Mercaptopropyl-functionalized Silica Research Articles

Silica-based ionic liquid coating for 96-blade system for extraction of aminoacids from complex matrixes

1-Vinyl-3-octadecylimidazolium bromide ionic liquid [C18VIm]Br was prepared and used for the modification of mercaptopropyl-functionalized silica (Si-MPS) through surface radical chain-transfer addition. The synthesized octadecylimidazolium-modified silica (SiImC18) was characterized by thermogravimetric analysis (TGA), infrared spectroscopy (IR), 13C NMR and 29Si NMR spectroscopy and used as an extraction phase for the automated 96-blade solid phase microextraction (SPME) system with thin-film geometry using polyacrylonitrile (PAN) glue. The new proposed extraction phase was applied for extraction of aminoacids from grape pulp, and LC–MS–MS method was developed for separation of model compounds. Extraction efficiency, reusability, linearity, limit of detection, limit of quantitation and matrix effect were evaluated. The whole process of sample preparation for the proposed method requires 270min for 96 samples simultaneously (60min preconditioning, 90min extraction, 60min desorption and 60min for carryover step) using 96-blade SPME system.Inter-blade and intra-blade reproducibility were in the respective ranges of 5–13 and 3–10% relative standard deviation (RSD) for all model compounds. Limits of detection and quantitation of the proposed SPME-LC–MS/MS system for analysis of analytes were found to range from 0.1 to 1.0 and 0.5 to 3.0μgL−1, respectively. Standard addition calibration was applied for quantitative analysis of aminoacids from grape juice and the results were validated with solvent extraction (SE) technique.

Investigation of π–π and ion–dipole interactions on 1-allyl-3-butylimidazolium ionic liquid-modified silica stationary phase in reversed-phase liquid chromatography

1-Allyl-3-butylimidazolium bromide ionic liquid [AyBIm]Br was prepared and used for the modification of mercaptopropyl-functionalized silica through surface radical chain-transfer addition. The obtained ionic liquid-modified silica (SiImBr) was characterized by elemental analysis, infrared spectroscopy, NMR spectroscopy, and thermogravimetric analysis. The selective retention behaviours of polycyclic aromatic hydrocarbons (PAHs) including some positional isomers were investigated using SiImBr as a stationary phase in reversed-phase liquid chromatography. The results showed that SiImBr presented multiple interactions including hydrophobic, π–π, and ion–dipole interactions during the separation of PAHs and dipolar compounds. However, it is proposed that π–π and ion–dipole interactions play important roles in the separation of PAHs and dipolar compounds. These results indicate that the ionic liquid-modified silica stationary phase is promising for future applications. A commercially available monomeric octadecylated silica (ODS) column and a custom-made poly(styrene)-grafted silica (Sil-St n) column were used as references.

Factors affecting the reactivity of thiol-functionalized mesoporous silica adsorbents toward mercury(II)

Numerous mercaptopropyl-functionalized silica spheres have been prepared by either post-synthesis grafting of MCM-41 and MCM-48 or self-assembly co-condensation of mercaptopropyltrimethoxysilane (MPTMS) or mercaptopropyltriethoxysilane (MPTES) and tetraethoxysilane (TEOS) precursors in hydroalcoholic medium in the presence of a cationic surfactant as templating agent and ammonia as catalyst. These materials of approximately the same particle size and morphology featured different functionalization levels, various degrees of structural order, and variable distribution of thiol groups in the mesopores. Their reactivity in solution has been studied using Hg(II) as model analyte. Total accessibility (on a 1:1 S:Hg stoichiometry basis) was demonstrated and quantified for well-ordered materials whereas less open and less organized structures with high degrees of functionalization were subject to less-than-complete loadings. Capacities measured at pH 2 were lower than at pH 4 because of distinct mercury-binding mechanisms. Kinetics associated to the uptake process were studied by in situ electrochemical monitoring of Hg(II) consumption from aqueous suspensions containing the various adsorbents. They indicate only little difference between materials of the MCM-41 and MCM-48 series at similar functionalization levels, fast mass transport in well-ordered mesostructures in comparison to the poorly or non-ordered ones (except at pH 2 where charge formation induced some restriction in materials characterized by long-range structural order), and even faster processes in the wormlike frameworks (characterized by shorter range structural order). Hg(II) binding to thiol-functionalized materials obtained by post-synthesis grafting was found to occur more rapidly in the early beginning of the uptake process as a result of a higher concentration of binding sites at the pore entrance in comparison to the more homogeneous distribution of these groups in the mesochannels of materials obtained by co-condensation.

Enhanced removal of arsenite from water by a mesoporous hybrid material – Thiol-functionalized silica coated activated alumina

A novel mesoporous hybrid adsorbent prepared by coating an activated alumina (AA) with a mercaptopropyl-functionalized silica was tested for removal of arsenite [As(III)]. Batch experimental results indicated that the thiol-functionalized AA (AA–SH) had an improved adsorption capacity and an enhanced adsorption rate for As(III) compared with AA. In the pH range from 4 to 11, AA–SH exhibited much higher removal efficiency than AA, and the maximum percent removal appeared at pH 7.0 and 8.5 for AA–SH and AA, respectively. The advantages of the hybrid material were further demonstrated by column filtrations using As(III)-spiked aged tap water and groundwater. Approximately 3200 and 350 bed volumes of spiked tap water containing 300 μg/L of As(III) were filtered by AA–SH and AA at pH 7, respectively, before the effluent arsenic concentration increased to the USEPA MCL of 10 μg/L. In a field column test with actual raw groundwater containing ∼70 μg/L of total arsenic (∼80% as As(III)) and having a pH value of ∼7.3, the breakthrough bed volumes were found to be ∼3100 and ∼800 for the AA–SH and AA, respectively. Batch and column studies also indicated that the AA–SH performed better than or similar to some common adsorbents such as granular ferric oxide (GFO) and granular TiO 2.

Preparation and evaluation of thiol-functionalized activated alumina for arsenite removal from water

Arsenic species such as arsenite [As(III)] and arsenate [As(V)] are known human carcinogens. Though lots of metal oxide adsorbents have been developed for removal of As(V), they are much less effective for As(III) adsorption. In this study, various inorganic–organic hybrid adsorbents bearing thiol groups have been prepared by modifying activated alumina (AA) with mercaptopropyl-functionalized silica under different experiment conditions. Raman spectra demonstrated the successful functionalization of AA and verified the formation of As–S complexes after As(III) adsorption. Batch experiments were applied to evaluate the As(III) adsorption performance of the hybrid adsorbents. Compare with AA, the hybrid adsorbents exhibited enhanced adsorption abilities for As(III) due to the introduction of thiol groups, and as the thiol loading increased, the uptake of As(III) increased. Experimental results indicated that the hybrid adsorbents still maintained the merit of the AA for As(V) adsorption. Based on the results, one hybrid adsorbent referred to as BL(AA) 30(MPTS) 3.3 has been selected by consideration of not only the adsorption capacity but also its environmentally friendly and cost-effective production. The investigation has indicated that the hybrid adsorbents are very promising for As(III) removal from water.

One-step preparation of thiol-modified mesoporous silica spheres with various functionalization levels and different pore structures

A wide range of mercaptopropyl-functionalized silica spherical particles of MCM-41 and MCM-48 (M41S family) have been prepared by co-condensation of mercaptopropyl trimethoxysilane (MPTMS) or mercaptopropyl triethoxysilane (MPTES) and tetraethoxysilane (TEOS) precursors in hydroalcoholic medium in the presence of a cationic surfactant as templating agent and ammonia as catalyst. It was possible to control the mesostructure type (hexagonal or cubic) by monitoring the water-to-ethanol ratio and the type of organoalkoxysilane precursor employed. Materials displaying various functionalization levels were obtained by varying the MPTMS or MPTES contents from 3 to 50% in the co-condensation synthesis medium. This gave rise to a wide range of porous solids with approximately the same particle size and morphology but featuring different functionalization levels and various degrees of structural order. They were characterized by X-ray diffraction (XRD), N2 adsorption-desorption isotherms and BET analysis, scanning and transmission electron microscopy, 29Si and 13C solid state nuclear magnetic resonance (NMR), particle size distribution measurements, and elemental chemical analysis. Mercaptopropyl groups were readily incorporated with high yields (>90%) by the co-condensation route. All samples exhibited spherical morphology with similar particle size but both the level of ordering and porosity of solids obtained by co-condensation were found to decrease when increasing the amount of organo-functional groups.

Synthesis and characterization of a novel resorcinarene-based stationary phase bearing polar headgroups for use in reversed-phase high-performance liquid chromatography

A novel silica-bonded stationary phase containing a functionalized resorcinarene selector was prepared by a straightforward synthesis. The complete modification of all resorcinic hydroxyl groups was achieved by reaction with isopropyl isocyanate. The derivatized resorcinarene selector was subsequently immobilized via the four alkenyl chains containing a terminal double bond by a free radical-induced reaction on mercaptopropyl-functionalized silica. A comprehensive characterization of the resulting bonded stationary phase was carried out by solid state NMR, IR and elemental analysis. The resulting selector is defined as a “polar headed” reversed phase since the highly ordered polar carbamate groups of the new stationary phase are located, compared to conventional polar embedded stationary phases, at a greater distance from the silica surface. Thus a new concept is introduced in the field of polar modified reversed-phase HPLC. The properties of the novel stationary phase are demonstrated by comparison with commercially available reversed phases.

1,3,5-Triaryl-2-penten-1,5-dione anchored to insoluble supports as heterogeneous chromogenic chemosensor

N-Allyl substituted 1,5-diphenyl-3-(4- N-methylaminophenyl)-2-penten-1,5-dione ( 1a ) has been immobilized on a polystyrene backbone, on the surface of mercaptopropyl-functionalized silica or inside the cavities of zeolite NaY. These solids either in suspension or in films act as chemosensors of Fe 3+ and other strong Lewis acid metal ions such as Cu 2+ and Pb 2+ in buffered water or ethanol. Brönsted acids in low pH aqueous solutions also produce the response of the sensor. For sensing of Fe 3+, depending on the loading of 1a (typically from 2.5 to 0.5 wt%) the solids can test from 10 −2 to 10 −4 M aqueous solutions. The time response can vary from tens of minutes to below a minute depending on hydrophilic/hydrophobic nature of the support and also on the 1a loading. The solid sensor was reused up to 10 times by regenerating after every use the initial form with NaAcO treatment.

Rate of Access to the Binding Sites in Organically Modified Silicates. 3. Effect of Structure and Density of Functional Groups in Mesoporous Solids Obtained by the Co-Condensation Route

Mercaptopropyl-functionalized silica spheres have been prepared by self-assembly co-condensation of mercaptopropyltrimethoxysilane (MPTMS) and tetraethoxysilane (TEOS) precursors in the presence of a cationic surfactant as templating agent and ammonia as catalyst. Several materials have been obtained by varying the MPTMS content from 5 to 100% in the synthesis medium, giving rise to a wide range of porous solids featuring different functionalization levels (denoted MPS-n%, with n ranging from 5 to 100) and distinct structural order/disorder over different length scales. They were characterized by N2 sorption isotherms, XRD, scanning and transmission electron microscopy, and particle size analysis. Their reactivity in aqueous media was studied with respect to their binding properties toward HgII species by complexation with thiol groups. Total accessibility (expressed on the basis of a 1:1 S/Hg stoechiometry) was demonstrated and quantified for well-ordered materials containing up to 30% MPTMS. Less open s...

Optical Properties of Inverse Opal Photonic Crystals

Colloidal crystal-templating methods have been used to prepare inverse opal photonic crystals of silica, mercaptopropyl-functionalized silica, titania, and zirconia. Ordered arrays of uniformly sized polymer spheres were infiltrated with fluid precursors capable of condensation or crystallization. After solidification of the material in the void spaces between the spheres, the polymer templates were removed by calcination or solvent extraction, leaving inverse replicas of the template arrays. By carefully controlling the synthetic procedures, gram-scale quantities of powdered macroporous materials exhibiting photonic crystal properties were obtained. For materials with crystalline walls (titania and zirconia), this required minimization of the size of the nanocrystalline grains. Because the periodicity introduced into the wall structure by the colloidal crystal templates was on the order of optical wavelengths, Bragg diffractions from the planes produced photonic stop bands in the visible spectra of these materials. The stop bands were manifested as brightly colored reflections and an optical filtering behavior of the materials. A crystallographic indexing of the optical spectrum of a polycrystalline inverse opal confirmed the fcc ordering of the pores. The optical properties of these materials were modified in predictable manners by numerous methods, including tailoring the pore size, filling the pores with fluids of various refractive indices, and changing the compositions of the solid material. The wavelengths of the colorful reflections (stop bands) were found to be proportional to the pore size and to vary linearly with the refractive index of the fluid filling the pores. The physical and synthetic modifications reported here allowed for the preparation of powders with optical reflections and bright colors spanning the entire visible spectrum.