Functionalized Silica Materials Research Articles

Tailoring the pore structure of amine-functionalized KCC fibrous nanosilica for efficient CO2 adsorption

Controlling the emission of greenhouse gases such as CO2 by adsorption has been extensively investigated over various solid adsorbents to achieve effectual capture. The present work studied the fabrication of mesoporous nanosilica materials, KCC-1, KCC-2, KCC-3, and their corresponding amine-functionalized NH2-KCC, as potential adsorbents for CO2 capture. The KCC-1, KCC-2, and KCC-3 silica were prepared using the hydrothermal and reflux methods under various parameters. The NH2-functionalized materials were obtained by grafting the KCC materials with 3-aminopropyltriethoxysilane (APTES). The synthesized materials were characterized by XRD, FTIR, N2-sorption, CHN elemental analysis, SEM-EDX, TEM, and TGA techniques. Results showed that the NH2-KCC materials retained the original KCC structure. Adsorption experiments revealed that the maximum CO2 capture capacity was 0.997 mmol g-1 at 1 bar (60 °C) and 0.715 mmol g-1 at 1 bar (25 °C) by NH2-KCC fibrous nanosilica. Furthermore, the CO2/N2 selectivity of KCC-3-APTES was 36 at 50 mbar (25 °C). The pores and surface silanol groups of the mesoporous silica, with NH2 functionalities, possess unique textural and binding properties that assess the efficient adsorption of CO2. The adsorption data were fitted using Langmuir and Freundlich models. Moreover, the NH2-KCC material was recycled and reused for five cycles and retained 99% adsorption efficiency. The results suggest that the synthesized functional porous silica (NH2-KCC) materials are potential adsorbents for advanced adsorption and CO2 capture processes.

Hybrid material for ferric ion detection & remediation: Exceptional selectivity & adsorption capacity with biological applications

In this work, naphthalimide derived functionalized silica material SiO2@NAPIA (2,2‘((((propylazanediyl)bis(methylene))bis(2,1-phenylene))bis(oxy))bis(N-(1,3-dioxo-1H-benzo[de]isoquinoline-2(3H)-yl)acetamide)) was constructed as a dual signaling and remediation material for ferric ions from a pool of 35 common ions (cations and anions) in the aqueous system. The material Cubic SiO2 shows a high surface area (1104 m2/g, pore volume (1.510 cm3/g), and pore diameter (6.3 nm) in the mesoporous range, which reduces further on functionalization to get the final material SiO2@NAPIA. The ferric ion selectivity through fluorescence quenching displays a Stern-Volmer quenching constant (Ksv) of 7.8 × 108 M−1 with a LOD (Limit of detection) value of 0.11 μM for ferric-ion, which is 48 times lower than the USEPA (United States Environmental Protection Agency) maximum contaminant level (5.35 μM) in drinking water. This material also shows a very high adsorption capacity (664 mg/g) for ferric ions fitting the Langmuir model isotherm with R2 = 0.99, which can be easily stripped out, and the material can be recycled. This material was also used as a sensory probe material for biosensing of ferric ions through fluorescence imaging in living organisms like Artemia salina and quantification in the real environmental sample. Furthermore, the antibacterial activity inspired by the ferric ion chelating affinity shows good potency against several Gram-negative and Gram-positive bacterial strains. The Minimum Inhibitory Concentration (MIC) & Minimal Bactericidal Concentration (MBC) of the material against these pathogens were found to be 100 & 200 μg/mL respectively. This material signifies superior activity with respect to the ferric-ion selective materials known in the literature.

The effects of amidophosphonate ligand immobilization method on the uranium extraction efficiency of functionalized silica

The effects on the uranium extraction efficiency of the functionalization method of three kinds of functionalized silica materials were evaluated in low sulfate (pH = 2) and high sulfate (pH = 1) solutions, with compositions representative of typical effluents from uranium mines and leaching solutions from uranium ore treatment, respectively. Silica supports were functionalized with amidophosphonate moieties either by peptide grafting or by non-covalent impregnation. Prior to impregnation, the surface of the silica supports was modified with either alkyl chains or ionic liquid groups. The selectivity of the modified silica supports for uranium was determined in the presence of iron and molybdenum as competing cations. Our results show that both incorporation methods yield materials with good extraction efficiency and selectivity in low sulfate solutions. EXAFS data indicate that uranyl species have to first be desulfurized to be extracted by the phosphonate ligand. This process appears more energetically favorable for the impregnated ligands than for the grafted ones under high sulfate conditions; likely because the grafted ligands compete less efficiently with the bidentate sulfates coordination in uranyl coordination sphere.

Recovering Nutrients from Waste Black Water Through Multi-Functional Mesoporous Silica.

In order to prevent the harmful effects in water phase such as eutrophication, industrial and urban sewages must be treated before discharging into the aquatic environment. In this work, amine grafted magnetic nanoporous silica materials are synthesized and applied as an adsorbent for the recovery of nutrients from waste black water. The magnetic force could separate the surface func-tionalized nanoporous silica materials from aqueous medium after treatment, and showed the higher adsorption capacity of nutrients than that of the original mesoporous silica. The multi-functional nanoporous silica adsorbents were effectively removed phosphate and nitrate at 20 °C with the maximum adsorption capacities of 42.5 and 34.9 mg/g, respectively. The overall results indicated that the synthesized multi-functional nanoporous silica sorbents can be a candidate material for the nutrient recovery in wastewater treatment system.

Facile and scalable synthesis of functional Janus nanosheets – A polyethoxysiloxane assisted surfactant-free high internal phase emulsion approach

HypothesisJanus nanosheets, which have two surfaces of different functionalities, exhibit unique interfacial properties. In this work, we propose a facile and scalable technique for preparation of silica-based Janus nanosheets, which is based on formation of high internal phase water-in-oil emulsions stabilized solely by alkyl-substituted polyethoxysiloxanes due to their hydrolysis-induced interfacial activity. ExperimentsJanus nanosheets are then obtained by crushing the silica foams converted from such emulsions. The morphology of Janus nanosheets is investigated by field-emission scanning electron microscopy (FE-SEM) and transmission electron microscopy (TEM). The chemical structure of functional silica materials is characterized by Fourier transform infrared spectroscopy (FT-IR). The asymmetric structure of silica nanosheets is observed by confocal laser scanning microscopy. FindingsThe resulting nanosheets have a rough hydrophobic surface and a smooth hydrophilic one, and are capable of stabilizing Pickering oil-in-water emulsions. Remarkably, pH-responsiveness of emulsions can be attained using the nanosheets whose hydrophilic surface is substituted with amino groups. Fast oil–water separation is achieved by the Janus nanosheets, which has been demonstrated by the nanosheets with a polystyrene-coated hydrophobic surface. This work paves a new avenue for large-scale production of functional silica-based Janus nanosheets suitable for numerous promising applications.

Efficiency analysis of helium-cooled MAS DNP: case studies of surface-modified nanoparticles and homogeneous small-molecule solutions.

Despite the growing number of successful applications of dynamic nuclear polarization (DNP)-enhanced magic-angle spinning (MAS) NMR in structural biology and materials science, the nuclear polarizations achieved by current MAS DNP instrumentation are still considerably lower than the theoretical maximum. The method could be significantly strengthened if experiments were performed at temperatures much lower than those currently widely used (∼100 K). Recently, the prospects of helium (He)-cooled MAS DNP have been increased with the instrumental developments in MAS technology that uses cold helium gas for sample cooling. Despite the additional gains in sensitivity that have been observed with He-cooled MAS DNP, the performance of the technique has not been evaluated in the case of surfaces and interfaces that benefit the most from DNP. Herein, we studied the efficiency of DNP at temperatures between ∼30 K and ∼100 K for organically functionalized silica material and a homogeneous solution of small organic molecules at a magnetic field B0 = 16.4 T. We recorded the changes in signal enhancement, paramagnet-induced quenching and depolarization effects, DNP build-up rate, and Boltzmann polarization. For these samples, the increases in MAS-induced depolarization and DNP build-up times at around 30 K were not as severe as anticipated. In the case of the surface species, we determined that MAS DNP at 30 K provided ∼10 times higher sensitivity than MAS DNP at 90 K, which corresponds to the acceleration of experiments by multiplicative factors of up to 100.

Removal of biogenic amines from wines by chemisorption on functionalized silica and effects on other wine components

The effectiveness of several functionalized silica materials (cation-exchange materials) for the removal of biogenic amines from wines, and the effects on other wine components and organoleptic characteristics were evaluated. Results have shown that mesoporous silica material bi-functionalized with phosphonic and sulfonic acids allowed the removal of histamine, putrescine, cadaverine, spermine and spermidine from wines, although the dose must be adapted for each wine according to the removal requirements and wine characteristics. A plus of the adsorbent developed is that it can be recovered and re-used for at least 3 treatments. Immediately following the treatments, a decrease in the levels of linear ethyl esters (ethyl hexanoate, ethyl octanoate and ethyl decanoate) was observed, although these levels were re-equilibrated after several days reducing this undesired side effect. A slight, but perceptible, effect on wine color was observed, probably due to the slight decrease in the pH of the wine produced by the treatments. On the basis of the sensory analysis that focused only on the aroma of the wines, the proposed technique would be more adequate for wines aged in barrels than for young wines.

Adsorption of bentazone and imazapyc from water by using functionalized silica: Experimental and computational analysis

In this study, silica and functionalized silica materials (3-aminopropyl and 3-mercapto derivatives) were successfully used for the removal of the pesticides bentazone and imazapyc from aqueous solutions. Adsorbent materials were characterized by BET isotherms and FT-IR spectroscopy (confirming the functionalization), and their equilibrium adsorption capacity was evaluated at different ionic strengths. It is observed that the maximum adsorption capacities decrease in the order 3-aminopropyl-derivative > silica >3-mercaptopropyl derivative. An increase in ionic strength produces an enhancement in the removal of pesticides. All isotherms are Ib-type and follow the Langmuir model, suggesting a monolayer physical adsorption process.

Tailoring Mesoporous Silica Nanoparticles and Thin Films: Synthesis, Characterization and Electrochemical Applications

Mesoporous silica materials have played great roles in widespread application areas like adsorption, catalysis, and separation due to their high surface area, large pore volume and tunable pore size and structure. One of the approaches for extending the application of mesoporous silica materials is tailoring their wall with various functional groups. However, the conventional post-grafting method results in lightly dense, heterogeneously distributed and less accessible functional groups. In our work, a new method that leads to dense and uniform functionalization of the wall without clogging of the pores has been employed. The hybrid silica-based materials are fabricated either through diblock copolymer templated sol-gel method or through electro-assisted self-assembly method. In the former case, since the template is self-assembled functional amphiphilic diblock copolymer, the selective removing of the hydrophobic block results in porous and PEO functionalized silica materials. Textural and structural properties of the hybrid porous materials will be presented. Furthermore, their application in the area of Li-ion battery as solid composite polymer electrolytes will be discussed. In the later case, surfactant templated mesoporous silica films have been fabricated on conductive substrates via electro-assisted self-assembly method. Hexagonally well-ordered and vertically oriented mesochannels with a diameter of 3nm are obtained in a large domain across the resulted films. The permeability, morphology and nanostructure of the films will be presented. Figure 1

Amine functionalized mesoporous hybrid materials: influence of KCl and xylene on the textural characteristics and CO2 sorption

Amine-functionalized mesoporous silica materials were prepared by sol–gel method in the system tetraethylortosilicate: bis[(3- trimethoxysilyl)propyl]amine (TEOS: BTPA). The hybrid amine functionalized silica materials were synthesized by co-condensation reaction between TEOS and BTPA precursors in acidic media. Soft template approach for pore formation was applied and as a structural directing agent was used surfactant Pluronic P123. For improving of pore ordering and textural characteristics xylene and KCl were used and their influence on the structural and morphological characteristics was investigated by FTIR, 13C CP MAS NMR, 29Si MAS NMR, BET, PSD and XRD techniques. CO2 adsorption properties of the synthesized amine functionalized hybrid materials were investigated. The simultaneous presence of xylene and KCl leads to improvement of the pore ordering, increasing of the textural characteristics values and formation of cylindrical pores. The determined heats of CO2 adsorption evidenced chemisorption process between CO2 and the amine groups of the hybrid materials.

Functionalized silica materials synthesized via co-condensation and post-grafting methods

Mesoporous silica particles have been prepared with functionalized precursors, used either in situ co-condensation process or as post-synthesis grafting agents, in order to deliver surface functionalisation. Aminopropyl, mercaptopropyl, vinyl and hexyl organosilanes were used as funtionalized precursors, tetraethyl orthosilicate as the base silica precursor material, hexadecyl-trimethylammonium bromide (CTAB) as directing agent and water-ethanol mixture as solvent, with ammonia catalyst. The aim was to explore the effect of various recipes on the structural properties of the composite materials. The samples’ microstructures have been evaluated using nitrogen sorption and small angle neutron scattering. Ordered mesoporous structures were obtained, for almost all synthesis conditions, after the solvent-extraction of the template agent. Only in one case, for the materials functionalized by mercaptopropyl groups in co-condensation route, disordered amorphous structure was obtained. All samples functionalized by post-grafting presented well-ordered mesoporous structures. The results have potential use for easy design of sorbent materials for drug loading or pollutant adsorption applications.

Use of Materials Based on Polymeric Silica as Bone-Targeted Drug Delivery Systems for Metronidazole.

Mesostructured ordered silica-based materials are the promising candidates for local drug delivery systems in bone disease due to their uniform pore size and distribution, and high surface area which affect their excellent adsorption properties, good biocompatibility and bioactivity, and versatile functionalization so that their properties can be controlled. Ordered mesoporous silica (MCM-41 type) was synthesized by a surfactant-assisted sol-gel process using tetraethoxysilane as a silica precursor and hexadecyltrimethylammonium bromide as the structure-directing agent. Functionalized silica materials containing various types of organic groups (3-aminopropyl, 3-mercaptopropyl, or 3-glycidyloxypropyl groups) were synthesized by the post-grafting method onto pre-made mesoporous silica. Comparative studies of their structural characteristics, the surface mineralization activity and release properties for the model drug Metronidazole (MT) were then conducted. It has been found that porosity parameters, mineralization activity and adsorption/release of metronidazole from mesoporous channels of silica can be regulated using functional groups which are chemically bounded with an outer silica surface. The preferential mineral nucleation was found on negatively charged surfaces—MCM-41, and mercaptopropyl and glycidyloxypropyl functionalized silica (MCM-SH and MCM-epoxy, respectively) in simulated body fluid (SBF solution), as well as a sustained release of MT. In contrast to them, aminopropyl-functionalized samples (MCM-NH2) achieved a high MT release rate. These results confirm the potential of silica-based materials for local therapeutic applications (as drug carriers and bone substitutes) in bone disease.

Tuning molecular structure of tertiary amine catalysts for glucose isomerization

The structure of alkyl substituents on tertiary amines can impact catalytic performance for the isomerization of glucose to fructose. When using the same concentration, homogeneous amines with similar values of pKa result in different glucose conversions. The observed differences can be attributed to how the steric bulk of substituents on the amine impact the accessibility. Amines with less bulky substituents achieve higher glucose conversion than sterically hindered amines, indicating that the amine is involved in a catalytically relevant step. Analogues of these homogeneous tertiary amines with different alkyl substituents are immobilized onto mesoporous silica materials. Contrary to the trend with homogeneous amines, the steric bulk of isopropyl substituents for tertiary amine functionalized silica materials leads to higher glucose conversion than less bulky substituents. The differences are associated with interactions with the silica surface. Catalytic testing with homogeneous amines in presence of silica demonstrate that the amines with bulky substituents are impacted less by the silica than less sterically hindered amines. Overall, these results demonstrate that amines are a tunable catalyst for the isomerization of glucose to fructose.

Preparation of glutathione-functionalized zwitterionic silica material for efficient enrichment of sialylated N-glycopeptides.

A glutathione (GSH)-functionalized silica material was prepared using divinyl sulfone activation chemistry (named SiO2-DVS-GSH). The successful synthesis of the SiO2-DVS-GSH material was confirmed by FT-IR, elemental analysis, and zeta potential analysis. The effects of water content, pH value, and salt concentration in the mobile phase on the model compound (uracil, uridine, cytosine, cytidine, guanosine, xanthosine, orotic acid) retention was studied, and a hydrophilic interaction liquid chromatography (HILIC) retention feature together with electrostatic interaction of the SiO2-DVS-GSH material was observed. The prepared stationary phase was further applied for the separation of oligosaccharide. In addition, the SiO2-DVS-GSH material displayed remarkable selectivity and specificity for the sialylated N-glycopeptides' enrichment from bovine fetuin tryptic digests, even at a mass ratio of 1:1000 (w/w) to bovine serum albumin (BSA, non-glycosylated protein), showing superior performance compared to commercial ZIC-HILIC material. Moreover, the SiO2-DVS-GSH material behaved well in the N-glycopeptides' enrichment from human serum, demonstrating its promising potential for glycoproteomics of complex biological samples. Graphical Abstract A glutathione (GSH)-functionalized silica material was prepared using divinyl sulfone activation chemistry, and it shows remarkable selectivity and specificity for the sialylated N-glycopeptides' enrichment.

Latest progress on the typical mesoporous Si-based solid acid catalysts

Serious environment and safety issues by the wide application of inorganic mineral acids have attracted worldwide attention from fundamental science and application point of view. Under such circumstances, the development of the solid acid catalysts is a very hot topic currently. The ideal solid acid catalysts possess appropriate Bronsted and Lewis acidic nature, good porosity, high stability and unique morphology. Among them, the morphological nanostructure of catalysts is one of the important factors that can have a profound influence on their catalytic performance. Compared with a number of other supports of the solid acid catalysts, the silica-based materials are considered as promising candidates because of their diverse composition, physicochemical property and morphology as well as excellent porosity property. Among them, mesoporous silica-based materials possess lager pore compared with the microporous silica materials (e.g., ZSM-5, H-beta, etc.). They enable to catalyze reactions efficiently involving bulky substrates and/or products, and facilitate mass transfer. Meanwhile, the larger pore favors the dispersion of the active sites and hinders the accumulation of coke on the surface to avoid pore blocking. As a result, one of the important strategies to prepare novel solid acid catalysts is to immobilize the active sites on mesoporous silica materials. The as-prepared mesoporous silica-based solid acid catalysts have shown great potential for application in the field of environment, energy and industrial catalysis. In this paper, the latest progress on the morphology-controlled preparation of mesoporous silica−based materials and their applications in catalysis are summarized. In the case of the silica-based materials, it can be dated back to the early 1990s, and Mobil Company synthesized various M41S materials firstly (MCM-41, MCM-48 and MCM-50) by using the alkyl quaternary ammonium salt cationic surfactant as the template agent. Compared with the amorphous silica materials, M41S possess ordered mesoporous structure, uniform pore size (2‒5 nm), large pore volume and BET surface area (1000 m2 g-1). Subsequently, various SBA materials (such as SBA-15 and SBA-16) with large pore size were prepared successfully. It has attracted wide attention to functionalize the silica materials by incorporating the active sites and maintaining the morphological structure. With the development of silica-based materials, periodic mesoporous organosilicas (PMO) were synthesized by surfactant-directed sol-gel method, which opened a new pathway to prepare functional mesoporous silica materials. Up to now, a number of functionalized organosilica materials have been reported and exhibited great potential in the fields of catalysis, sensing, chromatography analysis, metal adsorption and bio-pharmacy etc. Herein, the mesoporous silica-based solid acid catalysts by the morphology-controlled preparation of functionalized organosilicas showed highly ordered, tubular or hollow spherical nanostructure by P123-directed sol-gel co-condensation. The as-prepared mesoporous silica-based solid acid catalysts possessed hydrophobic surface, excellent porosity property and strong Bronsted acidic nature. Moreover, the catalysts with well-defined morphology exhibited high catalytic performance for synthesis of the biomass-derived platform molecules or high value-added chemicals. Owing to the accelerated diffusion, transmission and improved accessibility of substrates to active sites, the mesoporous silica-based solid acid catalysts with hollow nanosphere morphology showed the highest activity compared with the tubular or ordered analogues. On the other hand, the covalent bond between active sites and silica framework can avoid the leaching issue of the solid acid catalysts. In addition, the hydrophobic character of alkyl-containing organosilica can reduce acid sites deactivation associated with adsorption of polar byproducts, which can improve the stability of as-prepared catalysts. To summarize, this review aims to provide important reference value for development of novel solid acid catalysts.

IR spectroscopy study of SBA-15 silicas functionalized with the ethylthiocarbamidepropyl groups and their interactions with Ag(I) and Hg(II) ions

Mesoporous structure of silica is determined by the type of template, but the introduction of functional groups during the synthesis has additional influence. The structure of SBA-15 may be violated by the introduction of long functions, such as ≡Si(CH2)3NHC(=S)NHC2H5. These ethylthiocarbamidepropyl groups can form complexes with metal ions in thiol or thione tautomeric forms. We determined that the 2D hexagonal p6 mm structure is preserved for SBA-15 with thiourea groups at maximal TEOS:trifunctional silane ratio (mol) = 10:2, which was confirmed by TEM and by the presence of an intense reflex in the small-angle region of diffractograms of the final product. It was shown that the obtained sorbents possess high kinetic characteristics. The experimental data fit pseudo-second-order kinetic equation, but the rate constants depend on the content of functional groups in the surface layer. Template Pluronic P-123 defines the porosity of functional mesoporous silica materials even at increasing content of trifunctional silane in the initial solution. Infrared spectroscopy analysis showed that thione form of thiourea ligand is prevalent on the surface of pores of mesoporous samples. However, during the sorption of silver(I) ions, there are both thione and thiol forms on the surface. Thione form is transformed into thiol with increasing concentration of mercury(II) ions in the sorption solution. Adsorption experiments showed that the SBA-15 silicas functionalized with ethylthiocarbamidepropyl groups had high selectivity for silver(I) ions and could concentrate Ag(I) ions from metal ions mixture at pH ~ 2.

Dual Functions of Selective Ferric Ion Detection and Removal by a Recyclable Fluorescence Active Multifunctional Silica Material and Toxic Dye Removal from Aqueous Solution

Excess iron and its toxic dye Naphthol Green B is a threat to aquatic environment and human health. Therefore, effective detection and remediation of ferric ion and Naphthol Green B in aqueous system is a necessity. In our paper, to bring out synergy in dual functions of ferric ion sensing and extraction/removal by same material, a new ionophore based functionalized silica material (SiO2@Nap) was synthesized by immobilization of bis (tetradentate) naphthalene ligand on silica surface. Physicochemical properties of the adsorbent were studied by scanning and transmission electron microscopy, atomic force microscopy, XRD, FT-IR, thermo-gravimetric analysis and elemental (CHN) analysis. The selective sensing studies by SiO2@Nap material towards ferric ion in presence of 17 other relevant metal ions were evaluated through the fluorescence quenching phenomenon which gives limit of detection value of 74 ppb (1.31 μM). The adsorption studies for ferric ion were assessed in view of effect of solution pH, extraction efficiency (99%), adsorption capacity (79 mg/g) and adsorption isotherms. This material can be recycled upon simple acid-base treatments for further usage after recovery of ferric ions which is supported by reversibility studies. The strong affinity towards ferric ion enabled this material to remove iron containing industrial toxic dye Naphthol Green B with 99.5% efficiency with recyclability. Adsorption, striping and regeneration studies reveals that SiO2@Nap is a recyclable extracting cum sensory probe material for ferric ions.

Surface-functionalization of mesoporous SBA-15 silica materials for controlled release of methylprednisolone sodium hemisuccinate: Influence of functionality type and strategies of incorporation

Mesoporous SBA-15 silica materials functionalized with several organic moieties, that include different polarities and hydrophobicities, were investigated as matrices for controlled drug delivery. The functionalities were incorporated into SBA-15 using two methods: direct synthesis or co-condensation route and post-synthesis grafting. Methylprednisolone sodium hemisuccinate, a synthetic pharmaceutical compound used as anti-inflammatory and immunosuppressant, was loaded onto the pristine and functionalized mesoporous SBA-15 silica materials. The influence of the type of organic moieties as well as their incorporation method onto the inorganic silica framework has been evaluated. The results show that SBA-15 functionalized with aminopropyl trimethoxysilane groups has the largest capacity of drug adsorption, clearly higher than the provided by materials functionalized with other groups, independently of the synthesis route. Additionally, materials synthesized by the co-condensation approach show a lower degree of drug retention than the same material synthesized by grafting technique. This fact is attributed to the distinct localization of the functionality, more accessible in the case of the grafting procedure, and hence suggesting that stronger interactions among the SBA-15 functionalized surfaces and the model drug are established. To ascertain whether other organosilanes containing amino groups can provide more effective loading and controlled drug delivery, at neutral and acidic conditions (pH of 7.4 and 4.6, respectively), it was also investigated the incorporation by grafting of several amino organic moieties onto the SBA-15 silica materials. It was concluded that as the number of amino groups incorporated into SBA-15 material increased, not only the drug loading capacity was higher, but the functionalized silica material vehicles slowed down the drug delivery. Finally, it was confirmed that cell viability was largely unaffected by amino-functionalized mesoporous SBA-15 silica materials after 72 h of incubation time.

Fabrication of diverse pH-sensitive functional mesoporous silica for selective removal or depletion of highly abundant proteins from biological samples

In proteomic studies, poor detection of low abundant proteins is a major problem due to the presence of highly abundant proteins. Therefore, the specific removal or depletion of highly abundant proteins prior to analysis is necessary. In response to this problem, a series of pH-sensitive functional mesoporous silica materials composed of 2–(diethylamino)ethyl methacrylate and methacrylic acid units were designed and synthesized via atom transfer radical polymerization. These functional mesoporous silica materials were characterized and their ability for adsorption and separation of proteins was evaluated. Possessing a pH-sensitive feature, the synthesized functional materials showed selective adsorption of some proteins in aqueous or buffer solutions at certain pH values. The specific removal of a particular protein from a mixed protein solution was subsequently studied. The analytical results confirmed that all the target proteins (bovine serum albumin, ovalbumin, and lysozyme) can be removed by the proposed materials from a five–protein mixture in a single operation. Finally, the practical application of this approach was also evaluated by the selective removal of certain proteins from real biological samples. The results revealed that the maximum removal efficiencies of ovalbumin and lysozyme from egg white sample were obtained as 99% and 92%, respectively, while the maximum removal efficiency of human serum albumin from human serum sample was about 80% by the proposed method. It suggested that this treatment process reduced the complexity of real biological samples and facilitated the identification of hidden proteins in chromatograms.

Calixarene ionic liquid modified silica gel: A novel stationary phase for mixed-mode chromatography

A novel calixarene ionic liquid functionalized silica material was synthesized by the preparation of a new calixarene monomer and its grafting on mercaptopropyl modified silica gel. The material was characterized by infrared spectra, elemental analysis, and thermogravimetric analysis. To explore the retention mechanism of the stationary phase, linear solvation energy relationships (LSER) equation as an effective mathematical model was used. In addition to this, the distinct separation mechanisms were outlined by selected examples of chromatographic separations in the different modes. In reversed-phase liquid chromatography, this new stationary phase presented specific chromatographic performance when evaluated using alkylbenzenes, PAHs and phenols as solutes. Due to the existing polar functional groups, this stationary phase can also be used in hydrophilic interaction chromatography, six nucleosides and four ginsenosides were separated successfully in hydrophilic mode. Furthermore, anions can be separated on the column in anion exchange mode. Thus, this new material was can be applied as a new kind of mixed-mode stationary phase in liquid chromatography, which allows an exceptionally flexible adjustment of retention and selectivity by tuning the experimental conditions.