Microwave-Assisted Synthesis of Pt/SnO2 for the Catalytic Reduction of 4-Nitrophenol to 4-Aminophenol.

In this study, we present a new approach for the synthesis of Pt/SnO2 catalysts using microwave radiation. Pt(IV) and Sn(IV) inorganic precursors (H2PtCl6 and SnCl4) and ammonia were used, which allowed the controlled formation of platinum particles on the anisotropic SnO2 support. The synthesized Pt/SnO2 samples are mesoporous and exhibit a reversible physisorption isotherm of type IV. The XRD patterns confirmed the presence of platinum maxima in all Pt/SnO2 samples. The Williamson-Hall diagram showed SnO2 anisotropy with crystallite sizes of ~10 nm along the c-axis (< 00l >) and ~5 nm along the a-axis (< h00 >). SEM analysis revealed anisotropic, urchin-like SnO2 particles. XPS results indicated relatively low average oxidation states of platinum, close to Pt metal. 119Sn Mössbauer spectroscopy indicated electronic interactions between Pt and SnO2 particles. The synthesized samples were used for the catalytic reduction of 4-nitrophenol (4-NP) to 4-aminophenol (4-AP) in the presence of excess NaBH4. The catalytic activity of the Pt/SnO2 samples for the reduction of 4-NP to 4-AP was optimized by varying the synthesis parameters and Pt loading. The optimal platinum loading for the reduction of 4-NP to 4-AP on the anisotropic SnO2 support is 5 mol% with an apparent rate constant k = 0.59 × 10-2 s-1. The Pt/SnO2 sample showed exceptional reusability and retained an efficiency of 81.4% after ten cycles.

Change in Magnetic Anisotropy at the Surface and in the Bulk of FINEMET Induced by Swift Heavy Ion Irradiation.

57Fe transmission and conversion electron Mössbauer spectroscopy as well as XRD were used to study the effect of swift heavy ion irradiation on stress-annealed FINEMET samples with a composition of Fe73.5Si13.5Nb3B9Cu1. The XRD of the samples indicated changes neither in the crystal structure nor in the texture of irradiated ribbons as compared to those of non-irradiated ones. However, changes in the magnetic anisotropy both in the bulk as well as at the surface of the FINEMET alloy ribbons irradiated by 160 MeV 132Xe ions with a fluence of 1013 ion cm-2 were revealed via the decrease in relative areas of the second and fifth lines of the magnetic sextets in the corresponding Mössbauer spectra. The irradiation-induced change in the magnetic anisotropy in the bulk was found to be similar or somewhat higher than that at the surface. The results are discussed in terms of the defects produced by irradiation and corresponding changes in the orientation of spins depending on the direction of the stress generated around these defects.

Magnetic Anisotropy and Microstructure in Electrodeposited Quaternary Sn-Fe-Ni-Co Alloys with Amorphous Character.

Sn-Fe-Ni-Co quaternary alloys, in the composition range of 37-44 at% Sn, 35-39 at% Fe, 6-8 at% Ni and 13-17 at% Co, were prepared by direct current (DC) and pulse plating (PP) electrodeposition. The alloy deposits were characterized by XRD, 57Fe and 119Sn conversion electron Mössbauer spectroscopy, SEM-EDX and magnetization measurements. XRD revealed the amorphous character of the quaternary alloy deposits. The dominant ferromagnetic character of the deposits was shown by magnetization and Mössbauer spectroscopy measurements. Room temperature Mössbauer spectra showed minor paramagnetic phases, where their occurrences (~3-20%) are correlated to the electrodeposition parameters (Jdep from -16 to -23 mA/cm2 for DC, Jpulse from -40 to -75 mA/cm2 for PP), the composition and the saturation magnetization (~52-73 emu/g). A considerable difference was found in the magnetization curves applying parallel or perpendicular orientation of the applied fields, indicating magnetic anisotropy both in DC and pulse plated alloy coatings.