Synthesis and Characterization of Rutile TiO2Nanopowders Doped with Iron Ions

Titanium dioxide nanopowders doped with different amounts of Fe ions were prepared by coprecipitation method. Obtained materials were characterized by structural (XRD), morphological (TEM and SEM), optical (UV/vis reflection and photoluminescence, and Raman), and analytical techniques (XPS and ICP-OES). XRD analysis revealed rutile crystalline phase for doped and undoped titanium dioxide obtained in the same manner. Diameter of the particles was 5–7 nm. The presence of iron ions was confirmed by XPS and ICP-OES. Doping process moved absorption threshold of TiO2into visible spectrum range. Photocatalytic activity was also checked. Doped nanopowders showed normal and up-converted photoluminescence

Спинална и церебрална тумороподобна МС, клинични и невроизобразяващи корелации

Откриването на тумороподобна МС често води до диагностична несигурност, особено ако лезиите се появяват при пациен ти без известно към момента демиелинизиращо заболяване. Супратенториалната ТМС може да бъде отграничена от тумор по някои специфични образни характеристики: несъответствие между големината на лезията и мас-ефектът и; специфичен патерн на контрастиране – отворен пръстен насочен към сивото вещество. Голямо предизвикателство е разграничаването на ТМС от първичен ЦНС лимфом (PCNSL). Подозренията за мозъчен тумор често налагат биопсия, която също може да покаже подвеждаща патохистологична находка. При солитарна тумороподобна лезия в миелона диагностичните усилия са насочени към изключване на спинални интрамедуларни тумори. Представени са два клинични случая, суспектни за тумороподибна МС в главен и гръбначен мозък с обсъждане и предложения за диагностични подходи за прецизиране на диагнозата. Тумороподобната МС е необичайна и трудна за диагностициране форма на първична демиелинизация, поради което е изключително важно интегрирането на клиничните и лабораторни данни с резултатите от образните изследвания и нерядко проследяване на случаите във времето

Degradation Mechanisms of Pt/C Fuel Cell Catalysts under Simulated Start−Stop Conditions

This manuscript investigates the degradation of a Pt/Vulcan fuel cell catalyst under simulated start stop conditions in an electrochemical half-cell. Identical location transmission electron microscopy (IL-TEM) is used to visualize the several different degradation pathways occurring on the same catalyst material under potential cycling conditions. The complexity of degradation on the nanoscale leading to macroscopic active surface area loss is demonstrated and discussed. Namely, four different degradation pathways at one single Pt/Vulcan aggregate are clearly observed. Furthermore, inhomogeneous degradation behavior for different catalyst locations is shown, and trends in degradation mechanisms related to the platinum particle size are discussed in brief. Attention is drawn to the vast field of parameters influencing catalyst stability. We also present the development of a new technique to study changes of the catalyst not only with 2D projections of standard TEM images but also in 3D. For this purpose, identical location tomography (IL-tomography) is introduced, which visualizes the 3D structure of an identical catalyst location before and after degradation

Toward Highly Stable Electrocatalysts via Nanoparticle Pore Confinement

The durability of electrode materials is a limiting parameter for many electrochemical energy conversion systems. In particular, electrocatalysts for the essential oxygen reduction reaction (ORR) present some of the most challenging instability issues shortening their practical lifetime. Here, we report a mesostructured graphitic carbon support, Hollow Graphitic Spheres (HGS) with a specific surface area exceeding 1000 m(2) g(-1) and precisely controlled pore structure, that was specifically developed to overcome the long-term catalyst degradation, while still sustaining high activity. The synthetic pathway leads to platinum nanoparticles of approximately 3 to 4 nm size encapsulated in the HGS pore structure that are stable at 850 degrees C and, more importantly, during simulated accelerated electrochemical aging. Moreover, the high stability of the cathode electrocatalyst is also retained in a fully assembled polymer electrolyte membrane fuel cell (PEMFC). Identical location scanning and scanning transmission electron microscopy (IL-SEM and IL-STEM) conclusively proved that during electrochemical cycling the encapsulation significantly suppresses detachment and agglomeration of Pt nanoparticles, two of the major degradation mechanisms in fuel cell catalysts of this particle size. Thus, beyond providing an improved electrocatalyst, this study describes the blueprint for targeted improvement of fuel cell catalysts by design of the carbon support