Industrial Titania Research Articles

Batch microreactor for photocatalytic reactions monitoring

Photocatalytic oxidation of organic contaminants is a hot topic in environmental research. However, an effective purification process needs an effective photoreactor. Typical light sources such as mercury and halogen lamps are replaced with more energy efficient Light Emitting Diodes. In the current work, a miniature photoreactor with low catalyst consumption was presented. The work of the micro-photoreactor is investigated using anatase and P25 industrial titania as model catalysts. The key element of the microreactor is replaceable UV-LED. The used 365 nm emission wavelength is optimal for the model pollutant Rhodamine B dye. The micro-photoreactor is able to mineralize the Rhodamine B dye almost completely.

Study of industrial titania synthesis using a hybrid particle-number and detailed particle model

We apply a hybrid particle model to study synthesis of particulate titania under representative industrial conditions. The hybrid particle model employs a particle-number description for small particles, and resolves complicated particle morphology where required using a detailed particle model. This enables resolution of particle property distributions under fast process dynamics. Robustness is demonstrated in a network of reactors used to simulate the industrial process. The detailed particle model resolves properties of the particles that determine end-product quality and post-processing efficiency, including primary particle size and degree of aggregate cohesion. Sensitivity of these properties to process design choices is quantified, showing that higher temperature injections produce more sintered particles; more frequent injections narrow the geometric standard deviation of primary particle diameter; and chlorine dilution reduces particle size and size variance. Structures of a typical industrial particle are compared visually with simulated particles, illustrating similar aggregate features with slightly larger primary particles.

Tuning the photocatalytic properties of sol–gel-derived single, coupled, and alloyed ZnO–TiO2 nanoparticles

Existing industrial titania production lines and their intermediate products are economically attractive precursors for synthesis of highly concentrated TiO2 coating sols and soluble nanopowders. Refluxing of aliphatic alcoholic TiOCl2 solutions (with up to 500 g TiO2/L) allows straightforward formation of nonaggregated anatase nanocrystals with size between 5 and 8 nm. Surface modification of these nanoparticles with organosilanes shifts the pH value of point of zero charge from initially 5.3 down to around 2.8. At appropriate Ti/Si ratios, complete suppression of the anatase ultraviolet (UV) photoactivity is possible. Furthermore, we address the optical and photocatalytic data of transparent nanocrystalline layers produced from superconcentrated ZnxTiyOz heterosols. Depending on the Zn/Ti ratio and processing temperature, colorless cubic c-ZnTiO3 and c-Zn2TiO4 spinel nanophases or coupled r-ZnTiO3-ilmenite/r-TiO2-rutile heterojunctions (Zn/Ti = 2/3) can be produced. The cubic spinel films are indirect semiconductors showing band gap transition of around 3.7 eV. In contrast, r-ZnTiO3-ilmenite films have slightly lower band gap of around 3.6 eV. Organic dye photodegradation studies reveal the highest catalytic activity for the coupled r-ZnTiO3-ilmenite/r-TiO2-rutile systems compared with colored (nitridated) or colorless cubic spinel film samples.

Dispersion of nanoparticles in media of biological interest

ABSTRACTNanoparticles (NP) are introduced in a growing number of commercial products, including food and beverage, daily use hygiene products such as toothpaste, or orally-administered drugs. To study the possible toxicity of these nanoparticles, a model system is the in vitro response of eukaryotic cells to the presence of NP. However, to understand the observed effects, it is clear that good physical and chemical characterization of NP, and in particular of their dispersion are needed. Indeed, the expected effects should be different if the study is dealing with agglomerates or isolated nanoparticles. For fundamental understanding, it appears important to work with nanoparticles as well dispersed as possible while being in relevant biological condition, i.e. cellular culture cell.In this context, we have studied the dispersion of a very common industrial titania NP (Degussa P25 produced in ton quantities). When dispersed in water, the suspensions of NP appear stable for weeks.. When transferred in the cell culture medium (DMEM) or if directly dispersed in DMEM, strong evolution of size is seen as well as sedimentation. To address this problem, we have compared different ways, coming from materials science, of dispersing NP in water with the idea to break in a preliminary step some of the necks between nanoparticles. The effect of dry ball milling, liquid ball milling, size of the balls and Ultrasonic dispersion will be compared. The best results were obtained from high power ultrasonic dispersion. To avoid direct aggregation, when going to DMEM, a “surfactant” relevant with biological studies (Foetal Bovine Serum (FBS)) was added in the suspension in order to coat the nanoparticles prior to transfer in DMEM (or other cell media). The result obtained with various surfactants and cell media will be presented. It must be noted that our best results were obtained in the FBS + DMEM medium.

Photocatalytic degradation of diuron in aqueous solution in presence of two industrial titania catalysts, either as suspended powders or deposited on flexible industrial photoresistant papers

In the present paper, the practical elimination of pesticides from water by photocatalysis has been studied by using two commercial titania photocatalysts (Degussa P25 (50m2/g) and Millennium PC500 (340m2/g)) and by choosing diuron as a model molecule. These two catalysts have been tested and compared in suspension in a slurry reactor. Their activities have been based on the rates of diuron disappearance diuron. In particular, comparisons have been made on their initial activities, which is independent of the influence of intermediates formed. Under identical conditions, Degussa P25 appeared substantially more active than Millennium PC500. However, since the final filtration of titania powders in suspension for the release of cleaned water and the recovery of the catalysts is a tedious process, titania has been successfully deposited on flexible photo-inert supports to be easily removed and recycled. The binding agent was an amorphous silica, transparent to UV. Depending on the nature of the industrial paper support used, both industrial titania photocatalysts behaved oppositely: for the same quantity of deposited titania samples, Degussa P25 was as active as in suspension when deposited on paper KN47 and substantially (20%) less active when deposited on NW10 whereas Millennium PC-500 behaved oppositely.

Effect of operating parameters on the testing of new industrial titania catalysts at solar pilot plant scale

A new granulated version of the well-known P-25 titanium dioxide (VP AEROPERL ® P-25/20 (Aeroperl)) has been tested to determine whether its photocatalytic efficiency is good enough for use in photocatalytic water purification and to find out if it can be separated from water more easily than its well-known homologue, powdered Degussa P-25, a significant technical improvement that might eliminate the tedious final filtration necessary with a slurry. Furthermore, a new commercial catalyst (PC-100 from Millennium Inorganic Chemicals), having a surface area and structure that are both different from Degussa P-25, has also been studied. All the experiments were carried out in sunlight in the pilot compound parabolic collector (CPC) plant at the Plataforma Solar de Almerı́a. Three different substrates were chosen as model molecules for this study: dichloracetic acid, phenol and the pesticide imidacloprid. Results show that Degussa Aeroperl is not a good alternative to powdered Degussa P-25 because of its spontaneous sedimentation during photocatalysis. Millennium PC-100 efficiency seems to be in the same range as that of Degussa P-25. In this work we also attempt to demonstrate that the comparison of efficiencies of different photocatalysts is not a trivial matter. Many factors are involved and interfere in the testing of photocatalyst behaviour during the degradation of a contaminant. A thorough comparison of photocatalyst activity should include reactions with several different substrates under varied experimental conditions.

New industrial titania photocatalysts for the solar detoxification of water containing various pollutants

A new series of titania industrial photocatalysts have been elaborated by Millennium Inorganic Chemicals and were denoted Millennium-PC/10, PC/25 and PC/50 with respective specific surface areas equal to 11, 23 and 43m2g−1. Their photocatalytic activities have been determined and compared in the solar pilot CPC-photoreactor at the Plataforma Solar de Almeria (PSA) (Spain) in the photocatalytic degradation of four different representative pollutants (4-chlorophenol, nitrobenzene, 2-chlorobenzoic acid and hydrobutanedioic (malic) acid), whose degradation pathways had previously been elucidated in laboratory experiments with artificial light, using titania Degussa P-25 as a reference photocatalyst. The study concerned the influence of (i) the nature of organic pollutants, (ii) the surface area and (iii) the concentration of suspended TiO2. The affinity of the pollutants for TiO2 and the presence of heteroatoms in the reactant molecules intervened on the activities of Millennium-PCs when compared to Degussa P-25. The higher the affinity of the organic pollutants for titania, the higher the efficiency of Millennium-PC/10 photocatalyst calibrated on the initial rate of pollutant disappearance. The degradation pathways were found similar for both photocatalysts and the primary steps of the degradation for the different types of molecules were discussed.4-Chlorophenol (4-CP), a model pollutant for waste waters, was then chosen for the study of the influence of the surface areas and of the concentration of Millennium-PC photocatalysts. The initial apparent rate constants of 4-CP degradation in presence of all Millennium-PC catalysts were all higher than that obtained with Degussa P-25. When choosing the total organic carbon (TOC) disappearance rate as an overall kinetic parameter, Millennium-PC/10 and PC/25 appeared as less active than Degussa P-25, with longer solar exposures (by about 10%) necessary to obtain a total mineralisation. However, Millennium-PC/50 resulted as the best catalyst in all cases. The optimal slurry concentration (gl−1) has been determined for each Millennium TiO2 sample.While the optimum of Degussa P-25 had previously been found equal to 0.2gl−1, higher amounts of Millennium-PC samples were required. A twice higher concentration (0.4gl−1) increased the activities by factors equal to 1.2 and 1.5 for Millennium-PC/50 and PC/10, respectively. The rate constants of disappearance of intermediates and of TOC were quantitatively affected by factors in agreement with a multiple consecutive reactions model. In any case, titania Millennium-PC/50 appeared as the best catalyst among all those tested, including Degussa P-25.

Advances in the Mechanism of Deposition of MoO2−4and Mo7O6−24Species on the Surface of Titania Consisted of Anatase and Rutile

The mechanism of deposition of MoO2−4and MoO7O6−24from electrolytic solution on the surface of industrial titania consisting of anatase and rutile patches was further investigated following a recently developed methodology. The methodology is based on the “2pk/one site” and “triple-layer” models. It involves the writing down of various deposition equilibria, derivation of the corresponding equations, calculation of the amount of each of the deposited Mo(vi)species and the total amount of deposited Mo(vi)at various pH and concentrations, calculation of the variation with pH of the ζ potentials and of the difference in H+ion consumption by the support surface in the presence and absence of MoO2−4and Mo7O6−24species in the impregnating solution. Comparison of the calculated parameters and variations mentioned above with the corresponding ones obtained by deposition experiments, potentiometric titrations, and microelectrophoresis allowed us to establish the mechanism of deposition of the Mo(vi)species on the surface of titania. It was found that the deposition of MoO2−4and Mo7O6−24species on the surface of “anatase regions” of the industrial titania takes mainly place by the following equilibria in the pH range 9.0–4.6:[formula]According to this mechanism, in the pH range 9–7 the deposition takes place exclusively through the first equilibrium, namely, by reaction of the MoO2−4ions, located in the inner Helmholtz place (IHP) of the double layer developed between the support surface and the impregnating solution, and the neutral surface hydroxyls in the “anatase regions” of the support. The deposition through adsorption of the MoO2−4and Mo7O6−24species, on the protonated surface hydroxyls of the support, starts at pH 7 and 6.4, respectively. The same equilibria are mainly responsible for the deposition on the rutile patches of the support, but the extent of deposition in this case is too small. A preference for deposition of MoO2−4with respect to Mo7O6−24ions was observed in almost the whole pH range studied. This was attributed to the negative charge developed in the IHP, which inhibits the location in it of highly charged Mo7O6−24species. Lateral, attractive, interactions are exerted between the deposited Mo(vi)species through water molecules being in the IHP. The intensity of these interactions is proportional to the charge of the deposited Mo(vi)species.

Investigation of Rutile, Anatase, and Industrial Titania/Water Solution Interfaces using Potentiometric Titration and Microelectrophoresis

The rutile, anatase, and industrial titania (used in catalysis as support and consisting of rutile and anatase)-water solution interfaces were studied using potentiometric titration and microelectrophoretic mobility measurements. Concerning the simple oxides it was found that specific adsorption of the ions of the background electrolyte (NH4NO3) does not take place. The electrical double layer developed in the anatase/aqueous solution and rutile/aqueous solution interfaces is described by the diffuse layer model. On the basis of this model the surface acidity constants, the point of zero charge, and the concentration of the various surface hydroxyls in the pH range 4-8 were calculated using a computer program called SURFEQL. It was confirmed that the surface of rutile is more acidic than the surface of anatase. Concerning industrial titania used in catalysis as support it was demonstrated that its surface has a patchwise structure consisting of rutile (10%) and anatase (90%) regions. The acid-base behavior of this material is identical to a mechanical mixture of rutile and anatase of the same composition. Taking into account its patchwise structure we calculated the variation, with pH, of the concentration of each surface hydroxyl of industrial titania [TirOH+2, TiIOH, TirO-, TiaOH+2, TiaOH, and TiaO-; a, r stand for anatase and rutile, respectively]. These variations allow one to model the deposition of species containing catalytically active ions on the surface of industrial titania.