Publications by authors named "Chunming Su"

41 Publications

Removal of Fluoride from Water Using a Calcium-Modified Dairy Manure-Derived Biochar.

J Environ Eng (New York) 2020 Dec;146(12):1-10

Dept. of Civil and Environmental Engineering, Southern Methodist Univ., Dallas, TX 75275.

This study investigated the removal of fluoride from water using a calcium-modified dairy manure-derived biochar (Ca-DM500). The Ca-DM500 showed a 3.82 - 8.86 times higher removal of fluoride from water than the original (uncoated) manure-derived biochar (DM500). This is primarily attributed to strong precipitation/complexation between fluoride and calcium. The Freundlich and Redlich-Peterson sorption isotherm models better described the experimental data than the Langmuir model. Additionally, the removal kinetics were well described by the intraparticle diffusion model. The Ca-DM500 showed high reactivity per unit surface area [0.0001, 0.03, 0.16 mg F per m for Douglas fir-derived biochar (DF-BC), DM500. and Ca-DM500, respectively] for retention of fluoride reflecting the importance of surface complexation. The copresence of anions reduced removal by Ca-DM500 in the order . The sorption behavior of fluoride in a continuous fixed-bed column was consistent with the Thomas model. Column studies demonstrated that the Ca-DM500 shows a strong affinity for fluoride, a low release potential, and a stable (unreduced) removal capacity through regeneration and reuse cycles.
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http://dx.doi.org/10.1061/(asce)ee.1943-7870.0001812DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7970507PMC
December 2020

Removal of Arsenate and Arsenite in Equimolar Ferrous and Ferric Sulfate Solutions through Mineral Coprecipitation: Formation of Sulfate Green Rust, Goethite, and Lepidocrocite.

Soil Syst 2020 Nov;4(68):1-16

Groundwater Characterization and Remediation Division, Center for Environmental Solutions and Emergency Response, Office of Research and Development, United States Environmental Protection Agency, 919 Kerr Research Drive, Ada, OK 74820, USA.

An improved understanding of in situ mineralization in the presence of dissolved arsenic and both ferrous and ferric iron is necessary because it is an important geochemical process in the fate and transformation of arsenic and iron in groundwater systems. This work aimed at evaluating mineral phases that could form and the related transformation of arsenic species during coprecipitation. We conducted batch tests to precipitate ferrous (133 mM) and ferric (133 mM) ions in sulfate (533 mM) solutions spiked with As (0-100 mM As(V) or As(III)) and titrated with solid NaOH (400 mM). Goethite and lepidocrocite were formed at 0.5-5 mM As(V) or As(III). Only lepidocrocite formed at 10 mM As(III). Only goethite formed in the absence of added As(V) or As(III). Iron (II, III) hydroxysulfate green rust (sulfate green rust or SGR) was formed at 50 mM As(III) at an equilibrium pH of 6.34. X-ray analysis indicated that amorphous solid products were formed at 10-100 mM As(V) or 100 mM As(III). The batch tests showed that As removal ranged from 98.65-100%. Total arsenic concentrations in the formed solid phases increased with the initial solution arsenic concentrations ranging from 1.85-20.7 g kg. Substantial oxidation of initially added As(III) to As(V) occurred, whereas As(V) reduction did not occur. This study demonstrates that concentrations and species of arsenic in the parent solution influence the mineralogy of coprecipitated solid phases, which in turn affects As redox transformations.
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http://dx.doi.org/10.3390/soilsystems4040068DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7898115PMC
November 2020

Surface heterogeneity mediated transport of hydrochar nanoparticles in heterogeneous porous media.

Environ Sci Pollut Res Int 2020 Sep 10;27(26):32842-32855. Epub 2020 Jun 10.

Oak Ridge Institute for Science and Education (ORISE), U. S. Environmental Protection Agency, Ada, OK, 74820, USA.

The effects of clay particles (montmorillonite, M) and phosphate (P) on the transport of hydrochar nanoparticles (NPs) in water-saturated porous media (uncoated and aluminum (Al) oxide-coated sands) were explored in NaCl (1-50 mM) solutions. Our results showed that the deposition behaviors of hydrochar NPs affected by M and phosphate were significantly different between pH 6.0 and pH 9.0, especially in Al oxide-coated sand. This can be attributed to their distinct surface characteristics: hydrochar agglomerates with a larger pore size distribution, more carboxylate groups, and less negative charges on the surface at pH 9.0 than those at pH 6.0. In Al oxide-coated sand, block adsorption of hydrochar was alleviated appreciably with the presence of M due to the preferential preoccupies of M on these favorable retention sites. On the contrary, M substantially increased the hydrochar retention on uncoated sand due to the formation of nanoaggregates between hydrochar and M. Differently, phosphate substantially enhanced the transport of hydrochar, even in coated sand, due to the strong phosphate adsorption onto Al oxide on the surface of sand and hydrochar. Our findings will provide useful insights into designing effective strategies for land application of hydrochar while minimizing potential environmental risks. Graphical abstract.
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http://dx.doi.org/10.1007/s11356-020-09482-wDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7520070PMC
September 2020

Facilitated transport of nTiO-kaolin aggregates by bacteria and phosphate in water-saturated quartz sand.

Sci Total Environ 2020 Apr 11;713:136589. Epub 2020 Jan 11.

Oak Ridge Institute for Science and Education, United States Environmental Protection Agency, Ada, OK 74820, USA. Electronic address:

The soil major component of clay plays an important role in governing the fate and transport of engineered nanomaterials (e.g., the most commonly used titanium dioxide nanoparticles; nTiO) in the subsurface environments via forming nTiO-clay aggregates. This research is designed to unravel the interplay of naturally-occurring bacteria (Escherichia coli) and phosphate on the transport and retention of nTiO-kaolin aggregates in water-saturated porous media. Our results showed that nTiO-nTiO homoaggregates and nTiO-kaolin heteroaggregates dominated in the nTiO-kaolin nanoaggregate suspension. Transport of nTiO-kaolin aggregates was enhanced with the copresence of E. coli and phosphate, particularly at the low pH of 6.0. This effect is due to the greater adsorption of phosphate and thus the greater enhancement in repulsive interaction energies between aggregates and sand grains at pH 6.0 (vs. pH 9.0). The charged "soft layer" of E. coli cell surfaces changed the aggregation state and the heterogeneous distribution of nTiO-kaolin aggregates, and subsequently stabilized the nTiO-nTiO homoaggregates and nTiO-kaolin heteroaggregates via TEM-EDX measurements and promoted the physical segregation between the aggregates (separation distance = 0.486 vs. 0.614 μm without vs. with the presence of E. coli) via 2D/3D AFM identifications, both of which caused greater mobility of nTiO-kaolin aggregates with the presence of E. coli. Nonetheless, transport of nTiO-kaolin aggregates was lower with the copresence of E. coli and phosphate vs. the singular presence of phosphate due to the competitive adsorption of less negatively charged E. coli (vs. phosphate) onto the aggregates. Taken altogether, our findings furnish new insights into better understanding the fate, transport, and potential risks of nTiO in real environmental settings (soil and sediment aquifer) where clay, bacteria, and phosphate ubiquitously cooccur.
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http://dx.doi.org/10.1016/j.scitotenv.2020.136589DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7252603PMC
April 2020

Toxicity of ZnO/TiO -conjugated carbon-based nanohybrids on the coastal marine alga Thalassiosira pseudonana.

Environ Toxicol 2020 Jan 13;35(1):87-96. Epub 2019 Sep 13.

Department of Biochemistry and Molecular Biology, University of Miami, Miller School of Medicine, Miami, Florida.

Increasing consumption of metal-oxide nanoparticles (NPs) and carbon-based nanomaterials has caused significant concern about their potential hazards in aquatic environments. The release of NPs into aquatic environments could result in adsorption of NPs on microorganisms. While metal-oxide NP-conjugated carbon-based nanohybrids (NHs) may exhibit enhanced toxicity toward microorganisms due to their large surface area and the generation of reactive oxygen species (ROS), there is a lack of information regarding the ecotoxicological effects of NHs on marine diatom algae, which are an indicator of marine pollution. Moreover, there is scant information on toxicity mechanisms of NHs on aquatic organisms. In this study, four NHs (ie, ZnO-conjugated graphene oxide [GO], ZnO-conjugated carbon nanotubes [CNTs], TiO -conjugated GO, and TiO -conjugated CNT) that were synthesized by a hydrothermal method were investigated for their toxicity effects on a Thalassiosira pseudonana marine diatom. The in vitro cellular viability and ROS formation employed at the concentration ranges of 50 and 100 mg/L of NHs over 72 hours revealed that ZnO-GO had the most negative effect on T. pseudonana. The primary mechanism identified was the generation of ROS and GO-induced dispersion that caused electrostatic repulsion, preventing aggregation, and an increase in surface areas of NHs. In contrast to GO-induced dispersion, large aggregates were observed in ZnO/TiO -conjugated CNT-based NHs. The scanning electron microscopy images suggest that NHs covered algae cells and interacted with them (shading effects); this reduced light availability for photosynthesis. Detailed in vitro toxicity effects and mechanisms that cause high adverse acute toxicity on T. pseudonana were unveiled; this implied concerns about potential hazards of these mechanisms in aquatic ecosystems.
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http://dx.doi.org/10.1002/tox.22845DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7144345PMC
January 2020

Antibacterial effects of graphene- and carbon-nanotube-based nanohybrids on Escherichia coli: Implications for treating multidrug-resistant bacteria.

J Environ Manage 2019 Oct 24;247:214-223. Epub 2019 Jun 24.

Department of Biochemistry and Molecular Biology, School of Medicine, University of Miami, 1011 NW 15th Street, Miami, FL, 33136, USA.

Some nanomaterials including Fe, Ag, and ZnO are well known for their antibacterial effects. However, very few studies have examined antibacterial effects of nanohybrids. Given that metal oxides, mainly ZnO and TiO, are known to increase mobility, surface area, and photocatalysis when combined with carbon-based nanomaterials, ZnO- and TiO-conjugated carbon nanotube and graphene oxide nanohybrids were investigated for their antibacterial effects on Escherichia coli (DH5α, a multidrug-resistant coliform bacterium). Graphene-oxide (GO)-based nanohybrids (ZnO-GO and TiO-GO) induced increased dispersion compared to carbon-nanotube (CNT)-based nanohybrids (ZnO-CNT and TiO-CNT). Among the four types of nanohybrids, ZnO-conjugated nanohybrids exhibited a higher antibacterial property, resulting in the antibacterial effect (measured with growth inhibition of cells) in the order ZnO-GO > ZnO-CNT > TiO-GO > TiO-CNT. Among four possible antibacterial mechanisms (generation of reactive oxygen species (ROS), physicochemical characteristics, the steric effect, and release of metal ions), a primary mechanism-ROS generation-was identified; whereas, physicochemical characteristics and the steric effect were part of contributing mechanisms. The increasing dispersion of TiO/ZnO on GO may have contributed to the antibacterial effects due to increasing surface areas. Similarly, significant damages to E. coli cell membranes were found by the GO sheet with its sharp edges. Our results suggest that applying GO-based ZnO or TiO could be an effective antibacterial method, especially for the treatment of multidrug-resistant bacteria in the water.
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http://dx.doi.org/10.1016/j.jenvman.2019.06.077DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7085116PMC
October 2019

Next-Generation Multifunctional Carbon-Metal Nanohybrids for Energy and Environmental Applications.

Environ Sci Technol 2019 07 24;53(13):7265-7287. Epub 2019 Jun 24.

Groundwater, Watershed, and Ecosystem Restoration Division, National Risk Management Research Laboratory, Office of Research and Development , United States Environmental Protection Agency , Ada , Oklahoma 74820 , United States.

Nanotechnology has unprecedentedly revolutionized human societies over the past decades and will continue to advance our broad societal goals in the coming decades. The research, development, and particularly the application of engineered nanomaterials have shifted the focus from "less efficient" single-component nanomaterials toward "superior-performance", next-generation multifunctional nanohybrids. Carbon nanomaterials (e.g., carbon nanotubes, graphene family nanomaterials, carbon dots, and graphitic carbon nitride) and metal/metal oxide nanoparticles (e.g., Ag, Au, CdS, CuO, MoS, TiO, and ZnO) combinations are the most commonly pursued nanohybrids (carbon-metal nanohybrids; CMNHs), which exhibit appealing properties and promising multifunctionalities for addressing multiple complex challenges faced by humanity at the critical energy-water-environment (EWE) nexus. In this frontier review, we first highlight the altered and newly emerging properties (e.g., electronic and optical attributes, particle size, shape, morphology, crystallinity, dimensionality, carbon/metal ratio, and hybridization mode) of CMNHs that are distinct from those of their parent component materials. We then illustrate how these important newly emerging properties and functions of CMNHs direct their performances at the EWE nexus including energy harvesting (e.g., HO splitting and CO conversion), water treatment (e.g., contaminant removal and membrane technology), and environmental sensing and in situ nanoremediation. This review concludes with identifications of critical knowledge gaps and future research directions for maximizing the benefits of next-generation multifunctional CMNHs at the EWE nexus and beyond.
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http://dx.doi.org/10.1021/acs.est.9b01453DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7388031PMC
July 2019

Adsorptive Removal of Fluoride from Water Using Nanomaterials of Ferrihydrite, Apatite, and Brucite: Batch and Column Studies.

Environ Eng Sci 2019 May;36(5):634-642

Department of Civil and Environmental Engineering, Southern Methodist University, Dallas, Texas.

This study investigated the adsorptive removal of fluoride from simulated water pollution using various (hydro)oxide nanomaterials, which have the potential to be used as sorbents for surface water and groundwater remediation. Tested nanomaterials include hematite, magnetite, ferrihydrite, goethite, hematite-alpha, hydroxyapatite (HAP), brucite, and four titanium dioxides (TiO-A [anatase], TiO-B [rutile], TiO-C [rutile], and TiO-D [anatase]). Among 11 (hydro)oxide nanomaterials tested in this study, ferrihydrite, HAP, and brucite showed two to five times higher removal of fluoride than other nanomaterials from synthetic fluoride solutions. Freundlich and Redlich-Peterson adsorption isotherms better described the adsorptive capacity and mechanism than the Langmuir isotherm based on higher values, indicating better fit of the regression predictions. In addition, the adsorption kinetics were well described by the intraparticle diffusion model. Column studies in a fixed bed continuous flow through system were conducted to illustrate the adsorption and desorption behavior of fluoride on ferrihydrite, HAP, or brucite. Experimental results fitted well with the Thomas model because of the values at least 0.885 or higher. By comparisons of the adsorption capacity and the rate constant, columns packed with ferrihydrite exhibited not only faster rates but also higher sorption capacity than those packed with HAP or brucite. Desorption tests in deionized water showed that the adsorbed fluoride could be desorbed at a lower efficiency, ranging from 4.0% to 8.9%. The study implicated that (hydro)oxide nanomaterials of iron calcium and magnesium could be effective sorptive materials incorporated into filtration systems for the remediation of fluoride polluted water.
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http://dx.doi.org/10.1089/ees.2018.0438DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7376914PMC
May 2019

Effect of various chemical oxidation reagents on soil indigenous microbial diversity in remediation of soil contaminated by PAHs.

Chemosphere 2019 Jul 27;226:483-491. Epub 2019 Mar 27.

U.S. Environmental Protection Agency, National Risk Management Research Laboratory, Ground Water and Ecosystems Restoration Division, Ada, OK, United States.

Chemical oxidation is a promising pretreatment step coupled with bioremediation for removal of polycyclic aromatic hydrocarbons (PAHs). The effectiveness of Fenton, modified Fenton, potassium permanganate and activated persulfate oxidation treatments on the real contaminated soils collected from a coal gas plant (263.6 ± 73.3 mg kg of the Σ16 PAHs) and a coking plant (385.2 ± 39.6 mg kg of the Σ16 PAHs) were evaluated. Microbial analyses showed only a slight impact on indigenous microbial diversity by Fenton treatment, but showed the inhibition of microbial diversity and delayed population recovery by potassium permanganate reagent. After potassium permanganate treatment, the microorganism mainly existed in the soil was Pseudomonas or Pseudomonadaceae. The results showed that total organic carbon (TOC) content in soil was significantly increased by adding modified Fenton reagent (1.4%-2.3%), while decreased by adding potassium permanganate (0.2%-1%), owing to the nonspecific and different oxidative properties of chemical oxidant. The results also demonstrated that the removal efficiency of total PAHs was ordered: permanganate (90.0%-92.4%) > activated persulfate (81.5%-86.54%) > modified Fenton (81.5%-85.4%) > Fenton (54.1%-60.0%). Furthermore, the PAHs removal efficiency was slightly increased on the 7th day after Fenton and modified Fenton treatments, about 14.6%, and 14.4% respectively, and the PAHs removal efficiency only enhanced 4.1% and 1.3% respectively from 1st to 15th day after potassium permanganate and activated persulfate treatments. The oxidants greatly affect the growth of soil indigenous microbes, which cause further influence for PAHs degradation by bioremediation.
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http://dx.doi.org/10.1016/j.chemosphere.2019.03.126DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6756151PMC
July 2019

Potential utility of graphene-based nano spinel ferrites as adsorbent and photocatalyst for removing organic/inorganic contaminants from aqueous solutions: A mini review.

Chemosphere 2019 Apr 9;221:392-402. Epub 2019 Jan 9.

Department of Civil and Environmental Engineering, University of South Carolina, Columbia, 300 Main Street, SC 29208, USA. Electronic address:

Toxic substances such as heavy metals or persistent organic pollutants raise global environmental concerns. Thus, diverse water decontamination approaches using nano-adsorbents and/or photocatalysts based on nanotechnology are being developed. Particularly, many studies have examined the removal of organic and inorganic contaminants with novel graphene-based nano spinel ferrites (GNSFs) as potential cost-effective alternatives to traditionally used materials, owing to their enhanced physical and chemical properties. The introduction of magnetic spinel ferrites into 2-D graphene-family nanomaterials to form GNSFs brings various benefits such as inhibited particle agglomeration, enhanced active surface area, and easier magnetic separation for reuse, making the GNSFs highly efficient and eco-friendly materials. Here, we present a short review on the state-of-the-art progresses on developments of GNSFs, as well as their potential application for removing several recalcitrant contaminants including organic dyes, antibiotics, and heavy metal ions. Particularly, the mechanisms involved in the adsorptive and photocatalytic degradation are thoroughly reviewed, and the reusability of the GNSFs is also highlighted. This review concludes that the GNSFs hold great potential in remediating contaminated aquatic environments. Further studies are needed for their practical and large-scale applications.
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http://dx.doi.org/10.1016/j.chemosphere.2019.01.063DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7373271PMC
April 2019

Evaluation of the colloidal stability and adsorption performance of reduced graphene oxide-elemental silver/magnetite nanohybrids for selected toxic heavy metals in aqueous solutions.

Appl Surf Sci 2019 ;471:8-17

Groundwater, Watershed, and Ecosystem Restoration Division, National Risk Management Research Laboratory, Office of Research and Development, U.S. Environmental Protection Agency, 919 Kerr Research Drive, Ada, OK 74820, USA.

Reduced graphene oxide (rGO) hybridized with magnetite and/or elemental silver (rGO/magnetite, rGO/silver, and rGO/magnetite/silver) nanoparticles were evaluated as potential adsorbents for toxic heavy metal ions (Cd (II), Ni(II), Zn(II), Co(II), Pb(II), and Cu(II)). Although the deposition of iron oxide and silver nanoparticles on the rGO nanosheets played an inhibitory role in metal ion adsorption, the metal adsorption efficiency by the nanohybrids (NHs) was still higher than that reported for many other sorbents (e.g., activated biochar, commercial resins, and nanosized hydrated Zr(IV) oxide particles). X-ray photoelectron spectroscopy analyses revealed that complexation with deprotonated adsorbents and cation exchange was an important mechanism for Cd(II) ion removal by the rGO and NHs. Competitive adsorption tests using multi metals showed that the adsorption affinity of metal ions on the rGO and its NHs follows the order (Cu(II), Zn(II)) > Ni(II) > Co(II) > (Pb(II), Cd(II)), which is similar to the order observed for single-metal adsorption experiments. These results can be explained by the destabilization abilities of the rGO and NHs, as well as the ionic radii of the considered metal ions. Our findings demonstrate the feasibility of using rGO-based NHs as highly efficient adsorbents for heavy metal removal from water.
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http://dx.doi.org/10.1016/j.apsusc.2018.11.240DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7424532PMC
January 2019

Enhanced degradation of polycyclic aromatic hydrocarbons by indigenous microbes combined with chemical oxidation.

Chemosphere 2018 Dec 17;213:551-558. Epub 2018 Sep 17.

U.S. Environmental Protection Agency, National Risk Management Research Laboratory, Ground Water and Ecosystems Restoration Division, Ada, OK, United States.

In this study, the removal efficiency PAHs by chemical oxidation combined with microbe remediation was evaluated in two contaminated soils. The number of indigenous soil microbes decreased after the addition of chemical oxidants and then increased by nutrients addition. The total removal efficiencies of PAHs by chemical oxidation and nutrient addition followed the order: activated persulfate > potassium permanganate > modified Fenton reagent > Fenton reagent. There are 24.29-27.97%, 22.00-23.67%, 10.24-13.74% and 1.9-2.5% contributions separately due to nutrient treatment in Fenton, modified Fenton, activated persulfate and potassium permanganate treatment, which show significantly difference. The different chemical oxidants exhibited 78-90% removal efficiency for 5-6 rings PAHs, while 52-85% removal efficiency for 2-4 rings PAHs. With the addition of nutrients, the growth of indigenous microbes was enhanced significantly, and the contents of 2-4 rings PAHs in the soil were further decreased. Furthermore, the removal efficiencies of NAP and ANY were increased by more than 45%, while the removal efficiencies of ANE, FLE and PHE were about 30% at Fenton system. There was a complementary enhancing effect of microbial remediation for PAHs degradation after chemical oxidation.
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http://dx.doi.org/10.1016/j.chemosphere.2018.09.092DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6775777PMC
December 2018

Heterogeneous activation of persulfate by reduced graphene oxide-elemental silver/magnetite nanohybrids for the oxidative degradation of pharmaceuticals and endocrine disrupting compounds in water.

Appl Catal B 2018 Jun;225:91-99

Department of Civil and Environmental Engineering, University of South Carolina, 300 Main Street, Columbia, SC 29208, USA.

Reduced graphene oxide hybridized with zero-valent silver and magnetite nanoparticles (NPs) (rGO-Ag/FeO nanohybrids) prepared via nucleation and crystallization was used to activate peroxydisulfate (PDS) for degradation of pharmaceuticals and endocrine disrupting compounds (phenol, acetaminophen, ibuprofen, naproxen, bisphenol A, 17β-estradiol, and 17α-ethinyl estradiol). The deposition of Ag and FeO in rGO nanosheet enhanced the catalytic removal of phenol in the heterogeneous activation of PDS. The adsorption capacities of rGO-Ag/FeO for 10 μM phenol were 1.76, 1.33, and 2.04 μmol g-adsorbent at pH 4, 7, and 10, respectively, which are much higher than those of single NPs studied (Ag, nanoscale zero-valent iron, and rGO). The rGO-Ag/FeO effectively activated PDS to produce strong oxidizing SO·and facilitate an electron transfer on the surface of the nanohybrid. The initial pseudo-first-order rate () constant for phenol degradation in PDS/rGO-Ag/FeO system was 0.46 h at pH 7, which is approximately eight times higher than that in the presence of single NPs ( = 0.04-0.06 h) due to the synergistic effects between adsorption and catalytic oxidation. Among various organic contaminants tested, the simultaneous use of rGO-Ag/FeO (0.1 g/L) and PDS (1 mM) achieved more than 99% degradation of acetaminophen and 17β-estradiol at pH 7. The radical scavenging studies with methanol and natural organic matter indicated that phenol was more likely to be degraded via free SO· and ·OH formation or a non-radical oxidative pathway. Our findings indicate that the rGO-Ag/Fe O nanohybrids can be used as an efficient magnetically-separable nanocatalyst for removal of organic compounds in water and wastewater treatment.
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http://dx.doi.org/10.1016/j.apcatb.2017.11.058DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7376738PMC
June 2018

Modeling the Transport of the "New-Horizon" Reduced Graphene Oxide-Metal Oxide Nanohybrids in Water-Saturated Porous Media.

Environ Sci Technol 2018 04 5;52(8):4610-4622. Epub 2018 Apr 5.

Department of Civil, Structural, and Environmental Engineering , University at Buffalo, The State University of New York , Buffalo , New York 14260 , United States.

Little is known about the fate and transport of the "new-horizon" multifunctional nanohybrids in the environment. Saturated sand-packed column experiments ( n = 66) were therefore performed to investigate the transport and retention of reduced graphene oxide (RGO)-metal oxide (FeO, TiO, and ZnO) nanohybrids under environmentally relevant conditions (mono- and divalent electrolytes and natural organic matter). Classical colloid science principles (Derjaguin-Landau-Verwey-Overbeek (DLVO) theory and colloid filtration theory (CFT)) and mathematical models based on the one-dimensional convection-dispersion equation were employed to describe and predict the mobility of RGO-FeO, RGO-TiO, and RGO-ZnO nanohybrids in porous media. Results indicate that the mobility of the three nanohybrids under varying experimental conditions is overall explainable by DLVO theory and CFT. Numerical simulations suggest that the one-site kinetic retention model (OSKRM) considering both time- and depth-dependent retention accurately approximated the breakthrough curves (BTCs) and retention profiles (RPs) of the nanohybrids concurrently; whereas, others (e.g., two-site retention model) failed to capture the BTCs and/or RPs. This is primarily because blocking BTCs and exponential/hyperexponential/uniform RPs occurred, which is within the framework of OSKRM featuring time- (for kinetic Langmuirian blocking) and depth-dependent (for exponential/hyperexponential/uniform) retention kinetics. Employing fitted parameters (maximum solid-phase retention capacity: S = 0.0406-3.06 cm/g; and first-order attachment rate coefficient: k = 0.133-20.6 min) extracted from the OSKRM and environmentally representative physical variables (flow velocity (0.00441-4.41 cm/min), porosity (0.24-0.54), and grain size (210-810 μm)) as initial input conditions, the long-distance transport scenarios (in 500 cm long sand columns) of the three nanohybrids were predicted via forward simulation. Our findings address the existing knowledge gap regarding the impact of physicochemical factors on the transport of the next-generation, multifunctional RGO-metal oxide nanohybrids in the subsurface.
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http://dx.doi.org/10.1021/acs.est.7b06488DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6818097PMC
April 2018

Aggregation of reduced graphene oxide and its nanohybrids with magnetite and elemental silver under environmentally relevant conditions.

J Nanopart Res 2018 ;20:93

Groundwater, Watershed and Ecosystem Restoration Division, National Risk Management Research Laboratory, Office of Research and Development, United States Environmental Protection Agency, 919 Kerr Research Drive, Ada, OK 74820, USA.

The aggregation and long-term (25 d) sedimentation behaviors of reduced graphene oxide (RGO) and its three successively self-assembled nanohybrids with magnetite (FeO) and zerovalent silver (Ag) nanoparticles have been investigated. The aggregation behaviors of the nanomaterials in NaCl and CaCl were found to be in good agreement with the Derjaguin-Landau-Verwey-Overbeek (DLVO)-type interactions and the Schulze-Hardy rule. The colloidal stability decreased with the increasing ratios of the edge-based functional groups (COO and C=O) to the total oxygen-containing functional groups decorated on the basal planes (C-O) and edges of RGO, as quantified by X-ray photoelectron spectroscopy analysis. In the presence of natural organic matter (NOM), the aggregation of RGO and its nanohybrids was greatly inhibited as a result of the enhanced electrosteric repulsions arising from the adsorbed NOM macromolecules. The long-term sedimentation kinetics results showed that the RGO nanohybrids were less stable in synthetic groundwater containing higher electrolyte concentrations, which was likely because of the greater charge screening or neutralization effect imparted by higher monovalent and divalent electrolyte concentrations. Our findings have important implications for evaluating the environmental impact and toxicity of the emerging class of multifunctional nanohybrids whose environmental behaviors are currently largely unknown.
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http://dx.doi.org/10.1007/s11051-018-4202-xDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6781226PMC
January 2018

Pilot-scale application of shotblast dust for phosphorus removal.

J Am Water Works Assoc 2018 ;110(11):64-68

Gulf Ecology Division, National Health and Environmental Effects Research Laboratory, Office of Research and Development, U.S. Environmental Protection Agency, 1 Sabine Island Drive, Gulf Breeze, FL 32561, USA.

Phosphorus contamination is a global issue, and cost-effective remediation is sought for removing phosphorus from water. We applied a novel use of waste material called shotblast dust in a pilot-scale reactor to remove phosphorus from water. Results indicate that shotblast dust was effective in treating phosphorus-laden water with 132 kg of the material treating 568 liters of 220 μg/L total phosphorus (T-P) water on a daily basis, achieving approximately 60% removal of T-P in 7 days.
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http://dx.doi.org/10.1002/awwa.1186DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6781228PMC
January 2018

Carboxymethylcellulose Mediates the Transport of Carbon Nanotube-Magnetite Nanohybrid Aggregates in Water-Saturated Porous Media.

Environ Sci Technol 2017 Nov 25;51(21):12405-12415. Epub 2017 Oct 25.

Department of Civil, Structural and Environmental Engineering, University at Buffalo, The State University of New York , Buffalo, New York 14260, United States.

Carbon-metal oxide nanohybrids (NHs) are increasingly recognized as the next-generation, promising group of nanomaterials for solving emerging environmental issues and challenges. This research, for the first time, systematically explored the transport and retention of carbon nanotube-magnetite (CNT-FeO) NH aggregates in water-saturated porous media under environmentally relevant conditions. A macromolecule modifier, carboxymethylcellulose (CMC), was employed to stabilize the NHs. Our results show that transport of the magnetic CNT-FeO NHs was lower than that of nonmagnetic CNT due to larger hydrodynamic sizes of NHs (induced by magnetic attraction) and size-dependent retention in porous media. Classical Derjaguin-Landau-Verwey-Overbeek (DLVO) theory can explain the mobility of NHs under varying experimental conditions. However, in contrast with colloid filtration theory, a novel transport feature-an initial lower and a following sharp-higher peaks occurred frequently in the NHs' breakthrough curves. The magnitude and location of both transport peaks varied with different experimental conditions, due to the interplay between variability of fluid viscosity and size-selective retention of the NHs. Promisingly, the estimated maximum transport distance of NHs ranged between ∼0.38 and 46 m, supporting the feasibility of employing the magnetically recyclable CNT-FeO NHs for in situ nanoremediation of contaminated soil, aquifer, and groundwater.
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http://dx.doi.org/10.1021/acs.est.7b04037DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7375327PMC
November 2017

Role of solution chemistry in the retention and release of graphene oxide nanomaterials in uncoated and iron oxide-coated sand.

Sci Total Environ 2017 Feb 17;579:776-785. Epub 2016 Nov 17.

Key Laboratory of Soil Environment and Pollution Remediation, Institute of Soil Science, Chinese Academy of Sciences, Nanjing 210008, China. Electronic address:

Understanding the fate and transport including remobilization of graphene oxide nanomaterials (GONMs) in the subsurface would enable us to expedite their benign use and evaluate their environmental impacts and health risks. In this study, the retention and release of GONMs were investigated in water-saturated columns packed with uncoated sand (Un-S) or iron oxide-coated sand (FeS) at environmentally relevant solution chemistries (1-100mM KCl and 0.1-10mM CaCl at pH7 and 11). Our results showed that increasing ionic strength (IS) inhibited GONMs' transport, and the impact of K was less than Ca. The positively charged iron oxide coating on sand surfaces immobilized the negatively charged GONMs (pH7) in the primary minimum, yielding hyperexponential retention profiles particularly in Ca. A stepwise decrease in pore-water IS caused detachment of previously retained GONMs. The mass of GONMs released during each detachment step correlated positively with the difference in secondary minimum depth (ΔΦ) at each IS, indicating that the released GONMs were retained in the secondary minimum. While most retained GONMs were re-entrained upon lowering pore-water IS in Un-S, decreasing IS only released limited GONMs in FeS, which were captured in the primary minimum. Introducing 1mM NaOH (pH11) released most retained GONMs in FeS; and average hydrodynamic diameters of the detached GONMs upon injecting NaOH were significantly smaller than those of GONMs in the influent and retentate, suggesting that NaOH induced GONMs disaggregation. Our findings advance current knowledge to better predict NMs' fate and transport under various solution chemistries such as during rainfall events or in the mixing zones between sea water and fresh water where transient IS changes drastically.
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http://dx.doi.org/10.1016/j.scitotenv.2016.11.029DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7372574PMC
February 2017

Effects of titanium dioxide nanoparticles derived from consumer products on the marine diatom Thalassiosira pseudonana.

Environ Sci Pollut Res Int 2016 Oct 5;23(20):21113-21122. Epub 2016 Sep 5.

Department of Marine Geosciences, University of Miami, 4600 Rickenbacker Causeway, Miami, FL, 33149-1098, USA.

Increased manufacture of TiO nanoproducts has caused concern about the potential toxicity of these products to the environment and in public health. Identification and confirmation of the presence of TiO nanoparticles derived from consumer products as opposed to industrial TiO NPs warrant examination in exploring the significance of their release and resultant impacts on the environment. To this end, we examined the significance of the release of these particles and their toxic effect on the marine diatom algae Thalassiosira pseudonana. Our results indicate that nano-TiO sunscreen and toothpaste exhibit more toxicity in comparison to industrial TiO and inhibited the growth of the marine diatom T. pseudonana. This inhibition was proportional to the exposure time and concentrations of nano-TiO. Our findings indicate a significant effect, and therefore, further research is warranted in evaluation and assessment of the toxicity of modified nano-TiO derived from consumer products and their physicochemical properties.
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http://dx.doi.org/10.1007/s11356-016-7556-6DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7337103PMC
October 2016

Environmental implications and applications of engineered nanoscale magnetite and its hybrid nanocomposites: A review of recent literature.

Authors:
Chunming Su

J Hazard Mater 2017 Jan 1;322(Pt A):48-84. Epub 2016 Jul 1.

Ground Water and Ecosystems Restoration Division, National Risk Management Research Laboratory, Office of Research and Development, United States Environmental Protection Agency, 919 Kerr Research Drive, Ada, OK 74820, USA. Electronic address:

This review focuses on environmental implications and applications of engineered magnetite (FeO) nanoparticles (MNPs) as a single phase or a component of a hybrid nanocomposite that exhibits superparamagnetism and high surface area. MNPs are synthesized via co-precipitation, thermal decomposition and combustion, hydrothermal process, emulsion, microbial process, and green approaches. Aggregation/sedimentation and transport of MNPs depend on surface charge of MNPs and geochemical parameters such as pH, ionic strength, and organic matter. MNPs generally have low toxicity to humans and ecosystem. MNPs are used for constructing chemical/biosensors and for catalyzing a variety of chemical reactions. MNPs are used for air cleanup and carbon sequestration. MNP nanocomposites are designed as antimicrobial agents for water disinfection and flocculants for water treatment. Conjugated MNPs are widely used for adsorptive/separative removal of organics, dyes, oil, arsenic, phosphate, molybdate, fluoride, selenium, Cr(VI), heavy metal cations, radionuclides, and rare earth elements. MNPs can degrade organic/inorganic contaminants via chemical reduction or catalyze chemical oxidation in water, sediment, and soil. Future studies should further explore mechanisms of MNP interactions with other nanomaterials and contaminants, economic and green approaches of MNP synthesis, and field scale demonstration of MNP utilization.
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http://dx.doi.org/10.1016/j.jhazmat.2016.06.060DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7306924PMC
January 2017

Influence of siloxane on the transport of ZnO nanoparticles from different release pathways in saturated sand.

RSC Adv 2016 ;6(102):100494-100503

Department of Chemistry, University of Miami, 1301 Memorial Drive, Coral Gables, FL 33146, USA.

The production of nanomaterials (NMs) is expected to grow continuously, yet their transformation, transport, release mechanisms, and interactions with contaminants under environmental conditions remain poorly understood. Few studies have investigated the effects of contaminants on fate and transport of NMs, especially siloxanes that are widely found in products. It is hypothesized that the model contaminant, siloxane (, 1,1,3,3-tetramethyldisiloxane (TMDS)) may influence the mechanisms and transport kinetics of NMs under different release pathways. Sand column experiments were carried out under two different scenarios: the release from a mixed TMDS and nano-ZnO suspension (A) and the release of nano-ZnO from sand contaminated with TMDS (B). Results show that interparticle reactions are dominant in (A) and particle-porous interactions are responsible for blocking effects governing in (B). Insights, especially the kinetics of nano-ZnO from co-transport by a contaminant and from porous media preloaded with a contaminant, and environmental factors affecting the release and retention of nano-ZnO in saturated sand are unveiled. These two dominant transport mechanisms (, interparticle reactions and blocking effects) were derived. This study indicates that the release of ZnO NPs is influenced by the presence of TMDS; the extent of mobility and their transport pathways depend on the pre-existence of TMDS in porous media.
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http://dx.doi.org/10.1039/C6RA22820HDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7037544PMC
January 2016

Transport and retention of zinc oxide nanoparticles in porous media: effects of natural organic matter versus natural organic ligands at circumneutral pH.

J Hazard Mater 2014 Jun 2;275:79-88. Epub 2014 May 2.

Ground Water and Ecosystems Restoration Division, National Risk Management Research Laboratory, Office of Research and Development, United States Environmental Protection Agency, 919 Kerr Research Drive, Ada, OK 74820, USA.

The potential toxicity of nanoparticles (NPs) has received considerable attention, but there is little knowledge relating to the fate and transport of engineered ZnO NPs in the environment. Column experiments were performed at pH 7.3-7.6 to generate effluent concentrations and retention profiles for assessing the fate and transport of ZnO NPs (PZC=9.3, nominal size 20 nm) in saturated quartz sands (256 μm) in the presence of low natural organic matter (NOM) concentrations (1 mg/L humic and fulvic acids) and millimolar natural organic ligands (NOL) levels (formic, oxalic, and citric acids). At circumneutral pHs, ZnO NPs were positively charged and immobile in sand. The presence of NOM decreased the attachment efficiency facilitating ZnO transport through sand columns. Conversely, ZnO transport in the presence of formic and oxalic acids was only slightly improved when compared to ZnO in DI water; whereas, citric acid showed no improvement. The distinct difference between NOM and NOL may have important implications with regard to ZnO transport in the subsurface environment. Experimental results suggested the presence of both favorable and unfavorable nanoparticle interactions causes significant deviations from classical colloid filtration theory (CFT).
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http://dx.doi.org/10.1016/j.jhazmat.2014.04.058DOI Listing
June 2014

Silicon impurity release and surface transformation of TiO2 anatase and rutile nanoparticles in water environments.

Environ Pollut 2014 Jan 1;184:570-8. Epub 2013 Nov 1.

National Research Council, 919 Kerr Research Drive, Ada, OK 74820, United States. Electronic address:

Surface transformation can affect the stability, reactivity, and toxicity of titanium dioxide (TiO2) nanoparticles (NPs) in water environments. Herein, we investigated the release kinetics of Si impurity frequently introduced during NP synthesis and the resulting effect on TiO2 NP transformation in aqueous solutions. The release of Si increased from 2 h to 19 d at three pHs with the order: pH 11.2 ≥ pH 2.4 > pH 8.2. The Si release process followed parabolic kinetics which is similar to diffusion controlled dissolution of minerals, and the release magnitude followed the order: 10 × 40 nm rutile > 50 nm anatase > 30 × 40 nm rutile. FTIR data indicated preferential dissolving of less polymerized Si species on NP surface. Surface potential and particle size of TiO2 NPs remained almost constant during the 42-day monitoring, implying the unaffected stability and transport of these NPs by the incongruent dissolution of impurities.
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http://dx.doi.org/10.1016/j.envpol.2013.10.011DOI Listing
January 2014

Release of phosphorous impurity from TiO2 anatase and rutile nanoparticles in aquatic environments and its implications.

Water Res 2013 Oct 31;47(16):6149-56. Epub 2013 Jul 31.

National Research Council, 919 Kerr Research Drive, Ada, OK 74820, United States. Electronic address:

Phosphorus-bearing materials as an additive have been popularly used in nanomaterial synthesis and the residual phosphorus within the nanoparticles (NPs) can be of an environmental concern. For instance, phosphorus within pristine commercial TiO2 NPs greatly influences the surface charge and aggregation behavior of the host TiO2 in aquatic environments; however, it is unknown whether and how fast phosphorus is released. In this study, we focus on the phosphorus release kinetics from five types of TiO2 NPs (i.e., 5, 10, and 50 nm anatase and 10 × 40, 30 × 40 nm rutile) under the influence of varying solution chemistries. The 50 nm anatase has the highest quantity of P (8.05 g/kg) and most leachable P dissolves within the first 2 h (i.e., 5.01 g/kg), which presents a potential pollutant source of P. Higher pH favors the phosphorus release (release order: pH 11.2 > pH 8.2 > pH 2.4), while variations in the environmentally relevant ionic strengths (0.01 M NaCl + 0.01 M NaHCO3 and 0.04 M NaCl + 0.01 M NaHCO3) and the presence of dissolved natural organic matter (10 mg/L) do not affect release rate greatly. X-ray Absorption Near Edge Structure results suggest that phosphate adsorbed on the pristine 50 nm anatase desorbs, and some dissolved phosphate again re-sorbs as a surface precipitate. The findings from this research may have important environmental implications such as accidental release of TiO2 NPs and other nanomaterials that are synthesized using phosphorus containing chemicals as an ingredient.
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http://dx.doi.org/10.1016/j.watres.2013.07.034DOI Listing
October 2013

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

Environ Sci Technol 2013 Aug 22;47(15):8391-8. Epub 2013 Jul 22.

Department of Civil Engineering, University of Nebraska-Lincoln , Lincoln, Nebraska 68583, United States.

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.
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http://dx.doi.org/10.1021/es4016124DOI Listing
August 2013

Travel distance and transformation of injected emulsified zerovalent iron nanoparticles in the subsurface during two and half years.

Water Res 2013 Aug 21;47(12):4095-106. Epub 2013 Mar 21.

Ground Water and Ecosystems Restoration Division, National Risk Management Research Laboratory, Office of Research and Development, United States Environmental Protection Agency, 919 Kerr Research Drive, Ada, OK 74820, USA.

Nanoscale zerovalent iron (NZVI) such as Toda Kogyo RNIP-10DS has been used for site remediation, yet information is lacking regarding how far injected NZVI can travel, how long it lasts, and how it transforms to other minerals in a groundwater system. Previously we reported effective mass destruction of chlorinated ethenes dominated by tetrachloroethene (PCE) using emulsified zerovalent iron (EZVI) nanoparticles of RNIP-10DS in a shallow aquifer (1-6 m below ground surface, BGS) at Site 45, Marine Corps Recruit Depot, Parris Island, South Carolina, USA. Here we report test results on transport and transformation of injected EZVI in the subsurface. We employed two EZVI delivery methods: pneumatic injection and direct injection. Effective delivery of EZVI to the targeted zone was achieved with pneumatic injection showing a travel distance from injection points of up to 2.1 m and direct injection showing a travel distance up to 0.89 m. X-ray diffraction and scanning electron microscopy studies on particles harvested from well purge waters indicated that injected black colored NZVI (α-Fe(0)) was transformed largely to black colored cube-like and plate-like magnetites (Fe3O4, 0.1-1 μm, 0-9 months), then to orange colored irregularly shaped lepidocrocite (γ-FeOOH, 0.1-1 μm, 9 months to 2.5 years), then to yellowish lath-like goethite (α-FeOOH, 2-5 μm, 2.5 years) and ferrihydrite-like spherical particles (0.05-0.1 μm) in the top portion of the aquifer (1-2 m BGS). No α-Fe(0) was found in most monitoring wells three months after injection. The formed iron oxides appeared to have a wider range of particle size (submicron to 5 μm) than the pristine NZVI (35-140 nm). Injected NZVI was largely transformed to magnetite (0.1-1 μm) during two and half years in the lower portion of the aquifer (3-6 m).
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http://dx.doi.org/10.1016/j.watres.2012.12.042DOI Listing
August 2013

Effects of dominant material properties on the stability and transport of TiO2 nanoparticles and carbon nanotubes in aquatic environments: from synthesis to fate.

Environ Sci Process Impacts 2013 Jan;15(1):169-89

Recently, increasing studies have focused on the environmental stability, transport, and fate of the anthropogenic nanomaterials in the environment, which contributes to the understanding of the potential risks when released. However, applying nanomaterials from different manufacturers and production methods tends to result in inconsistent experimental data and potentially a biased comparison. The aim of this review is to investigate the dominant material properties that determine the aggregation and deposition behavior of nanomaterials. Herein, we focus on two of the most popular anthropogenic nanomaterials, i.e., titanium dioxide (TiO2) and carbon nanotubes (CNTs). We start from the production methods of nanomaterials of different sources, and then examine their influence on the material properties and surface characteristics. The role of the material properties was carefully analyzed and correlated with the stability and transport in aquatic environments. These two case studies may be extended to other nanomaterials with similar surface properties, which will improve our understanding of the impact and risks of anthropogenic nanomaterials in the environment. This study highlights opportunities to design and produce "green" nanomaterials with less environmental risk and no sacrificing of the novel "nano" properties.
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http://dx.doi.org/10.1039/c2em30625eDOI Listing
January 2013

A two and half-year-performance evaluation of a field test on treatment of source zone tetrachloroethene and its chlorinated daughter products using emulsified zero valent iron nanoparticles.

Water Res 2012 Oct 7;46(16):5071-84. Epub 2012 Jul 7.

Ground Water and Ecosystems Restoration Division, National Risk Management Research Laboratory, Office of Research and Development, United States Environmental Protection Agency, 919 Kerr Research Drive, Ada, OK 74820, USA.

A field test of emulsified zero valent iron (EZVI) nanoparticles was conducted at Parris Island, SC, USA and was monitored for two and half years to assess the treatment of subsurface-source zone chlorinated volatile organic compounds (CVOCs) dominated by tetrachloroethene (PCE) and its chlorinated daughter products. Two EZVI delivery methods were used: pneumatic injection and direct injection. In the pneumatic injection plot, 2180 L of EZVI containing 225 kg of iron (Toda RNIP-10DS), 856 kg of corn oil, and 22.5 kg of surfactant were injected to remedy an estimated 38 kg of CVOCs. In the direct injection plot, 572 L of EZVI were injected to treat an estimated 0.155 kg of CVOCs. After injection of the EZVI, significant reductions in PCE and trichloroethene (TCE) concentrations were observed in downgradient wells with corresponding increases in degradation products including significant increases in ethene. In the pneumatic injection plot, there were significant reductions in the downgradient groundwater mass flux values for PCE (>85%) and TCE (>85%) and a significant increase in the mass flux of ethene. There were significant reductions in total CVOC mass (86%); an estimated reduction of 63% in the sorbed and dissolved phases and 93% reduction in the PCE DNAPL mass. There are uncertainties in these estimates because DNAPL may have been mobilized during and after injection. Following injection, significant increases in dissolved sulfide, volatile fatty acids (VFA), and total organic carbon (TOC) were observed. In contrast, dissolved sulfate and pH decreased in many wells. The apparent effective remediation seems to have been accomplished by direct abiotic dechlorination by nanoiron followed by biological reductive dechlorination stimulated by the corn oil in the emulsion.
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http://dx.doi.org/10.1016/j.watres.2012.06.051DOI Listing
October 2012

Distinct effects of humic acid on transport and retention of TiO2 rutile nanoparticles in saturated sand columns.

Environ Sci Technol 2012 Jul 14;46(13):7142-50. Epub 2012 Jun 14.

National Research Council Resident Research Associate, National Risk Management Research Laboratory, Office of Research and Development, US Environmental Protection Agency, 919 Kerr Research Drive, Ada, Oklahoma 74820, United States.

The distinct effects of humic acid (HA, 0-10 mg L(-1)) on the transport of titanium dioxide (rutile) nanoparticles (nTiO(2)) through saturated sand columns were observed under conditions of environmental relevance (ionic strength 3-200 mM NaCl, pH 5.7 and 9.0). Specifically, the transport of nTiO(2) was dramatically enhanced in the presence of HA at pH 5.7, even at a low HA concentration of 1 mg L(-1). The mobility of nTiO(2) was further increased with greater concentrations of HA. In contrast, this enhancement of the nTiO(2) transportability due to the presence of HA was limited at pH 9.0 because of the negligible adsorption of HA onto nTiO(2), regardless of the concentrations of HA examined in this study. The distinct effects can be explained by the adsorption behaviors of HA to nTiO(2) and sand surfaces and the resulting interactions between nTiO(2) and sand surfaces under different conditions, which resulted in a large variation of the nTiO(2) transport and deposition behaviors at various conditions. In addition, theoretical interaction energy calculations and additional elution experiments indicate that the secondary energy minimum played an important role in controlling the nTiO(2) transport and deposition in porous media observed in this study. Moreover, the interaction energy calculations suggest that at pH 5.7, HA affected nTiO(2) transport by increasing the negative surface charge of nTiO(2) at low HA adsorption densities; whereas, combinations of increased electrostatic and steric interactions due to the presence of HA were the main mechanisms of enhanced transportability of nTiO(2) at high HA adsorption densities. Overall, results from this study suggest that natural organic matter and solution pH are likely key factors that govern the stability and mobility of nTiO(2) in the natural aquatic environment.
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http://dx.doi.org/10.1021/es204010gDOI Listing
July 2012

Influence of collector surface composition and water chemistry on the deposition of cerium dioxide nanoparticles: QCM-D and column experiment approaches.

Environ Sci Technol 2012 Jun 1;46(12):6681-8. Epub 2012 Jun 1.

National Research Council Resident Research Associate, US Environmental Protection Agency, 919 Kerr Research Drive, Ada, Oklahoma 74820, United States.

The deposition behavior of cerium dioxide (CeO(2)) nanoparticles (NPs) in dilute NaCl solutions was investigated as a function of collector surface composition, pH, ionic strength, and organic matter (OM). Sensors coated separately with silica, iron oxide, and alumina were applied in quartz crystal microbalance with dissipation (QCM-D) to examine the effect of these mineral phases on CeO(2) deposition in NaCl solution (1-200 mM). Frequency and dissipation shift followed the order: silica > iron oxide > alumina in 10 mM NaCl at pH 4.0. No significant deposition was observed at pH 6.0 and 8.5 on any of the tested sensors. However, ≥ 94.3% of CeO(2) NPs deposited onto Ottawa sand in columns in 10 mM NaCl at pH 6.0 and 8.5. The inconsistency in the different experimental approaches can be mainly attributed to NP aggregation, surface heterogeneity of Ottawa sand, and flow geometry. In QCM-D experiments, the deposition kinetics was found to be qualitatively consistent with the predictions based on the classical colloidal stability theory. The presence of low levels (1-6 mg/L) of Suwannee River humic acid, fulvic acid, alginate, citric acid, and carboxymethyl cellulose greatly enhanced the stability and mobility of CeO(2) NPs in 1 mM NaCl at pH 6.5. The poor correlation between the transport behavior and electrophoretic mobility of CeO(2) NPs implies that the electrosteric effect of OM was involved.
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http://dx.doi.org/10.1021/es300883qDOI Listing
June 2012