Natural silicate nanoparticles: separation, characterization, and assessment of stability and perspectives of their use as reference nanomaterials.

Natural nanomaterials, which play a very important role in environmental processes, are so far poorly studied. Firstly, the separation of nanoparticles from the bulk sample is a challenge. Secondly, the absence of reference natural nanomaterials makes it impossible to compare the results obtained by different researchers and develop a unified methodology for the separation and characterization of natural nanomaterials. Therefore, the development of reference natural nanomaterials is an urgent need of the environmental analytical chemistry. In this work, mineral nanoparticles (kaolinite, montmorillonite, muscovite, and quartz) have been studied as potential reference natural nanomaterials. A set of analytical methods including coiled-tube field-flow fractionation, scanning electron microscopy, dynamic light scattering, laser diffraction, inductively coupled plasma atomic emission, and mass spectrometry are applied to the separation and characterization of nanoparticles. It has been shown by laser diffraction that 93-98% of separated mineral nanoparticles are in the size range from about 40 to 300 nm, while 2-7% have size up to 830 nm. The size range of particles is confirmed by electron microscopy. Major (Al, Na, K, Ca, Fe), trace (Ti, Co, Cu, Zn, Tl, Pb, Bi, etc.), and rare earth elements have been determined in the suspensions of kaolinite, montmorillonite, and muscovite nanoparticles. Based on Al content, the concentration of mineral nanoparticles in suspensions is estimated. Agglomeration stability (consistency of size distribution) of nanoparticles at pH 6-8 is assessed. It has been shown that muscovite nanoparticles are stable at pH 7-8, whereas montmorillonite nanoparticles are stable only at pH 8 for at least 4 weeks. A noticeable agglomeration of kaolinite nanoparticles is observed at pH 6-8. Due to the low concentration of quartz nanoparticles, their characterization and stability assessment are hindered. The challenges of the development of reference natural nanomaterials are discussed.

Assessment of elemental composition and properties of copper smelter-affected dust and its nano- and micron size fractions.

A comprehensive approach has been developed to the assessment of composition and properties of atmospherically deposited dust in the area affected by a copper smelter. The approach is based on the analysis of initial dust samples, dynamic leaching of water soluble fractions in a rotating coiled column (RCC) followed by the determination of recovered elements and characterization of size, morphology and elemental composition of nano-, submicron, and micron par ticles of dust separated using field-flow fractionation in a RCC. Three separated size fractions of dust (<0.2, 0.2-2, and >2 µm) were characterized by static light scattering and scanning electron microscopy, whereupon the fractions were analyzed by ICP-AES and ICP-MS (after digestion). It has been evaluated that toxic elements, which are characteristics for copper smelter emissions (As, Cu, Zn), are accumulated in fraction >2 µm. At the same time, up to 2.4, 3.1, 8.2, 6.7 g/kg of As, Cu, Zn, Pb, correspondently, were found in nanoparticles (<0.2 µm). It has been also shown that some trace elements (Sn, Sb, Ag, Bi, and Tl) are accumulated in fraction <0.2, and their content in this fraction may be one order of magnitude higher than that in the fraction >2 µm, or the bulk sample. It may be assumed that Sn, Sb, Ag, Bi, Tl compounds are adsorbed onto the finest dust particles as compared to As, Cu, Zn compounds, which are directly emitted from the copper smelter as microparticles.

A contribution of nanoscale particles of road-deposited sediments to the pollution of urban runoff by heavy metals.

Road-deposited sediments (RDS) present a sink for traffic-related pollutants including heavy metals (HMs). HMs associated with RDS particles enter the urban aquatic environment during rainfall events and have adverse effects for biota. RDS nanoscale particles (NSPs) require special consideration due to their specific properties, extremely high mobility in the environment, and ability to penetrate into living organisms. In the present work, the contribution of NSPs of RDS to the pollution of urban runoff by HMs has been evaluated for the first time. It has been shown that bulk RDS samples are polluted by HMs as compared to background urban soils (geo-accumulation indexes of Cu and Zn may attain 2-3). Meanwhile, NSPs of RDS are enriched by HMs as compared to bulk samples; concentration factor for Ni, Cu, Zn, Cd, Sn, and Pb in NSPs being varied from 2 to 10. The water-soluble fractions of RDS samples were also analyzed. Results have shown that the content of water-soluble HMs in RDS is insignificant and rarely exceeds 0.5% of the total contents of HMs in the bulk samples; the highest contents are identified for Cu and Pb. It should be noted that the water-soluble fraction is nearly free from Zn and this element is almost entirely present as particulate matter (NSPs). In general, the overall contribution of NSPs and water-soluble fraction of HMs to the pollution of urban runoff is comparable.

Assessment of elemental composition and properties of copper smelter-affected dust and its nano- and micron size fractions.

A comprehensive approach has been developed to the assessment of composition and properties of atmospherically deposited dust in the area affected by a copper smelter. The approach is based on the analysis of initial dust samples, dynamic leaching of water soluble fractions in a rotating coiled column (RCC) followed by the determination of recovered elements and characterization of size, morphology and elemental composition of nano-, submicron, and micron particles of dust separated using field-flow fractionation in a RCC. Three separated size fractions of dust (<0.2, 0.2-2, and >2 µm) were characterized by static light scattering and scanning electron microscopy, whereupon the fractions were analyzed by ICP-AES and ICP-MS (after digestion). It has been evaluated that toxic elements, which are characteristics for copper smelter emissions (As, Cu, Zn), are accumulated in fraction >2 µm. At the same time, up to 2.4, 3.1, 8.2, 6.7 g/kg of As, Cu, Zn, Pb, correspondently, were found in nanoparticles (<0.2 µm). It has been also shown that some trace elements (Sn, Sb, Ag, Bi, and Tl) are accumulated in fraction <0.2, and their content in this fraction may be one order of magnitude higher than that in the fraction >2 µm, or the bulk sample. It may be assumed that Sn, Sb, Ag, Bi, Tl compounds are adsorbed onto the finest dust particles as compared to As, Cu, Zn compounds, which are directly emitted from the copper smelter as microparticles.