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Superhydrophobic hierarchical biomass carbon aerogel assembled with TiO2 nanorods for selective immiscible oil/water mixture and emulsion separation Dengsen Yuan, Tao Zhang, Qing Guo, Fengxian Qiu, Dongya Yang, and Zhongping Ou Ind. Eng. Chem. Res., Just Accepted Manuscript • DOI: 10.1021/acs.iecr.8b03661 • Publication Date (Web): 11 Oct 2018 Downloaded from http://pubs.acs.org on October 12, 2018

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Industrial & Engineering Chemistry Research

Superhydrophobic hierarchical biomass carbon aerogel assembled with TiO2 nanorods for selective immiscible oil/water mixture and emulsion separation Dengsen Yuan a, Tao Zhang a,b* , Qing Guo a, Fengxian Qiu a,*, Dongya Yang a, Zhongping Ou a a

School of Chemistry and Chemical Engineering, Jiangsu University, Zhenjiang 212013, China

b

Institute of Green Chemistry and Chemical Technology, Jiangsu University, Zhenjiang 212013, China

*Corresponding authors: Tel./fax: +86 511 88791800. E-mail: [email protected] (T. zhang); [email protected] (F. Qiu) 1

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ABSTRACT: The hierarchical nanomaterials/biomass carbon aerogels are of great interest in various fields including oil/water separation, and oil absorption based on the synergistic effects of mechanical strength, recyclability and wettability together with the convenient separation. Here, we reported fabrication of the hybrid aerogel prepared simply by in situ growth of TiO2 nanorods on the surface of the biomass carbon aerogel under hydrothermal condition, followed by the surface modification in hydrogen atmosphere. The interconnected 3D network structure of hybrid aerogel could offer a passageway to transport oil and store the absorbed oils. The as-prepared aerogel could act as a membrane for separating oil from oil/water mixture and it also could separate effectively surfactant-stabilized water-intoluene emulsions. Furthermore, the aerogel exhibited the excellent reusability and durability after intensive compression and repeated oil absorption, which provides a reliable approach for the development of sustainable and efficient absorbents toward environmental protection applications. KEYWORDS: Micro-nano structure, TiO2 nanorods, Biomass carbon aerogel, Superhydrophobicity, Oils absorption. INTRODUCTION With the development of marine engineering, environmental pollution caused by frequent oil-spill accidents and industrial production has become one of the most urgent environmental problems.1-3 In addition, the leakage of water-insoluble organic solvents (such as toluene, carbon tetrachloride, acetone) also destroy ecological environment. In the 2


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past decades, traditional oil-recovery technologies and methods including physical methods (skimmer, absorbent), chemical methods (solidifier, dispersant, in-situ burning) and biologic methods (microbiological deterioration) could no longer meet all above requirements.4-6 Due to its low cost, recyclability, and no adverse effect to the environment, physical absorption via porous absorbent is the most promising and green method for oil collection and recovery among these methods.7-9 Currently, many porous materials (including sponge-based material,10 foam-based material11 and membrane material12) have been reported to separate oil from oily wastewater. However, they still suffer from some critical drawbacks such as low absorption capacities, expensive raw materials, and complicated fabrication processes, which limit their practical application in oil/water separation. Therefore, it is urgent to explore a facile, low cost and high absorption capacities porous materials to solve the oily wastewater. Carbon aerogels are attractive for their fascinating features (ultralow density, excellent electrical conductivity, large surface area, and high porosity), which have been widely applicated in biomedical, environmental, and energy fields.13-15 Currently, various raw materials (such as carbon fiber,16 carbon nanotubes17 and graphene,18) have been used to prepare multifunctional carbon aerogels. Although various carbon aerogels have been successfully prepared, most previous and existing carbon aerogels possessed the critical drawbacks of expensive precursors, complicated fabrication procedure, and restriction in scale up, which could limit greatly in industrial applications.19, 20 It is reported that the graphene aerogel was synthesize by a facile hydrothermal method and exhibited excellent 3



adsorption capacity, but the expensive cost of graphene limits its practical application.21 Therefore, there is a trend to use biomass as raw materials to fabricate carbon-based aerogel, as it is easy to obtain, abundant in nature and environmental benefits. Among them, cellulose is one of the most abundant renewable natural polymer, which has received increasing attention in the preparation of biomass carbon materials.22, 23 In this regard, the reported biomass carbon aerogels possess many favorable properties, but them still hold some shortcomings (such as wettability, stability).24 Furthermore, wettability is one of the important characteristics of solid surface, which is available for effectively removing oil from oily wastewater. Thus, it is of great significant to improve the wettability of porous materials. Wettability is influenceed by the chemical composition and the microstructure of the surface. Also, different wettability of surface could be obtained by controlling the two factors.25, 26 Jiang et al.27 found that there are micro-nano hierarchical structures on the lotus leaf surface and branch-like nanostructures on the top of micropapillae result in the formation of superhydrophobicity. Therefore, the presence of both micro-nano structures plays an important role in obtaining superhydrophobic surfaces. In addition, the low surface energy is the other important factor in obtaining the superhydrophobic surface.28, 29

It has been known that the chemical modifications can regulate the surface wettability in

order to improve chemical affinities for selectivity of oil or water molecules. Although the superhydrophobic surfaces could be successfully prepared, most previous and existing chemical modifications (such as organosilicons,30 polymers31) possessed the critical 4


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drawbacks of unstable superhydrophobicity, environmental pollution, and complicated process, which could limit greatly their practical applications. For example, the superhydrophobic surface of as-prepared sponge was obtained by dip-coating in a fluoropolymer aqueous solution, which exhibits excellent superhydrophobicity and superoleophilicity.32 Although wettability of sponge could be converted from superhydrophilicity to superhydrophobicity, the potential environmental pollution has restricted their practical applications due to the low surface energy of fluoropolymer (-CF2group). Therefore, a strategy for facile and green modification of surface, which renders hybrid aerogels more widespread applications, is still desirable. Herein, we reported a reliable route to prepare superhydrophobic hierarchical biomass carbon@TiO2 (SHBCT) aerogel that can be utilized as an advanced absorbent of oils and organic solvents. The aerogel was prepared simply by in situ growth of TiO2 nanorods on the surface of the biomass carbon aerogel under the hydrothermal condition and the surface modification of the aerogel was calcinated in hydrogen atmosphere. This method can endow biomass carbon aerogel with a robust micro-nano structure, enhanced roughness, and durable superhydrophobicity. The interconnected 3D network and micro-nano structure of as-prepared aerogel have been verified to selectively transport microdroplets through its network, which can absorb various oil from mixtures with a high storage capacity simultaneously, separate non-polar solvents from mixtures efficiently. Above all, this facile fluorine-free, environment-friendly, and inexpensive method is easily employed by industry as a reliable agent for wastewater treatment. 5



EXPERIMENTAL SECTION Materials Sisal leaves were collected from the campus of Jiangsu University, in Zhenjiang, China. Sodium chlorite (NaClO2), Acetic acid (CH3COOH), Sodium hydroxide (NaOH), Anhydrous ethanol (CH3CH2OH), Hydrochloric acid (HCl) and Titanium isopropoxide (C12H28O4Ti, 98%) were purchased from Sinopharm Chemical Reagent Co., in Shanghai, China. Deionized water (DI water) was used throughout the experiment. All chemicals in this experiment are of reagent grade and used without any further purification. Preparation of biomass carbon aerogel The biomass carbon aerogel (BC aerogel) was fabricated according to the method described by Liu and co-workers33. Typically, 20 g of the raw sisal leaves was firstly stirred in 5 wt% NaOH solution at 80 °C for 3 h, followed by in 5 wt% acidified NaClO2 solution for 3h. Then, 5 g of sisal cellulose was redispersed in solution to form the homogeneous suspensions, followed by freeze-drying process to achieve sisal cellulose aerogel (SC aerogel). Finally, the as-prepared SC aerogel was heated to 700 °C for 2 h and the BC aerogel was collected after the tubular furnace cooled down to room temperature naturally. Preparation of hierarchical biomass carbon@TiO2 aerogel The hierarchical biomass carbon@TiO2 aerogel (HBCT aerogel) was achieved by in situ growth of TiO2 nanorods on the surface of BC aerogel through a hydrothermal method. Briefly, 0.06 M of C12H28O4Ti was added into 30 mL of 5 M HCl, and then 0.5 g of HBCT aerogel was sealed in the precursor solution. Then, the suspension was transferred to a 6


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Teflon-lined stainless-steel autoclave in an air flow electric oven at 150 oC for 14 h. After the autoclave was cooled to room temperature, the sample was washed with ethanol and dried at 50 oC for 12 h to achieve HBCT aerogel. Hydrophobic modification of HBCT aerogel Oxygen deficiency was formed on the surface of titanium dioxide by heat treatment in a hydrogen atmosphere, which could improve the wettability of the as-prepared aerogel. So, the HBCT aerogel was further thermally annealed at a temperature of 400 °C in mixed Ar and H2 (90: 10 by flow) atmosphere for 1 h using a ramp rate of 3 °C min−1 to obtain superhydrophobic hierarchical biomass carbon@TiO2 aerogel (SHBCT aerogel). The preparation process of SHBCT aerogel is illustrated in Figure 1.

Figure 1. Schematic illustration of fabrication of the SHBCT aerogel. Characterization The phases of SC aerogel, BC aerogel, HBCT aerogel and SHBCT aerogel were 7



identified using X-ray diffraction in the 2θ range from 10o to 80o with a scanning rate of 4° min-1 (D8 ADVANCE). The microscopic structures and elements of SC aerogel, BC aerogel, and HBCT aerogel were investigated by scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX) measurements performing at accelerating voltage of 15 kV (JSM-7001F). The contact angle measurements of HBCT aerogel and SHBCT aerogel were carried out by applying 5 μL of deionized water and the water contact angel (WCA) values were the average of at least five measurements of a water droplet at different positions on each sample (CAM 200 optical system). The specific surface areas of BC aerogel and HBCT aerogel were calculated by the Brunauer–Emmett–Teller (BET) method from data in a relative pressure (P/P0) range between 0.05 and 1.0. Pore size distribution plots of BC aerogel and HBCT aerogel were calculated based on the Barrett– Joyner–Halenda (BJH) model (Micromeritics ASAP 2020 adsorption analyzer). Fourier transform infrared spectra (FT-IR) were used to analyze functional groups of SC aerogel, BC aerogel, HBCT aerogel and SHBCT aerogel by using KBr pellets in the range from 4000 to 400 cm-1 (Nicolet Nexus 470). Separation of emulsions The removal of tiny water droplets in Tween 80-stabilized water-in-toluene emulsions was performed by the following procedure. Firstly, 0.1 g of Tween 80 concentration was added into the 50 mL toluene, and the water-in-toluene mixtures (1: 50, V/V) were intensively stirred until a stable milk emulsion formed without any demulsification or precipitation. Next, the as-prepared SHBCT aerogel was inserted in the separation device 8


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and a variety of water-in-toluene emulsions were poured into the upper tube. Then, toluene penetrated the device into the beaker quickly while water was stuck on the top of aerogel. The separation process was only driven by gravity. Oil absorption capacity experiment The oil absorption capacity of SHBCT aerogel was determined by the weighing method. The absorption process is as follows: 0.1 g of SHBCT aerogel was forced into a 30 mL of liquid bath for about 60 s at room temperature, and then picked out from the bath and paused for 5 s to remove the redundant liquid. The oil-absorption SHBCT aerogel was measured again. The absorption capacity (Q) was calculated using the following equation (1): Q = (Mt - M0)/M0

(1)

where, M0 and Mt are the weights of the SHBCT aerogel before and after absorption, respectively. Reusability experiment The absorption-squeezing experiment was carried out to evaluate the recycling performance. To study the reusability of SHBCT aerogel, it was placed into the ethanol to remove the absorbed oils or organic solvents and dried at 50 oC. During the regeneration experiment, this operation reused for oil/water separation for 9 cycles were tested for each experiment. RESULTS AND DISCUSSION Morphology of aerogels 9



As a green resource in nature, cellulose has properties of high polymerization, chemical durability and mechanical stability due to the strong inter-molecular hydrogen bonding. Here, the biomass cellulose can be used as a potential raw material for preparation of absorption material to separate oil from oil/water mixtures. The structures of the SC aerogel, BC aerogel and HBCT aerogel were studied via SEM, and the representative images of these samples are shown in Figure 2 and Figure 3. It can be seen that the biomass cellulose cross each other to form interconnected 3D network structures, with the single cellulose having a diameter of 6 micrometers and the length of hundreds of micrometers to several millimeters after a series of treatments (Figure 2). Also, the obtained SC aerogel possesses high porosity and the pore sizes range from several of micrometers to dozens of micrometers, which can offer a passageway to transport oil and store the absorbed oils. The BC aerogel was obtained by carbonization of SC aerogel at 700 °C in a N2 atmosphere. The SEM images of BC aerogel with different magnifications displayed in Figure 3a-b. Compared with SC aerogel, the BC aerogel could maintain well the morphology of SC aerogel after carbonization, but it underwent about 30% shrinkage in diameter and the average diameter was approximately 4 μm. In addition, the surface of the BC aerogel was observed to be rougher after carbonization, which could improve effectively the storage of absorbed oils.

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Figure 2. Typical SEM images of (a-d) SC aerogel with different magnifications. With the introduction of the nanomaterials on the surface of BC aerogel, limitations of practical application could be overcome effectively, which is a versatile way for fabrication of absorbed materials. After in situ growth of TiO2 nanorods, the BC aerogel was covered by the flower-like TiO2 nanorods. As shown in Figure 3c-d, uniform cauliflower-like TiO2 nanorods on HBCT aerogel with an average diameter of around 2–3 μm were well dispersed and self-assembled on the surfaces of the HBCT aerogel after a facile hydrothermal reaction. The flower-like TiO2 nanorods were assembled by large number of single TiO2 nanorod having an average diameter of around 150–200 nm and the length of 1-2 μm, which leads to the hierarchical micro-nano structure on surface of BC aerogel and improving the wettability of HBCT aerogel. The elemental mapping (Figure 3e) reveals the homogenous distribution of C, O and Ti elements in the HBCT aerogel, indicating that 11



the TiO2 nanorods were homogeneously distributed on the surface of the HBCT aerogel. The image of Figure 3f shows a typical EDX spectrum recorded from the selected area, in which three elements of C, O and Ti are simultaneously presented and mainly dominated by Ti, with lower proportions of C and O. Consequently, combining the SEM and EDS results, it was obvious that the TiO2 nanorods were successfully distributed on the surface of the HBCT aerogel with a 3D interconnected network during the hydrothermal treatment. There is no significant change in the morphology of SHBCT aerogel after calcinated in hydrogen atmosphere (Figure S1).

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Figure 3. Typical SEM images of (a-b) BC aerogel and (c-d) HBCT aerogel with different magnifications. The right column shows (e) the EDS mapping images and (f) EDS images of HBCT aerogel. The inset in (d) is a typical picture of a cauliflower in nature. Chemical Structure of aerogels To investigate the transformation from the SC aerogel to the HBCT aerogel, the 13



surface functional groups of SC aerogel, BC aerogel and HBCT aerogel were investigated by FT-IR spectra (Figure 4a). In the FT-IR spectrum of the pure SC aerogel, the characteristic bands appeared at 3426, 2920, 1627, 1384, 1110 and 1057 cm-1 could be ascribed to O-H, CH3, C=C, C-H, C-O-C and C-O, respectively. Compared to the spectrum of the SC aerogel, the main absorption bands of the BC aerogel at 3426 cm-1 (stretching vibration O-H) became extremely weak and 2920 cm-1 (stretching vibration of C-H) and 1110 cm-1 (stretching vibration of C-O-C) disappeared after carbonization. In comparison of BC aerogel, the HBCT aerogel exhibits a broad absorption peak below 1000 cm-1 after the hydrothermal reaction, which is presumably ascribed to the combination of Ti-O-Ti and Ti-O-C vibration modes resulting from the chemical interaction between TiO2 and BC aerogel. This is in accordance with Wang et.al previous work34. By comparing spectra of the HBCT aerogel before and after modification, the characteristic peak of SHBCT aerogel at 3426 cm-1 (stretching vibration O-H) disappeared after H2 modification and it could also explain hydrophobicity of SHBCT aerogel. (Figure S2b). To further reveal the structural properties of SC aerogel, BC aerogel and HBCT aerogel, XRD patterns were measured and displayed in Figure 4b. As can be seen, the origin SC aerogel showed two strong characteristic peaks centered at 2θ = 15.24° and 22.67°, which can be attributed to the (110) and (200) diffraction peaks and correspond to typical of the cellulose I crystalline. After carbonization, the peak of BC aerogel at 2θ=15.24° and 22.67° became extremely weak and two broad peaks at 2θ=25°-35° and 38°-43° appeared, which can be attributed to the (002) and (100) diffraction peaks and may 14


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mean that the crystalline structure of the BC aerogel has been destroyed and amorphous carbon has been formed in the carbonization process. In comparison, the HBCT aerogel exhibited characteristic diffraction peaks at about 27.4°, 36.0°, 41.2° and 54.3°, indicate the (110), (101), (111) and (211) diffraction peaks of tetragonal rutile TiO2 (JCPDS NO. 21–1276). This implies that tetragonal rutile TiO2 formed during the hydrothermal process by the reversible reactions of C12H28O4Ti under acid condition.35 Compared with HBCT aerogel, no characteristic diffraction peaks can be observed in the XRD patterns of SHBCT aerogel (Figure S2a), which may hydrogen treatment only improve the wettability of the surface of HBCT aerogel and did not destroy the crystal structure of tetragonal rutile TiO2.

Figure 4. FT-IR spectra (a) and XRD patterns (b) of SC aerogel, BC aerogel and HBCT aerogel. Density, Porosity and BET Surface Area of aerogels The pore diameter, volume and specific surface area of SC aerogel and HBCT aerogel were measured through nitrogen adsorption-desorption isotherms to investigate the effect of TiO2 functional layers on the rough structure of the resulting HBCT aerogel and the 15



corresponding results were presented, respectively. As is shown in Figure 5a, the SC aerogel and HBCT aerogel both exhibited type IV isotherm with beautiful hysteresis loop according to IUPAC. Also, significant hysteresis characteristics of the isotherms at high relative pressures (0.4-1.0) were associated with capillary condensation, which indicated the existence of abundant mesopores. This observation is consistent with the results from the analysis to the pore size distribution of SC aerogel and HBCT aerogel by the BJH method (Figure 5b), where the pore sizes are mainly centered at 3-5 nm and 6-10 nm, and an obvious peak exists at 4 nm, indicating abundant mesopores are broadly distributed in SC aerogel. In comparison, the obvious broad peaks centered at 5-10 nm were observed for the HBCT aerogel, indicating the existence of TiO2 nanorod impacts the pore size of the composite aerogel. The detailed structural properties of SC aerogel and HBCT aerogel were depicted in Table S1. Compared with SC aerogel, the specific surface area of HBCT aerogel observed a decline, which may be attributed to a sudden increase in quality of HBCT aerogel with the introduction of TiO2 nanorods. However, the higher porous diameter, volume and micro-nano rough surface can enhance hydrophobicity and durability of HBCT aerogel and offer a passageway to transport oil or organic solvent, which has a great potential for handling oil-spill remediation and recovery.

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Figure 5. Nitrogen adsorption-desorption isotherms (a) and pore size distributions (b) for SC aerogel and HBCT aerogel. Wettability property of aerogels Effective oil/water selectivity was essential for oil absorption material during the separation process. The wettability of the SHBCT aerogels was characterized by the static water contact angles (WCA) of the selected surfaces. As shown in Figure 6a-b, a droplet of carbon tetrachloride could penetrate quickly into the SHBCT aerogel within 1 s. In comparison, a droplet of water could be repelled by the surface of the SHBCT aerogel and keep its original shape well without penetration within 30 s, which exhibited superhydrophobicity and excellent oil/water selectivity owing to its rough surface and low surface energy.

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Figure 6. Optical images and WCA photographs (inset) of (a) a drop of carbon tetrachloride and (b) water on the pristine SHBCT aerogel. (c) Contact angle of a droplet with different pH values on the as-prepared SHBCT aerogel. And the insets of (c) are the static shape of a water droplet on the corresponding samples. In addition to the good water repellency, the as-prepared SHBCT aerogel also exhibited a stable repellency towards corrosive liquids, such as acidic and basic solutions. The WCA of the as-prepared SHBCT aerogel over aqueous solutions with pH range from 2 to 12 was carried by contact angle test and the results were shown in Figure 6c. All the WCA values are above 150° with the pH value changing from 2 to 13, exhibiting remarkable repellency towards acid or alkaline solutions. The time dependence of the wettability was evaluated by the contact angles of water in different times. Figure 7 demonstrates the dynamic wetting behavior of water and superhydrophobic stability on the as-prepared surface. When the water droplet was falling on the selected surface, it bounced immediately without any delay and the water droplet could stand on the surface quickly within a very short time. The water droplets all could keep their original shapes well 18


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without penetration within 300 s in different conditions, indicating a stable superhydrophobicity of the SHBCT aerogel. In addition, the chemical durability of asprepared SHBCT aerogel ensured its access to widespread use in different aqueous conditions.

Figure 7. Dynamic photographs showing the long-term superhydrophobic property of the SHBCT aerogel with spherical water drops on it in pH=7 (a), pH=3 (b) and pH=13 (c). Emulsion separation of aerogels Due to the special selectively wettability toward oil and water, the SHBCT aerogel could be also utilized for removing water droplets from various water-in-oil emulsions. Figure 8a shows gravity-driven separation process of water-in-toluene emulsions and toluene quickly permeated through the as-prepared aerogel when the emulsion got in touch with the SHBCT aerogel. By comparing photographs of feed and filtrate (Figure 8b-c), the milky emulsion became colorless and transparent after separating treatment. 19



In addition, there is a significant difference in the phase composition between the feed and the collected filtrate, as revealed by the optical microscopy images (Figure 8d-e). It can be seen that there are numerous water droplets with a size of about 2000 nm in the feed solution, but no droplets are observed in the whole view of collected filtrate, indicating the excellent separating properties of the SHBCT aerogel. Furthermore, as shown in Figure 8fg, the droplet sizes of the toluene droplets dispersed in water are larger than 1000 nm in the feed and smaller than 300 nm in the filtrate.

Figure 8. (a) The process of water-in-toluene emulsion separation using SHBCT aerogel; (b) photographs of the water-in-toluene emulsion before and (c) after filtration; (d) the optical microscope images of the water-in-toluene emulsion before and (e) after filtration; (f) droplet size distribution of the feed and (g) filtrate of the water-in-toluene emulsion. Oil-water separation of aerogels In spite of the outstanding water repellency, the SHBCT aerogel can be easily wetted by organic liquids or oil with low surface tension. Therefore, it should be an excellent 20


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candidate for oil absorbent. As illustrated in Figure 9a, the carbon tetrachloride sunk at the bottom of water was quickly absorbed by a small piece of as-prepared aerogel and no excess carbon tetrachloride could be observed on the water, demonstrating good oilabsorption capacities of SHBCT aerogel. Meanwhile, the absorption capacity of SHBCT aerogel for various oils and organic solvents was investigated and the results are shown in Figure 9b. The SHBCT aerogel exhibited a superior absorption capacity in the range from 62.7 to 126.2 times of its own weight, which mainly depends on the surface tension, density and viscosity of the absorbed oils and solvents. In addition, the as-prepared aerogel could act as a membrane for gravity-driven separating efficiently carbon tetrachloride from mixture. As is shown in Figure 9c, once the carbon tetrachloride/water mixture was poured onto separating device contained a piece of the SHBCT aerogel, the carbon tetrachloride was quickly absorbed by the as-prepared aerogel or the excess carbon tetrachloride penetrated through the aerogel and dropped into the beaker beneath it, which depends on the volume of carbon tetrachloride and the absorption capacity of the aerogel. However, water was completely repelled on the superhydrophobic surface of the aerogel during the separation process, resulting in separating efficiently carbon tetrachloride from water. After separation, the aerogel was squeezed to recycle the absorbed carbon tetrachloride. Comparing with the volume of carbon tetrachloride before and after separation (Figure 9d-e), a part of carbon tetrachloride was absorbed by the SHBCT aerogel, which may explain why separating efficiency of the aerogel is not up to 100%. The whole separation process completely depends on the gravity 21



of the mixture without any external force.

Figure 9. (a) Removal of carbon tetrachloride from underwater by using SHBCT aerogel; (b) maximum absorption capacity of the SHBCT aerogel towards 10 different liquids; (c) the process of carbon tetrachloride/water separation using SHBCT aerogel, and the volume of carbon tetrachloride (d) before separation and (e) after separation, the magnification of (d) and (e) indicate the volumes in the measuring cylinder. Reusability and durability of aerogels The excellent elasticity would greatly facilitate the oil recovery and reuse of the SHBCT aerogels through a simple squeezing process. As is shown in insets of Figure 10a, 22


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the aerogel was extensively pressed using the slide glass, and the aerogel could almost recover it initial height after released of the pressure. In addition, the height of the SHBCT aerogel decreased from 100% to 94.3% after 30 compression-recovery cycles, which suggests the as-prepared aerogel possessed excellent elasticity and could greatly guarantees its promising application for oil/water separation. What is more, the stability is also a highly desirable property for practical application of the SHBCT aerogel. The recyclability was also tested to evaluate its oil cleanup application of the SHBCT aerogel. Figure 10b shows the recyclable use of the as-prepared aerogel for removal of carbon tetrachloride, DMF and THF. It can be seen that a slight decrease of the absorption capacity was found after 9 cycles of absorption-squeezing processes, indicating the excellent recycling performance of the SHBCT aerogel. The variation trend of absorption capacity to different oils or solvents is different, which may mainly be attributed to inherent stability of rough surface structure towards different liquids. The excellent elasticity and stability could guarantee its promising application for the oil recovery and reuse of the SHBCT aerogels.

Figure 10. (a) Height recovery of the SHBCT aerogel as a function of recycle number at 74% compression strain and insets of (a) shows compressing–releasing processes of 23



SHBCT aerogel; (b) The oil absorption capacity of SHBCT aerogel during the repeated absorption and squeeze of several solvents for 9 cycles. CONCLUSIONS In summary, we have developed a SHBCT aerogel based on biomass carbon aerogel via a facile hydrothermal reaction followed by the surface modification in hydrogen atmosphere. The flower-like TiO2 nanorods were observed on the surface of as-prepared aerogel to endow the micro-nanoscale roughness to SHBCT aerogel, which could improve the wetting property of aerogel. Compared to hydrophobic modification of other absorbents by organosilicons and polymers, the SHBCT aerogel modified by calcinated in hydrogen atmosphere is environmental friendly and no secondary pollution. The as-prepared aerogel exhibited the outstanding separation performance with high absorption capacity and the maximum absorption capacities was measured to be 126.2 times of its own weight. The aerogel could also absorb rapidly various sorts of oils and organic solvents from the oil/water mixture under extreme harsh conditions, and act as a membrane for oil/water separation. Moreover, the aerogel could maintain its absorption capacity without losing elasticity and hydrophobicity after intensive compression and repeated oil absorption, showing the excellent reusability and durability. Furthermore, the SHBCT aerogel could separate surfactant-stabilized water-in-toluene emulsions, and the excellent separation properties render the as-prepared aerogel potential application in oily wastewater treatment. ACKNOWLEDGEMENTS We gratefully acknowledge the support of the Natural Science Foundation of Jiangsu 24


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Province (BK20160500) and National Nature Science Foundation of China (21706100 and U1507115). This work was also supported by the Key Research and Development Program of Jiangxi Province (20171BBH80008), China Postdoctoral Science Foundation (2016M600373 and 2018T110452), China Postdoctoral Science Foundation of Jiangsu Province (1601016A) and Scientific Research Foundation for Advanced Talents, Jiangsu University (15JDG142). Supporting Information Textural properties of BC aerogel and HBCT aerogel (Table S1) ； Typical SEM images of (a-b) SHBCT aerogel with different magnifications (Figure S1); XRD pattern (a) and FT-IR spectrum (b) of SHBCT aerogel (Figure S2). REFERENCES 1.

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Schematic illustration of fabrication of the SHBCT 546x208mm (72 x 72 DPI)


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Superhydrophobic Hierarchical Biomass Carbon ... - ACS Publications

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