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Influence of copper content on NO removal of the activated carbon fibers produced by electroplating
Journal of Colloid and Interface Science 264 (2003) 39–42 www.elsevier.com/locate/jcis
Influence of copper content on NO removal of the activated carbon fibers produced by electroplating Soo-Jin Park ∗ and Jun-Sik Shin Advanced Materials Division, Korea Research Institute of Chemical Technology, P.O. Box 107, Yusong, Taejon 305-600, South Korea Received 10 December 2002; accepted 22 March 2003
Abstract In this study, the activated carbon fibers (ACFs) on which copper metal was deposited by electroplating were used to remove nitric oxide (NO). N2 /77 K adsorption isotherm characteristics, including the specific surface area and micropore volume, were investigated by BET and T -plot methods. NO removal efficiency was confirmed by gas chromatographic technique. From the experimental results, the copper content supported on ACFs led to an increase in the NO conversion, in spite of the decrease of the specific surface area or the micropore volume of ACFs. Consequently, the presence of Cu on ACFs played an important role in improving the NO reduction into O2 and N2 , which was mainly attributed to the catalytic reactions of C–NO–Cu. 2003 Elsevier Inc. All rights reserved. Keywords: Activated carbon fibers; Cu electroplating; Adsorption; NO removal; Catalytic reaction
1. Introduction Air pollution is not a new problem. It has been with society since at least the Middle Ages. But recent times, due largely to increased population and industrialization, it has come to the forefront of public concern. Especially, nitrogen oxides (NOx ) are major pollutants in the atmosphere, being a precursor to acid rain, photochemical smog, and ozone accumulation. Nitrogen oxide (NO) is not considered harmful to health. However, it can react with other gases present both in the exhaust and in the atmosphere to form nitrogen dioxide (NO2 ). Nitrogen dioxide is harmful to health and is also an important component in the formation of ozone [1–8]. There are several methods for controlling NOx emissions. Gas scrubbing is one of the most common forms of NOx treatment, with sodium hydroxide being the conventional scrubbing medium. Also, combustion systems have been used up to this day. However, they have problems such as complex, expensive setup, harmful gas emission, and metal corrosion. In recent years, to overcome these problems, some researchers [2,7,8] have reported that NO is reduced more effectively by using the adsorption characteristics of activated carbons (ACs) and activated carbon fibers (ACFs). * Corresponding author.
E-mail address: [email protected] (S.-J. Park). 0021-9797/03/$ – see front matter 2003 Elsevier Inc. All rights reserved. doi:10.1016/S0021-9797(03)00333-3
Also, other researchers have studied NO reduction using metals supported on ACs or ACFs by impregnation, metal plating, deposition, and so on [9–13]. Especially, ACFs have been actually used in waste water disposal plants, adsorption systems, and removal apparatus for noxious gas because of their extended specific surface area, high adsorption capacity, well-developed micropores, safety, reproductability, processability, and so on. However, metal-supporting methods on ACs or ACFs and their NO removal efficiency have not yet been studied systematically. The objective of the present work is to investigate the surface and adsorption characteristics of the electrolytic Cuplated ACFs by using pH, FTIR, and BET isotherms and to discuss the influence of NO removal on plating time and copper content of the ACFs studied.
2. Experimental For the present investigation, the ACFs were supplied from Taiwan Carbon Co. (AW2001, weight 45 g/m2, thickness 0.3 mm, and specific surface area 2121 m2 /g). Cudeposited ACFs were prepared by Cu electroplating at a constant velocity and same electric current. Electrolytic copper and graphite plate were used as an anode and a cathode, respectively. The samples with different plating times, 0, 2,
40
S.-J. Park, J.-S. Shin / Journal of Colloid and Interface Science 264 (2003) 39–42
5, 10, and 20 s, were denoted as-received, Cu-2, Cu-5, Cu10, and Cu-20, respectively. The compositions of the plating bath were CuSO4 (10 g/l) and H2 SO4 (20 ml/l) solutions. Prior to use following analyses, the residual solution of the electrolyte in the treated ACFs was washed several times with distilled water and dried in a drying oven at 60 ◦ C for 12 h. The amount of copper in Cu-plated ACFs was determined by atomic absorption spectrophotometry (AAS) and showed copper mg per carbon fiber g. Nitrogen isotherms were measured by using an ASAP (Micromeritics) at 77 K. Prior to each analysis, the samples were outgassed at 573 K for 10–12 h to obtain a residual pressure of less than 10−3 Torr. The amount of nitrogen adsorbed, used to calculate specific surface area and micropore volume was determined from the BET equation [14] and T -plot method [15], respectively. Also, the Horvath– Kawazoe model [16] was applied to the experimental nitrogen isotherms for pore size distribution. For the present experiment, a gas chromatograph (DS 6200 model, Donam Co., Korea) and a thermal collect detector were used to measure NO conversion. Reactor temperature was sustained constantly at 500 ◦ C using a P.I.D. temperature controller (UP-350, Yokokawa) and gas flow rate was maintained at 10 ml/min by a mass flow controller (GMC 1000, MKS). All samples were heated under a helium purge at 150 ◦ C for 1 h to remove residual H2 O before NO conversion test. The NO conversion was determined from the concentration of NO at the outlet reactor. Prior to each analysis, NO standard curve was gained by using the 300, 600, and 1000 ppm NO gas.
3. Results and discussion Figure 1 shows the content of copper on ACFs as a function of electroplating time. It is seen that the content of copper increases rapidly at the beginning of plating time, whereas the plating velocity is decreased with increasing the plating time. This probably indicates that plating is decreased because of Cu deposited on ACF surfaces. Also, the
Fig. 1. Cu quantification of electrolytically Cu-plated activated carbon fibers, measured by AAS.
Fig. 2. Adsorption isotherms of nitrogen at 77 K on electrolytically Cuplated activated carbon fibers.
Table 1 Textural properties of the electrolytically Cu-plated ACFs
BET surface area (m2 g−1 ) Micropore volume (cm3 g−1 ) Total pore volume (cm3 g−1 ) Fraction of micropore (%) Average pore diameter (Å)
As-received
Cu-2
Cu-5
Cu-10
Cu-20
2121
1709
1620
1534
1060
1.145
0.906
0.831
0.809
0.526
1.216
0.997
0.912
0.889
0.572
94
91
91
91
92
25.4
25.8
25.4
25.8
24.6
surface pore structures on ACFs undergo pore-blocking phenomena owing to deposition of copper metal on ACFs. An understanding of the porosity of an adsorbent can be achieved by the construction of an adsorption isotherm. The adsorption isotherms of the adsorbents are measured in the range 106 –100 Torr at 77 K. The results of nitrogen adsorption isotherms of the ACFs deposited with and without copper metal are shown in Fig. 2. All of the specimens are approximately the Type I isotherms having well-developed micropores according to the IUPAC’s classification [14]. It is evident that most of the pore volumes of the specimens are filled at low relative pressure, indicating that these ACFs are highly microporous. After a sharp increase of relative pressure, the isotherms show a small increment in the further adsorption, as indicated in the fraction of microporosity of Table 1. Figure 3 shows the pore size distributions of the ACFs measured by the Horvath–Kawazoe slit pore model [16]. All of the pore size distribution curves suggest a predominant micropore owing to the sharp increase of pore size distribution curves to pore radius less than 10 Å. Also, this confirms that the micropore volumes of Cu-plated specimens are slightly decreased. Table 1 shows the structural adsorption properties of the ACFs studied. As expected, the Cu plating on ACFs leads to a decrease in adsorption characteristics, including microporosity. Also, the volume fraction of micropores is decreased
S.-J. Park, J.-S. Shin / Journal of Colloid and Interface Science 264 (2003) 39–42
Fig. 3. Pore size distributions of electrolytically Cu-plated activated carbon fibers.
41
Fig. 5. Dependence of NO conversion on Cu content (R, coefficient of regression).
NO removal that is mainly due to the catalytic reactions of NO–Cu and NO–C.
4. Conclusions
Fig. 4. NO conversion of electrolytically Cu-plated activated carbon fibers.
with increasing Cu content on ACFs. It can be seen that copper plating shows pore blocking owing to deposition of copper metal on ACFs [12,17]. NO conversion of the electrolytic Cu-plated ACFs at 500 ◦ C is shown in Fig. 4. As-received has a low activity, whereas electrolytically Cu-plated ACFs have a high activity. It can be seen that NO conversion on the as-received is sharply decreased within a few hours, and it reaches about 14% after 180 min [3]. The reasons for this result are attributed to the direct reaction of NO with C (NO–C reactions) with time on stream at 500 ◦ C. NO conversions of Cu-2 and Cu-5 are slowly decreased within a few hours and then reach a constant conversion [18]. Also, in the case of Cu-20, NO conversion is almost constant at more than 99%, which can be attributed to the existence of optimal reduction of NO into O2 and N2 between direct reaction of NO with C and the catalytic NO reaction with C over a catalyst (NO–Cu and NO–C reactions). It is then considered that the metallic catalytic system of the adsorbents is very predominant, in which copper metal is activated for removing NO at 500 ◦ C. A linear relationship between NO conversion and Cu content on ACFs is shown in Fig. 5. As a result, NO conversion is greatly increased with increasing Cu content. Consequently, the copper content in the ACFs allows efficient
In this work, the effects of the surface properties and pore structure of copper-plated ACFs on NO removal were investigated. As experimental results, the copper metals appeared to produce an increase in the characteristics of NO removal in spite of the decrease of adsorption properties, including specific surface area, micropore volume, and microporosity of the ACFs. In addition, NO conversion was linearly increased with increasing copper content in the ACFs. It could be concluded that the copper content in ACFs played an important role in improving the NO removal, due to the catalytic reactions of C–NO–Cu. It is then noted that copper electroplating treatment on ACFs is a useful technique for the removal of NO with a viewpoint to highly functional metallic catalytic systems.
References [1] S. Calvert, H.M. Englund, Handbook of Air Pollution Technology, Wiley, New York, 1984. [2] B.J. Park, S.J. Park, S.K. Ryu, J. Colloid Interface Sci. 217 (1999) 142. [3] Z. Zhu, Z. Liu, S. Liu, H. Niu, Appl. Catal. B Environ. 29 (2001) 263. [4] Y. Hu, E. Ruckenstein, J. Catal. 172 (1997) 110. [5] R. Tsunoda, T. Ozawa, J. Ando, J. Colloid Interface Sci. 205 (1998) 265. [6] F. Adib, A. Bagreev, T.J. Bandosz, J. Colloid Interface Sci. 212 (1999) 186. [7] P. Denton, A. Giroir-Fendler, Y. Schuurman, H. Praliand, C. Mirodatos, M. Primet, Appl. Catal. A Gen. 220 (2001) 141. [8] S.K. Ryu, S.Y. Kim, N. Gallego, D.D. Edie, Carbon 37 (1999) 1619. [9] S.J. Park, K.D. Kim, J. Colloid Interface Sci. 212 (1999) 186. [10] S. Lowell, J.E. Shields, Power Surface Area and Porosity, Chapman & Hall, London, 1993. [11] S.J. Park, J.B. Donnet, J. Colloid Interface Sci. 200 (1998) 46. [12] S.J. Park, Y.S. Jang, J. Colloid Interface Sci. 237 (2001) 91. [13] D. Mehandjiev, E. Bekyarova, M. Khristova, J. Colloid Interface Sci. 192 (1997) 440.
42
S.-J. Park, J.-S. Shin / Journal of Colloid and Interface Science 264 (2003) 39–42
[14] S. Brunauer, P.H. Emmett, E. Teller, J. Am. Chem. Soc. 60 (1938) 309. [15] B.C. Lippens, J.H. de Boer, J. Catal. 4 (1965) 319. [16] G. Horvath, K. Kawazoe, J. Chem. Eng. Jpn. 16 (1983) 470.
[17] S.J. Park, Y.S. Jang, J. Korean Ind. Eng. Chem. 13 (2002) 1. [18] V.I. Parvulescu, P. Oelker, P. Grange, B. Delmon, Appl. Catal. B Environ. 16 (1998) 1.
Influence of copper content on NO removal of the activated carbon fibers produced by electroplating Soo-Jin Park ∗ and Jun-Sik Shin Advanced Materials Division, Korea Research Institute of Chemical Technology, P.O. Box 107, Yusong, Taejon 305-600, South Korea Received 10 December 2002; accepted 22 March 2003
Abstract In this study, the activated carbon fibers (ACFs) on which copper metal was deposited by electroplating were used to remove nitric oxide (NO). N2 /77 K adsorption isotherm characteristics, including the specific surface area and micropore volume, were investigated by BET and T -plot methods. NO removal efficiency was confirmed by gas chromatographic technique. From the experimental results, the copper content supported on ACFs led to an increase in the NO conversion, in spite of the decrease of the specific surface area or the micropore volume of ACFs. Consequently, the presence of Cu on ACFs played an important role in improving the NO reduction into O2 and N2 , which was mainly attributed to the catalytic reactions of C–NO–Cu. 2003 Elsevier Inc. All rights reserved. Keywords: Activated carbon fibers; Cu electroplating; Adsorption; NO removal; Catalytic reaction
1. Introduction Air pollution is not a new problem. It has been with society since at least the Middle Ages. But recent times, due largely to increased population and industrialization, it has come to the forefront of public concern. Especially, nitrogen oxides (NOx ) are major pollutants in the atmosphere, being a precursor to acid rain, photochemical smog, and ozone accumulation. Nitrogen oxide (NO) is not considered harmful to health. However, it can react with other gases present both in the exhaust and in the atmosphere to form nitrogen dioxide (NO2 ). Nitrogen dioxide is harmful to health and is also an important component in the formation of ozone [1–8]. There are several methods for controlling NOx emissions. Gas scrubbing is one of the most common forms of NOx treatment, with sodium hydroxide being the conventional scrubbing medium. Also, combustion systems have been used up to this day. However, they have problems such as complex, expensive setup, harmful gas emission, and metal corrosion. In recent years, to overcome these problems, some researchers [2,7,8] have reported that NO is reduced more effectively by using the adsorption characteristics of activated carbons (ACs) and activated carbon fibers (ACFs). * Corresponding author.
E-mail address: [email protected] (S.-J. Park). 0021-9797/03/$ – see front matter 2003 Elsevier Inc. All rights reserved. doi:10.1016/S0021-9797(03)00333-3
Also, other researchers have studied NO reduction using metals supported on ACs or ACFs by impregnation, metal plating, deposition, and so on [9–13]. Especially, ACFs have been actually used in waste water disposal plants, adsorption systems, and removal apparatus for noxious gas because of their extended specific surface area, high adsorption capacity, well-developed micropores, safety, reproductability, processability, and so on. However, metal-supporting methods on ACs or ACFs and their NO removal efficiency have not yet been studied systematically. The objective of the present work is to investigate the surface and adsorption characteristics of the electrolytic Cuplated ACFs by using pH, FTIR, and BET isotherms and to discuss the influence of NO removal on plating time and copper content of the ACFs studied.
2. Experimental For the present investigation, the ACFs were supplied from Taiwan Carbon Co. (AW2001, weight 45 g/m2, thickness 0.3 mm, and specific surface area 2121 m2 /g). Cudeposited ACFs were prepared by Cu electroplating at a constant velocity and same electric current. Electrolytic copper and graphite plate were used as an anode and a cathode, respectively. The samples with different plating times, 0, 2,
40
S.-J. Park, J.-S. Shin / Journal of Colloid and Interface Science 264 (2003) 39–42
5, 10, and 20 s, were denoted as-received, Cu-2, Cu-5, Cu10, and Cu-20, respectively. The compositions of the plating bath were CuSO4 (10 g/l) and H2 SO4 (20 ml/l) solutions. Prior to use following analyses, the residual solution of the electrolyte in the treated ACFs was washed several times with distilled water and dried in a drying oven at 60 ◦ C for 12 h. The amount of copper in Cu-plated ACFs was determined by atomic absorption spectrophotometry (AAS) and showed copper mg per carbon fiber g. Nitrogen isotherms were measured by using an ASAP (Micromeritics) at 77 K. Prior to each analysis, the samples were outgassed at 573 K for 10–12 h to obtain a residual pressure of less than 10−3 Torr. The amount of nitrogen adsorbed, used to calculate specific surface area and micropore volume was determined from the BET equation [14] and T -plot method [15], respectively. Also, the Horvath– Kawazoe model [16] was applied to the experimental nitrogen isotherms for pore size distribution. For the present experiment, a gas chromatograph (DS 6200 model, Donam Co., Korea) and a thermal collect detector were used to measure NO conversion. Reactor temperature was sustained constantly at 500 ◦ C using a P.I.D. temperature controller (UP-350, Yokokawa) and gas flow rate was maintained at 10 ml/min by a mass flow controller (GMC 1000, MKS). All samples were heated under a helium purge at 150 ◦ C for 1 h to remove residual H2 O before NO conversion test. The NO conversion was determined from the concentration of NO at the outlet reactor. Prior to each analysis, NO standard curve was gained by using the 300, 600, and 1000 ppm NO gas.
3. Results and discussion Figure 1 shows the content of copper on ACFs as a function of electroplating time. It is seen that the content of copper increases rapidly at the beginning of plating time, whereas the plating velocity is decreased with increasing the plating time. This probably indicates that plating is decreased because of Cu deposited on ACF surfaces. Also, the
Fig. 1. Cu quantification of electrolytically Cu-plated activated carbon fibers, measured by AAS.
Fig. 2. Adsorption isotherms of nitrogen at 77 K on electrolytically Cuplated activated carbon fibers.
Table 1 Textural properties of the electrolytically Cu-plated ACFs
BET surface area (m2 g−1 ) Micropore volume (cm3 g−1 ) Total pore volume (cm3 g−1 ) Fraction of micropore (%) Average pore diameter (Å)
As-received
Cu-2
Cu-5
Cu-10
Cu-20
2121
1709
1620
1534
1060
1.145
0.906
0.831
0.809
0.526
1.216
0.997
0.912
0.889
0.572
94
91
91
91
92
25.4
25.8
25.4
25.8
24.6
surface pore structures on ACFs undergo pore-blocking phenomena owing to deposition of copper metal on ACFs. An understanding of the porosity of an adsorbent can be achieved by the construction of an adsorption isotherm. The adsorption isotherms of the adsorbents are measured in the range 106 –100 Torr at 77 K. The results of nitrogen adsorption isotherms of the ACFs deposited with and without copper metal are shown in Fig. 2. All of the specimens are approximately the Type I isotherms having well-developed micropores according to the IUPAC’s classification [14]. It is evident that most of the pore volumes of the specimens are filled at low relative pressure, indicating that these ACFs are highly microporous. After a sharp increase of relative pressure, the isotherms show a small increment in the further adsorption, as indicated in the fraction of microporosity of Table 1. Figure 3 shows the pore size distributions of the ACFs measured by the Horvath–Kawazoe slit pore model [16]. All of the pore size distribution curves suggest a predominant micropore owing to the sharp increase of pore size distribution curves to pore radius less than 10 Å. Also, this confirms that the micropore volumes of Cu-plated specimens are slightly decreased. Table 1 shows the structural adsorption properties of the ACFs studied. As expected, the Cu plating on ACFs leads to a decrease in adsorption characteristics, including microporosity. Also, the volume fraction of micropores is decreased
S.-J. Park, J.-S. Shin / Journal of Colloid and Interface Science 264 (2003) 39–42
Fig. 3. Pore size distributions of electrolytically Cu-plated activated carbon fibers.
41
Fig. 5. Dependence of NO conversion on Cu content (R, coefficient of regression).
NO removal that is mainly due to the catalytic reactions of NO–Cu and NO–C.
4. Conclusions
Fig. 4. NO conversion of electrolytically Cu-plated activated carbon fibers.
with increasing Cu content on ACFs. It can be seen that copper plating shows pore blocking owing to deposition of copper metal on ACFs [12,17]. NO conversion of the electrolytic Cu-plated ACFs at 500 ◦ C is shown in Fig. 4. As-received has a low activity, whereas electrolytically Cu-plated ACFs have a high activity. It can be seen that NO conversion on the as-received is sharply decreased within a few hours, and it reaches about 14% after 180 min [3]. The reasons for this result are attributed to the direct reaction of NO with C (NO–C reactions) with time on stream at 500 ◦ C. NO conversions of Cu-2 and Cu-5 are slowly decreased within a few hours and then reach a constant conversion [18]. Also, in the case of Cu-20, NO conversion is almost constant at more than 99%, which can be attributed to the existence of optimal reduction of NO into O2 and N2 between direct reaction of NO with C and the catalytic NO reaction with C over a catalyst (NO–Cu and NO–C reactions). It is then considered that the metallic catalytic system of the adsorbents is very predominant, in which copper metal is activated for removing NO at 500 ◦ C. A linear relationship between NO conversion and Cu content on ACFs is shown in Fig. 5. As a result, NO conversion is greatly increased with increasing Cu content. Consequently, the copper content in the ACFs allows efficient
In this work, the effects of the surface properties and pore structure of copper-plated ACFs on NO removal were investigated. As experimental results, the copper metals appeared to produce an increase in the characteristics of NO removal in spite of the decrease of adsorption properties, including specific surface area, micropore volume, and microporosity of the ACFs. In addition, NO conversion was linearly increased with increasing copper content in the ACFs. It could be concluded that the copper content in ACFs played an important role in improving the NO removal, due to the catalytic reactions of C–NO–Cu. It is then noted that copper electroplating treatment on ACFs is a useful technique for the removal of NO with a viewpoint to highly functional metallic catalytic systems.
References [1] S. Calvert, H.M. Englund, Handbook of Air Pollution Technology, Wiley, New York, 1984. [2] B.J. Park, S.J. Park, S.K. Ryu, J. Colloid Interface Sci. 217 (1999) 142. [3] Z. Zhu, Z. Liu, S. Liu, H. Niu, Appl. Catal. B Environ. 29 (2001) 263. [4] Y. Hu, E. Ruckenstein, J. Catal. 172 (1997) 110. [5] R. Tsunoda, T. Ozawa, J. Ando, J. Colloid Interface Sci. 205 (1998) 265. [6] F. Adib, A. Bagreev, T.J. Bandosz, J. Colloid Interface Sci. 212 (1999) 186. [7] P. Denton, A. Giroir-Fendler, Y. Schuurman, H. Praliand, C. Mirodatos, M. Primet, Appl. Catal. A Gen. 220 (2001) 141. [8] S.K. Ryu, S.Y. Kim, N. Gallego, D.D. Edie, Carbon 37 (1999) 1619. [9] S.J. Park, K.D. Kim, J. Colloid Interface Sci. 212 (1999) 186. [10] S. Lowell, J.E. Shields, Power Surface Area and Porosity, Chapman & Hall, London, 1993. [11] S.J. Park, J.B. Donnet, J. Colloid Interface Sci. 200 (1998) 46. [12] S.J. Park, Y.S. Jang, J. Colloid Interface Sci. 237 (2001) 91. [13] D. Mehandjiev, E. Bekyarova, M. Khristova, J. Colloid Interface Sci. 192 (1997) 440.
42
S.-J. Park, J.-S. Shin / Journal of Colloid and Interface Science 264 (2003) 39–42
[14] S. Brunauer, P.H. Emmett, E. Teller, J. Am. Chem. Soc. 60 (1938) 309. [15] B.C. Lippens, J.H. de Boer, J. Catal. 4 (1965) 319. [16] G. Horvath, K. Kawazoe, J. Chem. Eng. Jpn. 16 (1983) 470.
[17] S.J. Park, Y.S. Jang, J. Korean Ind. Eng. Chem. 13 (2002) 1. [18] V.I. Parvulescu, P. Oelker, P. Grange, B. Delmon, Appl. Catal. B Environ. 16 (1998) 1.