Porous SiO2 Research Articles

Enhanced release rate of the poorly water-soluble ginsenoside Rg3 with ordered meso/macroporous silica

Although ginsenoside Rg3 is very important in pharmaceutical field, the application of this drug is greatly limited by the release rate due to its poor dissolution. Here we introduced a meso/macroporous SiO2 to assist dispersing Rg3. The as-obtained SiO2/Rg3 (m/M-SiO2/Rg3) with this well-designed support showed superior Rg3 release rate compared to a mesoporous SiO2/Rg3 (m-SiO2/Rg3) at the same release duration and Rg3 loading 20 wt%. The excellent performance of the carrier drug could be attributed to the structural characteristics of hierarchically porous SiO2. On one hand, the macropores (~ 270 nm) accommodate for the active ingredient as effective reservoirs, more importantly the interconnected macropores efficiently shortens the paths of transferring Rg3, which facilitates releasing Rg3 at the nearest mesoporous channels (~ 2.8 nm) penetrated on the wall of adjacent macropores.

Application of an immobilized ionic liquid for the preparation of hydroxylamine via hydrolysis of cyclohexanone oxime

AbstractPreparation of hydroxylamine via hydrolysis of cyclohexanone oxime was studied over porous SiO2 supported acid ionic liquid catalyst. The catalyst [SPIPTES]CF3SO3@SiO2 was prepared through sol‐gel method and characterized by elemental analysis, IR and TG, etc. Various parameters such as reaction temperature and time, catalyst amount were investigated systematically. The optimized reaction conditions investigated were catalyst:cyclohexanone oxime (mass ratio) 4 : 1, conducted at 60 °C for 1 h. Since the present hydrolysis reaction is controlled by thermodynamics, the conversion of cyclohexanone oxime could not be very high. However, reasonable result was achieved under the optimized reaction conditions. Cyclohexanone oxime conversion was 38.41 % and NH2OH yield was 37.65 %. Additionally, combining experiments with density functional theory calculations, a possible catalyst structure and reaction pathway involved protonated cyclohexanone oxime mechanism was proposed for the present hydrolysis in this study.

One-step synthesis of SiO2 α−Fe2O3 / Fe3O4 composite nanoparticles with magnetic properties from rice husks

This paper presents different methodologies for the preparation of Fe2O3@SiO2 nanoparticles (composites) and their characterization. The composite nanoparticles were prepared directly from rice husks. Two methodologies were used, (i) impregnation with an ionic iron solution of rice husks followed with a thermal treatment and (ii) impregnation of the pre-calcinated and lixiviated rice husks. In both methods, a low density, homogenous and highly porous SiO2 nanoparticles with a mean diameter of 20 nm and loaded with different types of iron oxide are generated. The synthetized products were systematically characterized by SEM, AFM, DLS, FT-IR, Mössbauer and VSM. The results show that two different composites were obtained, one mostly composed by α-Fe2O3@SiO2 and a second one mostly composed by γ-Fe2O3@SiO2. Mössbauer and VMS spectra show that iron oxide nanoparticles are formed in the pores of the SiO2 nanoparticles and the first method promote production of composites with magnetic properties. These results highlight a new one-step methodology to obtain silica nanoparticles loaded with iron oxides and with high magnetic properties.

Investigation into the adsorption of methylene blue on the surface of a "core–shell" type catalyst for the Fenton system

The catalytic oxidation of organic substances, in particular by the Fenton method, is one of the effective methods of wastewater treatment. The oxidation efficiency is affected by the adsorption properties of the catalyst when using heterogeneous catalysts in the Fenton process. In this work, the adsorption kinetics of methylene blue dye from aqueous solutions of different concentrations on the surface of the synthesized nanostructured magnetosensitive catalyst CoFe2O4/SiO2/CoMnO2 was studied by spectrophotometric analysis and the kinetic parameters of the process were determined. The CoMnO2-based "core–shell" catalyst has a magnetically sensitive cobalt ferrite core coated with a protective layer of porous SiO2, on the surface of which clusters of cobalt and manganese oxides are placed as catalytic centers. The process of adsorption of methylene blue from an aqueous solution can be considered as a quasi-chemical reaction of displacement of solvent molecules from the adsorption layer by dye molecules. The equilibrium state is described by the Langmuir equation, in which the effective adsorption constant is the ratio of the equilibrium constants of the Langmuir interactions of the dye and the solvent, respectively, with the active center of the adsorbent. The limiting adsorption of methylene blue and the adsorption constant characterizing the affinity of the dye to the catalyst surface were determined. The specific area of the catalyst was calculated under the condition of a known landing plane of the dye molecule. The influence of the adsorption properties of the catalyst on the efficiency of the Fenton process was established.

Self-Assembled Surfactant-Templated Synthesis of Porous Hollow Silica Nanoparticles: Mechanism of Formation and Feasibility of Post-Synthesis Nanoencapsulation.

SiO2 is bioinert and highly functionalizable, thus making it a very attractive material for nanotechnology applications such as drug delivery and nanoencapsulation of pesticides. Herein, we synthesized porous hollow SiO2 nanoparticles (PHSNs) by using cetyltrimethylammonium bromide (CTAB) and Pluronic P123 as the structure-directing agents. The porosity and hollowness of the SiO2 structure allow for the protective and high-density loading of molecules of interest inside the nanoshell. We demonstrate here that loading can be achieved post-synthesis through the pores of the PHSNs. The PHSNs are monodisperse with a mean diameter of 258 nm and a specific surface area of 287 m2 g-1. The mechanism of formation of the PHSNs was investigated using 1-D and 2-D solid-state nuclear magnetic resonance (SS-NMR) and Fourier-transform infrared spectroscopy (FTIR). The data suggest that CTAB and Pluronic P123 interact, forming a hydrophobic spherical hollow cage that serves as a template for the porous hollow structure. After synthesis, the surfactants were removed by calcination at 550 °C and the PHSNs were added to an Fe3+ solution followed by addition of the reductant NaBH4 to the suspension, which led to the formation of Fe(0) NPs both on the PHSNs and inside the hollow shell, as confirmed by transmission electron microscopy imaging. The imaging of the formation of Fe(0) NPs inside the hollow shell provides direct evidence of transport of solute molecules across the shell and their reactions within the PHSNs, making it a versatile nanocarrier and nanoreactor.

Quartz-Driven Quartz@WO3 Piezocatalyst for Hydrogen Evolution Reaction

Piezocatalyst is one of the most innovative catalysts for hydrogen evolution reaction in these years. It has attracted broad interest due to its ultra-high efficiency and renewability. In this study, we initiatively fabricate single-crystal quartz microrods (Quartz MRs) from rice husks, which possess excellent piezoelectricity. Firstly, the raw rice husks are washed and acidized with HCl solution for several hours, following by calcination at 550℃ for 6 hours to produce highly porous SiO2 (RH-SiO2) that serves as the precursor of quartz MRs. After that, some NaCl and 0.6M NaOH solution are mixed with the as-synthesized RH-SiO2. The final mixture is then poured into the Teflon-lined stainless-steel autoclave, undergoing hydrothermal process at 220℃ for 12 hours. To form the Quartz@WO3 heterostructure, Na2WO4·2H2O and citric acid are dissolved in DI water and the pH value is adjusted to 1.0 under stirring. After the solution is formed, the as-prepared quartz MRs are added into it and sealed in an autoclave, placing in the oven at 120℃ for 3 hours. Finally, the product is calcined to remove residual water and we can obtain the Quartz@WO3 heterostructure. The crystal structures of Quartz MRs and WO3 are well identified by XRD analysis, which corresponds to alpha quartz and monoclinic WO3 respectively. Though gas chromatography (GC) analysis, the hydrogen generation rate of Quartz@WO3 effectively enhances around 53% compared to that of pristine WO3 under ultrasonication as an external mechanical force, this may be associated with the piezoelectric effect from the quartz MRs.

Magnetic properties of γ-Fe2O3 nanoparticles in a porous SiO2 shell for drug delivery

A method is presented for synthesizing core–shell nanoparticles with a magnetic core and a porous shell suitable for drug delivery and other medical applications. The core contains multiple γ-Fe2O3 nanoparticles (∼15 nm) enclosed in a SiO2 (∼100–200 nm) matrix using either methyl (denoted TMOS-γ-Fe2O3) or ethyl (TEOS-γ-Fe2O3) template groups. Low-temperature Mössbauer spectroscopy showed that the magnetic nanoparticles have the maghemite structure, γ-Fe2O3, with all the vacancies in the octahedral sites. Saturation magnetization measurements revealed that the density of γ-Fe2O3 was greater in the TMOS-γ-Fe2O3 nanoparticles than TEOS-γ-Fe2O3 nanoparticles, presumably because of the smaller methyl group. Magnetization measurements showed that the blocking temperature is around room temperature for the TMOS-γ-Fe2O3 and around 250 K for the TEOS-γ-Fe2O3. Three dimensional topography analysis shows clearly that the magnetic nanoparticles are not only at the surface but have penetrated deep in the silica to form the core–shell structure.

Study on the removal of thiophene sulfides by porous core-shell SiO2 @Cu/Ni

Porous SiO2@Cu/Ni core-shell nanomaterials were prepared by the sol-gel method. The results of HADDF-STEM and XRD indicated that Cu and Ni were evenly distributed on the surface of the SiO2 supporter. XPS and H2-TPR showed that the chemical state of Cu and Ni were conducive to the desulfurization reaction. The catalytic performance of samples was evaluated through the desulfurization ratios using 4, 6-Dimethyldibenzothiophene as the model sulfide. The effect of metal loading, Ni:Cu ratios, and temperature on the desulfurization, the selectivity of sulfone and 3-3′-dimethylbiphenyl was investigated. The results suggested that the desulfurization activities of 20 wt % SiO2@Cu/Ni were much higher than those of the other catalysts. Due to the synergistic effect among Cu, Ni, and the supporter, the desulfurization rate and selectivity of sulfone and 3-3′-dimethylbiphenyl were all 100% under the suitable conditions. And after the reaction, ICP-OES results showed that the catalyst composition was unchanged, indicating that SiO2@Cu/Ni had good stability while maintaining excellent catalytic performance. Also, the desulfurization mechanism of SiO2@Cu/Ni core-shell nanomaterials was proposed in the present work.

Semihollow Core-Shell Nanoparticles with Porous SiO2 Shells Encapsulating Elemental Sulfur for Lithium-Sulfur Batteries.

Lithium-sulfur batteries have shown great promise as next-generation high energy density power sources, but their commercial applications are hindered by short battery cycle life arising from the dissolution and shuttling of polysulfides. To address this shortcoming, we prepared two types of semihollow core-shell nanoparticles in which (1) elemental sulfur is encapsulated within a porous silica shell (S@SiO2) and (2) elemental sulfur is encapsulated within a porous silica shell where the inner surface of the shell is decorated with small Au nanoparticles (S@Au@SiO2). These core-shell nanoparticles, both ∼300 nm in diameter, were generated from analogous zinc sulfide-based core-shell nanoparticles (ZnS@SiO2 and ZnS@Au@SiO2, respectively) by converting the ZnS cores to elemental sulfur upon treatment with Fe(NO3)3. With a high surface area and strong host-polysulfide interaction, the SiO2 shells effectively trap the polysulfides; moreover, the internal void space of these nanostructures accommodates the volume expansion of the sulfur core upon lithiation. By decorating ∼5-7 nm Au nanoparticles evenly on the inner surface of the porous SiO2 shells (i.e., S@Au@SiO2), electron transport is enhanced, with consequently enhanced sulfur conversion kinetics at high current rates. Studies of battery performance showed that the S@SiO2 cathode can deliver an initial capacity of 1153 mA h g-1 under 0.2 C and retain 816 mA h g-1 after 100 cycles. More importantly, the Au-decorated S@Au@SiO2 cathode can deliver a high capacity of 500 mA h g-1 under 5 C.

Color-changing refractive index sensor based on Fano-resonant filtering of optical modes in a porous dielectric Fabry-Pérot microcavity.

Refractometry is a ubiquitous technique for process control and substance identification in the chemical and biomedical fields. Herein, we present an all-dielectric, wafer-scalable, and compact Fabry-Pérot microcavity (FPMC) device for refractive index (RI) sensing. The FPMC consists of a highly porous SiO2 microcavity capped with a thin, quasi-periodically patterned TiO2 hole array partial reflector that enables rapid, nanoliter-scale analyte transport to and from the sensor. Liquid (alcohols) or condensed-vapor (water from human breath) infiltration resulted in spectral redshifts up to 100 nm, highly apparent visible color change, rapid recovery (< 20 s), and RI sensitivity of up to 680 nm/RIU. The sensor can also be used in spectral or single-wavelength detection modes. Effective-medium and finite-difference time-domain optical simulations identified that Fano-resonant scattering modes induced by the quasi-periodic TiO2 outcoupling layer effectively filter higher-order Fabry-Pérot cavity modes and thereby confer an easily identifiable red-to-green color transition during analyte infiltration.

Production of greener energy in microbial fuel cell with ceramic separator fabricated using native soils: Effect of lattice and porous SiO2

In this study, ceramic membranes with different compositions have been fabricated and used as a separator in two-chambers microbial fuel cells (MFCs). MFCs performance has been affected by properties of the clayware separator such as porosity, proton exchange, and electrical conductivity as well as the structure of the membrane. To study the effect of SiO2 on the composition of ceramic membrane soil, adding different amounts of SiO2 to two soil samples of Kalporgan and leached Kalporgan’s soil for fabricated ceramic membrane was investigated. The sintering phenomenon in the leaching process was reduced significantly and the membrane acted as an ideal substrate. The addition of SiO2 to the leached soil caused the melting point decreases and the sintering process increases slightly, thus have not a positive effect on the MFCs performance. However, when 30% SiO2 has been added to non-leached soil without proper support, its porous structure had a dominant effect on reducing the melting point, results in better performance of MFCs, decreasing the internal resistance from 977.36 to 115.96 Ω, growing up the current density from 102.00 to 769.23 mA/m2, increasing the power density by approximately 15-fold and gaining colombic efficiency from 27 to 79%.

Long-term ablation behavior and mechanisms of 2D-Cf/ZrB2-SiC composites at temperatures up to 2400 °C

Long-term ablation behavior and mechanisms of 2D-Cf/ZrB2-SiC composites are studied by air plasma test at temperatures up to 2400 °C. After ablation at temperatures lower than 1800 °C for 60 s, a porous SiO2 layer forms on the sample surface, which turns to a continuous ZrO2-SiO2 glassy layer at higher temperatures (2000−2400 °C). As ablation temperature increases and ablation time extends, ZrO2 grains are precipitated from the ZrO2-SiO2 glass, further coarsening and sintered via a quasi-liquid phase assisted route, finally form a dense ceramic layer. Consequently, the 2D-Cf/ZrB2-SiC composites show a superior anti-ablation property even at 2400 °C for 300 s.

Preparation of metal and metal oxide doped silica hollow spheres and the evaluation of their catalytic performance

The aim of this study was the synthesis of silica hollow spheres-based materials doped with metal nanoparticles or metal oxides. Two different strategies based on the use of polymer colloids and cetyltrimethylammonium bromide (CTAB) as dual templates were developed. The first strategy involves the use of soap-free emulsion polymerization for the trapping of metal nanoparticles (Ag and Ni) and in the polymer structure. The second strategy exploited carboxyl groups present on the surface of the polymer particles for the adsorption of metal salts (Ni and Fe). A complete porous SiO2 shell was generated around the polymer colloids using a Stober method and CTAB to guide the silica shell growth. The obtained silica hollow sphere displayed either yolk-shell distribution of the doping elements or a uniform oxide deposit on the interior surface of the silica capsules. The versatility of the synthesis method and the catalytic performance of the materials were demonstrated in the case of Fe@SiO2 for a Fischer-Tropsch process.

A combination of hierarchical pore and buffering layer construction for ultrastable nanocluster Si/SiOx anode

Porous Si can be synthesized from diverse silica (SiO2) via magnesiothermic reduction technology and widely employed as potential anode material in lithium ion batteries. However, concerns regarding the influence of residual silicon oxide (SiOx) component on resulted Si anode after reduction are still lacked. In this work, we intentionally fabricate a cauliflower-like silicon/silicon oxide (CF-Si/SiOx) particles from highly porous SiO2 spheres through insufficient magnesiothermic reduction, where residual SiOx component and internal space play an important role in preventing the structural deformation of secondary bulk and restraining the expansion of Si phase. Moreover, the hierarchically structured CF-Si/SiOx exhibits uniformly-dispersed channels, which can improve ion transport and accommodate large volume expansion, simultaneously. As a result, the CF-Si/SiOx-700 anode shows excellent electrochemical performance with a specific capacity of ~1,400 mA·h·g−1 and a capacity retention of 98% after 100 cycles at the current of 0.2 A·g−1.

Molecular imprinting of polymer films on 2D silica inverse opal via thermal graft copolymerization for bisphenol A detection

Bisphenol A (BPA), which is extensively used in the plastic industry, is a known endocrine disrupting chemical whose release into the environment from industrial products is detrimental to human health. In this study, to characterize BPA-detectable imprinted films on quartz crystals (QCs), sensitive molecularly imprinted quartz crystal microbalance (MIP-QCM) sensors were fabricated. The MIP films were synthesized on 2D porous SiO2 and Au pinholes that were generally observed from replica structures prepared using a polystyrene colloidal monolayer as an insulating mold. For MIP film formation, surface-initiated atom transfer radical polymerization was precisely controlled to adjust the MIP film growth on initiator-modified porous structures. Note that three BPA-imprinted poly(4-VP-co-EGDMA) films, i.e., MIP(8-h), MIP(16-h), and MIP(24-h), under reaction time control were successfully prepared. Furthermore, all imprinted patterned surfaces were characterized via atomic force microscopy (AFM) and scanning electron microscopy (SEM). The MIP(24-h) film demonstrated the highest imprinting factor (i.e., IF ≈ 2.4) and sensitivity (i.e., 1.219 ± 0.079 Hz nM−1), although the maximum binding capacity (Qmax) and binding capacity (Qe) at 1-h rebinding equilibrium was relatively lesser than those of the MIP(8-h) and MIP(16-h) owing to the differentiation of the deposited MIP mass. Using the Freundlich isotherm model, the binding affinity of the BPA imprinted MIP films measured in an aqueous solution of BPA whose concentration ranged between 45 and 225 nM was evaluated. Finally, the selectivity of the MIP-QCM sensors for BPA detection was investigated in aqueous solutions in the presence of other analogous chemicals such as bisphenol F (BPF), bisphenol AP (BPAP), and bisphenol B (BPB). The MIP(8-h) film showed extremely high recovery percentage (≈ 94.54 %) owing to the relatively thinner film formation, which was significantly comparable with that of other MIP films, i.e., 68.37 % for MIP(16-h) and 61.99 % for MIP(24-h). However, the MIP(24-h) film appeared to have higher selective features with selectivity coefficients and relative selectivity (k* and k’ ≈ 2.5, respectively) despite measurement in a limited period (i.e., 1-h rebinding process).

Stress distribution in highly porous SiO2 films: results of the molecular dynamics simulation

The stress distribution over the thickness of silicon dioxide thin films is studied using simulated thin film cluster. The atomistic cluster representing the film is deposited on a glassy substrate using the full-atomistic molecular dynamic simulation. The deposition angle is equal to 80°, which leads to the growth of a highly porous anisotropic film with low refractive index. The method for calculating the stress distribution is based on the integral relationship between the thickness-averaged stress and the stress distribution. In the present work, we focus on the application of this relationship to the atomistic modeling of stresses at the initial stage of thin film growth. It is found that in the transition layer between the substrate and the film the stress distribution function corresponds to the compressive stress. With the increase in film thickness, the stress distribution function changes sign and becomes tensile. It is shown that these results correspond to experimental data.

Porous SiO composite tailored by scalable mechanochemical oxidation of Si for Li-ion anodes

In this study, we propose a simple strategy for the mass-production of a porous SiO material as an anode material for rechargeable Li-ion batteries. The porous SiO composite was prepared by mechanochemically oxidizing inexpensive Si powder while simultaneously reducing ZnO powder using a high-energy ball milling process. The resulting Zn of the SiO/Zn composite was chemically removed by acid-aided etching. Both micro- and nano-sized Si powders were used as a starting material to compare their final microstructure and electrochemical properties. X-ray diffraction and X-ray photoelectron spectroscopy were employed to confirm the mechanochemical synthesis of the SiO materials. Electron microscopy analyses with elemental mapping demonstrated that the SiO composite had a Si nanocrystallite embedding microstructure in an amorphous silicon suboxide matrix with highly abundant inside mesopores. The porous SiO composite electrode exhibited improved electrochemical properties over a commercially available SiO electrode because of its microstructure modification. Also, the effects of the starting Si powder's particle size on the resulting microstructure and electrochemical properties were thoroughly investigated with the abovementioned material and electrochemical characterization tools.

Formation mechanisms and photoluminescence properties of self-organized porous Si/SiO2 structures formed by electrochemical etching of n-type of Si

An ordered array of silicon dioxide pyramids were obtained in the course of silicon substrates etching in viscous solution of dimethylformamide. Systematic study was made to establish the influence of etching current and solution composition on the size, density and the shape of SiO2 pyramids. In general, the formation of the structure involves following steps: (i) the porous silicon layer formation at the interface with monocrystalline silicon, (ii) a sol-gel synthesis of the porous SiO2 area on top of the por-Si layer, (iii) formation of cracks in the por-Si layer and (iv) dissolution of the por-Si layer and as consequence the growth of the Si/SiO2 pyramids. The photoluminescence properties of the samples (λex = 405 nm) are determined by morphology of pyramids array.

A Novel Microstructural Evolution Model for Growth of Ultra-Fine Al2O3 Oxides from SiO2 Silica Ceramic Decomposition during Self-Propagated High-Temperature Synthesis.

In this paper, experimental verification of the microstructural evolution model during sintering of aluminum, iron and particulate mullite ceramic powders using self-propagated high-temperature synthesis (SHS) was performed. The powder mixture with 20% wt. content of reinforcing ceramic was investigated throughout this research. The mixed powders were cold pressed and sintered in a vacuum at 1030 °C. The SHS reaction between sintered feed powders resulted in a rapid temperature increase from the heat generated. The temperature increase led to the melting of an aluminum-based metallic liquid. The metallic liquid infiltrated the porous SiO2 ceramics. Silicon atoms were transited into the intermetallic iron–aluminum matrix. Subsequently, a ternary matrix from the Fe–Al–Si system was formed, and synthesis of the oxygen and aluminum occurred. Synthesis of both these elements resulted in formation of new, fine Al2O3 precipitates in the volume of matrix. The proposed microstructural evolution model for growth of ultra-fine Al2O3 oxides from SiO2 silica ceramic decomposition during SHS was successfully verified through scanning electron microscopy (SEM), X-ray energy-dispersive spectroscopy (EDS) analysis and X-ray diffraction (XRD).

Spherical porous SiO2 supported CuVOS catalyst with an efficient catalytic reduction of pollutants under dark condition

Herein, the copper-based bimetallic oxysulfide (CuVOS) coated on the surface of porous SiO2 sphere abbreviated as CuVOS@SiO2 was prepared with a simple technique. The characterizations of the resulting CuVOS@SiO2 catalysts were performed by using different instruments. The reductive activities of the CuVOS@SiO2 catalysts were investigated through the decolorization of methyl orange (MO), methylene blue (MB), rhodamine-B (RhB), 4-nitrophenol (4-NP), and hexavalent chromium (Cr(VI)) in aqueous solutions under dark condition. Complete reduction of 100 mL (50 ppm) Cr(VI) solution was achieved by10 mg of CuVOS@SiO2-3 catalyst within 4 min. In addition to Cr(VI) reduction, 20 ppm of 4-NP solution (100 mL) took only 2 min for complete reduction with 5 mg of CuVOS@SiO2-3 catalyst. Moreover, the reductions of MO, MB, and RhB organic dyes were also reduced by 5 mg of CuVOS@SiO2-3 catalyst and took only 4, 3, and 3 min, respectively. The results indicated that the CuVOS@SiO2-3 catalyst prepared with the addition of optimum hydrazine amount exhibited excellent activity towards the reduction of both inorganic and organic pollutants.