Effects of Cellulose, Hemicellulose, and Lignin on the Structure and

Subscriber access provided by UCL Library Services

Article

Effects of Cellulose, Hemicellulose, and Lignin on the Structure and Morphology of Porous Carbons Jiang Deng, Tianyi Xiong, Haiyan Wang, Anmin Zheng, and Yong Wang ACS Sustainable Chem. Eng., Just Accepted Manuscript • DOI: 10.1021/ acssuschemeng.6b00388 • Publication Date (Web): 24 May 2016 Downloaded from http://pubs.acs.org on May 29, 2016

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a free service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are accessible to all readers and citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

ACS Sustainable Chemistry & Engineering is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 23

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

ACS Sustainable Chemistry & Engineering

Effects of Cellulose, Hemicellulose, and Lignin on the Structure and Morphology of Porous Carbons Jiang Deng†, Tianyi Xiong†, Haiyan Wang†, Anmin Zheng‡, and Yong Wang*† †Advanced Materials and Catalysis Group, Center for Chemistry of High-performance and Novel Materials, Department of Chemistry, Zhejiang University, Hangzhou, 310028, P. R. China *Corresponding Author: Yong Wang, [email protected] ‡State Key Laboratory of Magnetic Resonance and Atomic and Molecular Physics, National Center for Magnetic Resonance in Wuhan, Wuhan Institute of Physics and Mathematics, Chinese Academy of Sciences, Wuhan 430071, China

KEYWORDS: Cellulose; Lignin; Hemicellulose; Porous carbon, Supercapacitor

ABSTRACT: Porous carbon stemmed from biomass have drawn increasing interest because of their sustainable properties. Cellulose, hemicellulose and lignin are the three basic components of crude biomass, and were investigated to reveal their influence on the derived carbonaceous materials. Huge amount of oxygen-containing functional groups in cellulose and hemicellulose tend to be eliminated as H2O, CO2, and CO and give micropores during pyrolysis. Whereas, lignin contains plentiful aromatic units which are chemical inert, and thus produce nonporous carbon materials. When the KHCO3 was introduced during the pyrolysis process, the plentiful

ACS Paragon Plus Environment

1


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 2 of 23

hydroxyl in cellulose and hemicellulose underwent dehydration condensation among different parent polymers, which are responsible for the formation of macroporous structure. By contrast, The β-O-4 bands in lignin experience homolysis and give rise to benzene-containing units, which finally result in carbon nanosheets. Furthermore, we demonstrated the mixture of cellulose, hemicellulose, and lignin can display a three-dimensional porous structure (containing macropores, mesopores and micropores) when less than 50% of lignin contains.

INTRODUCTION Carbonaceous materials, benefiting from their adjustable microstructure, large specific surface area, and easy processability, are widely used in technologically important applications, such as heterogeneous catalyst supports,1, 2 water or gas purification filters,3, 4

and electrodes materials for energy storage and conversion.5-9 Generally, carbonaceous

materials can be fabricated from lots of carbon-rich precursors essentially through thermal treatment (direct pyrolysis or hydrothermal carbonization).10, 11 There has been growing interest in the conversion of biomass to carbonaceous materials recently, since biomass is a carbon-neutral resource that derived from photosynthesis making use of CO2 and H2O.12-14 The performance of carbonaceous materials in specific applications highly rely on their size-/surface-dependent (e.g., morphological, electrical, and mechanical) properties.15 Hence, the controlling of porous structure as well as functional surface is extremely important. The recently developed hydrothermal carbonization (HTC) usually cooperated with templating or additives-assisted method is a powerful tool to control the size-/surface-dependent

properties

of

carbonaceous

materials.10,

16

Nanocasting

approaches typically combine the hard-templates such as SBA-15,17 SiO2 spheres,18 AAO membrane19 etc. with carbon-rich molecules, and subsequently remove the templates after


2

Page 3 of 23

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


carbonization. However, the removal of templates would consume the hazardous reagents which result in the environmental pollution besides the fussy processes.20 Compared with nanocasting, soft-templating based on the micelle formed by surfactant that can be removed through pyrolysis, is easier to handle and more sustainable to some extent.21 However, the high cost of surfactants and weak self-assembly between biomassderivatives and micelle hinder their industrial feasibility.22 More importantly, these methods particularly designed for water-soluble biomass derivatives are incapable for accurate control of porous structure towards polysaccharides, such as cellulose and crude biomass which is abundant on the earth. Although, ionothermal and molten-salt carbonization are explored for effective conversion of biomass to carbonaceous materials, their high price and special equipment requirement hinder them from wider use.23,

24

Hence, it remains great challenge to fabricate functional carbonaceous materials from polysaccharides and particular crude biomass. The group of Clark has pioneered a work of making porous carbonaceous materials from starch, which is well known as starbon®.25 Three steps including gelatinization, solution exchanging, and acid-assistant pyrolysis are needed among the fabrication process of starbon®.26 Although other biomass such as alginic acid and pectin can also serve as the raw materials for starbon® materials, the multi-steps processes and lack of micropores still restrict their wide applications. Hence, it is highly desired to develop a simple approach to prepare porous carbonaceous materials with upgraded pore structure, which leads to advanced applications and possibilities.15 In this respect, the activator-assisted pyrolysis strategy (leavening method) recently developed by our group was a good choice.27 The leavening method was implemented by mixing carbon


3


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 4 of 23

resources with KHCO3 and then undergoing elevated temperature treatment, which generated hierarchical porous carbonaceous materials (HPCs). (Containing pores at different scales, from micropores to mesopores, up to macropores) This method is applicative for many carbon-rich resources, varying from monosaccharide (glucose, xylose) to crude biomass such as bamboo and straw. However, when lignin the basic component of crude biomass was served as the carbon precursor, the as-obtained products show dissimilar morphologies as HPCs. Cellulose, hemicellulose, and lignin are the three basic components of crude biomass, whose intrinsic structure are different from each other. It is vital to throw light on the pyrolysis mechanism of the basic units of biomass. In this paper, we focused on disclosing the influence of cellulose, hemicellulose, and lignin on the porous structure and morphologies of the porous carbons. Also, the ternary mixtures of cellulose, hemicellulose, and lignin were implemented to uncover the effect of different proportions of each component on the pyrolytic carbon. EXPERIMENTAL SECTION Materials: α-cellulose (Aladdin), KHCO3 (Sinopharm Chemical Reagent Co., Ltd.), Lignin (TCI Co., Ltd. were used as received. Xylan from beechwood purchased from Sigma-Aldrich was used as the model polymer of hemicellulose. Water used throughout all experiments was purified through a Millipore system. Sample Preparation. Synthesis of leaven method derived products (Cx-LE-T, x represents the first three letters of the name of raw materials, LE means that the asobtained products derived from leaven method, and T stands for the pyrolysis temperature). firstly, 2 g cellulose mixed with 8 g potassium bicarbonate. Then, the mixture undergone the thermal treatment with Muffle furnace at programmed temperature in N2 flow (400 mL/min). The temperature program was shown as follow: the


4

Page 5 of 23

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


temperature rose from ambient temperature to desired temperature with heat rate of 15 o

C/min and remained for another 1 hour. Particularly, when the calcining temperature is

400 oC, the thermal treatment time was prolonged to 3 hours to make sure complete carbonization of carbon resources. The final products was acquired after thorough rinse with DI water (deionized water) and followed by drying overnight in 70 oC oven. Directly pyrolysis products (Cx-T, x represents the first three letters of the carbon resource, T stands for the pyrolysis temperature). firstly, carbon precursor was calcined in a Muffle furnace at the same programmed temperature as Cx-LE-T’s. Then the black solid was ground into black powder. Thermogravimetric-mass spectrometry (TG-MS). All experiments were performed using METTLER TOLEDO TGA/DSC 1100SF and ThermoStar gas mass spectrometry. 5 mg sample was put into alumina crucible and then was put into the automatic sampler. The temperature programming was the same as the calcination procedure of the corresponding products. Since the mass of nitrogen is the same as carbon monoxide, high purity argon was used as the protective gas and also as the carrier gas instead. The gas speed was set as 20 ml/min in order to keep high concentrate of the pyrolysis products making sure a high sensitivity of MS. Electrochemical characterization. All the samples were tested on a two-electrode system for determining their capacitive performance. Each carbon sample was mixed with carbon black and polyvinylidene fluoride (PVDF) with a weight ratio of 8:1:1 and rolled into slices. Pieces of 1.4 cm in diameter were stamped. The mass loading for each electrode is about 1.6 mg/cm2.The electrode plates were then dried in a vacuum at 40 oC for 24 h. Two electrode plates with similar mass loads were assembled in a two-electrode


5


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 6 of 23

system with 1 M EmimBF4/AN (1-Ethyl-3-methylimidazolium tetrafluoroborate was dissolved into acetonitrile) sealed in the 2032 button cell. The cyclic voltammetry (CV), galvanostatic charge-discharge (GCD), and electrochemical impedance spectrum (EIS) were measured on a Gamry Reference 600 electrochemical workstation. The voltage window for the organic electrolyte was set to be 0 - 2 V. The scan rate was in a range 20 200 mV/s. GCD measurement was conducted under a current density ranging from 0.1 to 1 A g-1. EIS were collected with frequencies ranging from 100 kHz to 10 mHz with an AC amplitude of 5 mV. The specific capacitance of the single electrode is calculated as Cs = I∆t/Um (F g-1) where I is the current, ∆t is the discharge time, U is the potential range and m is the total mass of the porous carbon materials on two electrode. General Characterization. SEM images were obtained on a Hitachi SU-8010. TEM studies were performed on a Hitachi HT-7700. The diffraction data were collected at room temperature with 2θ scan range between 10° and 60° using a wide-angle X-ray diffraction (Model D/tex-Ultima TV, 1.6 kV, Rig-aku, Japan) equipped with Cu Ka radiation (1.54 Å). The N2 adsorption–desorption isothermal analysis were determined by Micromeritics ASAP 2020 HD88, Brunauer–Emmett–Teller (BET) equation was used to calculate the surface areas and pore volume and samples were degassed at 200 oC for 8 h until the residual pressure was less than 10-4 Pa. All

13

C NMR experiments were carried

out on a Varian Infinityplus-300 spectrometer with the use of a 4 mm double-resonance MAS probe at a spinning rate of 10 kHz. The Larmor resonance frequencies for 1H and 13

C were 299.78 and 75.38 MHz, respectively.

13

C MAS NMR spectra with high power

proton decoupling were recorded using a π/2 pulse length of 4.1 us and a recycle delay of 10 s. The chemical shift of 13C was externally referenced to adamantane.


6

Page 7 of 23

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


RESULTS AND DISCUSSION Cellulose, hemicellulose, and lignin are the three main components of biomass. Alkaline lignin was chosen as the representative of lignin and xylan derived from beechwood was regarded as the substitute of hemicellulose. Alpha-cellulose, which is composed of a linear chain of different number of β (1→4) linked D-glucose units as see from the Scheme S1, was chosen as the representative of cellulose.28 As presented in Scheme S1, cellulose is a polyhydroxy polymer containing lots of adjacent hydroxyls, while the basic monomeric units of lignin are p-hydroxyphenyl, guaiacyl, and syringyl.29-31 Moreover, hemicellulose contains branched structure consisting of both pentose and hexose. The polymerized degree of hemicellulose is 50 ~ 200 which is lower than that of cellulose.32 It is obviously that both cellulose and hemicellulose contain plenty of hydroxyl and lignin is characterized as polyacromatic units.


7


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 8 of 23

Figure 1. SEM images of (a) Ccel-LE-400, (b) Chem-LE-400, (c) Clig-LE-400. (d) Ccel-LE-900, and (e) Clig-LE-900; TEM images of (f and e) Ccel-LE-900 and (h) Clig-LE-900 These three components, serving as the raw materials, were conducted according to the leavening process. As reported in our previous work, KHCO3 decomposed firstly and give rise to macropores in derived products, while the activators such as K2CO3, H2O, and CO2 would etch the carbon and produce mesopores and micropores. The mixture of precursor and KHCO3 was under the elevated-temperature treatment for an hour with a heating rate of 15 oC/min. The final products were obtained after the removal of the by-products and were named as Cx-LE-T, where x stands for the first three letters of the precursors and T represents the calcination temperature. The yields of Ccel-LE-900 and Clig-LE-900 are ~ 9% and 39%. However, hemicellulose decomposed easily so there were almost no product for Chem-LE-900, as the TGA results presented. When the calcination temperature was set as 400 oC, the yield of Ccel-LE-400, Chem-LE400, and Clig-LE-400 were 21%, 4.6%, and 52%, respectively. Ccel-LE-400 (Figure 1a) and ChemLE-400

(Figure 1b) display the similar morphologies and possess plentiful correlative

macropores with pore width of ~ 700 nm as characterized by scanning electron microscope (SEM). However, Clig-LE-400 (Figure 1c) give a totally bulk shape with smooth surface. The morphologic evolutions of the sample were presented at Figure S1. The original shape of cellulose is rod like while hemicellulose and lignin exhibit globular shape. The direct pyrolysis at 400 oC gives rise to morphologies changes for both cellulose and hemicellulose. On the contrary, the morphologies of lignin almost didn’t change even after three hours’ calcination at 400 oC. As for Ccel-LE-900, the macroporous structures of Ccel-LE-900 are both observed at SEM image and TEM image as is described in our former work. When enlarging the TEM image, the mesopores embedded at the macropore walls are also clearly seen (Figure 1f and e). Compared with Ccel-LE-


8

Page 9 of 23

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


900, Clig-LE-900 (Figure 1e) shows nanosheets with lots of wrinkles which can be seen from the TEM image (Figure 1h). The β-O-4 bands in lignin experience homolysis and the as-obtained aliphatic units are easily etched by activator while leaving behind intact nanosheets. However, these ultrathin carbon nanosheets tend to aggregate and stack together.33, 34 The SEM images of Clig-LE-900 (Figure S2) in absence of ultrasonic-assisted dispersion gave a monolithic morphology. The digital pictures (Figure S3) of Ccel-LE-900 display a distinctly larger volume than that of Clig-LE-900 with the same mass, which is a direct evidence for the rich porous structure of Ccel-LE-900. Within the assistant of KHCO3, it seems that cellulose and hemicellulose are favourable for the formation of three-dimensional and interconnected porous structure, while lignin trends to transform to nanosheet instead. The pore structures of Ccel-LE-900 and Clig-LE-900 were further characterized by nitrogen sorption measurements, as is shown in Figure S4a. Both Ccel-LE-900 and Clig-LE-900 give a type I adsorption–desorption isotherm which micropore filling occurs at low pressure. A gradual increase in adsorption continues up to P/P0 of 1 indicates an interconnected pore system exhibiting constrictions. Figure S4b shows the pore size distribution (PSD) from nitrogen adsorption, which reveals that Ccel-LE-900 contain higher mesopore volume than that of Clig-LE900. The pore structures of these two samples are unraveled by cumulative surface area vs. pore width (Figure S5). These results demonstrate that micropores (< 1.6 nm) in Clig-LE-900 contribute more to the surface area than that of Ccel-LE-900, while Ccel-LE-900 contains larger micropores and mesopores. The same conclusions can be made based on the data presented in Table S1. The VTotal and VMicro of Ccel-LE-900 is 0.93 and 0.74 cm3/g, giving a VMicro/VTotal of 80% which is lower than that of Clig-LE-900 (87%). It seems that the pyrolysis of lignin with the assistance of KHCO3 have a tendency to form smaller micropores. Besides the differences in the


9


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 10 of 23

pore structure, the distinctions of texture between Ccel-LE-900 and Clig-LE-900 were characterized by X-ray diffraction (XRD) (Figure S4c). The XRD patterns of both Ccel-LE-900 and Clig-LE-900 show broadened humps, demonstrating a glass-like structure. The diffraction peaks at 2θ values

Figure 2. TG-MS results of (a) cellulose, (b) hemicellulose, and (c) lignin under the atmosphere of helium with thermal rate of 15 oC/min. of 24o and 44° are assigned to the 002 and 100 reflection of graphite. Note that the 002 peak of Clig-LE-900 is narrower than that of Ccel-LE-900, revealing a higher graphitization degree.35 It suggested that KHCO3 tend to destroy the graphitic structure of cellulose derived carbon but contribute to the higher graphitic degree of Clig-LE-900. According to the above results, it is obviously that the raw materials make great effect to the properties of its porous carbon. Hence, thermogravimetric-mass spectrometry (TG-MS) was firstly conducted under the atmosphere of helium to test the mechanism of the direct pyrolysis of cellulose, hemicellulose, and lignin. In Figure 2a, the remarkable weight loss between 300 - 370 o

C correspond to the decomposition processes of the cellulose releasing CO2 (m/z = 44), CO

(m/z = 28), CH4 (m/z = 16), and H2O (m/z = 18). Also, the decomposition of cellulose under inert gas would result in carbonaceous materials. (rough 20% retention at 400 oC) The asprepared carbonaceous materials would undergo aromatization with the further elevated temperature. The summits of CO2, CO, and H2 at ~ 770 oC are ascribed to the self-activation


10

Page 11 of 23

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


process.36 Compared with cellulose, the initially decomposed temperature of hemicellulose (Figure 2b) is lower because of its low polymerized degree. In contrast with the sharp weigh loss of cellulose at ~ 350 oC, the decomposition of hemicellulose is to some extent tardy and last from 200 oC to 580 oC. The MS results show that hemicellulose is favourable to releasing H2, CO, and CO2 at low temperature (< 400 oC). According to the curve of lignin (Figure 2c), it can be divided into three stages, whose first stage was removal of physically adsorbed water, and the following two stages were ascribed to the decomposition of lignin. Compared with cellulose and hemicellulose, the temperature of self-activation, releasing CO2, CO, CH4, and H2 at the same time, moved to a higher temperature of ~ 830 oC and there was not a distinct peak of H2 anymore which may be attributed to the stable polyaromatic structure of lignin. The releasing of small molecules during the decomposition of biomass is essential for the formation of micropores in their direct pyrolysis products. To verity this, cellulose, hemicellulose, and lignin were also conducted at directly pyrolysis process and gave products donated as Ccel-400, Chem-400, and Clig-400, (400 represent the final isothermal temperature) respectively. The N2 sorption analyses give a BET specific surface (Table S1) are of 0.59 and 11 m2/g for Ccel-400 and Chem-400. However, Clig-400 displays a nonporous structure. It is clearly that the intensity of υC-O-C, υC-H and υ-OH decrease in all three component according to the infrared spectroscopy (IR) results (Figure S6) due to the dehydration and condensation. However, the aromatic skeletal vibration (~ 1496 cm-1) and asymmetric C-H bending of methoxyl group (~ 1452 cm-1) were still observed in Clig-400 because of the robust stability of aromatic units. When the calcination temperature was set at 900 oC, which is higher than the selfactivation temperature of cellulose or lignin, the as-obtained Ccel-900 and Clig-900 exhibit significantly increasing specific surface area (527 m2/g for Ccel-900 and 73 m2/g for Clig-900 as is


11


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 12 of 23

shown in Table S1), but there is hardly any product for Chem-900 as hemicellulose decomposed easily. These results show that cellulose and hemicellulose undergo decomposition/condensation procedures at relatively low temperature and mainly release

Figure 3. (a) DTG results of mixture of KHCO3 and cellulose, KHCO3, and cellulose, (b) DTG results of mixture of KHCO3 and hemicellulose, KHCO3, and hemicellulose (c) DTG results of mixture of KHCO3 and lignin, KHCO3, and lignin. TGA-MS results of the mixture of (d) KHCO3&Cel, (e) KHCO3&Hem, and (c) KHCO3&Lig, where the mass ratio of KHCO3 to cellulose, hemicellulose, or lignin is 4. CO, CO2, and H2O which may account for the formation of pores. The self-activation process of cellulose and lignin under higher temperature treatment may result in micropores. However, because lignin contains the robust aromatic structure, its products at low temperature (Clig-400) is featured by nonporous structure or gives an extremely low specific surface area even at high temperature. (73 m2/g for Clig-900)


12

Page 13 of 23

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


The mixture of KHCO3 and cellulose (hemicellulose, lignin) labelled as KHCO3&Cel (Hem, Lig) was also conducted to TG-MS to explore the effect of KHCO3. KHCO3 decomposed at ~ 200 oC and produced CO2 and H2O which were both observed in KHCO3&Cel, KHCO3&Hem, and KHCO3&Lig (Figure 3a-c). Compared with sole cellulose and hemicellulose, the decomposition of both cellulose in KHCO3&Cel and hemicellulose in KHCO3&Hem put ahead due to the catalysis of KHCO3 (Figure 3a and b). The decomposition temperature of KHCO3 among KHCO3&Cel put off compared with sole KHCO3 (from ~ 200 to 230 oC), which may be attributed to the endothermic actions of cellulose (Figure S7). The initial decomposition temperature put ahead (140 oC vs. 250 oC) and the long decomposition process was also shortened (140 ~ 250 oC vs. 250 ~ 600 oC). However, most of oxygen-containing groups in lignin are existed in stable forms such as ether bond or phenolic hydroxyl groups, which are inert to some extent. Therefore, the decomposition of lignin did not change even in the presence of KHCO3 at relatively low temperature. The obvious activation process of KHCO3&Cel and KHCO3&Hem is observed after 400 oC for the characteristics of the continuing releasing of H2.37 However, this similar process begins only after 500 oC for KHCO3&Lig, which is due much to the relative stable structure of aromatic rings in lignin. When the temperature was set higher, KHCO3&Lig release CH4 and H2. But the corresponding temperature is lower than that of sole lignin, which suggests that the activator and its by-products (K, K2CO3, and K2O) would catalyze the decomposition of the intermediate products. There are not any gas released after 700 oC for KHCO3&Hem, which due to the totally decomposition of hemicellulose at elevated temperature. Another distinct difference is that KHCO3&Cel releases CO at ~ 770 oC, while KHCO3&Lig produced CH4 at higher


13


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 14 of 23

temperature. These phenomena indicate that lots of adjacent hydroxyl groups in cellulose undergo dehydration and produce C=O, which is related to the release of CO under the higher temperature. While lignin tend to produce CO at first and generate C-C, then the C-H located at edges would leave as CH4.38 The similar conclusion can be made on the basis of solid-state NMR (Figure S8) which was discussed in Supporting Information. The pristine structures of biomass derivatives show significant influence on the morphologies, porous structure, and texture of resultant carbonaceous materials, which also determinate the performance in specific applications. Herein, Ccel-LE-900 and Clig-LE900 were served as the electrode materials for two-symmetric supercapacitors in 1 M EmimBF4/AN. The cyclic voltammogram (CV) measurements were firstly conducted to test the performance of Ccel-LE-900 and Clig-LE-900. The CV curves of both Ccel-LE-900 and Clig-LE-900 display rectangular shape (Figure S9), demonstrating a typical characteristic of the double-layer capacitance. Ccel-LE-900 gives the larger specific capacitance (21 F/g vs. 13.3 F/g at 5 mv/s) due to its higher specific surface area. The capacitive retention of Ccel-LE-900 is 73.2% from 0.1 A/g (23.1 F/g) to 1 A/g (16.9 F/g ) which is higher than that of Clig-LE-900 (16.7 F/g at 0.1 A/g to 11.7 F/g at 1 A/g) due to the often cited


14

Page 15 of 23

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Scheme 1. The possible structure revolution of cellulose, hemicellulose, and lignin under the thermal treatment with assistance of KHCO3 hierarchically porous structure which is good for the electrolytes diffusion. (All the capacitance was calculated based on the full cell) Compared with Clig-LE, the high O-H content contained in Ccel-LE-900 give rise to increased charge transfer resistance (Rct) (80.2 vs. 16.1Ω) (Figure S9) due to the reaction of O-H and ionic liquid in the electrolyte. In contrast, the optimized hierarchical pores of Ccel-LE-900 are responsible for the lower solution resistance (Rs, 3.12 Ω) and the steeper slope in the low frequency zone. On the basis of the observations above, we can conclude the following tips (as presented at Scheme 1: 1) large amount of hydroxyl in cellulose and hemicellulose would result in oxygen heterocyclic rings which finally transform into aromatic rings. The decomposing of oxygen-containing groups at elevated temperature would produce micropores; 2) the hydroxyl in cellulose and hemicellulose would experience dehydration and condensation and link with each other, thus, resulting in three-dimensional and interconnect structure; 3) lots of aromatic rings in lignin lead to a robust structure which hardly forms micropores.


15


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 16 of 23

The aromatic rings also show inert properties to activator and only produce small micropores; 4) a series condensation and addition reaction would happen during the pyrolysis of lignin. However, unlike the oxygen-rich cellulose and hemicellulose, the aromatic rings tend to form two-dimensional structure (Figure 1e); 5) carbonaceous materials derived from cellulose contain hierarchical pores which are favourable for fast electrolytes diffusion, and products from lignin tend to characterize at high graphitization degree and thus lead to a lower charge transfer resistance. As described above, Ccel-LE-900 possesses hierarchically porous structure (containing macro-, meso-, and micropores) while Clig-LE-900 is characterized by two-dimensional nanosheets. However, Cbam-LE-900 which was fabricated by using bamboo, containing 43%~50% cellulose,

Figure 4. (a) Table 1 name of different tertiary mixture with different proportion of specific component, (b) the morphological evolution of carbon stemmed from different tertiary mixture via leaven method 15%~22% hemicellulose, and ~35% lignin,39 as the raw materials had the similar morphology as Ccel-LE-900. It seems that cellulose and hemicellulose are able to act as the framework during the


16

Page 17 of 23

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


KHCO3-assisted pyrolysis. To verify the general applicability of leavening method, it is vital to undertake the model reaction. Hence, the tertiary mixture of cellulose, lignin and hemicellulose with different mass ratio were studied (Figure 4a). The effect of the cellulose: hemicellulose: lignin on the macroporsity of products is shown in the ternary plot in Figure 4b, Figure S10 and Figure S11. It is clear that the SEM images in the lower-left corner of triangular chart in which the proportion of lignin is high (mainly >50%) exhibit bulky morphology, while the rest consistently show macroporous shape. (also see from Figure S11) All the N2 sorption isotherms and PSD curves (Figure S12-1 and S12-2, and Table S2) demonstrate those products contain hierarchically porous structure (containing macropores, mesopores, and micropores). Notably, there were hardly products when hemicellulose was conducted under the same experiment conditions as cellulose. To uncover the contribution of each component to the yield of the final resultants, the yield against each component was analyzed in detail. From Figure S13a, the yield is almost proportional to the mass ratio of lignin. Then, the yield of samples with the same mass ratio of lignin was also analyzed. (Figure S13b-c) The total yields increased with the mass of cellulose when the mass ratio of lignin is 17% and 34%. However, higher content of hemicellulose seems to give higher yield when mass ratio of lignin is 50%. These results show that all the components contribute to the yield of activated products. Moreover, the leaven method was also applied to different kinds of crude biomass. As shown in Figure 5, all the products derived from leaven method exhibited a macroporous morphology on the basis of different biomass. By contrast, the directly pyrolytic products give a bulky morphology. (Figure S14) These results illustrated that leaven method is general toward to crude biomass.


17


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 18 of 23

Figure 5. SEM images of carbon materials derived from leaven method on the basis of different kinds of crude biomass CONCLUSIONS In summary, hydroxyl in cellulose and hemicellulose decomposed easily because of their higher activity compared with stably aromatic compounds in lignin. While hemicellulose tends to decompose thoroughly at high temperature (~ 900 oC) because of its low polymeric degree. Within abundant hydroxyl, cellulose and hemicellulose undergoes decomposition and dehydration condensation leading to plentiful micropores. These hydroxyls in different cellulose or hemicellulose polymers interconnect with each other and undergo dehydration as well as condensation which would result in three-dimensional structure. On the other hand, aromatic rings in lignin provide robust structure leading nonporous carbonaceous materials under the treatment of direct pyrolysis. With the assistance of KHCO3, the carbon stemmed for lignin exhibits two-dimensional nanosheets due to the insertion of activator. Given that the content of lignin are less than 50% in most crude biomass, experimental study on mixed ternary natural polymer (cellulose, hemicellulose, and lignin) with the assistance of KHCO3 give a possibility of wide applications of leavening method for biomass. Furthermore, this leaven method is very


18

Page 19 of 23

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


easy-to-handle with wide raw material sources and the relative products are going to produce commercially by Zhejiang NHU Company LTD.. ASSOCIATED CONTENT Supporting Information This material is available free of charge via the Internet at http://pubs.acs.org. TEM images, SEM images, XRD results, solid-state NMR results, N2 sorption, CV and GCD curves, of the supercapacitor electrode AUTHOR INFORMATION Corresponding Author *E-mail: [email protected] Author Contributions All authors have given approval to the final version of the manuscript. Notes The authors declare no competing financial interest ACKNOWLEDGMENT Financial support from the National Natural Science Foundation of China (91534114 & 21376208), the Zhejiang Provincial Natural Science Foundation for Distinguished Young Scholars of China (LR13B030001), the Fundamental Research Funds for the Central Universities (2016FZA3006), and the Partner Group Program of the Zhejiang University and the Max-Planck Society are greatly appreciated.


19


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 20 of 23

REFERENCES 1.Joo, S. H.; Choi, S. J.; Oh, I.; Kwak, J.; Liu, Z.; Terasaki, O.; Ryoo, R. Ordered nanoporous arrays of carbon supporting high dispersions of platinum nanoparticles. Nature 2001, 412, 169172. 2.Xu, X.; Li, Y.; Gong, Y.; Zhang, P.; Li, H.; Wang, Y. Synthesis of Palladium Nanoparticles Supported on Mesoporous N-Doped Carbon and Their Catalytic Ability for Biofuel Upgrade. J. Am. Chem. Soc. 2012, 134, 16987-16990. 3.Wickramaratne, N. P.; Jaroniec, M. Importance of small micropores in CO2 capture by phenolic resin-based activated carbon spheres. J. Mater. Chem. A 2013, 1, 112-116. 4.Wang, H.; Gong, Y.; Wang, Y. Cellulose-based hydrophobic carbon aerogels as versatile and superior adsorbents for sewage treatment. RSC Adv. 2014, 4, 45753-45759. 5.Yan, J.; Wang, Q.; Wei, T.; Fan, Z. J. Recent Advances in Design and Fabrication of Electrochemical Supercapacitors with High Energy Densities. Adv. Energy Mater. 2014, 4, 43. 6.Beguin, F.; Presser, V.; Balducci, A.; Frackowiak, E. Carbons and Electrolytes for Advanced Supercapacitors. Adv. Mater. 2014, 26, 2219-2251. 7.Han, C.; Wang, J.; Gong, Y.; Xu, X.; Li, H.; Wang, Y. Nitrogen-doped hollow carbon hemispheres as efficient metal-free electrocatalysts for oxygen reduction reaction in alkaline medium. J. Mater. Chem. A 2014, 2, 605-609. 8.Gong, K. P.; Du, F.; Xia, Z. H.; Durstock, M.; Dai, L. M. Nitrogen-Doped Carbon Nanotube Arrays with High Electrocatalytic Activity for Oxygen Reduction. Science 2009, 323, 760-764. 9.Hou, J.; Cao, C.; Idrees, F.; Ma, X. Hierarchical Porous Nitrogen-Doped Carbon Nanosheets Derived from Silk for Ultrahigh-Capacity Battery Anodes and Supercapacitors. ACS Nano 2015, 9, 2556-2564. 10.Hu, B.; Wang, K.; Wu, L.; Yu, S. H.; Antonietti, M.; Titirici, M. M. Engineering carbon materials from the hydrothermal carbonization process of biomass. Adv. Mater. 2010, 22, 813828. 11.Jin, Y. Z.; Gao, C.; Hsu, W. K.; Zhu, Y. Q.; Huczko, A.; Bystrzejewski, M.; Roe, M.; Lee, C. Y.; Acquah, S.; Kroto, H.; Walton, D. R. M. Large-scale synthesis and characterization of carbon spheres prepared by direct pyrolysis of hydrocarbons. Carbon 2005, 43, 1944-1953. 12.Wang, H.; Xu, Z.; Kohandehghan, A.; Li, Z.; Cui, K.; Tan, X.; Stephenson, T. J.; King'ondu, C. K.; Holt, C. M. B.; Olsen, B. C.; Tak, J. K.; Harfield, D.; Anyia, A. O.; Mitlin, D. Interconnected Carbon Nanosheets Derived from Hemp for Ultrafast Supercapacitors with High Energy. ACS Nano 2013, 7, 5131-5141. 13.Ding, J.; Wang, H.; Li, Z.; Kohandehghan, A.; Cui, K.; Xu, Z.; Zahiri, B.; Tan, X.; Lotfabad, E. M.; Olsen, B. C.; Mitlin, D. Carbon Nanosheet Frameworks Derived from Peat Moss as High Performance Sodium Ion Battery Anodes. ACS Nano 2013, 7, 11004-11015. 14.Wu, X. L.; Wen, T.; Guo, H.-L.; Yang, S.; Wang, X.; Xu, A.-W. Biomass-Derived Spongelike Carbonaceous Hydrogels and Aerogels for Supercapacitors. ACS Nano 2013, 7, 3589-3597. 15.Dutta, S.; Bhaumik, A.; Wu, K. C. W. Hierarchically porous carbon derived from polymers and biomass: effect of interconnected pores on energy applications. Energy Environ. Sci. 2014, 7, 3574-3592. 16.Titirici, M.-M.; White, R. J.; Brun, N.; Budarin, V. L.; Su, D. S.; del Monte, F.; Clark, J. H.; MacLachlan, M. J. Sustainable carbon materials. Chem. Soc. Rev. 2015, 44, 250-290. 17.Ryoo, R.; Joo, S. H.; Kruk, M.; Jaroniec, M. Ordered Mesoporous Carbons. Adv. Mater. 2001, 13, 677-681.


20

Page 21 of 23

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


18.Han, C.; Wang, S.; Wang, J.; Li, M.; Deng, J.; Li, H.; Wang, Y. Controlled synthesis of sustainable N-doped hollow core-mesoporous shell carbonaceous nanospheres from biomass. Nano Res. 2014, 7, 1809-1819. 19.Kubo, S.; Tan, I.; White, R. J.; Antonietti, M.; Titirici, M.-M. Template Synthesis of Carbonaceous Tubular Nanostructures with Tunable Surface Properties. Chem. Mater. 2010, 22, 6590-6597. 20.Jache, B.; Neumann, C.; Becker, J.; Smarsly, B. M.; Adelhelm, P. Towards commercial products by nanocasting: characterization and lithium insertion properties of carbons with a macroporous, interconnected pore structure. J. Mater. Chem. 2012, 22, 10787-10794. 21.Yang, Z. C.; Zhang, Y.; Kong, J. H.; Wong, S. Y.; Li, X.; Wang, J. Hollow Carbon Nanoparticles of Tunable Size and Wall Thickness by Hydrothermal Treatment of alphaCyclodextrin Templated by F127 Block Copolymers. Chem. Mater. 2013, 25, 704-710. 22.Kubo, S.; White, R. J.; Yoshizawa, N.; Antonietti, M.; Titirici, M.-M. Ordered carbohydratederived porous carbons. Chem. Mater. 2011, 23, 4882-4885. 23.Zhang, P.; Gong, Y.; Wei, Z.; Wang, J.; Zhang, Z.; Li, H.; Dai, S.; Wang, Y. Updating Biomass into Functional Carbon Material in Ionothermal Manner. ACS Appl. Mater. Interfaces 2014, 6, 12515-12522. 24.Liu, X. F.; Fechler, N.; Antonietti, M. Salt melt synthesis of ceramics, semiconductors and carbon nanostructures. Chem. Soc. Rev. 2013, 42, 8237-8265. 25.White, R. J.; Budarin, V.; Luque, R.; Clark, J. H.; Macquarrie, D. J. Tuneable porous carbonaceous materials from renewable resources. Chem. Soc. Rev. 2009, 38, 3401-3418. 26.Budarin, V.; Clark, J. H.; Hardy, J. J. E.; Luque, R.; Milkowski, K.; Tavener, S. J.; Wilson, A. J. Starbons: New starch-derived mesoporous carbonaceous materials with tunable properties. Angew. Chem. Int. Ed. 2006, 45, 3782-3786. 27.Deng, J.; Xiong, T.; Xu, F.; Li, M.; Han, C.; Gong, Y.; Wang, H.; Wang, Y. Inspired by bread leavening: one-pot synthesis of hierarchically porous carbon for supercapacitors. Green Chem. 2015, 17, 4053-4060. 28.Updegraff, D. M. Semimicro determination of cellulose inbiological materials. Anal. Biochem. 1969, 32, 420-424. 29.Braun, J.; Holtman, K.; Kadla, J. Lignin-based carbon fibers: Oxidative thermostabilization of kraft lignin. Carbon 2005, 43, 385-394. 30.Sevilla, M.; Fuertes, A. B. The production of carbon materials by hydrothermal carbonization of cellulose. Carbon 2009, 47, 2281-2289. 31.Baccile, N.; Falco, C.; Titirici, M.-M. Characterization of biomass and its derived char using 13C-solid state nuclear magnetic resonance. Green Chem. 2014, 16, 4839-4869. 32.Kitani, O.; Hall, C. W.; Wagener, K. Biomass handbook. 1989. 33.Ding, J.; Wang, H.; Li, Z.; Cui, K.; Karpuzov, D.; Tan, X.; Kohandehghan, A.; Mitlin, D. Peanut shell hybrid sodium ion capacitor with extreme energy-power rivals lithium ion capacitors. Energy Environ. Sci. 2015, 8, 941-955. 34.Wang, H.; Mitlin, D.; Ding, J.; Li, Z.; Cui, K. Excellent energy-power characteristics from a hybrid sodium ion capacitor based on identical carbon nanosheets in both electrodes. J. Mater. Chem. A 2016, 4, 5149-5158. 35.Luo, W.; Wang, B.; Heron, C. G.; Allen, M. J.; Morre, J.; Maier, C. S.; Stickle, W. F.; Ji, X. Pyrolysis of cellulose under ammonia leads to nitrogen-doped nanoporous carbon generated through methane formation. Nano Lett. 2014, 14, 2225-2229.


21


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 22 of 23

36.Jeon, J. W.; Zhang, L.; Lutkenhaus, J. L.; Laskar, D. D.; Lemmon, J. P.; Choi, D.; Nandasiri, M. I.; Hashmi, A.; Xu, J.; Motkuri, R. K. Controlling Porosity in Lignin-Derived Nanoporous Carbon for Supercapacitor Applications. ChemSusChem 2015, 8, 428-432. 37.Wang, J. C.; Kaskel, S. KOH activation of carbon-based materials for energy storage. J. Mater. Chem. 2012, 22, 23710-23725. 38.Yang, H.; Yan, R.; Chen, H.; Lee, D. H.; Zheng, C. Characteristics of hemicellulose, cellulose and lignin pyrolysis. Fuel 2007, 86, 1781-1788. 39.Chen, W. J.; Cheng, X. S. Research on Preparation of Fiber and Lignin from Bamboo with High-boiling Alcohol Solvent. Chemistry and Industry of Forest Products 2004, 24, 34-38.


22

Page 23 of 23

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


For Table of Contents Use Only

Effects of Cellulose, Hemicellulose, and Lignin on the Structure and Morphology of Porous Carbons Jiang Deng†, Tianyi Xiong†, Haiyan Wang†, Anmin Zheng‡, and Yong Wang*†

Effects of cellulose, hemicellulose, and lignin on morphology and porous structure of porous carbons are presented.


23

Effects of Cellulose, Hemicellulose, and Lignin on the Structure and

Recommend Documents