Aleksander Gurlo

Synthesis and sensoric response of ZnO decorated carbon nanotubes

ZnO nanoparticles of size 2–10 nm were generated in situ from the single source precursor [2-(methoxyimino)propanoato]zinc(II), ([CH3ONCCH3COO]2Zn·2H2O) onto multiwalled carbon nanotubes (MWCNTs) at low temperature (150 °C). The degree of ZnO coverage on the MWCNTs can be tuned and is dependent upon the ZnO precursor concentration. A plausible growth mechanism based on surface saturation of as-deposited precursor on the MWCNTs has been proposed. The X-ray diffraction (XRD) pattern and transmission electron microscopy (TEM) indicate the nano-crystalline nature of the ZnO particles. Scanning electron microscopy (SEM) and TEM investigations of the ZnO deposition revealed a dense and homogeneous deposition along the complete periphery of the MWCNT. The ZnO/MWCNT nanocomposite hybrid materials were further electronically characterized by micro-Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), ultraviolet-visible spectroscopy (UV-Vis) as well as room temperature photoluminescence (PL). The nanostructured ZnO/MWCNT composite shows a better sensing performance when compared to bare MWCNTs in the detection of low CO levels (20–200 ppm).

Nanosensors: does crystal shape matter?

Crystal morphology changes the gas sensing activity! A recent study by X. G. Han et al. evidences the crystal morphology influence on the sensing activity of metal oxides. The sensor response of SnO2 nanocrystals increases symbatly with increasing ratio of the high-energy {221} facets.

Molecular based, chimie douce approach to 0D and 1D indium oxide nanostructures. Evaluation of their sensing properties towards CO and H2

The synthesis of a new molecular In(III) precursor complex, the generation of nanoscaled In2O3 (bixybyte structure) in 0D and 1D morphology, and the sensoric behavior of the 0D and 1D In2O3 nanostructures towards reducing gas atmospheres is studied. The indium precursor complex can be converted to a ceramic green body under mild reaction temperatures (160 °C), followed by conversion into crystalline indiumoxide at higher temperatures (350 °C). Geometric confinement by endotemplating of the molecular In precursor in track-etched polycarbonate templates yields polycrystalline indium oxide nanotubes in high yields. Controlled conversion of the molecular precursor without geometric confinement gives nanoparticulate crystalline In2O3. Both morphologically different In2O3 nanomaterials are sensitive to reducing gas conditions, however they show distinct differences towards reducing H2 and CO gas atmospheres.

Structural stability of high-pressure polymorphs in In2O3 nanocrystals: evidence of stress-induced transition?

Size matters: Both high-pressure and nanoscale syntheses can lead to the same indium oxide polymorph. Recent work by Farvid et al. provide an explanation: metastable high-pressure rh-In2O3 is stabilized by surface forces in nanoscale particles, whereas in larger particles only the stable cubic c-In2O3 polymorph exists; this is evident in the energy diagrams.

Orthorhombic In2O3: A Metastable Polymorph of Indium Sesquioxide

The way is open for the physical and chemical characterization and single-crystal growth of the orthorhombic o′-In2O3 polymorph. Orthorhombic In2O3 is synthesized from rhombohedral corundum-type rh-In2O3 under moderately high-pressure and high-temperature conditions (8–9 GPa, 600–1100 °C) followed by recovery to ambient pressure and temperature. The crystal-structure data at ambient conditions confirm unambiguously the Rh2O3(II)-type structure.

NH3-assisted synthesis of microporous silicon oxycarbonitride ceramics from preceramic polymers: a combined N2 and CO2 adsorption and small angle X-ray scattering study

We have developed a simple and general synthesis strategy to tune the chemical composition and pore size as well as the surface area of microporous ceramics. This method is based on modifying the structure of preceramic polymers through chemical reactions with NH3 at 300–800 °C, followed by thermolysis under an Ar atmosphere at 750 °C. Under these synthesis conditions polysiloxane (SPR-212a, Starfire® Systems) and polysilazane (HTT-1800, KiON Specialty Polymers) transform to microporous ceramics, while materials derived from polycarbosilane (SMP-10, Starfire® Systems) remain non-porous, as revealed by N2 and CO2 adsorption isotherms. Small angle X-ray scattering (SAXS) characterization indicates that samples prepared from polycarbosilane possess latent pores (pore size < 0.35 nm) which are not accessible in the gas adsorption experiments. The microporous silicon oxycarbonitride (SiCNO) ceramics synthesized from polysilazane and polysiloxane by the above-mentioned route possess a surface area and micropore volume of as high as 250–300 m2 g−1 and 0.16 cm3 g−1, respectively, as determined by the N2 adsorption method. The analysis of CO2 adsorption isotherms by the Dubinin–Astakhov equation confirms a narrow pore size distribution in the ceramics derived from polysilazane. Our synthesis strategy provides tools to engineer the microstructure, that is the chemical structure and porosity, of microporous SiCNO ceramics for potential applications in the fields of catalysis, gas adsorption and gas separation.

Can we predict the formability of perovskite oxynitrides from tolerance and octahedral factors

Perovskite oxynitrides AB(O,N)3 represent an emerging class of materials suitable for applications in the fields of clean energy and environmental protection. Nitrogen substitution for oxygen allows for a significant enrichment of possible perovskite structures for combinations of cations that are not achievable in perovskite oxides. A model that utilizes the tolerance and octahedral factors is developed for assessing the formability of the perovskite structure in oxynitrides and for predicting new perovskite oxynitrides that have not been synthesized so far. Our model considers the alteration of the interatomic distances and cationic radii in oxynitrides when compared to those in oxides and nitrides. In the first step we identify the stability field of the perovskite structure in oxynitrides from the crystal structure data for perovskite oxynitrides synthesized so far. In the next step we address the formability of the perovskite structure for compositions not studied yet. For instance, we predict that among potentially piezoelectric oxynitrides, YSiO2N and YGeO2N are not stable in the perovskite-type structure; YZrO2N and YSnO2N are in turn formable, whereas for possible candidate of photocatalytic oxynitrides according to DFT calculations MgTaO2N is not formable in perovskite structure; YTiO2N, CdTaO2N and CdNbO2N appear to be feasible. Moreover, we predict the formability of perovskite structures for Zn2+, Cd2+, Y3+, Hf4+, Fe4+and Sn4+, as well as Pr3+, Nd3+, and Sm3+ oxynitrides. As none of these compounds has been yet synthesized, our model can be applied for designing and guiding the synthesis of novel perovskite structures in oxynitrides.

A molecular approach to Cu doped ZnO nanorods with tunable dopant content

A novel molecular approach to the synthesis of polycrystalline Cu-doped ZnO rod-like nanostructures with variable concentrations of introduced copper ions in ZnO host matrix is presented. Spectroscopic (PLS, variable temperature XRD, XPS, ELNES, HERFD) and microscopic (HRTEM) analysis methods reveal the +II oxidation state of the lattice incorporated Cu ions. Photoluminescence spectra show a systematic narrowing (tuning) of the band gap depending on the amount of Cu(II) doping. The advantage of the template assembly of doped ZnO nanorods is that it offers general access to doped oxide structures under moderate thermal conditions. The doping content of the host structure can be individually tuned by the stoichiometric ratio of the molecular precursor complex of the host metal oxide and the molecular precursor complex of the dopant, Di-aquo-bis[2-(methoxyimino)-propanoato]zinc(II) 1 and -copper(II) 2. Moreover, these keto-dioximato complexes are accessible for a number of transition metal and lanthanide elements, thus allowing this synthetic approach to be expanded into a variety of doped 1D metal oxide structures.

In situ formation of tungsten oxycarbide, tungsten carbide and tungsten nitride nanoparticles in micro- and mesoporous polymer-derived ceramics

We present a facile approach to design micro- and mesoporous ceramic nanocomposites, which avoids the sintering of nanoparticles even at high synthesis temperatures and in situ forms nanoparticles in high temperature stable porous silicon oxycarbonitride (SiOC(N)) matrices. Our case study includes the synthesis of micro- and mesoporous polymer nanocomposites (c-WO3−x/WO3×H2O/[–Si(O)CH2–]n) which contain cubic tungsten oxide and tungsten oxide monohydrate (c-WO3−x/WO3×H2O) nanowhiskers in highly micro- and mesoporous polycarbosilane–siloxane matrices. The thermolysis of c-WO3−x/WO3×H2O/[–Si(O)CH2–]n nanocomposites under a suitable atmosphere and temperature leads to the in situ formation of well-dispersed nanoparticles of cubic tungsten oxide (c-WO3−x), tungsten oxycarbide (W2CO), tungsten carbide (WC) and tungsten nitride (WN) in micro- and mesoporous matrices.

Monitoring Gas Sensors at Work: Operando Raman–FTIR Study of Ethanol Detection by Indium Oxide

Gas sensors at work: The mode of operation of metal-oxide gas sensors can be studied by simultaneous measurement of the sensor response, adsorbates, changes in the metal-oxide material, and gas-phase composition by operando Raman–FTIR spectroscopy. Depending on the gas environment and temperature, for EtOH sensing by In2O3, a correlation has been found between the sensor signal, presence of adsorbates, oxidation state of the sensor material, and intensity of surface hydroxy groups.