Environmental nanoparticles

A corollary to (2) is that environmental nanoparticles will be generally surrounded by water, either due to saturated conditions, or adsorbed water. Hence the surfaces of the particles must adjust to the bonding with water molecules, and possibly excess or surplus protons as dictated by the pH. This alone may cause a significant difference in the nature of the particle surface relative to a dry surface, e.g., a cleaved particle exposed to a dry atmosphere of pressure with sufficient oxygen partial pressure to maintain all metal valence states as in the bulk. 

State lifetimes and modes of energy transfer within the structure. Examples of this are photoluminescence of ZnS nanoparticles studied by Wu et al. (1994), and Mn doped ZnS nanoparticles by Bhargava et al. (1994). In the latter study, the doped nanocrystals were found to have higher quantum efficiency for fluorescence emission than bulk material, and a substantially smaller excited state lifetime. In the case of environmental nanoparticles of iron and manganese oxides, photoluminescence due to any activator dopant would be quenched by magnetic coupling and lattice vibrations. This reduces the utility of photoluminescence studies to excited state lifetimes due to particle-dopant coupling of various types. The fluorescence of uranyl ion sorbed onto iron oxides has been studied in this way, but not as a function of particle size. 

Table 6.2. Comparison of Environmental Nanoparticles in a Variety of Workplaces ...

The most important environmental nanoparticles are carbon nanotubes (CNTs), fullerenes (such as Ceo), nanowires, Ti02, ZnO, Ce02, Si02 (silica), iron oxides, alumina, hydroxyapatite and metallic nanoparticles such as Fe, Ag and Au. World production of Ti02 is estimated to be in excess of 40,000 tons per annum with most of the material being nano-sized. ... 

Given the absolute and increasing scale of production of nanomaterials allied to their uncertain effects on human health it is important that the presence of nanoparticles in the environment can be measured and monitored along with their chemical identification and concentration. The quantification of environmental nanoparticles represents a significant analytical challenge. In the next section (8.2), we veiy briefly outline existing non-electrochemical methods before considering in detail electrochemical alternatives in Sect. 8.3. 

Non-electrochemical Approaches to the Quantification of Environmental Nanoparticles and Their Limitations... 

We have reported a simple, green, bench top, economical and environmentally benign room temperature synthesis of MSe (M=Cd or Zn) nanoparticles using starch, PVA and PVP as passivating agents. The whole process is a redox reaction with selenium acting as the oxidant and MSe as the reduction product. An entire "green" chemistry was explored in this synthetic procedure and it is reproducible. The optical spectroscopy showed that all the particles are blue shifted from the bulk band gap clearly due to quantum confinement. Starch capped CdSe nanoparticles showed the presence of monodispersed spherical... 

Mueler et al. and Gottschalk et al. [43, 44] presented a model for predicting concentrations of nanoparticles including nano-Ag, nano-Ti02, nano-ZnO, fullerenes, and carbon nanotubes (CNT) in different environmental compartments. The results of this study demonstrated that modeling is a meaningful utility to carry out quantitative risk assessment of nanoparticles. 

One method of overcoming the detrimental solvent dewetting effects is to use liquid C02 as the solvent for nanoparticle dispersions [52], since C02 does not experience the dewetting instabilities due to its extremely low surface tension [53]. In this case, nanoparticles must be stabilized with fluorinated ligands [30, 33, 54—65] or other C02-philic ligands [60,66-76], such that they will disperse in the C02 prior to dropcasting. These fluorinated ligands tend be toxic and environmentally persistent and, typically, only very small nanoparticles can be dispersed at low concentrations. 

Calza, P., Pelizzetti, E., Mogyorosi, K, Kun, R., and Dekany, I. (2007) Size dependent photocatalytic activity of hydrothermally crystallized titania nanoparticles on poorly adsorbing phenol in absence and presence of fluoride ion. Applied Catalysis B Environmental, 72 (3 1), 314-321. 

Lorret, O., Franco va, D., Waldner, G., and Stelzer, N. (2009) W-doped titania nanoparticles for UV and visible-light photocatalytic reactions. Applied Catalysis B Environmental, 91 (1-2), 39-46. 

Fresno, F., Coronado, J.M.,Tudela, D., and Soria, J. (2005) Influence of the structural characteristics of Ti], .Sn,.02 nanoparticles on their photocatalytic activity for the elimination of methylcyclohexane vapors. Applied CatalysisB Environmental, 55 (3), 159-167. 

Oberdorster, G Oberdorster, E., and Oberdorster, J. (2007) Concepts of nanoparticle dose metric and response metric. Environmental Health Perspectives, 115 (6), A290. 

Murr, L.E., Garza, K.M., Soto, K.F., Carrasco, A., Powell, T.G., Ramirez, D.A., Guerrero, P.A., Lopez, D.A., and Venzorlll, J. (2005) Cytotoxicity assessment of some carbon nanotubes and related carbon nanoparticle aggregates and the implications for anthropogenic carbon nanotube aggregates in the environment. International Journal of Environmental Research and Public Health, 2 (1), 31-42. 

The particle size was below 50 nm (as determined by TEM image analysis), considerably smaller than that of the starting nanoemulsion, and showed a slight mean particle size increase and a broader size distribution with increasing O/S ratio, supporting the template effect of the nanoemulsion. The authors showed that these nanoparticles are interesting not only from a basic viewpoint but also for applications where safety and environmental concerns are important issues. 

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