Mesoporous System Research Articles

Microstructural characterisation of lightweight granules made from masonry rubble

The pore structure of lightweight granules made from masonry rubble was studied in order to better understand their engineering properties. Thermally and hydrothermally hardened granules were tested. Analysis by ESEM, mercury porosimetry and sorption methods yield important insight into their microstructure. The thermal granules are characterised by partly melted vitreous areas and large internal macropores that are connected via narrow throats. They show a marginal specific surface area along with a hydrophobic behaviour. In contrast, the hydrothermal granules have an accessible mesoporous system containing plate-like and ink-bottle pores. The shape of their water isotherms depending on the granules’ CaO content is sensitive to the morphology of calcium silicate hydrate phases (CSH). The hysteresis changes from a narrow loop that closes at low pressures, which can be attributed to coarser more crystalline CSH, to a large triangular-shaped loop along with a low pressure hysteresis, which is characteristic for fine fibre-like CSH with ink-bottle and plate-like pore morphologies. Granules with fibre-like CSH have the higher specific surfaces areas but those with more crystalline CSH show stronger physisorption of water molecules.

Selective intracellular free radical generation against cancer cells by bioactivation of low-dose artesunate with a functionalized mesoporous silica nanosystem.

Excessive free radicals are noxious for living organisms and lead to cell death. Destruction of malignant cells by reactive free radicals has been widely used in cancer treatment. A key consideration is how to allow targeted free radical attack on cancer cells and avoid unwanted side-effects. Herein, we develop an efficient intracellular free radical generation strategy against cancer cells by delivering active ingredients into cancer cells, where free radicals are selectively generated by a lysosomal bioactivation process. Artesunate (ART), which is non-toxic to normal cells, was chosen as the free radical source and transported into cells with a hollow mesoporous silica-based delivery system (ART@HMS). To selectively activate the ART@HMS inside cancer cells, a high-bioactive Fe/O cluster-mesoporous silica nanosystem (Fe/O-MSN) was elaborately prepared. Under the bioactivation of the lysosome, the low-dose ART@HMS together with biocompatible Fe/O-MSN induced significant intracellular generation of toxic free radicals and efficient death of cancer cells. This selective intracellular free radical generation strategy is encouraging for its development into an effective low-cost cancer therapy.

Functional nanovalves on protein-coated nanoparticles for in vitro and in vivo controlled drug delivery.

A multifunctional mesoporous drug delivery system that contains fluorescent imaging molecules, targeting proteins, and pH-sensitive nanovalves is developed and tested. Three nanovalve-mesoporous silica nanoparticle (NV-MSN) systems with varied quantities of nanovalves on the surface are synthesized. These systems are characterized and tested to optimize the trade-off between the coverage of nanovalves on the MSNs to effectively trap and deliver cargo, and the remaining underivatized silanol groups that can be used for protein attachments. The NV-MSN system that has satisfactory coverage for high loading and spare silanols is chosen, and transferrin (Tf) is integrated into the system. Abiotic studies are performed to test the operation of the nanovalve in the presence of the protein. In vitro studies are carried out to demonstrate the autonomous activation and function of the nanovalves in the system under biological conditions. Enhanced cellular uptake of the Tf-modified MSNs is seen using fluorescence microscopy and flow cytometry in MiaPaCa-2 cells. The MSNs are then tested using SCID mice, which show that both targeted and untargeted NV-MSN systems are fully functional to effectively deliver cargo. These new multifunctional nanoparticles serve proof of concept of nanovalve functionality in the presence of large proteins and demonstrate another dimension of MSN-based theranostic platforms.

Carbonate pore system evaluation using the velocity–porosity–pressure relationship, digital image analysis, and differential effective medium theory

Abstract Carbonate reservoirs exhibit heterogeneous pore systems and a wide variety of grain types, which affect the rock's elastic properties and the reservoir parameter relationships. To study the Albian carbonates in the Campos Basin, a methodology is proposed to predict the amount of microporosity and the representative aspect ratio of these inclusions. The method assumes three pore-space scales in two representative inclusion scenarios: 1) a macro–mesopore median aspect ratio from the thin-section digital image analysis (DIA) and 2) a microporosity aspect ratio predicted based on the measured P-wave velocities. Through a laboratory analysis of 10 grainstone core samples of the Albian age, the P- and S-wave velocities (Vp and Vs) are evaluated at effective pressures of 0–10 MPa. The analytical theories in the proposed methodology are functions of the aspect ratios from the differential effective medium (DEM) theory, the macro–mesopore system recognized from the DIA, the amount of microporosity determined by the difference between the porosities estimated from laboratorial helium-gas and the thin-section petrographic images, and the P-wave velocities under dry effective pressure conditions. The DIA procedure is applied to estimate the local and global parameters, and the textural implications concerning ultrasonic velocities and image resolution. The macro–mesopore inclusions contribute to stiffer rocks and higher velocities, whereas the microporosity inclusions contribute to softer rocks and lower velocities. We observe a high potential for this methodology, which uses the microporosity aspect ratio inverted from Vp to predict Vs with a good agreement. The results acceptably characterize the Albian grainstones. The representative macro–mesopore aspect ratio is 0.5, and the inverted microporosity aspect ratio ranges from 0.01 to 0.07. The effective pressure induced an effect of slight porosity reduction during the triaxial tests, mainly in the microporosity inclusions, slightly changing the amount and the aspect ratio of the microporosity.

A smart upconversion-based mesoporous silica nanotheranostic system for synergetic chemo-/radio-/photodynamic therapy and simultaneous MR/UCL imaging

To achieve the accurate diagnosis and efficient in situ therapy of malignant tumors is encouraging but still remains a big challenge. The integration of upconversion nanoparticles and mesoporous silica that can combine the diagnostic/therapeutic functions within a single platform, may provide a more advanced way for the efficient theranostics of cancer. In this study, sub-80 nm rattle-structured multifunctional Gd-UCNPs core/mesoporous silica shell nanotheranostics (UCMSNs) were successfully constructed for the co-delivery of a radio-/photo-sensitizer hematoporphyrin (HP) and a radiosensitizer/chemodrug docetaxel (Dtxl). Upon NIR excitation and X-ray irradiation, the complete tumor elimination has been achieved by the synergetic chemo-/radio-/photodynamic tri-modal therapy under the assistance of simultaneous magnetic/upconversion luminescent (MR/UCL) bimodal imaging. To the best of our knowledge, this study is the first example of achieving tri-modal synergetic therapy in one single nanotheranostic system, and we anticipate that it may serve as a particularly useful platform for the clinical diagnosis and efficient treatment of cancer from bench to beside.

New method for preparation of delivery systems of poorly soluble drugs on the basis of functionalized mesoporous MCM-41 nanoparticles

MCM-41 silica with spherical morphology and small particle sizes (100nm) was synthesized and modified by post-synthesis method with amino and/or carboxylic groups. Solid state reaction was applied for the first time for loading of poorly soluble drug mesalazine (5-aminosalicylic acid – 5-ASA). The non-loaded and drug loaded mesoporous silicas were characterized by XRD, TEM, N2 physisorption, elemental analysis, thermal analysis, FT-IR and solid state NMR spectroscopy. Quantum-chemical calculations were used to predict the interactions between the drug molecule and the functional groups of the carrier. The nanoparticles were post-coated with sodium alginate and the coating modified the rate of mesalazine release from MCM-41NH2 and MCM-41NH2COOH particles. Cytotoxic evaluation on colon adenocarcinoma cell line revealed that the alginate coating reduced cytotoxicity of mesalazine loaded in the post-coated particles compared to the pure mesalazine. The functionalized, polymer coated mesoporous systems are suitable oral drug delivery systems providing an opportunity to modify drug release.

Photocatalytic and biocidal activities of novel coating systems of mesoporous and dense TiO2-anatase containing silver nanoparticles

Here we describe the development of novel nanostructured coating systems with improved photocatalytic and antibacterial activities. These systems comprise a layer of SiO2 followed by a layer of mesoporous or dense TiO2-anatase, and doping with silver nanoparticles (Ag NPs). The coatings were synthesized via a sol–gel technique by combining colloidal Ag NPs with TiO2 and SiO2 sols.The photocatalytic activity was studied through methyl orange decomposition under UV light. Results showed a great increase of photocatalytic activity by Ag NPs doping. The most active photocatalyst corresponded to the Ag–SiO2/TiO2 mesoporous system, associated with the porosity of the coatings and with the decrease of e–h recombination for the presence of Ag NPs.All the TiO2 coatings showed a strong bactericidal activity against planktonic forms of Gram-negative (enterohemorrhagic Escherichia coli) and Gram-positive (Listeria monocytogenes) pathogens, as well as a strong germicidal effect against deadly spores of human gas gangrene- and anthrax-producing bacteria (Clostridium perfringens and Bacillus anthracis, respectively). The bactericidal and sporocidal activity was improved by doping the coatings with Ag NPs, even more when nanoparticles were in the outer layer of TiO2, because they are more accessible to the environment.The mechanisms responsible for the increase of photocatalytic and bactericidal behaviors related to Ag NP doping were studied by spectroscopic ellipsometry, UV–vis spectroscopy, photoluminescence and anodic stripping voltammetry. It was found that the separation of the electron–hole pair contributed to the enhancement of photocatalysis, whereas the effect of the local electric field reinforcement was probably present. A possible involvement of a decrease of band-gap energy and dispersion by silver nanoparticles is ruled out. bactericidal efficacy was increased by Ag+ ion release.Overall, the results included in this article show that the architecture of the films may tune photocatalytic and bactericidal properties.

Silver nanoparticle-containing submicron-in-size mesoporous silica-based systems for iodine entrapment and immobilization from gas phase

Submicron-in-size silica particles with controllable morphology, particle size and mesoporosity, have been prepared under basic conditions making use of cationic alkyltrimethylammonium surfactants (CnTAB, n=12,16,18) as porogens. Gaseous nitrogen adsorption, XRD and TEM experiments revealed quasi-spherical homodispersed objects possessing regular mesopores of the MCM-41 type; lengthening of the hydrophobic tail of the template resulted in smaller particles with greater intraparticle pores. The aggregation and sintering of individual silica particles during the calcination step led to the formation of particle clusters comprising interparticle voids, as evidenced by the 129Xe NMR and TEM studies. The calcined particles were subsequently loaded with metallic silver. The measurements of iodine adsorption onto Ag-functionalized materials from the gas phase were supplemented by XRD, SEM/EDX, and TGA/DTA studies. It was demonstrated that the functionalized silica retained much gaseous iodine in an irreversible manner, mainly as an ‘interfacial’ AgI. The best compromise between the textural parameters and the post-synthesis functionalization was obtained for the large-pore silica templated with C18TAB. Indications about the presence of silver metal nanoparticles, displaying certain heterogeneity in size and shape, within the pores of this sample were given based on the analysis of 129Xe NMR spectra supplemented by UV–Visible absorption spectra and powder XRD patterns in the wide-angle region. The material can be recommended for the entrapment and immobilization of radioactive iodine in the nuclear industry since it guarantees that the adsorbed pollutant is primarily localized within the material pores and is thermally stable up to 800K in air.

2,6-Di-tert-butylpyridine Sorption Approach to Quantify the External Acidity in Hierarchical Zeolites

This work was aimed to evidence that substituted pyridine, 2,6-di-tert-butylpyridine, is a suitable probe for the quantitative investigation of the external acidity in hierarchically structured zeolites. The 2,6-di-tert-butylpyridine was too large to enter the micropores, even in wide pore zeolites, and nearly no sites in nonmesoporous zeolites were available. Accessibility studies of acid sites in zeolites TNU-9 and BEA involving quantitative IR measurements with hindered 2,6-di-tert-butylpyridine as a probe were performed. The extinction coefficients of the 1615 cm–1 diagnostic bands of 2,6-di-tert-butylpyridine interacting with Brønsted acid sites were determined. Lewis acid sites were not detected with the probe. The accessibility factor (AF) for the 2,6-di-tert-butylpyridine probe molecule was defined as the number of sites detected by adsorption of the dTBPy (external sites) divided by the total amount of acid sites in the studied zeolites as quantified by pyridine sorption. Upon desilication resulting in the fabrication of the secondary mesopores, the enhanced accessibility of the protonic sites was observed. In comparison to the mesoporous zeolites with the secondary system of mesopores generated by alkaline leaching, considerably higher accessibility of protonic sites was evidenced in both ultrathin ZSM-5 and delaminated ITQ-2 zeolite.

Formation of pyridine N-oxides using mesoporous titanium silicalite-1

Mesoporous titanium silicalite-1 (TS-1) prepared by carbon-templating is significantly more active than conventional TS-1 for the oxidation of pyridine derivatives using aqueous hydrogen peroxide as oxidant. The catalytic activity is increased by the system of mesopores that helps to overcome the configurational diffusion limitations within the microporous catalyst. The use of a carbon-template for generation of secondary porosity is more effective than desilication. The desilicated catalyst is slightly more active than conventional TS-1, probably due to a decrease of the mean diffusion path length. In contrast, carbon-templated mesopores provides an efficient transport throughout the zeolite, thus preventing deactivation due to product confinement. All catalysts were characterised by X-ray powder diffraction, scanning electron microscopy, UV–Vis spectroscopy and nitrogen physisorption. The results indicate that desilication may cause a surface densification of less catalytically active extra-framework Ti species. Carbon-templating is thus a more gentle and effective method for generating secondary porosity. Utilization of carbon-templated mesoporous TS-1 for oxidation of pyridine derivatives represents a new and environmentally friendly method to synthesise N-oxides.

Eu3+-modification of luminescent hybrid bimodal mesoporous silicas with various anions (NO3−, CH3COO−, and Cl−)

In order to enhance the intensity of luminescent hybrid bimodal mesoporous silica (LHMS), the rare earth Eu3+ ion was employed as an enhancer to modify 1,8-naphthalic anhydride (NA) molecules. The modified LHMS were prepared with various anions of europium salts including Cl−, NO3−, and CH3COO−. The structure and photoluminescence properties of the obtained samples were characterized by XRD, TEM, N2-adsorption/desorption, FT-IR, TGA, ICP-OES, and PL measurements. The results showed that the bimodal mesoporous system of BMMs could be preserved after functionalization via grafted Eu3+-modified NA molecules onto mesoporous matrix. However, the structure parameters and textural properties of resultant LHMS series were obviously influenced by the anions volume. Meanwhile, the luminescent performances of LHMS series were seriously impacted by both of the binding force between Eu3+ and various anions and steric hindrance of the anions, resulting in the intensity of emission peak of obtained LHMS series declining as following order: LHMS-EN (NO3−) > LHMS-EA (CH3COO−) > LHMS-EC (Cl−). Finally, the related mechanism was discussed in-depth.

Enhanced Quantum Confined Stark Effect in a mesoporous hybrid multifunctional system

Quantum Confined Stark Effect in hybrid of CdTe quantum dot with superparamagnetic iron oxide nanoparticles in both nonporous and mesoporous silica matrix has been realized. The observed QCSE is due to the local electric field induced by charge dispersion at SiO2/polar solvent interface. Enhanced Stark shift of 89.5meV is observed in case of mesoporous hybrid structure and the corresponding local electric field has been evaluated as 4.38×104V/cm. The enhancement is assumed to be caused by greater density of charge in the mesoporous hybrid. The conjugation of superparamagnetic nanoparticles in this tailored hybrid microstructure has not imparted any alteration to the Stark shift, but has added multifunctional attribute. The present study on the local electric field induced enhanced QCSE with wavelength modulation towards red end paves the way of developing magneto-fluorescent hybrid systems for biomedical imaging application.

Hierarchical Hybrid Organic–Inorganic Materials with Tunable Textural Properties Obtained Using Zeolitic-Layered Precursor

Novel layered zeolitic organic-inorganic materials have been synthesized using a two-dimensional zeolite precursor IPC-1P prepared by a top-down approach from zeolite UTL. The formation of porous materials containing organic linkers or polyhedral oligomeric siloxane covalently bonded to zeolite layers in the interlayer space was confirmed by a variety of characterization techniques (N2/Ar sorption analysis, XRD, (29)Si and (13)C NMR, TEM). The organic-inorganic porous hybrids obtained by intercalation with silsesquioxane posessed layered morphology and contained large crystalline domains. The hybrids exhibited mesoporous or hierarchical micro-/mesoporous systems, stable up to 350 °C. Textural properties of the formed zeolitic organic-inorganic materials can be controlled by varying the linker or synthetic conditions over a broad range. Surface areas and pore volumes of synthesized hybrids significantly exceed those for parent zeolite UTL and corresponding swollen material; the amount of micropores increased with increasing rigidity and size of the organic linker in the order biphenyl > phenylene > ethanediyl.

Kroll-carbons based on silica and alumina templates as high-rate electrode materials in electrochemical double-layer capacitors

Hierarchical Kroll-carbons (KCs) with combined micro- and mesopore systems are prepared from silica and alumina templates by a reductive carbochlorination reaction of fumed silica and alumina nanoparticles inside a dense carbon matrix. The resulting KCs offer specific surface areas close to 2000 m2 g−1 and total pore volumes exceeding 3 cm3 g−1, resulting from their hierarchical pore structure. High micropore volumes of 0.39 cm3 g−1 are achieved in alumina-based KCs due to the enhanced carbon etching reaction being mainly responsible for the evolution of porosity. Mesopore sizes are uniform and precisely controllable over a wide range by the template particle dimensions. The possibility of directly recycling the process exhaust gases for the template synthesis and the use of renewable carbohydrates as the carbon source lead to a scalable and efficient alternative to classical hard- and soft templating approaches for the production of mesoporous and hierarchical carbon materials. Silica- and alumina-based Kroll-carbons are versatile electrode materials in electrochemical double-layer capacitors (EDLCs). Specific capacitances of up to 135 F g−1 in an aqueous electrolyte (1 M sulfuric acid) and 174 F g−1 in ionic liquid (1-ethyl-3-methylimidazolium tetrafluoroborate) are achieved when measured in a symmetric cell configuration up to voltages of 0.6 and 2.5 V, respectively. 90% of the capacitance can be utilized at high current densities (20 A g−1) and room temperature rendering Kroll-carbons as attractive materials for EDLC electrodes resulting in high capacities and high rate performance due to the combined presence of micro- and mesopores.

Gate Control of Mesoporous Silica with α-Synuclein-Coated Au Nanoparticles via Particles-On-A-Particle Assembly

Efficient encapsulation, targeted delivery, and controlled release of drugs are critical prerequisites in current efforts to design advanced drug delivery systems. In particular, the development of release-controllable delivery systems is of importance to curb a substantial risk of systemic side effects and greatly enhance pharmacological effect of drugs at the desired target. In this study, we have developed a novel mesoporous silica-based delivery system in which the function of protein ligand-responsive gate control was embedded. The nanocomposite, named 'raspberry-type PoP', was constructed by incorporating αSyn-functionalized AuNPs onto the surface of a mesoporous silica nanoparticle (MSN) via acidic pH-induced non-covalent interaction of αSyn on hydrophilic surface, which provides controlled release behavior of its entrapped cargo mediated by ligand interaction to the protein. The PoP on which 5 nm AuNP was incorported could retain about 30% of pre-soaked Rh6G within MSN by blocking leaking-out of the dye, and the percentage was dramatically decreased as AuNP size increased. Thus, by tuning sizes of pore and/or surface nanoparticles, one can improve the efficiency of cargo entrapment. Because of human-originated α-Syn on the surface of the PoP, non-specific adsorption of plasma proteins that enhance renal and immunological clearance of intravenously-injected drug carriers might be prevented. The PoP released its entrapped dye in response to interaction of various ions with αSyn. Particularly, Ca2+ whose cytoplasmic concentration is tightly controlled could play as a key to open the AuNP-αSyn gate, suggesting the potential application of the PoP delivery system in Ca2+-involved diseases such as cancers and cardiovascular diseases.

Homogeneous precipitation method preparation of modified red mud supported Ni mesoporous catalysts for ammonia decomposition

Red mud modified by an acid digestion and alkali reprecipitation approach was employed as support for the preparation of Ni/MRM catalysts using the homogeneous precipitation method. The textural and structural properties of the as-received red mud (RM), the modified red mud (MRM) and the as-prepared Ni/MRM catalysts were characterized by X-ray diffraction (XRD), energy dispersive X-ray fluorescence (EDXRF), thermogravimetry-differential scanning calorimetry analysis (TG-DSC), Fourier transform infrared spectra (FT-IR), transmission electron microscopy (TEM) combined with energy-dispersive X-ray spectroscopy (EDX) and N2 sorption techniques. The analysis results revealed a mesoporous nanocatalyst system with high surface area and uniform pore-size distribution. The results of the catalytic activity measurements showed that these mesoporous nanostructured Ni/MRM catalysts were very active for ammonia decomposition. The catalyst with 15% Ni loading and calcined at 600 °C exhibited the highest catalytic activity. Due to its unique properties and the feature of resource utilization of industrial solid waste, MRM holds great promise for developing catalysts and catalyst supports for applications in various catalytic reactions including catalytic ammonia decomposition.

Morphology-driven electrical and optical properties in graded hierarchical transparent conducting Al:ZnO

ABSTRACTGraded Al-doped ZnO layers, constituted by a mesoporous forest-like system evolving into a compact transparent conductor, were synthesized by Pulsed Laser Deposition with different morphologies to study the correlation with functional properties. Morphology was monitored by Scanning Electron Microscopy images and by measuring the resulting surface roughness. Its effects on electrical conductivity – especially carrier mobility, which significantly decreases with increasing roughness – allow to discuss the limitations in conduction mechanisms. Significant changes in light scattering capability due to variations in morphology are also investigated and discussed to study the correlation between morphology and functional properties.

Design considerations for mesoporous silica nanoparticulate systems in facilitating biomedical applications

Abstract Mesoporous silica nanoparticles (MSNs) have advanced to the forefront of multifunctional nanoparticulate systems in nanomedicine, owing to this highly fexible materials platform enabling a multitude of design options, often in a modular fashion. Drug delivery ability, detectability via diferent imaging modalities, and stimuliresponsiveness are often combined into one particle system. Very sophisticated and versatile designs along with impressive demonstrations of applicability have been reported to date, but a common ground when it comes to some critical considerations valid for any nanoparticle intended for biomedical purposes is lacking to some degree. In this study, we attempt to take a glance at some of the most crucial aspects of biomedical nanoparticulate design and relate how they apply specifically toMSNs. These considerations include fuorophore labeling and leaching with respect to immobilization to MSNs, the surrounding conditions, carrier biodegradability, and surface coating. Surface modifcation strategies and surface charge tuning are further considered in conjunction to the relative amount of cellular uptake and serum protein adsorption. Cellular internalization routes and biological techniques used to evaluate especially in vitro biobehavior are discussed. Our attempt is hereby to draw attention to some of the most frequently occurring issues to be considered in the design of MSN systems for biomedical applications

Effect of mesopore structure of TNU-9 on methane dehydroaromatization

A series of micro-mesoporous molecular sieves TNU-9-x (TNU-9 Taejon National University no. 9) were prepared by a hydrothermal reaction method for non-oxidative aromatization of methane. The physical properties of the synthesized samples were characterized by XRD, SEM, TEM, BET, NH3-TPD and FT-IR spectroscopy. Characterization results suggested that the micro-mesoporous molecular sieves TNU-9-x exhibited similar geometrical shapes, but different pore properties with conventional microporous molecular sieve TNU-9. Catalytic tests indicated that Mo–TNU-9-20 showed excellent catalytic performance with a 14.9% conversion of methane and a 9.9% yield of aromatics. In addition, the catalytic stability of Mo–TNU-9-20 was better than the conventional microporous material Mo–TNU-9. The improved catalytic behaviour might be attributed to the generation of a secondary mesoporous system within the hierarchical pore materials.

Adsorption studies and release of selected dyes from functionalized mesoporous MCM-41 silica

Abstract Functionalized mesoporous MCM-41 silica was subjected to adsorption and release studies of encapsulated guest molecules of three chosen dyes. These mesoporous systems were composed of three different capping reagents introduced by grafting method on the silica surface to control the release of dye molecules at two different pH values. The amounts of dyes adsorbed on the silica surface were measured using ultraviolet-visible (UV-VIS) spectrophotometry. The efficiency of grafting was calculated on the basis of differential thermal analysis (TG) results and elemental analysis. The release profiles were determined for all obtained systems using USP Dissolution Apparatus 2. Adsorption of the two azo dyes used was the most efficient after the positively charged functionalization and lower after functionalization with neutral and negatively charged capping reagents, while the phthalocyanine dye adsorption was almost functionalization-independent. Grafting efficiency was the highest for neutral capping reagent and much lower for electrically charged molecules of other reagents. Release studies showed clearly that desorption was pH-dependent for azo dyes and pH independent for Alcian Blue. The adsorption and release seem to be connected with the electrical charge of all constituents of these systems. Results obtained can be used for further analysis of different electrically charged molecules.