Channels Of Silica Research Articles

Electrochemical determination of chloramphenicol in milk and honey using vertically ordered silica mesochannels and surfactant micelles as the extraction and anti-fouling element

Chloramphenicol (CAP), an antibiotic, is closely related to the food safety, ecological environment and human health. It is therefore of great importance to develop simple and rapid methods for CAP determination. We report in this work the utilization of indium tin oxide (ITO) electrodes modified with a binary assembly of vertical silica mesochannels (VSMs) and cylindrical surfactant micelles (CSMs) for the electrochemical detection of CAP. Each hard VSM of 2–3nm in diameter supports and confines a soft CSM of cetyltrimethylammonium bromide (CTAB), which has a hydrocarbon core capable of extracting and concentrating lipophilic organic analytes from sample solutions. So the CSM@VSM modified electrode exhibited an analytical performance for CAP apparently superior to bare and VSM modified electrodes. Under optimized conditions, two linear dynamic concentration ranges were obtained for CAP determination using differential pulse voltammetry, namely 0.1 to 3.6ppm and 3.6 to 15.0ppm, as well as a low limit of detection at 40ppb. Moreover, thanks to the ultrasmall size of silica channels and the lipophilic microenvironment of micelle cores, the CSM@VSM film displayed an excellent hydrophobic selectivity and anti-fouling ability by preventing unwanted substances from accessing to and contaminating the underlying electrode surface. Therefore, reliable results were obtained for direct electrochemical determination of CAP in real samples, such as milk and honey, without pre-treatment.

Enantioselective Optical Trapping of Chiral Nanoparticles with Plasmonic Tweezers

Enantiomer separation is a critical step in many chemical syntheses, particularly for pharmaceuticals, but prevailing chemical methods remain inefficient. Here, we introduce an optical technique to sort chiral specimens using coaxial plasmonic apertures. These apertures are composed of a deeply subwavelength silica channel embedded in silver and can stably trap sub-20 nm dielectric nanoparticles. Using both full-field simulations and analytic calculations, we show that selective trapping of enantiomers can be achieved with circularly polarized illumination. Opposite enantiomers experience distinct trapping forces in both sign and magnitude: one is trapped in a deep potential well, while the other is repelled with a potential barrier. These potentials maintain opposite signs across a range of chiral polarizabilities and enantiomer–aperture separations. Our theory indicates that the interaction of chiral light and chiral specimens can be mediated by achiral plasmonic apertures, providing a possible route to...

Relaxation and magnetocaloric effect in the Mn12 molecular nanomagnet incorporated into mesoporous silica: a comparative study

Successful incorporation of the Mn12 molecules into silica channels has been attested with AC susceptometry and magnetocaloric effect measurements.

A Facile Approach to Upconversion Crystalline CaF2:Yb3+,Tm3+@mSiO2 Nanospheres for Tumor Therapy.

A new facile approach, namely chemical-assisted sol-gel growth (CASGG), was successfully developed to induce the formation of fine CaF2:Yb3+, Tm3+ nanocrytals within the pore channels of mesoporous silica (mSiO2) nanoparticles. A series of upconversion photoluminescent crystalline CaF2:Yb3+,Tm3+@mSiO2 nanospheres with controlled diameters from ~65 nm to ~290 nm were fabricated. All nanospheres presented sound cyto-compatibility and unique ratiometric spectral monitoring functionalities for drug release kinetics. The nanospheres with smallest dimension (UCNP-2.5, ~65nm) induced the most sustained DOX release kinetics. More importantly, the in-vitro study demonstrated that the DOX loaded UCNP-2.5 nanopheres presented the strongest anti-cancer efficacy to MCF-7 human breast cancer cells due to its stronger penetration ability to cell nuclei due to the size effect.

A General Synthetic Approach for Integrated Nanocatalysts of Metal-Silica@ZIFs

Integration of different nanocomponents into a greater assemblage or object for applications poses a significant challenge to materials chemists. At present, it still remains extremely difficult to achieve high monodispersivity for such assembled products. To gain better synthetic controllability, ideally, an integration of this type should be done in a stepwise manner. Herein, we report a versatile stepwise approach for preparation of integrated nanocatalysts of metal-mSiO2@ZIFs (metal = Pt, Pd, Ru, Ag, and Pt53Ru47; mSiO2 = mesoporous silica; and ZIFs = ZIF-8 and ZIF-67). Starting with uniform solid Stober silica spheres in submicrometer scale, mesoporous channels with desired length and diameter can be created for silica which serves as a support. With measurements of amino-modification of mesopores and selection of metal precursors applied, subsequently, ultrafine metal nanoparticles (2–5 nm) can be deposited evenly onto the inner walls of silica channels. Resultant metal-mSiO2 spheres are then modifi...

Janus colloidal copolymers

We propose a new type of nanocomposite that we call Janus colloidal copolymers (JCCPs). JCCPs have two different polymers conjugated on opposite sides of a nanosized colloid. Janus clusters of copolymer PS-b-PAA (where PS is polystyrene and PAA is poly(acrylic acid)) are self-organized within confined mesoporous silica channels onto the surface of iron oxide (Fe3O4) core particles by coordination-induced adsorption. PScPAA diblock JCCPs are fabricated by selective crosslinking of the nanosized PAA domains. In addition, the crosslinked PAA domains are terminated with amine-capped polyethylene glycol (PEG) to form PS-cPAA-PEG triblock JCCPs. The cPAA domain containing functional groups can serve as a nanoreactor to allow in situ preparation of functional materials. The composite JCCPs combine the functionality of nanosized colloids with the amphiphilic performance and self-organization capability of copolymers.

In English

Selectively modified silica materials with uniform hexagonally ordered cylindrical mesopores were synthesized by combination of sol‑gel condensation and postsynthetic chemical modification. Hexagonally arranged porous structure of silica carriers was confirmed by X-ray diffraction and low‑temperature ad‑desorption of nitrogen. Content of functional groups immobilized onto external surface of silica particles was determined from chemical analysis of surface reaction products. Release capability of MCM‑41 mesoporous silicas selectively modified with N‑(2‑aminoethyl)‑3‑aminopropyl or N‑[N’-(N’-phenyl)-2-aminophenyl]‑3‑aminopropyl groups was studied by use of para‑aminobenzoic acid as model biologically active substance. It has been found that desorption of aromatic amino acid from mesoporous channels of silica can be regulated using pH-sensitive functional groups which are chemically bounded with outer silica surface.

Electrokinetic transport in silica nanochannels with asymmetric surface charge

The characteristic high surface area to volume ratio causes ionic transport in nanofluidic devices to be governed by surface properties like surface charge. In recent years, experimental demonstrations have shown gate electrodes embedded in the nanochannel wall to systematically alter the surface potential to manipulate ionic transport in nanochannels. Using state-of-the-art non-equilibrium molecular dynamics simulations, electrokinetic transport of an aqueous KCl solution confined in a ~7 nm deep silica nanochannel is reported under the influence of asymmetric surface charge to investigate the effect of engineered surface charge on the resulting velocity and ion number density profiles within these nanochannels. Significant changes in the velocity magnitude and profile were observed in the silica nanochannels with two charged surface patches compared to a homogenously charged silica channel. The surface charged patches cause regions of local flow reversal which were indicated by an observed negative velocity. The simulations provide a theoretical foundation to systematically manipulate electrokinetic flow inside nanochannels by using engineered surface charge at the nanochannel walls.

High performance nanocomposite electrodes of mesoporous silica platelet-polyaniline synthesized via impregnation polymerization

A novel high specific capacitance mesoporous polyaniline (PANI)/silica platelet nanocomposite electrode material for supercapacitors was prepared by an impregnation polymerization. The initiator was embedded firstly in the mesoporous silica pores and channels and then initiated the polymerization of aniline (AN). Compared with the other mesoporous silica materials, the mesoporous silica platelets possess a relative shorter mesoporous channels, leading an easier penetration process of initiator and AN to the inner of mesoporous silica platelets. The structures, morphologies and electrochemical properties of the nanocomposites were thoroughly studied by a series of methods, such as X-ray diffractometry, scanning electron microscope, nitrogen adsorption-desorption tests, infrared spectroscopy, thermogravimetric analysis, and electrochemical measurements. The results revealed that the PANI existed both in the inner and surface of the mesoporous silica platelets, leading a continual conductive network and a large specific surface area. These features provide the nanocomposites an excellent electrochemical performance. The biggest specific capacitance is 1598 F g−1 at a current density of 0.5 A g−1. POLYM. COMPOS., 2015. © 2015 Society of Plastics Engineers

Rapid functionalization of as-synthesized KIT-6 with nickel species occluded with template for adsorptive desulfurization

Nickel-containing mesoporous silica, Ni-KIT-6, was prepared by directly grinding nickel nitrate into the as-synthesized KIT-6 occluded with template for adsorptive desulfurization of fuels. The obtained materials were well-characterized by N2 adsorption, XRD, HRTEM, H2-TPR, FT-IR, XPS and TG/DTG. The results reveal that the abundant silanols, as well as the confined space between silica walls and template in as-synthesized KIT-6 are highly efficient in dispersing large amount of nickel oxide in the channels of mesoporous silica. Compared with the material synthesized using calcined KIT-6, Ni-KIT-6 demonstrates extremely smaller Ni particles on the support, stronger interaction of Ni with silica matrix and higher content of active Ni0 in the KIT-6. As a result, the adsorptive desulfurization performance of Ni-KIT-6, both in commercial and model fuels was enhanced. The present strategy not only saves time and energy, but also allows template removal and precursor conversion in one step instead of repeated calcinations in conventional methods. After regeneration of spent sorbent, approximately 100% of adsorption capacity was recovered.

N-Functionalized L-proline anchored MCM-41: a novel organic-inorganic hybrid material for solvent-free aminolysis of styrene oxide under microwave irradiation.

A novel organic-inorganic hybrid material, namely L-prol-N-pMCM-41, was synthesized via two steps by covalently anchoring N-functionalized proline derivative (L-prol-N-pTMS) into the pore channels of MCM-41 silica. The prepared material was characterized by X-ray diffraction (XRD), thermogravimetric analysis (TGA), nitrogen adsorption-desorption isotherm, Brunauer-Emmett-Teller (BET) surface area analysis, and Fourier Transform Infrared spectroscopy (FTIR). The immobilized catalyst demonstrated moderate to high catalytic activity and excellent regioselectivity for the ring opening of styrene oxide with aniline derivatives under microwave irradiation and solvent-free conditions. The catalyst could be rapidly separated from the reaction mixture and reused up to five runs with good conversion and high regioselectivity.

Complete magnesiothermic reduction reaction of vertically aligned mesoporous silica channels to form pure silicon nanoparticles.

Owing to its simplicity and low temperature conditions, magnesiothermic reduction of silica is one of the most powerful methods for producing silicon nanostructures. However, incomplete reduction takes place in this process leaving unconverted silica under the silicon layer. This phenomenon limits the use of this method for the rational design of silicon structures. In this effort, a technique that enables complete magnesiothermic reduction of silica to form silicon has been developed. The procedure involves magnesium promoted reduction of vertically oriented mesoporous silica channels on reduced graphene oxides (rGO) sheets. The mesopores play a significant role in effectively enabling magnesium gas to interact with silica through a large number of reaction sites. Utilizing this approach, highly uniform, ca. 10 nm sized silicon nanoparticles are generated without contamination by unreacted silica. The new method for complete magnesiothermic reduction of mesoporous silica approach provides a foundation for the rational design of silicon structures.

The role of oxide location in HMF etherification with ethanol over sulfated ZrO2 supported on SBA-15

The etherification of 5-hydroxymethyl-2-furfural (HMF) over ZrO2 and sulfated ZrO2-SBA-15 was chosen as a case study to analyze (i) the quantitative relationship between the concentration of Lewis and Brønsted acid sites and the catalytic behavior in the above reaction, which is also of industrial relevance for the production of biodiesel additives, and (ii) how the location of zirconia nanoparticles inside or outside the mesoporous channels of SBA-15 could significantly influence the specific reactivity in this reaction, both before and after sulfation. Depending on the loading of zirconia (about 10 or 35wt%), the characterization data by different techniques (TEM, XRD, BET, Dr-UV–vis, and XPS) agree in indicating that zirconia is located predominantly outside the mesoporous channels as small zirconia nanoparticles for the lower loading, and predominantly inside the mesoporous channels for the higher loading. The concentration of medium–strong Lewis and Brønsted acid sites were determined by pyridine chemisorption monitored by IR spectroscopy. While the concentration of Brønsted acid sites (formed after sulfation) is linearly dependent on the amount of zirconia in SBA-15, a marked deviation is observed for Lewis acid sites. The same conclusion was derived from analysis of the dependence of the catalytic activity in Lewis- or Brønsted-acid-site-promoted reactions. The analysis of these results indicated that the characteristics of the zirconia nanoparticles deposited outside or inside the mesoporous silica channels differ in terms of acid features and in turn of catalytic reactivity.

Evaluation of mesoporous SBA-15 for the controlled delivery of ciprofloxacin hydrochloride

Controlled drug release of ciprofloxacin hydrochloride monohydrate has been investigated by loading into the channels of SBA-15 mesoporous silica. Three categories of SBA-15 were prepared by a sol-gel process according to blank SBA-15, calcined SBA-15 and SBA-15 functionalised with 3-aminopropyltriethoxysilane (APTS) in a 1:1 ratio prior to drug loading. The carrier and drug samples were characterised by small-angle X-ray diffraction (SAXRD), N2 adsorption–desorption isotherm measurements, fourier transform infrared spectroscopy (FT-IR) and ultraviolet (UV) spectrophotometry. Controlled drug release was conducted in buffered neutral conditions at room temperature for 24, 48 and 120 h. Maximum desorption was observed in the case of the amino-functionalised SBA-15 after 120 h corresponding to 72·16%, whereas for calcined SBA-15 this amounted to 71·35% and in the case of blank SBA-15 48·34% of the total amount of loaded drug was liberated demonstrating the slow release effect of mesoporous silica.

Electroviscous resistance of nanofluidic bends.

Analysis tools that quantify the pressure and potential changes occurring over pressure-driven electrokinetic device elements are necessary for the design of optimal laboratory-on-a-chip devices. In this study, the resistance of a nanofluidic silica channel with negatively charged walls containing a 90^{∘} bend to the electroviscous flow of a potassium chloride salt solution is quantified in terms of two equivalent lengths using numerical analysis. One equivalent length is based on the excess pressure drop and the other on the excess potential rise. Over the entire range of simulations conducted, these equivalent lengths are relatively independent of salt concentration, flow velocity, channel size, and surface charge, remaining within the approximate ranges of 1.3-1.5 for the pressure equivalent length and 0.8-1.05 for the potential equivalent length.

Insights into Nanoscale Electrophoresis of Single Dye Molecules in Highly Oriented Mesoporous Silica Channels

Electrophoresis is a very important tool in chemistry, biochemistry, and biology and is commonly used for the separation and analysis of molecules. Typically, electrophoresis is performed at the macroscopic level. With a view on integrating molecular separations into micro- and nanofluidic and massively parallel systems, it would be highly desirable to obtain detailed knowledge about electrophoretic separation at the nanoscale. Here, we describe an in situ single molecule fluorescence imaging approach to provide insights into the controlled movement and separation of charged molecules in highly oriented silica nanochannels under the influence of an electric field. The velocity of the charged single molecules increases with increasing electric field strength and can therefore be directly controlled by an external stimulus. On the basis of the single molecule trajectories, we propose a model for the internal structure of the host and for the diffusion of charged and uncharged species in the nanoscale channels. In order to prove that the molecules move along the aligned pores, we applied an electric field diagonally to the pores. The molecules that were located in the mesopores showed a directed movement along the mesoporous silica channels, whereas molecules next to, but outside of, the structure followed the electric field lines. Leaky defects in the side walls of the pores were indicated by molecules switching into and out of the pores. In addition, we show the application of the mesoporous host material for separation of molecules according to their mobility and charge.

Electrochemically assisted deposition by local pH tuning: a versatile tool to generate ordered mesoporous silica thin films and layered double hydroxide materials

This review presents the interest of electrochemistry for the preparation of two families of porous materials (ordered mesoporous silica and layer\ed double hydroxide), generated as thin films on solid electrode surfaces via an electrochemically assisted local pH tuning. The deposition mechanism is dependent on the target material. The driving force to get the ordered mesoporous silica thin films is the combination of electrochemical interfacial surfactant templating to the electro-assisted sol-gel deposition, leading to the growth of vertically aligned mesopore channels of surfactant-templated silica. The mechanism involved in the generation of layered double hydroxide (LDH) thin films is the electrochemically induced precipitation of the material by the electrogenerated hydroxide anions, which can be also applied to the formation of LDH-based composites. After a presentation of the materials that can be synthesized by the electrochemical manipulation of localized pH at electrode/solution interfaces, their characterization and applications are also briefly discussed.

Synthesis of Mesoporous Silica Nanocomposites for Preparation of Gold Nanoparticles

Gold nanoparticles (AuNPs) having particle size less than 10 nm can exhibit enhancement of surface area to give high activity such as in catalytic reaction. However, it is hard to synthesize AuNPs with small particle size due to the strong agglomeration. Herein we report that channels of mesoporous silica synthesized via the template sol-gel synthesis can be used to prepare AuNPs by calcination method. Mesoporous silica with an interpore distance of 4.1 nm was successfully fabricated as transparent thin film by using an amphiphilic trinuclear gold (I) pyrazolate complex as a template for the sol-gel synthesis. Upon calcination at 450 °C for 3 h, silica film nanocomposites showed red-shifting of surface plasmon resonance (SPR) bands from 518 (AuNPs from the bulk) to 544 nm owing to decreasing of the average particle size. The formation of AuNPs was also supported by the appearance of diffraction peaks of d111 at 2θ = 38.20° having a cubic phase. Moreover, transmission electron microscope (TEM) images and X-ray diffraction (XRD) peaks also showed smaller and more homogenous distribution of AuNPs.

Solvent Free Highly Dispersed Zinc Oxide within Confined Space of Al- Containing SBA-15 as an Efficient Catalyst for Knoevenagel Condensation

A mesoporous silica-supported zinc oxide catalyst was successfully synthesized by directly grinding zinc nitrate into the as-prepared Al-Containing SBA-15 occluded with template and characterized by powder X-ray diffraction (XRD), BET nitrogen adsorption-desorption methods, IR spectroscopy, transmission electron microscopy and diffuse reflectance UV-Vis spectroscopy. This solvent-free method not only saves the time and energy, but also enables a high dispersion of zinc oxide without pore blocking in the channels of mesoporous silica. The XRD and TEM analyses show that textural properties of Al-SBA-15 retained after coating process. The resulting material was successfully applied as a heterogeneous catalyst for Knoevenagel Condensation in good to excellent yields under mild conditions. Keywords: ZnO. Al-SBA-15, mesoporous, heterogeneous catalyst, solvent-free, knoevenagel condensation.

Mesostructured Arrays of Nanometer‐spaced Gold Nanoparticles for Ultrahigh Number Density of SERS Hot Spots

A novel one‐trough synthesis via an air‐water interface is demonstrated to provide hexagonally packed arrays of densely spaced metallic nanoparticles (NPs). In the synthesis, a mesostructured polyoxometalate (POM)‐silicatropic template (PSS) is first self‐assembled at the air‐water interface; upon UV irradiation, anion exchange cycles enable the free‐floating PSS film to continuously uptake gold precursors from the solution subphase for diffusion‐controlled and POM‐site‐directed photoreduction inside the silica channels. NPs ≈ 2 nm can hence be homogeneously formed inside the silica‐surfactant channels until saturation. As revealed via X‐ray diffraction, small‐angle X‐ray scattering (SAXS), grazing incidence SAXS, and transmission electron microscopy, the Au NPs directed by the PSS template are arrayed into a 2D hexagonal lattice with inter‐channel spacing of 3.2 nm and a mean along‐channel NP spacing of 2.8 nm. This corresponds to an ultra‐high number density (≈1019 NPs cm−3) of narrowly spaced Au NPs in the Au‐NP@PSS composite, leading to 3D densely deployed hot‐spots along and across the mesostructured POM‐silica channels for surface‐enhanced Raman scattering (SERS). Consequently, the Au‐NP@PSS composite exhibits prominent SERS with 4‐mercaptobenzoic acid (4‐MBA) adsorbed onto Au NPs. The best 4‐MBA detection limit is 5 nm, with corresponding SERS enhancement factors above 108.