The release of anthropogenic toxic pollutants into the atmosphere is a worldwide threat of growing concern. In this regard, it is possible to take advantage of the high versatility of MOFs materials ...in order to develop new technologies for environmental remediation purposes. Consequently, one of the main scientific challenges to be achieved in the field of MOF research should be to maximize the performance of these solids towards the sensing, capture and catalytic degradation of harmful gases and vapors by means of a rational control of size and reactivity of the pore walls that are directly accessible to guest molecules.
Tunable hydrophobicity: Efficient air filters for the protection against chemical warfare agents might be achieved by surface functionalization of the pores in robust metal–organic frameworks (MOFs) ...with fluoroalkyl residues and the precise control of their pore size (see picture). These MOFs capture harmful volatile organic compounds even under extremely moist conditions (80 % relative humidity).
We present the novel potential application of imine-based covalent organic frameworks (COFs), formed by the direct Schiff reaction between 1,3,5-tris(4-aminophenyl)benzene and ...1,3,5-benzenetricarbaldehyde building blocks in m-cresol or acetic acid, named RT-COF-1 or RT-COF-1Ac/RT-COF-1AcB. The post-synthetic treatment of RT-COF-1 with LiCl leads to the formation of LiCl@RT-COF-1. The ionic conductivity of this series of polyimine COFs has been characterized at variable temperature and humidity, using electrochemical impedance spectroscopy. LiCl@RT-COF-1 exhibits a conductivity value of 6.45 × 10–3 S cm–1 (at 313 K and 100% relative humidity) which is among the highest values so far reported in proton conduction for COFs. The mechanism of conduction has been determined using 1H and 7Li solid-state nuclear magnetic resonance spectroscopy. Interestingly, these materials, in the presence of controlled amounts of acetic acid and under pressure, show a remarkable processability that gives rise to quasi-transparent and flexible films showing in-plane structural order as confirmed by X-ray crystallography. Finally, we prove that these films are useful for the construction of proton exchange membrane fuel cells (PEMFC) reaching values up to 12.95 mW cm–2 and 53.1 mA cm–2 for maximum power and current density at 323 K, respectively.
The current technology of air‐filtration materials for protection against highly toxic chemicals, that is, chemical‐warfare agents, is mainly based on the broad and effective adsorptive properties of ...hydrophobic activated carbons. However, adsorption does not prevent these materials from behaving as secondary emitters once they are contaminated. Thus, the development of efficient self‐cleaning filters is of high interest. Herein, we report how we can take advantage of the improved phosphotriesterase catalytic activity of lithium alkoxide doped zirconium(IV) metal–organic framework (MOF) materials to develop advanced self‐detoxifying adsorbents of chemical‐warfare agents containing hydrolysable PF, PO, and CCl bonds. Moreover, we also show that it is possible to integrate these materials onto textiles, thereby combining air‐permeation properties of the textiles with the self‐detoxifying properties of the MOF material.
The silk of human kindness: Insertion of lithium alkoxides in zirconium metal–organic frameworks (MOF) which are then deposited on silk fibers gives rise to protective fabrics capable of self‐detoxifying chemical‐warfare agents. The fabrics combine the air‐permeation properties of the textiles with the highly active phosphotriesterase catalytic activity of the MOF for the hydrolysis of PF, PO, and CCl bonds.
This work describes synthesis at the nanoscale of the isoreticular metal–organic framework (MOF) series ZnBDP_X, based on the assembly of ZnII metal ions and the functionalized organic spacers ...1,4-bis(1H-pyrazol-4-yl)-2-X-benzene (H2BDP_X; X = H, NO2, NH2, OH). The colloidal stability of these systems was evaluated under different relevant intravenous and oral-simulated physiological conditions, showing that ZnBDP_OH nanoparticles exhibit good structural and colloidal stability probably because of the formation of a protein corona on their surface that prevents their aggregation. Furthermore, two antitumor drugs (mitroxantrone and Ru(p-cymene)Cl2(pta) (RAPTA-C) where pta = 1,3,5-triaza-7-phospaadamantane) were encapsulated within the pores of the ZnBDP_X series in order to investigate the effect of the framework functionalization on the incorporation/delivery of bioactive molecules. Thus, the loading capacity of both drugs within the ZnBDP_X series seems to directly depend on the surface area of the solids. Moreover, ligand functionalization significantly affects both the delivery kinetics and the total amount of released drug. In particular, ZnBDP_OH and ZnBDP_NH2 matrixes show a slower rate of delivery and higher percentage of release than ZnBDP_NO2 and ZnBDP_H systems. Additionally, RAPTA-C delivery from ZnBDP_OH is accompanied by a concomitant and progressive matrix degradation due to the higher polarity of the BPD_OH ligand, highlighting the impact of functionalization of the MOF cavities over the kinetics of delivery.
The ionic conductivity properties of the face‐centered cubic Ni8(OH)4(H2O)2(BDP_X)6 (H2BDP_X=1,4‐bis(pyrazol‐4‐yl)benzene‐4‐X with X=H (1), OH (2), NH2 (3)) metal–organic framework (MOF) systems as ...well as their post‐synthetically modified materials KNi8(OH)5(EtO)(BDP_X)5.5 (1@KOH, 3@KOH) and K3Ni8(OH)3(EtO)(BDP_O)5 (2@KOH), which contain missing‐linker defects, have been studied by variable temperature AC impedance spectroscopy. It should be noted that these modified materials exhibit up to four orders of magnitude increase in conductivity ‐values in comparison to pristine 1–3 systems. As an example, the conductivity value of 5.86×10−9 S cm−1 (activation energy Ea of 0.60 eV) for 2 at 313 K and 22 % relative humidity (RH) increases up to 2.75×10−5 S cm−1 (Ea of 0.40 eV) for 2@KOH. Moreover, a further increase of conductivity values up to 1.16×10−2 S cm−1 and diminution of Ea down to 0.20 eV is achieved at 100 % RH for 2@KOH. The increased porosity, basicity and hydrophilicity of the 1@KOH–3@KOH materials compared to the pristine 1–3 systems should explain the better performance of the KOH‐modified materials.
The missing link: The deliberate introduction of defects on fcu frameworks by KOH/EtOH, leading to missing‐linker defects and metal cluster basification, is responsible for a boosting of the ion conductivity and depletion of activation energy.
Two isoreticular series of pyrazolate-based 3D open metal–organic frameworks, MBDP_X, adopting the NiBDP and ZnBDP structure types H2BDP = 1,4-bis(1H-pyrazol-4-yl)benzene, were synthesized with the ...new tagged organic linkers H 2 BDP_X (X = −NO2, −NH2, −OH). All of the MBDP_X materials have been characterized through a combination of techniques. IR spectroscopy proved the effective presence of tags, while X-ray powder diffraction (XRPD) witnessed their isoreticular nature. Simultaneous TG/DSC analyses (STA) demonstrated their remarkable thermal stability, while variable-temperature XRPD experiments highlighted their high degree of flexibility related to guest-induced fit processes of the solvent molecules included in the channels. A structural isomer of the parent NiBDP was obtained with a sulfonate tagged ligand, H 2 BDP_SO 3 H. Structure solution from powder diffraction data collected at three different temperatures (room temperature, 90, and 250 °C) allowed the determination of its structure and the comprehension of its solvent-related flexible behavior. Finally, the potential application of the tagged MOFs in selective adsorption processes for gas separation and purification purposes was investigated by conventional single component adsorption isotherms, as well as by advanced experiments of pulse gas chromatography and breakthrough curve measurements. Noteworthy, the results show that functionalization does not improve the adsorption selectivity (partition coefficients) for the resolution of gas mixtures characterized by similar high quadrupole moments (e.g., CO2/C2H2); however, the resolution of gas mixtures containing molecules with highly differentiated polarities (i.e., N2/CO2 or CH4/CO2) is highly improved.
The widespread emissions of toxic gases from fossil fuel combustion represent major welfare risks. Here we report the improvement of the selective sulfur dioxide capture from flue gas emissions of ...isoreticular nickel pyrazolate metal organic frameworks through the sequential introduction of missing-linker defects and extra-framework barium cations. The results and feasibility of the defect pore engineering carried out are quantified through a combination of dynamic adsorption experiments, X-ray diffraction, electron microscopy and density functional theory calculations. The increased sulfur dioxide adsorption capacities and energies as well as the sulfur dioxide/carbon dioxide partition coefficients values of defective materials compared to original non-defective ones are related to the missing linkers enhanced pore accessibility and to the specificity of sulfur dioxide interactions with crystal defect sites. The selective sulfur dioxide adsorption on defects indicates the potential of fine-tuning the functional properties of metal organic frameworks through the deliberate creation of defects.
The dynamic art of growing COF crystals Navarro, Jorge A R
Science (American Association for the Advancement of Science),
07/2018, Volume:
361, Issue:
6397
Journal Article
Peer reviewed
Growth modulation leads to large, high-quality covalent organic framework crystals
Diamonds consist of an ordered array of tetrahedral carbon atoms, held together by strong covalent bonds. Despite ...this simple structure, making diamond crystals is difficult, requiring extremely high pressures and temperatures that can only be achieved deep in Earth's crust or through sophisticated experiments. Building covalent organic frameworks (COFs) similarly involves the ordered spatial arrangement, in a two- or three-dimensional crystalline network, of organic units linked together by strong covalent bonds. Growing single crystals of robust COFs is challenging because it requires the dynamic formation and cleavage of strong covalent bonds. On page 48 of this issue, Ma
et al.
(
1
) report a simple method for growing large, high-quality single crystals of COF networks held together by strong imine covalent bonds.
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