Nanocomposite Foam Involving Boron Nitride Nanoplatelets and

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Nanocomposite foam involving boron nitride nanoplatelets and polycaprolactone: porous structures with multiple length scales for oil spill cleanup Li Hao, I-Cheng Chen, Jun Kyun Oh, Nirup Nagabandi, Felipe Ramos Bassan, Shuhao Liu, Ethan Scholar, Luhong Zhang, Mustafa Akbulut, and Bin Jiang Ind. Eng. Chem. Res., Just Accepted Manuscript • DOI: 10.1021/acs.iecr.7b03911 • Publication Date (Web): 17 Nov 2017 Downloaded from http://pubs.acs.org on November 18, 2017

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Industrial & Engineering Chemistry Research

Nanocomposite foam involving boron nitride nanoplatelets and polycaprolactone: porous structures with multiple length scales for oil spill cleanup Li Hao,a,b I-Cheng Chen,b Jun Kyun Oh,b Nirup Nagabandi,b Felipe Bassan,b Shuhao Liu,c Ethan Scholar,b Luhong Zhang,a Mustafa Akbulut,b,c,d* Bin Jiang,a**

a

School of Chemical Engineering and Technology, Tianjin University, Tianjin 300072, China;

b

Artie McFerrin Department of Chemical Engineering, Texas A&M University, College Station, Texas 77843-3122, USA; c

Department of Materials Science and Engineering, Texas A&M University, College Station, Texas 77843-3003, USA;

d

Texas A&M Energy Institute, Texas A&M University, College Station, Texas 77843-3372, USA;

1

ACS Paragon Plus Environment


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ABSTRACT: Herein, we report a facile approach to fabricate highly porous nanocomposites made from polycaprolactone (PCL) and boron nitride (BN) nanoplatelets using co-precipitation mixing and supercritical CO2 drying. The presence of boron nitride nanoplatelets in polycaprolactone matrix enhanced porosity of polycaprolactone foams and also improved the interfacial compatibility with oils and nonpolar organic solvents. Through a synergistic combination of surface morphology and interfacial tension effect, PCL:BNNP foams achieved a high hydrophobicity with a contact angle of 135º while being strongly oleophilic with a near zero contact angle for oils and nonpolar organic solvents. The absorption capacity was 6.1, 5.8, 4.3, 3.7, and 3.4 for paraffin oil, silicone oil, corn oil, hexadecane, and n-hexane, respectively. Additionally, the nanocomposite foam also demonstrated promising reusability and oil-stability. Overall, this study offers a novel and facile strategy for fabricating porous nanocomposite materials with a strong potential in the applications of environmental remediation.

KEYWORDS: polymer foam, boron nitride, hybrid composites, supercritical CO2, water cleanup

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1 Introduction

An increasing amount of accidental discharge of crude oil into the sea during marine transportation, leakage of underwater oil pipelines, chemical spills due to natural disasters, and production of industrial oily wastewater and wastewater containing nonpolar organic solvents threatens public health and the terrestrial and aquatic ecosystem.1 Effective oil/water separation and removal of organic pollutants from water by taking advantage of new materials and techniques is essential for the protection of water sources and bodies throughout the world.2

Traditional methods for water remediation include oil absorbent materials, oil skimmers, centrifugation, flocculation, settling tanks, depth filters, magnetic separations, and in situ burning.3-12 Oil-absorption is considered to be one of the simplest and the most attractive ways for oil-spill remediation and organic pollution purification because of the possibility of collection and complete removal of the oil without bringing any adverse effect to the environment. The ideal absorbent material is to satisfy several requirements such as high hydrophobicity, light-weight for high-gravimetric capacity, easy separation from cleaned water, cost-effectiveness, and environmentally benign components.13 To date, a variety of absorbent materials have been employed in the field of water cleanup, including activated carbon,14 zeolites,15 natural fibers,16 and exfoliated graphite17.

Recently, polymeric composite materials have been the focus of intense research owing to the synergistic combination of desirable polymer properties such as flexibility, easy processability, low cost, and potential for scale-up.18 Particulate fillers possess properties 3



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such as high surface-to-volume ratio, enhanced absorption of nonpolar molecules promoted by increased attractive van der Waals interactions relative to polymers, and possibility to manipulate and tailor the internal nanostructure of polymeric base matrix to achieve high porosity and surface area. To this end, various types of fillers, including carbon black, carbon fibers, carbon nanotubes, silica, titanium dioxide, graphene, and boron nitride platelets, have been incorporated into polymer matrix with the purpose of improving oil spill capture.19-24 For instance, Zha et al.21 reported the development of hydrophobic polyvinylidene fluoride (PVDF)/graphene hybrid porous materials using slow solvent-exchange and subsequent freeze-dying method to achieve 3-4 times of their own weights oil absorption capacity. Liu et al.22 described a multifunctional composite membrane based on the incorporation of BN nanosheets into the polymeric matrix PVDF, which improved water permeation flux and led to an excellent separation efficiency in excess of 99.99%. Likewise, Yu et al.23 fabricated porous BN nanosheet/PVDF composite materials by gelation and freeze-drying methods, applied for oil-polluted water cleanup and absorbed a mass of oil about 3.3-8.9 times of its dry weight.

The main challenge to the large-scale production and application of porous nanocomposites containing the abovementioned fillers is the poor dispersion and distribution of the nanoparticles in polymeric hosts mostly due to aggregation. Fractures and interfacial defects induced by aggregation tend to compromise the mechanical integrity, reliability, and reusability of such materials.25;18;26 To overcome these challenges, approaches relying on melt blending and co-precipitation have been developed.19;27 Recently, it has been demonstrated that with the use of supercritical drying, it is possible to minimize the damage on the internal 4


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nanostructure of high porosity composite materials.28;29 Among various types of fillers, boron nitride nanoplatelets, consist of several layers of hexagonal BN planes, have attracted intense attention in both scientific and engineering fields owing to its intriguing properties such as a wide energy band gap, high thermal conductivity and stability, electrical insulation, remarkable mechanical property, high resistance to oxidation and good chemical inertness within the past decade.30-33 Additionally, BN nanoplatelets can be used as an ideal absorbent filler candidate for removing pollutant and oil spill clean-up because of its high surface area, hydrophobicity, and ease of large scale production.34;35

Another challenge with fluoropolymer-based oil absorbing materials is the environmental

impact

of

fluoro-residues

and

its

toxicity

to

aquafauna

and

microorganisms.36,37 As such, in this work, we consider polycaprolactone (PCL), which is a linear aliphatic polyester, known for its biocompatibility and biodegradability,38 and may even be synthesized from milk in a sustainable manner.39 Because of its biocompatibility and biodegradability, PCL is a valuable material in biomedical applications and used as resorbable sutures, drug delivery devices, and bone graft substitutes.20;40 Furthermore, PCL is fairly hydrophobic and displays remarkable toughness, which amplifies its potential applications to other fields.41

The aim of the current study is to develop mechanically stable, ultraporous nanocomposite materials for improved capture efficiency of oil and nonpolar organic pollutants from aqueous media. For this purpose, we relied on high-energy intensity sonication-assisted co-precipitation of BN nanoplatelets and PCL by suddenly decreasing the

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quality of solvent from organic solvent to water, which is followed by supercritical CO2 drying to yield highly porous hybrid nanostructures. The hydrophobic, low-density, and high porosity PCL:BNNP foams are found to possess a unique capability to remove oil and organic solvents rapidly and efficiently.

2 Experimental Section

2.1 Materials

Hexagonal boron nitride (h-BN) platelets (98%, APS; 0.5 µm) was received from Lower Friction-MK IMPEX Corp. (Mississauga, Ontario, Canada), which was produced by the reaction of boric acid and ammonia at 900 °C: B(OH)3+NH3→BN+3H2O.42 Polycaprolactone (PCL, Mw=14000 g·mol-1), tetrahydrofuran (THF, ≥99.9%), and hexadecane (≥99%) were obtained from Sigma-Aldrich (St. Louis, MO). Isopropyl alcohol (IPA, 99.5%, ACS grade) and n-hexane (ACS grade) were procured from Macron Chemicals (Center Valley, PA). Paraffin oil was purchased from Fluka (St. Louis, MO). Silicone oil was obtained from ACE Glass (Vineland, NJ). Corn oil was purchased from local market. OrcoSolve Blue was obtained from Organic Dyestuffs Corp (Concord, NC). Deionized water was used in all experiments.

2.2 Preparation of nanostructured PCL:BNNP foam

The h-BN powder dispersed in IPA was exfoliated by ultrasonication using a high-intensity ultrasonic probe (SJIA-2000W, Syclon Electronic Instrument Comp., Zhejiang, China) for 60 min at power of 400 W. After the ultrasonication step, the dispersion was

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centrifuged at 4000 rpm for 90 min to remove the large unexfoliated h-BN particles. Next, the supernatant primarily consisting of BN nanoplatelets (BNNP) was collected and washed with ethanol several times and dried for 24 hours at 85 °C. The resultant nanoplatelets were used as the building block of porous PCL:BNNP foam.

The PCL/BNNP nanocomposites were prepared by a co-precipitation technique. PCL was first fully dissolved in THF (10 wt%) to form a homogeneous solution in a vial. Afterwards, BNNP was added into the polymer solution at a mass ratio of 7:100 BNNP: PCL, followed by the addition of IPA to assist the dispersion of BNNP. Then, the dispersion was homogenized via the application of ultrasonication for 30 min at 800 W. Finally, the PCL/BNNP dispersion was precipitated by the addition of excess water and the precipitate was placed in a fume hood to evaporate the solvents until the formation of a gel was observed. The gel was supercritically dried to obtain a porous foam structure using supercritical carbon dioxide (CO2; Brazos Valley Welding Supply Inc., Bryan, TX) at the critical point (31.1 °C, 72.9 bar) for 3 hours. Upon bringing samples to atmospheric conditions, the aerated composite with high porosity was formed. As control experiments, porous PCL material without BNNP was also prepared using the same procedure. In addition, non-porous PCL/BNNP was also produced by skipping the supercritical drying step.

2.3 Characterization of BNNP and PCL/BNNP nanostructures

Particle size distribution of BNNP was determined using dynamic light scattering (DLS) (Zetasizer Nano ZS90, Malvern Instr. Inc., Westborough, MA). Attenuated total reflectance-Fourier transform infrared (ATR-FTIR) spectra were used to identify bonding 7



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between boron and nitrogen within PCL/BNNP composites via an IRPrestige-21 (Shimadzu Corp., Kyoto, Japan) system and analyzed using IRsolution (Shimadzu Corp., Kyoto, Japan) software version 1.40.

The foam nanostructure and morphology were observed by scanning electron microscopy (SEM, JSM-7500F; JEOL, Tokyo, Japan) equipped with EDX detector. Before SEM examination, the samples were coated with 8 nm platinum/palladium to minimize possible charging effects. The SEM micrographs were obtained at an accelerating voltage of 1 kV and emission current of 20 µA. The porosity of porous foam was calculated according to the following formula43: ‫ = ݕݐ݅ݏ݋ݎ݋݌‬ሺܸ௧ − ܸ௔ ሻ ×

ଵ଴଴ ௏೟

= ቀܸ௧ −

ௐ೟ ఘ

ቁ×

ଵ଴଴ ௏೟

[1]

where Vt is the total volume of porous foam (cm3) by measuring the length, height, and width of rectangular cuboid-shaped porous sample, while Va is the actual volume taken by PCL or PCL/BNNP composite (cm3), which is equal to Wt divided ρ. Wt is the mass of foam (g), and ρ is the density of porous foam, which was determined gravimetrically to be 0.313 g/cm3 for porous PCL foam and 0.292 g/cm3 for porous PCL:BNNP foam.

The surface wettability of samples was analyzed using contact angle goniometry at room temperature44-46 and the image analysis was conducted via contact angle plug-in for ImageJ (National Institute of Health (NIH), Bethesda, MD, USA) software. The water contact angle (WCA) values reported on each surface were the average of five measurements on five different batches samples.

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2.4 Oil and organic solvent removal tests

In this study, five different kinds of oils and organic solvents with different densities, including paraffin oil, silicone oil, corn oil, hexadecane, and n-hexane were used to investigate the absorption capacity of the developed foams. The samples were left submerged in the oils or organic solvents fully for overnight to ensure full saturation was obtained before weighing. To test the stability and reuseability of the porous PCL:BNNP foam, the absorption experiment was repeated for ten times. After each absorption, the porous PCL:BNNP foam was washed with ethanol in sonication bath for 30 min and dried in air. The porous PCL foams and non-porous PCL/BNNP composites were also tested with the abovementioned procedure as controls. The absorption capacity, R, was obtained by measuring the weight of porous PCL:BNNP foam before and after absorption and taking the ratios of the weights, i.e. R﹦Wsatureted_foam/Wdry_foam. The error bars are equal to the standard deviation from the mean, and calculated from the experimental data, which are replicated three times for each condition and parameter.

3 Results and discussion

3.1 Characterization of h-BN and BNNP

It is well-established the mechanical and structural properties of composite materials strongly depend on the filler geometry and size.23,42 As such, we first characterized the h-BN and exfoliated BNNP using dynamic light scattering and scanning electron microscopy (Fig. 1). The intensity-averaged hydrodynamic size of h-BN was found to be 535±126 nm while the analysis of SEM micrographs yielded an average thickness value of 101±7 nm (Fig. 9



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1a&c). The exfoliated particles, i.e., BNNP, had much uniform shapes with an intensity averaged hydrodynamic size of 95±9 nm and an average thickness of 19±1 nm. Considering each layer of BN is about ~1 nm 47-49, it can be stated that BNNP contained on average of 19 layers. (a)

(b)

100 nm

(c)

size=535±126 nm

100 nm

(d)

size = 94.56±9.43 nm

Figure 1.SEM and particle size distribution of starting h-BN and exfoliated BN nanoplatelets (BNNPs): SEM image of (a) h-BN powder and (b) exfoliated BNNPs, the intensity-averaged hydrodynamics size distribution of (c) h-BN powder and (d) exfoliated BNNPs. 3.2 Chemical interactions of PCL and BNNP and composition of PCL:BNNP

The existence of boron nitride incorporated into PCL polymer matrix in PCL:BNNP composite foam was confirmed by ATR-FTIR spectroscopy. Figure 2 compares the ATR-FTIR spectra of BNNP, PCL foam, and PCL:BNNP foam. For the case of bare BNNP, two key characteristics absorption bands were located at 1327 and 754 cm-1 where the former is attributed to in-plane B-N stretching mode while the latter is ascribed to out-of-plane B-N-B bending vibrations.30 For the case of bare PCL (porous form), the strong peak at 1722 cm-1 was due to the stretching of ring carbonyl of PCL.20,40, 50 Peak located 1173 cm-1 was 10


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likely owing to symmetric C‒O‒C stretching groups. Other significant peaks were at 1240 cm-1 (asymmetric C‒O‒C stretching), 1292 cm-1 (C‒O and C‒C stretching in the crystalline phase), and 1363 cm-1 (CH2 band vibrations of PCL).51-53 For the case of PCL:BNNP nanocomposite, as the majority of the composite was PCL, the main characteristics of spectra were similar to the PCL spectra. However, some differences compared to bare PCL and BNNP were also observed: For instance, the emergence of a peak at 796 cm-1, which is because of CO2 residue trapped in the foam during the supercritical drying, was observed. CO2 detected in FTIR measurements is likely due to the internally trapped gas molecules not owing to gas molecules on the sample surface, which can readily diffuse away and mixed with environmental gases. As such, while the wettability can be altered in the presence of supercritical CO2 54,55, the detected internally trapped CO2 is not expected to influence the oleophilic properties significantly. Also, the relative magnitude of peak at 1363 cm-1 noticeably increased, indicating a decrease in the carbonyl index, which is the ratio of the absorbance intensities of carbonyl at 1722 cm-1 and CH2 at 1363 cm-1.56 The reduction in the carbonyl index implies the cleavage of the polymer chains to allow a less restricted stretching of CH2 groups in the presence of BNNP to some extent. Furthermore, elemental analysis by EDX spectroscopy also confirmed the presence of B and N atoms at a number percentage of 9.3±3.5%.

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BNNP PCL PCL:BNNP Composite

(i)

(ii)

(iii)

(iv)

(v)

Figure 2. ATR-FTIR spectra of BN nanoplatelets (black), polycaprolactone (red), and PCL:BNNP nanocomposite (blue). The comparison of peaks at wavenumbers revealed that the largest differences between the spectra of PCL and PCL:BNNP nanocomposite are at 796 cm-1 (i) and 1363 cm-1(iv). 3.3 Morphological characterization of PCL:BNNP foam

SEM micrographs revealed that PCL:BNNP composites prepared by supercritical drying involved macroscopic cellular networks that are connected to microscopic pores on the walls of the network channels (Fig. 3). For a given preparation conditions, PCL:BNNP composite foam had smaller macroscopic channels than PCL foam. The reason for this difference is most likely due to increased rigidity of PCL:BNNP composite due to BNNP building blocks, which hinders the expansion of CO2 upon the phase transition.

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Figure 3. SEM micrographs displaying the morphology and cell-size distribution of (a) PCL foam and (b) porous PCL:BNNP nanocomposite foam. Figure 4 compares high-magnification SEM images of nonporous PCL/BNNP composite, porous PCL foam, and porous PCL:BNNP foam. Randomly but mostly homogenously distributed nanoplatelets were observed within nonporous PCL/BNNP composites (Fig. 4a). The absence of large aggregates of nanoplatelets indicates favorable interactions between BNNP and PCL. The walls of network channels in porous PCL foam was fairly smooth (Fig. 4b). On the other hand, porous PCL:BNNP foam was not only very rough compared to PCL foam, but also involved smaller pores at much higher number density. It is important to underline that the increased surface roughness implies a high surface area that can come in contact with contaminant and allowing a higher loading efficiency and capacity. The possible reason for the enhanced porosity is probably because interaction between PCL and PCL is stronger than that between PCL and BNNP. In addition, since boron nitride has much higher thermal conductivity than PCL and supercritical drying was conducted in a nonequilibrium state, the phase change of CO2 should initiate from the local hot spots on BNNP. Average porosity of PCL foam and PCL:BNNP composite foam was determined to be 33.4±3.2% and 42.8±4.1%, respectively via gravimetric analysis.

Figure 4. SEM micrographs of (a) nonporous PCL/BNNP bulk composite, (b) porous PCL foam, (c) porous PCL:BNNP composite foam.

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3.4 Wettability of porous PCL:BNNP composite foam

To evaluate the wetting characteristics of samples, static contact angle measurements were carried out as shown in Figure 5. It was found that porous PCL foam was hydrophobic with a contact angle of 95.2±1.4° (Fig.5a). Consistent with the literature data,57 pristine h-BN showed a hydrophobic character with a water contact angle of 130°. The water contact angle of nonporous PCL/BNNP composite was 112.5±2.3° (Fig.5b). Considering composite system averages out the interfacial properties in accordance with the Clausius-Mossotti equation, the resultant contact angle is fairly reasonable. On the other hand, the contact angle increased to 135.2±1.0° for the case of porous PCL:BNNP composite foam (Fig. 5c). This observation can be ascribed to the surface roughness/texture of foam and the formation of air pockets at the Cassie state.58 Namely, as air is very hydrophobic material, the interfacial effects of PCL and air counteract and return the contact angle from 112° back to 135°. Regarding the interactions of oil and PCL:BNNP foam, paraffin oil droplets were found to rapidly spread on with a nearly zero oil contact angle and penetrate into the foam upon contact (Supporting Information Movie S1). The difference in the wetting characteristics of water and oil of PCL:BNNP foam satisfies an essential requirement for oil-water separation applications.

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Figure 5. Water contact angles of (a) porous PCL foam, (b) nonporous PCL/BNNP bulk composite, and (c) porous PCL:BNNP composite foam. 3.5 Removal of oil and organic solvent from water

Porous PCL:BNNP composite foam exhibited strong absorbance towards oils and nonpolar organic solvents from water. Figure 6 demonstrates how as-prepared white PCL:BNNP composite foam absorb paraffin oil (while trace amount of dye was added into oil for visualization purposes, quantitative measurements were conducted in the absence of dye). As shown in Figure 6d-f, placing PCL:BNNP composite foam in contact with paraffin oil floating on water resulted in complete absorption of oil within 1 minute (Supporting Information Movie S2). Furthermore, no water was observed in the foam after taking foam from water reservoir.

Figure 6. Photographs of (a-b) porous PCL:BNNP foam, (c) porous PCL:BNNP composite foam saturated with oil, (d-f) oil absorption process from water utilizing porous PCL:BNNP foam. Porous PCL:BNNP composite foam was a promising absorbent for the cleanup and 15



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removal of organic pollutants with various densities and viscosities. Figure 7a describes the uptake of different oils and organic solvents such as paraffin oil, silicone oil, corn oil, hexadecane, and n-hexane by the developed nanostructured foam. The absorption capacity ranged from 6.1 to 3.4 for these oils and nonpolar solvents, which are higher than the reported absorption capacity of activated carbon, commercial BN particles, and graphene/polymer composite in the literatures.13;21 The absorption capacity of PCL:BNNP composite foam was two to three times larger than that of porous PCL foam and nonporous PCL:BNNP composite, showing a synergistic effect of nanostructure and composition in enhancing absorption behavior. Namely, it is essential to have BN nanoplatelets as well as increased surface area to achieve a high absorption capacity.

The porous PCL:BNNP foam can be reused several times by directly washing with ethanol and drying, which is equally important from a perspective of application. The nanocomposite foam reached a steady-state performance with an absorption capacity of 4.1±0.1 after 10 cycles.

ATR-FTIR spectra of porous PCL:BNNP foam after the complete washing in ethanol and drying is shown in Figure 8, which demonstrates that even after uptake of paraffin oil and cleaning with ethanol, the nanocomposite foam still had the similar characteristic bands with the original foam and maintained the chemical integrity in the presence of oil. Overall, these desirable features of PCL:BNNP composite foam makes them a promising material suitable for oil-spill clean-up.

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(a)

(b)

porous PCL:BNNP foam

porous PCL foam non-porous PCL/BNNP bulk composite

(c)

Figure 7. (a) absorption capacities of the porous PCL:BNNP composite foam for five different oils and organic solvents, (b) comparison of the absorption capacities of porous PCL:BNNP composite foam, porous PCL foam and non-porous PCL/BNNP bulk composite, (c) absorption recyclabilities of the porous PCL:BNNP composite foam for paraffin oil.

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porous PCL:BNNP foam porous PCL:BNNP foam after cleaning and recycling

Figure 8. ATR-FTIR spectra of the porous PCL:BNNP composite foam after cleaning and recycling. The mechanism of oil absorption can be ascribed to several phenomena. First, hexagonal boron nitride demonstrates sp2 hybridization with strong directional bonding between adjacent coplanar atoms.48, 59 Honeycomb structure of h-BN is covered with π electrons, which tend to localize around the nitrogen atomic centers because of the electronegativity differences between the boron and the nitrogen atoms.60, 61 These electronics characteristics of h-BN impart it with hydrophobic properties, favoring the absorption of nonpolar oil molecules. Second, the existence of multiscale porous structure implies a large distribution of curvature length scales, which result in long-range attractive interactions between nanocomposite surface and oil film,62,

63

i.e. further favoring oil absorption. Third, the

resultant surface texture with nanoscale roughness promotes the formation of air-pockets (i.e. the Cassie state) upon contacting oil in the presence of atmospheric air. Similar interstitial air has been observed in various boron nitride textures.64, 65 Given that air is very hydrophobic due to very nonpolar nitrogen gas, the entrapment of air in the nanorough areas of nanocomposites increases the effective hydrophobicity of the nanocomposite, providing

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another mechanism of enhanced oil absorption.

4 Conclusions

In summary, a novel nanocomposite foam involving BN nanoplatelets and PCL with macroscopic and microscopic pores was successfully prepared via co-precipitation and supercritical CO2 drying method with a specific aim of cleaning up and recycling oil and nonpolar solvents from water surface. The absorption capacity was 6.1, 5.8, 4.3, 3.7, and 3.4 for paraffin oil, silicone oil, corn oil, hexadecane, and n-hexane, respectively. The incorporation of BN nanoplatelets (BNNP) had two key benefits on PCL foam: First, the presence of BNNP enhanced the porosity and internal roughness of PCL foam. Second, BNNP also improved oil compatibility due to its nonpolar nature. Additionally, the developed nanocomposite foam also exhibited promising reusability and oil-stability. Overall, this study offers a novel and facile strategy for fabricating porous nanocomposite materials with a strong potential in the applications of environmental remediation.

Supporting Information Movie S1: Contact angle measurement on porous PCL:BNNP composite foam using paraffin oil droplets. Movie S2: The absorption process of paraffin oil from water using porous PCL:BNNP composite foam. AUTHOR INFORMATION

Corresponding Authors

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*Telephone: 979-847-8766. Fax: 979-845-6446. E-mail: [email protected] (Mustafa Akbulut), Artie McFerrin Department of Chemical Engineering, Texas A&M University, College Station, Texas 77843-3122, United States.

**E-mail: [email protected] (Bin Jiang), School of Chemical Engineering and Technology, Tianjin University, Tianjin 300072, P. R. China.

Notes

The authors declare no competing financial interest.

Acknowledgements

The authors gratefully appreciate the financial support from the China Scholarship Council (CSC).

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Captions of figures Figure 1.SEM and particle size distribution of starting h-BN and exfoliated BN nanoplatelets (BNNPs): SEM image of (a) h-BN powder and (b) exfoliated BNNPs, the intensity-averaged hydrodynamics size distribution of (c) h-BN powder and (d) exfoliated BNNPs. Figure 2. ATR-FTIR spectra of BN nanoplatelets (black), polycaprolactone (red), and PCL:BNNP nanocomposite (blue). The comparison of peaks at wavenumbers revealed that the largest differences between the spectra of PCL and PCL:BNNP nanocomposite are at 796 cm-1 (i) and 1363cm-1(iv). Figure 3. SEM micrographs displaying the morphology and cell-size distribution of (a) PCL foam and (b) porous PCL:BNNP nanocomposite foam. Figure 4. SEM micrographs of (a) nonporous PCL/BNNP bulk composite, (b) porous PCL foam, (c) porous PCL:BNNP composite foam. Figure 5. Water contact angles of (a) porous PCL foam, (b) nonporous PCL/BNNP bulk composite, and (c) porous PCL:BNNP composite foam. Figure 6. Photographs of (a-b) porous PCL:BNNP foam, (c) porous PCL:BNNP composite foam saturated with oil, (d-f) oil absorption process from water utilizing porous PCL:BNNP foam. Figure 7. (a) absorption capacities of the porous PCL:BNNP composite foam for five different oils and organic solvents, (b) comparison of the absorption capacities of porous PCL:BNNP composite foam, porous PCL foam and non-porous PCL/BNNP bulk composite, (c) absorption recyclabilities of the porous PCL:BNNP composite foam for paraffin oil. Figure 8. ATR-FTIR spectra of the porous PCL:BNNP composite foam after cleaning and recycling.

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Table of Contents Graphic

Polycaprolactone-based Nanocomposite Sponge

Porous PCL:BNNP foam

Nano- and Micropores

Boron Nitride Nanoplatelets

Porous PCL:BNNP foam after oil absorption

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Nanocomposite Foam Involving Boron Nitride Nanoplatelets and

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