Research Article Cite This: ACS Appl. Mater. Interfaces 2018, 10, 27416−27423
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Lotus-Seedpod-Bioinspired 3D Superhydrophobic Diatomite Porous Ceramics Comodified by Graphene and Carbon Nanobelts Yubao Bi,†,‡ Lei Han,† Yangfan Zheng,† Yunpeng Guan,† Haijun Zhang,*,† Shengtao Ge,† Huifang Wang,†,‡ Quanli Jia,§ Yuxin Zhang,∥ and Shaowei Zhang*,⊥
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†
The State Key Laboratory of Refractories and Metallurgy, Wuhan University of Science and Technology, Wuhan 430081, P. R. China ‡ High Temperature Materials Institute, Henan University of Science & Technology, Luoyang 471003, P. R. China § Henan Key Laboratory of High Temperature Functional Ceramics, Zhengzhou University, Zhengzhou 450052, P. R. China ∥ College of Materials Science and Engineering, Chongqing University, Chongqing 400044, P. R. China ⊥ College of Engineering, Mathematics and Physical Sciences, University of Exeter, Exeter EX4 4QF, United Kingdom S Supporting Information *
ABSTRACT: Hydrophobic and oleophilic sorbents play an important role in the remediation processes of oil spills/leakages occurring globally from time to time. In this work, for the first time, lotus-seedpod-bioinspired 3D superhydrophobic diatomite porous ceramics with good mechanical strength and thermal stability were fabricated, using inexpensive porous diatomite as a substrate, and graphene/carbon nanobelts as modifiers. Thanks to the presence of graphene coating and in situ formed carbon nanobelts, the surface energy of the final porous ceramics was reduced and their surface roughness increased, conferring superhydrophobicity on them. As-prepared porous ceramics demonstrated 3−30 times higher adsorption capacity in oil/water separation than their conventional inorganic sorbent materials, and had compressive strength 70−270 times higher than that of a sponge/graphene-based sorbent material. The present work could additionally offer a new strategy for the treatment/recycle of waste plastics, the so-called “white pollution”. KEYWORDS: hierarchical pore ceramic, graphene, carbon nanobelt, superhydrophobicity, oil/water separation
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INTRODUCTION
structures and larger sizes than their 0D and 2D counterparts.16−21 However, as they were generally prepared from sponges,22,23 and graphene24,25 or carbon-nanotube-based foams,26,27 most of them were too weak/fragile to withstand harsh conditions. For example, in the cases of graphene-oxidebased (GO-based) monolithic adsorbents, their compressive strength was only as low as 10−40 KPa.28,29 Such low strength would not enable them to perform safely in rough weather at sea or on rivers where oil spill/leakage accidents occurred more often. Therefore, development of robust 3D porous materials with high oil/water separation efficiency, good mechanical properties, and chemical stability is of great importance.
Oil spill/leakage accidents occur around the world from time to time, bringing about catastrophic effects on local environmental and ecological systems. Among the approaches used to tackle the problem, physical absorption is commonly employed and considered as one of the most economical, efficient, and green ways because of its great potential in complete removal of organic liquids from water, while bringing no negative effects to the environment. 1 Numerous functionalized materials with superhydrophobicity have been manufactured and applied recently for oil/water separation, 2−8 selfcleaning,9,10 and antifogging.11,12 Inspired by nature, e.g., lotus leaves,13 many metamaterials with superhydrophobicity have been developed on the basis of surface energy reduction along with surface roughening.14,15 Among them, those with 3D porous architectures in particular showed great oil/water separation efficiency due to their intrinsic hierarchical porous © 2018 American Chemical Society
Received: April 11, 2018 Accepted: July 23, 2018 Published: July 23, 2018 27416
DOI: 10.1021/acsami.8b05878 ACS Appl. Mater. Interfaces 2018, 10, 27416−27423
Research Article
ACS Applied Materials & Interfaces
Figure 1. Fabrication process of GCMD: (a) Digital image of a lotus seedpod. Schematic of fabrication process of GCMD: (b) Diatomite porous ceramics immersed in GO suspension. (c) Diatomite porous ceramics coated by reduced GO sheets. (d) Carbon nanobelts deposited on reducedGO-coated porous ceramics. (e) Final diatomite porous ceramics comodified by graphene and carbon nanobelts. surfaces and pores’ inside walls. The coated blocks were dried at 60 °C for 24 h in a vacuum dryer before being reduced by hydrazine hydrate vapor at 85 °C for 24 h. The reduced-GO-coated blocks after another 24 h of vacuum drying were dipped in Ni(NO3)2·6H2O solution of 0.5 wt % concentration. The polyethylene was loaded with 0.75 wt % Ni(NO3)2·6H2O via an incipient-wetness impregnation method. In a typical process, 0.5 g of Ni(NO3)2·6H2O was dissolved in 73 mL of ethanol and stirred for 30 min. Then, 67 g of polyethylene was immersed in the Ni(NO3)2·6H2O solution and stirred vigorously to achieve homogeneous adsorption of Ni(NO3)2· 6H2O onto its surface. The reduced diatomite porous ceramics prepared earlier were embedded in such polyethylene powders contained in an alumina crucible covered with a lid, and then fired at 700 °C for 2 h in N2 atmosphere to form in situ carbon nanobelts to further modify the reduced-GO-modified porous ceramics. The resultant GCMD was subjected to detailed characterization. The typical fabrication process of GCMD is schematically illustrated in Figure 1. The porous structure of GCMD overall is quite analogous to that of a lotus seedpod. The reduced GO functioned like the epicuticular wax of a lotus seedpod, decreasing the surface energy of porous diatomite ceramics, and the in situ carbon nanobelts increased the surface roughness of porous diatomite ceramics, functioning like the multiscale surface of a lotus seedpod. Sample Characterization. Morphologies and microstructures were observed by a scanning electron microscope (SEM, JSM-6610) equipped with an X-ray energy-dispersive spectroscope (EDS, Oxford, U.K.). A high-resolution transmission electron microscope (TEM, JEM-2100F HRSTEM) was employed for lattice-resolved imaging. Thermogravimetry and differential scanning calorimetry (TG-DSC, Netzsch STA 449C) analyses were carried out to evaluate thermal behaviors of samples. The content of carbon was assist measured by high-frequency infrared carbon and sulfur analyzer (CS-8800). Infrared spectra of samples were collected by a Fourier transform infrared spectrophotometer (FT-IR, Thermo Nicolet 6700) using the KBr pellet technique. X-ray photoelectron spectroscopy (XPS) was performed using a Thermo Scientific Escalab 250Xi electron spectrometer. Water wettability of samples was evaluated by measuring the water contact angle (WCA) using a video-based optical contact angle measuring system with a high-speed USB camera (DataPhysics OCA15Pro). Bulk density and apparent porosity of fired porous samples were measured by using the Archimedes’ method and their compressive strength values (sample sizes: 20 × 20 × 20 mm3) measured by using a digitally controlled tester (LM-02, Longsheng Test Facility Co. Ltd.) (cross-head speed: 0.5 mm/min). Adsorption Experiment. A series of digital photographs of organic solvent floating on deionized water were taken to monitor the dynamic oil adsorption. The adsorption capacity of a sample was evaluated by measuring weight gain values. Samples were soaked in the organic solvent for 5 min, and taken out and weighed after no residual liquid droplets were left on their surfaces. Each adsorption test was performed with three blocks, and the average values were taken. The adsorption capacity Q (g-organic liquid/g-GCMD) of a sample was calculated on the basis of eq 1:
As is well-known, a lotus seedpod (Figure 1a) which possesses a micro-/nanoscaled hierarchical structure exhibits superhydrophobicity.30 Bioinspired by this, we have successfully designed and fabricated 3D robust graphene/carbon nanobelts comodified superhydrophobic diatomite porous ceramics (referred to as GCMD) with a hierarchical pore structure analogous to that of the lotus seedpod, for highefficiency oil/water separation. Porous diatomite with a hierarchical pore structure was chosen as the substrate material, and GO and polyethylene were employed as carbon sources to functionalize the former, on the basis of the following considerations: (1) Diatomite is characterized by a porous structure with pore size ranging from micrometers to nanometers.31,32 It is nontoxic and readily available in a large quantity at a low cost, and does not cause any environmental concern after using. (2) Despite their brittleness, such porous ceramics possess sufficiently high compressive strength, and have better abrasion resistance compared to their polymerbased counterparts. Also, they can be readily manufactured in the large monolithic form and safely applied under harsh conditions. (3) Porous ceramics can be used over a broader range of temperatures and at a higher service temperature than their polymer-based counterparts. (4) The porous diatomite substrate functionalized by in situ formed carbon nanobelts from polyethylene can be used as a new material for treatment/recycle of the so-called “white pollution” of waste plastics. (5) The reduced GO and in situ carbon nanobelts can decrease the surface energy and improve the surface roughness of the porous diatomite substrate, enhancing oil/water separation efficiency.
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EXPERIMENTAL SECTION
Materials. Diatomite powder (∼45 μm, SiO2 ≥ 92 wt %, Hebei Haoying Minerals Co., Ltd.), graphite flakes (∼100 μm, C ≥ 99 wt %, Dongguang Xiangyang Graphite Fabricating Factory), and linear lowdensity polyethylene (∼3 mm, Shanghai LINGS Packaging Materials Co., Ltd.) were used as starting materials. Hydrazine hydrate (N2H4· H2O, 80 wt %, Sinopharm Chemical Reagent Co., Ltd.) and Ni(NO3)2·6H2O (AR, Sinopharm Chemical Reagent Co., Ltd.) were used as the reducing agent and catalytic precursor, respectively. Preparation of Diatomite Porous Ceramics. In a typical preparation, 40 wt % of diatomite powder, 1.25 wt % isobutylenemaleic anhydride copolymer, 0.25 wt % sodium carboxymethyl cellulose, and deionized water were mixed under mechanical stirring. A 0.6 vol % of triethanolamine lauryl sulfate was then added to form foams. The resultant slurry was cast into a mold and subsequently gelled. After demolding, the samples were dried and then fired at 1200 °C for 2 h. Preparation of GCMD. Diatomite porous ceramics were cut into small blocks of ∼1.5 × 1.5 × 1 cm, immersed in the GO suspension, and kept in vacuum (∼10 par) for 24 h for GO sheets to cover their 27417
DOI: 10.1021/acsami.8b05878 ACS Appl. Mater. Interfaces 2018, 10, 27416−27423
Research Article
ACS Applied Materials & Interfaces
Figure 2. Preliminary characterization of GCMD. (a) Unmodified diatomite porous ceramics with a WCA of 25°. (b, c) SEM images showing macropores in unmodified diatomite porous ceramics. (d) TEM image showing mesopores in unmodified diatomite porous ceramics. (e) Black reduced-GO-modified porous ceramics with a WCA of 98°. (f) Reduced GO present in pores of the porous ceramics shown in part e. (g) SEM image showing reduced GO membrane covering the inside wall of a pore in the porous ceramics shown in part f. (h) High-magnification SEM image showing wrinkles of reduced GO membrane shown in part g.
Figure 3. Water wettability and microstructure characterization of GCMD. (a) GCMD floated in water but sank in toluene. (b) GCMD with a WCA of 150°. (c) Many nanofibrous phases generated on diatomite particles. (d) High-magnification SEM of nanofibrous phases shown in part c. (e) TEM image of the carbon nanobelts. (f) HRTEM lattice image of the carbon nanobelts.
Q=
(m − m0) m0
where Qt is the adsorption capacity of a sample after t cycles, and Q0 is the initial adsorption capacity of a sample.
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(1)
RESULTS AND DISCUSSION The WCA of unmodified porous diatomite substrate was determined as 25°, indicating its good hydrophilicity (Figure 2a). SEM and TEM images reveal that it contained a significant number of macropores (Figures 2b,c) and mesopores (Figure 2d) (Figure S1, Supporting Information). Its apparent porosity was 80% and bulk density as low as 0.45 g/cm3. Furthermore, its room-temperature compressive strength after firing at 1200 °C was up to 2.7 MPa. After modification by reduced GO, the color of the porous diatomite substrate was changed from white to black, and the WCA
where m0 (g) and m (g) are, respectively, the masses before and after adsorption. After each cycle, the sample was dried for 6 h at 100 °C (above the boiling point of trihalomethanes, 61 °C) to remove the trihalomethanes and regenerate it for the next test cycle. The residual adsorption ratio R was calculated by eq 2 to evaluate the recyclability of samples: R=
Qt Q0
× 100% (2) 27418
DOI: 10.1021/acsami.8b05878 ACS Appl. Mater. Interfaces 2018, 10, 27416−27423
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ACS Applied Materials & Interfaces
be enhanced. In addition to their reinforcement effects,37 1D nanomaterials could contribute to the increase in the roughness of a solid material. A 2.8% weight loss, corresponding to an exothermic peak at 476 °C, was recorded by TG-DSC (Figure S5, Supporting Information), indicating that the total load of graphene and carbon nanobelts in GCMD was 2.8 wt %. As seen from Figure 3c, many nanobelts were formed on diatomite particles. A high-magnification SEM image (Figure 3d) further shows that the nanobelts were several microns long and about 300 nm wide but were very thin. They were confirmed by EDS to be carbon nanobelts (Figure S6, Supporting Information). Figure 3e presents a typical TEM image of some of the nanobelts, also showing that they were several microns in length. The EDS result in this case also confirmed that the nanobelts consisted of C (Figure S7, Supporting Information). The selected area electron diffraction (SAED) pattern additionally revealed that the carbon nanobelts were polycrystalline C (inset in Figure 3e). According to the high-resolution TEM (HRTEM) lattice image in Figure 3f, the lattice fringe spacing is 0.337 nm, which matches with the (002) plane of graphite (0.335 nm). During firing in N2 at 700 °C, the polyethylene precursor decomposed and released gaseous carbon-containing species which were subsequently deposited on diatomite as carbon nanobelts under the catalysis of Ni nanoparticles (the black particles shown in Figure 3e,f, whose EDS is illustrated in Figure S8). The carbon nanobelts were observed both on the surface and inside of GCMD (Figure S9, Supporting Information). On the basis of our own results and those reported previously by others,38−40 the growth mechanism of carbon nanobelts could be briefly described as follows: On heating, hydrocarbon gases such as propane, ethane, and methane were generated from the catalytic pyrolysis of polyethylene, and dissolved in nanosized catalyst droplets. Upon reaching carbon saturation, the dissolved carbon atoms would precipitate from the droplets as carbon nanobelts.38 The vapor−liquid−solid (VLS) mechanism is believed to have governed the overall growth process of nanobelts. At the firing temperature, NiO generated from the decomposition of Ni(NO3)2·6H2O was reduced to Ni which subsequently vaporized and then condensed to form a significant number of tiny Ni droplets on the porous ceramics substrate. Some of the tiny droplets linked with more neighbor droplets because of the gradually increased droplet size with the continuous Ni vapor supply, but the other droplets linked with fewer neighbor droplets. During the process, elliptical interfacial layers with different width/ thickness ratios would form between the Ni droplets, which then induced the growth of nanobelts. The small elliptical interfacial layer, formed between less linked Ni droplets, and the large elliptical interfacial layer, formed between more linked Ni droplets, were responsible for the formation of narrow nanobelts with small width/thickness ratio and wide nanobelts with large width/thickness ratio, respectively.39 Differently from in the case of unmodified diatomite porous ceramics, Fourier transform infrared (FT-IR) spectra of GCMD (Figure S10, Supporting Information) showed an additional weak peak at 1619 cm−1 corresponding to the characteristic peaks for aromatic CC.41 X-ray photoelectron spectra (XPS) exhibited the signal peaks of Si 2p, C 1s, and O 1s. The deconvoluted C 1s XPS spectrum indicated that the peak is composed of three Gaussian peaks, centered at the binding energies of 284.8, 286.6, and 288.8 eV, corresponding to CC, COC, and CO, respectively.42 The Si 2p
increased to 98° (Figure 2e), indicating the change from the original hydrophilicity to hydrophobicity, which might arise from the lowered surface energy caused by the reduced GO.33 TG-DSC analysis was carried out in air to measure the contents of reduced GO in the reduced-GO-modified porous ceramics. Differently from the case of unmodified porous diatomite ceramics (Figure S2, Supporting Information), in the case of reduced-GO-modified porous ceramics, about 0.40% weight loss was seen from the TG curve, which corresponded to the exothermic peak at 443 °C in the DSC curve (Figure S3, Supporting Information), suggesting that the total load of reduced GO in the modified diatomite porous ceramics was about 0.40%.34 Moreover, high-frequency infrared carbon and sulfur analysis was further performed to assist measure the amount of reduced GO in the reduced-GO-modified porous ceramics, and the result indicated that the amount of reduced GO was 0.4003 wt %, which is consistent with the result measured by TG. SEM shows that the reduced GO (indicated by green color in Figure 2f) was mainly present in the pores of modified ceramics. Figure 2g further reveals that the inside wall of a pore was entirely covered by reduced GO, suggesting the formation of reduced GO membrane via self-assembly.35 The wrinkles of the membrane also indirectly indicated the presence of reduced GO (Figure 2h). EDS (from the area highlighted by the red dot in Figure 2g) detected C, Si/O, and Ni, respectively from reduce GO, diatomite, and the catalyst employed (Figure S4, Supporting Information), further confirming the formation of reduced GO membrane. In addition, SEM observations reveal that pore pathways in the reduced-GO-modified porous ceramics were not blocked by the reduced GO membrane, so the overall pore volumes were not decreased significantly, which would be beneficial to their adsorption capacity of organic liquids. The bulk density and porosity of reduced-GO-modified porous ceramics were 0.45 g/cm3 and 79%, respectively, which were very close to those of unmodified porous ceramics (bulk density of 0.45 g/cm3 and porosity of 80%), further suggesting that the total pore volumes were not decreased significantly. Surface roughness of the reduced-GO-modified diatomite porous ceramics was improved by further depositing carbon nanobelts on their surface via in situ chemical vapor deposition using polyethylene as a carbon source. The resultant graphene/ carbon nanobelts comodified porous ceramics (i.e., GCMD) could float in water but sink in toluene (Figure 3a). They exhibited a WCA of about 150° (Figure 3b) (Video S1, Supporting Information), which was higher than those reported for many other adsorbent materials (Table S1, Supporting Information), indicating its superhydrophobic and oleophilic nature. This indicated that the hydrophobicity of diatomite porous ceramics was further enhanced by additional formation of carbon nanobelts. The wettability of a solid usually can be changed by roughening its surface. Assuming a 180° liquid contact angle for air, the contact angle (θ) on a rough surface can be described by the Cassie equation:36 cos θ = f (cos θ* + 1) − 1
(3)
where f is the fraction of solid surface area wetted by the liquid, and θ* is the contact angle of smooth surface. On increasing the roughness of solid surface, gaps between protrusions on the solid surface would be filled with air rather than water, thus decreasing the f value. Consequently, the contact angle (θ) would become bigger, and the hydrophobicity of solid would 27419
DOI: 10.1021/acsami.8b05878 ACS Appl. Mater. Interfaces 2018, 10, 27416−27423
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Figure 4. Adsorption capacity, recyclability, and separation efficacy of GCMD. (a) Adsorption capacity of GCMD for carbon tetrachloride, toluene, trihalomethanes, vacuum pump oil, and vegetable oil. (b) Recyclability of GCMD. (c) GCMD fixed in a fixture. (d, e) Before and after separation of GCMD ceramics for paraffin oil/water mixture.
Table 1. Comparison of Adsorption Capacity Values of Various Adsorbent Materials Developed to Date adsorbent material
adsorbate
viscosity (mPa s)
density (g/cm3)
adsorption capacity (g/g)
ref
sepiolite bentonite zeolite modified silica particles phenyltriethoxysilane-modified diatomite diatomite/silicalite-1 composite seeded diatomite GCMD
motor oil motor oil motor oil motor oil benzene benzene benzene toluene vacuum pump oil
10.88 10.88 10.88 393.00 0.64 0.64 0.64 0.58 40.00
0.89 0.89 0.89 0.89 0.88 0.88 0.88 0.87 0.87
0.174−0.184 0.150−0.176 0.166−0.192 0.330 0.028 0.095−0.246. 0.027−0.046 0.815 1.025
46 46 46 47 48 49 50 this work this work
XPS spectrum also showed only one single peak centered at the binding energy of 102.6 eV, corresponding to SiO (Figure S11, Supporting Information). No CSi peak appeared, suggesting that the reduced GO and carbon nanobelts were only physically bound with the diatomite. All of these results confirmed again the presence of reduced GO and carbon nanobelts in the GCMD. As is well-known, the wettability of a solid surface depends on its chemical composition and topographical structure.43,44 The surface energy of the GCMD was lowered by graphene, and their surface roughness was further increased by carbon nanobelts, explaining well their superhydrophobicity. The adsorption capacity of GCMD for organic liquids was evaluated in terms of weight gain.45 Several organic liquids with various viscosity and density values were employed, including common organic liquids (trihalomethanes, carbon tetrachloride, and toluene), vegetable oil, and commercial petroleum product (vacuum pump oil). The adsorption capacity values for carbon tetrachloride, toluene, trihalomethanes, vacuum pump oil, and vegetable oil were 1.801, 0.815, 1.544, 1.025, and 1.090 g-organic liquid/g-GCMD, respectively (Figure 4a). Compared to the inorganic sorbent materials reported previously by others, GCMD developed in this work demonstrated considerably improved adsorption
capacity (3−30 times better) for these organic liquids (Table 1). In addition to adsorption capacity, the recyclability of an adsorbent material needs to be considered for practical applications. The recyclability of as-prepared GCMD was tested by using trihalomethanes as an example organic liquid. The adsorption capacity values after 1, 2, 3, and 4 cycles were determined as 1.544, 1.548, 1.512, and 1.516 g/g, respectively. Correspondingly, the residual adsorption ratios were 100.0%, 100.3%, 97.9%, and 98.2%, respectively (Figure 4b). These results indicated that the adsorption capacity had only decreased very slightly (by only 1.8%) after 4 cycles, verifying the excellent recyclability of as-prepared GCMD. The performance of as-prepared GCMD in oil/water separation was further demonstrated using mixed toluene/ water as an example. Initially, toluene stained with Sudan Red III was mixed with deionized water, and the former was floating on the latter. Then, as-prepared GCMD ceramics were placed in the mixed liquid, and a series of digital photos were taken to assist in evaluating the dynamic adsorption process (Figure S12, Supporting Information). It was found that the toluene diffused through the water under no additional stirring and became absorbed completely by the GCMD in just 1 min, revealing evidently that as-prepared GCMD ceramics were 27420
DOI: 10.1021/acsami.8b05878 ACS Appl. Mater. Interfaces 2018, 10, 27416−27423
Research Article
ACS Applied Materials & Interfaces
recyclability and more diverse service conditions. The high mechanical strength, low bulk density, good chemical inertness, and thermal stability of as-prepared GCMD could enable them to be utilized reliably under harsh conditions and in rough environments. They could be potentially used as a promising material for addressing oil and organic solvent leakage problems.
highly effective/efficient in separating toluene from its mixture with water. More importantly, compared to the other passive adsorption materials, GCMD could be designed to actively and continuously separate organic liquids from their mixtures with water via a self-priming pump system because of its high mechanical strength and highly selective adsorption for organic liquid. GCMD ceramics were connected with a self-priming pump (power: 15 W) through a self-designed device (Figure 4c), and placed in a paraffin oil/water solution (paraffin oil dyed with Sudan Red III). As shown in Figure 4d,e, paraffin oil was selectively removed from its mixture with water with assistance of the pump. Ultimately, it was separated completely from the mixed solution within a short time (Video S2, Supporting Information). Although 3D polyurethane (onset pyrolysis temperature of 170 °C51) and graphene-foam-based adsorbent materials showed higher adsorption capacity, GCMD ceramics prepared in this work were more durable and could be potentially used under more diverse conditions. In the present work, no reduced GO or carbon nanobelts were observed in the organic liquids after the adsorption and oil/water separation test, suggesting that the reduced GO and carbon nanobelts were well-bound with the porous ceramics substrate. The durability of as-prepared GCMD ceramics was also evaluated by subjecting them to abrasion and high-temperature heat treatment. After 1 mm deep abrasion by a sandpaper, they still exhibited a WCA of 130°. Moreover, after 2 h of heat treatment in air at 200 °C, their WCA also only decreased slightly to 135°. For comparison, graphene-/carbon-nanotubemodified 3D polyurethane foams would start to pyrolyze and lose their 3D structure at only about 170 °C. Also, their compressive strength generally was as low as 10−40 KPa,28,29 about 70−270 times lower than in the case of the present GCMD. In addition, another distinct advantage of the present GCMD is that the diatomite substrate after use could be readily regenerated by simply heating it at above 600 °C in air. Pore structures in the regenerated diatomite substrate remained undamaged/undestroyed thanks to the high mechanical strength and thermal stability of the substrate. Therefore, the degraded diatomite substrate could be ecofriendly reused/recycled to fabricate new GCMD porous ceramics. In contrast, the recycle of polyurethane is one of the big global challenges. Considerable environmentally unfriendly/toxic gases will be released with its burning. The heat treatment of diatomite might lead to the transformation from amorphous silica into crystalline cristobalite; however, unlike its powder-formed counterpart which enters into the human body more easily through the respiratory system and potentially causes silicosis, cristobalite in the present case (if formed) would still be “immobilized” in situ in the highstrength bulk products, and thus would hardly pose any potential health risk during the production and application processes.
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ASSOCIATED CONTENT
* Supporting Information S
The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acsami.8b05878. Additional figures including EDS, TG-DSC, FT-IR, and XPS curves (PDF) Video S1: GCMD exhibiting a WCA of about 150° (AVI) Video S2: paraffin oil selectively removed from its mixture with water with assistance of a pump, ultimately being separated completely from the mixed solution within a short time (AVI)
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AUTHOR INFORMATION
Corresponding Authors
*E-mail:
[email protected]. *E-mail:
[email protected]. ORCID
Haijun Zhang: 0000-0002-9546-8524 Yuxin Zhang: 0000-0003-4698-5645 Notes
The authors declare no competing financial interest.
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ACKNOWLEDGMENTS This work was financially supported by National Natural Science Foundation of China, Grant 51472184 and 51672194; Key Program of Natural Science Foundation of Hubei Province, China, Contract 2017CFA004; and Program for Innovative Teams of Outstanding Young and Middle-aged Researchers in the Higher Education Institutions of Hubei Province, Grant T201602.
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REFERENCES
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CONCLUSION Robust high-performance GCMD were successfully fabricated for the first time, via cofunctionalizing a diatomite porous substrate with reduced GO sheets and carbon nanobelts. Adsorption test results indicated some outstanding features of as-prepared GCMD, including excellent adsorption capacity for various viscous organic liquids, continuous and efficient separation of oil from its mixture with water, and better 27421
DOI: 10.1021/acsami.8b05878 ACS Appl. Mater. Interfaces 2018, 10, 27416−27423
Research Article
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DOI: 10.1021/acsami.8b05878 ACS Appl. Mater. Interfaces 2018, 10, 27416−27423
