Opening of an Accessible Microporosity in an Otherwise Nonporous Metal–Organic Framework by Polymeric Guests

The development of highly porous metal–organic frameworks (MOFs) is greatly sought after, due to their wide range of applications. As an alternative to the development of new structures, we propose to obtain new stable configurations for flexible MOFs by insertion of polymeric guests. The guests prevent the otherwise spontaneous closing of the host frameworks and result in stable opened forms. Introduced at a fraction of the maximal capacity, polymer chains cause an opening of the occupied nanochannels, and because of the MOF reticular stiffness, this opening is propagated to the neighboring nanochannels that become accessible for adsorption. Composites were obtained by in situ polymerization of vinyl monomers in the nanochannels of an otherwise nonporous MOF, resulting in homogeneously loaded materials with a significant increase of porosity (<i>S</i>_BET = 920 m²/g). In addition, by limiting the accessible configurations for the framework and forbidding the formation of a reactive intermediate, the polymeric guest prevented the thermal degradation of the host MOF even at very low loading (as low as 3 wt %) and increased its stability domain by more than 200 °C

Mass Transport Properties of Silicified Graphite Felt Electrodes

Mass transport properties of electrodes prepared from graphite felt, as such and after silicification, have been studied using cyclic voltammetry. Within the graphite felt, the mass transport of a probe changes with decreasing scan rate, from a radial diffusion around fibers to a regime that is analogous to “thin-layer” systems. Furthermore, unlike classical “thin-layer” systems, the volume comprised in the felt is macroscopic (resulting in high current densities), while the time required to consume all diffusive species remains in the 1 min range. Silicification of graphite felt does not impact on the mass transport of the negatively charged molecular probe Fe­(CN)₆^3– but significantly slows mass transport of positively charged Ru­(NH₃)₆³⁺. In the latter case, a parallel decrease of peak current intensity reflects limited mobility of the probe due to its strong interaction with the surface of the pore walls. These data provide important information for the optimization of the working conditions of these electrodes for the design of biosensors and biofuel cells

Nanostructuration of PEDOT in Porous Coordination Polymers for Tunable Porosity and Conductivity

A series of conductive porous composites were obtained by the polymerization of 3,4-ethylenedioxythiophene (EDOT) in the cavities of MIL–101­(Cr). By controlling the amount of EDOT loaded into the host framework, it was possible to modulate the conductivity as well as the porosity of the composite. This approach yields materials with a reasonable electronic conductivity (1.1 × 10⁻³ S·cm^–1) while maintaining high porosity (<i>S</i>_BET = 803 m²/g). This serves as a promising strategy for obtaining highly nanotextured conductive polymers with very high accessibility for small gas molecules, which are beneficial to the fabrication of a chemiresistive sensor for the detection of NO₂

DWCNT-Doped Silica Gel Exhibiting Both Ionic and Electronic Conductivities

Silica gels doped with double-walled carbon nanotubes (DWCNTs) were prepared using an aqueous sol–gel route in mild conditions (neutral pH, room temperature). The wet gels exhibited both ionic and electronic conduction. Electrochemical impedance spectroscopy was used to study these two different conduction pathways that prevail at different characteristic time scales. The ionic conduction in the silica network was found to be independent of the DWCNT-doping rate. The electronic conduction through the DWCNT network was found to occur above a critical concentration (0.175 wt %) corresponding to nanotube percolation threshold. The highest content in DWCNTs (0.8 wt %) exhibited a conductivity of 0.05 S/m. Furthermore, the DWCNTs network was found to evolve even after the macroscopic solidification of the gel, suggesting a reorganization of the DWCNTs at the molecular level. This phenomenon could be attributed to the polarization effect of the electrode and was confirmed by Raman spectroscopy studies. Such materials can be useful for the design of sensors incorporating electroactive chemical or biological species

Core–Shell Silver Nanoparticles in Endodontic Disinfection Solutions Enable Long-Term Antimicrobial Effect on Oral Biofilms

To achieve effective long-term disinfection of the root canals, we synthesized core–shell silver nanoparticles (AgNPs@SiO₂) and used them to develop two irrigation solutions containing sodium phytate (SP) and ethylene glycol-bis­(β-aminoethyl ether)<i>N</i>,<i>N</i>,<i>N</i>′,<i>N</i>′-tetraacetic acid (EGTA), respectively. <i>Ex vivo</i> studies with instrumented root canals revealed that the developed irrigation solutions can effectively remove the smear layer from the dentinal surfaces. Further <i>in vitro</i> experiments with single- and multispecies biofilms demonstrated for the first time that AgNPs@SiO₂-based irrigation solutions possess excellent antimicrobial activities for at least 7 days, whereas the bare AgNPs lose the activity almost immediately and do not show any antibacterial activity after 2 days. The long-term antimicrobial activity exhibited by AgNPs@SiO₂ solutions can be attributed to the sustainable availability of soluble silver, even after 7 days. Both solutions showed lower cytotoxicity toward human gingival fibroblasts compared to the conventionally used solution (3% NaOCl and 17% EDTA). Irrigation solutions containing AgNP@SiO₂ may therefore be highly promising for applications needing a long-term antimicrobial effect