Photocatalytic TiO2 Nanoparticles Research Articles

Boosting Membrane Interactions and Antimicrobial Effects of Photocatalytic Titanium Dioxide Nanoparticles by Peptide Coating.

Photocatalytic nanoparticles offer antimicrobial effects under illumination due to the formation of reactive oxygen species (ROS), capable of degrading bacterial membranes. ROS may, however, also degrade human cell membranes and trigger toxicity. Since antimicrobial peptides (AMPs) may display excellent selectivity between human cells and bacteria, these may offer opportunities to effectively "target" nanoparticles to bacterial membranes for increased selectivity. Investigating this, photocatalytic TiO2 nanoparticles (NPs) are coated with the AMP LL-37, and ROS generation is found by C11-BODIPY to be essentially unaffected after AMP coating. Furthermore, peptide-coated TiO2 NPs retain their positive ζ-potential also after 1-2h of UV illumination, showing peptide degradation to be sufficiently limited to allow peptide-mediated targeting. In line with this, quartz crystal microbalance measurements show peptide coating to promote membrane binding of TiO2 NPs, particularly so for bacteria-like anionic and cholesterol-void membranes. As a result, membrane degradation during illumination is strongly promoted for such membranes, but not so for mammalian-like membranes. The mechanisms of these effects are elucidated by neutron reflectometry. Analogously, LL-37 coating promoted membrane rupture by TiO2 NPs for Gram-negative and Gram-positive bacteria, but not for human monocytes. These findings demonstrate that AMP coating may selectively boost the antimicrobial effects of photocatalytic NPs.

Conformational control of antimicrobial peptide amphiphilicity: consequences for boosting membrane interactions and antimicrobial effects of photocatalytic TiO2 nanoparticles.

This study reports on the effects of conformationally controlled amphiphilicity of antimicrobial peptides (AMPs) on their ability to coat TiO2 nanoparticles (NPs) and boost the photocatalytic antimicrobial effects of such NPs. For this, TiO2 NPs were combined with AMP EFK17 (EFKRIVQRIKDFLRNLV), displaying a disordered conformation in aqueous solution but helix formation on interaction with bacterial membranes. The membrane-bound helix is amphiphilic, with all polar and charged amino acid residues located at one side and all non-polar and hydrophobic residues on the other. In contrast, the d-enantiomer variant EFK17-d (E(dF)KR(dI)VQR(dI)KD(dF)LRNLV) is unable to form the amphiphilic helix on bacterial membrane interaction, whereas the W-residues in EFK17-W (EWKRWVQRWKDFLRNLV) boost hydrophobic interactions of the amphiphilic helix. Circular dichroism results showed the effects displayed for the free peptide, to also be present for peptide-coated TiO2 NPs, causing peptide binding to decrease in the order EFK17-W > EFK17 > EFK17-d. Notably, the formation of reactive oxygen species (ROS) by the TiO2 NPs was essentially unaffected by the presence of peptide coating, for all the peptides investigated, and the coatings stabilized over hours of UV exposure. Photocatalytic membrane degradation from TiO2 NPs coated with EFK17-W and EFK17 was promoted for bacteria-like model bilayers containing anionic phosphatidylglycerol but suppressed in mammalian-like bilayers formed by zwitterionic phosphatidylcholine and cholesterol. Structural aspects of these effects were further investigated by neutron reflectometry with clear variations observed between the bacteria- and mammalian-like model bilayers for the three peptides. Mirroring these results in bacteria-like model membranes, combining TiO2 NPs with EFK17-W and EFK17, but not with non-adsorbing EFK17-d, resulted in boosted antimicrobial effects of the resulting cationic composite NPs already in darkness, effects enhanced further on UV illumination.

A facile strategy for fabrication of nanocomposite ultrafiltration membrane: oily wastewater treatment and photocatalytic self-cleaning

Understanding the importance of reclaiming water from a huge oily wastewater stream generated during the drilling of oil in the petroleum industry and mitigating membrane fouling, a polymeric-inorganic nanocomposite membrane was fabricated with self-cleaning properties. The photocatalytic TiO2 nanoparticles were embedded in the polyvinylidene fluoride (PVDF) matrix during wet phase inversion. To enhance the separation potential and photocatalytic activity of TiO2 nanoparticles, a conjugated polypyrrole (PPy) was grown on the membrane through oxidative polymerization leading to an active layer composed of PPy@TiO2 nano-photocatalyst. The study of membrane wettability revealed the hydrophilic and underwater superoleophobic nature of the PPy@TiO2/PVDF membrane. The PPy@TiO2/PVDF membrane was applied for treating water-containing emulsified oily feed. Different types of feeds contaminated by different oils such as motor oil, diesel oil, and crude oil were studied. The separation efficiency of the PPy@TiO2/PVDF membrane stayed above 99% as the membrane allowed only water to permeate while oil was rejected. The permeate pure water flux was found to be dependent upon feed pressure and the nature of oil in the feed. While keeping the separation efficiency constant at 99%, the flux was decreased with increasing concentration of oil in the feed which is attributed to the fouling of the membrane. The fouled membrane was photo-catalytically cleaned by exposing the fouled PPy@TiO2/PVDF membrane to solar-simulated visible light as the surface features of the cleaned membrane completely resembled that of the pristine PPy@TiO2/PVDF membrane.

PAN/TiO2 Ultrafiltration Membrane for Enhanced BSA Removal and Antifouling Performance

Membrane separation has been widely utilized to eliminate pollutants from wastewater. Among them, a polyacrylonitrile (PAN) ultrafiltration (UF) membrane has presented outstanding stability, and distinguished chemical and thermal properties. However, UF membranes inevitably incur fouling issues during their operation procedure caused by contaminant adhesion on the membrane surface, which would restrict the operational efficiency and increase the maintenance cost. The conventional physical and chemical cleaning is not an effective technique to reduce the fouling due to the additional chemical addition and inevitable structure damage. Recently, UF membranes combined with photocatalytic materials are suggested to be a useful approach to conquer the membrane fouling issues. Herein, TiO2 nanoparticles were utilized to blend with a PAN casting solution for fabricating a composite UF membrane via a phase inversion method. With a certain TiO2 addition, the obtained membranes presented an enhancement of hydrophilicity, which could promote the water permeability and antifouling performance. The optimized M3 membrane prepared with 15.0 wt% PAN and 0.6 wt% TiO2 exhibited an excellent water permeability up to 207.0 L m−2 h−1 bar−1 with an outstanding 99.0% BSA rejection and superior antifouling property. In addition, the photocatalytic TiO2 nanoparticles endowed the M3 membrane with a remarkable self-cleaning ability under the UV irradiation. This facile construction method offered new insight to enhance the UF membrane separation performance with an enhanced antifouling ability.

Design of TiO2-Surfactin Hybrid Systems with Multifunctional Properties

In recent years, multifunctional inorganic-organic hybrid materials have been widely investigated in order to determine their potential synergetic, antagonist, or independent effects in terms of reactivity. The aim of this study was to design and characterize a new hybrid material by coupling well-known photocatalytic TiO2 nanoparticles with sodium surfactin (SS), a biosurfactant showing high binding affinity for metal cations as well as the ability to interact with and disrupt microorganisms' cell membranes. We used both chemical and colloidal synthesis methodologies and investigated how different TiO2:SS weight ratios affected colloidal, physicochemical, and functional properties. We discovered a clear breaking point between TiO2 and SS single-component trends and identified different ranges of applicability by considering different functional properties such as photocatalytic, heavy metal sorption capacity, and antibacterial properties. At low SS contents, the photocatalytic properties of TiO2 are preserved (conversion of organic dye = 99% after 40 min), and the hybrid system can be used in advanced oxidation processes, taking advantage of the additional antimicrobial SS properties. At high SS contents, the TiO2 photoactivity is inhibited, and the hybrid can be usefully exploited as a UV blocker in cosmetics, avoiding undesired oxidative effects (UV adsorption in the range between 300-400 nm). Around the breaking point (TiO2:SS 1:1), the hybrid material preserves the high surface area of TiO2 (specific surface area around 180 m2/g) and demonstrates NOx depletion of up to 100% in 80 min, together with improved adhesion of hybrid antibacterial coating. The last design demonstrated the best results for the concurrent removal of inorganic, organic, and biological pollutants in water/soil remediation applications.

Gaseous ethylbenzene removal by photocatalytic TiO2 nanoparticles immobilized on glass fiber tissue under real conditions: evaluation of reactive oxygen species contribution to the photocatalytic process.

Photocatalytic oxidation (PCO) using a TiO2 catalyst is an effective technique to remove gaseous volatile organic compounds (VOCs). Herein, a lab-scale continuous reactor is used to investigate the photocatalytic performance toward ethylbenzene (EB) vapor removal over TiO2 nanoparticles immobilized on glass fiber tissue. The role of the reactive species in the removal of EB and the degradation pathway were studied. Firstly, the effect of key operating parameters such as EB concentration (13, 26, 60mg/m3), relative humidity levels (From 5 to 80%), gas carrier composition (dry air + EB, O2 + EB and N2 + EB) and ultraviolet (UV) radiation wavelength (UV-A 365nm, UV-C 254nm) were explored. Then, using superoxide dismutase and tert-butanol as trapping agents, the real contribution of superoxide radical anion (O2.-) and hydroxyl radicals (OH.) to EB removal was quantified. The results show that (i) small water vapor content enhances the EB degradation; (ii) the reaction atmosphere plays an important role in the photocatalytic process; and (iii) oxygen atmosphere/UV-C radiation shows the highest EB degradation percentage. The use of radical scavengers confirms the major contribution of the hydroxyl radical to the photocatalytic mechanism with 75% versus 25% for superoxide radical anion.

Exposure to low levels of photocatalytic TiO2 nanoparticles enhances seed germination and seedling growth of amaranth and cruciferous vegetables

Titanium dioxide (TiO2) is one of the most common compounds on Earth, and it is used in natural forms or engineered bulks or nanoparticles (NPs) with increasing rates. However, the effect of TiO2 NPs on plants remains controversial. Previous studies demonstrated that TiO2 NPs are toxic to plants, because the photocatalytic property of TiO2 produces biohazardous reactive oxygen species. In contrast, another line of evidence suggested that TiO2 NPs are beneficial to plant growth. To verify this argument, in this study, we used seed germination of amaranth and cruciferous vegetables as a model system. Intriguingly, our data suggested that the controversy was due to the dosage effect. The photocatalytic activity of TiO2 NPs positively affected seed germination and growth through gibberellins in a plant-tolerable range (0.1 and 0.2 mg/cm2), whereas overdosing (1 mg/cm2) induced tissue damage. Given that plants are the foundations of the ecosystem; these findings are useful for agricultural application, sustainable development and maintenance of healthy environments.

Metal oxide-doped elastomeric materials for amplifying visible light-based antimicrobial activity

Healthcare-associated infection through transmission of pathogenic bacteria poses a huge threat to public health. One of the main transmission routes is via contaminated surfaces, including those of medical devices, and therefore significant efforts are being invested in developing new surface decontamination strategies. This includes visible light-based approaches, which offer improved compatibility with mammalian cells but lower germicidal efficacy with respect to UV-light. This study investigates the potential to enhance the antimicrobial efficacy of 405 nm light for surface decontamination through use of a photocatalytic TiO2-doped elastomer, elastomers being selected due to their wide use in biomaterials. Poly(dimethylsiloxane) (PDMS) was doped with TiO2 nanoparticles and the surface elastomer etched to expose the embedded nanoparticles. As etching results in increased surface roughness, samples with control nanoparticles (SiO2 and Fe3O4) were also investigated to decouple the effects of roughness and photoinactivation upon bacterial attachment and inactivation. Characterisation by SEM, AFM and contact angle analysis confirmed that etching produced a rougher (39.3 ± 15.3 versus 5.11 ± 1.29 nm RMS roughness; etched versus unetched TiO2-PDMS), more hydrophobic surface (water contact angle of 120 ± 2.5° versus 110 ± 1.0°; etched TiO2-PDMS versus native PDMS). This surface, rich in exposed photocatalytic TiO2 nanoparticles, allows direct contact between contaminating bacteria and nanoparticles, enabling ROS generation in closer proximity to the bacteria and consequent enhancement of visible light treatment. Incorporating TiO2 into PDMS significantly improved the photoinactivation efficacy (mean bacterial count for light-treated samples normalised to untreated samples of 0.043 ± 0.0081) compared to PDMS alone (0.19 ± 0.036), when seeded with Staphylococcus aureus and exposed to 405 nm, 60 J cm−2 light. However, photoinactivation efficacy was significantly (p < 0.001) enhanced by etching the TiO2-PDMS surface (0.015 ± 0.0074), resulting in greater photoinactivation than that obtained for etched (47.0 ± 14.5 nm RMS roughness), non-photocatalytic SiO2-PDMS (0.10 ± 0.093). Results suggest this doping and etching strategy shows significant potential for facilitating decontamination of elastomer-based biomaterials.

Photolytic Controlled Release Formulation of Methotrexate Loaded in Chitosan/TiO2 Nanoparticles for Breast Cancer.

A new system composed of chitosan nanoparticles loaded with methotrexate (MTX-CS-NPs) and functionalized with photocatalytic TiO2 nanoparticles (TiO2-NPs) was prepared. This system is expected to initiate polymeric rupture of MTX-CS-NPs and subsequently release MTX, upon illumination with UV light. MTX-CS-NPs were prepared and characterized in terms of particle size, charge, polydispersity and drug release before and after coating with TiO2-NPs. The release of MTX in vitro was studied in dark, light and UV light. Finally, coated and uncoated MTX-CS-NPs were studied in vitro using MCF-7 cell line. The functionalized NPs were larger in size, more polydisperse and carried higher positive charges compared to the unfunctionalized NPs. The entrapment efficacy was high reaching 75% and was not affected by coating with MTX-CS-NPs. Further, less than 5% of methotrexate was released after 80 h from uncoated NPs and the release was not enhanced by UV illumination of the particles. In contrast, the release from functionalized NPs was enhanced, reaching 40% after 80 h, as the particles were stroked with UV light and as the amount of TiO2-NPs used in coating increased. Finally, coating the MTX-CS-NPs with TiO2-NPs significantly enhanced their cytotoxicity on MCF-7 cells. The coated MTX-CS-NPs recorded low cell viabilities compared to the other formulations. In conclusion, the drug release of MTX-CS-NPs could be triggered and controlled remotely by coating with TiO2-NPs, which maybe more effective in cancer treatment.

Mesoporous silica as a matrix for photocatalytic titanium dioxide nanoparticles: lipid membrane interactions.

In the present study, we investigate the combined interaction of mesoporous silica (SiO2) and photocatalytic titanium dioxide (TiO2) nanoparticles with lipid membranes, using neutron reflectometry (NR), cryo-transmission electron microscopy (cryo-TEM), fluorescence oxidation assays, dynamic light scattering (DLS), and ζ-potential measurements. Based on DLS, TiO2 nanoparticles were found to display strongly improved colloidal stability at physiological pH of skin (pH 5.4) after incorporation into either smooth or spiky ("virus-like") mesoporous silica nanoparticles at low pH, the latter demonstrated by cryo-TEM. At the same time, such matrix-bound TiO2 nanoparticles retain their ability to destabilize anionic bacteria-mimicking lipid membranes under UV-illumination. Quenching experiments indicated both hydroxyl and superoxide radicals to contribute to this, while NR showed that free TiO2 nanoparticles and TiO2 loaded into mesoporous silica nanoparticles induced comparable effects on supported lipid membranes, including membrane thinning, lipid removal, and formation of a partially disordered outer membrane leaflet. By comparing effects for smooth and virus-like mesoporous nanoparticles as matrices for TiO2 nanoparticles, the interplay between photocatalytic and direct membrane binding effects were elucidated. Taken together, the study outlines how photocatalytic nanoparticles can be readily incorporated into mesoporous silica nanoparticles for increased colloidal stability and yet retain most of their capacity for photocatalytic destabilization of lipid membranes, and with maintained mechanisms for oxidative membrane destabilization. As such, the study provides new mechanistic information to the widely employed, but poorly understood, practice of loading photocatalytic nanomaterials onto/into matrix materials for increased performance.

Green Synthesis of Photocatalytic TiO2 Nanoparticles for Potential Application in Photochemical Degradation of Ornidazole

The present paper reports the green synthesis of TiO2 NPs to evaluate its photocatalytic activity. In this synthesis we use Aegle marmelos leaf extract as reducing and stabilizing agent. The TiO2 nanoparticles were characterized by using various advance analytical tools. The FTIR analysis revels the presence of different functional group present on the surface of the fabricated nanoparticles. The result of SEM analysis indicated that the prepared nanoparticles were almost spherical in nature and particles are in agglomerated state with bunch size less than 150 nm. The X-ray analysis of our synthesized nanoparticles clearly indicated that the particles are exit in anatase phase. Photocatalytic degradation studies of our nanoparticles were also evaluated against the most common nitroimidazole derivative drug ornidazole (ODZ) and the result of this study provide a good alternative path to remove the ODZ contaminants from waste water. The photocatalytic degradation of selected drug follow pseudo-first order reaction.

Sensitization of TiO2 nanoparticles with natural dyes extracts for photocatalytic activity under visible light

Titanium dioxide (TiO2) is the most used semiconductor for heterogeneous photocatalysis. However, TiO2 is activated only by ultraviolet radiation (wavelength less than 390 nm) and only 5% of the sunlight spectrum corresponds to the UV radiation, therefore restricting the efficiency of titania catalysts. Aiming to obtain more efficient photocatalytic TiO2 nanoparticles under visible light, the goal of this study is the sensitization of this semiconductor with natural dye extracts, consequently enabling the absorption of energy in the visible light spectrum. Four natural dyes were used, blackberry and hibiscus (anthocyanins group) and urucum and curcuma (carotenoids group), which were extracted by the solid-liquid extraction method. The Evonik P25 titanium dioxide was used and the sensitization of the nanoparticles was by the liquid route. Samples were characterized by UV–visible spectrophotometry, differential thermal analysis and thermal gravimetric analysis (DTA/TGA), Fourier-transform infrared spectroscopy (FTIR) and pH control. A solution of curcuma was used to determine the photocatalytic activity of the sensitized TiO2 NPs under visible light. As a result, TiO2 without sensitization degraded only 11% of the dye solution, whereas the sensitized catalysts degraded on a range of 51–73%, showing that sensitized TiO2 nanoparticles have a significant increase in the degradability of organic compounds under visible light. The sensitization of TiO2 nanoparticles with natural dye extract has a great potential to increase the photocatalytic efficiency in the visible spectrum, especially in environments without ultraviolet radiation.

Photoelectrochemical CO2 Reduction to Formate with the Sacrificial Reagent Free System of Semiconductor Photocatalysts and Formate Dehydrogenase

AbstractEfficient sacrificial reagent free (and no external bias) photoelectrochemical CO2 reduction to formate with a hybrid system consisting of semiconductor‐based photocatalytic TiO2 nanoparticles, methylviologen (MV) as an electron carrier, and biocatalytic formate dehydrogenase (FDH) was investigated. To develop the sacrificial reagent free photoelectrochemical cell for the CO2 reduction to formate, the photoanode based on TiO2 film and cathode based on the carbon fabric paper (CFP) were separated into two compartments using a proton‐permeable Nafion film to prevent gas diffusion. When the anode was irradiated with Xenon lamp (&gt;300 nm), MV reduction and CO2 reduction to formate with FDH on the cathode side proceeded in this system. For MV reduction with photoelectrochemical cell, MV was reduced using TiO2 film at each pH (6, 7 and 8) without bias, the reduction of MV did not progressed at pH 6. In contrast, MV reduction was progressed at pH 7 or 8. For CO2 reduction to formate in the presence FDH on the cathode side with photoelectrochemical cell, the rate of formate production was estimated to be 31.9 nmol h−1 at pH 8 under continuous irradiation without bias. Moreover, the rates of formate production at pH 7 and 8 were estimated to be 56.5 and 168.8 nmol h−1, respectively under continuous irradiation with bias (0.4 V vs. cathode). By using this system, we have succeeded in constructing CO2 reduction to formate using water as an electron donor, which does not require a sacrificial reagent.

In-situ synthesis of TiO2 nanoparticles in ACF: Photocatalytic degradation under continuous flow

In this work, photocatalytic TiO2 nanoparticles (NPs) were in-situ synthesized on an activated carbon fiber (ACF) substrate and the prepared material was successfully used for the catalytic degradation of an organic pollutant in water under continuous (dynamic) flow conditions. Briefly, titanium tetraisopropoxide (TTIP) was immobilized within the pores of ACF using wet impregnation method followed by hydrothermal treatment. ACF played the dual role of an adsorbent as well as a support to the TiO2 NPs by preventing the NPs from eluting into the flowing effluent stream. Successful immobilization (31 mg/g) of TiO2 within the pores of ACF was confirmed through different spectroscopic techniques. The photocatalytic activity of the material for methylene blue (MB) was tested under a continuous flow in an especially designed photochemical reactor. The effects of TiO2/ACF dose and inlet concentration of MB on degradation were studied. The data showed the prepared material to be an effective photocatalyst without leaching of the TiO2 NPs. Even at the sparse loading of TiO2 on ACF, the photocatalytic degradation kinetic rate was competitive to that reported in literature for MB degradation on the solid supported and composite catalysts. This is the first study to show an effective approach towards remediation of wastewater contaminated with methylene blue under continuous flow using the ACF-supported TiO2 NPs.

Preparation and characterization of photocatalytic Gd-doped TiO2 nanoparticles for water treatment.

In recent years, the photocatalytic process by using TiO2 nanoparticles (NPs) has produced a great interest in wastewater treatment due to its interesting features such as low-cost, environmental compatibility, and especially capacity to eliminate persistent organic compounds as well as microorganisms in water. In the present work, the photocatalytic activity of Gd-doped TiO2 nanopowders, with different doping amount 0.1, 1, and 5mol% synthesized by the sol-gel method, was studied under UV/Visible irradiation for water treatment application. The Gd-doped TiO2 nanoparticles were investigated for their photocatalytic degradation of methylene blue (MB) dye and antibacterial activities against two bacterial strains namely Stenotrophomonas maltophilia (S. maltophilia) and Micrococcus luteus (M. luteus). MB dye was used as a pollutant model to estimate reactive oxygen species (ROS) generation and to correlate killing action of nanoparticles with the generation of ROS. Scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), and Raman spectroscopy were used to characterize the as-synthesized nanomaterials. Photocatalytic, as well as antibacterial tests, showed that doping with an appropriate amount of Gd could reduce the radiative recombination process of photogenerated electron-hole pairs in TiO2 and induce a significant enhancement in photocatalytic and consequently antibacterial activity. The experimental sequence of bactericidal activity and photocatalytic degradation efficiency exhibited by the different gadolinium-doped nanoparticles was the following: 0.1mol% Gd-doped TiO2 > 1mol% Gd-doped TiO2 > 5mol% Gd-doped TiO2 > pure titania.

Synthesis and characterization of photocatalytic polyurethane and poly(methyl methacrylate) microcapsules for the controlled release of methotrexate

The aim of this work is to prepare ultraviolet (UV) triggered controlled release of compounds from microcapsule systems (MCs). Polyurethane (PU) and poly(methyl methacrylate) (PMMA) microcapsules were studied with/without chemical functionalization using photocatalytic TiO2 nanoparticles (NPs) on their surface. Once TiO2 nanoparticles are illuminated with UV light (λ = 370 nm), they initiate the rupture of the polymeric bonds of the microcapsule and subsequently initiate the encapsulated compound release, methotrexate (MTX) or rhodamine (Rh), in the present work. The size, polydispersity, charge, and yield of all MCs were measured, being the methotrexate drug release for all systems determined and compared with and without functionalization with TiO2 NPs, under dark, visible light and UV illumination in vitro. Finally, the Rh release was characterized using fluorescence microscopy. The TiO2 NPs size is around 10 nm, as determined by X-ray diffraction experiments. The PU MCs average size is around 60 µm, its electric charge +3.11 mV and yield around 85%. As for the PMMA MCs, the average size is around 280 µm, its electric charge −7.2 mV and yield around 25% and 30% for both MTX and Rh, respectively. In general, adding TiO2 NPs or the encapsulated products to the MCs does not affect the size but functionalization with TiO2 NPs lowers the electric charge. Microcapsules functionalized with TiO2 nanoparticles and irradiated with UV light presented the highest release of MTX and Rh. All other samples showed lower drug release levels when studied under the same conditions.

Synthesis of High Crystalline TiO2 Nanoparticles on a Polymer Membrane to Degrade Pollutants from Water

Titanium dioxide (TiO2) is described as an established material to remove pollutants from water. However, TiO2 is still not applied on a large scale due to issues concerning, for example, the form of use or low photocatalytic activity. We present an easily upscalable method to synthesize high active TiO2 nanoparticles on a polyethersulfone microfiltration membrane to remove pollutants in a continuous way. For this purpose, titanium(IV) isopropoxide was mixed with water and hydrochloric acid and treated up to 210 °C. After cooling, the membrane was simply dip-coated into the TiO2 nanoparticle dispersion. Standard characterization was undertaken (i.e., X-ray powder diffraction, scanning electron microscopy, X-ray photoelectron spectroscopy, water permeance, contact angle). Degradation of carbamazepine and methylene blue was executed. By increasing synthesis temperature crystallinity and photocatalytic activity elevates. Both ultrasound modification of nanoparticles and membrane pre-modification with carboxyl groups led to fine distribution of nanoparticles. The ultrasound-treated nanoparticles gave the highest photocatalytic activity in degrading carbamazepine and showed no decrease in degradation after nine times of repetition. The TiO2 nanoparticles were strongly bound to the membrane. Photocatalytic TiO2 nanoparticles with high activity were synthesized. The innovative method enables a fast and easy nanoparticle production, which could enable the use in large-scale water cleaning.

Photocatalytic hydroxyapatite-titania nanocomposites for preventive conservation of marble

Soiling of external surfaces is an increasing issue for conservation of architectural heritage. Providing architectural surfaces with self-cleaning ability is one of the most promising routes of preventive conservation. To this aim, several methods have been proposed in the literature, based on the use of photocatalytic TiO2 nanoparticles, either directly applied onto the surfaces or incorporated in protective coatings. However, when nano-TiO2 is directly applied onto architectural surfaces, the particles are easily removed by rain. When TiO2 is incorporated in polymeric coatings, durability issues arise as well, because the photoactivity of TiO2 nanoparticles can promote degradation of the polymer. Here, we present an innovative alternative method, based on combination of TiO2 nanoparticles and hydroxyapatite (HAP). The incorporation of nano-TiO2 into an HAP coating protects the nanoparticles from leaching by rain, thanks to the chemical bonding between TiO2 and HAP, without diminishing their photoactivity. As a result, marble treated with HAP-TiO2 composites exhibits high self-cleaning ability and high durability, with results superior to those achieve by direct application of nano-TiO2 onto the surface, as frequently performed on site.

Dip coating of air purifier ceramic honeycombs with photocatalytic TiO2 nanoparticles: A case study for occupational exposure

Nanoscale TiO2 (nTiO2) is manufactured in high volumes and is of potential concern in occupational health. Here, we measured workers exposure levels while ceramic honeycombs were dip coated with liquid photoactive nanoparticle suspension and dried with an air blade. The measured nTiO2 concentration levels were used to assess process specific emission rates using a convolution theorem and to calculate inhalation dose rates of deposited nTiO2 particles. Dip coating did not result in detectable release of particles but air blade drying released fine-sized TiO2 and nTiO2 particles. nTiO2 was found in pure nTiO2 agglomerates and as individual particles deposited onto background particles. Total particle emission rates were 420×109min−1, 1.33×109μm2min−1, and 3.5mgmin−1 respirable mass. During a continued repeated process, the average exposure level was 2.5×104cm−3, 30.3μm2cm−3, <116μgm−3 for particulate matter. The TiO2 average exposure level was 4.2μgm−3, which is well below the maximum recommended exposure limit of 300μgm−3 for nTiO2 proposed by the US National Institute for Occupational Safety and Health. During an 8-hour exposure, the observed concentrations would result in a lung deposited surface area of 4.3×10−3cm2g−1 of lung tissue and 13μg of TiO2 to the trachea-bronchi, and alveolar regions. The dose levels were well below the one hundredth of the no observed effect level (NOEL1/100) of 0.11cm2g−1 for granular biodurable particles and a daily no significant risk dose level of 44μgday−1. These emission rates can be used in a mass flow model to predict the impact of process emissions on personal and environmental exposure levels.

Extended hydrophobicity and self-cleaning performance of waterborne PDMS/TiO2 nanocomposite coatings under accelerated laboratory and outdoor exposure testing

It has been shown that incorporation of TiO2 nanoparticles into hydrophobic coatings can show self-cleaning performance. Accelerated laboratory testing indicated that the coats retain their hydrophobic nature for an extended time period. In this paper, hydrophobic polydimethylsiloxane (PDMS)/TiO2 nanocomposite coatings with a TiO2 content of 0–40% were fabricated by simple blending of a PDMS dispersion with an aqueous TiO2 nanoparticle dispersion. Their long-term hydrophobicity and self-cleaning performance were investigated both in laboratory and real-world outdoor testing. As expected, TiO2 nanoparticle-based coatings exhibited better self-cleaning relative to the TiO2-free PDMS control coating as measured by methylene blue degradation testing. Excellent long-term hydrophobicity was observed in accelerated weathering testing when they contained the appropriate levels of TiO2 nanoparticles (i.e., 0–30%). However, the same PDMS/TiO2 coatings did not show self-cleaning performance, and instead, exhibited improved dirt pickup resistance, in outdoor exposure testing. Sustained hydrophobicity was observed in outdoor exposure testing for the clear films except when TiO2 levels were at 40%. The hysteresis of water contact angle (HWCA) significantly increased for the PDMS control coating, and water beading was lost as the film surface picked up dirt. In contrast, the TiO2-based coatings with appropriate TiO2 levels maintained a relatively low HWCA after outdoor exposure and no water sheeting on rainy days was observed. This result demonstrates that while photocatalytic TiO2 nanoparticles can maintain coating hydrophobicity upon outdoor exposure, long-term self-cleaning performance in polluted environments has not yet been achieved with this type of coating under real-world conditions.