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561.
Botelho J. R. Souza A. G. Nunes L. M. Chagas A. P. Garcia dos Santos I. M. da Conceição M. M. Dunstan P. O. 《Journal of Thermal Analysis and Calorimetry》2002,67(2):413-417
The standard molar enthalpies of formation of crystalline dialkyldithiocarbamates chelates, [Pd(S2CNR2)2], with R=C2H5, n-C3H7, n-C4H9 and i-C4H9, were determined through reaction-solution calorimetry in acetone, at 298.15 K. From the standard molar enthalpies of formation
of the gaseous chelates, the homolytic (172.4±3.8, 182.5±3.2,150.9±3.1 and 162.6±3.1 kJ mol−1) and heterolytic (745.0±3.8, 803.7±3.3,834.3±3.1 and 735.2±3.0 kJ mol−1) mean palladium-sulphur bond-dissociation enthalpies were calculated.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
562.
By dissolution of PVC and polyaniline in dimethylformamide, a series of blends PVC-polyaniline were produced which were studied
by scanning electron microscopy and thermogravimetry. Special attention is focused on the kinetic study of the thermal degradation
steps by using non-isothermal thermogravimetric data. The results show that the thermal stability of the synthesized blend
is decreased as the total amount of polyaniline is enhanced. Furthermore, the Brřnsted acid doped blend is more stable than
the corresponding undoped one. PVC and the PVC-polyaniline blends exhibit two mass loss steps which activation energy values
are in the range from 176 to 283 kJ mol-1 and 306 to 322 kJ mol-1, respectively.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
563.
Comprehension of short- and medium-range order of phosphate glasses is a topic of interest, due to the close relation between network structure and mechanical, thermal, and optical properties. In this work, the short-range structure of glasses (1 - x)Ca(PO(3))(2).xAl(PO(3))(3) with 0 < or = x < or = 0.47 was studied using solid-state nuclear magnetic resonance spectroscopy, Raman spectroscopy, density measurements, and differential scanning calorimetry. The bonding between a network modifier species, Al, and the network forming phosphate groups was probed using high-resolution nuclear magnetic resonance spectroscopy of (27)Al and (31)P. Changes in the compositional behavior of the density, glass transition temperature, PO(2) symmetric vibrations, and Al coordination number were verified at around x = 0.30. (31)P NMR spectra show the presence of phosphorus in Q(2) sites with nonbridging oxygens (NBOs) coordinated by Ca ions and also Q(2) sites with one NBO coordinated by Al (namely, Q(2)(1Al)). The changes in the properties as a function of x can be understood by considering the mean coordination number measured for Al and the formation of only Q(2) and Q(2)(1Al) species. It is possible to calculate that a network formed only by Q(2)(1Al) phosphates can just exist up to the upper limit of x = 0.48. Above this value, Q(2)(2Al) species should appear, imposing a major reorganization of the network. Above x = 0.30 the network undergoes a progressive reorganization to incorporate Al ions, maintaining the condition that only Q(2)(1Al) species are formed. These observations support the idea that bonding principles for cationic species inferred originally in binary phosphate glasses can also be extended to ternary systems. 相似文献
564.
S.C. Nunes V. de Zea Bermudez D. Ostrovskii L.D. Carlos 《Vibrational Spectroscopy》2006,40(2):278-288
The interactions occurring in di-urea (NHC(O)NH) cross-linked poly(oxyethylene) (POE)/siloxane hybrids (di-ureasils) doped with zinc triflate (Zn(CF3SO3)2) were investigated by Fourier Transform infrared (FT-IR) and Raman (FT-Raman) spectroscopies. Bonding of the Zn2+ ions to the urea carbonyl oxygen atoms occurs in the entire range of compositions studied (∞ > n ≥ 1, where n, salt content, is the molar ratio of oxyethylene moieties per Zn2+ ion). At n > 20 the incorporation of the guest cations progressively reduces the number of free CO groups. At n = 20 the saturation of the urea cross-links is attained and the Zn2+ ions start to coordinate to the POE chains giving rise to the formation of a crystalline POE/Zn(CF3SO3)2 complex. The latter process occurs at the expense of the destruction of the hydrogen-bonded POE/urea structures of the host di-ureasil structure. New hydrogen-bonded associations, more ordered than the urea–urea aggregates present in the non-doped matrix and including Zn2+OC coordination, emerge in parallel. “Free” and weakly coordinated CF3SO3− ions, present in all the xerogels studied, appear to be the main charge carriers of the conductivity maximum of this family of ormolytes located at n = 60 at 30 °C. In materials with n ≤ 20 contact ion pairs, “cross-link separated” ions pairs and higher ionic aggregates appear. The data reported demonstrate that the behaviour of the di-ureasils doped with triflate salts depends on the type of cation. 相似文献
565.
Madeira P Nunes MR Borges C Costa FM Florêncio MH 《Rapid communications in mass spectrometry : RCM》2005,19(14):2015-2020
The benzidine photodegradation process was studied using UV/Vis spectroscopy and electrospray ionization mass spectrometry (ESI-MS) combined with collision-induced dissociation (CID) and tandem mass spectrometry (MS/MS). Mass spectrometry was used to characterize benzidine and to identify and characterize possible degradation products and intermediates. The MS data showed that benzidine is quite persistent in aqueous medium. Moreover, the MS analysis enabled us to propose the following three degradation products/intermediates: 4'-nitro-4-biphenylamine, tetrahydroxybiphenyl and 4,4'-dinitrobiphenyl. For the benzidine molecular ion and protonated molecule and for the protonated molecules of the degradation products/intermediates detected, fragmentation patterns are proposed based on CID and MS/MS data. For the photodegradation process different catalysts were used, namely the commercial TiO2 Degussa P25, and the laboratory-prepared ZnO, TiO2 anatase and a titanium-zinc oxide with a perovskite type structure. Comparison of the different catalysts showed that degradation was favoured with the commercial TiO2. Nevertheless, the other catalysts appear to be promising and economic alternatives for potential future remediation studies. 相似文献
566.
Rodella Cristiane B. Franco Roberto W.A. Magon Claudio J. Donoso Jose P. Nunes Luis A.O. Saeki Margarida J. Aegerter Michel A. Florentino Ariovaldo O. 《Journal of Sol-Gel Science and Technology》2002,25(1):75-82
This work describes a modified sol-gel method for the preparation of V2O5/TiO2 catalysts. The samples have been characterized by N2 adsorption at 77 K, X-ray Diffractometry (XRD), Scanning Electronic Microscopy (SEM/EDX) and Fourier Transform Infrared Spectroscopy (FT-IR). The surface area increases with the vanadia loading from 24 m2 g–1 for pure TiO2 to 87 m2 g–1 for 9 wt% of V2O5. The rutile form is predominant for pure TiO2 but becomes enriched with anatase phase when vanadia loading is increased. No crystalline V2O5 phase was observed in the diffractograms of the catalysts. Analysis by SEM showed heterogeneous granulation of particles with high vanadium dispersion. Two species of surface vanadium were observed by FT-IR spectroscopy: a monomeric vanadyl and polymeric vanadates. The vanadyl/vanadate ratio remains practically constant. Ethanol oxidation was used as a catalytic test in a temperature range from 350 to 560 K. The catalytic activity starts around 380 K. For the sample with 9 wt% of vanadia, the conversion of ethanol into acetaldehyde as the main product was approximately 90% at 473 K. 相似文献
567.
568.
569.
Rapee Gosalawit Suwabun Chirachanchai Sergey Shishatskiy Suzana P. Nunes 《Journal of membrane science》2008
A nanocomposite membrane of sulfonated montmorillonite/sulfonated poly(ether ether ketone) (SMMT/SPEEK) is proposed for direct methanol fuel cells (DMFCs). The SMMT is clay modified with silane of which the structure consists of a sulfonic acid group for proton conductivity improvement. The micro- and nano-scaled morphologies of the membranes perform the increase in inorganic aggregation with SMMT loading content as confirmed by SEM and AFM. The membrane stability, i.e., the liquid uptake in water and in methanol aqueous solution, as well as the mechanical stability increases with the SMMT loading content whereas thermal stability does not improve significantly. The methanol permeability reduction is obtained when the SMMT loading content increases for various methanol concentrations (1.5–4.5 M). A comparative study of the SPEEK nanocomposite membranes with SMMT and with pristine MMT shows fourfold proton conductivity enhancement after sulfonation. The DMFC single cell tests inform us that all nanocomposite membranes give the significant performance revealed by the plot of current density–voltage and power density. 相似文献
570.
Joyce Nunes Bianchin Renata Mior Cleide Sandra Tavares Araújo Eduardo Carasek 《Talanta》2009,78(2):333-2300
In this study a method for the determination of cadmium in fuel alcohol using solid-phase extraction with a flow injection analysis system and detection by flame atomic absorption spectrometry was developed. The sorbent material used was a vermicompost commonly used as a garden fertilizer. The chemical and flow variables of the on-line preconcentration system were optimized by means of a full factorial design. The selected factors were: sorbent mass, sample pH, buffer concentration and sample flow rate. The optimum extraction conditions were obtained using sample pH in the range of 7.3-8.3 buffered with tris(hydroxymethyl)aminomethane at 50 mmol L−1, a sample flow rate of 4.5 mL min−1 and 160 mg of sorbent mass. With the optimized conditions, the preconcentration factor, limit of detection and sample throughput were estimated as 32 (for preconcentration of 10 mL sample), 1.7 μg L−1 and 20 samples per hour, respectively. The analytical curve was linear from 5 up to at least 50 μg L−1, with a correlation coefficient of 0.998 and a relative standard deviation of 2.4% (35 μg L−1, n = 7). The developed method was successfully applied to spiked fuel alcohol, and accuracy was assessed through recovery tests, with recovery ranging from 94% to 100%. 相似文献