Browsing by Author "Wang, Tianxiao"

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    Co-transport of Carboxyl-functionalized Multi-walled Carbon Nanotubes and Kaolinite in Saturated Porous Media
    (2015-04-22) Wang, Tianxiao; Li, Qilin; Alvarez, Pedro J; Tomson, Mason B
    Co-transport behavior of carboxylated multiwalled carbon nanotubes (COOH-MWCNTs) and kaolinite in various solution ionic strength (IS) and pH were investigated. Results on electrophoretic mobility of CNT, kaolinite and quartz sand as well as particle size of CNT-kaolinite mixture, CNT alone and kaolinite alone were consistent with the DLVO theory. Large particle sizes of kaolinite-CNT mixture revealed potential heteroaggregations especially at 1 mM NaCl, pH=3 and 10 mM NaCl and pH=9. Deposition of CNT was enhanced during the co-transport at 1mM NaCl and pH=3 due to the low mobility of CNT-kaolinite heteroaggregate while decreased at pH=5 in 1 mM NaCl, pH=9 in 10 mM NaCl and pH=9 in 100 mM NaCl because of site blocking by kaolinite. Kaolinite mobility increased in the presence of CNT at pH=3 in 1 mM NaCl caused by site blocking and at pH=9 in 10 mM NaCl resulted from low single collector efficiency of large particles.
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    Effect of Kaolinite on the Fate and Transport of Carbon Nanotubes
    (2018-02-15) Wang, Tianxiao; Li, Qilin
    Fate and transport of the engineered nanomaterials (ENMs) in aquatic systems has been increasingly concerned due to their potential human exposure and reported toxicity to the living organisms. The ubiquitous naturally occurring colloids (NOC) is an important impacting factor controlling the aqueous stability and subsurface transport of ENMs in porous media. This study investigated the effect of kaolinite on the aggregation, stability and subsurface mobility of carboxyl-functionalized multi-walled carbon nanotubes (COOH-MWCNT) under a range of environmentally relevant solution conditions. The increase of ionic strength and decrease of pH enhanced the heteroaggregation. CNT and kaolinite can form both primary and secondary heteroaggregates under different solution conditions. The effect of heteroaggregation strongly depends on the CNT-to-kaolinite ratio; it can either increase or decrease the stability of the suspension depending on the structure of the heteroaggregates formed. Ca2+ and dissolved NOM played opposite roles on the stability of CNT. The addition of Ca2+ induced the heteroaggregation through bridging effect and charge screening while NOM hindered the aggregation via steric effect in low Ca2+ conditions. When Ca2+ reached a high concentration range, the effect of Ca2+ dominated and induced large heteroaggregates, destabilizing the CNT-kaolinite system. In natural surface waters, CNT exhibits decreased stability, a notable portion of which is attributed to the naturally occurring colloids. The effect of other water quality parameters (e.g., ionic composition) also contributes to the decreased stability. Flow cytometry, a common technique for cell analysis in biological field, was applied in analyzing aggregations in Alexa Fluor 633 dyed carbon nanotubes (AFCNT) and kaolinite mixture under various pH and ionic strength conditions. By testing the extremely low concentrations of AFCNT and kaolinite mixture samples, the flow cytometer rapidly provided data needed in quantitatively determining the degree of homo- and heteroaggregations. It can be applied on future aggregation studies of ENM-NOC systems and provide meaningful information for the risk management of ENMs in aquatic environments. The mobility of CNT in porous media is strongly dependent on the degree of CNT-kaolinite heteroaggregation and the formation of the aggregates. Results demonstrated that significant CNT-kaolinite heteroaggregations occurred under extremely low pH (pH=3 in 1 mM NaCl) or extremely high ionic strength (pH=9, 100 mM NaCl) conditions. Under the conditions when large secondary aggregation formed at low pH, kaolinite hindered CNT mobility through straining effect. However, CNT transport was facilitated by kaolinite when primary heteroaggregates are the main formation in high ionic strength and high pH. When there were no CNT-kaolinite interactions, CNT mobility was enhanced probably because kaolinite competed with CNT for the adsorption sites on porous media. Findings in the study highlighted the important role of naturally occurring colloids, dissolved natural organic matter and solution chemistry on the environmental fate and transport of CNT. It provides fundamental information for the risk assessment of CNT in natural water systems.
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    Multi-endpoint, High-Throughput Study of Nanomaterial Toxicity in Caenorhabditis elegans
    (American Chemical Society, 2015) Jung, Sang-Kyu; Qu, Xiaolei; Aleman-Meza, Boanerges; Wang, Tianxiao; Riepe, Celeste; Liu, Zheng; Li, Qilin; Zhong, Weiwei
    The booming nanotechnology industry has raised public concerns about the environmental health and safety impact of engineered nanomaterials (ENMs). High-throughput assays are needed to obtain toxicity data for the rapidly increasing number of ENMs. Here we present a suite of high-throughput methods to study nanotoxicity in intact animals using Caenorhabditis elegans as a model. At the population level, our system measures food consumption of thousands of animals to evaluate population fitness. At the organism level, our automated system analyzes hundreds of individual animals for body length, locomotion speed, and lifespan. To demonstrate the utility of our system, we applied this technology to test the toxicity of 20 nanomaterials at four concentrations. Only fullerene nanoparticles (nC60), fullerol, TiO2, and CeO2 showed little or no toxicity. Various degrees of toxicity were detected from different forms of carbon nanotubes, graphene, carbon black, Ag, and fumed SiO2 nanoparticles. Aminofullerene and ultraviolet-irradiated nC60 also showed small but significant toxicity. We further investigated the effects of nanomaterial size, shape, surface chemistry, and exposure conditions on toxicity. Our data are publicly available at the open-access nanotoxicity database www.QuantWorm.org/nano.