Effect Of Surface Chemistry Research Articles

Probing the effect of surface chemistry on the electrical properties of ultrathin gold nanowire sensors

Ultrathin metal nanowires are ultimately analytical tools that can be used to survey the interfacial properties of the functional groups of organic molecules immobilized on nanoelectrodes. The high ratio of surface to bulk atoms makes such ultrathin nanowires extremely electrically sensitive to adsorbates and their charge and/or polarity, although little is known about the nature of surface chemistry interactions on metallic ultrathin nanowires. Here we report the first studies about the effect of functional groups of short-chain alkanethiol molecules on the electrical resistance of ultrathin gold nanowires. We fabricated ultrathin nanowire electrical sensors based on chemiresistors using conventional microfabrication techniques, so that the contact areas were passivated to leave only the surface of the nanowires exposed to the environment. By immobilizing alkanethiol molecules with head groups such as -CH3, -NH2 and -COOH on gold nanowires, we examined how the charge proximity due to protonation/deprotonation of the functional groups affects the resistance of the sensors. Electrical measurements in air and in water only indicate that beyond the gold-sulfur moiety interactions, the interfacial charge due to the acid-base chemistry of the functional groups of the molecules has a significant impact on the electrical resistance of the wires. Our data demonstrate that the degree of dissociation of the corresponding functional groups plays a major role in enhancing the surface-sensitive resistivity of the nanowires. These results stress the importance of recognizing the effect of protonation/deprotonation of the surface chemistry on the resulting electrical sensitivity of ultrathin metal nanowires and the applicability of such sensors for studying interfacial properties using electrodes of comparable size to the electrochemical double layer.

Cellulose Nanocrystal-Mediated Synthesis of Silver Nanoparticles: Role of Sulfate Groups in Nucleation Phenomena

Developing sustainable chemical methods to synthesize silver nanoparticles has drawn significant research interest. Due to their unique and well-defined physical-chemical properties, cellulose nanocrystals (CNCs) have become one of the most promising renewable nanomaterials. Here we use CNC to mediate silver nanoparticle synthesis and elucidate the effect of CNC surface chemistry (as defined by sulfate groups) in nanoparticle formation and nucleation in the presence of borohydride reduction. Pristine CNCs produced by sulfuric acid hydrolysis and partially desulfated CNCs mediated the formation of silver nanoparticles of different sizes (and size distribution) following different rates of formation, as determined by transmission electron microscopy (TEM) and UV-vis spectroscopy. The results shed light on methods to stabilize silver nanoparticles, control their nucleation, and highlight the potential of CNCs in metal nanoparticle synthesis.

Tunable self-discharge process of carbon nanotube based supercapacitors

Self-discharge tuning of supercapacitors is critical in prolonging their energy retention, which would significantly benefit their applications in energy storage if the self-discharge process can be controlled. This report on self-discharge mechanisms of supercapacitors built with single-walled carbon nanotubes (SWNTs) demonstrates the effects of surface chemistry on self-discharge by interfering in the electrostatic interaction between electrolytic ions and the SWNT surface and also explores the tunability of the self-discharge process. Experimental results give decent correlation between the self-discharge performance and the concentration of functional groups attached to the electrode surface. The time the self-discharge process takes to reach half of the charged voltage is extended by ~5 times with functional group decreasing by ~13%. Tuning of the self-discharge rate is therefore feasible for the SWNT supercapacitors by simply trimming the surface chemistry of the nanotubes.

Aerobic oxidation of benzyl alcohol to benzaldehyde catalyzed by carbon nanotubes without any promoter

Carbon nanotubes (CNTs) were used as metal-free catalysts for selective oxidation of benzyl alcohol (BzOH) to benzaldehyde (BzH) with molecular oxygen as the terminal oxidant in the absence of any promoter. The effects of reaction conditions, solvent and surface chemistry of CNTs on the catalytic performances have been investigated. The results showed that the solvent has a remarkable effect on oxidation of BzOH. The effect of the CNTs surface chemistry on the catalytic activity was revealed, and the surface carboxylic groups were particularly detrimental for the catalytic activity. A reasonable mechanism responsible for the liquid-phase oxidation of BzOH on CNTs was proposed, and electron transfer in graphene skeletons played an important role. Nitrogen doping efficiently enhanced the catalytic activity of CNTs for aerobic oxidation of BzOH, arising from improving electron transfer. In addition, the NCNTs revealed outstanding recyclability and exhibited excellent potential for industrial application of the BzOH oxidation to BzH.

Combining Nitrogen, Argon, and Water Adsorption for Advanced Characterization of Ordered Mesoporous Carbons (CMKs) and Periodic Mesoporous Organosilicas (PMOs)

Ordered mesoporous CMK carbons and periodic mesoporous organosilica (PMO) materials have been characterized by combining nitrogen (77.4 K) and argon (87.3 K) adsorption with recently developed quenched solid density functional theory (QSDFT). Systematic, high-resolution water adsorption experiments have been performed in the temperature range from 298 to 318 K in order to ascertain the effect of surface chemistry (using periodic mesoporous organosilicas (PMOs) of given pore size) and pore size/pore geometry (using CMK-3, CMK-8 carbons) on the adsorption, pore filling, condensation and hysteresis behavior. These data reveal how the interplay between confined geometry effects and the strength of the adsorption forces influence the adsorption, wetting, and phase behavior of pore fluids. Further, our results indicate that water adsorption is quite sensitive to both small changes in pore structure and surface chemistry, showing the potential of water adsorption as a powerful complementary tool for the characterization of nanoporous solids.

Effects of Al/Si ordering on feldspar dissolution: Part II. The pH dependence of plagioclases’ dissolution rates

The rate of mineral dissolution in an aquatic environment is sensitive to the pH of the contacting solution. The pH dependence of mineral dissolution rate has been interpreted by the Transition State Theory-Surface Complexation Model (TST-SCM) formalism in terms of pH-sensitive variability in surface chemistry. In this study, we provide an alternative interpretation for the experimentally observed nonlinear pH dependence of feldspar dissolution rates. The interpretation is based on a new formalism for feldspar dissolution which, while compatible with the TST-SCM formalism, incorporates the effects of both surface chemistry and bulk chemistry on feldspar dissolution into the quantification of dissolution rate. The pH dependence of dissolution rate varies from one feldspar specimen to another because different TOT linkages within one solid matrix can respond differently to the attack of proton. Our results suggest that the pH dependence of feldspar dissolution rate is not a constant in general, and could be affected by pH, substitutional Al/Si ordering, chemical composition of the specimen, and the relative rapidness of linkage hydrolysis according to different mechanisms. The rate law proposed in this study is able to capture the experimentally observed pH dependence of the dissolution rates of a series of plagioclases, including albite, andesine, labradorite, bytownite, and anorthite. The effectiveness of the newly proposed formalism for feldspar dissolution, hence, suggests that dissolution reactions of minerals are combinations of surface renewal and heterogeneous chemical reactions. The currently widely used TST-SCM-based rate laws can be further improved by taking into account the effects of bulk chemistry and surface renewal in the prediction of mineral dissolution rates. An improved formalism for mineral dissolution will be mineral-specific, and will reflect the effects of the temporal decay in the availability of reactive surface sites as well as the interconnectivities of atoms within the solid matrix of a mineral.

Molecular simulation and experimental characterization of the nanoporous structures of coal and gas shale

Characterization of coal and shale is required to obtain pore size distribution (PSD) in order to create realistic models to design efficient strategies for carbon capture and sequestration (CCS) at full scale. Proton nuclear magnetic resonance (NMR) cryoporometry and low-pressure gas adsorption isothermal experiments, conducted with N2 at 77K over a P/P0 range of 10−7 to 0.995, were carried out to determine the PSD and total pore volumes to provide insight into the development of realistic simulation models for the organic matter comprising coal and gas shale rock. The PSDs determined on the reference materials (SiliaFlash F60 and Vycor 7930) show a reasonable agreement between low-pressure gas adsorption and NMR cryoporometry showing complementarity of the two independent techniques. The PSDs of coal and shale samples were determined with low-pressure gas adsorption isothermal experiments, but were unable to be measured by NMR cryoporometry. This is likely due to a combined size and pore surface chemistry effect that prevents the water from condensing in the pores, such that when the sample is heated there is no distinction based upon melting or phase change. Molecular modeling is carried out to create the pore structure network in which the transport and adsorption predictions are based. The three-dimensional (3D) pore network, representative of porous carbon-based materials, has been generated atomistically using the Voronoi tessellation method. A comparison of the computed PSD using this method was made to the measured PSD using isothermal low-pressure gas adsorption isothermal experiments on coal and gas shale samples. Applications of this work will lead to the development of more realistic 3-D models from which enhanced understanding of gas adsorption and transport for enhanced methane recovery and CO2 storage applications can be developed.

The effects of surface chemistry of mesoporous silica materials and solution pH on kinetics of molsidomine adsorption

Adsorption kinetics of molsidomine on mesoporous silica material (UMS), the phenyl- (PhMS) and mercaptopropyl-functionalized (MMS) derivatives from solution with different pH and 298K was studied. The adsorption kinetics was found to follow the pseudo-second-order kinetic model for all studied silica materials and pH. Effects of surface functional groups and pH on adsorption efficiency and kinetic adsorption parameters were investigated. At all studied pH, the highest molsidomine amount is adsorbed on PhMS due to π–π interactions and hydrogen bonding between surface groups of PhMS and molsidomine molecules. An increase of pH results in a decrease of the amounts of adsorbed molsidomine onto the silica materials. Furthermore, the highest adsorption rate kinetically evaluated using a pseudo-second-order model, is observed onto UMS and it strongly depends on pH. The mechanism of the adsorption process was determined from the intraparticle diffusion and Boyd kinetic film–diffusion models. The results showed that the molsidomine adsorption on the silica materials is controlled by film diffusion. Effect of pH on the diffusion parameters is discussed.

Bi1–xSbx Alloy Nanocrystals: Colloidal Synthesis, Charge Transport, and Thermoelectric Properties

Nanostructured Bi1-xSbx alloys constitute a convenient system to study charge transport in a nanostructured narrow-gap semiconductor with promising thermoelectric properties. In this work, we developed the colloidal synthesis of monodisperse sub-10 nm Bi1-xSbx alloy nanocrystals (NCs) with controllable size and compositions. The surface chemistry of Bi1-xSbx NCs was tailored with inorganic ligands to improve the interparticle charge transport as well as to control the carrier concentration. Temperature-dependent (10-300 K) electrical measurements were performed on the Bi1-xSbx NC based pellets to investigate the effect of surface chemistry and grain size (∼10-40 nm) on their charge transport properties. The Hall effect measurements revealed that the temperature dependence of carrier mobility and concentration strongly depended on the grain size and the surface chemistry, which was different from the reported bulk behavior. At low temperatures, electron mobility in nanostructured Bi1-xSbx was directly proportional to the average grain size, while the concentration of free carriers was inversely proportional to the grain size. We propose a model explaining such behavior. Preliminary measurements of thermoelectric properties showed a ZT value comparable to those of bulk Bi1-xSbx alloys at 300 K, suggesting a potential of Bi1-xSbx NCs for low-temperature thermoelectric applications.

The combined effects of size and surface chemistry on the accumulation of boronic acid-rich protein nanoparticles in tumors

The high drug concentration and long-acting time within tumor tissues are a key challenge in cancer treatment. Here we prepare the boronic acid-rich bovine serum albumin nanoparticles with the size of 70 nm, 110 nm and 150 nm, and subsequently decorate particle surface with polyethyleneimine–polyethylene glycol copolymer and cRGD peptide. We demonstrated that the drug accumulation and particle residence time at tumor site can be significantly improved by incorporating boronic acid group into the bovine serum albumin nanoparticles, optimizing particle size and decorating particle surface. We show that the size- and surface chemistry-driven dual-actions lead to the doxorubicin accumulation at tumor site go beyond 12% injected dose per gram of tumor through such delivery system, which is 16-fold higher than that of free doxorubicin injected. Based on the systemic, tissue and cell level analysis, we demonstrated that the incorporated boronic acid group into the nanoparticles enhances the recognition ability of nanoparticles to cancer cells, and prolongs the action time of nanoparticles at tumor sites since the boronic acid group can reversibly and rapidly react with sialic acid residues which are overexpressed in cancer cells. These features make that this drug delivery system not only has significantly superior ability in impeding tumor growth, but also induces distinct shrinkage and apoptosis of tumor.

HPLC analysis of synthetic polymers on short monolithic columns

Ultrashort monolithic columns (disks) were thoroughly studied as efficient stationary phases for precipitation-dissolution chromatography of synthetic polymers. Gradient elution mode was applied in all chromatographic runs. The mixtures of different flexible chain homopolymers, such as polystyrenes, poly(methyl methacrylates), and poly(tert-butylmethacrylates) were separated according to their molecular weights on both commercial poly(styrene-co-divinylbenzene) disks (12 id × 3 mm and 5 × 5 mm) and lab-made monolithic columns (4.6 id × 50 mm) filled with supports of different hydrophobicity. The experimental conditions were optimized to reach fast and highly efficient separation. It was observed that, similar to the separation of monoliths of other classes of (macro)molecules (proteins, DNA, oligonucleotides), the length of column did not affect the peak resolution. A comparison of the retention properties of the poly(styrene-co-divinylbenzene) disk-shaped monoliths with those based on poly(lauryl methacrylate-co-ethylene dimethacrylate), poly(butyl methacrylate-co-ethylene dimethacrylate), and poly(glycidyl methacrylate-co-ethylene dimethacrylate) supports demonstrated the obvious effect of surface chemistry on the resolution factor. Additionally, the results of the discussed chromatographic mode on the fast determination of the molecular weights of homopolymers used in this study were compared to those established by SEC on columns packed with sorbent beads of a similar nature to the monoliths.

Effect of microstructure and surface chemistry in liquid-phase adsorptive nicotine by almond-shell-based activated carbon

The effect of microstructure and surface chemistry on nicotine adsorption capacity of almond-shell-based activated carbon was studied. Almond-shell-based activated carbon was reactivated or modified with steam, ZnCl2 and NaHSO4 separately. The surface area and pore structure parameters of activated carbon were determined from the adsorption-desorption isotherm of nitrogen at 77 K. Boehm titration and FTIR were explored to determine the surface oxygen groups. The results revealed that nicotine adsorption from solution on carbons depend on the micropores and phenolic groups. A strong correlation between the amounts of adsorbed nicotine and the phenolic groups was observed, whereas the higher amounts of carboxylic groups decrease the nicotine adsorption capacity on activated carbons.

Adsorption of carbon dioxide-methane mixtures in porous carbons: effect of surface chemistry

A combined experimental and molecular simulation study of the coadsorption of CO2 and CH4 in porous carbons is reported. We address the effect of surface chemistry by considering a numerical model of disordered porous carbons which has been modified to include heterochemistry (with a chemical composition consistent with that of the experimental sample). We discuss how realistic the numerical sample is by comparing its pore size distribution (PSD), specific surface area, porous volume, and porosity with those for the experimental sample. We also discuss the different criteria used to estimate the latter properties from a geometrical analysis. We demonstrate the ability of the MP method to estimate PSD of porous carbons from nitrogen adsorption isotherms. Both the experimental and simulated coadsorption isotherms resemble those obtained for pure gases (type I in the IUPAC classification). On the other hand, only the porous carbon including the heterogroups allows simulating quantitatively the selectivity of the experimental adsorbent for different carbon dioxide/methane mixtures. This result shows that taking into account the heterochemistry present in porous carbons is crucial to represent correctly adsorption selectivities in such hydrophobic samples. We also show that the adsorbed solution theory describes quantitatively the simulated and experimental coadsorption isotherms without any parameter adjustment.

An Overview on the Pharmacokinetics of Quantum Dots

Recent developments in nanotechnology have paved the way for using quantum dots (QDs) in nanodiagnostics and nanotherapeutics. Careful design and preparation of QDs are guided by these application-specific requirements. QDs will probably be one of the first nanomaterial to reach clinical applications, however many challenges in this field have yet to be overcome. In this article, we present an extensive review of the pharmacokinetic properties of QDs. The representative studies responsible for observing quantitative determination of QDs biodistribution in vivo are presented. The effects of size, surface chemistry, and target moiety on their pharmacokinetics are discussed. Finally, future directions for improving the pharmacokinetics of QDs and perspectives in the field are discussed. The understanding of its absorption, distribution, metabolism, and excretion from the body will provide important guidelines for the successful clinical use of QDs.

Smooth Perfluorinated Surfaces with Different Chemical and Physical Natures: Their Unusual Dynamic Dewetting Behavior toward Polar and Nonpolar Liquids

The effects of surface chemistry and the mobility of surface-tethered functional groups of various perfluorinated surfaces on their dewetting behavior toward polar (water) and nonpolar (n-hexadecane, n-dodecane, and n-decane) liquids were investigated. In this study, three types of common smooth perfluorinated surfaces, that is, a perfluoroalkylsilane (heptadecafluoro-1,1,2,2-tetrahydrooctyl-dimethylchlorosilane, FAS17) monomeric layer, an amorphous fluoropolymer film (Teflon AF 1600), and a perfluorinated polyether (PFPE)-terminated polymer brush film (Optool DSX), were prepared and their static/dynamic dewetting characteristics were compared. Although the apparent static contact angles (CAs) of these surfaces with all probe liquids were almost identical to each other, the ease of movement of liquid drops critically depended on the physical (solidlike or liquidlike) natures of the substrate surface. CA hysteresis and substrate tilt angles (TAs) of all probe liquids on the Optool DSX surface were found to be much lower than those of Teflon AF1600 and FAS17 surfaces due to its physical polymer chain mobility at room temperature and the resulting liquidlike nature. Only 6.0° of substrate incline was required to initiate movement for a small drop (5 μL) of n-decane, which was comparable to the reported substrate TA value (5.3°) for a superoleophobic surface (θ(S) > 160°, textured perfluorinated surface). Such unusual dynamic dewetting behavior of the Optool DSX surface was also markedly enhanced due to the significant increase in the chain mobility of PFPE by moderate heating (70 °C) of the surface, with substrate TA reducing to 3.0°. CA hysteresis and substrate TAs rather than static CAs were therefore determined to be of greater consequence for the estimation of the actual dynamic dewetting behavior of alkane probe liquids on these smooth perfluorinated surfaces. Their dynamic dewettability toward alkane liquids is in the order of Optool DSX >> Teflon AF1600 ≈ FAS17.

The role of surface chemistry in determining in vivo biodistribution and toxicity of CdSe/ZnS core–shell quantum dots

To examine the effect of surface chemistry and surface charge on in vivo biodistribution and toxicity of CdSe/ZnS core–shell quantum dots (QDs), QDs with positive, negative, or PEG coating are used in this study for in vivo evaluation in a mouse model. The results suggest that QDs coated with cationic polydiallyldimethylammonium chloride (PDDA) preferentially deposit in the lung other than in the liver, while the negative and PEGylated QDs render abundant accumulation in the liver. At higher doses positive QDs with PDDA coating show severe acute toxicity due to pulmonary embolism. Independent of their surface coatings, all QDs cause injuries in specific tissues like liver, spleen, lung, and kidney, after acute and long-term exposure, and the degree of injuries is dominated by their surface properties. For the positively charged QDs, the acute phase toxicity is primarily contributed by the coating material PDDA, while coating on QDs may amplify both in vitro and in vivo toxicity of PDDA. PEGylated QDs display the slightest chronic injuries in the long-term toxicity examination in comparison to positive or negative ones.

Diagnosis of the Surface Chemistry Effects on Fine Coal Flotation Using Saline Water

In the present investigation, two coal samples were obtained from a typical Australian coal flotation plant using saline water and examined to identify surface chemistry effects on fine coal flotation which is an important issue confronting the coal industry. The speciation modeling indicated that hydrophilic precipitates may occur in the flotation circuits as a result of the use of high ionic strength water, negatively impacting the coal flotation. Meanwhile, Cryo-SEM (scanning electron microscopy) detected the presence of clay minerals on the coal surface which has a deleterious effect on the flotation. Surface oxidation was also found on both coal samples by XPS (X-ray photoelectron spectroscopy) analysis and well correlated with their flotation behavior. This study suggests mitigating the slime coating and addressing the oxidized coal surface simultaneously to improve the coal flotation.

Extraordinary Shifts of the Leidenfrost Temperature from Multiscale Micro/Nanostructured Surfaces

In the present work, the effects of surface chemistry and micro/nanostructuring on the Leidenfrost temperature are experimentally investigated. The functional surfaces were fabricated on a 304 stainless steel surface via femtosecond laser surface processing (FLSP). The droplet lifetime experimental method was employed to determine the Leidenfrost temperature for both machine-polished and textured surfaces. A precision dropper was used to control the droplet size to 4.2 μL and surface temperatures were measured by means of an embedded thermocouple. Extraordinary shifts in the Leidenfrost temperatures, as high as 175 °C relative to the polished surface, were observed with the laser-processed surfaces. These extraordinary shifts were attributed to nanoporosity, reduction in contact angle, intermittent liquid/solid contacts, and capillary wicking actions resulting from the presence of self-assembled nanoparticles formed on the surfaces. In addition to the shift in the Leidenfrost temperature, significant enhancement of the heat transfer in the film boiling regime was also observed for the laser-processed surfaces; water droplet evaporation times were reduced by up to 33% for a surface temperature of 500 °C.

The mechanisms of surface chemistry effects of mesoporous silicon nanoparticles on immunotoxicity and biocompatibility

Despite steadily increasing insights on the biocompatibility of PSi nanoparticles (NPs), an extensive biosafety study on the immune and red blood cells (RBCs) is still lacking. Herein, we evaluated the impact of the PSi NPs' surface chemistry on immune cells and human RBCs both in vitro and in vivo. Negatively charged hydrophilic and hydrophobic PSi NPs caused less ATP depletion and genotoxicity than the positively charged amine modified hydrophilic PSi NPs, demonstrating the main role of PSi NPs' surface charge on the immunocompatibility profile. Furthermore, cells with lower metabolic activity, longer doubling time, and shorter half-life were more sensitive to the concentration- and time-dependent toxicity in the following order: T-cells ≈ monocytes > macrophages ≈ B-cells. RBC hemolysis and imaging assay revealed a significant correlation between the surface chemistry, the amount of the PSi NPs adsorbed on the cell surface and the extent of morphological changes. The in vivo results showed that despite mild renal steatosis, glomerular degeneration, hepatic central vein dilation and white pulp shrinkage in spleen, no notable changes were observed in the serum level of biochemical and hematological factors. This study is a comprehensive demonstration of the mechanistic direct and indirect genotoxicity effects of PSi NPs, elucidating the most influencing properties for the PSi NPs' design.

Effect of surface chemistry of porous silicon microparticles on glucagon-like peptide-1 (GLP-1) loading, release and biological activity

Recently, mesoporous silicon (PSi) microparticles have been shown to extend the duration of action of peptides, reducing the need for frequent injections. Glucagon-like peptide 1 (GLP-1) is a potential novel treatment for type 2 diabetes. The aim of this study was to evaluate whether GLP-1 loading into PSi microparticles reduce blood glucose levels over an extended period. GLP-1 (pI 5.4) was loaded and released from the negatively charged thermally oxidized (TOPSi, pI 1.8) and thermally carbonized (TCPSi, pI 2.6) PSi microparticles and from the novel positively charged amine modified microparticles, designated as TOPSi-NH2-D (pI 8.8) and TCPSi-NH2-D (pI 8.8), respectively. The adsorption of GLP-1 onto the PSi microparticles could be increased 3-4-fold by changing the PSi surface charge from negative to positive, indicating that the positive surface charge of PSi promoted an electrostatic interaction between the negatively charged peptide. All the GLP-1 loaded PSi microparticles lowered the blood glucose levels after a single s.c. injection but surprisingly, TOPSi-NH2-D and TCPSi-NH2-D were not able to prolong the effect when compared to TOPSi, TCPSi or GLP-1 solution. However, TOPSi-NH2-D and TCPSi-NH2-D microparticles were able to carry improved payloads of active GLP-1 encouraging continuing further attempts to achieve sustained release.