Al‐for‐Fe substitution in hematite: the effect of low Al concentrations in the Raman spectrum of Fe2O3

Five different mixed Al‐hematites with an aluminium molar content varying from 0 to 10% were investigated by micro‐Raman spectroscopy to study the effect of Al‐for‐Fe substitution on the hematite lattice. A red shift of hematite vibrational wavenumbers and a line broadening were observed; also a shoulder located near 430 cm⁻¹ and a broad band at 670 cm⁻¹ developed. The variation of the spectral features is discussed in terms of a local disorder correlated to the insertion of Al³⁺ ions into the Fe(O)₆ octahedra constituting hematite structure. A multivariate analysis was also carried out on the spectral data to distinguish between the doped samples analysed. Copyright © 2007 John Wiley & Sons, Ltd.     

Low‐Cost,Thermoresponsive Wettability of Surfaces: Poly(N‐isopropylacrylamide)/Polystyrene Composite Films Prepared by Electrospinning

Low‐cost, responsive poly(N‐isopropylacrylamide)/polystyrene composite films were prepared by a facile electrospinning technique. The surface structures and wettabilities of the composite films are tunable by simply controlling the concentration of polymer. With a proper proportion of each polymer, the wettability of the surface can be switched between superhydrophilicity and superhydrophobicity when the temperature is changed from 20 °C to 50 °C. The combination of a stimuli‐responsive polymer with micro/nanostructures on the surface of the composite film contributes to this unique surface property.

     

High‐pressure studies of the micro‐Raman spectra of iron cyanide complexes: Prussian blue (Fe4[Fe(CN)6]3), potassium ferricyanide (K3[Fe(CN)6]), and sodium nitroprusside (Na2[Fe(CN)5(NO)]·2H2O)

The pressure dependences of the peaks observed in the micro‐Raman spectra of Prussian blue (Fe₄[Fe(CN)₆]₃), potassium ferricyanide (K₃[Fe(CN)₆]), and sodium nitroprusside (Na₂[Fe(CN)₅(NO)]·2H₂O) have been measured up to 5.0 GPa. The vibrational modes of Prussian blue appearing at 201 and 365 cm⁻¹ show negative dν/dP values and Grüneisen parameters and are assigned to the transverse bending modes of the Fe C N Fe linkage which can contribute to a negative thermal expansion behavior. A phase transition occurring between 2.0 and 2.8 GPa in potassium ferricyanide is shown by changes in the spectral region 150–700 cm⁻¹. In the spectra of the nitroprusside ion, there are strong interactions between the FeN stretching mode and the FeNO bending and the axial CN stretching modes. The pressure dependence of the NO stretching vibration is positive, 5.6 cm⁻¹ GPa⁻¹, in contrast to the negative behavior in the iron(II)‐meso‐tetraphenyl porphyrinate complex. Copyright © 2011 John Wiley & Sons, Ltd.     

An integrated spectroscopic approach to investigate pigments and engobes on pre‐Roman pottery

Painted Canosa ceramics were examined to identify the nature of the pigments employed and their manufacturing technology. A multi‐technique approach was used, comprising Raman microspectroscopy and laser ablation hyphenated to inductively coupled plasma‐mass spectrometry (LA‐ICP‐MS). The analysed samples were mainly produced for burial in tombs and were not intended for everyday use. They belong to the period between the end of the mid‐7th century and the first half of the 4th century BC, and were excavated from the Toppicelli archaeological district near the suburbs of Canosa (Puglia, Italy). Forty‐eight pottery fragments were available for this study. No handling of the samples was required for the Raman study, and it was possible to excise the pigmented layer in such a way that the lacunae were not distinguishable to the naked eye due to the micrometric size of the laser spot as far as LA‐ICP‐MS is concerned. Their combination turned out to be quite useful for the investigation of these archaeological materials: the chemical nature of the white, red, brown and black pigments employed in the pottery manufacture was investigated. Iron and manganese compounds were identified as the red and brown/black main colouring substances, respectively; on the other hand, whites and engobes (whitish slips) were based on kaolinite. This set of colouring substances is of importance, as it enabled the artisan to obtain in one oxidising firing cycle brown, black and red paints. Finally, the finding of manganese black in these Canosa potsherds confirms that Canosa was an important centre connecting the near East to central Italy and Europe since the pre‐Roman age. Copyright © 2010 John Wiley & Sons, Ltd.     

Nonlinear optics in spheres: from second harmonic scattering to quasi‐phase matched generation in whispering gallery modes

Over the last fifteen years, a series of theoretical and experimental investigations have demonstrated the usefulness of circular geometries to tailor second‐order nonlinear optical effects. However, until recently, such effects have remained rather weak, calling for their enhancement. In parallel, developments in the field of high quality factor spherical or ring resonators have shown that many different types of light‐matter interactions can be dramatically amplified when light is coupled in the whispering gallery modes of such resonators. In high‐quality spherical micro‐resonators, close to one million interactions can occur between a nonlinear molecule and a circulating light pulse. Recent research on nonlinear optics in spherical geometry is reviewed, from micrometer‐size spheres to whispering gallery mode resonators.     

Micro/Nanoengineered α-Fe2O3 Nanoaggregate Conformably Enclosed by Ultrathin N-Doped Carbon Shell for Ultrastable Lithium Storage and Insight into Phase Evolution Mechanism

The Fe-based transition metal oxides are promising anode candidates for lithium storage considering their high specific capacity, low cost, and environmental compatibility. However, the poor electron/ion conductivity and significant volume stress limit their cycle and rate performances. Furthermore, the phenomena of capacity rise and sudden decay for α-Fe₂O₃ have appeared in most reports. Here, a uniform micro/nano α-Fe₂O₃ nanoaggregate conformably enclosed in an ultrathin N-doped carbon network (denoted as M/N-α-Fe₂O₃@NC) is designed. The M/N porous balls combine the merits of secondary nanoparticles to shorten the Li⁺ transportation pathways as well as alleviating volume expansion, and primary microballs to stabilize the electrode/electrolyte interface. Furthermore, the ultrathin carbon shell favors fast electron transfer and protects the electrode from electrolyte corrosion. Therefore, the M/N-α-Fe₂O₃@NC electrode delivers an excellent reversible capacity of 901 mA h g⁻¹ with capacity retention up to 94.0 % after 200 cycles at 0.2 A g⁻¹. Notably, the capacity rise does not happen during cycling. Moreover, the lithium storage mechanism is elucidated by ex situ XRD and HRTEM experiments. It is verified that the reversible phase transformation of α↔γ occurs during the first cycle, whereas only the α-Fe₂O₃ phase is reversibly transformed during subsequent cycles. This study offers a simple and scalable strategy for the practical application of high-performance Fe₂O₃ electrodes.     

Monodisperse silica nanoparticles coated with gold nanoparticles as a sorbent for the extraction of phenol and dihydroxybenzenes from water samples based on dispersive micro‐solid‐phase extraction: Response surface methodology

A selective and sensitive method was developed based on dispersive micro‐solid‐phase extraction for the extraction of hydroquinone, resorcinol, pyrocatechol and phenol from water samples prior to high‐performance liquid chromatography with UV detection. SiO₂, SiO₂@MPTES, and SiO₂@MPTES@Au nanoparticles (MPTES = 3‐mercaptopropyltriethoxysilane) were synthesized and characterized by scanning electronic microscopy, thermogravimetric analysis, differential thermogravimetric analysis, and infrared spectroscopy. Variables such as the amount of sorbent (mg), pH and ionic strength of sample the solution, the volume of eluent solvent (μL), vortex and ultrasonic times (min) were investigated by Plackett–Burman design. The significant variables optimized by a Box–Behnken design were combined by a desirability function. Under optimized conditions, the calibration graphs of phenol and dihydroxybenzenes were linear in a concentration range of 1–500 μg/L, and with correlation coefficients more than 0.995. The limits of detection for hydroquinone, resorcinol, pyrocatechol, and phenol were 0.54, 0.58, 0.46, and 1.24 μg/L, and the limits of quantification were 1.81, 1.93, 1.54, and 4.23 μg/L, respectively. This procedure was successfully employed to determine target analytes in spiked water samples; the relative mean recoveries ranged from 93.5 to 98.9%.