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Facile Fabrication of Plasmonic Enhanced Noble-Metal-Decorated ZnO Nanowire Arrays for Dye-Sensitized Solar Cells

Tan WK, Muto H, Ito T, Kawamura G, Lockman Z, Matsuda A

J Nanosci Nanotechnol, 2020 Jan 01;20(1):359-366.
PMID: 31383179 DOI: 10.1166/jnn.2020.17223

Novel decoration of high aspect ratio zinc oxide nanowires (ZnO NWs) with noble metals such as Ag and Au nanoparticles (NPs) was demonstrated in this work. A facile method of chemical deposition with good controllability, as well as good homogeneity would be a huge advantage towards large scale fabrication. The highlight of this work is the feasibility of multiple component decoration such as a hybrid (co-exist) Ag-Au NPs decorated ZnO NWs formation that could be beneficial towards the development of nanoarchitectured materials with the most desired properties. The local surface plasmon effect (LSPR) of Ag and Au NPs were confirmed using extinction spectra and significant photoelectrochemical conversion efficiency (PCE) enhancement of dye-sensitized solar cells (DSSCs) was achieved. The Ag-NPs and hybrid Ag-Au NPs decorated ZnO NWs marked an impressive 125 and 240% efficiency improvement against pure ZnO NWs. The improved dye light extinction resulted from the LSPR effect that had enabled greater electron generation leading to improved PCE. As the complex design of oxides' nanoarchitectures have reached a point of saturation, this novel method would enable further enhancement in their photoelectrochemical properties through decoration with noble metals via a simple chemical deposition route.
Nanoporous anodic Nb2O5 with pore-in-pore structure formation and its application for the photoreduction of Cr(VI)

Alias N, Hussain Z, Tan WK, Kawamura G, Muto H, Matsuda A, et al.

Chemosphere, 2021 Nov;283:131231.
PMID: 34144283 DOI: 10.1016/j.chemosphere.2021.131231

An anodic film with a nanoporous structure was formed by anodizing niobium at 60 V in fluorinated ethylene glycol (fluoride-EG). After 30 min of anodization, the anodic film exhibited a "pore-in-pore" structure; that is, there were smaller pores growing inside larger pores. The as-anodized film was weakly crystalline and became orthorhombic Nb2O5 after heat treatment. The energy band gap of the annealed nanoporous Nb2O5 film was 2.9 eV. A photocatalytic reduction experiment was performed on Cr(VI) under ultraviolet (UV) radiation by immersing the nanoporous Nb2O5 photocatalyst in a Cr(VI) solution at pH 2. The reduction process was observed to be very slow; hence, ethylenediaminetetraacetic acid (EDTA) was added as an organic hole scavenger, which resulted in 100% reduction after 45 min of irradiation. The photocatalytic reduction experiment was also performed under visible light, and findings showed that complete reduction achieved after 120 min of visible light exposure.
Fulltext Formation of Dense and High-Aspect-Ratio Iron Oxide Nanowires by Water Vapor-Assisted Thermal Oxidation and Their Cr(VI) Adsorption Properties

Budiman F, Tan WK, Kawamura G, Muto H, Matsuda A, Abdul Razak K, et al.

ACS Omega, 2021 Oct 26;6(42):28203-28214.
PMID: 34723018 DOI: 10.1021/acsomega.1c04280

Coral-like and nanowire (NW) iron oxide nanostructures were produced at 700 and 800 °C, respectively, through thermal oxidation of iron foils in air- and water vapor-assisted conditions. Water vapor-assisted thermal oxidation at 800 °C for 2 h resulted in the formation of highly crystalline α-Fe2O3 NWs with good foil surface coverage, and we propose that their formation was due to a stress-driven surface diffusion mechanism. The Cr(VI) adsorption property of an aqueous solution on α-Fe2O3 NWs was also evaluated after a contact time of 90 min. The NWs had a removal efficiency of 97% in a 225 mg/L Cr(VI) solution (pH 2, 25 °C). The kinetic characteristic of the adsorption was fitted to a pseudo-second-order kinetic model, and isothermal studies indicated that the α-Fe2O3 NWs exhibited an adsorption capacity of 66.26 mg/g. We also investigated and postulated a mechanism of the Cr(VI) adsorption in an aqueous solution of α-Fe2O3 NWs.
Photoreduction of Cr(VI) in wastewater by anodic nanoporous Nb2O5 formed at high anodizing voltage and electrolyte temperature

Alias N, Hussain Z, Tan WK, Kawamura G, Muto H, Matsuda A, et al.

Environ Sci Pollut Res Int, 2022 Aug;29(40):60600-60615.
PMID: 35426025 DOI: 10.1007/s11356-022-20005-7

In this study, nanoporous anodic film was produced by anodization of niobium, Nb in a fluoride ethylene glycol electrolyte. The effect of anodization voltage and electrolyte temperature was studied to find an optimum condition for circular, ordered, and uniform pore formation. The diameter of the pores was found to be larger when the applied voltage was increased from 20 to 80 V. The as-anodized porous film was also observed to comprise of nanocrystallites which formed due to high field-induced crystallization. The nanocrystallites grew into orthorhombic Nb2O5 after post-annealing treatment. The Cr(VI) photoreduction property of both the as-anodized and annealed Nb2O5 samples obtained using an optimized condition (anodization voltage: 60 V, electrolyte temperature: 70 °C) was compared. Interestingly, the as-anodized Nb2O5 film was found to display better photoreduction of Cr(VI) than annealed Nb2O5. However, in terms of stability, the annealed Nb2O5 presented high photocatalytic efficiency for each cycle whereas the as-anodized Nb2O5 showed degradation in photocatalytic performance when used continually.
Fulltext Ag nanoparticle-deposited TiO2 nanotube arrays for electrodes of Dye-sensitized solar cells

Kawamura G, Ohmi H, Tan WK, Lockman Z, Muto H, Matsuda A

Nanoscale Res Lett, 2015;10:219.
PMID: 26019696 DOI: 10.1186/s11671-015-0924-1

ABSTRACT: Dye-sensitized solar cells composed of a photoanode of Ag nanoparticle (NP)-deposited TiO2 nanotube (TNT) arrays were fabricated. The TNT arrays were prepared by anodizing Ti films on fluorine-doped tin oxide (FTO)-coated glass substrates. Efficient charge transportation through the ordered nanostructure of TNT arrays should be carried out compared to conventional particulate TiO2 electrodes. However, it has been a big challenge to grow TNT arrays on FTO glass substrates with the lengths needed for sufficient light-harvesting (tens of micrometers). In this work, we deposited Ag nanoparticles (NPs) on the wall of TNT arrays to enhance light-harvesting property. Dye-sensitized solar cells with these Ag NP-deposited TNT arrays yielded a higher power conversion efficiency (2.03 %) than those without Ag NPs (1.39 %).
PACS CODES: 06.60.Ei Sample preparation, 81.05.Bx Metals, Semimetals, Alloys, 81.07.De Nanotubes.