Separation of caustic nano-emulsions and macromolecular

Subscriber access provided by TULANE UNIVERSITY

Applications of Polymer, Composite, and Coating Materials

Separation of caustic nano-emulsions and macromolecular conformations with nanofibrous membrane of marine chitin Zengbin Wang, Jie Xu, Mingjie Li, Chunlei Su, Xiaochen Wu, Yue Zhang, Jun You, and Chaoxu Li ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.8b21847 • Publication Date (Web): 01 Feb 2019 Downloaded from http://pubs.acs.org on February 6, 2019

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 27 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

ACS Applied Materials & Interfaces

Separation of caustic nano-emulsions and macromolecular conformations with nanofibrous membrane of marine chitin Zengbin Wang,1,2 Jie Xu,2 Mingjie Li,

2

Chunlei Su,3 Xiaochen Wu,2 Yue Zhang,1,* Jun You,2,* and

Chaoxu Li2,* 1Institute

of Material Science and Engineering, Ocean University of China, Qingdao, Shandong, 266100

P.R. China. 2CAS

Key Lab of Biobased Materials, Qingdao Institute of Bioenergy and Bioprocess Technology,

Chinese Academy of Sciences, Songling Road 189, Qingdao 266101, P. R. China. 3Key

Laboratory of Green Process and Engineering, Institute of Process Engineering, Chinese Academy

of Sciences, Beijing 100190, PR China.

*Corresponding author: C. Li (Email: [email protected]), J. You (Email: [email protected]), Y. Zhang (Email: [email protected])

ACS Paragon Plus Environment

ACS Applied Materials & Interfaces 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 2 of 27

ABSTRACT Sustainable development of nanotechnology is challenged by nanoscale pollutants and oily water. Bio-based nanoporous membranes, though serving as one of the eco-friendliest separation technologies, have been hindered for wide applications due to their broad pore distributions, poor solvent resistance and structural instability. In order to avoid possible leakage of nanoscale objects in caustic and organic solvents, herein we endeavored to exfoliate chitin nanofibrils with identical chemical and crystalline structures to pristine chitin in portunid carapace, and further produce nanoporous and mesoporous membranes with super structural stability, endurance, permeation flux and rejection. The final membranes had minimal ionization, controllable thickness, tunable and narrow distribution of pore size, being able to separate nano-emulsions, nanoparticles and rigid macromolecules in caustic aqueous solutions and organic solvents. Thus, these scalable, low-cost and sustainable membranes may promise applications as diverse as in separating and concentrating nanoparticles in nanotechnology, oil/water separation in wastewater treatment, and molecular sieving in biomedicine and material science. KEYWORDS: Chitin nanofibrils, nanoporous membranes, nanoemulsion, caustic resistance, nanoparticles


Page 3 of 27 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


INTRODUCTION Sieving nano-objects (e.g. nanoparticles, nanoemulsion droplets and macromolecules) in liquid systems has aroused great interests in diverse fields of science and technology, not only owing to rapidly development of nanotechnology and its wide applications,1 but also owing to ecologic and health concerns of discarded nanomaterials and oily water.2,3 Among various separation technologies of nano-objects (e.g. density gradient centrifugation, chromatography, electrophoresis, dielectrophoresis, and filtration), membrane-based separation gains particular attention on account of its scalability, low cost, high throughput, time-saving and energy-conservation.4-7 In comparison to commercial membranes produced from synthetic polymers, bio-based membranes, though having unambiguous advantages of maximal eco-friendliness, sustainability and preference in biologic applications, have been hindered for wide applications due to their broad pore distributions, poor solvent resistance and structural instability. In principle, separation efficiency of solid nanoparticles depends on the pore size and pore stability of filtration membranes. The broad pore distribution and variation of pore sizes would produce nano-objects leakage, and hereby loss of synthesis yield as well as ecologic and health concerns, which become even more severe when caustic systems were utilized in synthesis and application of nanoparticles. In the case of nanoscale fluid droplets and soluble macromolecules, their translation through porous media depend additionally on membrane surfaces, filtration pressure and solvent viscosity. These nano-subjects may deform and pass through a smaller pore above a critical intrusion pressure8 or a critical flow rate.9 And super-wetting surfaces of separation membranes further favor infiltration of the corresponding fluid droplets. Thus the pore structures and surface properties of the separation membranes have to be more precisely controlled in order to balance the permeation flux and separation performance. There have developed a variety of techniques to produce porous membranes, such as block



Page 4 of 27

copolymer-assembly10, track-etching technique11, template synthesis12 and direct filtration.13 In comparison, flexible organic nanofibrils with the diameter ˂50 nm showed distinct superiority to produce high porosity, nanoscale pore size and interconnected open pore structures with tunable pore surfaces.14 Several types of biologic nanofibrils have been endeavored to produce porous membranes.4,13,15,16 Biologic nanofibrils are nanoscale building blocks of many natural materials, and can be extracted with physical/chemical treatments.17,18 They not only possess unique structural features (e.g. high aspect ratio up to 103), but also combine mechanic strength, toughness and excellent dispersibility in many solvents. For example, cellulose nanofibrils with the diameter ˂10 nm enabled homogeneous nanoporous morphologies, adjustable membrane thickness and high permeability, being able to separate 5-nm Au nanoparticles with 93.8 % rejection for a 47-nm-thick membrane.6 Nanofibrils of bombyx mori silk produced nanoporous membranes with the pore size of 8~12 nm, and showed water fluxes of 1.3  104 L h-1 m-2 bar-1 as well as efficient separation performance for proteins and colloids.5 Despite much success has been made in biologic nanofibrils, their fibous membranes were still limited for applications owing to their instability in chemical and pore structures. Firstly, many biologic nanofibrils may undergo chemical degradation (e.g. hydrolysis of proteins) under caustic conditions (e.g. acidic, ionic and highly polar). Secondly, partial ionization was normally adopted to exfoliate biologic nanofibrils (e.g. carboxy and quaternary ammonium groups of cellulose nanofibrils),8,19 which, howerver, would hydrate/loose the porous structures gradually in polar (e.g. aqueous) systems and thus lower the nanoparticles rejection. Thirdly, some biologic nanofibrils may not be rigid enough to withstand high pressure, which thus varies the pore size in the vacuum-filtration process and give low and unstable rejection. In order to separate nano-objects, in particlar deformable nano-droplets and macromolecules in caustic aqueous systems, we aimed to select biologic nanofibrils with sufficient chemical stability,


Page 5 of 27 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


mechanic rigidity, superlytropic surfaces while less ionization. Chitin nanofibrils (ChitinNFs) in portunid carapace have the chemical structure of linear polymer of β-(1→4)-linked 2-acetamido-2-deoxy-β-D-glucose, and the Type I crystalline form. When exfoliating in dimethyl sulfoxide (DMSO) saturated with KOH,20 they may appropriately combine the nanoscacle size, stability, rigidity and superlyophilic surfaces to deposite on commercial macroporous supports. The membrane, with the tunable porosity, narrow distribution of pore sizes and less ionization, could not only withstand caustic conditions (e.g. strong acid, base, salty, and polar solvents), but also separate nanoscale nanoparticles, nanoemulsion and rigid macromolecules with high rejection and flux (higher than many commercial membranes). Thus these broad-spectrum filtration membranes are highly promising for applications as diverse as in separating and concentrating nanoparticles in nanotechnology, wastewater (e.g. oily and nano-polluted) treatment, and molecular sieving in biomedicine and material science. Their low-cost, environmental friendliness, solvent/corrosion resistance and facile procedures also benefit to large-scale production and practical utilization.

 EXPERIMENTAL SECTION Materials Portunid carapace were collected from food waste and purified according to the literature.20 In brief, after steaming for 15 min, crab shells were peeled off and washed with abundant deionized water. Then they were treated with 2M HCl for 48h and 4wt % NaOH for 48h to remove minerals and proteins, respectively. Finally, purified chitin was obtained by bleaching treatment in 0.3 wt% NaClO2 at 80 oC for 3.5 h. Filter membranes with a cut-off of 220 nm were purchased from Xinya purification Co., Ltd (Shanghai, China), and utilized as the macroporous support to fabricate the separation membranes. Dimethyl sulfoxide (DMSO) was supplied by Hengxing chemical preparation Co., Ltd (Tianjin, China).



Page 6 of 27

Oil red and polyethylene oxide (PEO) were obtained from Macklin Biochemical Co., Ltd (Shanghai, China). Sodium alginate and isooctane were purchased from Aladdin Bio-Chem Technology Co., Ltd (Shanghai, China). All other reagents (HCl, NaOH, KOH, hydrazine hydrate, NaCl, acetone, toluene, chloroform, petroleum ether etc.) were supplied by Sinopharm Chemical Reagent Co., Ltd, and used without further purification. Deionized water (resistance: 18.2 MΩ/cm) were used during all the experiments. Fabrication of Nanofibrous Membranes Chitin nanofibrils were directly extracted from purified crab shells through a green deprotonation-assisted liquid exfoliation protocol:20 2 g of purified chitin was treated with 500 mL of DMSO solution containing 3 mg/mL KOH for 1 week. After centrifugally washing with deionized water, the product was treated by a Vibra-Cell Ultrasonic Processor (BILON92-II, Shanghai, China) with the power of 300 W for 9 min to obtain the expected chitin nanofibrils suspensions (0.37 mg/mL). A desired volume of chitin nanofibrils suspension was filtered onto a macroporous filter membrane (cellulose acetate membranes for aqueous phase filtration and polyvinylidene fluoride membranes for organic phase filtration) with a pore size of 220 nm by vacuum filtration under 0.95 bar. During filtration, chitin nanofibrils were deposited on the support to form a thin layer. The thickness of the skin layer could be tuning by adjusting the suspension volume of chitin nanofibrils. Pore size of the membranes can be regulated by carefully engineering the drying process. Typically, nanoporous membranes with sub-10 nm pores were prepared by ambient drying (45±2 % RH, 25±2 oC). Mesoporous membranes with approximately 22 nm pores were obtained by solvent exchange to t-BuOH and subsequent freeze-drying. Membrane Characterization Surfaces and cross-section morphologies of fibrous membranes were characterized using a Hitachi


Page 7 of 27 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


S-4800 instrument operated at 3 kV for gold-sputtered samples. The thickness of the membranes was statistically calculated from their cross-section SEM images. FT-IR spectra were conducted on a Nicolet 6700 Fourier transform infrared spectrometer. X-ray diffraction patterns (XRD) were recorded on a Bruker D8 ADVANCE X-ray diffractometer with a CuKα radiation (=1.5406A), and scanned with a 2θ angle from 5 to 60o with a step speed of 5o /min. Nitrogen physisorption measurements were conducted at 77 K on a Quantachrome Autosorb iQ surface analyzer (Quantachrome, USA). Brunauer-Emmett-Teller (BET) analysis was performed under relative vapor pressures of 0.05-0.3. The samples were degassed at 80 oC in vacuum to remove all the adsorbed species. Mechanical properties of free-standing ChitinNFs membranes were evaluated using a universal tensile-compressive machine (CMT 6503, MTS systems China Co. Ltd). The contact angle was tested by a drop shape analysis system (JC2000DM, China). In order to quantitatively evaluate the membrane permeability, deionized water (5 mL) was filtered across the membranes to calculate the pure water flux (J, L m−2 h−1 bar−1) according to the equation J=V/(Atp), where V is the volume of the permeated water (510-3 L), A is the effective area of ChitinNFs membrane (2.0110-4 m2), t is the filtration time (h), and p is the suction pressure across the membrane (0.95 bar). The porosity (P) of membranes was calculated by P=1-ρ/ρc, where ρ and ρc are the density of membranes and bulk chitin (1.425 g/cm3) respectively. The density of chitin nanofibrils membranes was determined by weighting the samples and testing its volumes. Separation Performance of Nanoemulsions Four kinds of oil (toluene, petroleum ether, chloroform and isooctane) were used to prepare various oil/water emulsions. The surfactant-stabilized oil-in-water nanoemulsions were prepared by mixing oils and deionized water (containing 0.1 wt% Tween 80 for chloroform, toluene and 0.2 wt% Tween 80 for isooctane, petroleum ether) in a volume ratio of 1:99, and the mixtures were treated by a Vibra-Cell



Page 8 of 27

Ultrasonic Processor (BILON92-II, Shanghai, China) with the power of 300 W for 9 min to obtain the emulsified, milky solutions with oil droplet size ranging from 50 to 200 nm. To prepare the surfactant-stabilized oil-in-water and water-in-oil microemulsions, oil containing 0.2 wt% Tween 80 and water containing 0.2 wt% Span 80 were mixed in a volume ratio of 3/7 and 7/3, and the mixtures were under mechanical agitation (1000 rpm) for 12 h to produce a milky emulsion. All the emulsions could keep stable for at least 12 h. The droplet size of nanoemulsions and microemulsions was characterized by dynamic light scattering (Malvern, UK) and optical microscope (CX-31), respectively. A dead-end filtration apparatus equipped with a water pump were used to evaluate the oil/water emulsion separation performance. After pre-wetting of the membranes, the emulsions were poured in the upper tube, and the water permeated membranes under a pressure difference of 0.95 bar. After separation, the filtrate was collected and the permeation flux was calculated with its volume during 5 min according to the previous reports4. The residual oil was evaluated by the average total organic carbon (TOC) contents in the filtrate, which was determined using an organic carbon analyzer (TOC-V CSH). The organic rejection (R, %) was approximate calculated according to the equation R=(1-cf/c0)100%, where cf (mg/mL) and c0 (mg/mL) are the TOC content in the feed emulsion and the corresponding filtrate, respectively. Notable, the obtained rejection of non-polar fluids would be slightly lower than the actual value because the presence of surfactants was not excluded from the TOC value of the filtrate. During cyclic separation tests of toluene-in-water nanoemulsions, the membranes were cleaned by carefully flushing its surface with deionized water 5 times to remove the oil cake. Separation Performance of nanoparticles and rigid macromolecules The separation performance was also evaluated using a dead-end filtration apparatus equipped with a water pump under 0.95 bar. Various colloidal nanoparticles with different sizes (Au NPs, Ag NPs, Pt NPs,


Page 9 of 27 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


graphene quantum dot), and macromolecules with different molecular weight and conformations (e.g. quaternized chitosan (QCh), chitosan, alginate, hydroxy propyl cellulose (HPC), polyvinyl alcohol (PVA), polyethylene oxide (PEO)) were used to evaluate the membranes’ rejection. The preparation methods for various nanoparticles were described in detail in the Supporting Information. The feed solution/suspension (5 mL) was filtered across the membrane under 0.95 bar. After separation, the filtrates were collected to calculate the flux and rejection. The concentrations of colloidal nanoparticles suspensions were determined using an UV–vis spectrophotometer (DU800). The filtrates of macromolecular solutions were freeze-dried and weighted to calculate their concentrations. The rejection (R, %) was calculated by R=(1-cf/c0)100%, where cf (mg/mL) and c0 (mg/mL) are the concentration of nanoparticles/macromolecules in the feed and filtrate, respectively.

 RESULTS AND DISCUSSION ChitinNFs are abundant in marine crustaceans and responsible for mechanic properties and structural stability of their body “armors” (Fig. 1A). Having strong inter-fibril attraction (e.g. H-bonding and Van de Waal’s interactions), these 1D crystalline structures were normally exfoliated through partial ionization (e.g. sulphonation in sulfuric acid, amination in NaOH and carboxylation by TEMPO-oxidation). During the exfoliation process, ionization not only balanced the attraction between ChitinNFs, but also increased their aqueous dispersibility. However, when engineering ionized fibrils into separation membranes, ionization may induce membrane swelling in polar systems and thus low separation efficiency of nano-objects. In order to minimize this negative effect, here ChitinNFs were exfoliated through deprotonation of amide groups in DMSO saturated with KOH.20 The resultant nanofibrils had a diameter of 3~8 nm and a contour length over 10 μm (Fig. 1B), giving an aspect ratio up to 103.



Page 10 of 27

By depositing these nanofibrils on filtering membranes through vacuum-filtration, nanoporous and mesoporous membranes were produced by different drying protocols. In the case of ambient air-drying, a low porosity of 8.4% and sub-10 nm pores were obtained (with the membrane thickness of 10 m) owing to significant shrinkage of fibrous networks resulted from strong capillary forces among ChitinNFs (Fig. 1C).13 Such nanoporous membranes was evaluated by N2 adsorption-desorption analysis to have the narrow distrubution of pore sizes maximized at ~4.1 nm (Fig. 1E). In the case of solvent exchange to tertiary butanol and frezze-drying, a porosity up to 78.2% was produced for the meso-porous membrane (with the thickness of 24 m) with a broad distribution of pore sizes maximized at 22 nm (Fig. 1D & 1E). The cross-sectional SEM images showed in Fig. S2A certified a homogeneous porous morphology throughout the ChitinNFs membranes. To be noted, besides negligible ionization and strong interfibril H-bonding in anlogue to natural carapace of shrimp and crab, either nanoporous or mesoporous membranes could have their thickness tuned precisely within 97 nm ~ 25 μm, whereas without sacrificing their porous structures (Fig. S1A & S2B). Maximally maintaining chemical and crystalline structures of pristine chitin (Fig. S3A & S3B), these stubborn membranes not only had robust mechanical properties (Figure S1B), but could also maintain their porous structures when immerging in various solvents and under corrosive environments (Fig. S3C). For example, the ultimate tensile strength of nanoporous and mesoporous membranes was 91.4 and 10.9 MPa, respectively, being comparable to the other chitin nanofibrils based membranes and much higher than those of commercial filtration membranes (Figure S1B & Table S1). Moreover, both mesoporous and nanoporous membrane show weak volume swelling and negligible variation of water flux (Fig. 2A), which would promise great potential for longtime and cyclic uses in membrane separation. In contrast, ionized ChitinNFs (e.g. via oxidation, esterification and deacetylation) and cellulose nanofibrils (e.g


Page 11 of 27 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


TEMP-cellulose) showed serious swelling of their porous structures (Fig. S4A).6 Meanwhile, these ChitinNF membranes also inherited super stability under caustic conditions from pristine chitin (Fig. S5). There occurred only very weak flux variation in acidic (1 M HCl), alkaline (1 M NaOH), salty (1 M NaCl), reductive (1 M hydrazine) and oxidative (1 M NaClO2) systems (Fig. 2B), with comparison to gradual hydrolysis of silk nanofibrils (Fig. S4B). In polar organic solvents, the flux followed the Hagen-Poiseuille model6 and was inversely proportional to the solvent viscosity (Fig. 2C), in contrast to dissolution of commercial cellulose acetate membranes (Fig. S4C). Thus, these stable and endurable membranes could serve for diverse separation applications in caustic and polar organic systems. In spite of having negligible ionization, these nanoporous and mesoporous membranes did not sacrifice their hydrophilic surfaces for high flux of polar solvents, owing to the presence of plentiful polar groups. The water flux followed the Hagen-Poiseuille model with the increasing membrane thickness within 97 nm ~ 25 m (Fig. 2D & S6).21 If calculating the membrane resistance (Rc) according to the equation F = P/0.89(Rs+Rc) (where 0.89 mPa•s is the viscosity of pure water, F is the water flux, P is the applied pressure difference and Rs is the support resistance), the nanoporous membrane (with the thickness of 45 nm) gave a resistance as low as 9.96  1010 bar/m, being comparable to the values of macro-porous supporters (7.19  1010 bar/m) and nano-porous membranes of cellulose fibrils (8.7  1010 bar/m for the membrane thickness of 40 nm).6 It could produce a high water flux of 2230 L h-1 m-2 bar-1, being comparable to certain membranes with sub-10 nm pores and two orders of magnitudes higher than those of commercial filtration membranes (e.g. HFM-100 and HFM-116).22-27 In analogue, the mesoporous membrane (with the thickness of 436 nm) gave a water flux of 2630 L h-1 m-2 bar-1, being also superior to state-of-art filtration membranes with the similar thickness and two orders of magnitudes higher than those of commercial filtration membranes (e.g. UE 50 and PLHK).5, 28-31



Page 12 of 27

The intrinsic hydrophilicity of chitin also offered underwater super-oleophobicity for the nanoporous and mesoporous membranes.32,33 Water could wet and hydrate the membranes within 0.5 s (Fig. 3A), offering hydrated surfaces to repel non-polar fluids (e.g. heavy and light oils). An ellipsoidal droplet of chloroform could detach easily from the hydrated membrane (Fig. 3B & S7), and many non-polar solvents showed a contact angle larger than 140, even for the membranes hydrated with caustic solvents (Fig. 3C & S8).34 Besides the contact angel, a critical intrusion pressure (Pc) was also utilized frequently to quantitatively evaluate the permeation resistance of fluids into a membrane. In the equation Pc=-2cos/R,35  refers to the surface tension,  refers to the static contact angle and R is the equivalent pore radius of the membrane. The high Pc beyond 2.5 MPa in Fig. 2G suggests that these non-polar solvents were hindered across the membranes. The underwater super-oleophobicity of these ChitinNF membranes immediately evoked their application of separating non-polar fluids from their nano-emulsions. Many commercial membranes, which may lack the ability of separating nano-emulsions due to their large pores (Fig. S9),36,37 could be adapted by sequentailly filtering the disperion of ChitinNFs and t-butanol (Fig. 4A). Non-polar fluids such as toluene, either as the droplets in oil-in-water emulsions or as the continuous phases in water-in-oil emulsions, were rejected nearly completely by the mesoporous ChitinNF layer with the thickness of >97 nm (Fig. S10A-S10C). And no toluence droplet was detected in the transparent fitrate by optic microscope, light scattering and UV-vis spectra (Fig. 4B-4C & S10D). For the membrane thickness of 97 nm, a high flux of 563 L h-1 m-2 and a rejection of 91 % were obtained to separate toluene droplets (the droplets were stabilized by the surfactant of Tween 80 and having the size as low as 50 nm) from water (Fig. 4D), which were also superior to many membranes in the literature.38-45 Moreover, after flushing with water (Fig. 5A & S11), the ChitinNF membrane could be recovered for cyclic utilization. Both the


Page 13 of 27 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


permeation flux and rejection recovered to the original level by removing the layer of non-polar solvents from the membrane (Fig. 5A). In the case of separating other non-polar fluids (e.g. chloroform, isooctane and petroleum ether), a high permeation flux (>33 L h-1 m-2 bar-1) and rejection (>83 %) still remained for the ChitinNF membrane with the thickness of 970 nm, even under caustic environments (Fig. 5B & S12-S14). To be noted, the differences in the permeation flux and rejection in Fig. 5B were associated with different sizes and viscosities of non-polar droplets.4 The ChitinNF membranes combined perfectly nanoporous structures and structural stabilization, enabling to separate and/or recycle diverse nanoparticles in nanotechnology. The nanoporous membrane could be integrated into a commercial syringe filter by simply filtering the dispersion of ChitinNFs before air-drying (Fig. 6A). With the membrane thickness of >68 nm (Fig. S15), Au nanoparticles with the size of 5.3 nm were separated with the rejection of >99 %, while graphene oxide (GO) dots with the size of ~2.1 nm could freely pass the nanoscale pore (Fig. 6B-6C). Although the rejection of nanoporous membranes could be further improved by decreasing the external driving pressure, the permeation flux dramatically decreased at the same time (Fig. S18). Thus, a driven pressure of 0.95 bar was used for the following experiments without further specification. Moreover, both the high flux (870.1 L m-2 h-1 bar-1) and rejection remained stable during hours’ filtration (Fig. 6D), which were also higher than those of many filtration membranes in the literature (Fig. 7A), such as with the building units of cellulose nanofibrils, silk nanofibrils, 2D nanosheets and nanoparticles.5, 31, 46-49 Thus these ChitinNF membranes seemed to show a perfect balance of permeability and separation performance. The cut-off between 2.1~5.3 nm was also confirmed by separating other nanoparticles with different sizes (Fig. S16-S17), including Pt NPs (2.7 nm), Au NPs (5.3 nm & 20.2 nm) and Ag NPs (8.7 nm). The nanoparticles with the size  5.3 nm all gave a high rejection >99% (Fig. 7B).



Page 14 of 27

In theory, a flexible macromolecule could translocate through a nanoscale pore by stretching its random coil conformation.50 Thus, it is possible to separate rigid macromolecules from flexible ones by forcing their mixing solution through stable nanoscale pores (Fig. 8A). As the matter of fact, flexible macromolecules such as polyvinyl alcohol (PVA, Mw~31 kDa), bovine serum albumin (BSA, Mw ~66 kDa) and polyethylene epoxide (PEO, Mw ~100 kDa) showed a lower rejection (˂35%) for the nanoporous ChitinNF membrane with the thickness of 102 nm (Fig. 8B & Table S2), in contrast to high rejection (>95%) of relatively rigid macromolecules such as chitosan (Mw ~87 kDa), alginate (Mw ~150 kDa), quaternized chitosan (QCh, Mw ~210 kDa) and hydroxy propyl cellulose (HPC, Mw ~100 kDa) (Fig. S19). Removal of chitosan from its mixture with PEO was confirmed by lack of characteristic 1H NMR chemical shift (i.e. 3.15 ppm in Fig. 8C) and FTIR vibration (e.g. 1480~1490 cm-1 in Fig. S20) of chitosan in the filtrate. Although, the macromolecules fouling of the membranes were unavoidable during the separation process, its flux could be partially recovered by fluxing with deionized water (Fig. S21).

CONCLUSIONS In summary, we reported a facile approach to prepare novel porous chitin membranes consisting of natural chitin nanofibrils, which directly exfoliated from portunid carapace to retain chemical and crystalline structures. The resulting membranes, with adjustable thickness, tunable porosity, narrow distribution of pore sizes and minimal ionization, allowed rapid permeation of water and most organic solvents that higher than commercial membranes. Typically, the resistance of 45 nm-thick nanoporous membrane and 436 nm-thick mesoporous membrane was 9.96  1010 bar/m and 7.36  1010 bar/m, respectively, which was close to the macroporous support resistance (7.19  1010 bar/m). Moreover, these membranes could not only withstand caustic conditions, but also separate nanoscale nanoparticles, nanoemulsion and rigid macromolecules with high rejection and efficiency. For example, 97 nm-thick


Page 15 of 27 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


mesoporous ChitinNF membranes were capable of efficiently separating toluene nano-droplets from water with a high flux of 563 L h-1 m-2 and a rejection of 91 %, even under caustic environments. While, nanoporous ChitinNF membranes could be used to sieve ultra-small nanoparticles with different sizes and macromolecules with different conformations. Thus, we speculate that our broad-spectrum ChitinNF membranes are highly promising for applications as diverse as in food, wastewater treatment, nanotechnology, biomedicine and material science.

ASSOCIATED CONTENT Supporting Information The Supporting Information is available free of charge on the ACS Publications website at DOI: Photographs, SEM images, microscope images, Zeta potential, XRD patterns, FT-IR, contact angle, size distributions, total organic content (TOC), UV-vis absorption, tables summarizing the ChitinNF membranes properties (PDF).

ACKNOWLEDGEMENTS Y. J. and L. C. thank the National Natural Science Foundation of China (No. 51603224 and 21474125) for financial support, L. C. also thank Chinese “1000 Youth Talent Program”, Shandong “Taishan Youth Scholar Program”, Natural Science Foundation of Shandong Province (JQ201609) and Shandong Collaborative Innovation Centre for Marine Biomass Fiber Materials and Textiles, for financial support.

REFERENCES (1) Jiang, X.; Du, B.; Huang, Y.; Zheng, J. Ultrasmall Noble Metal Nanoparticles: Breakthroughs and Biomedical Implications. Nano Today 2018, 21, 106-125. (2) BATLEY, G. E.; KIRBY, J. K.; MCLAUGHLIN, M. J. Fate and Risks of Nanomaterials in Aquatic



Page 16 of 27

and Terrestrial Environments. Accounts. Chem. Res. 2013, 46, 854-862. (3) Gupta, R. K.; Dunderdale, G. J.; England, M. W.; Hozumi, A. Oil/water Separation Techniques: a Review of Recent Progresses and Future Directions. J. Mater. Chem. A 2017, 5, 16025–10658. (4) Cheng, Q.; Ye, D.; Chang, C.; Zhang, L. Facile Fabrication of Superhydrophilic Membranes Consisted of Fibrous Tunicate Cellulose Nanocrystals for Highly Efficient Oil/Water Separation. J. Membr. Sci. 2017, 525, 1-8. (5) Ling, S.; Jin, K.; Kaplan, D. L.; Buehler, M. J. Ultrathin Free-Standing Bombyx Mori Silk Nanofibril Membranes. Nano Lett. 2016, 16, 3795-3800. (6) Zhang, Q. G.; Deng, C.; Soyekwo, F.; Liu, Q. L.; Zhu, A. M. Sub-10 nm Wide Cellulose Nanofibers for Ultrathin Nanoporous Membranes with High Organic Permeation. Adv. Funct. Mater. 2016, 26, 792-800. (7) Wang, Y.; Zhu, L.; You, J.; Chen, F.; Zong, L.; Yan, X.; Li, C. Catecholic Coating and Silver Hybridization of Chitin Nanocrystals for Ultrafiltration Membrane with Continuous Flow Catalysis and Gold Recovery. ACS Sustain. Chem. Eng. 2017, 5, 10673-10681. (8) Li, L.; Chen, Q.; Jin, F.; Wu, C. How Does a Polymer Chain Pass Through a Cylindrical Pore Under Anelongational Flow Field? Polymer 2015, 67, A1-A13. (9) Zheng, T.; Yang, J.; He, J.; Li, L. Origin of Inconsistency in Experimentally Observed Transition Widths and Critical Flow Rates in Ultrafiltration Studies of Flexible Linear Chains. Macromolecules 2018, 51, 6504-6512. (10) Phillip, W. A.; Dorin, R. M.; Werner, J.; Hoek, E. M.; Wiesner, U.; Elimelech, M. Tuning Structure and Properties of Graded Triblock Terpolymer-Based Mesoporous and Hybrid Films. Nano Lett. 2011, 11, 2892-2900. (11) Eguizábal, A.; Sgroi, M.; Pullini, D.; Ferain, E.; Pina, M. P. Nanoporous PBI Membranes by Track Etching for High Temperature PEMs. J. Membr. Sci. 2014, 454, 243-252. (12) Kellenberger, C. R.; Luechinger, N. A.; Lamprou, A.; Rossier, M.; Grass, R. N.; Stark, W. J. Soluble Nanoparticles as Removable Pore Templates for the Preparation of Polymer Ultrafiltration Membranes. J. Membr. Sci. 2012, 387, 76-82. (13) Sehaqui, H.; Michen, B.; Marty, E.; Schaufelberger, L.; Zimmermann, T. Functional Cellulose Nanofiber Filters with Enhanced Flux for the Removal of Humic Acid by Adsorption. ACS Sustain. Chem. Eng. 2016, 4, 4582-4590. (14) Bolisetty, S.; Arcari, M.; Adamcik, J.; Mezzenga, R. Hybrid Amyloid Membranes for Continuous Flow Catalysis. Langmuir 2015, 31, 13867-13873. (15) Bolisetty, S.; Mezzenga, R. Amyloid–Carbon Hybrid Membranes for Universal Water Purification. Nat. Nanotechnol. 2016, 11, 365-371. (16) Bolisetty, S.; Reinhold, N.; Zeder, C.; Orozco, M. N.; Mezzenga, R. Efficient Purification of Arsenic-Contaminated Water Using Amyloid-Carbon Hybrid Membranes. Chem. Commun. 2017, 53, 5714-5717. (17) Zhu, L.; Zong, L.; Wu, X.; Li, M.; Wang, H.; You, J.; Li, C. Shapeable Fibrous Aerogels of Metal-Organic-Frameworks Templated with Nanocellulose for Rapid and Large-Capacity Adsorption. ACS Nano 2018, 12, 4462-4468. (18) Ling, S.; Chen, W.; Fan, Y.; Ke, Z.; Jin, K.; Yu, H.; Buehler, M. J.; Kaplan, D. L. Biopolymer Nanofibrils: Structure, Modeling, Preparation, and Applications. Prog. Polym. Sci. 2018, 85, 1-56. (19) Saito, T.; Kimura, S.; Nishiyama, Y.; Isogai, A. Cellulose Nanofibers Prepared by TEMPO-Mediated Oxidation of Native Cellulose. Biomacromolecules 2007, 8, 2485-2491. (20) You, J.; Zhu, L.; Wang, Z.; Zong, L.; Li, M.; Wu, X.; Li, C. Liquid Exfoliated Chitin Nanofibrils


Page 17 of 27 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


for Re-Dispersibility and Hybridization of Two-Dimensional Nanomaterials. Chem. Eng. J. 2018, 344, 498-505. (21) Baker, R. W. Membrane Technology and Applications, 2nd ed., New York: 2004. (22) Song, J. J.; Huang, Y.; Nam, S.-W.; Yu, M.; Heo, J.; Her, N.; Flora, J. R.; Yoon, Y. Ultrathin Graphene Oxide Membranes for the Removal of Humic Acid. Sep. Purif. Technol. 2015, 144, 162-167. (23) Han, Y.; Xu, Z.; Gao, C. Ultrathin Graphene Nanofiltration Membrane for Water Purification. Adv. Funct. Mater. 2013, 23, 3693-3700. (24) Zhang, Q.; Ghosh, S.; Samitsu, S.; Peng, X.; Ichinose, I. Ultrathin Freestanding Nanoporous Membranes Prepared from Polystyrene Nanoparticles. J. Mater. Chem. 2011, 21, 1684-1688. (25) Wang, J.; Zhang, P.; Liang, B.; Liu, Y.; Xu, T.; Wang, L.; Cao, B.; Pan, K. Graphene Oxide as an Effective Barrier on a Porous Nanofibrous Membrane for Water Treatment. ACS Appl. Mater. Interfaces 2016, 8, 6211-6218. (26) Wang, Y.; Liu, L.; Xue, J.; Hou, J.; Ding, L.; Wang, H. Enhanced Water Flux Through Graphitic Carbon Nitride Nanosheets Membrane by Incorporating Polyacrylic Acid. Aiche J. 2018, 64, 2181-2188. (27) Gao, S. J.; Qin, H.; Liu, P.; Jin, J. SWCNT-Intercalated GO Ultrathin Films for Ultrafast Separation of Molecules. J. Mater. Chem. A 2015, 3, 6649-6654. (28) Deng, C.; Zhang, Q. G.; Han, G. L.; Gong, Y.; Zhu, A. M.; Liu, Q. L. Ultrathin Self-Assembled Anionic Polymer Membranes for Superfast Size-Selective Separation. Nanoscale 2013, 5, 11028-11034. (29) Zhou, K.; Zhang, Q. G.; Li, H. M.; Guo, N. N.; Zhu, A. M.; Liu, Q. L. Ultrathin Cellulose Nanosheet Membranes for Superfast Separation of Oil-in-Water Nanoemulsions. Nanoscale 2014, 6, 10363-10369. (30) Ma, H.; Burger, C.; Hsiao, B. S.; Chu, B. Ultrafine Polysaccharide Nanofibrous Membranes for Water Purification. Biomacromolecules 2011, 12, 970-976. (31) Ling, S.; Qin, Z.; Huang, W.; Cao, S.; Kaplan, D. L.; Buehler, M. J. Design and Function of Biomimetic Multilayer Water Purification Membranes. Sci. Adv. 2017, 3, e1601939. (32) Chang, C.; Chen, S.; Zhang, L. Novel Hydrogels Prepared Via Direct Dissolution of Chitin at Low Temperature: Structure and Biocompatibility. J. Mater. Chem. 2011, 21, 3865-3871. (33) Xu, D.; Huang, J.; Zhao, D.; Ding, B.; Zhang, L.; Cai, J. High-Flexibility, High-Toughness Double-Cross-Linked Chitin Hydrogels by Sequential Chemical and Physical Cross-Linkings. Adv. Mater. 2016, 28, 5844-5849. (34) Blanco, M. V. D.; Fischer, E. J.; Cabane, E. Underwater Superoleophobic Wood Cross Sections for Efficient Oil/Water Separation. Adv. Mater. Interfaces 2017, 4, 1700584. (35) Dou, Y.; Tian, D.; Sun, Z.; Liu, Q.; Na, Z.; Kim, J. H.; Lei, J.; Shi, X. D. Fish Gill Inspired Crossflow for Efficient and Continuous Collection of Spilled Oil. ACS Nano 2017, 11, 2477-2485. (36) Yang, J.; Wen, G.; Gou, X.; Song, H.; Guo, Z. A Study on the Manufacture of Kevlar Membrane Modified by Inorganic Nanoparticles with Universal Applicability in Separating Diffident Types of Emulsions. J. Membr. Sci. 2018, 563, 326-335. (37) Ge, J.; Zong, D.; Jin, Q.; Yu, J.; Ding, B. Biomimetic and Superwettable Nanofbrous Skins for Highly Effcient Separation of Oil-in-Water Emulsions. Adv. Funct. Mater. 2018, 28, 1705051. (38) Wang, M.; Cao, Y.; Xu, Z.-L.; Li, Y.-X.; Xue, S.-M. Facile Fabrication and Application of Superhydrophilic Stainless Steel Hollow Fiber Microfiltration Membranes. ACS Sustain. Chem. Eng. 2017, 5, 10283-10289. (39) Sun, F.; Liu, W.; Dong, Z.; Deng, Y. Underwater Superoleophobicity Cellulose Nanofibril Aerogel Through Regioselective Sulfonation for Oil/Water Separation. Chem. Eng. J. 2017, 330, 774-782. (40) Yang, H.-C.; Liao, K.-J.; Huang, H.; Wu, Q.-Y.; Wan, L.-S.; Xu, Z.-K. Mussel-Inspired



Page 18 of 27

Modification of a Polymer Membrane for Ultra-High Water Permeability and Oil-in-Water Emulsion Separation. J. Mater. Chem. A 2014, 2, 10225-10230. (41) Rajasekhar, T.; Trinadh, M.; Veera Babu, P.; Sainath, A. V. S.; Reddy, A. V. R. Oil–Water Emulsion Separation Using Ultrafiltration Membranes Based on Novel Blends of Poly(Vinylidene Fluoride) and Amphiphilic Tri-Block Copolymer Containing Carboxylic Acid Functional Group. J. Membr. Sci. 2015, 481, 82-93. (42) Yuan, T.; Meng, J.; Hao, T.; Zhang, Y.; Xu, M. Polysulfone Membranes Clicked with Poly (Ethylene Glycol) of High Density and Uniformity for Oil/Water Emulsion Purification: Effects of Tethered Hydrogel Microstructure. J. Membr. Sci. 2014, 470, 112-124. (43) Moghimifar, V.; Livari, A. E.; Raisi, A.; Aroujalian, A. Enhancing the Antifouling Property of Polyethersulfone Ultrafiltration Membranes Using NaX Zeolite and Titanium Oxide Nanoparticles. RSC Advances 2015, 5, 55964-55976. (44) Wang, G.; He, Y.; Wang, H.; Zhang, L.; Yu, Q.; Peng, S.; Wu, X.; Ren, T.; Zeng, Z.; Xue, Q. A Cellulose Sponge with Robust Superhydrophilicity and Under-Water Superoleophobicity for Highly Effective Oil/Water Separation. Green Chem. 2015, 17, 3093-3099. (45) Milić, J. K.; Petrinić, I.; Goršek, A.; Simonič, M. Ultrafiltration of Oil-in-Water Emulsion by Using Ceramic Membrane: Taguchi Experimental Design Approach. Cent. Eur. J. Chem. 2014, 12, 242-249. (46) Krieg, E.; Weissman, H.; Shirman, E.; Shimoni, E.; Rybtchinski, B. A Recyclable Supramolecular Membrane for Size-Selective Separation of Nanoparticles. Nat. Nanotechnol. 2011, 6, 141-146. (47) Liang, H. W.; Wang, L.; Chen, P. Y.; Lin, H. T.; Chen, L. F.; He, D.; Yu, S. H. Carbonaceous Nanofiber Membranes for Selective Filtration and Separation of Nanoparticles. Adv. Mater. 2010, 22, 4691-4695. (48) Huang, H.; Song, Z.; Wei, N.; Shi, L.; Mao, Y.; Ying, Y.; Sun, L.; Xu, Z.; Peng, X. Ultrafast Viscous Water Flow Through Nanostrand-Channelled Graphene Oxide Membranes. Nat. Commun 2013, 4, 2979. (49) Sun, L.; Ying, Y.; Huang, H.; Song, Z.; Mao, Y.; Xu, Z.; Peng, X. Ultrafast Molecule Separation Through Layered WS2 Nanosheet Membranes. ACS Nano 2014, 8, 6304-6311. (50) Jin, F.; Wu, C. Observation of the First-Order Transition in Ultrafiltration of Flexible Linear Polymer Chains. Phys. Rev. Lett. 2006, 96, 237801.


Page 19 of 27 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 1. Procedures followed to fabricate nanoporous and mesoporous membranes of ChitinNFs. (A) Aligned ChitinNFs in Portunid carapace. (B) ChitinNFs exfoliated in DMSO saturated with KOH under sonication. (C) Nanoporous membranes produced through filtering aqueous suspension of ChitinNFs and air-drying. (D) Mesoporous membranes produced through filtering aqueous suspension of ChitinNFs, solvent exchange to t-butanol and freeze-drying. (E) Pore size distribution of nanoporous (black) and mesoporous (red) membranes determined by nitrogen physisorption measurements.



Page 20 of 27

Figure 2. Stability of nanoporous and mesoporous membranes of ChitinNFs. (A) Time dependence of water flux and water uptake. Thickness of nanoporous membrane: 307 nm; Thickness of mesoporous membrane: 0.97 μm. (B) Flux stability for caustic aqueous solutions. Thickness of nanoporous membrane: 102 nm; Thickness of mesoporous membrane: 4.8 μm. (C) Flux of organic polar solvents. Thickness of nanoporous membrane (dark yellow): 307 nm; Thickness of mesoporous membrane (dark cyan): 4.8 μm. The Hagen-Poiseuille equation was used for data fitting. (D) Water flux of membranes with different pore sizes. Building units of membranes: 1-sulfonated polyetherketone;28 2-graphene oxide (GO);22 3-silk NFs hybridized with hydroxyapatite;31 4-cellulose;29 5-silk NFs;5 6-graphene with 2D nanochannels;23 7-polystyrene nanoparticles;24 8-cellulose NFs;30 9-GO/polyacrylonitrile nanofibers;25 10-graphitic carbon nitride nanosheets;26 11-single-walled carbon nanotube/GO.27


Page 21 of 27 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 3. Superlyophilicity of mesoporous membranes of ChitinNFs. (A) Dynamic wetting behavior of mesoporous membrane to water. (B) Dynamic adhesive behavior of chloroform droplets on wet mesoporous membrane. (C) Contact angle and intrusion pressures of organic non-polar solvents to mesoporous membranes wetted with H2O (Left) and caustic aqueous solutions (Right).



Page 22 of 27

Figure 4. Separation of nanoemulsions with mesoporous membrane of ChitinNFs. (A) Illustration of processing commercial membrane into mesoporous membrane of ChitinNFs for emulsion separation. Step І: Filtering ChitinNFs suspension and t-butanol; Step П: Filtering emulsion; Step Ш: Water flushing. (B-C) Optic microscopy of toluene-in-water microemulsions (B) and droplet size distribution of toluene-in-water nanoemulsion (C) before and after passing mesoporous membrane. Toluene/Water: 3:7 vol/vol. (D) Toluene rejection vs. flux of mesoporous membranes producing by different building components.

1-polyethersulfone-titanium

fluoride)-tri-block

copolymer;41

dioxide;43

2-polyethersulfone;43

4-polydopamine/

3-poly(vinylidene polyethyleneimine;40

5-polysulfone/propargyl-poly(ethylene glycol);42 6-steel hollow fibers;38 7-ceramic;45 8-cellulose NFs aerogel;39 9-cellulose sponge.44


Page 23 of 27 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 5. Stability of mesoporous membranes of ChitinNFs during the emulsions separation process. (A) Stability of flux and toluene rejection during cyclic application of mesoporous membrane. Water flush was adopted to recover the membrane. (B) Flux and oil rejection for emulsions of organic non-polar solvents in H2O (Left) and caustic aqueous solutions (Right). Thickness of mesoporous membranes: 970 nm.



Page 24 of 27

Figure 6. Separation of nanoparticles with nanoporous membrane of ChitinNFs. (A) Illustration of processing syringe filter into nanoporous membrane of ChitinNFs for nanoparticle separation. Step І: Filtering ChitinNFs suspension and air-drying; Step П: Filtering nanoparticles. (B-C) UV-vis absorption (B) and TEM image (C) of mixture dispersion of Au nanoparticles and GO quantum dots before and after passing nanoporous membrane. Sizes of Au nanoparticles and GO quantum dots: ~5 and ~2.1 nm. Thickness of nanoporous membranes: 102 nm. (D) Time dependence of permeation flux and rejection of Au nanoparticles. Thickness of nanoporous membranes: 68 nm.


Page 25 of 27 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 7. Comparison of separation performance. (A) Permeation flux vs. thickness of membranes produced by different building components. Color-scale indicates rejection of Au nanoparticles with ~5 nm in size. PS: polystyrene;24 SNF: silk NFs;5 CNF: carbonaceous nanofibers;47 WS2: tungsten disulfide;49

NSC-GO:

hydroxyapatite;31

nanostrand-channelled

PP2b:

GO;48

SNF/HAP:

(5,5′-bis(1-ethynyl-7-polyethylene

silk

NFs

hybridized

with

glycol-N,N′-bis(ethylpropyl)

perylene-3,4,9,10-tetracarboxylic diimide)-2,2′-bipyridine).46 (B) Permeation flux and rejection for nano-objects with different sizes. Thickness of nanoporous membranes: 102 nm.



Page 26 of 27

Figure 8. Separation of soluble macromolecules with nanoporous membrane of ChitinNFs. (A) Illustration of flexible macromolecules translocating across nanoscale pore by stretching their conformation. (B) Rejection of macromolecules with different chain rigidity. QCh: quaternized chitosan; HPC: hydroxypropyl cellulose; PVA: polyvinyl alcohol; PEO: polyethylene oxide. (C) Separation rigid QCh (210 kDa) from flexible polyethylene oxide (PEO, 100 kDa). Thickness of nanoporous membranes: 102 nm.


Page 27 of 27 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


TOC

Separation of caustic nano-emulsions and macromolecular conformations with nanofibrous membrane of marine chitin Zengbin Wang,1,2 Jie Xu,2 Mingjie Li,

2

Chunlei Su,3 Xiaochen Wu,2 Yue Zhang,1,* Jun You,2,* and

Chaoxu Li2,*


Separation of caustic nano-emulsions and macromolecular

Recommend Documents