Feng He

Auburn University, Auburn, AL, United States

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Publications (13)41.49 Total impact

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    ABSTRACT: Zero valent iron (ZVI) nanoparticles have been studied extensively for degradation of chlorinated solvents in the aqueous phase, and have been tested for in-situ remediation of contaminated soil and groundwater. However, little is known about its effectiveness for degrading soil-sorbed contaminants. This work studied reductive dechlorination of trichloroethylene (TCE) sorbed in two model soils (a potting soil and Smith Farm soil) using carboxymethyl cellulose (CMC) stabilized Fe-Pd bimetallic nanoparticles. Effects of sorption, surfactants and dissolved organic matter (DOC) were determined through batch kinetic experiments. While the nanoparticles can effectively degrade soil-sorbed TCE, the TCE degradation rate was strongly limited by desorption kinetics, especially for the potting soil which has a higher organic matter content of 8.2%. Under otherwise identical conditions, ∼ 44% of TCE sorbed in the potting soil was degraded in 30 h, compared to ∼ 82% for Smith Farm soil (organic matter content = 0.7%). DOC from the potting soil was found to inhibit TCE degradation. The presence of the extracted SOM at 40 ppm and 350 ppm as TOC reduced the degradation rate by 34% and 67%, respectively. Four prototype surfactants were tested for their effects on TCE desorption and degradation rates, including two anionic surfactants known as SDS (sodium dodecyl sulfate) and SDBS (sodium dodecyl benzene sulfonate), a cationic surfactant hexadecyltrimethylammonium (HDTMA) bromide, and a non-ionic surfactant Tween 80. All four surfactants were observed to enhance TCE desorption at concentrations below or above the critical micelle concentration (cmc), with the anionic surfactant SDS being most effective. Based on the pseudo-first-order reaction rate law, the presence of 1 × cmc SDS increased the reaction rate by a factor of 2.5 when the nanoparticles were used for degrading TCE in a water solution. SDS was effective for enhancing degradation of TCE sorbed in Smith Farm soil, the presence of SDS at sub-cmc increased TCE degraded by ∼ 10%. However, effect of SDS on degradation of TCE in the potting soil was more complex. The presence of SDS at sub-cmc decreased TCE degradation by 5%, but increased degradation by 5% when SDS dosage was raised to 5 × cmc. The opposing effects were attributed to combined effects of SDS on TCE desorption and degradation, release of soil organic matter and nanoparticle aggregation. The findings strongly suggest that effect of soil sorption on the effectiveness of Fe-Pd nanoparticles must be taken into account in process design, and soil organic content plays an important role in the overall degradation rate and in the effectiveness of surfactant uses.
    Water Research 03/2011; 45(7):2401-14. · 4.66 Impact Factor
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    ABSTRACT: This paper describes the results of a series of single well push-pull tests conducted to evaluate the in situ transport of carboxymethyl cellulose (CMC) stabilized nanoscale zero-valent iron (ZVI) particles in saturated sediments and their reactivity toward chlorinated ethenes. CMC-stabilized nanoscale ZVI particles were synthesized on site by reducing ferrous ions with borohydride in water in the presence of CMC. Nanoscale ZVI and bimetallic ZVI-Pd nanoparticle suspensions were prepared and injected into depth-discrete aquifer zones during three push-pull tests. The injected nanoparticle suspensions contained a conservative tracer (Br(-)) and were allowed to reside in the aquifer pore space for various time periods prior to recovery by groundwater extraction. The comparison between Br(-) and Fe concentrations in extracted groundwater samples indicated that the CMC-stabilized nanoscale ZVI particles were mobile in the aquifer but appeared to lose mobility with time, likely due to the interactions between particles and aquifer sediments. After 13 h in the aquifer, the nanoscale ZVI particles became essentially immobilized. During the push-pull test with injection of Fe-Pd nanoparticles, ethane concentrations increased from non-detectable to 65 microg/L in extracted groundwater within less than 2 h of reaction time, indicating the rapid abiotic degradation of chlorinated ethenes. The amount of total chlorinated ethene mass destroyed was low presumably because the injected solutions "pushed" the dissolved chlorinated ethenes away from the injection well, without substantial mixing, and because stationary (sorbed) chlorinated ethene mass on the aquifer sediments was low. In situ remediation programs using highly reactive metallic nanoparticles should incorporate delivery methods that maintain high groundwater pore velocities during injection to increase advective transport distances (e.g. groundwater circulation wells). Also, source zones with abundant stationary contaminant mass that is accessible by advective transport should be targeted for remediation with the nanoparticles, as opposed to portions of dissolved plumes, in order to maximize the in situ destruction of contaminants.
    Journal of contaminant hydrology 07/2010; 116(1-4):35-46. · 2.01 Impact Factor
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    ABSTRACT: This study pilot-tested carboxymethyl cellulose (CMC) stabilized zero-valent iron (ZVI) nanoparticles (with a trace amount of Pd catalyst) for in situ destruction of chlorinated ethenes such as perchloroethylene (PCE) and trichloroethylene (TCE) and polychlorinated biphenyls (PCBs) that had been in groundwater for decades. The test site was located in a well-characterized secondary source zone of PCBs and chlorinated ethenes. Four test wells were installed along the groundwater flow direction (spaced 5 ft apart), including one injection well (IW), one up-gradient monitoring well (MW-3) and two down-gradient monitoring wells (MW-1 and MW-2). Stabilized nanoparticle suspension was prepared on-site and injected into the 50-ft deep, unconfined aquifer. Approximately 150 gallons of 0.2 g/L Fe-Pd (CMC = 0.1 wt%, Pd/Fe = 0.1 wt%) was gravity-fed through IW-1 over a 4-h period (Injection #1). One month later, another 150 gallons of 1.0 g/L Fe-Pd (CMC = 0.6 wt%, Pd/Fe = 0.1 wt%) was injected into IW-1 at an injection pressure <5 psi (Injection #2). When benchmarked against the tracer, approximately 37.4% and 70.0% of the injected Fe was detected in MW-1 during injection #1 and #2, respectively, confirming the soil mobility of the nanoparticles through the aquifer, and higher mobility of the particles was observed when the injection was performed under higher pressure. Rapid degradation of PCE and TCE was observed in both MW-1 and MW-2 following each injection, with the maximum degradation being observed during the first week of the injections. The chlorinated ethenes concentrations gradually returned to their pre-injection levels after approximately 2 weeks, indicating exhaustion of the ZVI's reducing power. However, the injection of CMC-stabilized nanoparticle and the abiotic reductive dechlorination process appeared to have boosted a long-term in situ biological dechlorination thereafter, which was evidenced by the fact that PCE and TCE concentrations showed further reduction after two weeks. After 596 days from the first injection, the total chlorinated ethenes concentration decreased by about 40% and 61% in MW-1 and MW-2, respectively. No significant long-term reduction of PCB 1242 was observed in MW-1, but a reduction of 87% was evident in MW-2. During the 596 days of testing, the total concentrations of cis-DCE (dichloroethylene) and VC (vinyl chloride) decreased by 20% and 38% in MW-1 and MW-2, respectively. However, the combined fraction of cis-DCE and VC in the total chlorinated ethenes (PCE, TCE, cis-DCE and VC) increased from 73% to 98% and from 62% to 98%, respectively, which supports the notion that biological dechlorination of PCE and TCE was active. It is proposed that CMC-stabilized ZVI-Pd nanoparticles facilitated the early stage rapid abiotic degradation. Over the long run, the existing biological degradation process was boosted with CMC as the carbon source and hydrogen from the abiotic/biotic processes as the electron donor, resulting in the sustained enhanced destruction of the chlorinated organic chlorinated ethenes in the subsurface.
    Water Research 04/2010; 44(7):2360-70. · 4.66 Impact Factor
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    ABSTRACT: Mercury (Hg) immobilization using stabilized iron sulfide (FeS) nanoparticles was investigated through a series of batch and column experiments. The nanoparticles were prepared using a low-cost, food-grade cellulose (sodium carboxymethyl cellulose, CMC) as the stabilizer. The hydrodynamic diameter of fresh FeS-CMC nanoparticles was measured to be 38.5+/-5.4nm. Batch tests showed that the nanoparticles can effectively immobilize Hg in a clay loam sediment. The Hg distribution coefficient for the nanoparticles was determined to be 8930+/-1480L/g, which is >4 orders of magnitude greater than for the sediment. When the Hg-laden sediment was treated at an FeS-to-Hg molar ratio of 26.5, the Hg concentration leached into water was reduced by 97% and the TCLP (toxicity characteristic leaching procedure) leachability of Hg was reduced by 99%. Column tests showed that water-leachable mercury from the sediment containing 3120mg/L Hg was reduced by 67% and the TCLP leachability by >77% when the sediment was treated with 67 pore volumes (PVs) of a 0.5g/L FeS nanoparticle suspension. Column tests proved that the stabilized nanoparticles were highly mobile in the sediment and full breakthrough of the nanoparticles occurred at approximately 18 PVs.
    Water Research 08/2009; 43(20):5171-9. · 4.66 Impact Factor
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    ABSTRACT: We present here a straightforward, one-step “green” approach for preparing Pd nanoparticles of controlled size and size distribution. The new catalysts were synthesized using a low-cost, biocompatible cellulose, sodium carboxymethyl cellulose (CMC), as a stabilizer and ascorbic acid as a reducing agent at temperatures ranging from 22 to 95 °C. The mean size and polydispersivity (expressed as standard deviation, SD) of the Pd nanoparticles was exponentially reduced by increasing the preparation temperature from 22 to 95 °C. At 95 °C, nearly monodisperse Pd nanoparticles were obtained with a mean diameter of 3.6 nm (SD = 0.5 nm). The Pd nanoparticles exhibited high catalytic reactivity when tested for hydrodechlorination of trichloroethene in the presence of H2. The observed pseudofirst-order reaction rate constant, kobs, was up to 692 L g−1 min−1, which is comparable to the Pd nanoparticles synthesized per the conventional borohydride reduction method. This new approach not only offers a simple way to manipulate particle size and size distribution but also eliminates the need of borohydride, which is much more costly and less environmentally friendly than the ascorbic acid used in this work.
    Industrial & Engineering Chemistry Research - IND ENG CHEM RES. 06/2009; 48(14).
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    ABSTRACT: Carboxymethyl cellulose (CMC) can facilitate in situ delivery of zero-valent iron (ZVI) nanoparticles in contaminated aquifer. This work investigated transport of CMC-stabilized ZVI nanoparticles (CMC-Fe) using column breakthrough experiments and model simulations. The nanoparticles (18.1+/-2.5 nm) were transportable through four saturated model porous media: coarse and fine glass beads, clean sand, and sandy soil. The transport data were interpreted using both classical filtration theory and a modified convection-dispersion equation with a first-order removal rate law. At full breakthrough, a constant concentration plateau (Ce/C0) was reached, ranging from 0.99 for the glass beads to 0.69 for the soil. While Brownian diffusion was the predominant mechanism for particle removal in all cases, gravitational sedimentation also played an important role, accounting for 30% of the overall single-collector contact efficiency for the coarse glass beads and 6.7% for the soil. The attachment efficiency for CMC-Fe was found to be 1-2 orders of magnitude lower than reported for ZVI nanoparticles stabilized with other commercial polymers. The particle removal and travel distance are strongly dependent on interstitial flow velocity, but only modestly affected by up to 40 mM of calcium. Simulation results indicate that once delivered, 99% of the nanoparticles will be removed by the soil matrix within 16 cm at a groundwater flow velocity of 0.1 m/day, but may travel over 146 m at flow velocity of 61 m/day.
    Journal of Colloid and Interface Science 05/2009; 334(1):96-102. · 3.55 Impact Factor
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    ABSTRACT: In this paper, we present a "green" and size-controlled seed-mediated growth method by which differently sized palladium (Pd) nanoparticles, spanning from 3.4 to 7.6 nm, with an increment of 1.4 nm, were synthesized. Monodisperse Pd nanoparticles (ca. 3.4 nm, standard deviation = 0.7 nm) were first synthesized and stabilized in an aqueous solution at 95 degrees C using nontoxic ascorbic acid and sodium carboxymethyl cellulose (CMC) as reducing agent and capping agent, respectively. These Pd nanoparticles were subsequently employed as seeds on the surface of which fresh Pd (2+) ions were reduced by the weak reducing agent ascorbic acid. Optimal conditions were determined that favored the homogeneous and sequential accumulation of Pd atoms on the surface of the Pd seeds, rather than the formation of new nucleation sites in the bulk growth solution, thereby achieving atomic-level control over particle sizes. The adsorbed CMC molecules did not inhibit the addition of Pd atoms onto the seeds during the growth but provided stabilization of the Pd nanoparticles in aqueous solution after the growth. Potential mechanisms that underpin this seed-mediated growth process are provided and discussed. One advantage of this seed growth process is that it provides stoichiometric control over the size of the Pd nanoparticles by simply varying Pd(2+) added during the growth stage. Furthermore, the use of ecologically friendly reagents, such as water (solvent), CMC (capping agent), and ascorbic acid (reducing agent), in both the seed synthesis and subsequent seed-mediated growth provides both "green" and economic attributes to this process.
    Langmuir 04/2009; 25(12):7116-28. · 4.38 Impact Factor
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    ABSTRACT: Remediation of soils and sediments contaminated with chlorinated solvents and heavy metals has been a major environmental challenge for decades. Yet, cost-effective in situ remediation technology remains lacking. While zero-valent iron (ZVI) nanoparticles have been found effective in reducing various chlorinated hydrocarbons, rapid agglomeration of the particles rendered the particles undeliverable in soils. To address this issue, we developed a particle stabilization strategy using starch or carboxymethyl cellulose (CMC) as a stabilizer. We found that the use of the stabilizers can facilitate controlling the size, delivery and transport of the nanoparticles and resulted faster reaction rate. The stabilized ZVI nanoparticles can be readily delivered to the targeted contaminated zones, and can in situ effectively destroy chlorinated solvents such as trichloroethylene (TCE). Bench- and field scale experimental data showed that the stabilized ZVI nanoparticles can in situ completely and rapidly dechlorinate TCE in water and soils. Field tests also indicated that the application of stabilized ZVI nanoparticles can boost long-term biodegradation of chlorinated solvents. Based on the stabilized ZVI nanoparticles, we also developed an technology for in situ reductive immobilization of Cr(VI) in soils and groundwater. When a Cr(VI)-laden soil column was treated with 5.7 bed volumes of 0.06 g/L of the nanoparticles at pH 5.60, only 4.9% of the total Cr was eluted compared to 12% for untreated soil under otherwise identical conditions. Moreover, the ZVI treatment reduced the TCLP leachability of Cr in the soil by 90%, and the California WET leachability by 76%. The stabilized nanoparticles may offer a powerful alternative for in situ dechlorination or in situ reductive immobilization of redox-sensitive heavy metals.
    2008 AIChE Annual Meeting; 11/2008
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    ABSTRACT: In this paper, we present a straightforward and environmentally friendly aqueous-phase synthesis of small Pd nanoparticles (approximately 2.4 nm under the best stabilization) by employing a "green", inexpensive, and biodegradable/biocompatible polysugar, sodium carboxymethylcellulose (CMC), as a capping agent. The Pd nanoparticles exhibited rather high catalytic activity (observed pseudo-first-order reaction kinetic rate constant, k(obs), is up to 828 L g(-1) min(-1)) for the hydrodechlorination of environmentally deleterious trichloroethene (TCE) in water. Fourier transform IR (FT-IR) spectra indicate that CMC molecules interact with the Pd nanoparticles via both carboxyl (-COO-) and hydroxyl (-OH) groups, thereby functioning to passivate the surface and suppress the growth of the Pd nanoparticles. Hydrodechlorination of TCE using differently sized CMC-capped Pd nanoparticles as catalyst was systematically investigated in this work. Both the catalytic activity (k(obs)) and the surface catalytic activity (turnover frequency, TOF) of these CMC-capped Pd nanoparticles for TCE degradation are highly size-dependent. This point was further verified by a comparison of the catalytic activities and surface catalytic activities of CMC-capped Pd nanoparticles with those of beta-D-glucose-capped Pd and neat Pd nanoparticles for TCE degradation.
    Langmuir 02/2008; 24(1):328-36. · 4.38 Impact Factor
  • Feng He, Dongye Zhao
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    ABSTRACT: This study investigated the effects of carboxymethyl cellulose (CMC) as a stabilizer on the reactivity of CMC-stabilized Fe-Pd bimetallic nanoparticles toward trichloroethene (TCE). Overall, the particle stabilization prevented particle agglomeration and resulted in greater particle reactivity. The pseudo-first order TCE degradation rate increased from 0.86 h−1 to 6.8 h−1 as the CMC-to-Fe molar ratio increased from 0 to 0.0124. However, a higher CMC-to-Fe ratio inhibited the TCE degradation. Within the same homologous series, CMC of greater molecular weight resulted in more reactive nanoparticles for TCE hydrodechlorination. Hydrogen (either residual hydrogen from zero-valent iron (ZVI) nanoparticle synthesis or hydrogen evolved from ZVI corrosion) can serve as effective electron donors for TCE dechlorination in the presence of Pd (either coated on ZVI or as separate nanoparticles). Decreasing reaction pH from 9.0 to 6.0 increased the TCE reduction rate by 11.5 times, but enhanced the Fe corrosion rate by 31.4 times based on the pseudo-first order rate constant. Decreasing pH also shifted the rate controlling step of TCE reduction from Fe corrosion to hydrodechlorination. Ionic strength (<0.51 M) did not significantly affect the TCE reduction.
    Applied Catalysis B: Environmental. 01/2008;
  • Feng He, Dongye Zhao
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    ABSTRACT: Zerovalent iron (ZVI) nanoparticles of various sizes were synthesized by applying various types of carboxymethyl cellulose (CMC) as a stabilizer. At an initial Fe2+ concentration of 0.1 g/L and with 0.2% (w/w) of CMC (Mr = 90 000), nanoparticles with a hydrodynamic diameter of 18.6 nm were obtained. Smaller nanoparticles were obtained as the CMC/Fe2+ molar ratio was increased. When the initial Fe2+ concentration was increased to 1 g/L, only 1/4 of the CMC was needed to obtain similar nanoparticles. On an equal weight basis, CMC with a greater Mr or higher D.S. (degree of substitution) gave smaller nanoparticles, and lower the synthesizing temperature favored the formation of smaller nanoparticles. It is proposed that CMC stabilizes the nanoparticles through the accelerating nucleation of Fe atoms during the formation of ZVI nanoparticles and, subsequently, forms a bulky and negatively charged layer via sorption of CMC molecules on the ZVI nanoparticles, thereby preventing the nanoparticles from agglomeration through electrosteric stabilization. In agreement with the classical coagulation theory, the presence of high concentrations of cations (Na+ and Ca2+) promoted agglomeration of the nanoparticles. The strategy for manipulating the size of the ZVI nanoparticles may facilitate more effective applications of ZVI nanoparticles for in situ dechlorination in soils and groundwater.
    Environmental Science and Technology 10/2007; 41(17):6216-21. · 5.48 Impact Factor
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    ABSTRACT: This study reports a new strategy for stabilizing palladized iron (Fe−Pd) nanoparticles with sodium carboxymethyl cellulose (CMC) as a stabilizer. Compared to nonstabilized Fe−Pd particles, the CMC-stabilized nanoparticles displayed markedly improved stability against aggregation, chemical reactivity, and soil transport. Transmission electron microscopy (TEM) and dynamic light scattering (DLS) analyses indicated that the CMC-stabilized nanoparticles with a diameter <17.2 nm are highly dispersed in water. Fourier transform infrared (FTIR) spectroscopy results suggested that CMC molecules were adsorbed to iron nanoparticles primarily through the carboxylate groups through monodentate complexation. In addition, −OH groups in CMC were also involved in interactions with iron particles. Batch dechlorination tests demonstrated that the CMC-stabilized nanoparticles degraded trichloroethene (TCE) 17 times faster than their nonstabilized counterparts based on the initial pseudo-first-order rate constant. Last, column tests showed that the stabilized nanoparticles can be readily transported in a loamy-sand soil and then eluted completely with three bed volumes of deionized (DI) water.
    Industrial & Engineering Chemistry Research 11/2006; 46(1). · 2.24 Impact Factor
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    Feng He, Dongye Zhao
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    ABSTRACT: Dechlorination of TCE and PCBs using bimetallic nanoparticles has received increasing interest in recent years. However, due to the extremely high reactivity, nanoparticles prepared using current methods tend to either react with surrounding media or agglomerate, resulting in the formation of much larger flocs and significant loss in reactivity. To overcome these drawbacks, we developed a simple and green approach for synthesizing palladized iron (Fe-Pd) nanoparticles. We modified the conventional methods by applying a water-soluble starch as a stabilizer. The starched nanoparticles displayed much less agglomeration but greater dechlorination power than those prepared without a stabilizer. TEM analyses indicated that the starched nanoparticles were present as discrete particles as opposed to dendritic flocs for nonstarched particles. The mean particle size was estimated to be 14.1 nm with a standard deviation of 11.7 nm, which translated to a surface area of approximately 55 m2 g(-1). While starched nanoparticles remained suspended in water for days, nonstarched particles agglomerated and precipitated within minutes. The starched nanoparticles exhibited markedly greater reactivity when used for dechlorination of TCE or PCBs in water. At a dose of 0.1 g L(-1), the starched particles were able to destroy 98% of TCE (C0 = 25 mg L(-1)) within 1 h. While trace amounts (<25 microg L(-1)) of 1,1-DCE were detected in the initial stage (<20 min) of degradation, no other intermediate byproducts such as vinyl chloride, cis-, or trans-dichloroethene were detected. The starched nanoparticles at approximately 1 g L(-1) were able to transform over 80% of PCBs (C0 = 2.5 mg L(-1)) in less than 100 h, as compared to only 24% with nonstarched Fe-Pd nanoparticles. The application of an innocuous stabilizer may substantially enhance the performances of palladized iron nanoparticles for environmental applications.
    Environmental Science and Technology 05/2005; 39(9):3314-20. · 5.48 Impact Factor