Sol-gel Reactor Research Articles

Photocatalytic activity of TiO2-P25@n-TiO2@HAP composite films for air depollution.

We report on an elaboration of new composite photocatalysts (TiO2-P25@ n-TiO2@HAP) based on grafted size-selected 5-nm titanium-oxo-alkoxo nanoparticles on P25-TiO2 nanoparticles and HAP obtained by co-precipitation of salts. The 5-nm oxo-TiO2 particles were prepared in a sol-gel reactor with rapid reagents micromixing. The photocatalytic test of ethylene degradation, in a continuous-flow fixed-bed reactor, showed an increase of the photocatalytic yield for the composite photocatalysts with an addition of HAP. This result was interpreted by a synergy between adsorption and photo-oxidation.

Nucleation-growth of salicylic acid-oxoTiO2 colloids synthesized by sol-gel processing

In this work, the preparation of hybrid oxo-TiO2 nanoparticles modified by salicylic acid (SA) is reported. The size-selected TiO2 nanoparticles were synthesized in a sol-gel reactor with rapid micromixing of reagents and binding of SA molecules occurs at the nucleation stage. UV-visible absorption, Raman spectroscopy and Light scattering measurements evidence the formation of a SA–oxo-TiO2 charge-transfer complex. In particularly, the CO vibration mode of SA shifts to lower frequencies upon complexation while the C-O vibration modes of both carboxylate and phenolic groups retain their position. The absence of C-O shift comes from two effects that cancel each other, i.e. the hardening of this mode related to the CO mode changes and its softening due to the replacement of hydrogen in COH group by Ti atoms. Kinetic studies of the oxo-TiO2 nanoparticles nucleation and growth in presence of SA show that the acidic ligand at the nanoparticle surface acts as an attractor for another oxo-TiO2 nanoparticle leading to polycondensation. This mechanism is responsible for the acceleration of the nanoparticle aggregation kinetics and shortening of the induction time. The hybrid nanoparticles are stable at pH ≤ 7.7 and release SA molecules at pH ≥ 8.5.

Isolation of titania nanoparticles in monolithic ultraporous alumina: Effect of nanoparticle aggregation on anatase phase stability and photocatalytic activity

We report on the preparation of a new photocatalyst by impregnation of size-selected TiO 2 nanoparticles into monolithic ultraporous alumina of θ and α polymorphs. The alumina matrix is prepared by selective surface oxidation of liquid Hg-alloys in a humid atmosphere at room temperature with subsequent annealing at 1100–1300 °C. An additional treatment with trimethylethoxysilane was used to mechanically reinforce the ultraporous structure. Monodispersed titanium-oxo-alkoxy nanoparticles were generated in a sol–gel reactor with rapid micromixing, then deposited by liquid colloid impregnation and thermally treated above 350 °C to form anatase TiO 2. High-resolution TEM images show evidence of non-aggregated 5-nm nanoparticles in θ-alumina matrix at a mass loading of 26 wt.%, which conserve their anatase crystalline structure after the thermal treatment at temperatures as high as 1000 °C. The rutile phase appears only at T ≥ 1100 °C when particle size increases to ∼17 nm due to the aggregation. The photocatalytic activity (ethylene decomposition) of the non-aggregated nanoparticles is conserved over a wide temperature range, and it decreases as soon as the aggregation takes place.

Novel nanostructured pHEMA–TiO2 hybrid materials with efficient light-induced charge separation

We report on a new approach to the fabrication of an electronic material: organic-inorganic pHEMA-oxo-TiO(2) hybrid with efficient light-induced separation of charges. Particular attention is paid to the material nanoscale morphology. The size-selected 5.0 nm titanium oxo-alkoxy nanoparticles are prepared in a sol-gel reactor with rapid (turbulent) fluid micromixing and the ligand exchange results in a stable nanoparticulate precursor in HEMA solution, in which polymerization can be induced thermally or by photons. The obtained hybrid materials demonstrate the highest quantum yield of photoinduced charge separation of 50% and can store photoinduced electrons at a number density above 10% Ti atoms.

Elaboration of pure and doped TiO 2 nanoparticles in sol–gel reactor with turbulent micromixing: Application to nanocoatings and photocatalysis

Pure and doped nanocoatings were prepared of from chemically active TiO 2 colloids. The colloids are generated in sol–gel reactor with turbulent mixing of two reactive fluids, containing titanium tetra-isopropoxide and water, in T-mixer. The particle size is measured by the light-scattering technique using optical-fibre probe. The TiO 2 nanoparticles doped with nitrogen are obtained by the injection of a doping agent into the reaction zone at the mixing stage. The mixing at the nucleation stage has a strong impact on the nanoparticles polydispersity and mean size. The prepared nanocoatings show photocatalytic activity under UV and visible light illumination.

Degradation of 1,4-dioxane in water using TiO 2 based photocatalytic and H 2O 2/UV processes

1,4-dioxane is a synthetic compound found in industrial effluent and subsequently contaminates water bodies due to its high solubility and high volatility. It is of concern due to its toxic and hazardous nature and has been listed as a class 2B carcinogen. This study involved optimisation of the photocatalytic and H 2O 2/UVC processes for 1,4-dioxane removal. Different photocatalysts and loadings were investigated for the degradation of low concentrations of 1,4-dioxane in water including a commercial P25, a synthesised magnetic photocatalyst and an immobilised sol–gel system. A commercial catalyst (Degussa P25) was the most efficient. A lifetime study of the sol–gel reactor showed that the coating was stable over the time period studied. The optimum H 2O 2 concentration in the H 2O 2/UVC process was found to be 30 ppm. The addition of H 2O 2 to the photocatalytic process for 1,4-dioxane removal caused a decrease in rate for the commercial P25 photocatalyst and an increase in rate for the lab-made magnetic photocatalyst.

Supported Nanometric Titanium Oxide Sols as a New Efficient Photocatalyst

We report on the first study of the photocatalytic performance of immobilized smallest titanium oxide oxoparticles of the size 2R = 5.0 nm on a glass support. The nanometric particles are prepared in the sol-gel reactor with rapid reagent mixing and temperature, atmosphere, and particle size control. The surface coverage is achieved by inserting the support into the reactor solution during the induction period, where chemically active nanoparticles are relatively stable. We show that this immobilized amorphous oxo phase of titanium oxide exhibits considerable activity toward photocatalytic degradation of trichloroethylene in the gas phase. Moreover, one of the important factors appears to be the catalyst surface preparation, which has to be free of the adsorbed alcohol molecules. UV-assisted exchange between propoxy and hydroxy groups is suggested as the surface activation mechanism. The film thickness is expected to strongly affect the material photocatalytic efficiency because of the internal traps population.

Sol–Gel Reactor With Rapid Micromixing: Modelling and Measurements of Titanium Oxide Nano-particle Growth

We present a concept of the sol–gel reactor with injection of stock solutions through a T mixer, environmental gas control, thermal control of the reactive medium and in–situ particle size measurement using a monomode optical fibre probe. The rapid injection of the whole amount of reagents leads to short time of nucleation, and the micro-mixer eliminates gradients of concentrations, which results in higher local nucleation and aggregation rates. The reactor is used for production of mono-disperse nanometric titanium oxide sols. With this reactor, induction kinetics are reproducible and agree with a model describing the mean particle size increase by a slow aggregation process. As well as the in–situ size measurement technique, the reactor is a kinetic tool for determination of the sol aggregation rate. As the rules for scale-up of its equipment are already established, it is of interest for the operation and the design of industrial-scale sol–gel reactors.

Temperature dependence of the titanium oxide sols precipitation kinetics in the sol–gel process

We report on observations of the temperature dependence ( T = 5–40 °C) of the titanium oxide sols precipitation kinetics in the sol–gel process using Ti(OPr i ) 4 as a metal organic precursor. The nanometric sol particles are produced in the sol–gel reactor with rapid reagent mixing and temperature and atmosphere control. Precipitation kinetics was followed in situ by the light scattering method using an optical fibre probe. From these measurements the activation energy E a = 0.33 ± 0.02 eV has been obtained and assigned to the secondary hydrolysis–condensation reactions between surface Ti–OPr i groups. Careful analysis of experimental data allows concluding about a decrease of the fractal dimension D f of the precipitate with an increase of the temperature, which provides D f = 1 at 35 °C.

Fate of Cryptosporidium oocysts in an immobilised titanium dioxide reactor with electric field enhancement

We have undertaken simple proof of principle experiments to find out if electric field enhanced photo-oxidation using immobilised titanium dioxide will damage Cryptosporidium oocysts. Using a simple Petri dish reactor and two forms of immobilised titanium catalyst (sol-gel and thermal-film) we have tested the ability of this technology to affect Cryptosporidium oocysts permeability assessed by propidium iodide exclusion. Test and control reactor runs were significantly different ( P=0.007). The thermal-film reactor had the greatest effect (approximately 27% of the seed) and was statistically distinguishable from the sol-gel reactor and the controls. The sol-gel reactor showed an increase in oocyst permeability, but was not statistically distinguishable from one of the controls. The enhanced performance of the thermal film reactor is attributed to the superior conversion of photochemical holes to hydroxyl radicals at the surface of this catalyst.