- Email: [email protected]
Nano-zerovalent iron contained porous carbons developed from waste biomass for the adsorption and dechlorination of PCBs
Bioresource Technology 101 (2010) 2562–2564
Contents lists available at ScienceDirect
Bioresource Technology journal homepage: www.elsevier.com/locate/biortech
Short Communication
Nano-zerovalent iron contained porous carbons developed from waste biomass for the adsorption and dechlorination of PCBs Zhengang Liu a,b, Fu-Shen Zhang a,* a b
Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, 18 Shuangqing Road, Beijing 100085, China EcoTopia Science Institute, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8603, Japan
a r t i c l e
i n f o
Article history: Received 8 September 2009 Received in revised form 12 November 2009 Accepted 18 November 2009 Available online 21 December 2009 Keywords: Waste biomass Carbonization Pyrolysis Catalytic dechlorination Polychlorinated biphenyls
a b s t r a c t The low-cost composite, nano-zerovalent iron (NZVI) contained in porous carbon (PC), was prepared using pinewood sawdust and ferric chloride as starting materials. The key point of this strategy was that the production of PC and the formation of NZVI were accomplished simultaneously through a simple process. The composite PC/NZVI was characterized by XRD, BET and the adsorption and simultaneous dechlorination of PCBs were efficiently demonstrated. The results showed the pinewood sawdust was activated by ferric chloride and the surface area and the pore volume of obtained composite were 423 m2/g and 0.23 cm3/g, respectively. The produced NZVI, around 27 nm in diameter, catalyzed the formation of substantial mesopores in the composite. PC/NZVI exhibited an efficient dechlorination of PCBs at room temperature, and the dechlorinated-products could be completely adsorbed onto the composite. Accordingly, it is believed that PC/NZVI developed in the present study is practically applicable for PCBscontaminated water purification. Ó 2009 Elsevier Ltd. All rights reserved.
1. Introduction Biofuel production and carbonaceous materials synthesis from waste biomass have attracted much attention due to the increased energy shortage and environmental concerns. Due to the lower economical competitiveness of biofuel production in comparison with crude energy, synthesis of functional carbonaceous materials is viewed as most promising utilization of biomass at present. In addition, the transformation of biomass toward carbonaceous material has the advantage of sequestering carbon from plant biomass, therefore binding CO2 in atmosphere efficiently (Nunes et al., 2009). Due to the strong attachment of organic pollutants to carbonaceous material in environmental media, the porous carbon (PC) acting as adsorbent/catalysis support has shown insignificant application for the pollution control (Choi et al., 2008; Yoon et al., 2006; Sevilla et al., 2007). PC supported zerovalent iron (ZVI) insignificantly enhanced the reactivity of ZVI during treating PCBs-contaminated water (Sun et al., 2006). The preparation of PC/ NZVI was generally carried out via several tedious consecutive steps including incipient wet impregnation of commercial PC, chemicals reduction of iron salt and heat treatment (Choi et al., 2008; Sun et al., 2006). The time-consuming synthetic processes
* Corresponding author. Tel./fax: +86 10 62849515. E-mail address: [email protected] (F.-S. Zhang). 0960-8524/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.biortech.2009.11.074
together with the high production cost of PC limited large-scale application of PC/NZVI in practice. In this paper, for the first time, a novel PC/NZVI composite was synthesized using pinewood sawdust and ferric chloride as starting materials through simple one-step pyrolysis. The PC/NZVI composite was characterized and utilized in adsorption and simultaneous dechlorination of PCBs from aqueous solutions. 2. Methods 2.1. Preparation of PC/NZVI Analytical grade ethanol and ferric chloride were purchased from Beijing Chemicals Company. Waste biomass (pinewood sawdust) was obtained from a wood processing factory in Beijing suburb (C 43.25%; H 6.01%; N 0.21%; S 0.10% and O 50.43% calculated by difference). Prior to impregnation with FeCl3, the pinewood sawdust was firstly dried at 105 °C for 24 h in an oven followed by ground into 680 meshes. Two gram of the sawdust sample was immersed into 20 ml of 1 mol/L FeCl3 solution and the resulting mixture was subsequently ultrasonicated for 2 h at room temperature. After stirred at 60 °C for 12 h, the mixture was separated through vacuum filtration. The recovered residue was dried at 100 °C in vacuum for 2 h followed by pyrolyzing under continuous N2 with flow rate 30 ml/min. The sample was heated from room temperature to final 800 °C with heating rate 20 °C/min and hold for 40 min
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Z. Liu, F.-S. Zhang / Bioresource Technology 101 (2010) 2562–2564
at 800 °C. The sample was cooled inside the furnace, maintaining the N2 flow, and then washed with de-ionized water and ethanol for several times. The resulting product was vacuum dried for use (the product was designated as A800). For comparison, the sawdust without ferric chloride impregnation was pyrolyzed under the same procedure at 800 °C (the corresponding product was designated as P800). 2.2. Characterization The crystal property of the composite were determined by XRD (Shimadazu Corporation, Japan) within 2°/min using graphite monochromatic copper radiation (CuKa) at 40 kV and 30 mA over the 2h range 10–80°. The BET surface area was obtained from nitrogen adsorption isotherms at 196 °C using an ASAP 2010 analyzer (Micromeritics, USA). Prior to the N2 sorption analysis, the sample was degassed at 150 °C for 8 h. 2.3. PCBs removal from aqueous solution by A800 Considering the existence form in environment media (commercial PCBs typically come with a mixture of different chlorinate-substituted biphenyls and isomers) and the adsorption interaction of different PCBs (Nollet et al., 2003), Aroclor 1242 (di-, tri-, tetra- and penta-chlorinated PCBs mainly contained) was selected as a representative PCBs sample in present study. Acetone and n-hexane were chromatographic grade purchased form Alfa. Batch experiments were conducted in a 50-mL serum bottle capped with viton stops and sealed with aluminum cap. Two gram of A800 was added to 25 mL of 10 mg/L PCBs aqueous solution and the mixture was agitated at 200 rpm at room temperature for 9 days. Samples (0.5 mL) were taken at predetermined interval (the interval was 2 h within initial 24 h and then changed to 48 h) with a glass syringe from the close-reaction system and collected in 2.5-mL glass vessels filled with 1 mL n-hexane. Then the samples were extracted on a platform shaker at 200 rpm and 25 °C for 24 h followed by centrifugation for 20 min. The water-insoluble layer was analyzed for the concentration of PCBs remained and the complete dechlorinated product biphenyl. After 9 days, the solid/liquid mixture was separated through vacuum filtration and the solid residue recovered was extracted by 20 mL acetone/n-hexane (v/ v = 1) in Soxhlet extraction equipment to analyze the residual PCBs and the adsorbed biphenyl. The analysis was carried on gas chromatograph equipped with mass selective detector (GC-MS, Agilent 7890A/5975C, USA) and HP-5 column (5% phenyl methyl siloxane, 30 m 250 lm 0.25 lm) was used.
comparison with P800, the porous property of A800 was significantly enhanced by the addition of FeCl3, which indicated that the FeCl3 acted as activation agent in the sawdust carbonization. In addition, isotherms of A800 showed a significant adsorption up to relative pressure 0.06 and the hysteresis loop between adsorption and desorption isotherms at higher relative pressure, indicating the presence of substantial amount of mesopores in microporous A800. The formation of mesopores was catalyzed by NZVI and the similar phenomena have been observed in aerogel carbonization process (Maldonado-Hodar et al., 2000). 3.2. PCBs adsorption and dechlorination The different chlorinated biphenyls were represented as selected compounds (2,3- and 2,60 -dichloro-1,10 -biphenyl represented di-chlorinated biphenyls (2CB); 2,5,50 - and 2,3,4-trichloro1,10 -biphenyl represented tri-chlorinated biphenyls (3CB); 2,3,40 ,60 - and 2,4,40 ,6-tetrachloro-1,10 -biphenyl represented tetrachlorinated biphenyls (4CB); 2,3,4,40 ,5- and 2,30 ,40 ,5,60 -penta-1,10 biphenyl represented penta-chlorinated biphenyls (5CB)). Fig. 1 shows the removal rate (%) of different chlorinated biphenyls in terms of time. The PCBs was completely removed from the aqueous solution after 16 h. Pseudo-first-order and pseudo-second-order equation were also employed to study PCBs removal process by A800 (here PCBs as a whole and the removal rate from the average removal rate of representative 2CB, 3CB, 4CB and 5CB). The higher correction coefficient R2 (R2 were 0.855 and 0.998 for pseudo-firstorder and pseudo-second-order equation, respectively) indicated that the pseudo-second-order equation can satisfactorily approximate the removal of the PCBs from aqueous solution as a result of synergistically combination of adsorption and dechlorination. The chlorination is summarized by the following equations:
Fe0 ! Fe2þ ðaqÞ þ 2e þ
Ar2 Clm þ mH þ ne
E0 ¼ þ0:447 V
ð1Þ
! Ar2 Hm þ ðn mÞCl
ð2Þ
Fig. 2 shows the dechlorination rate of the different chlorinated biphenyls. As can be seen from Fig. 2, more than 70% of PCBs (except 2CB) were dechlorinated after 9 days at room temperature. Taking into account of the fact that the dechlorination of 3CB, 4CB and 5CB could transform into 2CB, it was safely concluded the actual dechlorination rate of 2CB exceeded the observed dechlorination rate (68.4%). In addition, it was worthily noted that only small
100
80
3.1. Characterization of the composite XRD patterns of A800 presents the characteristic peaks 2h = 44.57 and 64.94° and these two peaks were assigned to the 1 1 0 and 2 0 0 plane reflections of the ZVI with a body centered cubic (bcc) structure (Hoch et al., 2008). The crystal size of the ZVI particles in A800 was calculated using the full width at half maximum of the XRD peaks according to Scherrer equation (Cullity and Stock, 2001). The estimated size of ZVI from the 1 1 0 plane diffraction was 27 nm in A800. As for P800, the XRD pattern was simple, and the broad weak bands around 2h = 22° together with the deviation of the baseline between 20° and 30° indicated the amorphous carbonaceous structure of organic matrix (Mochidzuki et al., 2003). The BET surface area, pore volume were 423 m2/g and 0.23 cm3/ g for A800 and 20 m2/g and 0.04 cm3/g for P800, respectively. In
Removal rate (%)
3. Results and discussion
60
2CB 3CB 4CB 5CB
40
20
0 0
4
8 Time (h)
12
16
Fig. 1. Removal rate of different chlorinated PCBs as a function of time (PCBs concentration 10 mg/L; A800 dose 80 g/L).
2564
Z. Liu, F.-S. Zhang / Bioresource Technology 101 (2010) 2562–2564
Cl
80
adsorption and dechlorination onto the PC/NZVI resulted in a mostly complete PCBs removal from aqueous solution.
Cl
Acknowledgements
Cl Cl
Dechlorination rate (%)
Cl Cl
Cl
Cl Cl
Cl
Cl Cl
Cl
Cl
Cl
Cl Cl
Cl
Cl Cl
Cl
Cl Cl
70
This work was financially supported, in part, by the National Key Technology R&D Program (2008BAC32B03) and the National Basic Research Program of China (2007CB407303) of China. The authors greatly appreciate Dr. Nengmin Zhu for providing the PCBs samples.
Cl Cl
Cl
Cl
Cl
References
60 1
2
3 4 5 Different chlorinated biphenyls
6
Fig. 2. Dechlorination rate of different chlorinated PCBs (A800 dose 80 g/L; reaction time 9 days).
amount of biphenyl, the completely dechlorinated product, was detected in the aqueous solution, indicating even the dechlorinated products preferentially adsorbed on the composite A800 rather than diffused into the aqueous solutions. In comparison with other NZVI reduction, the quick dechlorination and high destruction rate onto PC/NZVI was attributed to the enhanced contacting between the PCBs and NZVI due to the PCBs strong adsorption on PC (Lowry et al., 2004). On the other hand, the presence of a transport pores (i.e., mesopores) also played an important role to accelerate the adsorption and dechlorination (Tseng et al., 2003; Sabio et al., 2004; Yoon et al., 2006).
4. Conclusions A simple process for preparing functional PC/NZVI composite was developed using pinewood sawdust and ferric chloride as starting materials. The sawdust could be significantly activated by ferric chloride, and subsequently NZVI was formed in the carbonization process. The synergistic and simultaneous function of
Choi, H., Al-Abed, S.R., Agarwal, S., Dionysiou, D.D., 2008. Synthesis of reactive nanoFe/Pd bimetallic system-impregnated activated carbon for the simultaneous adsorption and dechlorination of PCBs. Chem. Mater. 20, 3649–3655. Cullity, B.D., Stock, S.R., 2001. Elements of X-Ray Diffraction, third ed. Prentice-Hall, New York. Hoch, L.B., Mack, E.J., Hydutsky, B.W., Hershman, J.M., Skluzacek, J.M., Mallouk, T.E., 2008. Carbothermal synthesis of carbon-supported nanoscale zero-valent iron particles for the remediation of hexavalent chromium. Environ. Sci. Technol. 42, 2600–2605. Lowry, G.V., Johnson, K.M., 2004. Congener-specific dechlorination of dissolved PCBs by microscale and nanoscale zerovalent iron in a water/methanol solution. Environ. Sci. Technol. 38, 5208–5216. Maldonado-Hodar, F.J., Moreno-Castilla, C., Rivera-Utrilla, J., Hanzawa, Y., Yamada, Y., 2000. Catalytic graphitization of carbon aerogels by transition metals. Langmuir 16, 4367–4373. Mochidzuki, K., Soutric, F., Tadokoro, K., Antal, M.J., Toth, M., Zelei, B., Varhegyi, G., 2003. Electric and physical properties of carbonized charcoals. Ind. Eng. Chem. Res. 42, 5140–5151. Nollet, H., Roels, M., Lutgen, P., Van der Meeren, P., Verstraete, W., 2003. Removal of PCBs from wastewater using fly ash. Chemosphere 53, 655–665. Nunes, A.A., Franca, A.S., Oliveira, L.S., 2009. Activated carbons from waste biomass: an alternative use for biodiesel production solid residues. Bioresour. Technol. 100, 1786–1792. Sabio, E., Gonzalez, E., Gonzalez, J.F., Gonzalez-Garcia, C.M., Ramiro, A., Ganan, J., 2004. Thermal regeneration of activated carbon saturated with p-nitrophenol. Carbon 42, 2285–2293. Sevilla, M., Lota, G., Fuertes, A.B., 2007. Saccharide-based graphitic carbon nanocoils as supports fror PtRu nanoparticles for methanol electrooxidation. J. Power Sources 171, 546–551. Sun, Y., Takaoka, M., Takeda, N., Matsumoto, T., Oshita, K.M., 2006. Kinetics on the decomposition of polychlorinated biphenyls with activated carbon-supported iron. Chemosphere 65, 183–189. Tseng, R.L., Wu, F.C., Juang, R.S., 2003. Liquid-phase adsorption of dyes and phenols using pinewood-based activated carbons. Carbon 41, 487–495. Yoon, T.H., Benzerara, K., Ahn, S., Luthy, R.G., Tyliszczak, T., Brown, G.E., 2006. Nanometer-scale chemical heterogeneities of black carbon materials and their impacts on PCB sorption properties: soft X-ray spectromicroscopy study. Environ. Sci. Technol. 40, 5923–5929.
Contents lists available at ScienceDirect
Bioresource Technology journal homepage: www.elsevier.com/locate/biortech
Short Communication
Nano-zerovalent iron contained porous carbons developed from waste biomass for the adsorption and dechlorination of PCBs Zhengang Liu a,b, Fu-Shen Zhang a,* a b
Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, 18 Shuangqing Road, Beijing 100085, China EcoTopia Science Institute, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8603, Japan
a r t i c l e
i n f o
Article history: Received 8 September 2009 Received in revised form 12 November 2009 Accepted 18 November 2009 Available online 21 December 2009 Keywords: Waste biomass Carbonization Pyrolysis Catalytic dechlorination Polychlorinated biphenyls
a b s t r a c t The low-cost composite, nano-zerovalent iron (NZVI) contained in porous carbon (PC), was prepared using pinewood sawdust and ferric chloride as starting materials. The key point of this strategy was that the production of PC and the formation of NZVI were accomplished simultaneously through a simple process. The composite PC/NZVI was characterized by XRD, BET and the adsorption and simultaneous dechlorination of PCBs were efficiently demonstrated. The results showed the pinewood sawdust was activated by ferric chloride and the surface area and the pore volume of obtained composite were 423 m2/g and 0.23 cm3/g, respectively. The produced NZVI, around 27 nm in diameter, catalyzed the formation of substantial mesopores in the composite. PC/NZVI exhibited an efficient dechlorination of PCBs at room temperature, and the dechlorinated-products could be completely adsorbed onto the composite. Accordingly, it is believed that PC/NZVI developed in the present study is practically applicable for PCBscontaminated water purification. Ó 2009 Elsevier Ltd. All rights reserved.
1. Introduction Biofuel production and carbonaceous materials synthesis from waste biomass have attracted much attention due to the increased energy shortage and environmental concerns. Due to the lower economical competitiveness of biofuel production in comparison with crude energy, synthesis of functional carbonaceous materials is viewed as most promising utilization of biomass at present. In addition, the transformation of biomass toward carbonaceous material has the advantage of sequestering carbon from plant biomass, therefore binding CO2 in atmosphere efficiently (Nunes et al., 2009). Due to the strong attachment of organic pollutants to carbonaceous material in environmental media, the porous carbon (PC) acting as adsorbent/catalysis support has shown insignificant application for the pollution control (Choi et al., 2008; Yoon et al., 2006; Sevilla et al., 2007). PC supported zerovalent iron (ZVI) insignificantly enhanced the reactivity of ZVI during treating PCBs-contaminated water (Sun et al., 2006). The preparation of PC/ NZVI was generally carried out via several tedious consecutive steps including incipient wet impregnation of commercial PC, chemicals reduction of iron salt and heat treatment (Choi et al., 2008; Sun et al., 2006). The time-consuming synthetic processes
* Corresponding author. Tel./fax: +86 10 62849515. E-mail address: [email protected] (F.-S. Zhang). 0960-8524/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.biortech.2009.11.074
together with the high production cost of PC limited large-scale application of PC/NZVI in practice. In this paper, for the first time, a novel PC/NZVI composite was synthesized using pinewood sawdust and ferric chloride as starting materials through simple one-step pyrolysis. The PC/NZVI composite was characterized and utilized in adsorption and simultaneous dechlorination of PCBs from aqueous solutions. 2. Methods 2.1. Preparation of PC/NZVI Analytical grade ethanol and ferric chloride were purchased from Beijing Chemicals Company. Waste biomass (pinewood sawdust) was obtained from a wood processing factory in Beijing suburb (C 43.25%; H 6.01%; N 0.21%; S 0.10% and O 50.43% calculated by difference). Prior to impregnation with FeCl3, the pinewood sawdust was firstly dried at 105 °C for 24 h in an oven followed by ground into 680 meshes. Two gram of the sawdust sample was immersed into 20 ml of 1 mol/L FeCl3 solution and the resulting mixture was subsequently ultrasonicated for 2 h at room temperature. After stirred at 60 °C for 12 h, the mixture was separated through vacuum filtration. The recovered residue was dried at 100 °C in vacuum for 2 h followed by pyrolyzing under continuous N2 with flow rate 30 ml/min. The sample was heated from room temperature to final 800 °C with heating rate 20 °C/min and hold for 40 min
2563
Z. Liu, F.-S. Zhang / Bioresource Technology 101 (2010) 2562–2564
at 800 °C. The sample was cooled inside the furnace, maintaining the N2 flow, and then washed with de-ionized water and ethanol for several times. The resulting product was vacuum dried for use (the product was designated as A800). For comparison, the sawdust without ferric chloride impregnation was pyrolyzed under the same procedure at 800 °C (the corresponding product was designated as P800). 2.2. Characterization The crystal property of the composite were determined by XRD (Shimadazu Corporation, Japan) within 2°/min using graphite monochromatic copper radiation (CuKa) at 40 kV and 30 mA over the 2h range 10–80°. The BET surface area was obtained from nitrogen adsorption isotherms at 196 °C using an ASAP 2010 analyzer (Micromeritics, USA). Prior to the N2 sorption analysis, the sample was degassed at 150 °C for 8 h. 2.3. PCBs removal from aqueous solution by A800 Considering the existence form in environment media (commercial PCBs typically come with a mixture of different chlorinate-substituted biphenyls and isomers) and the adsorption interaction of different PCBs (Nollet et al., 2003), Aroclor 1242 (di-, tri-, tetra- and penta-chlorinated PCBs mainly contained) was selected as a representative PCBs sample in present study. Acetone and n-hexane were chromatographic grade purchased form Alfa. Batch experiments were conducted in a 50-mL serum bottle capped with viton stops and sealed with aluminum cap. Two gram of A800 was added to 25 mL of 10 mg/L PCBs aqueous solution and the mixture was agitated at 200 rpm at room temperature for 9 days. Samples (0.5 mL) were taken at predetermined interval (the interval was 2 h within initial 24 h and then changed to 48 h) with a glass syringe from the close-reaction system and collected in 2.5-mL glass vessels filled with 1 mL n-hexane. Then the samples were extracted on a platform shaker at 200 rpm and 25 °C for 24 h followed by centrifugation for 20 min. The water-insoluble layer was analyzed for the concentration of PCBs remained and the complete dechlorinated product biphenyl. After 9 days, the solid/liquid mixture was separated through vacuum filtration and the solid residue recovered was extracted by 20 mL acetone/n-hexane (v/ v = 1) in Soxhlet extraction equipment to analyze the residual PCBs and the adsorbed biphenyl. The analysis was carried on gas chromatograph equipped with mass selective detector (GC-MS, Agilent 7890A/5975C, USA) and HP-5 column (5% phenyl methyl siloxane, 30 m 250 lm 0.25 lm) was used.
comparison with P800, the porous property of A800 was significantly enhanced by the addition of FeCl3, which indicated that the FeCl3 acted as activation agent in the sawdust carbonization. In addition, isotherms of A800 showed a significant adsorption up to relative pressure 0.06 and the hysteresis loop between adsorption and desorption isotherms at higher relative pressure, indicating the presence of substantial amount of mesopores in microporous A800. The formation of mesopores was catalyzed by NZVI and the similar phenomena have been observed in aerogel carbonization process (Maldonado-Hodar et al., 2000). 3.2. PCBs adsorption and dechlorination The different chlorinated biphenyls were represented as selected compounds (2,3- and 2,60 -dichloro-1,10 -biphenyl represented di-chlorinated biphenyls (2CB); 2,5,50 - and 2,3,4-trichloro1,10 -biphenyl represented tri-chlorinated biphenyls (3CB); 2,3,40 ,60 - and 2,4,40 ,6-tetrachloro-1,10 -biphenyl represented tetrachlorinated biphenyls (4CB); 2,3,4,40 ,5- and 2,30 ,40 ,5,60 -penta-1,10 biphenyl represented penta-chlorinated biphenyls (5CB)). Fig. 1 shows the removal rate (%) of different chlorinated biphenyls in terms of time. The PCBs was completely removed from the aqueous solution after 16 h. Pseudo-first-order and pseudo-second-order equation were also employed to study PCBs removal process by A800 (here PCBs as a whole and the removal rate from the average removal rate of representative 2CB, 3CB, 4CB and 5CB). The higher correction coefficient R2 (R2 were 0.855 and 0.998 for pseudo-firstorder and pseudo-second-order equation, respectively) indicated that the pseudo-second-order equation can satisfactorily approximate the removal of the PCBs from aqueous solution as a result of synergistically combination of adsorption and dechlorination. The chlorination is summarized by the following equations:
Fe0 ! Fe2þ ðaqÞ þ 2e þ
Ar2 Clm þ mH þ ne
E0 ¼ þ0:447 V
ð1Þ
! Ar2 Hm þ ðn mÞCl
ð2Þ
Fig. 2 shows the dechlorination rate of the different chlorinated biphenyls. As can be seen from Fig. 2, more than 70% of PCBs (except 2CB) were dechlorinated after 9 days at room temperature. Taking into account of the fact that the dechlorination of 3CB, 4CB and 5CB could transform into 2CB, it was safely concluded the actual dechlorination rate of 2CB exceeded the observed dechlorination rate (68.4%). In addition, it was worthily noted that only small
100
80
3.1. Characterization of the composite XRD patterns of A800 presents the characteristic peaks 2h = 44.57 and 64.94° and these two peaks were assigned to the 1 1 0 and 2 0 0 plane reflections of the ZVI with a body centered cubic (bcc) structure (Hoch et al., 2008). The crystal size of the ZVI particles in A800 was calculated using the full width at half maximum of the XRD peaks according to Scherrer equation (Cullity and Stock, 2001). The estimated size of ZVI from the 1 1 0 plane diffraction was 27 nm in A800. As for P800, the XRD pattern was simple, and the broad weak bands around 2h = 22° together with the deviation of the baseline between 20° and 30° indicated the amorphous carbonaceous structure of organic matrix (Mochidzuki et al., 2003). The BET surface area, pore volume were 423 m2/g and 0.23 cm3/ g for A800 and 20 m2/g and 0.04 cm3/g for P800, respectively. In
Removal rate (%)
3. Results and discussion
60
2CB 3CB 4CB 5CB
40
20
0 0
4
8 Time (h)
12
16
Fig. 1. Removal rate of different chlorinated PCBs as a function of time (PCBs concentration 10 mg/L; A800 dose 80 g/L).
2564
Z. Liu, F.-S. Zhang / Bioresource Technology 101 (2010) 2562–2564
Cl
80
adsorption and dechlorination onto the PC/NZVI resulted in a mostly complete PCBs removal from aqueous solution.
Cl
Acknowledgements
Cl Cl
Dechlorination rate (%)
Cl Cl
Cl
Cl Cl
Cl
Cl Cl
Cl
Cl
Cl
Cl Cl
Cl
Cl Cl
Cl
Cl Cl
70
This work was financially supported, in part, by the National Key Technology R&D Program (2008BAC32B03) and the National Basic Research Program of China (2007CB407303) of China. The authors greatly appreciate Dr. Nengmin Zhu for providing the PCBs samples.
Cl Cl
Cl
Cl
Cl
References
60 1
2
3 4 5 Different chlorinated biphenyls
6
Fig. 2. Dechlorination rate of different chlorinated PCBs (A800 dose 80 g/L; reaction time 9 days).
amount of biphenyl, the completely dechlorinated product, was detected in the aqueous solution, indicating even the dechlorinated products preferentially adsorbed on the composite A800 rather than diffused into the aqueous solutions. In comparison with other NZVI reduction, the quick dechlorination and high destruction rate onto PC/NZVI was attributed to the enhanced contacting between the PCBs and NZVI due to the PCBs strong adsorption on PC (Lowry et al., 2004). On the other hand, the presence of a transport pores (i.e., mesopores) also played an important role to accelerate the adsorption and dechlorination (Tseng et al., 2003; Sabio et al., 2004; Yoon et al., 2006).
4. Conclusions A simple process for preparing functional PC/NZVI composite was developed using pinewood sawdust and ferric chloride as starting materials. The sawdust could be significantly activated by ferric chloride, and subsequently NZVI was formed in the carbonization process. The synergistic and simultaneous function of
Choi, H., Al-Abed, S.R., Agarwal, S., Dionysiou, D.D., 2008. Synthesis of reactive nanoFe/Pd bimetallic system-impregnated activated carbon for the simultaneous adsorption and dechlorination of PCBs. Chem. Mater. 20, 3649–3655. Cullity, B.D., Stock, S.R., 2001. Elements of X-Ray Diffraction, third ed. Prentice-Hall, New York. Hoch, L.B., Mack, E.J., Hydutsky, B.W., Hershman, J.M., Skluzacek, J.M., Mallouk, T.E., 2008. Carbothermal synthesis of carbon-supported nanoscale zero-valent iron particles for the remediation of hexavalent chromium. Environ. Sci. Technol. 42, 2600–2605. Lowry, G.V., Johnson, K.M., 2004. Congener-specific dechlorination of dissolved PCBs by microscale and nanoscale zerovalent iron in a water/methanol solution. Environ. Sci. Technol. 38, 5208–5216. Maldonado-Hodar, F.J., Moreno-Castilla, C., Rivera-Utrilla, J., Hanzawa, Y., Yamada, Y., 2000. Catalytic graphitization of carbon aerogels by transition metals. Langmuir 16, 4367–4373. Mochidzuki, K., Soutric, F., Tadokoro, K., Antal, M.J., Toth, M., Zelei, B., Varhegyi, G., 2003. Electric and physical properties of carbonized charcoals. Ind. Eng. Chem. Res. 42, 5140–5151. Nollet, H., Roels, M., Lutgen, P., Van der Meeren, P., Verstraete, W., 2003. Removal of PCBs from wastewater using fly ash. Chemosphere 53, 655–665. Nunes, A.A., Franca, A.S., Oliveira, L.S., 2009. Activated carbons from waste biomass: an alternative use for biodiesel production solid residues. Bioresour. Technol. 100, 1786–1792. Sabio, E., Gonzalez, E., Gonzalez, J.F., Gonzalez-Garcia, C.M., Ramiro, A., Ganan, J., 2004. Thermal regeneration of activated carbon saturated with p-nitrophenol. Carbon 42, 2285–2293. Sevilla, M., Lota, G., Fuertes, A.B., 2007. Saccharide-based graphitic carbon nanocoils as supports fror PtRu nanoparticles for methanol electrooxidation. J. Power Sources 171, 546–551. Sun, Y., Takaoka, M., Takeda, N., Matsumoto, T., Oshita, K.M., 2006. Kinetics on the decomposition of polychlorinated biphenyls with activated carbon-supported iron. Chemosphere 65, 183–189. Tseng, R.L., Wu, F.C., Juang, R.S., 2003. Liquid-phase adsorption of dyes and phenols using pinewood-based activated carbons. Carbon 41, 487–495. Yoon, T.H., Benzerara, K., Ahn, S., Luthy, R.G., Tyliszczak, T., Brown, G.E., 2006. Nanometer-scale chemical heterogeneities of black carbon materials and their impacts on PCB sorption properties: soft X-ray spectromicroscopy study. Environ. Sci. Technol. 40, 5923–5929.