Surface-functionalized Silica Research Articles

Surface Functionalization of Silica with 2‐Vinylfuran by Cationic Polymerization

AbstractCationic surface polymerization of 2‐vinylfuran with chlorotriphenylmethane as initiator has been used for the functionalization of silica particles. The influence of monomer/initiator ratio and temperature on grafting efficiency, yield, and degree of grafting has been investigated. Grafting efficiency is a significant function of temperature and monomer/initiator ratio, because crosslinking reactions between cationically active chains increases the amount of the immobilized polyvinylfuran fraction. Thus, larger initiator concentrations on the silica cause higher polymer content on the surface. Polymer structure elucidation and surface properties are analyzed by means of solid‐state NMR spectroscopy, UV‐vis spectroscopy, BET – measurements, and scanning electron microscopy. magnified image

Microfluidic enzyme immunoassay using silicon microchip with immobilized antibodies and chemiluminescence detection.

Silicon microchips with immobilized antibodies were used to develop microfluidic enzyme immunoassays using chemiluminescence detection and horseradish peroxidase (HRP) as the enzyme label. Polyclonal anti-atrazine antibodies were coupled to the silicon microchip surface with an overall dimension of 13.1 x 3.2 mm, comprising 42 porous flow channels of 235-microm depth and 25-microm width. Different immobilization protocols based on covalent or noncovalent modification of the silica surface with 3-aminopropyltriethoxysilane (APTES) or 3-glycidoxypropyltrimethoxysilane (GOPS), linear polyethylenimine (LPEI, MW 750,000), or branched polyethylenimine (BPEI, MW 25,000), followed by adsorption or covalent attachment of the antibody, were evaluated to reach the best reusability, stability, and sensitivity of the microfluidic enzyme immunoassay (microFEIA). Adsorption of antibodies on a LPEI-modified silica surface and covalent attachment to physically adsorbed BPEI lead to unstable antibody coatings. Covalent coupling of antibodies via glutaraldehyde (GA) to three different functionalized silica surfaces (APTES-GA, LPEI-GA, and GOPS-BPEI-GA) resulted in antibody coatings that could be completely regenerated using 0.4 M glycine/HCl, pH 2.2. The buffer composition was shown to have a dramatic effect on the assay stability, where the commonly used phosphate buffer saline was proved to be the least suitable choice. The best long-term stability was obtained for the LPEI-GA surface with no loss of antibody activity during one month. The detection limits in the microFEIA for the three different immuno surfaces were 45, 3.8, and 0.80 ng/L (209, 17.7, and 3.7 pM) for APTES-GA, LPEI-GA, and GOPS-BPEI-GA, respectively.

Functionalization of silica particles towards cationic polyelectrolytes using vinylformamide and 1,3-divinylimidazolidin-2-one as monomers

The use of vinylformamide and 1,3-divinylimidazolidin-2-one, bisvinylethylene-urea (BVU). as well as of the poly(vinylformamide-vinylamine) copolymer (PVFA-co-PVAm) for silica surface functionalization has been investigated Various procedures such as grafting from, crosslinking surface polymerization, and post-functionalization of adsorbed PVAm chains have been experimentally applied The advantage of the different synthetic methods is discussed with regard to the resulting surface structure of the organic/inorganic hybrid materials.

Solid-State 31P NMR Study of Phosphonate Binding Sites in Guanidine-Functionalized, Molecular Imprinted Silica Xerogels

Phosphonate binding sites in guanidine and ammonium surface-functionalized silica xerogels were prepared via the molecular imprinting technique and characterized using solid-state 31P MAS NMR. One-point, two-point, and nonspecific host−guest interactions between phenylphosphonic acid (PPA) and the functionalized gels were distinguished by characteristic chemical shifts of the observed absorption peaks. Using solid-state as well as solution-phase NMR analyses, absorptions observed at 15.5 and 6.5 ppm were identified as resulting from the 1:1 (one-point) and 2:1 (two-point) guanidine to phosphonate interactions, respectively. Similar absorptions were observed with the ammonium functionalized gels. By examining the host−guest interactions within the gels, the efficiency of the molecular imprinting procedure with regard to the functional monomer-to-template interaction could be readily assessed. Template removal followed by substrate adsorption studies conducted on the guanidine-functionalized gels provided a method to evaluate the binding characteristics of the receptor sites to a phosphonate substrate. During these experiments, 29Si and 31P MAS NMR acted as diagnostic monitors to identify structural changes occurring in the gel matrix and at the receptor site from solvent-mediated processes.

Immobilization and catalytic properties of perfluorinated ruthenium phthalocyanine complexes in MCM-41-type molecular sieves

Ruthenium perfluorophthalocyanine complexes were immobilized in the channels of MCM-41-type molecular sieves using three different methods: (1) ship-in-the-bottle synthesis (in situ assembling of the metal complex from smaller moieties); (2) the synthesis method (addition of the preformed complex during synthesis of the molecular sieve); and (3) grafting the complex to the functionalized silica surface of MCM-41. The resulting host/guest compounds were characterized by X-ray powder diffraction, nitrogen adsorption and solid-state infrared and ultraviolet/visible spectroscopy, and tested as catalysts for the oxidation of n-hexane or cyclohexane under ambient conditions using tertiary-butylhydroperoxide as oxidant. Depending on the synthesis method, the materials obtained differ strongly in their composition (i.e., loading with complexes) and in their catalytic activities.

Zinc, Cadmium, and Lead Separation from Aqueous Streams Using Solid-Phase Extractants

The separation of cadmium, zinc, and lead from aqueous solutions using inorganic solid-phase extractants has been examined. An inorganic solid-phase extractant (ISPE-302) was prepared by attachment of bis (2,4,4-trimethyl)monothiophosphonic acid on a functionalized silica surface. Results of preparation and characterization studies are presented here. FTIR spectral studies show van der Waals type interactions between the alkyl chain of the extractant and the functional groups bonded to the silica surfaces. ISPE-302 exhibits the selectivity series of cadmium > lead > zinc. The initial capacity of 0.175 × 10-3 mol of cadmium/g of ISPE-302 achieved is 89% of the theoretical capacity. The capacity of ISPE-302 decreases to 0.5 × 10-4 mol/g, which is likely due to loss of extractant. Cadmium, lead, and zinc were separated by selective stripping from the bed saturated with these metal ions. These results indicate ISPE-302 has potential for separation of these metal ions from dilute aqueous solutions.

Determination of Functional Groups on Particle Surfaces by Fluorescence and Reflection Spectroscopy

The application of fluorescence and reflection (absorption) measurements for the determination of functional groups on surfaces has been investigated. As an example, aminofunctionalized silica surfaces have been studied that were functionalized silica surfaces have been studied that were labeled with the strongly colored fluorodinitrobenzene (FDNB) and the fluorescent Lucifer Yellow VS (LY). Both with reflection measurements and with fluorescence detection, amino groups could be quantified with concentrations as low as 10 mmol/kg, which is significantly lower than the detection limit attainable with conventional titration appraoches

Polymerization of vinyl monomers in the presence of silica having surface functional groups

The surface of silica was modified by mercaptopropyl, chloropropyl, aminopropyl, and methacryloxypropyl groups by the treatment of silica with the corresponding silane coupling agents, and the effects of functional groups on the surface on the polymerization of vinyl monomers initiated by benzoyl peroxide or 2,2′-azobisisobutyronitrile were investigated. Although the rate of the polymerization of vinyl monomers in the presence of silica was almost equal to that in the absence of silica, a part of polymer formed was grafted onto silica surface. The polymerization was considerably retarded in the presence of these functionalized silicas and the corresponding polymers were effectively grafted onto the surface. The molecular weight of ungrafted polymer formed in the presence of the functionalized silica was lower than that formed in the presence of unmodified silica. This indicates that the chain transfer reaction of growing polymer radical to functionalized silica surface forms radicals on the surface, which then couples with growing polymer radical and/or reinitiates the polymerization to give rise to the grafting of polymers onto the surface. In the case of silica having methacryloxypropyl groups, the grafting based on the copolymerization of vinyl monomer with the surface methacryloxypropyl groups was considered to successfully proceed.

ゾルーゲル法で合成した官能基をもつシリカゲルからのエポキシドと環状酸無水物のアニオングラフト重合

ゾルーゲル法で合成した官能基をもつシリカゲルからのエポキシドと環状酸無水物のアニオングラフト重合

Preparation and characterization of silica-bound tetrairidium carbonyl cluster compounds

Supported tetrairidium carbonyl cluster compounds were synthesized in the presence of a functionalized silica surface. The activity of the catalysts for ethylene hydrogenation and synthesis gas conversion was determined in an infrared flow reactor cell. The structure of the cluster was investigated in situ by Fourier transform infrared spectroscopy (FTIR). Preparation of the silica bound cluster compounds involved: (1) silica surface functionalization performed in a batch reactor at 90 °C under 1 atm of nitrogen, with beta-diphenylphosphinoethyltriethoxysilane; and (2) tetrairidium cluster synthesis in the presence of the functionalized silica, performed in a batch reactor at 90 °C under 5 atm of carbon monoxide. The supported cluster compounds were successfully identified as Ir 4(CO) 11-(PPh 2)SIL and Ir 4(CO) 10(PPh 2) 2SIL using Fourier transform infrared spectroscopy. Reaction kinetics for ethylene hydrogenation were determined for temperatures between 25 °C and 200 °C and for pressures between 1.0 atm and 1.5 atm. The reactor system, consisting of a differential flow reactor situated in the sample beam of a FTIR spectrometer and including an on-line gas chromatograph, was constructed for simultaneous monitoring of kinetics and infrared spectra. Ethylene hydrogenation orders at 27.5 °C of 0.7 and 1.2 were found for ethylene and hydrogen respectively. Catalytic enhancement of synthesis gas conversion was not detected.