Surface Properties and Chemical Constitution as Crucial Parameters for the Sorption Properties of Ionosilicas: The Case of Chromate Adsorption

We report ionosilicas with different chemistries, textures, and morphologies and their use as adsorbents for chromium­(VI). All studied materials are highly efficient anion exchange materials with adsorption capacities between 1.6 and 2.6 mmol/g. The ion exchange capacity of the materials reaches up to 91% of the theoretical value, that is, the molar amount of ionic groups immobilized within the material, indicating a very high accessibility of the organo-ionic groups. Noticeable differences were found regarding the ion exchange properties in terms of capacity and kinetics according to the used material, in particular, its porosity. High specific surface areas favor the adsorption process and result in high adsorption capacity. However, even a nonporous material displays high adsorption capacity of 1.7 mmol/g. This result can be attributed to the high hydrophilicity of ionosilicas that favors diffusion and mass transfer throughout the material. The adsorption kinetics are fast, as 80–90% of the adsorption capacity is reached after ∼10 min. Finally, isotherm titration calorimetry evidences the influence of the constitution of the cationic group on the displacement enthalpy, in relationship with the steric hindrance of the alkyl groups that surround the cationic center

Tuning the Interfacial Properties of Mesoporous Ionosilicas: Effect of Cationic Precursor and Counter Anion

Ionosilica are mesoporous silica-based hybrid materials containing covalently bound ionic groups. The mixed ionic mineral nature confers particular properties to these materials. Here, we focus on the tailoring of the interfacial properties of ionosilicas. Three materials were synthesized from three different oligosilylated ammonium precursors. Furthermore, anion exchange allowed replacing the halide in the parent ionosilicas by more hydrophobic anions, e.g., thiocyanate (SCN^–) and bis­(trifluoromethane)­sulfonimide (NTf₂^–). Both the constitution of the ammonium substructure of the precursor and the nature of the counteranion allow controlling the interfacial properties in terms of hydrophilicity and affinity toward different types of solvents. Although all studied ionosilica are highly hydrophilic mesoporous materials, significant differences and clear trends could be observed. As shown via competitive 1-butanol adsorption measurements in the liquid phase and solvent vapor adsorption from the gas phase, the interfacial properties of ionosilicas can be fine-tuned either by the use of more hydrophobic ammonium precursors or the incorporation of hydrophobic anions. We therefore show that ionosilicas combine high porosity, regular architecture on the mesoscopic level with an unmatched chemical versatility, induced by the high variability and the high number of homogeneously distributed ionic species. Ionosilicas appear as highly adaptable materials and can be considered as “<i>designer materials</i>”, which are interesting for applications in catalysis, sorption, and separation

Confinement Effects on the Ionic Liquid Dynamics in Ionosilica Ionogels: Impact of the Ionosilica Nature and the Host/Guest Ratio

Ionosilica ionogels have been lately introduced as emerging all-ionic designer materials. They consist of an ionic liquid (IL) guest trapped within a solid ionosilica support host. In this work, we investigate the influence of the (i) ionosilica nature and (ii) the ionosilica/IL ratio on the mobility of the confined IL. We report the elaboration of various ionosilica ionogels via a nonhydrolytic sol–gel process, using namely tris­(3-(trimethoxysilyl)­propyl)­amine (TTA), methyl-tris­(3-(trimethoxysilyl)­propyl)­ammonium iodide (MTTA), and tetrakis­(3-(trimethoxysilyl)-propyl)­ammonium iodide (TKTA) as ionosilica precursors, with the IL butyl-methyl imidazolium bis­(trifluoromethanesulfonyl)­imide ([BMIM] TFSI). Various ionogels were prepared from different ratios between the ionosilica host and the IL guest. The host/guest interactions, i.e., the change in the conformational contribution of the IL counter-anion, were explored by means of Raman spectroscopy. In addition, the transport properties of the confined species were probed via spin echo solid-state NMR experiments and Complex Impedance Spectroscopy (CIS) measurements. Raman experiments revealed different conformational equilibrium for the TFSI anion in the various ionosilica ionogels, with an increase in the cisoid form compared to the bulk IL due to confinement effects. The TFSI anion seems to experience different degrees of confinement and thus different interactions with the ionosilica scaffold as a function of the investigated parameters. Concomitantly, the 1H spin echo NMR and CIS measurements revealed a significantly higher ionic mobility in the materials synthesized from the tris-trialkoxysilylated ammonium precursor compared to the one synthesized from the tetra-trialkoxysilylated ammonium precursor. These results may reflect stronger host–guest interactions in the latter case related to the higher degree of the network reticulation. All these techniques give concordant results and highlight an effect of the chemical constitution of the ionosilica scaffold and the amount of confined IL on its dynamics within the network

Eu³⁺@Organo-Si(HIPE) Macro-Mesocellular Hybrid Foams Generation: Syntheses, Characterizations, and Photonic Properties

The elaboration of organosilica-based hybrid monoliths exhibiting a hierarchically structured bimodal porous structure with chelating functionality have been synthesized under interplay between high internal phase emulsion (HIPE) and lyotropic mesophases. For the first time grafted Eu3+@gβ-diketone-Si(HIPE) and Eu3+@gmalonamide-Si(HIPE) hybrid foams have been synthesized while a related Eu3+@β-diketone-Si(HIPE) material has been obtained under a one-step co-condensation process. The loading of monoliths with lanthanides was performed by impregnation of an europium(III) salt in solution. The resulting materials have been thoroughly characterized via a large set of techniques including scanning electron microscopy (SEM), transmission electron microscopy (TEM), small angle X-ray scattering (SAXS), mercury porosimetry, nitrogen sorption isotherms, Fourier transform infrared (FTIR) spectroscopy, and 29Si and 13C magic angle spinning nuclear magnetic resonance (MAS NMR). This new series of luminescent Eu3+ containing Organo-Si(HIPE) materials has a large potential of promising applications in catalysis, optics, sensors, chromatographic supports, and so forth. For the first time, optical properties of these versatile materials with macro- and microporosity have been addressed thorough their absorption and emission spectra along with their relaxation luminescence properties

Ionothermal Carbonization of Sugarcane Bagasse in 1‑Alkyl-3-methylimidazolium Ionic Liquids: Insights into the Role of the Chloroferrate Anion

We report the ionothermal carbonization (ITC) of lignocellulosic biomass in imidazolium tetrachloroferrate ionic liquids (ILs) as an advantageous approach for the preparation of nanostructured carbonaceous materials, namely, ionochars. In a previous study, we investigated the role of the imidazolium cation and demonstrated the possibility of controlling both the textural and morphological properties of ionochars by cation engineering. Although essential for providing intermediate Lewis acidity and relatively high thermal stability, the role of the chloroferrate anion is still open to debate. Herein, we investigated the ITC of sugarcane bagasse and its main component, cellulose, in 1-alkyl-3-methylimidazolium ILs with different chloroferrate anions. We identified anionic speciation and its impact on the properties of the IL by Raman spectroscopy, thermogravimetric analysis, and differential scanning calorimetry. The obtained ionochars were characterized by gas physisorption, electron microscopy, Raman spectroscopy, Fourier transform infrared (FTIR) spectroscopy, and 13C solid-state CP-MAS NMR spectroscopy. We show that the anionic species have a predominant impact on the textural and morphological properties of the ionochars

Hybrid Materials and Periodic Mesoporous Organosilicas Containing Covalently Bonded Organic Anion and Cation Featuring MCM-41 and SBA-15 Structure

We report the synthesis of a new trialkoxysilylated ionic liquid based on disilylated guanidinium and monosilylated sulfonimide species. This compound allowed the successful preparation of new periodic mesoporous organosilicas containing covalently anchored ion-pair through both organo-cationic and organo-anionic moieties which have never been reported up to now. Two classes of hybrid materials containing guanidinium−sulfonimide ion-pairs (IPs) have been synthesized. The first type of material was prepared by grafting the silylated IP onto both MCM-41-type and SBA-15-type silicas according to a surface sol−gel polymerization. The second class was synthesized following a one-pot sol−gel procedure using silylated IP and tetraethoxysilane as framework precursors. These latter materials correspond to so-called periodic mesoporous organosilicas (PMOs) and gave “organo-ionically” modified MCM-41 and SBA-15 related solids. The materials were characterized by a series of techniques including XRD, nitrogen sorption, solid-state NMR, FTIR, transmission electronic microscopy, and elemental analysis. The highest structural regularity in terms of pore size distribution and channel size homogeneity was observed for IP-PMOs possessing SBA-15-type architecture due to an enhanced trialkoxysilylated IP precursor/surfactant interaction. Solvatochromic experiments with Reichardt’s dye showed good accessibility of the silica-supported ion-pair and suggested the formation of monophasic materials