Photoelectrochemical Behavior of Silver Nanoparticles inside Mesoporous Titania: Plasmon-Induced Charge Separation Effect

Fabrication of silver nanoparticles within chitosan based microgels for catalysis

Chitosan based monodisperse poly[chitosan-N-isopropylmethacrylamide-acrylic acid] [P(CNA)] microgels were produced via precipitation polymerization. Resulting crosslinked P(CNA) micro particles were used as micro-reactors to prepare silver nanoparticles within the polymeric network by chemical reduction of Ag⁺ ions with sodium borohydride. Various techniques including transmission electron microscopy (TEM), Fourier transform infrared (FTIR) spectroscopy and ultraviolet-visible (UV-vis) spectroscopy were used to analyze P(CNA) microgels and Ag-P(CNA) hybrid microgels. Catalytic potential of Ag-P(CNA) hybrid system towards individual and simultaneous reduction of various nitroarenes like p-nitrophenol (pNP), o-nitrophenol (oNP), p-nitroaniline (pNA) and o-nitroaniline (oNA) into corresponding aminoarenes using sodium borohydride as a reductant in aqueous medium was evaluated. The catalytic activity of Ag-P(CNA) system towards both the individual and simultaneous reduction of nitroarenes was examined at various concentrations of catalyst. The values of pseudo first order rate constant (k₁) for reduction of individual nitroarene and multiple nitroarenes were determined for comparison. The Ag-P(CNA) hybrid microgel system was found to be stable, economical and efficient catalyst for rapid individual and simultaneous reduction of nitroarenes.

Chemical Interface Damping in Nonstoichiometric Semiconductor Plasmonic Nanocrystals: An Effect of the Surrounding Environment

Semiconductor plasmonic nanocrystals (NCs) have been utilized for an enormous number of plasmon-enhanced spectroscopic and energy conversion applications. Plasmonic NCs are extremely high light absorbers, and optical properties can be easily manipulated across the UV-vis-NIR spectrum region by changing mere chemical compositions and the surrounding environment of the NCs. This feature article focuses on reassessing plasmon dynamics by changing the interface composition between NCs and the surrounding medium to ascertain the damping contribution from chemical interface damping (CID). Also, this feature article deciphers a fundamental understanding of hot-carrier relaxation and extraction from plasmonic materials. On the route to determining the different relaxation dynamics of nonstoichiometric Cu_2-xS/Se NCs, we have employed a transient ultrafast pump-probe broadband spectrometer. First, we have described the ultrafast plasmon relaxation dynamics of nonstoichiometric Cu_2-xS NCs by varying the copper to sulfur ratio, and then we carefully compare how two surface ligands (oleylamine and 3-mercaptopropionic acid) lead to significantly different transient kinetics of the same plasmonic (Cu_2-xSe) NCs because of different capping agents. Along with this, we have described the impact of a molecular adsorbate (methylene blue) on ultrafast plasmon relaxation dynamics of the nonstoichiometric Cu_2-xSe NCs system. Finally, the chemical interface damping effect has been compared in the Cu_2-xS NCs system after capping with two distinct capping ligands: oleylamine and oleic acid. For the proof of concept, plasmonic thin-film devices were fabricated and exhibited higher conductivity/photoconductivity performance in oleic acid-capped NCs because of a deprotonated carboxyl functional group. We have also introduced a model and mechanism of chemical interface damping in a nonstoichiometric plasmonic semiconductor (Cu_2-xS/Se) NC system. This feature article highlights the importance of the surface functionalization of nonstoichiometric plasmonic semiconductors to develop new advanced semiconductor-based devices such as infrared photodetectors, plasmonic solar cells, and efficient NIR phototransistors.

Decoration of titanium dioxide nanotubes with silver nanoparticles using the photochemical deposition method and their application as an electrocatalyst to determine tinidazole

In this study, titanium nanotube electrodes were decorated with silver nanoparticles (AgNPs/TiO₂NTs) and used as an electrocatalyst for the reduction of tinidazole. AgNPs/TiO₂NTs are constructed by anodization of titanium sheet metal and photochemical deposition of AgNPs on TiO₂NTs. The structural and elemental analysis characteristics of the AgNPs/TiO₂NT electrode have been studied by scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), and X-ray diffraction (XRD) methods. Based on the cyclic voltammetric data, it has been confirmed that the AgNPs/TiO₂NT electrode has good electrocatalytic activity to reduce tinidazole. Two liner concentration ranges of 0.2-55.0 μM and 55.0-111.2 μM were obtained by amperometric method. A detection limit of 60.9 nM was obtained for measuring tinidazole at the AgNPs/TiO₂NT electrode surface. In addition, the designed sensor has been successfully used for quantitative measurement of tinidazole in pharmaceutical and human urine samples.

In Situ Synthesis of Mesoporous TiO2 Nanofibers Surface-Decorated with AuAg Alloy Nanoparticles Anchored by Heterojunction Exhibiting Enhanced Solar Active Photocatalysis

We designed an electrospinning synthesis protocol to obtain in situ, the mesoporous TiO₂ nanofibers, which are surface-decorated with plasmonic AuAg nanoparticles (AuAg-mTNF-H). Such alloy nanoparticles are found to be partially exposed on the surface of the nanofibers. Characterization by HRTEM and EDS confirmed the formation of 1:1 AuAg alloy nanoparticles on the surface of TiO₂ nanofibers with heterojunction at the interfaces. On the basis of electron microscopic characterization, we proposed that, during the formation of the nanofibers, the incorporated metal ions with surface capping of negative charges migrated toward the outer surface of the nascent fibers under the influence of high positive voltage required for electrospinning. As a result, after the subsequent thermal treatment, the crystallization of TiO₂ nanofibers and the formation of alloy nanoparticles took place, leading to the formation of a deep heterojunction through partial embedment of the nanoparticles. The formation of AuAg alloy also restricted the oxidation of Ag, thus making the nanoparticles highly stable in ambient condition. Accordingly, such unique AuAg-mTNF-H photocatalyst shows strong light absorption property covering the entire range of visible wavelengths with stability. The solar light harvesting property of AuAg-mTNF-H was verified by monitoring solar light induced H₂ evolution via water splitting and photodecomposition of MB. In both the cases AuAg-mTNF-H showed excellent H₂ evolution and photodecomposition of dye.

Electroactive Area from Porous Oxide Films Loaded with Silver Nanoparticles: Electrochemical and Electron Tomography Observations

Electrochemical studies of nanomaterial-based electrodes have been widely developed for catalyst and energy-harvesting applications. The evolution of these electrodes over time and their efficiency have been extensively studied and analyzed in order to optimize their performance. However, the electrochemical responses of electrodes are rarely studied in terms of the position of the active species within these electrodes. In this paper, we highlight that the spatial location of silver nanoparticles (NPs) embedded inside semiconductive porous films, TiO₂ or Fe₂O₃, is crucial for the electrochemical response. In fact, by using cycling voltammetry and electron tomography experiments, we show the existence of an "electroactive area", corresponding to a reduced thickness of the sample in close vicinity to a fluorine-doped tin oxide substrate where most of the electrochemical responses originate. Our results demonstrate that, for a film thickness of several hundred nanometers, only less than 30 nm close to the substrate responds electrochemically. However, cyclic voltammetry empties the electroactive area of silver NPs. Therefore, application of chronoamperometry coupled to irradiation allowed regeneration of this area thanks to an increased diffusion of silver species. In this paper, we also show the significant diffusion of silver species within the film during electrochemical experiments, a phenomenon even increased by irradiation. These results are therefore an important step that shows the importance of the localization of active species within a porous film and help in understanding and increasing the durability of nanomaterial-based electrodes.