Environmental Remediation of Chlorinated Hydrocarbons Using

Subscriber access provided by Eastern Michigan University | Bruce T. Halle Library

Article

Environmental Remediation of Chlorinated Hydrocarbons Using Biopolymer Stabilized Iron Loaded Halloysite Nanotubes Yang Su, Yueheng Zhang, Hang Ke, Gary L. McPherson, Jibao He, Xu Zhang, and Vijay T. John ACS Sustainable Chem. Eng., Just Accepted Manuscript • DOI: 10.1021/ acssuschemeng.7b02872 • Publication Date (Web): 10 Oct 2017 Downloaded from http://pubs.acs.org on October 17, 2017

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a free service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are accessible to all readers and citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

ACS Sustainable Chemistry & Engineering is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 30

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

ACS Sustainable Chemistry & Engineering

Environmental Remediation of Chlorinated Hydrocarbons Using Biopolymer Stabilized Iron Loaded Halloysite Nanotubes

Yang Su1, Yueheng Zhang1, Hang Ke2, Gary McPherson3, Jibao He4, Xu Zhang2, Vijay T. John1*

1. Department of Chemical & Biomolecular Engineering, Tulane University, 6823 St. Charles Avenue, New Orleans, Louisiana 70118, United States 2. School of Environment, Tsinghua University, 30 Shuangqing Rd, Beijing 100084, China 3. Department of Chemistry, Tulane University, 6823 St. Charles Avenue, New Orleans, Louisiana 70118, United States 4. Coordinated Instrumentation Facility, Tulane University, 6823 St. Charles Avenue, New Orleans, Louisiana 70118, United States

* To whom correspondence should be addressed. Email: [email protected]

1 ACS Paragon Plus Environment


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

ABSTRACT Dense non-aqueous phase chlorinated compounds such as trichloroethylene (TCE) and tetrachloroethylene (PCE) are widespread groundwater and soil contaminants which cause long-term environmental pollution. Extensive efforts have been carried out to develop materials for in-situ remediation particularly using nanoscale zero-valent iron (NZVI) to reduce TCE to relatively innocuous products such as ethane and ethylene. A novel technology is described here that uses earth-abundant natural tubular aluminosilicate clays known as halloysite (HNT) to support NZVI. These systems are efficient at the reductive dechlorination of such chlorinated hydrocarbons indicating a pseudo-first order rate constant of 0.1 L g-1h-1 with NZVI particle size between 5-10 nm. The adsorption of the naturally derived polyelectrolytes chitosan and carboxymethyl cellulose on the surface of HNT provides easy dispersibility in aqueous solutions and colloidal stability to the NZVI supported on HNT, with chitosan adsorption leading to stability over a period of 60 hours. Observations of transport through packed capillaries using optical microscopy indicate that these biopolymerstabilized composites transport efficiently through porous media at flow rates representative of groundwater flow. Such efficient transport is attributed to the tubular morphology with the particles aligning along flow streamlines. Calculations of the sticking coefficient indicate values as low as 0.1 indicating low attachment to sediment. Such composite materials using sustainable biopolymers and earth abundant clay minerals have potential in the groundwater remediation of chlorinated ethenes. KEYWORDS: Halloysite nanotubes, NZVI, DNAPL, chlorinated ethene


Page 2 of 30

Page 3 of 30

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


INTRODUCTION Trichloroethylene (TCE) is a widespread soil and groundwater contaminant that causes long-term environmental pollution.1-3 TCE is sparingly soluble in water (solubility of 1100 ppm) and has a density of 1.46 g/ml. Due to these properties, TCE spills travel deep into the subsurface of aquifers and the contaminant accumulates in bedrock fractures and in aquifer pores, from which it slowly dissolves in groundwater forming a plume of contaminated ground water that is difficult to remediate.1 Extensive efforts have been carried out to develop remediation methods for TCE pollution such as soil vapor extraction, bioremediation and in-situ injection of reactive agents.4-8 Among these approaches, the in-situ injection of nanoscale zero-valent iron (NZVI) particles into contaminant plumes is a simple, low cost and environmentally benign technology and has become a preferred method.5, 6, 9 The decontamination reaction follows the overall redox reaction: C2HCl3+ 4 Fe0 +5 H+ → C2H6+ 4 Fe2++ 3 Cl-

(1)

The objective of in-situ injection is to have the dechlorination agent (NZVI) stay colloidally suspended in groundwater and follow groundwater migration, thus continually breaking down the dissolved TCE in a contaminant plume.

Compared to

granular iron particles, NZVI particles exhibit superior reactivity towards TCE dechlorination because of the large specific surface area of nanoparticles.10 However, the high surface energy and the intrinsic ferromagnetism of NZVI particles larger than the superparamagnetic limit lead to a rapid aggregation of NZVI particles. These agglomerates decrease the mobility of NZVI particles, thus limiting the application of NZVI particles in in-situ injection processes. Various hydrophilic or amphiphilic species such as starches, vegetable oils, surfactants and some polyelectrolytes such as sodium carboxymethyl cellulose (CMC) and poly (acrylic acid) (PAA) have been used 3 ACS Paragon Plus Environment


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

to stabilize the NZVI particles in order to prevent the particle aggregation.11-18 These organic species can be adsorbed to the surfaces of NZVI particles and provide steric or electrostatic repulsions between particles. A second approach is to stabilize NZVI particles by immobilizing the NZVI particles on solid supports, such as porous silica particles, carbon particles19-22 and activated carbon.23 Such immobilization follows principles of supported catalyst systems used in heterogeneous catalytic reactions, with the objective of achieving high surface areas for reaction and preventing metal particle aggregation. In contrast to supported metal catalysis in a stationary reactor however, there is the added aspect that the particles move with groundwater flow, leading to the requirement of a colloidally stable particulate system. In-situ injection requires large quantities of material, and there is therefore the need to use earth abundant materials both to mitigate manufacturing costs and to minimize the environmental footprint of manufactured materials. In this paper, we report our findings on the use of halloysite, a natural aluminosilicate clay with a nanotubular morphology, as a support for NZVI. The use of halloysite nanotubes as a support material for metal particles is of much interest due to their high porosities, their inertness and abundance leading to potential applications in catalysis.2427

Halloysite nanotubes (HNTs) constitute a 1:1 aluminosilicate clay mineral,

chemically similar to kaolin with the empirical formula Al2Si2O5(OH)4. As shown in Figure 1, HNTs naturally occur as small scroll-like clay sheets which are caused by a lattice mismatch between the two different layers comprising the clay sheet. The external surface consists of siloxane (Si-O-Si) groups and the internal surface consists of aluminol (Al-OH) groups. The structural isomorphic substitution of Si for Al leads to the unequal charge distribution between the cationic Al-rich inner surface and the anionic Si-rich outer surface.28 Naturally occurring HNTs have lengths varying from 4 ACS Paragon Plus Environment

Page 4 of 30

Page 5 of 30

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


0.5 to 10 m although a typical length is around 0.5-2 µm as shown in Figure 1. The outer diameter of halloysite is around 100 nm with the inner lumen approximately 20 nm. Halloysites thus have aspect ratios ranging from 5 to 20.29 The spacing between the scrolled layers is 0.7 nm in the dehydrated state leading to 10-15 sheets per nanotube.

Figure 1. (a) SEM and TEM images of halloysite nanotubes. (b) Halloysite structure showing the Si rich outer layer and the Al rich inner structure of a scroll leaflet. Our objective in this work is to demonstrate the use of halloysite as a support for NZVI to conduct the dechlorination reaction in groundwater saturated sediments. Of relevance is the development of methods to prevent aggregation of the particles and to retain colloidal suspension stability in groundwater. Additionally, the tubular morphology of halloysite allows it to align axially with groundwater streamlines and may enhance transport through porous media. Figure 2 illustrates such transport through porous media indicating that the relatively narrow diameter of halloysite allows penetration through pores not accessible to the isometric spherical morphology. These concepts are elaborated upon in subsequent sections. 5 ACS Paragon Plus Environment


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 6 of 30

Figure 2. Schematic of tubular particles that align along groundwater flow streamlines. Such alignment allows transport through pores that are impenetrable by isometric spherical particles.

EXPERIMENTAL SECTION Materials Ferric chloride hexahydrate (FeCl3.6H2O), sodium borohydrate (NaBH4, 99%), tetrachloroethylene (PCE, C2Cl4, 99%), trichloroethylene (TCE, C2HCl3, 99%), 1,2 dichloroethylene (mixture of cis- and trans- 1,2-DCE, C2H2Cl2, 99%), 1,1 dichloroethylene (1,1-DCE, C2H2Cl2, 99%), sodium carboxymethyl cellulose (mean MW=90000),

chitosan

(low

molecular

weight,

60K-120K),

Rose

Bengal

(C20H2Cl4I4Na2O5, dye content 95%) were purchased from Sigma-Aldrich and used as received. Halloysite nanotubes (HNTs) were obtained from Sigma-Aldrich. Ottawa sand particles (EMD, CAS 14808-60-7, Fisher) were sieved and sand grains >300 µm were used in capillary and column experiments. Deionized (DI) water, produced from an Elga water purification system (Medica DV25) to a resistance of 18.2 MΩ was used in all experiments.


Page 7 of 30

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Halloysite-NZVI Composite Preparation The wetness impregnation method was used to prepare halloysite-FeCl3 (HNT-FeCl3) composites. In detail, 0.3 g of HNTs were loosely packed in a container with dropwise addition of FeCl3 solution (184 g/L) up to 500 µL. The dense slurry was then dried into powder. Nanoscale zero-valent iron loaded halloysite (HNT-NZVI) was prepared by using liquid phase NaBH4 reduction as previously reported,30 leading to an iron loading amount of 6.4 wt%. Specifically, 0.8 g of HNT-FeCl3 particles were placed in a vial followed by the dropwise addition of 5 ml of 0.5 M NaBH4 solution. After cessation of visible hydrogen evolution, the particles were centrifuged and washed with N2 purged D.I. water before use. The HNTs were labeled with Rose Bengal according to the procedures reported by Dorota.31 Thus, 2.5 g of HNTs was added into 100 ml of 10 x 10-5 M Rose Bengal aqueous solution and the suspension was stirred continuously for 96 h at ambient temperature while being kept in the dark. The excess Rose Bengal was washed away by centrifugation until the supernatant showed no adsorption at 548 nm (the maximum absorption band for Rose Bengal) using UV/Vis adsorption spectroscopy. Characterization and Analysis Scanning electron microscopy (SEM, Hitachi S-4800, operated at 3 kV) and transmission electron microscopy (TEM, FEI Tecnai G2 F30, operated at 200 kV) along with energy-dispersive spectroscopy (EDS) were used to characterize the pristine HNT and the HNT-NZVI composite. The dechlorination reactivity was tested through batch experiments using TCE dechlorination as the specific example. Thus 0.8 g of HNT-NZVI was dispersed in 20 ml of water and placed in a 40 ml reaction vial equipped with a Mininert valve. 0.1% Pd (w/w of NZVI) was added using K2PdCl6 aqueous solution.32 15 l of a TCE stock solution (20 g/L TCE in methanol) was spiked into this vial, resulting in an initial TCE 7 ACS Paragon Plus Environment


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

concentration of 15 ppm. The reactions were monitored through headspace analysis 33 using a HP 6890 gas chromatograph (GC) equipped with a J&W Scientific capillary column (30 m x 0.32 mm) and a flame ionization detector (FID). The sample was injected splitless at 220 oC. The oven temperature was held at 75 oC for 2 min and then ramped to 150 oC at a rate of 25 oC /min and maintained at 150 oC for 8 min to ensure adequate peak separation. Optical microscopy (Leica DMI REZ) was used to characterize the transport properties of the HNT-NZVI composite in packed capillary systems. We also used confocal microscopy (Leica SP2 AOBS 2004) to observe the transport of Rose Bengallabeled halloysites (HNT-RB) through the packed capillaries. To facilitate discussion of the results, further aspects of the capillary transport experiments are described in conjunction with the observations. The colloidal stability of HNT-NZVI suspensions was monitored with a nephelometric turbidimeter (DRT100B, Scientific Inc.) over a period of 60 hours. Zeta potential values of the HNT-NZVI suspensions were done by measuring the electrophoretic mobility using the phase analysis light scattering (PALS) technique (Nanobrook ZetaPALS, Brookhaven Instruments). Macroscopic method (column breakthrough tests) combined with capillary microscopy method were used to study the transport characteristics of HNT-NZVI particles.


Page 8 of 30

Page 9 of 30

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


RESULTS AND DISCUSSION Morphological Characterizations Figure 3a shows the TEM image of HNT-NZVI. The inset is a high resolution TEM, indicating NZVI particles in the 5-10 nm range have been deposited on the HNT surface and are relatively evenly distributed. EDS analysis (Figure 3bi) confirms the presence of iron on the HNT. The control sample of pristine HNT (Figure 3bii) only exhibits elemental peaks of Al, Si and O, with the Cu elemental peak attributed to the TEM sample grid. The X-ray diffraction and X-ray photoelectron spectroscopy data of the HNT-NZVI composite are shown in supporting information S1.

Figure 3. (a) TEM images of HNTs loaded with iron nanoparticles with the inset being a high resolution image of iron nanoparticles. Loading of iron within the lumen of halloysite is due to capillary influx of the precursor solution into the lumen. (b) EDS analysis of HNT-NZVI and pristine HNT.



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Reactivity Characteristics of Pristine HNT -NZVI Composites Figure 4a illustrates the removal of TCE from solution indicating both removal of TCE and evolution of the gaseous product. The corresponding chromatogram in Figure 4b indicates negligible intermediates and an evolving gaseous product (ethane+ ethylene lumped into a single chromatographic peak). A pseudo first order initial rate constant km of 0.0912 L g-1h-1 is calculated based on the mass of zero-valent iron, with the assumption of first order kinetics serving as a quantitative guideline to compare various systems.34 The fast evolution of the major products, the relative absence of intermediates such as dichloroethylene and vinyl chloride which tend to stay adsorbed till complete conversion to ethane, indicate that the HNT-NZVI system is effective in the reductive dechlorination of TCE. The morphology of the HNT-NZVI composite particles after reaction is shown in Figure S2a (Supporting Information) indicating transformation of spherical particles of zerovalent iron to sheet-like structures after oxidation.


Page 10 of 30

Page 11 of 30

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 4: (a) TCE removal from solution and gas product evolution rates for HNTNZVI composite. M/Mo is the fraction of the original TCE remaining and P/Pf is the ratio of the gas product peak to the gas product peak at the end. (b) Representative GC trace of headspace chromatographic analyses showing TCE degradation and reaction product evolution at various reaction times.



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 12 of 30

Enhancement of Colloidal Stability through Polymer Adsorption The colloidal stability of HNT particles is essential to assess the ability of these materials to follow contaminant plumes in groundwater and thus design appropriate insitu remediation methods. In this experiment, the sedimentation of a suspension containing 250 mg/L of HNT-NZVI was used to monitor colloidal stability, with the addition of electrolyte (1 mM NaCl) to simulate natural groundwater conditions.35 Results of the sedimentation experiment are shown in Figure 5b. We note that even pristine HNT-NZVI particles take approximately 24 hours to sediment, an indication of minimal aggregation. Subsequent experiments were done with the addition of the water-soluble biopolymers carboxymethylcellulose (CMC) chitosan. Structures of the two sustainable polymers are shown in Figure 5a. CMC is a cellulose derivative which can be easily obtained by replacing the CH2OH group in the glucose unit with a carboxymethyl group. As a food-grade additive, CMC has been widely used as a costeffective stabilizer in industries, food and medical fields.36-38 Chitosan is a cationic linear polysaccharide obtained from the deacetylation of chitin. Derived from species of fungi as well as seafood processing wastes such as shrimp and crab shells, chitin is the second most abundant natural biopolymer, after cellulose.39,

40

Chitosan is

biodegradable and biocompatible and has been extensively studied in a variety of applications including water treatment, biomaterials and food additives. Both CMC and chitosan are widely available and inexpensive.


Page 13 of 30

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 5. (a) Structures of carboxymethyl cellulose (CMC) and chitosan. (b) Sedimentation curves of 0.25 g/L HNT-NZVI in 0.5% (w/w) CMC solution, 0.5% (w/w) chitosan solution and water. 1 mM NaCl was added as the electrolyte. The normalized turbidity is defined as the ratio of the measured time-dependent turbidity to the initial turbidity of the colloidal suspensions. We observe that the colloidal stability of the HNT-NZVI composite is greatly enhanced with the addition of these polymers, with 60% of HNT-NZVI particles remaining suspended after 60 hours in 0.5% (w/w) CMC solution and 76% of HNTNZVI particles remaining suspended in 0.5% (w/w) chitosan solution. Zeta potential measurements shown in Table 1, indicate the reversal of charge from a negative zeta potential upon CMC adsorption, to a strongly positive zeta potential upon chitosan adsorption. We propose that the enhancement of stability with chitosan is the result of adsorption of the cationic biopolymer to the Si rich anionic exterior of halloysite. With CMC, adsorption may primarily occur within the lumen on the cationic inner surface 13 ACS Paragon Plus Environment


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

of halloysite, and the greater enhancement in colloidal stability with chitosan may reflect the attachment of chitosan to the external surface. The choice of biopolymer to be used is a function of the porous media characteristics, as it is important that the polyelectrolyte coated particles do not become adsorbed onto the sediment grains. Nevertheless, the use of widely available biopolymers such as CMC and chitosan to enhance HNT-NZVI colloidal stability points to the development of sustainable technology. Supporting information S3 lists viscosity versus shear rate for CMC and chitosan stabilized HNT suspensions indicating that viscosity levels remain close to those of water (1mPa.s) at polymer concentrations up to 2.5 g/L. The low viscosities imply applicability of such material suspensions for direct injection into TCE contaminated groundwater saturated sediments.

Table 1. Zeta Potential Measurement of HNT-NZVI suspensions

The question arises as to whether the adsorbed polymer layer on the HNT nanotubes inhibits reactivity. Accordingly, we conducted dechlorination reactivity tests with the adsorbed polymer. The reactivity of HNT-NZVI particles with 0.5% (w/w) CMC towards TCE is shown in Figure 6a, with the corresponding test of HNT-NZVI particles with 0.5% (w/w) chitosan shown in Figure 6b. In all experiments, 0.8 g of HNT-NZVI particle was used and the initial TCE concentration was 15 ppm. Both systems indicate 14 ACS Paragon Plus Environment

Page 14 of 30

Page 15 of 30

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


efficient reaction with the pseudo first order rate constant km determined as 0.104 L g1 -1

h and 0.121 L g-1h-1 for the CMC and chitosan stabilized HNT-NZVI composite,

respectively. The values are fully comparable to the values obtained for pristine HNTNZVI and the slight enhancement may be a consequence of TCE adsorption to the polymer thus enhancing the local concentration of TCE in the vicinity of the NZVI.

Figure 6. TCE removal from solution and gas product evolution rates for HNT-NZVI composite with (a) 0.5% w/w CMC and (b) 0.5% w/w chitosan. M/Mo is the fraction of the original TCE remaining and P/Pf is the ratio of the gas product peak to the gas product peak at the end.

Dechlorination reactivity tests of HNT-NZVI particles towards PCE, 1,2-DCE and 1,1-DCE are shown in the Supporting Information (S4). In all cases, high reactivities 15 ACS Paragon Plus Environment


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

to the chlorinated ethenes are observed indicating the efficiency of HNT-NZVI composite particles.

Transport Characteristics of HNT-NZVI Composite Particles Transport characteristics of the HNT-NZVI particles were examined through capillary transport experiments that we had developed earlier.41 The advantage of capillary experiments is the minimal use of materials, and the ability to visualize bands of the dark colored HNT-NZVI particles moving through the capillary. Additionally, optical microscopy imaging of the capillary enables visualization of particle aggregates deposited on sediment grains. Figure 7a shows the schematic experimental setup. In detail, a glass capillary open at both ends (1.5-1.8mm i.d x 100 mm length, Corning, NY) was packed with wet Ottawa sands to a 3 cm length. 30 l of particle suspension was injected into the capillary and the capillary was placed horizontally to simulate horizontal groundwater flow. A continuous water flow was provided by a syringe pump at a flow rate of 0.1 mL/min for 5 min. The exit point of the capillary was plugged with glass wool in order to maintain the capillary packing during water flush, and also to collect the eluted particles. Optical microscopy was used to observe the transport of the particles through the packed sand grains. Figure 7b shows the photograph of the capillary with the HNT-NZVI suspension and Figure 7c shows the same capillary after the water flush. As shown in Figure 7c, the particles were collected by the glass wool and there is a small evidence of particle aggregates on the sand grains. In contrast, RNIP particles (10DS, Toda Kogyo) quickly aggregate even prior to the water flush, as shown in Figure 7d. Figure 7e shows that most of the RNIP particles are trapped between the sand grains after the water flush. Capillary transport experiments for CMC and chitosan stabilized HNT-NZVI suspensions are shown in the Figure 8. The sand grains were 16 ACS Paragon Plus Environment

Page 16 of 30

Page 17 of 30

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


notably clean after water flush. These images directly demonstrate that the CMC and chitosan stabilized HNT-NZVI particles can readily transport through the porous media of the capillary and become captured by the glass wool. The added polyelectrolytes, adsorbed onto the surface of HNT-NZVI particles, prevent particle aggregation and increase colloidal stability of the suspension through steric and electrostatic repulsion.

Figure 7. Characterization of the capillary transport experiments. (a) Experimental setup: flow rate, 0.1 ml/min; sand length, 3 cm; the injected suspension volume, 0.03 ml. Photographs of capillary (b) containing HNT-NZVI particles and (c) after water flush, (d) containing RNIP suspension and (e) after water flush. Panels i-iii show optical micrographs of particles at different locations. All scale bars are 100 µm. 17 ACS Paragon Plus Environment


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Figure 8. Characterization of the capillary transport experiments with polymer stabilized HNT-HZVI. Photographs of capillary (a) containing HNT-NZVI particles with 0.5% w/w CMC and (b) after water flush, (c) containing HNT-NZVI particles with 0.5% w/w chitosan and (d) after water flush. Panels i-ii show optical micrographs of sediments and particles at different locations. Panel iii illustrates accumulation on glass wool at the end of the capillary. All scale bars are 100 µm. To increase sensitivity of the capillary set-up to microscopic observation, we used Rose Bengal-labeled HNTs (HNT-RB) for the transport experiments that would allow the use of confocal microcopy for fluorescence imaging of the capillary. As shown in Figure 9, after the water flush, there is no fluorescence observed in the sand grain section of the capillary indicating negligible adsorption of HNT-RB to sand grains. The glass wool at the end of the column captures the HNT-RB particles and fluorescence is clearly observed in this section of the column. 18 ACS Paragon Plus Environment

Page 18 of 30

Page 19 of 30

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 9. Characterization of HNT-RB particles in capillary transport experiment. (a) HNT-RB suspension with 0.5% w/w CMC and (b) HNT-RB suspension with 0.5% w/w chitosan. The particle suspension was injected in the capillary followed by a continuous water flush. Confocal images of i) sand grains and iii) glass wool taken in the brightfield mode and ii) the same sand grains and iv) glass wool taken in the fluorescence mode (λexc=561nm). All scale bars shown in the images represent 10 µm.

While qualitative, the capillary transport experiments are instructive and illustrate the ability of HNTs to move readily through groundwater saturated sediments. As stated earlier, the facile transport characteristics of HNT are ascribed to their tubular structure. Such tubular particles can readily mobilize through porous media in comparison to isometric spherical particles due to their tendency to align with the groundwater flow when their aspect ratio is sufficiently large. Penetration of sediment pores is thus a function of their circular cross sections.42-44 To quantify such an effect, we calculated the single collector efficiency of tubular particles. The collector efficiency ( 0 ) represents the frequency of a particle colliding with the surface of a collector (sediment grain)45 with low collector efficiencies implying enhanced mobility through porous media. To calculate the collector efficiency of the HNTs, the mathematical model developed by Carroll and co-workers46 for the mobility of multi19 ACS Paragon Plus Environment


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 20 of 30

walled carbon nanotubes in porous media, was applied. The collector efficiency is the contribution of effects from particle diffusion ( D ), particle interception by collector grains ( I ) and particle sedimentation due to gravity ( G )

47

with the resulting

expression derived for the “side-contact” (the sidewall of the tubular particle contacting the collector) mechanism of collection:

 0   D   I  G 1 d 1  (1  ( P ) 2 ) 2 2 1 2 1 2 3 d l  4.03[kTln( )] 3  (3 dC0 ( d P 2 l ) 3 ( l ) 3 (1  ( P ) 2 ) 2 ) 3 d l dP P 2 l dP 1 d [ ( P ) 2 (3  )] (2) 2 dC d P  dC

d P 2 12 2 2 3 1  [1  ( ) ] 0.146(    ) g(d l) d l P P ( P ) 3 ( ) ln( ) 1 l dP 2 2 dP 0 [1  ( l ) ] l where l is the length of the tubular particle (m), dc is the diameter of the collector (m) 2

and dP is the particle diameter (m),  P is the particle density (g.cm-3),  is the fluid density (g.L-1) and  is the fluid viscosity (kg.m-1·s-1),  0 is the undisturbed uniform flow velocity (m.s-1), T is the absolute temperature (K), and k is the Boltzmann constant. For a typical 1 µm long HNT with a diameter of 100 nm, the collector efficiency is calculated to be 0.00087. The single-collector efficiency of the isometric spherical particle (same volume as a cylinder with length 1 µm and diameter 100 nm) with particle diameter dp = 246.6 nm, calculated using the well-established TufenkjiElimelech model (T-E)47 (details in the Supporting Information section S5) is 0.0027, clearly showing the increased probability of spherical particles being trapped onto sand grains. We note that the greater diameter of the isometric spherical particle implies a greater proximity of the spherical particle to the collector surface. In other words, when the longitudinal axis of the cylinder and the center of the isometric sphere both lie along a streamline, the sphere surface is closer to the collector thus increasing van der Waals 20 ACS Paragon Plus Environment

Page 21 of 30

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


forces and enhancing the probability of capture by the collector. By collecting the particles eluted out of the capillary and the particles adhering to the glass wool, it is possible to determine the attachment efficiency (α) defined as the ratio of particles that attach to the sediment to the particles that collide with the grains.45, 47 Thus,   

dC 2 ln(C ) C0 3 (1  f ) L0

(3)

where dc is the average diameter of sand grains (dc = 500 µm), C

C0

is the ratio of

particle concentration in the effluent to that in the influent, f is the porosity of the packed sand grains (f = 0.32), and L is the length of the column (L= 0.03 m), 0 is the single collector efficiency. Regardless of whether CMC or chitosan is used as the colloidal stabilizer, we have found that over 95% of the particles are eluted within one elution volume, with α values in the range of 0.1, the low values indicating rapid elution as indicated by equation 2 (C/C0 → 1). The attachment efficiency can also be determined from column elution experiments

20, 48, 49

and Supporting Information section S6 describes such elution

experiments using a 50 ml glass burette (diameter = 1.3 cm) packed with wet Ottawa sand. Again, we note the removal of almost all particles within one elution volume when stabilized with CMC or chitosan. The control experiment of non-functionalized halloysite shows a reduced level of 60% removal over a single elution volume further implying the advantage of stabilization with sustainable biopolymers.



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

CONCLUSIONS In summary, we have described a technology for the reductive in-situ remediation of chlorinated compounds by using earth-abundant, environmentally benign and sustainable materials. Important aspects of the technology are the following (1) the use of earth abundant halloysite nanotubes as a support for nanoscale zerovalent iron with the 5-10 nm NZVI particles exhibiting high levels of reactivity in the reductive dechlorination of chlorinated ethenes (2) the use of sustainable biopolymers such as carboxymethylcellulose and chitosan to enhance colloidal stability of the HNT-NZVI composites in aqueous solutions (3) the tubular morphology of HNT that facilitates transport through porous media as seen in capillary and column transport experiments. We feel that these characteristics of the biopolymer-stabilized HNT nanotubes indicate potential for using these materials in in-situ remediation where the particles are injected into plumes of dissolved contaminants in groundwater saturated sediments, travel with the plumes and break down the contaminants to light gases that gradually volatilize out of the sediment. While we have introduced the first application of halloysites to in-situ groundwater remediation, there are significant opportunities for further improvement. Novel methods of introducing metal particles between the sheets and in cracks of halloysite have recently been introduced by Vinokurov and coworkers.50 Such methods may enhance NZVI loading on halloysite and make the composites less susceptible to reactive site deactivation by groundwater foulants such as natural organic matter. Carbonization of halloysite may additionally improve reactivity by creating adsorption sites for chlorinated compounds thus increasing local concentrations near the reactive iron species.20,

51

In contaminated groundwater sediments, the TCE can exist as

dissolved contaminants and as bulk material sequestered in pores. The advantage of 22 ACS Paragon Plus Environment

Page 22 of 30

Page 23 of 30

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


particle supported NZVI is that the particles can adsorb to the bulk TCE-water interface to form particle stabilized emulsions (Pickering emulsions) to degrade bulk TCE.52 Storage of HNT-NZVI and delivery are additional important factors with storage in an inert atmosphere or as suspensions in NaBH4 serving to prevent oxidation.9 All of these are aspects of continuing research essential to translating the concepts described here to technological application.

Supporting Information: X-ray diffraction characterization of HNT-NZVI composite particles (S1), characterizations of HNT-NZVI composite particles after dechlorination reaction (S2), viscosity of CMC and chitosan stabilized HNT suspensions (S3), dechlorination reactivity tests of HNT-NZVI particles towards PCE, 1,2-DCE and 1,1-DCE (S4), calculations of the single-collector efficiency for spherical particles (S5) and calculations of the attachment coefficient (S6).

Acknowledgements Support by the National Science Foundation (Grant 1236089) is gratefully acknowledged.



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

REFERENCES (1) Al-Abed, S.; Chen, J.-L., Transport of Trichloroethylene (TCE) in Natural Soil by Electroosmosis. In Physicochemical Groundwater Remediation, Smith, J.; Burns, S., Eds. Springer US: 2002; 91-114. (2) Saleh, N.; Sirk, K.; Liu, Y. Q.; Phenrat, T.; Dufour, B.; Matyjaszewski, K.; Tilton, R. D.; Lowry, G. V., Surface modifications enhance nanoiron transport and NAPL targeting in saturated porous media. Environ. Eng. Sci. 2007, 24, (1), 45-57. DOI: 10.1089/ees.2007.24.45 (3) Dowideit, P.; von Sonntag, C., Reaction of ozone with ethene and its methyl- and chlorine-substituted derivatives in aqueous solution. Environ. Sci. Technol. 1998, 32, (8), 1112-1119. DOI:10.1021/es971044j (4) Switzer, C.; Kosson, D. S., Soil vapor extraction performance in layered vadose zone materials. Vadose Zone J. 2007, 6, (2), 397-405. DOI: 10.2136/vzj2005.0131 (5) Phenrat, T.; Saleh, N.; Sirk, K.; Tilton, R. D.; Lowry, G. V., Aggregation and sedimentation of aqueous nanoscale zerovalent iron dispersions. Environ. Sci. Technol. 2007, 41, (1), 284-290. DOI: 10.1021/es061349a (6) Elliott, D. W.; Zhang, W. X., Field assessment of nanoscale biometallic particles for groundwater treatment. Environ. Sci. Technol. 2001, 35, (24), 4922-4926. DOI: 10.1021/es0108584 (7) Scherer, M. M.; Richter, S.; Valentine, R. L.; Alvarez, P. J. J., Chemistry and microbiology of permeable reactive barriers for in situ groundwater clean up. Critical Reviews in Environmental Science and Technology 2000, 30, (3), 363-411. DOI: 10.1080/10643380091184219 (8) Nakano, Y.; Hua, L. Q.; Nishijima, W.; Shoto, E.; Okada, M., Biodegradation of trichloroethylene (TCE) adsorbed on granular activated carbon (GAC). Water Res. 2000, 34, (17), 4139-4142. DOI: 10.1016/S0043-1354(00)00199-8 (9) He, F.; Zhao, D. Y.; Paul, C., Field assessment of carboxymethyl cellulose stabilized iron nanoparticles for in situ destruction of chlorinated solvents in source zones. Water Res. 2010, 44, (7), 2360-2370. DOI: 10.1016/j.watres.2009.12.041 (10) Liu, Y. Q.; Choi, H.; Dionysiou, D.; Lowry, G. V., Trichloroethene hydrodechlorination in water by highly disordered monometallic nanoiron. Chem. Mater. 2005, 17, (21), 5315-5322. DOI: 10.1021/cm0511217 (11) Alessi, D. S.; Li, Z. H., Synergistic effect of cationic surfactants on perchloroethylene degradation by zero-valent iron. Environ. Sci. Technol. 2001, 35, (18), 3713-3717. DOI: 10.1021/es010564i (12) He, F.; Zhao, D. Y., Preparation and characterization of a new class of starchstabilized bimetallic nanoparticles for degradation of chlorinated hydrocarbons in water. Environ. Sci. Technol. 2005, 39, (9), 3314-3320. DOI: 10.1021/es048743y (13) He, F.; Zhao, D. Y., Manipulating the size and dispersibility of zerovalent iron nanoparticles by use of carboxymethyl cellulose stabilizers. Environ. Sci. Technol. 2007, 41, (17), 6216-6221. DOI: 10.1021/es0705543 24 ACS Paragon Plus Environment

Page 24 of 30

Page 25 of 30

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(14) Kanel, S. R.; Choi, H., Transport characteristics of surface-modified nanoscale zero-valent iron in porous media. Water Sci. Technol. 2007, 55, (1-2), 157-162. DOI: 10.2166/wst.2007.002 (15) Quinn, J.; Geiger, C.; Clausen, C.; Brooks, K.; Coon, C.; O'Hara, S.; Krug, T.; Major, D.; Yoon, W. S.; Gavaskar, A.; Holdsworth, T., Field demonstration of DNAPL dehalogenation using emulsified zero-valent iron. Environ. Sci. Technol. 2005, 39, (5), 1309-1318. DOI: 10.1021/es0490018 (16) Saleh, N.; Phenrat, T.; Sirk, K.; Dufour, B.; Ok, J.; Sarbu, T.; Matyiaszewski, K.; Tilton, R. D.; Lowry, G. V., Adsorbed triblock copolymers deliver reactive iron nanoparticles to the oil/water interface. Nano Lett. 2005, 5, (12), 2489-2494. DOI: 10.1021/nl0518268 (17) Schrick, B.; Hydutsky, B. W.; Blough, J. L.; Mallouk, T. E., Delivery vehicles for zerovalent metal nanoparticles in soil and groundwater. Chem. Mater. 2004, 16, (11), 2187-2193. DOI: 10.1021/cm0218108 (18) Zhang, M.; He, F.; Zhao, D. Y.; Hao, X. D., Degradation of soil-sorbed trichloroethylene by stabilized zero valent iron nanoparticles: Effects of sorption, surfactants, and natural organic matter. Water Res. 2011, 45, (7), 2401-2414. DOI: 10.1016/j.watres.2011.01.028 (19) Zhan, J. J.; Zheng, T. H.; Piringer, G.; Day, C.; McPherson, G. L.; Lu, Y. F.; Papadopoulos, K.; John, V. T., Transport Characteristics of Nanoscale Functional Zerovalent Iron/Silica Composites for in Situ Remediation of Trichloroethylene. Environ. Sci. Technol. 2008, 42, (23), 8871-8876. DOI: 10.1021/es800387p (20) Zhan, J. J.; Kolesnichenko, I.; Sunkara, B.; He, J. B.; McPherson, G. L.; Piringer, G.; John, V. T., Multifunctional Iron-Carbon Nanocomposites through an AerosolBased Process for the In Situ Remediation of Chlorinated Hydrocarbons. Environ. Sci. Technol. 2011, 45, (5), 1949-1954. DOI: 10.1021/es103493e (21) Zhan, J. J.; Sunkara, B.; Tang, J. J.; Wang, Y. Q.; He, J. B.; McPherson, G. L.; John, V. T., Carbothermal Synthesis of Aerosol-Based Adsorptive-Reactive IronCarbon Particles for the Remediation of Chlorinated Hydrocarbons. Ind. Eng. Chem. Res. 2011, 50, (23), 13021-13029. DOI: 10.1021/ie200783z (22) Sunkara, B.; Zhan, J. J.; Kolesnichenko, I.; Wang, Y. Q.; He, J. B.; Holland, J. E.; McPherson, G. L.; John, V. T., Modifying Metal Nanoparticle Placement on Carbon Supports Using an Aerosol-Based Process, with Application to the Environmental Remediation of Chlorinated Hydrocarbons. Langmuir 2011, 27, (12), 7854-7859. DOI: 10.1021/la200657m (23) Choi, H.; Al-Abed, S. R.; Agarwal, S.; Dionysiou, D. D., Synthesis of reactive nano-Fe/Pd bimetallic system-impregnated activated carbon for the simultaneous adsorption and dechlorination of PCBs. Chem. Mater. 2008, 20, (11), 3649-3655. DOI: 10.1021/cm8003613 (24) Lvov, Y.; Wang, W. C.; Zhang, L. Q.; Fakhrullin, R., Halloysite Clay Nanotubes for Loading and Sustained Release of Functional Compounds. Adv. Mater. 2016, 28, (6), 1227-1250. DOI: 10.1002/adma.201502341 (25) Zhang, Y.; Yang, H. M., Co3O4 nanoparticles on the surface of halloysite nanotubes. Phys. Chem. Miner. 2012, 39, (10), 789-795. 25 ACS Paragon Plus Environment


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

DOI: 10.1007/s00269-012-0533-9 (26) Peng, H. X.; Liu, X. H.; Tang, W.; Ma, R. Z., Facile synthesis and characterization of ZnO nanoparticles grown on halloysite nanotubes for enhanced photocatalytic properties. Sci Rep 2017, 7:2250. DOI: 10.1038/s41598-017-02501-w (27) Lvov, Y. M.; DeVilliers, M. M.; Fakhrullin, R. F., The application of halloysite tubule nanoclay in drug delivery. Expert. Opin. Drug Del. 2016, 13, (7), 977-986. DOI: 10.1517/17425247.2016.1169271 (28) Tari, G.; Bobos, I.; Gomes, C. S. F.; Ferreira, J. M. F., Modification of surface charge properties during kaolinite to halloysite-7 angstrom transformation. J. Colloid Interf. Sci. 1999, 210, (2), 360-366. DOI: 10.1006/jcis.1998.5917 (29) Rawtani, D.; Agrawal, Y. K., Multifarious Applications of Halloysite Nanotubes: A Review. Rev. Adv. Mater. Sci. 2012, 30, (3), 282-295. (30) Wang, C. B.; Zhang, W. X., Synthesizing nanoscale iron particles for rapid and complete dechlorination of TCE and PCBs. Environ. Sci. Technol. 1997, 31, (7), 21542156. DOI: 10.1021/es970039c (31) Bielska, D.; Karewicz, A.; Lachowicz, T.; Berent, K.; Szczubialka, K.; Nowakowska, M., Hybrid photosensitizer based on halloysite nanotubes for phenolbased pesticide photodegradation. Chem. Eng. J. 2015, 262, 125-132. DOI: 10.1016/j.cej.2014.09.081 (32) Yan, W. L.; Herzing, A. A.; Li, X. Q.; Kiely, C. J.; Zhang, W. X., Structural Evolution of Pd-Doped Nanoscale Zero-Valent Iron (nZVI) in Aqueous Media and Implications for Particle Aging and Reactivity. Environ. Sci. Technol. 2010, 44, (11), 4288-4294. DOI: 10.1021/es100051q (33) Zheng, T. H.; Zhan, J. J.; He, J. B.; Day, C.; Lu, Y. F.; Mcpherson, G. L.; Piringer, G.; John, V. T., Reactivity characteristics of nanoscale zerovalent iron-silica composites for trichloroethylene remediation. Environ. Sci. Technol. 2008, 42, (12), 4494-4499. DOI: 10.1021/es702214x (34) Sunkara, B.; Zhan, J. J.; He, J. B.; McPherson, G. L.; Piringer, G.; John, V. T., Nanoscale Zerovalent Iron Supported on Uniform Carbon Microspheres for the In situ Remediation of Chlorinated Hydrocarbons. Acs Applied Materials & Interfaces 2010, 2, (10), 2854-2862. DOI : 10.1021/am1005282 (35) Atekwana, E. A.; Richardson, D. S., Geochemical and isotopic evidence of a groundwater source in the Corral Canyon meadow complex, central Nevada, USA. Hydrological Processes 2004, 18, (15), 2801-2815. DOI: 10.1002/hyp.1495 (36) Johnson, R. L.; Nurmi, J. T.; Johnson, G. S. O.; Fan, D. M.; Johnson, R. L. O.; Shi, Z. Q.; Salter-Blanc, A. J.; Tratnyek, P. G.; Lowry, G. V., Field-Scale Transport and Transformation of Carboxymethylcellulose-Stabilized Nano Zero-Valent Iron. Environ. Sci. Technol. 2013, 47, (3), 1573-1580. DOI: 10.1021/es304564q (37) Panca, M.; Cutting, K.; Guest, J. F., Clinical and cost-effectiveness of absorbent dressings in the treatment of highly exuding VLUs. J. Wound Care 2013, 22, (10), 568568. (38) Ranjbar, S. M., S.; Nematti, N.; Sokotifar, R. , Evaluation of the Effect of Carboxy Methyl Cellulose on Sensory Properties of Gluten-Free Cake. Research Journal of 26 ACS Paragon Plus Environment

Page 26 of 30

Page 27 of 30

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Applied Sciences, Engineering and Technology 2012, 4, (19). (39) Aberg, C. M.; Chen, T. H.; Olumide, A.; Raghavan, S. R.; Payne, G. F., Enzymatic grafting of peptides from casein hydrolysate to chitosan. Potential for value-added byproducts from food-processing wastes. J. Agr. Food Chem. 2004, 52, (4), 788-793. DOI: 10.1021/jf034626v (40) Wu, G. G., H.; Ma, J. , Chitosan-based Biomaterials. Material Matters 2012, 7, 3. (41) Zhan, J. J.; Sunkara, B.; Le, L.; John, V. T.; He, J. B.; McPherson, G. L.; Piringer, G.; Lu, Y. F., Multifunctional Colloidal Particles for in Situ Remediation of Chlorinated Hydrocarbons. Environ. Sci. Technol. 2009, 43, (22), 8616-8621. DOI: 10.1021/es901968g (42) Dong, R.-Y.; Cao, B.-Y., Anomalous orientations of a rigid carbon nanotube in a sheared fluid. Sci. Rep. 2014, 4:6120. DOI: 10.1038/srep06120 (43) Feng, Y.; Kleinstreuer, C., Analysis of non-spherical particle transport in complex internal shear flows. Physics of Fluids 2013, 25, (9), 091904. DOI: 10.1063/1.4821812 (44) Xu, S. P.; Liao, Q.; Saiers, J. E., Straining of nonspherical colloids in saturated porous media. Environ. Sci. Technol. 2008, 42, (3), 771-778. DOI: 10.1021/es071328w (45) Kuan-Mu Yao, M. T. H., Charles R. O'Melia, Water and waste water filtration: concept and applications. Environ. Sci. Technol. 1971, 5, (11). DOI: 10.1021/es60058a005 (46) Liu, X. Y.; O'Carroll, D. M.; Petersen, E. J.; Huang, Q. G.; Anderson, C. L., Mobility of Multiwalled Carbon Nanotubes in Porous Media. Environ. Sci. Technol. 2009, 43, (21), 8153-8158. DOI: 10.1021/es901340d (47) Tufenkji, N.; Elimelech, M., Correlation equation for predicting single-collector efficiency in physicochemical filtration in saturated porous media. Environ. Sci. Technol. 2004, 38, (2), 529-536. DOI: 10.1021/es034049r (48) Xiao, Y.; Wiesner, M. R., Transport and Retention of Selected Engineered Nanoparticles by Porous Media in the Presence of a Biofilm. Environ. Sci. Technol. 2013, 47, (5), 2246-2253. DOI: 10.1021/es304501n (49) He, F.; Zhang, M.; Qian, T. W.; Zhao, D. Y., Transport of carboxymethyl cellulose stabilized iron nanoparticles in porous media: Column experiments and modeling. J. Colloid Interf. Sci. 2009, 334, (1), 96-102. DOI: 10.1016/j.jcis.2009.02.058 (50) Vinokurov, V. A.; Stavitskaya, A. V.; Chudakov, Y. A.; Ivanov, E. V.; Shrestha, L. K.; Ariga, K.; Darrat, Y. A.; Lvov, Y. M., Formation of metal clusters in halloysite clay nanotubes. Sci. Technol. Adv. Mat. 2017, 18, (1), 147-151. DOI: 10.1080/14686996.2016.1278352 (51) Owoseni, O.; Zhang, Y. H.; Su, Y.; He, J. B.; McPherson, G. L.; Bose, A.; John, V. T., Tuning the Wettability of Halloysite Clay Nanotubes by Surface Carbonization for Optimal Emulsion Stabilization. Langmuir 2015, 31, (51), 13700-13707. DOI: 10.1021/acs.langmuir.5b03878 (52) Venkataraman, P.; Sunkara, B.; St Dennis, J. E.; He, J. B.; John, V. T.; Bose, A., Water-in-Trichloroethylene Emulsions Stabilized by Uniform Carbon Microspheres. Langmuir 2012, 28, (2), 1058-1063. 27 ACS Paragon Plus Environment


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

DOI: 10.1021/la204215x


Page 28 of 30

Page 29 of 30


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 30 of 30

Sustainable polysaccharide biopolymers maintain colloidal stability of earth abundant halloysite nanotubes containing zerovalent iron, for facile transport and reaction with chlorinated groundwater contaminants.

ACS Paragon Plus Environment

Environmental Remediation of Chlorinated Hydrocarbons Using

Recommend Documents