Helder T. Gomes

Catalytic properties of carbon materials for wet oxidation of aniline

A mesoporous carbon xerogel with a significant amount of oxygen functional groups and a commercial activated carbon, were tested in the catalytic wet air oxidation of aniline at 200 degrees C and 6.9 bar of oxygen partial pressure. Both carbon materials showed high activity in aniline and total organic carbon removal, a clear increase in the removal efficiency relatively to non-catalytic wet air oxidation being observed. The best results in terms of aniline removal were obtained with carbon xerogel, an almost complete aniline conversion after 1h oxidation with high selectivity to non-organic compounds being achieved. The materials were characterized by thermogravimetric analysis, temperature programmed desorption, N(2) adsorption and scanning electron microscopy, in order to relate their performances to the chemical and textural characteristics. It was concluded that the removal efficiency, attributed to both adsorption and catalytic activity, is related to the mesoporous character of the materials and to the presence of specific oxygen containing functional groups at their surface. The effect of catalytic activity was found to be more important in the removal of aniline than the effect of adsorption at the materials surface. The results obtained indicate that mesoporous carbon xerogels are promising catalysts for CWAO processes.

Liquid‐Phase Hydrogenation of Unsaturated Aldehydes: Enhancing Selectivity of Multiwalled Carbon Nanotube‐Supported Catalysts by Thermal Activation

Platinum and iridium organometallic precursors are used to prepare nanosized, thermally stable multiwalled carbon nanotube‐supported catalysts. The materials are characterized by N2 adsorption at 77 K, temperature‐programmed desorption coupled with mass spectrometry, H2 chemisorption, transmission electron microscopy and thermogravimetric analysis; they are tested in the selective hydrogenation of cinnamaldehyde to cinnamyl alcohol under mild conditions (363 K and 1 MPa). A thermal activation at 973 K is found to have a very positive effect over both activity and selectivity, leading to selectivities of approximately 70 %, at 50 % conversion, regardless of the active metal phase (Pt or Ir). Since no noticeable differences in the metal particle sizes are detected, the results are interpreted in light of an enhanced metal/support interaction. This effect, induced by the removal of oxygenated surface groups, is thought to change the adsorption mechanism of the cinnamaldehyde molecule.

A new OMCVD iridium precursor for thin film deposition

Deposits of noble metals, particularly Pt, Pd, Rh, or Ir, prepared by CVD are of particular interest because of their low resistivity and high thermal stability. The major application is in microelectronics where they can replace gold as interconnectors and contacts; other potential applications are protective coatings, gas sensors, or catalysts. Our interest in the latter field has prompted us to develop a CVDfluidized bed reactor in order to prepare supported catalysts that are highly dispersed on porous substrates. Among the noble metals cited above, iridium has been the subject of only a few studies, and suitable CVD precursors (i.e., volatile, easily synthesized, thermally stable during gas phase transport, characterized by a clean decomposition, and non-toxic) are relatively scarce. Iridium halides yield high quality films on graphite substrates at temperatures near 800 C under an H2/CO/Ar atmosphere. [3] Iridium acetylacetonates provide deposits with measurable impurity levels above 500 C, but addition of a small amount of oxygen gas allows the production of high-purity films in the same temperature range. Tris-(allyl)-iridium(III), an airsensitive precursor, was used to produce clean deposits at temperatures as low as 100 C, under H2, on SiO2 substrates. (1,5-COD)(Cp)Ir and (1,5-COD)(CpMe)Ir were used by Hoke et al. to produce high purity films in the range 120±160 C. Finally, very recently (1,5-COD) (hfac)Ir and (1,5-COD)(thd)Ir (where hfac = 1,1,1,5,5,5-hexafluoroacetylacetonate and thd = 2,2,6,6-tetramethyl-3,5-heptanedionate) were used to deposit thin films at 250 C to 400 C on SiO2/Si, Pt/Si, and Cu/Si substrates. [7] The easy and highyield synthesis of a new iridium volatile precursor was desirable. Surprisingly, although carbonyl complexes are often used in OMCVD, they have not yet been used for deposition of iridium. In this work, we report a new and simple synthesis of [Ir(l-SC(CH3)3)(CO)2]2 (tetracarbonyl bis(l-(2methyl-2-propane-thiolato))diiridium), and the preliminary studies of its use as precursor for OMCVD on planar graphitic carbon substrates. The previously reported synthesis of [Ir(l-SC(CH3)3)(CO)2]2 requires three steps and produces a clean complex with a 60 % yield based on iridium salt; no particular information concerning its volatility is available. We describe here a facile one-step synthesis that consists of the production of the [IrX2(CO)2] ± (X = Cl, I) anion from iridium salts and of its reaction with 2-methyl-2-propanethiol. This complex (Fig. 1), stable to air and moisture, has been characterized by H and C NMR, FTIR, and mass spectrometry

In vitro biomineralization by osteoblast-like cells II. Characterization of cellular culture supernatants

The quantification of total calcium, phosphorus, iron, chromium and nickel in cell culture medium by electrochemical or spectroscopic means may require digestion of samples. Nevertheless, when pH adjustment is performed for values higher than about 6.5, the formation of two phases occurs: a white precipitate and a clear solution. Analysing both phases using microelectrodes, atomic absorption spectrometry (AAS), diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy, X-ray dispersive (XRD) analysis, scanning electron microscopy (SEM) and energy dispersive spectroscopic (EDS) analysis, it was observed that iron, chromium and nickel are not co-precipitating with the white solid phase. If quantification of calcium, phosphorus and magnesium is intended, a ten-fold dilution at least, must be performed to avoid most of these elements going into the precipitate. This knowledge is crucial if a mineralization study is going to be made.

Role of nitrogen doping on the performance of carbon nanotube catalysts: a catalytic wet peroxide oxidation application

Four magnetic carbon nanotube (CNT) samples (undoped, completely N‐doped, and two selectively N‐doped) were synthesized by chemical vapor deposition. The materials were tested in the catalytic wet peroxide oxidation (CWPO) of highly concentrated 4‐nitrophenol solutions (4‐NP, 5 g L−1). Relatively mild operating conditions were considered (atmospheric pressure, T=50 °C, pH 3), using a catalyst load of 2.5 g L−1 and the stoichiometric amount of H2O2 needed for the complete mineralization of 4‐NP. N‐doping was identified to influence considerably the CWPO performance of the materials. In particular, undoped CNTs, with a moderate hydrophobicity, favor the controllable and efficient decomposition of H2O2 into highly reactive hydroxyl radicals (HO.), thus showing high catalytic activity for 4‐NP degradation. On the other hand, the completely N‐doped catalyst, fully hydrophilic, favors a quick decomposition of H2O2 into nonreactive O2 and H2O species. The selectively N‐doped amphiphilic catalysts, that is, hybrid structures containing undoped sections followed by N‐doped ones, provided intermediate results, namely, a higher N content favored H2O2 decomposition towards nonreactive H2O and O2 species, whereas a lower N content resulted in the formation of HO., increasing 4‐NP mineralization. Catalyst stability and reusability were also investigated by consecutive CWPO runs.

Thermal Infrared Image Processing to Assess Heat Generated by Magnetic Nanoparticles for Hyperthermia Applications

Magnetic fluid hyperthermia (MFH) is considered a promising therapeutic technique for the treatment of cancer cells, in which magnetic nanoparticles (MNPs) with superparamagnetic behavior generate mild-temperatures under an AC magnetic field to selectively destroy the abnormal cancer cells, in detriment of the healthy ones. However, the poor heating efficiency of most NMPs and the imprecise experimental determination of the temperature field during the treatment, are two of the majors drawbacks for its clinical advance. Thus, in this work, different MNPs were developed and tested under an AC magnetic field (~1.10 kA/m and 200 kHz), and the heat generated by them was assessed by an infrared camera. The resulting thermal images were processed in MATLAB after the thermographic calibration of the infrared camera. The results show the potential to use this thermal technique for the improvement and advance of MFH as a clinical therapy.

Multifunctional graphene-based magnetic nanocarriers for combined hyperthermia and dual stimuli-responsive drug delivery

The synthesis of hydrophilic graphene-based yolk-shell magnetic nanoparticles functionalized with copolymer pluronic F-127 (GYSMNP@PF127) is herein reported to achieve an efficient multifunctional biomedical system for mild hyperthermia and stimuli-responsive drug delivery. In vitro tests revealed the extraordinary ability of GYSMNP@PF127 to act as smart stimuli-responsive multifunctional nanomedicine platform for cancer therapy, exhibiting (i) an outstanding loading capacity of 91% (w/w, representing 910 μg mg-1) of the chemotherapeutic drug doxorubicin, (ii) a high heating efficiency under an alternating (AC) magnetic field (intrinsic power loss ranging from 2.1-2.7 nHm2 kg-1), and (iii) a dual pH and thermal stimuli-responsive drug controlled release (46% at acidic tumour pH vs 7% at physiological pH) under AC magnetic field, in just 30 min. Additionally, GYSMNP@PF127 presents optimal hydrodynamic diameter (DH = 180 nm) with negative surface charge, high haemocompatibility for blood stream applications and tumour cellular uptake of drug nanocarriers. Due to its physicochemical, magnetic and biocompatibility properties, the developed graphene-based magnetic nanocarrier shows high promise as dual exogenous (AC field)/endogenous (pH) stimuli-responsive actuators for targeted thermo-chemotherapy, combining magnetic hyperthermia and controlled drug release triggered by the abnormal tumour environment. The presented strategy and findings can represent a new way to design and develop highly stable added-value graphene-based nanostructures for the combined treatment of cancer.

The Effect of a Static Magnetic Field on the Flow of Iron Oxide Magnetic Nanoparticles Through Glass Capillaries

Iron oxide nanoparticles were developed using solvothermal synthesis and suspended in a physiological fluid constituted by erythrocytes in order to perform studies of flow behaviour in glass microchannels. The main purpose of this work was to study the influence of different iron oxide nanoparticles and magnetic fields in the plasma layer thickness and also the influence of the magnetic field in the area composed of nanoparticles attracted to the wall of the microchannel. The results obtained show that nanoparticles with magnetic characteristics promote the thinning of the plasma layer, in contrast to the behaviour observed with nanoparticles without magnetic characteristics. It was also observed upon application of magnetic fields with different intensities, the plasma layer tend to disappear in some areas depending on the type of particles. Moreover, the area of nanoparticles attracted to the microchannel wall increases with the increase of the magnetic field intensity.