes

Porous membranes having various average pore sizes, ranging from 1 to 4 nm, were prepared from silica–zirconia composite colloidal sols by sol–gel processes, and were used for nanofiltration (NF) experiments in non-aqueous solutions of ethanol and methanol. Silica–zirconia membranes, which were tested in pure alcohol solutions for the first time after the preparation of the membrane, showed a gradual decrease in flux for approximately 100 h and then reached a steady flux. When the feed, after reaching the steady flux with ethanol, was changed to another alcohol, steady flux was attained after only several hours. Ethylene glycol, diethylene glycol, triethylene glycol, polyethylene glycol (PEG) of various molecular weights (PEG400, 600, 1000, and 2000) were nanofiltrated in methanol and ethanol solutions at 50°C. Rejections in non-aqueous solutions increased with applied pressure, which is similar to aqueous solutions. Control of pore size of silica–zirconia membranes showing molecular weight cut-offs in methanol solutions at 300, 600, 1000, and >1000, respectively, was possible by the appropriate choice of colloidal particle sizes. Rejection in methanol solution showed a tendency similar to that in ethanol solution, while rejection in methanol was slightly larger than in ethanol solutions. In addition, rejection in water was much smaller than in methanol solution. For example, the rejection of PEG600 in water and methanol was 0.03 and 0.74, respectively. These results suggest that solvent type plays an important role in determining rejection, as a result of the interaction with solvents and/or membrane surface.     

Stability and performance of porous silica–zirconia composite membranes for pervaporation of aqueous organic solutions

Porous silica–zirconia membranes were fabricated by the sol–gel techniques to study their stability against water and the pervaporation performance of aqueous solutions of organic solvents. Zirconia (10–70 mol%) was added to silica to obtain silica–zirconia composite membranes by firing at 400–500 °C for pervaporation tests with organic solvent/water mixtures, such as iso-propyl alcohol (IPA)/water and tetrahydrofuran (THF)/water mixtures at their normal boiling points.The membrane coatings have been done effectively by the hot-coating methods proposed previously. Boiling water treatments introduced in the coating processes have made the membranes quite stable even in the high water concentration region of aqueous organic solutions at their normal boiling points. Zirconia contents larger than about 40 mol% have made the silica–zirconia membranes quite stable. The membranes of zirconia contents less than about 30 mol% were found not stable in a dilute aqueous solution of IPA. The membranes fabricated by the conventional dip-coating methods with slow drying were not stable against water because of the probable segregation of silica and/or silica-rich phases during drying.The membranes fired at lower temperature (400 °C) gave a higher water flux of around 500 mol m⁻² h⁻¹ (9 kg m⁻² h⁻¹) with a separation factor larger than 1500 at 10 wt.% of water in the boiling feed of IPA/water mixture, for example.     

Janus Gold Nanostars–Mesoporous Silica Nanoparticles for NIR-Light-Triggered Drug Delivery

Janus gold nanostar–mesoporous silica nanoparticle ( AuNSt–MSNP ) nanodevices able to release an entrapped payload upon irradiation with near infrared (NIR) light were prepared and characterized. The AuNSt surface was functionalized with a thiolated photolabile molecule ( 5 ), whereas the mesoporous silica face was loaded with a model drug (doxorubicin) and capped with proton-responsive benzimidazole-β-cyclodextrin supramolecular gatekeepers ( N 1 ). Upon irradiation with NIR-light, the photolabile compound 5 photodissociated, resulting in the formation of succinic acid, which induced the opening of the gatekeeper and cargo delivery. In the overall mechanism, the gold surface acts as a photochemical transducer capable of transforming the NIR-light input into a chemical messenger (succinic acid) that opens the supramolecular nanovalve. The prepared hybrid nanoparticles were non-cytotoxic to HeLa cells, until they were irradiated with a NIR laser, which led to intracellular doxorubicin release and hyperthermia. This induced a remarkable reduction in HeLa cells viability.     

Hexafluoropropylene Oxide–Alcohol: A Convenient System for Silica Dissolution

Abstract

A new method of silica dissolution is described. It involves the formation of a stable SiF₄ · n ROH complex (1, 1a) just from SiO₂ and anhydrous alcoholic HF generated in situ from commercially available hexafluoropropene oxide. Alcoholic SiF₄ complexes can be easily converted to different organosilicon compounds of the type SiF₄L₂ and (LH)₂SiF₆ [L = 1,10-phenantroline (2a), 2,2′-dipyridyl (2b), Me₂SO (2c), pyridine (2d), triethanolamine (3a)]. Different silica-containing compounds can be used in this strategy—silicagel, sand, alumosilicates, and even rice husk.

GRAPHICAL ABSTRACT     

Polyaphrons as Templates for the Sol–Gel Synthesis of Macroporous Silica

Macroporous silica was synthesized using polyaphrons as shape-directing templates in a sol–gel hydrolysis scheme using tetraethyl orthosilicate (TEOS). Polyaphrons are a special class of high internal phase ratio emulsions (HIPRE) that can potentially be used in the continuous processing of long range ordered macroporous solids. The structures so formed were examined using a scanning electron microscope after thermal curing to 400C. The majority of the pores in the silica structures were in the range between 0.1 and 10 m. Key parameters affecting the polyaphrons template characteristics were varied and their effects on the final silica structure were studied.     

Platinum nanoparticles supported on zirconia–carbon black nanocomposites for methanol oxidation reaction

Platinum (Pt) nanoparticles supported on zirconia–carbon black nanocomposites (Zr–C), which annealed at different temperatures, used as Pt/Zr–C electrocatalysts for methanol oxidation reaction (MOR) are prepared and characterized in this study. Transmission electron microscope images and X-ray diffraction analysis showed that the diameters of Pt nanoparticles are around 3–4 nm. Electrocatalytic MOR performances of these Pt/Zr–C electrocatalysts are investigated by cyclic voltammetry, CO-stripping voltammetry, and chronoamperometry. All the Pt/Zr–C electrocatalysts synthesized in this study exhibited higher MOR efficiency than that of the commercial E-TEK Pt/C electrocatalyst, and the electrocatalyst using Zr–C support annealed at 300 °C, achieving the highest MOR efficiency among all the electrocatalysts.     

Ceramic–glass composite high temperature seals for dense ionic-conducting ceramic membranes

A basic principle for selecting inorganic sealing materials for dense ionic-conducting ceramic membranes is described for high temperature permeation/reaction experiments. Based on this principle ceramic–glass composite seals consisting of the Pyrex glass and the ceramic powder of the membrane were developed and successfully used to seal a number of different dense ceramic membranes at high temperatures. The ceramic–glass composite seal is typically composed of 40–50 wt.% membrane material powder, 20–50 wt.% Pyrex glass and 5–20 wt.% additive such as sodium aluminate and boron oxide. The properties of ceramic–glass composite seal can be tailored to obtain suitable wettability, viscosity, chemical inertness, thermal expansibility, and bonding strength for good sealing results. A success rate for sealing these ceramic membranes of nearly 100% is possible using the ceramic–glass composite recipe if the correct sealing procedure, including seal paste preparation, is carefully followed.     

Synthesis and morphology of polycaprolactone–block-polyimide–block-polycaprolactone triblock copolymers for film separation membranes

Triblock copolymers with the central polyimide block and peripheral polycaprolactone blocks were synthesized by controlled ring-opening anionic coordination polymerization of ε-caprolactone on polyimide macroinitiators with terminal hydroxy groups. The chemical structure of the products was determined by spectroscopic methods, and the molecular-mass characteristics of the triblock copolymers and their separate blocks were determined by size-exclusion chromatography. Examination of the phase morphology of strong self-supporting films formed from the copolymer solutions revealed microphase segregation on the nanometer level in the films.     

PPO-based acid–base polymer blend membranes for direct methanol fuel cells

New acid–base polymer blend membranes for direct methanol fuel cells (DMFC) have been designed using a very accessible commercial polymer, poly(2,6-dimethyl-1,4-phenylene oxide) (PPO). The preparation begins with the sulfonation and bromination of PPO to sulfonated PPO (SPPO) and bromomethylated PPO (BrPPO), respectively. Blend membranes are formed by mixing n-propylamine(PrNH₂)-neutralized SPPO and PrNH₂-aminated BrPPO solutions in N-methyl-2-pyrrolidone (NMP), and casting the mixed solution on glass petri dishes followed by acidification with aqueous hydrochloric acid. The compatibility between the acid and base components of the blend is assured by using acidic and basic polymers deriving from the same parent polymer (PPO). Ionic crosslinking is established between the sulfonic groups of SPPO and the amine groups of aminated BrPPO. The ionic crosslinking strengthens the membrane dimensional stability by reducing water uptake and membrane swelling up to temperatures as high as 80 °C. The membranes fabricated as such display good resistance to methanol crossover amidst some, but acceptable loss of proton conductivity. The characteristic factor (i.e. the ratio of proton conductivity to methanol permeability) increases noticeably with the BrPPO content, with the sample containing 30 wt.% BrPPO showing a 16-fold improvement over Nafion 117. The mechanical properties and oxidative stability of the blend membranes also satisfy the requirements for fuel cell assembly and operation.     

Stabilized superhydrophobic composite membranes prepared by electrospinning for oil–water separation

In dealing with the oil–water separation process, improving the oil–water selectivity of the membrane surface and increasing the porosity within the membrane are effective means to achieve durable and efficient oil–water separation. Therefore, polystyrene/polyacrylonitrile-polyvinylidene fluoride/Polydimethylsiloxane Fe₃O₄ nanoparticles (PS/PAN-PVDF/PDMS@Fe₃O₄) composite membranes with superhydrophobicity and lipophilicity were prepared by electrospinning technique. By controlling the filling concentration of Fe₃O₄ nanoparticles, a stable superhydrophobic and lipophilic rough structure was constructed, and micro–nano multilayer rough voids existed inside the membrane. The results showed that the composite fiber membrane exhibited exceptional superhydrophobicity (156.2°), thermal stability (338°C), mechanical properties (tensile strength of 3.0 MPa, elongation of 33.9%), and oil adsorption capacity (30–100 g/g). Moreover, even under corrosive environments, this composite fiber membrane maintained its superhydrophobic properties (above 152°) and achieved high oil–water separation efficiency (above 97%). Remarkably, after 40 cycles, the composite membrane could sustain a separation flux of 5000 L m⁻² h⁻¹. Consequently, the composite fiber membrane manufactured using this strategy exhibits promising potential for applications in oil–water separation.     

Metal–organic framework-based mixed-matrix membranes for gas separation: An overview

Mixed-matrix membranes (MMMs) have been studied widely in the field of gas separation due to their potential to overcome performance barriers found in traditional polymeric membranes. Most polymeric membranes exhibit a trade-off between permeation and selectivity, which has limited their development in many challenging separation applications. One solution to this issue utilizes the introduction of fillers into the polymer matrix to produce MMMs. Out of the many different fillers, metal–organic frameworks stand out as a promising candidate due to their highly tunable structure, molecular sieving effect, and superior compatibility with the polymer matrix. This review will provide an in-depth look into the basic mechanisms of MMMs for gas separation and different approaches to model the permeation of gases through the membrane. In addition, challenges facing the field and recent research trends for MMMs will be discussed as well as their many applications for different gas separations. Finally, some insight on the future direction for MMMs will be covered, focusing on many intriguing opportunities and challenges that must be further explored to advance this technology.     

Silica–gelatin hybrids for tissue regeneration: inter-relationships between the process variables

Owing to their diverse range of highly tailorable material properties, inorganic/organic hybrids have the potential to meet the needs of biodegradable porous scaffolds across a range of tissue engineering applications. One such hybrid platform, the silica–gelatin sol–gel system, was examined and developed in this study. These hybrid scaffolds exhibit covalently linked interpenetrating networks of organic and inorganic components, which allows for independent control over their mechanical and degradation properties. A combination of the sol–gel foaming process and freeze drying was used to create an interconnected pore network. The synthesis and processing of the scaffolds has many variables that affect their structure and properties. The focus of this study was to develop a matrix tool that shows the inter-relationship between process variables by correlating the key hybrid material properties with the synthesis parameters that govern them. This was achieved by investigating the effect of the organic (gelatin) molecular weight and collating previously reported data. Control of molecular weight of the polymer is as an avenue that allows the modification of hybrid material properties without changing the surface chemistry of the material, which is a factor that governs the cell and tissue interaction with the scaffold. This presents a significant step forward in understanding the complete potential of the silica–gelatin hybrid system as a medical device.     

Influence of the zirconia transformation on the thermal behavior of zircon–zirconia composites

During a heating?Ccooling cycle, zirconia (ZrO₂) undergoes a martensitic transformation from monoclinic to tetragonal structure phases, which presents special hysteresis loop in the dilatometry curve at temperatures between 800 and 1100?°C. Monoclinic zirconia (m-ZrO₂) particles reinforced ceramic matrix composites not always present this behavior. In order to elucidate this fact a series of zircon?Czirconia (ZrSiO₄?CZrO₂) ceramic composites have been obtained by slip casting and characterized. The final properties were also correlated with the zirconia content (0?C30?vol.%). The influence of the martensitic transformation (m?Ct) in well-dispersed zirconia grains ceramic composite on the thermal behavior was analyzed. Thermal behavior evaluation was carried out; the correlation between the thermal expansion coefficients with the zirconia content showed a deviation from the mixing rule applied. A hysteresis loop was observed in the reversible dilatometric curve of composites with enough zirconia grains (??10?vol.%). Over this threshold the zirconia content is correlated with the loop area. The transformation temperatures were evaluated and correlated with the zirconia addition. When detected the m?Ct temperature transformation is slightly influenced by the zirconia content (due to the previously evaluated decrease in the material stiffness) and similar to the temperature reported in literature. The reverse (cooling) transformation temperature is strongly decreased by the ceramic matrix. The DTA results are consistent with the dilatometric analysis, but this technique showed more reliable results. Particularly the endothermic m?Ct transformation temperature showed to be easily detected even when the only m-ZrO₂ present was the product of the slight thermal dissociation of the zircon during the processing of the pure zircon material.     

Structural and mechanical characterizations of microporous silica–boron membranes for gas separation

This paper presents structural and mechanical characterizations of microporous silica membranes for gas separation. The membrane separative layer is made of microporous silica–B₂O₃ produced via a sol–gel process. This layer of about 200 nm of thickness is deposited on the internal surface of a tubular asymmetric γ-alumina/α-alumina support. FTIR and Raman analyses indicate the presence of the boron in the silica net and the above methods in conjunction with ¹¹B MAS NMR analyses of the samples indicate that boron is located mainly in the tetrahedral framework position. Such membranes present interesting gas separation properties at temperatures up to 500 °C and transmembrane pressures lower than 8 bar. He permeance values close to 10⁻¹⁰ kmol m⁻² s⁻¹ Pa⁻¹ are obtained, associated with ideal selectivity α(He/CO₂) which can reach 55. Mechanical properties of separative silica-modified layers are measured by nanoindentation and the coefficient of thermal expansion is obtained from pure material.     

Dimensionally stable Nafion–polyethylene composite membranes for direct methanol fuel cell applications

Nafion^® impregnated Solupor^®, microporous UHMWPE film, (N-PE), Nafion^®117 (N117) and a membrane prepared using a DE2020 Nafion^® dispersion (DE2020) were characterized with respect to their swelling degree (SD), methanol cross-over, proton conductivity and DMFC performance at various methanol concentrations in order to understand the effect of impregnation of an ion-conductive polymer membrane to the fuel cell performance.     

Quasi-solid electrolyte membranes with percolated metal–organic frameworks for practical lithium-metal batteries

High-energy Li-metal batteries (LMBs) suffer from short cycle life and safety issues due to severe parasitic reactions and dendrite growth of Li metal anode (LMA) in liquid electrolytes [1–3].It is generally believed that replacing liquid electrolytes with solidstate electrolytes (SSEs) would be a feasible approach for practical LMBs [4,5]. Conventional SSEs including ceramic and polymer electrolytes have been studied for decades.     

Silica–PSCl3: A Mild and Efficient Reagent for Deoxygenation of Sulfoxides

A new solid supported reagent, silica–PSCl₃, has been developed for deoxygenation of sulfoxides. With this reagent, conversion of sulfoxides to sulfides occurred cleanly and efficiently at room temperature. Facile isolation of the product was achieved by simple filtration of the by‐products without any extensive workup.     

Silica–Sulfuric Acid Catalyzed Nitrodeiodination of Iodopyrazoles

Abstract

We report here the synthesis of nitropyrazoles in good to excellent yields from iodopyrazoles over silica–sulfuric acid catalyst for the first time. The present procedure require less acid, offers a simplified workup procedure, and may be applied for the nitration of a wide variety of iodoazoles in drug and pharmaceutical industries.