Adsorption | EPFL Graph Search

En chimie, l’adsorption est un phénomène de surface par lequel des atomes, des ions ou des molécules - des adsorbats - se fixent sur une surface solide - l'adsorbant - depuis une phase gazeuse, liquide ou une solution solide. Dans le cas d'un atome adsorbé, on parle d'adatome. Ce phénomène est différent de l'absorption, par lequel un fluide ou le composant d'une solution solide rentre dans le volume d'une autre phase liquide ou solide, mais les deux effets sont similaires et sont facilement (et à tort) confondus, notamment dans des applications pour le grand public. Un exemple usuel typique est la fixation de vapeur d'eau sur une vitre. Industriellement, l'adsorption s'effectue à l'intérieur de grains d'adsorbant, sur la surface développée par les pores afin d'obtenir une grande quantité fixée dans un minimum de volume. Le processus d'adsorption est donc basé sur l'interaction de l'adsorbat avec une surface, ce qui peut faire intervenir divers processus plus ou moins intenses comme

Characterization and prediction of peptide structures on inorganic surfaces

Dmitrii Maksimov

Interfaces between peptides and metallic surfaces are the subject of great interest for possible use in technological and medicinal applications, mainly since organic systems present an extensive range of functionalities, are abundant, cheap, and exhibit low toxicity. Exemplary applications are biosensors that may be sensitive to specific metabolites or harmful compounds. However, these hybrid interfaces pose a challenge to computational modelling, particularly regarding predicting the most relevant configurations at the surface, which determines the electronic properties of the system as a whole. From a theoretical point of view, predicting the most stable interface configuration requires searching through the enormous structure space of flexible biomolecules with respect to the surface for different configurations and performing computational calculations of their properties. However, it is impossible to investigate those parts separately due to complex interactions during adsorption. In order to capture these complex interactions, one has to employ accurate theoretical methods, which are very computationally expensive. In this thesis, we provide a comprehensive description of the complex nature of the interaction of selected amino acids with metallic surfaces using state-of-the-art dimensionality reduction techniques and accurate ab initio theoretical methods and creation of tools tailored for the high-throughput investigations of interface systems. The theoretical methods used in the thesis are described in the first part of the thesis. The second section looks into the conformational space changes of Arginine (Arg) and its protonated counterpart after adsorption on three noble metallic surfaces. Arg is an excellent testbed because it is tiny enough to be treated using density functional theory, which is considered the best compromise between accuracy and computational efficiency. At the same time, Arg is complex enough due to a highly flexible side-chain that allows for hundreds of different configurations in the gas phase alone. The examination of adsorption behavior requires creating a database by performing a large number of geometry optimizations of various conformations and orientations. The investigation of that database includes creating a low-dimensional representation of the conformational spaces using recent dimensionality reduction techniques, followed by examining various bonding and charge transfer patterns and how they affect the available conformational spaces.The third section of the thesis is concerned with developing tools for the automated structure search of interface systems and the modelling of self-assembly patterns formed after adsorption. Different geometry optimization algorithms and a flexible method of preconditioning the quasi-Newton optimization algorithms are implemented in the GenSec package that was developed. Together, these enable a more straightforward interface with a wide range of quantum chemistry packages for sampling the conformational spaces of flexible molecules in 1D (ions), 2D (surfaces), and 3D (cavities and molecules) systems. Structure search of the conformational space of a flexible molecule using GenSec provided satisfactory results for di-L-alanine adsorbed on Cu(110) surface.

EPFL2022

Controlled protein adsorption for microimmunoassays

Andrea Lionello

This dissertation addresses the adsorption of proteins in microchannels with the aim of improving the result of an immunoassay. To observe the adsorption of fluorescently labelled immunoglobulins G in laser ablated polymer microchannels, a confocal microscope was built. By optically scanning the specimen, and observing one focal plane at time, this tool allows for a high signal-to-background, which leads to a low limit of detection (10-9 M). A numerical model for the adsorption kinetics of proteins on the walls of a microchannel has been developed using the finite element method (FEM). The model illustrates the adsorption limitation sometimes observed when the microdimensions of these systems induce a global depletion of the bulk solution. A new non-dimensional parameter is introduced to predict the final value of the coverage of any microsystem under static adsorption. A working curve and a criteria (h/KΓmax > 10) are provided in order to choose, for given adsorption characteristics, the value of the volume-to-surface ratio (i.e. the channel height h) avoiding depletion effects on the coverage (relative coverage at least 90% of the theoretical one). Simulations were compared with confocal microscopy measurements of IgG antibody adsorption on the walls of a PET (poly(ethylene terephthalate)) microchannel. The fit of the model to the experimental data show that the adsorption is under apparent kinetic control. Two ways of loading proteins on microchannel surfaces for immunological applications have been analysed with the FEM model: the "stop-flow" and the continuous flow processes. The "stop-flow" method consists of successive static incubation periods where the bulk solution depletes upon the adsorption process. A multi-step "stop-flow" protein coating is studied and compared to a coating under continuous flow conditions. For the "stop-flow", a non-dimensional parameter is here introduced, indicating the adsorbing capacity of the system, by which it is possible to calculate the number of loads necessary to reach the optimum coverage. For the continuous flow, the effects on the adsorption of the kinetic rates, flow velocity and wall capacity have been considered. This study shows the importance of a careful choice of the fluid velocity to minimise the sample waste. For diffusion controlled and kinetics controlled processes, two flow velocity criteria are provided in order to obtain the best possible coverage, with the same amount of sample as with the "stop-flow". Surface modifications have been conceived in order to improve the adsorption and the activity of the physisorbed antibodies. The microchannels have been coated with titania nanomaterials, chosen because of their biocompatible properties. Crystalline and amorphous TiO2 have been used and the adsorption with respect to the native PET was improved by 3 times. A study of adsorption as a function of the pH solution and different ionic strengths has been done in order to infer the forces acting during the adsorption: it was found that hydrophobic forces helped by electrostatic ones occur during IgG adsorption onto titania phases. The "stop-flow" method was employed to coat the TiO2 modified microchannels with the capture antibodies and improve the result of a microimmunoassay. When strong adsorbing phases are used, the limit of detection of the assay was lowered by one order of magnitude. The FEM model was used to obtain the kinetic rates of adsorption and desorption of IgG antibodies on PET with a novel biosensor conceived in this lab, which measures capacitive changes in the surface microchannel while the adsorption takes place. As the FEM model foresees a three-dimension region where the adsorption might take place, it can be used to study the adsorption in TiO2 gels developed in our lab.

EPFL2006

Adsorptive Removal of Pb(II) and As(V) from Aqueous Solution by PVDF/HMO Ultrafiltration Mixed Matrix Membrane

Younes Lucas Seghrouchni

Lead and arsenic are among the designated chemicals of major concern by the World Health Organization, they affect millions of people worldwide with both acute and chronic effects on human health. In the current study, mixed matrix membranes (MMMs) were fabricated using polyvinylidene fluoride (PVDF) for the matrix and hydrous manganese dioxide nanoparticles to remove lead, Pb(II), and arsenic, As(V), form water. The objectives of the study were to fabricate membrane with HMO:PVDF ratios from 0 to 1 and to characterize their adsorption properties on the two metals and their filtration performances. The HMO nanoparticles were synthesized using manganese sulfate monohydrate and potassium permanganate. The membranes were fabricated using phase inversion, a dope solution was prepared with HMO:PVDF ratios between 0 and 1, NMP as a solvent at an NMP:PVDF ratio of 5.57 and PVP at a PVP:PVDF ratio of 0.1 to increase the permeance of the membranes. The dope solution was casted and then soaked in a water coagulation bath for phase inversion. The structure of the nanoparticles was observed using TEM, and the structure of the membranes was described using SEM. The adsorption tests assessed the adsorption capacity, the adsorption kinetic and the effect of the pH on the adsorption capacity for the two metals. The concentration in the samples was measured with ICP-OES. A FTIR analysis was performed as a proof of adsorption. The tests that were run to assess the filtration performance of the membranes were the following ones: pure water permeance test, hydrophilicity test, surface analysis using XPS, pore size with AFM and finally filtration capacity on lead and arsenic. The HMO particles that were produced had sizes in the nanometer range and were elongated, which provided them a large surface-to-volume ratio. The membranes had asymmetric structures and the membrane with large HMO ratios had the surface of their pores covered uniformly with HMO particles. The adsorption capacities of pure HMO particles were 36 [mg/g] for arsenic and 283 [mg/g] for lead. The adsorption capacity of the membranes with an HMO:PVDF ratio of 1 was 11 [mg/g] for arsenic and 146 [mg/g] for lead. The Freundlich isotherm was used to describe the adsorption capacity of the membranes for both lead and arsenic. The adsorption kinetic was described by a pseudo-second order kinetic model for arsenic and the results were not significant enough the assess the adsorption kinetic model for lead. The equilibrium was almost reached in 30 minutes for the adsorption of the two metals on pure HMO. The adsorption capacity was enhanced with increasing pH for lead adsorption and it was the opposite for arsenic adsorption. The sensitivity to the pH was higher for lead compared to arsenic and this sensitivity to the pH could be used to regenerate the membrane in case of lead adsorption. The average permeance of the membranes was around 1500 [L/m2h bar], the pore sizes were in the ultrafiltration range, between 41 [nm] and 70 [nm] and the membranes were in the hydrophilic range, with an average contact angle of 69 [°]. The HMO ratio in the membranes had a limited impact on these three parameters. The filtration capacity on arsenic was too low to remove arsenic at ppb concentrations and the results of this test on lead were not significant enough to be interpreted.

2018