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Metalized nanocellulose composites as a feasible material for membrane supports: Design and applications for water treatment Perla Cruz-Tato, Edwin O. Ortiz-Quiles, Karlene Vega-Figueroa, Liz Noemi Santiago-Martoral, Michael Flynn, Liz M Diaz-Vazquez, and Eduardo Nicolau Environ. Sci. Technol., Just Accepted Manuscript • DOI: 10.1021/acs.est.6b05955 • Publication Date (Web): 20 Mar 2017 Downloaded from http://pubs.acs.org on March 21, 2017

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Environmental Science & Technology

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Metalized nanocellulose composites as a feasible material for

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membrane supports: Design and applications for water treatment

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Perla Cruz-Tato1,2, Edwin O. Ortiz-Quiles1,2, Karlene Vega-Figueroa1,2, Liz Santiago-Martoral1,2,

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Michael Flynn3, Liz M. Díaz-Vázquez1and Eduardo Nicolau*1,2

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1

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Puerto Rico USA 00931-3346

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2

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Juan Puerto Rico USA 00931-3346

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Department of Chemistry, University of Puerto Rico, Rio Piedras Campus, PO Box 23346, San Juan,

Molecular Sciences Research Center, University of Puerto Rico, 1390 Ponce De Leon Ave, Suite 2, San

NASA Ames Research Center, Bioengineering Branch, Moffett Field, California 94036 USA

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Corresponding Author

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*Phone: 787-292-9820, fax: 787-522-2150; email: [email protected]

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ACS Paragon Plus Environment


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Abstract

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Herein, we study the feasibility of using nanocellulose (NC)-based composites with silver and platinum

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nanoparticles as additive materials to fabricate the support layer of thin film composite (TFC) membranes

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for water purification applications. In brief, the NC surface was chemically modified and then was

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decorated with silver and platinum nanoparticles, respectively by chemical reduction. These metalized

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nanocellulose composites (MNC) were characterized by several techniques including: FTIR, XPS, TGA,

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XRD and XANES to probe their integrity. Thereafter, we fabricated the MNC-TFC membranes and the

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support layer was modified to improve the membrane properties. The membranes were thoroughly

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characterized and the performance was evaluated in forward osmosis (FO) mode with various feed

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solutions: nanopure water, urea and wastewater samples. The fabricated membranes exhibited finger-like

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pore morphologies and varying pore sizes. Interestingly, higher water fluxes and solute rejection was

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obtained with the MNC-TFC membranes with wastewater samples. The overall approach of this work

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provides an effort to fabricated membranes with high water flux and enhanced selectivity.

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KEYWORDS

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Nanocellulose, water purification, membrane supporting layer, metal nanoparticles

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Introduction

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According to the World Health Organization (WHO) there are 663 million of human beings worldwide

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with limited access to fresh water for consumption and hygiene. Moreover, water-related diseases are

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known to affect more than 1.5 billion people every year.1 Thus, finding cost-effective approaches for

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water recycling, water purification and wastewater reclamation are of urgent need.

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Current state-of-the-art for water reclamation strategies rely on the use of membrane-based processes. The

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most widely used membrane processes in water purification applications are microfiltration (MF),2-3

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ultrafiltration (UF),4-5 nanofiltration (NF)6-7 and reverse osmosis (RO).8-9 The membrane characteristics

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for these processes are very similar and only vary in the pore size of the membrane for each application.

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Nevertheless, these technologies employ high pressures to drive the flux of water making the overall

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process energy-intensive.10 In contrast, osmotically driven membrane processes have the potential to

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sustainably produce and reclaim water.11 Forward osmosis (FO) is a membrane process driven by the

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osmotic pressure gradient across a semi-permeable membrane (Figure 1), where water is extracted across

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the membrane from a regime of low osmotic pressure in the feed solution (FS) to a high-osmotic-pressure

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in the draw solution (DS).12 Forward osmosis has captured the attention of researchers mainly because it

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is a technology that helps alleviate the issues encountered with the aforementioned technologies (e.g. high

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pressure requirements, fouling and concentrate management).13 This membrane-based water separation

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process is less prone to fouling because it generates a lower transmembrane pressure. Moreover, FO

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membranes also allow for high water flux with minimum energy consumption, making FO a feasible and

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cost-effective approach for wastewater treatment. Even when FO exhibits lower membrane fouling, the

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technology still suffers from some fouling effects. The membrane fouling process in osmotically driven

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membranes is known to be different in pressure driven processes due to the low hydraulic pressure being

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employed.13 Interestingly, membrane fouling may improve the solute rejection and permeability of the FO

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membrane. 14-15



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Figure 1. Representation of the FO membrane process 69

In the area of FO membranes the use of the thin film composites (TFC) polyamide membranes are

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considered at the forefront for the actual application. These membranes are composed of a porous

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support, typically polysulfone (PSF), and a non-porous highly crosslinked polyamide selective layer. TFC

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polyamide membranes can achieve higher water permeability and comparable salt rejection than

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asymmetric cellulose-acetate-based membranes, such as the commercial membrane from Hydration

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Innovation Technologies (HTI-CTA).16 The rational design of TFC membranes for FO processes requires

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a thin support layer with high porosity and low tortuosity in order to increase the flux of water across the

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membrane. Moreover, the support layer must be hydrophilic while providing chemical and thermal

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stability within reasonable mechanical strength.17

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A variety of technologies and approaches has been studied to improve the membrane performance (e.g.

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higher water fluxes), most of these are focused on chemical modifications and in the development of

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mixed matrix membranes, i.e. using additives. Reported chemical modifications and mixed matrix

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membranes include: polymers18-19 and its variations

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, nanoparticles22-23, organic


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and inorganic

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compounds.25-26 These modifications are performed via chemical or physical interactions on the active

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side or in the support layer of the membrane.27

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As previously shown by Tarabara27, the use of nanoparticles in polymeric membranes may have direct

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influence on important characteristics such as the porosity, the pore size and the morphology of the

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asymmetric support layer which affects the water permeability, the salt rejection and the interfacial

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polymerization reaction. Also an increase in the thickness and changes in the contact angle can be

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obtained, depending on the nature of the nanoparticles. Nevertheless, metallic nanoparticles are

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thermodynamically unstable and without the use of capping agents, ligands or supports tend to

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aggregation.28 Nanocellulose (NC) is considered an ideal support for depositing metal nanoparticles

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owing to their high surface area-to-volume ratio, reductive surface, mechanical strength (i.e. Young’s

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Module in the range of 100-130GPa), biodegradability, non-toxicity and low cost.29-31 In fact, NC

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biopolymer has been recently considered as a candidate for novel water treatment technologies, and have

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been shown that low loadings of NC into polymeric membrane support layer have the effect of increasing

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the tensile strength while exhibiting increased porosity, larger pore sizes and enhanced water permeability

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when compared to other materials.32

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In this study, we present the synthesis and characterization of metallized nanocellulose (MNC)

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composites as candidate materials to incorporate in the support layer of a forward osmosis membrane to

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improve its performance. The nanocellulose-based composites combine the advantages of both the guest

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nanomaterial and the nanocellulose substrate that are known to exhibit synergetic properties.29 As

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mentioned previously, the inclusion of metallic nanoparticles in the structural framework of the

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membrane may help enhance the membrane properties and performance. Therefore in this work we

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studied two types of metal nanoparticles (silver and platinum) as they both exhibit particular and

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interesting properties for further applications. The silver nanoparticles (AgNP) have been widely studied

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as antimicrobial agent33, and the platinum nanoparticles (PtNP) are well-known for its catalytic



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properties.34 The nanoparticles were immobilized in the support layer as a way to decrease the risk of

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leaching.27, 33

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By linking the advantages of the different materials we present the composites characterization and

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respective membrane performance. The combination of NC with the advantages of metallic nanoparticles

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could present a way to generate outstanding support layers for water purification membranes with

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possible capabilities beyond reclaiming water.

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Materials and Methods

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2.1 Materials

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Nanocellulose (NC, 11.8%) aqueous solution was purchased from University of Maine Process and

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Development Center (Onoro, USA). 3-aminopropyltriethoxysilane (APTES, 97%), silver nitrate (AgNO3,

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99%), potassium tetrachloroplatinate (K2PtCl4, 99.99%), sodium borohydride (NaBH4, 99%), polysulfone

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(PSF, average Mn ~22,000), N-methyl-2-pyrrolidone (NMP, 99%), m-phenylenediamine (MPD, 99%), 1,

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3, 5-benzenetricarbonyl trichloride (TMC, 98%), hexane (anhydrous 95%), sodium chloride (NaCl, ACS

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reagent 99.0%) and urea (ACS reagent, 99.0-100.5%) were all purchased from Sigma-Aldrich. All

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chemicals and solvents were used as received without further purification. Nanopure water (18.2

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MΩ·cm2, MilliQ Direct 16) was used at all times.

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2.2 Preparation of amino-modified nanocellulose (NC-NH2)

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The surface of the NC was modified to incorporate amino silane functionalities following published

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procedures with minor modifications.35 Amino modified nanocellulose (NC-NH2) were prepared by

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reacting 15 mL of a 3% w/v aqueous solution of NC and 15 mL of APTES 0.1M in 80% EtOH. First, the

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NC 3% solution was placed on a hot plate at 60ºC under constant stirring while APTES solution was

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slowly added to the reaction vessel. The reaction was carried out under these conditions for 2 hours, after

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completing the reaction, the NC-NH2 composite was allowed to reach ambient temperature.


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2.3 Deposition of silver and platinum nanoparticles to NC-NH2

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The deposition of the metal nanoparticles to the NC-NH2 was performed by an in-situ chemical reduction

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of the precursor materials using sodium borohydride as a reducing agent. Briefly, 10 mL of a 0.05M

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AgNO3 solution was thoroughly mixed with 30 mL of the NC-NH2. Thereafter, 15 mL of a 0.1 M NaBH4

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solution was used to titrate the mixture promoting the reduction of the silver ions in solution to silver

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metal nanoparticles (NC-NH2Ag). This reaction was conducted on an ice bath under constant stirring. The

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mixture was stirred for 15 minutes after reaction. The composites were washed in a vacuum filtration

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system using nanopure water and a 50% v/v ethanol solution. The same procedure was employed to

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generate the platinum NC-based composite (NC-NH2Pt) where 10 mL of a 0.05 M K2PtCl4 solution was

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thoroughly mixed with 30mL of the NC-NH2. The mixture was titrated with 15 mL of the reducing agent,

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the solution turned black after addition of reducing agent and left reacting for 15 minutes and, then

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filtered. All composites were lyophilized and pulverized for further characterization.

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2.4 Physical and chemical characterization of nanocellulose based composites

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Freeze-dried samples were analyzed, the infrared spectra were recorded on a Thermo Scientific

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TM Nicolet TM Continuµm TM infrared (IR) microscope using transmittance mode. X-ray diffraction

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measurements were conducted over 10 to 90º 2θ range using a Rigaku SmartLab diffractometer at 40 kV

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and 44 mA equipped with monochromatic CuKα (1.54 Å) X-ray source. X-Ray Photoelectron

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spectroscopy (XPS) binding energy were obtained using a PHI 5600 spectrometer equipped with an Al

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Kα mono and polychromatic X-ray source operating at 15 kV, 350 W and pass energy of 58.70 eV. A

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Perkin-Elmer STA 6000 simultaneous thermal analyzer was used to measure the changes in weight and

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heat flow as a function of temperature. X-Ray Absorption spectroscopy (XAS) was performed at Cornell

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High Energy Synchrotron Source (CHESS) using line F3. The Ag K edge (25,514 eV) and Pt L3 edge

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(11,563 eV) were measured for the NC-NH2Ag and NC-NH2Pt samples in transmission mode. The

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antimicrobial properties were tested using the Kirby-Bauer diffusion method and the electrochemical



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profile was evaluated by cyclic voltammetry. Detailed information of these measurements is included at

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the Supporting Information.

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2.5 Fabrication of NC-TFC mesh-embedded supports

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The NC-PSF membranes were prepared using the non-solvent induced phase separation (NIPS) process

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as published elsewhere.36 The dope solution was prepared with 12% w/v PSF and 0.5% w/v NC-

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composites in NMP. To dissolve the materials, the solutions were stirred at room temperature for 24

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hours. The polyester (PE) mesh was attached to a clean glass plate, and a dust magnet was employed to

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remove the particles over the surface. The solution was casted over the PE using a casting knife adjusted

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to 150 µm. The film was immediately immersed in a nanopure water precipitation bath for 10 minutes

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before transferring the membrane to a nanopure water bath for storage. Thereafter, the NC-TFC

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membranes were fabricated by fixing the NC-PSF membranes over a glass plate to allow coating of only

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the top surface. A 2% w/v MPD aqueous solution was poured to the membranes until it was completely

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soaked for 2 minutes and the excess was removed using an air knife. Next, a 0.1% w/v TMC aqueous

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solution in hexane was poured to the membranes for 1 minute and the excess was removed by using an air

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knife. Finally, the membrane was soaked in 0.2% w/v sodium carbonate solution for 5 minutes, rinsed

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and stored in nanopure water.

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2.6 Characterization of MNC-TFC membranes

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Scanning electron microscopy images were performed in a high-resolution field emission JEOL JSM-

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7500F SEM to analyze the surface morphology of the NC-TFC membranes. Samples were lyophilized,

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placed in sample holders and sputtered with a thin gold film (ca. 20 nm thick). The TFC membranes

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performance was tested using an in-house FO system (Figure 2) with nanopure water (18 MΩ·cm2), urea

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solution (1.3% w/v) and wastewater samples as the feed. These membranes were screened against

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commercially available membranes Hydration Technology Innovation (HTI-CTA). The exposed area of

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the membrane was 4.25 cm2, the active layer was facing the feed solution and the results were collected at


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constant pressure (1 bar). To evaluate the performance of the membrane, water flux rate from the feed to

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the draw solution side is determined using the following equation:

‫= ݓܬ‬

߂ܸ ‫ܲ߂ݐ ܯܣ‬

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(1)

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where, Jw is the water flux rate in LMH/bar (L·m-2·h-1/bar), ∆V is the volume increment in the osmotic

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solution in L, AM is active membrane area, t is time or duration of test in hours and ∆P is the

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transmembrane pressure in bar.

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The concentration of salt in the feed was determined by ion chromatography, using a cation column:

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CS12 and anion column: AS4A with a conductivity detector and preparing a calibration curve with a

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standard solution of ions. The reverse salt flux from the draw solution to the feed side was obtained with

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the following equation:

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Js =

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where Js is the reverse salt flux in GMH (g·m-2·h-1), Ct and Vt are the salt concentration and the feed

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volume at the end of the FO tests, respectively. Total organic carbon content was also determined using a

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TOC from Shimadzu model TOC-LCCH.

∆(CtVt ) AM t

(2)



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Figure 2. Experimental setup diagram for the FO performance test. The 1-hour experiments were performed by recirculating the feed and draw solutions continuously with the aid of a peristaltic pump through the custom-made cell containing the membrane. The arrows represent the flow of each solution and the conductivity was monitored at each solution using the conductometers. 191

Results and discussion

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3.1 Metalized nanocellulose-based composites characterization

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Considering the abovementioned properties attributed to NC, the use of this biopolymer as an additive for

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functional materials presents an interesting approach. In this study, the surface of the nanocellulose was

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modified and functionalized through the addition of amino-silane groups. Presumably, the incorporation

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of -SiO and -NH functional groups provide more nucleation sites where metallic nanoparticles can be

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localized at the expense of a slight decrease in NC hydrophilicity.37-38 In order to assure chemical integrity

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of modified-NC, FT-IR and XPS were employed as characterization tools. Figure S1 shows the FTIR

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spectrum of NC and the amino modified-NC where absorption signals are constant suggesting that NC

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structural functional groups remain unaltered after the synthesis process. An obvious absorption band is


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observed at ca. 1560 cm-1 attributed to the bending vibration of primary amines (N-H).39 The

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characteristic two bands of the N-H stretching vibration are observed in the region of 3500-3200 cm-1

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while presence of silanes (νSi-O) can be observed at absorption signals around 820 cm-1.

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Moreover, XPS was performed and survey results confirm the presence of carbon, oxygen, nitrogen and

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silicon in the NC-NH2 composite (see supporting information, Figure S2a). Also, to further evaluate the

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integrity of the modified material a high-energy photoelectron spectrum deconvolution procedure was

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performed, see Figure S2b. FTIR and XPS results confirm successful incorporation of the amino-silane

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group to the NC surface.

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The deposition of metallic nanoparticles within the NC-NH2 network was achieved via a wet chemical

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approach and using a reducing agent. We performed a thermogravimetric analysis of the composites to

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study the thermal stability of the materials. Changes in the thermal decomposition transitions can account

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to verify the presence of the metal nanoparticles (see Figure S3). The TG curve suggests a metal loading

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of 12% Ag and 20% Pt. More important, is the XRD analysis for all the materials shown in Figure S4

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where it can be observed the characteristic diffraction signals for NC (type I and II) at low angles for all

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composites,30 suggesting the presence of NC with a crystalline structure, which provides an indication

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that the crystallinity of the NC was not perturbed by the chemical reaction at the surface. Moreover, the

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presence of metallic nanoparticles was verified, and crystalline phases for Ag and Pt are in agreement

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with the literature.40-41

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Additional XPS analyses were also utilized in this study to account for the presence of all the elements

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and to obtain information of the main interactions between elements in each composite. Survey results

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confirm the presence of carbon, oxygen, nitrogen and silicon in all composites whereas silver and

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platinum were also detected in the respective composites. Moreover, Figure S5 (a) and (b) presents the

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high-resolution photoelectron spectrum deconvolution of the composites and suggests the presence of the

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metallic nanoparticles in both the metal and oxide forms. To further elucidate the electronic structure and



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provide qualitative information of the electronic environment within the composites, X-Ray Absorption

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Near Edge Spectroscopy (XANES) was performed. The XANES spectra of Ag K-edge and Pt LIII edge,

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respectively, suggest the presence of the nanoparticles mainly in their reduced form, which is in

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agreement with the XPS results (see Figure S5 c and d). We evaluate the electronic environment of the

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composites containing the metal nanoparticles because differences at the nanoparticle surface could

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generate significant changes in the support layer. These changes may include hydrophilicity, which will

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directly affect the water permeability and also the membrane selectivity.27

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Physical characterizations confirmed the successful modification of the nanocellulose with the amino-

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silane group and the deposition of metal nanoparticles. The principal objective of incorporating AgNP

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and PtNP was due to the inherent properties of each material, antimicrobial and catalytic respectively. We

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evaluated the NC-NH2Ag biocidal potential using a Kirby-diffusion test (Figure S6) suggesting

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antimicrobial properties for AgNP. The NC-NH2Pt electrochemical properties were studied by cyclic

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voltammetry (Figure S7), which indicate that the PtNP are electrochemically active. Even though this

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work focused on the effect of these metal nanoparticles at the supporting layer, these types of materials

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could also be incorporated at the membrane’s surface in the future to generate reactive FO membranes.

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3.2 Nanocellulose-based thin film composite (NC-TFC) membranes

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The fabricated mesh-reinforced thin film composite membranes for FO were prepared using the phase

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inversion method, illustrated in Figure 3. A polyester (PE) mesh was employed as mechanical reinforcing

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material followed by a porous mid-layer made of polysulfone (PSF) and the NC-composites. Afterwards,

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the membrane’s surface was modified with a thin polyamide layer through the interfacial polymerization

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of MPD and TMC to improve the permeability, the selectivity and the water fluxes of the membranes.42

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Recent investigations have explored the advantages and the importance of the rational design and

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development of PSF supports for FO applications.11,

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formation is one of the most important factors to evaluate. Herein, we used the phase inversion method,

36, 43

When fabricating a FO membrane, pore


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which is governed by the solvent exchange rate. Depending on this solvent exchange rate, also known as

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the precipitation rate, the pores morphology and size may vary. The polymer precipitation rates affect the

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pore morphology as rapid precipitation creates finger-like pores and slow precipitation produces sponge-

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like pores. Membranes with finger-like pores present higher water fluxes while sponge-like pores present

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higher salt rejection. NMP was used as the solvent because it has been known that induces a high

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precipitation rate where the non-solvent influx (i.e. water) directs the net flux during the phase inversion

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process.44

Figure 3. Two-step fabrication of NC embedded TFC membranes. 256



a) a)

f)

b)

g) g)

c)

h)

d) d)

i)

e)

j)j)

Figure 4. SEM micrographs of non-polymerized support layer (a-e) active side and (f-j) back side of the membrane, where P represents polysulfone (PSF). 257


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Figure 4 shows the top (a)-(e) and bottom (f)-(j) SEM micrographs of the non-polymerized support layers

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used for the TFC-membranes. The membrane’s surface porosity plays a key role in the interfacial

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polymerization reaction because it essentially determines the amount of MPD molecules that can

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penetrate the support layer. As can be observed in the figure, the surface of the non-polymerized supports

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present homogeneous pores sizes in the range of ca. PtNP

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suggesting that the particle size affects the FO performance of the membrane. The reverse salt flux was

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calculated and similarly, all membranes showed a low reverse salt flux. The selectivity of the membrane

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can be assessed from the total organic carbon (TOC) rejection. The TOC was measured in both solutions

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(feed and draw solution) before and after each run. All the membranes present high TOC rejection values

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although the commercial membrane still has the higher performance (96.9%) followed by the NC (94.6%)

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and PSF (90.3%) membranes. The membrane with NC-NH2 (90.3%) presented the lowest rejection, which

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also suggests that the urea molecules in the draw solution could contribute to higher gradient in osmotic

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pressure. The incorporation of metal nanoparticles to the membranes, also seem to have an opposite trend

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in the TOC rejection, AgNP (92.4%) < PtNP (94.0%).

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Another parameter that helps to determine membrane selectivity is the specific reverse salt flux, Js/Jw.

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The specific reverse salt flux takes into consideration the amount of draw solute leakage per unit of water

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permeated across the membrane. As shown in Figure S10, all membranes have a low Js/Jw value (less

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than 0.22 g/L) with both feed solutions (DI water and urea) meaning that the leakage of salt is minimum

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compared to the permeated water through the membrane.

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Figure 8. Puerto Nuevo Regional Wastewater Treatment Plant: municipalities45 and facilities46, and a schematic illustration of primary treatment (from wastewater to primary effluent) and the experimental setup employed for the FO membrane system. 355

As a proof-of-concept and in an effort to assess the effectiveness of the fabricated membranes we tested

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the membranes containing the composites with the metal nanoparticles using wastewater from the Puerto

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Nuevo Regional Wastewater Treatment Plant (RWWTP), a primary water treatment plant in Puerto Rico.

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The Puerto Nuevo RWWTP is located in San Juan, Puerto Rico and serves the municipalities of the

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metropolitan area (Figure 8). The facility’s layout includes a pumping station, mechanical bar screen, grit

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removal mechanism, primary clarifiers, sludge handling facilities and a disinfection area. The treated

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effluent from the Puerto Nuevo RWWTP is then discharged approximately 7,365 ft (2,246 m) from the

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shoreline into the Atlantic Ocean.47 Figure 8 also shows a schematic representation of the overall

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treatment that samples from RWWTP received, starting at the wastewater treatment plant through the FO

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system employed in this work.


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a)

b)

Figure 9. Results after wastewater treatment: a) SEM micrographs, and b) table summarizing the bacteria per membrane area and the obtained water fluxes with each membrane 365

We analyze the membrane surface using SEM after the FO performance evaluation with raw wastewater.

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The micrographs are shown in Figure 9a, and when compared to the membranes before the FO process

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(Figure 5) significant differences can be noticed. After the performance test structures consistent with the

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basic shape and size of bacteria48 appears, suggesting the attachment of microorganisms. A semi-

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quantitative analysis of the SEM micrographs (0.12 mm x 0.09 mm) was performed in order to compare

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the number of microorganisms per area of membrane. The results are summarized in Figure 9b, and it

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suggests that fewer microorganisms were able to attach onto the fabricated membranes. Specifically, the

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P:NC-NH2Ag membrane reduced in 87% and 67% the amount of microorganisms on the membrane’s

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surface when compared to the HTI-CTA and P:NC-NH2Pt, respectively. Nguyen, T. et al.49 have

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previously identified the surface roughness, surface hydrophilicity, surface charge and membrane material

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as the main factors that affect the attachment of microorganisms onto a membrane. Based on these

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factors, all of the fabricated membranes are similar in all of the surface properties (roughness,



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hydrophilicity and charge) due to the polyamide layer, but for the membrane material. Therefore,

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differences (i.e. microorganisms per area) between the MNC-TFC membranes are due to the nature of the

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nanoparticles.

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We measured the efficiency of the membranes by the water fluxes and contaminant rejection using GC-

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MS. The water fluxes obtained are shown in Figure 9b and it can be observed that the performance of the

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fabricated membranes was higher than the HTI-CTA. As in our previous trend, the membrane containing

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the AgNP exhibited higher water fluxes suggesting that the pore distribution also enhanced its

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performance using a real wastewater sample. The FO membrane performance with various feed solutions

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were compared and we recorded an increment in the water flux for both MNC-TFC membranes when raw

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wastewater was used as the feed solution: P:NC-NH2Ag increased 15% and P:NC-NH2Pt 33%. It was also

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of interest to determine the identity of the compounds that cross over the membrane. In order to

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accomplish this we utilized a GC-MS to account for the contaminants in the draw solution after the

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experiment, see Figure S11. These results suggest that the fabricated membranes can be considered as

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promising materials as to their high rejection of contaminants. Unexpectedly, both membranes containing

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the metallic nanoparticles have higher contaminant rejection than the HTI-CTA. We can notice that the

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membranes P:NC-NH2Ag and P:NC-NH2Pt only allow the passage across the membrane of linear alkanes

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and ester-based contaminants while the HTI-CTA also allows other contaminants: aromatics, cyclic and a

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wide variety of molecules with other functional groups. Therefore, a significant difference can be

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appreciated when comparing the results from the MNC-TFC with the HTI-CTA membranes. The MNC-

396

TFC allows for higher water fluxes and also higher contaminant rejection.

397

Closer examination of the SEM micrographs (Figure 9a) allows to further identify the organized

398

structures at the membrane’s surface. These organized structures are more apparent in the P:NC-NH2Pt

399

surface, by its particular arrangement and similarity to reported results48, 50 we can speculate that a biofilm

400

forms at the membrane surface. As previously reported,14, 49, 51 studies utilizing raw wastewater promotes

401

membrane fouling and this is considered as one of the major problems in membrane-based processes23, 51.


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402

However it could also play a favorable role in the water extraction and solute rejection of the

403

membranes.15 By virtue of the polyamide layer properties (higher roughness, more hydrophobicity and

404

higher negative charge), the MNC-TFC membranes might suffer from biofilm formation. In regards to the

405

P:NC-NH2Ag membrane it is apparent that a biofilm did not formed, yet an improvement in water flux

406

and contaminant rejection was obtained. Overall, the results with wastewater samples suggest a better

407

performance for the fabricated MNC-TFC membranes than the HTI-CTA.

408

In summary, we successfully synthesized promising MNC-based composites that exhibit electrochemical

409

and antimicrobial activity and certainly could be utilized for FO membrane fabrication. These composites

410

were well characterized by several techniques, which verified the crystallinity of NC after surface

411

modifications and confirmed the presence of each metal nanoparticle (Ag and Pt). We fabricated the TFC

412

membranes using the NIPS technique and the support layer of the membranes was modified by the

413

incorporation of the NC-based composites. The fabricated membranes exhibited finger-like pore

414

morphologies and varying pore sizes. These results directly affect the FO performance using different

415

feed solutions: DI water, urea aqueous solution and raw wastewater samples. Interestingly, higher water

416

fluxes and solute rejection were obtained with the MNC-TFC membranes when using wastewater sample

417

due to the formation of a biofilm. This approach provides an effort to produce membranes with high water

418

fluxes, high selectivity and low reverse salt fluxes that could further degrade contaminants and prevent

419

bacterial growth. In future studies we will address the electrochemical and bactericidal properties of the

420

MNC-TFC membranes, to further improve their properties under operating conditions.

421

BRIEFS

422

This work presents the synthesis, characterization and application of metalized nanocellulose composites

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for the fabrication of forward osmosis membranes.

424 425

SYNOPSIS (TOC)*



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426

427

AKNOWLEDGEMENTS

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This work was supported by the NASA Experimental Program to Stimulate Competitive Research

429

(EPSCoR) under grant #NNX14AN18A and the NASA Advanced STEM Training and Research

430

(ASTAR) Fellowship under grant #NNX15AU27H.

431

The authors acknowledge the UPR Materials Characterization Center (MCC) for the provided support

432

during the attainment of this work. We would also like to thank Institute for Functional Nanomaterials

433

Nanoscopy Facility and the CHESS facilities for their help supported by the NSF & NIH/NIGMS via

434

NSF award DMR-1332208. Also we want to thank Dina Bracho, Valerie Ortíz and Dr. Carlos González

435

for their help with the microbiological assays. Also, we would like to thank Luis Betancourt for the X-ray

436

absorption analysis and Dr. Craig Priest, from the University of South Adelaide for the contact angle

437

measurements. Finally, special thanks are due to Arnulfo Rojas for helping with the GC-MS analysis.

438

AUTHORS INFORMATION

439

Corresponding Author, * Prof. Eduardo Nicolau, [email protected]

440

Perla Cruz-Tato, [email protected]

441

Edwin Ortiz-Quiles, [email protected]

442

Karlene Vega-Figueroa, [email protected]

443

Liz Santiago Martoral, [email protected]


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444

Michael Flynn, [email protected]

445

Liz M. Díaz-Vázquez, [email protected]

446

Present Addresses

447

(E.N.) Department of Chemistry, University of Puerto Rico, Rio Piedras Campus, PO Box 23346, San

448

Juan, Puerto Rico USA 00931-3346// Molecular Science Research Center, University of Puerto Rico,

449

1390 Ponce De Leon Ave, Suite 2, San Juan Puerto Rico USA 00931-3346

450

Author Contributions

451

The manuscript was written through contributions of all authors. All authors have given approval to the

452

final version of the manuscript. PCT is the main author of this work.

453

Notes

454

The authors declare no competing financial interest.

455

Supporting Information

456 457 458

Supporting information contains: FTIR, XRD, XPS, XANES, microbial and electrochemical characterizations of the MNC-composites, AFM and SEM images, roughness, contact angle and GC-MS results of the prepared membranes. The material is complementary to the main work.

459

References

460 461 462 463 464 465 466 467 468 469 470 471 472 473 474

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SYNOPSIS (TOC)


Metalized nanocellulose composites as a feasible ... - ACS Publications

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