A.O. Porto

Pyrolysis of organotin compounds: A preparative method for nanometric tin dioxide powders

Nanometric tin dioxide powders were obtained by pyrolysis of organotin oxide based compounds such as Sn3O3Bu6 (1) and Sn4O6Bu4 (2) (Bu = n-butyl). The thermal behaviour of 1 and 2 was studied by thermogravimetric analysis (TG) and with simultaneous differential thermal analysis (DTA). Pyrolysis experiments were carried out in three different atmospheres (N2, air and O2) and the residual powders were characterised by X-ray diffraction (XRD) and the morphology was investigated by scanning electron microscopy (SEM). The XRD data showed the formation of pure SnO2 when the decomposition process was accomplished in air or O2, however, in N2, and for Sn4O6Bu4, the X-ray study indicated the formation of a mixture of SnO/SnO2. The micrographs revealed grains of 30–40 nm, approximately.

119Sn Mössbauer spectroscopic study of nanometric tin dioxide powders prepared by pyrolysis of organotin oxides

Abstract This paper reports the results of 119 Sn Mossbauer Spectroscopy of residues from the pyrolysis of Sn 3 O 3 Bu 6 ( 1 ) and Sn 4 O 6 Bu 4 ( 2 ) (Bu= n -butyl) in air, O 2 , and N 2 . The isomer shift and quadrupole splitting parameters of the samples allowed the identification of the tin oxidation states, as well as the number of non-equivalent coordinated tin sites. The result of the 119 Sn Mossbauer study correlates perfectly with those of X-ray electron probe microanalysis, scanning electron microscopy and X-ray powder diffraction for the formation of pure SnO 2 from the decomposition of ( 1 ) and ( 2 ) in air or O 2 . However, in N 2 , evidences suggest the formation of a mixture of SnO 2 and SnO.

Inhibition of positronium formation and its quenching reactions in binary solid solutions and mixtures of metal tris-2,2,6,6-tetramethyl-3,5-heptanedionate (dpm) complexes

Abstract The inhibition of positronium formation and its quenching reactions have been studied in binary solid solutions formed by Al(dpm) 3 as a matrix, and Co(dpm) 3 , Fe(dpm) 3 and Mn(dpm) 3 as guest molecules, by lifetime and Doppler broadening spectroscopies. In all the solid solutions studied the quenching of positronium lifetime by redox reactions was observed. The total inhibition and quenching rate constants determined for each system are similar. The full-width at half-maximum of the annihilation line increases with increasing guest molecule mole fraction, indicating the presence of redox reactions combining with inhibition processes. The corresponding mixtures were studied as blanks.

Positron annihilation study in binary molecular solid solutions of metal acetylacetonate complexes using positron annihilation lifetime (PAL) and Doppler broadening (DBS) spectroscopies

Abstract PAL and DBS techniques have been used to study inhibition of positronium (Ps) formation in binary molecular solid solutions of Al(III) (tris)-acetylacetonate (acac), as matrix, and Co(III), Fe(III), Ru(III), Rh(III), and Ir(III) (tris)-acetylacetonates, as guest molecules. For all the studied systems, no Ps quenching reactions have been observed. For Al (1− x ) Co ( x ) (acac) 3 , Al (1− x ) Fe ( x ) (acac) 3 , and Al (1− x ) Ru ( x ) (acac) 3 systems, a strong inhibition of Ps formation was observed with increasing of guest molecule concentration. The obtained Ps yields measured by PAL were fitted by the Stern-Volmer equation. The DBS results confirm the inhibition constants ( k ) previously determined by PAL technique, except for the Al (1− x ) Ru ( x ) (acac) 3 system, where the experimental and calculated Doppler broadening curves are quite different. Only in Al (1− x ) Ir ( x ) (acac) 3 system, the inhiition effect was not detected. The highest total inhibition constants belong to Al (1− x ) Co ( x ) (acac) 3 and Al (1− x ) Ru ( x ) (acac) 3 systems and the smallest one to Al (1− x ) Rh ( x ) (acac) 3 system. The magnitude of the obtained k values was associated with the ability of the guest complexes to scavenge electrons and are closely related to the redox properties of the complexes. X-ray diffraction measurements were made to confirm the hypothesis that all studied samples are single phase systems and that the introduction of the guest molecules in the matrix lattice does not result in significant crystalline changes. These results are well explained in the framework of the spur model and show that the chemical properties determine the Ps yields in molecular solids, regardless of their free volume characteristics.

ANALYTICAL APPLICATION OF POSITRON LIFETIME SPECTROSCOPY IN THE CHARACTERIZATION OF BINARY SOLID SOLUTIONS

Positron Lifetime Spectroscopy (LS) measurements were performed in a series of binary molecular solid solutions of the general formula M1−xGxL3, where L(ligand)=acetylacetone, dipivaloylmethane, or N-benzoyl-N-phenylhydroxylamine, M=Al(III), Ga(III) or In(III), as matrix, and G=Cr(III), Mn(III), Fe(III), Co(III), Ru(III), Rh(III) and Ir(III), as guest molecules, and the corresponding mechanical mixtures. For the solid solutions, the o-Ps yield values (I3) decrease very rapidly with the increase of the guest mole fraction, showing a high efficient Ps inhibition process, while for the corresponding mechanical mixtures, these values decrease linearly with the increase of the “guest” molecule concentration, indicating the presence of two distinct phases. These results confirm our previous proposal that the LS technique is able to characterize solid solutions formed by one matrix, in whichI3 values are high, and one guest, in which theI3 values are very low.

One-pot synthesis of amine-functionalized graphene oxide by microwave-assisted reactions: an outstanding alternative for supporting materials in supercapacitors

A simple and straightforward method using microwave-assisted reactions is presented for the functionalization of graphene oxide with aromatic and non-aromatic amines, notedly dibenzylamine (DBA), p-phenylenediamine (PPD), diisopropylamine (DPA) and piperidine (PA). The as-synthesized amine-functionalized graphene oxide materials (amine-GO) were characterized using spectroscopic techniques including XRD, FTIR, 13C NMR, XPS, TEM for imaging and thermogravimetric analysis (TGA). The characterization confirmed the functionalization for all amines, reaching relatively high surface nitrogen atomic concentrations of up to 8.8%. The investigations of electrochemical behavior for the amine-GOs show the significant improvement in GOs electrochemical properties through amine functionalization, exhibiting long life cycle stability and reaching specific capacitance values of up to 290 F g−1 and 260 F g−1 for GO-PA and GO-DPA samples, respectively, confirming their potential application as alternative supporting materials in supercapacitors.

Thermal Decomposition of Dibutyltin(IV) Sulphide Supported on α-Αl2ο3

In this paper we report the preparation of tin sulphides on the surface of α-Α1203. The starting material was prepared by a mixture of dibutyltin(IV) sulphide dissolved in ethanol with a suspension of alumina in the same solvent. The residues were obtained after removing the solvent and subsequent pyrolysis of the supported product. The samples were prepared in order to have, after pyrolysis, ratios of Sn/a-Al203 of 5% (1), 10% (2), 15% (3), 30% (4), 40% (5) and 60% (6) in weight. The X-ray powder diffraction results were not conclusive since lines of some phases of SnS, SnS2, Sn2S3 and Sn3S4 are too close one to another. However, Sn Mössbauer experiments suggest that SnS2 is formed at first, and then Sn2S3 and finally Sn3S4, as the Sn(IV) concentration increases. Scanning electron microscopy (SEM) revealed that crystals of tin sulphides have grown on the surface of big crystals of α-Α1203. Finally, X-ray electron probe microanalyses (ΕΡΜΑ) shows the presence of ΑΙ, Ο, S and Sn in all samples.

Direct Synthesis of Porous Carbon Materials Prepared from Diethyldithiocarbamate Metal Complexes and Their Electrochemical Behavior

Porous carbon materials were prepared at low temperatures via thermal decomposition of iron, nickel and cobalt N,N-diethyldithiocarbamates (DDT). X-ray diffraction data showed two peaks at 2θ (25.5° and 43.5°) that indicate the presence of graphite-like structures. Raman spectra displayed D and G bands in the range from 1312 to 1321 cm and 1587 to 1593 cm, respectively, which were fitted with 4 components. All spectra showed two low intensity D* (1190 cm) and D’’ (1500 cm) bands, assigned to sp–sp bonds in disordered carbonaceous materials and amorphous carbon, respectively. Transmission electron microscopy images showed agglomerates of spherical particles formed by graphitic segments. The results showed that the carbon material obtained from iron N,N-diethyldithiocarbamate, Fe(DDT)3, is structurally better organized than the others and the pore size distribution curves confirmed that this material presents high degree of mesoporosity. Voltammetric curves obtained using KOH and H2SO4 electrolytes showed hysteresis behavior typical of capacitors charge/discharge process. The carbon material prepared from Fe(DDT)3 displayed the highest specific capacitance in acidic media, 59 F g, which was associated to its high degree of mesoporosity.