Adsorption Of Molecular Probes Research Articles

Measuring the Accessible Surface Area within the Nanoparticle Corona Using Molecular Probe Adsorption.

The corona phase-the adsorbed layer of polymer, surfactant, or stabilizer molecules around a nanoparticle-is typically utilized to disperse nanoparticles into a solution or solid phase. However, this phase also controls molecular access to the nanoparticle surface, a property important for catalytic activity and sensor applications. Unfortunately, few methods can directly probe the structure of this corona phase, which is subcategorized as either a hard, immobile corona or a soft, transient corona in exchange with components in the bulk solution. In this work, we introduce a molecular probe adsorption (MPA) method for measuring the accessible nanoparticle surface area using a titration of a quenchable fluorescent molecule. For example, riboflavin is utilized to measure the surface area of gold nanoparticle standards, as well as corona phases on dispersed single-walled carbon nanotubes and graphene sheets. A material balance on the titration yields certain surface coverage parameters, including the ratio of the surface area to dissociation constant of the fluorophore, q/KD, as well as KD itself. Uncertainty, precision, and the correlation of these parameters across different experimental systems, preparations, and modalities are all discussed. Using MPA across a series of corona phases, we find that the Gibbs free energy of probe binding scales inversely with the cube root of surface area, q. In this way, MPA is the only technique to date capable of discerning critical structure-property relationships for such nanoparticle surface phases. Hence, MPA is a rapid quantitative technique that should prove useful for elucidating corona structure for nanoparticles across different systems.

Piezoelectric immunochip coated with thin films of bacterial cellulose nanocrystals for dengue detection

Low-cost piezoelectric devices, such as simple frequency monitoring quartz crystal microbalance (QCM) devices, have good clinical utility as fast diagnostic tools for the detection of several diseases. However, unspecific antigen recognition, poor molecular probe adsorption and the need for sample dilution are still common drawbacks that hinder their use in routine diagnosis. In this work, piezoelectric sensors were previously coated with thin films of bacterial cellulose nanocrystals (CN) to provide a more sensitive and adapted interface for the attachment of monoclonal immunoglobulin G (IgGNS1) and to favor specific detection of non-structural protein 1 (NS1) of dengue fever. The assembly of the immunochip surface was analyzed by atomic force microscopy (AFM) and the NS1 detection was followed by quartz crystal microbalance with (QCM-D) and without energy dissipation monitoring (QCM). The CN surface was able to immobilize 2.30±0.5mgm−2 of IgGNS1, as confirmed by AFM topography and phase images along with QCM-D. The system was able to detect the NS1 protein in serum with only 10-fold dilution in the range of 0.01–10µgmL−1 by both QCM and QCM-D. The limits of detection of the two devices were 0.1μgmL−1 for QCM-D and 0.32μgmL−1 for QCM. As a result, QCM-D and QCM apparatuses can be used to follow NS1 recognition and have good potential for more sensitive, fast and/or less expensive diagnostic assays for dengue.

Synthesis and characterization of small-mesopore-added silicalite-1 zeolites using single wall carbon nanohorn templating

Small-mesopore-added silicalite-1 zeolites were prepared by using single wall carbon nanohorn (SWCNH) as a template. The samples were characterized with X-ray powder diffraction, field emission scanning electron microscopy, transmission electron microscopy (TEM) and molecular probe adsorption methods. The pore size distributions determined with N2 adsorption at 77 K showed the presence of small mesopores in 2–4 nm pore widths, in addition to their intrinsic micropores of 0.58 nm. The mesopore volume was 0.06 cm3 g−1. The presence of small mesopores in the SWCNH-templated silicalite-1 zeolites was supported with TEM observation as well as the liquid phase adsorption of methylene blue, which was much higher than that on a bulk (purely microporous) silicalite-1.

Dramatic change of water-cluster accessibility of highly pure double-walled carbon nanotubes with high temperature annealing

Highly pure double-walled carbon nanotubes (DWCNTs) synthesized by a catalytic chemical vapour deposition method have a well-ordered bundle structure giving explicit diffraction peaks by synchrotron X-ray diffraction measurement. The changes of nanopore structural properties and water adsorptivity of DWCNTs with high-temperature heat treatment were investigated using molecular probe adsorption methods. It was founded that their nanoporosities and apparent hydrophilicities decreased with thermal annealing. However, a specific surface area of 275 m(2) g(-1) and the residual microporosity of more than 60% even after heat treatment at 2673 K suggest their unique applications.

Evidence of Water Adsorption in Hydrophobic Nanospaces of Highly Pure Double-Walled Carbon Nanotubes

Highly pure double-walled carbon nanotubes synthesized by a catalytic chemical vapor deposition method have a quasi one-dimensional nanopore system. We determined these nanotubes' nanopore structures by means of molecular probe adsorption using N(2) at 77 K, CO(2) at 273 K, and water at 298, 308, and 318 K, as well as high-resolution transmission electron microscopy. The water vapor adsorption behavior of this system was quite unusual. At a lower relative pressure of P/P(0) = 0.3-0.65, water filled the interstitial nanopores, and at relative pressures higher than this range, water also filled the interbundle nanopores. This study is the first to our knowledge that has provided direct evidence of water adsorption in hydrophobic nanospaces of highly pure double-walled carbon nanotubes.

Developing Ion Electroadsorption Stereoselectivity, by Pore Size Adjustment with Chemical Vapor Deposition onto Active Carbon Fiber Electrodes. Case of Ca2+/Na+ Separation in Water Capacitive Desalination

By using carbon chemical vapor deposition (CVD) onto active porous carbon fibers, we were able to reduce the pore size of the active carbon to obtain selective carbon molecular sieves (CMS) of variable properties. The pore size of these carbons was characterized by the adsorption of molecules of different dimensions (molecular probe adsorption) from the gas phase. By manipulating the several experimental parameters of the CVD process, the pore size of the CMS could be finely tuned to fall between sizes of alkaline earth cations (Ca2+; Mg2+, 6−7 A in diameter), and the much smaller size of hydrated monovalent cations (4 A in diameter). This was proven by voltammetric measurements of the pore-tailored carbon electrodes in the corresponding salt solutions, which also provided a measure of the differential capacity of the electrical double layer (EDL) vs the potential (e.g., at potentials negative to the potential of the zero charge, the EDL capacity was very small for CaCl2 and MgCl2 solutions, while it was ...

Assessing optimal pore-to-ion size relations in the design of porous poly(vinylidene chloride) carbons for EDL capacitors

In order to maximize the capacitance of electrical double layer (EDL) capacitors per unit electrode volume, higher surface areas are required. This leads to an increasingly greater subdivision of the carbon electrode, namely to pore systems of smaller pore size. When the pore size approaches the ion size, the EDL charging kinetics lows down because of multiple interactions of the ions with the surrounding pore walls. On the other hand, the ion electroadsorption capacity increases just because of this enhanced interaction. Therefore, there is a conflict between improving discharge kinetics and improving capacity. Knowing the effective ion size relative to the pore size can be helpful in optimizing the pore system design in electrodes for EDL capacitors. A thorough technique based on the adsorption of molecular probes in the gas phase and the electroadsorption of different ions was developed to assess pore dimensions. In this report, the technique is applied to the unique case of polyvinylidene chloride (PVDC) based carbon electrodes in an attempt to elucidate its extraordinary high EDL capacitance, in terms of the relation between effective ion size and pore size.

Studies of surfaces through molecular probe adsorption and solid-state NMR.

The interaction between the basic probe trimethylphosphine oxide and the Brønsted acid sites of a silica-alumina has been spectroscopically resolved for the first time using a new solid-state NMR approach that opens the possibilities for the investigation of surfaces.

Characterization of Silica Xerogels Surfaces by Inverse Gas Chromatography (IGC)

Abstract Silylated silica xerogels, with controlled specific surface area and porosity, were prepared by a two-step procedure. In the first step, hydrogels were treated “in-situ” with hexamethyldisiloxane (HMDS) in the presence of 2-propanol and acid. In the second step, the hydrophobic gel was transferred into an organic solvent, the residual water removed by azeotropic distillation and the dried xerogel isolated by evaporating the solvent. Using this procedure, structure collapse of the hydrogels was minimized and it was possible to make xerogels with controlled specific surface area and porosity by varying the aging conditions of the hydrogels. The surface properties of both the untreated and the “in-situ” treated silica xerogels were examined by inverse gas chromatography (IGC) at either infinite dilution conditions (IGC-ID) or finite concentration conditions (IGC-FD). The former method was used to monitor the thermodynamic parameters of adsorption of molecular probes in interaction with the sites having the highest energies, while the latter method was used to provide information about the surface energy heterogeneity of the whole surface. The results for the xerogels are also compared to those obtained on untreated and silylated fumed silicas. After silylation, a systematical surface energy decrease has been observed at both ID and FD conditions of IGC for the two types of silica. However, the modified xerogels with higher surface coverage than silylated fumed silica show some different behaviors.

Characterisation of zeolitic catalysts by the adsorption of molecular probes

Few examples of the characterisation by FTIR spectroscopy supplemented by the use of CO2, CO and NO molecular probes of acid, base and redox centres in zeolites (NaX and NaY) and zeolitetype (HSAPO-34, a silicon-aluminophosphate, and CoAPO-18, a cobalt-aluminophosphate) catalysts, are illustrated.

ChemInform Abstract: Characterization of Microporous and Mesoporous Materials by the Adsorption of Molecular Probes: FTIR and UV—VIS Studies

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Characterisation of microporous and mesoporous materials by the adsorption of molecular probes: FTIR and UV–Vis studies

This contribution describes with a few, properly selected, examples the spectroscopic characterisation of acid, base and redox centres in microporous and mesoporous molecular sieves. FTIR studies of the adsorption of molecular probes that lead to weak H-bonding (N 2 and CO), medium–strong H-bonding (H 2O) and proton-transfer reactions (NH 3) with the Brønsted acid hydroxyl groups of zeolites and aluminophosphates (HSAPO-34 and CoAPO-18) are illustrated. The acid Lewis sites (countercations) and the acid–base couples in NaX and NaY zeolites are monitored by CO and CO 2 adsorption respectively. Finally, FTIR and UV–Vis studies of the H 2O and NH 3 adsorption that probe the transition metal cation centres in mesoporous Ti–MCM41 and microporous CoAPO-18 catalysts are described.

“Figure/Ground” Study of Colloidal Silica Nanoparticles and Corresponding Microporous Xerogels

A critical hurdle in the development of sol−gel techniques for the preparation of microporous inorganic materials is elucidating the effect of key synthesis and processing parameters on the structure of the resulting sols. Characterization of colloidal particles with diameters of less than approximately 10 nm is problematic using conventional techniques such as dynamic light scattering. Similarly, quantitative determination of pore size distribution in the resulting materials using gas adsorption isotherms is difficult in the microporous regime. The present work extends these traditional methods with the objective of obtaining information both on the particle size in an inorganic sol and on the pore size distribution in the resulting microporous xerogel. Silica sols synthesized at pH 3 and an H2O/TEOS ratio of r = 83 were shown by atomic force microscopy to have a distribution of particle diameters centered around approximately 4−6 nm. Nitrogen and molecular probe adsorption studies on xerogels derived fr...

112. Molecular probe adsorption analysis of activated carbons

112. Molecular probe adsorption analysis of activated carbons