Agglomeration and sedimentation of titanium dioxide nanoparticles (n-TiO2) in synthetic and real waters (original) (raw)
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Environmental Science & Technology, 2011
The Supporting Information consists of 11 pages, 4 tables and 5 figures. Nanoparticles. The TiO 2 stock dispersions for the matrix testing were prepared by suspending TiO 2 particles (50 mg L-1) in Milli-Q water, followed by 30 minutes of ultrasonication (2×60 W indicated power, Sonorex RK 106 from Bandelin, Germany). The water used (Milli-Q-water) was from a Millipore Advantage A10 system (Millipore, Billerica, US) equipped with a Bio-Pak TM ultrafilter (5000 Dalton molecular weight cutoff) for final clean-up. Suwannee River natural organic matter purchased from the International Humic Substances Society (8) was used as an NOM surrogate. The relationship of NOM to dissolved organic carbon (DOC) has been calculated (with a factor of 0.41) and it is therefore used as a synonym for DOC unless otherwise stated. Stock solutions of 10 mM HCl and NaHCO 3 were prepared for titration. All reagents were of analytical grade, purchased from Fisher Scientific in Austria. The final TiO 2 concentration in the test vessels prior to the aggregation/settling period was 25 mg L-1. Water chemistry. Dissolved organic carbon (DOC) was measured using a GE Power & Water DOC analyzer (Sievers 900, USA). The pH and electrical conductivity (EC) were measured using a portable pH/conductivity meter (SenTix 61 and TetraCon 325 probes, respectively: WTW, Germany). Inductively coupled plasma optical emission spectroscopy (ICP-OES) (Optima 5300 DV, Perkin-Elmer, Austria) was used to analyze major cations, i.
The Procedure for e Ffi Cient Dispersion of Titanium Dioxide Nanoparticles in Aqueous Samples
2016
The widespread use of titanium dioxide nanoparticles (TiO2NPs) in consumer products has led to an increase of their concentrations in the environment. For reliable determination of their total concentrations, the microwave assisted digestion procedure for the decomposition of nanoscale anatase and rutile was optimized and Ti concentrations were determined by inductively coupled plasma mass spectrometry (ICP-MS). To determine the TiO2NP concentration in environmental water samples, sample treatments, which maintain NPs dispersed and stabilized in solution, enabling quantitative transfer of TiO2NPs during the analytical procedure, are of crucial importance. In the present work, several dispersion approaches by the use of different mechanical and ultrasonication procedures in combination with various dispersing agents were examined in order to prepare aqueous suspensions of stable and homogeneously dispersed TiO2NPs. Experiments were performed with commercially available rutile and ana...
The aggregation of TiO 2 nanoparticles under different aqueous matrixes representative of natural waters was experimentally investigated. Conditions included indiferent electrolytes (NaCl) and specifically adsorbing cations (CaCl 2 and MgCl 2), in the presence and absence of natural organic matter. The nanoparticles of 21 nm primary particle size, formed stable aggregates of aproximately 250 nm under conditions unfavorable for aggregation, while size increased significantly at pHs near or at the pzc of the material (pzc TiO 2 6.3). The pH for favorable aggregation was affected by the presence of divalent cations and natural organic matter, turning the nanoparticles mobile at conditions were otherwise limited mobility should be expected. DLVO calculations confirmed the experimental observations, if the stable aggregate size was applied as the primary size of the particles. Aggregate morphology observed by SEM was in agreement with proposed mechanisms.
Nanoscale Research Letters, 2011
Characterizing nanoparticle dispersions and understanding the effect of parameters that alter dispersion properties are important for both environmental applications and toxicity investigations. The role of particle surface area, primary particle size, and crystal phase on TiO2 nanoparticle dispersion properties is reported. Hydrodynamic size, zeta potential, and isoelectric point (IEP) of ten laboratory synthesized TiO2 samples, and one commercial Degussa TiO2 sample (P25) dispersed in different solutions were characterized. Solution ionic strength and pH affect titania dispersion properties. The effect of monovalent (NaCl) and divalent (MgCl2) inert electrolytes on dispersion properties was quantified through their contribution to ionic strength. Increasing titania particle surface area resulted in a decrease in solution pH. At fixed pH, increasing the particle surface area enhanced the collision frequency between particles and led to a higher degree of agglomeration. In addition to the synthesis method, TiO2 isoelectric point was found to be dependent on particle size. As anatase TiO2 primary particle size increased from 6 nm to 104 nm, its IEP decreased from 6.0 to 3.8 that also results in changes in dispersion zeta potential and hydrodynamic size. In contrast to particle size, TiO2 nanoparticle IEP was found to be insensitive to particle crystal structure.
Environmental Science & Technology, 2009
The extensive use of titanium dioxide nanoparticles (nano-TiO 2 ) in many consumer products has raised concerns about possible risks to the environment. The magnitude of the threat may depend on whether nano-TiO 2 remains dispersed in the environment, or forms much larger-sized aggregates or clusters. Currently, limited information is available on the issue. In this context, the purpose of the present article is to report initial measurements of the morphology and rate of formation of nano-TiO 2 aggregates in aqueous suspensions as a function of ionic strength and of the nature of the electrolyte in a moderately acid to circumneutral pH range typical of soil and surface water conditions. Dynamic light scattering results show that 4-5 nm titanium dioxide particles readily form stable aggregates with an average diameter of 50-60 nm at pH ∼4.5 in a NaCl suspension adjusted to an ionic strength of 0.0045 M. Holding the pH constant, but increasing the ionic strength to 0.0165 M, leads to the formation of micron-sized aggregates within 15 min. At all other pH values tested (5.8-8.2), micron-sized aggregates form in less than 5 min (minimum detection time), even at low ionic strength (0.0084-0.0099 M with NaCl). In contrast, micronsized aggregates form within 5 min in an aqueous suspension of CaCl 2 at an ionic strength of 0.0128 M and pH of 4.8, which is significantly faster than observed for NaCl suspensions with similar ionic strength and pH. This result indicates that divalent cations may enhance aggregation of nano-TiO 2 in soils and surface waters. Optical micrographs show branching aggregates of sizes ranging from the 1 µm optical limit of the microscope to tens of micrometers in diameter.
Water, Air, & Soil Pollution, 2017
A comprehensive ecotoxicity assessment of three different nanosized TiO 2 (with 16, 36 and 89 nm particle diameter) and one microscale TiO 2 suspension (with 3264 nm particle diameter) was carried out with a special emphasis on the relation between product characteristics and toxic effect. The applied test battery included the combination of modified standardized tests (Aliivibrio fischeri bioluminescence inhibition test, Lemna minor growth inhibition test), and nonstandardized bioassays with unconventional physiological endpoints (Tetrahymena pyriformis phagocytic activity, the Daphnia magna heartbeat rate). Based on the lowest significant effect values, the tested aquatic organisms were the most sensitive to the microscale TiO 2 suspension (with 3264 nm particle size). Although the three nanoscale TiO 2 particles were aggregated in the A. fischeri and the L. minor growth media, significant inhibition rates were experienced at 0.1 and at 1 μg L ─1 concentration of nTiO 2 suspensions with 16 and 36 nm primary particle size, respectively. Larger aggregates may have also high impact on biological organisms. In case of the D. magna heartbeat rate test rapid agglomeration was avoided, but lower responses were found compared to other investigated systems. The short term T. pyriformis phagocytic activity test demonstrated outstanding sensitivity; three TiO 2 suspensions were significantly toxic even at 0.1 μg L ─1. The consequences of our study clearly indicated that nanoscale TiO 2 may have an impact on the aquatic ecosystem which is strongly influenced by aggregation. The effect of exposure duration and concentration as contributing factors in nanotitanium dioxide mediated toxicity was also demonstrated.
Journal of Colloid and Interface Science, 2011
This study investigated the sedimentation and aggregation kinetics of titanium dioxide (TiO 2 ) nanoparticles with varying material properties (i.e., crystallinity, morphology, and chemical composition). Used in the study were various types of commercially available TiO 2 nanoparticles: three spherical anatase (nominal diameters of 5, 10, and 50 nm) and two rutile nanoparticles (10 Â 40 and 30 Â 40 nm). The 50 nm anatase and 10 Â 40 nm rutile showed higher stability in deionized water and 5 mM NaCl solutions at pH 7 than the 5, and 10 nm anatase nanoparticles in sedimentation experiments. In aggregation experiments, critical coagulation concentration values for the 50 nm anatase were the highest, followed by the 10 Â 40 nm rutile and the 5 nm anatase nanoparticles in NaCl and CaCl 2 solutions. The aggregation kinetics was fitted reasonably well with the Derjaguin-Landau-Verwey-Overbeek (DLVO) equations for the TiO 2 nanoparticles tested. Results showed that crystallinity and morphology are not influential factors in determining the stability of TiO 2 nanoparticle suspensions; however, the differences in their chemical compositions, notably, the varying concentrations of impurities (i.e., silicon and phosphorus) in the pristine materials, determined the surface charge and therefore the sedimentation and aggregation of TiO 2 nanoparticles in the aqueous phase.
Analytical and Bioanalytical Chemistry, 2020
Due to their omnipresence in consumer products, there is a growing concern about the potential effects of nanoparticles on human health. Toxicological assessment and NP end-product studies require proper quantification of these materials in biological fluids. However, their quantifications in these media require stable predispersed NP solutions in aqueous media to enable the fortification in the matrices of interest or the preparation of calibration standards. In this study, a sample preparation scheme was developed by studying various dispersion media (polyvinylpyrrolidone and polyethylene glycol) and sonication strategies (bath and ultrasonic probe) to ensure homogeneous dispersion of titanium dioxide nanoparticles. Optimization of the various parameters was performed using SRM NIST 1898 NP reference material, composed of rutile and anatase phases. Number-based size distribution for titanium dioxide NPs was determined by dynamic light scattering and single-particle inductively coupled plasma mass spectrometry to evaluate the procedure efficiency. Changes in mean size and most frequent size distribution were also studied to determine if the agglomeration of nanoparticles occurs at the various dispersion conditions tested. Among the different dispersion parameters tested herein, the use of polyvinylpyrrolidone combined with a sonication process generated by a probe leads to a significant improvement in terms of suspension efficiency and stability over 72 h. The dispersion efficiency of the proposed methodology was assessed by single-particle inductively coupled plasma mass spectrometry with spiked biological fluids such as urine and blood.