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Hierarchical porous nanosheet-assembled MgO microrods with high adsorption capacity
Materials Letters 116 (2014) 332–336
Contents lists available at ScienceDirect
Materials Letters journal homepage: www.elsevier.com/locate/matlet
Hierarchical porous nanosheet-assembled MgO microrods with high adsorption capacity Tao Wang a,b, Youfeng Xu b, Qiying Su b, Rong Yang b, Linfei Wang b, Bo Liu b, Shen Shen b, Guohua Jiang a,b, Wenxing Chen a,b, Sheng Wang a,b,n a Key Laboratory of Advanced Textile Materials and Manufacturing Technology, Ministry of Education, Zhejiang Sci-Tech University, Hangzhou 310018, PR China b Department of Materials Engineering, College of Materials and Textile, Zhejiang Sci-Tech University, Hangzhou 310018, PR China
art ic l e i nf o
a b s t r a c t
Article history: Received 2 July 2013 Accepted 12 November 2013 Available online 20 November 2013
Hierarchical porous nanosheet-assembled MgO microrods (PS-MgO) are synthesized by a simple surfactant-assisted method. Because of its unique porous nanosheet-assembled structure, the specific surface area of PS-MgO reaches 72 m2/g. Congo red adsorption experiments indicate that PS-MgO shows an adsorption capacity that is three times higher than that of MgO microrods. & 2013 Elsevier B.V. All rights reserved.
Keywords: Water treatment Microstructure MgO microrods Porous materials Adsorption capacity
1. Introduction Water pollution has many sources, and the most polluting is the large amount of industrial waste water released into the environment. In particular, effluents from textile plants, paper mills and plastic industries can contain dyes that are deeply colored, difficult to degrade, and even potentially carcinogenic and toxic, so they are detrimental to the environment and human health [1–4]. To date, many technologies have been developed to remove dyes from water, including physical adsorption [5,6], chemical coagulation [7], photodegradation [8], biological [9] and electrochemical processes [1]. Of these methods, physical adsorption is considered to be the most effective and economical method because of its simplicity, high efficiency and low operating cost. Metal oxides are well known because of their industrial applications as adsorbents, catalysts, and catalyst supports [10,11]. Magnesium oxide (MgO) is an important functional metal oxide that has been widely used in various fields such as catalysis, refractory materials, paints, and superconductors [12,13]. Recently, nanosized MgO has been explored as a nontoxic and environmentally friendly adsorbent to remove toxic metal ions and organic pollutants from water [14,15]. When compared with its commercial analogs, the advantages of nanosized MgO include high degradation ability, surface reactivity, and adsorption capacity, as well as simple production from abundant natural minerals [16].
n
Corresponding author.
0167-577X/$ - see front matter & 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.matlet.2013.11.053
In this work, hierarchical porous nanosheet-assembled MgO microrods (PS-MgO) were synthesized using a simple surfactant-assisted method. Because of the unique porous nanosheet-assembled structure of PS-MgO, its specific surface area reached 72 m2/g. Adsorption experiments using Congo red (CR) indicate that compared with untreated MgO nanorods, PS-MgO shows excellent adsorption capacity.
2. Experimental In general, MgO microrods as an adsorbent is easy to be collected as compared with simple MgO nanoparticles. PS-MgO microrods were prepared in four steps (Scheme 1). First, sodium dodecyl sulfate (SDS; 0.044 g) was added to an aqueous solution of MgCl2 (0.6 M, 20 mL). Aqueous NH4HCO3 (0.5 M, 24 mL) was added to the mixture, which was then stirred at 40 1C for 1 h to produce a white precipitate. The precipitate was isolated by centrifugation, washed thoroughly with deionized water and ethanol several times, and finally dried at 60 1C overnight to obtain surfactant-assisted MgCO3 nanorods. SDS is a widely used amphipathic anion surfactant, and the presence of SDS in the mixed aqueous solution played important role in the morphology and size of MgCO3 crystals, which was beneficial for oriented growth of one-dimensional MgCO3 crystals [17] (ESI, S1). The MgCO3 nanorods were calcined in air at 500 1C for 2 h to produce nanoparticle-assembled MgO microrods (P-MgO). P-MgO (0.2 g) in deionized water (40 mL) was placed in a Teflon-lined autoclave. After hydrothermal reaction at 120 1C for 1 h, the sample was isolated by centrifugation, washed with water and ethanol several
T. Wang et al. / Materials Letters 116 (2014) 332–336
times, and dried at 60 1C overnight to obtain nanosheet-assembled Mg(OH)2 microrods (S-Mg(OH)2). Finally, S-Mg(OH)2 was calcined in air at 500 1C for 2 h to produce PS-MgO.
3. Results and discussion Fig. 1a shows an SEM image of P-MgO. The sample consists of rod-like structures with a length of about 500 nm covered with
Scheme 1. Formation of PS-MgO.
333
numerous small nanoparticles (about 50 nm in diameter). After hydrothermal treatment to form S-Mg(OH)2, the diameter of the rods increased to 2.5 μm (Fig. 1b). As we known, brucite Mg(OH)2 tends to form into hexagonal platelets. Therefore S-Mg(OH)2 showed a hierarchical structure, in which a large number of hexagonal-shaped nanosheets with a uniform size of 500 nm, well-defined facets, straight edges, and flat smooth exterior surfaces grew on the microrods. The individual nanosheets were separated and crossed each other. Calcination of S-Mg(OH)2 gave PS-MgO. The diameter of the microrods decreased to 1.0 μm and the size of the nanosheets decreased to 200 nm. Fig. 1c–d shows that the edges of the nanosheets of PS-MgO are rather irregular, and many tiny dark spots are observed on the nanosheets. A high-magnification TEM image (Fig. 1e) reveals that the tiny dark spots are a large number of nanopores with diameters of less than 40 nm. A HRTEM image of PS-MgO is depicted in Fig. 1f. The lattice fringe had a lattice distance of 0.21 nm, [18] which is consistent with the spacing between the (200) planes of MgO. The clear lattice fringe indicates the highly crystalline nature of PS-MgO. In addition, the circular rings in the selected area electron diffraction (SAED) pattern of PS-MgO (inset of Fig. 1f) suggested the formation of a well-grown polycrystalline phase.
Fig. 1. SEM images of (a) P-MgO, (b) S-Mg(OH)2, (c) and (d) PS-MgO. (e) TEM and (f) high resolution TEM images of PS-MgO (SAED pattern inset).
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Fig. 2. (a) Nitrogen adsorption–desorption isotherms and (b) pore size distributions.
Fig. 3. (a) UV–vis absorption spectra of CR solution after 18 h of adsorption. Concentrations of adsorbents were (1) 0, (2) 0.05, (3) 0.1, (4) 0.3 and (5) 0.5 g L 1. (b) UV–vis. absorption spectra of CR solutions after different adsorption times. The adsorbent concentration is 0.5 g L 1. Adsorption rate (c) and adsorption capacity (d) of P-MgO, S-Mg(OH)2 and PS-MgO (0.5 g L 1).
T. Wang et al. / Materials Letters 116 (2014) 332–336
X-ray diffraction (XRD) patterns of the samples are shown in ESI S2. All of the diffraction peaks in the XRD pattern of S-Mg (OH)2 correspond to hexagonal magnesium hydroxide (JCPDS no. 44-1482). Both P-MgO and PS-MgO can be indexed to cubic MgO (JCPDS no. 71-1176). Nitrogen adsorption–desorption isotherms of P-MgO, S-Mg (OH)2 and PS-MgO are presented in Fig. 2a. All of the samples show typical type IV adsorption isotherms with H3-type hysteresis loops according to BDDT classification, indicating the samples contain mesopores (2–50 nm). Specific surface area (SBET) data were derived from the nitrogen adsorption–desorption isotherms. SBET increases considerably with the appearance of hierarchical structure. When P-MgO is transformed into Mg (OH)2, SBET increases from 38 to 51 m2/g, which is caused by the formation of nanoplatelets from nanoparticles. After calcination, SBET increases further to 72 m2/g, which is attributed to the formation of nanopores on the surface of the nanosheets. The corresponding pore size distributions of the samples are depicted in Fig. 2b. Unlike P-MgO and S-Mg(OH)2, PS-MgO exhibits a peak between 30 and 40 nm, which corresponds to the pores on the nanosheets. This result is consistent with the morphology of PS-MgO observed in Fig. 1e.
335
In this study, the adsorption capacity of the samples was investigated by their ability to remove Congo red (CR) dye, which is a common azo dye in the textile industry. In general, MgO charges positively in a neutral aqueous solution, on the other hand, CR is transformed into anion by dissociation. As a result, the adsorption of CR might proceed via an electrostatic interaction between them [19,20]. As shown in Fig. 3a, the adsorbents were added to CR solutions (200 mg L 1, 50 mL) and allowed to adsorb CR for 18 h. The adsorption capacities of the samples differed considerably. For example, in the case where 0.05 g L 1 of each adsorbent was added, the adsorption capacity of PS-MgO was about 1.5 times higher than that of S-Mg(OH)2, and 3.6 times higher than that of P-MgO. Similar results were obtained for other concentrations of adsorbents (0.025–0.5 g L 1 (ESI, S3)). The adsorption rate of the samples was also investigated, as shown in Fig. 3b. After adding the same amount of each adsorbent (0.05 g L 1), the CR remaining in solution was determined by UV–Vis spectroscopy. PS-MgO removed ca. 80% of CR within 10 min, and completely adsorbed CR within 120 min, which was the highest adsorption rate of the samples (Fig. 3c–d). Moreover, we compare the adsorption capacity of PS-MgO with those of other hierarchical structure materials (ESI S4). Interestingly,
Fig. 4. (a) and (b) SEM images of PS-MgO after CR adsorption for 120 min. (c) and (d) SEM images of PS-MgO after being added into water for 120 min. (e) Schematic of CR adsorption on porous PS-MgO.
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T. Wang et al. / Materials Letters 116 (2014) 332–336
even with the lowest SBET value (72 m2 g 1), PS-MgO shows the highest adsorption capacity. The adsorption capacity by surface area (qm0 value) is normalized and it is clear that PS-MgO remains the highest normalized adsorption capacity (6.67 mg m 2) among all of the hierarchical adsorbents. After adsorption for 120 min, the color of PS-MgO changed from white to red. SEM observation of this red precipitate showed that the nanosheet-crossed structures remained, indicating dye was adsorbed uniformly on the surface of the nanosheets (Fig. 4a). It should be noted that the original porous structure of the nanosheets had disappeared (Fig. 4b). However, the sample was then soaked in Milli-Q water for 120 min and the original porous structure of the nanosheets returned (Fig. 4c–d). As we have described in our previous work, for materials with large specific surface area and high surface energy, it is energetically favorable to decrease their surface area and energy to reach a more stable state [21,22]. Although the energy of the electronic beam used in TEM is too high to allow the sample to be observed, we suggest that large specific surface area is the reason for the increased adsorption capacity of PS-MgO compared with those of other materials. That is, PS-MgO readily adsorbs dye molecules to cover its pore structure and to reduce its specific surface area, which allows it to reach a lower surface energy (Fig. 4e). This strongly suggests that besides the electrostatic attraction between the absorbent and CR, and the high surface areas of the hierarchical structures, the superior performance of PS-MgO could be also attributed to embedding of dye molecules in porous structure during the adsorption process. 4. Conclusions In conclusion, hierarchical porous nanosheet-assembled MgO microrods (PS-MgO) were successfully synthesized. Because of its high specific surface area and unique hierarchical porous nanosheet-crossed structure, PS-MgO exhibited an excellent adsorption capacity for CR dye, so it shows great potential for practical application in water treatment.
Acknowledgment This work was supported by NSFC (50802088, 31070888, 21103152, 51133006, 51372227), ZJNSF (R2101054, Y4080392), ZJ-LTSTI (2011R50003), ZJ-WTARP (2012C23050) and 521 Talent Project of ZSTU. Appendix A. Supplementary material Supplementary data associated with this article can be found in the online version at http://dx.doi.org/10.1016/j.matlet.2013.11.053. References [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14] [15] [16] [17] [18] [19] [20] [21] [22]
Martine-Huitle CA, Brillas E. Appl Catal B-Environ 2009;87:105–45. Ollera I, Malatoa S, Sánchez-Pérez JA. Sci Total Environ 2011;409:4141–66. Singh K, Arora S. Crit Rev Environ Sci Technol 2011;41:807–78. Ong ST, Keng PS, Lee WN, Ha ST, Hung YT. Water 2011;3:157–76. Sharma P, Kaur H, Sharma M, Sahore V. Environ Monit Assess 2011;183:151–95. Rafatullah M, Sulaiman O, Hashim R, Ahmad A. J Hazard Mater 2010;177: 70–80. Alexander JT, Hai FI, Al-aboud TM. J Environ Manag 2012;111:195–207. Chong MN, Jin B, Chow CWK, Saint C. Water Res 2010;44:2997–3027. Solis M, Solis A, Perez HI, Manjarrez N, Flores M. Process Biochem 2012;112:429–48. Thakuria H, Borah BM, Das G. J Mol Catal A: Chem 2007;274:1–10. Ren YH, Yue B, Gu M, He HY. Materials 2010;3:764–85. Zavyalova U, Geske M, Horn R, Weinberg G, Frandsen W, Schuster M, et al. Chemcatchem 2011;3:949–59. Heidari H, Abedini M, Nemati A, Amini MM. Catal Lett 2009;130:266–70. Ai LH, Yue HT, Jiang J. Nanoscale 2012;4:5401–8. Yu XY, Luo T, Jia Y, Zhang YX, Liu JH, Huang XJ. J Phys Chem C 2011;115: 22242–50. Richards R, Mulukutla RS, Mishakov I, Chesnokov V, Volodin A, Zaikovski V, et al. Scr Mater 2001;44:1663–6. Yang C, Song X, Sun S, Sun Z, Yu J. Adv Power Technol 2013;24:585–92. Cao CY, Qu J, Wei F, Liu H, Song WG. ACS Appl Mater Interface 2012;4:4283–7. Crittenden JC, Trussell RR, Hand DW, Howe KJ, Tchobanoglous G. Water treatment: principals and design. 2nd ed. MWH: John Wiley and Sons, Inc.; 2005. Moussavi G, Mahmoui M. J Hazard Mater 2009;168:806–12. Wang T, Wang S, Chen WX, Wang W, Xu ZL, Liu Y, et al. J Mater Chem 2009;19:4692–4. Wang S, Wang T, Gao YL, Ding YW, Jiang GH, Chen WX. J Mater Chem 2011;21:19337–43.
Contents lists available at ScienceDirect
Materials Letters journal homepage: www.elsevier.com/locate/matlet
Hierarchical porous nanosheet-assembled MgO microrods with high adsorption capacity Tao Wang a,b, Youfeng Xu b, Qiying Su b, Rong Yang b, Linfei Wang b, Bo Liu b, Shen Shen b, Guohua Jiang a,b, Wenxing Chen a,b, Sheng Wang a,b,n a Key Laboratory of Advanced Textile Materials and Manufacturing Technology, Ministry of Education, Zhejiang Sci-Tech University, Hangzhou 310018, PR China b Department of Materials Engineering, College of Materials and Textile, Zhejiang Sci-Tech University, Hangzhou 310018, PR China
art ic l e i nf o
a b s t r a c t
Article history: Received 2 July 2013 Accepted 12 November 2013 Available online 20 November 2013
Hierarchical porous nanosheet-assembled MgO microrods (PS-MgO) are synthesized by a simple surfactant-assisted method. Because of its unique porous nanosheet-assembled structure, the specific surface area of PS-MgO reaches 72 m2/g. Congo red adsorption experiments indicate that PS-MgO shows an adsorption capacity that is three times higher than that of MgO microrods. & 2013 Elsevier B.V. All rights reserved.
Keywords: Water treatment Microstructure MgO microrods Porous materials Adsorption capacity
1. Introduction Water pollution has many sources, and the most polluting is the large amount of industrial waste water released into the environment. In particular, effluents from textile plants, paper mills and plastic industries can contain dyes that are deeply colored, difficult to degrade, and even potentially carcinogenic and toxic, so they are detrimental to the environment and human health [1–4]. To date, many technologies have been developed to remove dyes from water, including physical adsorption [5,6], chemical coagulation [7], photodegradation [8], biological [9] and electrochemical processes [1]. Of these methods, physical adsorption is considered to be the most effective and economical method because of its simplicity, high efficiency and low operating cost. Metal oxides are well known because of their industrial applications as adsorbents, catalysts, and catalyst supports [10,11]. Magnesium oxide (MgO) is an important functional metal oxide that has been widely used in various fields such as catalysis, refractory materials, paints, and superconductors [12,13]. Recently, nanosized MgO has been explored as a nontoxic and environmentally friendly adsorbent to remove toxic metal ions and organic pollutants from water [14,15]. When compared with its commercial analogs, the advantages of nanosized MgO include high degradation ability, surface reactivity, and adsorption capacity, as well as simple production from abundant natural minerals [16].
n
Corresponding author.
0167-577X/$ - see front matter & 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.matlet.2013.11.053
In this work, hierarchical porous nanosheet-assembled MgO microrods (PS-MgO) were synthesized using a simple surfactant-assisted method. Because of the unique porous nanosheet-assembled structure of PS-MgO, its specific surface area reached 72 m2/g. Adsorption experiments using Congo red (CR) indicate that compared with untreated MgO nanorods, PS-MgO shows excellent adsorption capacity.
2. Experimental In general, MgO microrods as an adsorbent is easy to be collected as compared with simple MgO nanoparticles. PS-MgO microrods were prepared in four steps (Scheme 1). First, sodium dodecyl sulfate (SDS; 0.044 g) was added to an aqueous solution of MgCl2 (0.6 M, 20 mL). Aqueous NH4HCO3 (0.5 M, 24 mL) was added to the mixture, which was then stirred at 40 1C for 1 h to produce a white precipitate. The precipitate was isolated by centrifugation, washed thoroughly with deionized water and ethanol several times, and finally dried at 60 1C overnight to obtain surfactant-assisted MgCO3 nanorods. SDS is a widely used amphipathic anion surfactant, and the presence of SDS in the mixed aqueous solution played important role in the morphology and size of MgCO3 crystals, which was beneficial for oriented growth of one-dimensional MgCO3 crystals [17] (ESI, S1). The MgCO3 nanorods were calcined in air at 500 1C for 2 h to produce nanoparticle-assembled MgO microrods (P-MgO). P-MgO (0.2 g) in deionized water (40 mL) was placed in a Teflon-lined autoclave. After hydrothermal reaction at 120 1C for 1 h, the sample was isolated by centrifugation, washed with water and ethanol several
T. Wang et al. / Materials Letters 116 (2014) 332–336
times, and dried at 60 1C overnight to obtain nanosheet-assembled Mg(OH)2 microrods (S-Mg(OH)2). Finally, S-Mg(OH)2 was calcined in air at 500 1C for 2 h to produce PS-MgO.
3. Results and discussion Fig. 1a shows an SEM image of P-MgO. The sample consists of rod-like structures with a length of about 500 nm covered with
Scheme 1. Formation of PS-MgO.
333
numerous small nanoparticles (about 50 nm in diameter). After hydrothermal treatment to form S-Mg(OH)2, the diameter of the rods increased to 2.5 μm (Fig. 1b). As we known, brucite Mg(OH)2 tends to form into hexagonal platelets. Therefore S-Mg(OH)2 showed a hierarchical structure, in which a large number of hexagonal-shaped nanosheets with a uniform size of 500 nm, well-defined facets, straight edges, and flat smooth exterior surfaces grew on the microrods. The individual nanosheets were separated and crossed each other. Calcination of S-Mg(OH)2 gave PS-MgO. The diameter of the microrods decreased to 1.0 μm and the size of the nanosheets decreased to 200 nm. Fig. 1c–d shows that the edges of the nanosheets of PS-MgO are rather irregular, and many tiny dark spots are observed on the nanosheets. A high-magnification TEM image (Fig. 1e) reveals that the tiny dark spots are a large number of nanopores with diameters of less than 40 nm. A HRTEM image of PS-MgO is depicted in Fig. 1f. The lattice fringe had a lattice distance of 0.21 nm, [18] which is consistent with the spacing between the (200) planes of MgO. The clear lattice fringe indicates the highly crystalline nature of PS-MgO. In addition, the circular rings in the selected area electron diffraction (SAED) pattern of PS-MgO (inset of Fig. 1f) suggested the formation of a well-grown polycrystalline phase.
Fig. 1. SEM images of (a) P-MgO, (b) S-Mg(OH)2, (c) and (d) PS-MgO. (e) TEM and (f) high resolution TEM images of PS-MgO (SAED pattern inset).
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Fig. 2. (a) Nitrogen adsorption–desorption isotherms and (b) pore size distributions.
Fig. 3. (a) UV–vis absorption spectra of CR solution after 18 h of adsorption. Concentrations of adsorbents were (1) 0, (2) 0.05, (3) 0.1, (4) 0.3 and (5) 0.5 g L 1. (b) UV–vis. absorption spectra of CR solutions after different adsorption times. The adsorbent concentration is 0.5 g L 1. Adsorption rate (c) and adsorption capacity (d) of P-MgO, S-Mg(OH)2 and PS-MgO (0.5 g L 1).
T. Wang et al. / Materials Letters 116 (2014) 332–336
X-ray diffraction (XRD) patterns of the samples are shown in ESI S2. All of the diffraction peaks in the XRD pattern of S-Mg (OH)2 correspond to hexagonal magnesium hydroxide (JCPDS no. 44-1482). Both P-MgO and PS-MgO can be indexed to cubic MgO (JCPDS no. 71-1176). Nitrogen adsorption–desorption isotherms of P-MgO, S-Mg (OH)2 and PS-MgO are presented in Fig. 2a. All of the samples show typical type IV adsorption isotherms with H3-type hysteresis loops according to BDDT classification, indicating the samples contain mesopores (2–50 nm). Specific surface area (SBET) data were derived from the nitrogen adsorption–desorption isotherms. SBET increases considerably with the appearance of hierarchical structure. When P-MgO is transformed into Mg (OH)2, SBET increases from 38 to 51 m2/g, which is caused by the formation of nanoplatelets from nanoparticles. After calcination, SBET increases further to 72 m2/g, which is attributed to the formation of nanopores on the surface of the nanosheets. The corresponding pore size distributions of the samples are depicted in Fig. 2b. Unlike P-MgO and S-Mg(OH)2, PS-MgO exhibits a peak between 30 and 40 nm, which corresponds to the pores on the nanosheets. This result is consistent with the morphology of PS-MgO observed in Fig. 1e.
335
In this study, the adsorption capacity of the samples was investigated by their ability to remove Congo red (CR) dye, which is a common azo dye in the textile industry. In general, MgO charges positively in a neutral aqueous solution, on the other hand, CR is transformed into anion by dissociation. As a result, the adsorption of CR might proceed via an electrostatic interaction between them [19,20]. As shown in Fig. 3a, the adsorbents were added to CR solutions (200 mg L 1, 50 mL) and allowed to adsorb CR for 18 h. The adsorption capacities of the samples differed considerably. For example, in the case where 0.05 g L 1 of each adsorbent was added, the adsorption capacity of PS-MgO was about 1.5 times higher than that of S-Mg(OH)2, and 3.6 times higher than that of P-MgO. Similar results were obtained for other concentrations of adsorbents (0.025–0.5 g L 1 (ESI, S3)). The adsorption rate of the samples was also investigated, as shown in Fig. 3b. After adding the same amount of each adsorbent (0.05 g L 1), the CR remaining in solution was determined by UV–Vis spectroscopy. PS-MgO removed ca. 80% of CR within 10 min, and completely adsorbed CR within 120 min, which was the highest adsorption rate of the samples (Fig. 3c–d). Moreover, we compare the adsorption capacity of PS-MgO with those of other hierarchical structure materials (ESI S4). Interestingly,
Fig. 4. (a) and (b) SEM images of PS-MgO after CR adsorption for 120 min. (c) and (d) SEM images of PS-MgO after being added into water for 120 min. (e) Schematic of CR adsorption on porous PS-MgO.
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even with the lowest SBET value (72 m2 g 1), PS-MgO shows the highest adsorption capacity. The adsorption capacity by surface area (qm0 value) is normalized and it is clear that PS-MgO remains the highest normalized adsorption capacity (6.67 mg m 2) among all of the hierarchical adsorbents. After adsorption for 120 min, the color of PS-MgO changed from white to red. SEM observation of this red precipitate showed that the nanosheet-crossed structures remained, indicating dye was adsorbed uniformly on the surface of the nanosheets (Fig. 4a). It should be noted that the original porous structure of the nanosheets had disappeared (Fig. 4b). However, the sample was then soaked in Milli-Q water for 120 min and the original porous structure of the nanosheets returned (Fig. 4c–d). As we have described in our previous work, for materials with large specific surface area and high surface energy, it is energetically favorable to decrease their surface area and energy to reach a more stable state [21,22]. Although the energy of the electronic beam used in TEM is too high to allow the sample to be observed, we suggest that large specific surface area is the reason for the increased adsorption capacity of PS-MgO compared with those of other materials. That is, PS-MgO readily adsorbs dye molecules to cover its pore structure and to reduce its specific surface area, which allows it to reach a lower surface energy (Fig. 4e). This strongly suggests that besides the electrostatic attraction between the absorbent and CR, and the high surface areas of the hierarchical structures, the superior performance of PS-MgO could be also attributed to embedding of dye molecules in porous structure during the adsorption process. 4. Conclusions In conclusion, hierarchical porous nanosheet-assembled MgO microrods (PS-MgO) were successfully synthesized. Because of its high specific surface area and unique hierarchical porous nanosheet-crossed structure, PS-MgO exhibited an excellent adsorption capacity for CR dye, so it shows great potential for practical application in water treatment.
Acknowledgment This work was supported by NSFC (50802088, 31070888, 21103152, 51133006, 51372227), ZJNSF (R2101054, Y4080392), ZJ-LTSTI (2011R50003), ZJ-WTARP (2012C23050) and 521 Talent Project of ZSTU. Appendix A. Supplementary material Supplementary data associated with this article can be found in the online version at http://dx.doi.org/10.1016/j.matlet.2013.11.053. References [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14] [15] [16] [17] [18] [19] [20] [21] [22]
Martine-Huitle CA, Brillas E. Appl Catal B-Environ 2009;87:105–45. Ollera I, Malatoa S, Sánchez-Pérez JA. Sci Total Environ 2011;409:4141–66. Singh K, Arora S. Crit Rev Environ Sci Technol 2011;41:807–78. Ong ST, Keng PS, Lee WN, Ha ST, Hung YT. Water 2011;3:157–76. Sharma P, Kaur H, Sharma M, Sahore V. Environ Monit Assess 2011;183:151–95. Rafatullah M, Sulaiman O, Hashim R, Ahmad A. J Hazard Mater 2010;177: 70–80. Alexander JT, Hai FI, Al-aboud TM. J Environ Manag 2012;111:195–207. Chong MN, Jin B, Chow CWK, Saint C. Water Res 2010;44:2997–3027. Solis M, Solis A, Perez HI, Manjarrez N, Flores M. Process Biochem 2012;112:429–48. Thakuria H, Borah BM, Das G. J Mol Catal A: Chem 2007;274:1–10. Ren YH, Yue B, Gu M, He HY. Materials 2010;3:764–85. Zavyalova U, Geske M, Horn R, Weinberg G, Frandsen W, Schuster M, et al. Chemcatchem 2011;3:949–59. Heidari H, Abedini M, Nemati A, Amini MM. Catal Lett 2009;130:266–70. Ai LH, Yue HT, Jiang J. Nanoscale 2012;4:5401–8. Yu XY, Luo T, Jia Y, Zhang YX, Liu JH, Huang XJ. J Phys Chem C 2011;115: 22242–50. Richards R, Mulukutla RS, Mishakov I, Chesnokov V, Volodin A, Zaikovski V, et al. Scr Mater 2001;44:1663–6. Yang C, Song X, Sun S, Sun Z, Yu J. Adv Power Technol 2013;24:585–92. Cao CY, Qu J, Wei F, Liu H, Song WG. ACS Appl Mater Interface 2012;4:4283–7. Crittenden JC, Trussell RR, Hand DW, Howe KJ, Tchobanoglous G. Water treatment: principals and design. 2nd ed. MWH: John Wiley and Sons, Inc.; 2005. Moussavi G, Mahmoui M. J Hazard Mater 2009;168:806–12. Wang T, Wang S, Chen WX, Wang W, Xu ZL, Liu Y, et al. J Mater Chem 2009;19:4692–4. Wang S, Wang T, Gao YL, Ding YW, Jiang GH, Chen WX. J Mater Chem 2011;21:19337–43.