Theoretical and experimental approaches
II.2.1 Materials .1 CeO 2 NPs .1 CeO2 NPs
II.2.2.2 Nanoparticle tracking analysis method
12
, (II.13)where ζ-potential is expressed in mV and electrophoretic mobility UE in µms–1/Vcm–1.
The advantages of DLS method are fast measurements (2-5 min per sample), easy sample handling, good reproducibility. Parameters (particle z-average hydrodynamic diameter and particle size distributions) are obtained in the same time and measurements are made in a broad range of sizes and concentrations of particle (1 – 1000 nm and 108 - 1012 particles/mL). However, the main drawback of the technique is an inaccurate determination of a particle size for a polydisperse sample. It happens because the results are biased toward bigger size particles due to the intensity of scattered light is proportional to the sixth power of particle radius (I ~ d6) (Boyd et al., 2011; Hanus and Ploehn, 1999).
II.2.2.2 Nanoparticle tracking analysis method
Visualization and distribution of particles by size were investigated using nanoparticle tracking analysis (NTA) technique with a NanoSight LM14 instrument (NanoSight Ltd, UK).
The instrument uses a laser light source to illuminate nanoscale particles. The particles appear individually as point-scatterers moving under Brownian motion, the dispersed light is being captured by a high sensitivity camera, via the microscope (Fig.
II.13). Particles are individually tracked and visualised on the screen of the control computer. NTA instrument captures a video of particles moving under Brownian motion and automatically locates and follows the centre of each particle. The device determines the average distance moved by each particle in x and y direction. The measurement is
36
done simultaneously for all particles. This value allows to obtain the diffusion coefficient and using the Stokes-Einstein equation (II.11) to calculate the sphere-equivalent, hydrodynamic diameter (Carr and Malloy, 2006; Hole et al., 2013).
Fig. II.13. A schematic illustration of the nanoparticle visualisation using the NTA instrument. The main steps of particle tracking and analysis consist in capturing the video, tracking of individual particles moving under Brownian motion and analysis of the data (Image from NanoSight Ltd).
In order to visualize as many particles as possible and to reduce the noise to minimum level the camera settings should be appropriately adjusted during the video recording. The capture time is also to be adjusted according to the polydispersity of the sample. Higher sample polydispersity need longer capture times (from 90 to 160 sec).
There are many advantages of NTA technique such as an accurate measurement of the particle size for both monodisperse and polydisperse samples, a high peak resolution, the measurement of hydrodynamic diameter dh directly and the size number distribution.
The results obtained are based on particle by particle analysis and the possibility to visualize the sample. However, the results of measurements are highly dependent of the processing parameters and experimental protocol. The technique can be applied in a limited size and concentration range (size: 30 – 1000 nm and concentration: 107 – 109 particles/mL). The measurement and sample preparation are time consuming and labour intensive (Gallego-Urrea et al., 2010; Hole et al., 2013).
37 II.2.2.3 Electron microscopy methods
In order to obtain images of individual particles and aggregates and to visualise the morphology of particles, scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were used. The schematic representation of the types of electrons detected by the techniques and schematic view of the both instrument are presented in Fig. II.14.
Fig. II.14. Schematic illustration of the working principle of electron microscopy methods (SEM and TEM).
SEM method provides the topographical information and chemical composition of the sample. A basic SEM consists of an electron gun that produces the electron beams with energy from 0.2 to 40 keV (Egerton, 2006). Electromagnetic optics is used to guide the beam and focus it. The detectors collect the electrons that come from the sample. When the electron beam interacts with the sample, different signals are emitted from different parts of the interaction volume. Typically, SEM detects secondary emitted electrons. The energy of the detected electron, its intensity and location of emission is used to put together the image. Other information that can be obtained using SEM is X-ray energy which depends on the elemental composition of the sample (Egerton, 2006). In our work we used a JEOL JSM-7001FA SEM operated with a following parameters: voltage 15 kV, probe current 1 nA.
In TEM, an electron beam penetrates a thin specimen and transmitted electrons are used to obtain the morphological information about the sample. The TEM is able to display the magnified images and to produce the electron-diffraction patterns in order to obtain crystallographic information.
38
TEM consists of the three main parts: the illumination system with the source of the electrons and lenses; the specimen stage, which contains the sample; and the imaging system with lenses. Electron beam can generate energy from 100 to 400 keV (Williams et al., 1998). The imaging lenses of a TEM produce a magnified image or an electron-diffraction pattern of the specimen on a viewing screen or camera system. The spatial resolution of the image is largely dependent on the quality and design of these lenses.
Hitachi A7650 TEM was used in our work with a large aperture (100µm apparent diameter) operating under a 80 keV accelerating voltage.
The advantages of microscopic techniques are the possibility of a direct measurement of particle morphology and size, imaging of surface coating and modification. There are some drawbacks of the technique such as it is a time consuming analysis (image acquisition and analysis). During sample preparation the formation of artefacts is possible because of the drying process (aggregation). The equipment is expensive and the analysis is a subject of personal bias because the operator might overlook some particles. The operator should perform a particle-by-particle analysis in order to determine the particle edge in a consistent and reproducible manner.
II.3 References
Ball, J.W., Jenne, E.A., Nordstrom, D.K., 1980. Additional and revised thermochemical data and computer code for WATEQ2: A computerized chemical model for trace and major element speciation and mineral equilibria of natural waters. Water Resources Division, US Geological Survey.
Barnum, D.W., 1983. Hydrolysis of cations. Formation constants and standard free energies of formation of hydroxy complexes. Inorg. Chem. 22, 2297–2305.
https://doi.org/10.1021/ic00158a016
Boyd, R.D., Pichaimuthu, S.K., Cuenat, A., 2011. New approach to inter-technique comparisons for nanoparticle size measurements; using atomic force microscopy, nanoparticle tracking analysis and dynamic light scattering. Colloids Surf.
Physicochem. Eng. Asp. 387, 35–42.
Carr, B., Malloy, A., 2006. NanoParticle Tracking Analysis–The NANOSIGHT system.
Chaukura, N., Gwenzi, W., Bunhu, T., Ruziwa, D.T., Pumure, I., 2016. Potential uses and value-added products derived from waste polystyrene in developing countries: A
review. Resour. Conserv. Recycl. 107, 157–165.
https://doi.org/10.1016/j.resconrec.2015.10.031
Chen, K.L., Elimelech, M., 2007. Influence of humic acid on the aggregation kinetics of fullerene (C60) nanoparticles in monovalent and divalent electrolyte solutions. J.
Colloid Interface Sci., Matijevic Festschrift 309, 126–134.
https://doi.org/10.1016/j.jcis.2007.01.074
39
Chen, K.L., Mylon, S.E., Elimelech, M., 2006. Aggregation kinetics of alginate-coated hematite nanoparticles in monovalent and divalent electrolytes. Environ. Sci.
Technol. 40, 1516–1523.
Chen, Q., Xu, S., Liu, Q., Masliyah, J., Xu, Z., 2016. QCM-D study of nanoparticle interactions.
Adv. Colloid Interface Sci., Clayton Radke Festschrift 233, 94–114.
https://doi.org/10.1016/j.cis.2015.10.004
Cornell, R.M., Schwertmann, U., 2003. The iron oxides: structure, properties, reactions, occurrences and uses. John Wiley & Sons.
Derjaguin, B., Landau, L., 1941. The theory of stability of highly charged lyophobic sols and coalescence of highly charged particles in electrolyte solutions. Acta Physicochim URSS 14, 58.
Egerton, R., 2006. Physical principles of electron microscopy: an introduction to TEM, SEM, and AEM. Springer Science & Business Media.
Elimelech, M., Jia, X., Gregory, J., Williams, R., 1998. Particle deposition & aggregation:
measurement, modelling and simulation. Butterworth-Heinemann.
Felmy, A.R., Girvin, D.C., Jenne, E.A., 1984. MINTEQ--a Computer Program for Calculating Aqueous Geochemical Equilibria: February 1984. National Technical Information Service.
Gallego-Urrea, J.A., Tuoriniemi, J., Pallander, T., Hassellöv, M., 2010. Measurements of nanoparticle number concentrations and size distributions in contrasting aquatic environments using nanoparticle tracking analysis. Environ. Chem. 7, 67–81.
Gregory, J., 2005. Particles in water: properties and processes. CRC Press.
Hanus, L.H., Ploehn, H.J., 1999. Conversion of intensity-averaged photon correlation spectroscopy measurements to number-averaged particle size distributions. 1.
Theoretical development. Langmuir 15, 3091–3100.
Hole, P., Sillence, K., Hannell, C., Maguire, C.M., Roesslein, M., Suarez, G., Capracotta, S., Magdolenova, Z., Horev-Azaria, L., Dybowska, A., Cooke, L., Haase, A., Contal, S., Manø, S., Vennemann, A., Sauvain, J.-J., Staunton, K.C., Anguissola, S., Luch, A., Dusinska, M., Korenstein, R., Gutleb, A.C., Wiemann, M., Prina-Mello, A., Riediker, M., Wick, P., 2013. Interlaboratory comparison of size measurements on nanoparticles using nanoparticle tracking analysis (NTA). J. Nanoparticle Res. 15, 1–12. https://doi.org/10.1007/s11051-013-2101-8
Israelachvili, J.N., 2011. Intermolecular and surface forces. Academic press.
Kaplan, D.L., Hartenstein, R., Sutter, J., 1979. Biodegradation of polystyrene, poly (metnyl methacrylate), and phenol formaldehyde. Appl. Environ. Microbiol. 38, 551–553.
Lee, K.Y., Mooney, D.J., 2012. Alginate: properties and biomedical applications. Prog.
Polym. Sci. 37, 106–126.
Leenheer, J.A., Wershaw, R.L., Reddy, M.M., 1995. Strong-acid, carboxyl-group structures in fulvic acid from the Suwannee River, Georgia. 2. Major structures. Environ. Sci.
Technol. 29, 399–405.
LeRoux, M.A., Guilak, F., Setton, L.A., 1999. Compressive and shear properties of alginate gel: effects of sodium ions and alginate concentration. J. Biomed. Mater. Res. 47, 46–53.
Metreveli, G., Philippe, A., Schaumann, G.E., 2015. Disaggregation of silver nanoparticle homoaggregates in a river water matrix. Sci. Total Environ., Special Issue:
Engineered nanoparticles in soils and waters 535, 35–44.
https://doi.org/10.1016/j.scitotenv.2014.11.058
Overbeek, J.T.G., Verwey, E.J.W., 1948. Theory of the Stability of Lyophobic Colloids: The interaction of Sol Particles Having an Electric Double Layer.
40
Peterson, S.R., Hostetler, C.J., Deutsch, W.J., Cowan, C.E., 1987. Minteq User’s Manual (No.
NUREG/CR-4808; PNL-6106). Pacific Northwest Lab., Richland, WA (USA);
Nuclear Regulatory Commission, Washington, DC (USA). Div. of Waste Management.
Pettit, R.E., 2004. Organic matter, humus, humate, humic acid, fulvic acid and humin: Their importance in soil fertility and plant health. CTI Res.
Plastics-the Facts 2016. An analysis of European plastics production, demand and waste data, 2016. . Plastics Europe.
Praetorius, A., Labille, J., Scheringer, M., Thill, A., Hungerbühler, K., Bottero, J.-Y., 2014.
Heteroaggregation of Titanium Dioxide Nanoparticles with Model Natural Colloids under Environmentally Relevant Conditions. Environ. Sci. Technol. 48, 10690–
10698. https://doi.org/10.1021/es501655v
Rehm, B.H., 2009. Alginates: biology and applications. Springer.
Singh, C., Friedrichs, S., Ceccone, G., Gibson, N., Jensen, K.A., Levin, M., Infante, H.G., Carlander, D., Rasmussen, K., 2014. Cerium Dioxide, NM-211, NM-212, NM-213.
Characterisation and test item preparation. European Commission, Joint Research Centre, European Union. https://doi.org/10.2788/80203
Smoluchowski, M. v, 1918. Versuch einer mathematischen Theorie der Koagulationskinetik kolloider Lösungen. Z. Für Phys. Chem. 92, 129–168.
Stefánsson, A., 2007. Iron (III) hydrolysis and solubility at 25 C. Environ. Sci. Technol. 41, 6117–6123.
Williams, D.B., Carter, C.B., Veyssiere, P., 1998. Transmission electron microscopy: a textbook for materials science. Springer.
Zhang, W., Crittenden, J., Li, K., Chen, Y., 2012. Attachment Efficiency of Nanoparticle Aggregation in Aqueous Dispersions: Modeling and Experimental Validation.
Environ. Sci. Technol. 46, 7054–7062. https://doi.org/10.1021/es203623z