For one part, calculations are done at the French National Supercomputers GENCI on the CINES/IDRIS supercomputer. In addition, the IFPEN supercomputer (BULLxB510) is also used. Electronic calculations are performed at the density functional theory (DFT) level, for which IFPEN, LAMBE and IRCP are recognized experts for their applications in oxide surfaces, interfaces and liquids either with the CP2K and VASP packages. Born-Oppenheimer DFT-based AIMD simulations at finite temperature are performed for extracting pKa values and adsorption enthalpies.
Simulation cell for α-alumina/water interface
ENER110, Bull 110 Tflops
IFP Energies nouvelles
The electrokinetic analysis of the streaming potential enables the automatic determination of zeta potential on macroscopic planar surfaces. This is done with a commercial set-up available from Anton Parr (SurPASS), which allows one to study, not only surface potentials, but also surface adsorption processes through the time-resolved measurements of the streaming potential during the adsorption process. This commercial apparatus bas been acquired by the LRS through the ANR funding.
Anton Parr Surpass analyzer
Atomic force microscopy (AFM) is used to determine the local charges on a surface in electrolyte solution. This is performed by probing the interaction between the AFM tip and the surface by recording force-distance curves, while varying physicochemical parameters of the medium (pH, ionic strength, temperature). The uncertainties related to (i) imperfections in geometry of the tip, (ii) locating zero distance position and (ii) the contribution of “non-electrostatic forces”, including hydration, steric, etc., can be better controlled by using a colloidal probe. This is obtained by attaching a colloidal particle (few µm in diameter) to a cantilever with an appropriate spring constant. The experimental data are analyzed using the DLVO theory.
Grazing Incidence-EXAFS (GI-EXAFS) measurements (at European synchrotrons) will be performed to study the surface speciation of CoII in the absence and in the presence of organic additives on single α-Al2O3 crystals. In addition, polarization dependent measurements help to constrain the orientation of adsorbates. Moreover, GI-EXAFS data are often simpler to interpret because the use of a hydrated single crystal sorbent with known surface structure imposes constraints on the types of possible surface sites.
Attenuated Total Reflection Infrared (ATR-IR) measurements are performed with a a Thermo Scientific Nicolet 6700 with a MCT detector and horizontal single reflection ZnSe/diamond Pike accessory. Two types of samples can be probed: either an equilibrated concentrated suspension spread on the ATR crystal, or film of particles in contact with a solution containing the adsorbate. This technique is adequate to probe the interactions of the organic ligands with alumina surface, or Co ions in the case of the formation of a ternary surface complex. This technique is adequate to probe the interactions of the organic ligands with alumina surface, or Co ions in the case of the formation of a ternary surface complex. The evolution of the surface charge vs. pH can also be studied by measuring the intensity of ions electrostatically adsorbed, following the STIRS (surface titration by internal reflection spectroscopy) protocol developed by Dobson et al. (Langmuir, 1997).
Second Harmonic Generation (SHG) experiments are performed through a collaborative convention between ICGM and the Marcoule Institute for Separative Chemistry (ICSM, UMR 5257). The measurements are done with an oblique incidence through the liquid phase and are collected in reflection onto the solid surface. The SHG light is detected with a water-cooled CCD camera (PIXIS 400, Princeton Instrument) placed after a spectrometer (ACTON SP 2300, Princeton Instrument). The input polarization angle is selected with a rotating half-wave plate to vary the polarization of the incident beam. The solution pH is continuously monitored and measured using a microelectrode.
Calorimetry measurements will be performed by ICGM in order to perform surface characterization. The key point in the SLIMCAT project is the valuation adsorption enthalpies. The adsorption at the PZC leads to rather small amount of adsorbed species, thus leading to small measured heat values which are thereby difficult to be detected. It is worth stressing that with the recent progress in ultra-sensitive heat flow measurements and the use of a wide variety of accessories to control the experimental conditions, it is now possible to study the adsorption phenomena in liquid phase with increased sensitivity and low detection limits as provided by TAM III thermostat (TA Waters) (50 nW signal resolution). Three nanocalorimeters equipped with titration cells will be used in the SLIMCAT project, to evaluate cobalt and additives adsorption enthalpy, together with flow calorimeter, in liquid or in gas phase, to determine the hydrophobic-hydrophilic balance and access number and strengths of acid sites respectively. Immersion will also be tested to evaluate polar-apolar and acid-base components of the surface energy. Up to now, only 2 labs in France have access to such a complete set of calorimeters (5 types of calorimeters, of which 4 will be devoted for the SLIMCAT project).
|TAM III thermostat and Nanocalorimeter - TA Instrument||
Flow microcalorimeter (gas or liquid) - Microscal