Constructing Three-Dimensional Hierarchical ... - ACS Publications

2 downloads 0 Views 627KB Size Report
Feb 23, 2016 - As such, the versatile [email protected] monoliths show great application potential for water treatment. KEYWORDS: Hierarchical carbon nanofiber ...

Research Article pubs.acs.org/journal/ascecg

Constructing Three-Dimensional Hierarchical Architectures by Integrating Carbon Nanofibers into Graphite Felts for Water Purification Yi Shen,*,† Ling Li,† Kaijun Xiao,† and Jingyu Xi*,‡ †

School of Food Science and Technology, South China University of Technology, Tianhe District, Guangzhou 510640, China Laboratory of Advanced Power Sources, Graduate School at Shenzhen, Tsinghua University, Shenzhen 518055, China



S Supporting Information *

ABSTRACT: Developing high-performance nanostructured sorbents for water treatment is of great importance. Herein, we report a facile strategy to fabricate three-dimensional hierarchical architectures by integrating carbon nanofibers (CNFs) into macroscopic graphite felt (GF) supports. The physicochemical properties of [email protected] monoliths including surface areas, densities, porosities, and pore structures could be conveniently tuned by varying reaction time. The [email protected] monoliths were utilized as advanced sorbents for the removal of Pb2+, Congo red, organic solvents, and oils from aqueous solutions. The characteristics of adsorption processes including kinetics, isotherms, and regeneration were investigated. It is demonstrated that the [email protected] exhibits outstanding performance for water treatment in terms of adsorption capacities, recovering, and recyclability. As such, the versatile [email protected] monoliths show great application potential for water treatment. KEYWORDS: Hierarchical carbon nanofiber arrays, Water purification, Lead ions, Congo red, Oil cleanup, Sorption isotherms and kinetics



are very difficult to handle in terms of shape figuration, porosity control, and toxicity concerns. To address these issues, one common strategy is to fabricate free-standing carbon aerogels.17−21 To date, considerable carbon-based aerogels with remarkable performance for pollutant removal have been reported.22−25 Generally, the synthesis of these aerogels is always a very complicated and costly process, making their massive production infeasible. Constructing three-dimensional (3D) hierarchically structured materials by integrating lowdimensional carbon nanomaterials, such as carbon nanotubes (CNTs) and graphene, into proper supports is regarded as an alternative solution to the aforementioned issues.26−30 One advantage of 3D hierarchical materials lies in the combination of the merits of different components and the achievement of synergistic effects via the tuning of the nanostructures. In this study, we synthesized 3D hierarchical architectures, consisting of vertically aligned carbon nanofiber (CNF) arrays anchored to macroscopic graphite felt (GF) supports, via ambientpressure chemical-vapor deposition (APCVD). The resulting [email protected] monoliths were evaluated as advanced sorbents to remove various pollutants including Pb2+, Congo red (CR), organic solvents, and oils from aqueous solutions.

INTRODUCTION Nowadays, a large number of pollutants such as oils, organic solvents, dyes, and heavy metal ions discharged from the metallurgy, textile, paper, tannery, and paint industries are entering into water sources, leading to inadequate access to clean and safe water supplies for the increasing global population.1 In this context, a series of approaches such as precipitation, coagulation−flocculation, oxidation, membrane filtration, and sorption are employed to remove pollutants from large volumes of aqueous solutions.2 Of these techniques, sorption is considered to be one of the most suitable and effective choices because of its simplicity, high efficiency, and low cost.3 Developing high-performance and cost-effective sorbents is crucial for the application of sorption in water cleanup. So far, many materials such as carbons,4 zeolite,5 oxides,6 nitrides,7 clays8, and polymer gels9 have been studied as sorbents. However, their widespread application in water cleanup is limited by some drawbacks, such as low adsorption capacity and removal efficiency.10 As a result, continuous efforts are directed in searching for high-performance sorbents which can be practically used in water treatment.11 Carbon nanomaterials such as activated carbon,12 ordered mesoporous carbon,13 carbon nanotube (CNT)14, and graphene15,16 have been extensively studied as sorbents for water treatment because of the high surface-to-volume ratio, low cost, abundant availability, and environmental friendliness. Nevertheless, for the practical application these powder-formed carbon materials © 2016 American Chemical Society

Received: January 5, 2016 Revised: February 1, 2016 Published: February 23, 2016 2351

DOI: 10.1021/acssuschemeng.6b00030 ACS Sustainable Chem. Eng. 2016, 4, 2351−2358

Research Article

ACS Sustainable Chemistry & Engineering



EXPERIMENTAL SECTION

Synthesis of [email protected] Composite. [email protected] was prepared by an APCVD method. Typically, nickel−copper oxalate (atomic Ni/Cu ratio 75:25) obtained from a simple precipitation process31 was transferred to thermally treated GF supports via an impregnation method.32 The nickel−copper oxalate was in situ reduced and the resulting Ni−Cu alloy nanoparticles served as catalysts for the growth of CNFs. The details of procedures were reported in our previous work.33,34 Characterization Methods. A field emission scanning electron microscope (FESEM) (JSM-7600F, JEOL) and a transmission electron microscope (TEM) (JEM2010, JEOL) were used to observe the morphology of the samples. X-ray diffraction (XRD) patterns were obtained by a diffractometer (PW1830, Philips) equipped with Cu Kα radiation of 1.54 Å. The N2 adsorption−desorption isotherm was obtained using the accelerated surface area porosimetry system (ASAP 2020, Micromeritics). The wetting property of samples was analyzed by contact angle tests (JGW-360C, Chenghui testing machine Co. Ltd.). Sorption of Pb2+ Ions and CR Dye. To evaluate the adsorption performance of the [email protected], both batch mode adsorption and dynamic filtration adsorption tests were conducted. In a typical batch adsorption test, [email protected] monoliths with a dimension of 15 × 15 × 5 mm were first thermally activated in an air flow at a temperature of 430 °C for 24 h.32 Then, one piece of activated [email protected] monolith was immersed into pollutant solution with a given concentration. The pH of the pollutant solution was set to be 5. The variations in the concentration of Pb2+ ions and CR were monitored as a function of time using a UV−visible spectrophotometer and inductively coupled plasma atomic emission spectrometry, respectively. The adsorption up-take qt (mg g−1) at time t (min) was calculated using eq 1 qt =

(C0 − Ct )V W −1

Figure 1. Procedures of preparation of 3D hierarchical [email protected] composite and the corresponding FESEM micrographs of the samples at different stages.

geometry shape and excellent chemical stability. Nickel−copper oxalate nanofibers (Figure S1) obtained from a precipitation process31 were transferred to the carbon fibers using an impregnation method32 (Figure 1b) and subsequently reduced by methane gas, forming Ni−Cu alloy nanoparticles which were intimately immobilized to the surface of carbon fibers (Figure 1c). The resulting Ni−Cu nanoparticles served as catalysts for the growth of CNFs via the catalytic decomposition of methane.33,34 FESEM micrographs (Figure 1d) reveal that the as-prepared [email protected] exhibits a well-defined 3D hierarchical structure, consisting of the secondary CNF arrays anchored to the primary carbon fibers. The crystalline structures of the samples at different stages of the preparation process were ex-situ examined by XRD as shown in Figure S2. The peaks in the XRD patterns of the samples could be well indexed. It was confirmed that the catalyst precursor, i.e., nickel−copper oxalate, was fully reduced to Ni−Cu alloy nanoparticles by methane before the CVD process. To further characterize the nanostructures, the CNFs were isolated from the carbon fiber by intense ultrasonication in ethanol and transferred to copper grids for TEM observation. Shown in Figure 2, the CNFs exhibited a herringbone structure consisting of obliquely aligned graphene layers with respect to the fiber axis. The diameters of the CNFs were in the range of 20−30 nm. The conical Ni−Cu nanoparticles were located in the tips of CNFs, indicating the tip-growth mode of the CNFs.34 The lattice fringes with spacing values of 0.21 and 0.34 nm shown in Figure 2D correspond to the interdistance of the Ni−Cu (111) and graphitic (002) planes, respectively. It was noted that the cover density of the CNFs could be conveniently tuned by varying CVD time during the synthesis process. Figure 3 shows the FESEM micrographs of the [email protected] GF samples synthesized with reaction times of 30, 60, 120, and 240 min (for convenience, the samples were denoted as [email protected] CF-30, [email protected], [email protected], and [email protected], respectively). The coverage and length of CNFs increased with increasing reaction time. For instance, at a reaction time of 30 min, the CNFs attached to the carbon fibers were quite short and some areas in the carbon fiber surface were not covered by CNFs. Comparatively, at a reaction time of 240 min, the carbon fibers were fully wrapped by CNFs, leading to

(1) −1

where C0 (mg L ) is the initial pollutant concentration, Ct (mg L ) is the concentration at time t (min) in the liquid phase, V (L) is the volume of the solution, and W (g) is the weight of the monolith. To determine the maximum adsorption capacity qe (mg g−1), the sorbent was immersed into the pollution solution at least for 24 h to achieve the equilibrium state of adsorption. In the experiments of studying adsorption kinetics, the initial pollutant concentration was 500 mg L−1. For the dynamic filtration adsorption test, one piece of the [email protected] monolith was fixed into a dead-end filtration device. The CR solution (100 mL) with a concentration of 100 mg L−1 was forced to filter through the monolith with a constant flow rate of 2.5 mL min−1 using a mechanical pump. The effluent was collected and analyzed to determine the CR concentration. For each sample, at least three tests were conducted and the average results were presented. Sorption of Solvents and Oils. To determine the adsorption capacities of solvents and oils, a piece of the as-prepared [email protected] monolith was immersed into a solvent or oil until it was completely saturated with the liquid adsorbate. To abate the evaporation of the absorbed solvent, the weight measurement was completed in several seconds. For each adsorbate, the adsorption test was repeated for five times and the average adsorption capacity was recorded. To demonstrate the superoleophilicity, [email protected] monoliths were utilized to adsorb oil from water. For the sake of observation, the oil was stained with a trace of Sudan red 3B dye.



RESULTS AND DISCUSSION Synthesis and Characterization of [email protected] Composite. The 3D [email protected] composite was prepared by an APCVD method using methane as carbon source. The experimental procedures of the preparation of [email protected] composite are schematically shown in Figure 1. The GF fabric consisting of numerous carbon microfibers with diameters ranging from 10 to 15 μm (Figure 1a) was utilized as support to fabricate 3D [email protected] composite by virtue of its well-defined 2352

DOI: 10.1021/acssuschemeng.6b00030 ACS Sustainable Chem. Eng. 2016, 4, 2351−2358

Research Article

ACS Sustainable Chemistry & Engineering

with increasing reaction time, manifesting increases in CNF deposition in the GF support. Figure S5 displays the N2 adsorption−desorption isotherms of the samples. The Brunauer−Emmett−Teller (BET) surface area of the [email protected] GF composite was calculated accordingly. The [email protected], [email protected], [email protected], and [email protected] possessed BET surface areas of 21.5, 62.2, 94.7, and 144.2 m2 g−1, respectively, which were much larger than that of the pristine GF support (less than 1 m2 g−1). Sorption of Pb2+ and CR. It was demonstrated that the asprepared [email protected] monoliths exhibited a well-defined 3D hierarchical structure, large surface areas, and high porosities, which rendered them as ideal sorbents for water treatment. As a proof of concept, the [email protected] monoliths were first utilized to remove Pb2+ ions and CR dye from aqueous solutions. Figure 4 (A and B) displays the adsorption isotherms of Pb2+ and CR. For comparison, the adsorption isotherms obtained from the pristine GF support were included. The isotherms were fitted by the Langmuir model (eq 2): Figure 2. TEM micrographs of CNFs. (A) Overview, (B) a representative CNT, (C) NiCu catalyst particle located in the tip of a CNF, and (D) high-resolution TEM.

qe =

qmax bCe 1 + bCe

(2)

where qe is the adsorption capacity of the sample at the equilibrium concentration (C e ), q max is the maximum adsorption capacity, and b is the Langmuir isotherm constant. The fitting results are listed in Table S1. For the adsorption of Pb2+, the qmax values of 11.5, 30.7, 52.5, 73.9, and 113 mg g−1 were obtained from the GF, [email protected], [email protected], [email protected], and [email protected], respectively. For the adsorption of CR, the GF, [email protected], [email protected],

the formation of dense CNF arrays. The thickness of the CNF arrays was up to 10 μm. It is noteworthy that the growth of CNFs on the carbon fiber support is remarkably uniform throughout the whole GF support as verified by the crosssectional view of the [email protected] composite (see Figure S3). The [email protected] monoliths obtained from varying reaction times were characterized by XRD as shown in Figure S4. The relative peak intensity C(002)/NiCu(111) in the XRD patterns increased

Figure 3. FESEM micrographs of [email protected] composites prepared with different reaction times: (A) 30, (B) 60, (C) 120, and (D) 240 min. The magnifications of the SEM micrographs increase from the left to right. 2353

DOI: 10.1021/acssuschemeng.6b00030 ACS Sustainable Chem. Eng. 2016, 4, 2351−2358

Research Article

ACS Sustainable Chemistry & Engineering

Figure 4. Adsorption isotherms of Pb2+ (A) and CR (B), and adsorption kinetics curves of Pb2+ (C) and CR (D) on the samples. (a) Pristine GF support, (b) [email protected], (c) [email protected], (d) [email protected], and (e) [email protected]

[email protected], and [email protected], exhibited qmax values of 21.8, 37.3, 83.3, 120.2, and 162.2 mg g−1, respectively. Shown in Figure S6, the qmax values were well correlated with the surface areas of the samples. The maximum adsorption capacities of the [email protected] samples were compared with those of adsorbents reported in the literature as shown in Tables S2 and S3. It is noteworthy that the adsorption capacities of the [email protected] sample are higher than those of carbonaceous adsorbents35,36 and even close to those of some oxides.37,38 The outstanding adsorption capacities of the [email protected] are attributed to its large BET surface area, which provides abundant sites for the adsorption of pollutants. One type of site could be the oxygencontaining species arisen from the thermal treatment, which could immobilize Pb2+ via complexing or electrostatic interactions. The adsorption of CR to the sorbents could be due to the π−π interaction. In addition, the defects in the carbon materials could also play an important role in the adsorption of pollutants. To study the kinetics of the adsorption process, the adsorption up-takes of the pollutants (qt) were recoded as a function of time as shown in Figure 4 (C and D). The adsorption up-takes increased sharply with increasing contact time in the initial stage and gradually reached to a saturated state with further increases in contact time. The adsorption data were fitted by using the pseudo-first-order equation, log(qe − qt ) = log qe −

k1 t 2.303

The resulting kinetic parameters and corresponding linear correlation coefficients (R2) are shown in Table S4. It reveals that the equilibrium adsorption up-takes of the samples also increase with increasing CVD time. For the adsorption of Pb2+ ions, the equilibrium adsorption up-takes of 9.1, 19.5, 33.8, 56, and 85.7 mg g−1 are obtained from the GF, [email protected], [email protected], [email protected], and [email protected] samples, respectively, while those of 16.1, 23.9, 43.8, 78.2, and 113.1 mg g−1 are obtained for the adsorption of CR. One significant advantage of 3D macroscopic porous monoliths for water treatment lies in the convenience of fixbed filtration adsorption. The filtration adsorption performance of the [email protected] monoliths was evaluated. Figure 5 shows the

(3) Figure 5. Breakthrough curves for the dynamic adsorption of CR to the [email protected] composite. (a) GF support, (b) [email protected], (c) [email protected], (d) [email protected], and (e) [email protected] monoliths.

where qe is the equilibrium adsorption up-take, k1 is the constant, and t is the contact time. 2354

DOI: 10.1021/acssuschemeng.6b00030 ACS Sustainable Chem. Eng. 2016, 4, 2351−2358

Research Article

ACS Sustainable Chemistry & Engineering breakthrough curves of dynamic adsorption of CR (initial concentration 100 mg L−1) through the [email protected] monoliths at a constant flow rate of 2.5 mL min−1. It revealed that most of the CR molecules were immobilized in the [email protected] monoliths in the initial filtration stage, e.g., the CR concentrations of the effluents in the initial stage were ca. 6.2, 5.7, 5.3, and 3.2 mg L−1 for the [email protected], [email protected], [email protected], and [email protected] monoliths, respectively, which were much lower than that of 48.7 mg L−1 obtained from the GF support. At 10% breakthrough point (defined as the point where the CR concentration in the effluent is 10% of the initial concentration), 21, 26, 36, and 50 mL of CR solution was filtrated through the [email protected], [email protected], [email protected], [email protected], and [email protected] monoliths, respectively. The penetration filtration adsorption results indicated that the [email protected] sample showed the best adsorption performance, which was consistent with the static batch adsorption results. Sorption of Organic Solvents and Oils. The bulk densities and porosities of the [email protected] monoliths were determined as shown in Table 1. The bulk densities were

Figure 6. Contact angle (a) and adsorption capacity (b) of the adsorbents.

the surface became progressively hydrophobic as the CNFs were continuously deposited to the GF support. The vertically aligned CNF arrays significantly enhanced surface roughness, leading to the superhydrophobicity of the [email protected] monoliths because of the minimization of contact areas between the surface and water droplet arisen from the trapped air.48 Notably, the [email protected] monolith possessed a maximum contact angle of 162°, manifesting the remarkable superhydrophobicity. The adsorption capacities of the sorbents for the adsorption of pump oil were evaluated. In Figure 6b, the volume-based adsorption capacities expressed with a unit of kilogram of organic compounds adsorbed per cubic meter sorbents (kg m−3) were used. It was revealed that the adsorption capacity of the sorbents also increased with increasing CVD time. The formation of CNF arrays in the GF support resulted in numerous superoleophilic pores, which provided a large volume of void space for oil capture via capillary forces.49 The [email protected] sorbent exhibited an adsorption capacity of 1100 kg m−3 for the adsorption of chloroform, which is larger than those of ultralight carbonbased aerogels (600−1000 kg m−3)50−52 and CNT foams (650 kg m−3),53 but lower than those of activated carbon-coated sponges (1380 kg m−3)54 and superhydrophobic sponges (3640 kg m−3).55 To further study the performance of the sorbents, the utilization efficiency of pore volume, defined as the ratio of adsorbed oil volume to the apparent volume of the sorbent, was calculated. As shown in Table 1, the porosity decreased while the utilization efficiency of pore volume increased with increasing CVD time. The growth of CNF arrays on the GF support reduced the total pore volume but significantly enhanced the utilization efficiency of pore volume. In particular, among the sorbents, the [email protected] exhibited a maximum utilization efficiency of pore volume of 91.7%, indicating that the total volume of the foam is almost fully utilized for oil capture. The [email protected] showed much higher utilization efficiency of pore volume than many previously reported sorbents, such as carbonaceous nanofiber aerogels (22.8%),56 polyurethane sponges (11.5%),57 graphene oxide foams (58.9%),58 ultralight carbon aerogels (25.6%),45 nanocellulose aerogels (70%), 59 and N-doped graphene frameworks (78.1%).46 The [email protected] monoliths also showed superoleophilicity for the absorption of organic solvents. Figure 7a depicts the adsorption of Sudan red III-dyed hexane on the surface of water. As soon as the [email protected] sorbent was put in contact with the mixture, the colored hexane was selectively adsorbed to the sorbent in less than 1 min (see the movie in the Supporting Information). To further demonstrate the superoleophilicity and high selectivity for oil adsorption, the [email protected] CF-240 sorbent was forced into water to adsorb chloroform at

Table 1. Physicochemical Properties and Oil Adsorption Performance of the Adsorbents sample GF [email protected] GF-30 [email protected] GF-60 [email protected] GF120 [email protected] GF240

bulk density (g cm−3)

contact angle (deg)

porosity (%)

adsorption capacity (kg m−3)

utilization efficiency of pore volume (%)

0.13 0.19

140 142

93.9 91.0

37.3 161.7

4.3 19.3

0.23

154

89.1

432.5

52.7

0.25

160

88.1

603.0

74.3

0.28

162

86.8

733.2

91.7

determined to be 130, 190, 230, 250, and 280 mg cm−3 for the GF, [email protected], [email protected], [email protected], and [email protected] GF-240, respectively, which are comparable to those of the reported conventional sponges (100−800 mg cm−3)39,40 and poly(dimethylsiloxane) sponges (170−420 mg cm−3),41 but much larger than those of CNT sponges (5.8 mg cm−3),42 CNT aerogels (4.0 mg cm−3),43 aerographite (0.18 mg cm−3),44 CNT/rGO aerogel (0.75 mg cm−3 ), 45 nitrogen-doped graphene framework (2.1 mg cm−3),46 and electrospun carbon−silica sponge (9.6 mg cm−3).47 The porosity, defined as the volume fraction of the void space within the sorbent, was calculated on the basis of the apparent and actual densities of the sorbent. By using an actual density of 2.17 g cm−3 for CNFs,47 porosities of 93.9, 91, 89.1, 88.1, and 86.8% were obtained from the GF, [email protected], [email protected], [email protected] CF-120, and [email protected], respectively. The increases in bulk densities and decreases in porosities with increasing reaction time were attributed to the accumulation of CNFs in the voids of the GF skeleton. The surface wettability of the sorbents was studied by the water contact angle measurements as shown in Figure 6a. The pristine GF support exhibited a contact angle of 140°, which was attributed to the high carbonization temperature during the preparation process. The contact angles of the [email protected] monoliths increased with increasing CVD time, indicating that 2355

DOI: 10.1021/acssuschemeng.6b00030 ACS Sustainable Chem. Eng. 2016, 4, 2351−2358

Research Article

ACS Sustainable Chemistry & Engineering

Figure 7. Digital photographs showing the sorption processes of (a) Sudan red 5B-dyed heptane and (b) Sudan red 5B-dyed chloroform by using the [email protected] monolith, (c) sorption capacities of the [email protected] monolith for various organic liquids, and (d) cyclic sorption and regeneration of the [email protected] sample via combustion.

the bottom of water. Shown in Figure 7b (and the movie in the Supporting Information), a mirror-like reflection was noted when the [email protected] monolith was immersed into water, which was ascribed to the formation of interface between the water and the air entrapped in the sorbent.60 The [email protected] monolith quickly adsorbed the chloroform in less than 1 s, indicating an excellent absorptive oil/water selectivity. Such fast kinetics of oil-adsorption from water were attributed to the superhydrophobic and superoleophilic surface, as well as the large surface area of the [email protected] sorbent. The adsorption performance of the [email protected] was further evaluated in terms of the absorption capacities toward a series of organic solvents and oils. Shown in Figure 7c, the [email protected] monolith exhibited volume-based capacities in the range of 200−1200 kg m −3 depending on the physicochemical properties, i.e., density, viscosity, and surface tension of the liquid sorbates. Table S5 summarizes the adsorption performance of various sorbents. It revealed that the [email protected] monolith exhibited larger volume-based capacities as compared with most reported sorbents. Admittedly, as the bulk density of the [email protected] sorbent is in the range of 100−300 mg cm−3, the mass-based absorption capacity is much lower (2−10 times its own weight) as compared with that of the reported aerogel sorbents (50−200 times) (see Table S5 in the Supporting Information). Nevertheless, the advantage of the [email protected] for water treatment is the well-defined geometric shape and excellent mechanical strength, which greatly facilitates its manipulation, transport, and recovering. It is worth noting that the [email protected] sorbents well maintain their hierarchical structural integrity and that no CNFs were isolated

from the GF support during the adsorption tests. In addition, the outstanding volume-based capacity of the [email protected] sorbent is also beneficial to its practical application in water treatment.53 For the practical application, the regeneration and recyclability of the sorbent are also important. The recyclability of the [email protected] sorbent was evaluated as shown in Figure 7d. The oil-saturated [email protected] could be facilely regenerated by combustion in air (see the movie in the Supporting Information). In the cyclic adsorption−combustion process, the adsorbed mass slightly decreased with increasing cycle number, indicating the excellent recyclability of the sorbent. Throughout the cyclic tests, the well-defined hierarchical structure of the [email protected] sorbent was well preserved (see Figure S7), and no isolated CNFs were observed.



CONCLUSION

We synthesized 3D porous [email protected] composite by an APCVD method. The as-prepared [email protected] monoliths exhibited a hierarchical porous structure, consisting of secondary vertically aligned CNF arrays anchored to the primary GF support. The surface areas, densities, and porosities of the monoliths could be facilely tuned by varying CVD times. The thermally treated [email protected] monoliths were utilized to remove Pb2+ and CR from aqueous solutions. It was found that the adsorption of Pb2+ and CR to the [email protected] sorbents could be described by the pseudo-first-order equation and that the isotherms could be well fitted by the Langmuir equation. The [email protected] showed the maximum adsorption capacities of 113 and 162.2 mg g−1 for the removal of Pb2+ and CR, 2356

DOI: 10.1021/acssuschemeng.6b00030 ACS Sustainable Chem. Eng. 2016, 4, 2351−2358

Research Article

ACS Sustainable Chemistry & Engineering

(5) Wang, S. B.; Peng, Y. L. Natural Zeolites as Effective Adsorbents in Water and Wastewater Treatment. Chem. Eng. J. 2010, 156, 11−24. (6) Suma, D.; Deng, D. Facile Synthesis of [email protected] Nanorods for Reversible Adsorption of Molecules and Absorption of Ions. ACS Sustainable Chem. Eng. 2015, 3, 133−139. (7) Lei, W. W.; Portehault, D.; Liu, D.; Qin, S.; Chen, Y. Porous Boron Nitride Nanosheets for Effective Water Cleaning. Nat. Commun. 2013, 4, 1777. (8) Unuabonah, E. I.; Gunter, C.; Weber, J.; Lubahn, S.; Taubert, A. Hybrid Clay: A New Highly Efficient Adsorbent for Water Treatment. ACS Sustainable Chem. Eng. 2013, 1, 966−973. (9) Zhou, G. Y.; Liu, C. B.; Tang, Y. H.; Luo, S. L.; Zeng, Z. B.; Liu, Y. T.; Xu, R.; Chu, L. Sponge-Like Polysiloxane-Graphene Oxide Gel as a Highly Efficient and Renewable Adsorbent for Lead and Cadmium Metals Removal from Wastewater. Chem. Eng. J. 2015, 280, 275−282. (10) Ali, I.; Gupta, V. K. Advances in Water Treatment by Adsorption Technology. Nat. Protoc. 2007, 1, 2661−2667. (11) Ali, I. New Generation Adsorbents for Water Treatment. Chem. Rev. 2012, 112, 5073−5091. (12) Namasivayam, C.; Kavitha, D. Removal of Congo Red from Water by Adsorption onto Activated Carbon Prepared from Coir Pith, an Agricultural Solid Waste. Dyes Pigm. 2002, 54, 47−58. (13) Zhuang, X.; Wan, Y.; Feng, C. M.; Shen, Y.; Zhao, D. Y. Highly Efficient Adsorption of Bulky Dye Molecules in Wastewater on Ordered Mesoporous Carbons. Chem. Mater. 2009, 21, 706−716. (14) Stafiej, A.; Pyrzynska, K. Adsorption of Heavy Metal Ions with Carbon Nanotubes. Sep. Purif. Technol. 2007, 58, 49−52. (15) Niu, Z. Q.; Liu, L. L.; Zhang, L.; Chen, X. D. Porous Graphene Materials for Water Remediation. Small 2014, 10, 3434−3441. (16) Sen Gupta, S.; Chakraborty, I.; Maliyekkal, S. M.; Adit Mark, T.; Pandey, D. K.; Das, S. K.; Pradeep, T. Simultaneous Dehalogenation and Removal of Persistent Halocarbon Pesticides from Water Using Graphene Nanocomposites: A Case Study of Lindane. ACS Sustainable Chem. Eng. 2015, 3, 1155−1163. (17) Yang, Y.; Tong, Z.; Ngai, T.; Wang, C. Y. Nitrogen-Rich and Fire-Resistant Carbon Aerogels for the Removal of Oil Contaminants from Water. ACS Appl. Mater. Interfaces 2014, 6, 6351−6360. (18) Cheng, Z. H.; Liao, J.; He, B. Z.; Zhang, F.; Zhang, F. A.; Huang, X. H.; Zhou, L. One-Step Fabrication of Graphene Oxide Enhanced Magnetic Composite Gel for Highly Efficient Dye Adsorption and Catalysis. ACS Sustainable Chem. Eng. 2015, 3, 1677−1685. (19) Bi, H. C.; Huang, X.; Wu, X.; Cao, X. H.; Tan, C. L.; Yin, Z. Y.; Lu, X. H.; Sun, L. T.; Zhang, H. Carbon Microbelt Aerogel Prepared by Waste Paper: An Efficient and Recyclable Sorbent for Oils and Organic Solvents. Small 2014, 10, 3544−3550. (20) Gao, Y.; Zhou, Y. S.; Xiong, W.; Wang, M. M.; Fan, L. S.; Rabiee-Golgir, H.; Jiang, L. J.; Hou, W. J.; Huang, X.; Jiang, L.; Silvain, J. F.; Lu, Y. F. Highly Efficient and Recyclable Carbon Soot Sponge for Oil Cleanup. ACS Appl. Mater. Interfaces 2014, 6, 5924−5929. (21) Wu, Z. Y.; Li, C.; Liang, H. W.; Chen, J. F.; Yu, S. H. Ultralight, Flexible, and Fire-Resistant Carbon Nanofiber Aerogels from Bacterial Cellulose. Angew. Chem., Int. Ed. 2013, 52, 2925−2929. (22) Nguyen, D. D.; Tai, N. H.; Lee, S. B.; Kuo, W. S. Superhydrophobic and Superoleophilic Properties of GrapheneBased Sponges Fabricated Using a Facile Dip Coating Method. Energy Environ. Sci. 2012, 5, 7908−7912. (23) Hayase, G.; Kanamori, K.; Fukuchi, M.; Kaji, H.; Nakanishi, K. Facile Synthesis of Marshmallow-like Macroporous Gels Usable under Harsh Conditions for the Separation of Oil and Water. Angew. Chem., Int. Ed. 2013, 52, 1986−1989. (24) Zhao, J. P.; Ren, W. C.; Cheng, H. M. Graphene Sponge for Efficient and Repeatable Adsorption and Desorption of Water Contaminations. J. Mater. Chem. 2012, 22, 20197−20202. (25) Chen, H.; Wang, X. X.; Li, J. X.; Wang, X. K. Cotton Derived Carbonaceous Aerogels for the Efficient Removal of Organic Pollutants and Heavy Metal Ions. J. Mater. Chem. A 2015, 3, 6073− 6081. (26) Su, D. S.; Chen, X. W.; Weinberg, G.; Klein-Hofmann, A.; Timpe, O.; Hamid, S. B. A.; Schlogl, R. Hierarchically Structured

respectively. Owing to the well-defined macroscopic hierarchical structures, the [email protected] monoliths were conveniently employed in fix-bed filtration adsorption. As advanced adsorbents, the as-prepared [email protected] monoliths showed outstanding efficiency to remove various organic solvents and oils. Notably, the [email protected] exhibited a remarkable volume-based adsorption capacity of 1100 kg m−3 for the adsorption of chloroform. The sorbent could be regenerated by combustion in air and showed outstanding recyclability for oil adsorption. The strategy disclosed in this study can be extended to integrate CNFs into other macroscopic supports, and the resulting 3D architectures could show great application in water treatment because of the structural merits.



ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acssuschemeng.6b00030. Modeling analyses of the adsorption data, comparison of adsorption performance of the sorbents, morphology of the catalyst precursor, XRD patterns, FESEM image of the cross-section and N2 adsorption−desorption isotherms of the samples, FESEM images of the regenerated sample (PDF) Movie 1 showing the adsorption of 0.5 mL hexane in the surface of water using the [email protected] (AVI) Movie 2 showing the adsorption of 1 mL hexane in the surface of water using the [email protected] (AVI) Movie 3 showing the adsorption of 0.5 mL chloroform in the surface of water using the [email protected] (AVI) Movie 4 showing the adsorption of 1 mL chloroform in the surface of water using the [email protected] (AVI) Movie 5 showing the regeneration of the spent [email protected] GF-240 sorbent by combustion (AVI)



AUTHOR INFORMATION

Corresponding Authors

*[email protected] *[email protected] Notes

The authors declare no competing financial interest.



ACKNOWLEDGMENTS The project was financially supported by the Scientific Research Foundation for the Returned Overseas Chinese Scholars, State Education Ministry, and the Natural Science Foundation of Guangdong Province, China (2014A030310315).



REFERENCES

(1) Voeroesmarty, C. J.; McIntyre, P. B.; Gessner, M. O.; Dudgeon, D.; Prusevich, A.; Green, P.; Glidden, S.; Bunn, S. E.; Sullivan, C. A.; Liermann, C. R.; Davies, P. M. Global Threats to Human Water Security and River Biodiversity. Nature 2010, 467, 555−561. (2) Fu, F. L.; Wang, Q. Removal of Heavy Metal Ions from Wastewaters: A Review. J. Environ. Manage. 2011, 92, 407−418. (3) Bhatnagar, A.; Sillanpaa, M. Utilization of Agro-Industrial And Municipal Waste Materials As Potential Adsorbents For Water Treatment-A Review. Chem. Eng. J. 2010, 157, 277−296. (4) Chen, B.; Ma, Q. L.; Tan, C. L.; Lim, T. T.; Huang, L.; Zhang, H. Carbon-Based Sorbents with Three-Dimensional Architectures for Water Remediation. Small 2015, 11, 3319−3336. 2357

DOI: 10.1021/acssuschemeng.6b00030 ACS Sustainable Chem. Eng. 2016, 4, 2351−2358

Research Article

ACS Sustainable Chemistry & Engineering

Outstanding Mechanical Performance. Adv. Mater. 2012, 24, 3486− 3490. (45) Sun, H. Y.; Xu, Z.; Gao, C. Multifunctional, Ultra-Flyweight, Synergistically Assembled Carbon Aerogels. Adv. Mater. 2013, 25, 2554−2560. (46) Zhao, Y.; Hu, C. G.; Hu, Y.; Cheng, H. H.; Shi, G. Q.; Qu, L. T. A Versatile, Ultralight, Nitrogen-Doped Graphene Framework. Angew. Chem., Int. Ed. 2012, 51, 11371−11375. (47) Tai, M. H.; Tan, B. Y. L.; Juay, J.; Sun, D. D.; Leckie, J. O. A Self-Assembled Superhydrophobic Electrospun Carbon−Silica Nanofiber Sponge for Selective Removal and Recovery of Oils and Organic Solvents. Chem. - Eur. J. 2015, 21, 5395−5402. (48) Hu, H.; Zhao, Z. B.; Gogotsi, Y.; Qiu, J. S. Compressible Carbon Nanotube−Graphene Hybrid Aerogels with Superhydrophobicity and Superoleophilicity for Oil Sorption. Environ. Sci. Technol. Lett. 2014, 1, 214−220. (49) Chen, N.; Pan, Q. M. Versatile Fabrication of Ultralight Magnetic Foams and Application for Oil/Water Separation. ACS Nano 2013, 7, 6875−6883. (50) Xiao, N.; Zhou, Y.; Ling, Z.; Qiu, J. S. Synthesis of a Carbon Nanofiber/Carbon Foam Composite from Coal Liquefaction Residue for the Separation of Oil and Water. Carbon 2013, 59, 530−536. (51) Gui, X. C.; Zeng, Z. P.; Lin, Z. Q.; Gan, Q. M.; Xiang, R.; Zhu, Y.; Cao, A. Y.; Tang, Z. K. Magnetic and Highly Recyclable Macroporous Carbon Nanotubes for Spilled Oil Sorption and Separation. ACS Appl. Mater. Interfaces 2013, 5, 5845−5850. (52) Inagaki, M.; Kawahara, A.; Konno, H. Sorption and Recovery of Heavy Oils Using Carbonized Fir Fibers and Recycling. Carbon 2002, 40, 105−111. (53) Liu, Y. F.; Ba, H.; Nguyen, D. L.; Ersen, O.; Romero, T.; Zafeiratos, S.; Begin, D.; Janowska, I.; Cuong, P. H. Synthesis of Porous Carbon Nanotubes Foam Composites with a High Accessible Surface Area and Tunable Porosity. J. Mater. Chem. A 2013, 1, 9508− 9516. (54) Sun, H. X.; Li, A.; Zhu, Z. Q.; Liang, W. D.; Zhao, X. H.; La, P. Q.; Deng, W. Q. Superhydrophobic Activated Carbon-Coated Sponges for Separation and Absorption. ChemSusChem 2013, 6, 1057−1062. (55) Huang, S. Y. Mussel-Inspired One-Step Copolymerization to Engineer Hierarchically Structured Surface with Superhydrophobic Properties for Removing Oil from Water. ACS Appl. Mater. Interfaces 2014, 6, 17144−17150. (56) Liang, H. W.; Guan, Q. F.; Chen, L. F.; Zhu, Z.; Zhang, W. J.; Yu, S. H. Macroscopic-scale Template Synthesis of Robust Carbonaceous Nanofiber Hydrogels and Aerogels and Their Applications. Angew. Chem., Int. Ed. 2012, 51, 5101−5105. (57) Zhu, Q.; Pan, Q. M.; Liu, F. T. Facile Removal and Collection of Oils from Water Surfaces through Superhydrophobic and Superoleophilic Sponges. J. Phys. Chem. C 2011, 115, 17464−17470. (58) Niu, Z. Q.; Chen, J.; Hng, H. H.; Ma, J.; Chen, X. D. A Leavening Strategy to Prepare Reduced Graphene Oxide Foams. Adv. Mater. 2012, 24, 4144−4150. (59) Korhonen, J. T.; Kettunen, M.; Ras, R. H. A.; Ikkala, O. Hydrophobic Nanocellulose Aerogels as Floating, Sustainable, Reusable, and Recyclable Oil Absorbents. ACS Appl. Mater. Interfaces 2011, 3, 1813−1816. (60) Bi, H. C.; Yin, Z. Y.; Cao, X. H.; Xie, X.; Tan, C. L.; Huang, X.; Chen, B.; Chen, F. T.; Yang, Q. L.; Bu, X. Y.; Lu, X. H.; Sun, L. T.; Zhang, H. Carbon Fiber Aerogel Made from Raw Cotton: A Novel, Efficient and Recyclable Sorbent for Oils and Organic Solvents. Adv. Mater. 2013, 25, 5916−5921.

Carbon: Synthesis of Carbon Nanofibers Nested Inside or Immobilized onto Modified Activated Carbon. Angew. Chem., Int. Ed. 2005, 44, 5488−5492. (27) Vieira, R.; Pham-Huu, C.; Keller, N.; Ledoux, M. J. New Carbon Nanofiber/Graphite Felt Composite for Use as a Catalyst Support for Hydrazine Catalytic Decomposition. Chem. Commun. 2002, 9, 954− 955. (28) García-Bordejé, E.; Kvande, I.; Chen, D.; Ronning, M. Carbon Nanofibers Uniformly Grown on Gamma-Alumina Wash Coated Cordierite Monoliths. Adv. Mater. 2006, 18, 1589−1592. (29) Worsley, M. A.; Stadermann, M.; Wang, Y. M. M.; Satcher, J. H., Jr; Baumann, T. F. High Surface Area Carbon Aerogels as Porous Substrates for Direct Growth of Carbon Nanotubes. Chem. Commun. 2010, 46, 9253−9255. (30) Pint, C. L.; Alvarez, N. T.; Hauge, R. H. Odako Growth of Dense Arrays of Single-Walled Carbon Nanotubes Attached to Carbon Surfaces. Nano Res. 2009, 2, 526−53. (31) Shen, Y.; Zhang, Z. H.; Xiao, K. J. Evaluation of Cobalt Oxide, Copper Oxide and Their Solid Solutions as Heterogeneous Catalysts for Fenton-Degradation of Dye Pollutants. RSC Adv. 2015, 5, 91846− 91854. (32) Shen, Y.; Lua, A. C.; Xi, J. Y.; Qiu, X. P. Ternary Platinum− Copper−Nickel Nanoparticles Anchored to Hierarchical Carbon Supports as Free-Standing Hydrogen Evolution Electrodes. ACS Appl. Mater. Interfaces 2016, 8, 3464−3472. (33) Shen, Y.; Lua, A. C. A Facile Method for the Large-Scale Continuous Synthesis of Graphene Sheets Using a Novel Catalyst. Sci. Rep. 2013, 3, 3037. (34) Shen, Y.; Lua, A. C. Synthesis of Ni and Ni-Cu Supported on Carbon Nanotubes for Hydrogen and Carbon Production by Catalytic Decomposition of Methane. Appl. Catal., B 2015, 164, 61−69. (35) Yu, X. Y.; Luo, T.; Zhang, Y. X.; Jia, Y.; Zhu, B. J.; Fu, X. C.; Liu, J. H.; Huang, X. J. Adsorption of Lead(II) on O2-Plasma-Oxidized Multiwalled Carbon Nanotubes: Thermodynamics, Kinetics, and Desorption. ACS Appl. Mater. Interfaces 2011, 3, 2585−2593. (36) Sui, Z. Y.; Meng, Q. H.; Zhang, X. T.; Ma, R.; Cao, B. Green Synthesis of Carbon Nanotube-Graphene Hybrid Aerogels and Their Use as Versatile Agents for Water Purification. J. Mater. Chem. 2012, 22, 8767−8771. (37) Song, L. X.; Yang, Z. K.; Teng, Y.; Xia, J.; Du, P. Nickel Oxide Nanoflowers: Formation, Structure, Magnetic Property and Adsorptive Performance towards Organic Dyes and Heavy Metal Ions. J. Mater. Chem. A 2013, 1, 8731−8736. (38) Li, H.; Li, W.; Zhang, Y. J.; Wang, T. S.; Wang, B.; Xu, W.; Jiang, L.; Song, W. G.; Shu, C. Y.; Wang, C. R. Chrysanthemum-like alphaFeOOH Microspheres Produced by a Simple Green Method and Their Outstanding Ability in Heavy Metal Ion Removal. J. Mater. Chem. 2011, 21, 7878−7881. (39) Wu, D. C.; Fu, R. W.; Zhang, S. T.; Dresselhaus, M. S.; Dresselhaus, G. Preparation of Low-Density Carbon Aerogels by Ambient Pressure Drying. Carbon 2004, 42, 2033−2039. (40) Fu, R. W.; Zheng, B.; Liu, J.; Dresselhaus, M. S.; Dresselhaus, G.; Satcher, J. H.; Baumann, T. E. The Fabrication and Characterization of Carbon Aerogels by Gelation and Supercritical Drying in Isopropanol. Adv. Funct. Mater. 2003, 13, 558−562. (41) Zhang, A. J.; Chen, M. J.; Du, C.; Guo, H. Z.; Bai, H.; Li, L. Poly(dimethylsiloxane) Oil Absorbent with a Three-Dimensionally Interconnected Porous Structure and Swellable Skeleton. ACS Appl. Mater. Interfaces 2013, 5, 10201−10206. (42) Gui, X. C.; Wei, J. Q.; Wang, K. L.; Cao, A. Y.; Zhu, H. W.; Jia, Y.; Shu, Q. K.; Wu, D. H. Carbon Nanotube Sponges. Adv. Mater. 2010, 22, 617−621. (43) Zou, J. H.; Liu, J. H.; Karakoti, A. S.; Kumar, A.; Joung, D.; Li, Q. A.; Khondaker, S. I.; Seal, S.; Zhai, L. Ultralight Multiwalled Carbon Nanotube Aerogel. ACS Nano 2010, 4, 7293−7302. (44) Mecklenburg, M.; Schuchardt, A.; Mishra, Y. K.; Kaps, S.; Adelung, R.; Lotnyk, A.; Kienle, L.; Schulte, K. Aerographite: Ultra Lightweight, Flexible Nanowall, Carbon Microtube Material with 2358

DOI: 10.1021/acssuschemeng.6b00030 ACS Sustainable Chem. Eng. 2016, 4, 2351−2358

Suggest Documents