Preparation of industrial sisal fiber waste derived activated carbon by chemical activation and effects of carbonization parameters on surface characteristics

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Preparation of industrial sisal fiber waste derived activated carbon by chemical activation and effects of carbonization parameters on surface characteristics Melike Dizbay-Onat a,∗ , Uday K. Vaidya b,1 , Claudiu T. Lungu c a Interdisciplinary Engineering/Department of Materials Science and Engineering, Materials Processing & Applications Development (MPAD) Center, University of Alabama at Birmingham, 1150 10th Avenue South BEC 254, Birmingham, AL, 35294-4461, United States b Department of Materials Science and Engineering, Materials Processing & Applications Development (MPAD) Center, University of Alabama at Birmingham, Birmingham, AL, 1150 10th Avenue South BEC 360C, Birmingham, AL, 35294-4461, United States c School of Public Health, Department of Environmental Health Sciences, University of Alabama at Birmingham, RPHB 530, 1720 2nd Ave S. Birmingham, AL 35294 United States

a r t i c l e

i n f o

Article history: Received 5 July 2016 Received in revised form 6 November 2016 Accepted 8 November 2016 Available online xxx Keywords: Industrial fiber waste Activated carbon Chemical activation Carbonization temperature Flow rate Carbonization time

a b s t r a c t This study investigates the use of industrial sisal (agave sisalana) fiber waste in activated carbon preparation via chemical activation and the influence of carbonization conditions on surface properties. Experiments have been conducted to study the effects of different carbonization temperatures (550, 600 and 650 ◦ C) with varied carbonization (hold) time (1 h and 3 h) at different nitrogen flow rates (94.4, 188.8 and 377.6 ml/min). The results showed that carbonization temperature and carbonization time have positive impact on Brunauer, Emmett, and Teller (BET) surface area, total pore volume and carbon percentages whereas flow rate has negative impact. The highest BET surface area of activated carbon obtained at 650 ◦ C with carbonization time of 3 h and 94.4 ml/min flow rate was 1297 m2 /g where total pore volume and carbon percentages were 0.64 cm3 /g and 81%, respectively. In conclusion, high surface area activated carbons could be produced from industrial sisal fiber waste by properly selecting carbonization parameters. © 2016 Elsevier B.V. All rights reserved.

1. Introduction Activated carbon (AC) has significant adsorptive, environmental, thermal, electrical and mechanical characteristics for novel applications of ACs (Abdul Khalil et al., 2013). Since the commercial AC prepared from the coal is expensive, cheaper alternatives such as agricultural biomass (Senthilkumar et al., 2013). Coconut shell (Yang et al., 2010) is the most common ‘green’ potential precursor option. Lignocellulosic fibers such as kenaf fiber (Aber and Sheydaei, 2011), and jute fiber (Senthilkumaar et al., 2006) have also been used as precursors to prepare AC. Sisal fiber is one of the most widely used natural fibers because it is very easily cultivated

∗ Corresponding author at: College of Arts and Sciences, Center for Community Outreach Development (CORD), University of Alabama at Birmingham, 933 Nineteenth Street South, Birmingham, AL, 35294, United States. E-mail addresses: [email protected], [email protected] (M. Dizbay-Onat), [email protected] (U.K. Vaidya), [email protected] (C.T. Lungu). 1 Department of Mechanical, Aerospace and Biomedical Engineering, Department of Materials Science & Engineering, University of Tennessee Knoxville, TN 37996, United States.

in large quantities (Chand et al., 1989). It is grown about 4.5 million tons per year in tropical countries of Africa, the West Indies, India, Tanzania and Brazil (Li et al., 2000). Sisal fiber is extracted from the leaves of the sisal plant and its general applications are in carpets, ropes, mats, and twines. Natural fibers used in the industry produce more than 50 wt% waste which occupies a huge amount of landfill space (Williams and Reed, 2003). Hence, the motivation for this study is to use industrial sisal fiber waste to produce AC. There are two significant steps to producing AC (Chowdhury et al., 2013); (a) carbonization which is pyrolysis of the precursors in an inert atmosphere. During this step, the organic substances’ carbon content enhances and the narrow or blocked pores are formed. Carbonization temperature of lignocellulosic biomass is at lower than 800 ◦ C; and (b) Activation: Physical activation and chemical activation are two activation processes for the additional development of the pores. During physical activation, a precursor is carbonized in an inert atmosphere and then activated with steam or carbon dioxide to develop internal porosity. Typically, activation the temperature is ranging from 800 to 1000 ◦ C for lignocellulosic carbon (Guo and Lua, 2000; Herawan et al., 2013a). In chemical activation, a precursor is impregnated with activa-

http://dx.doi.org/10.1016/j.indcrop.2016.11.016 0926-6690/© 2016 Elsevier B.V. All rights reserved.

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tion agents such as zinc chloride (ZnCl2 ), phosphoric acid (H3 PO4 ), sodium hydroxide (NaOH), and potassium hydroxide (KOH) and carbonized (Katesa et al., 2011; Sricharoenchaikul et al., 2007). They develop the porosity based on dehydration and degradation (Nor et al., 2013). Chemical activation usually takes place at lower temperature and shorter treatment time than physical activation. (Guo and Lua, 2000; Nor et al., 2013). The energy consumption and the cost are also reduced with lower temperatures (Guo and Lua, 2000; Herawan et al., 2013b). Additionally, chemical activation retains larger surface area and higher carbon yield than physical activation (Nor et al., 2013). Typically, H3 PO4 and KOH have been used for the lignocellulosic materials activation (Lozano-Castello et al., 2001). H3 PO4 has some advantages such as low energy cost and high carbon yield. Therefore, it has become a popular activation agent for lignocellulosic materials activation (Hernández-Montoya et al., 2012). The pore structure of AC is divided into three categories according to their pore diameters – microporous (<2 nm), mesoporous (2 nm–50 nm), and macroporous (>50 nm)(Liang et al., 2008). AC with high surface area and microporous structure has the good adsorptive capability for small molecules (e.g. acetone, dichloromethane-ethyl formate), but is not very attractive for larger molecules or ions. AC with high surface area and mesoporous structure are appropriate for large molecules (e.g. dyes, proteins, polycyclic aromatic hydrocarbons) adsorption (Ramalingama et al., 2012; Song et al., 2012; Wang et al., 2008). Carbonization and activation conditions are both important steps that influence the AC’s physical properties (Katesa et al., 2013). The activation conditions (activation temperature, activation time) studies are very common in literature. During the carbonization step, the carbonization temperatures and the carbonization time (hold time) are the two key parameters to be considered. Moreover, ‘flow rate’ is also another parameter (Malhotra et al., 2016; Mohameda et al., 2010), but is not common in the literature. Therefore, the present research has been directed towards studying all three carbonization factors, namely – carbonization temperature, carbonization time and flow rate. The first aim of this study is to explore the production of AC from industrial sisal fiber waste by chemical activation. Chemical activation is completed in a single step. This procedure combines the carbonization and activation process which provides better development of porous structure. (Tiwari et al., 2013). The second aim is to examine the effects of carbonization parameters by characterizing the surface area, elemental analysis, pore characteristics and morphological properties. 2. Materials and methods 2.1. Materials Industrial sisal fiber waste (Supplier Miller Waste Mills, Winona, MN) was used as a precursor material to produce activated carbon in this study. H3 PO4 and hydrochloric acid (HCl) were obtained from Fisher Scientific (Pittsburg, PA). High purity (99.99%) nitrogen (N2 ) was also used for carbonization process. 2.2. Activated carbon sample preparation In this study industrial sisal fiber was activated with chemical activation method using H3 PO4 acid as an activating agent. Industrial sisal fiber waste was impregnated with 30 wt% diluted H3 PO4 in 3:1 (acid: precursor) ratio and soak time of one hour. H3 PO4 was sprayed onto sisal fiber waste to achieve uniform impregnation. The impregnated samples were located in a three-zone temperature system horizontal furnace (Lindberg/Blue M) and N2

Table 1 List of six industrial sisal waste derived activated carbon samples prepared under different carbonization parameters. Samples

SWAC1 SWAC2 SWAC3 SWAC4 SWAC5 SWAC6

Carbonization Temperature (◦ C)

Carbonization Time (Hold Time) (h)

Nitrogen Flow Rate (ml/min)

1 1 1 3 3 3

94.4 94.4 94.4 94.4 188.8 377.6

550 600 650 650 650 650

gas was used at the carbonization step, for carbon formation. In each run, a heating rate of 10 ◦ C/min was used. Carbonization of lignocellulosic precursors starts above 170 ◦ C and it is nearly completed between 550 ◦ C–650 ◦ C (Cuhadar, 2005). As illustrated in Table 1, six Sisal Waste Activated Carbon (SWAC) samples were prepared under different carbonization conditions. Samples SWAC1, SWAC2 and SWAC3 focused on effects of carbonization temperatures (550, 600 and 650 ◦ C) where carbonization time (1 h) and N2 flow rate (94.4 ml/min) were kept constant. Effects on carbonization times (1 h and 3 h) on SWAC3 and SWAC4 were studied by keeping the carbonization temperature (650 ◦ C) and carbonization flow (94.4 ml/min) stable. The effects of flow rate were studied on SWAC4, SWAC5 and SWAC6 (94.4, 188.8, 377.6 ml/min), where carbonization temperature (650 ◦ C) and time (3 h) were fixed. The samples were then cooled down to ambient temperature and repeatedly washed with HCl, hot water and distilled water respectively. The washed sample was dried at 100 ◦ C for 2 h. At the final preparation step, activated carbon samples were crushed and sieved in mesh size 32 (U.S Standard Testing Sieve) or 0.5 mm to obtain uniform particle size. 2.3. Characterization of activated carbon 2.3.1. Surface characteristics The N2 adsorption-desorption isotherms, BET surface area, and pore size characteristics (surface area, pore volume, mesopore size distribution) of SWAC samples were measured by using Micromeritics ASAP2020-Accelerated Surface Area and Porosime◦ try Analyzer (Micromeritics Corp., Norcross, Georgia) at 77 K. The t-plot method was used to determine the mesoporous surface area and micropore volume. For micropore size distribution, Carbon◦ dioxide (CO2 ) adsorption at 273.15 K has been preferred since CO2 adsorption is faster (∼3 h) compared to N2 adsorption (∼30 h). Furthermore, this adsorption leads to assurance that measured adsorption points are equilibrated (Cazorla-Amoros et al., 1996; Garcia-Martinez et al., 2000; Garrido et al., 1987). It was measured with Quantachrome instrument applying Density Functional Theory (DFT) (Wang et al., 2013). The mesopore size distribution was estimated by using the Barrett-Joyner-Halenda (BJH) method (Barrett et al., 1951) which calculates pore size distributions from adsorption isotherms on mesoporous and small macroporous materials. The total pore volume is the volume of liquid nitrogen at a relative pressure of about 0.99. The mesopore volume was calculated by subtracting the micropore volume from the total pore volume (Hu et al., 2000). Three analyses (n = 3) were performed for each carbonization condition. 2.3.2. Ultimate analysis Ultimate analyzers determine the elemental compositions of materials such as C, H, and N (Pradhan, 2011). Ultimate analysis was carried out in the Perkin-Elmer CHN 2400 analyzer (PerkinElmer, Waltham, Massachusetts). The results are based on as-received basis.

Please cite this article in press as: Dizbay-Onat, M., et al., Preparation of industrial sisal fiber waste derived activated carbon by chemical activation and effects of carbonization parameters on surface characteristics. Ind. Crops Prod. (2016), http://dx.doi.org/10.1016/j.indcrop.2016.11.016

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475 450 425 400 375 350 325 300 275 250 225 200

(a)

3

700

SWAC2 SWAC3 SWAC4 SWAC5 SWAC6 0

0.2

0.4

0.6

0.8

1

Relative Pressure (P/Po) Fig. 1. N2 adsorption and desorption isotherms of industrial sisal waste derived activated carbon samples at varied carbonization conditions.

2.3.3. Proximate analysis Proximate analysis separates the products into four groups as moisture, ash, volatile matter and fixed carbon content based on their weights (Goswami, 2014). Moisture: It presents the mass of water content in the sample and ASTM D2867-99 method is used to determine moisture content (ASTM, 2014). Ash: It indicates some inorganic compounds in the carbon and measured by ASTM D2866-94 (ASTM, 2011; Baseri et al., 2012). Volatile matter: It shows the presence of organic substituents, CO2 , N and S containing substitutes. They are released from the sample during the heating process and it is calculated by ASTM D5832-98 (ASTM, 2008; Goswami, 2014). Fixed carbon: Typically it refers carbon content. However, it might also include H, S, and N. It is reported by subtracting the moisture content, volatile matter content and ash content from 100% (Goswami, 2014). 2.3.4. Scanning electron microscope (SEM) analysis Surface texture and porosity of the industrial sisal fiber waste and SWAC samples were carried out using an FEI, Quanta FEG 690 and the analysis was operated at a 10 kV accelerating potential. The samples were coated in a sputter coating unit to avoid charging and improve the electron signals for imaging before the analysis.

Carbonization Temperature (oC)

SWAC1

650

600

550

500 1075.3

(b)

1193 BET Surface Area (m2/g)

1245.3

400 350

Flow Rate (ml/min)

Quantity Adsorbed (cm3/g)

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300 250 200 150 100 50 1008.3

1028 BET Surface Area (m2/g)

1296.7

Fig. 2. (a) Effect of carbonization temperature on Brunauer, Emmett, Teller surface area. (b) Effects of flow rates on Brunauer, Emmett, Teller surface area.

et al., 2003) prepared sisal fiber derived activated carbon with H3 PO4 (35 wt%) activation and 24 h soaking time. BET surface areas obtained in that study were between 900–950 m2 /g. The highest BET surface area was found at 1000 ◦ C.

3. Results and discussion 3.1. Surface characteristics 3.1.1. Adsorption isotherms Chemical characteristics, porous structure and heat adsorption of the adsorbent are determined with the adsorption isotherms. The porosity of activated carbon materials is commonly identified by using N2 adsorption technique (Wang et al., 2013). Fig. 1 displays the N2 adsorption/desorption isotherms at 77 K of the six different activated carbon samples produced from industrial sisal fiber waste. The isotherm plots generated from these studies were found to follow the trend of mixed Type I and Type IV isotherms according to the International Union of Pure and Applied Chemistry (IUPAC) (Sing, 1982). These types of isotherms exhibit the micro/mesopore structure of the materials (Vasanth Kumara et al., 2010). At low relative pressure, the curves indicate adsorption into the micropores (Wang and Yuan, 2014). The hysteresis loop shows the pore widening and development of the mesopores (Gregg and Sing, 1982). 3.1.2. Surface area The BET method was used to determine surface areas (Brunauer et al., 1938). Senthilkumar et al. (Senthilkumar et al., 2013) reported BET surface area for H3 PO4 activated sisal fiber as 885 m2 /g with 3.8:1 impregnation ratio and 24 h soaking time. Fu et al. (Fu

3.1.2.1. Effects of carbonization temperature on surface area. Fig. 2(a) shows the effects of the carbonization temperature (550, 600 and 650 ◦ C) on the BET surface areas of activated carbons for SWAC1, SWAC2, SWAC3 and their average BET surface areas are 1075.3 ± 89.7, 1193 ± 2.6, 1245.3 ± 9.9 m2 /g, correspondingly (n = 3). The carbonization temperature at 650 ◦ C produces the highest surface area. It was found that there is a linear relationship between the surface area and the carbonization temperature. Rosas et al. (Rosas et al., 2009) proved that BET surface areas increase (from 1141 m2/g to 1355 m2/g) at elevated carbonization temperatures (from 450 ◦ C to 550 ◦ C) for H3 PO4 (85 wt.%) activated hemp fibers with 3:1 impregnation ratio. Inagaki et al. (Inagaki et al., 2004) also proved this for kenaf fibers. Li et al. (Li et al., 2008) observed that the BET surface area of the coconut shell activated carbon increased (from 130 m2 /g to 702 m2 /g) with increasing carbonization temperatures (from 400 ◦ C to 1000 ◦ C). Dehydration, linkage breaking off reactions, structural ordering process of residual carbon and polymerization reaction of the hemicellulose, cellulose and lignin in sisal fibers occurs during the carbonization process. Rising carbonization temperatures of SWAC samples increases the BET surface area because of tar release from cross-linked framework generated by H3 PO4 activation and the volatile organic compounds release from the precursor material (Demiral et al., 2007; Li et al., 2008). As a result, SWAC samples will have a possibility of having better adsorption capacity because

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(a) 0.14

Pore Volume (cm3/g)

0.12 0.1 0.08 0.06 0.04 0.02

Pore Diameter (nm)

SWAC3 SWAC4 SWAC5 SWAC6

SWAC2

SWAC1

3.45

3.80

4.56

4.15

5.66

5.06

41.92 24.39 15.84 12.51 10.32 8.57 7.33 6.41

0

(b) 0.07

Pore Volume (cm3/g)

0.06 0.05 0.04 0.03 0.02 0.01

SWAC1 SWAC2 SWAC3 SWAC4 SWAC5 SWAC6

1.41

1.29

1.18

Pore Diameter (nm)

1.08

0.98

0.90

0.75

0.82

0.63

0.69

0.52

0.57

0.31 0.33 0.37 0.40 0.44 0.48

0.00

Fig. 3. (a) Mesopore size distribution of industrial sisal waste derived activated carbon samples. (b) Micropore size distribution of industrial sisal waste derived activated carbon samples.

of the effects of pore widening and external carbon removal at higher carbonization temperatures (Prahas et al., 2008; Teng and Hsu, 1999).

3.1.2.2. Effects of carbonization time (holding time) on surface area. Samples were held at 650 ◦ C for carbonization times of 1 h and 3 h. Average BET surface areas for SWAC3 and SWAC4 were obtained as 1245.3 ± 9.9 and 1296.7 ± 29.3 m2 /g for 1 h, 3 h carbonization time, respectively (n = 3). These results show that the carbonization time has no significant effect on BET surface area. Sudaryanto et al. prepared activated carbon from cassava peel (agricultural waste) by chemical activation method (Sudaryanto et al., 2005). They have also concluded that surface area (1154 m2 /g–1183 m2 /g)

stays stable at elevated carbonization times (from 1 h to 3 h) at 650 ◦ C carbonization temperature.

3.1.2.3. Effects of N2 flow rate on surface area. In contrast to carbonization temperature and carbonization time, the BET surface area decreased at increasing N2 flow rate which may be caused by the broken walls of porosities and closed pores (Fig. 2(b)). In more details, when the flow rate was increased from 94.4 ml/min to 377.6 ml/min, average BET surface areas were decreased from 1296.7 ± 29.3, 1028 ± 13, 1008.3 ± 11.9 m2 /g for SWAC4, SWAC5, SWAC6 samples, respectively (n = 3). Fierroa et al. also obtained the parallel correlation for chemically activated kraft lignin carbon (Fierroa et al., 2007).

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Fig. 4. Scanning Electron Microscope images : (a) a raw industrial sisal waste fiber, bar length: 500 ␮m, (b) industrial sisal waste fiber derived activated carbon sample 4, bar length: 500 ␮m, (c) industrial sisal waste derived activated carbon sample 4, bar length: 400 ␮m, (d) industrial sisal waste derived activated carbon 4, bar length:100 ␮m.

3.1.3. Pore volume According to samples SWAC1, SWAC2 and SWAC3 in Table 2, the effect of carbonization temperature in pore development is significant since the total pore volume (Vt ) and mesopore volume (Vme ) enhances at increasing carbonization temperatures. At higher temperatures, volatile matter is released from the precursor material during carbonization and this causes pore development, pore widening of micropores to mesopores as well as creation of new pores (Huang et al., 2014; Sudaryanto et al., 2005). This table also clearly shows that the BET surface area, the pore volumes as well as the mesopore volume increase when the carbonization temperature increases. When SWAC3 and SWAC4 were compared, Vt and BET surface area did not change at higher carbonization times. Sudaryanto et al. also found the same relationship for cassava peel derived activated carbon samples (Sudaryanto et al., 2005). However, mesopore vol-

ume reduces by 10%, since higher carbonization time might cause the shrinkage of mesopores. The total pore volume and BET surface area decreases with increasing N2 flow rate for SWAC4, SWAC5, and SWAC6 respectively as shown in Table 2. The lower number of pores might be the reason for lower pore volume (Fierroa et al., 2007). Lozano-Castello et al. (2001) found that increasing N2 flow rate enhances the pore volume for Spanish anthracite precursor. On the other hand Fierroa et al. (Fierroa et al., 2007) used kraft lignin as a precursor and stated that rising N2 flow rate reduces the pore volume. These two opposite statements show that effects of flow rate during carbonization step depends on the precursor. As shown in Table 2, mesopore volume is higher than micropore volume, which indicates that the activated carbons derived from industrial sisal fiber waste have mesoporous structures.

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Table 2 Effects of carbonization parameters on average pore volume for industrial sisal waste derived activated carbon samples (n = 3). Samples

BET (m2 /g)

Vtot (cm3 /g)

Vmi (cm3 /g)

Vme (cm3 /g)

Vme /Vtot (%)

SWAC1 SWAC2 SWAC3 SWAC4 SWAC5 SWAC6

1075.3 ± 89.7 1193 ± 2.6 1245.3 ± 9.9 1296.7 ± 29.3 1028 ± 13 1008.3 ± 11.9

0.64 ± 0.08 0.65 ± 0.00 0.69 ± 0.004 0.67 ± 0.02 0.50 ± 0.007 0.49 ± 0.005

0.26 ± 0.06 0.24 ± 0.002 0.20 ± 0.002 0.27 ± 0.01 0.22 ± 0.001 0.23 ± 0.002

0.38 0.41 0.49 0.40 0.27 0.26

59 63 71 60 54 53

3.1.4. Pore size distribution Pore size distribution is used to characterize the structural heterogeneity of porous materials. It shows that a solid internal structure of regularly shaped, not interacting pores could represent the complex void spaces within the real solid (Sudaryanto et al., 2005). The efficiency and selectivity of adsorption are related to pores size distribution changes with the type of raw material (Binti Jabit, 2007). When micropores in the porous materials can adsorb the small molecules (0.6–0.8 nm), mesopores can adsorb larger molecules such as color molecules and humid acid (1.5–3.0 nm). The pore size distribution was determined using two methods; BJH method for mesopore size distribution and DFT method for micropore size distribution. 3.1.4.1. Mesopore size distribution. The mesopore size distributions of SWAC samples were determined by the BJH method. As seen in Fig. 3(a), pore diameters are concentrated between 2–50 nm, indicating the presence of mesopores. SWAC samples appear to have mainly narrow mesopores with the existence of a sharp peak size from about 3.5 nm. They also have a low contribution of mesopores with size larger than 4 nm. The maxima of the distribution curves occurred at 3.3–3.5 nm for each SWAC sample. An increase of carbonization temperature over the range from 550 ◦ C to 650 ◦ C results in higher mesopore size distribution. The area under the curve represents the value of the pore volume. Therefore, it is clear that mesopore volumes increase with increasing carbonization temperatures. An increase of the hold time (1 h to 3 h) and flow rate (94.4 ml/min to 188.8 ml/min) reduces the number of narrow mesopores and mesopore volume. On the other hand, the increase of flow rate from 188.8 ml/min to 377.6 ml/min doesn’t effect on pore size distribution and the volume. It can be concluded that preparation of activated carbon by H3 PO4 provides wide pores consisting of mesoporous activated carbon. Fig. 3(a) also presents that pore volume is proportional to the surface area for the SWAC samples. 3.1.4.2. Micropore size distribution. DFT method was used to examine the micropore size distribution of SWAC samples. As it is displayed in Fig. 3b, a heterogeneous micropore size distribution between 0.3 nm to 1.4 nm with three similar peaks was obtained for all SWAC samples. This shows that carbonization parameters (temperature, time, and flow rate) don’t significantly affect micropore size distribution of the SWAC samples. The most of the micropores have a diameter at around 0.5 nm as can be seen from the highest peak of each SWAC sample where pore volume range is between 0.048 cm3 /g and 0.059 cm3 /g. The samples also have two smaller peaks at 0.3 nm and 0.8 nm where pore volume is between 0.017 cm3 /g and 0.025 cm3 /g. According to the micro and mesopore size distribution results, all SWAC samples were mixed (microporous/mesoporous) structure. 3.1.5. Ultimate analysis The elemental composition of typical AC consists of 85–90% C, 0.5% H, 0.5% N, 5% O, and 1% S (Cuhadar, 2005). Small amount of N can be chemisorbed during carbonization step (Cuhadar, 2005).

As it is shown in Table 3, SWAC samples have N less than 1% (0.380.57%). H element is chemically bonded to carbon atoms (Cuhadar, 2005). Water molecules, polar substances, polarizable gasses and vapors can be adsorbed at the sites of the H functional group (Smisek and Cerny, 1970). The highest H content was observed for SWAC1 (2.05%), and the lowest for SWAC4 (0.84%) respectively, as seen from Table 3. The reason for high H content values is the hydrogen group in H3 PO4 activation agent structure. ACs produced in this study contains about 72.93-81.48% C. Carbon content in the AC and its BET surface area is directly proportional. BET surface area is one of the most significant parameters for AC (Cuhadar, 2005). Therefore, the high C content is desirable to obtain high BET surface area. Table 3 also shows that the H content of SWAC samples (SWAC1, SWAC2, SWAC3, SWAC4) decreased from 2.05% to 0.84% with increasing carbonization temperature from 550 ◦ C to 650 ◦ C and hold time from 1 h to 3 h. Additionally, the H content of SWAC samples (SWAC4, SWAC5, SWAC6) increased from 0.84% to 1.21% when the flow rate increased from 94.4 ml/min to 377.6 ml/min. On the other hand, C percentage and N percentage increased from 78.64% to 81.48% and 0.38% to 0.57%, respectively with elevated carbonization temperature (550 ◦ C to 650 ◦ C) and carbonization time (1 h to 3 h). C percentage and N percentage reduced (C: 81.48% to 72.92%, N: 0.57% to 0.41%) at increasing flow rates (94.4 ml/min to 377.6 ml/min). 3.1.6. Proximate analysis Fixed carbon content is the main parameter in the proximate analysis since carbon surface captures the adsorbate molecules. A typical AC contains low ash content between 2 and 10% (Binti Jabit, 2007). Pore surface area could be significantly reduced due to blockage of the pores by the ash presence which reduces the adsorption properties of activated carbon (Binti Jabit, 2007; Herawan et al., 2013b). Moreover, high ash content might cause hydrophilicity and catalytic effects that lead to restructuring process during activated carbon regeneration (Binti Jabit, 2007). It can be observed from Table 3 that the fixed carbon content gets raised with increasing carbonization temperature (550 ◦ C–650 ◦ C) and carbonization time (1 h to 3 h) over the range from 71.33–79.5%. On the other hand, it reduces from 79.5% to 69.48% with increasing flow rate (94.4 ml/min to 377.6 ml/min). SWAC4 has the highest carbon percentage (79.5%) which provides us the highest surface area (1296.67 ± 15.3 m2 /g). 3.1.7. Scanning electron microscopy (SEM) analysis The microstructure of the industrial sisal fiber waste and SWAC4 (which has the highest carbon percentage and the best BET surface area) is illustrated in between Fig. 4(a)–(d). According to Fig. 4(a), sisal fiber does not have a porous structure and the external surface is quite smooth. From Fig. 4(b)–(d); it was found that there is the formation of pores on the surface of SWAC. The activation of sisal fiber by H3 PO4 degrades the low volatile substances present in the fiber causing the formation of pores. Washing with HCl/water removes the blockage and exposes the porosity of the product (Senthilkumar et al., 2013). In H3 PO4 treated carbon, well-developed pores were seen. There are many clear fine pores visible within the microstructure of activated carbons. It is, fur-

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Table 3 Ultimate and proximate analysis of industrial sisal waste derived activated carbon samples. Samples

SWAC1 SWAC2 SWAC3 SWAC4 SWAC5 SWAC6

Ultimate Analysis (wt%)

Proximate Analysis (wt%)

Carbon

Hydrogen

Nitrogen

Moisture

Ash

Volatile

Fixed Carbon

78.64 78.80 79.04 81.48 75.79 72.93

2.05 1.63 1.11 0.84 1.15 1.21

0.38 0.39 0.41 0.57 0.47 0.41

17.27 14.01 14.04 14.96 18.01 18.86

3.9 4.53 3.16 4.18 6.11 3.32

7.5 7.52 4.88 1.36 4.76 8.34

71.33 73.94 77.92 79.5 71.12 69.48

ther, observed from Fig. 4(d) that the pores developed are highly non-uniform regarding their shapes which are a mixture of circular and irregular shapes. The SEM images of SWAC show that the activation stage produced extensive external surfaces with irregular cavitation and pores. These pores result from the evaporation of the chemical reagent H3 PO4 during carbonization leaving empty spaces (Deng et al., 2010). 4. Conclusions Industrial sisal fiber waste is a good precursor alternative for AC preparation since as an industrial waste material, it can provide environmentally friendly, cost effective solutions. SWAC would be a good adsorbent alternative with its high surface area, high carbon percentage. High surface areas (>1000 m2 /g) were observed for all SWAC samples from chemical (H3 PO4 ) activation. The carbonization temperature at 650 ◦ C with 3 h carbonization time is considered as an optimum condition for industrial sisal waste to develop AC. However, AC prepared at 650 ◦ C with 1 h carbonization time with the second highest surface area is preferable due to low energy consumption. Acknowledgements The authors gratefully acknowledge the support of NSF-EPSCoR under award number EPS-1158862; Deep South Center, Pilot Project Research Grant number 2T42OH008436 from NIOSH and the Center for Forest Sustainability, Auburn University. References ASTM, 2008. Standard Test Method for Volatile Matter Content of Activated Carbon Samples. ASTM Committee on Standards, ASTM D5832-98. ASTM, 2011. Standard Test Method for Total Ash Content of Activated Carbon. ASTM committee on standards, ASTM D2866-94. ASTM, 2014. Standard Test Methods for Moisture in Activated Carbon. ASTM Committee on Standards, ASTM D2867-99. Abdul Khalil, H.P.S., Jawaid, M., Firoozian, P., Rashid, U., Islam, A., Akil, H., 2013. Activated carbon from various agricultural wastes by chemical activation with KOH: preparation and characterization. J. Biobased Mater. Bioenergy 7, 1–7. Aber, S., Sheydaei, M., 2011. Removal of COD from industrial effluent containing indigo dye using adsorption method by activated carbon cloth: optimization, kinetics, and isotherm studies. Clean Soil Air Water 40, 87–94. Barrett, E.P., Joyner, L.G., Halenda, P.P., 1951. The determination of pore volume and area distributions in porous substance I computations from nitrogen isotherms. J. Am. Chem. Soc. 73, 373–380. Baseri, J.R., Palanisamy, P.N., Sivakumar, P., 2012. Preparation and characterization of activated carbon from thevetia peruviana for the removal of dyes from textile waste water. Adv. Appl. Sci. Res. 3, 377–383. Binti Jabit, N., 2007. The Production and Characterization of Activated Carbon Using Local Agricultural Waste Through Chemical Activation Process. School of Material and Mineral Engineering, Malaysia. Brunauer, S., Emmett, P.H., Teller, E., 1938. J. Am. Chem. Soc. 60. Cazorla-Amoros, D., Alcaniz-Monje, J., Linares-Solana, A., 1996. Langmuir, 12. Chand, N., Tiwary, R.K., Rohatgi, P.K., 1989. Bibiliography: resource structure properties of natural cellulosic fibres −an annotated bibliography. J. Mater. Sci. 23. Chowdhury, Z.Z., Hamid, S.B.A., Das, R., Hasan, R., Mohd Zain, S., Khalid, K., Uddin, N., 2013. Preparation of carbonaceous adsorbents from lignocellulosic biomass and their use in removal contaminants from aqueous solution. BioResources 8, 6523–6555.

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Please cite this article in press as: Dizbay-Onat, M., et al., Preparation of industrial sisal fiber waste derived activated carbon by chemical activation and effects of carbonization parameters on surface characteristics. Ind. Crops Prod. (2016), http://dx.doi.org/10.1016/j.indcrop.2016.11.016