Tungsten Nitride, Well-Dispersed on Porous Carbon: Remarkable Catalyst, Produced without Addition of Ammonia, for the Oxidative Desulfurization of Liquid Fuel.

Polyanilines (pANIs), loaded with phosphotungstic acid (PTA), are pyrolyzed to get WO3 or W2 N (≈6 and ≈7 nm, respectively), which is well-dispersed on pANI-derived porous carbons (pDCs). Depending on the pyrolysis temperature, WO3 /pDC, W2 N/pDC, or W2 N-W/pDCs could be obtained selectively. pANI acts as both the precursor of pDC and the nitrogen source for the nitridation of WO3 into W2 N during the pyrolysis. Importantly, W2 N could be obtained from the pyrolysis without ammonia feeding. The obtained W2 N/pDC is applied as a heterogeneous catalyst for the oxidative desulfurization (ODS) of liquid fuel for the first time, and the results are compared with WO3 /pDC and WO3 /ZrO2 . The W2 N/pDC is very efficient in ODS with remarkable performance compared with WO3 /pDC or WO3 /ZrO2 , which is applied as a representative ODS catalyst. For example, W2 N/pDC shows around 3.4 and 2.7 times of kinetic constant and turnover frequency (based on 5 min of reaction), respectively, compared to that of WO3 /ZrO2 . Moreover, the catalysts could be regenerated in a facile way. Therefore, W2 N/pDC could be produced facilely from pyrolysis (without ammonia feeding) of PTA/pANI, and W2 N, well-dispersed on pDC, can be suggested as a very efficient oxidation catalyst for the desulfurization of liquid fuel.

Hydrophobic Cobalt-Ethylimidazolate Frameworks: Phase-Pure Syntheses and Possible Application in Cleaning of Contaminated Water.

Two highly porous Co-based metal-azolate frameworks (MAFs), MAF-5(Co) and MAF-6(Co), which are isostructural with MAF-5(Zn) and MAF-6(Zn), respectively, were first synthesized in high yield and purity at room temperature. The syntheses compared two mixing methods, slow and fast, using cobalt acetate as the metal ion (Co2+) source and 2-ethylimidazole as the ligand. Triethylamine was applied as an additive/promoter in aqueous/ethanol solutions, and benzene and cyclohexane were used as hydrophobic templates. Phase-pure MAF-5(Co) and MAF-6(Co) were obtained in high yield by optimizing the mixing speed, reactant composition, and solvent/template ratio. It was found that fast mixing of the reactant mixtures was effective for synthesizing MAF(Co) materials. MAF-5(Co) and MAF-6(Co) were found to be very hydrophobic, similar to the MAFs composed of Zn, suggesting possible applications in water purification. MAF-5(Co) and MAF-6(Co) were then applied to adsorb n-octane as a model oil and nonpolar adsorbate from water, and the obtained results were compared to those of related materials, i.e., MAF-4(Co and Zn), MAF-5(Zn), and MAF-6(Zn), as well as with Cu-BTC (Cu-benzenetricarboxylate) and a conventional adsorbent, activated carbon. Surprisingly, despite having low porosity, MAF-5(Co) showed remarkable competitiveness among the typical porous materials for n-octane removal. The results suggest that the framework structure such as cavity and aperture sizes rather than surface area plays a significant role in n-octane removal. Moreover, MAF-5(Co) can easily be regenerated by simple evacuation and reused, and thus it was found to be a potential adsorbent for the removal of spilled oil from water. Additionally, MAFs were applied in the adsorption of diclofenac sodium from water, showing the competitiveness of MAFs in water purification probably because of hydrophobicity.

Scandium-Triflate/Metal-Organic Frameworks: Remarkable Adsorbents for Desulfurization and Denitrogenation.

Scandium-triflate (Sc(OTf)3) was introduced for the first time on metal-organic frameworks (MOFs), to utilize acidic Sc(OTf)3 for adsorptive desulfurization and denitrogenation of fuel containing benzothiophene (BT), dibenzothiophene (DBT), quinoline (QUI), and indole (IND). A remarkable improvement in the adsorption capacity (about 65% based on the weight of adsorbents; 90% based on the surface area of the adsorbents) was observed with the Sc(OTf)3/MOFs as compared to the virgin MOFs for the adsorption of BT from liquid fuel. The basic QUI was also adsorbed preferentially onto the acidic Sc(OTf)3/MOFs. However, nonsupported Sc(OTf)3 showed negligible adsorption capacities. The improved adsorptive performance for BT, DBT, and QUI might be derived from acid-base interactions between the acidic Sc(OTf)3 and basic adsorbates. On the other hand, the Sc(OTf)3, loaded on MOFs, reduced the adsorption capacity for neutral IND due to lack of interaction between the neutral adsorbate and acidic adsorbent and the reduced porosities of the modified adsorbents. The reusability of the adsorbents was found satisfactory up to the fourth run. On the basis of the result, it is suggested that metal-triflates, such as Sc(OTf)3, can be prospective materials for adsorptive desulfurization/denitrogenation of fuels when supported on porous materials such as MOFs.

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.

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.

Adsorptive removal of bisphenol-A from water with a metal-organic framework, a porous chromium-benzenedicarboxylate.

Adsorptive removal of bisphenol-A (BPA) using a MOF, Cr-benzenedicarboxylate (MIL-53), has been studied to understand the applicability of MOFs for the removal of hazardous endocrine disturbing chemicals from water. MIL-53 shows very fast adsorption in an hour and the adsorption capacity of MIL-53 is higher than that of activated carbon. Importantly, the adsorption of BPA over MIL-53 is very favorable especially at very low concentrations of BPA. Therefore, MOFs such as MIL-53 can be one of adsorbents that may be used in the adsorptive removal of BPA from contaminated water.

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.

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.

Rapid syntheses of a metal-organic framework material Cu3(BTC)2(H2O)3 under microwave: a quantitative analysis of accelerated syntheses.

A typical MOF material, Cu-BTC has been synthesized with microwave and conventional electric heating in various conditions to elucidate, for the first time, the quantitative acceleration in the synthesis of a MOF by microwaves. The acceleration by microwaves is mainly due to rapid nucleation rather than rapid crystal growth, even though both stages are accelerated. The acceleration in the nucleation stage by microwaves is due to the very large pre-exponential factor (about 1.4 x 10(10) times that of conventional synthesis) in the Arrhenius plot. However, the activation energy for the nucleation in the case of microwave synthesis is higher than the activation energy of conventional synthesis. The large acceleration in the nucleation, compared with that in the crystal growth, is observed once again by the syntheses in two-steps (changing heating methods from microwave into conventional heating or from conventional heating into microwave heating just after the nucleation is completed). The crystal size of Cu-BTC obtained by microwave-nucleation is generally smaller than the Cu-BTC made by conventional-nucleation, probably due to rapid nucleation and the small size of nuclei with microwave-nucleation.

Adsorptive removal of bulky dye molecules from water with mesoporous polyaniline-derived carbon.

Polyaniline-derived carbon (PDC) was obtained via pyrolysis of polyaniline under different temperatures and applied for the purification of water contaminated with dye molecules of different sizes and charge by adsorption. With increasing pyrolysis temperature, it was found that the hydrophobicity, pore size and mesopore volume increased. A mesoporous PDC sample obtained via pyrolysis at 900 °C showed remarkable performance in the adsorption of dye molecules, irrespective of dye charge, especially in the removal of bulky dye molecules, such as acid red 1 (AR1) and Janus green B (JGB). For example, the most competitive PDC material showed a Q 0 value (maximum adsorption capacity) 8.1 times that of commercial, activated carbon for AR1. The remarkable adsorption of AR1 and JGB over KOH-900 could be explained by the combined mechanisms of hydrophobic, π-π, electrostatic and van der Waals interactions.

Synthesis of Cu-Doped Mn3O4@Mn-Doped CuO Nanostructured Electrode Materials by a Solution Process for High-Performance Electrochemical Pseudocapacitors.

Cu-doped Mn3O4 and Mn-doped CuO (CMO@MCO) mixed oxides with isolated phases together with pristine Mn3O4 (MO) and CuO (CO) have been synthesized by a simple solution process for applications in electrochemical supercapacitors. The crystallographic, spectroscopic, and morphological analyses revealed the formation of all of the materials with good crystallinity and purity with the creation of rhombohedral-shaped MO and CMO and a mixture of spherical and rod-shaped CO and MCO nanostructures. The ratio of CMO and MCO in the optimized CMO@MCO was 2:1 with the Cu and Mn dopants percentages of 12 and 15%, respectively. The MO-, CO-, and CMO@MCO-modified carbon cloth (CC) electrodes delivered the specific capacitance (C s) values of 541.1, 706.7, and 997.2 F/g at 5 mV/s and 413.4, 480.5, and 561.1 F/g at 1.3 A/g, respectively. This enhanced C s value of CMO@MCO with an energy density and a power density of 78.0 Wh/kg and 650.0 W/kg, respectively, could be attributed to the improvement of electrical conductivity induced by the dopants and the high percentage of oxygen vacancies. This corroborated to a decrease in the optical band gap and charge-transfer resistance (R ct) of CMO@MCO at the electrode/electrolyte interface compared to those of MO and CO. The net enhancement of the Faradaic contribution induced by the redox reaction of the dopant and improved surface area was also responsible for the better electrochemical performance of CMO@MCO. The CMO@MCO/CC electrode showed high electrochemical stability with a C s loss of only ca. 4.7%. This research could open up new possibilities for the development of doped mixed oxides for high-performance supercapacitors.

Facile purification of porous metal terephthalates with ultrasonic treatment in the presence of amides.

A facile purification method for metal-organic frameworks (MOFs), especially the ones containing insoluble 1,4-benzenedicarboxylic acid (terephthalic acid) in the pore, has been suggested. The purification method consists of the treatment of the MOF with amides such as N,N-dimethylformamide, especially under ultrasound treatment. The purification is completed within 1 h at 70 degrees C as has been confirmed by XRD, nitrogen adsorption, FTIR and TGA measurements. The purification method proved to be simple, one-step, fast and energy-efficient. The MOFs purified by the proposed method show high surface area and micropore volume, confirming the efficiency of the method. The proposed method will lead to a new access to activate (for example, to remove carboxylic acids) MOFs that are unstable above around 100 degrees C. Additionally, the method may be used to transform a non-porous MOF-type material into a porous MOF structure. However, adequate solvents will be necessary for the facile purification of MOFs.

Polyaniline-Encapsulated Metal-Organic Framework MIL-101: Adsorbent with Record-High Adsorption Capacity for the Removal of Both Basic Quinoline and Neutral Indole from Liquid Fuel.

Polyaniline-encapsulated metal-organic frameworks (MOFs; MIL-101, Cr-benzenedicarboxylate) were prepared via a ship-in-bottle strategy and applied in liquid phase adsorptions. The modified MIL-101s showed record-high adsorptions for both basic and neutral nitrogen-containing compounds (NCCs) from liquid model fuel. For example, the maximum adsorption capacities ( Qo) of the protonated polyaniline (pANI)@MIL-101 for the basic quinoline and neutral indole from n-octane were 556 and 602 mg/g, respectively. The plausible adsorption mechanisms such as hydrogen bonding, acid-base interaction, and cation-π interaction were proposed to explain the extraordinary adsorptions of the studied adsorbates. Moreover, the adsorbents could be recycled via a simple approach and reused in adsorptions without noticeable decrease in performances. Therefore, the pANI-encapsulated MOFs could be recommended as a new type of adsorbents for very efficient removal of both basic and neutral NCCs from liquid fuel.

Polyaniline-derived porous carbons: Remarkable adsorbent for removal of various hazardous organics from both aqueous and non-aqueous media.

Polyaniline (pANI) was pyrolyzed under a nitrogen atmosphere to get porous pANI-derived carbons (PDCs). To increase the porosity of the carbons further, the PDCs were activated at 600-800 °C in the presence of KOH. The obtained PDCs were firstly applied in liquid-phase adsorptions in order to remove hazardous organics from both water and fuel effectively via adsorption. PDC-700, activated at 700 °C, showed record high adsorption capacities from water for the removal of hazardous organics such as diethyl phthalate and Janus Green B, as representative organics for industrial chemicals (endocrine disturbing agent) and organic dyes, respectively. Moreover, PDC-700 had record high adsorption capacity for the removal of 4,6-dimethyldibenzothiophene from a model fuel. The plausible mechanisms were also suggested to explain the remarkable adsorptions both from water and fuel. The adsorbents could be regenerated in a facile way and reused in adsorption up to several cycles. Therefore, the PDCs could be suggested as a new class of adsorbents for the purification of both water contaminated with organics and fuel having a high concentration of thiophenics.

Adsorptive removal and separation of chemicals with metal-organic frameworks: Contribution of π-complexation.

Efficient removal and separation of chemicals from the environment has become a vital issue from a biological and environmental point of view. Currently, adsorptive removal/separation is one of the most promising approaches for cleaning purposes. Selective adsorption/removal of various sulfur- and nitrogen-containing compounds, olefins, and π-electron-rich gases via π-complex formation between an adsorbent and adsorbate molecules is very competitive. Porous metal-organic framework (MOF) materials are very promising in the adsorption/separation of various liquids and gases owing to their distinct characteristics. This review summarizes the literature on the adsorptive removal/separation of various π-electron-rich compounds mainly from fuel and gases using MOF materials containing metal ions that are active for π-complexation. Details of the π-complexation, including mechanism, pros/cons, applications, and efficient ways to form the complex, are discussed systematically. For in-depth understanding, molecular orbital calculations regarding charge transfer between the π-complexing species are also explained in a separate section. From this review, readers will gain an understanding of π-complexation for adsorption and separation, especially with MOFs, to develop new insight for future research.

TiO2-Containing Carbon Derived from a Metal-Organic Framework Composite: A Highly Active Catalyst for Oxidative Desulfurization.

A new metal-organic framework (MOF) composite consisting of Ti- and Zn-based MOFs (ZIF-8(x)@H2N-MIL-125; in brief, ZIF(x)@MOF) was designed and synthesized. The pristine MOF [H2N-MIL-125 (MOF)]- and an MOF-composite [ZIF(30)@MOF]-derived mesoporous carbons consisting of TiO2 nanoparticles were prepared by pyrolysis (named MDC-P and MDC-C, respectively). MDC-C showed a higher surface area, larger pore sizes, and larger mesopore volumes than MDC-P. In addition, the TiO2 nanoparticles on MDC-C have more uniform shapes and sizes and are smaller than those of MDC-P. The obtained MDC-C and MDC-P [together with MOF, ZIF(30)@MOF, pure/nanocrystalline TiO2, and activated carbon] were applied in the oxidative desulfurization reaction of dibenzothiophene in a model fuel. The MDC-C, even with a lower TiO2 content than that of MDC-P, showed an outstanding catalytic performance, especially with a very low catalyst dose (i.e., a very high quantity of dibenzothiophene was converted per unit weight of the catalyst), fast kinetics (∼3 times faster than that for MDC-P), and a low activation energy (lower than that for any reported catalyst) for the oxidation of dibenzothiophene. The large mesopores of MDC-C and the well-dispersed/small TiO2 might be the dominant factors for the superior catalytic conversions. The oxidative desulfurization of other sulfur-containing organic compounds with various electron densities was also studied with MDC-C to understand the mechanism of catalysis. Moreover, the MDC-C catalyst can be reused many times in the oxidative desulfurization reaction after a simple washing with acetone. Finally, composing MOFs and subsequent pyrolysis is suggested as an effective way to prepare a catalyst with well-dispersed active sites, large pores, and high mesoporosity.

Nitrogen-Doped Porous Carbons from Ionic Liquids@MOF: Remarkable Adsorbents for Both Aqueous and Nonaqueous Media.

Porous carbons were prepared from a metal-organic framework (MOF, named ZIF-8), with or without modification, via high-temperature pyrolysis. Porous carbons with high nitrogen content were obtained from the calcination of MOF after introducing an ionic liquid (IL) (IL@MOF) via the ship-in-bottle method. The MOF-derived carbons (MDCs) and IL@MOF-derived carbons (IMDCs) were characterized using various techniques and used for liquid-phase adsorptions in both water and hydrocarbon to understand the possible applications in purification of water and fuel, respectively. Adsorptive performances for the removal of organic contaminants, atrazine (ATZ), diuron, and diclofenac, were remarkably enhanced with the modification/conversion of MOFs to MDC and IMDC. For example, in the case of ATZ adsorption, the maximum adsorption capacity of IMDC (Q0 = 208 m2/g) was much higher than that of activated carbon (AC, Q0 = 60 m2/g) and MDC (Q0 = 168 m2/g) and was found to be the highest among the reported results so far. The results of adsorptive denitrogenation and desulfurization of fuel were similar to that of water purification. The IMDCs are very useful in the adsorptions since these new carbons showed remarkable performances in both the aqueous and nonaqueous phases. These results are very meaningful because hydrophobic and hydrophilic adsorbents are usually required for the adsorptions in the water and fuel phases, respectively. Moreover, a plausible mechanism, H-bonding, was also suggested to explain the remarkable performance of the IMDCs in the adsorptions. Therefore, the IMDCs derived from IL@MOF might have various applications, especially in adsorptions, based on high porosity, mesoporosity, doped nitrogen, and functional groups.

Protonated MIL-125-NH2: Remarkable Adsorbent for the Removal of Quinoline and Indole from Liquid Fuel.

The removal of nitrogen-containing compounds (NCCs) from fossil fuels prior to combustion is currently of particular importance, and so we investigated an adsorptive method using metal-organic frameworks (MOFs) for the removal of indole (IND) and quinoline (QUI), which are two of the main NCCs present in fossil fuels. We herein employed an amino (-NH2)-functionalized MIL-125 (MIL-125-NH2) MOF, which was further modified by protonation (P-MIL-125-NH2). These modified MOFs exhibited extraordinary performance in the adsorption of both IND (as representative neutral NCC) and QUI (as representative basic NCC). These MOFs were one of the most efficient adsorbents for the removal of NCCs. For example, P-MIL-125-NH2 showed the highest adsorption capacity for QUI among ever reported adsorbent. The improved adsorption of IND was explained by H-bonding and cation-π interactions for MIL-125-NH2 and P-MIL-125-NH2, respectively, while the mechanisms for QUI were H-bonding and acid-base interactions, respectively. This is a rare phenomenon for a single material (especially not with very high porosity) to exhibit such remarkable performances in the adsorption of both basic QUI and neutral IND. The adsorption results obtained using regenerated MIL-125-NH2 and P-MIL-125-NH2 also showed that these materials can be used several times without any severe degradation.

Ionic liquid@MIL-101 prepared via the ship-in-bottle technique: remarkable adsorbents for the removal of benzothiophene from liquid fuel.

Ionic liquids (ILs) were synthesized inside a porous metal-organic framework (MIL-101) via a ship-in-bottle (SIB) technique. Unlike previously reported IL-incorporated MIL-101s, IL@MIL-101 prepared by the SIB approach was very stable over several cycles for the liquid phase adsorption of benzothiophene from liquid fuel.