Modular Molecular Nanoplastics | ACS Nano

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Modular Molecular Nanoplastics Angelica Niazov-Elkan, Xiaomeng Sui, Ifat Kaplan-Ashiri, Linda J.W. Shimon, Gregory Leitus, Erez Cohen, Haim Weissman, H. Daniel Wagner, and Boris Rybtchinski ACS Nano, Just Accepted Manuscript • Publication Date (Web): 12 Aug 2019 Downloaded from pubs.acs.org on August 12, 2019

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Modular Molecular Nanoplastics

Angelica Niazov-Elkan,† XiaoMeng Sui, ‡* Ifat Kaplan-Ashiri, § Linda J.W. Shimon, § Gregory Leitus, § Erez Cohen, † Haim Weissman, † H. Daniel Wagner, ‡* and Boris Rybtchinski†*

Departments of †Organic Chemistry, ‡Materials and Interfaces, and §Chemical Research Support, Weizmann Institute of Science, Rehovot, 76132701, Israel

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ABSTRACT In view of their facile fabrication and recycling, functional materials that are built from small molecules (“molecular plastics”) may represent a cost-efficient and sustainable alternative to conventional covalent materials. We show how molecular plastics can be made robust and how their (nano)structure can be tuned via modular construction. For this purpose, we employed binary composites of organic nanocrystals (ONCs) based on a perylene diimide (PDI) derivative, with graphene oxide (GO), bentonite nano-clay (NC), or hydroxyethyl cellulose (HEC) that both reinforce and enable tailoring the properties of the membranes. The hybrids are prepared via a simple aqueous deposition method, exhibit enhanced mechanical robustness, and can be recycled. We utilized these properties to create separation membranes with tunable porosity that are easy to fabricate and recycle. Hybrids 1/HEC and 1/NC are capable of ultrafiltration, and 1/NC removes heavy metals from water with high efficiency. Hybrid 1/GO shows mechanical properties akin to covalent materials with just 2-10% (by weight) of GO. This hybrid was used as a membrane for immobilizing β-galactosidase that demonstrated long and stable biocatalytic activity. Our findings demonstrate the utility of modular molecular nanoplastics as robust and sustainable materials that enable efficient tuning of structure and function, and are based on self-assembly of readily available inexpensive components.

Keywords:

supramolecular

materials,

self-assembly,

nanofiltration, biocatalysis,


membranes,

ultra-filtration,

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We define molecular plastics as robust macroscopic noncovalent materials based on noncovalent self-assembly of small molecules,1, 2 in contrast to conventional plastics that are based on covalent polymers. Because of the facile fabrication and recycling typical of noncovalent materials, molecular plastics can represent a sustainable and cost-efficient alternative to polymer-based materials. Targeting molecular plastics, we showed that organic nanocrystals (ONCs) can afford cohesive bulk materials that are thermally robust and easy to fabricate and recycle.3 However, the mechanical strength of these ONC materials is much inferior to polymeric ones, and their structural tunability is limited. Separation membranes are of high importance in industry, and are typically based on polymers or ceramics.4-8 Membranes with diverse separation properties (cutoff, affinity, biocompatibility, etc.) are available,9-11 however, their modification entails a redesign of membrane material, involving considerable synthetic and fabrication effort. Recently, supramolecular12-14 and nanoparticle-based15 membranes have enabled facile fabrication/recycling and retrieval of retentates. Besides precise control of their porosity, mechanical and thermal robustness of the membranes are of paramount importance since robust membrane materials are less susceptible to deformation, fractures, and morphological changes, thus enabling sustainable performance. Hence, separation membranes are excellent systems to test the viability of molecular plastics as alternatives to covalent materials.

Advantageously, supramolecular approach allows

combining various nanoscale modules via solution-based fabrication. We envisaged that ONCs can be hybridized with a variety of building blocks via a noncovalent “Lego” methodology, which can be applied to engineer strong and tunable molecular plastics capable of membrane function. Herein, we report on a family of membrane materials based on ONCs of 1 (Figure 1a, b) that are integrated with graphene oxide (GO), nano-clay (NC), or with a linear polysaccharide, hydroxyethyl cellulose (HEC, Figures 1c-e). All the resultant hybrids possess enhanced mechanical robustness. Hybrids 1/HEC and 1/NC are capable of ultra- and nanofiltration (with 5 and 1 nm cutoffs respectively); 1/NC is also capable of removing heavy metal contamination from water. Hybrid 1/GO shows excellent biocatalytic activity and exhibits mechanical properties akin to covalent materials, with just 5% wt of GO. All the hybrids are prepared by simple aqueous fabrication and can be easily disassembled and reassembled. Modular design from simple components, mechanical robustness, recyclability and diverse membrane function introduces a general platform for cost-efficient and sustainable membrane materials, demonstrating feasibility and utility of molecular nanoplastics.


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Figure 1. (a) Molecular structure of 1 and its ORTEP representation (derived from a single crystal Xray analysis), with thermal ellipsoids at 50% probability. Hydrogen atoms omitted for clarity. (b) SEM image of ONCs of 1. (c) Hydroxyethyl cellulose structure (R = Ethyl). (d) Structure of nano-sheets of bentonite clay, the counter cations are marked in blue, Si in yellow, Al in grey, O in red. (e) Representative GO sheet structure.

RESULTS AND DISCUSSION Macroscopic materials made from ONCs of 1 have relatively large pores (60 nm cutoff), which cannot be tuned as their porosity is a consequence of ONC dimensions (Figure S1).3 Young’s modulus of pristine ONC 1 films is relatively low (140 ± 50 MPa), and the films are brittle (elongation of ~1%).3 Integration of the films with a linear polysaccharide (HEC), or 2D nanomaterials (NC and GO) was performed in order to modify porosity and improve mechanical properties, resulting in reinforced materials with valuable membrane functions.


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Ultrafiltration membrane: 1/HEC hybrid. HEC is a linear cellulose derivative of high molar mass and toughness,16, 17 which is water processible. HEC is blended with various materials, such as cellulose nanofibers, N-vinylformamide, and gluten for the production of composite films with high ductility and toughness.18-22 In a typical procedure used for 1/HEC fabrication (see Experimental Section for details), ONC dispersion in THF: water mixture (3:7, v/v) is deposited on a Polyvinylidene fluoride (PVDF) support (with 0.45-μm pore size). Then HEC (1300 kDa) solution in water is deposited on top of the ONCs film to yield hybrid membrane with 10 wt% HEC content. The resulting film is dried on air, and the membrane is manually detached from the PVDF support, affording a freestanding film with average thickness of 40 µm. In the absence of ONC film, HEC passes through the PVDF support (0.45 μm) and cannot be deposited as a membrane. Scanning electron microscopy (SEM) imaging of the composite reveals that the ONC layer is covered with a polymer film (Figure 2a) that has nanometric channels (Figure 2d-c). The film does not penetrate into the bulk of the ONCs matrix (Figure 2b). The mechanical properties of the composite are given in Tables 1 and S1, indicating substantial enhancement in the mechanical robustness, with the toughness of the composite film (1.8±0.3 MPa) being more than two orders of magnitude higher than that of the pristine ONCs film ((7±4)·10-3 MPa). Both the pristine ONC film and the composite have approximately the same elastic modulus (114±17.0 MPa). Unlike the brittle ONCs film, HEC/ONCs composite has a yield point, after which there is plastic deformation, exhibiting average elongation of 31.5±4.3 %. While the tensile properties of the pristine ONCs film involve elastic deformation and yield due to the disentanglement of the ONCs,3 neat HEC polysaccharide film has an elastic deformation followed by yield and strain hardening (Figure S2). Thus, the tensile behavior of the hybrid 1/HEC is strongly influenced by the presence of the polysaccharide.


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Figure 2. (a) SEM image of the cross-section of 1/HEC hybrid film. (b) The cross-section of the ONC layer of the membrane. (c) SEM image of the cross-section of HEC polymer deposited on top of ONCs film. (d) Zoom in of the HEC layer (c). The nanometric channels are marked by yellow arrows.

Young’s Modulus [MPa]

Yield Strength [MPa]

Tensile Strength [MPa]

Elongation [%]

Toughness [MPa]

140±50 438±104

19.4±3.9

1.3±0.5 43.2±10.7

0.9±0.1 44.0±9.9

0.007±0.004 12.05±3.31

ONC/HEC (9:1)

114±17

5.7±0.6

7.3±0.8

31.5±4.3

1.80±0.31

ONC/HEC recycled

104±23

5.9±0.3

8.5±0.4

29.6±8.1

1.90±0.51

ONC 1 film

HEC film (neat)

Table 1. The mechanical properties of membrane of pristine ONC 1 film, pristine HEC film, and 1/HEC hybrids, measured by tensile test.

We utilized the 1/HEC membrane for filtration of aqueous dispersion of gold nanoparticles (Au NPs) with sizes of 2-20 nm. We found that the cutoff of the membrane is 5 nm (defined here

as a size larger than 98% of the particles in the filtrate, Figure 3), and the flux is 40 6 ACS Paragon Plus Environment

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L·h-1·m-2·bar-1. The retention of the NPs within the HEC layer was confirmed by Energydispersive X-ray spectroscopy (EDS, Figure S3). 1/HEC membranes can be kept dry for weeks, maintaining their filtration performance. Pristine HEC films do not perform size-selective separation of 2-20 nm Au NPs (Figure S4). Thus, the ONCs and HEC show structural synergy, as apparently, the ONCs layer templates HEC porous structure (Figure 2d), and restrains the HEC swelling, enabling ultrafiltration. After the filtration, the membrane can be disassembled, cleaned from the deposited NPs, recycled and reused (Figure 4). The mechanical properties and performance of the recycled membrane are similar to the original one (Tables 1 and S1, Figures S2, S3d and S5). The assembly/disassembly cycle can be also used in order to clean membranes that undergo fouling, which represents one of key challenges in membrane technology.23

Figure 3. (a) UV/Vis spectrum of Au NPs stock solution (red) and the filtrate (black). (b) Representative TEM image of Au NPs stock solution before filtration. (c) The corresponding size distribution histogram of the stock solution. (d) TEM image of the filtrate. (e) The corresponding size distribution histogram of the filtrate. (f) Photograph of the membrane before filtration (left) and after filtration (showing dark red Au NPs deposit, right).

Importantly, the hybridization of the ONCs with HEC gives rise to a highly valuable filtration function as the hybrid membrane operates in the regime of ultrafiltration with 5 nm cutoff, comparing to 60 nm cutoff of pristine ONCs material.3 Preparation of polymeric membranes with 5 nm cutoff requires substantial synthetic and fabrication effort, such as copolymerization,24 electro-spinning25 and other surface properties modifications,26 while our system is based on simple components and can be easily fabricated and recycled. 7 ACS Paragon Plus Environment

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Figure 4. Recycling of 1/HEC. (1) The film is immersed into THF to dissolve the ONCs of 1. (2) The solution of 1 is removed and the HEC film is dried. (3) HEC is dissolved in water by gentle heating to 80°C. (4) The solutions of 1 and HEC are used to re-form the 1/HEC hybrid.

Nanofiltration and water-purification membrane: 1/NC hybrid. Bentonite is a layered material consisting mostly of montmorillonite. The bentonite lattice can be cleaved along the basal surface to form clay nano-sheets with permanent negative charge that can be dispersed in aqueous medium, and have high surface area, in excess of 1000 m2·gr-1.27 In order to fabricate a hybrid of bentonite NC and the ONCs, bentonite clay was dispersed in water by tip-sonication. The resulting dispersion was centrifuged, and an aliquot of NC solution was added to a THF solution of 1. The resulting mixture of 1 and NC was deposited on PVDF support (with 0.45-μm pores) in a controlled pressure setup to yield hybrid films with ~1:1 NC to ONC ratio by weight (see Experimental Section for details). SEM imaging showed homogeneous distribution of the NCs platelets in the ONCs matrix (Figures 5a, b and S6). This was confirmed by EDS, indicating that the bentonite Al and Si are distributed within the entire cross-section of the hybrid film (Figure 5c, d). The thickness of 1/NC membranes is 27±3 µm.


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Figure 5. (a) SEM image of 1/NC hybrid film, the ONCs and the NC are marked by yellow arrows. (b) Zoom into marked area in (a). (c) EDS spectrum of the 1/NC hybrid film cross-section. (d) EDS of the membrane cross-section (red: Si, green: Al, blue: C).

The mechanical properties of the composite were examined by a tensile test (Table S2). The results reveal enhancement of the mechanical robustness of the composites: 1/NC exhibited an elastic modulus of 659.6±94.4 MPa, and toughness of 0.086± 0.4 MPa, that is, an order of magnitude higher than those of the film constructed from pristine ONCs. A representative stress/strain curve is shown in Figure S7. SEM images of the composite after tensile failure reveal that the ONCs and the NC sheets slide and do not break, therefore there is moderate effect on the film resilience (Figure S8). Incorporation of NC into the ONC matrix enabled both nanofiltration and ion exchange separations. We performed filtration of a mixture of Au NPs, 1–13 nm in size. The clear and


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transparent filtrate was examined by UV/Vis spectroscopy (Figure 6), Dynamic Light Scattering (DLS), and TEM. No Au NPs were present in the filtrate as revealed by TEM imaging, while DLS is consistent with the membrane cutoff of less than 1 nm (Figure S9). The retained Au NPs were detected in the membrane by SEM and EDS (Figure S10).

Figure 6. UV/Vis spectrum of Au NP stock solution (green) and the filtrate (black). Inset: photograph of the filtration experiment, showing a colorless filtrate drop.

We also constructed a membrane with reduced NC content of 20% wt that was as efficient at nanofiltration, although it did not show significant reinforcement of the mechanical properties (Table S3). Bentonite has excellent sorption properties, and is used for barriers at the waste disposal areas.28-32 Furthermore, dispersed nano-clay shows enhanced surface activity towards removal of toxic heavy metals from water.33-36 We investigated the ion exchange capabilities of 1/NC membrane with diameter of 1 cm and 30 µm thickness (1.4±0.2 mg NC) to remove the salts of the contaminant metals: lead (Pb), nickel (Ni), cobalt (Co), and cadmium (Cd). Aqueous solutions of the salts were filtered using the hybrid membrane at a high (10-40 ppm) and low (up to 1000 ppb) concentrations (pH=6.5), at 2 bar overpressure (flux: 20 L·h-1·m-2·bar-1). The concentrations typical for industrial wastewater are in the area of hundreds of ppb. 37 The stock solutions and filtrates were analyzed using inductively coupled plasma mass-spectrometry (ICP-MS), see Table 2. The membrane showed excellent retention, above 99.5% of the contaminants, in all cases. In terms of the ion exchange capacity, the membrane exhibited greater affinity towards Cd and Pb salts.

Notably, 1/NC hybrid membrane displayed

significantly greater metal retention capacity than bentonite.36 The membrane also efficiently


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purified heavy metal salts from tap water containing Na, Mg and Ca salts (Na~150 ppm; Mg = 23 ppm; Ca=15ppm; pH=7.2), see Table 3.

Salt

Initial

Concentration

Removed

Initial

Concentration

Removed

Exchange

concentration

after filtration

[%]

concentration

after filtration

[%]

capacity

[ppb]

[ppb]

[ppb]

[ppb]

NiSO4

1011

0.24

99.98

10428

3.60

99.96

40

CoCl2

1044

0.46

99.95

9704

0.97

99.98

39

CdSO4

1029

0

100

10293

0

100

80

Pb(NO )

610

0.28

99.95

40800

149

99.63

100

3 2

[mg/g]

Table 2. Retention of Ni2+, Co2+, Pb2+, and Cd2+ by the hybrid membrane.

Salt

Initial concentration

Concentration

Removed

[ppb]

after filtration

[%]

[ppb] NiSO4

9279

223

97.6

CoCl2

8610

57

99.3

CdSO4

8496

144

98.3

Pb(NO3)2

1882

0.4

99.9

Table 3. Removal of salts from tap water (containing Na ~ 150 ppm; Mg = 23 ppm; Ca = 15 ppm; pH=7.2) by the 1/NC membrane.

Finally, the hybrid membrane was disassembled, upon immersing into chloroform, where the ONCs of 1 dissolved, releasing an NC film, which was subsequently dispersed in water by sonication (Figure 7). The dispersion requires a centrifugation step prior to the hybridization, which leads to some material loss, while the organic component is fully recyclable. The nano-clay dispersion alone can be deposited on the PVDF membrane forming a nano-clay gel membrane capable of nanofiltration, but the NC gel matrix collapses upon drying (Figure S9), while the NC/ONC hybrid could be kept dry and functional for at least six months. Thus, the ONCs and the NC have synergistic effect, as NC provides the membrane with improved mechanical robustness and filtration performance, while the ONC network incorporated with the nano-sheets enables prolonged shelf life.

.


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Figure 7. Membrane recycling. (1) The film is immersed in chloroform to dissolve the ONCs of 1. (2) The solution of 1 is removed and the NC is immersed in water. (3) NC is redispersed in water by sonication.

Today, polymer-based or ceramic membranes are typically used for water purification. Preparation of polymeric membranes requires synthesis of polymers with well-defined structure,4, 38 preparation of mixed matrix,39-41 surface functionalizations,26, 42, 43 and gaining control over templating involved in the polymerization process.

44

Ceramic materials are

fabricated by coating porous materials by several layers of materials with decreasing porosity, and often require sintering at high temperatures.45-47 In addition, fouling represents a severe problem in usage of conventional membranes.23 In contrast, ONC hybrids are based on readily available materials that are processed in aqueous medium, and are capable of highly demanded separations: nanofiltration and toxic cation removal. The organic component is recyclable, while bentonite is an inexpensive abundant material.

Mechanical robustness and biocatalysis: 1/GO hybrid. GO is an oxidized water-soluble derivative of graphene that has been used in various composite materials48, 49 owing to its high stiffness. GO sheets have Young’s modulus of 40 GPa.50 We fabricated 1/GO with variable GO contents (2.5-10 wt%). In a typical procedure, aqueous GO dispersion was diluted with water and bath-sonicated. After the sonication, the GO dispersion was quickly added to a THF solution of 1 and sonicated for 10 min (see Experimental


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Section for details). The dispersion was deposited on PVDF support (with 45-µm pores) in a controlled pressure setup at 2 bars overpressure. The membrane was dried and manually detached from the PVDF support as a free-standing film. The morphology of the hybrids was studied by SEM, revealing that ONCs of 1 are homogeneously mixed with nano-sheets of GO (Figures 8a, b). The cross-section image shows that the membrane is porous (Figure 8c). The composite is recyclable, as the ONCs of 1 are soluble in chloroform releasing a GO residue, which can be redispersed in water by sonication (Figure 8d). The 1/GO was reassembled from the recycled components, and the resulting hybrid showed morphological and mechanical properties very similar to the initial film (Figure S11)

Figure 8. (a, b): SEM images of 1/GO hybrid, the GO is clearly visible and marked by yellow arrows. (c) Cross-section of the 1/GO film, the GO sheets are marked by yellow arrows. (d) Recycling process: (1) The film is immersed in chloroform to dissolve the ONCs of 1; (2) The solution of 1 is removed and the GO film is dried. (3) GO is re-dispersed in water by sonication. (4) The dispersions of ONC 1 and GO are recombined to form the 1/GO hybrid.


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The composite was examined by a tensile test (Tables 4 and S4, Figures S13), revealing significant enhancement of the mechanical properties. Both the modulus and the toughness grow with increasing amount of GO. Thus, the hybrids with 5 wt% GO are tougher by an order of magnitude than the film built from ONCs of 1, and their elastic modulus is comparable to polymers such as Polytetrafluoroethylene (PTFE)51 and poly butene (PB).52 SEM imaging of the films following yield upon tensile test revealed that films made of 1/GO and of pristine ONCs exhibited different failure mechanisms. Pristine ONCs material showed significant disentanglement of the crystalline fibers upon failure, while 1/GO failure involved breaking of the ONCs (Figure S12). Apparently, the ONCs are strongly attached to the GO, as they break on the edges of the GO sheets rather than disentangle (Figure S14). Film

Young’s Modulus [MPa]

Tensile strength [MPa]

Elongation [%]

Toughness [MPa]

1 ONCs film

140±50

1.3±0.5

0.9±0.1

0.007±0.004

1/GO (2.5 wt% GO) 1/GO (5wt% GO)

216±41

3.8±0.7

2.0±0.2

0.042±0.009

558±79

8.5±0.9

1.7±0.3

0.073±0.018

1/GO (10wt% GO) 1/GO (10wt% GO) recycled

1040±167 1019±145

13.5±1.3 12.8±2.8

1.7±0.3 1.6±0.3

0.099±0.028 0.086±0.027

Table 4. The mechanical properties of 1/GO hybrid with various GO contents from tensile test

Previous studies showed that GO can immobilize enzymes due to a large specific surface area and abundant functional hydrophilic groups along.53-55 The 1/GO with GO content of 5% wt was used as a support for immobilization of β-galactosidase (β-Gal) that is widely used in biotechnological applications.56 The enzyme was deposited by simple filtration of β-Gal solution through the membrane, followed by rinsing with phosphate buffer (pH=7). UV/Vis spectroscopy indicates excellent enzyme retention (Figure S15). The adsorbed enzyme clusters were observed by SEM (Figure S16). To test activity of the immobilized enzyme, we performed heterogeneous catalysis with commonly used β-Gal substrate, o-nitrophenol-β-galactoside (ONPG, Figures 9a and S17). UV/Vis indicated that the conversion from ONPG to ONP is close to 100% (Figure 9a). The membrane clearly shows dose-responsive activity in a broad range of ONPG concentrations (0.1 mg·ml-1 - 2mg·ml-1, Figure 9b). We also studied the performance under constant substrate flux. The hybrid filter was connected to a UV/Vis flow cuvette, and the absorbance of the filtrate at 420 nm was monitored. Stable conversion over 120 minutes of uninterrupted substrate flow was observed (Figure S18), with a flux of 70 L·h-1·m-2 14 ACS Paragon Plus Environment

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(higher than biocatalytic membranes based on GO as the dominant component).57 Importantly, the membrane performed the flow catalysis in multiple runs for two weeks, without any decrease in the conversion (Figure S18a-e). The membrane was rinsed with buffer and kept dry between catalytic runs, indicating excellent preservation of the biocatalytic activity of β-Gal.

Figure 9. (a) UV/Vis spectrum of ONPG stock solution before filtration (black) and the filtrate after reaction (red), the feed is colorless while the filtrate is bright yellow (inset). (b) UV/Vis spectrum showing the dose response to different cincentrations of ONPG substrate (0.1 mg·ml-1 – 2 mg ·ml-1), the inset shows the calibration curve.

Heterogenous biocatalysis is valuable for the preparation of various chemical compounds58-60 with high efficiency and selectivity under mild conditions; it is increasingly applied in environmentally friendly industrial processes.61 Employing 1/GO hybrid membrane for enzyme biocatalysis has several advantages: the membrane is constructed by self-assembly and the enzyme is immobilized via simple filtration, no synthetic modification or complex covalent attachment of the enzyme to a stationary phase is necessary. Moreover, the membrane is reusable after simple rinsing with buffer for at least two weeks of multiple runs. Potentially, the membrane could facilitate a more complex cascade reactions if two or more enzymes are immobilized.62 Finally, the membrane is easily recyclable.

CONCLUSIONS In summary, we developed a modular platform for tunable membranes based on ONCs, advancing a paradigm of molecular nanoplastics as cost-efficient sustainable materials with adjustable properties. The hybrids are easy to fabricate by simple filtration from aqueous media. The membranes are capable of ultra-filtration, nano-filtration, water purification, and biocatalysis. This broad range of separation properties is achieved using a single type of ONCs. All the building blocks of 1/GO and 1/HEC are recyclable, and the recycled membranes show properties almost identical to initial ones. In the case of 1/NC, the organic component is 15 ACS Paragon Plus Environment

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recyclable, and NC is partially recyclable. The fact that the membrane materials can be easily disassembled and reassembled also enables membrane cleaning and reuse after fouling. The membrane platform is sustainable and cost efficient, representing a green alternative to the materials based on polymers. Modular remodeling of structure and function introduces hybrid molecular plastics as valuable materials for industrially-relevant applications.

METHODS Solvents and reagents were purchased from commercial sources and used as received, unless otherwise indicated. For all aqueous mixtures, double-distilled water (DDW) was used (Barnstead NANOpure Diamond water system). Organic solvents for spectroscopic and microscopic studies were of HPLC grade. 2-hydroxyethyl cellulose (Mw: 1.3x106 g·mol-1) was used for 1/HEC; Nano-clay, hydrophilic bentonite, was used to prepare NC; GO (2 mg·ml-1) dispersion in water was used for 1/GO. βGal from E. coli was used for bio-catalysis (Sigma-Aldrich). Au NPs with SH-PEG capping were purchased from Nanocomposix. PVDF support with 0.45-μm pores (GE HealthcareLife Sciences, RPN1416F) was used for membrane fabrication. Controlled pressure setup and general membrane preparation schemes are described in the Supporting information (Figures S17, S18). UV/Vis absorption measurements were carried out on a Cary-5000 spectrometer (Varian). Flow cell connected to syringe pump was used for the kinetic measurements ICP-MS was measured using Agilent 7700 Series instrument. Scanning electron microscope (SEM) and EDS Imaging was performed using a Zeiss Supra 55 FEG-SEM or Ziess Ultra 55 FEG-SEM operating at 1-20 kV. Images were obtained using working distance (WD) of 3-5 mm. for 1-20 kV a standard aperture (30micrometer) was used. The samples were stuck directly on a carbon tape. For EDS (Bruker, Quantax, X-Flash, 60mm silicon drift detector) working distance (WD) of 6-7 mm was used at 10 kV tension (high tension or landing voltage). Transmission electron microscopy (TEM) imaging was performed using Tecnai T12 transmission electron microscope operated at 120 kV. Sample-preparation: 2.5 µl of each sample was applied to a 300-mesh copper grid coated with holey carbon (Pacific Grid-Tech supplies). Images were process using iTEM 5.2.3553 Olympus Soft Imaging Solutions GmbH. Tensile tests. For the tensile test experiments, all samples were cut into thin strips of 0.5-1 mm width, thickness of 30-50 μm, and gauge length of ~4 mm, and measured with an Instron Model 16 ACS Paragon Plus Environment

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5965 Materials Testing System, equipped with a 10 N load cell. The deformation rate was 0.2 mm/min. At least 5 specimens of each type were tested. The samples’ thickness and width were measured by SEM. Bath Sonication was performed using MRC Ultrasonic Cleaner D80H. Model: D80, Operation frequency: 43KHz, Power: 80Watt. Tip Sonication was performed with SONICS instrument (Sonics & Materials, Inc.), model Vibra-Cell VCX 750 (750 Watt; Tip: CV334, 25% amplitude at 20 kHz frequency).

Synthesis and structural characterization of 1: Compound 1 was synthesized according to a literature procedure.63 Single crystals for X-Ray structure determination: Compound 1 (5 mg) was dissolved in toluene (0.5 ml), and the solution was placed in an NMR tube, the toluene was slowly evaporated, and needle-like crystals of 1 precipitated. X-ray structure analysis of 1 was done at temperature 100 K, using Rigaku XtaLAB diffractometer, radiation CuK, graphite monochromator. 14395 reflections were collected, 2929 independent reflections (R-int =0.0677). CIF file containing all parameters obtained after structure solution and refinement was deposited in the database CCDC 1900061.

Membrane preparation, function, and recycling. The general procedure for membrane preparation constructed from pristine ONCs of 1 was described elsewhere.3 Briefly, DDW (14 ml) was quickly added to a THF solution of 1 (0.16 mg·ml-1, 6 ml), and the resulting dispersion was sonicated for 10 min. Then compound 1 (3 mg) in THF (1 ml) was rapidly injected into the ONC dispersion, which was divided into two fractions, and each fraction was deposited over PVDF support enclosed in a 13 mm stainless steel Swinny filter holder (Pall Biotech) in a controlled pressure setup, the trans-membrane overpressure during filtration was set at 2 bars. The film was dried and manually detached from the support to yield free standing membrane.

1/ HEC DDW (14 ml) was quickly added to a THF solution of 1 (0.16 mg·ml-1, 6 ml), and the resulting dispersion was sonicated for 10 min. Then compound 1 (3 mg) in THF (1 ml) was rapidly injected into the ONC dispersion, which was divided into two fractions, and each fraction was


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deposited over PVDF support enclosed in a 13 mm stainless steel Swinny filter holder (Pall Biotech) in a controlled pressure setup, the transmembrane overpressure during filtration was set at 2 bars. Hydroxyethyl cellulose (1300 kDa, 20mg) was dissolved in 10 ml of water by heating the mixture to 80 °C. Within minutes the polymer was fully dissolved, the solution the was cooled to r.t. and 200 µl of it was deposited on top of the ONC film by filtration at 2 bar. The resulting film was either used for the ultra-filtration of NPs or allowed to dry in air, and manually detached from the PVDF support to yield a free-standing film for mechanical measurements. The composition of the film was determined as following: the dry film was weighed using analytic balance, and then the ONCs were dissolved in THF, while the HEC residue was washed, dried and weighed. The content of the HEC was found to be 10 wt %. Filtration. The Au NP solution (5 ml), containing 2–20 nm particles, covered with PEG-SH capping layer was filtered over the hybrid membrane at an overpressure of 2 bar, using the setup shown in Figure S19. Recycling. The ONCs of 1 were dissolved using THF leaving HEC film, the HEC film was removed and the THF solution was dried to yield pristine compound 1 which was recrystallized and re-deposited as described above. HEC film was transferred to a 4 ml vial followed by addition of 1 ml of DDW, the vial was heated to 80 °C under stirring until a clear solution of HEC was obtained; the solution was divided to two fractions (500 µl) and each fraction was deposited on top of ONCs layer to afford two hybrid membranes. Hybrid membrane recycling after Au NPs filtration. The ONCs of 1 were dissolved using THF, leaving HEC film with Au NPs, the HEC film was removed and the THF solution was dried to yield pristine compound 1 which was recrystallized and re-deposited (see above). HEC film was transferred to a 4 ml vial followed by addition of water (1.5 ml), the vial was heated to 80 °C under stirring until HEC was dissolved, while the Au NPs precipitated. Then the vial was centrifuged, subsequently the supernatant was divided into two fractions and each fraction was deposited on top of ONCs layer to afford two hybrid membranes. Pristine HEC films Hydroxyethyl cellulose (1300 kDa, 20mg) was dissolved in 10 ml of water by heating the mixture to 80 °C, the solution was poured into a petri dish; after allowing the mixture to dry in air the HEC film was manually detached from the petri-dish. 1/NC 18 ACS Paragon Plus Environment

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Bentonite (2 or 5 mg) was dispersed in DDW (15 ml) by tip-sonication for 5 minutes, the resulting dispersion was centrifuged (3000 rpm, 5 min) and 14 ml of the clear supernatant was quickly added to THF solution of 1 (0.16 mg/ml, 6 ml), the resulting dispersion was sonicated for 10 min and then compound 1 (3 mg) dissolved in THF (1 ml) were injected rapidly. The final dispersion was divided into two fractions, each fraction was deposited over PVDF support enclosed in a 13 mm in-line stainless steel Swinney filter holder (Pall) in controlled pressure setup, the transmembrane pressure during filtration was set 3 bars. Filtration. 5 ml of Au NP solution (1–13 nm in size, average 5.1±2.1 nm) covered with neutral PEG-SH capping layer was filtered over the hybrid membrane at a constant pressure of 2 bar using the setup shown in Figure S20. Salt filtration test: 3 ml of salt (NiSO4; CdSO4; CoCl2; PbNO3) solutions in DDW and in tap water were filtered, fractions of 1 ml were collected and analyzed by ICP-MS. The membrane capacity was measured by filtering each salt (3 ml, 50 ppm) and measuring the maximal loading before the membrane began to leach. Recycling. The ONCs of 1 were dissolved in CHCl3, releasing NC film. It was removed and the CHCl3 solution was dried to yield pristine compound 1, which was recrystallized and redeposited. NC film was transferred to a vial followed by addition of 15 ml of water, and the vial was tip-sonicated for 5 min to yield aqueous NC dispersion, which was re-deposited to create a recycled 1/HEC membrane.

1/GO 50-200 μl of aqueous GO dispersion (2 mg·ml-1) was added to DDW (14 ml). The resulting dispersion was bath-sonicated for 30 minutes. After the sonication, the GO dispersion was quickly added to a THF solution of 1 (0.16 mg·ml-1, 6 ml), and sonicated for 10 min in order to fragment the ONCs prior to their precipitation,64 then compound 1 (3 mg) dissolved in 1 ml of THF was injected rapidly. The final dispersion was divided into two fraction, each fraction was deposited over PVDF support enclosed in a 13 mm in-line stainless steel Swinney filter holder in a controlled pressure setup, the transmembrane overpressure during filtration was set at 3 bars. The film was then dried and manually detached from the PVDF support to yield a free standing film. Enzyme immobilization. 1/GO with GO content of 5% wt was used as a support for immobilization of β-galactosidase (β-Gal). The enzyme was deposited by simple filtration of 1


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ml of β-Gal solution (0.2 mg·ml-1) through the membrane, followed by rinsing with 20 ml of phosphate buffer (10mM; pH=7; KCl, 50 mM; MgSO4, 5 mM). Concentrations of 0.1mg·ml-1 – 2 mg·ml-1 of ONPG in buffer (10 mM; pH=7; KCl, 50 mM; MgSO4, 5 mM) were used for dose response experiment. Solution of 0.2 mg·ml-1 ONPG was used for flow experiments. Recycling. The ONCs of 1 were dissolved in CHCl3 releasing GO film. It was removed and the CHCl3 solution was dried to yield compound 1, which was re-dissolved in THF (1 ml). The THF solution was divided into two fractions of 250 and 750 µl (fractions A and B respectively), the volume of fraction A was adjusted to 6 ml by adding THF, while the volume of fraction B was adjusted to 1 ml with THF. GO was re-dispersed in water (14 ml) by bath sonication, the GO dispersion was then quickly added to solution A and the resulting dispersion was bath sonicated for 10 min, followed by injection of solution B. The final dispersion was divided into two fractions, each fraction was deposited over PVDF support enclosed in a 13 mm in-line stainless steel Swinney filter holder in a controlled pressure setup, the transmembrane pressure during filtration was set at 3 bars

ASSOCIATED CONTENT Supporting Information Mechanical and filtration data, electron microscopy images, biocatalysis data. This material is available free of charge via the Internet at http://pubs.acs.org. The authors declare no competing financial interests.

AUTHOR INFORMATION Corresponding Authors * [email protected] *[email protected] *[email protected]

ACKNOWLEDGEMENTS


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This work was supported by grants from the Israel Science Foundation and the Helen and Martin Kimmel Center for Molecular Design. A. N.-E. is a recipient of the Adams Fellowship for PhD studies. This research was made possible in part by the generosity of the Harold Perlman family. H.D.W. is the recipient of the Livio Norzi Professorial Chair in Materials Science.

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