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Reduction of chlorinated methanes with nano-scale Fe particles Effects

Reduction of chlorinated methanes with nano-scale Fe particles:Effects of amphiphiles on the dechlorination reaction and two-parameter regression for kinetic prediction

Jing Feng *,Bao-wei Zhu,Teik-Thye Lim

School of Civil and Environmental Engineering,Nanyang Technological University,50Nanyang Avenue,Singapore 639798,Republic of Singapore

a r t i c l e i n f o Article history:

Received 1April 2008

Received in revised form 12August 2008Accepted 13August 2008

Available online 21September 2008Keywords:

Nano-scale Fe particle Carbon tetrachloride Chloroform Humic acid Surfactant

a b s t r a c t

The in?uences of amphiphiles,including humic acid (HA)and various types of surfactants,on dechlori-nation of carbon tetrachloride (CTC)and chloroform (CF)by the nano-scale Fe particles were investigated.Since the amphiphiles would modify the surface tension between the liquid–liquid and solid–liquid interface,in the presence of amphiphile matrix solution the Fe corrosion rate and the parent compound dechlorination rate would be different from those in the ultrapure water.Among the four amphiphile solutions,Fe corrosion rate was the highest in the anionic surfactant sodium dodecyl sulfate (SDS)solu-tion,presumably due to the existence of chemisorption between the hydrophilic head of SDS and Fe par-ticles.The dechlorination rates of CTC and CF could be described with the pseudo-?rst order kinetic model.The in?uences of amphiphiles on the dechlorination reaction rate were related to the species of parent compound and concentration of the matrix solution.The in?uences of HA on the dechlorination of CTC and CF were the most signi?cant compared to other matrix solutions.At relatively low HA concen-tration (<0.1g L à1),the HA molecules (serving as electron transfer mediator)would signi?cantly acceler-ate the dechlorination rate of CF.The two-parameter regression with energy of the lowest unoccupied molecular orbital (E LUMO )and HA concentration as the descriptors was developed to predict the speci?c reduction rate constants of chlorinated methanes in HA solution.The analysis of variance (ANOVA)indi-cated the existence of signi?cant relationship between the dechlorination rate constants and the two descriptors.

1.Introduction

Treatment with zero-valent Fe (ZVI)has been proven to be a feasible option for removal of halogenated organic compounds (HOCs)(Choe et al.,2001;Lien and Zhang,2001;Schrick et al.,2002;Doong and Lai,2005;Liu et al.,2005;Nurmi et al.,2005).In the absence of electron transfer mediator,the reductive dechlo-rination reaction with ZVI is generally a surface mediated reaction,which requires direct contact between the HOCs and Fe particles.The presence of co-contaminants with different chemical proper-ties in water may show signi?cant in?uence on the dechlorination ef?ciency of HOCs.One important group of co-solutes that can in?uence the dechlorination kinetics is amphiphilic compounds (Chen et al.,2001;Tratnyek et al.,2001;Doong and Lai,2005;Li et al.,2006).The main effects of amphiphiles on the dechlorination reaction include solubilization enhancement,sorption enhance-ment,competitive sorption and mediation of electron transfer (Tratnyek et al.,2001).

The most commonly found natural amphiphiles in wastewater and natural water are natural organic matters (NOMs),e.g.,humic acids (HAs)and fulvic acids (FAs).The humic substances include a skeleton of alkyl and aromatic units with various functional groups attached,such as carboxylic acid,phenolic hydroxyl,and quinine groups (Giasuddin et al.,2007).Klausen et al.(2003)found that NOMs had adverse effect on the reduction of chlorinated carbons and nitroaromatic compounds by granular Fe in their column reduction system.Tratnyek et al.(2001)showed that HAs had greater inhibitory effect than FAs on carbon tetrachloride (CTC)reduction.The adsorption of HA on ZVI surface appeared to be the main reason for the decreased contaminant removal ef?ciency (Tratnyek et al.,2001;Klausen et al.,2003).Giasuddin et al.(2007)con?rmed that nano-scale ZVI and HA can form an inner-sphere surface complexation.Meanwhile,the accumulation of HA on the iron–water interface could also inhibit the ZVI corrosion,which might adversely affect the contaminant reduction (Bouayed et al.,1998).Doong and Lai (2005)reported the inhibition effects of HA on perchloroethylene (PCE)dechlorination by Pd/Fe particles.After 24h equilibrium between HA and Pd/Fe,the PCE dechlorination rate increased with the increasing HA concentration,probably

*Corresponding author.Tel.:+6567906814.E-mail address:fengjing@https://www.wendangku.net/doc/2c1773520.html,.sg (J.Feng).

Chemosphere 73(2008)

1817–1823

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Chemosphere

j o u r n a l h o m e p a g e :w w w.e l s e v i e r.c o m /l o c a t e /c he m o s p h e r

due to electron shuttling between the Pd/Fe and PCE through the adsorbed HA layer.

Anthropogenic surfactants have been extensively used to mod-ify the surface or interfacial properties.Surfactant micellar cataly-ses have been widely applied in industry.In contaminated site remediation,surfactants are added to the saturated zone to mobi-lize the non-aqueous phase liquids.Therefore,surfactant is another important group of amphiphiles often found in wastewater and natural water systems.The in?uences of surfactants on the reduc-tion kinetics of HOCs are usually related to the chemical character-istics of HOCs and the surfactant used.Tratnyek et al.(2001) reported that the in?uences of surfactants on the ZVI reduction system were moderate.Others have found that some surfactants could effectively improve the performance of ZVI(Larson et al., 2000;Alessi and Li,2001;Zhang et al.,2002;Li et al.,2006).Studies on PCE dechlorination showed that in the presence of cationic sur-factant hexadecyltrimethylammonium(HDTMA)the reduction rate increased signi?cantly(Alessi and Li,2001;Zhang et al., 2002;Li et al.,2006).Sayles et al.(1997)indicated that the pres-ence of non-ionic surfactant Triton X-114would increase DDT reduction rate.The higher reduction rate of PCE observed by Li et al.(2006)was attributed to the higher distribution coef?cient of PCE adsorbed on the surfactant-modi?ed ZVI.Loraine(2001)ob-served that once the concentration of anionic sodium dodecyl sul-fate(SDS)was above its critical micelle concentration(CMC),PCE and trichloroethylene(TCE)dechlorination reactions would be inhibited.Alessi and Li(2001)observed that the PCE reduction rate would increase as the chain length of surfactant hydrophobic tail increased.They attributed this phenomenon to the better admi-celle formation of surfactants with longer hydrophobic tail,which promoted PCE partition in the aqueous phase and on the ZVI sur-face reactive sites.Signi?cant amount of reactive intermediate (TCE)was observed in the PCE reduction system with the presence of HDTMA-modi?ed ZVI(Li et al.,2006),indicating the favoring of hydrogenolysis over b-elimination in the HDTMA-modi?ed dechlo-rination system.

In this study,the effects of various amphiphiles on the reduc-tion of CTC and chloroform(CF)with the nano-scale ZVI particles were investigated.The amphiphiles included a natural amphiphile (e.g.HA)and three different anthropogenic surfactants,e.g.anionic SDS,cationic cetyltrimethylammonium bromide(CTAB),and non-ionic nonylphenol ethoxylate(NPE).A two-parameter regression model was developed for prediction of the dechlorination reaction kinetics.

2.Materials and methods

2.1.Chemicals

The chemicals used are:CTC(BDH,UK),CF(Merck,Germany), methylene chloride(DCM)(J.T.Baker,NJ),ferrous sulfate(FeS-O4á7H2O)(Reachim,Russia),methane(5%,National Oxygen Pte Ltd,Singapore),sodium hydroxide(Merck,Germany),sodium borohydride(Lancaster,UK),SDS(J.T.Baker,NJ),NPE(Aldrich, USA),CTAB(Aldrich,USA),methanol(Merck,Germany),and HA (sodium salt)(Aldrich,USA).All the aqueous solutions were pre-pared with the ultrapure water(18.2M X cm).

2.2.Nano-scale particles preparation and characterization

The nano-scale ZVI particles were synthesized by adding so-dium borohydride(NaBH4)solution to ferrous sulfate solution. The detailed procedure has been described in the previous publica-tion(Feng and Lim,2005).Brunauer–Emmett–Teller(BET)surface area analyses of the nano-scale Fe particles were analyzed with Quanta Chrome autosorb automated gas absorption system. X-ray diffraction(XRD)analyses of mineralogical characteristics of the synthesized nano-scale particles were carried out with Bru-ker Dt8advanced XRD diffractometer at40kV and40mA.Copper metal radiation was used to produce X-rays(k=1.5406?).The scan rate was set at2h of0.75°per min.Transmission electron microscope(TEM)images were obtained with a JEM-2010micro-scope at200kV.The particles dispersed in methanol were mounted on a carbon coated copper grid before analysis.The water wettability of the Fe particles was determined by observing the contact angles between the particles and various solutions with contact angle system OCA20.The surface charge of the Fe particles in the solution was measured with alkalimetric and acidimetric titration method(Stumm,1992).

2.3.Adsorption isotherm and Fe corrosion experiments

The adsorption of amphiphiles(e.g.HA,anionic SDS,non-ionic NPE,and cationic CTAB)on the nano-scale ZVI surface was investi-gated in the single species batch adsorption system with60mL TFE-sealed serum bottles.The freshly synthesized0.1g nano-scale ZVI particles were soaked in40mL amphiphile solution.The sur-factant concentrations investigated ranged from lower than CMC to several times of CMC.The HA concentrations investigated were from50mg Là1to1000mg Là1.After2h of equilibration,20mL solution was withdrawn with syringe and?ltered through 0.45l m nylon membrane syringe?lter.The amphiphile concen-trations were determined by total organic carbon analyzer (ASI-V,Shimadzu)after dilution of the samples to below 1000mg-C Là1.After adsorption experiments,the particles were separated with glass?ber membrane,and rinsed with ultrapure water for three times.The particles were dried in vacuum freeze drier over night.Spectra were carried out with spectrum GX Fou-rier transform infrared spectrometer(100scans)to detect the functional groups on the ZVI surface.

The ZVI corrosion experiments were carried out in the similar batch systems.The amounts of hydrogen evoluted and Fe ion lea-ched to the aqueous phase were monitored to assess the extent of Fe corrosion in the amphiphile solution.The hydrogen amounts evoluted in the various amphiphile solutions were compared with the percentages of hydrogen gas in the headspace.Hydrogen per-centage at the end of the experiments(at96h)was determined by gas chromatography(GC,HP5890)equipped with thermal con-ductivity detector.The dissolved ferrous/ferric ion was measured with the inductively coupled plasma optical emission spectrome-ter(Perkin–Elmer,Optima2000DV).

2.4.Dechlorination experiments

Batch reduction experiments were performed with60mL TFE-sealed serum bottles covered with aluminum foil.The initial pH of ultrapure water was adjusted to7.0with3.8M sodium hydroxide.The batch tests were carried out with20mL headspace left in each bottle.The ZVI loading in the experiments was 2.5g Là1.CTC or CF was introduced to the batch reduction system through a methanol spike that produced an initial concentration of 80mg Là1.The bottles were placed horizontally on an orbital sha-ker which operated at300rpm at room temperature(23±1°C). The concentrations of CTC or CF as well as their transformation intermediates and end products were determined by periodically removing80l L gas phase from the vials with a gas tight syringe. The gas withdrawn was then directly injected to GC with?ame ionization detector(FID)and an HP-5-mega column(30m-long?0.53mm-ID with1.5l m?lm thickness).Temperature con-ditions of GC/FID were programmed as follows:oven temperature at110°C,injector port temperature at200°C,and detector tem-

1818J.Feng et al./Chemosphere73(2008)1817–1823

perature at250°C.In the parallel experiment,5mL solution was withdrawn from the sacri?ced bottle for chloride ion analysis.Dis-solved chloride ion was measured with?ow injection analysis with ion chromatography(Lachat,QuickChem8000).

3.Results and discussion

3.1.Characterizations

Diameters of the nano-scale ZVI particles observed with TEM were smaller than100nm(Feng and Lim,2005).The BET surface area of the ZVI particles was around26m2gà1.Peaks identi?ed on the XRD patterns were con?rmed to associate with the body centered cubic Fe(?gure not shown).The peaks belonging to iron oxides(e.g.magnetite,etc.)were not apparent in the XRD pattern of the freshly synthesized ZVI particles.After ageing for over24h,

the peaks belonging to magnetite began to appear in the XRD pat-tern.The fresh particle showed wetting property with a contact an-gle of21°with ultrapure water.After24h,due to the formation of magnetite,the contact angle between Fe and ultrapure water in-creased to77°,which indicated that the particles became increas-ingly hydrophobic with the elapse of time.The contact angle was lower between ZVI and surfactant solution compared to that be-tween ZVI and ultrapure water,since the surfactant can decrease the surface tension of the liquid–liquid and liquid–solid interfacial energy.The point of zero charge(PZC)determined from the alkali-metric and acidimetric titration curves was around pH7.9,which agreed with the observations reported by other researchers(Kanel et al.,2005).

Fig.1shows the adsorption isotherms of various amphiphiles on the nano-scale ZVI particles,plotted on the log–log scale.A typ-ical four-region adsorption isotherm for amphiphile adsorption on a hydrophilic solid surface was shown previously(Atkin et al., 2003;Paria and Khilar,2004).At low concentrations,a linear rela-tionship exists between the amount of amphiphile adsorbed and the corresponding aqueous phase concentration.Further increase in the amount of adsorption enhances the molecular repulsion through the hydrophobic tails,which leads to decreasing slope of the adsorption isotherm.When the aqueous phase concentration reaches CMC,the maximum adsorption by the particle surface is achieved,limited by constant monomer activity in solution as a result of bulk micellization.

SDS adsorption was by far higher than those of HA,cationic CTAB and non-ionic NPE.It was proposed to be due to the occur-rence of the speci?c interaction between the ZVI particles and the sulfonate functional group on SDS hydrophilic head.Fig.2pre-sents the FTIR spectra of the ZVI particles after soaking in various amphiphile solutions.For the ZVI samples soaked in the NPE,HA and CTAB solutions,no apparent peaks were identi?ed.It was probably because the Fe particles did not retain the weakly-ad-sorbed layer during the sample treatment process for the FTIR analysis.Although Xie and Shang(2005)observed the aromatic COOH and hydroxyl or phenolic OH functional groups of HA ad-sorbed on the ZVI surface in their FTIR spectra,similar results were not found in this study.For the Fe samples soaked in SDS solution, peaks belonging to SDS were identi?ed on the FTIR spectrum, which was proposed to be due to the formation of speci?c interac-tion(chemisorption)between the SDS and Fe particles.The sulfo-nate hydrophilic head of SDS would combine with the ferrous/ ferric ion on the iron particle surface to form a compound similar to green rust II(Genin et al.,1998).

During the dechlorination of HOCs in the anoxic system,ZVI particles undergo anodic reaction which release electrons to HOCs and water.Meanwhile,the electron acceptors(HOCs or water)will be reduced accordingly,as illustrated below

Anodic reaction:Fe0!Fe2tt2eàe1TCathodic reaction:C x H y X ztz Htt2z eà!C x H ytztz Xàe2T2H2Ot2eà!H2"t2OHàe3TIt is noted that in the dechlorination experiments,the molar amounts of HOCs are usually negligible as compared to those of Fe particles and water.Therefore,monitoring of the Fe released and hydrogen evolution would be helpful to provide indication of the ZVI corrosion rates and the corresponding cathodic reaction rates in the presence of an amphiphile.Fig.3shows the concentra-tions of Fe released to the aqueous phase and hydrogen percent-ages in the headspace after96h reaction.The amounts of hydrogen evoluted in all amphiphile solutions were higher than

Hydrogen

J.Feng et al./Chemosphere73(2008)1817–18231819

that in the ultrapure water.Based on these observations,a general conclusion in this study was that amphiphiles could accelerate Fe corrosion rate.Among the amphiphile solutions,SDS solution emitted the highest amount of hydrogen but the concentration of Fe released to the aqueous phase was the lowest.For the SDS con-centrations higher than CMC,the nano-scale ZVI particles would partition in the interior of SDS micelles which avoided the Fe par-ticles from aggregation.The larger contact area between the parti-cles and the solution would lead to the higher Fe corrosion rate.The lower Fe aqueous phase concentration in SDS system,which seemed to be contradictory to the hydrogen evoluted percentage result,was proposed to be due to the formation of speci?c interac-tion between the ferrous/ferric ion and the sulfonate group of SDS,as discussed earlier.As shown in Fig.3,HA solution appeared to signi?cantly promote iron corrosion.Relatively low amount of fer-rous/ferric ion leached out was due to the existence of various functional groups (e.g.hydroxyl and carboxyl)on the HA molecular skeleton,which could form complexes with ferrous/ferric ion through complexiation or chelation (Tan,2003).3.2.In?uences on reduction kinetics

A previous study showed that the transformations of chlori-nated methanes with the nano-scale ZVI particles in the absence of amphiphile usually follow the pseudo-?rst order kinetics (Feng and Lim,2005).The results of this study indicated that transforma-tion of CTC and CF with the presence of amphiphile could also be described with the pseudo-?rst order kinetic model.An exception case was that in the presence of SDS solution the reduction of CF deviated from the ?rst-order kinetics after 24h reaction (?gure not shown).The deviation might be related to the highest corro-sion rate of ZVI in SDS solution and the longer reaction time of CF.At the initial 24h,the amount of target compound was negligi-ble compared to that of the ZVI particles,which satis?ed the assumption of a pseudo-?rst order kinetics.However,with the elapse of time,large amount of Fe was consumed or blocked in the interior of SDS micelles,which gradually made the amount of ZVI and CF comparable.The assumption of pseudo-?rst order kinetics was broken,and led to the deviation.Therefore,the reduc-tion rate constants of CF in SDS solution were regressed with the data within 24h.The pseudo-?rst order rate constants (k obs )and speci?c reduction rate constants (k SA )of CTC and CF dechlorination are summarized in Table 1.Generally,in the presence of the same amphiphile solution,the observed reduction rate constants of CTC were always higher than those of CF.The amphiphiles promoted CF reduction,but they could affect CTC reduction adversely or bene?-cially,depending on the amphiphile type.

In the absence of electron transfer mediators for reductive dechlorination reaction,CTC or CF must be ?rst adsorbed to the Fe surface,where they could interact with reactive or nonreactive sites.Dechlorination occurred at the reactive sites,and adsorption occurred at the nonreactive sites.The presence of amphiphiles in the nano-scale ZVI/water system could have multiple effects on CTC and CF reductive dechlorination processes.The effects in-cluded (1)enhancing solubilization of CTC and CF,(2)facilitating adsorption of CTC and CF at the metal surface through formation of hydrophobic interfacial layer on the ZVI surface,(3)serving as competitive adsorbates competing for the ZVI surface reactive/non-reactive sites,(4)serving as alternative electron acceptors,(5)partitioning the nano-scale ZVI particles in the interior of mi-celle to avoid particles from aggregation,and (6)passivating ZVI surface via formation of precipitates or adsorption layer over the Fe surface reactive sites.For HA,other effects are possible in additional to the abovementioned,such as mediating electron transfer and sequestrating Fe ions which resulted in accelerating iron corrosion.As these effects are concurrently operational and their relative signi?cance also depends on the amphiphile–con-taminant interactions,their combined effects determine the ulti-mate in?uences of the amphiphiles on the dechlorination reaction.

In the presence of HA,the reduction rates of CTC and CF were affected differently.For example,in the solution with HA concen-tration at 50mg L à1,the observed reduction rate constant of CF was over 20times higher than that of the ultrapure water with the presence of ZVI particles.The CF reduction rate decreased with the increase of HA concentration from 200mg L à1to 1000mg L à1.On the contrary,the CTC reduction rate constants were slightly lower than that in the ultrapure water (observed from the data of the ?rst hour),but they also decreased gradually with the in-crease of HA concentration.With the CTC dechlorination,CF pro-duced as an intermediate could be rapidly degraded (?gure not shown),especially in HA solution.

One possible explanation for the accelerating effect of HA on the dechlorination reaction was that the adsorbed HA layer could serve as a mediator for electron transfer from the underlying Fe particles to overlying target compounds.The possible process of these func-tions could be illustrated as follows:

Table 1

Summary of reduction rate constants of CTC and CF with Fe

Concentration

CTC CF

k obs (h à1)

k SA (L h à1m à2)?10à2R 2k obs (h à1)?10à2k SA (L h à1m à2)?10à4R 2Ultrapure water 6.24±1.259.60±1.92>0.994 1.29±0.31 1.98±0.48>0.938HA

50mg L à1

4.50±0.49 6.92±0.75

>0.93532.4±3.5749.8±5.49>0.996200mg L à1 2.81±0.56 4.32±0.86>0.938 5.51±0.698.48±1.06>0.9821000mg L à1 2.68±0.47 4.12±0.72>0.995 2.21±0.43 3.40±0.66>0.931SDS

0.125CMC 1.18±0.23 1.82±0.35>0.961 2.07±0.71 3.18±1.09>0.9711CMC 1.47±0.25 2.26±0.38>0.966 5.39±0.468.29±0.71>0.974CMC =8.0mM 3CMC 1.60±0.08 2.46±0.12>0.9528.20±0.1312.6±0.20>0.951CTAB

0.1CMC 9.58±1.6914.7±2.60>0.990 1.54±0.10 2.37±0.15>0.9201CMC 7.74±1.0511.9±1.62>0.980 2.51±0.87 3.86±1.34>0.956CMC =1.0mM 10CMC 9.43±1.3614.5±2.09>0.989 3.65±0.54 5.48±0.83>0.953NPE

0.167CMC 5.17±0.077.95±0.11>0.994 1.51±0.12 2.32±0.18>0.9711CMC 9.62±1.7914.8±2.75>0.988 1.34±0.10 2.06±0.15>0.968CMC =0.1mM

10CMC

7.11±1.00

10.9±1.60

>0.955

1.02±0.33

1.57±0.51

>0.959

Fe 2+ HA (e - acceptor) Chlorinated compound Fe HA (e - donor) Dechlorination product

e -

e -1820J.Feng et al./Chemosphere 73(2008)1817–1823

In the dechlorination system,CTC and CF might be reduced through two mechanisms,including direct electron transfer on the Fe surface and indirect dechlorination mechanism.For the CTC reduction system,the dechlorination reaction could complete within half an hour,therefore the surface mediated mechanism would be the dominant one.Since the HA adsorbed on the Fe sur-face would affect the direct contact between the target compound and the ZVI surface reactive sites,the inhibition effect on CTC dechlorination was more signi?cant than that on CF.For the case of CF as the electron acceptor,the presence of small amount of HA would enhance the effect of electron shuttling.However,the excess HA molecule accumulated on the Fe surface blocked Fe sur-face reactive sites,and formed a mass transfer or electron transfer barrier for the target compounds.In addition,further increase of the HA concentration would increase the parent compound parti-tion in the bulk aqueous phase,thus limited its surface concentra-tion on ZVI.Thus,these aspects weakened the roles of HA in electron shuttling and decreased the CF reduction rates as the HA concentration increased.

In the presence of SDS,the CF dechlorination rate was higher than that in the ultrapure water.On the contrary,the CTC dechlo-rination was inhibited.As shown in the previous part,SDS could form speci?c adsorption layer on the Fe surface.Thus,it indicated that SDS molecules would compete for the Fe surface reactive sites with the target compounds and partially deactivate the Fe surface reactive sites.On another hand,the presence of SDS increased the hydrogen evoluted amount,which was bene?cial to hydrodechlo-rination mechanism.Once the SDS concentration was higher than CMC,the SDS micelles inhibited aggregation of the Fe particles through partitioning the Fe particles in the interior of the micelles. However,the SDS chemisorption layer interfered with the mass transfer of the target compound to the ZVI surface.Therefore,the presence of SDS in the Fe mediated dechlorination system appar-ently showed opposite in?uences on the CF dechlorination rate.

One conclusive observation was that CTAB accelerated the dechlorination rates of CTC and CF.Fig.3shows that CTAB did not apparently accelerate the Fe corrosion rate.The competition between the target compound and CTAB for the Fe direct reductive sites was not signi?cant in the dechlorination system.The effect of CTAB on the dechlorination reaction might be related to the con-centration of CTC or CF on the ZVI surface,which indicated that the presence of cationic surfactant CTAB could increase the surface concentration of CTC and CF on the ZVI(Larson et al.,2000;Alessi and Li,2001;Zhang et al.,2002;Li et al.,2006).

For the case of NPE,the in?uences on CTC and CF dechlorination were minor.Similar to CTAB,NPE did not serve as a competitor for the Fe reactive sites in the dechlorination system.The non-speci?c adsorption of NPE(e.g.electrostatic interactions,hydrophibic bonding,and van der Waals force)on the Fe particle surface was the dominant interaction.However,the non-speci?c adsorption, as a weak interaction,could be substituted by the strong interac-tions(e.g.,chemisorption)of the target compound.Therefore,the in?uences of NPE on the dechlorination reaction were insigni?cant.

3.3.Two-parameter regression for kinetics prediction

Goss and Schwarzenbach(2001)proposed that poly-parameter regression could be a powerful tool in the?eld of environmental partitioning processes.Liu et al.(2003)developed two-parameter linear relationships for the dechlorination rate constants of chloro-benzenes,which provided a possibility of application of the multi-parameter regression to kinetics prediction of the dechlorination reactions.The energy of the lowest unoccupied molecular orbital (E LUMO)and standard heat of formation are two independent descriptors in Liu’s optimal model.The lowest unoccupied molec-ular orbital(LUMO)is de?ned as the frontier molecular orbit where the electron transfer takes place(Fleming,1976).For kinetics pre-diction,E LUMO as a descriptor for linear free energy relationships is better than other descriptors(e.g.one-electron reduction potential E1,two-electron reduction potential E2,etc.),since each target compound has one E LUMO value,which is not in?uenced by the sol-vation of different halide ions.It essentially avoids the complica-tion arising from the in?uence of different reduction pathways and different groups of halogenated compounds.Therefore,in this study,E LUMO was chosen as one independent variable for linear free energy relationships.Meanwhile,amphiphile can in?uence the dechlorination kinetics signi?cantly,as discussed in Section3.2. The in?uences of amphiphile on the reduction kinetics are usually related to the properties of the parent compounds.HA was chosen as the representative amphiphile for the linear regression model, for its omnipresence in natural environment.Table2summarizes the speci?c reduction rate constants for CTC and CF with the Fe particles.

From the preliminary analysis,second order polynomial equa-tion with?ve parameters could not produce satisfactory regression equation.Therefore,to simplify the process of establishing correla-tion,third order polynomial equation was applied to model the possible relationships.Basically,ten terms are included in the gen-eral equation as follows:

log k SA?atbáE LUMOtcáHAtdáE LUMO HAteáE2

LUMO

tfáHA2tgáE2

LUMO

HAtháE LUMO HA2tiáE3

LUMO

tjáHA3e4Twhere a,b,c,d,e,f,g,h,i,j are constants;HA is the HA concentration in the aqueous phase(g Là1).The analysis of variance(ANOVA)is used to check the correlations of each term and the standard errors of the model.The regression process is explained below.Firstly,the equation was regressed with the ten coef?cients.Although the ad-justed R2was higher than0.95,the coef?cient of HA was calculated to be zero.Therefore,the term HA was deleted from the regression. The regression process was repeated until all the coef?cients were not equal to zero or the p-values of the coef?cients were all lower than0.01(which indicated that it was uncertain to reject the hypothesis that the coef?cient was equal to zero).

For the reduction of chlorinated methanes,the simulation equa-tion is eventually derived to be the following:

Table2

Speci?c reduction rate constants with Fe particles in HA solutions

No Compounds HA Concentration

(g Là1)

E LUMO

(mV)a

k SA

(L hà1mà2)

Log

k SA

1CTC0à3.28 1.28Eà1à0.89 2CTC0à3.28 1.15Eà1à0.94 3CTC0à3.289.06Eà2à1.04 4CTC0.05à3.289.91Eà2à1.00 5CTC0.05à3.288.49Eà2à1.07 6CTC0.05à3.288.20Eà2à1.09 7CTC0.2à3.28 4.77Eà2à1.32 8CTC0.2à3.28 4.88Eà2à1.31 9CTC0.2à3.28 3.32Eà2à1.48 10CTC1à3.28 4.80Eà2à1.31 11CTC1à3.28 4.18Eà2à1.38 12CTC1à3.28 3.37Eà2à1.47 13CF0à2.54 2.40Eà4à3.62 14CF0à2.54 2.17Eà4à3.66 15CF0à2.54 1.91Eà4à3.72 16CF0.05à2.54 5.38Eà3à2.27 17CF0.05à2.54 4.60Eà3à2.34 19CF0.2à2.549.23Eà4à3.03 20CF0.2à2.547.74Eà4à3.11 22CF1à2.54 2.94Eà4à3.53 23CF1à2.54 3.88Eà4à3.41 a Totten and Roberts(2001).

J.Feng et al./Chemosphere73(2008)1817–18231821

log k SA?à5:02t76:0HA3à91:7HA2à10:9E LUMO HA

à1:87E2

LUMO HAà0:105E3

LUMO

e5T

The R2of this equation was0.93,and the adjusted R2was equal to 0.91.Based on the ANOVA,the F value was calculated to be40.7, which was higher than2.85(f0.05,5,16),indicated the existence of signi?cant relationship between the log k SA and the two descriptors (e.g.HA concentration and E LUMO).The standard errors of coef?cient are shown in Table3.Fig.4shows the contour plots of the com-bined effects of E LUMO and HA concentration on the speci?c reduc-tion rate constants.Several general conclusions can be inferred from the?gure.Firstly,in the same HA solution,the more oxidiz-able species(represented by the lower E LUMO)showed higher spe-ci?c reduction rate constants.Secondly,if the concentration of HA solution was lower than0.1g Là1,the presence of HA could acceler-ate the dechlorination rate of chlorinated methanes with Fe parti-cles.However,this effect was more signi?cant for the less oxidizable species,such as CF(E LUMO=à2.54mV).

In principle,the derived equation and the plot can be used to predict the rate of reduction of other halogenated methanes with Fe particles in the presence of the HA solution.It is worthy to note that the stand error for the coef?cients(Table3)was slightly high. Therefore,adding more experimental points,such as adding other target compounds of similar group and more HA concentration lev-els,will improve the reliability of the regression equation.The pre-ceding correlation analysis for reductive dehalogenation of halogenated methanes with the nano-scale particles is still in a for-mative stage.To obtain more robust regression equation for prac-tical applications,more effort should be made on this aspect.

4.Conclusions

The in?uences of four amphiphile matrix solutions,including various surfactants and HA,on the dechlorination of CTC and CF were investigated.Generally,the effects of amphiphiles on dechlo-rination reaction were mainly related to following aspects,such as modifying the Fe surface properties through the formation of amphiphile adsorption layer,competing for the Fe surface reduc-tive sites and adsorption sites,and increasing the solubility of hydrophobic target compound,etc.The adsorption of amphiphiles might follow different mechanisms,for examples speci?c interac-tion(SDS),non-speci?c interaction(NPE),and combination of these two aspects(HA),etc.In the presence of amphiphiles,the reductions of CTC and CF by Fe particles followed the pseudo-?rst order kinetics.The in?uences of amphiphiles on the CF dechlorina-tion were more signi?cant than those on the CTC dechlorination. Two-parameter regression model developed in this study indicated that in the same HA solution the species with a lower E LUMO showed a higher speci?c reaction rate constant.HA solution with a relatively low concentration(<0.1g Là1)would accelerate the dechlorination of the chlorinated methanes,especially for the spe-cies with higher E LUMO.More species of halogenated methanes could be added to the regression list to increase the reliability of the two-parameter regression model for further practical applications.

References

Alessi, D.S.,Li,Z.,2001.Synergistic effect of cationic surfactants on perchloroethylene degradation by zero-valent iron.Environ.Sci.Technol.35, 3713–3717.

Atkin,R.,Craig,V.S.J.,Wanless,E.J.,Biggs,S.,2003.Mechanism of cationic surfactant adsorption at the solid–aqueous interface.Adv.Colloid Interface103,219–304. Bouayed,M.,Rabaa,H.,Srhiri, A.,Saillard,J.Y.,Bachir, A.B.,Beuze, A.L.,1998.

Experimental and theoretical study of organic corrosion inhibitors on iron in acidic medium.Corros.Sci.41,501–517.

Chen,J.L.,Al-Abed,S.R.,Ryan,J.A.,Li,Z.,2001.Effects of pH on dechlorination of trichloroethylene by zero-valent iron.J.Hazard.Mater.B83,243–254.

Choe,S.,Lee,S.-H.,Chang,Y.-Y.,Hwang,K.-Y.,Khim,J.,2001.Rapid reductive destruction of hazardous organic compounds by nano-scale Fe0.Chemosphere 42,367–372.

Doong,R.-A.,Lai,Y.-J.,2005.Dechlorination of tetrachloroethylene by palladized iron in the presence of humic acid.Water Res.39,2309–2318.

Feng,J.,Lim,T.-T.,2005.Pathways and kinetics of carbon tetrachloride and chloroform reductions by nano-scale Fe and Fe/Ni particles:comparison with commercial micro-scale Fe and Zn.Chemosphere59,1267–1270.

Fleming,I.,1976.Frontier Orbitals and Organic Chemical Reactions.John Wiley& Sons Ltd.,England.

Genin,J.-M.R.,Bourrie,G.,Trolard,F.,Abdelmoula,M.,Jaffrezic,A.,Refait,P.,Maitre, V.,Humbert, B.,Herbillon, A.,1998.Thermodynamic equilibria in aqueous suspensions of synthetic and natural Fe(II)–Fe(III)green rusts:occurrences of the mineral in hydromorphic soils.Environ.Sci.Technol.32,1058–1068.

Table3

Values of regression coef?cients and their standard errors

Variable Coef?cients Standard error

Interceptà5.02 2.80Eà1

HA37.60E+1 2.53E+1

HA2à9.17E+1 3.06E+1

E?HAà1.09E+1 3.79

HA?E2à1.87 6.64Eà1

E3à1.05Eà1 1.00Eà2

1822J.Feng et al./Chemosphere73(2008)1817–1823

Giasuddin,A.B.M.,Kanel,S.R.,Choi,H.,2007.Adsorption of humic acid onto nano-scale zerovalent iron and its effect on arsenic removal.Environ.Sci.Technol.41, 2002–2027.

Goss,K.U.,Schwarzenbach,R.P.,2001.Linear free energy relationships used to evaluate equilibrium partitioning of organic compounds.Environ.Sci.Technol.

35,1–9.

Kanel,S.R.,Manning,B.,Charlet,L.,Choi,H.,2005.Removal of arsenic(III)from groundwater by nano-scale zero-valent iron.Environ.Sci.Technol.39,1291–1298. Klausen,J.,Vikesland,P.J.,Kohn,T.,Burris,D.R.,Ball,W.P.,Roberts,A.L.,2003.

Longevity of granular iron in groundwater treatment processes:solution composition effects on reduction of organohalides and nitroaromatic compounds.Environ.Sci.Technol.37,1208–1218.

Larson,R.A.,Jafvert, C.T.,Bosca, F.,Marley,K.A.,Miller,P.L.,2000.Effects of surfactant on reduction and photolysis(>290nm)of nitroaromatic compounds.

Environ.Sci.Technol.34,505–508.

Li,Z.,Willms,C.,Alley,J.,Zhang,P.,Bowman,R.S.,2006.A shift in pathway of iron-mediated perchloroethylene reduction on the presence of sorbed surfactant-A column study.Water Res.40,3811–3819.

Lien,H.L.,Zhang,W.-X.,2001.Nano-scale iron particles for complete reduction of chlorinated ethenes.Colloids Surf.,A191,97–105.

Liu,Y.,Yang,F.,Chen,J.,Gao,L.,Chen,G.,2003.Linear free energy relationships for dechlorination of aromatic chlorides by Pd/Fe.Chemosphere50,1275–1279. Liu,Y.,Choi,H.,Dionysiou, D.,Lowry,G.V.,2005.Trichloroethene hydrodechlorination in water by highly disordered monometallic nanoiron.

Chem.Mater.17,5315–5322.

Loraine,G.A.,2001.Effects of alcohols,anionic and nonionic surfactants on the reduction of pce and tce by zero-valent iron.Water Res.35,1453–1460.Nurmi,J.T.,Tratnyek,P.G.,Sarathy,V.,Baer,D.R.,Amonette,J.E.,Pecher,K.,Wang,C., Linehan,J.C.,Matson,D.W.,Penn,R.L.,Driessen,M.D.,2005.Characterization and properties of metallic iron nanoparticles:spectroscopy,electrochemistry, and kinetics.Environ.Sci.Technol.39,1221–1230.

Paria,S.,Khilar,K.C.,2004.A review on experimental studies of surfactant adsorption at the hydrophilic solid–water interface.Adv.Colloid Interface 110,75–95.

Sayles,G.D.,You,G.,Wang,M.,Kupferle,M.J.,1997.DDT,DDD,and DDE dechlorination by zero-valent iron.Environ.Sci.Technol.31,3448–3454. Schrick,B.,Blough,J.L.,Jones,A.D.,2002.Hydrodechlorination of trichloroethylene to hydrocarbons using bimetallic nickel-iron nano-particles.Chem.Mater.14, 5140–5147.

Stumm,W.,1992.Chemistry of the Solid–Water Interface.John Wiley&Sons,Inc., United States of America.

Tan,K.H.,2003.Humic Matter in Soil and Environment.Marcel Dekker,New York. Totten,L.A.,Roberts, A.L.,2001.Calculated one-and two-electron reduction potentials and related molecular descriptors for reduction of alkyl and vinyl hylide in water.Crit.Rev.Environ.Sci.Technol.31,175–221.

Tratnyek,P.G.,Scherer,M.M.,Deng, B.,Hu,S.,2001.Effects of natural organic matter,anthropogenic surfactants,and model quinines on the reduction of contaminants by zero-valent iron.Water Res.35,4435–4443.

Xie,L.,Shang, C.,2005.Role of humic acid and quinine model compounds in bromate reduction by zerovalent iron.Environ.Sci.Technol.39,1092–1100.

Zhang,P.,Tao,X.,Li,Z.,Bowman,R.,2002.Enhanced perchloroethylene reduction in column systems using surfactant-modi?ed zeolite/zero-valent iron pellets.

Environ.Sci.Technol.36,3597–3603.

J.Feng et al./Chemosphere73(2008)1817–18231823

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