Yonas Chebude

Synthesis of metal–organic frameworks in water at room temperature: salts as linker sources

Exponential growth in the interest in MOF (Metal–Organic Framework) materials in both scientific and industrial spheres has been flourishing in the last fifteen years. However, certain environmental and economic limitations could slow down their industrial establishment. Here we present an innovative, widely applicable, straightforward, rapid, inexpensive and environmentally friendly method to prepare high-quality carboxylate-based MOFs with properties rarely obtained under conventional conditions. The method is based on the use of organic salts (instead of their homologous protonated organic ligands) as anionic linker sources, so that their solubility and the deprotonation steps, which necessarily take place in the formation of MOFs, are notably favoured in aqueous solution. As an example, the preparation of X-MIL-53-Al (X = none, NH2, NO2) materials is reported at room temperature, with the following additional advantages for some applications: they (i) are nanocrystalline, (ii) have notable and ordered inter-crystalline mesoporosity, and (iii) contain a reduced or even a negligible amount of unreacted linker within the pores. To the best of our knowledge, this is the first preparation of a 3-D highly-porous MOF under these two industrially-demanded synthesis conditions: room temperature and water as the sole solvent. The scarce commercial availability of these linker salts is a limitation that can be easily circumvented by replacing the salts with their protonated analogue plus a base. Following this method, a high-quality MOF-74 material, so far only prepared in organic solvents, could be also prepared in water and at room temperature. Even in organic media, in which this approach could be a priori unfavourable from a linker solubility point of view, MOFs with properties unattainable through conventional methods of synthesis can be prepared following this approach. That is the case for the synthesis of MOF-5 with the highest interpenetration degree ever described by just replacing terephthalic acid with disodium terephthalate as the linker source and maintaining the otherwise conventional conditions including the use of DMF as the solvent.

Template synthesis of symmetrical transition metal dithiocarbamates

Novel transition metal dithiocarbamates of the type [M2(etdtc)2] and [M1(etdtc)Cl]2 where M = Mn(II), Fe(II), Co(II), Ni(II), Cu(II), Zn(II), Cd(II) and Hg(II), M1 = Cr(III), Fe(III) and etdtc = (S4N4C11H18 ) have been synthesized by the use of self-assembly techniques. The metal dithiocarbamates were prepared from the primary amine, CS2 and metal chloride. They have been characterized by spectroscopic, TGA/DSC, magnetic susceptibility and conductivity data. The complexes, [Mn2(etdtc)2], [Fe2(etdtc)2], [Co2(etdtc)2], [Zn2(etdtc)2], [Cd2(etdtc)2] and [Hg2(etdtc)2] have been suggested to be tetrahedral while [Ni2(etdtc)2] and [Cu2(etdtc)2] have square-planar geometry. [Cr(etdtc)Cl]2 and [Fe(etdtc)Cl]2 have chlorine bridged distorted-octahedral geometry. It has been observed that the dithiocarbamato moiety is symmetrically bonded in all the cases. A three stage TGA profile is observed for all the complexes leading to the formation of respective metal sulfide as the end-product. The molar conductance of 10-3 mol L-1 solution of the complexes measured in DMSO is indicative of their non-ionic nature.

Room temperature synthesis of metal organic framework MOF-2

One of the pioneering metal organic framework material, called MOF-2 and having the formula [Zn2(BDC)2], still continues awakening interest amongst the scientific community in spite of its layered character. However, the synthesis methods are either experimentally complicated or in two steps through the transformation of MOF-1. Here, we describe the preparation of a high-quality MOF-2 under more sustainable conditions, including room temperature, absence of any amine or any other pH-controller, partial substitution of the harmful organic solvent (N,N-dimethylformamide) by water, and by simply mixing linker and metal sources, the latter being zinc acetate, carefully selected as a function of their solubility in the solvent mixture. The optimum ratio of Zn(OAc)2·4H2O to terephthalic acid (H2BDC) is 1.74 and H2O to DMF is 3. MOF-2 [Zn2(BDC)2] has been characterized using powder X-ray diffraction, thermogravimetric analysis, N2 adsorption/desorption and scanning electron microscopy, all of them supporting the good quality of the material.

Synthesis, Characterization and Thermal Studies of Bipyridine Metal Complexes Containing Different Substituted Dithiocarbamates

Complexes of the type [Mpy2(dedtc)2], and [Mpy2(dpdtc)2], where M=Mn(II), Fe(II), Co(II), Ni(II), Cu(II), Zn(II), py=pyridine, dedtc=diethyldithiocarbamate and dpdtc=diphenyldithiocarbamate, have been synthesized and characterized by elemental analyses, magnetic susceptibility, TGA/DSC and IR in the solid-state, and electronic spectroscopy and conductivity measurement studies in solution. The dithiocarbamato moiety has been found to be symmetrically bonded to the metal. The complexes are proposed to have a distorted-octahedral structure. The ligand field parameters 10 Dq, B and β have also been evaluated. The value of β indicates a considerable orbital overlap in the complexes. A two-stage decomposition pattern leading to the formation of respective metal sulfide as the end-product has been observed in all the complexes. Their molar conductance indicated them to be non-electrolyte in nitrobenzene.

Synthesis of perfluoroalkylnitroborates: structure of Cs[(C2F5)3BNO2]

Abstract (CF 3 ) 2 BNMe 2 reacts with CF 3 (CF 2 ) n I/tetrakisdimethylaminoethylene (TDAE) to form the dimethylamine boranes CF 3 (CF 2 ) n (CF 3 ) 2 B·NHMe 2 ( n =1 ( 2 ), 3 ( 3 )). Reacting C 2 F 5 I with Br 2 BNMe 2 and TDAE, (C 2 F 5 ) 3 B·NHMe 2 ( 4 ) was obtained in low yield. Compounds 2 – 4 react with ozone in CsOH solution to form the corresponding nitroborates Cs[CF 3 (CF 2 ) n (CF 3 ) 2 BNO 2 ] ( 2a ), ( 3a ) and Cs[(C 2 F 5 ) 3 BNO 2 ] (4a) . The structure of 4a has been determined by X-ray diffraction.

Comparison of glucose conversion to 5-HMF using different modified mordenites in ionic liquid and biphasic media

Modified mordenites have been used in the direct conversion of glucose into 5-hydroxymethylfurfural (5-HMF) in two different media: the ionic liquid 1-butyl-3-methylimidazolium bromide ([BMIM]Br) and a biphasic system composed of water–acetone and ethyl acetate. The results revealed that there are crucial differences in the final catalytic performances. Modified mordenite treated with 1 M NH4Cl only, with a moderate Si/Al ratio of 11.2 and a high content of strong Bronsted acid sites (TPDNH3 acidity of 1.39 mmol g−1), possessed the highest catalytic activity resulting in 64% 5-HMF yield with 97% glucose conversion in the ionic liquid system. On the other hand, the mordenite treated with 1 M NH4Cl and 2.4 M NH4F, with a total acidity of 1.51 mmol g−1, mainly due to Lewis acid sites, gave 50% 5-HMF yield with 98% conversion in the biphasic system. The presence of strong Lewis acid sites has a major effect on the catalytic activity in aqueous–organic biphasic medium, in agreement with earlier works that showed that the reaction proceeds via Lewis acid-catalyzed isomerization followed by Bronsted acid-catalyzed dehydration. In contrast, the quick adsorption and strong interaction of the ionic liquid with the zeolite, which hinders the diffusion of the products, enhances the role of zeolite mesoporosity in the catalytic activity when the reaction is carried out in ionic liquid solution.

Controlled growth of hydroxyapatite on the surface of natural stilbite from Ethiopia: application in mitigation of fluorosis

This contribution reports the preparation of a composite material based on a natural zeolite rich in calcium, stilbite, on which surface nanosized hydroxyapatite is grown under controlled conditions. Low crystallisation temperatures enable the crystallisation of nano-sized hydroxyapatite crystals, which display a very high intrinsic capacity (based on weight of hydroxyapatite) of fluoride removal. The low cost and easy accessibility of the materials employed for its preparation, as well as the simplicity of the synthesis procedure, make these materials suitable candidates for their use in fluoride removal from drinking water.

ELECTROCHEMICAL AND OZONE OXIDATION OF (CF3)3B.NH3 : FORMATION AND CHARACTERIZATION OF PRODUCTS WITH NONDEGRADATED (CF3)3B GROUPS

(CF3)3B · NH3 (1) has been oxidized in aqueous solution using a platinum anode. At pH = 8–9 in CsOH/Cs2CO3 solution Cs[(CF3)3B–NO2] (2), Cs2[(CF3)3B–N(O)=N(O)–B(CF3)3] (3) and Cs2[(CF3)3B–N=N(O)–B(CF3)3] (4) are formed. Compound 3 slowly hydrolyses to yield the hydroxyborate Cs[(CF3)3B–OH] (5). Compound 2 and traces of 3 and 5 were also formed by oxidation of 1 or (CF3)3B · NHEt2 with ozone. The constitution of the novel borates has been deduced from multinuclear NMR, IR and mass spectra. The structures of 2–5 have been investigated by single-crystal X-ray diffraction.

Synthesis of zeolite A using kaolin from Ethiopia and its application in detergents

Most commercial manufacturers of soap and detergents in developing countries and few developed countries are still using environmentally unfriendly phosphate based materials like sodium tripolyphosphate as detergent builders. Detergents that contain phosphorus contribute to the eutrophication of fresh water bodies. To surmount this problem, many detergent manufacturers are currently using zeolite A as the builder material which has proved to be a better substitute for phosphorus containing additives. Despite its remarkable potential, the high cost of zeolite A has limited its effective use in detergents. In this work detergent-grade zeolite A has been synthesized from the Ethiopian kaolin collected from the southern part of the country with the molar gel composition of Na2O:Al2O3:2SiO2:37H2O. Two routes are surveyed for the synthesis of zeolite A: alkali fusion using raw kaolin and conventional hydrothermal synthesis. The resulting zeolite A samples are studied by X-ray diffraction (XRD), scanning electron microscopy (SEM), chemical analysis (ICP) and thermogravimetry (TGA). Moreover, the cation exchange capacity (CEC) of >310 mg CaCO3 per g as well as the average particle size of 3 μm of zeolite A is found to be satisfactory to be used as a detergent builder. This study also focused on evaluating its potential use as a detergent by analyzing some physicochemical properties like foam height, pH value, moisture content and alcohol and water insolubility of the formulated detergent using our synthetic zeolite A. The result showed that the synthesized detergent has comparable detergency to commercial brands of powder detergents.

Piperazine-bridged homodinuclear transition metal complexes

Piperazine-bridged transition metal complexes of the type [M(etdtc)]2ppzdtc and [M1(etdtc)2]2ppzdtc [where M = Mn(II), Fe(II), Co(II), Ni(II), Cu(II), Zn(II), Cd(II) and Hg(II), M1 = Cr(III), Fe(III), etdtc = (S2NC5H10) and ppzdtc = [S2C(NCH2CH2)2CS2] have been synthesised and characterised by elemental analyses, magnetic susceptibility measurements, TGA/DSC, IR and electronic spectroscopy and conductivity measurements. The presence of only one (C–S) stretching frequency at around 1000 cm−1 supports symmetrical bonding of the dithiocarbamato-moiety. The low molar conductance value of the complexes in DMSO at 25 °C indicates their non-electrolytic behaviour. Thermogravimetric analysis showed only two-step, simple pyrolysis. The decomposition is generally exothermic, leading to the formation of metal sulfide as the final product. The complexes of divalent metal ions appear to be tetrahedral, excepting Cu(II) and Ni(II) which are square-planar, while those of trivalent metal ions are octahedral, which is also corroborated from their electronic spectra and magnetic moment data.