- Email: [email protected]
Catalytic behavior of graphene oxide for cement hydration process
Journal of Physics and Chemistry of Solids 89 (2016) 128–133
Contents lists available at ScienceDirect
Journal of Physics and Chemistry of Solids journal homepage: www.elsevier.com/locate/jpcs
Catalytic behavior of graphene oxide for cement hydration process Changqing Lin a,b, Wei Wei a, Yun Hang Hu a,n a b
Department of Materials Science and Engineering, Michigan Technological University, 1400 Townsend Drive, Houghton, MI 49931-1295, USA Department of electrical and Mechanical Engineering, Qiqihar Institute of Technology, Qiqihar, Heilongjiang, 161005, PR China
art ic l e i nf o
a b s t r a c t
Article history: Received 23 September 2015 Received in revised form 30 October 2015 Accepted 2 November 2015 Available online 10 November 2015
Hydration is a critical step that determines the performance of cement-based materials. In this paper, the effect of GO on the hydration of cement was evaluated by XRD and FTIR. It was found that GO can remarkably accelerate the hydration rate of cement due to its catalytic behavior. This happened because the oxygen-containing functional groups of GO provide adsorption sites for both water molecules and cement components. & 2015 Elsevier Ltd. All rights reserved.
Keywords: Graphene oxide Concrete Hydration Catalysis
1. Introduction Cement composites are the most important and most abundant building material [1,2]. Concrete is a composite material (primarily of cement, sand, and water) with nano-structures and multiphases. As an important engineering material, concrete possesses an excellent compressive strength. However, it suffers several issues, such as brittle nature due to its poor resistance to crack formation, low tensile strength, and strain capacities. Many efforts have been made to enhance the performance of cement-based materials by manipulating their properties with admixtures [3–6], supplementary cementitious materials [7–10], and fibers [11,12]. Progress in nanomaterials created invaluable opportunities to enhance the performance of cementitious composites. The incorporation of nanomaterial additions as partial replacement for cement can improve the properties of the high-strength and especially ultrahigh-performance concrete with relatively highcementitious binder content and high-lacking density, producing better dispersion and interaction of the reinforcement systems and achieving significantly higher mechanical strength and durability [13]. Carbon based materials have drawn attention and were incorporated in the cement matrix for strengthening. Carbon nanotubes and nanofibers were explored as promising promoters for reinforcements in cement-based materials at nanoscale [14]. Graphene, which consists of a one-atom-thick planar sheet n
Corresponding author. E-mail address: [email protected] (Y.H. Hu).
http://dx.doi.org/10.1016/j.jpcs.2015.11.002 0022-3697/& 2015 Elsevier Ltd. All rights reserved.
comprising a sp2-bonded carbon structure with exceptionally high crystal and electronic quality, is a novel material that has emerged as a rapidly rising star in the field of material science [15–18]. Graphene oxide (GO) has unique properties, such as a very high surface area [16], surface functionalization [16], and good dispersibility in aqueous solvents [17,18]. GO sheets bear various oxygen-containing groups, mainly epoxides and hydroxyls on their basal planes and carboxyls on the edges, which can facilitate the dispersion of GO in water [19,20]. Therefore, GO has been accepted as an efficient agent to improve the interfacial properties between fiber and matrix [21]. It was reported that small content (0.01– 0.06%) of GO can remarkably improve compressive strength of concrete [22–24]. Recently, our group found that the mixture of graphene oxide (GO) sheets and single-walled carbon nanotubes (SWCNTs) exhibited an excellent co-effect, leading to 72.7% increase in bending strength of cement, which is much higher than the strength enhancements of 51.2% by GO and 26.3% by SWCNTs [25]. It is well-known that the structure and properties of concrete are strongly dependent on hydration reactions of major components (silicates and aluminates of calcium) in the cement [26–29], producing complex products, such as calcium hydroxide (CH), ettringite (AFt), and monosulfates (AFm). Furthermore, the contents and crystal shapes of those hydrates determine the final strength of concrete [30]. However, a little effort was made to explore the effect of GO on the cement hydration. In this paper, we report that GO can play a catalytic role for the hydration process of cement, which can remarkably accelerate the production of hydrates.
C. Lin et al. / Journal of Physics and Chemistry of Solids 89 (2016) 128–133
129
Fig. 1. (A) XRD pattern of graphene oxide and (B) TEM image of graphene oxide sheets.
Fig. 2. (A) XRD patterns of concrete nanocomposites without GO and with 0.5 wt% GO at 10 min and (B) FTIR spectra of concrete nanocomposites without GO and with 0.5 wt%, 1.5 wt%, and 2.5 wt% GO at 10 min.
2. Experimental 2.1. Materials Portland cement type II (No. 1124), which was used in this work, consists typically of 51% tricalcium silicate (C3S), 24% dicalcium silicate (C2S), 6% dicalcium aluminate (C3A), 11% tetracalcium aluminoferrite (C4AF), 2.9% MgO, 2.5% SO3, 0.8% Ignition loss, and 1.0% CaO. Graphene oxide (GO) was synthesized from graphite powders (Sigma-Aldrich) with the modified Hummers method described as follows [31,32]: potassium permanganate (3 g) was added into the mixture of graphite (0.5 g), sodium nitrate (0.5 g), and sulfuric acid (25 mL) at room temperature, followed by heating to 35 °C with a water-bath and then stirring at 35 °C for 5 h to form a thick paste. Deionized water (40 mL) was added into the thick paste with stirring, followed by heating to 90 °C over 30 min, then adding more deionized water (100 mL), and finally gradually adding 10 mL of H2O2 (30%). The obtained sample was filtered and washed with 100 mL of deionized water. The filter sediment was dispersed in deionized water again, followed by
ultrasonic treatment for 24 h and then centrifugal treatment to separate the solid from the water. The obtained solid sample of graphite oxide was dried in a vacuum furnace at 50 °C. The asprepared graphite oxide was re-dissolved in deionized water, followed by ultrasonic treatment (for 48 h) to achieve full exfoliation from graphite oxide to graphene oxide (GO).
2.2. Concrete sample preparation Four concrete samples were prepared by mixing 40 g cement, 120 g stand sand, 12 g water, and 4 g polycarboxylate superplasticizer (PC) solution (that contains 0, 0.5, 1.5, and 2.5 wt% GO, respectively) as follows: GO was suspended in distilled water and sonicated for 3 h until the homogeneous solution was obtained. Then, polycarboxylate superplasticizer (PC), which is an indispensably admixture for a cement composite to reduce water consumption without losing fluidity of the cement paste, was added to the mixture. The water to cement ratio was kept the same. Finally, the cement and sand were added.
130
C. Lin et al. / Journal of Physics and Chemistry of Solids 89 (2016) 128–133
Fig. 3. FTIR spectra of concrete composite with (A) 0.5 wt% GO, (B) 1.5 wt% GO, and (C) 2.5 wt% GO with/without water content.
C. Lin et al. / Journal of Physics and Chemistry of Solids 89 (2016) 128–133
131
Fig. 4. XRD patterns of concrete nanocomposites at different hydration time. (A) Without GO; (B) with 0.5 wt% GO; (C) with 1.5 wt% GO, and (D) with 2.5 wt% GO.
Fig. 5. IR spectra of concrete nanocomposites at different hydration time. (A) Without GO; (B) with 0.5 wt% GO; (C) with 1.5 wt% GO, and (D) with 2.5 wt% GO.
Fig. 6. Schematic diagram of catalytic mechanism of GO for cement hydration.
2.3. Material characterization The composition of GO sheets was evaluated by Elemental Analysis (Control Equipment Corporation, Model 240XA). GO surface area was measured with a Micromeritics ASAP 2000 adsorption instrument using nitrogen adsorption at liquid-nitrogen temperature (77 K). Before nitrogen adsorption measurement, the sample was degassed at 100 °C. Furthermore, microstructures of GO sheets were examined by JEOL JEM-2010F transmission electron microscopy (TEM). Fourier transform infrared (FTIR) spectra of GO sheets were obtained using FT/IR-4200 spectrometer. Crystal structures of cement composites were determined by using Scintag XDS 2000 powder diffractometer with Cu Kα (λ ¼1.5406 Å) radiation at a scan speed of 1°/min and a step size of 0.03°.
3. Results and discussion Graphene oxide (GO), which is a layered material with rich oxygen functional groups, was prepared by oxidizing graphite with modified Hummers method. The elemental analysis revealed that the obtained GO contains about 64 mol% carbon and 36 mol% oxygen. The oxygen-containing functional groups of GO constitute its ability to absorb water molecules. Furthermore, as shown in Fig. 1A, one can see two broad peaks at about 23° and 43°
corresponding to the (002) and (100) plane reflections in the X-ray diffraction patterns of GO. The interlayer distance for graphene oxide is 0.39 nm, which is significantly larger than that 0.335 nm for pristine graphite. This is due to the intercalating oxide functional groups. The morphology of the graphene oxide was analyzed with transmission electron microscopy (TEM). GO is a wrinkled layer, which can be attributed to effective exfoliation of graphite oxide (Fig. 1B). Furthermore, GO (as a two dimensional nanosheets) possesses a high surface area of 103 m2/g, which provides significant contact area with the cement material. Cement in unhydrous state mainly consists of tricalcium silicate C3S (Ca3SiO5), dicalcium silicate C2S (Ca2SiO4), tricalcium aluminate C3A (Ca3Al2O6), and tetracalcium aluminoferrite C4AF (Ca4Aln Fe2 nO7) as well as small amount of gypsum (CaSO4 2H2O). In the hydration process, C3A, C4AF, C3S, and C2S react with water to form ettringite (Ca6Al2(SO4)3(OH)12 26H2O, Aft), calcium hydroxide (Ca(OH)2, CH), and calcium silicate hydrate (3CaO 2SiO2 4H2O, C–S–H) gel, which can be briefly described by the following equations: 3CaO Al2O3 þ3(CaSO4 2H2O) þ26H2O3CaO 3Al2O3 3CaSO4 32H2O
(1)
2(3CaO SiO2)þ6H2O-3CaO 2SiO2 3H2O þ3Ca(OH)2
(2)
2(2CaO SiO2)þ4H2O-3CaO 2SiO2 3H2O þCa(OH)2
(3)
132
C. Lin et al. / Journal of Physics and Chemistry of Solids 89 (2016) 128–133
To evaluate the effect of GO on the hydration of concrete composite, the concrete matrices were subjected to XRD measurements. The content of calcium hydroxide (a major crystalline phase) was used as the degree of hydration. The peaks for portlandite (C–H or Ca(OH)2) appear at positions of 18.2°, 34.2°, 47.1°, and 50.1° (Fig. 2A). The introduction of GO into the concrete remarkably increased the intensities of the peaks corresponding to C–H crystals even in the first 10 min, indicating that GO accelerated the hydration of cement. Furthermore, the sizes of crystal C–H particles, which were calculated from XRD peak widths at half-height using Debye–Scherrer equation, are 175 and 95 nm for concretes with and without 0.5 wt% GO, respectively. This indicates that GO can remarkably enhance the formation of nucleus and the crystal growth of C–H particles. Functional groups in GO were evaluated using FTIR spectroscopy. As shown in Fig. 2B, an absorption peak for the –C¼ C– stretch was observed at 1629 cm 1, indicating alkenic bonds in GO. Hydroxyl groups (–OH) and carbonyl groups (C ¼O) were also present with peaks at 3300 and 1735 cm 1, respectively, confirming the –COOH group. A peak at 937 cm 1 is characteristic of the C–O stretch in epoxides, which was further supported by the absorption peak at 1026 cm 1. These results were consistent with incorporated oxygen-containing functional groups in the GO nanosheets reported in literature [33–36]. These oxygen functional groups rendered layers of GO hydrophilic and provide effective sites for further functionalization to enhance properties such as charges and interactions with water [37–39]. Furthermore, the band at 970 cm 1 is assigned to C–S–H gel [40–41]. Characteristic sulfate absorption bands are generally found in the range 1100–1200 cm 1 due to the u3 vibration of the SO42 group in sulfates [42–44]. Increase in GO content enhanced the peak intensity, which can further confirm that GO can accelerate the hydration reaction. The hydration process was monitored by XRD and FTIR for 120 h. The recorded spectra of dry and hydrated concrete are displayed in Fig. 3. We can observe the development and saturation of the band (at 1100–1200 cm 1) of hydrated samples. The oxygen functional groups of GO remain unchanged with the hydration time for all cases. This indicates that the hydration of cement in the GO/cement composites did not cause any change in GO functional groups. In other words, the acceleration of hydration by GO suggests that GO would be a catalyst instead of a reactant for the cement hydration. This can be further supported by the relationship between GO content and hydrate production. As shown in Figs. 4 and 5, one can see that the content of hydrates (Aft, CH, and C–S–H) increased not only with increasing hydration time, but also with increasing concentration of GO in the concrete matrix. This catalytic behavior of GO for cement hydration can be explained as follows (Fig. 6): The surface of GO possesses rich oxygen functional groups (mainly –OH and –COOH). Those oxygen-containing groups have two main functions: (1) the active functional groups would be active sites to interact with cement, and (2) the functional groups can absorb water molecules, generating a water reservoir and water transport channels. When GO was highly dispersed in cement, C3A, C4AF, C3S, and C2S should have a strong interaction with oxygen-containing functional groups of GO, namely, GO-connected components (C3A, C4AF, C3S, and C2S) of cement can easily react with water molecules adsorbed on functional groups of GO, forming crystal nucleuses of hydrates. Furthermore, water molecules on GO constitute a water reservoir and thus water transport channels for the hydration of C3A, C4AF, C3S, and C2S, accelerating the hydration rate.
4. Conclusions The effect of GO on the hydration of cement was evaluated by XRD and FTIR. It was found that GO played a catalytic role in the hydration of cement. This happened because (1) the oxygen-containing function groups provide adsorption sites for water and cement, leading to the crystal nucleuses for cement hydrates; and (2) water molecules on GO constitute a water reservoir and water transport channels for further hydration of cement. This would provide a novel approach to promote the hydration of cement.
Acknowledgment This work was supported by the ACS Petroleum Research Fund (PRF-51799-ND10). The author also thanks Charles and Carroll McArthur for their great support.
References [1] S. Chakraborty, S.P. Kundu, A. Roy, B. Adhikari, S.B. Majumder, Ind. Eng. Chem. Res. 52 (2013) 1252–1260. [2] S.L. Xu, B.W. Zhang, Z.R. Chen, J.H. Yu, D.G. Evans, F.Z. Zhang, Ind. Eng. Chem. Res. 50 (2011) 6567–6572. [3] S. Hanehara, K. Yamada, Cem. Concr. Res. 29 (1999) 1159–1165. [4] K. Jae Hong, M. Beacraft, S.P. Shah, Cem. Concr. Compos. 32 (2010) 665–671. [5] M.-H. Zhang, K. Sisomphon, T.S. Ng, D.J. Sun, Constr. Build. Mater. 24 (2010) 1700–1707. [6] J. Cheung, A. Jeknavorian, L. Roberts, D. Silva, Cem. Concr. Res. 41 (2011) 1289–1309. [7] B. Lothenbach, K. Scrivener, R.D. Hooton, Cem. Concr. Res. 41 (2011) 217–229. [8] K. Sobolev, Cem. Concr. Compos. 27 (2005) 848–853. [9] C. Shi, J. Qian, Resour. Conserv. Recycl. 29 (2000) 195–207. [10] M. Sahmaran, H.A. Christianto, I.O. Yaman, Cem. Concr. Compos. 28 (2006) 432–440. [11] S.P. Shah, O. Chengsheng, J. Am. Ceram. Soc. 74 (1991) 2727–2738. [12] J.-Y. Wang, N. Banthia, M.-H. Zhang, Cem. Concr. Compos. 34 (2012) 443–450. [13] K. Wille, A.E. Naaman, S. El-Tawil, G.J. Parra-Montesinos, Mater. Struct. 45 (2012) 309–324. [14] G.Y. Li, P.M. Wang, X. Zhao, Cem. Concr. Compos. 29 (2007) 377–382. [15] (a) H. Wang, K. Sun, F. Tao, D.J. Stacchiola, Y.H. Hu, Angew. Chem. Int. Ed. 52 (2013) 9210–9214; (b) H. Wang, Y.H. Hu, Energy Env. Sci. 5 (2012) 8182–8188; (c) L. Chang, W. Wei, K. Sun, Y.H. Hu, J. Mater. Chem. A 3 (2015) 10183–10187; (d) W. Wei, K. Sun, Y.H. Hu, J. Mater. Chem. A 2 (2014) 16842–16846. [16] (a) Y.W. Zhu, S. Murali, W.W. Cai, X.S. Li, J.W. Suk, J.R. Potts, R.S. Ruoff, Adv. Mater. 22 (2010) 3906–3924; (b) S. Stankovich, D.A. Dikin, R.D. Piner, K.A. Kohlhaas, A. Kleinhammes, Y. Jia, Y. Wu, S.T. Nguyen, R.S. Ruoff, Carbon 45 (2007) 1558–1665. [17] D. Konios, M.M. Stylianakis, E. Stratakis, E. Kymakis, J. Colloid Interface Sci. 430 (2014) 108–112. [18] J.I. Paredes, S. Villar-Rodil, A. Martinea-Alonso, J.M.D. Tascon, Langmuir 24 (2008) 10560–10564. [19] Z. Tang, H. Kang, Z. Shen, B. Guo, L. Zhang, D. Jia, Macromolecules 45 (2012) 3444–3445. [20] D.R. Dreyer, S. Park, C.W. Bielawski, R.S. Ruoff, Chem. Soc. Rev. 39 (2010) 228–240. [21] J. Chen, D. Zhao, X. Jin, C. Wang, D. Wang, H. Ge, Compos. Sci. Technol. 97 (2014) 41–45. [22] S. Lv, Y. Ma, C. Qiu, T. Sun, J. Liu, Q. Zhou, Constr. Build. Mater. 49 (2013) 121–127. [23] S. Chual, Z. Pan, J.G. Sanjayan, C.M. Wang, W.H. Duan, Constr. Build. Mater. 73 (2014) 113–124. [24] H. Alkhateb, A. Al-Ostaz, A.H.-D. Cheng, X.B. Li, J. Nanomech, Micromech 3 (2013) 67–77. [25] X. Li, W. Wei, H. Qin, Y.H. Hu, J. Phys. Chem. Solids 85 (2015) 39–43. [26] S. Chakraborty, S.P. Kundu, A. Roy, B. Adhikari, S.B. Majumder, Ind. Eng. Chem. Res. 52 (2013) 1252–1260. [27] M.S. Konsta-Gdoutos, Z.S. Metaxa, S.P. Shah, Cem. Concr. Res. 40 (2010) 1052–1059. [28] R. Alizadeh, J.J. Beaudoin, Mater. Struct. 44 (2011) 13–28. [29] M. Atkins, F. Glasser, A. Kindness, Cem. Concr. Res. 22 (1992) 241–246. [30] A. Goldman, A. Bentur, Cem. Concr. Res. 23 (1993) 962–972. [31] W. Hummers, R. Offeman, J. Am. Chem. Soc. 80 (1958) 1339. [32] (a) H. Wang, Y.H. Hu, J. Colloid Interface Sci. 391 (2013) 21–27; (b) H. Wang, Y.H. Hu, Ind. Eng. Chem. Res. 50 (2011) 6132–6137.
C. Lin et al. / Journal of Physics and Chemistry of Solids 89 (2016) 128–133
[33] S. Sharma, N.C. Kothiyal, RSC Adv. 5 (2015) 52642–52657. [34] X. Sun, Z. Liu, K. Welsher, J.T. Robinson, A. Goodwin, S. Zaric, H. Dai, Nano Res. 1 (2008) 203–212. [35] G. Wang, B. Wang, J. Park, J. Yang, X. Shen, J. Yao, Carbon 47 (2009) 68–72. [36] J.I. Paredes, S. Villar-Rodil, A. Martinez-Alonso, J.M.D. Tascon, Langmuir 24 (2008) 10560–10564. [37] H. He, J. Klinowski, M. Forster, A. Lerf, Chem. Phys. Lett. 287 (1998) 53–56. [38] H. He, T. Riedl, A. Lerf, J. Klinowski, J. Phys. Chem. 100 (100) (1996) 19954–19958. [39] A. Buchsteiner, A. Lerf, J. Pieper, J. Phys. Chem. B 110 (2006) 22328–22338.
133
[40] I. García-Lodeiro, A. Fernández-Jiménez, M.T. Blanco, A. Palomo, J. Sol–Gel Sci. Technol. 45 (2008) 63–72. [41] P. Yu, R.J. Kirkpatrick, B. Poe, P.F. McMillan, J.X. Cong, J. Am. Ceram. Soc. 82 (1999) 742–748. [42] M.Y.A. Mollah, W. Yu, R. Schennach, D.L. Cocke, Cem. Concr. Res. 30 (2000) 267–273. [43] T.L. Hughes, C.M. Methven, T.G.J. Jones, S.E. Pelham, P. Fleccher, C. Hall, Adv. Cem. Based Mater. 2 (1995) 91–104. [44] S.N. Ghosh, S.K. Handoo, Cem. Concr. Res. 10 (1980) 771–778.
Contents lists available at ScienceDirect
Journal of Physics and Chemistry of Solids journal homepage: www.elsevier.com/locate/jpcs
Catalytic behavior of graphene oxide for cement hydration process Changqing Lin a,b, Wei Wei a, Yun Hang Hu a,n a b
Department of Materials Science and Engineering, Michigan Technological University, 1400 Townsend Drive, Houghton, MI 49931-1295, USA Department of electrical and Mechanical Engineering, Qiqihar Institute of Technology, Qiqihar, Heilongjiang, 161005, PR China
art ic l e i nf o
a b s t r a c t
Article history: Received 23 September 2015 Received in revised form 30 October 2015 Accepted 2 November 2015 Available online 10 November 2015
Hydration is a critical step that determines the performance of cement-based materials. In this paper, the effect of GO on the hydration of cement was evaluated by XRD and FTIR. It was found that GO can remarkably accelerate the hydration rate of cement due to its catalytic behavior. This happened because the oxygen-containing functional groups of GO provide adsorption sites for both water molecules and cement components. & 2015 Elsevier Ltd. All rights reserved.
Keywords: Graphene oxide Concrete Hydration Catalysis
1. Introduction Cement composites are the most important and most abundant building material [1,2]. Concrete is a composite material (primarily of cement, sand, and water) with nano-structures and multiphases. As an important engineering material, concrete possesses an excellent compressive strength. However, it suffers several issues, such as brittle nature due to its poor resistance to crack formation, low tensile strength, and strain capacities. Many efforts have been made to enhance the performance of cement-based materials by manipulating their properties with admixtures [3–6], supplementary cementitious materials [7–10], and fibers [11,12]. Progress in nanomaterials created invaluable opportunities to enhance the performance of cementitious composites. The incorporation of nanomaterial additions as partial replacement for cement can improve the properties of the high-strength and especially ultrahigh-performance concrete with relatively highcementitious binder content and high-lacking density, producing better dispersion and interaction of the reinforcement systems and achieving significantly higher mechanical strength and durability [13]. Carbon based materials have drawn attention and were incorporated in the cement matrix for strengthening. Carbon nanotubes and nanofibers were explored as promising promoters for reinforcements in cement-based materials at nanoscale [14]. Graphene, which consists of a one-atom-thick planar sheet n
Corresponding author. E-mail address: [email protected] (Y.H. Hu).
http://dx.doi.org/10.1016/j.jpcs.2015.11.002 0022-3697/& 2015 Elsevier Ltd. All rights reserved.
comprising a sp2-bonded carbon structure with exceptionally high crystal and electronic quality, is a novel material that has emerged as a rapidly rising star in the field of material science [15–18]. Graphene oxide (GO) has unique properties, such as a very high surface area [16], surface functionalization [16], and good dispersibility in aqueous solvents [17,18]. GO sheets bear various oxygen-containing groups, mainly epoxides and hydroxyls on their basal planes and carboxyls on the edges, which can facilitate the dispersion of GO in water [19,20]. Therefore, GO has been accepted as an efficient agent to improve the interfacial properties between fiber and matrix [21]. It was reported that small content (0.01– 0.06%) of GO can remarkably improve compressive strength of concrete [22–24]. Recently, our group found that the mixture of graphene oxide (GO) sheets and single-walled carbon nanotubes (SWCNTs) exhibited an excellent co-effect, leading to 72.7% increase in bending strength of cement, which is much higher than the strength enhancements of 51.2% by GO and 26.3% by SWCNTs [25]. It is well-known that the structure and properties of concrete are strongly dependent on hydration reactions of major components (silicates and aluminates of calcium) in the cement [26–29], producing complex products, such as calcium hydroxide (CH), ettringite (AFt), and monosulfates (AFm). Furthermore, the contents and crystal shapes of those hydrates determine the final strength of concrete [30]. However, a little effort was made to explore the effect of GO on the cement hydration. In this paper, we report that GO can play a catalytic role for the hydration process of cement, which can remarkably accelerate the production of hydrates.
C. Lin et al. / Journal of Physics and Chemistry of Solids 89 (2016) 128–133
129
Fig. 1. (A) XRD pattern of graphene oxide and (B) TEM image of graphene oxide sheets.
Fig. 2. (A) XRD patterns of concrete nanocomposites without GO and with 0.5 wt% GO at 10 min and (B) FTIR spectra of concrete nanocomposites without GO and with 0.5 wt%, 1.5 wt%, and 2.5 wt% GO at 10 min.
2. Experimental 2.1. Materials Portland cement type II (No. 1124), which was used in this work, consists typically of 51% tricalcium silicate (C3S), 24% dicalcium silicate (C2S), 6% dicalcium aluminate (C3A), 11% tetracalcium aluminoferrite (C4AF), 2.9% MgO, 2.5% SO3, 0.8% Ignition loss, and 1.0% CaO. Graphene oxide (GO) was synthesized from graphite powders (Sigma-Aldrich) with the modified Hummers method described as follows [31,32]: potassium permanganate (3 g) was added into the mixture of graphite (0.5 g), sodium nitrate (0.5 g), and sulfuric acid (25 mL) at room temperature, followed by heating to 35 °C with a water-bath and then stirring at 35 °C for 5 h to form a thick paste. Deionized water (40 mL) was added into the thick paste with stirring, followed by heating to 90 °C over 30 min, then adding more deionized water (100 mL), and finally gradually adding 10 mL of H2O2 (30%). The obtained sample was filtered and washed with 100 mL of deionized water. The filter sediment was dispersed in deionized water again, followed by
ultrasonic treatment for 24 h and then centrifugal treatment to separate the solid from the water. The obtained solid sample of graphite oxide was dried in a vacuum furnace at 50 °C. The asprepared graphite oxide was re-dissolved in deionized water, followed by ultrasonic treatment (for 48 h) to achieve full exfoliation from graphite oxide to graphene oxide (GO).
2.2. Concrete sample preparation Four concrete samples were prepared by mixing 40 g cement, 120 g stand sand, 12 g water, and 4 g polycarboxylate superplasticizer (PC) solution (that contains 0, 0.5, 1.5, and 2.5 wt% GO, respectively) as follows: GO was suspended in distilled water and sonicated for 3 h until the homogeneous solution was obtained. Then, polycarboxylate superplasticizer (PC), which is an indispensably admixture for a cement composite to reduce water consumption without losing fluidity of the cement paste, was added to the mixture. The water to cement ratio was kept the same. Finally, the cement and sand were added.
130
C. Lin et al. / Journal of Physics and Chemistry of Solids 89 (2016) 128–133
Fig. 3. FTIR spectra of concrete composite with (A) 0.5 wt% GO, (B) 1.5 wt% GO, and (C) 2.5 wt% GO with/without water content.
C. Lin et al. / Journal of Physics and Chemistry of Solids 89 (2016) 128–133
131
Fig. 4. XRD patterns of concrete nanocomposites at different hydration time. (A) Without GO; (B) with 0.5 wt% GO; (C) with 1.5 wt% GO, and (D) with 2.5 wt% GO.
Fig. 5. IR spectra of concrete nanocomposites at different hydration time. (A) Without GO; (B) with 0.5 wt% GO; (C) with 1.5 wt% GO, and (D) with 2.5 wt% GO.
Fig. 6. Schematic diagram of catalytic mechanism of GO for cement hydration.
2.3. Material characterization The composition of GO sheets was evaluated by Elemental Analysis (Control Equipment Corporation, Model 240XA). GO surface area was measured with a Micromeritics ASAP 2000 adsorption instrument using nitrogen adsorption at liquid-nitrogen temperature (77 K). Before nitrogen adsorption measurement, the sample was degassed at 100 °C. Furthermore, microstructures of GO sheets were examined by JEOL JEM-2010F transmission electron microscopy (TEM). Fourier transform infrared (FTIR) spectra of GO sheets were obtained using FT/IR-4200 spectrometer. Crystal structures of cement composites were determined by using Scintag XDS 2000 powder diffractometer with Cu Kα (λ ¼1.5406 Å) radiation at a scan speed of 1°/min and a step size of 0.03°.
3. Results and discussion Graphene oxide (GO), which is a layered material with rich oxygen functional groups, was prepared by oxidizing graphite with modified Hummers method. The elemental analysis revealed that the obtained GO contains about 64 mol% carbon and 36 mol% oxygen. The oxygen-containing functional groups of GO constitute its ability to absorb water molecules. Furthermore, as shown in Fig. 1A, one can see two broad peaks at about 23° and 43°
corresponding to the (002) and (100) plane reflections in the X-ray diffraction patterns of GO. The interlayer distance for graphene oxide is 0.39 nm, which is significantly larger than that 0.335 nm for pristine graphite. This is due to the intercalating oxide functional groups. The morphology of the graphene oxide was analyzed with transmission electron microscopy (TEM). GO is a wrinkled layer, which can be attributed to effective exfoliation of graphite oxide (Fig. 1B). Furthermore, GO (as a two dimensional nanosheets) possesses a high surface area of 103 m2/g, which provides significant contact area with the cement material. Cement in unhydrous state mainly consists of tricalcium silicate C3S (Ca3SiO5), dicalcium silicate C2S (Ca2SiO4), tricalcium aluminate C3A (Ca3Al2O6), and tetracalcium aluminoferrite C4AF (Ca4Aln Fe2 nO7) as well as small amount of gypsum (CaSO4 2H2O). In the hydration process, C3A, C4AF, C3S, and C2S react with water to form ettringite (Ca6Al2(SO4)3(OH)12 26H2O, Aft), calcium hydroxide (Ca(OH)2, CH), and calcium silicate hydrate (3CaO 2SiO2 4H2O, C–S–H) gel, which can be briefly described by the following equations: 3CaO Al2O3 þ3(CaSO4 2H2O) þ26H2O3CaO 3Al2O3 3CaSO4 32H2O
(1)
2(3CaO SiO2)þ6H2O-3CaO 2SiO2 3H2O þ3Ca(OH)2
(2)
2(2CaO SiO2)þ4H2O-3CaO 2SiO2 3H2O þCa(OH)2
(3)
132
C. Lin et al. / Journal of Physics and Chemistry of Solids 89 (2016) 128–133
To evaluate the effect of GO on the hydration of concrete composite, the concrete matrices were subjected to XRD measurements. The content of calcium hydroxide (a major crystalline phase) was used as the degree of hydration. The peaks for portlandite (C–H or Ca(OH)2) appear at positions of 18.2°, 34.2°, 47.1°, and 50.1° (Fig. 2A). The introduction of GO into the concrete remarkably increased the intensities of the peaks corresponding to C–H crystals even in the first 10 min, indicating that GO accelerated the hydration of cement. Furthermore, the sizes of crystal C–H particles, which were calculated from XRD peak widths at half-height using Debye–Scherrer equation, are 175 and 95 nm for concretes with and without 0.5 wt% GO, respectively. This indicates that GO can remarkably enhance the formation of nucleus and the crystal growth of C–H particles. Functional groups in GO were evaluated using FTIR spectroscopy. As shown in Fig. 2B, an absorption peak for the –C¼ C– stretch was observed at 1629 cm 1, indicating alkenic bonds in GO. Hydroxyl groups (–OH) and carbonyl groups (C ¼O) were also present with peaks at 3300 and 1735 cm 1, respectively, confirming the –COOH group. A peak at 937 cm 1 is characteristic of the C–O stretch in epoxides, which was further supported by the absorption peak at 1026 cm 1. These results were consistent with incorporated oxygen-containing functional groups in the GO nanosheets reported in literature [33–36]. These oxygen functional groups rendered layers of GO hydrophilic and provide effective sites for further functionalization to enhance properties such as charges and interactions with water [37–39]. Furthermore, the band at 970 cm 1 is assigned to C–S–H gel [40–41]. Characteristic sulfate absorption bands are generally found in the range 1100–1200 cm 1 due to the u3 vibration of the SO42 group in sulfates [42–44]. Increase in GO content enhanced the peak intensity, which can further confirm that GO can accelerate the hydration reaction. The hydration process was monitored by XRD and FTIR for 120 h. The recorded spectra of dry and hydrated concrete are displayed in Fig. 3. We can observe the development and saturation of the band (at 1100–1200 cm 1) of hydrated samples. The oxygen functional groups of GO remain unchanged with the hydration time for all cases. This indicates that the hydration of cement in the GO/cement composites did not cause any change in GO functional groups. In other words, the acceleration of hydration by GO suggests that GO would be a catalyst instead of a reactant for the cement hydration. This can be further supported by the relationship between GO content and hydrate production. As shown in Figs. 4 and 5, one can see that the content of hydrates (Aft, CH, and C–S–H) increased not only with increasing hydration time, but also with increasing concentration of GO in the concrete matrix. This catalytic behavior of GO for cement hydration can be explained as follows (Fig. 6): The surface of GO possesses rich oxygen functional groups (mainly –OH and –COOH). Those oxygen-containing groups have two main functions: (1) the active functional groups would be active sites to interact with cement, and (2) the functional groups can absorb water molecules, generating a water reservoir and water transport channels. When GO was highly dispersed in cement, C3A, C4AF, C3S, and C2S should have a strong interaction with oxygen-containing functional groups of GO, namely, GO-connected components (C3A, C4AF, C3S, and C2S) of cement can easily react with water molecules adsorbed on functional groups of GO, forming crystal nucleuses of hydrates. Furthermore, water molecules on GO constitute a water reservoir and thus water transport channels for the hydration of C3A, C4AF, C3S, and C2S, accelerating the hydration rate.
4. Conclusions The effect of GO on the hydration of cement was evaluated by XRD and FTIR. It was found that GO played a catalytic role in the hydration of cement. This happened because (1) the oxygen-containing function groups provide adsorption sites for water and cement, leading to the crystal nucleuses for cement hydrates; and (2) water molecules on GO constitute a water reservoir and water transport channels for further hydration of cement. This would provide a novel approach to promote the hydration of cement.
Acknowledgment This work was supported by the ACS Petroleum Research Fund (PRF-51799-ND10). The author also thanks Charles and Carroll McArthur for their great support.
References [1] S. Chakraborty, S.P. Kundu, A. Roy, B. Adhikari, S.B. Majumder, Ind. Eng. Chem. Res. 52 (2013) 1252–1260. [2] S.L. Xu, B.W. Zhang, Z.R. Chen, J.H. Yu, D.G. Evans, F.Z. Zhang, Ind. Eng. Chem. Res. 50 (2011) 6567–6572. [3] S. Hanehara, K. Yamada, Cem. Concr. Res. 29 (1999) 1159–1165. [4] K. Jae Hong, M. Beacraft, S.P. Shah, Cem. Concr. Compos. 32 (2010) 665–671. [5] M.-H. Zhang, K. Sisomphon, T.S. Ng, D.J. Sun, Constr. Build. Mater. 24 (2010) 1700–1707. [6] J. Cheung, A. Jeknavorian, L. Roberts, D. Silva, Cem. Concr. Res. 41 (2011) 1289–1309. [7] B. Lothenbach, K. Scrivener, R.D. Hooton, Cem. Concr. Res. 41 (2011) 217–229. [8] K. Sobolev, Cem. Concr. Compos. 27 (2005) 848–853. [9] C. Shi, J. Qian, Resour. Conserv. Recycl. 29 (2000) 195–207. [10] M. Sahmaran, H.A. Christianto, I.O. Yaman, Cem. Concr. Compos. 28 (2006) 432–440. [11] S.P. Shah, O. Chengsheng, J. Am. Ceram. Soc. 74 (1991) 2727–2738. [12] J.-Y. Wang, N. Banthia, M.-H. Zhang, Cem. Concr. Compos. 34 (2012) 443–450. [13] K. Wille, A.E. Naaman, S. El-Tawil, G.J. Parra-Montesinos, Mater. Struct. 45 (2012) 309–324. [14] G.Y. Li, P.M. Wang, X. Zhao, Cem. Concr. Compos. 29 (2007) 377–382. [15] (a) H. Wang, K. Sun, F. Tao, D.J. Stacchiola, Y.H. Hu, Angew. Chem. Int. Ed. 52 (2013) 9210–9214; (b) H. Wang, Y.H. Hu, Energy Env. Sci. 5 (2012) 8182–8188; (c) L. Chang, W. Wei, K. Sun, Y.H. Hu, J. Mater. Chem. A 3 (2015) 10183–10187; (d) W. Wei, K. Sun, Y.H. Hu, J. Mater. Chem. A 2 (2014) 16842–16846. [16] (a) Y.W. Zhu, S. Murali, W.W. Cai, X.S. Li, J.W. Suk, J.R. Potts, R.S. Ruoff, Adv. Mater. 22 (2010) 3906–3924; (b) S. Stankovich, D.A. Dikin, R.D. Piner, K.A. Kohlhaas, A. Kleinhammes, Y. Jia, Y. Wu, S.T. Nguyen, R.S. Ruoff, Carbon 45 (2007) 1558–1665. [17] D. Konios, M.M. Stylianakis, E. Stratakis, E. Kymakis, J. Colloid Interface Sci. 430 (2014) 108–112. [18] J.I. Paredes, S. Villar-Rodil, A. Martinea-Alonso, J.M.D. Tascon, Langmuir 24 (2008) 10560–10564. [19] Z. Tang, H. Kang, Z. Shen, B. Guo, L. Zhang, D. Jia, Macromolecules 45 (2012) 3444–3445. [20] D.R. Dreyer, S. Park, C.W. Bielawski, R.S. Ruoff, Chem. Soc. Rev. 39 (2010) 228–240. [21] J. Chen, D. Zhao, X. Jin, C. Wang, D. Wang, H. Ge, Compos. Sci. Technol. 97 (2014) 41–45. [22] S. Lv, Y. Ma, C. Qiu, T. Sun, J. Liu, Q. Zhou, Constr. Build. Mater. 49 (2013) 121–127. [23] S. Chual, Z. Pan, J.G. Sanjayan, C.M. Wang, W.H. Duan, Constr. Build. Mater. 73 (2014) 113–124. [24] H. Alkhateb, A. Al-Ostaz, A.H.-D. Cheng, X.B. Li, J. Nanomech, Micromech 3 (2013) 67–77. [25] X. Li, W. Wei, H. Qin, Y.H. Hu, J. Phys. Chem. Solids 85 (2015) 39–43. [26] S. Chakraborty, S.P. Kundu, A. Roy, B. Adhikari, S.B. Majumder, Ind. Eng. Chem. Res. 52 (2013) 1252–1260. [27] M.S. Konsta-Gdoutos, Z.S. Metaxa, S.P. Shah, Cem. Concr. Res. 40 (2010) 1052–1059. [28] R. Alizadeh, J.J. Beaudoin, Mater. Struct. 44 (2011) 13–28. [29] M. Atkins, F. Glasser, A. Kindness, Cem. Concr. Res. 22 (1992) 241–246. [30] A. Goldman, A. Bentur, Cem. Concr. Res. 23 (1993) 962–972. [31] W. Hummers, R. Offeman, J. Am. Chem. Soc. 80 (1958) 1339. [32] (a) H. Wang, Y.H. Hu, J. Colloid Interface Sci. 391 (2013) 21–27; (b) H. Wang, Y.H. Hu, Ind. Eng. Chem. Res. 50 (2011) 6132–6137.
C. Lin et al. / Journal of Physics and Chemistry of Solids 89 (2016) 128–133
[33] S. Sharma, N.C. Kothiyal, RSC Adv. 5 (2015) 52642–52657. [34] X. Sun, Z. Liu, K. Welsher, J.T. Robinson, A. Goodwin, S. Zaric, H. Dai, Nano Res. 1 (2008) 203–212. [35] G. Wang, B. Wang, J. Park, J. Yang, X. Shen, J. Yao, Carbon 47 (2009) 68–72. [36] J.I. Paredes, S. Villar-Rodil, A. Martinez-Alonso, J.M.D. Tascon, Langmuir 24 (2008) 10560–10564. [37] H. He, J. Klinowski, M. Forster, A. Lerf, Chem. Phys. Lett. 287 (1998) 53–56. [38] H. He, T. Riedl, A. Lerf, J. Klinowski, J. Phys. Chem. 100 (100) (1996) 19954–19958. [39] A. Buchsteiner, A. Lerf, J. Pieper, J. Phys. Chem. B 110 (2006) 22328–22338.
133
[40] I. García-Lodeiro, A. Fernández-Jiménez, M.T. Blanco, A. Palomo, J. Sol–Gel Sci. Technol. 45 (2008) 63–72. [41] P. Yu, R.J. Kirkpatrick, B. Poe, P.F. McMillan, J.X. Cong, J. Am. Ceram. Soc. 82 (1999) 742–748. [42] M.Y.A. Mollah, W. Yu, R. Schennach, D.L. Cocke, Cem. Concr. Res. 30 (2000) 267–273. [43] T.L. Hughes, C.M. Methven, T.G.J. Jones, S.E. Pelham, P. Fleccher, C. Hall, Adv. Cem. Based Mater. 2 (1995) 91–104. [44] S.N. Ghosh, S.K. Handoo, Cem. Concr. Res. 10 (1980) 771–778.