Andrei Jitianu

Comparative study of the sol–gel processes starting with different substituted Si-alkoxides

Abstract In the present work a comparative study of the hydrolysis–polycondensation processes of different Si-substituted alkoxides, leading to hybrid materials with covalent –Si–C– bonds, was carried out. The following alkoxides were used: tetraethoxysilane (TEOS), methyltriethoxysilane (MTEOS) and vinyltriethoxysilane (VTEOS). Using gas chromatography coupled with mass spectrometry (CG-MS), nuclear magnetic resonance (29Si-NMR) and infrared spectrometry (IR), information about the sol–gel process in the mentioned systems were obtained. The differences in the reactivity of the studied alkoxides are connected with the steric effect of the organic substituents. The reactivity of the alkoxides in the early stages of the hydrolysis-polycondensation process increased in the order TEOS

Core/shell nanoparticles as hybrid platforms for the fabrication of a hydrogen peroxide biosensor

Core/shell nanoparticles consisting of a Fe3O4 nanoparticle core and a mesoporous silica shell (Fe3O4/m-silica) were used as a matrix for immobilization of horseradish peroxidase (HRP) enzyme and subsequent design of an amperometric hydrogen peroxide biosensor. HRP enzyme was immobilized on the core/shell nanoparticles through the electrostatic interaction between oppositely charged HRP enzyme and the silica shell at neutral pH. The enzyme–core/shell nanoparticle hybrid material was deposited on screen printed electrodes and further characterized by ultraviolet–visible (UV-vis) spectroscopy and scanning electron microscopy (SEM). This set up was used as a biosensor to detect hydrogen peroxide. The hydrogen peroxide biosensor showed a detection limit of 4.3 × 10−7 M, at a signal-to-noise ratio of 3, and a sensitivity of 84.4 μA mM−1 cm2.

Sol-gel processing for conventional and alternative energy

Overview of conventional energy sources and alternative energy sources.- Energy conversion and energy storage nanoarchitectures.- Energy Conversion.- Batteries and Energy Storage.- Photovoltaics.- Carbon Dioxide Sequestration.- Catalysts for biofuels.- Photocatalysts.- Electrochromics.- Electrodes in Electrochemical Cells.- Thermoelectrics.- Ferroelectrics.- Heat exchangers.- Energy conservation through solid state lighting.- Hydrogen storage in porous materials.- Nuclear Fuels.

New SnO2 Nano-Clusters Obtained by Sol-Gel Route, Structural Characterization and Their Gas Sensing Applications

SnO2 is a well known and widely studied sensor material for the detection of CO and flammable gases like H2. Here we discuss the use of porous networks of SnO2 nanoparticles for an optical detection of the reducing gas CO. Nano-sized SnO2 clusters were prepared by the sol-gel method using an organically modified Sn precursor. After thermal treatment at 550°C the mean diameters of the primary SnO2 nanoparticles constructing the network were estimated to ∼25 nm and ∼15 nm, respectively, for particles obtained in acid and basic catalysis. The reversible redox behavior of SnO2 nano-clusters in reducing and oxidizing atmospheres (CO, O2) was studied optically by in-situ DR-UV/VIS spectroscopy.

Comparative Study of Sol-Gel and Coprecipitated Ni-Al Hydrotalcites

Hydrotalcite is an anionic clay mineral (layered double hydroxide) whose general formula is [M(II)1−xM(III)x(OH)2]x+Xx/nn−·mH2O. Anionic clays with a hydrotalcite-type are widely used as useful precursors of multicomponent catalysts. Hydrotalcites with Ni/Al molar ratio 2.5 have been synthesised both by the coprecipitation method, starting with nickel and aluminium nitrates and by the sol-gel method, using nickel acetylacetonate and aluminium isopropylate as precursors. The NiO-Al2O3 oxidic forms have been obtained by the thermal treatment of the precursors at 450°C and 900°C, respectively, and were characterised by DTA, XRD, IR spectroscopy and temperature programmed reduction (TPR). TPR clearly demonstrated a higher reducibility of the oxidic forms derived from the sol-gel synthesised precursors.

Organic–inorganic sol-gel thick films for humidity barriers

Hybrid thick films were deposited on Surlyn, a copolymer of poly(ethylene- co-methacrylic acid) and a common adhesion film for metal surfaces. Hybrid organic–inorganic materials were prepared by a sol-gel process. Methyltriethoxysilane (MTES) with tetraethoxysilane (TEOS), phenyltriethoxysilane (PhTES) with TEOS, and methyltrimethoxysilane (MTMS) with tetramethoxysilane (TMOS) were investigated. The inorganic component was selected to form the network for the film, while the organic component was selected to repel water and fill porosity. The films were deposited on Surlyn and on glass slides. The properties of the films were investigated using attenuated total reflection Fourier transform infrared (FTIR) and Raman spectroscopy. Contact-angle measurements indicated that the contact angle increased from ∼76.5° for Surlyn alone to ∼89.6° for Surlyn coated with MTES.

The Sol-Gel Route in Synthesis of Cr(III)-Containing Clays. Comparison Between Mg-Cr and Ni-Cr Anionic Clays

Mg/Cr and Ni/Cr hydrotalcites (HTs) were synthesised by the sol-gel method. This route was for the first time explored for Cr(III)-containing HTs. The hydrotalcite were synthesised starting with magnesium ethoxyde and nickel acetylacetonate, respectively, as divalent cation precursors and chromium acetylacetonate as trivalent cation precursor using basic catalysis (sodium hydroxide). Pure hydrotalcites containing materials with M(II)/Cr(III) = 3 were obtained. The presence of Ni(II) favoured the increasing of hydrotalcite crystallinity. The samples were investigated using X-ray diffraction and spectroscopic techniques, DTA/TGA measurements and transmission electron microscopy (TEM). The obtained compounds were pure hydrotalcite phases with very similar structural features, but exhibited particularities depending on the M(II) cation. The compounds were nanosized in both cases. The IR spectroscopy evidenced that the Ni(II) samples retained some organic groups on the surface, thus the decomposition processes of the Ni(II) containing sample being different from that of Mg(II) containing one. The decomposition process ended at lower temperature in the case of Ni/Cr hydrotalcite.

Sol–Gel Hybrids for Electronic Applications: Hermetic Coatings for Microelectronics and Energy Storage

Hermetic seals are an essential part of microelectronics, namely, micro-electromechanical systems (MEMS) displays using organic-light emitting diodes (OLEDs) and electrochemical devices, such as microbatteries. Hermetic seals have to prevent humidity and other gases from reaching devices and degrading their performance. Typically, the barriers are applied once the devices have been assembled, and, consequently, the sealing material has to be hermetic at low processing temperatures. Hybrid organic–inorganic materials are capable of being applied in a sol–gel process at low temperature. A survey of sol–gel hybrid materials that are finding use in microelectronics is presented.

Obtaining Thickness-Limited Electrospray Deposition for 3D Coating

Electrospray processing utilizes the balance of electrostatic forces and surface tension within a charged spray to produce charged microdroplets with a narrow dispersion in size. In electrospray deposition, each droplet carries a small quantity of suspended material to a target substrate. Past electrospray deposition results fall into two major categories: (1) continuous spray of films onto conducting substrates and (2) spray of isolated droplets onto insulating substrates. A crossover regime, or a self-limited spray, has only been limitedly observed in the spray of insulating materials onto conductive substrates. In such sprays, a limiting thickness emerges, where the accumulation of charge repels further spray. In this study, we examined the parametric spray of several glassy polymers to both categorize past electrospray deposition results and uncover the critical parameters for thickness-limited sprays. The key parameters for determining the limiting thickness were (1) field strength and (2) spray temperature, related to (i) the necessary repulsive field and (ii) the ability for the deposited materials to swell in the carrier solvent vapor and redistribute charge. These control mechanisms can be applied to the uniform or controllably-varied microscale coating of complex three-dimensional objects.

Sol-Gel Packaging for Electrochemical Devices

Packaging is an essential part of manufacturing electrochemical devices, such as micro-batteries and super-capacitors. Hermetic packaging is required to prevent humidity and gases from degrading components and interconnects. Typically, packaging is the last step in assembling such devices. Consequently, packaging materials have to be applied at low processing temperatures. Sol-gel processed hybrid organic–inorganic materials are convenient low temperature materials for packaging. This chapter, which surveys the use of sol-gel hybrids in packaging of electronic devices, is based, in part (Jitanu and Klein In Hybrid nanocomposites for nanotechnology: electronic optical magnetic and bio/medical applications. Springer, Berlin, pp. 429–453, 2009), which appeared in 2009. The survey has been updated and focused on electrochemical systems.