Módosított titanát nanocsövek szerkezete és stabilitása: ioncsere, adalékolás és heterostruktúrák

Increasing atmospheric concentration of CO2 and depletion of fossil energy sources are just a few examples for today’s major environmental challenges that materials science needs to be working on. Nanotechnology offers a new point of view because it deals with matter with at least one dimension in the 1 to 100 nm range and the size control brings about different physical and chemical properties compared to the bulk phase. There are many kinds of nanomaterials such as quantum dots, nanotubes and nanowires, nanosheets with thickness of a few atomic layers, or hierarchical structures. These materials can be applied as sensors, in energy storage, biomedicine or as catalyst supports because of their favorable properties. Discovery of carbon nanotubes made the ‘90s the decade of tubular nanostructures. In 1998, Kasuga firstly reported about trititanate nanotubes synthesized by an alkaline hydrothermal route. These rolled-up nanotubes have layered structure with a length of 100-200 nm, diameter of 10-12 nm and specific surface area of 200-300 m2/g. Protonated trititanate nanotubes (TiONT) transform into different types of titanium-dioxides upon heat treatment. Thus, from the application point of view, the investigation of TiONTs is as appropriate as that of TiO2. Since 1972, TiO2 has become one of the most investigated semiconductors especially in the field of heterogeneous photocatalysis, owing largely to Fujishima’s and Honda’s groundbreaking photoelectrochemical study. Titanium-dioxide exhibits photocatalytic activity only under UV irradiation. However, modifications such as doping or the formation of heterostructures can push its activity into the visible light region. The Department of Applied and Environmental Chemistry has been active in 1D titananate nanostructure research for nearly 15 years now. This was the research direction that I joined when I started my work at the Department. The goals of my doctoral studies were to prepare modified (ion-exchanged, doped, heterostructure based) titanate nanotubes and to investigate their heat stability and photocatalytic properties. In order to deepen our understanding of these nanostructures the following particular topics were investigated: Synthesis and heat stability of bismuth and/or antimony ion-exchanged titanate nanotubes: structural and morphological investigation. Investigation of nitrogen doping by thermal and ion-implantation methods. Study of the chemical environment of the incorporated nitrogen. Revealing the effect of dopants and post heat treatments on the structure and morphology of TiONT. Preparation of bismuth- and antimony-oxychloride based TiONT heterostructures by immobilization of oxychloride nanoparticles on the surface of nanotubes. Investigation the heat stability of composites and studying their photo-activated methyl orange dye decolorization properties.

Titania nanotube stabilized BiOCl nanoparticles in visible-light photocatalysis

Photocatalysis is a green approach in environmental organic pollutant decomposition. Lately, considerable improvement in the activity of photocatalysts has been achieved with the realization of p-n heterostructures due to the lifetime extension of the photogenerated charge carriers. Herein, we report a facile synthesis approach for decorating n-type titanate nanotubes with p-type V-VI-VII compound semiconductor BiOCl nanoparticles. It is well-known that BiOX (X = Cl, Br, I) materials form nanometer-thick platelets, which can eventually assemble into micrometer size flower-like 3D structures. Here, we demonstrate that the tubular titanate support can stabilize BiOCl on its surface in the form of nanoparticles measuring a few nanometers in diameter, instead of forming the well-known bismuth-oxyhalide nanoflowers. Subsequent calcination at 400 °C transforms the pristine titanate structures into one-dimensional anatase nanotubes, along with the formation of a heterojunction at the interface of the emerging Bi2Ti2O7 and anatase phases. The resulting nanocomposite shows activity in visible-light photocatalytic test reactions. © The Royal Society of Chemistry

pH-regulated Antimony Oxychloride Nanoparticle Formation on Titanium Oxide Nanostructures: A Photocatalytically Active Heterojunction

Improving the catalytic activity of heterogeneous photocatalysts has become a hot topic recently.</p

Structure and stability of boron doped titanate nanotubes and nanowires

Abstract Boron doped titanate nanoparticles were prepared from protonated (H-form) titanate nanotubes (TiONT) and nanowires (TiONW). The chemical nature and morphology of boron were monitored by X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD) and transmission electron microscopy (TEM). XPS proved that significant part of the boron incorporated into interstitial position (TiOB) of titanate nanotubes and nanowires, while a smaller part of the boron formed boron titanates via ion-exchange process. In the case of titanate nanotubes the presence of boron induced morphological (tubular to rod-like) and structural (trititanate to anatase) changes. These effects were not so pronounced on titanate nanowires

Low-temperature conversion of titanate nanotubes into nitrogen-doped TiO2 nanoparticles

We report on the lowest synthesis temperature recorded for nitrogen-doped titanate nanostructures and their subsequent conversion into N-doped TiO2.</p

Morphology conserving high efficiency nitrogen doping of titanate nanotubes by NH3 plasma

Titanate nanotubes offer certain benefits like high specific surface area, anisotropic mesoporous structure and ease of synthesis over other nanostructured titania forms. However, their application in visible light driven photocatalysis is hindered by their wide band-gap, which can be remedied by, e.g., anionic doping. Here we report on a systematic study to insert nitrogen into lattice positions in titanate nanotubes. The efficiency of N2+ bombardment, N2 plasma and NH3 plasma treatment is compared to that of NH3 gas synthesized in situ by the thermal decomposition of urea or NH4F. N2+ bombarded single crystalline rutile TiO2 was used as a doping benchmark (16 at.% N incorporated). Surface species were identified by diffuse reflectance infrared spectroscopy, structural features were characterized by scanning electron microscopy and powder X-ray diffraction measurements. The local chemical environment of nitrogen built into the nanotube samples was probed by X-ray photoelectron spectroscopy. Positively charged NH3 plasma treatment offered the best doping performance. This process succeeded in inserting 20 at.% N into nanotube lattice positions by replacing oxygen and forming Ti–N bonds. Remarkably, the nanotubular morphology and titanate crystal structure were both fully conserved during the process. Since plasma treatment is a readily scalable technology, the suggested method could be utilized in developing efficient visible light driven photocatalysts based on N-doped titanate nanotubes

Evolution of the Gram-Negative Antibiotic Resistance Spiral over Time: A Time-Series Analysis

We followed up the interplay between antibiotic use and resistance over time in a tertiary-care hospital in Hungary. Dynamic relationships between monthly time-series of antibiotic consumption data (defined daily doses per 100 bed-days) and of incidence densities of Gram-negative bacteria (Escherichia coli, Klebsiella spp., Pseudomonas aeruginosa, and Acinetobacter baumannii) resistant to cephalosporins or carbapenems were followed using vector autoregressive models sequentially built of time-series ending in 2015, 2016, 2017, 2018, and 2019. Relationships with Gram-negative bacteria as a group were fairly stable across years. At species level, association of cephalosporin use and cephalosporin resistance of E. coli was shown in 2015–2017, leading to increased carbapenem use in these years. Association of carbapenem use and carbapenem resistance, as well as of carbapenem resistance and colistin use in case of A. baumannii, were consistent throughout; associations in case of Klebsiella spp. were rarely found; associations in case of P. aeruginosa varied highly across years. This highlights the importance of temporal variations in the interplay between changes in selection pressure and occurrence of competing resistant species