RESUMEN
HYPOTHESIS: One of the main drawbacks of metal-supported materials, traditionally prepared by the impregnation of metal salts onto pre-synthesized porous supports, is the formation of large and unevenly dispersed particles. Generally, the larger are the particles, the lower is the number of catalytic sites. Maximum atom exposure can be reached within single-atom materials, which appear therefore as the next generation of porous catalysts. EXPERIMENTS: Herein, we designed single iron atom-supported silica materials through sol-gel hydrothermal treatment using mixtures of a non-ionic surfactant (Pluronic P123) and a metallosurfactant (cetyltrimethylammoniumtrichloromonobromoferrate, CTAF) as porogens. The ratio between the Pluronic P123 and the CTAF enables to control the silica structural and textural properties. More importantly, CTAF acts as an iron source, which amount could be simply tuned by varying the non-ionic/metallo surfactants molar ratio. FINDINGS: The fine distribution of iron atoms onto the silica mesopores results from the iron distribution within the mixed micelles, which serve as templates for the polymerization of the silica matrix. Several characterization methods were used to determine the structural and textural properties of the silica material (XRD, N2 sorption isotherms and TEM) and the homogeneous distribution and lack of clustering of iron atoms in the resulting materials (elemental analysis, magnetic measurements, pair distribution function (PDF), MAS-NMR and TEM mapping). The oxidation and spin state of single-iron atoms determined from their magnetic properties were confirmed by DFT calculations. This strategy might find straightforward applications in preparing versatile single atom catalysts, with improved efficiency compared to nanosized ones.
RESUMEN
PURPOSE: Comparing Power Doppler imaging versus technetium-dimercapto-succinic-acid (Tc-DMSA) scintigraphy in acute pyelonephritis of childhood. INCLUSION CRITERIA: First episode of urinary tract infection, clinical and biological findings suggesting an upper lesion, absence of urological malformation or obstruction, absence of reflux (or vesico-ureteral reflux inferior to grade 3). Number of patients: 49, length of the study: 26 months (from November 95 to January 98). METHODS: Tc99m-DMSA scintigraphy (after five days), B mode and Power Doppler imaging (on the day of admission or the following day). Systematic cystography (day 5 to day 30). RESULTS: In terms of positive diagnosis, scintigraphy was superior to Power Doppler, and the latter was superior to B mode ultrasonography. Sensitivity (scintigraphy being the gold standard) was equal for both B mode and Power DopplerUS imaging, but combined Power Doppler and B mode US provided improved results. CONCLUSION: Currently, the results with Power Doppler imaging are insufficient to replace DMSA scintigraphy. However, Power Doppler is a good complement to B mode US.