A considerable increase in the saturation magnetization, M s (40%), and initial susceptibility of ultrasmall (<5 nm) iron oxide nanoparticles prepared by laser pyrolysis was obtained through an optimized acid treatment. Moreover, a significant enhancement in the colloidal properties, such as smaller aggregate sizes in aqueous media and increased surface charge densities, was found after this chemical protocol. The results are consistent with a reduction in nanoparticle surface disorder induced by a dissolutionÀ recrystallization mechanism.

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Thin films composed of Au nanoparticles dispersed inside a TiO 2 -NiO mixed oxide matrix are prepared by the sol-gel method, resulting in nanostructured composites with a morphology and crystallinity that depend on synthesis parameters and thermal treatment. Their functional activity as hydrogen sulfide optical sensors is due to Au-localized surface plasmon resonance (SPR) which is reversible. The detection sensitivity is shown to be down to a few parts per million of H 2 S, and almost no interference in response is observed during simultaneous exposure to CO or H 2 , resulting in a highly sensitive and selective sensor for hydrogen sulfide detection. For mechanistic studies, experimental evidence using reaction product analysis and thin film surface characterization suggests a direct catalytic oxidation of H 2 S over the Au-TiO 2 -NiO nanocomposite film.

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