Commercial Metal-organic Framework Research Articles

Catalysts by pyrolysis: Transforming metal-organic frameworks (MOFs) precursors into metal-nitrogen-carbon (M-N-C) materials

Metal-organic framework (MOF) materials are promising precursors to transition into metal-nitrogen-carbon (M-N-C) catalysts with high catalytic performance. Pyrolysis is one of the most common ways to convert MOFs into electrically conductive MOF-derived M-N-C catalysts. General interests in using MOFs as precursors derive from changing the MOFs’ porous structure into the carbonaceous frame. However, this favorable structure is not always maintained, with the reason unidentified since pyrolysis is currently still more of an empirical process. Understanding the pyrolysis processes leading to the transformation of MOFs into M-N-C catalysts is essential to broaden the development of MOF-derived catalysts. We report here complete chemical and morphological evolution and transformation of two commercial MOFs with the same sodalite topology, the ZIF-8 and ZIF-67, via series of in situ and ex situ techniques. The results reveal that the structure of the ZIF-67 collapses after the pyrolysis due to the graphitization of the carbon. Graphitization is catalyzed by the metallic cobalt particles formed when the temperature rose above 460 °C. The ZIF-8 was found to be a promising precursor material since most of the metal evaporates at the early stages and does not aggregate to form metal particles. However, the insufficient metal-N active sites and intrinsic low electrocatalysis availability of Zn limit the performance of the final catalyst. To maintain the porous structure of MOFs it is important to control the metal species and prevent them from agglomeration. Direct utilization of high-concentration MOFs as pyrolysis precursors is not recommended without rational design to inhibit agglomeration and graphitization that are undesirable for catalyst activity.

Modeling High-Pressure Hydrogen Uptake by Nanoporous Metal–Organic Frameworks: Implications for Hydrogen Storage and Delivery

Due to their very high porosity and superior textural properties, metal–organic frameworks (MOFs) are promising nanoporous materials for hydrogen storage by cryocompression. Herein, we investigated hydrogen adsorption on four commercial MOFs, namely, MIL53-Al, MOF-5, HKUST-1, and MOF-177, over a temperature range of 77 to 273 K and pressures up to 14 MPa. The modified Dubinin–Astakhov equation was used to fit the experimental adsorption data, and six parameters (m, nmax, α, β, P0, and Va) were obtained. We concluded that the parameters nmax and Va are related to the micropore volume, while α, β, m, and P0 are related to the average micropore size. Compared to hydrogen compression in an empty tank, the introduction of MOF-5 enhanced the volumetric hydrogen storage at 77 K and 10 MPa from 31 to 42 kg m–3. The released H2 capacities of MOFs from a loading pressure of 10 MPa to a discharge pressure of 0.5 MPa were determined for either isothermal discharge at 77 K or after temperature increase to 160 K. For MOF-5, the amount of usable hydrogen increased up to 10.6 wt % (40.8 mg cm–3) by pressure drop (from 10 to 0.5 MPa) and temperature increase (from 77 to 160 K).

Use of Basolite® F300 metal-organic framework for the dispersive solid-phase extraction of phthalic acid esters from water samples prior to LC-MS determination

In the present work, a commercial metal-organic framework (Basolite® F300) has been applied for the first time as dispersive solid-phase extraction (dSPE) sorbent of eight phthalic acid esters (PAEs) (butyl benzyl phthalate, bis-2-n-butoxyethyl phthalate, bis-isopentyl phthalate, bis-n-pentyl phthalate, dicyclohexyl phthalate, di-(2-ethylhexyl) phthalate -DEHP-, di-n-octyl phthalate and diisononyl phthalate) and an adipate (bis (2-ethylhexyl) adipate), which is utilized as a PAE substitutive. Milli-Q, pond, tap and waste water were selected as samples. Dihexyl phthalate-3,4,5,6-d4 was used as procedural internal standard. High-performance liquid chromatography mass spectrometry was used for the determination of the target compounds. Optimum dSPE conditions were the following: 50 mL of the water sample (pH 6.0), 120 mg of sorbent and 15 mL of ACN as elution solvent. For the validation of the method, matrix-matched calibration and trueness of the method were addressed, obtaining determination coefficients (R2) higher than 0.9905 and relative recovery values between 70 and 118 % (RSDs < 20 %). The limits of quantification of the method were in the range 22–69 ng/L. Matrix effects were also studied. Different real samples were analysed, finding DEHP in all of them at the low µg/L level.

Benzene adsorption on synthesized and commercial metal–organic frameworks

Benzene adsorption on four synthesized metal–organic frameworks (MOFs): MOF-520(Al), MOF-5(Zn), ZIF-8(ZnO–Zn), MOF-74(Mg) and three commercial MOFs: Basolite C300, Basolite F300 and Basolite Z377 at 20 °C is investigated. The materials studied feature high surface areas ranging from 950 to 3760 m2/g and large micropore volumes varying from 0.37 to 1.79 cm3/g. Nevertheless, the volume of supermicropores is one of the main factors that determines C6H6 adsorption performance of MOFs. Additionally, in the case of some MOFs, open metal sites enhance interactions between gas molecules and the surrounding framework.

Electrical and humidity-sensing properties of flexible metal-organic framework M050(Mg) and KOH/M050 and AuNPs/M050 composites films

A commercial metal-organic framework (MOF) of Basosiv M050 and its composite materials potassium hydroxide/M050 (KOH/M050) and Au nanoparticles/M050 (AuNPs/M050) were coated on a polyethylene terephthalate (PET) substrate to form novel flexible impedance-type humidity sensors. The electrical properties of M050 to which were added various amounts of KOH or AuNPs were studied in detail as functions of relative humidity (RH). The contributions of the KOH or the AuNPs to the humidity-sensing (linearity and sensitivity) properties and flexibility were thus elucidated. The M050 and composites of KOH/M050 and AuNPs/M050 films that were coated on PET substrates were analyzed using scanning electron microscopy (SEM), atomic force microscopy (AFM), UV–vis spectroscopy and infrared spectrometry. The sensor that was made of KOH/M050 film with 0.05 M added KOH exhibited high flexibility, the highest sensitivity, acceptable linearity, a short response time, a low temperature coefficient and long-term stability. The humidity-sensing mechanism of the KOH/M050 film was explained using complex impedance spectra.

Robust microporous organic copolymers containing triphenylamine for high pressure CO2 capture application

Various adsorbents including zeolites, activated carbon and metal-organic frameworks have demonstrated a potential capability for applications in pre-combustion carbon capture and H2 purification owing to their large surface areas and affinity for CO2. However, most adsorbents showing promising performances in dry condition are not stable or lose their capability for capturing CO2 in the presence of H2O and acidic gases such as H2S. To address this issue, a series of triphenylamine-containing microporous organic copolymers (PP-N-x) possessing high surface areas (1010–1251m2g−1) as well as excellent hydrolytic and acid stability were synthesized and evaluated for potential application in high pressure CO2 capture above-mentioned. Among the adsorbents tested, PP-N-25 exhibited the highest CO2/H2 selectivity over the entire pressure range along with the good CO2 uptake capability which is comparable to HKUST-1, a commercial metal-organic framework possessing coordinatively open metal sites. Subsequent breakthrough experiment revealed that PP-N-25 maintains decent CO2 adsorption capability even in the presence of H2O while HKUST-1 lost CO2 capturing capability in humid condition.

Amino-impregnated MOF materials for CO2 capture at post-combustion conditions

Three different commercial Metal-Organic Frameworks (HKUST-1, MIL-53(Al) and ZIF-8) were modified by wetness impregnation of tetraethylenepentamine (TEPA) molecules. These amino-containing MOF materials were studied in CO2 adsorption under post-combustion conditions (45°C and 1bar) using a simulated exhausted flue gas stream of power plants (75% inert gas; 5% O2; 14% CO2; 6% H2O; % in vol.). The yield of TEPA incorporation was significantly affected by the physicochemical properties of the MOF precursors. The presence of reactive sites of HKUST-1 (unsaturated copper sites) or MIL 53(Al) (exposed hydroxyl bridges (µ2-OH)) as well as their worst textural properties as compared to ZIF-8,led to lower TEPA loadings and porosities of the resultant amino-impregnated HKUST-1 and MIL 53(Al) materials. The ZIF-8 material showed a better distribution of TEPA since reactive surface sites are not present in this support with a higher superficial development. Amino-impregnated ZIF-8 samples exhibited enhanced adsorption capacities by combination of physical and chemical adsorption of CO2 over the TEPA-impregnated microporous framework. The increase of the TEPA content in the ZIF-8 material led to CO2 uptake up to 67mgCO2/gads using pure CO2 at 0.15bar and 45°C. Under post-combustion CO2 capture conditions, TEPA-impregnated ZIF-8 samples underwent a remarkable increase of the carbon dioxide uptake up to 104mgCO2/gads, due to the presence of moisture, which is responsible of increasing the CO2 capture efficiency of amino groups. After several adsorption/desorption cycles at post-combustion adsorption conditions, TEPA-containing ZIF-8 samples have shown a high structural stability, maintaining the CO2 uptake practically constant.

Hydrocarbons adsorption on metal trimesate MOFs: Inverse gas chromatography and immersion calorimetry studies

Two commercial metal-organic frameworks, Cu3(BTC)2 and Fe(BTC), have been selected to compare the adsorption parameters obtained on these materials by two different techniques: immersion calorimetry and inverse gas chromatography (IGC), in order to find a relationship between thermodynamic parameters obtained by so different techniques. From comparison between the enthalpy of adsorption obtained from IGC and the enthalpy of immersion, three molecules of the same number of carbon atoms have been selected: n-heptane, methylcyclohexane and toluene. Both by IGC and immersion calorimetry, the interaction is stronger in Fe(BTC), being the aromaticity of TOL determinant in the strength of the interaction. However, splitting of the enthalpy of adsorption into the dispersive and specific components allows to deduce that both parameters are more important on the Cu3(BTC)2, due to the higher available surface area in the case of the dispersive interaction; and for the specific interaction, due to the high potential of interaction into the micropores.

Hollow carbon nano-onions with hierarchical porosity derived from commercial metal organic framework

We report on the synthesis of new metal–organic framework derived carbons using a two-step process employing for the first time a commercially available iron-containing metal–organic framework. The resulting carbons consist mainly of highly graphitic shells due to the highly dispersed iron in the precursor structure which catalyzes the formation of graphitic carbon. In addition, a distinct onion-like morphology is observed, with high total pore volumes of up to 1cc/g and a hierarchically structured porosity in which the hollow cores of the carbon onions are accessible via smaller micro- and mesopores. As a proof of concept we furthermore demonstrate the inherent structure of this carbon being advantageous for the application in lithium–sulfur batteries as a both confining and contacting host for the active material, yielding capacities of up to 550mAh/g after 40 cycles.

ChemInform Abstract: Commercial Metal—Organic Frameworks as Heterogeneous Catalysts

AbstractReview: 101 refs.

Commercial metal–organic frameworks as heterogeneous catalysts

Metal-organic frameworks (MOFs) are porous crystalline materials that have promising applications as heterogeneous catalysts. After describing the composition, textural properties and crystal structure of four commercially available MOFs, we summarize organic transformations for which these commercial MOFs exhibit higher catalytic activity than the corresponding soluble metal salts or metal ion-exchanged zeolites. In the present article, we have focused on reactions requiring Lewis-acid sites or redox centers to illustrate the potential applications and limitations of commercial MOFs. In a final section, we provide our views on future developments whose ultimate target will be the use of a commercial MOF as a heterogeneous catalyst for a real industrial process in fine chemistry, thus, realizing the advantages of these materials with respect to zeolites or other solid catalysts in liquid-phase reactions.

Chemical instability of Cu3(BTC)2 by reaction with thiols

In contrast to Fe(BTC) (BTC: 1,3,5-benzenetricarboxylate), the crystal structure of Cu3(BTC)2, a commercial metal organic framework widely used as solid catalyst, collapses when contacted with thiols under mild reaction conditions forming copper nanoparticles.