Suspensions Of TiO2 Nanoparticles Research Articles

Impact of TiO₂ nanoparticles on Vicia narbonensis L.: potential toxicity effects.

This work was aimed to provide further information about toxicology of TiO2 nanoparticles (NPs) on Vicia narbonensis L., considering different endpoints. After exposure to TiO2 nanoparticle suspension (mixture of rutile and anatase, size <100 nm) at four different concentrations (0.2, 1.0, 2.0 and 4.0 ‰), the seeds of V. narbonensis were let to germinate in controlled environmental conditions. After 72 h, the extent of the success of the whole process (seed germination plus root elongation) was recorded as the vigour index, an indicator of possible phytotoxicity. After the characterisation of the hydric state of different materials, oxidative stress and enzymatic and nonenzymatic antioxidant responses were considered as indicators of possible cytotoxicity and to assess if damage induced by TiO2 NPs was oxidative stress-dependent. Cytohistochemical detection of in situ DNA fragmentation as genotoxicity endpoint was monitored by TUNEL reaction. The treatments with TiO2 NPs in our system induced phytotoxic effects, ROS production and DNA fragmentation. The nonenzymatic and enzymatic antioxidant responses were gradually and differentially activated and were able to maintain the oxidative damage to levels not significantly different from the control. On the other hand, the results of DNA fragmentation suggested that the mechanisms of DNA repair were not effective enough to eliminate early genotoxicity effects.

Synthesis, Antibacterial Activity of Tio2 Nanoparticles Suspension Induced by Laser Ablation in Liquid

Synthesis, Antibacterial Activity of Tio2 Nanoparticles Suspension Induced by Laser Ablation in Liquid

Biphase TiO2 Microspheres with Enhanced Photocatalytic Activity

TiO2 microspheres (TMS) with perfect spherical morphology were synthesized by spray drying of a hydrothermally cured aqueous suspension of TiO2 nanoparticles. TiO2 powders (TP) obtained by drying the nanoparticle suspension were studied simultaneously to determine which was the most efficient photocatalyst. SEM images and laser granulometry on TMS show spherical morphology with the diameter ranging from 2 to 10 μm. TMS had high specific surface area after annealing as seen from BET analyses. XRD analyses show that TMS consist of anatase and rutile crystalline phases where the rutile fraction increases with annealing temperature and above 500 °C rutile dominates anatase. Raman spectroscopy shows several Raman bands from anatase and rutile phases and supports the XRD results of phase transformation with increasing annealing temperature. Photodegradation of organic pollutants in aqueous solution under UV light irradiation establishes the higher photocatalytic activity of TMS with respect to TP. The highest e...

Effects of pH, ionic strength and humic acid on the removal of TiO2 nanoparticles from aqueous phase by coagulation

The increasing use of nanotechnology will most likely lead to the appearance of nanoparticles in aqueous phase. It is necessary to find effective methods to remove these nanoparticles from water. In this study, we found TiO2 nanoparticles (NPs) could be removed effectively by poly-ferric sulfate (PFS) and ferric chloride (FeCl3) coagulants. The effects of pH, ionic strength and humic acid (HA) on the performance of these two coagulants in this application were investigated. The effective pH range of FeCl3 is very narrow (9.5–10.6). For PFS, its effective pH range is broader (7–10.8). The behaviour of PFS is different from FeCl3 for the removal of TiO2 NPs. Liquid PFS contains many polymerization cations, which have the role of charge neutralization and bridging flocculation in the removal of TiO2 NPs. The main mechanism for removing TiO2 NPs by PFS is the formation of polymerization cations during the hydrolysis process. For both PFS and FeCl3 coagulants, the increase of ionic strength can significantly improve the coagulation effect, although this effect is influenced by pH. For both coagulants, higher HA concentration makes the TiO2 NPs suspension more stable, and the TiO2 NPs removal rate decreased significantly because of the steric hindrance effect of HA molecules.

Behavior and Determination of Titanium Dioxide Nanoparticles in Nitric Acid and River Water by ICP Spectrometry

ICP spectrometry (ICPMS, ICPOES) are classical techniques for the determination of solubilized or suspended elements. Unfortunately, their relevance for nanoparticles at low concentration (below 10 ppm) is rarely called into question, even if literature reports are not always coherent. This work is a systematic study based on the measurement of TiO2 nanoparticle suspensions, as a model of quasi-insoluble material, by plasma spectrometry. It studies both sample treatment and measurement in the 10 ppb to 30 ppm concentration range. Realized on a set of four engineered nanoparticles suspensions at low concentration, it shows the existence of three different regimes of stability that affect concentration measurement. Above a C(S) stability concentration value, suspensions are stable in time; below a low-concentration C(E) value, the signal loss is at a maximum, and a final partition is reached between the container walls and the suspension. Between these two regimes, the suspension aging varies with concentration. C(E) and C(S) depend on nanoparticle characteristics and the suspension medium, whereas the evolution kinetic is volume-dependent. Because TiO2 nanoparticles are present in the environment at concentrationd below C(S), it is then necessary to find a way to rehomogenize the suspension between sampling and analyzing. Soft sonication, minimizing the sample temperature, and trapping of free radicals is proposed and evaluated. Homogenization is traced by the addition of an internal standard before storage. The procedure is applied to a real sample, Seine River water. The amount of total titanium found, 48.7 ppb, is in good agreement with the result of the reference method.

Removal of Metal Oxide Nanoparticles from Aqueous Suspensions

An experimental investigation was carried out to assess the removal efficiency of metal oxide nanoparticles from aqueous suspensions via sedimentation and the added benefit of membrane filtration. The study was conducted with aqueous suspensions of TiO2, ZnO, and CeO2 nanoparticles (NPs) of primary size of 10 nm–21 nm. The removal of NPs by gravitational settling was carried out with suspensions that were pretreated via pH adjustment and coagulant addition in order to increase the agglomerate size. Removal efficiencies were as high as 72.3–98.6% for the studied NPs with subsequent ultrafiltration of the remaining suspensions (post sedimentation) enabling essentially complete NP removal.

Effectiveness Study of a Shell and Tube Heat Exchanger Operated with Nanofluids at Different Mass Flow Rates

Several challenging issues, such as global warming, greenhouse effect, fuel security, and the high price of energy, motivate people to think about energy savings. Energy can be saved by effectively using available materials and facilities. Heat exchangers play a significant part in the field of energy conservation, conversion, and recovery. Nanofluids can be used in the heat exchangers to reduce global energy losses. Thermal performance of a shell and tube heat exchanger operated with nanofluids has been analytically investigated at different mass flow rates and compared with water as the base fluid. Suspensions of ZnO, CuO, Fe3O4, TiO2, and Al2O3 nanoparticles in water (W) at 0.03 volumetric fractions have been considered. It is found that, for a certain mass flow rate (50 kg/min) of tube side and shell side fluid, the highest heat transfer coefficient (h) belongs to Al2O3-Wnanofluid and the lowest to CuO-W nanofluid. However, maximum energy effectiveness (ϵ) improvement took place by 43% for ZnO-W nanofluid and minimum ϵ improvement that was around 31% happened for Al2O3-W nanofluid. Furthermore, this energy effectiveness also improved with the decrease of the mass flow rates of nanofluids and increasing the mass flow rates of the base fluid. However, changing the base fluid's mass flow rate has a limited effect on this improvement of energy effectiveness. For example, a maximum overall heat transfer coefficient was found to vary from 18.31 to 18.35 W/m² · K for Al2O3-W nanofluid when changing the mass flow rate of nanofluid from 50 to 70 kg/min. On the other hand, with the same changes of hot water mass flow rates, a maximum overall heat transfer coefficient was obtained to shift from 18.31 to 22 W/m².K for the same nanofluid. Viscosity and specific heat of nanofluids are responsible for these phenomena. However, energy effectiveness of the shell and tube heat exchanger can be increased by using metal oxide nanofluids, and better performance can be achieved by maintaining higher mass flow rates of shell side fluid and lower mass flow rates for tube side fluid.

Effect of Variable Nanogeometry of Titanium oxide-gold Nanocomposite: Application in Electrochemical Sensing of Hydrazine

3-Aminopropyltrimethoxysilane (3-APTMS) and 3-glycidoxypropyltrimethoxy-silane (3-GPTMS) mediated synthesis of gold nanoparticles (AuNPs) of two different sizes [AuNP1 (10 nm) and AuNP2 (20 nm)] were made and used for nano-composite formation with TiO2 nanoparticle suspension. The resulting TiO2-AuNP1 and TiO2-AuNP2 nanocomposites were used for making chemically modified electrodes to understand the role of nanogeometry in chemical sensing. TiO2-AuNP1 and TiO2-AuNP2 nanocomposites were characterized by transmission electron microscopy and UV-VIS spectroscopy. The analytical results revealed the average size of the nanocomposite in the range of 20-25nm. The nanocomposites were employed for modification of graphite paste electrodes and applied in electrochemical sensing of hydrazine. The results demonstrated that TiO2-AuNP1 exhibit better electrocatalytic activity as compared to that of TiO2-AuNP2 and only TiO2 towards oxidation of hydrazine. Amperometric analysis of hydrazine on these electrodes at the applied potential of 0.4 V vs Ag/AgCl was made to quantify the sensing ability of modified electrodes. The sensitivity and lowest detection limit was found as 25, 57.2 and 145.7 μAmM-1cm-2 and 50, 100, 20 nM for TiO2, TiO2-AuNP2 and TiO2-AuNP1 respectively.

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.

SiO2@TiO2/Acrylic Transparent UV Protective Layer for Cool Color Roofing Application

ABSTRACTTransparent UV protective coatings were developed by incorporating nano-TiO2 into waterborne acrylic systems to provide long-term UV protection for UV sensitive cool color roofing. Water based high crystalline TiO2 nanoparticle suspension was prepared via a gel-sol method at a basic pH. The TiO2 nanoparticles have an average size of 20 nm and are stable against agglomeration. As prepared TiO2 nanosuspension is ready to be well dispersed in commercial waterborne acrylic resin system without extra surface modification. The fabricated TiO2/acrylic nanocomposite coating achieved an UV cut-off below 350 nm with a visible transmission greater than 85% at 700 nm. It is also demonstrated that surface modification of Nano-TiO2 with a SiO2 insulation layer would suppress the catalytic activity of Nano-TiO2 and improve the UV protection for UV and photocatalysis sensitive dyes.

Humidity Effect on Transport Properties of Titanium Dioxide Nanoparticles

Rutile TiO2 nanoparticles were synthesized using co-precipitation method with an average diameter of ∼30 nm TiO2 nanoparticle device was then fabricated on glass substrate. Aluminum electrodes were defined using photolithography and vacuum evaporation. A suspension of TiO2 nanoparticles was prepared in isopropanol using ultrasonic agitation. The nanoparticles were deposited between the electrodes. The device was tested by AC electrical measurements at 40%–90% relative humidity (RH). The impedance of the TiO2 nanoparticles decreases by about 80 times with the increase in RH from 40% to 90% at 100 Hz. The response time and the recovery time were 4 s and 5 s, respectively between 40% and 90% RH. At 100 Hz, the sensitivity of the aluminum electrode TiO2 nanoparticle device in the range of 40%–90% RH was 17 MΩ/%RH. Complex modulus analysis also confirms the increase in DC conductivity of TiO2 nanoparticles as RH increases.

Nanotitania-coated multi-walled carbon nanotube composite by facile colloidal processing route for photocatalytic applications

Multi-walled carbon nanotubes (MWCNTs) and titanium dioxide nanocomposites (MWCNTs/TiO2) were fabricated by a simple novel colloidal processing route and tested as a photocatalyst for degradation of methylene blue under UV irradiation. The novel idea behind this work is to make MWCNTs and TiO2 nanoparticle suspensions separately highly oppositely charged and utilize the electrostatic force of attraction between two entities to deposit nanotitania onto MWCNTs surface. Particle charge detector, scanning electron microscopy, transmission electron microscope, energy dispersive X-rays, X-rays diffraction (XRD), and Raman spectroscopy were used to characterize the composite. XRD and Raman spectroscopic analysis showed the crystalline structure of deposited TiO2 over MWCNTs surface structure as anatase phase. It was found that MWCNTs/TiO2 composite structure have much higher photocatalytic activity compared to TiO2 nanoparticles. The composite material developed may find potential applications in the degradation of organic pollutants in aqueous medium under UV irradiation.

Electrospray Dense Suspensions of TiO2Nanoparticles for Dye Sensitized Solar Cells

We report the feasibility of using electrospray to atomize dense suspension of nanoparticles with high solid concentrations. We demonstrate this principle through electrospraying dense suspensions of TiO2 nanoparticles with 40 wt.% in ethylene glycol. A dye sensitized solar cell (DSSC) is fabricated by electrospray deposition and the power conversion efficiency up to 6.81% is demonstrated. This simple, one-step process can fabricate the active layer with uniform thickness and multiple length scales, including 25 nm TiO2 nanoparticles, ∼2 μm micro spherical particles, and ∼20-μm-thick film. A judicious choice of drying temperature is important to ensure complete drying of suspension droplets while avoiding creation of hollow particles, because the hollow particles exhibit significantly lower carrier mobility and short circuit current. The very high solid concentration demonstrated in this work can potentially reduce the manufacturing cost of DSSC because less energy will be wasted on evaporating and/or rec...

Generation of TiO2Aerosols from Liquid Suspensions: Influence of Colloid Characteristics

The influence of the colloidal characteristics of aqueous TiO2 nanoparticle suspensions and of the operating conditions on the total particle concentration and the particle size distribution of aerosols generated by nebulization has been studied. A commercial nebulization unit coupled to a diffusion dryer was used to generate aerosols using two different sources of titanium dioxide nanoparticles. Stable, concentration-tunable aerosols could be obtained for both types of nanoparticle suspensions. The effect of operating conditions during nebulization (air flow rate, purity of water source, nanoparticle concentration, and pH of the precursor suspension) was studied. The results obtained indicate that the degree of agglomeration in the liquid phase previous to aerosol formation has a direct influence both on the total nanoparticle count and on the particle size distribution of the generated aerosols.Copyright 2013 American Association for Aerosol Research

Membrane Performance: TiO2 Nanoparticles Coated on Polysulfone (PSf) Ultrafiltration Membrane Surfaces

This study focuses on the modification polysulfone (PSf) ultrafiltration membrane surfaces via coated and irradiated with titanium dioxide (TiO2) nanoparticles with UV lights respectively. Basically, the flat sheet membrane was prepared using phase inversion technique with three conditions: (i) uncoated PSf membrane, (ii) coated PSf membrane with TiO2 and (iii) PSf membrane coated with TiO2 irradiated to UV. The coating process was carried out using dipping method into TiO2 nanoparticles suspension at different concentrations (0.01, 0.03 and 0.05 wt.%). Membrane was immersed in all suspension for 15 and 30 minutes. Then, coated membranes were exposured under 184 Watts UV lamp at two different durations, 15 and 30 minutes. The performance of membranes was evaluated in terms of pure water flux (PWF) and humic acid (HA) rejection. The morphology of membranes was characterized using scanning electron microscopy (SEM). Analysis of the result revealed that 15 minutes immersion of membrane in TiO2 suspension showed a better performance in term permeation and rejection of compared to 30 min immersion. This is due to the pore plugging as time of immersion increased. Therefore, the coated membranes with 0.03 wt.% of TiO2 nanoparticles at 15 minutes immersion and 15 minutes exposure of UV light irradiation were determined as an ideal performance of rejection and permeation compared to the other.

Facile detection of photogenerated reactive oxygen species in TiO2 nanoparticles suspension using colorimetric probe-assisted spectrometric method

This present study reports that reactive oxygen species (ROS), which mainly consist of hydroxyl (OH) and superoxide (O2-) radicals generated by the photocatalysis of TiO2 nanoparticles (TiO2 NPs) in suspension, can be quantitatively measured by the colorimetric probe-assisted spectrometric method without any interference by the TiO2 NPs. The interference effect of the TiO2 NPs with UV–vis spectroscopy was excluded by the selective separation of p-nitrosodimethylaniline (RNO) and tetrazolium salt (XTT) (probe compounds for OH and O2-, respectively) from the TiO2 NPs in the suspension by centrifugation at a specified ionic strength adjusted with phosphate buffer (KH2PO4/NaOH, PB) solution. This colorimetric probe-assisted spectrometric method was also successfully applied to measure the steady-state production of photogenerated ROS in a TiO2 NPs suspension.

TiO2 nanoparticles intake by fish gill cells following exposure

Engineered nanomaterials such as nanoparticles (NPs) are increasingly being used for commercial purposes in products within medicine, electronics, sporting goods, tires, textiles and cosmetics. They comprise diverse types of materials from metals, polymers, ceramic to biomaterials and have been defined as particles with at least one dimension in the order up to 100 nm1. The higher toxicological potential of NPs is mostly due to their small size, wide surface, increase of their chemical reactivity and biological activity and the capacity to generate free radicals. NPs also can have the ability to penetrate trough the biological barriers and to move easily through the biological systems. Therefore, is mandatory to assess the toxicity of these nanomaterials, since their industrial production and uses will also result in releases to the environment with unclear consequences.The aim of the present work is to evaluate the toxicity of titanium dioxide (TiO2) NPs on gill gluthatione-S-transferase activity (GST), lipid peroxidation and on structure of the gills of two freshwater fish species (Carassius auratus and Danio rerio). Suspensions of TiO2 NPs, with an average size of 21 nm, were prepared using distillate water and then ultrasonicated (10 min, 35 KHz). The suspensions were added to 10L of tap water in exposure tanks, to obtain nominal concentrations (0.01; 0.1; 1, 10; 100 TiO2 mg/L). The test fish, C. auratus (N=144) and D. rerio (N=80), were randomly distributed by 6 exposure tanks and an additional tank with clean tap water was used as control. Fish were sampled after 7, 14, and 21 days. Six fish from both species were left for depuration in clean tap water during 14 days and then sacrificed. The GST activity was determined by following the procedure described by Habig et al. and lipid peroxidation was measured based on the Thiobarbituric Acid Reactive Species method. The tissues were processed essentially according to Martoja and Martoja for light microscopy (LM). For transmission electron microscopy (TEM) the samples were fixed sequentially in glutaraldehyde, osmium tetroxide and uranyl acetate, dehydrated in ethanol and embedded in Epon-Araldite according to standard procedures. The histological and ultrastructural observations were performed using a Leica-ATC 2000 microscope and a JEOL 100-SX electron microscope respectively.The results show a significant increase of GST in gills tissues for C.auratus exposed to 10 and 100 mg/L TiO2 NPs and a decrease following the depuration period. With respect to D. rerio a significant increase was observed in fish exposed to 1, 10 and 100 mg/L TiO2 NPs. Lipid peroxidation are in agreement with GST results but showing a significant increase for fish (C.auratus and D. rerio) exposed to concentrations of 0.1 TiO2 mg/L NPs and higher. Usually, the oxidative stress caused by exposure to TiO2 NPs is attributed to hydroxyl radicals (OH) generated by photochemical (UV/vis) processes but it may be also related to specific properties of TiO2 NPs such as size, surface area and solubility that can influence the degree of toxicity. The results from LM observations (Fig. 1) showed that exposure to TiO2 NPs affected gill tissues, with changes being detected in both fish species exposed to 0.1 TiO2 mg/L NPs and higher which is in accordance with biochemical results. Changes include different degrees of hyperplasia (from low to complete fusion of lamellae). The TEM analysis revealed that TiO2 NPs were internalized by gills epithelial cells accumulating in vacuoles inside these cells (Fig. 2). After the depuration period it was observed that the capability for gills to recover was not complete. The results show a strong response to oxidative stress caused by exposure to TiO2 NPs, possibly because they are in direct contact with the exposure medium and function as a first barrier against external aggression. However, the gills changes observed following exposure and a partial recover after depuration suggest that TiO2 NPs may cause deleterious effects in fish gills compromising fish homeostasis.The authors acknowledge the funding by Fundação para a Ciência e Tecnologia through grant PTDC/CTM/099446/2008 and through project no. PEst-C/EQB/LA0006/2011 granted to Requimte.

Histological and biochemical effects of exposure to TiO2 nanoparticles in livers of two freshwater fish species: Carassius auratus and Danio rerio

Nanoparticles (NPs), particles with at least one dimension less than 100 nm, are used in many industrial applications and to produce new types of materials with unique physicochemical properties. The aquatic environment is commonly the ultimate recipient for NPs and there is uncertainty of exposure as understanding and data regarding the potential detrimental effects of NPs on aquatic biota are missing. In this study, titanium dioxide (TiO2) was chosen for its potential use in technology and diverse industrial applications. The objective of this work is to evaluate the toxicity of TiO2 NPs on total liver glutathione-S-transferase (GST), lipid peroxidation and tissue structure of the livers of two freshwater fish species (Carassius auratus and Danio rerio).Stock suspensions of TiO2 NPs, with an average size of 21 nm, were prepared using distilled water and then ultrasonicated (10 min, 35 KHz). The suspensions were added to 10L of tap water in exposure tanks, to obtain nominal concentrations (0.01; 0.1; 1, 10; 100 TiO2 mg/L). The test fish, C. auratus (N=144) and D. rerio (N=80), were randomly distributed by 6 exposure tanks and an additional tank with clean tap water was used as control. Fish were sampled after 7, 14, and 21 days. Six fish from both species were left for depuration in clean tap water during 14 days and then sacrificed. Immediately after sampling the fish were processed for enzymatic determination and histopathology. The GST activity was determined by following the procedure described by Habig et al. and lipid peroxidation was measured based on the Thiobarbituric Acid Reactive Species method. The tissues were processed essentially according to Martoja and Martoja for light microscopy (LM). For transmission electron microscopy (TEM) the samples were fixed sequentially in glutaraldehyde, osmium tetroxide and uranyl acetate, dehydrated in ethanol and embedded in Epon-Araldite according to standard procedures. The histological and ultra-structural observations were carried out using a Leica microscope (Leica-ATC 2000) and a JEOL 100-SX electron microscope respectively.The results showed increased activities of the GST in livers with increasing TiO2 NP concentrations after 7 days of exposure, however after 14 days a trend to decrease was observed for both species. The GST results suggest that the increase of activity of these detoxification enzymes can be a response to oxidative stress caused by the generation of reactive oxygen species by the NP. On the other hand, size, chemical composition, surface area, shape, solubility and aggregation may also contribute for NPs toxicity. The results from lipid peroxidation showed an increase according to tested concentrations suggesting that TiO2 NPs is able to cause cell damage and is in agreement with biochemical and histological findings. After 14 days of depuration, GST and lipid peroxidation levels were not significant different from controls suggesting that cells are able to recover in a certain degree. The results from LM (Fig. 1) showed that exposure to TiO2 NPs affected liver structure, with more pronounced changes detected in livers from fish exposed to higher concentrations. Observed changes include tissue degeneration, inflammation and pyknosis among others. The TEM analysis revealed also severe changes in liver cells compatible with oxidative stress. Hepatocytes of treated fish showed glycogen depletion, swollen mitochondria and increased lysosomes, compared to controls. After depuration, some cells recovered nearly normal morphology, but retained the lysosomes, while others underwent necrotic changes (Fig. 2). Differences among the two species studied were of a quantitative nature, and more pronounced in Danio rerio.The results suggest that potential risk to fish health exist related to the TiO2 NPs release to the aquatic environment and may cause deleterious effects in aquatic organisms. It is evident that the effects of TiO2 NPs on environment is a matter of great concern and the precise mechanisms of toxicity of this and other types of NPs must be clarified.The authors acknowledge the funding by Fundação para a Ciência e Tecnologia through grant PTDC/CTM/099446/2008 and through project no. PEst-C/EQB/LA0006/2011 granted to Requimte.

Direct quantification of TiO2 nanoparticles in suspension by grazing-incidence X-ray fluorescence spectrometry: Influence of substrate pre-treatment in the deposition process

X-ray fluorescence at grazing incidence (GIXRF) was investigated as a method for the quantification of TiO2 nanoparticles in aqueous suspensions. One of the major advantages of this technique is the possibility to analyze the particles without pre-treatment, like harsh acid digestion, as required by most other conventional methods. However, reliable quantitative measurements require a number of precautions. Particularly, the deposition process of the sample on the flat reflecting substrate must maintain homogeneity in composition and concentration over the entire surface of the deposition residue once dried. Scanning electron microscopy showed that using an adhesive coating of the substrate significantly improves the morphology and chemical homogeneity of the residue, hence leading to better performance of the method from a quantitative point of view. Linear calibration curves using internal standardization were established with ionic Ti and with two different types of TiO2 nanoparticles. Low limits of detections of 18μgL−1 and 52μgL−1 at incident angles of 0.20° and 0.75°, respectively, were obtained. It was found that correlation factors of the calibration linear fits were particle-size dependent, which was assigned to sampling problems due to possible incomplete dispersion of the particles in suspensions. The measured fluorescence of the dried deposits changed within a 4-month timespan for both types of TiO2 nanoparticles, demonstrating the very peculiar behavior of these particulate samples.

The effect of UV radiant power on the rate of polysaccharide photocatalytic mineralization

Data are reported on photocatalytic mineralization rates of sodium alginate (SA), which is representative of polysaccharides commonly encountered in surface waters and effluents requiring purification. An agitated vessel-type photocatalytic reactor was employed, with suspended TiO2 nanoparticles, to study the effect of UV-A radiant power per unit volume PR (W per L reactor fluid) for which there are insufficient data. Using initial SA concentration ∼30mg/L, mineralization rates were determined, by monitoring Total Organic Carbon (TOC) reduction, in the range of UV-A PR=2.15 to 8.57 WL−1 and TiO2 concentrations 0.5 to 1.5g/L. For this well-mixed heterogeneous photocatalytic environment, the measured fairly high polysaccharide mineralization rates were fitted to a first order kinetic expression. In the parameter range studied, the kinetic constants k (of order 10−2min−1) were linearly dependent on PR with a slope in the range ∼0.6×10−2 to ∼1.0×10−2L/(Wmin). An optimum catalyst concentration near 1g/L TiO2 was observed. The experimental techniques developed and the type of kinetic data obtained are considered useful for designing photocatalytic reactors for practical applications. Moreover, it is encouraging that the measured mineralization rates are in accord with those from a continuously operated hybrid photocatalytic membrane reactor of different geometry.