Justyna Florek

On the origin of the high capacitance of carbon derived from seaweed with an apparently low surface area

Low surface area carbon materials, derived from pyrolyzing biomass or polymers, often possess high areal capacitances. However, the well-accepted pseudocapacitance introduced by heteroatoms could not explain this phenomenon without doubt. In order to explore the nature of the energy storage mechanism in these low surface area carbon materials, we prepared a series of laver-based carbon materials by regulating the heteroatom contents and investigated their electrochemical performance. Combining the results of advanced pore structure analyses and electrochemical measurements, we disclose that the presence of ultramicropores, which could not be probed by adsorbates such as nitrogen gas or argon, but are accessible to carbon dioxide or electrolyte ions, plays a most dominant role in the high capacitance of low surface area carbon materials. In this contribution, the previously accepted viewpoint that the capacitance is mainly derived from heteroatoms undergoing Faradaic reactions is challenged.

Selective recovery of rare earth elements using chelating ligands grafted on mesoporous surfaces

Nowadays, rare earth elements (REEs) and their compounds are critical for the rapidly growing advanced technology sectors and clean energy demands. However, their separation and purification still remain challenging. Among different extracting agents used for REE separation, the diglycolamide (DGA)-based materials have attracted increasing attention as one of the most effective extracting agents. In this contribution, a series of new and element-selective sorbents were generated through derivatisation of the diglycolamide ligand (DGA), grafted to mesoporous silica and tested for the separation of rare earth elements. It is shown that, by tuning the ligand bite angle and its environment, it is possible to improve the selectivity towards specific rare earth elements.

Support effects in rare earth element separation using diglycolamide-functionalized mesoporous silica

Due to the rapidly increasing energy demand and growing production of high technology devices, the development of new sequestration materials for rare earth elements (REEs) has become critical. Nowadays, REEs play a predominant role as supplies for the transition to cleaner energy and production of economically important modern devices, such as wind turbines (Pr, Nd, Sm, Dy), car catalysts (Ce) or hybrid vehicles (Dy, La, Nd). However, for all these applications, only a very pure and isolated form of element can be used. While several methods have been developed for REE extraction, such as liquid–liquid or liquid–solid extraction methods, the selective separation and purification of REEs still remain challenging. Industrially, the separation/purification process of REEs involves several liquid–liquid extraction (LLE) cycles. As a consequence, a large volume of solvents, time and labor are required. Moreover, LLE usually generates huge amounts of waste that is often environmentally harmful. Therefore, in our laboratories, we have recently focused on developing greener alternatives for the REE extraction process using solid extraction systems. In the present study, we use a tailored-made solid phase (SPE) extraction system, where appropriately modified mesoporous silica supports (i.e., SBA-15, SBA-16 and MCM-41) are used and compared as sorbents. As evidenced from our results, DGA-functionalized porous sorbents are characterized by a pronounced selectivity towards mid-size elements and high stability under the extraction conditions tested. Moreover, these sorbents show very fast REE uptake, in about 5 min. Furthermore, we focus our studies on elucidating the influence of the pore structure, pore size and pore connectivity of different silica materials on the static and dynamic extraction/purification of REEs.

A generalized method toward high dispersion of transition metals in large pore mesoporous metal oxide/silica hybrids

A series of transition metal acetylacetonates and acetates were used as precursors to generate high loadings of metal sites finely dispersed on SBA-15 silica. To achieve this, grafting of chelated transition metal precursors was performed directly to the surface of the as-synthesized SBA-15/P123 composite material. The thus-obtained metal/SBA-15 materials were studied by a variety of methods, e.g., elemental analysis, Fourier transform infrared spectroscopy (FTIR), powder X-ray diffraction (XRD), scanning electron microscopy (SEM), diffuse reflectance UV-visible spectroscopy (DR-UV-vis), X-ray photoelectron spectroscopy (XPS) and N2 physisorption measurements at -196 °C. From the results, the proposed functionalization method was found to be a highly tunable and reproducible strategy to disperse transition metal oxides in mesoporous silica materials. The results from elemental analysis of the modified materials confirmed that the amount of grafted species is a function of the initial concentration of precursor in the solution used for grafting. The chelated complexes were found to strongly interact with the silanol groups of the silica material, resulting in a ligand-exchange process, as corroborated by FTIR. However, different metal precursors showed distinct reactivity towards the surface of mesoporous silica, owing to differences in the stability of the complexes under the conditions used for grafting. DR-UV-vis and XPS analyses suggest that when the stability of a given precursor decreases, the grafting procedure can lead to the formation of small clusters of the metal oxide on the silica surface. XRD and SEM also show that grafting of lower stability complexes, such as Mn(acac)3, Cu(acetate)2 and VO(acac)2, on the silica surface can result in the formation of large crystals on the external surface of the SBA-15 particles. Nevertheless, it was established by XPS analysis that only a small percentage of the grafted species leads to the formation of bulk crystals while the remaining species are substituted into the silica framework. Obviously, a well-controlled and increased dispersion of the metal cations/oxides on the surface of highly porous silica materials is of great interest since these M(x)O(y)-SiO2 mixed oxides could demonstrate high catalytic activity in a large variety of reactions.

Functionalization of Mesoporous Carbon Materials for Selective Separation of Lanthanides under Acidic Conditions

New functional mesoporous carbon sorbents were successfully synthesized to overcome some issues of solid-liquid extraction (e.g., selectivity, extraction capacity, and reusability under acidic conditions) in production of pure lanthanides (Ln). Wet-oxidation technique was performed to increase the surface reactivity of pristine ordered mesoporous carbon (OMC), and, in a second step, a surface modification using diglycolamide-based (DGA-based) selective ligands toward Ln was performed. Two types of ligands were tested: the first contains a long spacer (e.g., between carbon support and chelating function), and the second has a shorter one. These materials have been characterized by X-ray photoelectron spectroscopy (XPS), low-angle X-ray diffraction (XRD), thermogravimetric analysis, nitrogen sorption, transmission electron microscopy (TEM), and scanning electron microscopy (SEM). These analyses confirmed that the carbon mesostructure was maintained after organo-functionalization of the surface and showed the covalent attachment of selective ligands. These new materials, and especially the system with a short spacer between the ligand and the surface, reveal unique Ln selectivity profiles with improved extraction performances for the recovery of lanthanides, in terms of both selectivity and adsorption capacity, and unprecedented stability under acidic conditions.

In vitro Dissolution, Cellular Membrane Permeability and Anti-Inflammatory Response of Resveratrol-Encapsulated Mesoporous Silica Nanoparticles

Sizing drugs down to the submicron and nanometer scale using nanoparticles has been extensively used in pharmaceutical industries to overcome the poor aqueous solubility of potential therapeutic agents. Here, we report the encapsulation and release of resveratrol, a promising anti-inflammatory and anticancer nutraceutical, from the mesopores of MCM-48-type silica nanospheres of various particle sizes, i.e., 90, 150, and 300 nm. Furthermore, the influence of the carrier pore size on drug solubility was also evaluated (3.5 vs 7 nm). From our results, it is observed that the saturated solubility could depend not only on the pore size but also on the particle size of the nanocarriers. Moreover, with our resveratrol-mesoporous silica nanoparticles formulation, we have observed that the permeability of resveratrol encapsulated in MCM-48 nanoparticles (90 nm) can be enhanced compared to a resveratrol suspension when tested through the human colon carcinoma cell monolayer (Caco-2). Using an in vitro NF-κB assay, we showed that resveratrol encapsulation did not alter its bioactivity and, at lower concentration, i.e., 5 μg mL-1, resveratrol encapsulation provided higher anti-inflammatory activity compared to both resveratrol suspension and solution. All combined, the reported results clearly highlight the potential of small size mesoporous silica nanoparticles as next generation nanocarriers for hydrophobic drugs and nutraceuticals.