Wiktoria Lipińska

Transition metal sulfides have been widely investigated as electrocatalysts for both the oxygen and hydrogen evolution reactions. Here, we synthesized copper, nickel, cobalt, and iron sulfides using a facile successive ionic layer adsorption reaction (SILAR) occurring in porous transparent titanium dioxide nanotubes. Nanotubes are fabricated by anodization of a titanium layer sputtered onto indium tin oxide‐coated glass slides. X‐ray photoelectron spectroscopy measurements confirmed the presence of copper oxides and sulfides, cobalt oxides and sulfides, nickel oxides and sulfides as well as iron oxides. Although the walls of the titania nanotubes are modified using 5 m m aqueous solutions containing the metal and sulfide ions, the initial transparency has been preserved. According to microscopic studies and elemental analysis, the sulfides are uniformly distributed on the walls forming a metal oxide/metal sulfide heterojunction. Among all investigated materials, titania overgrown by cobalt oxide and sulfide exhibits the highest current density of 28 mA cm ⁻² recorded at +2.1 V vs. RHE during oxygen evolution, while the non‐modified electrode reached only 1.5 mA cm ⁻² . Taking into account both the high transparency and activity toward oxygen evolution, the investigated electrodes are an important element for a semitransparent tandem device for overall water splitting.

Research on titanium nanotubes modified with metal sulfides, particularly bismuth sulfide (Bi₂S₃), aims to create heterostructures that efficiently absorb sunlight and then separate photogenerated charge carriers, thereby enhancing the energy conversion efficiency. This study shows a key role of solvent used for sulfide and bismuth salt solutions used during successive ionic layer adsorption and reaction (SILAR) onto the morphology, structure, and photoresponse of the heterojunction where one element is represented by semitransparent titania nanotubes (gTiNT) and the second is Bi₂S₃. Using 2-methoxyethanol and methanol during SILAR, results in remarkably photoactive 3D heterostructure and recorded photocurrents were 44 times higher compared to bare titania nanotubes. Additionally, methanol- and 2-methoxyethanol-based processing allowed uniform deposition of the sulfide, which was not reached for other solvents. XPS studies not only confirm formation of bismuth sulfides but also indicate that Bi_xTi_yO_z compound can arise that can affect both stability and photoactivity of the electrode material.

Highly ordered spaced titanium dioxide nanotubes were fabricated via electrochemical anodization and modified with titania nanoparticles and copper oxides. Such materials were rapidly annealed in hydrogen atmosphere or conventionally in a tube furnace in air, in which the temperature slowly increases. Applied synthesis procedure can be considered as simple, cost-effective, and environmentally friendly as it allows for reduction in used materials and enhances sustainable engineering. Manipulating the chemical composition of materials by different thermal treatments resulted in various photoelectrochemical activities and density of CO₂ adsorption sites. Rapidly annealed nanotubes decorated by copper oxides exhibit excellent electrochemical properties where one electrode combines both: solar to electricity conversion (photocurrent under visible light 30 µA/cm²) and CO₂ adsorption systems (18 times higher current after CO₂ saturation). Rapidly thermal hydrogenated TiO₂ nanotubes with copper oxides had 17 times higher photocurrent and wider absorption band (380–780 nm) than conventionally annealed ones. Furthermore, the crystal planes such as Cu (111), Cu (220), Cu₂O (110), CuO (002) and Cu⁰, Cu⁺, Cu²⁺ oxidation states, and oxygen vacancies were recognized for hydrogenated sample. It should be highlighted that thermal annealing conditions significantly affects ability of copper oxide to CO₂ adsorption and CO₂ reduction reaction for hydrogenated electrode. Graphical abstract

Thermal processing is an essential step during the synthesis of various metal nanostructures and for tailoring their morphology, optical, and electrochemical properties. Herein, a profound impact of the annealing rate and time on photoactivity of gold–copper nanostructures by changes in the position and alignment of energy levels and surface states is reported. AuCu nanoparticles (NPs) are fabricated by sputtering of thin metal layers on the Ti nanopatterned foil followed by slow (0.67 °C s⁻¹) or fast (30 °C s⁻¹) treatment in the rapid thermal annealing furnace and then utilized as photoanodes. Photocurrent in the visible range of the slow‐heated AuCu materials is 77 times higher, whereas for the fast heated 24 times higher than for pure Ti platform. On the other hand, the fast‐heated material exhibits higher photon‐to‐current efficiency, longer recombination rate which reaches 10s, and higher carrier transport rate of 150 μs. Based on the simulated projected local density of states analysis and the characteristics of intensity‐modulated spectra, this phenomenon is attributed to the presence of deeper midgap states in the electronic band structure for the fast‐heated samples. Furthermore, photocurrent is enhanced by the presence of Au inside NPs, which increases tunneling across copper oxides junction.

Gold–copper nanostructures are promising in solar-driven processes because of their optical, photocatalytic and photoelectrochemical properties, especially those which result from the synergy between the two metals. Increasing interest in their internal structure, such as the composition or distribution of the Au and Cu as well as the size and shape of the nanoparticles, have developed to define their physicochemical properties.In this work, we present the influence of thermal treatment in temperature ranges from 100 to 600 °C on the formation process of bimetallic AuCu structures and their properties. AuCu materials were placed on nanostructured titanium foil substrates that were fabricated using electrochemical anodisation and chemical etching. Thin layers of AuCu mixture, as well as Au and Cu, were sputtered on the obtained Ti nanodimples. The materials were then annealed in a rapid thermal annealing furnace in an air atmosphere. Thermal treatment strongly affected the morphology and optical properties of the fabricated materials. AuCu NPs formed at 400 °C in titanium dimples. The material exhibits absorption of visible light in the range from c.a. 400 to 700 nm. The characterisation of the chemical nature of the samples was determined using X-ray photoelectron spectroscopy. In addition, X-ray diffraction and Raman spectroscopy defined composition and crystallinity. Based on photoelectrochemical studies carried out with the use of linear voltammetry in 0.1 M NaOH, it is possible to distinguish two types of interactions of light with the materials such as photogenerated charge accumulation and electron–hole pair separation. A 10AuCu electrode annealed at 300 °C achieved the highest current registered under illumination at − 0.17 V vs. Ag/AgCl/0.1 M KCl. The value was 11 times higher than for a non-annealed structure.

In this article, we studied the annealing process of AuCu layers deposited on TiO₂ nanotubes (NTs) conducted in various atmospheres such as air, vacuum, argon, and hydrogen in order to obtain materials active in both visible and UV–vis ranges. The material fabrication route covers the electrochemical anodization of a Ti plate, followed by thin AuCu film magnetron sputtering and further thermal treatment. Scanning electron microscopy images confirmed the presence of spherical nanoparticles (NPs) formed on the external and internal walls of NTs. The optical and structural properties were characterized using UV–vis, X-ray diffraction, and X-ray photoelectron spectroscopies. It was proved that thermal processing under the argon atmosphere leads to the formation of a CuAuTi alloy in contrast to materials fabricated in air, vacuum, and hydrogen. The electrochemical measurements were carried out in NaOH using cyclic voltammetry, linear voltammetry, and chronoamperometry. The highest photoactivity was achieved for materials thermally treated in the argon atmosphere. In addition, the Mott–Schottky analysis was performed for bare TiO₂ NTs and TiO₂ NTs modified with gold copper NPs indicating a shift in the flatband potential. Overall, thermal processing resulted in changes in optical and structural properties as well as electrochemical and photoelectrochemical activities.

More than 50 years have passed since Clark and Lyon developed the concept of glucose biosensors. Extensive research about biosensors has been carried out up to this day, and an exponential trend in this topic can be observed. The scope of this review is to present various enzyme immobilization methods on gold nanoparticles used for glucose sensing over the past five years. This work covers covalent bonding, adsorption, cross-linking, entrapment, and self-assembled monolayer methods. The experimental approach of each modification as well as further results are described. Designated values of sensitivity, the limit of detection, and linear range are used for the comparison of immobilization techniques.