Igor Bezverkhyy

ZnO nanorods covered with a TiO2 layer: simple sol–gel preparation, and optical, photocatalytic and photoelectrochemical properties

In this work, composite core–shell ZnO/TiO2 materials were fabricated by deposition of TiO2 layers via a sol–gel method onto ZnO nanorods hydrothermally grown on an ITO electrode. Two approaches to the sol–gel procedure resulted in strongly different morphologies and thicknesses of the deposited TiO2 layer, as shown in electron microscopy studies. The decrease of the optical band gap energies of the ZnO/TiO2 composites by about 0.2–0.3 eV with respect to the TiO2 nanoparticles and ZnO nanorods was determined from UV-Vis diffuse reflectance spectra. The photocatalytic activities of the systems were determined by investigation of the decolorization of Methylene Blue (MB) in aqueous solution, irradiated with monochromatic light (LED, 400 nm). Depending on the TiO2 layer morphology, and therefore the accessibility of the ZnO/TiO2 heterojunction, the photocatalytic activities of the ZnO/TiO2 composite systems showed 2-fold and 6-fold higher efficiency than that of the non-covered ZnO system. Addition of a small amount of methanol (3% v/v) to the MB test solution resulted in a significant drop in performance of all the ZnO/TiO2 samples, suggesting that the photodegradation mechanism proceeds mostly via photogenerated holes and less likely via photoexcited electrons. Photoelectrochemical tests of ITO/ZnO/TiO2 electrodes carried out in an acetonitrile solution containing ferrocene as a redox probe showed an increase in photocurrents in comparison to ITO/ZnO electrodes upon illumination with a xenon arc lamp.

Mesoporous Silica‐Confined Manganese Oxide Nanoparticles as Highly Efficient Catalysts for the Low‐Temperature Elimination of Formaldehyde

Manganese(IV) oxide was synthesized through crystallization in confined space by using the SBA‐15 silica support. The evolution of textural, morphological, structural, and redox properties of the manganese phase in the composites has been studied in terms of different parameters such as impregnation route, manganese loading, and activation temperature. High performances of nanoscaled manganese(IV) oxide for low‐temperature formaldehyde oxidation have been obtained. The optimization of preparation parameters enabled the complete conversion of formaldehyde at temperatures as low as 130 °C, which is comparable to the activity of the reference platinum catalyst that demonstrates complete conversion at similar temperatures.

Hyperstoichiometric Interaction Between Silver and Mercury at the Nanoscale

Breaking through the stoichiometry barrier: as the diameter of silver particles is decreased below a critical size of 32 nm, the molar ratio of aqueous Hg(II) to Ag(0) drastically increases beyond the conventional Hg/Ag ratio of 0.5:1, leading to hyperstoichiometry with a maximum ratio of 1.125:1. Therein, around 99% of the initial silver is retained to rapidly form a solid amalgam with reduced mercury.

Capture of formaldehyde by adsorption on nanoporous materials

The aim of this work is to assess the capability of a series of nanoporous materials to capture gaseous formaldehyde by adsorption in order to develop air treatment process and gas detection in workspaces or housings. Adsorption-desorption isotherms have been accurately measured at room temperature by TGA under very low pressure (p<2 hPa) on various adsorbents, such as zeolites, mesoporous silica (SBA15), activated carbon (AC NORIT RB3) and metal organic framework (MOF, Ga-MIL-53), exhibiting a wide range of pore sizes and surface properties. Results reveal that the NaX, NaY and CuX faujasite (FAU) zeolites are materials which show strong adsorption capacity and high affinity toward formaldehyde. In addition, these materials can be completely regenerated by heating at 200°C under vacuum. These cationic zeolites are therefore promising candidates as adsorbents for the design of air depollution process or gas sensing applications.

Characterization of adsorbed water in MIL-53(Al) by FTIR spectroscopy and ab-initio calculations

Here, we report ab-initio calculations developed with a twofold purpose: understand how adsorbed water molecules alter the infrared spectrum of the metal-organic framework MIL-53(Al) and to investigate which are the associated physico-chemical processes. The analyzed structures are the two anhydrous narrow (np⊘) and large (lp⊘) pore forms and the hydrated narrow pore form (np-H2O) of the MIL-53(Al). For these structures, we determined their corresponding infrared spectra (FTIR) and we identified the vibrational modes associated to the dominant spectral lines. We show that wagging and scissoring modes of CO2 give flexibility to the structure for facilitating the lp⊘- np⊘ transition. In our studies, this transition is identified by eight vibrational modes including the δCH(18a) vibrational mode currently used to identify the mentioned transition. We report an exhaustive band identification of the infrared spectra associated to the analyzed structures. Moreover, the FTIR for the np-H2O structure allowed us to identify four types of water molecules linked to the host structure by one to three hydrogen bonds.

Preparation of magnetic composites of MIL-53(Fe) or MIL-100(Fe) via partial transformation of their framework into γ-Fe2O3

A novel two-step approach is proposed to obtain magnetically active composite materials consisting of MIL-53(Fe) or MIL-100(Fe) and γ-Fe2O3 particles. The first step consists in a partial transformation of the framework into a layer of γ-FeO(OH) (lepidocrocite) covering the MOF particles. We found that such a transformation can be realized under air-free conditions by hydrolysing the MOFs at pH 6.2 in the presence of FeSO4. In the second step the obtained γ-FeO(OH)/MOF composite is heated under an air flow at 250 °C in order to transform γ-FeO(OH) to γ-Fe2O3. The thus prepared composites containing 40 wt% of the magnetic phase were characterized in detail by XRD, HRTEM, FESEM, N2 adsorption and magnetic measurements. It was found that the diameter of γ-Fe2O3 crystallites is about 4 nm in both materials but the microstructure of the magnetic layer is different. While in the MIL-53(Fe)-based composite the crystallites of γ-Fe2O3 form polycrystalline needle-shaped particles, in the case of MIL-100(Fe) the crystallites are present mainly in the isolated form. Both composites are superparamagnetic at ambient temperature, however the saturation magnetization of the MIL-53(Fe)-based composite (12.7 emu g−1) is higher than that for the MIL-100(Fe)-based one (6.6 emu g−1) probably due to the difference in the microstructure of γ-Fe2O3. The specific surface area and pore volume of the prepared γ-Fe2O3/MIL-100(Fe) composite (699 m2 g−1 and 0.41 cm3 g−1) make it a promising magnetically active material for catalysis or adsorption.

Nanocrystalline ZnCO3—A novel sorbent for low-temperature removal of H2S

The reactivity of a nanocrystalline ZnCO3 toward H2S (0.2vol% in N2/H2 mixture) at 140-180°C was characterized by thermal gravimetric analysis and by breakthrough curves measurements. We have found that under used conditions transformation of ZnCO3 into ZnS is complete and the rate determining step of the sulfidation is the surface reaction. Such behavior is in strike contrast with that of ZnO whose sulfidation is severely limited by diffusion. The higher reactivity of ZnCO3 in comparison with ZnO is attributed to the different microstructure of ZnS layer formed in these materials after a partial sulfidation. As in ZnO-ZnS transformation the molar volume increases (from 14.5 to 23.8cm(3)/mol), a continuous protective ZnS layer is formed hampering the access of H2S to the non reacted ZnO core. By contrast, in ZnCO3-ZnS transformation the molar volume decreases (from 27.9 to 23.8cm(3)/mol), which produces a discontinuous non-protective ZnS layer enabling a complete transformation of ZnCO3 even at 140°C. The higher reactivity of ZnCO3 results in a considerable increase of the breakthrough sulfur capacity of the carbonate in comparison with oxide. The material has therefore a good potential for being used as a disposable sorbent for H2S capture at low temperature.

One-step and one-pot method for synthesis of hybrid composite palladium-polypyrrole-carbon (Pd/PPy/C) nanomaterials

63 A onestep and onepot method to design compos� ite nanomaterials based on conjugated polymer, poly� pyrrole, and palladium nanoparticles by the redox reaction of the monomer and a palladium salt in non� aqueous and aqueous media was described previously in the works of our team (1-3). These composite materials were successfully tested as heterogeneous catalysts for the most known organic syntheses (Suzuki reaction, direct C-C conjugation, Sonogash� ira reaction, etc.) and showed excellent catalytic activ� ity. This fact made such materials interesting for fur� ther investigation. The main feature of palladium-polypyrrole (Pd/PPy) composite nanomaterials consists is that the formation of palladium nanoparticles within polypyr� role globules requires no additional stabilizers in the system. Therefore, no protective layers appear on the surface of palladium nanoparticles so that it remains catalytically active. At the same time, the polymer resulting from the chemical reaction has a porous structure that favors the diffusion of reactants to cata� lytically active centers.

Mesoporous silicon carbide via nanocasting of Ludox® xerogel

Porous SiC with uniformly sized 12 nm and 22 nm spherical mesopores was synthesized from nanocomposites of polycarbosilane (PCS) preceramic polymer and xerogels of Ludox® SiO2 nanoparticles as templates. The influence of PCS type (Mw 800 and 2000 Da), PCS : SiO2 ratio, pyrolysis temperature 1200–1400 °C, and addition of Ni complex to the preceramic composite was studied with respect to the SiC porous morphology, crystalline structure and chemical properties. We found that the pore walls of Ni-free por-SiC are composed of relatively large (20 nm) crystallites embedded inside a poorly crystalline SiC/SiC1+x phase. Increasing the pyrolysis temperature resulted in an increase of the large crystallites fraction, as well as of the stability with regard to air oxidation; however, some degradation of the porous morphology was noted too. The presence of Ni (1.5% wt relatively to PCS) noticeably improved the crystallinity of por-SiC prepared at 1200–1300 °C, with no degradation of the porous morphology occurring. On the other hand, higher Ni loadings and temperatures led to the transformation of the porous morphology into aggregates of irregularly packed large crystallites.

Size and Surface Chemistry Tuning of Silicon Carbide Nanoparticles

Chemical transformations on the surface of commercially available 3C-SiC nanoparticles were studied by means of FTIR, XPS, and temperature-programmed desorption mass spectrometry methods. Thermal oxidation of SiC NPs resulted in the formation of a hydroxylated SiO2 surface layer with C3Si-H and CHx groups over the SiO2/SiC interface. Controllable oxidation followed by oxide dissolution in HF or KOH solution allowed the SiC NPs size tuning from 17 to 9 nm. Oxide-free SiC surfaces, terminated by hydroxyls and C3Si-H groups, can be efficiently functionalized by alkenes under thermal or photochemical initiation. Treatment of SiC NPs by HF/HNO3 mixture produces a carbon-enriched surface layer with carboxylic acid groups susceptible to amide chemistry functionalization. The hydroxylated, carboxylated, and aminated SiC NPs form stable aqueous sols.