Extremely high surface area of ordered mesoporous MCM-41 by atrane route

Silatrane synthesized from inexpensive oxide precursor, silica and TEA was used as the precursor for MCM-41 synthesis at low temperature because of its stability in aqueous solutions. Using cationic surfactant hexadecyltrimethyl ammonium bromide (CTAB) as a template, the resulting meso-structure mimics the liquid crystal phase. Varying the surfactant concentration, ion concentration and temperature of the system, changes the structure of the liquid crystal phase, resulting in different pore structures and surface area. After heat treatment, very high surface area mesoporous silica was obtained and characterized using XRD, BET and TEM. XRD and TEM results show a clear picture of hexagonal structure. The surface area is extraordinarily high, up to more than 2400 m² g⁻¹ at a pore volume of 1.29 cm³ g⁻¹. However, the pore volume is up to 1.72 cm³ g⁻¹ when the surface area is greater than 2100 m² g⁻¹.     

Synthesis of new silicas with high stable and large mesopores and macropores for biocatalysis applications

Monomodal or bimodal porous silicas with large mesopores, constituted by particles or having a monolithic (block type) morphology, respectively, are synthesized using sodium silicate as siliceous species source, cetyltrimethylammonium bromide (CTAB) as pore template and ethyl acetate (EtAc) as pH modifier. The monomodal porosity is represented by 20–30 nm pores and the bimodal one by these pores and also macropores. These characteristics are modulated in function of the CTAB and EtAc concentrations as well as the pH and hydrothermal treatment. The role of these reagents upon the porosity is rationalized. The presence of high CTAB concentration and a rather low pH decreasing rate (function of EtAc concentration and hydrothermal treatment) are essential for having the already known bimodal mesoporous silicas (BMS). On the contrary a rather high pH decreasing rate promotes the formation of the new bimodal mesoporous–macroporous silicas (BMMS) synthesized in this work, where the EtAc also plays the role of emulsion forming agent. The hydrolytic stability of the synthesized silica under aqueous conditions, at different pH values, makes these silicas good candidates for application in different areas of catalysis, especially in the enzymatic one.     

Synthesis and characterization of V,Mo and Nb incorporated micro–mesoporous MCM-41 materials

Highly microporous metal-MCM-41 ordered mesoporous structure catalysts having different metal/Si (V, Mo, Nb) atomic ratios and combinations of metal sources were hydrothermally synthesized. The structural properties estimated using different techniques were found to be in agreement with each other. Metals were successfully incorporated into MCM-41 without deteriorating the ordered hexagonal structure. The metal ions in the synthesis solutions probably settled on the hydrophilic end of the template hence the metal incorporation resulted improvements in the micropore structure. Low loading of metals caused an increase in the surface area and pore volume values of the catalysts. The highest total (1310 m² g^?1) and micropore surface area values (1083 m² g^?1) were obtained by Nb incorporation. The micro- and mesopore dimensions of MCM-41 increased from 0.5 to 1.1 nm and from 2.5 to 2.8 nm, respectively, with metal incorporation. Low V/Si ratios and presence of Nb in the starting solution enhanced narrow mesopore size distribution. The pore dimension and wall thickness values estimated from nitrogen adsorption and X-ray diffraction methods were consistent with the corresponding values obtained using transmission electron microscopy.     

Fabrication and characterization of a zirconia/multi-walled carbon nanotube mesoporous composite

A zirconia/multi-walled carbon nanotube (ZrO₂/MWCNT) mesoporous composite was fabricated via a simple method using a hydrothermal process with the aid of the cationic surfactant cetyltrimethylammonium bromide (CTAB). Transmission electron microscopy (TEM), N₂ adsorption–desorption, Fourier transform infrared spectroscopy (FT-IR) and X-ray diffraction (XRD) techniques were used to characterize the as-made samples. The cubic ZrO₂ nanocrystallites were observed to overlay the surface of MWCNTs, which resulted in the formation of a novel mesoporous–nanotube composite. On the basis of a TEM analysis of the products from controlled experiment, the role of the acid-treated MWCNTs and CTAB was proposed to explain the formation of the mesoporous–nanotube structure. The as-made composite possessed novel properties, such as a high surface area (312 m² · g^? 1) and a bimodal mesoporous structure (3.18 nm and 12.4 nm). It was concluded that this composite has important application value due to its one-dimensional hollow structure, excellent electric conductivity and large surface area.     

Highly ordered mesoporous bioactive glasses with Im3m symmetry

Highly 3D body centered cubic (Im3m) ordered mesoporous bioactive glasses (MBG) were synthesized by evaporation-induced self-assembly (EISA) in the presence of a nonionic triblock copolymer, EO₁₀₀PO₆₅EO₁₀₀ (F127), template. The influence of the F127 concentration on the mesostructure was examined. MBG calcined at 600 °C possessed a large specific surface area (∼ 520 m² g^− 1) and pore volume (0.51 cm³ g^− 1) and a uniformly distributed pore size (5.4 nm). In vitro bioactivity studies were carried out in simulated body fluid (SBF).     

Ultrafine porous fibers electrospun from cellulose triacetate

Ultrafine porous cellulose triacetate (CTA) fibers were prepared by electrospinning with methylene chloride (MC) and a mixed solvent of MC/ethanol (EtOH) and their intra- and inter-fiber pore structures was investigated. Ultrafine porous CTA fibers electrospun with MC had isolated circular shape pores with a narrow size distribution in the range of 50–100 nm. In the case of ultrafine CTA fibers electrospun with MC/EtOH (90 / 10 v/v), they had interconnected larger pores in the range of 200–500 nm. These porous structures were induced by phase separation resulting from the rapid evaporation of solvent during the electrospinning process. However, non-porous corrugated fibers were obtained from MC/EtOH (85 / 15 v/v) and MC/EtOH (80 / 20 v/v) due to their lower vapor pressure. The pore sizes in ultrafine CTA fibers electrospun with MC showed a bimodal distribution centered at ∼17 and ∼64 nm. CTA fibers electrospun with MC/EtOH (90 / 10 v/v) showed the greatest porosity due to their larger intra-fiber pores and fiber diameter.     

Mesoporous structure and evolution mechanism of hydroxycarbonate apatite microspheres

Monodisperse mesoporous hydroxycarbonate apatite microspheres (MHAMs) were fabricated by soaking calcium carbonate microspheres (CCMs) in a cetyltrimethylammonium bromide (CTAB)/Na₂HPO₄/cyclohexane/n-butanol emulsion system. After soaking CCMs in the emulsion system at 20 °C, hydroxycarbonate apatite nanocrystals nucleate heterogeneously on the surfaces of CCMs via a dissolution–precipitation reaction. The as-formed nanocrystals aggregate to form mesopores with the pore size of ～ 3.9 nm and ～ 9.0 nm. The smaller mesopores are derived from the direct aggregation of the nanocrystals, which do not change obviously with the reaction time. In contrast, the larger mesopores are formed by using CTAB micelles as templates, and their pore size decreases from ～ 9.0 nm to ～ 7.4 nm with increasing the reaction time from 6 h to 1 day. After reaction for 3 or 5 days, the larger mesopores disappear because of unstability of the CTAB micelles. If reaction temperature is kept at 50 °C, the conversion rate of CCMs to MHAMs is greater than that at 20 °C, and the corresponding mesoporous structure is unimodal with the pore size of ～ 3.9 nm. Simulated body fluid immersion tests reveal that MHAMs have a great in vitro bioactivity, which is attributed to the mesoporous structure and B-type CO₃^2? substitution of MHAMs.     

High yield growth of uniform ZnS nanospheres with strong photoluminescence properties

High yield ZnS nanospheres were generated conveniently in aqueous solution with the assistance of surfactant polyvinyl pyrrolidone (PVP). The products were characterized by XRD, EDX, XPS, FESEM, TEM and HRTEM. The as-prepared ZnS nanospheres were uniform with an average diameter of 80 nm. The role of PVP in the forming of ZnS nanospheres was investigated. The results indicated that surfactant PVP plays a crucial role on the morphology and size of the products. Moreover, a tentative explanation for the growth mechanism of ZnS nanospheres was proposed. UV–vis and PL absorption spectrum were used to investigate the optical properties of ZnS nanospheres. The UV–vis spectrum indicated that the sample exhibits a dramatic blue-shift. PL spectrum reveals that ZnS nanospheres have a strong visible emission peak centered at 516 nm with excitation light of 400 nm.     

One-step synthesis of hydrophobic mesoporous silica ellipsoidal particles with a bimodal mesopore system

Highly CH₃-functionalized mesoporous silica ellipsoidal particles with bimodal mesopore structure were prepared via a one-step route using polymethylhydrosiloxane (PMHS) and tetraethoxysilane (TEOS) with triblock copolymer P123 as template under acidic conditions. N₂ adsorption–desorption, XRD, HRTEM, SEM and ²⁹Si MAS NMR were used to characterize the obtained material. The introduction of PMHS into the synthetic system led to the formation of a bimodal mesopore system consisting of framework mesopores of ∼7.2 nm and textural mesopores of ∼29.4 nm. The two scale pores were directly observed in HRTEM images and indirectly proved by the two-step increase in N₂ adsorption–desorption isotherm. Also, PMHS played an important role in morphology controlling and organic functionalization, ensuring monodisperse ellipsoidal particle morphology and high CH₃ functionalization degree of the mesoporous silica product. Subjected to removing highly diluted nonylphenol from aqueous solution, the hydrophobic bimodal mesoporous silica ellipsoidal particles showed high adsorption performance.     

Surfactant-assisted synthesis of Sn nanoparticles via solution plasma technique

We have adopted a solution plasma synthesis for preparing Sn nanoparticles (Sn-NPs) directly from metallic Sn electrode. The Sn-NPs were synthesized in the presence of the surfactant, cetyltrimethylammonium bromide (CTAB), and the effect of the concentration of CTAB on the Sn-NPs was investigated. Without CTAB addition, SnO plates were precipitated. Sn-NPs with less than 200 nm were synthesized at a high concentration of 200 × 10⁻⁶ g ml⁻¹ of CTAB. Electrochemical properties of SnO plates and Sn-NPs were analyzed for use as an anode material in Li-ion batteries. A composite of Sn-NPs and graphite enhanced the cyclic stability owing to the buffer space provided by the graphite for volume expansion. In the case of the 30 wt% loaded Sn-NPs, the capacity was measured to be 414 mA h g⁻¹ after 20 cycles.     

Characterization of silica-coated Ag nanoparticles synthesized using a water-soluble nanoparticle micelle

This article describes the synthesis of silica-coated Ag nanoparticles using a water-soluble nanoparticle micelle under basic conditions. Monodispersed Ag nanoparticles with a mean particle size of 7 nm were synthesized using AgNO₃ in the presence of ascorbic acid as a reducing agent. The Ag nanoparticles were easily re-dispersed into an aqueous solution by surface adsorption of surfactant molecules, indicating formation of water-soluble nanoparticle micelles. Silica-coated Ag nanoparticles ranging in size from 50 to 100 nm were obtained by controlling the surfactant, Ag nanoparticle and tetraethylortho silicate (TEOS) concentrations. Adsorbed surfactant monolayers on Ag nanoparticles were used as a template for the silica shell because of the hydrophobicity of TEOS. In all cases, the size of the resulting particles increased linearly as these concentrations increased. Based on transmission electron microscopy, all the Ag nanoparticles were completely covered with a silica shell. In most samples, however, Ag nanoparticle size increased from 7 to 50 nm due to evaporation of hexane by heating. Although mean particle size of silica-coated Ag nanoparticles was drastically altered, characteristic absorption peaks were observed at approximately 410 nm.     

Surfactant-assisted hydrothermal synthesis of chains self-assembled by cobalt microspheres

Magnetic cobalt chains, self-assembled by microspheres of hexagonal-phase cobalt, have been synthesized at 100 °C via a hydrothermal reduction route in the presence of cobalt chloride, the surfactant sodium dodecylsulfate (SDS) (or cetyltrimethylammonium bromide CTAB) and the complex reagent sodium tartrate. As-synthesized, the chains are 100–300 μm in length and the cobalt microspheres, which consist of nanosheets with an average thickness of about 60 nm, are 5–10 μm in diameter. The magnetic hysteresis loops at 5 K and 300 K of the chains of microspheres show ferromagnetic characteristics. The morphologies of the microspheres can be controlled by adjusting the concentrations of the surfactant and the complex reagent and also the reaction temperature.     

A facile method for the production of high-surface-area mesoporous silica gels from geothermal sludge

Mesoporous silica gels were successfully produced from geothermal sludge by alkali extraction followed by acidification. The silica in the geothermal sludge was dissolved by NaOH solution to produce a sodium silicate solution, which was then reacted with HCl or tartaric acid to produce silica gels. The effects of silica concentration and pH on the silica gel properties were investigated. In addition, an improved method was proposed by incorporating two-step aging. The first aging step, which was conducted at pH 10, was used to induce Ostwald ripening to increase the size of the primary particles, and the second step was used to strengthen the gel network. Decreasing the silica concentration by diluting the as-prepared sodium silicate solution tended to increase the surface area and pore volume of the prepared silica gels. The silica gels produced by tartaric acid possessed higher surface area and pore volume than those by HCl. The surface area and pore volume reached approximately 450 m² g⁻¹ and 0.8 cm³ g⁻¹, respectively. When the gelation pH was decreased to 6, the surface area exceeded 600 m² g⁻¹. The first aging process increased the size and uniformity of the primary particles, which in turn increased the surface area of the particles. The pore diameter for all cases was greater than 5 nm, indicating that the silica gels were mesoporous.     

Formation of cobalt hollow nanospheres via surfactant-assisted hydrothermal progress

In the paper we present the synthesis of Co hollow nanospheres by surfactant-assisted hydrothermal method at mild condition. The XRD pattern indicates the sample is hexagonal close-packed (hcp) Co with cell constants a = 2.512 Å and c = 4.102 Å. The Co hollow nanospheres have the outer diameter of about 50–200 nm with the thin wall of 10–20 nm. Room temperature magnetic measurement of the Co hollow nanospheres demonstrates its enhanced ferromagnetic property. The surfactant CTAB might play a vital role in the formation of the hollow Co nanospheres, and simply adapting different reaction temperatures can control the size of these hollow nanospheres. The possible formation mechanism was also discussed.     

Synthesis and characterization of nanoporous hydroxyapatite using cationic surfactants as templates

Nanoporous hydroxyapatite was synthesized utilizing cationic surfactants as templates. The effects of cetyltrimethylammonium bromide and reaction temperatures on the phase and morphology of HA were investigated by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and transmission electron microscopy (TEM). The thermal stability of nanoporous structures was studied by XRD and thermal analyzers (TGA/DTA), while the pore structure of HA was observed using high resolution TEM. It was found that the pore size was about 1 nm, and the pore structure of HA was thermally stable up to 700 °C and the pore size did not change with reaction temperature and CTAB:PO₄^3? ratio. The possible formation mechanism of nanoporous structure was proposed.     

Surfactant-assisted hydrothermal synthesis and characterization of WS2 nanorods

WS₂ nanorods with diameters of about 20–100 nm and lengths of about 0.1–2 μm were successfully synthesized by a simple hydrothermal method with the help of the surfactant Cetyltrimethylammonium Bromide (CTAB). As-prepared WS₂ samples are characterized by X-ray diffraction, scanning electron microscopy, and transmission electron microscopy. Moreover, the influence of surfactant CTAB on the formation of WS₂ nanorods was investigated. A possible three-step growth mechanism of WS₂ nanorods, in which initial nucleation, self-assembly (oriented aggregation), and subsequent crystal growth (Ostwald ripening) is involved, is proposed to explain the formation of WS₂ nanorods on the basis of observations of a time-dependent morphology evolution process.     

Gel-like properties of MCM-41 material and its transformation to MCM-50 in a caustic alkaline surround

MCM-41 material, prepared by sol–gel method, reveals gel-like properties in a caustic alkaline environment, i.e., 6 M potassium hydroxide (KOH) electrolyte. The gellation of MCM-41 starts at a KOH weight ratio of 40 wt.%. The structural change of the material is verified with X-Ray diffractograms and supported by observation using Scanning Electron Microscope (SEM). As the KOH weight ratio increases, the MCM-41 hexagonal arrays structure gradually transforms into MCM-50 lamellar structure before disappearing completely at 80 wt.% KOH. The MCM gel phase is further characterized by rotational viscometry and texture analysis. The gel phase shows shear thinning or pseudoplastic behavior and possesses homogeneous matrix structure.     

Immobilization of cholesterol esterase in mesoporous silica materials and its hydrolytic activity toward diethyl phthalate

Cholesterol esterase (CE, cholesteryl ester hydrolase, EC 3.1.1.13) from porcine pancreas (molecular weight 400–500 kDa) exhibits hydrolytic activity toward various toxic organic phthalate esters. CE was confined in the nanospace (diameter 3–30 nm) of five types of mesoporous silica (MPS) that differ in structural properties such as pore diameter, pore volume, and particle morphology. These structural properties were characterized by transmission electron microscopy, small-angle X-ray diffraction, N₂ adsorption–desorption experiments, solid-state ¹³C nuclear magnetic resonance (NMR), and solid-state ²⁹Si NMR. Catalytic activities of immobilized and free CE were evaluated by the hydrolysis of diethyl phthalate in phosphate buffer solutions containing an organic cosolvent. Optimal activity recovery was achieved when CE was immobilized in n-decane-functionalized MPS, which had a large pore size (22.5 nm). The immobilization also protected against effects of temperature within the range 30 °C–60 °C; CE immobilized in n-decyl-functionalized MPS exhibited better thermal stability than in non-functionalized MPS or free CE. Moreover, it retained approximately 60% of its catalytic activity even after six catalytic cycles.     

Preparation and characterization of nano-porous silica aerogel from rice husk ash by drying at atmospheric pressure

Silica aerogel, a mesoporous material, was prepared from rice husk ash by sol–gel method and dried under atmospheric pressure. In this method, rice husk ash, which is rich in silica, was extracted with sodium hydroxide solution to produce a sodium silicate solution. This solution was neutralized with acid to form a silica hydrosol, and a small amount of tetraethyl silicate (TEOS) to form a gel. The aged gel was washed carefully by distilled water and ethanol and finally dried under atmospheric air. The prepared silica aerogels were characterized by XRF, FT-IR, TG, DTA, DTG, XRD, BET and SEM measurements. The synthesized TEOS-doped silica aerogel was a light solid with specific surface area of 315 m²/g, pore volume 0.78 cm³/g, average pore size 9.8 nm, bulk density 0.32 g/cm³ and porosity 85%.     

Hydrothermal synthesis and luminescent properties of EuW2O6(OH)3 red micro-phosphors

Red phosphors EuW₂O₆(OH)₃ were synthesized via a facile hydrothermal method at different pH values (1, 2, 3, 4, 5, 6 and 7) at 180 °C for 24 h. The XRD patterns indicate that as-obtained phosphors exhibit monoclinic phase. The SEM results show that the as-obtained phosphors exhibit micro-spherical morphologies. The emission spectra under 394 nm excitation exhibit dominant peaks centered at 617 nm. pH value has a strong effect on the phosphor morphology and the emission intensity. The strongest 617 nm red emission was obtained at pH 6. The influence of morphology and crystal size on the intensity of red emission were discussed. The as-obtained micro-phosphors are potential candidate for red-emitting LED phosphors.