Yusong Li

Influence of electrolyte species and concentration on the aggregation and transport of fullerene nanoparticles in quartz sands

The potential toxicity of nanoscale particles has received considerable attention, but the fate of engineered nanomaterials in the environment has been studied only under a limited set of conditions. In the present study, batch and column experiments were performed to assess the aggregation and transport of nanoscale fullerene (nC60) particles in water-saturated quartz sands as a function of electrolyte concentration and species. As the electrolyte concentration increased from 1 to 100 mM, the change in nC60 particle diameter was minimal in the presence of NaCl but increased by more than sevenfold in the presence of CaCl2. The latter effect was attributed to the agglomeration of individual nC60 particles, consistent with a net attractive force between particles and suppression of the electrical double layer. At low ionic strength (3.05 mM), nC60 particles were readily transported through 40- to 50-mesh quartz sand, appearing in the column effluent after introducing less than 1.5 pore volumes of nC60 suspension, with approximately 30% and less than 10% of the injected mass retained in the presence of CaCl2 or NaCl, respectively. At higher ionic strength (30.05 mM) and in finer Ottawa sand (100-140 mesh), greater than 95% of the introduced nC60 particles were retained in the column regardless of the electrolyte species. Approximately 50% of the deposited nC60 particles were recovered from 100- to 140-mesh Ottawa sand after sequential introduction of deionized water adjusted the pH to 10 and 12. These findings demonstrate that nC60 transport and retention in water-saturated sand is strongly dependent on electrolyte conditions and that release of deposited nC60 requires substantial changes in surface charge, consistent with retention in a primary energy minimum.

Enhanced Mobility of Fullerene (C60) Nanoparticles in the Presence of Stabilizing Agents

Experimental and mathematical modeling studies were performed to examine the effects of stabilizing agents on the transport and retention of fullerene nanoparticles (nC(60)) in water-saturated quartz sand. Three stabilizing systems were considered: naturally occurring compounds known to stabilize nanoparticles (Suwannee river humic acid (SRHA) and fulvic acid (SRFA)), synthetic additives used to enhance nanoparticle stability (Tween 80, a nonionic surfactant), and residual contaminants resulting from the manufacturing process (tetrahydrofuran (THF)). The results of column experiments demonstrated that the presence of THF, at concentrations up to 44.5 mg/L, did not alter nC(60) transport and retention behavior, whereas addition of SRHA (20 mg C/L), SRFA (20 mg C/L), or Tween 80 (1000 mg/L) to the influent nC(60) suspensions dramatically increased the mobility of nC(60), as demonstrated by coincidental nanoparticle and nonreactive tracer effluent breakthrough curves (BTCs) and minimal nC(60) retention. When columns were preflushed with surfactant, nC(60) transport was significantly enhanced compared to that in the absence of a stabilizing agent. The presence of adsorbed Tween 80 resulted in nC(60) BTCs characterized by a declining plateau and retention profiles that exhibited hyperexponential decay. The observed nC(60) transport and retention behavior was accurately captured by a mathematical model that accounted for coupled surfactant adsorption-desorption dynamics, surfactant-nanoparticle interactions, and particle attachment kinetics.

Transport and retention of colloids in porous media: does shape really matter?

The effect of particle shape on its transport and retention in porous media was evaluated by stretching carboxylate-modified fluorescent polystyrene spheres into rod shapes with aspect ratios of 2:1 and 4:1. Quartz crystal microbalance with dissipation (QCM-D) experiments were conducted to measure the deposition rates of spherical and rod-shaped nanoparticles to the collector (poly-l-lysine coated silica sensor) surface under favorable conditions. The spherical particles displayed a significantly higher deposition rate compared with that of the rod-shaped particles. Theoretical analysis based on Smoluchowski-Levich approximation indicated that the rod-shaped particles largely counterbalance the attractive energies due to higher hydrodynamic forces and torques experienced during their transport and rotation. Under unfavorable conditions, the retention of nanoparticles in a microfluidic flow cell packed with glass beads was studied with the use of laser scanning cytometry (LSC). Significantly more attachment was observed for rod-shaped particles than spherical particles, and the attachment rate of the rod-shaped particles showed an increasing trend with the increase in injection volume. Rod-shaped particles were found to be less sensitive to the surface charge heterogeneity change than spherical particles. Increased attachment rate of rod-shaped particles was attributed to surface heterogeneity and possibly enhanced hydrophobicity during the stretching process.

Development of a web-based mass transfer processes laboratory: System development and implementation

A web‐based environment is utilized as a means to introduce advanced mass transfer processes concepts in environmental engineering and science courses. System development and implementation is presented, including detailed descriptions of the techniques employed to link software written in high‐level computer languages such as C++ and FORTRAN to an internet‐based, user‐friendly graphical user interface for both program input and output.

Improving the sweeping efficiency of permanganate into low permeable zones to treat TCE: experimental results and model development.

The residual buildup and treatment of dissolved contaminants in low permeable zones (LPZs) is a particularly challenging issue for injection-based remedial treatments. Our objective was to improve the sweeping efficiency of permanganate into LPZs to treat dissolved-phase TCE. This was accomplished by conducting transport experiments that quantified the ability of xanthan-MnO4(-) solutions to penetrate and cover (i.e., sweep) an LPZ that was surrounded by transmissive sands. By incorporating the non-Newtonian fluid xanthan with MnO4(-), penetration of MnO4(-) into the LPZ improved dramatically and sweeping efficiency reached 100% in fewer pore volumes. To quantify how xanthan improved TCE removal, we spiked the LPZ and surrounding sands with (14)C-lableled TCE and used a multistep flooding procedure that quantified the mass of (14)C-TCE oxidized and bypassed during treatment. Results showed that TCE mass removal was 1.4 times greater in experiments where xanthan was employed. Combining xanthan with MnO4(-) also reduced the mass of TCE in the LPZ that was potentially available for rebound. By coupling a multiple species reactive transport model with the Brinkman equation for non-Newtonian flow, the simulated amount of (14)C-TCE oxidized during transport matched experimental results. These observations support the use of xanthan as a means of enhancing MnO4(-) delivery into LPZs for the treatment of dissolved-phase TCE.

Modeling the transport and retention of nC60 nanoparticles in the subsurface under different release scenarios.

The escalating production and consumption of engineered nanomaterials may lead to their increased release into groundwater. A number of studies have revealed the potential human health effects and aquatic toxicity of nanomaterials. Understanding the fate and transport of engineered nanomaterials is very important for evaluating their potential risks to human and ecological health. While there has been a great deal of research effort focused on the potential risks of nanomaterials, a limited amount of work has evaluated the transport of engineered nanomaterials under different release scenarios in a typical layered geological field setting. In this work, we simulated the transport of fullerene aggregates (nC(60)), a widely used engineered nanomaterial, in a multi-dimensional environment. A Modular Three-Dimensional Multispecies Transport Model (MT3DMS) was modified to evaluate the transport and retention of nC(60) nanoparticles. Hypothetical scenarios for the introduction of nanomaterials into the subsurface environment were investigated, including the release from an injection well and the release from a waste site. Under the conditions evaluated, the mobility of nC(60) nanoparticles was found to be very sensitive to the release scenario, release concentration, aggregate size, collision efficiency factor, and dispersivity of the nanomaterial.

Pore-Scale Investigation of Nanoparticle Transport in Saturated Porous Media Using Laser Scanning Cytometry

Knowledge of nanoparticle transport and retention mechanisms is essential for both the risk assessment and environmental application of engineered nanomaterials. Laser scanning cytometry, an emerging technology, was used for the first time to investigate the transport of fluorescent nanoparticles in a microfluidic flow cell packed with glass beads. The laser scanning cytometer (LSC) was able to provide the spatial distribution of 64 nm fluorescent nanoparticles attached in a domain of 12 mm long and 5 mm wide. After 40 pV of injection at a lower ionic strength condition (3 mM NaCl, pH 7.0), fewer fluorescent nanoparticles were attached to the center of the flow cell, where the pore-scale velocity is relatively higher. After a longer injection period (300 PV), more were attached to the center of the flow cell, and particles were attached to both the upstream and downstream sides of a glass bead. Nanoparticles attached under a higher ionic strength condition (100 mM NaCl, pH 7.0) were found to be mobilized when flushed with DI water. The mobilized particles were later reattached to some favorable sites. The attachment efficiency factor was found to reduce with an increase in flow velocity. However, torque analysis based on the secondary energy minimum could not explain the observed hydrodynamic effect on the attachment efficiency factor.

Effect of 17β-estradiol on stability and mobility of TiO2 rutile nanoparticles

Contaminants including titanium dioxide nanoparticles (n-TiO2), as well as organic wastewater contaminants (OWCs), have been detected in wastewater treatment plant effluents, however, no information is yet available on how OWCs may modify the surface properties of TiO2 nanoparticles, or influence their stability in water and subsequent mobility in porous media. In this study, 17β-estradiol (E2) was chosen as a representative OWC to investigate the interaction between OWCs and n-TiO2. Batch and kinetic sorption experiments and Fourier Transform Infrared (FTIR) Spectrometer measurements confirmed that E2 was quickly sorbed onto the surface of n-TiO2 aggregates in water. Aggregation experiments showed that the presence of E2 has a minor influence on the size of n-TiO2 aggregates under lower ionic strength conditions at natural pH. In high ionic strength solution, the presence of E2 led to an increased average hydrodynamic diameter and a wider distribution of n-TiO2 aggregate sizes. Interaction energy analyses indicated that steric repulsion likely contributed to the stability of the n-TiO2 suspension in the presence of E2. Mobility analysis based on the clean bed filtration theory indicated that the impact of E2 on the mobility of n-TiO2 in porous media is minimal in comparison to the influence of solution ionic strength.

Combined quartz crystal microbalance with dissipation (QCM-D) and generalized ellipsometry (GE) to characterize the deposition of titanium dioxide nanoparticles on model rough surfaces

Measuring the interactions between engineered nanoparticles and natural substrates (e.g. soils and sediments) has been very challenging due to highly heterogeneous and rough natural surfaces. In this study, three-dimensional nanostructured slanted columnar thin films (SCTFs), with well-defined roughness height and spacing, have been used to mimic surface roughness. Interactions between titanium dioxide nanoparticles (TiO2NP), the most extensively manufactured engineered nanomaterials, and SCTF coated surfaces were measured using a quartz crystal microbalance with dissipation monitoring (QCM-D). In parallel, in-situ generalized ellipsometry (GE) was coupled with QCM-D to simultaneously measure the amount of TiO2NP deposited on the surface of SCTF. While GE is insensitive to effects of mechanical water entrapment variations in roughness spaces, we found that the viscoelastic model, a typical QCM-D model analysis approach, overestimates the mass of deposited TiO2NP. This overestimation arises from overlaid frequency changes caused by particle deposition as well as additional water entrapment and partial water displacement upon nanoparticle adsorption. Here, we demonstrate a new approach to model QCM-D data, accounting for both viscoelastic effects and the effects of roughness-retained water. Finally, the porosity of attached TiO2NP layer was determined by coupling the areal mass density determined by QCM-D and independent GE measurements.

Influence of ligands on metal speciation, transport and toxicity in a tropical river during wet (monsoon) period

Metal speciation and transport are seldom assessed in densely populated Tropical River. An evaluation of the phase distribution for Copper (Cu), Lead (Pb) and Zinc (Zn) along with chemical speciation, variance with different water quality parameters and toxicity were conducted in the Brahmaputra River of India from upstream to downstream during wet (monsoon) periods in July 2014. Results indicated that metal free ions and carbonates were dominant in the inorganic fractions whereas metal concentrations were negligible in the anionic inorganic fractions. Due to high sediment load in the river during monsoon, metals were substantially higher in the particulate fractions than in the aqueous phase. Partition coefficient for Cu (3.1-6.1), Pb (3.4-6.5) and Zn (3.5-6.9), demonstrated strong adsorption of the metals on suspended matter. Q-mode hierarchical cluster analysis (HCA) illustrated groupings mainly governed by quality parameters rather than by the river course. R-mode results imply selectivity of the affinities of metals for different ligands. Health risk index (HRI) values were less than 1 for dissolved metal for Cu, Pb and Zn while it was greater than 1 for total metal for Pb and Cu indicating potential human health risk. The study demonstrated that binding of metals with naturally occurring dissolved organic matter or suspended particulate matter affects metal bioavailability in river during wet periods when sediment load is particularly high. A combination of empirical, computational and statistical relationships between ionic species and fractions of metals provided greater certitude in identifying the resemblance among the different locations of the river.