Accepted Manuscript Highly mesoporous activated carbon synthesized by pyrolysis of waste polyester textiles and MgCl2: Physiochemical characteristics and pore-forming mechanism Zhihua Xu, Zhihang Yuan, Daofang Zhang, Weifang Chen, Yuanxing Huang, Tianqi Zhang, Danqi Tian, Haixuan Deng, Yuwei Zhou, Zhenhua Sun PII:
S0959-6526(18)31334-9
DOI:
10.1016/j.jclepro.2018.05.007
Reference:
JCLP 12864
To appear in:
Journal of Cleaner Production
Received Date: 4 January 2018 Revised Date:
23 March 2018
Accepted Date: 1 May 2018
Please cite this article as: Xu Z, Yuan Z, Zhang D, Chen W, Huang Y, Zhang T, Tian D, Deng H, Zhou Y, Sun Z, Highly mesoporous activated carbon synthesized by pyrolysis of waste polyester textiles and MgCl2: Physiochemical characteristics and pore-forming mechanism, Journal of Cleaner Production (2018), doi: 10.1016/j.jclepro.2018.05.007. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
ACCEPTED MANUSCRIPT Highly mesoporous activated carbon synthesized by pyrolysis of waste polyester textiles and MgCl2: Physiochemical characteristics and pore-forming mechanism
Zhihua Xu, Zhihang Yuan, Daofang Zhang*, Weifang Chen*, Yuanxing Huang, Tianqi Zhang, Danqi Tian,
RI PT
Haixuan Deng, Yuwei Zhou, Zhenhua Sun. School of Environment and Architecture, University of Shanghai for Science and Technology, 516 Jungong Rd., Shanghai 200093, PR China.
SC
*Corresponding author. Email:
[email protected] (D.F. Zhang).
[email protected] (W.F. Chen).
M AN U
Abstract
Activation-pyrolysis of textile wastes was considered a sustainable technique to fabricate activated carbon. Highly mesoporous activated carbon was prepared from waste polyester textiles by employing MgCl2 as the activation and template agents. The influences of different preparation conditions on
TE D
textual property and crystalline structure of carbon were identified by N2 adsorption-desorption isotherms and X-ray diffraction. The optimum pyrolysis temperature, time and mixing ratio for MgCl2/waste polyester textiles are 900°C, 1.5 h and 5:5 with the carbon thus obtained manifested a
EP
surface area of 1307 m2/g, total pore volume of 3.56 cm3/g of which 98% is mesopore. The effect of
AC C
MgCl2 on the full-cycle pyrolysis pathway of waste polyester textiles was systematically investigated by various characterization methods to explore the pore-forming mechanism of activated carbon. The results demonstrated that MgCl2 was capable of catalyzing the dehydrogenation, decarboxylic and cross-linking reaction of waste polyester textiles and inhibited the formation of tars during pyrolysis process, indicating that the addition of MgCl2 was conducive to the formation of carbonaceous materials and open pores. Meanwhile, acted as the template, MgO particles derived from the decomposition of MgCl2 could develop massive homogeneous mesopores in the carbon matrix.
ACCEPTED MANUSCRIPT Keywords: Waste polyester textiles, MgCl2, Activated carbon, Pore-forming mechanism
1. Introduction
RI PT
Activated carbons have been extensively used for water treatment (Rodrigues et al., 2017; Yao et al., 2016; Zhou et al., 2014), air pollution control (Zhang et al., 2016) and energy storage (Nishihara and Kyotani, 2012; Prauchner et al., 2016) because of its higher specific surface area, various porous
SC
structures and abundant oxygen-containing groups. Generally, activated carbons can be prepared from
M AN U
any precursor of high carbon content, like resin (Ma et al., 2015), glucose (Falco et al., 2011) and cellulose etc (Zhu et al., 2011). However, the large-scale applications of some of these materials are often confined by economic reason since they are oftentimes costly and non-renewable. Therefore, investigations are being conducted worldwide to explore alternative raw materials for activated carbon
TE D
that are more abundant and cost-effective (Giri et al., 2012; Sahu et al., 2010; Tian et al., 2017). In recent years, the production of textile wastes in China is over 2×107 ton/year, and about 70 percent of which is chemical fiber (NDRC, 2014). It will certainly cause severe environmental problems if
EP
there is no proper treatment toward such a large amount of waste. Waste polyester textiles (WPT),
AC C
accounting for four-fifths of waste chemical fiber, is difficult to degrade in the environment. For rapid disposal, most of the waste is directly burned in open air, resulting in grievous atmosphere pollution (Nzihou, 2010). Researchers have attempted to use dissolution method for waste recycling (Negulescu et al., 1998; Vasconcelos and Cavaco-Paulo, 2006). Various organic solvents were used to separate cellulose and polyester from their mixed fabrics for the recycling of waste fabrics, and a higher separation rate (75%~80%) was achieved. However, dissolution consumes a large amount of chemicals and the processes are complex. To this end, some studies focused on utilizing waste textiles such as
ACCEPTED MANUSCRIPT acrylic textile (Nahil and Williams, 2010) and cotton woven (Bao and Li, 2012; Zheng et al., 2014) as a precursor to prepare activated carbon. In their studies, activated carbons with surface area ranged from 750~1000 m2/g were obtained and applied to dye adsorption and energy storage. Nevertheless, few
RI PT
investigations pay attention to the preparation of activated carbon using WPT as the precursor. With a high carbon content in the vicinity of 60 percent (Esfandiari et al., 2012), WPT can be considered as a potential raw material for the production of activated carbon.
SC
Activated carbons are commonly synthesized by pyrolysis-activation method using H3PO4, ZnCl2
M AN U
and KOH etc. as activating agent (Yahya et al., 2015). However, common synthesis present certain drawbacks: (1) It results in environmental pollution and equipment corrosion due to the volatility and corrosiveness of chemical by-products; (2) Activated carbons resultant are mainly microporous, which may be detrimental to the mass transfer during adsorption process (Gong et al., 2014). More efforts are
TE D
made to manipulate preparation method to synthesize carbons that present specific pore structures and high surface area. Recently, one of the novel approaches is the MgO-templating method, that employing MgO as the template to synthesize mesoporous carbon (Inagaki et al., 2007; Morishita et al.,
EP
2007; Morishita et al., 2010). The method has advantages to obtain high surface area and homogenous
AC C
pore structures without much complicated stabilization procedures. Different magnesium salts (e.g. magnesium acetate, magnesium citrate and magnesium gluconate) have been used as the precursor of MgO (He et al., 2012; Inagaki et al., 2016). Remarkably, the surface area (1080~1800 m²/g) of the carbons prepared from the above magnesium salts were obviously improved compared to the sample prepared from MgO (741~920 m²/g). MgCl2 is reported to also be able to decompose into MgO by pyrolysis, and has the characteristics of low cost and wide source (Huang et al., 2011; Liu et al., 2013). Therefore, it is logical to suppose that MgCl2 may be a potential candidate as template agents (Xu et al.,
ACCEPTED MANUSCRIPT 2017). There are some studies that have already investigated the feasibility of using MgCl2 as the activating agent to synthesize porous carbon (Liu et al., 2013; Rufford et al., 2011; Zhang et al., 2012), and the results suggested that MgCl2 showed strong dehydration capability toward polymers, which is
RI PT
beneficial to the formation of pores structures in the carbon matrix. While the surface area of the carbons prepared by the above studies is relatively low and the effect of MgCl2 on the full-cycle pyrolysis pathway of carbon precursor has not been clearly defined. Therefore, it is necessary to
SC
explore in more details the corresponding pore-forming mechanism for potential manipulation of
M AN U
activated carbons of high quality.
In this work, MgCl2 was employed as the activating agent and MgO template precursor for synthesis activated carbon from WPT. To the best of our knowledge, there were few investigations on co-pyrolysis of MgCl2 and WPT and the corresponding pore-forming mechanism. The N2
TE D
adsorption-desorption isotherms analysis and X-ray diffraction (XRD) were conducted to determine the effects of pyrolysis temperature and mixing ratio of MgO/WPT on surface area, pore size distribution and crystalline structure of the products. Thermogravimetric-Fourier infrared spectrum-Gas
EP
chromatography/Mass spectrum (TG-FTIR-GC/MS) technique was used to dynamically detect the
AC C
release of volatiles from WPT and the mixture of MgCl2/WPT during pyrolysis to further illuminate the carbon-forming and activation mechanism. In addition, the changes in morphology and crystalline structure of activated carbons before and after MgO dissolution were investigated in details to explore the templating effect of MgO.
ACCEPTED MANUSCRIPT 2. Experimental
2.1 Materials
RI PT
MgCl2·6H2O and HCl used (analytical grade) in this study were obtained from Sinopharm Chemical Reagent Co. (Shanghai, China). Waste polyester textiles was supplied by a textile factory in Shanghai. (It is mainly composed of polyester coated (around 90 wt.%) with a small amount of polyurethane hot
SC
melt adhesive (around 10 wt.%), and the chemical structures were shown in Fig. S1). All solutions
M AN U
employed were prepared with Milli-Q ultra-pure water and the purity of nitrogen was no less than 99.99%.
2.2 Preparation
TE D
Chunks of WPT was cut into small pieces of 1×1 cm and heated in muffle furnace at 265°C for 1 h under aerobic condition. After that, the cooled sample was ground into powder (40 meshes) and immersed in MgCl2·6H2O solution at MgO/WPT powder weight ratio of 3:7, 5:5 and 7:3, respectively.
EP
The mixture was stirred (600 rpm) by a magnetic stirrer for 12 h, and was then placed in drying oven at
AC C
80°C for 12 h. The dried WPT were heated to pyrolysis temperature (600°C, 750°C and 900°C) under the N2 atmosphere in a pipe furnace. The hearting rate was set to be 10°C/min and the residence time at the target temperature was 1.5 h. Upon completion of the pyrolysis, the resultant mixture was soaked in 10 vol% HCl solution (300 mL) for 8~12 h to remove MgO. In the end, the product was washed by deionized water until the pH of elution was ~7 and then dried in dryer at 105°C. The above mentioned samples were marked as AC-x-y (x is pyrolysis temperature, y is mixing ratio of MgO g/WPT g). The carbon prepared utilizing MgO as the template (temperature: 900°C, mixing ratio: 5:5, pyrolysis time:
ACCEPTED MANUSCRIPT 1.5 h) and carbonization sample (carbonization temperature: 900°C, pyrolysis time: 1.5 h) were denoted as AC-MgO and CS, respectively.
RI PT
2.3 Characterization
The approximate analysis of WPT was performed according to National Standard (GB/T 212-2008, China). The elements of WPT, CS, and AC-900-5:5 were determined by elemental analyzer
SC
(Elementar/MACRO Germany). The measurement of point of zero charge was conducted by adding 1 g
M AN U
sample into 20 mL of ultra-pure water and oscillated for 24 h, and pH of the slurry was determined utilizing pH meter (Mettler-Toledo/ FE20 Switzerland) as pHpzc (Moreno-Castilla et al., 2000). The yield was defined as the mass ratio of activated carbon to WPT, and the equations can be explained as (1):
(1)
TE D
Yield% = Mw/Ma × 100%
Where Mw is the mass of WPT, Ma is the mass of the sample after washing and drying. Textural properties of all carbons were investigated with N2 adsorption/desorption isotherms at 77 K
EP
using a surface area analyzer (Quantachrome/autosorb-iQ, USA). The specific surface area was
AC C
calculated by Brunauer-Emmett-Teller (BET) equation, and the mesoporous and microporous size distributions were determined with density functional theory (DFT). The total pore volume (Vtotal) was determined as the adsorption volume at 0.99 P/P0. The micropore surface area (Smicro), external surface area (Sext) and micropore volume (Vmicro) were calculated using the t-method. The crystallinity analysis was investigated with a 2θ scan range from 5° to 80° (scan speed was 3°/min) utilizing wide-angle X-ray diffraction (Bruker/D8 ADVANCE, Germany) equipped with Ni-filtered Cu Kα radiation (λ=1.540598 Å). The morphological properties of sample before and after HCl pickling were analyzed
ACCEPTED MANUSCRIPT by transmission electron microscopy (TEM) (FEI/Tecnai-G2-F20, USA) and scanning electron microscope-energy dispersive spectrometer (SEM-EDS) (HITACHI/S4800, Japan). The TG-FTIR-GC/MS analysis was performed using a thermogravimetric (TG) analyzer
RI PT
(PerkinElmer/STA 8000, USA) coupled with a FTIR spectrometer (PerkinElmer/Frontier, USA) and gas chromatograph/mass spectrometer (GC/MS) (PerkinElmer/Clarus680SQ8T, USA). Samples were pyrolyzed in TG analyzer at a heating rate of 10°C/min from 30°C to 900°C in N2 atmosphere. Then the
SC
changes of gaseous products were recorded by FTIR with the increasing temperature. In GC/MS
M AN U
system, the initial column temperature was held at 80°C for 0 min, and then raising to 280°C at a rate of 10°C /min. The split, carrier gas and solvent delay were 10:1, helium and 0 min, respectively.
3. Results and discussion
TE D
3.1 Specific surface area and pore structure
The N2 adsorption/desorption isotherms and the corresponding DFT pore size distribution of the
EP
prepared activated carbons were exhibited in Fig. 1. As shown in Fig. 1(a), all samples displayed the type-IV isotherm with a distinct H3 hysteresis loop, indicating that the pores were mainly created by
AC C
the accumulation of flake-shaped carbons (Sing, 1985). The samples prepared at 600°C exhibited lower adsorption capacity (around 1000 cm3/g) and lower nitrogen uptake at ~0.1 P/P0, manifesting insufficient micropores and lower surface area. Upon the pyrolysis temperature being raised to 750°C, the uptake of nitrogen at ∼0.1 P/P0 increased to a certain degree due to the existence of micropores. This may be related to the strong contractions of polyester-based carbonaceous material outside MgO particles at higher temperature, which contribute to the formation of slit-shaped pore structures in the carbon films (Morishita et al., 2010). Furthermore, for the sample prepared at 900°C, the maximum
ACCEPTED MANUSCRIPT adsorption quantity was significantly improved and reached nearly 2400 cm3/g, illustrating the presence of abundant pore structure in the carbon matrix. As demonstrated in Fig. 1(b), all the samples were mainly mesoporous (15~30 nm) along with a few micropores of 1.1~1.5 nm. It was noteworthy
RI PT
that the peaks of mesopore size distribution shift toward larger pore width with the increment of temperature, which was due to the fact that the crystallinity and crystal grains of MgO increasing slightly in higher temperature (Przepiórski et al., 2009). The textual property parameters of all carbons
SC
were summarized in Table 1. As the pyrolysis temperature increased from 600 to 900°C, the surface
M AN U
area and pore volume of the resultant carbons increased accordingly. Moreover, it could be obtained that the surface area increased firstly and then decreased with the mixing ratio from 3:7 to 7:3, and reached a maximum at the ratio of 5:5 at the same temperature. This can be interpreted as that the number of MgO templates increased along with the increase of MgCl2 content at first, as MgO was
TE D
conducive to the formation of porous structure. However, excessive MgO may lead to agglomeration that may be averse to the pore-forming. Overall, at the optimum condition, the total pore volume (Vtotal) reached 3.56 cm3/g for AC-900-5:5 which was far greater than those of many other studies (Inagaki et
EP
al., 2016; Libbrecht et al., 2017; Yahya et al., 2015; Yang et al., 2015). The beneficial effect by MgCl2
AC C
for pore-forming was further proven by the low specific surface area and total pore volume of CS (SBET: 171 m²/g, Vtotal: 0.15 cm3/g) and AC-MgO (SBET: 171 m²/g, Vtotal: 0.15 cm3/g) as shown in Fig. S2 and Table S1. All these means that MgCl2 can not only acts as the precursor of MgO template, but may also act both as a catalyst and activating agent toward WPT during the pyrolysis process. In summary, higher temperature and appropriate mixing ratio in MgCl2/WPT were propitious for the formation of pores structures. And the optimum activated carbon with maximum surface area of 1307 m²/g, total pore volume of 3.56 cm3/g and mesoporosity of 98% was obtained at pyrolysis temperature, time and
ACCEPTED MANUSCRIPT mixing ratio of 900°C, 1.5 h and 5:5.
3.2 Crystalline structure
RI PT
To investigate the structural order of the carbons prepared at different pyrolysis temperature and mixing ratios, XRD analysis was given in Fig. 2. In Fig. 2(a), the samples prepared at different pyrolysis temperature exhibited two broad peaks at around 25° and 43° ascribed to (002) and (100)
SC
interlayer reflection of amorphous carbon (Munoz et al., 2017; Tian et al., 2017). With the increase of
M AN U
pyrolysis temperature, the peak of (002) lattice plane shifted toward lower diffraction angle, implying higher degree of random stratification of samples (Yao et al., 2016). Meanwhile, the interlayer spacing d(002) could be calculated by Braggs equation d = λ/ sinθ , and the values were 0.349 nm for AC-900-5:5, 0.332 nm for AC-750-5:5 and 0.324 nm for AC-600-5:5. Larger interlayer spacing
TE D
contributed to the enhancement of surface activity as well as adsorption performance. In addition, AC-600-5:5 displayed a week broad peak in the range of 15~20°, this may be because of the diffraction peaks of insufficient carbonized polyester in relatively low temperature. Fig. 2(b) showed the effect of
EP
different mixing ratio on crystal structure of activated carbons. Among all the samples, the diffraction
AC C
angle of (002) lattice plane of AC-900-5:5 was the smallest, manifesting that proper mixing ratio (5:5) was also beneficial to the formation of turbostratic structure with irregularly oriented carbon sheets (Yi et al., 2006).
3.3 Pore-forming mechanism
3.3.1 TG-FTIR-GC/MS analysis
Thermogravimetric (TG) and differential thermogravimetric (DTG) analysis conducted in N2
ACCEPTED MANUSCRIPT atmosphere for WPT and the mixture of MgCl2/WPT (mixing ratio of 5:5) were exhibited in Fig. 3. According to Fig. 3(a), the pyrolysis process of WPT can be divided into two steps. The mass loss at the temperature from 300~450°C was the first stage. WPT decomposed and generated various
RI PT
polymers by radical polymerization reaction (Bertini and Zuev, 2006). A distinct peak at 370°C appeared on DTG curve due to the release of light components. Then these polymers were further decomposed at 450~500°C, followed by a peak at 485°C in DTG curve, which might be caused by the
SC
release of macromolecular aromatic compounds (Bertini and Zuev, 2006). Compared with WPT, the
M AN U
mixture of MgCl2/WPT showed a three-step pyrolysis process in Fig. 3(b). The initial mass loss of about 42% occurred at 100~300°C owing to partial decomposition of MgCl2 into Mg(OH)Cl through dehydration reaction (Fig. S3). After that, WPT began to decompose with a weight loss of 19% at the temperature range from 300 to 500°C. At around 480°C, a strong peak appeared on DTG curve
TE D
corresponding to the transformation of Mg(OH)Cl into MgO. In this stage, carbonized WPT gradually covered on MgO grains and inhibited the aggregation of MgO, thus promoting the formation of pore structures. Finally, the carbonization of decomposition product proceeded along with a slight mass loss
EP
(10%) at 500~650°C. Once the temperature reached 600°C, an obvious peak appeared on DTG curve
AC C
on account of the partially hydrated MgCl2 directly decomposing into MgO at around 570~620°C (Sugimoto et al., 2007). The conceivable pyrolysis pathway of MgCl2 in the mixture can be illustrated by (2~4):
100~300°C: MgCl · 6H O → MgOH Cl + 5H O + HCl
(2)
450~570°C: MgOH Cl → MgO + HCl
(3)
570~620°C: MgCl · 6H O → MgO + 5H O + 2HCl
(4)
The three-dimensional FTIR spectra of the gaseous products from WPT and mixture of MgCl2/WPT
ACCEPTED MANUSCRIPT were shown in Fig. 4. As depicted in Fig. 4(a), there were no gaseous products escaping from WPT before 300°C. While in the case of the mixture of MgCl2/WPT (Fig. 4(b)), weaker infrared absorption peaks attributed to O-H stretching was found at 3400 cm-1 and 1600 cm-1 owing to the decomposition
RI PT
of crystalline water in MgCl2·6H2O. With the increase of pyrolysis temperature, various infrared absorption peaks were found at the temperature range from 300 to 600°C, indicating that there were many gaseous products generated from WPT. After adding MgCl2, only a few gaseous products
SC
(3100~2850 cm-1: C-H, 2375~2250 cm-1:CO2) were detected, demonstrating that MgCl2 might change
M AN U
the decomposition pathway of WPT and inhibit the formation of volatile products to block the pores structures.
According to DTG analysis in Fig. 3, the maximum weight loss rate of WPT and MgCl2 was found at 370°C and 485°C, which means activating reaction occurred mainly in these periods. Thus the
TE D
corresponding FTIR diagrams at these temperatures were depicted in Fig. 5 and Fig. 6 to investigate the influence of MgCl2 and generated MgO on the pyrolysis pathway of WPT. At the temperature of 370°C, absorption peaks at 3668 cm-1, 3100~2850 cm-1, 2375~2250 cm-1, 1850~1600 cm-1, 1258 cm-1,
EP
1105 cm-1 and 600~900 cm-1 in the case of WPT (in Fig. 5(a)) were attributed to O-H stretching
AC C
vibration of H2O, C-H stretching vibration of benzene ring, characteristic bands of CO2, C=O stretching vibration, -C-O antisymmetric vibrations, C-O-C symmetric vibration and C-H out-of-plane bending, respectively (Liu et al., 2010; Moreno-Castilla et al., 1998; Sabio et al., 2004). As shown in Fig. 5(b), the release of organic volatiles (C-H, C=O and C-O-C) were markedly reduced after adding MgCl2, this should be ascribe to the catalytic degradation of alkaline earth metal cations (Mg2+) toward organic matter through the decarboxylic reaction (Yan et al., 2013). The probable chemical reaction may be described as Fig. 5(c). The decomposition of organic volatiles can effectively reduce the
ACCEPTED MANUSCRIPT formation of heavy tar which may block the pores, thus being conducive to the formation of open pores structure (Liu et al., 2013). In addition, as an activator, CO2 generated during pyrolysis could also react with disordered carbon and thereby further increased the porosity of activated carbon. As shown in Fig.
RI PT
6(a), when the pyrolysis temperature reached 485°C, C-H (3100~2850 cm-1), =CH2 (1426 cm-1) and -CH3 (1300 cm-1) of aromatic compounds were found in the curve of WPT, and accompanied with some week peaks corresponding to C-H bending vibration of saturated aliphatic hydrocarbons (1084
SC
cm-1) and characteristic bands of CO2 (742 cm-1) (Yan et al., 2013). After adding MgCl2, the
M AN U
characteristic peaks of aromatic were weakened or vanished, while the emission of CO2 increased significantly in Fig. 6(b). This might be related to the formation of MgO during pyrolysis at around 480°C, contributing to decreasing the formation of tar through inhibiting thermal chain lengthening reaction of radicals compounds (Simell et al., 1992). Furthermore, catalytical dehydrogenation of
TE D
macromolecular aromatic compounds on the surface of MgO can lead to the formation of polymeric carbon precursor or carbon compounds, which was beneficial to increase the yield of activated carbons. Most of these carbonaceous materials were coated on the surface of MgO to form carbon-encapsulated
EP
MgO accompanied by emission of CH4 and CO2, and the remaining would form carbon whiskers by
AC C
diffusion or precipitation reaction. The formation of carbon layer on MgO could prevent the growth of grain, so as to promote the formation of homogeneous pores. The proposed reaction pathway was described by Fig. 6(c).
GC/MS was employed to explore in more details the effects of MgCl2 on activation process of WPT. The chromatograms of gaseous products at 370°C and their identifications were shown in Fig. 7, Table S2 and Table S3. In the case of WPT, there were many peaks presented in the chromatographs attributing to aromatic compounds. Peaks at retention time of 6.24 min, 8.33 min and 11.51 min
ACCEPTED MANUSCRIPT corresponded to 1, 4-Dicyanobenzene, ethyl 4-cyanobenzoate and N-Arachidoyl-5-hydroxytryptamine, respectively. These macromolecules volatile matter not only inhibited the formation of pores, but also caused severe air pollution. It was remarkable that the chromatographs of MgCl2/WPT presented fewer
RI PT
and weaker peaks of volatiles compared to WPT, indicating that MgCl2 could effectively inhibit the production of tar. According to the gaseous product recorded at retention time 16.08 min corresponding to terephthalic acid, di (2-chloroethyl) ester, it could be assumed that MgCl2 might promote the
SC
cleavage of C-O in WPT through substitution reaction, thereby accelerating the pyrolysis speed of
M AN U
polyester. The possible reaction pathway may be described in Fig. 8(a). Firstly, polyester molecule (I) was decomposed into terephthalic acid, di (2-chloroethyl) ester (II) due to the cleavage of C-O. And then terephthalic acid, di (2-chloroethyl) ester could be further decomposed into terephthalic acid (III) and chlorethylidene (IV). Finally, some amounts of double bond (V) were formed by the
TE D
dehydrochlorination of chlorethylidene. In addition, some cyclization molecules like cinnoline (8.69 min) and 2(1H)-Quinolinone, 4-methyl- (11.34 min) were detected in chromatographs during pyrolysis. These cyclic carbon chain molecules were regarded as the precursors of polymeric carbon, indicating
EP
that MgCl2 can promote the cross-linking reaction of WPT to form carbonaceous materials (Pike et al.,
AC C
1997). The chain reaction was illustrated in Fig. 8(b). MgCl2 combined with Cl to form intermediate
products with carbonium ion (VI), due to its strong Lewis acidity. Then, the electrophilic addition reaction between the carbonium ion and double bond led to the crosslinking of the molecular chain to form long carbon chain. Furthermore, Lewis acid had catalytic action toward the dehydrogenation (like Dials-Alder cyclization reaction) of carbon chains, thus being favorable to the formation of carbon and inhibiting tar production (Stoeva et al., 1992). The above results can also be supported by elemental analysis and carbon yield of CS and AC-900-5:5. As shown in Table S4, the carbon content and carbon
ACCEPTED MANUSCRIPT yield of AC-900-5:5 were markedly higher than that of CS, whereas the hydrogen element of AC-900-5:5 was lower than that of CS, which further proved the dehydrogenation, cross-linking and carbon-forming effect of MgCl2.
RI PT
Overall, TG-FTIR-GC/MS analysis results revealed that MgCl2 possessed chemical activation effect toward WPT, and the specific activation mechanisms were proposed as follows: MgCl2 can inhibit the formation of tars through decarboxylic, dehydrogenation and catalytic reactions. Moreover, MgCl2 can
SC
also promote the cross-linking reaction of WPT to form more carbonaceous materials during pyrolysis
3.3.2 XRD and TEM analysis
M AN U
process, due to its Lewis acidity.
XRD and TEM analyses of the carbon synthesized at a mixture ratio and activation temperature of
TE D
5:5 and 900°C were employed to explore the templating effect of MgO generated from MgCl2. Fig. 9(a) was the XRD analysis of the activated carbon before pickling process. This sample exhibited obvious peaks at 37°, 43°, 62°, 75° and 79° corresponding to the (111), (200), (220), (311), and (222) plane
EP
interlayer reflection of MgO diffraction peak, respectively. The MgO crystallite size calculated from
AC C
Scherrer equation was around 40 nm. In Fig. 9(b), after pickling process, the peaks of MgO grain was vanished and two new diffraction peaks attributed to (100) and (002) lattice plane of amorphous carbon were found at about 24° and 43°. The above results can also be supported by SEM-EDS analyses of the samples before and after pickling (Fig. S4). Before pickling, few pores were found and a generous amount of Mg and O were detected on carbon surface. After pickling, no Mg was detected and abundant homogeneous pores structures appeared. In addition, TEM images of the samples before and after washing by HCl were shown in Fig. 9(c-d). It can be noticed that the MgO particles with uniform
ACCEPTED MANUSCRIPT size and good dispersibility were achieved as shown in Fig. 9(c), which proved the hypothesis that carbonaceous film coated on MgO particle could inhibit the agglomeration of grain during pyrolysis process. Furthermore, the size of MgO crystallites were mostly between around 20~50 nm, which in
RI PT
accordance with the conclusion from XRD results. After elimination of MgO (Fig. 9(d)), the pores with the similar size (20~30 nm) of MgO particles were formed in activated carbon. This conclusion also
templating agent to form porous structure during pyrolysis.
M AN U
4. Conclusion
SC
agreed well with the results of pore size distribution, which demonstrated that MgO acted as a
Highly mesoporous activated carbon was synthetized from WPT utilizing MgCl2 as activator and the precursor of MgO template. The highest surface area (1307 m2/g) and total pore volume (3.56 cm3/g)
TE D
was achieved at mixing ratio, pyrolysis temperature and time of 5:5, 900°C and 1.5 h, respectively. Meanwhile, more random stratification structures were found in AC-900-5:5, leading to the enhancement of sample surface reactivity. The pore-forming mechanism was confirmed as the
EP
synergistic effect of activation and templating. The specific effects of MgCl2 on the full-cycle pyrolysis
AC C
pathway of WPT were presented as follows: (1) MgCl2 inhibited the formation of macromolecule compounds (tars) through decarboxylic and dehydrogenation reactions, thus being favourable to the formation of open pores structure. (2) MgCl2 has the catalysis ability of cross-linking reaction of WPT due to its Lewis acidity, which is beneficial to the formation of carbonaceous materials during pyrolysis process. (3) As a templating agent, MgO particles formed by pyrolysis of MgCl2 were capable of forming porous wall on activated carbons.
ACCEPTED MANUSCRIPT Acknowledgements
This research was funded by National Natural Science Foundation of China (21707090), Chinese
RI PT
Postdoctoral Science Foundation (2017M611590) and Shanghai Natural Science Foundation (14ZR1428900).
SC
References
Bao, L., Li, X., 2012. Towards textile energy storage from cotton T-shirts. Adv Mater 24, 3246-3252.
polyesters:
M AN U
Bertini, F., Zuev, V.V., 2006. Investigation of the thermal degradation of fully aromatic regular Poly(oxy-1,4-phenyleneoxy-fumaroyl-bis-4-oxybenzoate).
Stability 91, 3214-3220.
Polymer
Degradation
&
TE D
Esfandiari, A., Kaghazchi, T., Soleimani, M., 2012. Preparation and evaluation of activated carbons obtained by physical activation of polyethyleneterephthalate (PET) wastes. Journal of the Taiwan Institute of Chemical Engineers 43, 631-637.
EP
Falco, C., Baccile, N., Titirici, M.M., 2011. Morphological and structural differences between glucose,
AC C
cellulose and lignocellulosic biomass derived hydrothermal carbons. Green Chemistry 13, 3273-3281. Giri, A.K., Patel, R., Mandal, S., 2012. Removal of Cr(VI) from aqueous solution by Eichhornia crassipes root biomass-derived activated carbon. Chemical Engineering Journal 185, 71-81. Gong, Y., Wang, H., Wei, Z., Xie, L., Wang, Y., 2014. An Efficient Way To Introduce Hierarchical Structure into Biomass-Based Hydrothermal Carbonaceous Materials. Acs Sustainable Chemistry & Engineering 2, 2435-2441. He, X., Li, R., Qiu, J., Xie, K., Ling, P., Yu, M., Zhang, X., Zheng, M., 2012. Synthesis of mesoporous carbons for supercapacitors from coal tar pitch by coupling microwave-assisted KOH activation with a
ACCEPTED MANUSCRIPT MgO template. Carbon 50, 4911-4921. Huang, Q., Lu, G., Wang, J., Yu, J., 2011. Thermal decomposition mechanisms of MgCl2•6H2O and MgCl2•H2O. Journal of Analytical and Applied Pyrolysis 91, 159-164.
carbon from a coal tar pitch. Carbon 45, 1121-1124.
RI PT
Inagaki, M., Kato, M., Morishita, T., Morita, K., Mizuuchi, K., 2007. Direct preparation of mesoporous
carbons: Synthesis and applications. Carbon 107, 448-473.
SC
Inagaki, M., Toyoda, M., Soneda, Y., Tsujimura, S., Morishita, T., 2016. Templated mesoporous
M AN U
Libbrecht, W., An, V., Thybaut, J.W., Voort, P.V.D., Clercq, J.D., 2017. Soft templated mesoporous carbons: Tuning the porosity for the adsorption of large organic pollutants. Carbon 116, 528-546. Liu, Q S., Zheng, T., Wang, P., Guo, L., 2010. Preparation and characterization of activated carbon from bamboo by microwave-induced phosphoric acid activation. Industrial Crops and Products 31,
TE D
233-238.
Liu, W.J., Jiang, H., Tian, K., Ding, Y.W., Yu, H.Q., 2013. Mesoporous carbon stabilized MgO nanoparticles synthesized by pyrolysis of MgCl2 preloaded waste biomass for highly efficient CO2
EP
capture. Environ Sci Technol 47, 9397-9403.
AC C
Ma, J., Zhou, L., Dan, W., Zhang, H., Shao, Y., Bao, C., Jing, L., 2015. Novel magnetic porous carbon spheres derived from chelating resin as a heterogeneous Fenton catalyst for the removal of methylene blue from aqueous solution. Journal of Colloid & Interface Science 446, 298-306. Moreno-Castilla, C., Carrasco-Marin, F., Maldonado-Hodar, F., Rivera-Utrilla, J., 1998. Effects of non-oxidant and oxidant acid treatments on the surface properties of an activated carbon with very low ash content. Carbon 36, 145-151. Moreno-Castilla, C., Lopez-Ramon, M., Carrasco-Marın, F., 2000. Changes in surface chemistry of
ACCEPTED MANUSCRIPT activated carbons by wet oxidation. Carbon 38, 1995-2001. Morishita, T., Ishihara, K., Kato, M., Inagaki, M., 2007. Preparation of a carbon with a 2 nm pore size and of a carbon with a bi-modal pore size distribution. Carbon 45, 209-211.
RI PT
Morishita, T., Tsumura, T., Toyoda, M., Przepiórski, J., Morawski, A.W., Konno, H., Inagaki, M., 2010. A review of the control of pore structure in MgO-templated nanoporous carbons. Carbon 48, 2690-2707.
SC
Munoz, M., Kolb, V., Lamolda, A., Pedro, Z.M.D., Modrow, A., Etzold, B.J.M., Rodriguez, J.J., Casas,
M AN U
J.A., 2017. Polymer-based spherical activated carbon as catalytic support for hydrodechlorination reactions. Applied Catalysis B Environmental.
Nahil, M.A., Williams, P.T., 2010. Activated carbons from acrylic textile waste. Journal of Analytical and Applied Pyrolysis 89, 51-59.
supervision 7, 3-8.
TE D
NDRC, 2014. Annual report on comprehensive utilization of resources in China. Equipment
Negulescu, I.I., Kwon, H., Collier, B.J., Collier, J.R., Pendse, A., 1998. Recycling cotton from
EP
cotton/polyester fabrics. Textile Chemist & Colorist 30, 31-35.
AC C
Nishihara, H., Kyotani, T., 2012. Templated nanocarbons for energy storage. Advanced Materials 24, 4473-4498.
Nzihou, A., 2010. Waste and Biomass Valorization. Waste & Biomass Valorization 1, 1-2. Pike, R.D., Jr, W.H.S., Jeng, J.P., Bryant, W.S., Kourtesis, P., Adams, C.W., Bunge, S.D., Kang, Y.M., Kim, A.S., Kim, J.H., 1997. Low-Valent Metals as Reductive Cross-Linking Agents: A New Strategy for Smoke Suppression of Poly(vinyl chloride). Macromolecules 30, 6957-6965. Prauchner, M.J., Sapag, K., Rodríguez-Reinoso, F., 2016. Tailoring biomass-based activated carbon for
ACCEPTED MANUSCRIPT CH4 storage by combining chemical activation with H3PO4 or ZnCl2 and physical activation with CO2. Carbon 110, 138-147. Przepiórski, J., Karolczyk, J., Takeda, K., Tsumura, T., Toyoda, M., Morawski, A.W., 2009. Porous
RI PT
carbon obtained by carbonization of PET mixed with basic magnesium carbonate: pore structure and pore creation mechanism. Industrial & Engineering Chemistry Research 48, 7110-7116.
Rodrigues, C.S.D., Soares, O.S.G.P., Pinho, M.T., Pereira, M.F.R., Madeira, L.M., 2017. p
SC
-Nitrophenol Degradation by Heterogeneous Fenton’s Oxidation Over Activated Carbon-Based
M AN U
Catalysts. Applied Catalysis B Environmental 219.
Rufford, T.E., Hulicova-Jurcakova, D., Zhu, Z., Lu, G.Q., 2011. A comparative study of chemical treatment
by
FeCl3,
MgCl2,
and
ZnCl2
on
microstructure,
surface
chemistry,
and
double-layercapacitance of carbons from waste biomass. Journal of Materials Research 25, 1451-1459.
TE D
Sabio, E., González, E., González, J., González-Garcıa, C., Ramiro, A., Ganan, J., 2004. Thermal regeneration of activated carbon saturated with p-nitrophenol. Carbon 42, 2285-2293. Sahu, J.N., Acharya, J., Meikap, B.C., 2010. Optimization of production conditions for activated
EP
carbons from Tamarind wood by zinc chloride using response surface methodology. Bioresource
AC C
technology 101, 1974-1982.
Simell, P.A., Leppälahti, J.K., Bredenberg, B.S., 1992. Catalytic purification of tarry fuel gas with carbonate rocks and ferrous materials. Fuel 71, 211-218. Sing, K.S.W., 1985. Reporting Physisorption Data for Gas/Solid Systems-With Special Reference to the Determination of Surface Area and Porosity. Pure & Applied Chemistry 57, 603-619. Stoeva, S., Karaivanova, M., Benev, D., 1992. Poly(vinyl chloride) composition. II. Study of the flammability and smoke-evolution of unplasticized poly(vinyl chloride) and fire-retardant additives.
ACCEPTED MANUSCRIPT Journal of Applied Polymer Science 46, 119-127. Sugimoto, K., Dinnebier, R.E., Hanson, J.C., 2007. Structures of three dehydration products of bischofite from in situ synchrotron powder diffraction data (MgCl2.nH2O; n = 1, 2, 4). Acta
RI PT
Crystallographica 63, 235-242. Tian, X., Ma, H., Li, Z., Yan, S., Ma, L., Yu, F., Wang, G., Guo, X., Ma, Y., Wong, C., 2017. Flute type micropores activated carbon from cotton stalk for high performance supercapacitors. Journal of Power
SC
Sources 359.
blends. Cellulose 13, 611-618.
M AN U
Vasconcelos, A., Cavaco-Paulo, A., 2006. Enzymatic removal of cellulose from cotton/polyester fabric
Xu, Z., Zhang, D., Yuan, Z., Chen, W., Zhang, T., Tian, D., Deng, H., 2017. Physicochemical and adsorptive characteristics of activated carbons from waste polyester textiles utilizing MgO template
TE D
method. Environmental Science & Pollution Research, 1-11.
Yahya, M.A., Al-Qodah, Z., Ngah, C.W.Z., 2015. Agricultural bio-waste materials as potential sustainable precursors used for activated carbon production: A review. Renewable and Sustainable
EP
Energy Reviews 46, 218-235.
AC C
Yan, J., Jiang, X., Han, X., Liu, J., 2013. A TG-FTIR investigation to the catalytic effect of mineral matrix in oil shale on the pyrolysis and combustion of kerogen. Fuel 104, 307-317. Yang, Z., Jing, R., Zhang, Z., Chen, X., Guan, G., Qiu, L., Ye, Z., Peng, H., 2015. Recent Advancement of Nanostructured Carbon for Energy Applications. Chemical Reviews 115, 5159. Yao, S., Zhang, J., Shen, D., Xiao, R., Gu, S., Zhao, M., Liang, J., 2016. Removal of Pb(II) from water by the activated carbon modified by nitric acid under microwave heating. Journal of colloid and interface science 463, 118-127.
ACCEPTED MANUSCRIPT Yi, Z.J., Yong, J.K., Chao, G., Yan, Q.Z., Huczko, A., Endo, M., Kroto, H.W., 2006. High temperature annealing effects on carbon spheres and their applications as anode materials in Li-ion secondary battery. Carbon 44, 724-729.
RI PT
Zhang, B., Zeng, X., Xu, P., Chen, J., Xu, Y., Luo, G., Xu, M., Yao, H., 2016. Using the Novel Method of Nonthermal Plasma To Add Cl Active Sites on Activated Carbon for Removal of Mercury from Flue Gas. Environmental Science & Technology 50.
SC
Zhang, M., Gao, B., Yao, Y., Xue, Y., Inyang, M., 2012. Synthesis of porous MgO-biochar
M AN U
nanocomposites for removal of phosphate and nitrate from aqueous solutions. Chemical Engineering Journal 210, 26-32.
Zheng, J., Zhao, Q., Ye, Z., 2014. Preparation and characterization of activated carbon fiber (ACF) from cotton woven waste. Applied Surface Science 299, 86-91.
TE D
Zhou, L., Shao, Y., Liu, J., Ye, Z., Zhang, H., Ma, J., Jia, Y., Gao, W., Li, Y., 2014. Preparation and characterization of magnetic porous carbon microspheres for removal of methylene blue by a heterogeneous Fenton reaction. Acs Appl Mater Interfaces 6, 7275-7285.
EP
Zhu, H.Y., Fu, Y.Q., Jiang, R., Jiang, J.H., Xiao, L., Zeng, G.M., Zhao, S.L., Wang, Y., 2011.
AC C
Adsorption removal of congo red onto magnetic cellulose/Fe3O4/activated carbon composite: Equilibrium, kinetic and thermodynamic studies. Chemical Engineering Journal 173, 494-502.
ACCEPTED MANUSCRIPT 3.5
AC-600-3:7 AC-600-5:5 AC-600-7:3 AC-750-3:7 AC-750-5:5 AC-750-7:3 AC-900-3:7 AC-900-5:5 AC-900-7:3
1600 1200
AC-600-3:7 AC-600-5:5 AC-600-7:3 AC-750-3:7 AC-750-5:5 AC-750-7:3 AC-900-3:7 AC-900-5:5 AC-900-7:3
(b)
3.0
3
(a)
dV(logd)/cm /g
800 400
2.5 2.0 1.5 1.0 0.5
0 0.0
0.2
0.4
0.6
0.8
0.0 0.5
1.0
1
2
RI PT
2000
3
dV(logd)/cm /g
2400
4
8
16
32
64
Pore Width / nm
P/P0
Fig. 1. N2 adsorption/desorption isotherms (a) and corresponding DFT pore size distributions (b) of activated
SC
carbons.
Table 1 Textual properties of activated carbons. SBET (m2/g)
Smicro(m2/g)
AC-600-3:7
483
24
AC-600-5:5
543
31
AC-600-7:3
489
34
AC-750-3:7
773
188
AC-750-5:5
808
113
AC-750-7:3
633
204
AC-900-3:7
1229
242
AC-900-5:5
1307
73
AC-900-7:3
1014
30
40
Vext(cm3/g)
0.01
1.58
513
1.86
0.01
1.85
455
1.58
0.01
1.57
585
2.20
0.09
2.11
696
2.53
0.07
2.46
429
1.53
0.09
1.44
987
3.14
0.12
3.02
1244
3.56
0.06
3.50
2.60
0.14
2.46
TE D
691
(a)
AC-900-5:5 AC-750-5:5
(002)
Intensity(arb.units.)
EP
AC C 20
Vmicro(cm3/g)
1.59
(100)
10
Vtotal(cm3/g)
460
323
(002)
Intensity(arb.units.)
Sext (m2/g)
M AN U
Sample
(b) (100) AC-900-3:7
AC-900-5:5
AC-900-7:3
AC-600-5:5 50
2θ(°)
60
70
80
10
20
30
40
50
60
2θ(°)
Fig. 2. XRD analysis of samples prepared under different temperatures (a) and mixing ratio (b).
70
80
-2 -4
60 -6
Peak X=485℃
40
-8
(a)
20
-10
Peak X=370℃
0
100
200
300
400
500
600
700
800
-12 900
0
80
-1 Peak X=600℃
60 40
-2
(b)
Peak X=480℃
20 100 200
Temperature (°C)
-3
300
400
500
600
Temperature (°C)
700
800
-4 900
Fig. 3. TG and DTG analysis for WPT (a) and the mixture of MgCl2/WPT (b).
(b)
M AN U
SC
(a)
TE D
Fig. 4. 3D-FTIR spectra of gaseous product from WPT (a) and mixture of MgCl2/WPT (b).
370°C
O-H
C-O-C C-O
CO2 C≡N
370°C
(b) Absorbance (%)
C=O
EP
Absorbance (%)
(a)
CO2
C-H
C-H
AC C
C-H
4000
3500
3000
2500
2000
1500 -1
1000
500
4000
3500
3000
Wavenumber (cm )
C=O 2500
2000
C-H C-O CO2
1500
1000
500
-1
Wavenumber (cm )
(c)
Fig. 5. FTIR diagrams of gaseous products from WPT (a) and the mixture of MgCl2/WPT (b) and the possible pyrolysis reaction pathway at 370°C.
Derivative Weight (%/min)
80
100
RI PT
0
Weight loss/mass (%)
100
Derivative Weight (%/min)
Weight loss / mass (%)
ACCEPTED MANUSCRIPT
ACCEPTED MANUSCRIPT 485°C
485°C
(b)
C-H
Absorbance (%)
Absorbance (%)
(a)
C-H
CO2
=CH2 -CH3 3500
3000
2500
2000
1500
1000
500
4000
-1
3500
3000
Wavenumber (cm )
2000
1500
-1
1000
500
Wavenumber (cm )
CmHnOk
CO2, CH4 C*
(CmHnOk)*
Cencapsulating
Diffusion/precipitation
MgO
SC
(c)
2500
RI PT
4000
CO2
Cwhisker
M AN U
Fig. 6. FTIR diagrams of gaseous products from WPT (a) and the mixture of MgCl2/WPT (b) and the possible
pyrolysis reaction pathway at 485°C.
EP
TE D
Abandance
WPT
AC C
Abandance
WPT+MgCl2
3
6
9
12
15
18
Time (min) Fig. 7. Gas chromatographs of WPT and the mixture of MgCl2/WPT at 370°C with the characteristic gaseous
products at different retention times.
ACCEPTED MANUSCRIPT
(IV) (III) (V)
M AN U
(a)
SC
(II)
RI PT
(I)
TE D
(VI)
(b)
AC C
EP
Fig. 8. Scheme of the decomposition (a) and crosslinking (b) process of WPT.
(b)
★MgO ★
★
unwashed ★
★
(002)
(100)
washed
★
10
20
30
40
50
60
70
80
10
20
40
50
60
70
80
2θ (°)
2θ (°)
(d)
M AN U
SC
(c)
30
RI PT
(a)
Intensity (arb.units)
Intensity (arb.units)
ACCEPTED MANUSCRIPT
AC C
EP
TE D
Fig. 9. XRD patterns and TEM images of samples before and after pickling. Before: (a) and (c). After: (b) and (d).
