Preparation and Characterization of Activated Carbon Fiber from Paper

Size: px

Start display at page:

Download "Preparation and Characterization of Activated Carbon Fiber from Paper"

Theresa Black
5 years ago
Views:

1 CHINESE JOURNAL OF CHEMICAL PHYSICS VOLUME 24, NUMBER FEBRUARY 27, 20 ARTICLE Preparation and Characterization of Activated Carbon Fiber from Paper Zong-jian Zhang a, Jia Li a, Fu-sheng Sun a, Dickon H. L. Ng b, Fung-luen Kwong b, Shi-quan Liu a a. School of Materials Science and Engineering, University of Ji nan, Ji nan , China b. Department of Physics, The Chinese University of Hong Kong, Hong Kong, China (Dated: Received on October 26, 200; Accepted on December 4, 200) Activated carbon fibers (ACFS) with surface area of 388 m 2 /g prepared from paper by chemical activation with KOH has been utilized as the adsorbent for the removal of methylene blue from aqueous solution. The experimental data were analyzed by Langmuir and Freundlich models of adsorption. The effects of ph value on the adsorption capacity of ACFS were also investigated. The rates of adsorption were found to conform to the kinetic model of Pseudo-second-order equation with high values of the correlation coefficients (R>0.998). The Langmuir isotherm was found to fit the experimental data better than the Feundlich isotherm over the whole concentration range. Maximum adsorption capacity of 520 mg/g at equilibrium was achieved. It was found that ph played a major role in the adsorption process, higher ph value favored the adsorption of MB. Key words: Activated carbon fiber, Paper, Microstructure, Adsorption, Methylene blue I. INTRODUCTION Activated carbons are important materials known for their great ability to adsorb various molecules on their surface [ 4]. The activated carbon has been produced from variety of biomass i.e., wood [5], rice husk [6], cellulose [7], lignin [8], coconut shells, and palm shells [9]. Activated carbon materials can be produced by physical or chemical activation. Chemical activation has been successfully applied to the production of activated carbons using various chemical reagents i.e., ZnCl 2 [0], H 2 SO 4 [], H 3 PO 4 [2], and HCl [3]. Recently, alkali hydroxides such as KOH, NaOH, and alkali carbonates such as K 2 CO 3 and Na 2 CO 3 have increasingly been used as activation reagents turning out high specific surface areas of the prepared activated carbons. Activated carbons prepared by pyrolysis of mixtures of carbon precursor/alkaline hydroxide were investigated. It was reported that KOH was more effective for the highly ordered materials, which indicated differences in the activation performance of both hydroxides [4 6]. In this work, activated carbon fibers were produced by chemical activation of paper. The advantages of using paper are that it provides excellent absorbent ability for easy infiltration of the activation reagents. Moreover, paper, being a mature industrial product compared with natural templates like wood and plant leaves, has stable properties like composition, porosity, and density [7, 8]. These properties and cellulosefiber structure of paper will be useful in fabricating Author to whom correspondence should be addressed. ljn964@gmail.com activated carbon fibers. In this work, paper activated carbon fibers were prepared by chemical activation with KOH and characterized, regarding their textural properties and adsorption capacity on methylene blue. The equilibrium and kinetic data of the adsorption process of methylene blue molecules onto the prepared activated carbon fibers were also studied. II. EXPERIMENTS We selected paper as precursor of activated carbon fiber in this work. The preparation of the activated carbons from paper was carried out in following steps. (i) Paper (Ji nan, China) was carbonized at 600 C under nitrogen (N 2 ) flow at a heating rate of 5 C/min. (ii) The carbonized sample was soaked in 30% hydrochloric acid for 2 h and then washed several times with distilled water until the ph of the filtrate became neutral, then the sample was impregnated in solutions of activating reagents (2 mol/l KOH, Tianjin Kermel Chemical Reagent, Tianjin, China) for 2 h. (iii) After impregnation, the samples were dried for 2 h at 60 C in a drying oven. (iv) The impregnated sample was activated in a tube furnace under N 2 flow at the temperature of 800 C for 2 and 3 h, respectively, at a heating rate of 5 C/min. (v) The activated sample was washed several times with distilled water until the ph of the filtrate became neutral. The washed samples were dried at 60 C for 2 h to prepare the activated carbon fibers. Adsorption kinetic experiments were carried out in a glass vessel, 200 ml methylene blue (0 mg/l MB) with 4 mg of activated carbon fibers (ACFS) at 25 C. The recording time started when ACFS was added to the vessel. Aqueous samples (3 ml) were taken from the solution at preset time intervals and the concentra- 03

2 04 Chin. J. Chem. Phys., Vol. 24, No. Zong-jian Zhang et al. FIG. XRD patterns of paper after carbonization and activation. (a) No activation, (b) activated by KOH at 800 C for 2 h, and (c) activated by KOH at 800 C for 3 h. FIG. 2 Raman Spectra of prepared ACFS. (a) Activated by KOH at 800 C for 2 h and (b) activated by KOH at 800 C for 3 h. tions were analyzed using a visual spectrophotometer (Model 722, Shanghai Jinghua, China) at 664 nm for methylene blue. The amount of adsorption q t at time t was calculated by q t = V (C 0 C t ) W () where C 0 and C t are the liquid concentrations at the start and t, respectively, V is the volume of aqueous solution, and W is the mass of ACFS. The phases of ACFS were analyzed using X-ray diffractometer (XRD with CuKα radiation source; Model D8-Advance, Germany) operated at 40 kv and 00 ma. Scanning electron microscopy (SEM, Model S- 2500, Hitachi, Japan) equipped with energy-dispersive X-ray spectrometer (EDS, Model INCA Energy 3294, Oxford, U.K.) was used to characterize the morphology and chemical composition of the samples. Specific surface areas and pore volumes of the samples were derived via N 2 adsorption at 77 K using a Micromeritics ASAP 2020M+C system. III. RESULTS AND DISCUSSION A. Characterization of ACFS XRD patterns of paper after carbonization and activation are shown in Fig.. Details of phase structure and the process of graphitization of carbon materials are obtained from XRD studies. It reveals that paper carbons are mainly amorphous after carbonization and activation. Raman spectra of prepared activated carbon materials are shown in Fig.2. The peaks centered around 600 and 350 cm are attributed to the graphitic and disordered carbon structure. The term graphitic means carbon atoms which are three coordinated and are bound by sp 2 type bonding orbital. The term graphitic has nothing to do with the stacking of layers along c-direction. The disorder in the carbon sheet TABLE I Textural characteristics of ACFS prepared by KOH activation of paper. ACFS S BET S micro V T d 2 h h S micro in m 2 /g, S micro is micropore area (in m 2 /g) deduced from t-plot, V T is total pore volume (in cm 3 /g), d is mean pore diameter (in nm), d=4v/a, where V is the total pore volume and A is the BET specific surface area. may be because of the non-planar microstructure distortions or the disorganized regions near the crystal edges. Lattice defects such as edge dislocation and lattice vacancies contribute to the band at 350 cm too. It indicates that the prepared activated carbon materials are graphitic and amorphous structure, which is consistent with the XRD analysis. Figure 3 shows a typical SEM micrograph of pure paper and activated carbon fiber in this work. It reveals that the paper contains networks of cellulose fibers with a diameter about 20 µm. The EDS (Fig.3(b)) confirms the presence of C and O in the fibers mostly, which is helpful to increase the amount of prepared carbon. SEM image of activated carbon fiber (Fig.3(c)) indicates the sample exhibited fiber structure with lots of micropores, which are confirmed by nitrogen adsorption-desorption isotherm. Figure 4 shows typical nitrogen adsorptiondesorption isotherm and the corresponding pore-size distributions of the sample activated at 800 C for 2 and 3 h. Details of texture properties of the carbon materials produced are given in Table I. The surface area of samples activated for 2 and 3 h are 388 and 353 m 2 /g, respectively, which lie in the range of commercial activated carbons. Close inspection of the isotherms give details of the type and nature of pores present in the carbon materials. The prepared activated carbon materials correspond to type I isotherms based on Brunauer, Deming, Deming,

Chin. J. Chem. Phys., Vol. 24, No. Preparation of Activated Carbon Fiber from Paper 05 Au (b) C O Au 20 0 (a) 2 3 4 Energy / kev (c) Au µm µm 50 nm (d) FIG.

3 Chin. J. Chem. Phys., Vol. 24, No. Preparation of Activated Carbon Fiber from Paper 05 Au (b) C O Au 20 0 (a) Energy / kev (c) Au µm µm 50 nm (d) FIG. 3 SEM images of paper and prepared activated carbon fiber. (a) SEM micrograph of pure paper, (b) EDS spectrum of pure paper, (c) and (d) SEM image of activated carbon fiber. FIG. 4 Nitrogen adsorption-desorption isotherms of the infiltrated samples activated for 2 h (a) and 3 h (c), the pore size distribution plots of samples activated for 2 h (b), 3 h (d). c 20 Chinese Physical Society

4 06 Chin. J. Chem. Phys., Vol. 24, No. Zong-jian Zhang et al. FIG. 5 Pseudo-second-order kinetic model for the removal of MB by adsorption on the prepared ACFS. (a) Activation for 2 h and (b) activation for 3 h. TABLE II Kinetic parameters for the adsorption of methylene blue (0 mg/l) onto the ACFS at room temperature. Type of ACFS Pseudo-first-order Pseudo-second-order k /h q e/(mg/g) R k /h q e/(mg/g) R Activation for 2 h Activation for 3 h and Teller (BDDT) classification [9]. According to the type of isotherm, the activated carbon fibers can be corroborated as microporous materials with the average pore diameter (<2 nm), which is in good agreement with Table I. B. Adsorption ability of ACFS. Adsorption kinetic In order to evaluate the kinetic mechanism that controls the adsorption process, the pseudo-first-order [20], pseudo-second-order [2], and intraparticle diffusion [22] were tested to interpret the experiment data. The above three kinetic mechanisms are expressed as following equations, respectively: = + k q t q e q e t (2) t = q t k 2 q 2 + t e q e (3) q t = k p t /2 + C (4) where t is the adsorption time, k is the constant, q e is the equilibrium adsorption, k 2 is the constant, k p is the constant, C is the intercept. Figure 5 shows pseudo-second-order kinetic model for the removal of MB by adsorption on the prepared activated carbon fibers. In this work, the adsorption data of sample fit better with Eq.(2) than other two, it means that physical adsorption rather than chemical adsorption occur during adsorption process. Kinetic parameters for the adsorption of MB (0 mg/l) onto the activated carbons paper at room temperature are shown in Table II. The MB adsorption onto the activated carbons from paper well follows the pseudosecond-order rate model with the correlation coefficients of high than for all sample in this work. The equilibrium adsorption of paper activated carbon are 507 and 52 mg/g, respectively for activation 2 and 3 h. 2. Adsorption isotherms The adsorption isotherm indicates how the adsorption molecules distribute between the liquid phase and the solid phase when the adsorption process reaches an equilibrium state. The analysis of the isotherm data by fitting them to different isotherm models is an important step to find the suitable model that can be used for design purpose. The Langmuir and Freundlich are the most frequently employed models. In this work, both models were used to describe the relationship between the amount of dye adsorbed and its equilibrium concentration. Langmuir isotherm model suggests that uptake occurs on homogeneous surface by monolayer sorption without interaction between adjacent sorbed molecules. The model assumes that all the sites available on the adsorbent surface are equivalent and the surface is perfectly uniform, that is flat. The linear form of Langmuir isotherm equation is represented by the following equation: C e q e = q max K L + C e q max (5) where C e is the equilibrium MB concentration in the solution, q max is the monolayer adsorption capacity of the activated carbon, k L is the Langmuir adsorption constant.

5 Chin. J. Chem. Phys., Vol. 24, No. Preparation of Activated Carbon Fiber from Paper 07 FIG. 7 The effect of ph value on adsorption capacities of ACFS based on pseudo-second-order kinetic model. FIG. 6 Linearized Langmuir isotherm (a) and linearized Freundlich isotherm (b) for MB adsorption by ACFS. TABLE III Langmuir and Freundlich isotherm constants for MB dye on paper-based ACFS. k/h q max/(mg/g) n R Langmuir Freundlich Freundlich isotherm is based on the assumptions that adsorption proceed beyond monolayer coverage and each layer followed the law of Langmuir adsorption. The linear form of Freundlich isotherm equation is represented by the following equation: lg q e = lg k F + n lg C e (6) where k F and n are the Freundlich adsorption constant. From Fig.6 we can see that the Langmuir isotherm fits better than the Feundlich isotherm. The Langmuir isotherm fits quite well with the experimental data (correlation coefficient R=0.9993), whereas the lower correlation coefficient (R=0.9875) shows poor agreement of Freundlich isotherm with the experimental data (Table III). Freundlich constants are listed in Table III. The slope /n ranging between 0 and, is a measure of adsorption intensity or surface heterogeneity, becoming more heterogeneous as its value gets closer to zero [23, 24]. A value of /n below one indicates a normal Langmuir isotherm while /n above one is indicative of cooperative adsorption. All above confirm that the MB dye uptake is due to monolayer coverage of solute particles onto the surface of the ACFS and the surface of TABLE IV Pseudo-second-order kinetic parameters for the adsorption of methylene blue onto ACFS. ph k /0 4 h q e/(mg/g) R ACFS is uniform. 3. Effect of ph value The ph of solution appears to be a key factor affecting the adsorption characteristics of MB onto the activated carbons fibers. As can be seen from Fig.7 and Table IV, it is evident that the adsorption capacities are significantly improved when ph value increase, indicating the adsorption of MB prefers a higher solution ph values. AC can be regarded as an amphoteric solid. Both negative and positively charged surface sites exist in aqueous solution, depending on the solution ph. When solution ph>carbon PZC (point of zero charge of the activated carbon), the surface of carbon is negatively charged and can attract cations from the solution. When solution ph<carbon PZC, the surface of carbon is positively charged and can attract anions from the solution [25, 26]. MB is cations, so higher ph value is better for adsorbing MB. IV. CONCLUSION Papers were used as raw materials for the production of activated carbon using KOH as activation agents. The chemical properties of ACFS produced, as well as their characteristics for liquid-phase adsorption were investigated. N 2 adsorption/desorption isotherms indicated that KOH-activation provided a carbon with a large surface area and a well-developed microporosity. The surface areas of 388 and 353 m 2 /g were obtained at 800 C with KOH activation for 2 and 3 h, respec-

6 08 Chin. J. Chem. Phys., Vol. 24, No. Zong-jian Zhang et al. tively, which lie in the range of commercial activated carbons. Liquid phase adsorption processes were employed and adsorption isotherms were constructed to investigate adsorption capacity and ability of the adsorbent to remove MB dye from aqueous solution. The MB adsorption onto the ACFS from paper well followed the pseudo-second-order rate model with the correlation coefficients of high than for all sample in this work. Higher ph value favored the adsorption of MB. The Langmuir isotherm was found to fit the experimental data better than the Feundlich isotherm over the whole concentration range. Maximum adsorption capacity of 520 mg/g at equilibrium was achieved. Consequently, the paper-based activated carbon fibers can be used as a low-cost alternative to commercial activated carbon fiber in the removal of various environmental applications including removing hazardous compounds from industrial waste gases or wastewater. V. ACKNOWLEDGMENTS This work was supported by the National Natural Science Foundation of China (No ) and the Shandong Provincial Natural Science Foundation of China (No.ZR2009FM068 and No.ZR2009FM072). [] S. Karagoz, T. Tay, S. Ucar, and M. Erdem, Bioresour. Technol. 99, 624 (2008). [2] S. Nagano, H. Tamon, T. Adzumi, K. Nakagawa, and T. Suzuki, Carbon 38, 95 (2000). [3] S. Karagoz, J. Yanik, S. Ucar, and C. Song, Energy Fuels 6, 30 (2002). [4] J. Guo and A. C. Lua, Sep. Purif. Technol. 8, 47 (2000). [5] I. A. Hared, J. L. Dirion, S. Salvador, M. Lacroix, and S. Rio, J. Anal. Appl. Pyrolysis 79, 0 (2007). [6] D. Kavitha and C. Namasivayam, Bioresour. Technol. 98, 4 (2007). [7] L. Ling, K. Li, L. Liu, S. Miyamoto, Y. Korai, S. Kawano, and I. Mochida, Carbon 37, 499 (999). [8] S. J. M. Carrott and M. M. L. R. Carrott, Bioresour. Technol. 98, 230 (2007). [9] W. M. A. W. Daud and W. S. W. Ali, Bioresour. Technol. 93, 63 (2004). [0] N. Yalcin and V. Sevinc, Carbon 38, 943 (2000). [] Y. Nakagawa, M. Molina-Sabio, and F. Rodrıguez- Reinoso, Microporous Mesoporous Mater. 03, 29 (2007). [2] P. Alvarez, C. Blanco, and M. Granda, J. Hazardous Mater. 44, 400 (2007). [3] O. Gercel and H. F. Gercel, Chem. Eng. J. 32, 289 (2007). [4] T. Tay, S. Ucar, and S. Karagoz, J. Hazardous Mater. 65, 48 (2009). [5] M. A. Lillo-Rodenas, J. P. Marco-Lozar, D. Cazorla- Amoros, and A. Linares-Solano, J. Anal. Appl. Pyrolysis 80, 66 (2007). [6] J. Guo and A. C. Lua, Microporous Mesoporous Mater. 32, (999). [7] S. Altenor, B. Carene, E. Emmanuel, J. Lambert, J. J. Ehrhardt, and S. Gaspard, J. Hazardous Mater. 65, 029 (2009). [8] J. Li, F. L. Kwong, and D. H. L. Ngw, J. Am. Ceram. Soc. 9, 350 (2008). [9] S. Brunauer, L. S. Deming, W. E. Deming, and E. Teller, J. Am. Chem. Soc. 62, 723 (940). [20] N. Kannan and M. M. Sundaram, Dyes Pigments 5, 25 (200). [2] Y. S. Ho and G. Mckay, Trans. IChemE B 76, 83 (998). [22] W. J. Weber and J. C. Morris, J. Sanit. Eng. Div. Am. Soc. Civ. Eng. 89, 2 (963). [23] F. Haghseresht and G. Q. Lu, Energy Fuels 2, 00 (998). [24] K. Fytianos, E. Voudrias, and E. Kokkalis, Chemosphere 40, 3 (2000). [25] L. R. Radovic, I. F. Silva, J. I. Ume, J. A. Menendez, C. A. Leon, Y. Leon, and A. W. Scaroni, Carbon 35, 339 (997). [26] D. Savova, N. Petrov, M. F. Yardim, E. Ekinci, T. Budinova, M. Razvigorova, and V. Minkova, Carbon 4, 897 (2003).

MOF-76: From Luminescent Probe to Highly Efficient U VI Sorption Material

MOF-76: From Luminescent Probe to Highly Efficient U VI Sorption Material Weiting Yang, a Zhi-Qiang Bai, b Wei-Qun Shi*, b Li-Yong Yuan, b Tao Tian, a Zhi-Fang Chai*, c Hao Wang, a and Zhong-Ming Sun*