Adsorption Of Silica Nanoparticles Research Articles

Preparation of ethanol-gels as hand sanitizers formed from chitosan and silica nanoparticles

The application of chitosan as a gelling agent in hydro-alcoholic hand sanitizers has rarely been studied due to its insolubility in ethanol. In this study, high-ethanol-content gels were prepared with chitosan in combination with silica nanoparticles. The properties of the gels were investigated by FTIR, XRD, SEM, rheological measurement and the zone of inhibition test against bacteria. The results showed that the adsorption of silica nanoparticles on the chitosan inhibited the precipitation of chitosan in ethanol. The chitosan/silica fibres entangled with each other, and gelation occurred in the solvent with high ethanol concentration due to the solvent-driven effect. The gelation process was related to the concentrations of ethanol, chitosan, and silica nanoparticles. A stable gel could be formed at a chitosan concentration as low as 0.5%, with an ethanol concentration up to 80%. All the gels exhibited pseudoplastic behaviour and had frequency-dependent profiles in the viscoelastic spectrum of non-Newtonian liquids, behaving in a solid-like manner. The limited linear viscoelastic region of all samples was<1%. The optimal silica concentrations (OSCs) for various chitosan concentrations in 75% ethanol were proposed by rheological analysis as a reference to optimize the sensory and textural properties of gels. These gels showed antibacterial activity, which introduced a potential application as hand sanitizers. This research provides a method of preparing novel high-ethanol-content gels, highlights the application of solvent-driven effects in gelation, and identified some suggestions for future research.

Fabrication and Characterization of Hydrophobic Cellulose Nanofibrils/Silica Nanocomposites with Hexadecyltrimethoxysilane.

Cellulose nanofibrils (CNFs) have attracted much attention because of their renewability and potential biocompatibility. However, CNFs are extremely hydrophilic due to the presence of a large number of hydroxyl groups, limiting their use as a water-resistant material. In this work, we controlled the adsorption behavior of silica nanoparticles on the surface of CNFs by adjusting the synthesis conditions. The silica nanoparticle size and packing efficiency on the CNF surface could be controlled by varying the ammonium hydroxide and water concentrations. In addition, hexadecyltrimethoxysilane (HDTMS) was successfully grafted onto CNF or CNF/silica nanocomposite surfaces, and the quantitative content of organic/inorganic substances in HDTMS was analyzed through XPS and TGA. The HDTMS-modified CNF/silica nanocomposites were more advantageous in terms of hydrophobicity than the HDTMS-modified CNF composites. This is because the silica nanoparticles were adsorbed on the surface of the CNFs, increasing the surface roughness and simultaneously increasing the amount of HDTMS. As a result, the HDTMS-modified CNFs showed a water contact angle (WCA) of ~80°, whereas HDTMS-modified CNF/silica nanocomposites obtained superhydrophobicity, with a WCA of up to ~159°. This study can provide a reference for the expansion of recyclable eco-friendly coating materials via the adsorption of silica nanoparticles and hydrophobic modification of CNF materials.

Ozone generation enhanced by silica catalyst in packed-bed DBD reactor

In this paper, three dielectric barrier discharge (DBD) configurations, which were plain DBD with no packing, DBD with packed pure quartz fibers and DBD with packed loaded quartz fibers, were employed to investigate the effect and catalytic mechanism of catalyst materials in a packed-bed ozone generator. From the experimental results, it was clear that the DBD configuration with packed pure fibers and packed loaded fibers promotes ozone generation. For the packed-bed reactor, ozone concentration and ozone yield were enhanced by an increase of electric field in the discharge gap with the packed-bed effect. Meanwhile, the enhancement of ozone concentration and yield for the DBD reactor packed by loaded fibers with silica nanoparticles was due to the catalysis of silica nanoparticles on the fiber surface. The adsorption of silica nanoparticles on the fiber surface can prolong the retention time of active species and enhance surface reactions.

Ion Transfer at Liquid | Liquid Interface Modified with Silica Nanoparticles

The interface formed between two immiscible electrolyte solutions (ITIES) is a highly reproducible, defect-free surface that allows the assembly of nanometer-sized objects. Their adsorption at the liquid-liquid interface is governed by their dimensions, zeta potential, wettability and the interfacial tension. The interest for the use of silica nanomaterials at the ITIES is due to their favourable adsorption kinetics and to their rich surface chemistry that can provide selectivity.At first, we followed the adsorption of silica nanoparticles (ø = 12 nm) at the ITIES by AC voltammetry and their interactions with methylene blue (MB+), selected as a model ion by cyclic voltammetry and UV-vis absorption spectroscopy. We determined the adsorption constant of the MB+ onto silica nanoparticles to be 1.66 × 105, which indicated a strong affinity between them. This is in contrast with two other ions tested (Eosin B and tetraethylammonium), which demonstrated low affinity for the silica nanoparticles.In a second step, we synthesized silica nanoparticles with diclofenac molecular imprint with the aim of selective accumulation of diclofenac, a commonly used nonsteroidal anti-inflammatory drug. The presence of imprint cavities greatly improved the affinity for diclofenac for the silica nanoparticles, in contrast with diclofenac analogue such as aceclofenac. Electrochemistry experiments (including cyclic and AC voltammetries) revealed that diclofenac transfer is blocked by the presence of molecularly imprinted nanoparticles at the ITIES.These two experimental examples show that target molecules can be accumulated at the ITIES by combining the ability of silica nanoparticles to adsorb onto the ITIES and their affinity for the targeted molecules. Such an accumulation localized at the interface could be of interest in sensing applications. Figure 1

Pickering emulsion stabilized by organoclay and intermediately hydrophobic nanosilica for high-temperature conditions

Pickering emulsions show great promise for many applications in the oil and gas industry. However, the thermal stability of Pickering emulsions reported thus far has been unfavorable for safe operation in the always high-temperature deep underground condition. Here we report a Pickering water-in-oil (W/O) emulsion that exhibits high temperature tolerance in the absence of any surfactant due to the synergistic effect between organoclay and silica nanoparticles (NPs) with intermediate hydrophobicity. The interaction between silica NPs and organoclay was characterized by X-ray diffraction, thermogravimetric analysis, zeta potentials, scanning electron microscopy and transmission electron microscopy. The results of gel volume and water contact angle measurement confirmed the hydrophobicity of the organoclay. The effects of varying the hydrophobicity and concentration of the silica NPs, the clay concentration of the organoclay, and the thermal-rolling temperature on the emulsion stability, droplet size, morphology, and rheology were investigated in detail. The optimal synergy for stabilizing the W/O emulsion was found to occur with 1 wt% silica NPs exhibiting intermediate hydrophobicity and 1 wt% organoclay. As expected, neither hydrophobic nor hydrophilic silica NPs could improve the emulsion stability due to inefficient adsorption at the water-oil interface. Organoclay was found to have a significant influence on the stability and rheological properties of the W/O Pickering emulsion since it dominates the formation of networks in the continuous phase due to its excellent swelling and exfoliation. The adsorption of silica NPs further enhanced the interactions between the particles and the medium, making it possible for the retainment of rheology even after thermal rolling at 220 ℃. The increase in temperature tolerance achieved through a simple and environmentally friendly method makes this Pickering emulsion applicable in potential drilling fluids for the oil and gas field.

Transport and Adsorption of Silica Nanoparticles in Carbonate Reservoirs: A Sand Column Study

The adsorption of nanoparticles onto mineral surfaces is a major limitation for applications that require long transport distances, such as enhanced oil recovery. This study investigates silica nanoparticle transport and adsorption in long granular columns, with emphasis on the adsorption onto carbonate substrates, given the fact that carbonate reservoirs host more than 60% of the world’s recoverable oil. The grain-scale particle–mineral interactions are characterized by zeta potential measurements. Ionic strength (especially potential-determining ions: Ca2+, Mg2+, CO32–, etc.) inherently influences the zeta potential of carbonates. Derjaguin–Landau–Verwey–Overbeek analyses show that low surface potential and high ionic concentration inhibit the electrostatic double-layer repulsion and lower the energy barrier of adsorption. Adsorption column experiments simulate a variety of fluid chemistry conditions: pH, ionic concentration, and ion type. Alkaline and low-salinity conditions favor silica nanoparticles transport in carbonate reservoirs. Both scanning electron microscopy images and adsorption mass analyses suggest that the adsorption of nanoparticles onto carbonate substrates is multilayered. A two-term adsorption model adequately captures the instantaneous adsorption and the subsequent kinetic adsorption. The instantaneous adsorption constant delays particle transport, and the kinetic adsorption rate determines the concentration profile of nanoparticles along the reservoir at the steady state. High advection velocity and low adsorption rate k1 are required to deliver high nanoparticle concentration to the far field in the reservoir.

Aggregation and Stabilization of Colloidal Spheroids by Oppositely Charged Spherical Nanoparticles.

Heteroaggregation of colloids is an important yet complex physical process involving colloidal/nanosized particles and is relevant in river delta formation, paper-making, water treatment, blood flocculation, and so on. Despite the earlier studies on oppositely charged spherical colloids, heteroaggregation of colloids of different shapes is less explored. In this regard, we report an experimental study to investigate the colloidal stability of mixture of positively charged spheroidal hematite and negatively charged spherical silica nanoparticles. In this study, pH and surface area ratio (silica to hematite, SS-H) are varied to tune the colloidal stability/instability of the suspension. At pH 6.5 and low SS-H, the silica particles adsorb onto the hematite particles and reduce the effective charge of the latter, leading to aggregation and resulting in unstable dispersions. At higher SS-H, adsorption of silica on hematite leads to overcharging and charge reversal, which leads to a stable dispersion. Similar experiments were performed at pH 2.4 and 3.5, and the crossover from unstable to stable dispersion is observed as a function of SS-H. Calculation of Derjaguin, Landau, Verwey, and Overbeek (DLVO) interaction between particles in the binary mixture, as a function of pH and SS-H, based on the aggregate size and zeta potential, explains the transition from unstable to stable dispersion. The size and zeta potential of heteroaggregates in the dispersion were analyzed by dynamic light scattering (DLS) technique. Adsorption of silica nanoparticles on hematite particles was visualized by scanning electron microscopy (SEM). The study provides a framework based on DLVO interactions to stabilize or destabilize a colloidal dispersion of nonspherical particles by controlled addition of oppositely charged spherical colloids, which is a feat that is not possible with simple salt. The stability ratio ( W) calculated from DLVO interactions demark the unstable-stable dispersion regions, which is found to be in agreement with the experimental results.

Peptide engineered microcantilevers for selective chemical force microscopy and monitoring of nanoparticle capture.

Engineered peptides capable of binding to silica have been used to provide contrast in chemical force microscopy and tested for their capacity to selectively capture silica nanoparticles (NPs). Gold coated atomic force microscopy (AFM) microcantilevers with integrated tips and colloidal probes were functionalized with engineered peptides through a thiol group of a terminal cysteine which was linked via a glycine trimer to a 12-mer binding sequence. The functionalized probes demonstrated a significantly increased binding force on silicon oxide areas of a gold-patterned silicon wafer, whereas plain gold probes, and those functionalized with a random permutation of the silica binding peptide motif or an all-histidine sequence displayed similar adhesion forces to gold and silicon oxide. As the functionalized probes also allowed contact mode imaging subsequently to the adhesion mapping, also the associated friction contrast was measured and found to be similar to the adhesion contrast. Furthermore, the adsorption of silica NPs onto planar gold surfaces functionalized in the same manner was observed to be selective. Notably, the surface coverage with silica NPs was found to decrease with increasing pH, implying the importance of electrostatic interactions between the peptide and the NPs. Finally, the adsorption of silica NPs was monitored via the decrease in fundamental resonance frequency of an AFM microcantilever functionalized with silica binding peptides.

Understanding adsorption behavior of silica nanoparticles over a cellulose surface in an aqueous medium

The suspension and adsorption of silica nanoparticles on a cellulose surface, in an aqueous medium is investigated using Brownian dynamic simulations. The inter particle and particle–surface interactions are modeled within the framework of the DLVO theory. Our analysis predicts the accumulation of negatively charged nanoparticles near a negatively charged surface depending on the Debye screening length of the medium. A crossover from the suspension to the adsorption of negatively charged silica nanoparticles onto a negatively charged cellulose surface has been reported as the screening length (k−1) of the medium increases. The crossover is observed at k−1=100nm, due to the interplay between the nanoparticle–nanoparticle and the nanoparticle–surface interactions. The adsorption behavior of nanoparticles is explained using the potential of mean force analysis. The amount of nanoparticles adsorbed depends on their bulk volume fraction (ϕ) and the screening length of the medium. Further, the effects of electrical potentials of nanoparticle (ΨP) and surface (ΨS) on the adsorption are reported. The data suggests that the adsorption of nanoparticles increases either with increasing ΨP magnitude, or/and, with decreasing ΨS magnitude. The adsorbed particles form a disordered monolayer, and undergo subdiffusive motion. We have also observed a transition from the gas-like structure to the liquid-like structure of nanoparticles in the adsorbed monolayer as their bulk volume fraction increases.

Adsorption of silica nanoparticles onto calcite: Equilibrium, kinetic, thermodynamic and DLVO analysis

Recently, application of silica nanoparticles (SNP) for enhancing oil recovery during water flooding has been much attended. However, understanding how rock and nanoparticles (NP) interacts through adsorption onto the carbonate reservoir rocks is not well discussed. In this work, adsorption behavior of SNP onto the calcite had been characterized, through kinetic, equilibrium, thermodynamics and electrokinetic studies as well as interaction energy analysis by DLVO theory. Also, field emission scanning electron microscopy (FESEM) was utilized to visualize the adsorption process. It had been found that kinetic behavior of SNP–calcite system followed the pseudo-second order model. Equilibrium study revealed that Langmuir model yielded a better fit which implied that monolayer coverage of SNP onto the calcite surfaces was more probable. Analysis of kinetic data indicated that the intraparticle diffusion mechanism was not the sole rate-controlling mechanism and the boundary layer diffusion affected the adsorption to some extent. Thermodynamic study showed that physical/electrostatic adsorption was expected to be the prevailing mechanism for the adsorption with a spontaneous and endothermic nature. Also, adsorption process was enhanced by lowering the pH and increasing ionic strength of the solutions. These findings were argued based on the equilibrium reactions of the SNP and calcite in water and DLVO theory. Results revealed that repulsive DLVO interaction energies predominated from which an unfavorable attachment condition was deduced. In such situation, ionic strength of solution controlled the extent of the SNP–calcite interaction. Reduction in the height of energy barrier and the formation of a secondary minimum were responsible for enhancing the adsorption process at higher ionic strengths. Furthermore, FESEM-observations depicted a spherical morphology for the adsorbed SNP that uniformly distributed on the calcite surface.

Adsorption of Surface-Modified Silica Nanoparticles to the Interface of Melt Poly(lactic acid) and Supercritical Carbon Dioxide.

With the purpose of fabricating polymer nanocomposite foams and preventing coalescence in foaming processes, the interfacial tension of poly(lactic acid) (PLA)-silica composites is investigated in this work. Synthesized silica nanoparticles (SNs) with a CO2-philic surface modification are used as the dispersed nanoparticles. Interfacial tension is a key parameter in processing of polymer foams since it directly affects the final foam properties, such as cell size and cell density. Interfacial tension of silica-containing PLA and supercritical carbon dioxide (CO2) is measured using axisymmetric drop shape analysis profile (ADSA-P) pendant drop method at high pressures and high temperatures. The interfacial tension between PLA and supercritical CO2 is observed to decrease as a result of the nanoparticles' adsorption to the interface. These results indicate that the reduction in interfacial tension with increasing silica content significantly deviates from a linear trend; there is a minimum at 2 wt % loading of the SNs and then the interfacial tension curve reaches a plateau. Contact angle measurements show an affinity of the SNs for the polymer-supercritical CO2 interface, and these obtained results are used to calculate the binding energy of the nanoparticles to the PLA/CO2 interface. In addition to interfacial properties, the adsorption of silica nanoparticles at the interface is also studied in detail with scanning electron microscopy.