Surface Capping Research Articles

Interaction and UV-Stability of Various Organic Capping Agents on the Surface of Anatase Nanoparticles.

Anatase nanoparticles synthesized by the sol-gel method were surface-functionalized with long alkyl chain coupling agents as compatibilizers for a nonpolar environment, containing different anchor groups for surface interaction namely phosphonate (dodecyl phosphonate), carboxylate (dodecanoic acid), sulfate (sodium dodecyl sulphate), and amine (dodecyl amine). It was shown that the surface of the nanoparticles can be functionalized with the various surface groups applying similar reaction conditions. The kind of surface interaction was analyzed applying FTIR spectroscopy. The phosphonate and the carboxylate groups interact with the surface via quite strong covalent or coordinative interactions, respectively. The sulfate and amine based coupling agents on the other hand exhibit electrostatic interactions. UV stability studies of the surface bound groups revealed different degradation mechanisms for the various functionalities and moreover showed that phosphonates are the most stable among the investigated surface capping groups.

Stability and aggregation of silver and titanium dioxide nanoparticles in seawater: Role of salinity and dissolved organic carbon

The behavior and fate of nanoparticles (NPs) in the marine environment are largely unknown and potentially have important environmental and human health implications. The aggregation and fate of NPs in the marine environment are greatly influenced by their interactions with seawater and dissolved organic carbon (DOC). In the present study, the stability and aggregation of 30-nm-diameter silver nanoparticles (AgNPs) capped with citrate and polyvinylpyrrolidone (PVP; AgNP-citrate and AgNP-PVP) and 21-nm-diameter titanium dioxide (TiO(2)) NPs as affected by seawater salinity and DOC were investigated by measuring hydrodynamic diameters and zeta potentials. The added DOC (in humic acid form) stabilized the 3 types of NPs when the seawater salinities were ≤5 parts per thousand (ppt), but the stabilizing effect of DOC was reduced by a higher salinity (e.g., 30 ppt). In addition, AgNP-PVP was more stable than AgNP-citrate in seawater, indicating that surface capping agents and stabilization mechanisms govern the stability and aggregation of NPs. Statistical analysis showed that salinity is the most dominant influence on the stability and aggregation of AgNPs and TiO(2) NPs, followed by DOC. These findings expand our knowledge on the behavior of AgNPs and TiO2 NPs in seawater and indicate that the fate of these NPs will be primarily to aggregate in the water column, precipitate, and accumulate in sediments following release into the marine environment.

Local impact effects on concrete target due to missile: An empirical and numerical approach

Concrete containment walls and internal concrete barrier walls of a Nuclear Power Plant safety related structures are often required to be designed for externally and internally generated missiles. Potential missiles include external extreme wind generated missiles, aircraft crash and internal accident generated missiles such as impact due to turbine blade failure and steel pipe missiles resulting from pipe break. The objective of the present paper is to compare local missile impact effects on reinforced concrete target using available empirical formulations with those obtained using LS-DYNA numerical simulation. The use of numerical simulations for capturing the transient structural response has become increasingly used for structural design against impact loads. They overcome the limits of applicability of the empirical formulae and also provide information on stress and deformation fields, which may be used to improve the resistance of the concrete. Finite element (FE) analyses of an experimental impact problem reported by Kojima (1991) are carried out that are able to capture the missile impact effects; in terms of local and global damage. The continuous surface cap model has been used for modelling concrete behaviour. A range of missile velocity has been considered to simulate local missile impact phenomenon and modes of failure and to capture the concrete response from elastic to plastic fracture. A comparison is then made between the empirical formulations, numerical simulation results, and available experimental results of slab impact tests. While the numerical simulation is able to capture the experimental trend and results, a comparison of penetration depth and scabbing and perforation limits as per different empirical formulation shows substantial divergence.

Controlling the electronic energy levels of ZnO quantum dots using mixed capping ligands

The surface passivation of nanocrystals with mixed ligands is an important way to enhance the performance of quantum dot based optoelectronic devices through tuning the electronic energy levels. By attaching two or three different ligands on the surface of a single nanoparticle, one can induce electric fields large enough to significantly alter the electronic and optoelectronic properties of the nanocrystals. By using the self-consistent-charge density-functional tight-binding (SCC-DFTB) method we demonstrate the tuning of the electronic energy levels of ZnO quantum dots (QDs) through exchanging the surface capping ligands. The tuning of the energy levels is largely dependent on the surface linking groups as well as on the ratio of the different passivated molecules attached on to the surface of the QDs.

BSA binding to silica capped gold nanostructures: effect of surface cap and conjugation design on nanostructure–BSA interface

This paper presents a detailed and systematic study of amine functionalization of silica coating of gold nanostructures and the electrostatic and covalent binding of the prepared silica capped gold nanostructures to BSA. The involvement of a Tryptophan residue in the hydrophobic pocket of BSA and its interaction with nanostructures was established. Fluorescence studies of tryptophan residues of the protein molecules after conjugation revealed that the method of crosslinking did not bring about major changes to the binding constant (1012 M−1) of BSA to nanostructures. Electrostatic binding indicated a larger number of binding sites (2.56) on the protein. Nanoparticle binding brought about a reduction in the characteristic negative ellipticity of BSA, indicating a change in the helical content. The reduction in the elliptical path of BSA was influenced by both nanoparticle curvature and crosslinker, such as in the case of glutaraldehyde or by the nanoparticle curvature alone as in the case of zero length crosslinker – EDC–NHS. Though not a subject matter of this study, the results obtained in this study could have implications in the design of nanobiomaterials, biosafety concerns and their cellular responses.

Visible light active Ru-doped sodium niobate pervoskite decorated with platinum nanoparticles via surface capping

An efficient visible light active NaNb1−xRuxO3 perovskite was hydrothermally fabricated and characterized. Various amounts of ruthenium substitution (0–5%) for Nb5+ in the niobate framework caused structural evolution from nanocubes to nanowires. 1% Ru-doped niobates [NR(1)], which had a highly crystalline orthorhombic structure, adsorbed visible light most substantially with an optical band gap of ∼2.3eV. With the aid of 1H MAS NMR examination, the addition of protons into the niobate by acid treatment was convinced and its projected structure of [RuO6] plus [NbO6] octahedra with some defects was proposed. NR(1) itself was not effective at carrying out photocatalytic decomposition of phenol in water. To enhance visible light driven charge separation, platinum was dispersed onto NR(1) using surface capped Pt nanoparticles (PtNP) and Pt complexes (e.g., [Pt(NH3)4]Cl2). PtNPs laden NR(1) exhibited superior photocatalytic degradation of phenol in water. This increased photocatalytic activity was attributable to synergistic effects of facilitated electron transfer by PtNPs.

The stabilization effect of surface capping on photocatalytic activity and recyclable stability of Ag3PO4

We find the stabilization effect of surface capping on the adsorption capacity and photocatalytic activity of Ag3PO4 in the recycling. The citrate anion complex (CAC) as the surface capping is confirmed to be constituted by citrate anion and silver citrate complex. The adsorption capacity of Ag3PO4 with CAC capping exhibits little increase in the subsequent cycle, whereas the one of the bare Ag3PO4 decreases by 25.8% for methylene blue (MB). The photocatalytic activity of Ag3PO4 with CAC capping is maintained, compared to marked 10% decrease of bare Ag3PO4 for degrading MB.

Influence of Soil Moisture on Soil Gas Vapor Concentration for Vapor Intrusion

Mathematical models have been widely used in analyzing the effects of various environmental factors in the vapor intrusion process. Soil moisture content is one of the key factors determining the subsurface vapor concentration profile. This manuscript considers the effects of soil moisture profiles on the soil gas vapor concentration away from any surface capping by buildings or pavement. The "open field" soil gas vapor concentration profile is observed to be sensitive to the soil moisture distribution. The van Genuchten relations can be used for describing the soil moisture retention curve, and give results consistent with the results from a previous experimental study. Other modeling methods that account for soil moisture are evaluated. These modeling results are also compared with the measured subsurface concentration profiles in the U.S. EPA vapor intrusion database.

Reagent control over the composition of mixed metal oxide nanoparticles

Binary (M1 − M2 − O) and ternary (M1 − M2 − M3 − O) metal-oxide nanoparticles (NPs) have been prepared by thermal decomposition in benzyl ether of the appropriate M(acac)n (M = Fe, Mn, Pd, Cu, Al, Gd) compounds in the presence of a mixture of oleic acid and oleylamine templating (surface capping) ligands, and 1,2-hexadecanediol as an accelerating agent. The metal percentage and the particle size were investigated as a function of the starting composition. The NP composition is controlled by the relative reaction rates of the particular precursors, such that prediction of NP composition from reagent ratios is not straightforward. However, understanding reaction rate limitations allows for alternative synthesis to be developed. In some cases, ligand exchange reaction and subsequent decomposition are possibly more important than thermal decomposition.

Cytotoxicity of Quantum Dots Used for In Vitro Cellular Labeling: Role of QD Surface Ligand, Delivery Modality, Cell Type, and Direct Comparison to Organic Fluorophores

Interest in taking advantage of the unique spectral properties of semiconductor quantum dots (QDs) has driven their widespread use in biological applications such as in vitro cellular labeling/imaging and sensing. Despite their demonstrated utility, concerns over the potential toxic effects of QD core materials on cellular proliferation and homeostasis have persisted, leaving in question the suitability of QDs as alternatives for more traditional fluorescent materials (e.g., organic dyes, fluorescent proteins) for in vitro cellular applications. Surprisingly, direct comparative studies examining the cytotoxic potential of QDs versus these more traditional cellular labeling fluorophores remain limited. Here, using CdSe/ZnS (core/shell) QDs as a prototypical assay material, we present a comprehensive study in which we characterize the influence of QD dose (concentration and incubation time), QD surface capping ligand, and delivery modality (peptide or cationic amphiphile transfection reagent) on cellular viability in three human cell lines representing various morphological lineages (epithelial, endothelial, monocytic). We further compare the effects of QD cellular labeling on cellular proliferation relative to those associated with a panel of traditionally employed organic cell labeling fluorophores that span a broad spectral range. Our results demonstrate the important role played by QD dose, capping ligand structure, and delivery agent in modulating cellular toxicity. Further, the results show that at the concentrations and time regimes required for robust QD-based cellular labeling, the impact of our in-house synthesized QD materials on cellular proliferation is comparable to that of six commercial cell labeling fluorophores. Cumulatively, our results demonstrate that the proper tuning of QD dose, surface ligand, and delivery modality can provide robust in vitro cell labeling reagents that exhibit minimal impact on cellular viability.

Long-Term Dispersion Stability and Adhesion Promotion of Aqueous Cu Nano-Ink for Flexible Printed Electronics

Aqueous Cu nanoparticles are synthesized using a reducing agent and surface capping molecule which prevents the interparticular agglomeration and surface oxidation. Aqueous conductive nano ink is prepared using the resulting Cu nanoparticles and conductive Cu layers are prepared via a wet coating process. The conductive Cu layers, metalized by annealing at 300 degrees C under vacuum atmosphere, exhibit excellent electrical resistivity, showing values as low as 12 microomega cm. The long-term dispersion stability for three months is monitored through an investigation on the rheological behavior of the conductive nano ink and the resistivity variation of the conductive Cu layer. The adhesion property of the conductive Cu layer is dramatically improved when using a primer-treated polyimide film, whereas the conductive Cu layer completely peels off on a pristine polyimide film. The epoxy-contained primer plays a critical role as an intermediary between the aqueous Cu nano ink and the polyimide film.

(Invited) Atomically Controlled CVD Processing of Group IV Semiconductors for Strain Engineering and Doping in Ultralarge Scale Integration

By atomic layer growth of C, Ge and B on Si (100) surface and subsequent Si cap layer growth, heavy atomic-layer doping is achieved at temperatures below 500 <sup>o<sup>C. Sub-atomic layer of C, Ge or B is confined within an about 1 nm-thick region. It is confirmed that the incorporation of C atoms at substitutional site in Si is influenced by substrate surface strain and is larger than that of in-situ doping. Atomic layer doping of Ge is enhanced by the tensile strain in the substrate, comparing with those of C and B. In the nm-thick region of atomic layer doping, strain generation is not observed. It is also confirmed that growth characteristics as well as electrical activity of impurity in the strained layer are influenced by the substrate surface strain before the layer growth. These results demonstrate the capability of atomically controlled CVD technology of group IV semiconductors for strain engineering and doping in ultralarge scale integration.

Rock failure induced by dynamic unloading under 3D stress state

A commercial finite element program, LS-DYNA, was employed to simulate the unloading process of rocks under three dimensional (3D) stresses. The continuous surface cap model (CSCM), was used to model rock behaviour. Using this model, the unloading failure mechanisms of hard rock in a confined state were investigated during the unloading process. The results indicated that when rocks under 3D stress state experience unloading, the process is dominated by strain energy density (SED) rate. The effects of different unloading paths and different confining stresses can be characterised by the SED rate. A significant finding of this study is that the SED rate can quantify the unloading process. Based on the findings, rock failure can be induced by rapid unload of initial stress. In the practical underground excavation engineering, dynamically controlling the SED rate can increase the excavation potential of rocks, minimising the required external excavation energy by using the energy of the stressed rock.

Surface modified fluorescent quantum dots with neurotransmitter ligands for potential targeting of cell signaling applications

The possibility of combining nanotechnology with nanomedicine opens a broad field of research which may truly revolutionize our society. The neural system plays a crucial role in the human body, and most related diseases can dramatically change the quality of life. Thus, the present study reports a novel approach for using neurotransmitters as ligands in the synthesis of surface-modified fluorescent nanocrystals for potential use in cell labeling applications. Briefly, CdS quantum dots (QDs) were prepared using l-glutamic and l-aspartic as surface capping agents via a one-step chemical processing method, which resulted in stable aqueous colloidal systems at room temperature and ambient pressure. UV–visible spectroscopy, photoluminescence spectroscopy (PL), Fourier transform infrared (FTIR) spectroscopy, and transmission electron microscopy (TEM) were used to characterize the synthesis and relative stability of peptide-capped CdS nanocrystals. The results demonstrate that both ligands were effective in nucleating and stabilizing CdS quantum dots in colloidal aqueous suspensions, with an estimated dimension below 3.3nm and with fluorescence activity. Thus, novel nanohybrids were developed based on QDs bioconjugated to surface-active neurotransmitter moieties suitable for investigation as potential biomarkers in cell targeting and signaling applications.

Evidence of trigonal dangling bonds at the Ge(111)/oxide interface by electrically detected magnetic resonance.

Despite a renewed interest in Ge as a competitor with Si for a broad range of electronic applications, the microstructure and the electronic properties of the dangling bonds that, in analogy with Si, are expected at the Ge/oxide interface have escaped a firm spectroscopy observation and characterization. Clear evidence based on contactless electrically detected magnetic resonance spectroscopy of a dangling bond at the Ge(111)/GeO(2) interface is reported in this Letter. This result supports the similarity between dangling bonds at the Si(111)/oxide and Ge(111)/oxide interfaces, both showing C(3v) trigonal point symmetry with the main axis oriented along the ⟨111⟩ direction. In contrast, at the Ge(001)/oxide interface the absence of the trigonal center in favor of a lower symmetry dangling bond marks the difference with the Si(001)/oxide interface, where both centers are present and the one having higher point symmetry prevails. This fact is rationalized in terms of suboxide interface rearrangement and oxide viscoelasticity, which promote the generation of the nonaxial centers at distorted dimers. The unambiguous identification of the centers at the Ge/oxide interfaces yields a deeper insight into the physical properties of the suboxide interface structure and offers a valid indicator for the evaluation of different surface capping and passivation techniques, with the potential to boost the Ge-related technology.

Lanthanide Clusters with Azide Capping Ligands

Weakly binding azide ligands have been used as surface caps in the synthesis of lanthanide oxo and selenido clusters. Addition of NaN3 and Na2O to in situ prepared solutions of Ln(SePh)3 in pyridine results in the formation of (py)18Sm6Na2O2(N3)16 or (py)10Ln6O2(N3)12(SePh)2 (Ln = Ho, Er), with the Sm and Er compounds characterized by low temperature single crystal X-ray diffraction. Attempts to prepare chalcogenido derivatives by ligand-based redox reactions using elemental Se were successful in the preparation of (py)10Er6O2(SeSe)2(N3)10, a diselenido cluster having crystallographic disorder due to some site sharing of both SeSe and N3 ligands. These compounds all detonate when heated.

Laux‐type Oxidation of In0 Nanoparticles to In2O3 Retaining Particle Size and Colloidal Stability

AbstractAs a conceptual study, In0 nanoparticles are obtained by NaBH4‐driven reduction of InCl3 · 4H2O and transferred from a polar/hydrophilic diethylene glycol phase to a non‐polar hydrophobic dodecane phase for purification and stabilization. Finally, the In0 nanoparticles are oxidized via a Laux‐like reaction with nitrobenzene to In2O3 nanoparticles. The challenge of the reaction is to perform the final oxidation to In2O3 under mild conditions with the colloidal stability, particle size and particle size distribution of the initial In0 nanoparticles retained. To this concern, the mean diameter of the initial In0 nanoparticles changed from 11(1) to 14(2) nm of the oxidized In2O3 nanoparticles. Such multi‐step reaction, including reduction, nucleation, phase transfer, exchange of surface capping and oxidation are of increasing importance for nanoparticles. Especially, Laux‐type conditions with nitrobenzene as a molecular oxidizing agent of nanoparticles have not been used till now. Particle size, size distribution and chemical composition of the In0 and In2O3 nanoparticles are analyzed by DLS, SEM, XRD, FT‐IR and HRTEM.

A top–down strategy towards monodisperse colloidal lead sulphide quantum dots

Monodisperse colloidal quantum dots with size dispersions <10% are of great importance in realizing functionality manipulation, as well as building advanced devices, and have been normally synthesized via 'bottom-up' colloidal chemistry. Here we report a facile and environmentally friendly 'top-down' strategy towards highly crystalline monodisperse colloidal PbS quantum dots with controllable sizes and narrow dispersions 5.5%<σ<9.1%, based on laser irradiation of a suspension of polydisperse PbS nanocrystals with larger sizes. The colloidal quantum dots demonstrate size-tunable near-infrared photoluminescence, and self-assemble into well-ordered two-dimensional or three-dimensional superlattices due to the small degree of polydispersity and surface capping of 1-dodecanethiol, not only serving as a surfactant but also a sulphur source. The acquisition of monodisperse colloidal PbS quantum dots is ascribed to both the quantum-confinement effect of quantum dots and the size-selective-vaporization effect of the millisecond pulse laser with monochromaticity and low intensity.

Seed Mediated Growth of Gold Nanoparticles Based on Liquid Arc Discharge

We report studies on the growth of gold nanoparticles by a seed-mediated approach in solution. The synthetic method is adapted from one we published earlier (Ashkarran et al. Appl. Phys. A 2009, 96, 423). The synthesized gold nanoparticles were characterized by X-ray diffraction (XRD), dynamic light scattering (DLS), UV-Vis spectroscopy, optical imaging and atomic force microscopy (AFM). Optical absorption spectroscopy of the prepared samples at 15 A arc current in HAuCl4 solution shows a surface plasmon resonance around 520 nm. It is found that sodium citrate acts as a stabilizer and surface capping agent of the colloidal nanoparticles. The intensity of the plasmonic peak of the prepared gold nanoparticles for 1 minute arc duration gradually increases due to seed mediation for up to 6 hours. The formation time of gold nanoparticles at higher seed concentrations is less than that at lower seed concentrations.

Magnetic–Plasmonic FePt@Ag Core–Shell Nanoparticles and Their Magnetic and SERS Properties

Magnetic-plasmonic FePt@Ag core-shell nanoparticles (NPs) with different Ag shell thicknesses were successfully synthesized using a seed-mediated method. They presented not only localized surface plasmon reso- nance in the visible region, but also superparamagnetic behavior at room temperature. When normalized by the weight of FePt, the saturation magnetization of the FePt@Ag NPs was found to be higher than that of FePt NPs, suggesting that the Ag shell effectively passivated the FePt NP surfaces, avoiding the direct interaction between the FePt core and surface capping ligands that typically forms a magnetically dead layer in FePt NPs. Despite the high colloidal stability and the small size of the FePt@Ag NPs, the NPs were easily separated using a permanent magnet. The surface enhanced Raman scattering (SERS) activity of the FePt@Ag NPs was then examined using thiophenol as a Raman reporter molecule and was found to be equivalent to that of Ag NPs. Moreover, the SERS activity of the FePt@Ag NPs was enhanced when a mag- netic field was applied during the preparation of the SERS substrate (FePt@Ag NP film). These FePt@Ag NPs hold promise as dual-functional sensing probes for environmen- tal and diagnostic applications.