Hollow Mesoporous Silica Spheres Research Articles

Sonochemical synthesis of ortho‐aminocarbonitrile tetrahydronaphthalenes using mesoporous yolk–shell nanocomposites as a recyclable heterogeneous catalyst and evaluation of their in vitro antimicrobial activities

A mobile Ca/Mg core was formed inside the silica shell of mesoporous yolk–shell nanocomposites (CaO‐MgO@SiO2). This new structure of hollow mesoporous silica spheres has been successfully synthesized inside the inner cavity. The used carbon spheres as a rigid template in the multi‐step synthetic process are covered with tetraethyl orthosilicate (TEOS) and a mixture of cetyltrimethylammonium bromide (CTAB). Then, the tetrahydronaphthalenes were synergistically synthesized using CaO‐MgO@SiO2 nanocomposites as a nanocatalyst under ultrasound irradiation. By this technique, the required items could be produced with a high to excellent efficiency between 90% and 98% and the reaction times of 5–15 min. As an effective and reusable catalyst in multicomponent processes, the CaO‐MgO@SiO2 catalyst exhibits high reactivity. The FT‐IR, 1H NMR, and melting point methods were used to identify all of the products. Moreover, FT‐IR, XRD, FE‐SEM, EDS, Mapping, and HR‐TEM techniques are used to characterize the prepared catalysts. Also, in vitro antibacterial activity of some synthetic compounds was evaluated.

Bio-inspired structural colors prepared by using hollow mesoporous silica spheres and carbon black

Solid silica or polystyrene spheres have been widely used to mimic solid melanin for fabricating amorphous photonic structures (APSs) and non-iridescent structural colors. However, few studies have been reported about mimicking APSs from hollow melanosomes in biology. A combination of HMSSs and carbon black (CB) is put forward to mimic hollow melanosomes for obtaining APSs and non-iridescent structural colors. Varied structural colors and reflection peaks of APSs are fabricated by adjusting diameters of HMSSs, amounts of CB and mixing ratios of different HMSSs. The stopband shift (137 nm) of the HMSS APSs infiltrated in ethanol is larger than the 40 nm red shift of solid silica photonic crystals (PCs) and the 105 nm red shift of HMSS PCs. The APSs from HMSSs show high sensitivity in visual detection for the chemicals with similar refractive indices, such as homologues and isomers. Based on structural difference of solid silica spheres and HMSSs, the combined APSs-LR could be obtained from the left side of solid silica spheres and the right side of HMSSs, the APSs-LU are from the lower layer of solid silica spheres and the upper layer of HMSSs. They could be used for information encryption and anti-counterfeiting by adjusting combination ways and the effective refractive indexes. The APSs show great potential applications in display, visual detection, information encryption and anti-counterfeiting.

Preparation of manganese dioxide/hollow mesoporous silica spheres (MnO2/HMSS) composites for removal of Sr(Ⅱ) from aqueous solution

Strontium ion in radioactive wastewater causes serious harm to the biological and ecological environment, so the removal of strontium ion is of great significance. We have prepared an inorganic adsorption material (MnO2/HMSS) by impregnation method. The adsorbent can effectively remove Sr2+ in radioactive wastewater. The synthetic materials were characterised by X-ray diffraction (XRD), Scanning electron microscope (SEM), X-ray spectroscopy (EDS), Fourier-transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS) and N2 adsorption-desorption isotherms. The effects of the mass ratio of manganese dioxide and hollow mesoporous silica spheres, pH, initial concentration of Sr2+, adsorption time, competitive ion and other parameters on the adsorption properties were systematically investigated. The results showed that the 4:1Mn02/HMSS composite had the highest adsorption capacity. The adsorption of Sr2+ on MnO2/HMSS is highly dependent on pH and initial solubility. Furthermore, the adsorption equilibrium is reached at 120 min, with a maximum adsorption capacity of 138.70 mg/g. In addition, the composite still maintains a good adsorption capacity under a variety of competitive ions. The Langmuir and pseudo-second-order models can better fit the adsorption isotherm and kinetic data than the Freundlich and pseudo-first-order models, respectively. The new composite obtained in this work has the advantages of rapid adsorption, large adsorption capacity, strong selectivity and capable of large-scale preparation, which makes it expected to play an important role in the removal of strontium ions.

In situ-synthesized Co and N-doped mesoporous hollow silica spheres for the selective oxidation of ethylbenzene.

Transition metal and nitrogen co-doped carbon materials (M-N-C) have attracted great attention in the field of catalysis due to their high atomic utilization and outstanding catalytic performance. Herein, a series of Co and N-doped carbon catalysts (Co-N-C@mSiO2-x) were successfully prepared by pyrolysis of cobalt porphyrins in situ synthesized in the cavity of mesoporous hollow silica spheres according to a ship-in-bottle method. The optimal catalyst exhibited excellent catalytic performance for the selective oxidation of ethylbenzene, with 95.5% conversion for ethylbenzene and 98.9% selectivity toward acetophenone. In combination with characterization techniques, acid treatment experiments and KSCN poisoning tests, the successful synthesis of cobalt-porphyrins in hollow silica spheres was demonstrated, and the excellent performance of Co-N-C@mSiO2-0.10 was attributed to the more acid-resistant Co-Nx species as the main metal active center. In addition, the N-containing groups could significantly facilitate the conversion of ethylbenzene. This work is expected to provide a straightforward and green approach to design metal and N co-doped carbon materials.

Fabrication and characterization of mesoporous yolk-shell nanocomposites as an effective reusable heterogeneous base catalyst for the synthesis of ortho-aminocarbonitrile tetrahydronaphthalenes.

Mesoporous yolk-shell nanocomposites (MYSNs) were loaded with a mobile CaMg core inside the silica shell. CaMg@MYS nanocomposites have been effectively prepared inside the inner cavity of a novel structure that consists of hollow mesoporous silica spheres. Tetraethyl orthosilicate (TEOS) and an amount of cetyltrimethylammonium bromide (CTAB) are coated on the carbon spheres used as a hard template in the multi-step synthetic procedure. In this method, the target products were obtained in high to excellent yields between 87-96% and quick response times between 10-20 minutes under mild conditions. The CaMg@MYS catalyst shows promise as an efficient and reusable catalyst in multicomponent processes. The CaMg@MYS multi-yolk spheres compared to metal oxide nanostructures indicated both high catalytic performance and a significant factor as a novelty. To identify each product, FT-IR, 1H NMR, and melting point techniques were applied. Also, in order to characterize the prepared catalysts, FT-IR, XRD, FE-SEM, EDS, elemental mapping, and HR-TEM techniques were applied.

Preparation of functional oils rich in diverse medium and long-chain triacylglycerols based on a broadly applicable solvent-free enzymatic strategy

To address the problems of long reaction times and limited range of adaptation in enzymatic synthesis medium- and long-chain triacylglycerols (MLCTs), a broadly applicable solvent-free enzymatic interesterification strategy was proposed. Candida sp. lipase (CSL) was immobilized on hydrophobic hollow mesoporous silica spheres (HHSS) to construct a biocatalyst designated as CSL@HHSS with a 15.3 % immobilization yield and a loading amount of 94.0 mg/g. The expressed activity and the specific activity were 20.14 U/g and 173.62 U/g, which were 4.6 and 5.6 times higher than that of free CSL, respectively. This biocatalyst demonstrated higher activity, wider applicability, and excellent reusability. Linseed oil, sunflower oil, perilla seed oil, algal oil, and malania oleifera oil were applied as substrates to produce MLCTs with medium-chain triacylglycerols (MCT) catalyzed by CSL@HHSS through interesterification in yields ranging from 69.6 % to 78.0 % within 20 min. Specific fatty acids, including linolenic acid, oleic acid, DHA, and nervonic acid (the first reported), were introduced into MLCT's skeleton, respectively. The structures were finely analyzed and identified by GC and UPLC-MS. The catalytic efficiency value of CSL@HHSS in catalyzing interesterification between linseed oil and MCT (70 ℃, 20 min, lipase 6 wt%) is 0.86 g/g∙min, which is the highest ever reported. This paper presents an effective and sustainable strategy for functional MLCTs production.

One-pot synthesis of bimetallic Fe/Co incorporated silica hollow spheres with superior peroxidase-like activity

Mesoporous silica hollow spheres with a homogenous and high content distribution of Fe and Co were synthesized by a facile one-pot hydrothermal process. The sub-nanometer bimetallic components inside the silica framework facilitate the stable fixation and the open accessibility to active sites. The co-doped Fe/Co in the spheres showed excellent peroxidase-like activity and much higher catalytic performance than their monometallic-supported spheres. The synergistic effect between Fe and Co promotes the continuous formation of functional radicals during the oxidation process and thus accelerates the reaction rate. When used for colorimetric detection of hydrogen peroxide (H2O2), the Fe/Co incorporated silica hollow spheres show the capability of detection of H2O2 in a wide range (10-250 µmol/L) and with the low detection limit of 0.012 ppm.

Preparation of immobilized Alcalase based on metal affinity for efficient production of bioactive peptides

The enzyme immobilization based on metal affinity has been applied in bioengineering and biochemical fields, but the effects of different metal ions on ligand and enzyme remain unexplored systematically. Here, different metal ions were initially chelated with triamino ligands on the Alcalase-immobilized hollow mesoporous silica spheres (HMSS) through metal–protein interaction forces. The results indicate the coordinated enzymes increased with the increase of metal ions, from which the transition metal ions (Zn2+, Cu2+ and Ni2+) were easier to chelate with triamino ligand than hard lewis acids (Fe3+, Ca2+). Compared to the free Alcalase which was deactivated at the condition of 85 °C incubation, the initial activity of immobilized Alcalase could be partially recovered with the highest activity recovery of 90% from Alcalase@HMSS-3N–Ni2+. Besides, all immobilized Alcalase maintained more than 40% of the initial activity after 5 cycles of successive reuse and Alcalase@HMSS-3N–Ni2+ particularly exhibited 75% of initial activity. Immobilized Alcalase could hydrolyze SPI （soy protein isolate）or WPI（whey protein isolate）to obtain the small peptides below 1500 Da, showing great hydrolysis efficiency for low-solubility proteins. Therefore, this study proposed the immobilized Alcalase on triamino-metal ions-functionalized materials to broaden the feasibility of immobilized enzymes on protein hydrolysis.

Boosting the quaternary ammonium halides catalyzed CO2 coupling with epoxides on the hollow mesoporous silica sphere

Although many efforts have been devoted to the development of novel catalytic protocols on the direct coupling of carbon dioxide with the epoxides, introducing simple, low cost and efficient catalysts, while can be operated under mild reaction conditions, remained with challenges. Herein, we wish to disclose the hollow sphere mesoporous silica (HMS) sphere concomitant with tetraethylammonium bromide (TEAB) can efficiently convert CO2 and various types of epoxide to the corresponding 5-ring carbonates under 10 bar CO2 at 70 °C within a short reaction time. The monodisperse HMS with oriented mesochannels was prepared through a simple hard-templating approache. Some commercially available quaternary ammonium salts such as tetrabutylammonium bromide, tetrabutylammonium iodide and tetrabutylammonium chloride as well as suitable reference catalysts for example sSiO2 hard template, sSiO2@mSiO2 without hollow region, mesoporous silica nanoparticle (MSN) and SBA-15 were also evaluated under optimized reaction conditions to gain more detail about the accurate role of quaternary ammonium halide and HMS structure in the catalyst activity. The results demonstrated that the presence of a hollow region in the interior of the catalyst increases the local concentration and retention time of CO2 in the catalyst pores where tetraethyl ammonium bromides through a confinement effect can lead to high conversion of CO2 molecules. The catalyst was easily recovered and reused in 6 successive reaction runs during coupling styrene oxide and CO2 with only a slight decrease of reactivity.

Synthesis of hollow mesoporous silica spheres functionalized with copper ferrocyanide and its application for Cs+ removal.

In this study, the potassium copper ferrocyanide-functionalized hollow mesoporous silica spheres was successfully prepared. SEM, FTIR, XRD, EDS, and XPS techniques were used to characterize the structure of materials before and after functionalization. The synthesized functionalized hollow mesoprous silica was applied to remove cesium from aqueous solution. The applicability of the adsorbent for the removal of cesium ions was assessed and the effective parameters such as solution pH, contacting time, initial Cs+ concentration, and competitive ions effect were evaluated systematically under the batch mode. The experimental results showed that the adsorbent exhibited high Cs+ selectivity even in the highly concentrated coexisting ions solution, which makes them to be used as potential adsorbents for the removal of cesium from nuclear wastewater or contaminated groundwater.

Robust Amino-Functionalized Mesoporous Silica Hollow Spheres Templated by CO2 Bubbles.

Hollow-structured mesoporous silica has wide applications in catalysis and drug delivery due to its high surface area, large hollow space, and short diffusion mesochannels. However, the synthesis of hollow structures usually requires sacrificial templates, leading to increased production costs and environmental problems. Here, for the first time, amino-functionalized mesoporous silica hollow spheres were synthesized by using CO2 gaseous bubbles as templates. The assembly of anionic surfactants, co-structure directing agents, and inorganic silica precursors around CO2 bubbles formed the mesoporous silica shells. The hollow silica spheres, 200–400 nm in size with 20–30 nm spherical shell thickness, had abundant amine groups on the surface of the mesopores, indicating excellent applications for CO2 capture, Knoevenagel condensation reaction, and the controlled release of Drugs.

Vanadia nanoparticles encapsulated in mesoporous silica as a rattle-like structure for oxidation of dibenzothiophene: A kinetic study

A rattle-like structure of V2O5 encapsulated in mesoporous silica was successfully prepared through a surfactant-supported selective etching strategy. The structural analysis showed that V2O5 nanoparticles in the core of mesoporous hollow silica spheres with void diameter ∼290 nm, V2O5 core diameter ∼93 nm, amorphous SiO2 shell thickness ∼17 nm, surface area of ∼368.19 m2/g and average pore radius of 16 nm. The as-prepared material was employed in catalytic oxidation of dibenzothiophene (DBT) in the presence of H2O2 as an oxidizing agent at different conditions of temperature, contact time and initial concentration using a batch system under either stirring or ultrasonication. The ultrasonication was found to be more effective (∼100%) and faster in oxidation process than the stirring (∼68%, after 5 h). The analysis of the outputs significantly indicated the adsorption of the produced sulfone onto the catalyst surface. The catalytic system exhibited high removal efficiency, qe (∼493 mg/g), as detected experimentally at ambient condition. The thermodynamic analysis confirms the spontaneous physic-sorption nature of the adsorption process with adsorption energy ∼2.155 kJ/mol. The intra-particle diffusion model indicates that the process passes through three stages to attain the equilibrium state.

One-pot pyrolysis method to fabricate Co/N co-doped hollow mesoporous spheres with carbon/silica binary shells for selective oxidation of arylalkanes

Hollow mesoporous silica spheres have an excellent application prospect in the field of catalysis due to high specific surface area, tunable pore size, structural stability and void-confinement effect. In this work, rasberry-like Co/N co-doped hollow mesoporous spheres with carbon/silica binary shells were synthesized by a facile one-pot pyrolysis method, and the catalysts with different properties can be obtained easily by adjusting the factors such as the pyrolysis temperature and the introduction approach of the active substance cobalt porphyrin. The results indicated that pyrolysis temperature could exert influence on the specific surface areas and defects of catalysts. Moreover, the active sites introduced through different ways played an important role in utilizing the enrichment effect of reactants originated from the void-confinement effect. As a result, the obtained catalysts showed remarkable activity and stability for selective oxidation of ethylbenzene under moderate reaction condition. Additionally, the optimal catalyst that achieved 95.9% ethylbenzene conversion and 99.3% acetophenone selectivity also exhibited outstanding catalytic performance for lots of arylalkanes. The superior performance was due to the large specific surface area and the well-dispersed active sites stabilized by the hollow structures with carbon/silica binary shells, which could maximize the enrichment of reactants to accelerate the reaction.

Highly dispersed Ni nanoparticles encapsulated in hollow mesoporous silica spheres as an efficient catalyst for quinoline hydrogenation

With the aim of studying the effect of support structure and preparation method on the hydrogenation performance of Ni-based catalysts. Hollow mesoporous silica spheres (hw-mSiO2) containing tiny Ni nanoparticles highly dispersed on the inner surface ([email protected]2) were synthesized by using carbon sphere as template with four continuous procedures, containing Ni deposition, silica shell coating, calcination and reduction. As demonstrated by SEM and TEM, the hollow structure was successfully obtained after calcination and the active Ni species was highly dispersed inside the porous silica shell, which is much smaller than the Ni-based catalysts prepared by a conventional impregnation method using hw-mSiO2 (Ni/hw-mSiO2) or commercial SiO2 (Ni/mSiO2) as supports. TPR and H2-chemisorption results revealed the existence of strong metal-interaction and more hydrogenation sites in [email protected]2. Therefore, [email protected]2 catalyst achieved an excellent catalytic activity and stability in the selective hydrogenation of quinoline into 1–4-tetrahydroquinoline (py-THQ), due to the more dispersed Ni species, strong metal-support interaction and confinement effect of porous silica shell.

Functionalized hollow mesoporous silica for detection of Staphylococcus aureus and sterilization

A dual-functional smart material for both bacterial detection and sterilization was prepared through the electrostatic interaction between Rhodamine B-loaded amino-modified hollow mesoporous silica spheres (RAHMSN) and Staphylococcus aureus (S. aureus)-specific aptamer-modified gold nanorods (AGNR). The internal RAHMSN portion was used for detection of S. aureus, while the external AGNR was used for photothermal sterilization. In the presence of S. aureus, it would specifically bind to the aptamer that modified on AGNR, resulting in the removal of AGNR from RAHMSN. Subsequently, Rhodamine B could be released from the AHMSN for the fluorescent detection of S. aureus. Then, upon near-infrared (NIR) light irradiation, the photothermal effect of AGNR was utilized to kill the specifically bound S. aureus, exerting the function of photothermal sterilization. When the ratio of RAHMSN to AGNR is 8 and the concentration of Rhodamine B is 11 μg/mL, the dual-functions of the composite material are harmoniously combined. The assay exhibited a wide detection range from 6.5 × 102 CFU/mL to 6.5 × 107 CFU/mL with the limit of detection of 51 CFU/mL, as well as good specificity. In terms of sterilization, 100% sterilization can be achieved after 5 min of irradiation. Based on these excellent properties, the dual-functional material will be very helpful to save resources and avoid the abuse of antibiotics in the potential applications in environmental sterilization and testing.

Thymol-functionalized hollow mesoporous silica spheres nanoparticles: preparation, characterization and bactericidal activity

Antimicrobial natural products show good antimicrobial activities; however, some of them have unpleasant odor or high volatility that limits their application in food industry. One of solutions is to introduce them in inorganic media. In this study, hollow mesoporous silica sphere (HS) was used to encapsulate natural organic antimicrobial agent thymol, and antimicrobial activity of the resulted antimicrobial agent (HST) was tested. Materials characterization revealed that the thymol was successfully introduced into the cavities of HS, and the inorganic host exhibited a high loading capacity of 1320 mg g−1. In addition, the antibacterial activities were tested by double-fold dilution method, the minimum bactericidal concentrations of HST against Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus) were decreased compared with that of thymol. Furthermore, scanning electron microscopy observation confirmed that HST indeed showed a notable inhibitory effect against E. coli and S. aureus by disrupting cell membrane structure.

Covalent Immobilization of Candida antarctica Lipase B on Functionalized Hollow Mesoporous Silica Nanoparticles

AbstractCandida antarctica lipase B (CALB) produced by recombinant Pichia pastoris was covalently immobilized to a carboxyl‐functionalized hollow mesoporous silica sphere (HMS) synthesized by sol‐gel precipitation. The HMS was characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X‐ray diffractometer (XRD), and Brunauer‐Emmett‐Teller (BET). The immobilized CALB was characterized through Fourier transform infrared spectra (FT‐IR) and elemental analysis to verify the binding of enzyme. The free and immobilized CALB were tested in tributyrin hydrolysis. Results revealed that CALB loading capacity of HMS‐COOH was about 28.6 mg/g support and the corresponding enzyme activity was up to about 2700 U/g support at optimal pH and temperature, which was 6.5 and 30 °C respectively. Moreover, compared with free CALB, the immobilized CALB presented more resistant towards the reaction pH and temperature changes. Furthermore, the immobilized CALB retained 60 % residual activity after eight batches of recycling and exhibited better thermal stability and storage stability, which was promising in the potential industrial applications.

Synthesis and Effective Thermal Conductivity Measurements of Hollow Mesoporous SiO2 Spheres for Heat‐Insulating Applications

Mesoporous silica hollow spheres are an excellent model system to investigate the thermal conductivity for an efficient heat‐insulating material with respect to its geometry. Four different monodisperse silica hollow spheres are synthesized via a three‐step synthesis consisting of emulsifier‐free emulsion polymerization, modified Stöber condensation process, and subsequent calcination. In this approach, cetyltrimethylammonium bromide (CTAB) is used as a structure directing component to produce a highly porous silica shell. The systematic investigations of the effective thermal conductivity (ETC) allow distinguishing the respective conduction pathways, such as solid conduction and gas conduction. The carried out thermal conductivity measurements reveal for all four samples promising low ETC values of ≈36 mW m−1 K−1 at 1013 mbar and 35 °C. In vacuum (0.03 mbar) all four samples showed, independent of shell thickness and inner diameter, a comparable reduced ETC of about 10 mW m−1 K−1. The comparison with previous studies on unstructured silica hollow spheres indicates that the solid state conductivity within the bulk is more dependent on the contact strengths and the number of contacts than on the thermal conductivity within the silica material, as the scattering probability of phonons is not influenced by an increased density of defects.

Thermodynamics and kinetics of Cu2+ adsorption of organic-inorganic hybrid hollow mesoporous silica spheres

In this work, organic–inorganic hybrid hollow mesoporous silica spheres (HMSs) have been synthesized by a core-template-free microemulsion method, and the thermodynamic and kinetic of the adsorption process of Cu2+ on the HMSs are detailly investigated. Thermodynamic results showed that the adsorption process obeyed the Langmuir model with a maximum adsorption capacity of 52.0 mg/g. Kinetic studies fitted well with the pseudo-second-order model, and the intraparticle diffusion model showed that the interparticle diffusion is not the sole adsorption rate-limiting step, the adsorption process was jointly controlled by both the external surface attraction interaction and interparticle diffusion interaction between the HMSs and Cu2+. The adsorption capacity of different HMSs is highly depended on the surface charge and their BET surface area. These experimental results provide some theoretical guidance for the metal ions adsorption on the HMSs.

Ultrasound-Assisted Interfacial Immobilization of Lipase on Hollow Mesoporous Silica Spheres in a Pickering Emulsion System: A Hyperactive and Sustainable Biocatalyst

Lipase immobilization processes have the potential to drive large-scale industrial applications through cost savings. Among them, the Pickering emulsion system has recently emerged as an ecofriendl...