Concept: Surface chemistry
We report the template-free, low-temperature synthesis of a stable, amorphous, and anhydrous magnesium carbonate nanostructure with pore sizes below 6 nm and a specific surface area of ∼ 800 m(2) g(-1), substantially surpassing the surface area of all previously described alkali earth metal carbonates. The moisture sorption of the novel nanostructure is featured by a unique set of properties including an adsorption capacity ∼50% larger than that of the hygroscopic zeolite-Y at low relative humidities and with the ability to retain more than 75% of the adsorbed water when the humidity is decreased from 95% to 5% at room temperature. These properties can be regenerated by heat treatment at temperatures below 100°C.The structure is foreseen to become useful in applications such as humidity control, as industrial adsorbents and filters, in drug delivery and catalysis.
Magnesium silicate as a high-performance adsorption material has attracted increasing attention for the removal of organic dye pollution. Here, we prepared a series of magnesium silicate hydrates (MSH) in a hydrothermal route, and carefully investigated the corresponding adsorption behavior towards methylene blue (MB) as well as the effect of surface charge on adsorption capacity. The results show that surface charge plays a key role in the adsorption performance of MSH for MB, a negative surface charge density follows the increase of Si/Mg feeding ratio from 1.00 to 1.75, and furthermore the higher negative charge favors the improvement of the adsorption capacity. Among four investigated samples (MSH = 1.00, 1.25, 1.50, and 1.75), MSH-1.75 has the highest negative surface charge and shows the largest adsorption capacity for MB. For example, the equilibrium adsorption quantity is 307 mg·g−1 for MSH-1.75, which is 35% higher than that of 227 mg·g−1 for MSH-1.00. Besides, for MSH-1.75, the as-prepared sample with negative charge exhibits ca. 36% higher adsorption quantity compared to the sample at the zero point of charge (pHZPC). Furthermore, magnesium silicate hydrate material with Si/Mg feeding ratio = 1.75 demonstrates the promising removal efficiency of beyond 98% for methylene blue in 10 min, and the maximum adsorption capacity of 374 mg·g−1 calculated from the Langmuir isotherm model.
The applicability of gallium-based liquid metal alloy has been limited by the oxidation problem. In this paper, we report a simple method to remove the oxide layer on the surface of such alloy to recover its non-wetting characteristics, using hydrochloric acid (HCl) vapor. Through the HCl vapor treatment, we successfully restored the non-wetting characteristics of the alloy and suppressed its viscoelasticity. We analyzed the change of surface chemistry before and after the HCl vapor treatment using x-ray photoelectron spectroscopy (XPS) and low energy ion scattering spectroscopy (LEIS). Results showed that the oxidized surface of Galinstan® (Ga2O3 and Ga2O) was replaced with InCl3 and GaCl3 after the treatment. Surface tension and static contact angle on a Teflon®-coated glass of the HCl vapor treated Galinstan® were measured to be 523.8 mN/m and 152.5°. A droplet bouncing test was successfully carried out to demonstrate the non-wetting characteristics of the HCl vapor treated Galinstan®. Finally, the stability of the transformed surface of the HCl vapor treated Galinstan® was investigated by measuring contact angle and LEIS spectra after re-oxidation in ambient environment.
Protein-surface interactions are crucial to the overall biocompatability of biomaterials, and are thought to be the impetus towards the adverse host responses such as blood coagulation and complement activation. Only a few studies hint at the ultra-low fouling potential of zwitterionic poly(carboxybetaine methacrylate) (PCBMA) grafted surfaces and, of those, very few systematically investigate their non-fouling behavior. In this work, single protein adsorption studies as well as protein adsorption from complex solutions (i.e. human plasma) were used to evaluate the non-fouling potential of PCBMA grafted silica wafers prepared by nitroxide-mediated free radical polymerization. PCBMAs used for surface grafting varied in charge separating spacer groups that influence the overall surface charges, and chain end-groups that influence the overall hydrophilicity, thereby, allows a better understanding of these effects towards the protein adsorption for these materials. In situ ellipsometry was used to quantify the adsorbed layer thickness and adsorption kinetics for the adsorption of four proteins from single protein buffer solutions, viz, lysozyme, α-lactalbumin, human serum albumin and fibrinogen. Total amount of protein adsorbed on surfaces differed as a function of surface properties and protein characteristics. Finally, immunoblots results showed that human plasma protein adsorption to these surfaces resulted, primarily, in the adsorption of human serum albumin, with total protein adsorbed amounts being the lowest for PCBMA-3 (TEMPO). It was apparent that surface charge and chain hydrophilicity directly influenced protein adsorption behavior of PCBMA systems and are promising materials for biomedical applications.
The advances in micro- and nanofabrication technologies enable the preparation of increasingly smaller mechanical transducers capable of detecting the forces, motion, mechanical properties and masses that emerge in biomolecular interactions and fundamental biological processes. Thus, biosensors based on nanomechanical systems have gained considerable relevance in the last decade. This review provides insight into the mechanical phenomena that occur in suspended mechanical structures when either biological adsorption or interactions take place on their surface. This review guides the reader through the parameters that change as a consequence of biomolecular adsorption: mass, surface stress, effective Young’s modulus and viscoelasticity. The mathematical background needed to correctly interpret the output signals from nanomechanical biosensors is also outlined here. Other practical issues reviewed are the immobilization of biomolecular receptors on the surface of nanomechanical systems and methods to attain that in large arrays of sensors. We then describe some relevant realizations of biosensor devices based on nanomechanical systems that harness some of the mechanical effects cited above. We finally discuss the intrinsic detection limits of the devices and the limitation that arises from non-specific adsorption.
The surface chemistry of GaAs (100) with 50-keV Ar+ ion beam irradiation at off-normal incidence has been investigated in order to elucidate the surface nano-structuring mechanism(s). Core level and valence band studies of the surface composition were carried out as a function of fluences, which varied from 1 [MULTIPLICATION SIGN] 1017 to 7 [MULTIPLICATION SIGN] 1017 ions/cm2. Core-level spectra of samples analyzed by X-ray photoelectron spectroscopy confirmed the Ga enrichment of the surface resulting in bigger sized nano-dots. Formation of such nano-dots is attributed to be due to the interplay between preferential sputtering and surface diffusion processes. Valence band measurement shows that the shift in the Fermi edge is higher for Ga- rich, bigger sized nano-dots due to the partial oxide formation of Ga. ‘One-dimensional power spectral density’ extracted from atomic force micrographs also confirms the significant role of surface diffusion in observed nano-structuring.
Aromatic organoarsenicals p-arsanilic acid (pAsA) and roxarsone (ROX) are used as feed additives in developing countries that allow the use of arsenic-containing compounds in their poultry industry. These compounds are introduced to the environment through the application of contaminated poultry litter. Little is known about the surface chemistry of these organoarsenicals at the molecular level with reactive components in soils. We report herein the first in-situ and surface-sensitive rapid kinetic studies on the adsorption and desorption of pAsA to/from hematite nanoparticles at pH 7 using ATR-FTIR. Values for the apparent initial rates of adsorption and desorption were extracted from experimental data as a function of spectral components. Hydrogen phosphate was used as a desorbing agent due to its ubiquitous presence in litter, and its adsorption kinetics was investigated on surfaces with and without surface arsenic. Initial first order pseudo adsorption rate constant for pAsA was lower by a factor of 1.6 than that of iAs(V) suggesting an average behavior for the formation of quantitatively more weakly-bonded monodentate and/or hydrogen-bonded complexes for the former relative to strongly-bonded bidentate surface complexes for the latter under our experimental conditions. Initial first order pseudo adsorption rate constants for hydrogen phosphate decreases in this order: fresh hematite > pAsA/hematite ≈ phenylarsonic acid (PhAs)/hematite > iAs/hematite by factors 1.5 and 3 relative to fresh films, respectively. Initial desorption kinetics of aromatic organoarsenicals due to flowing hydrogen phosphate proceed with a non-unity overall order suggesting a complex mechanism, which is consistent with the existence of more than one type of surface complexes. The impact of our studies on the environmental fate and transport of aromatic organoarsenicals in geochemical environments and their overall surface chemistry with iron (oxyhyr)oxides is discussed.
In this study, the adsorption/desorption characteristics of anthocyanins on five Amberlite resins (FPX-66, XAD-7HP, XAD-16N, XAD-1180 and XAD-761) were evaluated. FPX-66 and XAD-16N showed the highest adsorption and desorption capacities, and ratios for anthocyanins from muscadine pomace extract, while XAD-7HP had the lowest adsorption and desorption capacities, and ratios. Based on static adsorption and desorption tests three resins (FPX-66, XAD-16N and XAD-1180) were selected for adsorption kinetics and isotherms. The adsorption mechanism was better explained by the pseudo-first order kinetics for FPX-66 and XAD-16N; however, for XAD-1180 pseudo-second order kinetics was the most suitable model. The experimental data fitted best to Langmuir isotherm model for all the three resins. Dynamic testing was done on a column packed with FPX-66 resin and breakthrough volume was reached at 17 bed volumes of muscadine pomace water extract during adsorption. Three bed volumes of aqueous ethanol (70%) resulted in complete desorption. Resin adsorption resulted in a concentrated pomace extract that contained 13% (w/w) anthocyanins with no detectable sugars.
The assembly of artificial nanostructured and microstructured materials which display structures and functionalities that mimic nature’s complexity requires building blocks with specific and directional interactions, analogous to those displayed at the molecular level. Despite remarkable progress in synthesizing “patchy” particles encoding anisotropic interactions, most current methods are restricted to integrating up to two compositional patches on a single “molecule” and to objects with simple shapes. Currently, decoupling functionality and shape to achieve full compositional and geometrical programmability remains an elusive task. We use sequential capillarity-assisted particle assembly which uniquely fulfills the demands described above. This is a new method based on simple, yet essential, adaptations to the well-known capillary assembly of particles over topographical templates. Tuning the depth of the assembly sites (traps) and the surface tension of moving droplets of colloidal suspensions enables controlled stepwise filling of traps to “synthesize” colloidal molecules. After deposition and mechanical linkage, the colloidal molecules can be dispersed in a solvent. The template’s shape solely controls the molecule’s geometry, whereas the filling sequence independently determines its composition. No specific surface chemistry is required, and multifunctional molecules with organic and inorganic moieties can be fabricated. We demonstrate the “synthesis” of a library of structures, ranging from dumbbells and triangles to units resembling bar codes, block copolymers, surfactants, and three-dimensional chiral objects. The full programmability of our approach opens up new directions not only for assembling and studying complex materials with single-particle-level control but also for fabricating new microscale devices for sensing, patterning, and delivery applications.
Long term adsorption kinetics of asphaltenes at the oil-water interface: a random sequential adsorption perspective
- Langmuir : the ACS journal of surfaces and colloids
- Published over 5 years ago
Previous studies [1, 2] indicated that asphaltenes adsorbed as monomers on oil-water interfaces and the early stage kinetics of the process was controlled by diffusion and hence dependent on oil viscosity. By meas-uring interfacial tension (IFT) as a function of surface coverage during droplet expansions in pendant drop experiments, it was also concluded that the IFT data could be interpreted with a Langmuir Equation of State (EoS), which was independent of oil viscosity, time of adsorption and bulk asphaltenes concentration. The surface excess coverage was calculated to be ~0.3 nm2/molecule which suggested flat on adsorption of asphaltenes monomers at the interface and average PAH core per molecule of about 6 for the asphaltenes investigated, consistent with the Yen-Mullins model [3, 4] . The current study focuses on the kinetics of asphaltenes adsorption at longer times and higher interfacial coverage. Long term IFT data have been measured by the pendant drop method for different asphaltenes concentrations and for different bulk viscosities of the oil phase (0.5- 28cP). The data indicate that when coverage reaches 35-40%, the adsorption rates slow down considerably compared to the diffusion controlled rates at the very early stages. The surface pressure increase rate (or IFT decrease rate) at these higher coverages is now independent of oil viscosity but dependent upon both surface pressure itself and asphaltenes monomer concentration. The long term asymptotic behavior of surface coverage is found to be consistent with the predictions from surface diffusion mediated Random Sequential Adsorption (RSA) theory which indicates a linear dependency of surface coverage on 1/√t and an asymptotic limit corresponding to a ‘jammed’ state close to 2D random close packing of disks (85%). From these observations RSA theory parameters were extracted that enabled description of adsorption kinetics for the range of conditions above surface coverage of 35%.