We report the fabrication and characterization of hybrids of vertically-aligned carbon nanotube forests and gold nanoparticles for improved manipulation of their plasmonic properties. Raman spectroscopy of nanotube forests performed at the separation area of nanotube-nanoparticles shows a scattering enhancement factor of the order of 1 × 106. The enhancement is related to the plasmonic coupling of the nanoparticles and is potentially applicable in high-resolution scanning near-field optical microscopy, plasmonics, and photovoltaics.
Thin film sweat sensors utilizing ionophores have emerged as a powerful and non-invasive method for monitoring health. These sensors offer remarkable sensitivity, selectivity, and rapid response, making them a promising solution for personalized health tracking. Ionophores, specialized molecules with target-specific binding capabilities, enable accurate detection of biomarkers in real-time and continuous sweat analysis. Their integration into wearable devices allows for miniaturization and flexibility, ensuring seamless monitoring of athletes, patients, and individuals. By focusing on crucial biomarkers such as electrolytes and metabolites, these sensors provide valuable insights into dehydration, electrolyte imbalances, and metabolic disorders. Potential applications encompass health tracking, disease diagnosis, and sports performance optimization. With their exceptional performance and compatibility with wearable technology, these sensors hold great promise for enhancing personalized healthcare and promoting proactive well-being practices. In this study we will focus on the manual labor carried out for their fabrication and the improvement on its fabrication yield.
Controlling catalyst-particle formation is essential for the growth of single-wall carbon nanotube (SWCNT) arrays with improved alignment, areal mass, and height. We have previously reported the positive effect of CO2 on SWCNT growth via chemical vapor deposition, and in this study, we found its negative effect on catalyst-particle formation during annealing. A Fe (1 nm)/AlOx (15 nm) catalyst that was sputter-deposited on SiO2/Si substrates demonstrated a prolonged lifetime and enabled the growth of SWCNT arrays with better alignment, twice the height, and three times higher areal mass when the catalyst was annealed under 10 vol% H2/Ar without CO2 than with 1 vol% CO2. Detailed analysis indicated that the Fe particles could remain partially oxidized during annealing in H2 with mildly oxidative CO2, resulting in the bulk diffusion of Fe into the AlOx layer. In contrast, Fe is reduced sufficiently in H2 in the absence of CO2, thereby remaining on the AlOx surface and active for SWCNT growth. The findings of this study emphasize the importance of maintaining a highly reductive atmosphere during annealing to achieve active catalyst particles with a higher number density and longer lifetime.
Heteroepitaxial growth of rutile TiO2 nanorods from SnO2 seeds yielded radial heteromesocrystals consisting of SnO2(head) and rutile TiO2 nanorod(tail) with the SnO2(head) oriented toward the center (TiO2-NR//SnO2 HEMCs). Iron oxide clusters were formed on the surface by the chemisorption-calcination technique. The FeOx-surface modification gives rise to drastic increases in the photocatalytic activity for aerobic oxidation of 2-naphthol under irradiation of UV and visible light. As a 2D-model for 3D-TiO2-NR//SnO2 HEMC, electrochemical measurements were performed for the rutile TiO2-NR array formed on a fluorine-doped tin oxide (SnO2:F) electrode. The results showed that the FeOx clusters possess electrocatalytic activity for a multielectron oxygen reduction reaction, and the high photocurrent of the electrode is remarkably reduced by the FeOx-surface modification. Consequently, the striking photocatalytic activity of FeOx/TiO2-NR//SnO2 HEMCs was ascribable to the switching of the electron transport direction necessary for the charge separation from the long axis of the TiO2 NR to the short axis.
Cobalt chalcogenides are excellent oxygen evolution reaction (OER) precatalysts in alkaline medium as they readily form O2-evolving CoOOH entities in electrochemically accessible Co2+ sites when subjected to anodic potential. A key factor that determines the efficiency of OER in cobalt chalcogenides is the number of electrochemically accessible Co2+ sites. Here, an easy way of increasing the electrochemical accessibility of Co2+ sites in CoSe2 has been identified, which is the simple preoxidation of selenide to selenite. When screened for OER in alkali, it was found that the electrochemical accessibility of Co2+ after preoxidation of Se in CoSe2 was increased by 7.8 ± 2 times in the first cycle and 2–3 times after activation by potential sweeping and redox cycling. The corresponding OER activation energy lowered to ∼1/2 at overpotentials 450 mV or higher due to such preoxidation of Se. Irrespective of the lowering in the electrochemical accessibility of Co2+ sites from the 1st cycle to the 100th cycle, the overall OER activity was maintained to be the same. This is quite relatable as a major portion of Co2+ oxidized in the first cycle is shuttling between 3+ and 4+ states while evolving O2. Altogether, preoxidation of Se in CoSe2 benefitted the realization of increased electrochemical accessibility for Co2+ sites, improved ECSA, improved charge transfer at catalytic turnover conditions, and lowered OER activation energy.
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