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Preparation and characterization of novel carbon dioxide adsorbents based on polyethyleniminemodified Halloysite nanotubes a
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Haohao Cai , Feng Bao , Jie Gao , Tao Chen , Si Wang & Rui Ma a
Department of Chemistry, Central China Normal University, Wuhan 430079, People's Republic of China b
Engineering Research Center of Nano-Geomaterials of Ministry of Education, China University of Geosciences, Wuhan 430074, People's Republic of China Accepted author version posted online: 10 Nov 2014.Published online: 09 Dec 2014.
Click for updates To cite this article: Haohao Cai, Feng Bao, Jie Gao, Tao Chen, Si Wang & Rui Ma (2015) Preparation and characterization of novel carbon dioxide adsorbents based on polyethylenimine-modified Halloysite nanotubes, Environmental Technology, 36:10, 1273-1280, DOI: 10.1080/09593330.2014.984772 To link to this article: http://dx.doi.org/10.1080/09593330.2014.984772
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Environmental Technology, 2015 Vol. 36, No. 10, 1273–1280, http://dx.doi.org/10.1080/09593330.2014.984772
Preparation and characterization of novel carbon dioxide adsorbents based on polyethylenimine-modified Halloysite nanotubes Haohao Caia , Feng Baoa∗ , Jie Gaoa , Tao Chenb , Si Wangb and Rui Mab∗ a Department of Chemistry, Central China Normal University, Wuhan 430079, People’s Republic of China; b Engineering Research Center of Nano-Geomaterials of Ministry of Education, China University of Geosciences, Wuhan 430074, People’s Republic of China
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(Received 25 February 2014; accepted 26 September 2014 ) New nano-sized carbon dioxide (CO2 ) adsorbents based on Halloysite nanotubes impregnated with polyethylenimine (PEI) were designed and synthesized, which were excellent adsorbents for the capture of CO2 at room temperature and had relatively high CO2 adsorption capacity. The prepared adsorbents were characterized by various techniques such as Fourier transform infrared spectrometry, gel permeation chromatography, dynamic light scattering, thermogravimetry, thermogravimetry-Fourier transform-infrared spectrometry, scanning electron microscopy and transmission electron microscopy. The adsorption characteristics and capacity were studied at room temperature, the highest CO2 adsorption capacity of 156.6 mg/g-PEI was obtained and the optimal adsorption capacity can reach a maximum value of 54.8 mg/gadsorbent. The experiment indicated that this kind of adsorbent has a high stability at 80°C and PEI-impregnated adsorbents showed good reversibility and stability during cyclic adsorption–regeneration tests. Keywords: carbon dioxide; adsorbents; nanotubes; polymer; Halloysite
1. Introduction Recently, amine especially polyamine substance- [1–4] based adsorbents on mesoporous solids or nanoscale particles, such as MCM-41,[5] MCM-48,[6] SBA-15,[7] fumed silica,[8] etc., have attracted much attention on CO2 capture.[9–13] Support such as MCM-41, MCM-48, SBA15 and fumed silica which has larger specific surface area and pore volume can provide more active sites for amine substance to react with more CO2 molecules.[14–17] It is reported that the best result of CO2 absorption capacities for MCM-41-PEI was achieved with MCM-41-PEI containing 75 wt% of polyethylenimine (PEI) with 133 mg CO2 /g-sorbent at 75°C in pure CO2 and fumed silicaPEI-33 has a CO2 absorption capacity of 52 mg/g at room temperature (rt.) from the dry air.[18,19] So far, these kinds of adsorbents have the greatest possibility of practical application in large-scale CO2 capture [20] because of their high adsorption capacities and stable regenerative abilities.[21–25] However, preparation process of these supports is complex, very energy intensive and costly because it involves multistep synthesis, calcination and high-temperature reaction.[5–8,26,27] Halloysite nanotubes (HNTs) [28–31] are a kind of aluminosilicate clays with hollow nanotubular structure (about 20–50 nm in diameter and several hundred nanometres in length) mined from natural deposits and abundant at countries such as China, America, Brazil,
France and so on.[28] They are chemically similar to kaolinite which has relatively high chemical stability with specific surface area of 59.7 m2 /g generally.[31] In recent years, HNTs are used as nanotemplates or nanoscale reaction vessels instead of carbon nanotubes or boron nitride nanotubes and an additive to improve the properties of polymer nanocomposites.[28,32] In this paper, we will introduce a new polyamine-based adsorbent with HNTs support which was easily obtained and cheaper than those based on other supports, the most striking thing is that the adsorbent exhibited relatively high CO2 adsorption capacity from dry air, durable thermostability at desorption temperature and strong regenerative abilities. 2. Experimental section 2.1. Materials HNTs (99.8%) were purchased from Jiuchuan Technology Co. (Jiangsu, China), PEI with a high molecular weight (M w = 17,000, determined by gel permeation chromatography) was purchased from Qianglong New Chem. Mat. Co. (Hubei, China). Hydrochloric acid and methanol were purchased from Kaitong Chemical Reagent. Sodium hexametaphosphate was supplied by Sinopharm Chemical Reagent Co. Ltd. All other chemicals were of analytic grade and redistilled water was used throughout the experiment.
*Corresponding author. Emails: [email protected]; [email protected] © 2014 Taylor & Francis
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2.2. Pretreatment of HNTs The purchased HNTs were purified through a series of procedure before modification. The purchased HNTs were dispersed in a mass fraction 0.3% solution of sodium hexametaphosphate, stirred the mixture for 1 h to get slurry of 15% mass fraction HNTs.[28] Then the slurry was centrifuged at a speed of 3800 r/min for 30 min. The precipitate was removed and the supernatant was filtered to get this part of sediment. The sediment was washed with distilled water several times to remove the sodium hexametaphosphate. In order to remove the fragment in pre-purified HNTs, we dispersed the sediment in distilled water and centrifuged this slurry at a speed of 12,000 r/min for 1 h, then reserved the sediment. The sediment was dried at 95°C for 12 h.[33] Then, the pretreated HNTs with structural integrity and uniform size were obtained. 2.3.
The weight change of the adsorbent was monitored to determine the adsorption and desorption performance of the materials. In a typical adsorption/desorption process, about 10 mg of the adsorbent was placed in a small sample cell, prior to adsorption measurements and the adsorbent was heated up to 80°C under 10−5 bar vacuum to remove adsorbed CO2 and water until there was no noticeable weight loss. Then the temperature was decreased to 25°C and the dry air was introduced at a flow rate of 100 ml/min until there was no obvious weight loss. After the adsorption, the adsorbent was heated to 80°C under 10−5 bar vacuum [18] again to remove adsorbed CO2 completely for another adsorption measurement.[19] Adsorption capacity in mg of adsorbate/g-adsorbent and desorption capacity in percentage were used to evaluate the adsorbent and were calculated from the weight change of the sample in the adsorption/desorption process.
Preparation of HNTs-PEI adsorbents
The PEI-modified HNTs were prepared by a wet impregnation method. In a typical preparation, the desired amount of PEI (viscous liquid) was dissolved in 8 g of methanol under stirring for about 15 min at room temperature in the atmosphere, after which 2 g of purified HNTs was added to the PEI/methanol solution.[34] The resultant slurry was continuously stirred for about 30 min. Then the slurry was dried at 50°C under vacuum on a rotavapor followed by vacuum treatment overnight ( < 1 mmHg).[18] The asprepared adsorbent was denoted as HNTs-PEI-X, where X represents the loading of PEI as weight percentage in the sample. 2.4. Characterization FTIR adsorption was recorded on a Nicolet AVATAR360 instrument. The thermal stability and adsorption capacities were determined by thermogravimetric analysis (TGA) on a PE-TGA 7 thermal gravimeter. Dynamic light scattering (DLS) was conducted by a Britain Malvern Zetasizer ZEN3690 at room temperature. Transmission electron microscopy (TEM) was carried out on a Zeiss EM 912 Omega transmission electron microscope. The N2 adsorption/desorption was carried out on a Quantachrome Autosorb automated adsorption apparatus. Scanning electron microscopy was conducted by a Cambridge S-250MK3 UK microscope with an acceleration voltage of 5.0 kV. Zeta potential was measured by a Britain Malvern Zetasizer, ZEN3690. The thermogravimetryFourier transform-infrared spectrometry spectra were measured on a TG-209/Vector22 apparatus (Netzsch Co., Germany).
2.5. Adsorption and desorption measurement The adsorption and desorption performance of the adsorbents were measured using a PE-TGA 7 thermal analyser.
3. Results and discussion 3.1. Characterization of purified HNTs DLS results indicated that the average size (diameter) of purified HNTs was 427.3 nm, with a polydispersity index of 0.382 in distil water.[35] The TEM image (Figure 1) clearly showed the nanotube structure of purified HNTs, and the hollow lumens were easily observed. And the average inside diameter of these HNTs was approx. 30 nm which can be deduced from Figure 1. The following features are observed in the FTIR spectra of HNTs (Figure 2(a)): a broad, intense band at 3200–3500 cm−1 (O−H stretching vibrations, attributed to crystal water and slight absorbed water), the band at 910 cm−1 (Al−OH bending vibration), narrow bands at 1000–1100 cm−1 (Si−O stretching vibration) and 450–550 cm−1 (Si−O bending vibration).[31,36,37]
Figure 1.
The TEM image of the purified HNTs.
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supports such as fumed silica (approx. 200 m2 /g) [40–42] or MCM-41(approx. 1000 m2 /g).[18] But for effective CO2 absorption, the size of the support as well as its morphology was found to be of greater importance than the surface area of the support, as Olah et al. reported.[40]
In the characterization of thermogravimetry (TG), about 10 mg of the sample was heated at 10°C/min to 600°C in N2 flow (100 ml/min). Figure 3(a) shows the TGA profile of purified HNTs; there was tiny weight loss (about 1%) for HNTs until 100°C as a result of a small number of adsorbed water and free water (negligible gas).[20,38,39] As the CO2 adsorption capacity was calculated by weight loss, the practical adsorption capacity should take into account of lost weight of adsorbed water and free water at the first adsorption–regeneration measurement.[32] The HNTs gradually lost its crystal water with the increase in temperature until 490°C where the crystal structure was destroyed completely. This mass loss is mainly assigned to the dehydroxylation of structural Al−OH groups of HNTs. The result was accordant with the previous reports by Kepert et al.[30] and proved HNTs’ stability under 100°C. As shown in Figure 6, the surface area and pore volume of purified HNTs are 59.7 m2 /g and 0.861 cm3 /g, respectively, and lower than those of other
3.2. Characterization of adsorbents The reaction of PEI with CO2 is represented in different types of amines present in Scheme 1. The repeating unit of the polymer in this scheme is only a simplified model representation showing the three different types of amines present in PEI. The primary and secondary amino groups in PEI react with CO2 to form carbamates. In the presence of water, these carbamates can react further to form a bicarbonate species. In this case, only one amino group is necessary for every CO2 molecule instead of two in the case of carbamate formation in the absence of water.[19] It is reported by Iliuta et al. [42] that only carbamate formation of primary (RNH2 ) and secondary (R2 NH) amines took place through zwitterion (RNH2+ COO− ) formation and carbamate (RNHCOO− ) and protonated amine formation. Tertiary (R3 N) amines would not react with CO2 without water. In this paper, we mainly focus on the CO2 adsorption without water. Figure 2(b) shows the FTIR spectra of adsorbent HNTsPEI-30. According to Giannelis et al.,[36] the bands of PEI in the adsorbent at 3446, 3302 and 1570 cm−1 correspond to the asymmetric and symmetric NH2 stretching vibrations, while bands at 2881, 2814, 1457 and 1346 cm−1 can be due to CH2 vibrations. The absorption bands at 1650, 1540, and 1407 cm−1 can be assigned to N−H deformation in RNH3+ , C=O stretch and NCOO skeletal vibration respectively, due to the formed carbamate.[43] As expected, adsorbent shows characteristic peaks of both the HNTs and PEI, which indicated that PEI-decorated HNTs materials were successfully fabricated. Figures 3(b) and 4 show the TGA profile and the differential thermal gravimetric analysis (DTGA) of the adsorbent (HNTs-PEI-30, contained moisture), respectively. The DTGA of adsorbent indicates two maximum loss ratios at 80°C and 355°C with the loss percentage of 7.73% and 34.1% from TGA. The HNTs-PEI-30 lost its initiatory mass of 7.73% at 80°C, which can be mainly ascribed to the desorption of CO2 and moisture. This was confirmed by FTIR spectrum of gas released out at 80°C of HNTs-PEI30 pyrolysis from Figure 5. This also indirectly indicated that PEI has a low vapour pressure and unlike the commercially used amines such as diethanolamine, which makes
Figure 3. The TGA profiles of purified HNTs and adsorbent.
Scheme 1.
Figure 2. FTIR spectra of HNTs and HNTs-PEI-30.
Reaction of CO2 with amines.
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Figure 4. The DTGA profile of adsorbent.
PEI suitable for long-term use at relatively high temperature. As the adsorbent has a high loss ratio at 80°C and this mass loss mostly belongs to CO2 , we determine it the desorption temperature; while they are 75 and 85°C for MCM-41 and fumed silica supports adsorbents respectively, which can be explained by the uniform dispersion of PEI into the nanoscale-support pores of different sizes, since the melt or decomposition temperature will decrease when the particle size of a substance decreases.[18,19] The PEI of HNTs-PEI-30 began to decompose above 280°C and a sharp weight loss appeared at 355°C which are the start-to-decompose temperature and the maximum loss ratio temperature of PEI, respectively. Both of them were 130 and 150°C higher than other reported startto-decompose temperatures and the maximum loss ratio temperatures, respectively.[44] This may be explained by the opposite potentials between PEI and HNTs and more important high molecular weight. Because the HNTs and PEI in adsorbent had a very strong electrostatic attraction, and PEI with high molecular weight was more stable under high temperature condition which also led adsorbent to higher decomposition temperatures.[18,33] At 600°C the sample lost about 50% weight according to Figure 3(b), which was higher than total approx. 40% weight loss theoretically of designed PEI quantity (30%), complete weight loss of pure HNTs (9%) and captured CO2 (0.5%), the excess weight loss may be due to the absorbed water because polyamine adsorbents with large surface areas absorbed water easily [27] and amino function with water could have absorbed more CO2 as mentioned above.[42] Figure 5 shows the FTIR spectrum at 80, 490 and 600°C of TG. The relevant parameter on TG-209 is corresponding to the parameter on PE-TGA 7. Several representative times at each pyrolysis stage were selected to study the desorption condition and component part of volatiles. At the first stage, about 80°C, HNTs-PEI-30 lost its adsorbed water and free water as HNTs did (see 3700
Figure 5. FTIR spectrum of gas released out at three different times of an HNTs-PEI-30 pyrolysis process.
cm−1 around),[45] besides an amount of CO2 was detected in the volatile based on typical asymmetric stretching vibration (2350 cm−1 around) of CO2 .[21] The peak near 1500 cm−1 belonged to N−H bending vibration which was due to slightly volatile amino.[43] With the increase in the temperature until the second stage, the PEI began to decompose giving rise to the strong peak at 3260 cm−1 (N−H stretching vibration) and the weak peak at 2953 cm−1 (C−H stretching vibration). When the temperature was increased to 490°C, the PEI began decomposing into small molecule compounds which comprised methyl, methylene, amines, water, etc.[21,33,44,46] At about 600°C, the PEI was completely decomposed and removed as volatiles, while the HNTs structure was destroyed and lost the all crystal water.[47] The N2 adsorption/desorption was carried out on a Quantachrome Autosorb automated adsorption apparatus, from which the BET surface area, the pore volume and the pore size were obtained. The sample was out-gassed at 80°C for 48 h on a high vacuum line prior to adsorption. The pore volume of the HNTs was calculated from the adsorbed nitrogen after complete pore condensation (P/P0 = 0.995) using the ratio of the densities of liquid and gaseous nitrogen. The pore size was calculated by using the BJH method. Figure 6 shows the surface areas and pore volumes of HNTs-PEI with different PEI loadings. After the PEI was loaded into its hollow lumen, the pore volume decreased. The pore volume of HNTs-PEI-10 was 0.852 cm3 /g, smaller than that of the HNTs support, which confirmed that PEI was loaded into the HNTs inner lumen.[19] Abnormally with increasing PEI loadings, the pore volume increased slightly from 0.872 cm3 /g of 10% PEI-loading to 0.896 cm3 /g of 20% PEI-loading. This might be due to the
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example, when the PEI loading was 10 wt%, the adsorbent showed a pore volume of 0.852 ml/g, smaller than that of the HNTs support, which confirmed that PEI was loaded into the HNTs’ inner lumens. With increasing PEI loadings, the surface area further decreased. When the PEI loading was higher than 40 wt%, the surface area decreased sharply, which indicated that some of the mesoporous pores [43] were completely filled with PEI. The surface area was only 8.4 m2 /g and the residual pore volume was only 0.378 ml/g for HNTs-PEI-40 at the liquid nitrogen temperature (Table 1).
Figure 6. The surface areas and pore volumes of HNTs-PEI with different PEI loadings.
fact that PEI sticking outside HNTs forms agglomerates with large meso-and macropores. Because of the dispersed state of HNTs, pure HNTs scatter individually, but HNTs coated with PEI cluster and turn into large particles which have higher pore volume, as shown in Figure 6. When PEI is added to HNTs and fills in the inner lumen, the pore volume decreases. As more PEI is added to HNTs, a small portion of PEI that attached outside surface of HNTs made these nanotubes adhere to each other to create more pores (as shown in Scheme 2). With the proportion of PEI scaling up to 30%, the pore volume curved down. When the PEI loading further increased to 40 wt% around, the inner space was completely filled with PEI, restricting the access of nitrogen into the pores at the liquid nitrogen temperature. Therefore, information on the pore volume cannot be obtained from the N2 adsorption/desorption isotherms for PEI loading above 40 wt%.[19,42] The surface area of HNTs, after loading the PEI, exhibited the similar trends as the pore volume. The HNTs support had a surface area of 59.7 m2 /g. The surface area decreased after PEI was loaded into their inner lumens. For
Scheme 2. Schematic diagram of PEI loaded in the HNTs.
Table 1. Surface area, volume of pores and CO2 adsorption capacities to different PEI. PEI loading in adsorbent (%) 0 10 20 30 40
Surface area (m2 /g)
Volume of pores (cm3 /g)
CO2 adsorption capacity (mg/g)
59.7 52.6 40.2 25.9 8.4
0.861 0.852 0.886 0.702 0.378
– 15.3 30.7 48.6 24.3
3.3. Adsorption performance of HNTs-PEI adsorbents The weight of the sample after treatment was used to calculate the CO2 adsorption capacity under the assistance of TGA.[43] The influence of PEI loading on CO2 absorption performance in dry air at 25°C is shown in Figure 8.[44] The physical adsorption of pure HNTs comparing to chemical adsorption of amine adsorbent was so slight that could be negligible. When a small amount of PEI was loaded on HNTs, HNTs with larger specific surface area can provide more contact points for PEI to facilitate the reaction of amine with CO2 . As shown in Figure 8(a), at low PEI loading the linear relationship of adsorption capacity and incremental PEI illustrated the uniform distribution
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3.4.
Figure 8. CO2 adsorption capacity to PEI loading, (a) adsorbents and (b) PEI.
of PEI inside HNTs’ lumens and outside HNTs’ surface quite well, then all the amine group of PEI could effectively combine with CO2 molecule, as given in Scheme 2 (B is 3/4 cross-section of A). The highest CO2 adsorption capacity of 54.8 mg/g-adsorbent (35% PEI) was obtained, which was little higher than that of FS-PEI (33% PEI), as Olah et al. [44] reported earlier. Figure 8 shows the CO2 adsorption capacity in two ways: line (a) presents the adsorption of CO2 per 1 g adsorbent and line (b) presents the adsorption of CO2 per 1 g PEI in adsorbent. Although the surface area and pore volume were inclined to decrease, the absorption capacity increased with the increase in PEI loading as far as 35% PEI loading because incremental PEI could provide more amine groups to capture more CO2 molecules. As mentioned above, the adsorbent of 35% PEI loading performed the maximum adsorption capacity due to both adequate PEI loading and volume pore that the former provided contact points and the latter provided sufficient quantity of CO2 transfer channel (Scheme 2, D is partly zoomin of C). When the PEI loading increased to 40 wt% or higher, PEI filled the lumen completely and blocked the access of CO2 to inner polymer amine. However, excess
Figure 7. (a) The HNTs-PEI cluster and (b) larger HNTs-PEI cluster.
Cyclic adsorption–desorption performance of HNTs-PEI adsorbent For potential practical applications, in addition to high CO2 capturing capacity, the sorbent must possess long-term stability and regenerability with a minimum difference in adsorption/desorption temperatures or pressures, and lower cost. Figure 9 shows the regeneration behaviour of HNTsPEI-30 under the cyclic adsorption–desorption of dry air using a concentration sweep process. After CO2 capture at 25°C, the adsorbent was under 10−5 bar vacuum to remove CO2 at 80°C until there was no noticeable weight loss. The absorption capacity is 53.0 mg/g-adsorbent after 50 absorption–desorption cycles, only slightly lower than the value at the first cycle. The good cyclic performance may
Figure 9. Cyclic adsorption–desorption of HNTs-PEI-30 using a concentration sweep.
Environmental Technology be due to the higher boiling point of PEI, which contributes to better temperature stability.[25,27]
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4.
Conclusion
In conclusion, novel CO2 ‘HNTs-PEI’ adsorbents based on PEI-modified mesoporous compound of HNTs type have been successfully developed. The adsorbent of 35% PEI loading performed the maximum adsorption capacity due to both adequate PEI loading and volume pore that the former provided contact points and the latter provided sufficient quantity of CO2 transfer channel. The highest CO2 adsorption capacity of 156.6 mg/g-PEI was obtained in dry air and the features of long-term stability and regenerability were performed, which meets the demand of industrial application and the source of HNTs can be more environmental than other solid supports. In this paper, we pioneered combining TGA and FTIR spectrometry to investigate the CO2 desorption process for a better understanding how the adsorbate and adsorbent interact and relevant thermodynamic property. Disclosure statement
[8] [9] [10] [11] [12] [13] [14] [15]
[16]
No potential conflict of interest was reported by the author(s).
Funding This work was supported by the Fundamental Research Funds for the Central Universities [grant number CUGL100407 CUGL20118]; the National Natural Science Foundation of China [grant number 41372367]; the Natural Science Foundation of Hubei Province [grant number 2012FFA111], [grant number 2010BFA022] and the public service project of the Chinese Ministry of Land and Resources [grant number 201311024].
[17] [18]
[19]
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[26] Yue MB, Sun LB, Cao Y, Wang Y, Wang ZJ, Zhu JH. Efficient CO2 capturer derived from as-synthesized MCM-41 modified with amine. Chem Eur J. 2008;14:3442–3451. [27] Sayari A, Belmabkhout Y. Stabilization of aminecontaining CO2 adsorbents: dramatic effect of water vapor. J Am Chem Soc. 2010;132:6312–6314. [28] Du ML, Guo BC, Jia DM. Newly emerging applications of halloysite nanotubes: a review. Polym Int. 2010;59:574– 582. [29] Shchukin DG, Sukhorukov GB, Price RR, Lvov YM. Halloysite nanotubes as biomimetic nanoreactors. Small. 2005;1:510–513. [30] Yuan P, Southon PD, Liu Z, Green MER, Hook JM, Antill SJ, Kepert CJ. Functionalization of halloysite clay nanotubes by grafting with γ -aminopropyltriethoxysilane. J Phys Chem C. 2008;112(40):15742–15751. [31] Du ML, Guo BC, Lei YD, Liu MG, Jia DM. Carboxylated butadiene–styrene rubber/halloysite nanotube nanocomposites: interfacial interaction and performance. Polymer. 2008;49:4871–4876. [32] Yuan P, Southon PD, Liu ZW, Green MER, Hook JM, Antill SJ, Kepert CJ. Functionalization of halloysite clay nanotubes by grafting with γ -aminopropyltriethoxysilane. J Phys Chem C. 2008;112:15742–15751. [33] Xu XC, Song CS, Andresen JM, Miller BG, Scaroni AW. Novel polyethylenimine-modified mesoporous molecular sieve of MCM-41 type as high-capacity adsorbent for CO2 capture. Energy Fuels. 2002;16:1463–1469. [34] Yu H, Tian M, Shen C, Wang Z. Facile preparation of porous polybenzimidazole networks and adsorption behavior of CO2 gas, organic and water vapors. Polym Chem. 2013;4:961–968. [35] Gao J, Bao F, Feng LL, Shen KY, Zhu QD, Wang DF, Chen T, Ma R, Yan CJ. Functionalized graphene oxide modified polysebacic anhydride as drug carrier for levofloxacin controlled release. RSC Adv. 2011;1(9):1737–1744. [36] Qi GG, Wang YB, Estevez L, Duan XN, Anako N, Park AHA, Li W, Jones CW, Giannels EP. High efficiency nanocomposite sorbents for CO2 capture based on aminefunctionalized mesoporous capsules. Energy Environ Sci. 2011;4:444–452.
[37] Song WC, Xu XK, Chen Q, Zhuang ZZ, Bu XH. Nitrogenrich diaminotriazine-based porous organic polymers for small gas storage and selective uptake. Polym Chem. 2013;4:4690–4696. [38] Neti VSPK, Wu XF, Deng SG, Echegoyen L. Selective CO2 capture in an imine linked porphyrin porous polymer. Polym Chem. 2013;4:4566–4569. [39] Jackson KT, Rabbani MG, Reich TE, El-Kaderi HM. Synthesis of highly porous borazine-linked polymers and their application to H2 , CO2 , and CH4 storage. Polym Chem. 2011;2:2775–2777. [40] Goeppert A, Meth S, Prakash GKS, Olah GA. Nanostructured silica as a support for regenerable high-capacity organoamine-based CO2 sorbents. Energy Environ Sci. 2010;3:1949–1960. [41] Xiong YB, Wang YJ, Wang H, Wang RM. A facile onestep synthesis to ionic liquid-based cross-linked polymeric nanoparticles and their application for CO2 fixation. Polym Chem. 2011;2:2306–2315. [42] Bougie F, Iliuta MC. Sterically hindered amine-based absorbents for the removal of CO2 from gas streams. J Chem Eng Data. 2012;57:635–669. [43] Wang XX, Schwartz V, Clark JC, Ma XL, Overbury SH, Xu XC, Song CS. Infrared study of CO2 sorption over “Molecular Basket” sorbent consisting of polyethyleniminemodified mesoporous molecular sieve. J Phys Chem C. 2009;113:7260–7268. [44] Sayari A, Gorji AH, Yang Y. CO2 -induced degradation of amine-containing adsorbents: reaction products and pathways. J Am Chem Soc. 2012;134:13834–13842. [45] Ochiai B, Yokota K, Fujii A, Nagai D, Endo T. Reversible trap-release of CO2 by polymers bearing DBU and DBN moieties. Macromolecules. 2008;41:1229– 1236. [46] Xu XC, Song CS, Wincek R, Andresen JM, Miller BG, Scaroni AW. Separation of CO2 from power plant flue gas using a novel CO2 “Molecular Basket” adsorbent. Fuel Chem Div Preprints. 2003;48:162–163. [47] Olah GA, Prakash GKS, Goeppert A. Anthropogenic chemical carbon cycle for a sustainable future. J Am Chem Soc. 2011;133:12881–12898.
Environmental Technology Publication details, including instructions for authors and subscription information: http://www.tandfonline.com/loi/tent20
Preparation and characterization of novel carbon dioxide adsorbents based on polyethyleniminemodified Halloysite nanotubes a
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Haohao Cai , Feng Bao , Jie Gao , Tao Chen , Si Wang & Rui Ma a
Department of Chemistry, Central China Normal University, Wuhan 430079, People's Republic of China b
Engineering Research Center of Nano-Geomaterials of Ministry of Education, China University of Geosciences, Wuhan 430074, People's Republic of China Accepted author version posted online: 10 Nov 2014.Published online: 09 Dec 2014.
Click for updates To cite this article: Haohao Cai, Feng Bao, Jie Gao, Tao Chen, Si Wang & Rui Ma (2015) Preparation and characterization of novel carbon dioxide adsorbents based on polyethylenimine-modified Halloysite nanotubes, Environmental Technology, 36:10, 1273-1280, DOI: 10.1080/09593330.2014.984772 To link to this article: http://dx.doi.org/10.1080/09593330.2014.984772
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Environmental Technology, 2015 Vol. 36, No. 10, 1273–1280, http://dx.doi.org/10.1080/09593330.2014.984772
Preparation and characterization of novel carbon dioxide adsorbents based on polyethylenimine-modified Halloysite nanotubes Haohao Caia , Feng Baoa∗ , Jie Gaoa , Tao Chenb , Si Wangb and Rui Mab∗ a Department of Chemistry, Central China Normal University, Wuhan 430079, People’s Republic of China; b Engineering Research Center of Nano-Geomaterials of Ministry of Education, China University of Geosciences, Wuhan 430074, People’s Republic of China
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(Received 25 February 2014; accepted 26 September 2014 ) New nano-sized carbon dioxide (CO2 ) adsorbents based on Halloysite nanotubes impregnated with polyethylenimine (PEI) were designed and synthesized, which were excellent adsorbents for the capture of CO2 at room temperature and had relatively high CO2 adsorption capacity. The prepared adsorbents were characterized by various techniques such as Fourier transform infrared spectrometry, gel permeation chromatography, dynamic light scattering, thermogravimetry, thermogravimetry-Fourier transform-infrared spectrometry, scanning electron microscopy and transmission electron microscopy. The adsorption characteristics and capacity were studied at room temperature, the highest CO2 adsorption capacity of 156.6 mg/g-PEI was obtained and the optimal adsorption capacity can reach a maximum value of 54.8 mg/gadsorbent. The experiment indicated that this kind of adsorbent has a high stability at 80°C and PEI-impregnated adsorbents showed good reversibility and stability during cyclic adsorption–regeneration tests. Keywords: carbon dioxide; adsorbents; nanotubes; polymer; Halloysite
1. Introduction Recently, amine especially polyamine substance- [1–4] based adsorbents on mesoporous solids or nanoscale particles, such as MCM-41,[5] MCM-48,[6] SBA-15,[7] fumed silica,[8] etc., have attracted much attention on CO2 capture.[9–13] Support such as MCM-41, MCM-48, SBA15 and fumed silica which has larger specific surface area and pore volume can provide more active sites for amine substance to react with more CO2 molecules.[14–17] It is reported that the best result of CO2 absorption capacities for MCM-41-PEI was achieved with MCM-41-PEI containing 75 wt% of polyethylenimine (PEI) with 133 mg CO2 /g-sorbent at 75°C in pure CO2 and fumed silicaPEI-33 has a CO2 absorption capacity of 52 mg/g at room temperature (rt.) from the dry air.[18,19] So far, these kinds of adsorbents have the greatest possibility of practical application in large-scale CO2 capture [20] because of their high adsorption capacities and stable regenerative abilities.[21–25] However, preparation process of these supports is complex, very energy intensive and costly because it involves multistep synthesis, calcination and high-temperature reaction.[5–8,26,27] Halloysite nanotubes (HNTs) [28–31] are a kind of aluminosilicate clays with hollow nanotubular structure (about 20–50 nm in diameter and several hundred nanometres in length) mined from natural deposits and abundant at countries such as China, America, Brazil,
France and so on.[28] They are chemically similar to kaolinite which has relatively high chemical stability with specific surface area of 59.7 m2 /g generally.[31] In recent years, HNTs are used as nanotemplates or nanoscale reaction vessels instead of carbon nanotubes or boron nitride nanotubes and an additive to improve the properties of polymer nanocomposites.[28,32] In this paper, we will introduce a new polyamine-based adsorbent with HNTs support which was easily obtained and cheaper than those based on other supports, the most striking thing is that the adsorbent exhibited relatively high CO2 adsorption capacity from dry air, durable thermostability at desorption temperature and strong regenerative abilities. 2. Experimental section 2.1. Materials HNTs (99.8%) were purchased from Jiuchuan Technology Co. (Jiangsu, China), PEI with a high molecular weight (M w = 17,000, determined by gel permeation chromatography) was purchased from Qianglong New Chem. Mat. Co. (Hubei, China). Hydrochloric acid and methanol were purchased from Kaitong Chemical Reagent. Sodium hexametaphosphate was supplied by Sinopharm Chemical Reagent Co. Ltd. All other chemicals were of analytic grade and redistilled water was used throughout the experiment.
*Corresponding author. Emails: [email protected]; [email protected] © 2014 Taylor & Francis
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2.2. Pretreatment of HNTs The purchased HNTs were purified through a series of procedure before modification. The purchased HNTs were dispersed in a mass fraction 0.3% solution of sodium hexametaphosphate, stirred the mixture for 1 h to get slurry of 15% mass fraction HNTs.[28] Then the slurry was centrifuged at a speed of 3800 r/min for 30 min. The precipitate was removed and the supernatant was filtered to get this part of sediment. The sediment was washed with distilled water several times to remove the sodium hexametaphosphate. In order to remove the fragment in pre-purified HNTs, we dispersed the sediment in distilled water and centrifuged this slurry at a speed of 12,000 r/min for 1 h, then reserved the sediment. The sediment was dried at 95°C for 12 h.[33] Then, the pretreated HNTs with structural integrity and uniform size were obtained. 2.3.
The weight change of the adsorbent was monitored to determine the adsorption and desorption performance of the materials. In a typical adsorption/desorption process, about 10 mg of the adsorbent was placed in a small sample cell, prior to adsorption measurements and the adsorbent was heated up to 80°C under 10−5 bar vacuum to remove adsorbed CO2 and water until there was no noticeable weight loss. Then the temperature was decreased to 25°C and the dry air was introduced at a flow rate of 100 ml/min until there was no obvious weight loss. After the adsorption, the adsorbent was heated to 80°C under 10−5 bar vacuum [18] again to remove adsorbed CO2 completely for another adsorption measurement.[19] Adsorption capacity in mg of adsorbate/g-adsorbent and desorption capacity in percentage were used to evaluate the adsorbent and were calculated from the weight change of the sample in the adsorption/desorption process.
Preparation of HNTs-PEI adsorbents
The PEI-modified HNTs were prepared by a wet impregnation method. In a typical preparation, the desired amount of PEI (viscous liquid) was dissolved in 8 g of methanol under stirring for about 15 min at room temperature in the atmosphere, after which 2 g of purified HNTs was added to the PEI/methanol solution.[34] The resultant slurry was continuously stirred for about 30 min. Then the slurry was dried at 50°C under vacuum on a rotavapor followed by vacuum treatment overnight ( < 1 mmHg).[18] The asprepared adsorbent was denoted as HNTs-PEI-X, where X represents the loading of PEI as weight percentage in the sample. 2.4. Characterization FTIR adsorption was recorded on a Nicolet AVATAR360 instrument. The thermal stability and adsorption capacities were determined by thermogravimetric analysis (TGA) on a PE-TGA 7 thermal gravimeter. Dynamic light scattering (DLS) was conducted by a Britain Malvern Zetasizer ZEN3690 at room temperature. Transmission electron microscopy (TEM) was carried out on a Zeiss EM 912 Omega transmission electron microscope. The N2 adsorption/desorption was carried out on a Quantachrome Autosorb automated adsorption apparatus. Scanning electron microscopy was conducted by a Cambridge S-250MK3 UK microscope with an acceleration voltage of 5.0 kV. Zeta potential was measured by a Britain Malvern Zetasizer, ZEN3690. The thermogravimetryFourier transform-infrared spectrometry spectra were measured on a TG-209/Vector22 apparatus (Netzsch Co., Germany).
2.5. Adsorption and desorption measurement The adsorption and desorption performance of the adsorbents were measured using a PE-TGA 7 thermal analyser.
3. Results and discussion 3.1. Characterization of purified HNTs DLS results indicated that the average size (diameter) of purified HNTs was 427.3 nm, with a polydispersity index of 0.382 in distil water.[35] The TEM image (Figure 1) clearly showed the nanotube structure of purified HNTs, and the hollow lumens were easily observed. And the average inside diameter of these HNTs was approx. 30 nm which can be deduced from Figure 1. The following features are observed in the FTIR spectra of HNTs (Figure 2(a)): a broad, intense band at 3200–3500 cm−1 (O−H stretching vibrations, attributed to crystal water and slight absorbed water), the band at 910 cm−1 (Al−OH bending vibration), narrow bands at 1000–1100 cm−1 (Si−O stretching vibration) and 450–550 cm−1 (Si−O bending vibration).[31,36,37]
Figure 1.
The TEM image of the purified HNTs.
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supports such as fumed silica (approx. 200 m2 /g) [40–42] or MCM-41(approx. 1000 m2 /g).[18] But for effective CO2 absorption, the size of the support as well as its morphology was found to be of greater importance than the surface area of the support, as Olah et al. reported.[40]
In the characterization of thermogravimetry (TG), about 10 mg of the sample was heated at 10°C/min to 600°C in N2 flow (100 ml/min). Figure 3(a) shows the TGA profile of purified HNTs; there was tiny weight loss (about 1%) for HNTs until 100°C as a result of a small number of adsorbed water and free water (negligible gas).[20,38,39] As the CO2 adsorption capacity was calculated by weight loss, the practical adsorption capacity should take into account of lost weight of adsorbed water and free water at the first adsorption–regeneration measurement.[32] The HNTs gradually lost its crystal water with the increase in temperature until 490°C where the crystal structure was destroyed completely. This mass loss is mainly assigned to the dehydroxylation of structural Al−OH groups of HNTs. The result was accordant with the previous reports by Kepert et al.[30] and proved HNTs’ stability under 100°C. As shown in Figure 6, the surface area and pore volume of purified HNTs are 59.7 m2 /g and 0.861 cm3 /g, respectively, and lower than those of other
3.2. Characterization of adsorbents The reaction of PEI with CO2 is represented in different types of amines present in Scheme 1. The repeating unit of the polymer in this scheme is only a simplified model representation showing the three different types of amines present in PEI. The primary and secondary amino groups in PEI react with CO2 to form carbamates. In the presence of water, these carbamates can react further to form a bicarbonate species. In this case, only one amino group is necessary for every CO2 molecule instead of two in the case of carbamate formation in the absence of water.[19] It is reported by Iliuta et al. [42] that only carbamate formation of primary (RNH2 ) and secondary (R2 NH) amines took place through zwitterion (RNH2+ COO− ) formation and carbamate (RNHCOO− ) and protonated amine formation. Tertiary (R3 N) amines would not react with CO2 without water. In this paper, we mainly focus on the CO2 adsorption without water. Figure 2(b) shows the FTIR spectra of adsorbent HNTsPEI-30. According to Giannelis et al.,[36] the bands of PEI in the adsorbent at 3446, 3302 and 1570 cm−1 correspond to the asymmetric and symmetric NH2 stretching vibrations, while bands at 2881, 2814, 1457 and 1346 cm−1 can be due to CH2 vibrations. The absorption bands at 1650, 1540, and 1407 cm−1 can be assigned to N−H deformation in RNH3+ , C=O stretch and NCOO skeletal vibration respectively, due to the formed carbamate.[43] As expected, adsorbent shows characteristic peaks of both the HNTs and PEI, which indicated that PEI-decorated HNTs materials were successfully fabricated. Figures 3(b) and 4 show the TGA profile and the differential thermal gravimetric analysis (DTGA) of the adsorbent (HNTs-PEI-30, contained moisture), respectively. The DTGA of adsorbent indicates two maximum loss ratios at 80°C and 355°C with the loss percentage of 7.73% and 34.1% from TGA. The HNTs-PEI-30 lost its initiatory mass of 7.73% at 80°C, which can be mainly ascribed to the desorption of CO2 and moisture. This was confirmed by FTIR spectrum of gas released out at 80°C of HNTs-PEI30 pyrolysis from Figure 5. This also indirectly indicated that PEI has a low vapour pressure and unlike the commercially used amines such as diethanolamine, which makes
Figure 3. The TGA profiles of purified HNTs and adsorbent.
Scheme 1.
Figure 2. FTIR spectra of HNTs and HNTs-PEI-30.
Reaction of CO2 with amines.
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Figure 4. The DTGA profile of adsorbent.
PEI suitable for long-term use at relatively high temperature. As the adsorbent has a high loss ratio at 80°C and this mass loss mostly belongs to CO2 , we determine it the desorption temperature; while they are 75 and 85°C for MCM-41 and fumed silica supports adsorbents respectively, which can be explained by the uniform dispersion of PEI into the nanoscale-support pores of different sizes, since the melt or decomposition temperature will decrease when the particle size of a substance decreases.[18,19] The PEI of HNTs-PEI-30 began to decompose above 280°C and a sharp weight loss appeared at 355°C which are the start-to-decompose temperature and the maximum loss ratio temperature of PEI, respectively. Both of them were 130 and 150°C higher than other reported startto-decompose temperatures and the maximum loss ratio temperatures, respectively.[44] This may be explained by the opposite potentials between PEI and HNTs and more important high molecular weight. Because the HNTs and PEI in adsorbent had a very strong electrostatic attraction, and PEI with high molecular weight was more stable under high temperature condition which also led adsorbent to higher decomposition temperatures.[18,33] At 600°C the sample lost about 50% weight according to Figure 3(b), which was higher than total approx. 40% weight loss theoretically of designed PEI quantity (30%), complete weight loss of pure HNTs (9%) and captured CO2 (0.5%), the excess weight loss may be due to the absorbed water because polyamine adsorbents with large surface areas absorbed water easily [27] and amino function with water could have absorbed more CO2 as mentioned above.[42] Figure 5 shows the FTIR spectrum at 80, 490 and 600°C of TG. The relevant parameter on TG-209 is corresponding to the parameter on PE-TGA 7. Several representative times at each pyrolysis stage were selected to study the desorption condition and component part of volatiles. At the first stage, about 80°C, HNTs-PEI-30 lost its adsorbed water and free water as HNTs did (see 3700
Figure 5. FTIR spectrum of gas released out at three different times of an HNTs-PEI-30 pyrolysis process.
cm−1 around),[45] besides an amount of CO2 was detected in the volatile based on typical asymmetric stretching vibration (2350 cm−1 around) of CO2 .[21] The peak near 1500 cm−1 belonged to N−H bending vibration which was due to slightly volatile amino.[43] With the increase in the temperature until the second stage, the PEI began to decompose giving rise to the strong peak at 3260 cm−1 (N−H stretching vibration) and the weak peak at 2953 cm−1 (C−H stretching vibration). When the temperature was increased to 490°C, the PEI began decomposing into small molecule compounds which comprised methyl, methylene, amines, water, etc.[21,33,44,46] At about 600°C, the PEI was completely decomposed and removed as volatiles, while the HNTs structure was destroyed and lost the all crystal water.[47] The N2 adsorption/desorption was carried out on a Quantachrome Autosorb automated adsorption apparatus, from which the BET surface area, the pore volume and the pore size were obtained. The sample was out-gassed at 80°C for 48 h on a high vacuum line prior to adsorption. The pore volume of the HNTs was calculated from the adsorbed nitrogen after complete pore condensation (P/P0 = 0.995) using the ratio of the densities of liquid and gaseous nitrogen. The pore size was calculated by using the BJH method. Figure 6 shows the surface areas and pore volumes of HNTs-PEI with different PEI loadings. After the PEI was loaded into its hollow lumen, the pore volume decreased. The pore volume of HNTs-PEI-10 was 0.852 cm3 /g, smaller than that of the HNTs support, which confirmed that PEI was loaded into the HNTs inner lumen.[19] Abnormally with increasing PEI loadings, the pore volume increased slightly from 0.872 cm3 /g of 10% PEI-loading to 0.896 cm3 /g of 20% PEI-loading. This might be due to the
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example, when the PEI loading was 10 wt%, the adsorbent showed a pore volume of 0.852 ml/g, smaller than that of the HNTs support, which confirmed that PEI was loaded into the HNTs’ inner lumens. With increasing PEI loadings, the surface area further decreased. When the PEI loading was higher than 40 wt%, the surface area decreased sharply, which indicated that some of the mesoporous pores [43] were completely filled with PEI. The surface area was only 8.4 m2 /g and the residual pore volume was only 0.378 ml/g for HNTs-PEI-40 at the liquid nitrogen temperature (Table 1).
Figure 6. The surface areas and pore volumes of HNTs-PEI with different PEI loadings.
fact that PEI sticking outside HNTs forms agglomerates with large meso-and macropores. Because of the dispersed state of HNTs, pure HNTs scatter individually, but HNTs coated with PEI cluster and turn into large particles which have higher pore volume, as shown in Figure 6. When PEI is added to HNTs and fills in the inner lumen, the pore volume decreases. As more PEI is added to HNTs, a small portion of PEI that attached outside surface of HNTs made these nanotubes adhere to each other to create more pores (as shown in Scheme 2). With the proportion of PEI scaling up to 30%, the pore volume curved down. When the PEI loading further increased to 40 wt% around, the inner space was completely filled with PEI, restricting the access of nitrogen into the pores at the liquid nitrogen temperature. Therefore, information on the pore volume cannot be obtained from the N2 adsorption/desorption isotherms for PEI loading above 40 wt%.[19,42] The surface area of HNTs, after loading the PEI, exhibited the similar trends as the pore volume. The HNTs support had a surface area of 59.7 m2 /g. The surface area decreased after PEI was loaded into their inner lumens. For
Scheme 2. Schematic diagram of PEI loaded in the HNTs.
Table 1. Surface area, volume of pores and CO2 adsorption capacities to different PEI. PEI loading in adsorbent (%) 0 10 20 30 40
Surface area (m2 /g)
Volume of pores (cm3 /g)
CO2 adsorption capacity (mg/g)
59.7 52.6 40.2 25.9 8.4
0.861 0.852 0.886 0.702 0.378
– 15.3 30.7 48.6 24.3
3.3. Adsorption performance of HNTs-PEI adsorbents The weight of the sample after treatment was used to calculate the CO2 adsorption capacity under the assistance of TGA.[43] The influence of PEI loading on CO2 absorption performance in dry air at 25°C is shown in Figure 8.[44] The physical adsorption of pure HNTs comparing to chemical adsorption of amine adsorbent was so slight that could be negligible. When a small amount of PEI was loaded on HNTs, HNTs with larger specific surface area can provide more contact points for PEI to facilitate the reaction of amine with CO2 . As shown in Figure 8(a), at low PEI loading the linear relationship of adsorption capacity and incremental PEI illustrated the uniform distribution
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3.4.
Figure 8. CO2 adsorption capacity to PEI loading, (a) adsorbents and (b) PEI.
of PEI inside HNTs’ lumens and outside HNTs’ surface quite well, then all the amine group of PEI could effectively combine with CO2 molecule, as given in Scheme 2 (B is 3/4 cross-section of A). The highest CO2 adsorption capacity of 54.8 mg/g-adsorbent (35% PEI) was obtained, which was little higher than that of FS-PEI (33% PEI), as Olah et al. [44] reported earlier. Figure 8 shows the CO2 adsorption capacity in two ways: line (a) presents the adsorption of CO2 per 1 g adsorbent and line (b) presents the adsorption of CO2 per 1 g PEI in adsorbent. Although the surface area and pore volume were inclined to decrease, the absorption capacity increased with the increase in PEI loading as far as 35% PEI loading because incremental PEI could provide more amine groups to capture more CO2 molecules. As mentioned above, the adsorbent of 35% PEI loading performed the maximum adsorption capacity due to both adequate PEI loading and volume pore that the former provided contact points and the latter provided sufficient quantity of CO2 transfer channel (Scheme 2, D is partly zoomin of C). When the PEI loading increased to 40 wt% or higher, PEI filled the lumen completely and blocked the access of CO2 to inner polymer amine. However, excess
Figure 7. (a) The HNTs-PEI cluster and (b) larger HNTs-PEI cluster.
Cyclic adsorption–desorption performance of HNTs-PEI adsorbent For potential practical applications, in addition to high CO2 capturing capacity, the sorbent must possess long-term stability and regenerability with a minimum difference in adsorption/desorption temperatures or pressures, and lower cost. Figure 9 shows the regeneration behaviour of HNTsPEI-30 under the cyclic adsorption–desorption of dry air using a concentration sweep process. After CO2 capture at 25°C, the adsorbent was under 10−5 bar vacuum to remove CO2 at 80°C until there was no noticeable weight loss. The absorption capacity is 53.0 mg/g-adsorbent after 50 absorption–desorption cycles, only slightly lower than the value at the first cycle. The good cyclic performance may
Figure 9. Cyclic adsorption–desorption of HNTs-PEI-30 using a concentration sweep.
Environmental Technology be due to the higher boiling point of PEI, which contributes to better temperature stability.[25,27]
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4.
Conclusion
In conclusion, novel CO2 ‘HNTs-PEI’ adsorbents based on PEI-modified mesoporous compound of HNTs type have been successfully developed. The adsorbent of 35% PEI loading performed the maximum adsorption capacity due to both adequate PEI loading and volume pore that the former provided contact points and the latter provided sufficient quantity of CO2 transfer channel. The highest CO2 adsorption capacity of 156.6 mg/g-PEI was obtained in dry air and the features of long-term stability and regenerability were performed, which meets the demand of industrial application and the source of HNTs can be more environmental than other solid supports. In this paper, we pioneered combining TGA and FTIR spectrometry to investigate the CO2 desorption process for a better understanding how the adsorbate and adsorbent interact and relevant thermodynamic property. Disclosure statement
[8] [9] [10] [11] [12] [13] [14] [15]
[16]
No potential conflict of interest was reported by the author(s).
Funding This work was supported by the Fundamental Research Funds for the Central Universities [grant number CUGL100407 CUGL20118]; the National Natural Science Foundation of China [grant number 41372367]; the Natural Science Foundation of Hubei Province [grant number 2012FFA111], [grant number 2010BFA022] and the public service project of the Chinese Ministry of Land and Resources [grant number 201311024].
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