The role of surface stoichiometry in NO2 gas sensing using single and multiple nanobelts of tin oxide.

Typically used semiconducting metal oxides (SMOs) consist of several varying factors that affect gas sensor response, including film thickness, grain size, and notably the grain-grain junctions within the active device volume, which complicates the analysis and optimisation of sensor response. In comparison, devices containing a single nanostructured element do not present grain-grain junctions, and therefore present an excellent platform to comprehend the correlation between nanostructure surface stoichiometry and sensor response to the depletion layer (Debye length, LD) variation after the analyte gas adsorption/chemisorption. In this work, nanofabricated devices containing SnO2 and Sn3O4 individual nanobelts of different thicknesses were used to estimate their LD after NO2 exposure. In the presence of 40 ppm of NO2 at 150 °C, LD of 12 nm and 8 nm were obtained for SnO2 and Sn3O4, respectively. These values were associated to the sensor signals measured using multiple nanobelts onto interdigitated electrodes, outlining that the higher sensor signal of the Sn4+ surface (up to 708 for 100 ppm NO2 at 150°) in comparison with the Sn2+ (up to 185) can be explained based on a less depleted initial state and a lower surface electron affinity caused by the Lewis acid/base interactions with oxygen species from the baseline gas. To support the proposed mechanisms, we investigated the gas sensor response of SnO2 nanobelts with a higher quantity of oxygen vacancies and correlated the results to the SnO system.

Design of chitosan-based particle systems: A review of the physicochemical foundations for tailored properties.

Chitosan-based particles are widely proposed as biocompatible drug delivery systems with mucoadhesive and permeation enhancing properties. However, strategies on how to modulate the intended biological responses are still scarce. Considering that particle properties affect the biological outcome, the rational design of the synthesis variables should be proposed to engineer drug delivery systems with improved biological performance. The purpose of this review is to establish a deeper understanding of possible correlations between these variables and the particle properties from theoretical and experimental perspectives. The fundamental physicochemical knowledge of chitosan-based polyelectrolyte complexation and surface modification is discussed focusing on chitosan-TPP, polyelectrolyte complexes, and chitosan-surface modified PLGA or lipid particles. A set of design considerations is proposed to enable future investigation in the development of chitosan particles with modulated properties. The approach presented here contributes to the rational design of chitosan-based particles that meet different requirements for biological activities.

Relevance of electronic effects on the yield of CO2 from methanol oxidation.

The yields of products of methanol oxidation (HCHO, HCOOH, and CO(2)) were studied for carbon-supported PtRu nanoparticles having different amounts of alloyed and oxide phases. It is demonstrated that the increase in the Pt 5d-band vacancy enhances the production of CO(2), which is not directly related with the catalytic activity for CO oxidation. Results prove the relevant role of oxides and, at the same time, shed some new light on mechanistic aspects of methanol oxidation on PtRu nanocatalysts. It is also demonstrated that extrapolating from the behavior of smooth surfaces to nanoparticle systems is not always valid.

Electrochemical oxidation of hydroxylamine on gold in aqueous acidic electrolytes: an in situ SERS investigation.

The electrooxidation of hydroxylamine (HAM) on roughened Au electrodes has been examined in aqueous buffered electrolytes (pH 3) using in situ surface-enhanced Raman scattering (SERS). Two distinct spectral features were observed at potentials, E, within the range in which HAM oxidation was found to ensue, centered at 803 cm(-1) for 0.55 < E < 0.8 V and at 826 cm(-1) for 1.0 < E < 1.40 V versus SCE, attributed, respectively, to adsorbed nitrite and adsorbed NO(2). Similar experiments performed in solutions containing nitrite instead of HAM under otherwise identical conditions displayed only the peak ascribed to adsorbed nitrite over the range of 0.1 < E < 0.8 V versus SCE with no additional features at higher potentials. These observations strongly suggest that under the conditions selected for these studies the oxidation of HAM on Au proceeds at least in part through a pathway that does not involve nitrite as a solution-phase intermediate.