Synthesis of monodisperse silica microspheres and modification with diazoresin for mixed‐mode ultra high performance liquid chromatography separations

Monodisperse silica particles with average diameters of 1.9–2.9 μm were synthesized by a modified Stöber method, in which tetraethyl orthosilicate was continuously supplied to the reaction mixture containing KCl electrolyte, water, ethanol, and ammonia. The obtained silica particles were modified by self‐assembly with positively charged photosensitive diazoresin on the surface. After treatment with ultraviolet light, the ionic bonding between silica and diazoresin was converted into covalent bonding through a unique photochemistry reaction of diazoresin. Depending on the chemical structure of diazoresin and mobile phase composition, the diazoresin‐modified silica stationary phase showed different separation mechanisms, including reversed phase and hydrophilic interactions. Therefore, a variety of baseline separation of benzene analogues and organic acids was achieved by using the diazoresin‐modified silica particles as packing materials in ultra high performance liquid chromatography. According to the π–π interactional difference between carbon rings of fullerenes and benzene rings of diazoresin, C₆₀ and C₇₀ were also well separated by ultra‐high performance liquid chromatography. Because it has a small size, the ∼2.5 μm monodisperse diazoresin‐modified silica stationary phase shows ultra‐high efficiency compared with the commercial C₁₈‐silica high‐performance liquid chromatography stationary phase with average diameters of ∼5 μm.     

Effect of additives on the surface active and morphological features of 1-octyl-3-methylimidazolium halide aggregates in aqueous media

The influence of two salts as additives namely sodium chloride and sodium sulphate and a nonelectrolyte, 2-butoxyethanol on surface chemical and aggregation characteristics of ionic liquids (IL) of 1-octyl-3-methylimidazolium chloride, [C₈mim][Cl], 1-octyl-3-methylimidazolium bromide, [C₈mim][Br], and 1-octyl-3-methylimidazolium iodide, [C₈mim][I] in aqueous media were monitored through surface tension and small angle neutron scattering measurements. The addition of salts drastically decreased the critical aggregation concentration (CAC) and increased the area per adsorbed IL molecule. The co-ions of salts modify the surface of IL molecules and aggregates through various interactions such as charge neutralization, specific interactions and dehydration The results obtained by analyzing the SANS curves in the whole Q range showed that the oblate ellipsoidal shape of the aggregates of ionic liquids is un-altered upon the addition of additives. However the additives facilitate the growth of the aggregates in to microstructures with cubic packing at high salt concentrations.     

Analyzing the adsorption of blood plasma components by means of fullerene-containing silica gels and NMR spectroscopy in solids

The results from studying the adsorption of blood plasma components (e.g., protein, triglycerides, cholesterol, and lipoproteins of low and high density) using silica gels modified with fullerene molecules (in the form of C₆₀ or the hydroxylated form of C₆₀(OH) _x ) and subjected to hydration (or, alternatively, dehydration) are presented. The conditions for preparing adsorbents that allow us to control the adsorption capacity of silica gel and the selectivity of adsorption toward the components of blood plasma, are revealed. The nature and strength of the interactions of the introduced components (fullerene molecules and water) with functional groups on the silica surface are studied by means of solid state NMR spectroscopy (NMR-SS). Conclusions regarding the nature of the centers that control adsorption are drawn on the basis of NMR-SS spectra in combination with direct measurements of adsorption. The interaction of the oxygen of the hydroxyl group of silica gel with fullerene, leading to the formation of electron-donor complexes of C₆₀-H, C₆₀-OH, or C₆₀-OSi type, is demonstrated by the observed changes in the NMR-SS spectra of silica gels in the presence of fullerene.     

Magnetic properties and dye adsorption capacities of silica–hematite nanocomposites with well-defined structures prepared in surfactant solutions

Silica–hematite (α-Fe₂O₃) nanocomposites were synthesized by addition of aqueous solution containing ferrous ions (Fe²⁺), cetyltrimethylammonium bromide (CTAB) as a surfactant and tert-butanol (t-butanol) as a cosurfactant into colloidal silica solution. At alkaline atmosphere, silica surface with negative charges electrostatically attracts positively-charged iron hydroxide nuclei or particles which are stabilized by cationic CTAB molecules, and then silica–iron compound composites could be formed. Finally, the silica–hematite composite particles were obtained after calcination at 800 °C for 4 h. Through these processes, two types of composites having “core–shell type” or “decorated type” could be achieved. Morphology, BET surface area, crystallinity and magnetic properties of samples were analyzed by using TEM, BET, XRD and VSM, respectively. The “decorated type” composites had larger BET surface area and better magnetization. Also, to estimate the application in water treatment, adsorption properties of composites were studied through methylene blue (MB) adsorption which was characterized by UV–vis spectroscopy, involving collection of composites with neodymium magnet.     

Explaining Fullerene Dispersion by using Micellar Solutions

An effective computational strategy to describe the dispersion of C₆₀ by surfactants is presented. The influence of parameters such as surfactant concentration and molecular length on the final morphology of the system is explored to explain the experimental results and to understand the incorporation of C₆₀ inside micelles. Both neutral and charged amphiphilic molecules are simulated. The long‐discussed problem of the location of fullerenes in micelles is addressed and C₆₀ is found in the hydrocarbon‐chain region of the micelles. If the available hydrophobic space increases, C₆₀ is localized in the inner part of the micellar core. Short, charged amphiphilic stabilizers are more efficient at dispersing fullerenes monomolecularly. Two different phases of C₆₀ are observed as the C₆₀/surfactant ratio varies. In the first, aggregates of C₆₀ are entrapped inside the micelles, whereas, in the second, colloidal nanoC₆₀ is formed with surfactants adsorbed on the surface.     

Preparation of ultrathin membranes by layer-by-layer (LBL) deposition of oppositely charged inorganic colloids

Nanofilms were prepared by alternating deposition of Mg–Al (2:1) NO ₃ ⁻ layered double hydroxide (LDH), hectorite and silica particles present study. The charge density of the oppositely charged materials strongly affect film properties like thickness and ordering. The specific charge of the colloidal particles was measured with the particle charge detector. The sequential build up of the thin films was followed by spectrophotometry and X-ray diffraction (XRD). The surface morphology of the formed multilayers was characterized and film thickness determination was performed by atomic force microscopy. The influence of the charge density of hectorite and silica particles on the LDH/hectorite, LDH/silica film thickness was studied. The results reveal that the LDH concentration has a significant effect on the film thickness while the hectorite and silica concentration were not important. Films prepared from the different types of negatively charged inorganic particles in the same concentration range (0.25–1.0%) have similar thickness because of the much higher surface charge relative to the LDH lamellae.     

Preparation of poly(methyl methacrylate)/CaCO3/SiO2 composite particles via emulsion polymerization

A novel method to prepare organic/inorganic composite particles, i.e. poly(methyl methacrylate)/CaCO₃/SiO₂ three-component composite particles, using emulsion polymerization of methyl methacrylate with sodium lauryl sulfate as a surfactant in an aqueous medium was reported. CaCO₃/SiO₂ two-component inorganic composite particles were obtained firstly by the reaction between Na₂CO₃ and CaCl₂ in porous silica (submicrometer size) aqueous sol and the specific surface area of the particles was measured by the Brunauer–Emmett–Teller (BET) method. The results show that the BET specific surface area of the CaCO₃/SiO₂ composite particle is much smaller than that of the silica particle, indicating that CaCO₃ particles were adsorbed by porous silica and that two-component inorganic composite particles were formed. Before copolymerization with methyl methacrylate, the inorganic composite particles were coated with a modifying agent through covalent attachment. The chemical structures of the poly(methyl methacrylate)/CaCO₃/SiO₂ composite particles obtained were characterized by Fourier transform IR spectroscopy and thermogravimetric analysis. The results show that the surface of the modified inorganic particles is grafted by the methyl methacrylate molecules and that the grafting percentage is about 15.2%.     

Solubilization and stabilization of fullerene C60 in presence of poly(vinyl pyrrolidone) molecules in water

Solubilizing C₆₀ molecules in an aqueous medium is highly imperative in processing them in different forms of ionic or nonionic liquids, nanofluids, films and other derivatives. In this investigation, we report a facile chemical route using polymer molecules of poly(vinyl pyrrolidone) (PVP) which mediate C₆₀ molecules dissolving in water in a stable solution at room temperature. Poly(vinyl pyrrolidone) molecules, soluble in water as well as many organic liquids such as n-butanol, ethanol, or DMF, can be useful for transferring C₆₀ molecules from a non-aqueous to an aqueous system. A broad optical absorption arises over 270–520 nm when C₆₀ molecules are dissolved in water, 0.001–0.065 g/L in presence of 20–120 g/L PVP molecules. It consists of a strong π → π* absorption band (relatively sharp) lying at 294 nm in C(sp²) electrons from PVP-surface modified C₆₀ molecules followed by a broad charge transfer band which extends up to 520 nm. Upon a suitable surface modification, the C₆₀ molecules conquer enhanced optical absorption in both kinds of the bands. Dynamic light scattering reveals an average hydrodynamic length 181.5 nm and a polydispersity index 0.506 after a typical loading 0.065 g/L C₆₀. A zeta potential ?8.3 mV with a surface conductivity 0.064 mS/cm at 6.5 pH describes a negatively charged surface structure, showing an n-electron transfer from C=O (PVP) to a nanosurface in surface modified C₆₀ molecules in a weak donor–acceptor complex. Water soluble C₆₀ in presence of a biocompatible compound like PVP is useful for biological, medicinal, and other applications.     

Intumescent mineral fire retardant systems in ethylene-vinyl acetate copolymer: Effect of silica particles on char cohesion

Silica particles of different physical properties (particle size, morphology and specific surface area) were introduced into an ethylene-vinyl acetate copolymer filled with an intumescent mineral fire retardant system containing magnesium hydroxide and organo-modified montmorillonites. The effect of silica particles on the cohesion and strength of the foamed combustion residue was studied by micro-indentation, concurrently with the characterization of material's fire behavior.Silica particles seem to act as defects that generate cracks, decreasing the strength of the residue. This generation of cracks is connected to a lower cohesion of the residue, especially for silica particles of high specific surface area. In parallel, the presence of silica of high specific surface area, despite tending to decrease Time To Ignition, also improves self-extinguishing ability, thanks to a better thermal stability at higher temperatures, and reduces the maximum Heat Release Rate in cone calorimeter tests.     

Unique Separation Behavior of a C60 Fullerene‐Bonded Silica Monolith Prepared by an Effective Thermal Coupling Agent

Herein, we report a newly developed C₆₀ fullerene‐bonded silica monolith in a capillary with unique retention behavior due to the structure of C₆₀ fullerene. N‐Hydroxysuccinimide (NHS)‐conjugated C₆₀ fullerene was successfully synthesized by a thermal coupling agent, perfluorophenyl azide (PFPA), and assigned by spectroscopic analyses. Then, NHS‐PFPA‐C₆₀ fullerene was attached onto the surface of a silica monolith in a capillary. The capillary provided specific separation ability for polycyclic aromatic hydrocarbons in liquid chromatography by an effective π–π interaction. Furthermore, corannulene, which has a hemispherical structure, was selectively retained in the capillary based on the specific structural recognition due to the spherical C₆₀ fullerene. This is the first report revealing the spherical recognition ability by C₆₀ fullerene in liquid chromatographic separation.     

Formation of dimer, trimer, and tetramer of C60 and C70 by γ-ray, charged-particle irradiation, and their HPLC separation

C₆₀ and C₇₀ fullerenes were irradiated by high-energy γ-rays and charged particles. Coalesced products of C₆₀ and C₇₀ have been isolated and detected in the liquid phase by a radiochromatographic technique. It was found that not only ¹¹C radioactive fullerene dimer, trimer, and possibly tetramer were produced by a recoil implantation process following nuclear reaction, but also such non-radioactive coalesced products were produced by the recombination process after ionization by γ-rays or charged particles.     

PHOTOCHEMISTRY ON SURFACES. EXCITED STATE BEHAVIOR OF RUTHENIUM TRIS(BATHOPHENANTHROLINE DISULFONATE) ON COLLOIDAL ALUMINA-COATED SILICA PARTICLES*

Abstract— The excited state behavior of an anionic ruthenium(II) complex, RuL₃^4-(L=bathophen-anthroline disulfonate), that is electrostatically bound to positively charged alumina-coated silica particles is investigated. The apparent association constant for the binding of RuL₃^4-to the particles is 1.2 × 10⁴M^-1. Surface photochemical processes result in decreased emission yields and multiexponential excited state decay. Excited state quenching by ground-state molecules is evident at high surface coverages. The non-exponential decay kinetics observed at low surface coverages can be attributed either to clustering of the RuL₃^4-molecules or photoionization promoted by Lewis acid sites on the particle surface.     

Synthesis of fullerene-silica hybrid materials

Fullerene/silica hybrid materials were obtained by radiation grafting on silica surface of toluene or decalin solutions of C₆₀. As determined by thermogravimetric analysis, the amount of C₆₀ grafted on silica surface was dependent from the radiation dose administered and independent from the C₆₀ concentration and the nature of the organic solvent. In absence of air, a dose of 48 kGy was sufficient to ensure a grafting level of 30% by weight of C₆₀ in the hybrid material. The fullerene/silica hybrid material shows a remarkable thermal stability, since the early decomposition starts above 300 °C as measured by DTG and DTA. The chemical structure of the fullerene/silica hybrid material was determined by FT-IR spectroscopy and with solid state ¹³C CP-MAS NMR. The potential application of such materials has been outlined.     

The influence of mixed cationic–anionic surfactants on the three-phase contact parameters in silica–solution systems

The formation of thin wetting films on silica surface from aqueous solution of (a) tetradecyltrimetilammonium bromide (C₁₄TAB) and (b) surfactant mixture of the cationic C₁₄TAB with the anionic sodium alkyl- (straight chain C₁₂–, C₁₄– and C₁₆–) sulfonates, was studied using the microscopic thin wetting film method developed by Platikanov. Film lifetimes, three-phase contact (TPC) expansion rates, receding contact angles and surface tension were measured. It was found that the mixed surfactants caused lower contact angles, lower rates of the thin aqueous film rupture and longer film lifetimes, as compared to the pure C₁₄TAB. This behavior was explained by the strong initial adsorption of interfacial complexes from the mixed surfactant system at the air/solution interface, followed by adsorption at the silica interface. The formation of the interfacial complexes at the air/solution interface was proved by means of the surface tension data. It was also shown, that the chain length compatibility between the anionic and cationic surfactants controls the strength of the interfacial complex and causes synergistic lowering in the surface tension. The film rupture mechanism was explained by the heterocoagulation mechanism between the positively charged air/solution interface and the solution/silica interface, which remained negatively charged.     

Properties of the surface of silicas modified with bi-and trifunctional perfluorohexylsilanes: Adsorption of benzene

Diffuse reflection IR spectroscopy, static adsorption, and gas chromatography were used to study the chemistry and adsorption properties of the surface of silicas modified by chemically grafted bi-(C₆F₁₃(II)) and trifunctional (C₆F₁₃(III)) perfluorohexylsilanes. It was established that the modification of silica (SiO₂) results in a nearly complete screening of free silanols. At the same time, IR spectra featured absorption bands belonging to weakly perturbed OH groups capable of interacting with benzene molecules. The IR spectroscopy data on benzene adsorption were found to be in close agreement with the results of static adsorption and chromatographic measurements, according to which the specific amount of benzene adsorbed decreases in the series SiO₂ > C₆F₁₃(III) > C₆F₁₃(II). It was demonstrated that the heat of adsorption of benzene on the C₆F₁₃(III) sample is higher than that on the initial carrier. Grafted layers prepared from the trifunctional modifier exhibited higher efficiency in preventing benzene molecules from reaching the carrier surface.     

Polymer-silica nanocomposite membranes for CO2 capturing

Reducing carbon dioxide (CO₂) is an area of great interest in current international efforts geared toward lowering emissions and combating global warming. In this work, amino-silica composite membranes were prepared and used to capture carbon dioxide. The surface of silica particles was chemically modified with amine to efficiently capture carbon dioxide. The phase separation technique was used to prepare the membranes from a composite containing polyvinylidene-fluoride-hexafluoropropylene (PVDF-HFP), amino-silica particles, acetone and water. SEM images revealed that the membranes composed of multilayers of porous polymer uniformly impregnated with silica particles. Both XRD and FTIR results have validated the perfect integration of silica particles within the polymeric network. The mechanical properties of the membrane are improved by the presence of silica particles as proved by the high tensile strength value (1.5 N/cm²) obtained for the PVDF-HFP/SiO₂ membrane compared to 0.9 N/cm² obtained for bare PVDF-HFP membrane. Also, we succeeded in recording SEM images to show that the plastic deformation of the film is associated with the formation of macro-holes. To the best of our knowledge this is the first time for such results to be monitored with SEM to observe the macroscopic evolution of the structure. Additionally, the surface area was significantly increased from 3.8 m²/g for bare PVDF-HFP membrane to 116.4 m²/g for PVDF-HFP impregnated with silica particles. Moreover, the CO₂ separation efficiency depends on both surface area and the quantity of amino-SiO₂ added to the membrane. The addition of amino-silica particles leads to a significant uptake of carbon dioxide compared to non-modified polymer membrane. The results obtained indicated that combing the phase separation with amino silica particles provided a cost-effective route to scaling up the synthesis of membranes that were mechanically stable and highly efficient at CO₂ capture.     

Fabrication of silica-on-titania and titania-on-silica nanoparticle assemblies

Structures of silica particles on a titania surface and titania particles on a silica surface were formed by deposition of SiO₂ or TiO₂ nanoparticles on pre-patterned substrates. Photolithography was used to create a matrix for the selective deposition of nanoparticles by immersion in a colloidal suspension. Atomic force microscopy was used to investigate the topography of these inorganic assemblies. Whereas two-dimensional colloidal patches of TiO₂ nanoparticles are obtained on silica surfaces, SiO₂ nanoparticles form three-dimensional, U-shaped channels on titania surfaces.The influence of electrostatic forces on assembly structure is vital. The isoelectric points of the particles, the pre-patterned matrix and the photo-resist are key parameters and may be manipulated to achieve various microstructures. The 2D nanoparticle arrays of titania on silica and 3D channels (built of silica nanoparticles) on flat titania surfaces are of potential interest in lab-on-a-chip applications.     

C60 Based Hybrid Nanocomposites Obtained in the Presence of Ultrasounds

Since their discovery, fullerenes in general and buckminsterfullerene C₆₀ in particular, became a subject of great interest for studies. Being compatible with the sol–gel process, one of the promising approaches is to incorporate the fullerene molecules in sol–gel oxide matrices. Great part of studies deals with SiO₂ sol–gel oxide as the optimal matrix for entrapment of organic molecules. C₆₀-doped silica matrices used through our present study have been prepared by sol–gel processing, using different alkoxide precursors, as a silicon oxide source: tetraethoxysilane (a), methyltriethoxysilane (b), phenyltriethoxysilane (c) and a mixture of phenyltriethoxysilane and tetraethoxysilane (d). C₆₀-to-Si molar ratio was chosen to be 1.0 × 10^?3:1 for all materials synthesized, final oxide composition remaining unchanged in all cases. The effect of ultrasounds on the gelation process was established by preparing two series of samples, either via sonication or in the absence of ultrasound processing. The properties of the resulted materials were also established. The prepared samples were characterized by XRD, IR, RPE and UV-VIS spectrometry. All methods have put in evidence the embedment of the fullerene into the silica matrix.     

Zirconyl-containing microspheric silica gel surfaces

The adsorption properties of two samples of zirconyl-containing silica gels derived from zirconium oxychloride, polyetoxysiloxane oligomer 3% ZrOCl₂/SiO₂ (composite 1) and tetraetoxysilane 5% ZrOCl₂/SiO₂ (composite 2) were investigated by gas chromatography at low surface coverages. n-Alkanes and n-alkenes (C₆–C₈), C₆H₆ were used as test adsorbates, along with polar compounds whose molecules had different donor-acceptor interaction abilities. The dispersion and specific (electron-donor and electronacceptor) components of the energy of intermolecular interactions for the studied systems were determined from the experimental data on chromatographic retention. It was shown that composite 2 had a higher dispersion potential and higher surface energy characteristics of the surface’s electron-donating and electronacceptor centers, as compared to composite 1.     

Comparison of electrochemical properties of two-component C60-Pd polymers formed under electrochemical conditions and by chemical synthesis

The electrochemical behavior of C₆₀-Pd polymer formed under electrochemical conditions and by the chemical synthesis was examined. In these polymers, fullerene moieties are covalently bonded to palladium atoms to form a polymeric network. Both materials deposited at the electrode surface show electrochemical activity at negative potentials due to the reduction of fullerene cage. Electrochemically formed thin polymeric films exhibit much more reversible voltammetric response in comparison to chemically synthesized polymers. The morphology and electrochemical behavior of chemically synthesized C₆₀-Pd polymer depend on the composition of grown solution. Chemical polymerization results in formation of large, ca. 50 μm, crystallic superficial structures that are composed of regular spherical particles with a diameter of 150 nm. The capacitance properties of C₆₀-Pd films were investigated by cyclic voltammetry and faradaic impedance spectroscopy. Specific capacitance of chemically formed films depends on the conditions of film formation. The best capacitance properties was obtained for films containing 1:3 fullerene to Pd molar ratio. For these films, specific capacitance of 35 Fg^?1 was obtained in acetonitrile containing (n-C₄H₉)₄NClO₄. This value is much lower in comparison to the specific capacitance of electrochemically formed C₆₀-Pd film.