Surface Coverage Of Nanoparticles Research Articles

Silver nanoparticle coatings with adjustable extinction spectra produced with liquid flame spray, and their role in photocatalytic enhancement of TiO2

Silver nanoparticles deposits were produced with liquid flame spray (LFS) on glass and TiO2 substrates to study their optical response and photocatalytic enhancement. The correlation between extinction spectrum of the nanoparticle coating and the LFS process parameters was studied. The spectra consisted of two partly overlapping peaks: one centered in the UV region and the other in the visible light region. The visible light peak redshifted as either the silver mass concentration in the precursor solution or the precursor solution feed rate was increased, which also correlated with growing primary particle size. However, simultaneous correlation with photocatalytic activity of the decorated TiO2 surfaces was not observed, which was attributed to particle sintering on the surface. Instead, the photocatalytic activity was seen to change as the surface coverage of silver nanoparticles was varied. When the surface coverage was raised from ∼10 % to roughly 30 %, the activity, and then decreased as the loading was further raised. The increase was assumed to originate from plasmonic activation, and the decrease was attributed to the excessive amount of silver either blocking reactive area of the TiO2 or absorbing/scattering too much of the incoming light, which hindered the photocatalytic activity.

Investigating the Metallic Nanoparticles Decoration on Reduced Graphene Oxide-Based Sensors Used to Detect Sulfur Dioxide

This paper presents the impact of the decoration of reduced graphene oxide (rGO) with metallic nanoparticles to detect sulfur dioxide (SO2). Copper and platinum were employed to produce metal nanoparticles (NPs) for the chemical and physical decoration of rGO to form the nanocomposites (rGO/NPs). We optimized NP loading by varying the concentrations of metal ions and deposition times for chemical and physical decoration, respectively. The chemical decoration presents a random nanoparticle distribution on the rGO surface with a broad particle size distribution (1 to 100 nm with a majority less than 40 nm). In comparison, the physical decoration presents uniformly distributed nanoparticles with particles of a size between 1 and 20 nm, with a majority less than 10 nm. The chemically decorated structures present the best gas responses and show that lower NP loading provides better responses. The nanocomposites present responses owing to a better synergy between NPs and the rGO surface, combined with the catalytic action of the NPs on the rGO. The physical decoration allows higher NP surface coverage than the chemical one but implies a lower remaining rGO naked surface for gaseous molecule interaction. These results illustrate that the NPs’ surface and the uncovered rGO contribute to the gas response.

Surface‐Functionalized Nanoparticles as Catalysts for Artificial Photosynthesis

AbstractAnalogously to enzymatic catalysis, where the active metal sites and their environment are controlled by protein residues, the catalytic properties of metal nanoparticles (NPs) can be tuned by carefully selecting their surface‐coordinated species. In artificial photosynthesis, surface‐functionalization emerged in the last decade, grounded on the development of reliable methods for tailored synthesis, advanced characterization and theoretical modeling of metal NPs, altogether with the aim of transferring to the nanoscale the mechanistic knowledge acquired from molecular complexes. Metal NPs surface‐functionalization modulates the energetics of key catalytic intermediates, introduces second coordination sphere effects, influences the catalyst‐electrolyte interface, and determines the metal NPs surface coverage and, accordingly, the number of accessible active sites. In photoactivated systems, metal NPs surface‐functionalization may play a key role in modulating the charge transfers and recombination processes between the light absorber and the active sites and in the light absorber itself. Thus, after a presentation of the most relevant synthetic methods to produce well‐defined surface‐functionalized metal NPs, a critical analysis of why the above effects are the cornerstone in enhancing their catalytic performance in the key processes of artificial photosynthesis, namely the oxygen evolution reaction, the hydrogen evolution reaction, and the CO2 reduction reaction, is given.

Investigation of the surface tension of water-based Fe3O4 magnetic fluids under magnetic field: The effect of surfactants

In this work, water-based Fe3O4 magnetic fluids were prepared and the effect of surfactants on magnetic surface tension was investigated under a constant magnetic field. Different surfactants include anionic surfactants citric acid and sodium dodecyl sulfate (SDS); nonionic surfactants polyvinyl pyrrolidone (PVP K30) and polyethylene glycol(PEG-600) were employed to modify Fe3O4 nanoparticles. After the modification, the stability of Fe3O4-SDS magnetic fluid improved greatly, with the zeta potential improved to −40.5 mV compared to Fe3O4 magnetic fluid (−22 mV) without surfactants. X-ray diffraction and Fourier transform infrared spectroscopy were employed to characterize the crystalline and the surface changes. The results showed that the surfactant was successfully coated on the surface of Fe3O4 without changing the crystallinity. The surface coverage of nanoparticles by the surfactants caused a smaller saturation magnetization than uncoated Fe3O4 nanoparticles while keeping the superparamagnetic behavior. More importantly, the surface tension of the magnetic fluid was measured by the Du Noüy ring method, and an in-depth study of the magnetization time and direction on the magnetic surface tension has been carried out. Visual characterization of the cluster structure was carried out for an in-depth analysis of the influence of the external magnetic field on magnetic surface tension.

Generation of high-density nanoparticles in the carbothermal shock method.

The carbothermal shock (CTS) method has attracted considerable attention in recent years because it enables the generation of finely controlled polyelemental alloy nanoparticles (NPs). However, fabricating high surface coverage of NPs with minimized exposure of the carbon substrate is essential for various electrochemical applications and has been a critical limitation in CTS method. Here, we developed a methodology for creating NPs with high surface coverage on a carbon substrate by maximizing defect sites of cellulose during CTS. Cu NPs with high surface coverage of ~85%, various single NPs and polyelemental alloy NPs were densely fabricated with high uniformity and dispersity. The synthesized Cu NPs on cellulose/carbon paper substrate were used in electrocatalytic CO2 reduction reaction showing selectivity to ethylene of ~49% and high stability for over 30 hours of reaction. Our cellulose-derived CTS method enables the greater availability of polyelemental NPs for a wide range of catalytic and electrochemical applications.

Optimizing SERS performance through aggregation of gold nanorods in Langmuir-Blodgett films

Nanoparticles with a high degree of anisotropy are characterized by large electromagnetic field enhancements at the single-particle level; however, their arrangement into aggregated structures does not lead to significantly better performance. Surprisingly, for nanorods a superior accumulation of hot spots is present at surface coverages above 60%, which ensures a higher efficiency for surface-enhanced Raman spectroscopy (SERS). In this study, we produced pegylated gold nanorods in Langmuir-Blodgett layers in order to optimize SERS performance for the ultrasensitive detection of molecules, by tuning plasmonic coupling and nanoparticle surface coverage. To understand the arrangement of the nanorods in Langmuir and Langmuir-Blodgett layers, we performed spectroscopic and microscopic analysis of the obtained films. Based on the compression isotherms of the nanorods, we proposed the best conditions for nanoplatform design. The Raman enhancement factor was around 2·105 with a deposition surface pressure equal to 12 mN·m−1. Due to the polymer’s presence at the surface of the nanorods and the dewetting process, specific dendritic-like aggregates were observed on the solid substrate. The results obtained indicate the significance of further studies on the arrangement of metallic nanoparticles in monolayers, taking into account the size and shape of the nanoparticles, as well as the type of stabilizing ligands at their surface.

Electrochemically induced deposition of hydroxyl‐terminated poly(amidoamine) dendrimers encapsulating Pt nanoparticles on indium tin oxide for enhanced electrochemiluminescence

AbstractWe reported the electrochemically induced deposition of hydroxyl‐terminated poly(amidoamine) dendrimers encapsulating Pt nanoparticles on the surface of indium tin oxide (ITO). The electrochemical deposition led to significantly high surface coverage of Pt nanoparticles encapsulated inside the dendrimers on ITO surfaces, which allowed enhanced (i.e., ca. 212‐fold) electrochemiluminescence of Ru(bpy)32+/tripropylamine on the modified ITOs compared to unmodified ITO.

High performance SERS platforms via parametric optimization of the laser-assisted photodeposition of silver and gold nanoparticles

Parametric optimization of the laser-assisted photocatalytic growth of Ag and Au nanoparticles for high SERS enhancement factor performance informed by design of experiment is demonstrated. The photodeposition process was divided into two phases –seeding and growth– in order to achieve the highest possible nanoparticle surface coverage for the size range from 10 to 100 nm. A substantial difference in the parameter effects between the Ag and Au seeding and growth was found. The SERS performance of the photodeposited Ag and Au nanostructures was evaluated at 532, 633 and 785 nm with thiophenol as a probe molecule. A high-enhancement broadband SERS operation was attained with Ag nanostructure grown at high laser fluences. The SERS enhancement factors of 105 were achieved with both Ag and Au nanostructures.

Simulation tool for predicting and optimizing the performance of nanoparticle based strain sensors

In this work a Monte-Carlo tool simulating platinum nanoparticle (NP) based strain-sensors, on flexible substrates, is presented. The tool begins by randomly placing the NPs on the simulation area, with the ability to tune the NP surface coverage. After the calculation of the conductive paths that were generated in the previous step, the whole system is represented with an equivalent circuit; the NPs and the NP clusters act as nodes and the inter-particle gaps as resistances. The effective resistance is then calculated with the use of a Laplacian Matrix, which has proven extremely effective in significantly reducing the overall computational time. The simulation results are then benchmarked with experimental measurements from actual strain-sensing devices. The software is capable of predicting the strain-sensitivity for different NP sizes as well as surface coverages, emerging as a powerful computational tool for design-optimization of NP based devices in polymeric substrates, while it could well be extended to other nanocomposite materials used in flexible or stretchable electronic applications.

Electrochemically Decorated Iridium Electrodes with WS3−x Toward Improved Oxygen Evolution Electrocatalyst Stability in Acidic Electrolytes

AbstractIridium‐based oxides, currently the state‐of‐the‐art oxygen evolution reaction (OER) electrocatalysts in acidic electrolytes, are cost‐intensive materials which undergo significant corrosion under long‐term OER operation. Thus, numerous researchers have devoted their efforts to mitigate iridium corrosion by decoration with corrosion‐resistant metal oxides and/or supports to maximize OER catalyst durability whilst retaining high activity. Herein a one‐step, facile electrochemical route to obtain improved IrOx thin film OER stability in acid by decorating with amorphous tungsten sulphide (WS3−x) upon electrochemical decomposition of a [WS4]2− aqueous precursor is proposed. The rationale behind applying such WS3−x decoration stems from the generation of a tungsten oxide phase, a well‐known corrosion‐resistant photoactive OER catalyst. The study demonstrates the viability of the proposed WS3−x decoration, allowing the tailoring of experimental parameters responsible for WS3−x nanoparticle size and surface coverage. OER stability tests coupled by ex situ SEM and XPS corroborate the beneficial effect of WS3−x decoration, yielding improved OER specific activity metrics along with minimized Ir surface roughening, a characteristic of electrodissolution. Iridium decoration with electrodeposited, corrosion‐resistant oxides is consequently shown to be a promising route to maximize OER stabilities.

Boosting the Dynamic Range for Electrochemical Sensing of Hydrogen Peroxide by Enhanced Integration of Pd Nanoparticles in 3D Porous Si Framework

AbstractThree‐dimensional porous silicon framework (3D‐pSi) integrated with various nanostructures is highly potential for functional devices usage such as micro fuel cells or sensing chips. For noble metal deposition in highly directional Si nanowire array or porous Si with large aspect ratios, one difficulty is the restriction on the depth of deposition available. Herein, we would like to introduce a facile route to enhance the integration of Pd nanoparticles with anisotropic Si porous structure. By converting Si nanowire array into 3D‐pSi, the surface coverage of Pd nanoparticles is effectively improved as shown by scanning electron micrographs and cross‐sectional element mapping data. The relative electrochemical active surface area is increased by 3.5 folds. In order to demonstrate the merits brought by this morphological evolution, the electrochemical sensing devices are prepared for detecting H2O2 in PBS solution. As shown by differential pulse voltammetry, the upper limit of linear range of detection can be raised from 6.30 mM to 14.95 mM. This approach may indicate an alternative for boosting the performance of future sensing chips with progressively limited die area, especially attractive for those scenarios where large dynamic range is favourable.

Influence of Local Environments in Pores of Different Size on the Catalytic Liquid-Phase Oxidation of d-Glucose by Au Nanoparticles Supported on Nanoporous Carbon

Inorganic nanoparticles (NPs) dispersed on the surface of porous support materials play a dominant role in heterogeneous catalysis. Especially in liquid-phase catalysis, support materials may lead to nanoconfinement of solvent molecules, and the solute and can thus influence their local concentration and structure. This further affects the surface coverage of nanoparticles with reactants and other species, but these influences remain poorly understood—in particular under experimental conditions. Nanoconfinement effects are of particular importance in reactions such as liquid-phase oxidation with oxygen, i.e., when one reactant is a gas that has to be dissolved before reaching the NP surface. The significant influence of the pore structure of carbon materials on the catalytic activity of gold nanoparticles (AuNPs) with nearly similar size (4.1–4.7 nm) is demonstrated in this study. Experimental results on the oxidation of d-glucose with molecular oxygen in aqueous solution show that the “apparent catalytic activity” of AuNPs is a function of the carbon pore size and geometry. The architecture of the carbon pore size is determining the local concentration of reactants. Nanoconfinement of water in carbon nanopores can lead to enhanced solubility of reactants and therefore to their higher local concentration in proximity to the catalytically active sites. In contrast to purely microporous carbon support with the less wettable internal surface without any detectable catalytic activity, AuNPs supported on mesoporous carbons show a much higher metal time yield between 3.8 and 60.6 molGlc min–1 molAu–1, depending on volume and geometry of the mesopores.

Differences in corona formation of catalase immobilised on gold and silver nanoparticles

The adsorption process of proteins on nanoparticles (NPs) is spontaneous and depends on many factors, including the NP composition, size, shape, dispersity, and surface chemistry, as well the protein type, its chemical structure, affinity to NP surface, size, shape, availability of functional groups, etc. As a result, prediction of the adsorption process and the surface coverage of NPs with proteins remains a challenge. The theoretical coverage can obviously be calculated on the basis of geometric considerations, assuming that proteins remain globular on the NP surface; however, this is only a model approach, which does not always coincide with experimental results. Hence, experimental techniques are needed to characterise bioconjugates and to determine how many protein molecules bind to a NP surface.In this paper, we quantitatively characterise the surface coverage of NPs with catalase on the basis of polyacrylamide gel electrophoresis (PAGE). The surface coverage was investigated on two types of metallic NPs with a diameter equal 13 nm: i) gold and ii) silver. The obtained results prove that the protein corona formation significantly depends on the chemical composition of NPs and is difficult to predict how many protein molecules have to be incorporated into the colloid to attain assumed surface coverage.

In situ grown metallic nickel from X–Ni (X=La, Mg, Sr) oxides for converting plastics into carbon nanotubes: Influence of metal–support interaction

The process of pyrolysis and in-line catalysis was employed for converting plastics into value-added carbon nanotubes (CNTs). The metallic nickel catalysts Ni/X (X = La, Mg, Sr) were prepared through in situ growth from parent X–Ni oxides under reductive conditions and used for the catalytic synthesis of CNTs. The results showed that the activities of nickel catalysts decreased in the order of Ni/La > Ni/Sr > Ni/Mg, which strongly depended on the degree of metal–support interaction. The strong metal–support interaction in Ni/Mg catalyst was not favorable for the exsolution of large amount of metallic Ni, resulting in the lowest yield of CNTs. On the other hand, the weak metal–support interaction in Ni/Sr was unfavorable for the high coverage of Ni nanoparticles, leading to the simultaneous growth of carbon nano-onions and CNTs. The Ni/La catalyst with moderate metal–support interaction exhibited the highest yield of CNTs due to optimized amount, size and surface coverage of Ni nanoparticles. The microstructure, graphitization degree, quality and purity of obtained carbon products were characterized using X-ray diffraction, electron microscopy, Raman spectroscopy and thermogravimetric analysis. This study demonstrated an effective and delicate approach to tune the supported metal nanoparticles, leading to enhanced catalytic activity.

Magnetic properties, responsiveness, and stability of paramagnetic dumbbell and ellipsoid colloids

A layer-by-layer method is used to synthesize paramagnetic metal/polymer multi-layered colloidal particles. By taking advantage of recent advances in the synthesis of polymer colloids with various shapes and layer-by-layer assembly, superparamagnetic dumbbell colloids are fabricated with different aspect ratios and asymmetries between lobes. We characterize the surface coverage of magnetic nanoparticles on the anisotropic host particles and the magnetic response of the particles by magnetometry. The synthesized particles are colloidally stable, but in a magnetic field, form persistent microstructures through induced interactions. These column-like microstructures are reversible and readily disperse by Brownian motion. The magnetic nanoparticle concentration during synthesis provides a means to control the magnetic response of the composite nanoparticle. The method is extended to prolate ellipsoid nanoparticles with aspect ratios between 3.4 and 4.2.

Effect of silica nano-spheres on adhesion of oral bacteria and human fibroblasts

Objective This study investigated the effect of surface nano-patterning on adhesion of an oral early commensal colonizer, Streptococcus mitis and the opportunistic pathogen Staphylococcus aureus and human fibroblasts (HDFa) in a laminar flow cell. Methods Nanostructured surfaces were made by functionalizing glass substrates with 40 nm SiO2 nanoparticles. Gradients in nanoparticle surface coverage were fabricated to study the effect of nanoparticle spacing within a single experiment. Bacterial adhesion was investigated after 5 min of contact time by subjecting surfaces to a flow in a laminar flow cell. In addition, to examine the particles effect on human cells, the establishment of focal adhesion and spreading of primary human dermal fibroblasts (HDFa) were investigated after 4 and 24 h. Results Adhesion of both S. aureus and S. mitis decreased on surfaces functionalized with nanoparticles and coincided with higher nanoparticle surface coverage on the surface. Both strains were tested on three separate surfaces. The regression analysis showed that S. mitis was influenced more by surface modification than S. aureus. The establishment of focal adhesions in HDFa cells was delayed on the nanostructured part of the surfaces after both 4 and 24 h of culturing. Significance In the current manuscript, we have used a flow cell to investigate the effect of nanotopographies on S. aureus and S. mitis adhesion. The present findings are of relevance for design of future implant and prostheses surfaces in order to reduce adhesion of bacteria.

Self-terminating electrodeposition of Pt on WC electrocatalysts

Self-terminated electrochemical deposition is used to grow Pt nanoparticles on tungsten monocarbide (WC) from a pH 4 electrolyte of 3 mmol/L K2PtCl4-0.5 mol/L NaCl. An unconventional potentiodynamic deposition program is used where nucleation is promoted at large overpotentials followed by growth termination at still larger overpotentials to yield a high coverage of Pt nanoparticles. Following three deposition cycles between −0.8 VSCE and −0.45 VSCE, the surface is covered by a monolayer equivalent charge of Pt in the form of ≈3 × 1011 particles/cm2 that are ≈6.7 ± 1.1 nm in diameter. The number and size of nanoparticles increase monotonically for five deposition cycles. Area-normalized kinetics for hydrogen evolution (HER) and oxidation (HOR) on Pt-WC were determined in 0.5 mol/L H2SO4. For the lowest surface coverage of Pt nanoparticles on WC, ≈ 0.01, an exchange current density of ≈ 100 mA/cm2 is achieved, comparable to the highest reported values for Pt nanoparticles and ultramicroelectrodes. The area normalized apparent exchange current density decreases with increasing Pt coverage as the relative contribution of point versus planar diffusion decreases. Self-terminated electrodeposition of Pt provides an attractive approach to achieving ultra-low loadings of well-dispersed Pt nanoparticles on a non-precious metal support like WC.

Optimization of the surface coverage of metal nanoparticles on nanowires gas sensors to achieve the optimal sensing performance

The functionalization of noble metal nanoparticles (NPs) is a highly efficient method for increasing the sensing performance of metal oxide nanowire (NWs) gas sensors. Despite the well-established strategy, the level of the optimal functionalization for obtaining the maximum sensing response has rarely been reported. Herein, the surfaces of SnO2 NWs were functionalized with Pt and Pd NPs, and the gas sensing characteristics were then investigated using NO2 as an example gas. The sensing responses obtained at the optimal temperature showed a bell-shaped dependency on the proportion of surface coverage by Pd and Pt NPs. The sensing mechanism is explained and the results were also fitted to a simple theoretical model based on modulation in the conduction channel via the chemical and electronic sensitization on NWs. This study provides guidelines on the amount of metal NPs for achieving the optimal sensing responses in metal oxide NWs gas sensors.

Biocompatibility of Amine-Functionalized Silica Nanoparticles: The Role of Surface Coverage.

Here, amorphous silica nanoparticles (NPs), one of the most abundant nanomaterials, are used as an example to illustrate the utmost importance of surface coverage by functional groups which critically determines biocompatibility. Silica NPs are functionalized with increasing amounts of amino groups, and the number of surface exposed groups is quantified and characterized by detailed NMR and fluorescamine binding studies. Subsequent biocompatibility studies in the absence of serum demonstrate that, irrespective of surface modification, both plain and amine-modified silica NPs trigger cell death in RAW 264.7 macrophages. The in vitro results can be confirmed in vivo and are predictive for the inflammatory potential in murine lungs. In the presence of serum proteins, on the other hand, a replacement of only 10% of surface-active silanol groups by amines is sufficient to suppress cytotoxicity, emphasizing the relevance of exposure conditions. Mechanistic investigations identify a key role of lysosomal injury for cytotoxicity only in the presence, but not in the absence, of serum proteins. In conclusion, this work shows the critical need to rigorously characterize the surface coverage of NPs by their constituent functional groups, as well as the impact of serum, to reliably establish quantitative nanostructure activity relationships and develop safe nanomaterials.

Quenching of Luminol Fluorescence at Nano-Bio Interface: Towards the Development of an Efficient Energy Transfer System.

Surface modified colloidal gold (Au) and silver (Ag) nanoparticles (NPs) were used as efficient quenchers of luminol (LH2) fluorescence either in homogeneous aqueous medium or its noncovalent assembly with bovine serum albumin (BSA). The mechanism as well as the extent of fluorescence quenching was found to be strongly dependent on the nature of the nanoparticles. While simple static type fluorescence quenching mechanism was perceived with AuNP, a more complex protocol involving quenching sphere model was envisaged for AgNP quenching. Nevertheless, the magnitude of Stern-Volmer (SV) quenching constant (KSV ~ 108-1010M-1) was calculated to be ca. 104 times more for surface quoted NPs in comparison with BSA-NP bioconjugates system. On the other hand, a highly efficient (E ≈ 95%) energy transfer (ET) process was predicted for LH2 captured in the hydrophobic assembly with BSA in presence of AgNP as an acceptor. The ET efficiency is critically dependent on the concentration of BSA and nicely correlated with the extent of NP surface coverage. However, fluorescence quenching on AuNP surface is relatively less responsive towards protein concentration, primarily due to the difference in surface activity as well as the mode of interaction of the protein with NPs. Graphical Abstract Energy transfer from excited luminol to metal nanoparticles is strongly modulated in presence of serum albumins.