Photocatalytic TiO2 Nanoparticles Research Articles

Low cost and facile preparation of robust multifunctional coatings with self-healing superhydrophobicity and high conductivity

Superhydrophobic and conductive multifunctional coatings have been receiving great attention in recent years due to their wide potential applications. Nevertheless, a simple and cost-effective approach is still lacked. Herein, photocatalytic TiO2 nanoparticles and graphite particles were blended with fluorinated polysiloxane and methyltris(methylethylketoxime)silane, and followed by simply spraying onto various substrates for superhydrophobic functionalization under ambient-drying, in which the graphite particles and TiO2 nanoparticles could not only lead to the micro/nano-roughness structures for coatings but also endow the coatings with the conductivity and photocatalysis. These as-prepared coatings are not only superhydrophobic but also have the high conductivity. They also can be coated on the fabrics for the oil/water separation and deposited on flammable objects as the fire-shielding layer. This multifunctional coating is robust under the external taped or pressed forces and very stable whether in the acid-alkali and salty environment or during long hours of UV irradiation. And most of all, this coating could repair its superhydrophobicity even after mechanically abraded or polluted with organics. The design and fabrication of this multifunctional coating may find immediate usage in a wide range of areas.

Enhanced gas barrier properties of graphene-TiO2 nanocomposites on plastic substrates assisted by UV photoreduction of graphene oxide

Reduced graphene oxide (rGO) sheets have received great attention as a key element for thin barrier films that block the permeation of water vapor and other gases. However, it remains a challenge to prepare the rGO-based barrier films on plastic substrates through a chemically benign and low temperature fabrication route. Toxic chemicals or high temperature thermal treatments that are widely used for preparing rGO need to be avoided because they can damage the underlying plastic substrates. In this study, we report the fabrication of rGO/TiO2 composite films via an eco-friendly and low temperature ultraviolet (UV) photoreduction process and demonstrate their enhanced gas barrier properties by measuring water vapor transmission rates (WVTRs). When photocatalytic TiO2 nanoparticles are employed, UV exposure reduces the GO/TiO2 composite solution to form rGO/TiO2, which is subsequently deposited on plastic substrates. The rGO/TiO2 composites become resistant to water absorption because the UV photoreduction of GO/TiO2 effectively removes most polar groups on the GO sheets. We confirmed that rGO/TiO2 composites were successfully deposited onto the plastic substrate through a solution process and the barrier films led to a substantial reduction in WVTRs of the substrate. Our strategy for preparing graphene-based thin barrier films by using a UV photoreduction process enables the fabrication of solution-processed graphene-based encapsulation layers on plastic substrates with an eco-friendly and low temperature fabrication method.

Bactericidal effect of photocatalytically-active nanostructured TiO2 surfaces on biofilms of the early oral colonizer, Streptococcus oralis.

This study evaluated the photocatalytic bactericidal effect of nanostructured anatase-rich titanium dioxide (TiO2 ) on microbial biofilms. Commercially pure titanium discs were spin-coated with photocatalytic TiO2 nanoparticles (P25). Uncoated discs were used as control (CTRL). Half of the CTRL and half of the P25-coated surfaces were coated with purified saliva (SAL) to give four different groups (CTRL, CTRL + SAL, P25 and P25 + SAL). Streptococcus oralis were allowed to form biofilms on the discs for 18 h and non-adherent cells were rinsed off. Bacterial viability was assessed at time 0 with Live/Dead BacLight staining and epifluorescence microscopy. The remaining discs were divided into a non-UV group and UVA-irradiated (+UV) group (irradiation time, 6 or 24 h). Thereafter, viability was assessed as above. Viability at time 0 was high and no dead cells were seen on any of the surfaces, even after 24 h, in the absence of UVA. However, after 24 h of exposure, the proportion of viable cells was reduced by 40% on the P25 discs compared to 0 and 6 h, and this effect was enhanced with a salivary pellicle. Members of mixed species biofilms differ in their susceptibility to the bactericidal effect of the surfaces tested and further investigations are needed to optimize the conditions. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 105A: 2321-2328, 2017.

Doping polysulfone ultrafiltration membrane with TiO2-PDA nanohybrid for simultaneous self-cleaning and self-protection

To prepare an ultrafiltration membrane with simultaneous self-cleaning and self-protection abilities, TiO2-polydopamine (PDA) nanohybrid are facilely prepared and used to functionalize polysulfone (PSf) membrane matrix. In the TiO2-PDA nanohybrid, PDA spheres acts as an adhesive substrate to hold densely covered photocatalytic TiO2 nanoparticles, and also serves as a free-radical scavenger to protect PSf membrane against the damage by free radicals produced by TiO2 during UV exposure treatment. The spherical-shaped TiO2-PDA can be easily doped into PSf membrane via phase inversion method, which allows the hydrophilic TiO2-PDA spheres migrating to the hydrophobic PSf surface and benefiting the antifouling ability. As a result, the TiO2-PDA/PSf hybrid membrane exhibits excellent overall performances in separation efficiency, remarkable self-cleaning property and performance stability under UV irradiation, in comparison with PSf and TiO2/PSf membrane. The influence of TiO2-PDA content on the membrane properties is also investigated, and it is found the hybrid membrane with 0.8wt% TiO2-PDA possesses the optimal performance.

Biopolymer-based hydrogels for encapsulation of photocatalytic TiO2 nanoparticles prepared by the freezing/thawing method

We report a method of making biopolymer-based photocatalytic composite materials. The method is based on encapsulation of TiO2 nanoparticles into a porous polymer matrix by mixing the nanoparticles with a biopolymer, iota-carrageenan (CRG), and polyvinyl alcohol (PVA) followed by freezing/thawing cycles; the resulting material makes a stable hydrogel upon mixing with water. CRG-PVA and CRG-PVA-TiO2 hydrogels were characterized by X-ray diffraction, STEM, swelling capacity, TGA and FTIR. Mechanical properties of the gels were evaluated with use of tensile testing machine. The photocatalytic activity of the composites with concentrations of TiO2 0.25%, 0.5%, 0.75% was investigated by oxidative decomposition of organic dye, methyl orange.

Reusability of photocatalytic TiO2 and ZnO nanoparticles immobilized in poly(vinylidene difluoride)-co-trifluoroethylene

Pollutants present in water are increasingly becoming an important public health issue. After their transportation across the sewer network they can pass through the wastewater treatment plants (WWTPs) mostly unchanged because WWTPs are not designed to remove pollutants present at trace levels. Conventional treatments are therefore ineffective. Immobilized photocatalytic systems are thus an advantage for the treatment of contaminated water, because they are ecofriendly, cost-effective and allow reusability. This work reports on TiO2 and ZnO commercial nanoparticles immobilized in poly(vinylidene difluoride)-co-trifluoroethylene (P(VDF-TrFE)). Nanocomposites of P(VDF-TrFE) with different concentrations of TiO2 nanoparticles (5, 10, and 15wt.%) and ZnO nanoparticles (15wt.%) were produced by solvent casting and tested on the degradation of methylene blue, a model organic dye. Each nanocomposite was tested three times to assess its reusability. It is shown that increasing the photocatalyst concentration results in higher photocatalytic efficiencies; the degradation rates of 15% of TiO2 and ZnO are similar; and the photoactivity decreases 6%, 16%, 13%, and 11% after three utilizations, for TiO2 5%, TiO2 10%, TiO2 15%, and ZnO 15%, respectively. Thus, the low decrease in the photocatalytic activity after three uses makes the nanocomposites suitable for applications in which reusability is an important key factor.

Photocatalytic Nb2O5-doped TiO2 nanoparticles for glazed ceramic tiles

TiO2 nanoparticles are currently used as coating for self-cleaning building products. In order to achieve high self-cleaning efficiency for outdoor applications, it is important that titania is present as anatase phase. Moreover, it is desirable that the particle sizes are in nano-range, so that a large enough surface area is available for enhanced catalytic performance. In this work, TiO2 nanoparticles doped with 0–5mol% Nb2O5 were synthesized by co-precipitation. Nb2O5 postponed the anatase to rutile transformation of TiO2 by about 200°C, such that after calcination at 700°C, no rutile was detected for 5mol% Nb2O5-doped TiO2, while undoped TiO2 presented 90wt% of the rutile phase. A systematic decreasing on crystallite size and increasing on specific surface area of TiO2 were observed with higher concentration of Nb2O5 dopant. Photocatalytic activity of anatase polymorph was measured by the decomposition rate of methylene blue under ultraviolet and daylight illumination and compared to commercial standard catalyst (P25). The results showed enhanced catalysis under UV and visible light for Nb2O5-doped TiO2 as compared to pure TiO2. In addition, 5mol% Nb2O5-doped TiO2 presented higher photocatalytic activity than P25 under visible light. The enhanced performance was attributed to surface chemistry change associated with a slight shift in the band gap.

Nanostructured TiO2 for stone coating: assessing compatibility with basic stone’s properties and photocatalytic effectiveness

Many building materials have been functionalized to achieve photocatalytic properties, namely self-cleaning and depolluting abilities, through the application of photocatalytic TiO2 nanoparticles to those materials. These nanoparticles are able to preserve building facades by blocking the deposition of airborne particulates in polluted urban environments, and they are able to purify the air, thus benefiting the environment. In this study, the application of nanostructured TiO2 as a photoactive coating on two types of natural stone was investigated. A TiO2 sol obtained by sol–gel synthesis followed by hydrothermal processing was applied via spray deposition onto a compact limestone and a highly porous calcarenite. The effects of this coating on some basic properties of the stone, such as its color and water absorption, and the photocatalytic effectiveness of the coated surface were then studied. Scanning electron microscopy and energy-dispersive X-ray spectroscopy showed that the coating presented a uniform morphology on both types of stone, with the TiO2 nanoparticles penetrating <1 µm into the stone. The coating was found to be compatible with the properties of the investigated types of stone. Colorimetry indicated that the change in the color of the stone due to the coating was negligible. Measurements of the static contact angle and the results of the capillary water absorption test showed that photoinduced superhydrophilicity did not increase the amount of the water absorbed by the coated stone. A photodegradation test of rhodamine B demonstrated the self-cleaning ability of the coating on both types of stone. Conversely, the photocatalytic effectiveness of the coating—as measured by a nitrogen oxide abatement test—was found to be higher for the porous calcarenite than for the compact limestone, and to depend on the porosity and roughness of the substrate.

Mussel‐Inspired Immobilization of Catalysts for Microchemical Applications

Immobilization of photocatalytic TiO2 nanoparticles inside PDMS‐based microreactors was successfully attempted by sequential mussel‐inspired surface engineering of microchannels by using CA‐PVP and commercially available TiO2 nanoparticles, respectively. TiO2‐immobilized microreactors accomplished continuous photocatalytic degradation of MB for up to 30 days without releasing TiO2 nanoparticles from the surface of the microchannels, confirming the robustness of TiO2‐immobilization in photocatalysis media. Regeneration of microreactors with diminished photocatalytic activities was also possible with simple strong acid treatment, enabling efficient cleaning of used microreactors.

Study on nanocomposite construction based on the multi-functional biotemplate self-assembled by the recombinant TMGMV coat protein for potential biomedical applications.

Nowadays there is a growing interest in bio-scaffolded nanoarchitectures. Rapid progress in nanobiotechnology and molecular biology has allowed the engineering of inorganic-binding peptides termed as genetically engineered polypeptides for inorganics (GEPIs) into self-assembling biological structures to facilitate the design of novel biomedical or bioimaging devices. Here we introduce a novel nanocomposite comprising a self-assembled protein scaffold based on a recombinant tobacco mild green mosaic tobamovirus (TMGMV) coat protein (CP) and the photocatalytic TiO2 nanoparticles attached to it, which may provide a generic method for materials engineering. A template containing a modified TMGMV CP (mCP) gene, with the first six C-terminal amino acid residues deleted to accommodate more foreign peptides and expressing a site-directed mutation of A123C for bioconjugation utility, and two genetically engineered mutants, Escherichia coli-based P-mCP-Ti7 containing a C-terminal TiO2 GEPI sequence of seven peptides (Ti7) and Hi5 insect cells-derived E-CP-Ti7-His6 C-terminally fused with Ti7+His6 tag were created. Expression vectors and protocols for enriching of the two CP variants were established and the resultant proteins were identified by western blot analysis. Their RNA-free self-assembling structures were analyzed by transmission electron microscopy (TEM) and immuno-gold labeling TEM analysis. Adherence of nanoparticles to the P-mCP-Ti7 induced protein scaffold was visualized by TEM analysis. Also discussed is the Cysteine thiol reactivity in bioconjugation reactions with the maleimide-functionalized porphyrin photosensitizers which can function as clinical photodynamic therapy agents. This study introduced a novel approach to producing an assembly-competent recombinant TMGMV CP, examined its ability to serve as a novel platform for the multivalent display of surface ligands and demonstrated an alternative method for nanodevice synthesis for nanobiotechnological applications by combining GEPIs-mediated immobilization with the controllability of self-assembling recombinant TMGMV CP.

Slightly carbomethylated cotton supported TiO2 nanoparticles as self-cleaning fabrics

Effect of different levels of slight carboxymethylation of cotton cellulose was investigated for improved attachment of photocatalytic TiO2 nanoparticles on cotton fabrics using sodium monochloroacetate under an alkali condition. Surface modification was confirmed by FTIR using two characteristic peaks located at 1734 and 1594cm−1 which occur due to presence of carboxylic and carboxylate functionality on modified cotton fabrics. These fabrics were then grafted with TiO2 nanoparticles (Aeroxide©P25) using a special apparatus to obtain self-cleaning fabrics. Morphology of the treated samples was characterized by atomic force microscopy and scanning electron microscopy which showed uniform coating of TiO2 nanoparticles on surface modified fabrics. Crystallinity of the coatings was evaluated using X-ray diffraction spectroscopy. Photocatalytic performance was evaluated for methyl orange as a model stain under UV-A and B exposure (200W/m2) using a spectrophotometer. Results indicated that the number of surface carboxylic acid groups increase with the increase of concentration of sodium monochloroacetate used in surface modification reaction. Higher degree of surface modification increased the loading of TiO2 nanoparticles on cotton fabrics and hence the degree of photocataltic stain removal activity.

Cluster models of photocatalytic anatase TiO2 nanoparticles and their computational characterization

Modeling of anatase nanoparticles (ANP) with the size below 10nm represents great interest for development of insights into the mechanisms of processes taking place over nanopowders. Large fraction of surface atoms in the corners, vertices, edges, distortion of the lattice and consequent electronic structure changes make catalytic activity of ANP different. The goal of this study is creation of cluster models of ANP of size below 2.5nm and checking the applicability of modern semiempirical methods PM6 and PM7 for their description.The clusters were prepared by translation of the anatase elementary cell along [100], [010] and [001] directions. The clusters contained from 1×1×1 to 4×4×2 cells, (001), (010) as well as (001) facets, and were made charge neutral by adding oxygen atoms and hydroxyl groups which were then optimized. The frozen-core and fully relaxed clusters were (TiO2)13, (TiO2)34(H2O)2, (TiO2)59(H2O)2, (TiO2)114, and (TiO2)187(H2O)2 and they have TiO bonds at vertices of length 1.64–1.69Å in agreement with experiments. PM6 method was confirmed to describe anatase lattice much better than PM7 method but the geometries obtained differ somewhat from those obtained by DFT calculation. Fully relaxed clusters have a core with mean deviation from ideal lattice<0.32Å/atom and semiamorphous surface layer with mean deviation 0.44–1.06Å/atom in agreement with literature core–shell models for very small ANP. Enthalpy of formation (ΔfH) per TiO2 unit of the frozen-core and relaxed clusters agrees with the bulk anatase ΔfH to within 7% by subtracting surface tension contribution of 1.5 and 1J/m2 for non-relaxed and relaxed surfaces, respectively. The calculated with PM6 or PM7 optical band gap of the frozen-core clusters (2.9–3.5eV) is close to experimental values while optical band gap of relaxed clusters (4.6–5.7eV) is overestimated. Electronic band gap is always overestimated by ∼4eV but a clear quantum size effect is observed for relaxed clusters only. The clusters developed can be utilized in diverse catalytic studies.

Photocatalytic Finishing of Cotton Fabrics Based on Nano-Titanium Dioxide and Polyurethane Binder

In the textile industry, binders are used in fabric finishing processes to promote adhesion between a fiber surface and the particles of desired properties. In this research, a commercial polyurethane binder, Evo®Fin PUS, was used to attach photocatalytic TiO2nanoparticles (Degussa®, P-25) onto a cotton surface, in order to impart self-cleaning properties and to improve wash fastness. The cotton fabrics were finished with the aqueous dispersion of TiO2and the binder, consisting of 2, 4, and 6 % w/v for each component. Finishing was done via a pad-dry-cure process. Then a direct dye (C.I. Direct Blue 199), which was used as a model stain, was dropped onto each sample prior to 24-h illumination with simulated solar light. The self-cleaning properties were triggered by light and evaluated in terms of the reduction in color strength values (K/S) of the stain after exposure. The self-cleaning performance was preserved when the binder was added to the TiO2coating. However, washing reduced the self-cleaning performance of all samples because of the detachment of some TiO2particles, as observed by scanning electron microscopy. Overall, improved wash fastness was observed with the help of binder. Samples were further analyzed for mechanical properties, crease recovery, and drapeability.

Disinfection Kinetics and Contribution of Reactive Oxygen Species When Eliminating Bacteria with TiO&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt; Induced Photocatalysis

Titania (TiO2) induced photocatalysis has been widely investigated and applied as a disinfection strategy in many industrial and clinical applications. Reactive oxygen species (ROS), including hydroxyl radicals (&8226OH), superoxide radicals () and hydrogen peroxide (H2O2), generated in the photocatalytic reaction process are considered to be the active components prompting the bactericidal effect. In the present work, the kinetics of photocatalytic inactivation of Staphylococcus epidermidis and specific contributions of &#8226OH, and H2O2 to the bactericidal process were studied using two disinfection settings sutilizing photocatalytic resin-TiO2 nanocomposite surfaces and suspended TiO2 nanoparticles, respectively. In antibacterial tests against S. epidermidis with a layer of bacterial suspension on the resin-TiO2 surfaces, H2O2 was found to be the most efficient ROS component contributing to the antibacterial effect. Disinfection kinetics showed a two-step behavior with an initial region having a lower disinfection rate followed by a higher rate region after 10 min of UV irradiation. By contrast, in antibacterial tests with suspended bacteria and photocatalytic TiO2 nanoparticles, &#8226OH and H2O2 showed equal significance in the bacterial inactivation having a typical Chick-Watson disinfection kinetics behavior with a steady disinfection rate. The results contribute to the understanding of the bactericidal mechanism and kinetics of photocatalytic disinfection that are essential for designing specific antibacterial applications of photocatalytic materials.

Biomimetic photocatalytic reactor with a hydrogel-embedded microfluidic network

We present a light driven biomimetic reactor where photocatalytic TiO2 nanoparticles are embedded into water-based gels. Uniform supply of the reactants and extraction of the products is accomplished via a microfluidic channel network in a permeable hydrogel, broadly similar to the vein structure of live leaves. Quantitative analysis shows that the microvascular reactor has high quantum efficiency per mass of the catalyst.

The survey on use of photo-catalytic nanoparticles in Korea

Despite nanotechnology is an important and rapidly growing field of scientific and practical innovations, little is known about the potential risks of nanomaterials and nanotechnology to human health and environment. Titanium dioxide (TiO2) nanoparticle is important in consumer products because of its high stability and anticorrosion and photo-catalytic nature. It is frequently used in the cosmetics, pharmaceutical, paint, and paper industries. Recent studies, however, have shown that TiO2 nanoparticles induce cytotoxicity and genotoxicity in various lines of cultured cells as well as tumorigenesis in animal models. We do not have enough information on types and quantities of manufactured nanoparticles and the levels of exposure in Korea. To evaluate the use of photo-catalytic TiO2 nanoparticles, we have surveyed the use of photo-catalytic TiO2 nanoparticles from 94 Korean companies. The results indicate that forty-eight companies declared to use and/or produce nanoparticles. The results will be used for the basis of risk assessments and development of guidelines for the risk and safety decision framework.

Nano Titanium Dioxide Particles Promote Allergic Sensitization and Lung Inflammation in Mice

The purpose of this study was to investigate whether photocatalytic TiO2 nanoparticles have adjuvant effect, when administered in combination with ovalbumin (OVA) in mice. Mice were immunized via intraperitoneal injections of OVA, OVA + TiO2 or OVA + Al(OH)3 and challenged with aerosols of OVA. At the end of the study, serum was analysed for content of OVA-specific IgE, IgG1 and IgG2a antibodies, and the bronchoalveolar lavage fluid (BALF) was analysed for content of inflammatory cells and levels of interleukin (IL)-4, IL-5, IL-10 and interferon-γ. The TiO2 particles promoted a Th2 dominant immune response with high levels of OVA-specific IgE and IgG1 in serum and influx of eosinophils, neutrophils and lymphocytes in BALF. The TiO2 particles induced a significantly higher level of OVA-specific IgE than the standard adjuvant Al(OH)3. However, the two substances were comparable regarding the level of eosinophilic inflammation and interleukins present in BALF.

Comparative study of optically activated nanocomposites with photocatalytic TiO&lt;sub&gt;2&lt;/sub&gt; and ZnO nanoparticles for massive environmental decontamination

Nanocomposites that incorporate TiO2 and ZnO nanoparticles separately in three-dimensional solgel matrices through full chemical integration are prepared to perform highly efficient photocatalytic activities for applications of environmental decontamination. Spectral responses of photocatalytic TiO2 and ZnO nanoparticles exposed to UV activation for self-cleaning process were obtained as also their optical relative spectral efficiency curves from 270 to 370 nm in the UV regime. Our investigations of the optimal conditions to increase their spectral photocatalytic efficiencies resulted in remarkably high levels of optical recovery and efficiency.

Ecotoxic Effect of Photocatalytic Active Nanoparticles (TiO2) on Algae and Daphnids (8 pp)

Due to their large potential for manifold applications, the use of nanoparticles is of increasing importance. As large amounts of nanoparticles may reach the environment voluntarily or by accident, attention should be paid on the potential impacts on the environment. First studies on potential environmental effects of photocatalytic TiO2 nanoparticles have been performed on the basis of widely accepted, standardized test systems which originally had been developed for the characterization of chemicals. The methods were adapted to the special requirements of testing photocatalytic nanoparticles. Suspensions of two different nanoparticles were illuminated to induce their photocatalytic activity. For testing, the growth inhibition test with the green alga Desmodesmus subspicatus and the immobilization test with the daphnid Daphnia magna were selected and performed following the relevant guidelines (algae: ISO 8692, OECD 201, DIN 38412-33; daphnids: ISO 6341, OECD 202, DIN 38412-30). The guidelines were adapted to meet the special requirements for testing photocatalytic nanoparticles. The results indicate that it is principally possible to determine the ecotoxicity of nanoparticles. It was shown that nanoparticles may have ecotoxicological effects which depend on the nature of the particles. Both products tested differ in their toxicity. Product 1 shows a clear concentration-effect curve in the test with algae (EC50: 44 mg/L). It could be proven that the observed toxicity was not caused by accompanying contaminants, since the toxic effect was comparable for the cleaned and the commercially available product. For product 2, no toxic effects were determined (maximum concentration: 50 mg/L). In the tests with daphnids, toxicity was observed for both products, although the concentration effect-curves were less pronounced. The two products differed in their toxicity; moreover, there was a difference in the toxicity of illuminated and non-illuminated products. Both products differ in size and crystalline form, so that these parameters are assumed to contribute to the different toxicities. The concentration-effect curves for daphnids, which are less-pronounced than the curves obtained for algae, may be due to the different test organisms and/or the differing test designs. The increased toxicity of pre-illuminated particles in the tests with daphnids demonstrates that the photocatalytic activity of nanoparticles lasts for a period of time. The following conclusions can be drawn from the test results: (I) It is principally possible to determine the ecotoxicity of (photocatalytic) nanoparticles. Therefore, they can be assessed using methods comparable to the procedures applied for assessing soluble chemicals. (II) Nanoparticles may exert ecotoxicological effects, which depend on the specific nanoparticle. (III) Comparable to traditional chemicals, the ecotoxicity depends on the test organisms and their physiology. (IV) The photocatalytic activity of nanoparticles lasts for a relevant period of time. Therefore, pre-illumination may be sufficient to detect a photocatalytic activity even by using test organisms which are not suitable for application in the pre-illumination-phase. First results are presented which indicate that the topic 'ecotoxicity and environmental effects of nanoparticles' should not be neglected. In testing photocatalytic nanoparticles, there are still many topics that need clarification or improvement, such as the cause for an observed toxicity, the improvement of the test design, the elaboration of a test battery and an assessment strategy. On the basis of optimized test systems, it will be possible to test nanoparticles systematically. If a potential risk by specific photocatalytic particles is known, a risk-benefit analysis can be performed and, if required, risk reducing measures can be taken.

Water-repellent coating for mobile phone microphones

A water-repellent coating material has been developed which is composed of low molecular-weight poly(tetrafluoroethylene) (PTFE) particles and anatase-type photocatalytic TiO2 nano particles, fluoro-oil (perfluorinated polyether) and a polyvinylidene fluoride binder. The presence of these PTFE particles in the coating material makes it possible for the water-repellency properties of this material to be improved by achieving a water contact angle of more than 150°. The photocatalytic activity of the TiO2 particles incorporated in the water-repellent coating inhibits the surface contamination which previously had caused the deterioration of the water-repellent properties. This water-repellent coating can be applied to mobile phone microphones. The water repellency of the electret condenser microphone improves the durability of the mobile phone.