The role of particle size on the electrochemical properties at 25 and at 55 °C of the LiCr0.2Ni0.4Mn1.4O4 spinel as 5 V-cathode materials for lithium-ion batteries

The role of the particle size on the electrochemical properties at 25 and at 55 °C of the LiCr_0.2Ni_0.4Mn_1.4O₄ spinel synthesized by combustion method has been determined. Samples with different particle size were obtained by heating the raw spinel from 700 to 1100 °C, for 1 h in air. X-ray diffraction patterns revealed that all the prepared materials are single-phase spinels. The main effect of the thermal treatment is the remarkable increase of the particles size from 60 to 3000 nm as determined by transmission electron microscopy. The electrochemical properties were determined at high discharge currents (1C rate) in two-electrode Li-cells. At 25 and at 55 °C, in spite of the great differences in particle size, the discharge capacity drained by all samples is similar (Q_dch ≈ 135 mAh g⁻¹). Instead, the cycling performances strongly change with the particle size. The spinels with Φ > 500 nm show better cycling stability at 25 and at 55 °C than those with Φ < 500 nm. The samples heated at 1000 and 1100 °C, with high potential (E ≈ 4.7 V), elevate capacity (Q ≈ 135 mAh g⁻¹), and remarkable cycling performances (capacity retention after 250 cycles >96%) are very attractive materials as 5V-cathodes for high-energy Li-ion batteries.     

Synthesis of ZSM‐5 by hydrothermal method with pre‐mixing in a stirred‐tank reactor

This work proposed a synthesis route of ZSM‐5 via the hydrothermal method with premixing in a stirred tank reactor (STR). Effects of various operating conditions, including pre‐mixing time, molar ratio of SiO₂/Al₂O₃, TPAOH (organic template agents) concentration, NaCl (alkali metal cations) concentration, crystallization temperature, and crystallization reaction time, on the average particle size (PS) and particle size distribution (PSD) were investigated. It was found that the pre‐mixing time in the STR significantly affect the formation of proto‐nuclei in premixing process and crystal growth in hydrothermal reaction process, and consequently influence the PS and PSD of the prepared ZSM‐5. ZSM‐5 with good thermal stability, a PS of 380 nm, PSD of 0.17–0.9 µm, pore diameter of 2.31 nm, pore volume of 0.19 cm³ · g^?1 and specific surface area of 337.25 m² · g^?1 were obtained under the optimal conditions of a crystallization reaction time of 24 h, a crystallization temperature of 130 °C, a molar ratio of SiO₂/Al₂O₃ of 200, a TPAOH concentration of 3.5 mol · L^?1, NaCl concentration of 0.3 mol · L^?1, and a pre‐mixing time of 5 h. This work indicated that the operating conditions including premixing time have a significant effect on its PS and PSD.     

Acrylic polymers derived from high solid emulsions as excipients to pharmaceutical applications: synthesis and characterization

Novel polymeric excipients need to be designed to allow for the controlled delivery of many drugs to treat a variety of diseases. In this work, two polymers based on different proportions of ethyl acrylate, methyl methacrylate, and butyl methacrylate were synthesized by multistage emulsion polymerization using a redox initiator system to yield excipients for the manufacture of prolonged release tablets by the coating or compression technique. Fourier Transform Infrared spectrometer (FTIR) indicated that the polymerization reaction of the monomers was complete without carbon double bond absorption bands. Differential Scanning Calorimetry (DSC) analysis indicated that the glass transition temperature (T _g) of the polymers was around 50 °C. The dispersions obtained were characterized in terms of particle size and particle size distribution (PSD) using Dynamic Light Scattering (DLS), and the particle charge (zeta potential) was measured by electrophoretic mobility. The measurements showed particle diameters of approximately 200 nm and a zeta potential close to −60 mV. The low viscosity obtained for the polymers was attributed to bimodal PSD. The dispersions were freeze dried and the particles were submitted to in vitro cell tests to make a preliminary check of the toxicity of the materials. The low viscosity of the polymers, the absence of volatile solvents, and the high solid content (>50%) are ideal for these polymers to be used as coatings and matrices pharmaceutical excipients for prolonged release tablets. In vitro MTT tests suggested that the materials can be considered nontoxic.     

Effect of silica nanoparticle size on toughening mechanisms of filled epoxy

The addition of silica nanoparticles (23 nm, 74 nm, and 170 nm) to a lightly crosslinked, model epoxy resin, was studied. The effect of silica nanoparticle content and particle size on glass transition temperature (T_g), coefficient of thermal expansion (CTE), Young's modulus (E), yield stress (σ), fracture energy (G_IC) and fracture toughness (K_IC), were investigated. The toughening mechanisms were determined using scanning electron microscopy (SEM), transmission electron microscopy (TEM) and transmission optical microscopy (TOM). The experimental results revealed that the addition of silica nanoparticles did not have a significant effect on T_g or the yield stress of epoxy resin, i.e. the yield stress and T_g remained constant regardless of silica nanoparticle size. As expected, the addition of silica nanoparticles had a significant impact on CTE, modulus and fracture toughness. The CTE values of nanosilica-filled epoxies were found to decrease with increasing silica nanoparticle content, which can be attributed to the much lower CTE of the silica nanoparticles. Interestingly, the decreases in CTE showed strong particle size dependence. The Young's modulus was also found to significantly improve with addition of silica nanoparticles and increase with increasing filler content. However, the particle size did not exhibit any effect on the Young's modulus. Finally, the fracture toughness and fracture energy showed significant improvements with the addition of silica nanoparticles, and increased with increasing filler content. The effect of particle size on fracture toughness was negligible. Observation of the fracture surfaces using SEM and TOM showed evidence of debonding of silica nanoparticles, matrix void growth, and matrix shear banding, which are credited for the increases in toughness for nanosilica-filled epoxy systems. Shear banding mechanism was the dominant mechanism while the particle debonding and plastic void growth were the minor mechanisms.     

Microscopic Removal Function and the Relationship Between Slurry Particle Size Distribution and Workpiece Roughness During Pad Polishing

Various ceria and colloidal silica polishing slurries were used to polish fused silica glass workpieces on a polyurethane pad. Characterization of the slurries' particle size distribution (PSD) (using both ensemble light scattering and single particle counting techniques) and of the polished workpiece surface (using atomic force microscopy) was performed. The results show the final workpiece surface roughness is quantitatively correlated with the logarithmic slope of the distribution function for the largest particles at the exponential tail end of the PSD. Using the measured PSD, fraction of pad area making contact, and mechanical properties of the workpiece, slurry, and pad as input parameters, an Ensemble Hertzian Gap (EHG) polishing model was formulated to estimate each particle's penetration, load, and contact zone. The model is based on multiple Hertzian contact of slurry particles at the workpiece–pad interface in which the effective interface gap is determined through an elastic load balance. Separately, ceria particle static contact and single pass sliding experiments were performed showing ~1‐nm depth removal per pass (i.e., a plastic type removal). Also, nanoindentation measurements on fused silica were made to estimate the critical load at which plastic type removal starts to occur (P_crit~5 × 10^?5 N). Next the EHG model was extended to create simulated polished surfaces using the Monte Carlo method where each particle (with the calculated characteristics described above) slides and removes material from the silica surface in random directions. The polishing simulation utilized a constant depth removal mechanism (i.e., not scaling with particle size) of the elastic deformation zone cross section between the particle and silica surface, which was either 0.04 nm (for chemical removal) at low loads (<P_crit) or 1.0 nm (for plastic removal) at intermediate loads (>P_crit). The simulated surfaces quantitatively compare well with the measured rms roughness, power spectra, surface texture, absolute thickness material removal rate, and load dependence of removal rate.     

Synthesis of spinel Li4Ti5O12 anode material by a modified rheological phase reaction

Using lithium acetate dihydrate and tetra-n-butyl titanate as the raw materials, spinel Li₄Ti₅O₁₂ was successfully synthesized by a modified rheological phase method. Thermogravimetric analysis and differential scanning calorimetry (TG–DSC) of the thermal decomposition process of the precursor and X-ray diffraction (XRD) data indicate the crystallization of lithium titanates has occurred at 580 °C, and main phase Li₄Ti₅O₁₂ has obtained at 600 °C. Laser granulometer and scanning electron microscope (SEM) have been employed to estimate the particle size distribution, morphology and microstructure of the products. It reveals the prepared Li₄Ti₅O₁₂ powder had a small particle size (about 140 nm) and narrow size distribution (d_0.1 = 0.07, d_0.5 = 0.139, d_0.9 = 2.813 μm). Galvanostatic charge and discharge tests were carried out to characterize the electrochemical performances of Li₄Ti₅O₁₂. The result indicates that the Li₄Ti₅O₁₂ electrode material obtained from the precursor that had been experienced heat treatment at 110 °C exhibited discharge capacities of 161.6, 156.5 and 112.3 mAh g⁻¹ after 50 cycles at current rates 1, 2.5 and 10 C, respectively, demonstrating excellent high rate performance, due to the pure and well crystallized Li₄Ti₅O₁₂ with ultrafine particles and narrow size distribution.     

Application of the Volatility-TDMA Technique to Determine the Number Size Distribution and Mass Concentration of Less Volatile Particles

A Volatility-Tandem-Differential-Mobility-Analyzer (VTDMA) and a Differential Mobility Particle Sizer (DMPS) were used to determine the number and mass concentration of externally mixed aerosol particles in urban background air. In the VTDMA the less-volatile (LV) particle fraction was measured at 300°C for particles in the size range 20–250 nm. The LV particle fraction was converted to the number concentration of LV particles (N_LV) and the mass concentration (M_LV). M_LV was compared with the mass concentration of black carbon (M_BC) measured by a Multi-Angle Absorption Photometer (MAAP). The DMPS and VTDMA data were used for calculating scattering and absorption coefficients (σ_SP and σ _AP) with a Mie model and compared with σ _SP and σ _AP measured with a TSI nephelometer and the MAAP. The model was run by assuming external and internal mixing of absorbing and scattering aerosol. The best fit of measured and modeled σ _SP and σ _AP was sought by varying the refractive index. During periods dominated by local emissions LV particle fraction ??_LV ? was high ( >0.2). In these cases, the M_LV and the modeled σ _AP assuming external mixing agreed well with the measured M_BC and σ _AP, respectively. For the long-range transported aerosol ??_LV ? was small ( <0.1) and M_BC was higher than M_LV. For the whole period the average (± std) refractive index was 1.55 (± 0.09) – 0.04 (±0.02)i when internal mixing was assumed. When ??_LV ? was >0.2 the average refractive index of LV particles was 1.96 – 0.8 (±0.18)i when σ _AP was modeled assuming external mixing.     

Effect of the CoFe2O4 initial particle size when sintered by microwave on the microstructural,dielectric, and magnetic properties

The particle size of CoFe₂O₄ powders (average particle size of 350 nm) was reduced to 50 nm by high-energy milling. In this paper, special attention was given for analyzing the densification and grain growth of both particle sizes (350 and 50 nm) subject to ultrafast sintering assays using microwave sintering and their effect on the magnetic and electric properties. The results indicated that the grain growth was 10 times higher for the nanoparticle system, reaching similar sizes of ~1 μm in both cases after sintering. The relative density values were higher (95%) in the nanoparticle system due to the wide distribution of particle sizes generated in the grinding process. Qualitatively inferred microscopy analysis showed high sinterability of fine particles with a narrow distribution of grain size when subjected to ultrafast firing processes. Magnetization measurements at room temperature clearly show the reduction of Hc with increasing grain size. Electric resistivity, dielectric constant (ε′), and dielectric loss tangent (tan δ) were measured as a function of frequency at room temperature. The low values of dielectric constant (ε′) and dielectric loss (tan δ) in the low frequency range, shown for all samples sintered by microwave, prove the excellent uniformity in the microstructure.     

Performance of nanofiber/microfiber hybrid air filter prepared by wet paper processing

High-performance air filters composed of a hybrid structure of nanofiber/microfiber were fabricated using wet paper processing. Two types of nanofibers (NF) with average diameters of 180 and 234?nm were mixed with a suspension of microfibers (11.5 and 11.7?µm) in various mixing fractions. Then, the suspension was filtered to fabricate hybridized fiber sheets with a known nanofiber/microfiber composition. The effects of NF diameter and mixing fraction on the performance of the hybrid filters were experimentally investigated. With increasing NF fraction, both the particle collection efficiency and the pressure drop increased. The quality factor (Q_f) was used to evaluate the performance of the prepared filters. As predicted by the single fiber filtration theory, the experimentally obtained Q_f was almost independent of the mixing fraction of the NF. The collection efficiency and pressure drop of the hybrid filters could be controlled by the NF fraction at the same Q_f. Moreover, the inhomogeneity factor of fiber packing (δ) did not significantly affect Q_f over the δ range from 3 to 23 for our filters. This implies that the lower particle capturing efficiency due to heterogeneous packing could be compensated by a decrease in the pressure drop, resulting in the same Q_f value. Therefore, Q_f for particles smaller than 100?nm, which are in the diffusion-controlled regime, can be increased by reducing the NF diameter.

Copyright © 2019 American Association for Aerosol Research     

Effects of mesomorphic β nanograins on crystallization and photoexcited emission of poly(9,9-di-n-hexyl-2,7-fluorene)

Structural evolution processes of solution-cast and melt-quenched poly(9,9-di-n-hexyl- 2,7-fluorene) (PFH) were quantitatively examined using small/wide-angle X-ray scattering (SAXS/WAXS) and differential scanning calorimetry. SAXS/WAXS profiles of solution-cast PFH indicated presence of nanograins (radius of gyration R_g ≈ 5 nm) of 2D-ordered β phase. Upon heating above T_g, perfected packing order and growth of β nanograins up to R_g ≈ 10 nm result in suppressed formation of α crystallites up to 190 °C, beyond which extensive melting accompanied by significant (albeit partial) transformation of β nanograins into α nanocrystals of R_g ≈ 13 nm can be observed in a narrow temperature range of 190–200 °C. Thus transformed α crystallites remained stable in size before melting above 235 °C. The nanograin structures observed are correlated to phase-dependent optical absorption and photoexcited emission. Results suggest sensitive influences of the size/spatial distribution of β nanograins (particularly in the layering direction of the 2D-ordered chain packing) on photoexcited emission of the polyfluorene film.     

Fabrication of poly(lactic acid) nano‐ and microparticles using a nanomixer via nanoprecipitation or emulsion diffusion

In order to investigate the influence of mixing flow condition on particle generation, poly(lactic acid) (PLA) particles were fabricated at different mixing velocities (10–50 m s^?1) using a nanomixer through either the nanoprecipitation or the emulsion diffusion method. With a nanomixer (Couette–Taylor mixing geometry modified with cavitations), particles became smaller as the mixing velocity increased as long as the temperature was kept below the glass transition temperature (T_g) of PLA. Even in the emulsion diffusion method, it led to the formation of PLA nanoparticles in a short emulsification time (～1 min) and the mean diameter was less than 100 nm with deviation less than 10% (100 nm ± 10%). However, at high mixing velocity, the particle size was rapidly increased which was enhanced as mixing time increased. Dissipation rapidly increased the temperature inside the mixer above T_g of PLA, which caused smaller particles to agglomerate to form larger micron‐sized particles. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46199.     

Preparation of ferric oxide powders by ultrasonic-assisted impinging stream reaction

In this paper, Fe₃O₄ powder was prepared by the chemical precipitation method using impinging stream technology. The influences of feed flow rate, L/D, reactant concentration, ratio of iron ion concentration, reaction temperature, and impact time on the size and distribution of particles were investigated by the orthogonal experiment method. The microstructure and morphology of Fe₃O₄ powders were characterized by scanning electron microscopy, X-ray diffractometer, and granulometer. The results showed that when ratio of iron ion concentration c(Fe²⁺):c(Fe³⁺) = 0.75, reactant concentration c(Fe³⁺) = 0.4 mol · L⁻¹, feed flow rate Q = 800 L · h⁻¹, L/D = 3, reaction temperature T = 20°C, impact time t = 50 min, the prepared Fe₃O₄ had an average particle size of 1.815 μm and the most uniform distribution. The influence of ultrasonic enhancement on the mixing process and powder preparation in an impinging stream reactor was investigated. The size and distribution of the powders were significantly affected by ultrasonic enhancement. With the increase in ultrasonic power, the particle size of the powders decreased and the distribution became narrower. The particle size was reduced by 68.78%, and the particle distribution range was narrowed by 84.34% under ultrasound enhancement. This study promised the effective utilization of ultrasonic cavitation in the optimization of experimental equipment and the preparation of ultrafine powder, which provides a basis for process optimization of powder preparation.     

Optimization of a Continuous Precipitation Process to Produce Nanoscale BaSO4

The effect of supersaturation, reaction temperature, and mixing intensity on particle size was investigated. Sterical stabilization of barium sulfate suspensions was applied to prevent formation of agglomerates. This allowed a reactant ratio of 1:1, thus maximizing product yield. The local supersaturation is strongly affected by the mixing intensity that can be characterized by Reynolds numbers. The significant decrease in particle size was observed by increasing the Reynolds number from 600 to 8000. A higher reactant concentration leads to a higher degree of supersaturation, and finer particles are precipitated. The particle size can be reduced with increasing reactant concentration. The degree of supersaturation increases with temperature reduction, i.e., the particle size will be reduced at low temperature. In addition, nucleation and growth kinetics are changed in a way that reduces the particle size. The optimized lab‐scale process is capable of producing over 1 kg h^–1 of nanoscaled BaSO₄ with a median diameter of 75 nm.     

Generation and precipitation of paclitaxel nanoparticles in basil seed mucilage via combination of supercritical gas antisolvent and phase inversion techniques

In recent years, plant derived polymers have evoked tremendous interest in the field of drug delivery. In this work, a promising anticancer drug, paclitaxel, was precipitated in the basil seeds mucilage (BSM) using supercritical carbon dioxide (SC-CO₂). The employed SC-CO₂ process in this research is a combination of gas antisolvent and phase inversion techniques and consists of two steps: (1) casting solution preparation, a uniform mixture of BSM, water, paclitaxel and dimethyl sulfoxide (DMSO), (2) simultaneous generation and precipitation of nanoparticles in BSM structure using SC-CO₂ as antisolvent. The effect of DMSO/water ratio (4 and 6 (v/v)), pressure (10–16 MPa) and CO₂ addition rate (1–3 mL/min) on mean particle size (MPS), particle size distribution (PSD) and drug loading efficiency (DLE) were studied. Particle analyses were performed by scanning electron microscopy (SEM) and Zetasizer. High performance liquid chromatography was utilized for studying DLE. Nanoparticles of paclitaxel (MPS of 117–200 nm depending on process variables) with narrow PSD were successfully precipitated in BSM structure with DLE of 56.8–78.2%. The FTIR spectra confirmed that paclitaxel actually precipitated in basil seeds mucilage. Experimental results indicated that higher DMSO/water ratio, pressure and CO₂ addition decreased MPS and DLE.     

Synthesis of NdAlO3 with good microwave dielectric properties by stearic acid method

In this study, NdAlO₃ with perovskite structure was synthesized by the stearic acid method at relatively low temperature. The structural characteristics of the as-synthesized product were identified by TG–DSC, XRD, FT–IR, SEM, and TEM techniques. Using the powders as starting materials, NdAlO₃ bulk microwave ceramics were prepared, and the corresponding densification process, microstructural and dielectric properties were studied. The XRD and FI–IR results confirmed that single phase NdAlO₃ could be prepared at low temperature by the stearic acid method. A unique two-dimensional platelike morphology with an unevenly dispersed bubble shape structure was observed in the calcined powder. However, the TEM result revealed that the powder calcined at 800 °C had a good dispersity accompanied with narrow particle size distribution within a range of 20–35 nm. The average particle size of 27.3 nm was in accordance with that calculated from the XRD data. Using the powder calcined at 800 °C as raw materials, the as-obtained NdAlO₃ ceramics sintered at 1500 °C for 4 h possessed the highest density and favorable combined microwave dielectric properties (i.e., ε_r = 23.02, Q × f = 65320 GHz, and τ_f = −32.4 ppm/^°C). The present work developed a fast, energy-efficient approach to synthesize NdAlO₃ powder used as promising raw materials of microwave dielectric ceramics.     

Preparation and characterization of stable and high solid content St/BA emulsifier-free latexes in the presence of AMPS

Stable and high solid content (about 50 wt%) St/BA emulsifier-free latexes were successfully synthesized using emulsifier-free emulsion polymerization with the addition of a small amount of reactive emulsifier AMPS. Properties of the latexes, such as the average particle diameter and its distribution, the morphology of latex particles, and stability were investigated. Physical properties of the latex films, i.e., glass transition temperature (T _g), water resistance, and solvent resistance were investigated as well. The size of latex particles is 400–600 nm in diameter, which is larger than that prepared by conventional emulsion polymerization. And the particle size distribution is narrow and uniform. It was found that the diameter of the latex particles decreases with the increasing content of the initiator KPS and the reactive emulsifier AMPS. Compared with the film prepared by conventional emulsion polymerization, water resistant and solvent resistant of the films prepared by emulsifier-free emulsion polymerization are improved greatly.     

Effects of TiO2 starting materials on the synthesis of Li2ZnTi3O8 for lithium ion battery anode

Lithium zinc titanate (Li₂ZnTi₃O₈) anode materials have been successfully synthesized using rutile-TiO₂ with different particle sizes as titanium sources via a molten-salt method. Various physical and electrochemical methods are applied to characterize the effects of TiO₂ particle sizes on the structures and physicochemical properties of the Li₂ZnTi₃O₈ materials. When the particle size of TiO₂ is too small (10 nm), it is difficult to homogeneously mix TiO₂ with the other raw materials. Thus, the final product Li₂ZnTi₃O₈ has poor crystallinity, large particle size, small specific surface area, pore volume and average pore diameter, which are disadvantageous to its electrochemical performance. Using TiO₂ with the proper particle size of 100 nm as the titanium source, the Li₂ZnTi₃O₈ (R-100-LZTO) with excellent electrochemical performance can be obtained. At 1 A g⁻¹, 175.8 and 163.6 mA h g⁻¹ are delivered at the 1st and the 200th cycles, respectively. The largest capacities of 163, 133.3 and 122.5 mA h g⁻¹ are delivered at 2.5, 5 and 6 A g⁻¹, respectively. The good high-rate performance of the R-100-LZTO originates from the good crystallinity, small particle size, large specific surface area and average pore diameter, low charge-transfer resistance and high Li⁺ diffusion coefficient.     

Supercritical anti-solvent micronization of marigold-derived lutein dissolved in dichloromethane and ethanol

This work aims to study supercritical anti-solvent (SAS) micronization of lutein derived from marigold flowers. Lutein solution in dichloromethane (DCM) or ethanol was atomized into the stream of supercritical carbon dioxide (SC-CO₂) through a concentric nozzle in a pressurized vessel. The effects of pressure and SC-CO₂ flow rate on morphology, mean particle size (MPS) and particle size distribution (PSD) were investigated. The reduction in lutein MPS from 202.3 μm of unprocessed lutein to 1.58 μm and 902 nm could be achieved by SAS micronization using DCM and ethanol, respectively. In both solvent systems, no significant effects of pressure and SC-CO₂ flow rate on particle morphology were observed. However, pressure was found to have a significant effect on MPS and PSDs of lutein particles.     

Characterization of nanosized silica size standards

Nanosized silica size standards produced with a sol–gel synthesis process were evaluated for particle size, effective density, and refractive index in this study. Particle size and effective density measurements were conducted following protocol from the National Institute of Advanced Industrial Science and Technology (AIST) in Japan. Particle sizes were measured via electrical mobility analysis using a differential mobility analyzer (DMA) at sheath flow rates (Q_sh) of 3.0 and 6.0 L/min and a constant aerosol flow rate (Q_a) of 0.3 L/min. The measured mean and mode diameters agreed well with the labeled sizes in the size range 40–200 nm, with differences ranging from 0.03% to 0.8%, well within the labeled expanded uncertainties (95% confidence intervals) of 1.8%–2.2%. The coefficient of variation (CV) of the size distribution was 0.012–0.027 for 40–200 nm. Particle sizes measured for 20 nm and 30 nm standards showed size differences with respect to the certified sizes of 1.7% and 8.3% at Q_sh = 6.0 L/min, but the size distributions were narrow, with CV = 0.047–0.064. The average effective density for the range 40–200 nm measured with an aerosol particle mass analyzer (APM) was 1.9 g/cm³. The real component of the refractive index measured with an optical particle counter (OPC) was 1.41 at a wavelength of 633 nm. All properties (size, effective density, and refractive index) were stable and could be measured with good repeatability. From these evaluations, it was found that the nanosized silica size standards have good characteristics for use as size standards and constitute a feasible alternative to PSL particles.

© 2017 American Association for Aerosol Research     

Synthesis of onion-like mesoporous silica from sodium silicate in the presence of α,ω-diamine surfactant

Mesoporous silicas with vesicular and onion-like morphologies were assembled through hydrogen-bonding pathway from sodium silicate as silica source and electrically neutral α,ω-diamine, Jeffamine D2000 surfactant (H₂NCH(CH₃)CH₂[OCH₂CH(CH₃)]₃₃NH₂) as template in aqueous media at different synthesis temperatures (25, 60 and 100 °C). Assembling the material at 100 °C afforded onion-like core shell mesoporous silica, while at relatively lower temperature, e.g. 25 and 60 °C, multilamellar vesicles were obtained. Mesoporous silica with onion-like morphology was also obtained by a two-step synthesis involving an aging period of 20 h at room temperature followed by a hydrothermal stage (1–12 h) at 100 °C. The heavily cross-linked (Q⁴/Q³ ratio of 4.43) onion-like mesophase silica exhibited high hydrothermal stability. The BET surface area, pore volume and KJS (Kruk-Jaroniec-Sayari) pore diameter of the onion-like mesoporous silica were found to be 464 m² g⁻¹, 1.16 m³ g⁻¹ and 7.2 nm, respectively.