Ana Ruiz

Surface activation by Pt-nanoclusters on titania for gas sensing applications

Abstract Platinum supported on titania was prepared by two impregnation procedures using platinum chloride as a precursor. The catalytic precursor has been introduced before and after titania structural stabilisation, followed in both cases by a calcination process for chemical stabilisation. Anatase surface reactivity towards platinum is higher than rutile since better catalytic incorporation has been observed, by X-ray fluorescence (XRF) analyses, when introduced in anatase phase. Likewise, X-ray photoelectron spectroscopy (XPS) measurements show that the surface concentration of platinum nanoclusters is improved when adding the precursor in anatase phase. Depending on the additive concentration and the stabilisation temperature, platinum nanoclusters exhibit grain sizes between 2 and 4 nm, as shown by high resolution TEM (HRTEM) micrographs. However, concentrations higher than 2.5 at.% Pt/Ti, lead to a clustering phenomena to grain sizes up to 200 nm. Pt/TiO2 with 2.4 at.% metal content and calcined at 1100 °C shows maximum density of Pt nanoparticles and enhanced sensing behaviour. The response of thick-film Pt/TiO2 layers under gas exposures has been monitored showing that their suitability for in situ control of combustion processes is strongly related to the technological procedure used in sensor fabrication.

Study of the influence of Nb content and sintering temperature on TiO2 sensing films

Nb-doped TiO2 nanopowders have been synthesized with a wide range of Nb contents (0–10 at.%) and of calcination temperatures (600–900 °C). The materials have been structurally characterized by means of X-ray diffraction, Raman spectroscopy and transmission electron microscopy. The niobium introduction retards the anatase-to-rutile transformation and hinders grain growth mechanisms. The electrical behavior studied for CO and ethanol gases showed that the response to ethanol is slightly diminished by the incorporation of Nb atoms and not affected by the structure modification. However, the response to CO is modified by structure changes such as the anatase/rutile transformation, grain size and Nb segregation. For the samples treated at 700 °C, the best response to CO is achieved for 4 at.% of Nb.

Nanosized Nb-TiO/sub 2/ gas sensors derived from alkoxides hydrolization

Nanocrystalline TiO/sub 2/ modified with Nb has been produced through the sol-gel technique. Nanopowders have been obtained by means of the hydrolysis of pure alkoxides with deionized water and peptization of the resulting hydrolysate with diluted acid nitric at 100/spl deg/C. The addition of Nb stabilizes the anatase phase to higher temperatures. XRD spectra of the undoped and the Nb-doped samples show that the undoped sample has been almost totally converted to rutile at 600/spl deg/C, meanwhile the doped samples present still a low percentage of rutile phase. Nanocrystalline powders stabilized at 600/spl deg/C with grain sizes of about 17 nm have successfully been synthesized by the addition of Nb with a concentration of 2% at., which appears to be an adequate additive concentration to improve the gas sensor performances, such as it is suggested by the catalytic conversion efficiency experiments performed from FTIR measurements. FTIR absorbance spectra show that catalytic conversion of CO occurs at lower temperatures when niobium is introduced. The electrical response of the films to different concentrations of CO and ethanol has been monitored in dry and wet environments in order to test the influence of humidity in the sensor response. The addition of Nb decreases the working temperature and increases the stability of the layers. Also, large enhancement of the response time is obtained even with lower working temperatures. Moreover, humidity effects on the gas sensor response toward CO and ethanol are less important in Nb-doped samples than in the undoped ones.

Monitoring in resuscitation: Comparison of cardiac output measurement between pulmonary artery catheter and NICO

AIM The cardiac output and coronary perfusion pressure generated from chest compressions during resuscitation manoeuvres can predict effectiveness and successful outcome. Until now, there is no good method for haemodynamic monitoring during resuscitation. Noninvasive partial carbon dioxide rebreathing system (NICO, Novametrix Medical Systems, Inc., Wallingford, CT, USA) is a relatively new non-invasive alternative to thermodilution for measuring cardiac output. The accuracy of the NICO system has not been evaluated during resuscitation. The aim of this study is to compare thermodilution cardiac output method with NICO system and to assess the utility of NICO during resuscitation. METHODS AND DESIGN Experimental study in 24 Yorkshire pigs. Paired measurements of cardiac output were determined during resuscitation (before ventricular fibrillation and after 5, 15, 30 and 45 min of resuscitation) in the supine position. The average of 3 consecutive thermodilution cardiac output measurements (10 ml 20 degrees C saline) was compared with the corresponding NICO measurement. RESULTS Bland and Altman plot and Lins concordance coefficient showed a high correlation between NICO and thermodilution cardiac output measurements although NICO has a tendency to underestimate cardiac output when compared to thermodilution at normal values of cardiac output. CONCLUSIONS There is a high degree of agreement between cardiac output measurements obtained with NICO and thermodilution cardiac output during resuscitation. The present study suggests that the NICO system may be useful to measure cardiac output generated during cardiopulmonary resuscitation.