Chemical Engineering Journal 271 (2015) 195–203

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Chemical Engineering Journal

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Simultaneous adsorption and dechlorination of pentachlorophenol fromeffluent by Ni–ZVI magnetic biochar composites synthesized from papermill sludge

http://dx.doi.org/10.1016/j.cej.2015.02.0871385-8947/� 2015 Elsevier B.V. All rights reserved.

⇑ Corresponding author. Tel.: +91 1126591032; fax: +91 1126581020.E-mail address: aksaroha@chemical.iitd.ac.in (A.K. Saroha).

Parmila Devi, Anil K. Saroha ⇑Department of Chemical Engineering, Indian Institute of Technology, Delhi, Hauz Khas, New Delhi 110016, India

h i g h l i g h t s

� Ni–ZVI-MBC was synthesized frompaper mill sludge and used for PCPremoval.� PCP removal on Ni–ZVI-MBC occur by

simultaneous adsorption anddechlorination.� Ni acts as catalyst and help in

enhancement of PCP dechlorinationefficiency.� Adsorption and dechlorination

kinetics was used to determine ratelimiting step.� The feasibility of brick formation

from exhausted Ni–ZVI-MBC wasstudied.

g r a p h i c a l a b s t r a c t

a r t i c l e i n f o

Article history:Received 2 January 2015Received in revised form 24 February 2015Accepted 25 February 2015Available online 4 March 2015

Keywords:SludgeBiocharPentachlorophenolAdsorptionDechlorination

a b s t r a c t

The Ni–zero-valent iron magnetic biochar composites (Ni–ZVI-MBC) were synthesized from paper millsludge and used as an adsorbent for the removal of pentachlorophenol (PCP) from the synthetic and realpaper mill effluent. The synthesized Ni–ZVI-MBC was characterized and analyzed for the stability of Niand ZVI particles in the biochar matrix. The Ni–ZVI-MBC involves simultaneous adsorption anddechlorination mechanism resulting in higher PCP removal efficiency. The presence of Ni as a catalystin Ni–ZVI-MBC enhances the dechlorination rate and the adsorption of PCP by preventing the accumula-tion of PCP in the biochar matrix. The effect of operating parameters (solution pH, Ni loading, initial PCPconcentration in the solution and temperature) on adsorption and dechlorination efficiency was studied.The exhausted Ni–ZVI-MBCs were used for the brick formation and the bricks showed good compressivestrength and negligible heavy metal and PCP leaching.

� 2015 Elsevier B.V. All rights reserved.

1. Introduction

Pentachlorophenol (PCP), an organochlorine compound, is listedas a priority pollutant by U.S. Environmental Protection Agency(EPA) due to its toxic, carcinogenic and persistent nature [1]. PCP

can be found in air, water, and soil and the permissible limit (pre-scribed by US EPA) of PCP in drinking water is 0.3 lg/L. The chronicexposure of PCP can cause various health problems related tokidney, liver, blood and nervous system. It is widely used in theformulation of pesticides, herbicides, disinfectants and wood pre-servatives, thus finding its way in the effluent of these industries[2]. PCP is also generated during the industrial operations like pulpbleaching in pulp and paper industry [3]. Various processes such as

196 P. Devi, A.K. Saroha / Chemical Engineering Journal 271 (2015) 195–203

membrane filtration [4], biological treatment [5], adsorption [2]and advanced oxidation processes [6] are employed for the treat-ment of the effluent containing PCP and among these processes,adsorption is extensively used due to its relative simplicity ofdesign, operation, scale-up and low cost.

Biochar has attracted attention as an adsorbent for the treat-ment of effluent due to its extraordinary adsorption propertiesfor organic contaminants [7,8]. It has been reported that theadsorption capacity of the biochar is 10–1000 times more thanother type of carbon adsorbents due to its surface area, porosityand surface functional groups [9,10]. Various studies have beenreported in the literature on the use of biochar as an adsorbentfor the treatment of effluent containing various toxic pollutantslike phenol [11], atrazine [12], 4-chlorophenol [13], naphthalene[14] and polycyclic aromatic hydrocarbons [15]. Since the disposalof the exhausted adsorbent limits its practical applications, it isdesirable to desorb the adsorbate from the adsorbent to increasethe life of the adsorbent. The doping of the adsorbent materials(organobentonite, activated carbon, biochar) with zero-valent iron(ZVI) has been found to be a promising approach to remove thepollutant from the adsorbent insitu by reduction [1,16]. Theimpregnation of ZVI particles in the biochar matrix made frompulp and paper mill sludge [ZVI-magnetic biochar composites(ZVI-MBC)] facilitates the simultaneous adsorption anddechlorination of PCP in the effluent [1]. The combination of ZVIand carbon exert synergistic effect for the removal of pollutantfrom the effluent resulting in the high removal efficiency of theadsorbent. Wu et al. [16] reported that the bromate removal reac-tion rate was 4.15 times higher on ZVI immobilized activated car-bon compared to unsupported nZVI. Similarly, organobentonitesupported ZVI particles showed high PCP removal rate (4–6 times)than the unsupported ZVI due to the simultaneous adsorption andreduction of PCP on the organobentonite surface [17]. Although,ZVI-MBC was efficient in the dechlorination of PCP from the aque-ous solution but the dechlorination reaction was too slow toachieve the desired PCP removal. Devi and Saroha [1] obtained85% dechlorination efficiency of PCP in 24 h. One of the novelapproaches for enhancing the dechlorination rate of the ZVI-MBCinvolves impregnation of ZVI-MBC with some catalyst like nickel(Ni), copper (Cu), palladium (Pd) and platinum (Pt). The dopingof the metals such as Cu, Ni, Pt, and Pd has been reported in theliterature [18–20]. Nickel is a preferred doping metal in the ZVI-system because it is comparatively cheap and provides betterhydride generation potential [19]. Additionally, the Ni doping onZVI primarily controls the ZVI passivation by preventing its corro-sion and thereby enhancing the removal rate of the contaminants[20]. Therefore, it is proposed to synthesize the Ni–ZVI magneticbiochar composites (Ni–ZVI-MBC) by doping with Ni as a catalystfor the removal of PCP from the synthetic and real industrial efflu-ent. The synthesized adsorbent will provide higher PCP removalefficiency by utilizing the high adsorption capacity of biochar alongwith the high reductive potential of Fe–Ni bimetals.

In the present study, Ni–ZVI-MBC was synthesized by theimpregnation of ZVI on the biochar obtained by the pyrolysis ofpaper mill sludge and subsequent doping of Ni on ZVI-MBC. Thesynthesized Ni–ZVI-MBC was characterized for the surface area,porosity, surface morphology, surface functional groups and crys-tal structure. The ageing and leaching studies were performed todetermine the stability of Ni–ZVI-MBC. The Ni–ZVI-MBC was usedas an adsorbent for the removal of PCP from the synthetic and realindustrial effluent. The adsorption and dechlorination kinetics andthe thermodynamics studies were performed to characterize theadsorption and dechlorination mechanisms. Since, the disposal ofthe exhausted adsorbent after the adsorption process is a problem;the feasibility of using the exhausted Ni–ZVI-MBC for the brick for-mation was also explored.

2. Materials and methods

2.1. Chemicals

PCP (C6HCl5O; molecular weight – 266.34 g/mol) of 98% puritywas procured from Sigma–Aldrich chemical company. All reagentsused in the present study were of analytical grade.

2.2. Preparation of Ni–ZVI-MBC

The paper mill sludge was collected from dewatering unit ofpulp and paper mill and detailed characterization of paper millsludge is provided elsewhere [21]. The Ni–ZVI-MBC was synthe-sized from the paper mill effluent treatment plant (ETP) sludgein three steps. Initially, paper mill ETP sludge was pyrolyzed at700 �C [21] and the resultant biochar was used for the preparationof ZVI-MBC by impregnation of ZVI particles on paper mill sludgebiochar surface. The detailed procedure for ZVI and ZVI-MBC pre-paration is stated elsewhere [1]. Briefly, the preparation of ZVIwas carried out by reduction of FeSO4 to Fe(0) using NaBH4 solu-tion as a reducing agent (Eq. (1)). The NaBH4 solution was drop-wise added into the flask containing FeSO4 solution resulting inthe formation of ZVI as black precipitate:

4Fe3þ þ 3BH�4 þ 9H2O! 4Fe0 þ 3H2BO�3 þ 6H2 þ 12Hþ ð1Þ

The preparation of ZVI-MBC was performed by impregnation ofZVI on biochar-cetyltrimethylammonium bromide (CTMB) com-plex (5 g of biochar in the CTMB solution of known concentration(0.1–0.8%). To prepare ZVI-MBC, 5 g of biochar-CTMB complexwas added into the reaction mixture containing ZVI and stirred vig-orously at 1000 rpm for 30 min. The solid residue was separated byfiltration and washed with the distilled water. The solid residue(ZVI-MBC) was dried in the oven at 95 �C and stored in an air-tightcontainer for further use.

For the preparation of the Ni–ZVI-MBC, the doping of Ni wasperformed on the ZVI-MBC surface. A solution (50 mL) of nickelchloride (NiCl2�6H2O) of desired concentration (0.1–1.0 wt%) wasprepared and 5 g of ZVI-MBC was added in the solution. The mix-ture was ultra-sonicated for 20 min at 25 �C and the solid residuewas separated from the liquid by centrifugation at 1000 rpm. Thesolid residue was washed several times with ethanol to preventthe oxidation of the ZVI particles. After washing, the solid residuewas dried at 105 �C for 2 h to obtain Ni–ZVI-MBC. The Ni–ZVI-MBCwas stored in air-tight container for further use.

The synthesis of Ni–ZVI was performed by impregnation of Nion ZVI surface as per the above procedure without the additionof biochar-CTMB complex in reaction mixture.

2.3. Characterization of Ni–ZVI-MBC

The synthesized Ni–ZVI-MBC was characterized for the surfacearea, porosity, surface functional groups, surface morphology andcrystal structure. The BET surface area and porosity of the Ni–ZVI-MBC was analyzed using N2 adsorption–desorption isothermat 196 �C using a Micromeritics ASAP 2010 apparatus. The surfacefunctional groups of the Ni–ZVI-MBC was analyzed using FTIRspectrometer where the dried Ni–ZVI-MBC sample was mixed withthe dried KBr in a ratio of 1:30 and FTIR spectra was recorded at aresolution of 4 cm�1 in the region of 4000–400 cm�1. The surfacemorphology of the Ni–ZVI-MBC was determined using scanningelectron micrograph (SEM). The crystal structure of Ni–ZVI-MBCwas analyzed by X-ray diffraction (XRD) using Cu-Ka radiation(k = 1.54 Å) at 40 kV/40 mA. All the samples were scanned from5� to 60� 2h at a scanning rate of 3� 2h per min.

P. Devi, A.K. Saroha / Chemical Engineering Journal 271 (2015) 195–203 197

2.4. Adsorption experiments

The adsorption experiments were performed for the removal ofPCP from the synthetic and real industrial effluent using Ni–ZVI-MBC as an adsorbent. The stock solution of PCP (100 mg/L) wasprepared by dissolving analytical grade PCP in distilled water andthe working solution (10 mg/L) was prepared by dilution of thestock solution with distilled water. The initial PCP concentrationof 10 mg/L was chosen for batch experiments because the solubil-ity of PCP decrease as solution pH decreased from 7 to 4 and thereis the possibility of precipitation of PCP at higher concentrations(>10 mg/L) [22]. The batch adsorption experiments were con-ducted to study the effect of the solution pH (3–9), Ni loading(0.1–1.0 wt%), initial PCP concentration (5–50 mg/L) and tempera-ture (15–40 �C) on PCP removal by Ni–ZVI-MBC. The batch equilib-rium experiments were conducted in 250 mL conical flask bymixing 10 mg of adsorbent in 50 mL of PCP solution (10 mg/L)and the mixture was agitated (120 rpm) in an incubator shakerat 25 ± 1 �C. The samples were withdrawn at regular time intervalsto determine the residual concentration of PCP in the solution.

For comparison purpose, experiments were performed with ZVI,Ni–ZVI, biochar, ZVI-MBC at the optimized operational conditionsand results were compared with Ni–ZVI-MBC.

2.5. Analysis

The residual PCP concentration in the synthetic solution wasdetermined by UV–Vis spectrophotometer, while the residual PCPconcentration in the real industrial effluent was determined usinghigh pressure liquid chromatography (HPLC) equipped with anXDB-C18 analytical HPLC column and a 1200 diode-array detectorat a wavelength of 320 nm. The mobile phase for the PCP analysisconsisted of 90% methanol and 10% acidified distilled water (1 mLacetic acid in 100 mL distilled water) and the flow rate of themobile phase was kept 1 mL/min [23].

The removal of the PCP from the synthetic and the real indus-trial effluent by Ni–ZVI-MBC was analyzed in terms of the PCPremoval efficiency and adsorption capacity (qe), which have beendetermined as follows:

PCP removal efficiency ð%Þ ¼ Co � CCo

� �� 100 ð2Þ

qe ¼ðCo � CeÞ

W� V ð3Þ

where Co (mg/L) and C (mg/L) are the initial concentration and con-centration of PCP in the solution at any time t, respectively. Theadsorption capacity (qe) is the amount of PCP adsorbed per unitweight of the adsorbent (mg of PCP adsorbed/g of adsorbent), Ce

is the concentration of PCP in the solution at equilibrium, V is thevolume of the PCP solution (mL), and W is the adsorbent weight(mg).

The removal of PCP from synthetic and real industrial effluentusing Ni–ZVI-MBC as an adsorbent occurs by simultaneous adsorp-tion and dechlorination mechanism. The dechlorination of PCPresulted in the generation of chloride ions which get released inthe solution. The chloride ions in the aqueous solution weredetermined by the colorimetric method (APHA 4500-Cl-E).

2.6. Adsorption and dechlorination kinetics

The rate of dechlorination of PCP depends on the concentrationof adsorbed PCP on the Ni–ZVI-MBC matrix and the Ni concentra-tion. Since the Ni concentration in the Ni–ZVI-MBC matrix isconstant, the rate of PCP dechlorination is dependent only on thePCP concentration and the dechlorination reaction follows

pseudo-first order kinetics [18]. The adsorption kinetics and rateconstants were determined using Eqs. (4) and (5):

Cresidual PCP

Co¼ e�k1t ð4Þ

1� Cresidual PCP

Co¼ Cremoved PCP

Co¼ 1� e�k1t ð5Þ

where, Cresidual PCP (mg/L) is the residual concentration of PCP in thesolution, Co (mg/L) is the initial PCP concentration in the solution, k1

(min�1) is the adsorption kinetics rate constant and t (min) is thecontact time.

The dechlorination kinetics and rate constants were determinedusing Eqs. (6) and (7) [18]:

CPCP on adsorbent

Co¼ ð1� e�k1tÞ � ðe�k2tÞ ð6Þ

CPCP dechlorinated

Co¼ ð1� e�k1tÞ � ðe�k2tÞ ð7Þ

where, CPCP on adsorbent (mg/L)/Co (mg/L) is the fraction of PCPremoved from the solution remaining on Ni–ZVI-MBC afterdechlorination and CPCP dechlorinated (mg/L)/Co (mg/L) is thefraction of PCP removed from the solution being dechlorinated onNi–ZVI-MBC and k2 is dechlorination rate constant.

2.7. Extraction studies

The amount of PCP adsorbed on the exhausted Ni–ZVI-MBC sur-face was determined by soxhlet extraction method using methanolas a solvent [24].

2.8. Feasibility of brick formation

The exhausted Ni–ZVI-MBC after adsorption experiments wasused for the brick formation using geopolymerization technique.For brick formation, NaOH was used as an alkali activator and sandwas used as an additive. Initially, the exhausted Ni–ZVI-MBC andsand were weighed and mixed in 1:0.1 (w/w) ratio. A solution ofNaOH (15 M) was prepared and added in above mixture, followedby addition of 1 g each of calcium carbonate and silica dust. Thecontents were mixed properly to obtain a semi-slurry typehomogenous mixture which was poured into a mould and curedat room temperature for 24 h. The samples were demoulded andcured in an oven at 90 �C for 48 h to complete the geopolymeriza-tion reactions. The resultant geopolymeric brick samples were ana-lyzed for compressive strength, water adsorption (%) and leachingof heavy metals and PCP. The compressive strength of brick wasdetermined by pressing in hydraulic press. The water adsorption(%) of brick was analyzed by dipping in water for 48 h. The initialand final weight of the brick was noted. The difference in theweight was used to calculate the water adsorption (%) usingfollowing equation:

Water adsorption ¼W2 �W1

W2� 100 ð8Þ

where, W1 is the weight of dry brick and W2 is the weight of wetbrick.

The heavy metals leaching potential of brick samples (Cr, Cu, Ni,Zn, Pb and Cd) and Ni–ZVI-MBC (Fe, Ni) were analyzed using the USEPA toxicity characteristic leaching procedures (TCLP) and the con-centration of heavy metals in leachate was determined by atomicabsorption spectroscopy (PerkinElmer Analyst 100).

The reproducibility of the experimental results was alsochecked and the variation in the experimental results was foundto be ±2%.

Fig. 1. Characterization of Ni–ZVI-MBC (a) X-ray diffraction plot of Ni–ZVI-MBC atdifferent Ni loadings; (b) FTIR spectra of fresh and exhausted Ni–ZVI-MBC.

198 P. Devi, A.K. Saroha / Chemical Engineering Journal 271 (2015) 195–203

3. Results and discussion

3.1. Characterization of Ni–ZVI-MBC

The surface area and the porosity of the paper mill sludge bio-char, ZVI-MBC and Ni–ZVI-MBC are summarized in Table 1. It canbe noticed from Table 1 that the surface area of the Ni–ZVI-MBCis higher as compared to the ZVI-MBC and paper mill sludge bio-char as the immobilization of the Ni and ZVI on the biochar surfaceprovides the additional surface area. The micropore volume of theNi–ZVI-MBC was found higher in comparison to ZVI-MBC suggest-ing the higher adsorptive capability of Ni–ZVI-MBC in comparisonto ZVI-MBC and paper mill sludge biochar. The average porediameter of the Ni–ZVI-MBC was found to be 2.3 nm that allowsthe easy entry of the PCP molecules (size �1 nm) into the pores.

The XRD plot of the Ni-doped Ni–ZVI-MBC at various Ni loading(0–1.0 wt%) is shown in Fig. 1a. The peak at 2h = 44.32� is the char-acteristic peak of ZVI (Fe0), which indicates the adhesion of ZVIparticles on the surface of biochar. It was observed that the inten-sity of Fe0 peak at 2h = 44.32� decreased with an increase in the Niloading from 0.1 to 1.0 wt%, due to the formation of Fe–Ni alloy(FeNi3) and a new broad peak for Fe–Ni alloy appeared around2h = 45.32� [25]. The intensity of Fe–Ni alloy peak increased withan increase in Ni loading due to reaction of ZVI with Ni. The peakof high intensity was observed at 2h = 29.2� due to the presenceof CaO in biochar [26].

The SEM image of the paper mill sludge biochar, fresh andexhausted Ni–ZVI-MBC is shown in Fig. S1 (Supplementary infor-mation). It can be observed that the raw paper mill sludge containssmall fibrous structures due to the presence of cellulosic fibres inthe raw sludge (Fig. S1a). However these cellulosic fibrous struc-tures disappeared in the resultant biochar due to the carbonizationof cellulose and lead to the formation of uneven rough structure.The impregnation of Ni and ZVI on the biochar leads to the forma-tion of small globular chain like structures on the biochar surface(Fig. S1b). The biochar allows the proper dispersion of Ni and ZVIparticles and prevents aggregates formation, which might causereduction in the reactivity of Ni–ZVI-MBC. It can be observed fromFig. S1c that the size of the Ni–ZVI globular chain increased afterPCP adsorption due to the formation of iron oxides layer (Fe2O3,Fe3O4) on the Ni–ZVI-MBC surface.

The FTIR plot of ZVI-MBC (without Ni), the fresh and exhaustedNi–ZVI-MBC is shown in Fig. 1b. The spectra showed some broadand sharp peaks and some weak peaks, which were assigned cer-tain notations (A, B and C) for the comparison of the spectra. Thebroad peaks in the ZVI-MBC were assigned A1 and B1 while theweak peak was assigned C1. Similarly, the weak peaks in the Ni–ZVI-MBC and exhausted Ni–ZVI-MBC were assigned C2 and C3

while the broad peaks were assigned A2, B2 and A3, B3, respectively.The broad peaks (A1, A2, and A3) around 3350 cm�1 is due to the

presence of O–H bond of carboxylic acid. It was observed that thispeak (A3) shortened in the exhausted Ni–ZVI-MBC due to the pos-sible involvement of carboxylic acid in PCP adsorption which leadsto the breakage of O–H bond. The broad band around 1400 cm�1

and narrow band around 860 cm�1 can be attributed to the pres-ence of CaO and CaCO3 in the paper mill sludge biochar [27]. The

Table 1Surface area and porosity of paper mill sludge biochar and ZVI-MBC and Ni–ZVI-MBC.

Sample BET surfacearea (m2/g)

Microporevolume(cm3/g)

Total porevolume(cm3/g)

Porediameter(Å)

Biochar 67 0.026 0.083 31.7ZVI-MBC 101.23 0.029 0.079 47.83Ni–ZVI-MBC 167.86 0.045 0.087 23.16

weak (C) and broad (B) peaks observed at 1700 and 2340 cm�1 isindicative of the N–H band of the primary amines and the sharppeaks observed in the region 528–826 cm�1 are indicative of theC–Br and C–Cl stretch, which could be due to the impregnationof CTMB on the biochar surface [28]. The adsorption peaks noticedin exhausted Ni–ZVI-MBC in the region of 400–500 cm�1 can beattributed to the Fe–O stretch of Fe2O3 and Fe3O4. Moreover, thepeaks from 1126 to 1278 cm�1 may be due to the alcohols, car-boxylic acid and –N–H stretch of the amines indicating that thepresence of the organic compounds such as polymeric –CH2, ligninand polysaccharides in the precursor paper mill sludge remainedpreserved as such in the ZVI-MBC [27]. It can be noticed that Ni–ZVI-MBC is enriched in both acidic and basic functional groups,making it a suitable adsorbent for the removal of PCP, as the PCPexists in the molecular and the ionized form depending upon thesolution pH [1].

3.2. Comparison of PCP removal efficiency of Ni–ZVI-MBC withdifferent adsorbents

Batch adsorption experiments were performed to study the PCPremoval efficiency using biochar, ZVI, Ni–ZVI, ZVI-MBC and Ni–ZVI-MBC and the results are shown in Fig. S2 (Supplementaryinformation). It can be noticed from Fig. S2 that the very poorPCP removal efficiency (34.4%) was achieved using ZVI in a period

P. Devi, A.K. Saroha / Chemical Engineering Journal 271 (2015) 195–203 199

of 120 min, while the removal efficiency was comparativelyimproved (39.5%) after Ni doping on ZVI particles (Ni–ZVI com-plex). The increased efficiency was obviously related to the differ-ence of available surface area for PCP adsorption. The Ni–Fecomplex form larger specific surface area which offers more inter-faces for ZVI and PCP interactions [2]. It is worth noticing that rawbiochar alone has high adsorption capacity for PCP, which removedabout 65% of PCP in 120 min, which is far higher than ZVI andNi–ZVI respectively. The PCP removal efficiency obtained usingNi–ZVI-MBC was much higher compared to ZVI, Ni–ZVI and bio-char alone. A 97.5% PCP removal efficiency was obtained usingNi–ZVI-MBC for a contact time of 60 min while 86% PCP removalefficiency was obtained using ZVI-MBC for the same contact timeof 60 min. The higher PCP removal efficiency obtained for Ni–ZVI-MBC is due to the higher surface area available for adsorptionand the increase in the catalytic dechlorination rate of PCP by Ni–ZVI-MBC using Ni as a catalyst. The simultaneous dechlorination ofadsorbed PCP into chlorides and desorption of chlorides into solu-tion make the earlier PCP occupied sites vacant and available forfurther adsorption of PCP resulting in an increase in the PCPremoval efficiency. Similar results also reported by Choi et al.[18] for dechlorination of 2-chlorobiphenyl using reactive acti-vated carbon (granular activated carbon impregnated with reactiveiron/palladium (Fe/Pd) bimetallic nanoparticles).

3.3. Effect of operating parameters on removal efficiency of PCP

Experiments were performed to study the PCP removal from asynthetic solution containing PCP in batch mode of operation.The effect of the operating parameters such as solution pH, Ni load-ing in Ni–ZVI-MBC, initial PCP concentration and temperature onthe removal efficiency of PCP was studied.

3.3.1. Effect of solution pHThe effect of solution pH on PCP removal by Ni–ZVI-MBC was

studied by varying the solution pH from 3 to 9 and the resultsare shown in Fig. 2. The solution pH was adjusted by addingsodium hydroxide or hydrochloric acid to get the desired pH. Theadsorbent dosage and the initial PCP concentration of the solutionwere kept constant at 10 mg/50 mL and 10 mg/L, respectively. ThePCP removal from the aqueous solution occurs due to the adsorp-tion of PCP on Ni–ZVI-MBC surface and its subsequent dechlorina-tion. Hence, the PCP removal efficiency depends on the surfaceproperties of Ni–ZVI-MBC as well as its dechlorination behaviour.

Fig. 2. Effect of solution pH on PCP removal efficiency using Ni–ZVI-MBC(adsorbent dose – 10 mg/50 mL; Co – 10 mg/L; temperature – 25 �C; Ni loading –0.5 wt%).

It can be noticed from Fig. 2 that there was a decrease in the PCPremoval efficiency (79.9–70.4%) and adsorption capacity (39.95–35.2 mg/g) with an increase in the solution pH from 3 to 5 for acontact time of 240 min. This may be due to the enhanced corro-sion of iron which induces the formation of atomic hydrogen andsubsequently molecular hydrogen at lower solution pH [16,20].The Fe0 and H2 will react with PCP as reducing agents accordingto the following reactions [29]:

Fe0 þ 2H2O�!NiH2 þ 2OH� þ Fe2þ ð9Þ

H2 þ RCl�!RHþHþ þ Cl� ð10Þ

Overall reaction:

Fe0 þ RClþ 2H2O�!NiFe2þ þ RHþ Cl� þHþ þ 2OH� ð11Þ

At lower solution pH (pH 3), the increased H+ concentrationlead to an increase in nickel hydride formation, thereby enhancingthe PCP dechlorination efficiency. The higher PCP removal effi-ciency was obtained at solution pH 3 despite the fact that theadsorption capacity was lower at solution pH 3 due to an enhancedadsorption of protons (H+) by Ni–ZVI-MBC which suppresses PCPadsorption on the adsorbent surface [30].

The complete PCP removal was achieved at solution pH 6 due tothe presence of acidic functional groups on the Ni–ZVI-MBC sur-face for adsorption of PCP [22]. The increase in solution pH beyond7 leads to the reaction of the acidic functional groups with hydro-xyl ions resulting in a decrease in the adsorption capacity.Additionally, an increase in solution pH beyond 7 resulted in lowerPCP dechlorination efficiency due to the formation of hydroxideand oxide layers on the Ni–ZVI-MBC surface [20]. The oxide layerformation at Ni–ZVI-MBC surface prevents the direct contact ofthe PCP molecules with the reactive adsorbent sites, resulting ina decrease in the PCP dechlorination efficiency at alkaline solutionpH [31].

3.3.2. Effect of Ni loadingThe Ni loading is an important parameter affecting the PCP

dechlorination efficiency of Ni–ZVI-MBC. The effect of Ni loadingon PCP removal efficiency and dechlorination efficiency was stud-ied by varying the Ni loading from 0.1 to 1.0 wt% and the resultsare shown in Fig. 3. The initial PCP concentration and Ni–ZVI-MBC dosage were kept constant at 10 mg/L and 10 mg/50 mL

Fig. 3. Effect of Ni loading on PCP removal efficiency and dechlorination efficiency(solution pH – 6; adsorbent dose – 10 mg/50 mL; Co – 10 mg/L; temperature –25 �C).

Fig. 4. First order kinetics of PCP removal by Ni–ZVI-MBC; (a) at different initial PCPconcentrations; (b) at different Ni–ZVI-MBC dosage. The dotted lines represent firstorder kinetics fit of the experimental data (solution pH – 6; temperature – 25 �C; Niloading – 0.5 wt%).

Table 2PCP adsorption and dechlorination kinetics constants for Ni–ZVI-MBC.

Initial PCPconcentration (mg/L)

Ni–ZVI-MBC dosage(mg/50 mL)

k1

(min�1)R2 k2

(min�1)

5 10 0.119 0.915 0.14010 10 0.074 0.971 0.11620 10 0.031 0.948 0.03250 10 0.009 0.794 0.014

30 0.029 0.952 0.03540 0.106 0.994 0.55750 0.138 0.985 0.720

200 P. Devi, A.K. Saroha / Chemical Engineering Journal 271 (2015) 195–203

respectively. It can be observed from Fig. 3 that the rate of PCPremoval increased with an increase in Ni loading from 0.1 to0.5 wt% due to an increase in the availability of reactive sites forPCP adsorption. Similarly, the dechlorination efficiency of PCP alsoincreased from 86.05% to 100% with an increase in Ni loading from0.1 to 0.5 wt% over a contact time of 240 min. A significant increasein the rate of dechlorination (100% PCP dechlorination efficiency ina contact time of 240 min) was obtained using Ni impregnated Ni–ZVI-MBC (0.5 wt% Ni) as 85% PCP dechlorination efficiency wasobtained using ZVI-MBC as an adsorbent in a contact time of24 h by Devi and Saroha [1]. The coexistence of Fe0 and Ni in Ni–ZVI-MBC enhances the rate of dechlorination due to the catalyticeffect of Ni during dechlorination of PCP. It has been reported thatgalvanic cells are formed at each contact angle of Fe and Ni and anincrease in the Ni loading results in an increase in the formation ofgalvanic cells that accelerate the corrosion of Fe resulting in anincrease in the dechlorination efficiency [32,33]. Further, increasein Ni loading from 0.5 to 1.0 wt% resulted to a decrease in thePCP dechlorination efficiency and adsorption capacity from 100%to 78.15% and 50 to 48 mg/g respectively in a contact time of240 min. This is due to the fact that Ni loading beyond 0.5 wt% doesnot lead to an increase in the active catalyst sites as Ni forms multi-layer on the ZVI-MBC surface. The 0.5 wt% Ni loading was found tobe optimum for PCP removal and further experiments were per-formed using 0.5 wt% Ni loading.

3.4. Adsorption and dechlorination kinetics

Experiments were conducted by varying the initial PCP concen-trations in the solution (5–50 mg/L) to study the adsorption anddechlorination kinetics of PCP removal using Ni–ZVI-MBC as anadsorbent and the results are shown in Fig. 4a. It can be noticedfrom Fig. 4a that the complete removal of PCP was obtained atlower initial PCP concentrations (5–20 mg/L) whereas someamount of PCP remained in the solution at higher initial PCP con-centrations (50 mg/L) even after a contact time of 240 min. Thismight be due to two reasons: (i) accumulation of excess amountof PCP in Ni–ZVI-MBC matrix (ii) saturation of adsorption sites ofNi–ZVI-MBC at higher initial PCP concentrations in the solution.The rate of adsorption and dechlorination reaction plays an impor-tant role in the PCP removal by Ni–ZVI-MBC. If the rate ofdechlorination is slow compared to the rate of adsorption, it willcause accumulation of PCP in Ni–ZVI-MBC matrix and thus limitsthe rate of PCP removal. Further experiments were conductedusing different adsorbent dosages (30 mg/50 mL–50 mg/50 mL),by keeping initial PCP concentration in the solution constant(50 mg/L), to determine the rate limiting step i.e. adsorption ofPCP on Ni–ZVI-MBC or dechlorinaton of PCP and the results areshown in Fig. 4b. It can be noticed from Fig. 4b that the PCP resid-ual concentration in the solution decreases with an increase in theadsorbent dosage for a contact time of 30 min. The exhausted Ni–ZVI-MBC (after 240 min of contact time) was extracted withmethanol to determine the amount of PCP remaining in the Ni–ZVI-MBC matrix. It was found that the concentration of PCP inNi–ZVI-MBC matrix was negligible suggesting that dechlorinationis not the rate limiting step in PCP removal by Ni–ZVI-MBC. Sincethe PCP residual concentration in the solution was found to bedependent on the adsorbent dosage indicating that the adsorptionlimits the removal of PCP by Ni–ZVI-MBC.

The experimental data was fitted to the first order reactionkinetics and the experimental data was found to be in good agree-ment with the adsorption and dechlorination kinetic model (Fig. 4aand b). The estimated values of adsorption and dechlorinationkinetics rate constants are shown in Table 2. The value ofdechlorination rate constant k2 was determined by assuming thatthe concentration of PCP on the Ni–ZVI-MBC matrix is always

negligible since adsorption was found to be the rate limiting stepand the concentration of PCP in the exhausted Ni–ZVI-MBC wasfound to be negligible after a contact time of 240 min. It can benoticed from Table 2 that for a constant adsorbent dosage(10 mg/50 mL), the value of k1 decreased with an increase in theinitial PCP concentration in the solution. It can be further noticedthat for a fixed initial PCP concentration in the solution (50 mg/mL) the value of k1 increased with an increase in the adsorbentdosage. The value of k2 was found to be always more than k1 indi-cating that the rate of dechlorination of PCP is always more thanthe rate of adsorption of PCP from the solution.

3.5. Thermodynamics studies

The effect of temperature on the PCP removal using Ni–ZVI-MBC as an adsorbent was studied by varying the temperature from

Table 3Estimated values of thermodynamics parameters for removal of PCP by Ni–ZVI-MBC.

Temperature (�C) First order kineticsmodel

Arrhenius plot

k (min�1) R2 Ea (kJ/mol) R2

15 0.051 0.97 26.67 0.9425 0.074 0.9730 0.081 0.9840 0.093 0.98

P. Devi, A.K. Saroha / Chemical Engineering Journal 271 (2015) 195–203 201

15 to 40 �C and the results are shown in Fig. 5. It was observed thatthe PCP removal efficiency increased with an increase in the tem-perature and maximum PCP removal efficiency of 99% wasobtained at 40 �C after a contact time of 30 min. The adsorptioncapacity was also found to increase from 47 to 50 mg/g with anincrease in temperature from 15 to 40 �C. This increase might bedue to the effective collision of PCP molecules with Ni–ZVI-MBCparticles at higher temperature resulting in the enhanced removalefficiency.

The experimental data obtained at different temperatures wasfitted to pseudo first order kinetics model and the data is shownin Table 3. It was observed that the value of adsorption kineticsconstant (k) increased with an increase in temperature.

The Arrhenius plot of natural logarithm of adsorption kineticsrate constant (lnk) and reciprocal of temperature (1/T) resultedin a linear relationship and the value of activation energy of PCPadsorption on Ni–ZVI-MBC is shown in Table 3. The value of activa-tion energy describes the type of sorption process (physicaladsorption or chemical adsorption). In physical adsorption, thevalue of activation energy is usually lower (Ea 6 4.184 kJ/mol)due to lesser energy requirements for adsorption as the processis easily reversible and the equilibrium is attained easily.Contrary to this, the chemical adsorption processes have highervalue of activation energy due to the involvement of strong chemi-cal forces for adsorption that requires more energy in comparisonto physical adsorption [34]. The higher value of activation energy(26.67 kJ/mol) obtained in the present study indicates that theadsorption of PCP on Ni–ZVI-MBC is a chemisorption process.

3.6. Treatment of paper mill effluent

Experiments were conducted for the treatment of the realindustrial effluent containing PCP using Ni–ZVI-MBC as an adsor-bent (10 mg/50 mL) at 25 �C. No acid or acid or alkali was addedfor pH adjustment and experiments were performed at originalpH of the effluent. The real effluent, collected from the nearby pulpand paper mill, was characterized and the results are stated else-where [1]. The initial PCP concentration in the effluent was1.77 mg/L. The PCP removal efficiency of 100% was achieved after240 min of contact time using Ni–ZVI-MBC while ZVI-MBC took480 min to achieve 100% removal efficiency for same effluent asreported by Devi and Saroha [1]. The additional time needed toachieve 100% PCP removal efficiency for the treatment of the realindustrial effluent may be due to the presence of other chemicals

Fig. 5. Effect of temperature on PCP removal efficiency. Inset: first order kinetics ofPCP removal at different temperatures (solution pH – 6; adsorbent dose – 10 mg/50 mL; Co – 10 mg/L).

in the real industrial effluent. Moreover, no PCP was desorbed(soxhlet extraction) from the exhausted Ni–ZVI-MBC matrix,thereby suggesting the complete dechlorination of the PCP in theeffluent by Ni–ZVI-MBC matrix.

3.7. Ageing of Ni–ZVI-MBC

The Ni–ZVI-MBC were aged for 30 days (prior to performing theadsorption experiments) in three different environments (i) sub-merged in water (ii) aerobic conditions and (iii) anaerobic condi-tions, to study the effect of ageing on overall PCP removalefficiency and PCP dechlorination efficiency of Ni–ZVI-MBC andthe results are shown in Fig. 6a and b. It can be noticed that theageing of Ni–ZVI-MBC in absence of oxygen have no effect onPCP removal efficiency, however the dechlorination efficiencywas decreased slightly (2–3%). Similarly, the PCP removal effi-ciency of air aged samples remained almost same, while thedechlorination efficiency was slightly decreased after 30 days of

Fig. 6. Effect of ageing on efficiency of Ni–ZVI-MBC. (a) PCP removal efficiency, (b)PCP dechlorination efficiency.

202 P. Devi, A.K. Saroha / Chemical Engineering Journal 271 (2015) 195–203

ageing. The decline in the dechlorination efficiency was muchslower than the expected fast chemical corrosion of ZVI. This sug-gests that biochar helps in preventing the formation of oxide filmon the ZVI surface. In case of water aged samples, the PCP removalefficiency was decreased from 98% to 20% and a drastic decreasewas observed in dechlorination efficiency after 30 days of ageing.

3.8. Leaching studies

The leaching potential of Fe and Ni was studied under acidic (pH3), neutral (pH 7) and alkaline (pH 10) conditions of the solution. Itwas found that the Fe and Ni leaching potential was more underacidic conditions compared to the alkaline and the neutral solutionconditions. The concentrations of Fe and Ni in the leachate at solu-tion pH 3 were 2.58 and 1.19 mg/L respectively compared to 0.64and 0.48 mg/L at solution pH 10. However, the concentrations ofFe and Ni in the leachate were found negligible (0.034 mg/L (Fe);0.019 mg/L (Ni)) under neutral solution conditions (pH 7). Thismay be due to the variation in the dissolution and precipitationbehaviour of Fe at various solution pH. The rate of dissolution ofFe is faster than the rate of precipitation at acidic solution pH.Hence, no passivation layer is formed at the Ni–ZVI-MBC particlesurface resulting in high leaching potential of metal ions at acidicsolution pH. Conversely, the precipitation of Fe(II) and Fe(III)occurs at alkaline solution pH, which makes a passive layer onthe Ni–ZVI-MBC particle surface and hinders the Fe dissolution,resulting in the slow leaching of iron at alkaline solution pH [35].The formation of the passive layer at the Ni–ZVI-MBC particle sur-face prevents the leaching of Fe and Ni and hence, the leachingpotential of Ni–ZVI-MBC is low at alkaline solution pH.

3.9. Use of the exhausted adsorbent for brick formation

The disposal of exhausted adsorbent is a problem. So, thefeasibility of brick formation from exhausted Ni–ZVI-MBC obtainedafter the removal of PCP from the effluent was also investigated.The bricks were prepared from the exhausted Ni–ZVI-MBC bygeopolymerization mechanism in the presence of sodium hydrox-ide and the results were analyzed in terms of the compressivestrength and water adsorption (%) of the brick samples.Moreover, the heavy metal and PCP leaching potential of the bricksamples were analyzed to ensure the risk associated with theusage of exhausted Ni–ZVI-MBC made bricks. The mechanicalproperties and leaching potential of PCP and heavy metals frombrick samples are summarized in Table 4. The results showed thatthe bricks prepared using geopolymerization technique have goodcompressive strength and met the ASTM standard. The concentra-tion of the heavy metals in the leachate was found to be within the

Table 4Mechanical and leaching characteristics of bricks made from exhausted Ni–ZVI-MBC.

Parameters Values Standards

Compressive strength (MPa) 20.3 20.7a (severe weathering)17.2a (moderate weathering)

Water adsorption (%) 9.2 15a

Heavy metal concentration in leachateCr (mg/L) 0.21 2.0b

Cu (mg/L) 0.02 3.0b

Ni (mg/L) 1.4 3.0b

Zn (mg/L) 0.23 5.0b

Pb (mg/L) 0.01 0.1b

Cd (mg/L) Nil 2.0b

PCP (lg/L) Nil 0.3c

a American Standards for Testing and Materials (ASTM) specifications.b Indian Standards for Industrial and Sewage Effluents Discharge (inland surface

water).c USEPA [36].

permissible limits prescribed by Indian standards for Industrialand Sewage Effluents Discharge (inland surface water).

4. Conclusions

The Ni–ZVI-MBC was used as an adsorbent for the removal ofPCP from the synthetic and real industrial effluent. Since, the useof Ni–ZVI-MBC involves simultaneous adsorption and dechlorina-tion mechanism, the presence of Ni as catalyst enhanced the rateof dechlorination resulting in higher PCP removal efficiency. Theadsorption and dechlorination kinetics of PCP removal were stud-ied and it was found that adsorption is the rate limiting step. Theleaching and ageing studies confirmed stability of Ni–ZVI-MBC asthe biochar effectively immobilize Ni and ZVI and prevents theirleaching from Ni–ZVI-MBC matrix. The exhausted Ni–ZVI-MBCcan be used for brick formation as the bricks showed goodmechanical strength and low leaching potential.

Acknowledgement

The authors wish to acknowledge the funding received for theproject from Council of Scientific & Industrial Research, NewDelhi, India.

Appendix A. Supplementary data

Supplementary data associated with this article can be found, inthe online version, at http://dx.doi.org/10.1016/j.cej.2015.02.087.

References

[1] P. Devi, A.K. Saroha, Synthesis of the magnetic biochar composites for use as anadsorbent for the removal of pentachlorophenol from the effluent, Bioresour.Technol. 169 (2014) 525–531.

[2] Y. Li, Y. Zhang, J. Li, X. Zheng, Enhanced removal of pentachlorophenol by anovel composite: nanoscale zero valent iron immobilized on organobentonite,Environ. Pollut. 159 (2011) 3744–3749.

[3] U.D. Patel, S. Suresh, Electrochemical treatment of pentachlorophenol in waterand pulp bleaching effluent, Sep. Purif. Technol. 61 (2008) 115–122.

[4] J. Du, J. Bao, M. Tong, S. Yuan, Dechlorination of pentachlorophenol bypalladium/iron nanoparticles immobilized in a membrane synthesized bysequential and simultaneous reduction of trivalent iron and divalentpalladium ions, Environ. Eng. Sci. 30 (2013) 350–356.

[5] A.R. Reis, Y. Kyuma, Y. Sakakibara, Biological Fenton’s oxidation ofpentachlorophenol by aquatic plants, Bull. Environ. Contam. Toxicol. 91(2013) 718–723.

[6] P.K.A. Hong, Y. Zeng, Degradation of pentachlorophenol by ozonation andbiodegradability of intermediates, Water Res. 36 (2002) 4243–4254.

[7] R.M. Burgess, S.A. Ryba, M.G. Cantwell, J.L. Gundersen, R. Tien, M.M. Perron,Interaction of planar and nonplanar organic contaminants with coal fly ash:effects of polar and nonpolar solvent solutions, Environ. Toxicol. Chem. 25(2006) 2028–2037.

[8] H.W. Sun, Z.L. Zhou, Impacts of charcoal characteristics on sorption ofpolycyclic aromatic hydrocarbons, Chemosphere 71 (2008) 2113–2120.

[9] L. Luo, L. Lou, X. Cui, B. Wu, J. Hou, B. Xun, X. Xu, Y. Chen, Sorption anddesorption of pentachlorophenol to black carbon of three different origins, J.Hazard. Mater. 185 (2011) 639–646.

[10] X.L. Wang, B.S. Xing, Sorption of organic contaminants by biopolymer-derivedchars, Environ. Sci. Technol. 41 (2007) 8342–8348.

[11] Z. Liu, F.S. Zhang, Removal of copper(II) and phenol from aqueous solutionusing porous carbons derived from hydrothermal chars, Desalination 267(2011) 101–106.

[12] X. Cao, L. Ma, B. Gao, W. Harris, Dairy-manure derived biochar effectively sorbslead and atrazine, Environ. Sci. Technol. 43 (2009) 3285–3291.

[13] Y. Shih, Y. Su, R. Ho, P. Su, C. Yang, Distinctive sorption mechanisms of 4-chlorophenol with black carbons as elucidated by different pH, Sci. TotalEnviron. 433 (2012) 523–529.

[14] B. Chen, Z. Chen, Sorption of naphthalene and 1-naphthol by biochars oforange peels with different pyrolytic temperatures, Chemosphere 76 (2009)127–133.

[15] P. Oleszczuk, E.H. Hale, J. Lehmann, G. Cornelissen, Activated carbon andbiochar amendments decrease pore-water concentrations of polycyclicaromatic hydrocarbons (PAHs) in sewage sludge, Bioresour. Technol. 111(2012) 84–91.

P. Devi, A.K. Saroha / Chemical Engineering Journal 271 (2015) 195–203 203

[16] X. Wu, Q. Yang, D. Xu, Y. Zhong, K. Luo, X. Li, H. Chen, G. Zeng, Simultaneousadsorption/reduction of bromate by nanoscale zerovalent iron supported onmodified activated carbon, Ind. Eng. Chem. Res. 52 (2013) 12574–12581.

[17] G. Zhang, Q. Zhang, K. Sun, X. Liu, W. Zheng, Y. Zhao, Sorption of simazine tocorn straw biochars prepared at different pyrolytic temperatures, Environ.Pollut. 159 (2011) 2594–2601.

[18] H. Choi, S. Agarwal, S. Al-Abed, Adsorption and simultaneous dechlorination ofPCBs on GAC/Fe/Pd: mechanistic aspects and reactive capping barrier concept,Environ. Sci. Technol. 43 (2009) 488–493.

[19] C.L. Chun, D.R. Baer, D.W. Matson, J.E. Amonette, R.L. Penn, Characterizationand reactivity of iron nanoparticles prepared with added Cu, Pd, and Ni,Environ. Sci. Technol. 44 (2010) 5079–5085.

[20] B.S. Kadu, Y.D. Sathe, A.B. Ingle, R.C. Chikate, K.R. Patil, C.V. Rode, Efficiency andrecycling capability of montmorillonite supported Fe–Ni bimetallicnanocomposites towards hexavalent chromium remediation, Appl. Catal. B104 (2011) 407–414.

[21] P. Devi, A.K. Saroha, Effect of temperature on biochar properties during papermill sludge pyrolysis, Int. J. ChemTech Res. 5 (2013) 682–687.

[22] P.E. Diaz-Flores, R. Leyva-Ramos, R.M. Guerrero-Coronado, J. Mendoza-Barron,Adsorption of pentachlorophenol from aqueous solution onto activated carbonfiber, Ind. Eng. Chem. Res. 45 (2006) 330–336.

[23] L. Lou, L. Luo, G. Cheng, Y. Wei, R. Mei, B. Xun, X. Xu, B. Hu, Y. Chen, Thesorption of pentachlorophenol by aged sediment supplemented with blackcarbon produced from rice straw and fly ash, Bioresour. Technol. 112 (2012)61–66.

[24] B. Subramanian, V. Namboodiri, A.P. Khodadoust, D.D. Dionysiou, Extraction ofpentachlorophenol from soils using environmentally benign lactic acidsolutions, J. Hazard. Mater. 174 (2010) 263–269.

[25] D. Pandey, G. Deo, Promotional effects in alumina and silica supportedbimetallic Ni–Fe catalysts during CO2 hydrogenation, J. Mol. Catal. A: Chem.382 (2014) 23–30.

[26] P. Devi, A.K. Saroha, Risk analysis of pyrolyzed biochar made from paper milleffluent treatment plant sludge for bioavailability & eco-toxicity of heavymetals, Bioresour. Technol. 162 (2014) 308–315.

[27] A. Mendez, J. Paz-Ferreiro, F. Araujo, B. Gasco, Biochar from pyrolysis ofdeinking paper sludge and its use in the treatment of a nickel polluted soil, J.Anal. Appl. Pyrolysis 107 (2014) 46–52.

[28] M.K. Hossain, V. Strezov, K.Y. Chan, A. Ziolkowski, P.F. Nelson, Influence ofpyrolysis temperature on production and nutrient properties of wastewatersludge biochar, J. Environ. Manage. 92 (2011) 223–228.

[29] R. Cheng, W. Zhou, J.L. Wang, D. Qi, L. Guo, W.X. Zhang, Y. Qian, Dechlorinationof pentachlorophenol using nanoscale Fe/Ni particles: role of nano-Ni and itssize effect, J. Hazard. Mater. 180 (2010) 79–85.

[30] A. Dabrowski, P. Podkoscielny, Z. Hubicki, M. Barczak, Adsorption of phenoliccompounds by activated carbon—a critical review, Chemosphere 58 (2005)1049–1070.

[31] J. Xu, T. Sheng, Y. Hu, A.A. Baig, X. Lv, X. Xu, Adsorption–dechlorination of 2,4-dichlorophenol using two specified MWCNTs-stabilized Pd/Fenanocomposites, Chem. Eng. J. 219 (2013) 162–173.

[32] Y. Han, W. Li, M.H. Zhang, K.Y. Tao, Catalytic dechlorination ofmonochlorobenzene with a new type of nanoscale Ni(B)/Fe(B) bimetalliccatalytic reductant, Chemosphere 72 (2008) 53–58.

[33] N. Zhu, Y. Li, F.S. Zhang, Catalytic dechlorination of polychlorinated biphenylsin subcritical water by Ni/Fe nanoparticles, Chem. Eng. J. 171 (2011) 919–925.

[34] A. Kara, E. Demirbel, Kinetics, isotherm, thermodynamics analysis onadsorption of Cr(VI) ions from aqueous solutions by synthesis andcharacterization of magnetic-poly(divinylbenzene-vinylimidazole)microbeads, Water Air Soil Pollut. 223 (2012) 2387–2403.

[35] F. Xu, S. Deng, J. Xu, W. Zhang, M. Wu, B. Wang, J. Huang, G. Yu, Highly activeand stable Ni�Fe bimetal prepared by ball milling for catalytichydrodechlorination of 4-chlorophenol, Environ. Sci. Technol. 46 (2012)4576–4582.

[36] US EPA (Environmental Protection Agency), Integrated Risk InformationSystem on Pentachlorophenol, National Centre for Environmental Assessment,Office of Research and Development, Washington, DC, 1999.