Nazmul Abedin Khan

Adsorptive removal of hazardous materials using metal-organic frameworks (MOFs): a review.

Efficient removal of hazardous materials from the environment has become an important issue from a biological and environmental standpoint. Adsorptive removal of toxic components from fuel, waste-water or air is one of the most attractive approaches for cleaning technologies. Recently, porous metal-organic framework (MOF) materials have been very promising in the adsorption/separation of various liquids and gases due to their unique characteristics. This review summarizes the recent literatures on the adsorptive removal of various hazardous compounds mainly from fuel, water, and air by virgin or modified MOF materials. Possible interactions between the adsorbates and active adsorption sites of the MOFs will be also discussed to understand the adsorption mechanism. Most of the observed results can be explained with the following mechanisms: (1) adsorption onto a coordinatively unsaturated site, (2) adsorption via acid-base interaction, (3) adsorption via π-complex formation, (4) adsorption via hydrogen bonding, (5) adsorption via electrostatic interaction, and (6) adsorption based on the breathing properties of some MOFs and so on.

Synthesis of a metal-organic framework material, iron terephthalate, by ultrasound, microwave, and conventional electric heating: a kinetic study.

A metal-organic framework material named MIL-53(Fe), iron terephthalate, has been synthesized sovothermally at a relatively low temperature by not only conventional electric (CE) heating, but also by irradiation under ultrasound (US) and microwave (MW) conditions to gain an understanding of the accelerated syntheses induced by US and MW. The kinetics for nucleation and crystal growth were analyzed by measuring the crystallinity of MIL-53(Fe) under various conditions. The nucleation and crystal growth rates were estimated from crystallization curves of the change in crystallinity with reaction time. The activation energies and pre-exponential factors were calculated from Arrhenius plots. It was confirmed that the rate of crystallization (both nucleation and crystal growth) decreases in the order US>MW>>CE, and that the accelerated syntheses under US and MW conditions are due to increased pre-exponential factors rather than decreased activation energies. It is suggested that physical effects such as hot spots are more important than chemical effects in the accelerated syntheses induced by US and MW irradiation. The syntheses were also conducted in two steps to understand quantitatively the acceleration induced by MW and it was found that the acceleration in crystal growth is more important than the acceleration in nucleation, even though both processes are accelerated by MW irradiation.

Remarkable Adsorption Capacity of CuCl2‐Loaded Porous Vanadium Benzenedicarboxylate for Benzothiophene

There is a considerable demand to reduce the content of sulfur-containing compounds (S-compounds) such as thiophene (Th), benzothiophene (BT), and dimethyldibenzothiophene (DMDBT) in fuels like diesel and gasoline to a low level to prevent air pollution and deactivation of catalysts. So far, various methods have been investigated for sulfur removal, and adsorption has been regarded as one of the most competitive methods. For efficient adsorption, not only adequate porosity/pore size but also specific adsorption sites are required. Remarkable progress on porous materials has been achieved because of the developments of metal–organic framework materials (MOFs) and coordination polymers (CPs). The importance of MOF-type materials is due to the huge porosity, easy tunability of their pore size and shape, and potential applications. Recently, the MOF-type materials have also been investigated for the removal of harmful materials such as S-compounds, 2] dyes, N-containing compounds, and benzene from liquids. Gaseous sulfur compounds have also been removed using MOFs. 11] A few important factors, such as open metal sites, acid sites, and pore functionality have been suggested for the efficient removal of S-compounds. However, little has been understood for the high uptake of S-compounds with modified MOFs as adsorbents. Herein, we have shown the remarkable adsorption capacity for BT over a modified MOF, CuCl2-loaded MIL47 (MIL = materials of the Institute Lavoisier). MIL-47 is a typical MOF composed of vanadium and benzenedicarboxylate (BDC). The reduction of Cu to Cu has been observed in CuCl2/MIL-47 compounds without high-temperature calcination for the partial reduction. Moreover, CuCl2/ MIL-47 compounds have been prepared by a simple process of loading CuCl2 in the MIL-47 (purified at 70 8C) at room temperature. To understand the contribution of loaded CuCl2 to the adsorptive removal of BT, adsorption was done for various times over CuCl2(0.05)/MIL-47 and MIL-47. Here, MIL-47 is the MIL-47 purified in N,N-dimethylformamide (DMF) at 70 8C (see the Supporting Information). CuCl2(n)/MIL-47 denotes CuCl2 loaded onto the purified MIL-47 and n is the Cu/V ratio (mol/mol). The amount of adsorbed BT over CuCl2(0.05)/MIL-47 is much higher than that over MIL-47 without CuCl2 at all adsorption times (Figure 1). However,

Chemical and Thermal Stability of Isotypic Metal–Organic Frameworks: Effect of Metal Ions

Chemical and thermal stabilities of isotypic metal-organic frameworks (MOFs) like Al-BDC (Al-benzenedicarboxylate called MIL-53-Al), Cr-BDC (MIL-53-Cr) and V-BDC (MIL-47-V), after purification to remove uncoordinated organic linkers, have been compared to understand the effect of the central metal ions on the stabilities of the porous MOF-type materials. Chemical stability to acids, bases, and water decreases in the order of Cr-BDC>Al-BDC>V-BDC, suggesting stability increases with increasing inertness of the central metal ions. However, thermal stability decreases in the order of Al-BDC>Cr-BDC> V-BDC, and this tendency may be explained by the strength of the metal-oxygen bond in common oxides like Al(2)O(3), Cr(2)O(3), and V(2)O(5). In order to evaluate precisely the stability of a MOF, it is necessary to remove uncoordinated organic linkers that are located in the pores of the MOF, because a filled MOF may be more stable than the same MOF after purification.

Adsorption and removal of phthalic acid and diethyl phthalate from water with zeolitic imidazolate and metal–organic frameworks

ZIF-8 (zinc-methylimidazolate framework-8), one of the zeolitic imidazolate frameworks (ZIFs), has been used for the removal of phthalic acid (H2-PA) and diethyl phthalate (DEP) from aqueous solutions via adsorption. The adsorption capacity of the ZIF-8 for H2-PA was much higher than that of a commercial activated carbon or other typical metal-organic frameworks (MOFs). Because the surface area and pore volume of the adsorbents showed no favorable effect on the adsorption of H2-PA, the remarkable adsorption with ZIF-8 suggests a specific favorable interaction (electrostatic interaction) between the positively charged surface of ZIF-8 and the negatively charged PA anions. In addition, acid-base interactions also have a favorable contribution in the adsorption of H2-PA, based on the adsorptive performances of pristine and amino-functionalized MOFs and adsorption over ZIF-8 at acidic condition (pH=3.5). The reusability of ZIF-8 was also demonstrated after simple washing with methanol. On the other hand, ZIF-8 was not effective in adsorbing DEP probably because of little charge of DEP in a water solution.

Graphite Oxide/Metal–Organic Framework (MIL-101): Remarkable Performance in the Adsorptive Denitrogenation of Model Fuels

A highly porous metal-organic framework (MOF), MIL-101 (Cr-benzenedicarboxylate), was synthesized in the presence of graphite oxide (GO) to produce GO/MIL-101 composites. The porosity of the composites increased remarkably in the presence of a small amount of GO (<0.5% of MIL-101); however, further increases in GO reduced the porosity. GO also accelerated the synthesis of the MIL-101. The composites (GO/MIL-101) were used, for the first time, in liquid-phase adsorptions. The adsorptive removal of nitrogen-containing compounds (NCCs) and sulfur-containing compounds (SCCs) from model fuels demonstrated the potential applications of the composites in adsorptions, and the adsorption capacity was dependent on the surface area and pore volume of the composites. Most importantly, the GO/MIL-101 composite has the highest adsorption capacity for NCCs among reported adsorbents so far, partly because of the increased porosity of the composite. Finally, the results suggest that GO could be used in the synthesis of highly porous MOF composites, and the obtained materials could be used in various adsorptions in both liquid and gas/vapor phase (such as H2, CH4, and CO2 storage) adsorptions, because of the high porosity and functional GO.

Ionic Liquids Supported on Metal‐Organic Frameworks: Remarkable Adsorbents for Adsorptive Desulfurization

Acidic ionic-liquids (IL) supported on metal-organic frameworks (MOFs) have been shown to be beneficial for adsorptive desulfurization. A remarkable improvement in the adsorption capacity (ca. 71%) was observed in for ILs supported on MIL-101 compared with virgin MIL-101. The improved adsorptive performance might be explained by the acid-base interactions between the acidic ionic liquid and basic benzothiophene (BT). Moreover, from this study, it can be suggested that porous MOFs, supported with ionic liquids, may introduce a new class of highly porous adsorbents for the efficient adsorption of various compounds.

Analogous porous metal–organic frameworks: synthesis, stability and application in adsorption

So far, a huge number of metal–organic frameworks (MOFs) have been synthesized and studied very widely for various applications like gas adsorption/storage, separation, catalysis, drug delivery, luminescence, magnetism, etc. Some of the MOFs are isomorphous, isostructural or isoreticular in topologies having nearly similar (analogous) framework structures. On the other hand, some of the MOFs also have very similar structures with different functional groups via direct synthesis or post-modification. In this highlight, MOFs having very similar structures will be classified into three categories: (1) analogous MOFs with different metallic components; (2) analogous MOFs with different linkers; (3) analogous MOFs with different functional groups. Moreover, various MOFs with very similar structures composed of different metallic, organic or functional groups will be compared especially with regard to their synthesis kinetics, chemical/thermal stability and their applications in the adsorption of hydrogen, acetylene, propylene, carbon dioxide and sulfur-containing compounds, and so on. The synthesis rate and chemical stability of analogous MOFs depend on the lability and inertness, respectively, of metal ions. On the other hand, thermal stability may be explained with the bond strength of metal–oxygen in common oxides. The thermal or chemical stability of analogous MOFs having extra functional groups depends on the functional groups tagged on the linkers; however, no comprehensive explanation is available. Adsorption depends strongly on the property of the metallic or organic moiety of analogous MOFs, and important parameters (size, binding strength, ionic character, density, redox ability, softness and acidity of the metal ions; length, polarity, and hydrophobicity of the linkers) for adsorption can be suggested. Based on the analysis of the reported results, it can be concluded that the metallic, organic or functional groups of analogous MOFs have dominant roles in the synthesis, stability and adsorption even though contradictory results were also reported. Understanding the effects of metallic, organic or functional moieties of very similar MOFs on the synthesis, stability and adsorption will lead to a new way to develop MOF materials that have various commercial applications.

Low-temperature loading of Cu+ species over porous metal-organic frameworks (MOFs) and adsorptive desulfurization with Cu+-loaded MOFs.

Porous metal-organic frameworks (MOFs, MIL-100-Fe, iron-benzenetricarboxylate) supported with Cu(+) species were obtained for the first time under mild condition without high temperature calcinations. The Cu(+)-loaded MOFs were evaluated as efficient adsorbents for the liquid-phase adsorption of benzothiophene (BT). The effect of Cu(+) loading on the adsorption kinetics and maximum adsorption capacity (Q(0)) for the adsorption of BT was also studied. Q(0) increased with increasing copper loading up to a Cu/Fe (wt./wt.) ratio of 0.07 in Cu(+)-loaded-MIL-100-Fe, resulting in an increase in the Q(0) by 14% compared with the virgin MIL-100-Fe without Cu(+) ions. Since the surface area and pore volume decrease with the loading of copper, the increased Q(0) over the Cu(+)-loaded MIL-100-Fe adsorbents suggests specific favorable interactions (probably by π-complexation) between Cu(+) and BT.

Adsorptive denitrogenation of model fuels with porous metal-organic framework (MOF) MIL-101 impregnated with phosphotungstic acid: effect of acid site inclusion.

A metal-organic framework (MOF) MIL-101 was impregnated with phosphotungstic acid (PWA) and used as an adsorbent in liquid phase adsorption of nitrogen-containing compounds (NCCs) from a model fuel. The model fuel contained one sulfur-containing compound (SCC), benzothiophene (BT); one basic NCC, quinoline (QUI); and one neutral NCC, indole (IND). In both MIL-101 and PWA-impregnated MIL-101s, NCC adsorption selectivity was very high compared to the SCC selectivity. Additionally, the adsorption capacity of basic QUI increased by 20% with only 1% PWA impregnation in MIL-101. The adsorption of a neutral compound, IND, was slightly reduced with PWA impregnation in the MOF. The adsorption capacity/selectivity can be remarkably improved by a slight modification of MOFs, for example, to impart acidity. The MOF impregnated with PWA may be very interesting in commercial denitrogenation, especially for coal-derived fuels which contain mainly basic NCCs, by adsorption since the selectivity for NCCs (compared to SCCs) over the adsorbent is very high and the adsorbent can be reused many times.