Characteristics of activated carbon prepared from waste PET by carbon dioxide activation

Journal of Analytical and Applied Pyrolysis 100 (2013) 192–198

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Characteristics of activated carbon prepared from waste PET by carbon dioxide activation b ´ atkowski ˛ W. Bratek a , A. Swi , M. Pakuła c , S. Biniak d,∗ , M. Bystrzejewski e , R. Szmigielski f a

Faculty of Chemistry, Wrocław University of Technology, 50-344 Wrocław, Poland Faculty of Advanced Technology and Chemistry, Military University of Technology, 00-908 Warsaw, Poland c Faculty of Mechanical and Electrical Engineering, Naval University of Gdynia, 81-103 Gdynia, Poland d Faculty of Chemistry, Nicolaus Copernicus University, 87-100 Toru´ n, Poland e Faculty of Chemistry, Warsaw University, 02-093 Warsaw, Poland f Military Institute of Chemistry and Radiometry, 00-910 Warsaw, Poland b

a r t i c l e

i n f o

Article history: Received 6 August 2012 Accepted 22 December 2012 Available online 11 January 2013 Keywords: PET pyrolysis Char activation XRD Raman spectroscopy 4-Chlorophenol adsorption Voltammetry Hydrogen storage

a b s t r a c t Poly(ethylene)terephthalate (PET) waste was subjected to carbonization in a nitrogen stream at 1098 K. The coke was then activated in a carbon dioxide stream under various conditions: temperatures of 1173, 1198 and 1213 K as well as process times of 4, 5, 6 and 8 h. The activated carbons were characterized using various methods: the structure from Raman and XRD measurements, the porosity from low temperature nitrogen adsorption, the surface properties from cyclic voltammetry and the hydrogen storage capacity from the low temperature adsorption isotherm of H2 . The results demonstrated the importance of the temperature and the duration of the process. Higher temperatures result in the etching of graphitic domains of better crystallinity. A relatively small increase in activation time at the highest temperature used yielded a significant increase in the degree of burn-off and porous structure development. The microporosity of these carbons is similar to that of commercial activated carbons. They also have a similar capacity to adsorb water pollutants (e.g. 4-chlorophenol). The PET carbon sample with maximum burn-off exhibited higher values of the microporous structure parameters and the electric double layer capacity in electrolyte solution than the other three samples. The same sample exhibits a sufficient hydrogen storage capacity, which after optimization of the activation conditions should yield an effective storage material. This confirms the possibility of producing activated carbon from waste PET with satisfactory properties by the simple processes of carbonization and activation. The activated carbons obtained have potential use as water pollutant adsorbents, low-cost materials for hydrogen storage and electrode materials in supercapacitors or fuel cells. © 2012 Elsevier B.V. All rights reserved.

1. Introduction In recent years the production and consumption of poly (ethylene)terephthalate (PET) has recorded the fastest growth rate in the global plastics market, but the current consumption of plastic containers is generating a huge amount of this polymer waste. While this is not hazardous, it does unfortunately contribute a significant volume to solid wastes and is not biodegradable in real time. PET waste can, however, be recycled by different physical and chemical methods [1–3]. One interesting way of solving this problem is to convert this waste into valuable chemical products such as activated carbon materials [2,4–16]. The properties of these materials, especially their porous structure, may be well developed. The surface area often reaches values higher than those of other

∗ Corresponding author. Tel.: +48 566114338. E-mail address: [email protected] (S. Biniak). 0165-2370/$ – see front matter © 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.jaap.2012.12.021

commercial carbon adsorbents. There are also many reports on the production of activated carbons from commercial granulated PET [17–23]. The properties of the final carbon products from a PET precursor can be regulated by using various preparation methods and conditions (carbonization and activation) [5,11,21,24]. Depending on the temperature and time of activation (with CO2 ), amorphous carbon (formed by polymer degradation) is eliminated or a micropore texture develops (formation of new pores and widening of existing ones) [11]. The methods generally applied are more or less complicated and usually lead to a relatively high burn-off of carbonized polymer, which is economically disadvantageous. Owing to their wide application as sorbents, the porosity and surface chemistry of the carbons obtained were studied in detail. As a raw material, PET provides the opportunity of obtaining a highly ramified micropore structure in the final material [8,9,11,17]. Such microporous activated carbons have been proposed as a possible solution for hydrogen storage [8,9]. For this

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application an appropriate size pore distribution is necessary to ensure the highest possible adsorption capacity and the requisite strength of the interaction between H2 and the carbon surface. On the other hand, PET-based carbons are potentially applicable as electrode materials in supercapacitors [15,16]. These carbons follow the general trends observed for highly porous materials and display specific capacitances at low current density. Very good performance has also been achieved at high current densities, which confirms the potential of this type of material for electrical energy storage [16]. The aim of the present work was to obtain activated carbon from PET waste by taking into consideration (i) the possible simplification of the carbonization and activation methods, (ii) the small degree of char burn-off, and (iii) the microporosity development of the carbon products. The adsorption capacity toward nitrogen (gas) and 4-chlorophenol (aqueous solution) of PET carbons and commercial activated carbon were compared. Additionally, preliminary tests on the potential use of low-cost microporous PET carbon as electrodes with a high electric double layer capacity and for the storage of gaseous hydrogen were carried out. 2. Experimental 2.1. Sample preparation PET waste (old bottles, ground up) was carbonized in a quartz Gray-King retort placed in a vertical furnace (Carbolite Furnace, type MTF 12/38B) in a stream of nitrogen (10 dm3 /h). 5 g samples of PET (5 mm × 5 mm square) were heated from room temperature to 1098 K at a rate of 10 K/min. Samples were maintained at the final temperature for 15 min. Preliminary experiments indicate that these carbonization conditions ensured the formation of relatively small amounts of volatile degradation products of polymer. The yield ranged from 20 to 22%. The obtained char (after grinding) contain mainly (85%) particles of size 2–0.6 mm, and this fraction was selected for physical activation. Batches of ca 1.5 g of the carbonized sample (825-C) were activated in a quartz reactor placed in a vertical furnace (TERMOD PR-1000) using CO2 as activating agent (10 dm3 /h). Activation was carried out under various conditions: at 1173 K for 8 h, at 1198 K for 6 h, at 1213 K for 4 h and 5 h, the respective samples obtained being denoted by 900-8, 925-6, 940-4 and 940-5. The commercial activated carbon Norit R-3-ex (NR3ex) was selected as the reference material. It was previously de-mineralized HF and HCl acids to remove of inorganic impurities (absent in PET carbons)- sample UC1 from [25]. 2.2. Porosity The porosity of the activated carbons was characterized by lowtemperature nitrogen adsorption isotherms measured at 77.4 K on an ASAP 2010 volumetric adsorption analyzer (Micromeritics, Norcross, GA, USA). Before each adsorption measurement, the sample was outgassed under vacuum at 423 K. The specific surface areas (SBET ) and mesopore areas (Sme ) as well as micropore and mesopore volumes (Vmi and Vme ) were calculated from the adsorption isotherms [26,27]. 2.3. XRD and Raman spectroscopy X-ray diffraction (XRD) spectra were measured (D500 Diffractometer, Siemens, Germany) in conjunction with Cu K␣ radiation, in the 2 range from 10 to 60◦ with a 0.05◦ step. Raman spectra (T64000 Jobin Yvon, USA) were collected from 800 to 2000 cm−1 using a 514.5 nm excitation laser with a spectral resolution of 2 cm−1 . The spectra were deconvoluted and fitted using Lorentzian functions.

193

A scanning electron microscope (SEM, LEO 1430VP) integrated with an Energy Dispersive X-ray (EDS) analysis system (Quantax 200, Bruker-AXS Microanalysis) was used to obtain micrographs of selected samples and to estimate the total oxygen bonded to the carbon surface. Six different surface sites (0.2 cm2 ) were analyzed for each material. 2.4. Chlorophenol adsorption isotherms 4-Chlorophenol (4-CP) was adsorbed on the activated carbon samples 925-6 and NR3ex (for comparison) at 293 K from aqueous solutions with an adsorbate concentration < 0.05 M. The concentration of 4-chlorophenol was measured by HPLC [28] (DAD, Shimadzu LC-20, Kyoto, Japan). Analytes were separated on a Phenomenex Luna C18 (4.6 × 150 mm, 3 ␮m) column (Torrance, CA, USA). The chromatographic measurements were carried out under isocratic conditions on a Luna C18 (4.6 × 150 mm, 3 ␮m) column operated at 313 K with methanol and water adjusted to pH 3.0 with acetic acid (80:20, v/v). The mobile phase was pumped at a flow rate of 0.6 ml/min and peaks were monitored at 281 nm. 4-Chlorophenol (4-CP) was obtained from Sigma (St Louis, MO, USA), acetic acid was from POCH (Gliwice, Poland) and HPLC-grade methanol from Acros Organics (Geel, Belgium). 2.5. Cyclic voltammetry Electrochemical studies of all the samples (PET and commercial carbons) were carried out in 0.1 M sulfuric acid as blank electrolyte, using the powdered activated carbon electrode (PACE) technique [29,30]. After prior vacuum desorption (10−2 Pa), the powdered carbon (mass 50 mg) was placed in an electrode container and drenched with a de-aerated solution to obtain a ∼3 mm sedimentation layer. First, the potentiometric responses of the carbon electrodes were measured in an oxygen-free atmosphere once their values had stabilized (usually after 24 h). Next, cyclic voltammetry (CV) was performed using the typical three-electrode system and an Autolab (Eco Chemie) modular electro-chemical system equipped with a PGSTAT 10 potentiostat, driven by GPES 3 software (Eco Chemie). All potentials were measured, and are reported against a saturated calomel electrode (SCE). A platinum gauze served as counter electrode. First, CVs were recorded for different sweep amplitudes until the potentials of hydrogen or oxygen evaluation were achieved. The hydrogen and oxygen evolution potentials were determined for independently prepared electrodes. Next, with fresh electrode materials (previously impregnated with electrolyte for 24 h), the cyclizations were carried out from zero to positive potentials and in potential ranges precluding the electrolysis of water. The capacitive currents were visible on the CV curves for all samples in blank solutions and the electric double layer capacities (Cdl ) for +200 mV potential values were read off the curves [30,31]: Cdl =

i

v

(1)

where i is the capacitive current (mA/g) and v is the sweep rate (2 mV/s). For samples 925-6 and NR3ex the electrochemical studies were also performed in blank electrolyte with the addition of 2 mM 4-CP as depolarizer. 2.6. Hydrogen adsorption The hydrogen adsorption isotherm of the activated carbon sample with the best-developed microporosity (940-5) was measured at 77.4 K with a Micromeritics ASAP 2020 volumetric adsorption

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Table 1 Parameters of porous structure carbons tested. Sample

Burn-off (%)

SBET (m2 /g)

Sme (m2 /g)

Vme (cm3 /g)

Vmi (cm3 /g)

900-8 925-6 940-4 940-5 NR3ex

37.3 38.8 37.8 59.2 –

1210 1180 1110 1830 1120

26 15 8 61 28

0.052 0.027 0.010 0.096 0.040

0.413 0.405 0.397 0.604 0.404

analyzer (Micromeritics, Norcross, GA, USA). Before measurement the sample was outgassed under vacuum at 423 K. 3. Results and discussion As result of carbonization in a nitrogen atmosphere (1098 K) and subsequent activation in a CO2 stream at various temperatures (1173, 1198, 1213 K) and for different lengths of time (8, 6, 4, 5 h) several samples were obtained. The degrees of burn-off of activated carbons 900-8, 925-6 and 940-4 were relatively low and similar each to other (Table 1), but that of the 940-5 sample was markedly higher in value. The effect of activation was evaluated by lowtemperature nitrogen adsorption–desorption isotherms (Fig. 1a). On the basis of these, the parameters of porous structure – specific surface area (SBET ), mesopore surface area (Sme ) and microand mesopore volumes (Vmi and Vme ) were calculated [26,27] (see Table 1). For the first three samples, a rising temperature and shorter activation time was accompanied by a slight decrease in specific surface area and micropore volume. The mesopore volumes of the samples tested were distinctly lower and their changes are of lesser importance. Generally, these samples exhibited markedly microporous characters. Sample 940-5 with a high burn-off (1.5 times greater than that of the other three samples) exhibited a nearly 50% increase in SBET and Vmi , and the mesopore parameters were more than doubled. De-ashed activated carbon was used as the reference material. The external layer of its granules was abraded in a spouted bed to remove part of the material with to

Fig. 1. N2 adsorption–desorption isotherms at 77.4 K of activated carbons derived from waste PET (a) and isotherm comparison for NR3ex and 925-6 samples (b).

Fig. 2. Normalized X-ray powder diffraction patterns for as-obtained and activated carbonizates (a), diffraction pattern of sample 925-6 with marked areas background (b).

many mesopores. Fig. 1b compares the nitrogen isotherm of sample NR3ex with the most similar isotherm obtained for sample 925-6. The porous structure parameters for the reference carbon are listed in Table 1. PET carbons 925-6 and 940-4 with surface areas (1180 and 1110 m2 /g, respectively) similar to those of commercial carbon (1120 m2 /g) exhibit a more microporous character in comparison to the latter carbon (a higher value of Vmi /Vme ). The solid products obtained after carbonization and activation were structurally characterized by powder X-ray diffraction and Raman spectroscopy. Fig. 2a shows the XRD diffraction patterns for the as-obtained carbonizate and carbon materials activated at various temperatures and times. The XRD patterns of the samples do not exhibit any significant differences, but they do visualize the very low crystallinity ordering of the samples. There are two features appearing on the patterns. The first one is located at 22–23◦ and corresponds to the (0 0 2) reflections [32,33]. The second feature is of weaker intensity and is ascribed to the overlapping diffraction peaks (1 0 0) and (1 0 1). The increasing background in the 2 range between 10 and 30◦ is due to the presence of pores (primarily micropores) that continuously scatter the X-ray radiation [34]. The samples activated at 1213 K have the largest contribution of the background of all the carbon materials studied here. This is in agreement with textural data showing that activation at this temperature results in a product with the highest porosity. The structural details, i.e. the interlayer distance between graphene layers (d0 0 2 ) and the mean size of the graphitic domains, can be evaluated from the position and the width of the (0 0 2) reflection. Before the evaluation the background was subtracted using the polynomial function (Fig. 2b). The calculated interlayer distance from the position of the (0 0 2)

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Table 2 Structural parameters obtained from powder XRD patterns and Raman spectra. Sample

d0 0 2 (nm)

Lc (nm)

G/D

G/A

825-C 900-8 925-6 940-4 940-5 NR3ex

0.385 0.404 0.404 0.412 0.387 0.398

0.86 0.96 0.96 0.87 0.82 0.73

0.44 0.40 0.37 0.44 0.40 0.29

1.15 2.65 2.38 2.65 1.91 1.47

reflections are between 0.385 and 0.412 nm (Table 2). The Lc values varies in a relatively narrow range (0.82–0.96), which refers to statistical domains, which are built of 2–3 stacked graphene layers. Those values are typical for carbon materials of very low crystallinity ordering. This is an expected finding, because the low carbonization temperature applied can result in a material with a low degree of graphitization. Further structural details were obtained from Raman spectroscopy (Fig. 3). The wave number range between 800 and 2000 cm−1 is the spectral energy window that contains valuable information about solid carbon materials [35]. Two broad bands appear on the spectra of the samples (Fig. 3a). The feature located at 1600 cm−1 is the so-called G band, corresponding to the stretching vibrations in the basal graphene layer. The G band is upshifted by 18 cm−1 in comparison to the pyrolytic graphite, and this is a consequence of the small sizes of the basal graphene layers in the grains of the studied carbon materials. The band located at 1350 cm−1 (D band) is associated with a disordered graphite lattice, and is the more intense, the lower the structural ordering. The G/D integral intensity band ratio is a convenient and widely accepted indicator of the degree of graphitization [36]. This ratio is directly proportional to the basal plane diameter (La ) of graphene layers [37]. The G and D bands on the acquired Raman spectra are not resolved, so deconvolution is necessary. This procedure is successful (R2 > 0.997) when four bands are used (Fig. 3b). Band A appearing at 1530 cm−1 corresponds to the presence of solid carbon with a completely amorphous structure [38] whereas band I can be ascribed to polyenes [39]. The G/D ratios vary within a narrow range, i.e. between 0.37 and 0.44 (Table 2), and this shows that activation hardly modifies the basal size of graphene layers. This last finding is consistent with the XRD results (see the Lc values) and demonstrates that activation do not influence the crystallinity ordering both in a and c directions. Treatment with CO2 changes the amounts of the amorphous phase (this is illustrated in Fig. 3b and c). The G/A ratios were calculated for convenience (Table 2). Treatment with CO2 causes partial gasification of the solid carbon and results in the formation of a porous structure. Obviously, the carbon atoms in the amorphous part of the grain will be more reactive toward the gasification agent in comparison with the atoms in the small crystalline domains. This shows why the samples treated at low temperatures (900-8 and 925-6) or for short times (940-4) have a smaller amorphous phase fraction than the as-obtained carbonizate. With a further increase in temperature and activation time (sample 940-5) the amounts of amorphous phase also increase; this is accompanied by a decrease in the G/D ratio. Hence, at the highest temperature and the longest activation time the CO2 starts to gasify the carbon atoms from the small graphitic domains (this is also reflected by the largest burnoff). The structural parameters of the reference activated carbon NR3ex calculated from XRD and Raman spectra are shown in Table 2 for comparison. The results demonstrate that PET carbons exhibit better overall crystallinity than the reference commercial activated carbon. SEM micrographs (Fig. 4) of selected PET carbon (925-6) and NR3ex samples show differences in surface characteristics, such as topography and roughness. The PET carbon surface seems to be

Fig. 3. Normalized Raman spectra of as-obtained and activated carbonizates (a), deconvoluted spectra of carbonizat 825-C (b) and activated carbon 925-6 (c).

smoother and with a smaller number of macropores than the NR3ex sample. The adsorption ability toward 4-CP of PET activated carbon and reference material with a similar structure was examined; the relevant adsorption isotherms are presented at Fig. 5. The isotherms are similar to each other, and the experimental points are well described using Freundlich equation 1/n

qe = kCe

(2)

where k and 1/n are constants. The calculated parameters are as follows: k = 2.638, 1/n = 0.312; for 925-6 and k = 2.407, 1/n = 0.330 for NR3ex sample. In both cases R2 has very high value 0.9946 and 0.9974, respectively. The slightly smaller adsorption capacity toward 4-CP for NR3ex compared to

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W. Bratek et al. / Journal of Analytical and Applied Pyrolysis 100 (2013) 192–198 Table 3 Surface oxygen content and electrochemical parameters of the carbons tested. Sample

O (at%)a

Est (mV)

EH2 (mV)

EO2 (mV)

C (F/g)

825-C 900-8 925-6 940-4 940-5 NR3ex

3.8 1.8 2.2 2.1 2.3 5.4

+505 +354 +357 +339 +353 +533

−290 −410 −410 −410 −420 −500

+1350 +1680 +1640 +1640 +1710 +1850

0.95 14.5 13.8 13.5 19.2 20.5

a

From EDS.

PET carbon sample 925-6 (in spite of the close porous structure – see Table 1) is probably the result of a larger (nearly 2.5 fold) surface oxygen concentration (see Table 3). The carbon materials were used as powdered working electrodes in the electrochemical investigations [30]. First, potential responses (Est ) after stabilization were measured (see Table 3): there is a clear correlation between surface oxygen content and stationary potential. Then potential cyclization was carried out with a 2 mV/s sweep rate. For separated samples, the potential at which there is a rapid increase in anodic or cathodic current, before the generation of gaseous products (which could destroy the sedimentary layer of the powder electrode), is taken to be the potential at which oxygen or hydrogen is evolved. The estimated potential values from the recorded CV curves listed in Table 3 depends on the kind of material tested and are generally similar to those of other powdered activated carbon electrodes [30]. Further cyclovoltammetric measurements were carried out in a narrower range of sweep potentials. The CV curves presented in Fig. 6 are mostly very similar, but the current values measured for carbonizate 825-C are about fifty times smaller than those measured for the activated PET carbon

Fig. 4. SEM micrographs of 925-6 (a) and NR3ex (b) carbon samples.

5

925-6 4

q (mmol/g)

NR3ex 3

2

1

0 0

1

2

3

4

5

3

Ce (mmol/dm ) Fig. 5. 4-CP adsorption isotherms for 925-6 and NR3ex samples at 298 K.

Fig. 6. Cyclic voltammograms of the powdered carbon electrodes prepared from the samples tested: 1 – 825-C; 2 – 900-8; 3 – 925-6; 4 – 940-4; 5 – 940-5. Dashed line – NR3ex.

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197

Hydrogen uptake [ml (STP)/g]

200

160

120

80

40

0 0 Fig. 7. CVs of 925-6 (1) and NR3ex (2) samples in blank electrolyte (first cycle – solid line) and with 2 mM 4-CP (first cycle – dashed line; steady state – dotted line).

samples. The CV of the reference NRex activated carbon electrode recorded in blank solution is similar in shape and currents values to those of the PET activated carbons, as shown in Fig. 6 (dashed line). The parameters obtained from the cyclic voltammetric curves: the hydrogen and oxygen evolution potentials (EH2 , EO2 ) and the electric double layer capacity (Cdl ) are listed in Table 3. There is a linear correlation between the electric double layer capacity (Cdl ) and the specific surface areas (R2 = 0.9993) as well as the micropore volumes (R2 = 0.9947) of the carbon samples (see Table 1). In carbonizate 825-C, with has a specific surface area < 10 m2 /g, and also three activated carbons with only slightly varying values of EH2 , EO2 and Cdl , these parameters change in much the same way as the specific surface area (1100–1200 m2 /g). The last activated carbon 940-5, with electrochemical parameters significantly different from those of the three other carbons, also has the highest specific surface area (>1800 m2 /g). But the more evidently higher Cdl value of the reference activated carbon may be due to a higher degree of surface oxidation (see Table 3). The results of the electrochemical studies of PET carbon (925-6) and reference carbon (NRex) in electrolyte solution containing 4-CP as depolarizer are presented in Fig. 7. The changes in the CV during cyclization in the presence of a depolarizer are similar and rather slight (dotted lines – first cycle, dashed lines – steady state after 160 cycles). The 4-CP uptake in the electrochemical cell (on electrode material) during cyclization (measured by HPLC) is 2.4 mM/g for PET and 1.7 mM/g for NRex. The observed differences in up-take (in presence electrolyte) by 925-6 and for NRex samples resemble the mutual position of the 4-CP adsorption isotherms for these carbons (from pure water) (Fig. 5). PET activated carbon demonstrates a better capacity to remove 4-CP in both adsorption and electrochemical processes than commercial carbon with a similar porosity. H2 adsorption was measured in a preliminary study of the suitability of the materials obtained for hydrogen storage. The hydrogen storage capacity of the activated carbon sample with the best-developed microporosity (940-5) was calculated on the basis of the H2 adsorption isotherm (Fig. 5) determined at 77.4 K. The maximum hydrogen uptake (for p = 1 bar) was calculated to be 1.8 wt% for this sample. This value, as well as the dependence of hydrogen uptake on pressure (Fig. 5) is comparable to other results obtained with similar samples (see e.g. [8,9]). Optimization of the activation processes conditions (time and temperature of heat treatment in CO2 ) should enable a material with a better

200

400

600

800

Pressure (mm Hg) Fig. 8. Hydrogen adsorption isotherm for 940-5 activated carbon at 77.3 K.

hydrogen storage capacity to be obtained; this will be the subject of further studies. From the practical point of view, optimization should lead to a material with a >50% burn-off and a specific surface area a little above 2000 m2 /g (and a micropore surface area of ca. 1000 m2 /g). Further optimization should involve changing the time and temperature conditions of activation in a range close to those of the 940-5 sample (Fig. 8). 4. Conclusions Studies of the conditions under which activated carbon is produced from waste PET with CO2 as activating agent have demonstrated the importance of the temperature and the duration of the process. By increasing the temperature and simultaneously shortening the annealing time, a similar burn-off degree can be maintained and the parameters characterizing the porous structure decrease only slightly. All the carbons obtained are evidently microporous. Evidently, both factors – the temperature and time of activation – within the range of their variation, are important parameters driving pore formation in the carbon material. With increasing activation temperature, the time necessary to achieve the same level of burn-off decreased. Samples with similar specific surface area (and micropore volume) had similar levels of burnoff. Activation has no significant influence on sample crystallinity or on the size of the graphitic domains in the range of activation conditions used (mainly temperature). CO2 treatment preferentially removes the amorphous phase at lower temperatures and shorter times. Higher temperatures result in etching of graphitic domains of better crystallinity. Hardly any changes due to the activation temperature were observed in the CV curves or the hydrogen evolution potential. In contrast, a relatively small increase in activation time (from 4 h to 5 h) at the highest temperature used (940 ◦ C) yielded a significant increase in burn-off degree and porous structure development. This carbon sample exhibited higher values of the microporous structure parameters and the double layer capacity than the other three samples; its hydrogen evolution potential was slightly lower. This activated carbon possesses also a significant hydrogen storage capacity calculated on the basis of the measured low temperature adsorption isotherm. These investigations show that is possible to produce from waste PET activated carbon with satisfactory properties using the simple processes of carbonization and activation. In contrast to commercial activated carbon with a similar surface area, it exhibits

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a more microporous structure and a better capacity to remove 4-CP in both adsorption and electrochemical processes. The PET activated carbons obtained have a potential use as adsorbent and electrode materials in supercapacitors or fuel cells. Their porous structures are easily regulated by the temperature and/or the duration of activation. Acknowledgments This work was financially supported by Polish Ministry of Science and Higher Education (project no. N N209 099037) and partially by IP2011 006071. References [1] S. Mishra, A.S. Goje, V.S. Zope, Chemical recycling, kinetics, and thermodynamics of poly (ethylene terephthalate) (PET) waste powder by nitric acid hydrolysis, Polymer Reaction Engineering 11 (2003) 79–99. [2] M. Dias, M.C.M. Alvim-Ferraz, M.F. Almeida, J. Rivera-Utrilla, M. Sanchez-Polo, Waste materials for activated carbon preparation and its use in aqueousphase treatment: a review, Journal of Environmental Management 85 (2007) 833–846. [3] M.A. Migahead, A.M. Abdul-Raheim, A.M. Atta, W. Brostow, Synthesis and evaluation of a new water soluble corrosion inhibitor from recycled poly(ethylene terephthalate), Materials Chemistry and Physics 121 (2010) 208–214. ´ [4] M. Marzec, B. Tryba, R.J. Kalenczuk, A.W. Morawski, Poly(ethylene terephthalate) as a source for activated carbon, Polymer for Advanced Technologies 10 (1999) 588–595. [5] N.T. Kartel’, N.V. Gerasimenko, N.N. Tsyba, A.D. Nikolaichuk, G.A. Kovtun, Synthesis and study of carbon sorbent prepared from polyethylene terephthalate, Russian Journal of Applied Chemistry 74 (2001) 1765–1767. [6] J.B. Parra, C.O. Ania, A. Arenillas, J.J. Pis, Textural characterization of activated carbons obtained from poly(ethylene terephthalate) by carbon dioxide activation, Studies in Surface Science and Catalysis 144 (2002) 537–543. [7] K. Nakagawa, A. Namba, S.R. Mukai, H. Tamon, P. Ariyadejwanich, W. Tanthapanichakoon, Adsorption of phenol and reactive dye from aqueous solution on activated carbons derived from solid wastes, Water Research 38 (2004) 1791–1798. [8] J.B. Parra, C.O. Ania, A. Arenillas, F. Rubiera, J.J. Pis, High value carbon materials from PET recycling, Applied Surface Science 238 (2004) 304–308. [9] J.B. Parra, C.O. Ania, A. Arenillas, F. Rubiera, J.M. Palacios, J.J. Pis, Textural development and hydrogen adsorption of carbon materials from PET waste, Journal of Alloys and Compounds 379 (2004) 280–289. [10] A. Arenillas, F. Rubibiera, J.B. Parra, C.O. Ania, J.J. Pis, Surface modification of low cost carbon for their application in the environmental protection, Applied Surface Science 252 (2005) 619–624. [11] I. Fernández-Morales, M.C. Almazán-Almazán, M. Pérez-Mendoza, M. Domingo-García, F.J. López-Garzón, PET as precursor of microporous carbons: preparation and characterization, Microporous and Mesoporous Materials 80 (2005) 107–115. [12] M.T. Kartel, N.V. Sych, M.M. Tsyba, V.V. Strelko, Preparation of porous carbons by chemical activation of polyethyleneterephthalate, Carbon 44 (2006) 1019–1022. [13] N.V. Sych, N.T. Kartel, N.N. Tsyba, V.V. Strelko, Effect of combined activation on the preparation of high porous active carbons from granulated post-consumer polyethyleneterephthalate, Applied Surface Science 252 (2006) 8062–8066. [14] M.C. Almazán-Almazán, M. Pérez-Mendoza, F.J. López-Domingo, I. FernándezMorales, M. Domingo-García, F.J. López-Garzón, A new method microporous carbon from PET: characterisation by adsorption and molecular simulation, Microporous and Mesoporous Materials 106 (2007) 219–228. [15] T.A. Centeno, F. Rubiera, F. Stoeckli, Recycling of residues as precursors of carbons for supercapacitors, in: Proceedings of the 1st Spanish National

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