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Carbon Science Vol. 7, No. 1 March 2006 pp. 34-41 Characteristics of Surface Modified Activated Carbons Prepared by Potassium Salt Sequentially After Hydrochloric Acid Treatment Won-Chun Oh, Chong-Sung Park 1, Jang-Soon Bae 2 and Young-Shin Ko 3 Department of Advanced Materials & Science Engineering, Hanseo University, Chungnam 356-706, Korea 1 Department of Environmental Engineering, Hanseo University, Chungnam 356-706, Korea 2 Department of Industrial Chemistry, Dankook University, Chungnam 330-714, Korea 3 Department of Science Education, Seoul National University of Education, Seoul 137-700, Korea e-mail: wc_oh@hanseo.ac.kr (Received February 16, 2006; Accepted March 15, 2006) Abstract The objective of this paper is to compare the variation of surface properties by hydrochloric acid pre-treatment and of metallic potassium and their salts loading effect for activated carbon after surfaces transformation by acid. From the results of nitrogen adsorption, each isotherm shows a distinct knee band, which is closely related to the characteristic of microporous carbons with capillary condensation in micropores. In order to present the causes of the differences in surface properties and S BET after the samples were treated with hydrochloric acid, pore structure and surface morphology are investigated by adsorption analysis. X-ray diffraction (XRD) patterns indicate that activated carbons show better performance for metallic potassium and potassium salts by pre-treatment with hydrochloric acid. Scanning electron microscopy (SEM) pictures of potassium/activated carbon particles provide information about the homogeneous distribution of metal or metal complex on the surface. For the chemical composition microanalysis for potassium treatment of the activated carbon pre-treated with hydrochloric acid, samples were analyzed by energy disperse X-ray (EDX). Finally, the type and quality of oxygen groups are determined from the method proposed by Boehm. A positive influence of the acidic groups on the carbon surface by acid treatment is also demonstrated by an increase in the contents of potassium salts with increasing of acidic groups calculated from Boehm titration. Keywords : Activated carbon, isotherm, SEM, XRD, EDX, Boehm titration 1. ˆp, r r p n, ~ k~p rr rl v o np p. p l pnp p r, q r l p l ˆp o lv p. p l r p p, v,, p p oqp sq p [1]. ˆl p oq p sq p vp s, p m } m p r} o l v [2]. ˆl sq q tn oq p, ˆ r p qq l oqm p o l p. p l l p l q p r p e,, m Š p p [1, 3]. p p sq ˆ q~p m e t p p p m p p. k p } n, ˆ l } p p p p p p [4]. np, r rl qp l tn l p, r rl q p l q l t l p. r r l ˆp pnl p q m ~ q p v qm p v pl qrp p. ˆ p r ss l p p m n k l p lv. v v p, p m,, t,, rp msp ~ p l [5-7]. } r l l p k l r~ v eˆ o l o n p rp p. p p e m p v e ˆ l v eˆ l p. ˆ q~ vv~m l vpv, p p v p p oqp sql p q p p p l l v mm vl l o rp q n p. rsp ol, v p sq t p. ˆp p l sq p, k p m p vp r } p

Characteristics of Surface Modified Activated Carbons Prepared by Potassium Salt Sequentially After Hydrochloric Acid Treatment 35 pp pp ˆ mp [2]. k, p p l o l pl r, rp mm mm vp r l rp qn [8, 9]. l ˆl m p r} l ˆ l sq e mp } n p v eˆ q rp l. mp r p m p l ps l ˆ pp p, p p } ˆ vv l l t n p m. ˆp r p m p BET r, r~ m } s l p p ˆ l. ˆl p n p XRDl p sr p, SEM l p EDXl p o p l p m l ˆ l. 2. v n ˆp ˆpp vp n l rs l l pn m. 1 ˆ vp k 500 o Cl l} l e m, p p k 750 o C p m l v n l r l p l rs m. ˆ l p o l 0.05 m 0.1 Mp p m p n l p ˆ l n p v k } m [2, 4]. } k 1e r p m p m l e m. ˆp 3 v n l } mp, 323 Kl 24e k s m. m p m p } ˆp m p m HA 0.05 HA 0.1 p m. } o l, ˆp 50 mlp 0.1 M ˆ nkl eml 12 e k rl tl [4]. 30 k 1.33 Pap p k p ˆ n p l sq r m. k, r l kp r m. pm p } e p v s l 368 Kp m l 72e k s m. m } l p } ˆ le KMnO 4 -HA 0.05, KMnO 4 -HA 0.1, K 2 CO 3 - HA 0.05 K 2 CO 3 -HA 0.1 p p m. rl p m. m p r,, v p o q n m. ˆ l mp p l o l X- r p pn m. X- (Shimatz XD-D1, Japan)p s p Cu Kα p n m. m p l ps l p } ˆp ˆm sp o l rqt (SEM, JSM-5200 JOEL, Japan)p n m. ˆ l } p p o l SEMl EDX(Energy Disperse X-ray ) n m. #PFIN ˆ l p o l Boehm rr [10]p n m. p } r l ˆ e 1 g p 50 mlp 0.05 M, ˆ, tˆ m l m. d n l e l 24e k l tl. n k l ˆp psp n l r l p 5 mlp l 0.05 Mp m nk n kp rr m. l v ˆp p q o l, p e,, Š t eˆ, ˆ p e m Š t eˆ tˆ p Š t eˆ r l p m. ˆ l sq m q m l p l t kp m. 3. y pmp nkl } kq ˆl prl m srp [11, 12], } l m d } ˆp p kk o l, 77 Kl ASAP 2010(Micromeritics, USA)p n l v m p r m. r rl e p 1.33 10 3 Pap pr k p v l, 473 Kl l ˆ l Fig. 1. Adsorption isotherm obtained from Ks surface modified by pre-treatment with hydrochloric acid.

36 W.-C. Oh et al. / Carbon Science Vol. 7, No. 1 (2006) 34-41 } l ˆ p np ˆ p p ol ~ n p ˆ l. m } l p l p t l } ˆp v m p Fig. 1l ˆ l. p o l m p } l pmp nkl } l llv ˆ e l p v m p tn l p m p ˆm p p. p p n r p pp, p p sl r l p. p pv kkv m } r[12] m } l } mp s l 1~3%p p p p. Fig. 1l p, m } l mp } r l le o p p p. p e l m p ˆ p v ~ l ˆ rp Type Ip ˆ ˆ l, p m p sp knee mlp v t mlp p q ˆ ˆ. p m p HA 0.05 - AC p p ˆ lp, v HA 0.1, KMnO 4 - HA 0.05, KMnO 4 -HA 0.1, K 2 CO 3 -HA 0.05 K 2 CO 3 - HA 0.1 o s j p p ˆ l. m p kvl p ppp ˆ. m p } rl, t p } l l p p }n p Table 1. Comparison of Physical Parameters of K-Activated Carbon Pre-Treated with Hydrochloric Acid Parameter Sample S BET (m 2 /g) Micropore Volume (ml/g) Internal Surface Area (m 2 /g) Average Pore Diameter (Å) HA 0.05 HA 0.1 KMnO 4 -HA 0.05 KMnO 4 -HA 0.1 K 2 CO 3 -HA 0.05 K 2 CO 3 -HA 0.1 1423 1312 1145 1031 1217 1114 0.534 0.521 0.523 0.567 0.537 0.539 821.5 734.7 623.5 622.1 726.4 634.2 15.44 15.32 14.55 14.64 14.75 14.32 Fig. 2. XRD patterns for HA series; (a) KMnO 4 -HA 0.05, (b) KMnO 4 -HA 0.1, (c) K 2 CO 3 -HA 0.05 and (d) K 2 CO 3 -HA 0.1 - AC.

Characteristics of Surface Modified Activated Carbons Prepared by Potassium Salt Sequentially After Hydrochloric Acid Treatment 37 막으므로 인하여 미세동공 혹은 극미세 동공으로 변화한 것으 로 여겨진다. Table 1은 S, 미세동공부피, 외부 표면적 및 평균동공직경을 처리된 산의 양 및 칼륨염의 종류에 따라 비 교하여 나타내었다. 염산을 처리 시료 및 산처리 후에 칼륨염 을 처리한 활성탄 시료에 대한 비표면적은 1031~1423 m /g의 범위에 분포하였다. 이들에 대한 비표면적 값을 비교해 볼 때 상대적으로 약간 높은 값을 나타내고 있으며, 산처리가 동공 BET 2 변화에 영향을 주었으나 그다지 많은 영향을 주지 않은 것으 로 예상된다. 평균 동공직경은 14.32~15.44 Å의 범위에 존재 하였으나 큰 차이를 나타내지는 않았다. 미세동공부피와 미세 동공 면적의 경우도 큰 차이를 보이지 않았으나, 산처리 하지 않은 칼륨염-활성탄의 경우[12] 보다 약간 낮은 값을 나타내 었다. 물리적 파라메터의 감소하는 경향성과 관련하여 염산처리 SEM images obtained from HA series; (a) HA, (b) HA, (c) KMnO -HA, (d) KMnO -HA, (e) K CO -HA and (f) K CO -HA. Fig. 3. 2 3 0.05 0.05 2 3 0.1 0.1 4 0.05 4 0.1

38 W.-C. Oh et al. / Carbon Science Vol. 7, No. 1 (2006) 34-41 r l ˆ r qq ˆ l mp p o l X- r p m. m } ˆ l X- r Ž l Fig. 2l ˆ l. o l s p mp } n, r p mp, p lpp ˆ l. p mp kp r } l r p l ˆ v kp p m. p l kl np EDXp m l v v r p p } mp m p r t ˆ. p p r r rp k lp ˆ t l sq mp r rp ˆ pl. 2θ p 28.4 l p K m 40.5 l p p l. Fig. 4. EDX elemental micro-analysis spectra obtained from HAF series; (a) HA 0.05, (b) HA 0.1, (c) KMnO 4 -HA 0.05, (d) KMnO 4 -HA 0.1, (e) K 2 CO 3 -HA 0.05 and (f) K 2 CO 3 -HA 0.1.

Characteristics of Surface Modified Activated Carbons Prepared by Potassium Salt Sequentially After Hydrochloric Acid Treatment 39 Fig. 4. Continued. ˆ l mp ˆm p SEMl p l l. m } l l l m } ˆp SEM vp m l r r l t p. } v kp ˆp p [12]l re m p ˆ p, Fig. 3p m } l v m } ˆp p ˆ p vp. mp prp pp ˆl p p pp p p p ppˆ, p l l m p p v p v vp p. SEM l p l p mp t ˆ p p. p rl r rl r p v, n l m p t p. k, } m rp

40 W.-C. Oh et al. / Carbon Science Vol. 7, No. 1 (2006) 34-41, r q vl p nk m ˆ pl pp r p p [13]. } ˆp l [14, 15]l p sq p l v ˆ. p p ˆ vv p qn l p m p t p m. } l p ˆp p p ˆ lp, pl m ˆ l sq mp v p. o p r r p o l EDX n l p ll. p l Fig. 4m Table 2l ˆ l. p l p, d l Cm Op vrp ˆ p, p t (a)m (b) Cp p 91% p p ˆ p l (c), (d), (e) (f) 54.34-85.1%p o ˆ p. rp (c), (d), (e) (f)p n (a)m (b)p Op rp ˆ. pnl v rp Kp ˆ pp l t p. (a)m (b) p n rp qp p ˆ pp l (c), (d), (e) (f)p n 4.87-8.07% p j p o p ˆ l. } v e p n, p p e v l ˆ. k, (a), (b) (c)p d p Clp ˆ pp p. t n C, O K pp, } m v eˆl Kp v p ˆ p. (e) m (f)p d p (c)m (d)p d o p p pp, } mp p } n p v ppp ˆ p. p d p r m l r rp ˆ Table 2l p, ov e p m v p kp p ˆ l. } o p kp v p ˆ p. p ep kl r e p v p ˆ t l mp v p. ˆ p } e m p } e, o v p p p } e p l ˆ l. l l [1], p n l n l +m K MnO 4 pm, MnO 4 p p p e l v eˆ p p Table 2. EDX Elemental Microanalysis of K-Activated Carbon Pre-Treated with Hydrochloric Acid Sample C O Cl K Mn HA 0.05 HA 0.1 KMnO 4 -HA 0.05 KMnO 4 -HA 0.1 K 2 CO 3 -HA 0.05 K 2 CO 3 -HA 0.1 l p. Mn ˆ l displacing force n qp pm p l l p rp p l v. EDX l ˆ m p t p p l v, Mn p l p l v. ˆ tl p ˆ v v~ l tn l p p [10]. p p p kk o l Boehm rr p n mp, p r r l p l e, Š p r pp, p p l ps ˆ p m m r m. m p } n, p p p r ˆ p rp ˆ p m m le p p ˆ l. mp } n, ˆ l sq Š m r v mp pl p l v mpp ˆ l. ˆ p n v p ˆ v k pp, v eˆ l p p ˆ p. 4. 91.7 93.7 59.0 69.8 70.6 85.1 6.67 5.52 23.0 16.7 24.5 8.13 0.66 1.23 5.98 0.93 1.43 7.19 8.07 4.87 6.77 4.80 5.44 ˆl m p r} l p mp } n p v eˆ q l p rp lp, mp r p m p l ps l ˆ l. e l v m p ˆ p v ~ l ˆ rp Type Ip ˆ ˆ l, p m p sp knee mlp v t mlp Table 3. Number of Surface Species Obtained from Boehm Titration Sample HA 0.05 HA 0.1 KMnO 4 -HA 0.05 KMnO 4 -HA 0.1 K 2 CO 3 -HA 0.05 K 2 CO 3 -HA 0.1 Functional Group (meg/g) Carboxylic Lactonic Phenolic Acidic Basic 0.64 0.59 0.73 0.12 0.61 0.59 0.58 0.71 4.64 4.77 4.62 4.89 0.49 0.31 5.00 5.83 5.83 5.79 1.71 1.61 10.4 10.7 11.1 11.3 0.13 0.14 0.09 0.07 0.06 0.14

Characteristics of Surface Modified Activated Carbons Prepared by Potassium Salt Sequentially After Hydrochloric Acid Treatment 41 p q ˆ ˆ. p e p S BET, r, le p mp, p p m p m. mp } l p ˆ l mp sq p v o l XRD p mp, p ˆ t l sq mp r rp ˆ l. SEM mp } e p ˆ l p p pl. p e l EDX, r} m p l ps l kp v p ˆ l. Boehm rrp l p m p r} p r r ˆ l. k, p p l p ˆp v ˆ lp, } l m p tl. y [1] Puri, B. R. in Chemistry and Physics of Carbon Edited by P.J. Walker, Jr., Vol. 6, Dakker, New York, 1970, p. 191. [2] Oh, W. C.; Yum, M. H. Bull. Korean Chem. Soc. 2004, 25(8), 1189. [3] Avgul, N. N.; Kiselev, A. V. in Chemistry and Physics of Carbon Edited by P. J. Walker, Jr., Vol. 6, Dakker, New York, 1970, p. 3. [4] Oh, W. C. J. Ind. Eng. Chem. 2005, 11, 137. [5] Lisovski, A.; Semiat, R.; Aharoni, C. Carbon 1997, 35, 1639. [6] Pittman Jr., C. U.; He, G. R.; Wu, B.; Gardner, S. D. Carbon 1997, 35, 317. [7] Emolenko, I. N.; Lyubliner, I. P.; Gulko, N. V. In: Chemically modified carbon fibers and their application, New York: VCH, Chapter 6, 1990, p. 155. [8] Oh, W. C.; Lee, H. J.; Bae, J. S. J. Korean Ind. Eng. Chem. 2004, 15(4), 434. [9] Oh, W. C.; Lee, H. J.; Bae, J. S. Environ. Eng. Res. 2004, 9(5), 193. [10] Boehm, H.P. Advances in catalysis, Academic press, New York, 1966. [11] Oh, W. C.; Bae, J. S. J. Korean Ind. Eng. Chem. 2003, 14, 29. [12] Kim, J. K.; Oh, W. C.; Kim, M. K. J. Korean Ind. Eng. Chem. 1998, 9, 729. [13] Moreno-Castilla, C. Carbon 2004, 42, 83. [14] Oh, W. C.; Lim, C. S. Journal of Ceramic Processing Research 2005, 6, 73. [15] Oh, W. C.; Bae, J. S. Analytical science & Technology 2005, 18, 436.