Enamul Haque

Adsorptive removal of methyl orange and methylene blue from aqueous solution with a metal-organic framework material, iron terephthalate (MOF-235)

An iron terephthalate (MOF-235), one of the metal-organic frameworks (MOFs), has been used for the removal of harmful dyes (anionic dye methyl orange (MO) and cationic dye methylene blue (MB)) from contaminated water via adsorption. The adsorption capacities of MOF-235 are much higher than those of an activated carbon. The performance of MOF-235 having high adsorption capacity is remarkable because the MOF-235 does not adsorb nitrogen at liquid nitrogen temperature. Based on this study, MOFs, even if they do not adsorb gases, can be suggested as potential adsorbents to remove harmful materials in the liquid phase. Adsorption of MO and MB at various temperatures shows that the adsorption is a spontaneous and endothermic process and that the entropy increases (the driving force of the adsorption) with adsorption of MO and MB.

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.

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.

Superior adsorption capacity of mesoporous carbon nitride with basic CN framework for phenol

Highly basic 2D-mesoporous carbon nitride (MCN-1) shows the highest adsorption capacity and adsorption kinetic constant for phenol due to its well ordered porous structure with the in-built basic NH and NH2 groups on the surface, high surface area and large pore volume, suggesting the potential application of MCN-1 for the purification of contaminated water.

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.

Synthesis of isostructural porous metal-benzenedicarboxylates: Effect of metal ions on the kinetics of synthesis

A few porous isostructural metal-benzenedicarboxylates (Me-BDCs) such as MIL-47(V), MIL-53(Al) and MIL-53(Cr) have been synthesized hydrothermally from metal chlorides, TPA (terephthalic acid) and water to elucidate the relative rates (both in the nucleation stage and crystal growth stage) depending on the metal ions. The synthesis rates are rMIL-47(V) > rMIL-53(Al) > rMIL-53(Cr) for both in the nucleation and crystal growth stages at the same temperature, illustrating the importance of lability of the metal ions in the synthesis rate of a MOF material. The lability of metal ions is important in the kinetics of MOF synthesis because the synthesis may be carried out by simple complexation or ligand exchange. The importance of the lability of metal ions may suggest that the deprotonation rate of TPA (to BDC), even in acidic conditions, is relatively fast compared with the complexation rate of BDC on metal ions to form MOFs.

Facile synthesis of cuprous oxide using ultrasound, microwave and electric heating: effect of heating methods on synthesis kinetics, morphology and yield

Ultrasound (US) and microwave (MW) irradiation has been applied for rapid syntheses of cuprous oxides from copper sulfate, sodium citrate, sodium carbonate and polyvinylpyrrolidone in water at a relatively low temperature below 50 °C. Compared with conventional electric (CE) synthesis, US and MW heating lead very rapidly to cuprous oxides having a well-defined small cubic morphology in high yield. The rapid syntheses with US (acceleration degree: 48–81 times of CE synthesis) and MW (acceleration degree: 17–18 times of CE synthesis) are due to decreased activation free energy (ΔG≠, of the Eyring equation) or increased pre-exponential factor (A, of the Arrhenius equation). However, the activation energy (Ea) decreases in the order of US > MW > CE synthesis. The decreased activation free energy is due to a small decrease (or relatively high) in activation entropy (ΔS≠) rather than a decreased activation enthalpy (ΔH≠). The accelerated syntheses do not depend noticeably on reaction stages (nucleation and crystal growth) and synthesis methods (US and MW, excluding the acceleration degrees), suggesting the acceleration is mainly due to physical effects including hot spots or transient temperature rather than chemical ones.