Development of magnetic,ferrite supported palladium catalysts for 2,4-dinitrotoluene hydrogenation

Cobalt, copper, and nickel ferrite spinel nanoparticles have been synthesized by using a combination of sonochemical treatment and combustion. The magnetic nanoparticles have been used as supports to prepare ~4 wt% palladium catalysts. The ferrites were dispersed in an ethanolic solution of Pd(II) nitrate by ultrasonication. The palladium ions were reduced to metallic Pd nanoparticles, which were then attached to the surface of the different metal oxide supports. Thus, three different catalysts (Pd/CoFe₂O₄, Pd/CuFe₂O₄, Pd/NiFe₂O₄) were made and tested in the hydrogenation of 2,4-dinitrotoluene (DNT). A possible reaction mechanism, including the detected species, has been envisaged based on the results. The highest 2,4-diaminotoluene (TDA) yield (99 n/n%) has been achieved by using the Pd/NiFe₂O₄ catalyst. Furthermore, the TDA yield was also reasonable (84.2 n/n%) when the Pd/CoFe₂O₄ catalyst was used. In this case, complete and easy recovery of the catalyst from the reaction medium is ensured, as the ferrite support is fully magnetic. Thus, the catalyst is very well suited for applicationy in the hydrogenation of DNT or other aromatic nitro compounds.     

Biological Activity of Flavonoids Copper Complexes

Three flavonoid copper(II) complexes Cu₂(quercetin)(CH₃COO)₃(CH₃OH) ( 1 ), Cu(anthrarufin)(CH₃COO)·1/2H₂O ( 2 ) and Cu(naringin)(OCH₃)(CH₃OH)₂ ( 3 ) have been synthesized and characterized by elemental analysis, IR, electronic absorption and EPR (X‐band) spectroscopy. The complexes have a strong protective action over the Δsod1 mutant of S. cerevisiae against reactive oxygen radicals generated by an external source of free radicals (H₂O₂ or the superoxide‐generating, menadione). On the other hand, the complexes cleave DNA efficiently even in the absence of reducing agents. The main reactive oxygen species responsible for the DNA strand cleavage have been determined using radical scavengers. A probably mechanism of the DNA damage is proposed.     

Über das paramagnetische α-Fe2O3, das durch Spurenmengen gewisser Kationen ferromagnetisch wird,sowie deren Auswirkungen bei der Luftoxydation des Fe(OH)2

α-Fe₂O₃, containing small amounts of the oxides of Mg, Ni or Co, becomes ferromagnetic at 800°C, and this without any X-ray evidence for ferrite contaminations. The ferrites, and other ferromagnetic compounds, may, however, be prepared by air oxidation of Fe(OH)₂.     

New insight in the O2 activation by nano Fe/Cu bimetals: The synergistic role of Cu(0) and Fe(II)

This study demonstrated that as-synthesized nano Fe/Cu bimetals could achieve significant enhancement in the degradation of diclofenac (DCF), as compared to much slow removal of DCF by Cu(II) or zero valent iron nanoparticles (nZVI), respectively. Further observations on the evolution of O₂ activation process by nano Fe/Cu bimetals was conducted stretching to the preparation phase (started by nZVI/Cu²⁺). Interesting breakpoints were observed with obvious sudden increase in the DCF degradation efficiency and decrease in solution pH, as the original nZVI just consumed up to Fe(II) and Cu(II) appeared again. It suggested that the four-electrons reaction of O₂ and Cu-deposited nZVI would occur to generate water prior to the breakpoints, while Cu(0) and Fe(II) would play most important role in activation of O₂ afterwards. Through the electron spin resonance (ESR) analysis and quenching experiments, OH was identified as the responsible reactive species. Further time-dependent quantifications in the cases of Cu(0)/Fe(II) systems were carried out. It was found that the OH accumulation was positively and linearly correlated with nCu dose, Fe(II) consumption, and Fe(II) dose, respectively. Since either Cu(0) or Fe(II) would be inefficient in activating oxygen to produce OH, a stage-evolution mechanism of O₂ activated by nano Fe/Cu bimetals was proposed involving: (a) Rapid consumption of Fe(0) and release of Fe(II) based on the Cu-Fe galvanic corrosion, (b) adsorption and transformation of O₂ to O₂²⁻ at the nCu surface, and (c) Fe(II)-catalyzed activation of the adsorbed O₂²⁻ to OH.     

Thermal behavior of Ni,Co and Fe succinates embedded in silica matrix

This paper presents the thermal behavior of Co, Ni and Fe succinates obtained by sol-gel synthesis using Co(II), Ni(II) and Fe(III) nitrates, 1,4-butanediol and tetraethyl orthosilicate as reactants. The thermal analysis revealed the formation of succinates at 413–453 K and their decomposition to ferrites at 503–623 K. The rate constants for the decomposition of succinates to ferrites, calculated using the isotherms at 473, 523, 573 and 623 K, were used to determine the activation energy of each ferrite (NiFe₂O₄, Ni_0.3Co_0.7Fe₂O₄, Ni_0.7Co_0.3Fe₂O₄ and CoFe₂O₄) embedded in the silica matrix. By increasing the Ni content in the mixed Ni–Co ferrites, the activation energy decreases from 13.530 to 1.944 kJ mol^?1. The formation and decomposition of succinate precursors and the formation of silica matrix were confirmed by FT-IR spectroscopy, while the formation of CoFe₂O₄ and NiFe₂O₄ single-phases embedded in the silica matrix was confirmed by X-ray diffraction analysis. The nanocrystallites size decreases from 31.7 (CoFe₂O₄) to 18.5 nm (NiFe₂O₄). The optical band gap of mixed Co–Ni ferrites was significantly higher than that corresponding to CoFe₂O₄. The photocatalytic activity of the samples was evaluated against Rhodamine B under visible light. All the samples have photocatalytic activities, the best performance being obtained in the case of Ni_0.7Co_0.3Fe₂O₄.

     

Microwave Synthesis of Co,Ni, Cu,Zn Ferrites

Solid-phase synthesis of cobalt, nickel, copper, and zinc ferrites with spinel structure was performed from oxides of these metals and natural magnetite under the action of microwave radiation. The optimal conditions in which the corresponding ferrites can be formed were determined by varying the irradiation parameters affecting the reaction (magnetron power and reaction duration). It was found that the solid-phase interaction of oxides of Ni, Zn, Cu, Co(II) metals gives in practically acceptable yields metal-substituted ferrospinels (NiFe₂O₄, CoFe₂O₄, ZnFe₂O₄, CuFe₂O₄) constituting the main phase of the samples. A high capacity of the precursors and target synthesis products for absorption of the microwave radiation energy at a frequency of 2.45 GHz and its transformation into heat was demonstrated. This gives reason to use these compounds when preparing catalysts for microwave-stimulated reactions.     

Synthesis and neel temperature determination of ferrites from the MO−ZnO−Fe2O3 systems (M=Cu,Co and Ni)

The Curie (Neel) temperature is successfully determined by means of a simple magnetic device attached to the Q Derivatograph (MOM, Hungary), which is widely used in many laboratories. This possibility is demonstrated by a study of ferrite materials with general formula M_xZn_1?xFe₂O₄ (M=Cu, Co and Ni;x=0.0; 0.2; 0.4; 0.5; 0.6; 0.8; 1.0). X-ray phase analysis, Mössbauer spectroscopy and microscopic examinations revealed that the obtained ferrites are monophase samples. The mixed ferrites possess more strongly expressed magnetic properties than those of the individual ferrites; the maximum magnetic interaction in these ferrites is observed at different zinc contents.     

Thermal analysis of Y1−xCaxBa2Cu3O7−y

TG and DTA analysis of Y_1?xCa_xBa₂Cu₃O_7?y suggests that the stability of the 123 phase increases with increasing Ca contents. The O(1) in the Cu(1)-O chain is unstable but O(2) and O(3) in Cu(2)-O planes are very stable. There are hardly any oxygen vacancies in the Cu(2)-O plane. The replacement of Y by Ca does not make oxygen vacancies in Cu(2)-O planes but leads to an increase in the oxidation number of copper in Cu(2)-O planes.     

Preparation of magnesium and calcium ferrites from the thermolysis of M3[Fe(cit)2]2·xH2O precursors

Magnesium and calcium ferrites have been prepared from the thermolysis of M₃[Fe(C₆H₅O₇)₂]₂·xH₂0 (M=Mg, Ca) precursors. Thermal decomposition of the precursors has been studied employing various physico-chemical techniques, i.e., TG-DSC, XRD, IR and Mössbauer spectroscopy. After dehydration the anhydrous precursors undergo an abrupt oxidative pyrolysis to yield α-Fe₂O₃ and a metastable acetone-dicarboxylate intermediate. A subsequent exothermic decomposition leads to the formation of MgO and CaCO₃ from the respective intermediates. Finally ferrite is formed as a result of solid state reaction between MO/MCO₃ and α-Fe₂O₃. Nanosized ferrites of the stoichiometry MgFe₂O₄ and Ca₂Fe₂O₅ have been obtained from magnesium and calcium bis(citrato) ferrates(III). The temperature of ferrite formation is much lower than possible in conventional ceramic method. The results have been compared with the respective oxalate and maleate precursors.     

Complex of bis(hexafluoroacetylacetonato)copper(II) with a stable acyclic nitroxide (tert-butyl)(3-keto-2-methylbutyl-2) nitroxyl oxime

A complex of bis(hexafluoroacetylacetonato)copper(II) with a stable acyclic nitroxide (tert-butyl)(3-keto-2-methylbutyl-2)nitroxyl oxime (L), Cu(hfac)₂L, has been synthesized. The structure of the complex was studied by X-ray diffraction analysis. The compound has a molecular structure with chelate coordination of the nitroxide. The tetragonally distorted octahedral environment of the copper(II) ion is formed by the oxygen atoms of the hfac anions and by the nitrogen and oxygen atoms of the oxime and nitroxyl groups of L, respectively. The nitroxyl group lies in the equatorial plane of the octahedron (d_Cu?O=1.907 Å). This type of N?O coordination leads to strong antiferromagnetic exchange interactions between the unpaired electrons of the copper(II) ion and the coordinated nitroxyl group and, as a consequence, to diamagnetism of Cu(hfac)₂L.     

Synthesis, structure and physical properties of Ru ferrites: BaMRu5O11 (M=Li and Cu) and BaM′2Ru4O11 (M′=Mn, Fe and Co)

The synthesis, structure, and physical properties of five R-type Ru ferrites with chemical formula BaMRu₅O₁₁ (M=Li and Cu) and BaM′₂Ru₄O₁₁ (M′=Mn, Fe and Co) are reported. All the ferrites crystallize in space group P6₃/mmc and consist of layers of edge sharing octahedra interconnected by pairs of face sharing octahedra and isolated trigonal bipyramids. For M=Li and Cu, the ferrites are paramagnetic metals with the M atoms found on the trigonal bipyramid sites exclusively. For M′=Mn, Fe and Co, the ferrites are soft ferromagnetic metals. For M′=Mn, the Mn atoms are mixed randomly with Ru atoms on different sites. The magnetic structure for BaMn₂Ru₄O₁₁ is reported.     

Role of catechin on collagen type I stability upon oxidation: a NMR approach

Abstract

The study focuses on the understanding, at molecular level, the mechanism of interaction between protein and flavonoids. Collagen and catechin interactions were investigated by NMR in solution and solid state. The effect of catechin on the stability of collagen to oxidation was also explored. Collagen was treated with two concentrations of catechin solutions. Oxidation was carried out by incubation of collagen solution with three oxidation systems: Fe(II)/H₂O₂, Cu(II)/H₂O₂, and NaOCl/H₂O₂. The effects of oxidation systems were evaluated by high resolution 1?D and 2?D proton spectroscopy and solid state NMR (¹³C CP MAS) experiments. Interactions between collagen and catechin preferentially occur between catechin B ring and the amino acids Pro and Hyp of collagen. Results showed that both iron and copper oxidation systems were able to interact with collagen by site specific attack. Moreover, catechin protects collagen proline from oxidation by metal/H₂O₂ systems, preventing copper and iron approach to collagene molecule;this behaviour was more evident for the copper/H₂O₂ system.     

Preparation of CuFe2O4/SiO2 nanocomposite starting from Cu(II)–Fe(III) carboxylates embedded in hybrid silica gels

Nanocomposites of the type 30 % CuFe₂O₄/70 % SiO₂ were synthesized using the modified sol–gel method starting from tetraethylorthosilicate, metal nitrates (Fe(NO₃)₃·9H₂O, Cu(NO₃)₂·3H₂O) and the diol: 1,3-propane diol. The obtained hybrid gel, which contains within the pores, the metal nitrates and diol, was thermally treated at 140 °C, when the redox reaction between metal nitrates and 1,3-propane diol takes place forming Cu(II)–Fe(III) carboxylate compounds of malonate type. The thermal decomposition of the carboxylates within the gels pores, at ~300 °C, leads to simple or mixed metal oxides, uniformly distributed within the amorphous silica matrix. The spinel system CuFe₂O₄/SiO₂ was obtained starting with 700 °C. The evolution of the spinel phase with the annealing temperature was investigated and resulted that at 1,000 °C, the matrix crystallizes into cristobalite and quartz. The formation of bulk CuFe₂O₄, starting from the same type of Cu(II)–Fe(III) carboxylate compounds was also investigated. A comparison between the thermal evolution of bulk CuFe₂O₄ and CuFe₂O₄/SiO₂ starting from Cu(II)–Fe(III) carboxylate compounds was made. The magnetic behavior of the ferrite nanocrystallites depending on the annealing temperature was also investigated.     

Stoichiometry of superconducting YBa2Cu3Oy. Determination of Cu(III)/Cu(II) ratio and oxygen content

The electrical properties of the high T_c superconductor YBa₂Cu₃O_y depend on its oxygen content. The oxygen content is indirectly determined by iodimetric measurement of the oxidation state of copper. A combination of two titrations, with and without addition of KI, prior to dissolving the sample permits the determination of the two species Cu(II) and Cu(III). A simplified automatic titration with potentiometric detection of the end-point is described. The method is suitable for rapid and reliable determinations of the Cu(III)/Cu(II) ratio and total copper content and for controlling the stoichiometry of the compound.Samples of the superconductor were analysed and the stoichiometric coefficient y for oxygen was determined with excellent results. Typically, y=6.811 ± 0.0063 (s.d.) (n=5). A comparison of the total copper content (found by direct analytical determination) with the copper concentration calculated from the stoichiometric formula gives an evaluation of possible deterioration of the sample.     

Determination of Singlet Oxygen Production and Antibacterial Effect of Nonpolar Porphyrins In Heterogeneous Systems

ABSTRACT

The possibility of using the iodide method and the method of bleaching of 4-nitroso-N, N'-dimethylaniline, developed originally for homogeneous aqueous medium for the determination of singlet oxygen production, was tested for water-insoluble nonpolar senzitizers adsorbed on the silica gel support. Sensitizers of the porphyrin and metalloporphyrin type (tetraphenylporphin (TPP), protoporphyrin IX (PPIX), tetra(4-nitrophenyl)porphin (TPP(NO₂)₄ and complexes of TPP with some divalent and trivalent metals, Cd(II)TPP, Zn(II)TPP, Co(II)TPP, Cu(II)TPP, Ni(II)TPP, Mn(II)TPPCI, and Fe(II)TPPCl) were used as model compounds. It was found that both methods used gave similar values of ¹O₂. The relative ¹O₂ production of the compounds studied decreases in the order PP=Zn(II)TPP=Cd(II)TPP > TPP(NO₂)₄> PPIX> nonactive substances.

The cytotoxic effect of ¹O₂ Produced by these substances on the silica gel support was tested using E. coli DHS-alfa bacteria. The relative ¹O₂ production values correlate with the antibacterial activity of the adsorbed substances exposed to light.     

Thermomagnetometric analysis of lithium ferrites

In this work, the magneto-phase transitions in pure lithium (Li_0.5Fe_2.5O₄), lithium–zinc (Li_0.4Fe_2.4Zn_0.2O₄) and lithium–titanium (Li_0.6Fe_2.2Ti_0.2O₄) ferrites were studied by the thermogravimetric analysis in magnetic field, which is known as the thermomagnetometry method. The ferrites were prepared by the solid-state synthesis from oxides and carbonates. The Curie point of magnetic phase in ferrites and their composite mixtures was determined from the derivative thermogravimetric curve in the region of ferrite mass change associated with the ferrimagnet–paramagnet transition in the magnetic phase. The method based on the analysis of ferrite mass change at Curie temperature was developed to estimate the ferrite phase concentrations in composite magnetic materials.

     

Synthesis and Evaluation of Graphene Aerogel-Supported MnxFe3−xO4 for Oxygen Reduction in Urea/O2 Fuel Cells

Graphene aerogel-supported manganese ferrite (Mn_xFe_3−xO₄/GAs) and reduced-graphene oxide/manganese ferrite composite (MnFe₂O₄/rGO) were synthesized and studied as cathode catalysts for oxygen reduction reactions in urea/O₂ fuel cells. MnFe₂O₄/GAs exhibited a 3D framework with a continuous macroporous structure. Among the investigated Fe/Mn ratios, the more positive oxygen reduction onset potential was observed with Fe/Mn=2/1. The half-wave potential of MnFe₂O₄/GAs was considerably more positive than that of MnFe₂O₄/rGO and comparable with that of Pt/C, while the stability of MnFe₂O₄/GAs significantly higher than that of Pt/C. The best urea/O₂ fuel cell performance was also observed with the MnFe₂O₄/GAs. The MnFe₂O₄/GAs exhibited an OCV of 0.713 V and a maximum power density of 1.7 mW cm⁻² at 60 °C. Thus, this work shows that 3D structured graphene aerogel-supported MnFe₂O₄ catalysts can be used as an efficient cathode material for alkaline fuel cells.     

Synthesis,molecular structure and reactivity of sodium 5-sulfosalicylate dihydrate and sodium[triaqua(5-sulfosalicylato)copper(II)] 2 hemihydrate

The crystal and molecular structure of sodium 5-sulfosalicylate dihydrate, Na[(H₂Ssal)(H₂O)₂], (1) (H₃Ssal=5-sulfosalicylic acid) has been determined through X-ray diffraction analysis. The 5-sulfosalicylate anion has lost the proton at the SO₃H group but retains the usual intermolecular hydrogen bond between phenolic and carboxylic oxygen. The reaction in water of 1 with [Cu(II)(H₂O)₄]SO₄·H₂O, gives rise to the green sodium[triaqua(5-sulfosalicylato)copper(II)] 2 hemihydrate, Na[(H₂O)₃(Ssal)Cu(II)]·2×0.5H₂O, (2). The 5-sulfosalicylate anion, (Ssal³⁻), coordinates rather unusually in the syn–syn coordination mode since it binds bidentately the Cu(II) ion through the carboxylic and the phenolic oxygens, with Cu(II)O_carboxylic=1.909(4) Å and Cu(II)O_phenolic=1.885(4) Å distances. Copper(II) completes its square-planar coordination with two water molecules and in addition, perpendicularly to the square-planar coordination plane, another two water molecules with long bonds are present (Cu(II)O=2.518 and 2.912 Å). The green complex 2 reacts easily with adenine in water at pH 7 giving rise to the violet tetraadeninato(diaqua)-bis(copper(II)) dihydrate, [Cu₂(Ade)₄(H₂O)₂])]·2H₂O, (3) (Ade⁻=adeninato monoanion). This complex, that geometrically resembles copper(II) acetate monohydrate, was already described by Sletten. Finally, on the basis of the present results a possible mechanism for the anticancer activity of complex 2 and of other Cu(II)–salicylate complexes is proposed and discussed.     

New 1D and 2D metal oxygen connectivities in Cu(II) succinato and glutarato coordination polymers: [Cu3(H2O)2(OH)2(C4H4O4)2] · 4H2O, [Cu4(H2O)2(OH)4(C4H4O4)2] · 5H2O and [Cu5(OH)6(C5H6O4)2] · 4H2O

Two Cu(II) hydroxo succinates [Cu₃(H₂O)₂(OH)₂(C₄H₄O₄)₂]?·?4H₂O (1) and [Cu₄(H₂O)₂(OH)₄(C₄H₄O₄)₂]?·?5H₂O (2) and one Cu(II) hydroxo glutarate [Cu₅(OH)₆(C₅H₆O₄)₂]?·?4H₂O (3) have been prepared and structurally characterized by single crystal X-ray diffraction methods. They feature 1D and 2D copper oxygen connectivity of elongated {CuO₆} octahedra in “4?+?1?+?1” and “4?+?2” coordination geometries. Within 1, linear trimers of three edge-sharing {CuO₆} octahedra are connected into copper oxygen chains, which are bridged by the anti conformational succinate anions to generate 2D layers with mono terminally coordinating gauche succinate anions on both sides. The layers are assembled into a 3D framework by interlayer hydrogen bonds with lattice H₂O molecules distributed in channels. Different from 1, the principal building units in 2 are linear tetramers of four edge-sharing {CuO₆} octahedra. The tetramers are condensed into copper oxygen chains and the succinate anions interlink them into a 3D framework with triangular channels filled by lattice H₂O molecules. The {CuO₆} octahedra in 3 are edge-shared to form unprecedented 2D inorganic layers with mono terminally coordinating glutarate anions on both sides. Interlayer hydrogen bonding interactions are responsible for supramolecular assembly of the layers into a 3D framework with lattice H₂O molecules in the channels. The inorganic layers in 3 can be described as hexagonal close packing of oxygen atoms with the Cu atoms in the octahedral cavities. The title compounds were further characterized by elemental analyses, IR spectra and thermal analyses.     

Coordination of Deprotonated Saccharin in Copper(II) Complexes. Structural Role of the Saccharinate Directed by the Ancillary N‐heterocyclic Ligands

Four different coordination patterns were observed following the partial or complete thermodynamically‐controlled ligand substitution of the hydrated tetraaquabis(o‐sulfobenzimidato‐N)copper(II) complex with heterocyclic bases as examined by X‐ray diffraction. The N‐heterocycle directs the o‐sulfobenzimidate (saccharinate) anion into the immediate coordination polyhedron of the metal by any of the imido, carbonyl or sulfonyl functionalities, or as a lattice counter‐ion in the crystal lattice. Aqua(o‐sulfobenzimidato‐O)tetrakis(4‐methylpyridine)copper(II) o‐sulfobenzimidate hemihydrate ( 1 ) crystallizes in the monoclinic space group P2₁/n [a = 14.7858(2), b = 16.9090(1), c = 26.2350(2)Å; β = 92.861(1)°], aquadi(o‐sulfobenzimidato‐N)bis(4‐propylpyridine)copper(II) ( 2 ) in the tetragonal space group P4₂/n [a = 15.4127(1), c = 13.4604(1)Å], diaquatetrakis(3‐(2‐propenyl)imidazole)copper(II) di‐o‐sulfobenzimidate ( 3b ) in the monoclinic space group P2₁/c [a = 9.3959(5), b = 28.029(2), c = 8.8763(3)Å; β = 111.175(1)°] and di(o‐sulfobenzimidato)tetra(isoquinoline)copper(II) ( 4b ) in the orthorhombic space group Pna2₁ [a = 23.2132(6), b = 11.5760(2), c = 17.6297(4)Å]. The copper atom in 1 is six‐coordinate in a distorted trans‐N₄O₂Cu octahedron with elongated copper—oxygen bonds [Cu—O_water = 2.462(3), Cu—O_sulfonyl = 2.567(3)Å]. This adduct represents the first example of a combined O_sulfonyl/ionic coordination of the o‐sulfobenzimidate ion in the same crystal. The copper atom in 2 is five‐coordinate in the form of a N₄OCu square pyramid [Cu—O_water = 2.238(5)Å]. In 3 , the o‐sulfobenzimidate anions are linked to the copper atom through the coordinated water molecule forming a distorted octahedral N₄O₂Cu environment. In 4 , the copper atom is nearly octahedrally coordinated by four nitrogen atoms and a pair of o‐sulfobenzimidate carbonyl oxygen atoms. The structural details of the o‐sulfobenzimidate coordination pattern correspond well with the 298 and 77 K FT IR spectra of the adducts. The structures of two other solid adducts, tris(3‐(2‐propenyl)imidazole)copper(II) di‐o‐sulfobenzimidate trihydrate ( 3a ) and diaquabis(o‐sulfobenzimidato‐N)bis(isoquinoline)copper(II) ( 4a ) have been predicted by their spectral features. Alteration of the o‐sulfobenzimidate coordination mode upon changing the heterocycle ligand shows that this moiety is as a convenient polyfunctional structural tool for the construction of functional solids.