Prediction of Isoelectric Point of Manganese and Cobalt Lamellar Oxides: Application to Controlled Synthesis of Mixed Oxides

Abstract

To design novel layered materials, bottom-up strategy is very promising. It consists of (1) synthesizing various layered oxides, (2) exfoliating them, then (3) restacking them in a controlled way. The last step is based on electrostatic interactions between different layered oxides and is difficult to control. The aim of this study is to facilitate this step by predicting the isoelectric point (IEP) of exfoliated materials. The Multisite Complexation model (MUSIC) was used for this objective and was shown to be able to predict IEP from the mean oxidation state of the metal in the (hydr)oxides, as the main parameter. Moreover, the effect of exfoliation on IEP has also been calculated. Starting from platelets with a high basal surface area over total surface area, we show that the exfoliation process has no impact on calculated IEP value, as verified with experiments. Moreover, the restacked materials containing different monometallic (hydr)oxide layers also have an IEP consistent with values calculated with the model. This study proves that MUSIC model is a useful tool to predict IEP of various complex metal oxides and hydroxides.

Surface Reactivity and Surface Characterization of the Layered β(III)-CoOOH Material: an Experimental and Computational Study

“…Figure reports the SEM and transmission electron microscopy (TEM) images obtained on uncut samples (Figure a–c) and cut sample with the cross polisher of β­(III)-CoOOH (Figure d). The β­(III)-CoOOH material consists of well-defined hexagonal platelets of about 60–100 nm length and 10 nm thickness. ,, The low thickness of those particles corresponds to the coherent domain size, whereas the length coincides with 2 or 3 crystallites merged together. The platelets coalesce to form aggregates of various sizes, from few to several tens of micrometers (Figure a,b).…”

“…The β(III)-CoOOH material consists of well-defined hexagonal platelets of about 60−100 nm length and 10 nm thickness. 8,16,39 The low thickness of those particles corresponds to the coherent domain size, whereas the length coincides with 2 or 3 crystallites merged together. The platelets coalesce to form aggregates of various sizes, from few to several tens of micrometers (Figure 2a,b).…”

“…In this work, a focus is made on the layered β­(III)-cobalt oxyhydroxide phase (H w + Na y + Co x + O 2 n (H 2 O)) which possesses interesting characteristics for pseudo-capacitive electrode materials. Indeed, depending on the stoichiometry of H, which is linked to the amount of Co 4+ , this material has an excellent electronic conductivity (10 –3 up to 1 S cm –1 ) compared to most of the other pseudo-capacitive oxides and hydroxides, good stability in aqueous electrolytes, and can easily be synthesized as nanocrystalline powder with an SSA higher than 100 m 2 /g. − However, the experimental pseudo-capacitive response of β­(III)-cobalt oxyhydroxide, far below the theoretical expectation, leads us to perform a multiscale study to investigate in detail the reactivity of the different surfaces, the nature of the active sites and to identify the mechanisms involved in the charge storage. , To do this, the adsorption of gas such as SO 2 was carried out to probe the nature of the active sites. X-ray photoelectron spectroscopy (XPS) was used to characterize the surface in terms of electronic structure and composition of the material and also to determine the adsorption mode of SO 2 (redox and/or acid/base).…”

MUSIC Speciation of γ-Al2O3 at the Solid Liquid Interface: How DFT Calculations Can Help with Amorphous and Poorly Crystalline Materials

“…The so-called multi site complexation (MUSIC) model from Hiemstra and co-workers (see refs , for the original model and refs , for refinements of this work) allows for a prediction of the protonation constant (p K a ) of surface OH groups on metal (hydr)­oxides based on atomic scale information, mainly the number of bonds around surface species and their effective charge. Thus, MUSIC-based p K a constants in conjunction with an electrical double layer model have been successfully used to simulate the surface charge of complex metal oxides in water . The bottleneck for the application of this approach to an amorphous or poorly crystalline material is the lack of information about the structural parameters of the involved surfaces sites.…”

“…Thus, MUSIC-based pK a constants in conjunction with an electrical double layer model have been successfully used to simulate the surface charge of complex metal oxides in water. 19 The bottleneck for the application of this approach to an amorphous or poorly crystalline material is the lack of information about the structural parameters of the involved surfaces sites. In the literature, this problem has been resolved by a so-called pragmatic approach, where the authors described the mean surface reactivity with only one surface site (>SO 1/2− in its deprotonated state) and one equilibrium reaction (>SO 1/2− + H + = >SOH 1/2+ ) with a pK equal to the point of zero charge (PZC).…”