Presence Of Pt Nanoparticles Research Articles

Photoswitchable Electrocatalysis and Catalyzed Chemiluminescence Using Photoisomerizable Monolayer-Functionalized Surfaces and Pt Nanoparticles

A photoisomerizable monolayer consisting of carboxypropyl nitrospiropyran (1a) linked to an aminopropyl siloxane layer associated with an indium tin oxide surface is used to photoswitch the electrocatalyzed reduction of H2O2 in the presence of Pt nanoparticles (NPs) or to photostimulate the generation of chemiluminescence in the presence of Pt NPs, H2O2, and luminol. Photoisomerization of 1a to the protonated merocyanine, 1b, layer results in the electrostatic attraction of the negatively charged Pt NPs to the surface. This facilitates the electrocatalyzed reduction of H2O2 or the catalyzed generation of chemiluminescence in the presence of H2O2/luminol. Further photoisomerization of the 1b monolayer results in the formation of the nitrospiropyran layer that allows the washing off of the surface-bound Pt NPs. The resulting 1a-modified surface is inactive toward the reduction of H2O2 or toward the generation of chemiluminescence.

On a thermally induced readout mechanism in super-resolution optical disks

We have simultaneously measured the carrier-to-noise ratio (CNR) as well as the transmitted and reflected light intensities from platinum oxide based super-resolution near-field structure (PtOx super-RENS) disks. The the reflected and transmitted light intensities were found to decrease and increase, respectively, as the CNR value increased. The phase-change material AgInSbTe (AIST) used in PtOx super-RENS disks was found to exhibit a strong optical nonlinearity with respect to readout laser power. AIST becomes transparent at higher laser powers. To ascertain whether the presence of Pt nanoparticles is important to the readout mechanism, a super-RENS disk was fabricated in which the PtOx layer was replaced with a metal-free phthalocyanine (H2Pc) layer and the CNR of the H2Pc disk was measured. From the observation that the CNR value was equivalent to that of a disk made using PtOx, we conclude that the presence of nanoparticles does not play an important role in the super-RENS readout mechanism. Finally, we also investigated the use of Si and the alloy Ge2Sb2Te5 in lieu of AIST in a super-RENS disk and simple three layer structure disks. The super-resolution effect was observed for all disk types. Based upon these observations, we discuss the possibility of a thermal origin for the super-resolution effect in all super-resolution disks.

Catalytic reduction of Np(VI) with formic acid in the presence of platinum nanoparticles

The kinetics of catalytic reduction of Np(VI) with formic acid in the presence of Pt nanoparticles of different types (“brown” colloid stabilized with sodium polyacrylate and nonstabilized “gray” colloid) was studied. In both cases in the examined range of conditions ([Np(VI)]0 = 2.80 × 10−4−9.03 × 10−4 M; [HCOOH] = 0.03–1.0 M; [Pt] = 4 × 10−7 −2 × 10−5 M; T = 18–60°C) the reaction is zero-order with respect to [Np(VI)] and first-order with respect to [HCOOH]. The catalytic activity of the nonstabilized “gray” colloid exceeds by almost an order of magnitude that of the “brown” colloid, due to the blocking effect of stabilizing polyelectrolyte molecules on the active catalytic centers. The dependence of the reaction rate on the sodium polyacrylate concentration in the range 1 × 10−4−1 × 10−2 M is nonmonotonic, due to deflocculation of the nanoparticles. The mechanism of the catalytic reduction of Np(VI) with formic acid in the presence of Pt colloids is discussed; it involves a slow step of dissociative chemisorption of HCOOH molecules on the nanoparticle surface.