Desorption Of Particles Research Articles

Removal of thiol ligands from surface-confined nanoparticles without particle growth or desorption.

Size-dependent properties of surface-confined inorganic nanostructures are of interest for applications ranging from sensing to catalysis and energy production. Ligand-stabilized nanoparticles are attractive precursors for producing such nanostructures because the stabilizing ligands may be used to direct assembly of thoroughly characterized nanoparticles on the surface. Upon assembly; however, the ligands block the active surface of the nanoparticle. Methods used to remove these ligands typically result in release of nanoparticles from the surface or cause undesired growth of the nanoparticle core. Here, we demonstrate that mild chemical oxidation (50 ppm of ozone in nitrogen) oxidizes the thiolate headgroups, lowering the ligand's affinity for the gold nanoparticle surface and permitting the removal of the ligands at room temperature by rinsing with water. XPS and TEM measurements, performed using a custom planar analysis platform that permits detailed imaging and chemical analysis, provide insight into the mechanism of ligand removal and show that the particles retain their core size and remain tethered on the surface core during treatment. By varying the ozone exposure time, it is possible to control the amount of ligand removed. Catalytic carbon monoxide oxidation was used as a functional assay to demonstrate ligand removal from the gold surface for nanoparticles assembled on a high surface area support (fumed silica).

Modelling dimer–dimer reactions on supported catalysts

The kinetics of the dimer–dimer reaction, \(2A_2+B_2\rightarrow 2A_2B\), proceeding on supported catalysts is studied numerically using a phenomenological model which includes: the bulk diffusion of reactants from a bounded vessel towards the adsorbent and the product bulk one from the catalyst surface into the same vessel, adsorption and desorption of particles of both reactants, and surface diffusion of adsorbed particles. Two different arrangements of adsorption sites were used: (i) the same total amount of active and inactive in the surface reaction adsorption sites, (ii) the same concentrations of active and inactive sites. Two adsorption cases of both reactants for each arrangement of adsorption sites are considered: (i) each reactant adsorbs on both active and inactive sites, (ii) both reactants adsorb only on the support. The model where concentrations of both reactants at the catalyst surface are given is also studied. Simulations were performed using the finite difference technique. The influence of the size of the catalytic particle, surface diffusivity, adsorption rate constants, and particle jump rate constants via the catalyst-support interface on the catalytic reactivity of the supported catalyst is studied.

Effect of Adsorption Contact Time on Coking Coal Particle Desorption Characteristics

In this study, the effect of the adsorption contact time (ACT) on the desorption characteristics of coking coal particles is investigated using mercury intrusion, N2 adsorption/desorption, and methane adsorption equilibrium/desorption tests. The results of these tests reveal that the presence of micropores with one side closed, which we call half-open pores, in coal particles is the main factor affecting the duration of the equilibrium process. Coal particles subjected to different ACTs exhibit different adsorption contents, which strongly influences the desorption characteristics. The higher the ACT, the greater the volume being desorbed and the more durable it is. Considering that the adsorption content is equal to the limit of the desorption content, a new mathematical model of desorption under different ACTs is proposed, and the model output agrees well with the desorption curves. Using the diffusion coefficients fitted by this model, the adsorption equilibration period can be estimated, which will be...

Desorption of PAHs from solid phase into liquid phase during co-fermentation of municipal and coke sewage sludge

The work presents the results of the study that determined the changes in the concentration of polycyclic aromatic hydrocarbons (PAHs) in the sewage sludge and supernatants during the co-fermentation of municipal and coke sewage sludge. The municipal sewage sludge served as a control sample, and the mixture of municipal and coke sewage sludge was used as a test sample. The sewage sludge was incubated for 20 d at 37°C in the dark. The quantification of the PAHs was carried out simultaneously in both the solid and supernatant phases, the latter separated from the sludge during centrifugation. After 20 d, the solid phase was observed to have its PAHs content reduced by 60% in the control sample and 64% in the analyzed one, respectively. The decline in the solid phase PAHs content was accompanied by a significant quantitative increase of the PAHs in the liquid phase, which proves the desorption of solid particles. The control supernatants showed the total concentration of 16 PAHs of 1.1 μg/L prior to the treatment, and reaching 20.5 μg/L after 20 d of incubation, while for the supernatants separated from the mixture of municipal and coke sewage sludge, a 13-fold higher total concentration of the analyzed PAHs was determined

Fluctuations in transient response of adsorption-based plasmonic sensors

The basic parameters of a sensor element defining its ultimate performance are sensitivity and intrinsic noise. In plasmonic gas sensors both are determined by refractive index changes due to adsorption and desorption (a–d) of target analyte particles to the sensor active area. In this paper we present a general model that can be simultaneously used to determine sensitivity and intrinsic noise of a plasmonic sensor both during transients and in steady-state and is valid for multi-analyte environments. The model utilizes the conventional probabilistic approach. It is derived without any assumptions about the stochastic nature of the fundamental (a–d) process. It reveals how all stochastic properties of the processes with (pseudo) first order kinetics with the initial number of particles equal to zero can be fully determined from the deterministic solution, without any previous stochastic analysis. Based on the proposed model it is possible to establish the optimum moment for readout when fluctuations are minimal. Transients last longer and fluctuations are lower at lower temperatures. The insight into the transient dynamics opens the possibility to use a single element sensor for multiple analyte sensing. Another result is that a–d noise is higher for smaller adsorption areas, which may be important for micro and nanosystems generally, since each of them has to be kept immersed in some kind of environment and thus be subject to contamination by adsorption that can significantly influence their behavior. Besides being applicable for plasmonic sensors of trace amounts of gases and other nanoplasmonic devices used in sensing, the model is applicable for other adsorption-based sensors, as well as for the investigations of stochastic phenomena in micro and nanostructures.

Hybrid systems of gold and silver nanoparticles generated on cellulose surfaces

Developing methods for immobilizing metallic nanoparticles (NP) onto different surfaces is a subject of fundamental interest, as nanometric structures enable the appearance of novel properties, absent in bulk or even in micrometric dimensions. In fact, the presence of NP with different size and shape on surfaces can induce substantial modifications on their electronic, optical, magnetic, physical or chemical proprieties. This will be very useful for many applications in different areas ranging from electronics to biomedicine.In this work, we use a simple, reproducible and economic method to grow metallic gold and silver NP directly on cellulose surfaces. A prior chemical activation of the alcohol groups on the cellulose surface is needed for grafting amino functions, which will complex silver and gold ions. Therefore, NP nucleation is only allowed and selectively accomplished on these seed coordination sites. The growth of NP is achieved by the interaction of aqueous dilute solutions of AgNO3 or NaAuCl4 with the cellulose surface. The procedure limits the generation of NP only to the cellulose surface, keeping the dispersion medium completely exempt of them. The resulting NP are, consequently chemically immobilized on the cellulose surface. The chemical anchoring of the NP to the surface avoids particle desorption and extends the lifetime of the resulting hybrid materials. Following this procedure, silver and gold NP could be successfully created on cellulose and this was supported by transmission electron microscopy (TEM), scanning electron microscopy (SEM) and atomic force microscopy (AFM).The present AFM (Figure 1) study enabled to characterize the size and shape of silver NP: they are spherical and have a diameter of ~15 nm. SEM image of Ag NP (Figure 2) display the existence of NP agglomerates. Comparison of the two images suggests size and spatial distributions strongly non- uniform. It is now a challenge to deposit nanoparticles in an organized manner, achieving a regular surface functionalization of cellulose. In TEM (Figure 3) we see a sample where Ag and Au salts interacted simultaneously with the cellulose surface. Crossing the images with other information from analytical techniques, it seems that Ag NP and Au NP form mainly separately instead of presenting a core-shell structure. Also, there is evidence that larger NP are the ones made of silver which suggests that the final result is kinetically (and not thermodynamically) controlled.The authors acknowledge FCT for A.M. Ferraria Grant SFRH/BPD/26239/2006, for A. P. Carapeto Grant SFRH/BD/75734/2011 and strategic projects PEst-OE/CTM/LA0024/2011 and PEst-OE/CTM-UI0084/2011.

Removal of cadmium and lead from heavy metals loaded PVA–SA immobilized Lentinus edodes

This study, relates to results of Cd(II) and Pb(II) adsorption and removal efficiency from polyvinyl alcohol–Na-alginate (PVA–SA) immobilizing cells of Shi-take mushroom (Lentinus edodes) by H2SO4, HNO3, HCl, Na2CO3, NaHCO3, and NH4Cl solutions. Of these desorbing agents, H2SO4, HNO3, and HCl had strong desorbing potential, while HCl and HNO3 did better. The bio-sorbent particles, after desorption by both H2SO4 and HNO3 were found to be corroded. H2SO4 solution was most severe and it caused formation of amorphous matter at the surface that wrapped bio-sorbent particles and caused their round-shape coagulation. This membranes formed, further blocked desorption of Cd(II)/Pb(II). After desorption by HNO3, the particles were broken down due to strong oxidative power of the acid itself; while no obvious surface corrosion happened after desorption of the bio-sorbent particles when HCl was used as desorption agent. Since HCl solution had a weak influence on the bio-sorbent’s surface features, this acid was used as desorbing agent. An optimal time at equilibrium for Pb(II) desorption by 1 mol/L HCl was 90 min and for Cd(II) by 0.1 mol/L HCl was 60 min, with maximum efficiency of 90% and 81%, respectively. The pseudo-second-order model well-fitted to Cd(II)/Pb(II) desorption rates and the correlation coefficients (R2) were 0.9989 and 0.9969, respectively. From trial to trial as regeneration of bio-sorbent continued, its absorptive potential gradually weakened. Nevertheless, after three regeneration trials, the absorptive potential of reused bio-sorbent still reached 69% for Cd(II) and 85% for Pb(II), and what was displayed is that the immobilizing technology with the abandoned stipe of Shi-take mushroom can be feasible in practical application. After Pb(II) bio-sorption, the surface of bio-sorbent became rich in Pb(II) and energy spectra confirmed that the crystals found in scanning electron microscope (SEM) analysis were Pb(II) salts. On the other side, the spectral peak from Cd(II) was not as clear as from Pb(II). After desorption phase of Pb(II) and Cd(II), there were no spectral peaks from these heavy metals at the surface of the regenerated bio-sorbent.

Product desorption rate influence on catalytic reactivity of spatially inhomogeneous surfaces

We investigate numerically a phenomenological mathematical model of unimolecular reactions proceeding on inhomogeneous planar surfaces in the two-dimensional space case taking into account: the bulk diffusion of the reactant from the bounded vessel toward the adsorbent and the product bulk one from the adsorbent into the same vessel, the adsorption and desorption of reactant particles, long-range surface diffusion of the adsorbate, and a slow product desorption from the adsorbent. Simulations were performed using the finite difference technique. The influence of the long-range surface diffusion and product desorption rate on the kinetics of processes catalysed by inhomogeneous surfaces with different arrangements of reactive and nonreactive adsorption sites are studied.

Numerical study of long-range surface diffusion influence on catalytic reactivity of spatially inhomogeneous planar surfaces

A phenomenological (mean-field) mathematical model of unimolecular reactions proceeding onto inhomogeneous planar surfaces is presented and investigated numerically in two-dimensional in space case taking into account the adsorption and desorption of reactant particles, long-range surface diffusion of the adsorbed particles, and an instantaneous product desorption from an adsorbent. The model also involves the bulk diffusion of the reactant from the bounded vessel towards the adsorbent and the product bulk one from the adsorbent into the same vessel. Simulations were performed using the finite difference technique. The influence of the long-range surface diffusion of adsorbed particles on the kinetics for processes catalyzed by inhomogeneous surfaces with a different arrangement of reactive and non-reactive adsorption sites is studied.

Hematite nanoparticle monolayers on mica preparation by controlled self-assembly

A stable suspension of α-Fe2O3 (hematite) was synthesized according to the method of Matijevic and Scheiner by an acidic hydrolysis of ferric chloride. The average size of the particles was determined by dynamic light scattering (DLS) and atomic force microscopy (AFM) and was 22nm. The electrophoretic mobility and zeta potential of particles were determined as a function of ionic strength and pH. The zeta potential of the hematite particles was positive for pH<8.9 (isoelectric point) and negative otherwise. Using the suspension, systematic studies of particle deposition kinetics on mica were carried out. The coverage of self-assembled particle monolayers was determined by AFM and SEM imaging. Particle deposition was diffusion controlled, with the initial rate proportional to the bulk concentration of particles. On the other hand, for long times, the saturation coverage was attained, increasing systematically with ionic strength. The deposition kinetic runs were adequately reflected by the random sequential adsorption (RSA) model. Additionally, particle desorption kinetics, from previously formed monolayers, were studied using the AFM and SEM methods. It was confirmed that hematite particle desorption was practically negligible within the time period of 60h. Our experimental data proved, therefore, that it is feasible to produce uniform and stable hematite particle monolayers of desired coverage in self-assembly processes controlled by the bulk suspension concentration and the ionic strength.

A “place n play” modular pump for portable microfluidic applications

This paper presents an easy-to-use, power-free, and modular pump for portable microfluidic applications. The pump module is a degassed particle desorption polydimethylsiloxane (PDMS) slab with an integrated mesh-shaped chamber, which can be attached on the outlet port of microfluidic device to absorb the air in the microfluidic system and then to create a negative pressure for driving fluid. Different from the existing monolithic degassed PDMS pumps that are generally restricted to limited pumping capacity and are only compatible with PDMS-based microfluidic devices, this pump can offer various possible configures of pumping power by varying the geometries of the pump or by combining different pump modules and can also be employed in any material microfluidic devices. The key advantage of this pump is that its operation only requires the user to place the degassed PDMS slab on the outlet ports of microfluidic devices. To help design pumps with a suitable pumping performance, the effect of pump module geometry on its pumping capacity is also investigated. The results indicate that the performance of the degassed PDMS pump is strongly dependent on the surface area of the pump chamber, the exposure area and the volume of the PDMS pump slab. In addition, the initial volume of air in the closed microfluidic system and the cross-linking degree of PDMS also affect the performance of the degassed PDMS pump. Finally, we demonstrated the utility of this modular pumping method by applying it to a glass-based microfluidic device and a PDMS-based protein crystallization microfluidic device.

Tuning properties of silver particle monolayers via controlled adsorption–desorption processes

Using the well-defined silver particle suspension, systematic studies of adsorption kinetics on mica modified by poly(allylamine hydrochloride) (PAH) were carried out. The coverage of adsorbed particles was directly determined by AFM and SEM imaging. The dependence of the coverage on adsorption time, bulk suspension concentration, and ionic strength was systematically studied. It was confirmed that adsorption was diffusion controlled, with the initial rate proportional to the bulk concentration of particles. On the other hand, for long adsorption times, the saturation coverage was attained, which increased systematically with the ionic strength of the particle suspension. The adsorption kinetic runs were adequately reflected for the entire range of times and bulk concentration by the random sequential adsorption (RSA) model. Additionally, particle desorption kinetics from previously formed monolayers were studied. The decrease in the surface coverage of particles as a function of time was measured, which allowed one to determine the equilibrium adsorption constant Ka. The binding energy of silver particles (energy minimum depth) derived form these measurements varied between −16.9kT and −17.8kT, which suggests that it is mainly controlled by electrostatic interactions. Knowing the equilibrium adsorption constant, a particle adsorption isotherm was theoretically derived using the RSA model. Experimental data obtained for various bulk concentration of particles were in agreement with these theoretical predictions. These measurements suggest that it is feasible to produce uniform silver particle monolayers of desired coverage in the self-assembly process of particles.

High-throughput study of alpha-synuclein expression in yeast using microfluidics for control of local cellular microenvironment

Microfluidics is an emerging technology which allows the miniaturization, integration, and automation of fluid handling processes. Microfluidic systems offer low sample consumption, significantly reduced processing time, and the prospect of massive parallelization. A microfluidic platform was developed for the control of the soluble cellular microenvironment of Saccharomyces cerevisiae cells, which enabled high-throughput monitoring of the controlled expression of alpha-synuclein (aSyn), a protein involved in Parkinson's disease. Y-shaped structures were fabricated using particle desorption mass spectrometry-based soft-lithography techniques to generate biomolecular gradients along a microchannel. Cell traps integrated along the microchannel allowed the positioning and monitoring of cells in precise locations, where different, well-controlled chemical environments were established. S. cerevisiae cells genetically engineered to encode the fusion protein aSyn-GFP (green fluorescent protein) under the control of GAL1, a galactose inducible promoter, were loaded in the microfluidic structure. A galactose concentration gradient was established in the channel and a time-dependent aSyn-GFP expression was obtained as a function of the positioning of cells along the galactose gradient. Our results demonstrate the applicability of this microfluidic platform to the spatiotemporal control of cellular microenvironment and open a range of possibilities for the study of cellular processes based on single-cell analysis.

Laser-induced desorption of atomic and molecular fragments from a tin dioxide surface modified by a thin organic covering of copper phthalocyanine

The systematic features of laser-induced desorption from an SnO2 surface exposed to 10-ns pulsed neodymium laser radiation are studied at the photon energy 2.34 eV, in the range of pulse energy densities 1 to 50 mJ/cm2. As the threshold pulse energy 28 mJ/cm2 is achieved, molecular oxygen O2 is detected in the desorption mass spectra from the SnO2 surface; as the threshold pulse energy 42 mJ/cm2 is reached, tin Sn, and SnO and (SnO)2 particle desorption is observed. The laser desorption mass spectra from the SnO2 surface coated with an organic copper phthalocyanine (CuPc) film 50 nm thick are measured. It is shown that laser irradiation causes the fragmentation of CuPc molecules and the desorption of molecular fragments in the laser pulse energy density range 6 to 10 mJ/cm2. Along with the desorption of molecular fragments, a weak desorption signal of the substrate components O2, Sn, SnO, and (SnO)2 is observed in the same energy range. Desorption energy thresholds of substrate atomic components from the organic film surface are approximately five times lower than thresholds of their desorption from the atomically clean SnO2 surface, which indicates the diffusion of atomic components of the SnO2 substrate to the bulk of the deposited organic film.

Electrostatic interactions to modulate the reflective assembly of nanoparticles at the oil–water interface

The driving force for the adsorption of nanoparticles (5–10 nm) at the oil–water interface can be small and is particularly sensitive to the surface chemistry of the particles. Here we show that the interfacial assembly of 5 and 10 nm diameter gold nanoparticles functionalized with stoichiometric ion-pairs is reversible and can be tuned with the solution pH. We also show that at the interface the nanoparticles form a reflective layer with a mirror-like reflectance. Using titration we demonstrate that the mechanism for particle desorption from the interface is the electrostatic repulsion between the nanoparticles, likely due to pH-dependent adsorption of hydroxide ions. By controlling electrostatic repulsion we can control both the extent of adsorption at the interface and the separation between particles within the interfacial film. As such, we demonstrate two avenues to reversibly control the optical properties of the fluid interface: (1) increase the pH of the aqueous solution to desorb particles from the interface, and (2) decrease the ionic strength in the aqueous phase to increase the spacing of the nanoparticles at the oil–water interface.

Effect of pH on monolayer properties of colloidal silica particles at the air/water interface

Monodisperse colloidal silica particles were prepared by the Stober method and hydrophobized by grafting a silane coupling agent, octadecyltrimethoxysilane. Two different types of silica particles, i.e., hydrophilic and hydrophobic silica particles were spread at the air/water interface to form the Langmuir monolayers. Monolayer properties of those particles were investigated by measuring surface pressure–area (π–A) isotherms at different subphase pH. At pH above the isoelectric point (IEP) of silica, as pH increased the π–A isotherms for the hydrophobic particles slightly shifted to larger surface area whereas those for the hydrophilic particles showed a reverse trend. At pH below the IEP, the π–A isotherms for both types of particles shifted to much larger surface area with different shapes. In order to analyze the π–A isotherm results further, the time dependence of π was examined. When pH is above the IEP, the π for the hydrophilic particles significantly decreased with increasing time and it did more at higher pH. On the other hand, the decrease in π for the hydrophobic particles was insignificant regardless of pH. For both types of silica particles, the decrease in π was minimal at pH below the IEP. These results were discussed in terms of particle desorption into the water subphase and interparticle electrostatic repulsion which is directly influenced by zeta potential.

Adsorption on a surface with varying properties

We propose a self-consistent model taking into account the variations in adsorption properties of an adsorbent surface in the process of adsorption–desorption of gas particles on it. We introduce a dimensionless coupling parameter equal to the normalized adsorption-induced activation energy for desorption due to the substrate deformation caused by the adsorption-induced force. Bistability of the system of noninteracting adparticles is established in the case when the coupling parameter is greater than a critical value and the gas concentration belongs to a certain interval. We show that the adsorption isotherms obtained within the framework of the proposed model essentially differ from the Langmuir isotherms and we show that the Zeldovich hysteresis is possible. The kinetics of the surface coverage is analyzed in detail in the overdamped approximation. We show the possibility of a ‘quasi-stationary’ state of the system due to variations in adsorption properties of the surface in adsorption–desorption.

First field application of a thermal desorption resonance-enhanced multiphoton-ionisation single particle time-of-flight mass spectrometer for the on-line detection of particle-bound polycyclic aromatic hydrocarbons

The on-line analysis of single aerosol particles with mass spectrometrical methods is an important tool for the investigation of aerosols. Often, a single laser pulse is used for one-step laser desorption/ionisation of aerosol particles. Resulting ions are detected with time-of-flight mass spectrometry. With this method, the detection of inorganic compounds is possible. The detection of more fragile organic compounds and carbon clusters can be accomplished by separating the desorption and the ionisation in two steps, e.g. by using two laser pulses. A further method is, using a heated metal surface for thermal desorption of aerosol particles. If an ultraviolet laser is used for ionisation, a selective ionisation of polycyclic aromatic hydrocarbons (PAH) and alkylated PAH is possible via a resonance-enhanced multiphoton-ionisation process. Laser velocimetry allows individual laser triggering for single particles and additionally delivers information on aerodynamic particle diameters. It was shown that particles deriving from different combustion sources can be differentiated according to their PAH patterns. For example, retene, a C(4)-alkylated phenanthrene derivative, is a marker for the combustion of coniferous wood. In this paper, the first field application of a thermal desorption resonance-enhanced multiphoton-ionisation single particle time-of-flight mass spectrometer during a measurement campaign in Augsburg, Germany in winter 2010 is presented. Larger PAH-containing particles (i.e. with aerodynamic diameters larger than 1 μm), which are suspected to be originated by re-suspension processes of agglomerated material, were in the focus of the investigation. Due to the low concentration of these particles, an on-line virtual impactor enrichment system was used. The detection of particle-bound PAH in ambient particles in this larger size region was possible and in addition, retene could be detected on several particles, which allows to identify wood combustion as generic source of these particles. The observed diurnal distribution of these larger particles, however, support the origin by traffic induced re-suspension of sedimented/agglomerated material.

Modeling the system of electrogasdynamic final-control elements

A system of electrogasdynamic final-control elements (plasma actuators) intended for increasing the stability of the boundary layer on a swept wing is considered. The actuators operate on the basis of dielectric barrier discharge. The physical model of the discharge in the air is formulated in the diffusion-drift approximation with account for three charged ionized-gas components, namely, electrons, positive nitrogen and oxygen ions, and negative oxygen ions. The boundary conditions on the dielectric surface are formulated with account for finite desorption and recombination rates of the charged particles. The numerical modeling for an actuator system of particular geometry shows a slight influence of the negative ions on the bulk force generated by each actuator. The main actuator parameters, such as the total longitudinal force and heat release, are shown to considerably depend on the dielectric permeabilities of insulation layers separating the external and internal electrodes. The expressions are derived that make it possible to estimate the gas velocity induced by the bulk force action of the dielectric barrier discharge on the gas flow.

Surface functionalisation of cellulose with noble metals nanoparticles through a selective nucleation

Films and fibres of cellulose were functionalised with silver and gold nanoparticles directly generated on the surface. The present method lays on the cellulose surface pre-modification, replacing some of the hydroxyl groups by amino functions, which selectively act as the seed coordination sites. Nanoparticles can then grow through the interaction with aqueous dilute solutions of AgNO3 or NaAuCl4 at room temperature, without adding any reducing agent. The procedure offers the advantage of limiting the generation of nanoparticles to the cellulose surface, leaving the dispersion medium completely exempt of them. The cellulose pre-modification also ensures chemical anchoring of the nanoparticles to the surface, avoiding any risk of particle desorption and extending the lifetime of the resulting hybrid materials. Evidence of the formation of the NPs on the cellulose surfaces was supported by FE-SEM, AFM, XPS and XRD. The method is simple and reproducible.