Katarzyna Siuzdak

Enhanced photocatalytic, electrochemical and photoelectrochemical properties of TiO2 nanotubes arrays modified with Cu, AgCu and Bi nanoparticles obtained via radiolytic reduction

Graphical abstract

Novel nitrogen precursors for electrochemically driven doping of titania nanotubes exhibiting enhanced photoactivity

Nitrogen doped titania nanotubes were successfully sensitized by the electrochemical method, i.e. as-anodized titania was immersed in different amine (diethylenetriamine – DETA, triethylamine – TEA, and ethylenediamine – EDA) and urea (U) solutions and a constant potential was applied. The highly ordered morphology of fabricated N-TiO2 was investigated by scanning electron microscopy. Spectroscopic techniques, i.e. UV-Vis spectroscopy, Raman spectroscopy, X-ray photoelectron spectroscopy and photoluminescence spectroscopy, were utilized to characterize absorbance capability and the crystalline phase, to confirm the presence of nitrogen atoms and to study charge recombination, respectively. The highest photocurrent under both UV-Vis and visible illumination (λ > 420 nm) was registered for the N-TiO2 sample obtained from diethylenetriamine solution, used as a nitrogen precursor. The photocurrent density exhibited during UV-Vis irradiation by the most active nitrogen doped titania was 2.83 times higher compared to pure TiO2 nanotubes. The photocatalytic activity studies demonstrated a significant improvement when N-TiO2–DETA (52%) and N-TiO2–U samples (49%) where used instead of undoped TiO2 (27%). The presented results show that electrochemical doping with 0.5 M amine or urea solutions is a simple, cheap and effective strategy to introduce nitrogen atoms into the titania structure without affecting its morphology.

Enhanced photoelectrochemical and photocatalytic performance of iodine-doped titania nanotube arrays

The paper discusses the synthesis and performance of iodine doped titania nanotube arrays exhibited under irradiation. The doping procedure was performed as an additional, electrochemical process carried out after formation of nanotube arrays via anodization of the Ti substrate. The optical and structural properties were characterized using Raman, UV-vis, photoluminescence and X-ray photoelectron spectroscopy. The surface morphology and cross-section studies performed by means of scanning electron microscopy show that the ordered tubular architecture is not influenced by the doping method. However, iodine doping causes a reduction of bandgap energy and photoluminescence intensity. The nanotubular TiO2 electrodes have been monitored by electrochemical (using cyclic voltammetry and electrochemical impedance spectroscopy) and in situ UV-vis spectroelectrochemical measurements in contact with an aqueous electrolyte. Collected results show significant differences in electrochemical activity between pure and doped titania exhibited as i.e. change of Mott–Schottky relation or shift in the onset potential when a decrease in reflectance is initiated. The photocurrent density reached 155.2 and 142.2 μA cm−2 for iodine doped materials when KI and HIO4 were used as iodine precursors whereas only 25.6 μA cm−2 was registered for pure titania nanotubes under UV-vis illumination. Moreover, doped samples are far more efficient for the photodegradation progress than undoped material leading to decomposition of over 70% of methylene blue used as a model organic pollutant. The reported studies demonstrate for the first time the detailed optical, electrochemical and photoelectrochemical studies of iodine doped nanotube arrays.

Highly stable organic–inorganic junction composed of hydrogenated titania nanotubes infiltrated by a conducting polymer

A poly(3,4-ethylenedioxythiophene) conducting polymer doped with poly(2-styrene sulfonate) (pEDOT:PSS) was efficiently electrodeposited on a layer composed of ordered titania nanotubes. TiO2 nanotubes were formed during an anodization process and, after calcinations, a layer was subjected to hydrogen plasma. Hydrogenation leads to Ti(III) formation, a decrease in resistance, and a huge increase of donor density when compared with pure titania. According to a detailed structure analysis, the coverage by the polymer matrix is uniform on the entire titania surface as well as along the tubes. The composite material exhibits highly enhanced anodic photocurrent (106 μA cm−2) when compared with hydrogenated titania H–TiO2 (54 μA cm−2) or pure polymer film (2 μA cm−2). Moreover, H–TiO2/pEDOT:PSS is characterized with high photostability displayed during prolonged illumination. The proposed hydrogenation approach could be regarded as a facile titania modification for further electrochemical modifications.

Properties of plasmonic arrays produced by pulsed-laser nanostructuring of thin Au films

Summary A brief description of research advances in the area of short-pulse-laser nanostructuring of thin Au films is followed by examples of experimental data and a discussion of our results on the characterization of structural and optical properties of gold nanostructures. These consist of partially spherical or spheroidal nanoparticles (NPs) which have a size distribution (80 ± 42 nm) and self-organization characterized by a short-distance order (length scale ≈140 nm). For the NP shapes produced, an observably broader tuning range (of about 150 nm) of the surface plasmon resonance (SPR) band is obtained by renewal thin film deposition and laser annealing of the NP array. Despite the broadened SPR bands, which indicate damping confirmed by short dephasing times not exceeding 4 fs, the self-organized Au NP structures reveal quite a strong enhancement of the optical signal. This was consistent with the near-field modeling and micro-Raman measurements as well as a test of the electrochemical sensing capability.

Application of non-metal doped titania for inverted polymer solar cells

Inverted bulk-heterojunction polymer solar cells have been fabricated applying non-metal doped TiO2 as electron extraction buffer layers. Spin-coated films from nitrogen, sulphur, and iodine doped TiO2 nanoparticles dispersed in dimethyl sulphoxide showed comparable roughness and uniformity as those from the pure TiO2 nanoparticles. The highest power conversion efficiency (PCE) of 1.67% was obtained for N-doped TiO2, whereas in the case of pure TiO2, PCE was around 1%. The highest short circuit current density (Jsc = 10.66 mA cm−2) was achieved for I-doped TiO2. Moreover, it was observed that devices with doped TiO2 exhibit better stability under constant illumination comparing to the control devices with pure TiO2.

Boron-Enhanced Growth of Micron-Scale Carbon-Based Nanowalls: A Route toward High Rates of Electrochemical Biosensing

In this study, we have demonstrated the fabrication of novel materials called boron-doped carbon nanowalls (B:CNWs), which are characterized by remarkable electrochemical properties such as high standard rate constant (k°), low peak-to-peak separation value (ΔE) for the oxidation and reduction processes of the [Fe(CN)6]3-/4- redox system, and low surface resistivity. The B:CNW samples were deposited by the microwave plasma-assisted chemical vapor deposition (CVD) using a gas mixture of H2/CH4/B2H6 and N2. Growth results in sharp-edged, flat, and long CNWs rich in sp2 as well as sp3 hybridized phases. The achieved high values of k° (1.1 × 10-2 cm s-1) and ΔE (85 mV) are much lower compared to those of the glassy carbon or undoped CNWs. The enhanced electrochemical performance of the B:CNW electrode facilitates the simultaneous detection of DNA purine bases: adenine and guanine. Both separated oxidation peaks for the independent determination of guanine and adenine were observed by means of cyclic voltammetry or differential pulse voltammetry. It is worth noting that the determined sensitivities and the current densities were about 1 order of magnitude higher than those registered by other electrodes.

Titania nanotubes infiltrated with the conducting polymer PEDOT modified by Prussian blue – a novel type of organic–inorganic heterojunction characterised with enhanced photoactivity

A highly ordered p–n heterojunction was formed based on titania nanotubes containing a conducting polymer with Prussian blue matrix. The study demonstrates, for the first time, cases when a composite based on titania array scaffolding and Prussian blue embedded in PEDOT exhibits reversible FeII/FeIII redox activity. Highly enhanced photoactivity and capacitance of the obtained material are depicted in comparison to pristine titania. To the best of our knowledge this is the first report showing a heterojunction with titania nanotubes containing redox active species that may take part in efficient photocurrent generation.

Tin oxide nanoparticles from laser ablation encapsulated in a carbonaceous matrix – a negative electrode in lithium-ion battery applications

This report concerns carbonaceous electrodes doped with tin(II) oxide nanoparticles. Tin nanoparticles are obtained by pulsed laser ablation in water. Crystalline nanoparticles have been encapsulated in a carbonaceous matrix formed after pyrolysis of a mixture consisting of tin/tin(IV) oxide nanoparticles and gelatine. The obtained material is characterized by means of X-ray diffraction, selected area diffraction, scanning electron microscopy, transmission electron microscopy and energy dispersive X-ray analysis. Battery charging/discharging tests exhibit a capacity of 580 mA h g−1 for current densities of 100 mA g−1. The cycling performance of the material suggests that the tested nanocomposite can be used as an anode for lithium-ion batteries.

High Electrocatalytic Response of a Mechanically Enhanced NbC Nanocomposite Electrode Toward Hydrogen Evolution Reaction

Resistant and efficient electrocatalysts for hydrogen evolution reaction (HER) are desired to replace scarce and commercially expensive platinum electrodes. Thin-film electrodes of metal carbides are a promising alternative due to their reduced price and similar catalytic properties. However, most of the studied structures neglect long-lasting chemical and structural stability, focusing only on electrochemical efficiency. Herein we report on a new approach to easily deposit and control the micro/nanostructure of thin-film electrodes based on niobium carbide (NbC) and their electrocatalytic response. We will show that, by improving the mechanical properties of the NbC electrodes, microstructure and mechanical resilience can be obtained while maintaining high electrocatalytic response. We also address the influence of other parameters such as conductivity and chemical composition on the overall performance of the thin-film electrodes. Finally, we show that nanocomposite NbC electrodes are promising candidates toward HER and, furthermore, that the methodology presented here is suitable to produce other transition-metal carbides with improved catalytic and mechanical properties.