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From starch to carbon materials: insight into the crosslinking reaction and its influence on the carbonization process Maoqun Li, Zhihong Bi, Lijing Xie, Guohua Sun, Zhuo Liu, Qingqiang Kong, Xian-Xian Wei, and Cheng-Meng Chen ACS Sustainable Chem. Eng., Just Accepted Manuscript • DOI: 10.1021/acssuschemeng.9b02821 • Publication Date (Web): 27 Jul 2019 Downloaded from pubs.acs.org on July 29, 2019

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ACS Sustainable Chemistry & Engineering

From starch to carbon materials: insight into the cross-linking reaction and its influence on the carbonization process

Maoqun Li a,b, #, Zhihong Bi a,b, #, Lijing Xie a, Guohua Sun a*, Zhuo Liu a, Qingqiang Kong a, Xianxian Wei c, Cheng-Meng Chen a*

a

CAS Key Laboratory of Carbon Materials, Institute of Coal Chemistry, Chinese

Academy of Sciences, 27 Taoyuan South Road, YingZe District, Taiyuan 030001, P. R. China. b

University of Chinese Academy of Sciences, 19 Yuquan Road, Shijingshan District,

Beijing 100049, P. R. China. c

School of Environmentand Safety, Taiyuan University of Science and Technology, 66

WaLiu Road, WanBaiLin District, Taiyuan 030024, P. R. China. * Correspondence should be addressed Guohua Sun ([email protected]) and Cheng-Meng Chen ([email protected]).

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ABSTRACT As a renewable biomass product, starch is a fantastic source for preparing various advanced carbon materials. But starch shows poor thermal stability. Its original spherical morphology tends to be disrupted by direct pyrolysis, and the carbon yield is low. Thus, pre-stabilization by chemical cross-linking is an effective approach to address the above issue. Herein, corn starch was cross-linked by (NH4)2HPO4, followed by carbonization to obtain uniform carbon microspheres. The chemical evolution from starch to carbon was studied systematically using TG-MS, in-situ FTIR, XPS, NMR and in-situ XRD technique. The mechanism of the cross-linking reaction and its influence on the carbonization process were proposed. The introduction of (NH4)2HPO4 promoted the dehydrogenation reaction of starch and further improved its carbonization behaviors. With the increased temperature, more stable heterocyclic aromatic moieties, such as amines, pyridine, pyrrole and quaternary type N sites, formed in the carbon skeleton, which boosted the growth in cyclization and the size of the polyaromatic units. The further formation of C−O−PO3, C−P−O3 and C2−P−O2 played a critical role in cross-linking of polyaromatic unit fragments into graphitic crystalline, which facilitated the preservation of the natural microspheres morphology. The insights into the thermochemical conversion of starch paved a way for the controllable transformation from organic biomass to inorganic carbon materials, with desired structure and properties. KEYWORDS: starch, (NH4)2HPO4, carbon materials, cross-linking reaction, effect on carbonization


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INTRODUCTION Biomass was burned as fuel energy in a long time. But accompanied with the technology development, it’s considered to be a valuable source for preparing carbon materials, due to the widespread availability, renewable nature, low cost and precise biological structures. For instance, biochar,1 activated carbon2, 3 or rayon-based carbon fiber4 have already been industrially produced using wood,5-8 bamboo,9 coconut shell10, 11

and cotton12etc. as raw materials or precursor. Besides, other biomasses with unique

natural morphology, such as catkin,13, 14 peel,15, 16 carbohydrates,17-19 seaweed20-23 etc., were also highly concerned in recent years. In order to obtain materials with desired structure and properties, it is important to precisely control the thermo chemical conversion from organic biomass to inorganic carbons. However, the biomass is composed by a mixture of various macromolecule compounds, and its complexed components make a big challenge to clarify the chemistry mechanism of the carbonization process. Starch, as a biomass-based product, is widely existed in the root and seed of plants. It shows a fantastic spherical structure with high content of carbon, which is desirable for carbon precursor. For example, a facial method was proposed for the preparation of hierarchical porous carbon (HPC) with high surface area and controlled porosity, using starch as precursor and magnesium nitrate as oxidant.24 Yongil Kim et al. reported the starch-derived hard carbon used in sodium-based seawater battery and proved to be a good negative electrode active materials.25 In another example, hybrid structure of carbon nanofibers (CNFs) and activated carbon (AC) were both synthesized using



potato starch as the substrate for in-situ growth of the CNFs.26 Nevertheless, the basic structure of starch is a polysaccharide consisting of D-glucose units, which are easy to depolymerize to form small molecules during the direct pyrolysis process, thus resulting in low carbon yield and the disruption of the natural microstructure. To address this issue, different crosslinking agents such as air,27 pyromellitic dianhydride28 and (NH4)2HPO429-31 etc. are used in the pyrolysis process to improve the thermal stability of biomass, among which (NH4)2HPO4 is an efficient cross-linking agent. Recently, our group reported the kapok fiber cross-linked by (NH4)2HPO4 with simple heating treatment (200 oC for 2h), which efficiently prevented the destruction of the hollow tube structure during the carbonization process.27 (NH4)2HPO4 is an efficient cross-linking agent in many reports, while the improvement reason has not been reported and the cross-linking mechanism between (NH4)2HPO4 and biomass based precursor is not clear. Therefore, we chose starch as the precursor and (NH4)2HPO4 as cross-linking agent to clarify the two questions mentioned above. In this contribution, we provide a comprehensive study on the cross-linking mechanism of starch, as well as its influence on the carbonization process. The neat starch cannot maintain the initial morphology after direct pyrolysis. But if it was firstly cross-linked by (NH4)2HPO4, it can maintain its uniform spherical morphology after carbonization. In the process, SEM and TG-MS were used to observe the morphology transformation and the thermal decomposition behaviors of the materials, respectively. Moreover, the in-situ FTIR spectra, XPS analysis and NMR technique were combined together to characterize the chemical evolution from starch to carbon materials, and


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possible cross-linking mechanism was further proposed based on these results. EXPERIMENTAL SECTION Sample Preparation The corn starch was obtained from Linqing De Neng Golden Corn Biotechnology Co., Ltd. in P. R. China. Carbon microspheres were synthesized by a three-step process. In the first step, the corn starch was impregnated with (NH4)2HPO4 (M starch: M (NH4)2HPO4 = 5:1) solution for 12h and then dried overnight by vacuum freeze-drying to produce the impregnated corn starch (ICS). In the second step, the ICS was put into a tube furnace and stabilized under the Ar atmosphere at 160 oC for 4 h. The obtained sample was named ICS-160. Finally, sample ICS-160 was further heated under Ar atmosphere at 600 oC for 1h to prepare the final carbon micro spheres (ICS-600). For comparison, pristine corn starch (CS) was stabilized and carbonized in the same way to obtain sample of CS-160 and CS-600. Sample Characterizations The in-situ FTIR spectra were used for the identification of IR absorbance in the mid IR region (400-4000 cm-1). It was equipped with liquid nitrogen cooled MCT detector and low-volume gas cell (8.7 mL) with a 123 mm path length and KBr windows. The sample cell was heated from room temperature to 450 °C. The spectra are collected every 20 oC. The FTIR compartment was continuously purged by high purity nitrogen and molecular sieves/silica gel were used to minimize the water and carbon dioxide background in the recorded spectra. The resolution of the collected spectra was set to 4 cm-1 and co-addition of 32 scans per spectrum with a scan speed of 20 kHz. The



pyrolysis experiments were performed in a sensitive thermobalance (Netzsch, STA409PC) at a heating rate of 10 oC/min. The final pyrolysis temperature was 900 oC at N2atmosphere with the flow rate of 50 mL/min. A quadrupole mass spectrometer (Netzsch, QMS403C) coupled to the thermobalance was used for the evolved gas analysis. The transfer lines between the TGA and MS were heated to 200 oC in order to avoid cold spots, and thus prevent the condensation of the gaseous products. The signals for mass numbers of 17, 18, 28, and 44 were continuously detected. Then the mass numbers were converted to the concentrations of NH3, H2O, CO, and CO2 referring to the calibration curves constructed using the standard gases. The evolving rates of the gaseous products were estimated from the measurements. To characterize the morphology of the obtained samples, field-emission scanning electron microscope (JSM-700) at an accelerating voltage of 10.0 kV was used. X-ray photoelectron spectroscopy (XPS) studies were carried out. Elemental composition and bond configuration analyses of the samples were performed with an AXIS Ultra DLD spectrometer with an excitation source of Mg Kα (148.6 eV). The NMR spectra of ICS at different temperatures were measured on a Bruker AVANCE-600 (13C at 150.9 MHz) using a 5 mm TXI cryoprobe. The in-situ XRD measurements were carried out using a Bruker D8 Advance with a LynxEye array detector for data collection. The XRD data were continuously collected during thermal pyrolysis in the transmission mode. Diffraction patterns were acquired throughout the whole heat treatment in a 2θ range of 5o-80o. The heating program was determined by target temperature (20oC, 160oC, 180oC, 220oC, 250oC, 300oC, 450oC, 600oC). The ICS was heated to 600 oC with a


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heating rate of 2 oC/min and held at target temperature for 10 minutes before scanning. RESULTS AND DISCUSSION Figure 1 presents the preparation process of foamed carbon and spherical carbon. It also shows the structural evolution at the different stages. It can be seen that the raw corn starch presents an irregular polyhedral spherical structure with average diameter o

of ~10 μm, as shown in Figure 1a. After pyrolyzed at 160 C, there are no obvious morphology changes for samples CS and ICS, compared with that of raw corn starch (Figure 1b and d). However, there are some differences in color: the CS-160 presented light yellow while the ICS is reddish brown, confirming the catalytic effect of (NH4)2HPO4 on pyrolysis and dehydration of CS. When the pyrolysis temperature reaches 600 oC, the spherical structure of CS has been completely destroyed and become irregular overlapping lamellar structure in the final sample with a foamed form for lacking of (NH4)2HPO4, as shown in Figure 1c and its insert. This can be explained by the melting and swelling of starch caused by the volatile pyrolysis products, resulting in the collapse of spherical structure and the transformation into foaming and fluffy structure.32 In comparison, the carbon architecture of ICS, using (NH4)2HPO4 as crosslinking agent, inherits the natural spherical morphology well with a little shrinkage in the size. This is due to the rearrangement of carbon structure at higher heat treatment temperature. The insert in Figure 1e shows that the final sample is in powder form. The result indicates that (NH4)2HPO4 facilitates the formation of cross-linked corn starch and contributes to the preservation of the spherical structure of starch during the pyrolysis process.



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Figure1. SEM images of (a) CS, (b) CS-160, (c) CS-600, (d) ICS-160 and (e) ICS-600

TG and the DTG analysis are used to study the pyrolysis process of CS and ICS in Ar atmosphere. As shown in Figure 2a, the thermal decomposition of ICS is significantly ahead of CS, suggesting a significant difference in the thermal o

decomposition behavior between the two samples. From 280 to 350 C, the weight loss of CS with 81% is mainly due to the severe depolymerization and decarboxylation with releasinglarge volatile species simultaneously.33 Comparatively, since the thermal o

decomposition behavior of ICS is advanced to 220-270 C, its weight loss is only 56% and the corresponding weight retention rate is as high as 42%,which is more than twice o

that of CS (19%), after 600 C annealing treatment, it is much higher than that of CS. This indicates that the reaction of (NH4)2HPO4 with corn starch not only promotes the pyrolysis of ICS, but also plays an important role informing stabilized structure during thermal treatment.34 In the following discussion we will discuss its specific mechanism in depth.


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Figure 2. (a) TG-DTG curves for ICS and CS, (b) TG-MS analysis of ICS.

Additional insights into the thermochemistry of corn starch in the presence of (NH4)2HPO4 can be obtained from coupled TG-MS measurements in N2 atmosphere. The thermal decomposition features of the sample are well accompanied by the evolving behaviors of H2O, NH3, CO and CO2. As shown in Figure 2b, when the o

temperature rises from 20 to 180 C, the gases of H2O, NH3 and CO2 evolved. It is attributed to the desorption of physically adsorbed water and carbon dioxide as well as the partial decomposition of (NH4)2HPO4. The maximum release of CO2 takes place at o

around 248 C, which is associated to carboxylic acid due to phosphorus pentoxide (P2O5) produced by the decomposition of (NH4)2HPO4 oxidizes hydroxyl groups in the o

starch chains to carboxylic acid groups.35 In the range of 750-800 C, there is a process of CO evolution, indicating the presence of carboxyl anhydrides. The formation of these groups may be attributed to the decomposition of phosphate like-structures.36 Additionally, the evolution of NH3 indicates that the (NH4)2HPO4 has decomposed absolutely to form NH3 and H3PO4 etc. For the last stable weight loss from 300 to 900 o

o

C, a comparatively small MS peak at 785 C, corresponding to the trace of CO



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molecule, indicates the further deoxygenation from starch-based carbon skeleton. (The exothermic peaks of organic matter in DSC curves also correspond well to the gas products formed during starch decomposition as shown in supporting information (SI) Figure 1). According to TG-DTG curves, there are no relevant modifications among the FTIR o

o

spectra of ICS before 200 C. As shown in Figure 3, with the temperature up to 300 C, the typical absorption peaks of α-type starch at 900-750 cm-1 are almost disappear, indicating the first degradation of starch structure.37 As for CS, the same change o

happens above 400 C. Both two samples display two other main bands at 3600-3200 cm-1 and 2800 cm-1, of which the former is assigned to the stretching vibration of the −OH group and the latter corresponds to the stretching of aliphatic C−H (C−H2/C−H3). 38

With the temperature elevating, the intensity of the two bands tends to decrease,

demonstrating the dehydration and cyclization reaction, respectively. In addition, the new peaks of ICS at 1700 cm-1 and 1600 cm-1, attributed to the stretching of C=C and C=O group respectively, were stronger than those in CS. This implies the deeper aromatic character of ICS. Thus, the pyrolysis of starch can be effectively promoted via (NH4)2HPO4 treatment. It may due to the dehydration promoted by NH3 and phosphoric acid together.39 After (NH4)2HPO4 modification, new peaks appeared at around 1085 cm-1, which is ascribed to phosphorus and phosphor carbonaceous compounds (C−O−P).40-43 While the absorption in the region can have also been assigned to C−O stretching, 40 the intensities of the bands located in this area of CS are weaker than those of the ICS. Thereby, it discloses the existence of C−O−P groups.


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Figure 3. In situ FTIR spectroscopy spectra of (a), (c) CS and (b), (d) ICS.

The relative content of nitrogen species and phosphorus species from XPS in the sample ICS are listed in Tables 1 and 2, respectively. The data in parentheses represents the corresponding weighted concentration, which is calculated by multiplying relative concentrations in atomic% by the total atomic content of either phosphorus or nitrogen. This data treatment is done to account for different amounts of surface species at different temperatures. It should be stressed here that the amounts of surface phosphorus and nitrogen of CS were too low to deconvolution for the high-resolution P2p and N1s peaks (see in Figure 2 of SI). The deconvolution results of the N1s peak indicate that nitrogen species mainly exist



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in four forms, which are pyridine (N-6), amines/amides, pyrrolic /pyridone (N-5) and quaternary (N-Q) nitrogen and the weighted surface concentration ratio are calculated from the peak values, and corresponding binding energy are 398.7 eV, 399.6 eV, 400.3 eV and 401.8 eV, respectively, as show in Figure 4.44, 45 It can be seen from the relative o

content distribution and variation trend of nitrogen species in Table 1. Before 300 C, nitrogen species mainly exist in the form of amines/amides, N-5 and N-Q. While after o

450 C, N-6, N-5 and N-Q become the major species. The relative content of different o

nitrogen species are closely related to the temperature changes. From 300 to 450 C, amines/amides continuous decrease and finally disappear. While N-6 starts to form at o

o

450 C and continues to increase at up to 600 C, indicating a possible transition of o

nitrogen species between 300-450 C. This implies that the thermal stability of N-6 is o

higher than the amines/amides. For N-5, it kept stable from 160 to 300 C and started o

o

to drop from 300 to 600 C, while N-Q is constantly increasing from 160 to 600 C. o

And finally at 600 C, N-Q (42.4%)and N-6 (28.7%) are the major species, with a minority of N-5(28.9%).Through the above analysis, the order of thermal stability of different nitrogen species is N-Q > N-6 > N-5 > amines/amides, which is consistent with the conclusions of the reported work.46 The XPS N1s results seem to indicate the presence of mainly amines/amides, N-5 and N-Q groups on the activated carbon surface o

o

before 300 C. After the heat treatment to 450 C, N-5 and N-6 types are most abundant principally due to the cyclization of amines with H3PO4 as catalyst.47 Volatization of o

some organic matter upon heat treatment to 450 C results in an increase in the nitrogen o

content, which is in agreement with the TG-DTG data. At 600 C, the decrease in the


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weighted concentration of different nitrogen species is mainly due to the loss of gasification products resulting from pyrolysis and the formation of condensed aromatic rings, which in turn reduces the proportion of nitrogen.45, 48 Changes in the content of different type nitrogen species will lead to structural changes in carbon materials, which we will elaborate it in the subsequent mechanisms schemes.

396

160 OC

amines

N-5 N-Q

398

400

(b) Intensity (CPS)

Intensity (CPS)

(a)

402

404

300 OC N-5 N-Q

amines

396

398

(c)

396

N-5

398

N-Q

400

402

402

(d) Intensity (CPS)

450 OC

N-6

400

404

Binding energy (eV)

Binding energy (eV)

Intensity (CPS)

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


404

600 OC N-Q N-5 N-6

396

Binding energy (eV)

398

400

402

404

Binding energy (eV)

Figure 4. High resolution N1s XPS spectra of (a) ICS-160, (b) ICS-300, (c) ICS-450, (d) ICS-600.



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Table 1 Relative content and (Weighted surface content) of nitrogen species obtained by fitting the N1s core level peaks of XPS spectra. N1s peak (eV) Weighted concentration of nitrogen species (%)

Sample N-6

Amines, Amides

N-5

N-Q

398.7

399.6

400.3

401.8

ICS-160

--

46.7 (1.76)

41.8 (1.58)

11.5 (0.43)

ICS-300

--

28.3 (1.69)

51.1 (3.06)

20.6 (1.23)

ICS-450

21.5 (1.09)

--

38.9 (1.98)

39.6 (2.01)

ICS-600

28.7 (0.92)

--

28.9 (0.93)

42.4 (1.37)

Three peaks at 133.5, 133.9 and 134.5 eV were fitted out with respect to the P2p spectrum in Figure 5, wherein the peaks at 133.5 eV,133.9 eV, 134.5 eV were corresponding to C−P−O3, C-O-P, pentavalent tetra coordinated phosphorus (PO4) which may be in polyphosphates and/or phosphates, respectively.34 After the thermal o

treatment above 450 C, C2−P−O2 groups are appeared, as C−O−PO3 is reduced to C2−P−O2/C−P−O3 groups, in agreement with the result of Oh et al.49 The formation of C2−P−O2 groups indicates that more carbon atoms may be connected to the same phosphorus atom as the temperature increases. P bridging from C2−PO2 can further connect and crosslink aromatic unite fragments to form a more stabilized threedimensional network structure, which may be conducive to the preservation of natural microsphere morphology.50


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(a)

(b) 300 OC

Intensity (CPS)

Intensity (CPS)

160 OC

C-O-P

P-O4

C-P-O3

130

132

134

C-P-O3

C-O-P

130

136

132

PO4

134

136

Binding energy (eV)

Binding energy (eV)

(c)

(d) 600 oC

Intensity (CPS)

450 OC

Intensity (CPS)

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


C-O-P C-P-O3 PO4 C2-P-O2

130

132

134

C-P-O3

PO4

C2-P-O2

130

136

C-O-P

132

134

136

Binding energy (eV)

Binding energy (eV)

Figure 5. High resolution P2p XPS spectra of (a) ICS-160, (b) ICS-300, (c) ICS-450, (d) ICS-600.

Table 2 Relative content and (Weighted surface content) of phosphorus species obtained by fitting the P2p core level peaks of XPS spectra. P2p peak (eV) Weighted concentration of phosphorus species (%) Sample C2-P-O2

C-P-O3

C-O-P

PO4

132.7

133.5

133.9

134.5

ICS-160

--

24.1 (0.70)

40.1 (1.16)

35.8 (1.04)

ICS-300

--

49.3 (3.00)

26.4 (1.77)

24.3 (1.63)

ICS-450

4.1 (0.14)

31.4 (1.04)

38.7 (1.29)

25.8 (0.86)

ICS-600

15.3 (0.37)

24.7 (0.59)

27.1 (0.65)

32.9 (0.79)

High-resolution solid-state NMR is a powerful tool to investigate the thermal decomposition and carbonization behavior of polymers.40 Herein, we employ the

13

C

solid-state NMR to study the chemical structural evolution of ICS and CS at different



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temperatures. As shown in Figure 6, the signal from 78 to 80 ppm is the overlap region of C-2, C-3, and C-5, while the peaks at ~100 ppm,80-84 ppm and 62 ppm are assigned to C-1,C-4 and C-6 of the ordered starch polysaccharides, respectively.51, 52 The fade o

out of the C-4 (62 ppm) and C-1 (100 ppm) peaks after thermal treatment at 200 C is attributed to the disaggregate of the starch chain. This is in accordance with the initial o

weight loss of ICS from 100 to 200 C as shown in TG result.45 In comparison, the o

initial significant weight loss of CS was delayed to about 300 C. For ICS, the broadness of the resonances at 100, 78-80 and 62 ppm is due to the generation of a complex chemical shift distribution resulting from the thermal condensation or cross-linking o

between the starch chains/repeat units.45 When treated to 180 C, the peak at 62 ppm was weakened, indicating the C-6 substitution by the phosphate group.40 Comparing with the other C sites, the C-6 site, which was more active due to the weaker steric hindrance, is much easier to be substituted.40 The 62 ppm peak of ICS has almost o

disappeared at 180 C, possibly due to the removal or cross-linking of C-6 band. The appearance of new resonances at 20-40 ppm suggests the formation of −C= and −CH2− linkages or −CH3 end groups in the starch polymer chains due to the thermal o

degradation process. As the temperature increases from 220 to 450 C, a peak at around 129 ppm emerges gradually, which can be assigned to the aromatic region causing by aromatization/pseudo graphitization.45 The strong peaks at 150 ppm and 195 ppm are attributable to the formation of N-heterocyclic aromaticity and C=O of pyridinic, respectively.53, 54 It is noteworthy that the ICS start to show the strong aromatic signal o

at a low temperature of 300 C, while the CS does not show remarkable ordered carbon


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o

structure even at 450 C, which is in agreement with the FTIR results. This indicates that (NH4)2HPO4 is a very effective catalyst for the carbonization of starch.

Figure 6. 600 MHz 13C-NMR spectrum of (a) ICS and (b) CS at different temperature.

The in-situ XRD patterns of the ICS were collected and the results are shown in o

o

o

o

o

Figure 7. The peaks centered at ca. 15.0 , 17.1 , 17.9 , 20.0 and 23.1 for the ICS o

correspond to the typical A-type starch crystalline structure.55 During 220-250 C, the o

peaks centered at ca.18 correspond to the amorphous structure of the polymer-like carbons,56 indicating a transition state between starch and carbon. The transition state occurred in the maximum weight loss interval as shown in TG curves. From 300 to 600 o

C, the (002) peak, representing the inter-planar of graphitic carbons, are of low

intensity and are significantly broadened. The (100) peak signal representing the degree of graphitization-like begins to appear when the thermal treatment temperature reaches o

300 C. This is due to aromatization and condensation of the materials up to this temperature. The (100) peak become sharper upon increasing treatment temperature, indicating the increased structure order, and the results of 13C NMR also proved it.57



(002)

Intensity (a.u.)

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

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(100) 600OC 450OC 300OC 250OC O

17.1 17.9O 20 15

O

220OC

O

23.1

O

180OC 160OC 20OC

0

10

20

30

40 50 60 2θ (degree)

70

80

90

Figure 7. In-situ XRD patterns of the ICS.

The above characterization analysis results strongly confirm that the P and N atoms were simultaneously cross-linked into the carbon skeleton after the thermal treatment process. A possible reaction mechanism of corn starch cross-linked with (NH4)2HPO4 o

has been proposed as shown in Scheme 1. The ICS pyrolysis below 160 C mainly produces dehydrated dextran by dehydration and depolymerization with the elimination of H2O. Based on the results of XPS analysis, P and N atoms have been cross-linked into starch as the forms of C−O−P，amines and N-5. During the thermal treatment from o

160 to 250 C, ICS undergoes a large-scale depolymerization process, in which the C1 and C-4 shifts in NMR disappear and the opening reaction of glucose rings is exacerbated to produce many fatty side chain structures. The TG-DTG results also well demonstrate the occurrence of the large-scale depolymerization process. Meanwhile, the typical starch structure of ICS disappears and begin to transform into aromatic o

structure. For the aromatization process of ICS from 160 to 300 C, we further elaborated its deep mechanism of action. This can be attribute to (NH4)2HPO4


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undergoes a preliminary decomposition to release a part of ammonia molecules and o

phosphoric acid molecules after above 160 C as shown in reaction formulas 1 and 2 in Scheme 1 (see in SI).The initial part of the ammonia gas reacts with the pyrolysis starch product to form a substituted amines/amides.58 The hydroxyl group (-OH) of the phosphate molecule cross-inks with the side chain hydroxyl group of the starch decomposition product and dehydrates to form a C-O-P bond to provide more hydroxyl reaction sites for ammonia and its derivatives. As the temperature rises further above o

200 C, (NH4)2HPO4 was decomposed more fully, producing more products such as ammonia and its derivatives, phosphoric acid molecules, and P2O5. On the one hand, phosphoric acid molecules can produce more C-O-P bonds by dehydration condensation reaction and provide more hydroxyl reactive sites for amination reaction. Among them, rich hydroxyl site is highly reactive for ammonia and its derivatives, providing better adhesion conditions, which can be more easily replaced or attacked. This makes -OH, ether-like oxygen form intermediate state of carbon-containing oxynitride such as amines/amides, pyridine-N-oxide. On the other hand, P2O5 can oxidize -OH of the starch chain to carboxyl group (-COOH). Thereby it also provides a favorable active site for ammonization of ammonia to form imines. It is based on the aromatization process above that the predominant reactions can go smoothly including the cleavage of the aliphatic side groups and the cyclisation of the polymeric chain of o

precursor at 300 C. Moreover, the increased content of C−O−P in phosphate linkages that can connect and crosslink aromatic unit fragments. In this process, phosphate molecules or C-O-P bonds play a key role in the catalytic dehydrogenation and further



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aromatization of sugar molecules, and the corresponding key catalytic mechanism is shown in Scheme 2. In addition, the structure of graphite-N already exists surprisingly, indicating that N has been deeply doped into the starch and played an active role in the extension of the aromatic units via cyclisation and condensation. This can be further verified with the disappearance of amines/amides and the appearance of N-6 from 300 o

to 450 C according to Table.1. Moreover, the C−P−O3 groups can be observed o

decrease which seems to be transformed into C2-P-O2 groups during 300-450 C. While o

the C2-P-O2 begins to appear at 450 C, indicating a significant increase in the degree o

of aromatization. When it reached to 600 C, the further increase in the relative content of C2-P-O2, N-6 and N-Q is more suggestive of the formation of aromatic compounds, which merge into larger unites by rearrangements and self-cyclization, mainly due to the“bridging”function of P and N.


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Scheme 1. Possible scheme of the chemical evolution during thermal treatment for ICS.



Scheme 2. Dehydration reaction of sugar molecules catalyzed by phosphoric acid.59

CONCLUSION In this contribution, we described a comparative study of starch-derived carbon materials from pyrolysis of corn starch using (NH4)2HPO4 as cross-linker and direct pyrolysis of corn starch without any cross-linker. In comparison, it is found that corn starch cross-linked by (NH4)2HPO4 can still well maintain its natural spherical morphology after carbonization. By combination of advanced analytical tools, we provided a full understanding of the cross-link reaction mechanism. During the initial stage of pyrolysis, H3PO4 from (NH4)2HPO4 decomposition catalyzed the dehydration of starch and further restrained the formation of tar, resulting in a high carbon yield. With the temperature increasing, P atoms were successively connected to the starch molecular system in the form of C−O−PO3、C−PO3、C2−PO2. N was transformed in the order of amines/amides, N-5, N-6 and N-X. During the whole cross-linked reaction,


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N atoms contributed to the cyclization and growth of polyaromatic units, while P was responsible for the formation of phosphate and polyphoshate bridges that crosslink polyaromatic unit fragments into graphitic crystallines. Under the synergistic effect of P and N, starch has been successfully transformed from natural organic macromolecule compounds to carbon materials. Meanwhile it maintained its own natural spherical morphology. We believe that this study will provide the theoretical model and scientific foundation for the development of biomass-based carbon materials. Meanwhile, it also inspires that more natural products, such as lignin, cellulose, hemicellulose from other biomass need to be explored in the future.

ASSOCIATED CONTENT Supporting Information (SI) Figures S1-S5, Scheme S1 AUTHOR INFORMATION Corresponding Author *E-mail: [email protected]

[email protected] ORCID

Cheng-Meng Chen: 0000-0003-4259-9923 Author Contributions #

Maoqun Li and Zhihong Bi are co-first authors.

Notes The authors declare no competing financial interest.



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ACKNOWLEDGEMENTS We acknowledge the financial support by Scientific and Technological Key Project of Shanxi Province (MC2016-08, MC2016-04),the DNL Cooperation Fund, CAS (DNL180308), Scientific Research Foundation for Young Scientists of Shanxi Province (201601D021061, 201601D021134) and Youth Innovation Promotion Association of CAS.

REFERENCES

(1) Warnock, D. D.;

Mummey, D. L.;

McBride, B.;

Major, J.;

Lehmann, J.; Rillig, M. C.,

Influences of non-herbaceous biochar on arbuscular mycorrhizal fungal abundances in roots and soils: Results from growth-chamber and field experiments. Appl. Soil Ecol. 2010, 46 (3), 450-456. (2) Wang, S. Y.;

Tsai, M. H.; Lo, S. F.; Tsai, M. J., Effects of manufacturing conditions on the

adsorption capacity of heavy metal ions by Makino bamboo charcoal. Bioresource Technology 2008, 99 (15), 7027-7033. (3) Dalahmeh, S. S.;

Pell, M.; Hylander, L. D.;

Lalander, C.;

Vinneras, B.; Jonsson, H., Effects

of changing hydraulic and organic loading rates on pollutant reduction in bark, charcoal and sand filters treating greywater. J. Environ. Manage. 2014, 132, 338-345. (4) Zhu, C. Y.; Akiyama, T., Cotton derived porous carbon via an MgO template method for high performance lithium ion battery anodes. Green Chemistry 2016, 18 (7), 2106-2114. (5) Sun, Z. X.;

Zheng, M. T.; Hu, H.;

Dong, H. W.;

Liang, Y. R.;

Xiao, Y.;

Lei, B. F.; Liu, Y.

L., From biomass wastes to vertically aligned graphene nanosheet arrays: A catalyst-free synthetic strategy towards high-quality graphene for electrochemical energy storage. Chemical Engineering Journal 2018, 336, 550-561. (6) Wang, H.;

Xu, Z. W.;

King'ondu, C. K.;

Kohandehghan, A.;

Holt, C. M. B.;

Li, Z.;

Cui, K.; Tan, X. H.;

Olsen, B. C.; Tak, J. K.;

Stephenson, T. J.;

Harfield, D.; Anyia, A. O.; Mitlin,

D., Interconnected Carbon Nanosheets Derived from Hemp for Ultrafast Supercapacitors with High Energy. Acs Nano 2013, 7 (6), 5131-5141. (7) Zhou, D.;

Wang, H. L.;

Mao, N.;

Chen, Y. R.;

Zhou, Y.;

Yin, T. P.; Xie, H.; Liu, W.;

Chen, S. G.; Wang, X., High energy supercapacitors based on interconnected porous carbon nanosheets with ionic liquid electrolyte. Microporous Mesoporous Mat. 2017, 241, 202-209. (8) Tang, Z. J.; Pei, Z. X.; Wang, Z. F.; M. S.;

Xue, Q.;

Li, H. F.;

Zeng, J.;

Ruan, Z. H.;

Huang, Y.;

Zhu,

Yu, J.; Zhi, C. Y., Highly anisotropic, multichannel wood carbon with optimized


Page 25 of 29 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


heteroatom doping for supercapacitor and oxygen reduction reaction. Carbon 2018, 130, 532-543. (9) Deng, J.;

Xiong, T. Y.;

Xu, F.;

Li, M. M.; Han, C. L.;

Gong, Y. T.;

Wang, H. Y.; Wang,

Y., Inspired by bread leavening: one-pot synthesis of hierarchically porous carbon for supercapacitors. Green Chemistry 2015, 17 (7), 4053-4060. (10) Hulicova-Jurcakova, D.;

Seredych, M.;

Lu, G. Q.; Bandosz, T. J., Combined Effect of Nitrogen-

and Oxygen-Containing Functional Groups of Microporous Activated Carbon on its Electrochemical Performance in Supercapacitors. Advanced Functional Materials 2009, 19 (3), 438-447. (11) Sun, L.;

Tian, C. G.;

Li, M. T.; Meng, X. Y.;

Wang, L.;

Wang, R. H.;

Yin, J.; Fu, H. G.,

From coconut shell to porous graphene-like nanosheets for high-power supercapacitors. Journal of Materials Chemistry A 2013, 1 (21), 6462-6470. (12) Zhu, J. H.; T. C.;

Chen, M. J.;

Yerra, N.;

Hopper, J.; Young, D. P.;

Haldolaarachchige, N.;

Pallavkar, S.;

Luo, Z. P.;

Ho,

Wei, S. Y.; Guo, Z. H., Microwave synthesized magnetic tubular

carbon nanocomposite fabrics toward electrochemical energy storage. Nanoscale 2013, 5 (5), 1825-1830. (13) Li, Y. J.;

Wang, G. L.;

Wei, T.; Fan, Z. J.; Yan, P., Nitrogen and sulfur co-doped porous carbon

nanosheets derived from willow catkin for supercapacitors. Nano Energy 2016, 19, 165-175. (14) Xie, L.; Li, K.;

Sun, G.;

Su, F.;

Guo, X.;

Kong, Q.;

Li, X.;

Huang, X.;

Wan, L.;

song, W.;

Lv, C.; Chen, C.-M., Hierarchical porous carbon microtubes derived from willow catkins for

supercapacitor applications. Journal of Materials Chemistry A 2016, 4 (5), 1637-1646. (15) Xu, G. Y.;

Han, J. P.;

Ding, B.;

Nie, P.;

Pan, J.;

Dou, H.;

Li, H. S.; Zhang, X. G.,

Biomass-derived porous carbon materials with sulfur and nitrogen dual-doping for energy storage. Green Chemistry 2015, 17 (3), 1668-1674. (16) Liu, R. L.;

Liu, Y.;

Zhou, X. Y.;

Zhang, Z. Q.;

Zhang, J.; Dang, F. Q., Biomass-derived

highly porous functional carbon fabricated by using a free-standing template for efficient removal of methylene blue. Bioresource Technology 2014, 154, 138-147. (17) Krishnan, D.;

Raidongia, K.;

Shao, J. J.; Huang, J. X., Graphene Oxide Assisted Hydrothermal

Carbonization of Carbon Hydrates. Acs Nano 2014, 8 (1), 449-457. (18) Niu, Q. Y.;

Gao, K. Z.;

Tang, Q. H.;

Wang, L. Z.;

Han, L. F.;

Fang, H.;

Zhang, Y.;

Wang, S. W.; Wang, L. X., Large-size graphene-like porous carbon nanosheets with controllable N-doped surface derived from sugarcane bagasse pith/chitosan for high performance supercapacitors. Carbon 2017, 123, 290-298. (19) Pampel, J.;

Denton, C.; Fellinger, T. P., Glucose derived ionothermal carbons with tailor-made

porosity. Carbon 2016, 107, 288-296. (20) Kang, D. M.;

Liu, Q. L.;

Gu, J. J.;

Su, Y. S.;

Zhang, W.; Zhang, D., "Egg-Box"-Assisted

Fabrication of Porous Carbon with Small Mesopores for High-Rate Electric Double Layer Capacitors. Acs Nano 2015, 9 (11), 11225-11233. (21) Bichat, M. P.;

Raymundo-Pinero, E.; Beguin, F., High voltage supercapacitor built with seaweed

carbons in neutral aqueous electrolyte. Carbon 2010, 48 (15), 4351-4361. (22) Raymundo-Pinero, E.;

Cadek, M.; Beguin, F., Tuning Carbon Materials for Supercapacitors by

Direct Pyrolysis of Seaweeds. Advanced Functional Materials 2009, 19 (7), 1032-1039. (23) Raymundo-Pinero, E.;

Leroux, F.; Beguin, F., A high-performance carbon for supercapacitors

obtained by carbonization of a seaweed biopolymer. Advanced Materials 2006, 18 (14), 1877-1882. (24) Cao, J. H.;

Zhu, C. Y.;

Aoki, Y.; Habazaki, H., Starch-Derived Hierarchical Porous Carbon with

Controlled Porosity for High Performance Supercapacitors. ACS Sustain. Chem. Eng. 2018, 6 (6), 72927303.



(25) Kim, Y.;

Kim, J. K.;

Vaalma, C.;

Bae, G. H.;

Page 26 of 29

Kim, G. T.; Passerini, S.; Kim, Y., Optimized

hard carbon derived from starch for rechargeable seawater batteries. Carbon 2018, 129, 564-571. (26) Li, Q. Q.;

Liu, F.;

Zhang, L.;

Nelson, B. J.;

Zhang, S. H.;

Ma, C.; Tao, X. Y.; Cheng,

J. P.; Zhang, X. B., In situ construction of potato starch based carbon nanofiber/activated carbon hybrid structure for high-performance electrical double layer capacitor. Journal of Power Sources 2012, 207, 199-204. (27) Cao, Y. F.; Jiang, D.;

Xie, L. J.;

Sun, G. H.;

Su, F. Y.;

Kong, Q. Q.;

Li, F.;

Ma, W. P.; Shi, J.;

Lu, C. X.; Chen, C. M., Hollow carbon microtubes from kapok fiber: structural evolution

and energy storage performance. Sustainable Energy & Fuels 2018, 2 (2), 455-465. (28) Anceschi, A.;

Magnacca, G.;

Trotta, F.; Zanetti, M., Preparation and characterization of

microporous carbon spheres from high amylose pea maltodextrin. Rsc Advances 2017, 7 (57), 3611736123. (29) Li, Y. M.;

Wang, Z. G.;

Li, L. L.;

Peng, S. J.;

Zhang, L.;

Srinivasan, M.; Ramakrishna, S.,

Preparation of nitrogen- and phosphorous co-doped carbon microspheres and their superior performance as anode in sodium-ion batteries. Carbon 2016, 99, 556-563. (30) Qin, D. C.;

Liu, Z. Y.;

Zhao, Y. Z.;

Xu, G. Y.;

Zhang, F.; Zhang, X. G., A sustainable route

from corn stalks to N, P-dual doping carbon sheets toward high performance sodium-ion batteries anode. Carbon 2018, 130, 664-671. (31) Chen, Y.;

Yan, Q. Y.;

Zhang, S. S.;

Lu, L. H.;

Xie, B. Q.;

Xie, T.; Zhang, Y.;

Wu, Y. C.;

Zhang, Y. X.; Liu, D., Buffering agents-assisted synthesis of nitrogen-doped graphene with oxygen-rich functional groups for enhanced electrochemical performance. Journal of Power Sources 2016, 333, 125133. (32) Sharma, R. K.;

Hajaligol, M. R.;

Smith, P. A. M.;

Wooten, J. B.; Baliga, V., Characterization

of char from pyrolysis of chlorogenic acid. Energ Fuel 2000, 14 (5), 1083-1093. (33) Bardet, M.; Hediger, S.;

Gerbaud, G.;

Gambarelli, S.;

Jacquot, J. F.;

Foray, M. F.; Gadelle,

A., Investigation with C-13 NMR, EPR and magnetic susceptibility measurements of char residues obtained by pyrolysis of biomass. Fuel 2007, 86 (12-13), 1966-1976. (34) Valero-Romero, M. J.;

Garcia-Mateos, F. J.;

Rodriguez-Mirasol, J.; Cordero, T., Role of surface

phosphorus complexes on the oxidation of porous carbons. Fuel Processing Technology 2017, 157, 116126. (35) Ai, M., Oxidation of propane to acrylic-acid. Catal. Today 1992, 13 (4), 679-684. (36) Castro-Muniz, A.;

Suarez-Garcia, F.;

Martinez-Alonso, A.; Tascon, J. M. D., Activated carbon

fibers with a high content of surface functional groups by phosphoric acid activation of PPTA. J. Colloid Interface Sci. 2011, 361 (1), 307-315. (37) Vicentini, N. M.;

Dupuy, N.;

Leitzelman, M.;

Cereda, M. P.; Sobral, P. J. A., Prediction of

cassava starch edible film properties by chemometric analysis of infrared spectra. Spectr. Lett. 2005, 38 (6), 749-767. (38) Yu, L. H.;

Falco, C.;

Weber, J.; White, R. J.;

Howe, J. Y.; Titirici, M. M., Carbohydrate-

Derived Hydrothermal Carbons: A Thorough Characterization Study. Langmuir 2012, 28 (33), 1237312383. (39) Nabais, J. M. V.;

Carrott, P. J. M.; Carrott, M., From commercial textile fibres to activated carbon

fibres: Chemical transformations. Mater. Chem. Phys. 2005, 93 (1), 100-108. (40) Wang, J. L.;

Wang, Y. X.; Xu, L.;

Wu, Q. Q.; Wang, Q.;

Kong, W. B.;

Liang, J. Y.;

Yao,

J.; Zhang, J., Synthesis and structural features of phosphorylated Artemisia sphaerocephala


Page 27 of 29 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


polysaccharide. Carbohydr. Polym. 2018, 181, 19-26. (41) Zhang, Z. R.;

Macquarrie, D. J.; Clark, J. H.; Matharu, A. S., Chemical modification of starch

and the application of expanded starch and its esters in hot melt adhesive. Rsc Advances 2014, 4 (79), 41947-41955. (42) Puziy, A. M.;

Poddubnaya, O. I.;

Martinez-Alonso, A.;

Suarez-Garcia, F.; Tascon, J. M. D.,

Synthetic carbons activated with phosphoric acid - I. Surface chemistry and ion binding properties. Carbon 2002, 40 (9), 1493-1505. (43) Puziy, A. M.;

Poddubnaya, O. I.;

Martinez-Alonso, A.;

Suarez-Garcia, F.; Tascon, J. M. D.,

Surface chemistry of phosphorus-containing carbons of lignocellulosic origin. Carbon 2005, 43 (14), 2857-2868. (44) Cagniant, D.;

Gruber, R.;

Boudou, J. P.;

Bilem, C.;

Bimer, J.; Salbut, P. D., Structural

characterization of nitrogen-enriched coals. Energ Fuel 1998, 12 (4), 672-681. (45) Hulicova-Jurcakova, D.;

Seredych, M.;

Lu, G. Q.;

Kodiweera, N.;

Stallworth, P. E.;

Greenbaum, S.; Bandosz, T. J., Effect of surface phosphorus functionalities of activated carbons containing oxygen and nitrogen on electrochemical capacitance. Carbon 2009, 47 (6), 1576-1584. (46) Shen, W. Z.; Fan, W. B., Nitrogen-containing porous carbons: synthesis and application. Journal of Materials Chemistry A 2013, 1 (4), 999-1013. (47) Elmouwahidi, A.;

Bailon-Garcia, E.;

Perez-Cadenas, A. F.;

Maldonado-Hodar, F. J.;

Carrasco-Marin, F., Activated carbons from KOH and H3PO4-activation of olive residues and its application as supercapacitor electrodes. Electrochimica Acta 2017, 229, 219-228. (48) Hasegawa, G.;

Deguchi, T.;

Kanamori, K.;

Kobayashi, Y.;

Kageyama, H.;

Abe, T.;

Nakanishi, K., High-Level Doping of Nitrogen, Phosphorus, and Sulfur into Activated Carbon Monoliths and Their Electrochemical Capacitances. Chemistry of Materials 2015, 27 (13), 4703-4712. (49) Oh, S. G.; Rodriguez, N. M., In-situ electron-microscopy studies of the inhibition of graphite oxidation by phosphorus. J. Mater. Res. 1993, 8 (11), 2879-2888. (50) Jagtoyen, M.; Derbyshire, F., Activated carbons from yellow poplar and white oak by H3PO4 activation. Carbon 1998, 36 (7-8), 1085-1097. (51) Zhang, X. Q.;

Golding, J.; Burgar, I., Thermal decomposition chemistry of starch studied by C-

13 high-resolution solid-state NMR spectroscopy. Polymer 2002, 43 (22), 5791-5796. (52) Link, S.;

Arvelakis, S.;

Spliethoff, H.;

De Waard, P.; Samoson, A., Investigation of biomasses

and chars obtained from pyrolysis of different biomasses with solid-state C-13 and Na-23 nuclear magnetic resonance spectroscopy. Energ Fuel 2008, 22 (5), 3523-3530. (53) Cai, W. W.; Piner, R. D.; X.;

Velamakanni, A.;

Stadermann, F. J.;

Park, S.; Shaibat, M. A.;

An, S. J.; Stoller, M.; An, J. H.;

Ishii, Y.;

Yang, D.

Chen, D. M.; Ruoff, R. S., Synthesis and

solid-state NMR structural characterization of C-13-labeled graphite oxide. Science 2008, 321 (5897), 1815-1817. (54) Wang, T.; L. M.;

Shi, S. J.;

Li, Y. H.;

Zhao, M. X.;

Chang, X. F.;

Wu, D.;

Wang, H. Y.;

Peng,

Wang, P.; Yang, G., Study of Microstructure Change of Carbon Nanofibers as Binder-Free

Anode for High-Performance Lithium-Ion Batteries. Acs Applied Materials & Interfaces 2016, 8 (48), 33091-33101. (55) Gerard, C.; Planchot, V.; Colonna, P.; Bertoft, E., Relationship between branching density and crystalline structure of A- and B-type maize mutant starches. Carbohydr. Res. 2000, 326 (2), 130-144. (56) Wang, Q.;

Liang, X. Y.;

Qiao, W. M.;

Liu, C. J.;

Liu, X. J.;

Zhan, L. A.; Ling, L. C.,

Preparation of polystyrene-based activated carbon spheres with high surface area and their adsorption to



Page 28 of 29

dibenzothiophene. Fuel Processing Technology 2009, 90 (3), 381-387. (57) Zhao, L.;

Baccile, N.;

Gross, S.;

Zhang, Y. J.;

Wei, W.;

Sun, Y. H.;

Antonietti, M.;

Titirici, M. M., Sustainable nitrogen-doped carbonaceous materials from biomass derivatives. Carbon 2010, 48 (13), 3778-3787. (58) Hulicova-Jurcakova, D.;

Kodama, M.;

Shiraishi, S.;

Hatori, H.;

Zhu, Z. H.; Lu, G. Q.,

Nitrogen-Enriched Nonporous Carbon Electrodes with Extraordinary Supercapacitance. Advanced Functional Materials 2009, 19 (11), 1800-1809. (59) Molina-Sabio, M.; Rodriguez-Reinoso, F., Role of chemical activation in the development of carbon porosity. Colloid Surf. A-Physicochem. Eng. Asp. 2004, 241 (1-3), 15-25.


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For Table of Contents Use Only

The controllable transformation from organic starch to inorganic carbon materials by cross-linking of (NH4)2HPO4, with desired structure and properties.


From Starch to Carbon Materials: Insight into the ... - ACS Publications

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