Julien Reboul

Direct Carbonization of Al-Based Porous Coordination Polymer for Synthesis of Nanoporous Carbon

Nanoporous carbon (NPC) is prepared by direct carbonization of Al-based porous coordination polymers (Al-PCP). By applying the appropriate carbonization temperature, both high surface area and large pore volume are realized for the first time. Our NPC shows much higher porosity than other carbon materials (such as activated carbons and mesoporous carbons). This new type of carbon material exhibits superior sensing capabilities toward toxic aromatic substances.

Synthesis of Prussian Blue Nanoparticles with a Hollow Interior by Controlled Chemical Etching

Hollow particles, an important class of materials with large internal cavities and thin shells, present a wide range of potential applications, such as energy storage, chemical catalysis, photonics, and biomedical carriers. The properties of hollow particles are strongly affected by the compositions and exquisite nanostructures of the shell regions. Many efforts have been made to control these parameters. Recently, hollow particles with nanoporous shells have attracted great interest because the large pore volumes and high surface areas provided by the nanoporous shells show large storage capacity and allow guest species to pass easily into the internal cavity. For instance, metal oxide hollow particles present a superior lithium storage capacity and good cycle performance, 8] which could improve gas sensitivity and catalytic performance 10] in other applications. Inspired by the superiority of nanoporous shells, the creation of microporous crystal shells with outstanding properties is also expected. Porous coordination polymers (PCPs) (or metal–organic frameworks, MOFs) and zeolites are representative microporous crystals. Having adjustable porosity and properties, microporous crystals show great potential in applications such as separation, catalysis, adsorption, and gas storage. 13] To date, however, there have been no reports on the successful synthesis of uniformly nanosized hollow particles with microporous crystalline shells. 15] Very few reports on microporous zeolite and PCP hollow particles have been published, and several problems have been encountered. A major problem is that the synthesized hollow particles are very large and have a broad size distribution. Considering their practical use in various catalysis reaction processes, uniformly sized hollow particles are ideal because they can densely fill reactors or columns. Another problem is that the microporous crystallinity in the shells decreases seriously during the formation process (that is, amorphous regions are formed in the shells), causing a loss of thermal stability, acidic sites, and surface area. Therefore, the development of a general method of synthesizing uniformly nanosized hollow particles with highly crystalline microporous shells is in demand. Herein, we present a facile route to the fabrication of uniform-sized Prussian blue (PB) hollow particles by utilizing a controlled self-etching reaction in the presence of PVP. PB crystals consisting of metal ions coordinated by CN bridges are very typical coordination polymers with a high surface area, showing excellent properties in many applications such as catalysis, sensors, molecular magnets, gas storage, and bioimaging. The critical point in our procedure is the selection of PB mesocrystals as a starting material. PB mesocrystals are formed by the aggregation of PB nanocrystals in an oriented way, thereby showing single-crystal-like behavior. Through small pores (or defects) in the aggregated PB nanocrystals, the etching solution can be diffused into the core of the mesocrystals. We succeeded in the formation of an interior hollow cavity with the retention of the original PB crystallinity. Although a few attempts to prepare PB hollow structures have been reported, the obtained shells were amorphous or poorly crystalline, with large organic impurities. Such hollow particles cannot show high surface areas and good magnetic responses. Two types of PB mesocrystals with different particle sizes were used as starting materials (details regarding the synthetic conditions are given in the Experimental Section). SEM images indicated that the particle-size distributions of the original PB mesocrystals were very narrow and their average diameters were around 110 nm (Figure 1a) and 190 nm (Supporting Information, Figure S1a). From highly magnified SEM images (insets of Figure 1 a; Supporting Information, Figure S1a), very rough surfaces were observed at the edges and corners of the cubes, suggesting that the cube shapes were created by the aggregation of small PB nano[*] Dr. M. Hu, Dr. Y. Nemoto, Prof. Dr. Y. Yamauchi World Premier International (WPI) Research Center for Materials Nanoarchitectonics (MANA) National Institute for Materials Science (NIMS) 1-1 Namiki, Tsukuba, Ibaraki 305-0044 (Japan) E-mail: yamauchi.yusuke@nims.go.jp

Integration of porous coordination polymers and gold nanorods into core-shell mesoscopic composites toward light-induced molecular release.

Besides conventional approaches for regulating in-coming molecules for gas storage, separation, or molecular sensing, the control of molecular release from the pores is a prerequisite for extending the range of their application, such as drug delivery. Herein, we report the fabrication of a new porous coordination polymer (PCP)-based composite consisting of a gold nanorod (GNR) used as an optical switch and PCP crystals for controlled molecular release using light irradiation as an external trigger. The delicate core-shell structures of this new platform, composed of an individual GNR core and an aluminum-based PCP shell, were achieved by the selective deposition of an aluminum precursor onto the surface of GNR followed by the replication of the precursor into aluminum-based PCPs. The mesoscopic structure was characterized by electron microscopy, energy dispersive X-ray elemental mapping, and sorption experiments. Combination at the nanoscale of the high storage capacity of PCPs with the photothermal properties of GNRs resulted in the implementation of unique motion-induced molecular release, triggered by the highly efficient conversion of optical energy into heat that occurs when the GNRs are irradiated into their plasmon band. Temporal control of the molecular release was demonstrated with anthracene as a guest molecule and fluorescent probe by means of fluorescence spectroscopy.

Combining UV Lithography and an Imprinting Technique for Patterning Metal‐Organic Frameworks

Thin metal-organic framework (MOF) films are patterned using UV lithography and an imprinting technique. A UV lithographed SU-8 film is imprinted onto a film of MOF powder forming a 2D MOF patterned film. This straightforward method can be applied to most MOF materials, is versatile, cheap, and potentially useful for commercial applications such as lab-on-a-chip type devices.

Crystal morphology-directed framework orientation in porous coordination polymer films and freestanding membranes via Langmuir–Blodgettry

Porous coordination polymers (PCPs), with their ordered nanoporous systems and large surface areas, are very attractive for numerous applications that involve controlled molecular transport properties. To fully exploit their potential, a straightforward processing method to deposit the PCP crystals on various substrates and to create freestanding membranes with a controlled pore orientation is highly desirable. Here, we report a strategy to self-assemble PCP crystals into two-dimensional monolayers using Langmuir–Blodgettry. This approach allows the deposition on various substrates over several square centimeters, uniformly and with controllable density of the crystals. In addition we show that by controlling the morphology of the crystalline building blocks we can program their orientation on the substrates. Using a copper grid as the substrate, these assemblies can also be fabricated as freestanding sheets. This approach represents a very simple and scalable processing method to translate the orientation of the channel network from the individual crystal to the macroscopic scale, and can help to incorporate this interesting class of materials within advanced hierarchical systems.

Trapping of a Spatial Transient State During the Framework Transformation of a Porous Coordination Polymer

Structural transformability accompanied by molecular accommodation is a distinguished feature of porous coordination polymers (PCPs) among porous materials. Conventional X-ray crystallography allows for the determination of each structural phase emerged during transformation. However, the propagation mechanism of transformation through an entire crystal still remains in question. Here we elucidate the structural nature of the spatial transient state, in which two different but correlated framework structures, an original phase and a deformed phase, simultaneously exist in one crystal. The deformed phase is distinctively generated only at the crystal surface region by introducing large guest molecules, while the remaining part of crystal containing small molecules maintains the original phase. By means of grazing incidence diffraction techniques we determine that the framework is sheared with sharing one edge of the original primitive cubic structure, leading to the formation of crystal domains with four mirror image relationships.

Reductive coordination replication of V2O5 sacrificial macrostructures into vanadium-based porous coordination polymers

Vanadium-based porous coordination polymers (or metal–organic frameworks) possess both porous and electronic properties, which make these new materials appealing for applications in molecular separation, sensing and heterogeneous catalysis. Their integration into systems that fully exploit their intrinsic properties requires versatile methods allowing assembly of the PCP crystals into well-defined films, patterns, fibers or the formation of heterostructures. In this contribution, polycrystalline macrostructures and heterostructures made of [V(OH)ndc]n (ndc = 1,4-naphthalenedicarboxylate) PCP crystals were synthesized through a dissolution–recrystallization process, so-called coordination replication, where a pre-shaped V2O5 sacrificial phase was replaced by well-intergrown PCP crystals in the presence of H2ndc as an organic linker and under a reductive environment. In this process, V2O5 acts both as the metal source and as the template that provides the shape to the resulting mesoscopic polycrystalline architecture. Ascorbic acid, acting as the reducing agent, both promotes the dissolution of the sacrificial V2O5 phase and provides the VIII species required for the construction of the [V(OH)ndc]n framework. Two-dimensional patterns were successfully synthesized by applying this procedure.

L-Glutamic acid release from a series of aluminum-based isoreticular porous coordination polymers

We investigated the encapsulation of bioactive molecules such as l-glutamic acid (Glu) into a series of porous coordination polymers (PCPs) based on aluminum hydroxy dicarboxylates [Al(OH)(L)]n (L = dicarboxylate ligand) and the molecular release therefrom. The use of 2,6-naphthalene dicarboxylate (2,6-ndc), 1,4-benzene dicarboxylate (1,4-bdc) and 1,4-naphthalene dicarboxylate (1,4-ndc) as ligands allows us to systematically tune the pore size and the flexibility of frameworks while keeping the same topology and thus to investigate the effect of those parameters upon both adsorption and release of Glu. We revealed the impact of zwitterionic nature of Glu upon loading efficiency; optimal loading pH was shown to be that for which Glu bears both positive and negative charges. Whereas the loading capacity of PCPs is governed by the pore size ([Al(OH)(2,6-ndc)]n > [Al(OH)(1,4-bdc)]n > [Al(OH)(1,4-ndc)]n), the adsorption isotherm clearly revealed that small or flexible pores induce the stronger Glu-PCP interaction. The release experiments of Glu from PCPs in a physiological media (pH = 7.4, 37 °C) demonstrated the exceptional stabilization of Glu within [Al(OH)(1,4-bdc)]n, compared to those within the other frameworks; whereas the rigid frameworks of [Al(OH)(2,6-ndc)]n and [Al(OH)(1,4-ndc)]n spontaneously released almost the entire Glu contents within 10 h, 70% of Glu loaded within [Al(OH)(1,4-bdc)]n still remained therein over 24 h. Interestingly, the burst release of Glu was triggered by increasing temperature up to 80 °C, at which the framework changed its structure from a closed phase to the open phase.