Protein functionalised aerogel membranes (PFAMs) for gravity-driven

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Protein functionalised aerogel membranes (PFAMs) for gravity-driven separation Nilesh Vadodariya, and Ramavatar Meena ACS Sustainable Chem. Eng., Just Accepted Manuscript • DOI: 10.1021/ acssuschemeng.8b05100 • Publication Date (Web): 01 Feb 2019 Downloaded from http://pubs.acs.org on February 3, 2019

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ACS Sustainable Chemistry & Engineering

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Protein functionalised aerogel membranes (PFAMs) for gravity-driven separation

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Nilesh Vadodariyaa,b; Ramavatar Meenaa,b*

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aNatural

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Institute, G. B Marg, Bhavnagar-364002 (Gujarat), India

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bAcademy

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Research Institute, G. B. Marg, Bhavnagar-364002 (Gujarat), India.

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*Email: [email protected] / [email protected]; Phone No: +91-278-2567760

Products & Green Chemistry Division, CSIR-Central Salt & Marine Chemicals Research

of Scientific and Innovative Research (AcSIR)-Central Salt & Marine Chemicals

8 9

ABSTRACT

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In this research article bovine serum albumin (BSA), a protein with a free amine (-NH2) functional

11

groups, is demonstrated for the preparation of protein functionalised aerogel membranes (PFAMs)

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using naturally occurring genipin as a crosslinking agent. PFAMs were characterized using SEM,

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FT-IR, Solid-UV, and TGA. PFAMs are highly stable and recyclable under aqueous conditions and

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successfully tested for efficient separation of oil-spill as well as emulsion under gravity driven force.

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PFAMs produced ~98 % pure water with high flux rate ranging from 430 to 605 L.m-2.h-1 at lab scale

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separations under gravity. PFAMs were tested for the biodegradable possibility in the soil conditions.

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This work is one of the best examples for the development of environmentally friendly porous

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membranes using abundant seaweed biomass through crosslinking chemistry of protein.

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KEYWORDS: Protein, Agar, Aerogel, Oil-spill and oil/water separation, Reusability

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INTRODUCTION

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Several industries including mining, textiles, foods, petrochemicals, etc. produce substantial volumes

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of oily wastewater, which is now a common pollutant all over the world. 1, 2 According to report, a

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mining operation produces about 140000 L of oily wastewater every day. 3 The human activities such

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as marine transportation and oil production are another major causes of oil-leakages/spillages in

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marine environments and ecology1,2. Numerous types of mechanical devices such as oil skimmers or

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booms are used to purify these oil/water mixtures, but need an input of energy or high pressure to

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operate.4 Porous materials such as sponges, 5,6 foams,7,8 and textiles,9–11 are also generally used to

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overcome this issue, but such materials simultaneously absorb both water and oil, resulting in poor

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separation selectivity and efficiency. The recycling/ reuse of such materials and the adsorbed oils are

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normally difficult. Such types of materials are commonly burned in the ground, which produced

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pollutant in the environment.12 These prior arts speaks us that development of eco-friendly, green and

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recyclable materials technologies that can purify oil/water mixtures (including emulsions) in the

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industry are in high demand. Recent development on this field is mainly focused on surface

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superwettabilities

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superoleophilicity).13–16 However, hydrophilic membranes has advantages that it cannot be easily

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fouled by Oil during demulsification as compared to the hydrophobic and Oliophobic membrane.17,18

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Based on the superhydrophilicity diverse membrane have been recently reported like polyacrylamide

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(PAM) hydrogel-coated stainless steel mesh has been reported by Jiang's group in 2011, 19 Wang et.

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al. reported stainless steel hollow fibre microfiltration membrane,20 In the recent decade, researchers

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are focusing

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nanowhiskers co-crosslinked Poly N-isopropylacrylamide-co-N-methylolacrylamide membranes,21

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superhydrophilic fluorinated cellulose nanofibrils aerogel,22 superhydrophilic β-CD & Polydopamine

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modified Poly L-Lactic acid scaffold nanofibers membrane23 for the selective separation of water

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from oil-water mixture. Superhydrophobic and superoleophilic oil absorbent such as SiO2/Poly L-

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Lactic acid/polystyrene hybrid nonwoven has also been reported.24

(e.g.,

superhydrophobicity,

superhydrophilicity,

superoleophobicity,

and

on the development of eco-friendly and biodegradable materials such as chitin

2 ACS Paragon Plus Environment

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Membrane-based technologies such as ultrafiltration (UF), microfiltration (MF),

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nanofiltration (NF) and reverse osmosis (RO) have become potential candidates for such

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separations25. UF has been successfully applied for the separation of the surfactant-stabilized oil-

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water stable emulsion.

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In our laboratory, we have previously reported seaweed polymer agarose-based porous

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membrane systems for oil-water separation with flux in the range of 230-500 L m−2 h−1.26-27 These

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prior art encourage us to utilised agar for the development of aerogel membranes for oil-water

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separation. Furthermore, the above reports revealed that protein functionalised aerogel membranes

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are not reported in the literature for this purpose.

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In this study we describes a simple and eco-friendly method for the preparation of protein

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functionalised aerogel membrane (PFAMs) through crosslinking with natural crosslinker genipin. In

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this study a crosslinked system was developed in the form of aerogel membrane through crosslinking

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reaction with highly water soluble protein BSA. PFAMs is composed of 100 % bio-based raw

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materials including crosslinker and showed excellent soil degradability. In addition this work utilises

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seaweed polymer agar (linear hydrophilic galactan) as texturing polymer which is less expensive

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compared to agarose used in our previous studies. Flux rate and water purity were almost identical

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with our previous reports from expensive agarose seaweed polymer. So result of this work indicates

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that more expensive agarose polymer may be replaced by inexpensive agar polymer for designing

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such materials. This work also opens new research areas for polymer scientist to utilised seaweed

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polymers like agar to prepared biodegradable separation membranes for sustainable solutions.

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PFAMs tested for sustainable separation of oil-water mixtures; organic-water mixtures and emulsion.

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The purity of permeate water was >98 %, and water flux rate obtained up to 600 L·m−2·h−1.

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EXPERIMENT SECTION

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Materials



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Seaweed polysaccharide agar used in this work is extracted from Indian seaweed biomass using

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simple and cost-effective method using red seaweed Gelidella acerosa following the method reported

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in the literature.28, 29 BSA (Sigma-Aldrich), Genipin (Challenge Bioproducts Co. Ltd., Taiwan) and

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n-Hexane and toluene (S. D. Fine Chemicals) were purchased. Biodiesel procured from our institute

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pilot plant and used for emulsion formation by vigorous stirring in 20:80 v/v ratio (biodiesel: water)

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followed by addition of Sodium dodecyl sulphate (SDS). Oil-spill used in the present work was

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collected from Alang ship breaking yard, Gujarat, India and used directly for further treatments.

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Preparation of membrane

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This study provides a simple, green and eco-friendly process for the preparation of protein

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functionalised aerogel (PFAMs) membrane. For this used total polymer concentration in the range of

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1 % (w/v) to 3 % (w/v) keeping agar: BSA ratio constant (AG : P = 8: 2 w/w) in all PFAMs. In brief,

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1.8 g agar (AG) polymer dissolved in 80 mL distilled water under microwave heating at 100°C for 5

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min. Separately dissolved 0.2 g BSA in 20 mL water at room temperature. BSA solution adds into

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agar solution under stirring at 50°C followed by addition of 40 mg genipin as a crosslinker. Then the

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mixture was heated at 80 oC in the microwave for 1 minute and gradually cooled to room temperature

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to convert into the stable hydrogel. The appearance of bluish colored hydrogel on cooling indicates

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cross-linking reaction and becomes dark in color within 24 to 48 h due to the high crosslinking

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reaction of genipin with protein. In this work, the progress of blue color was observed physically up

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to 36 h. The cross-linked hydrogel was cut to small pieces (~0.5 mm thick slices) after 36 h, and

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lyophilised hydrogel slices to obtain the protein functionalised aerogel membranes (PFAMs), and

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used for separation applications. The control AG aerogel was prepared by following the above process

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without protein and genipin for comparative study.

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PFAMs obtained with 2 % total polymer concentration (AG: P = 8: 2 w/w) with 0.01 to 0.04

97

% genipin crosslinker exhibited swelling in the range of 280 - 350 % in water. The result shows that

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PFAMs obtained with 0.03 % and 0.04 % genipin crosslinker shows almost identical swelling (~280 4 ACS Paragon Plus Environment

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99

%). Figure S1b shows that PFAM obtained with 0.04 % genipin crosslinker showed the lowest

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swelling (150 %) in oil-water mixture compared to other membranes. Hence, PFAMs obtained from

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2 % total polymer concentration with 0.04 % genipin were tested for separation. PFAMs obtained in

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the present study shows significantly higher swelling in water and emulsion solution may be due to

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the more hydrophilic nature. Flux (J) of permeate and % rejection oil in permeate was calculated as

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method reported in our previous paper.26-27

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Membrane testing

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The resulting membrane materials were tested for the separation of oil-water and organic-water

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samples under gravity driven force in the laboratory using a simple funnel method. For this

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experiment, placing wet aerogel in the neck of the funnel. Afterward oil-spill, Biodiesel/water

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emulsion, n-hexane/water, and toluene/water feed samples were poured into the funnel. Permeation

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rate and purity were evaluated using the following equation (1): 𝐽 = 𝐴(𝑡

111

𝑉

..........(1)

0 −𝑡𝑛 )

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[J = flux (L·m−2·h−1); V = volume of permeate; A = effective area of the membrane used; t0 = at zero

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time interval; tn = at interval n]

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Membrane characterisation

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In this work, agar solutions were prepared using microwave or autoclave ES-315 (TOMY SEIKO

116

Co., Ltd., Japan). Further, protein functionalised aerogel membranes were obtained by small slices of

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the gel using lyophilisation (VirTis Benchtop, Freeze-dryer, United States). FTIR spectra of PFAMs

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recorded on a PerkinElmer (Spectrum GX, USA); surface morphology and porosity of uncross-linked

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and cross-linked PFAMs were done by scanning electron microscopy (SEM, Carl-Zeiss Leo VP 1430

120

instrument, Oxford INCA); thermogravimetric analysis (TGA) of PFAMs was carried out on Mettler

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Toledo Thermal Analyzer, (TGA/SDTA 851e, Switzerland) under N 2 atmosphere as described in our



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previous work26,

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spectrophotometer (JAPAN).

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RESULTS AND DISCUSSION

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Agar used in this work is well known hydrophilic seaweed polymer extracted from the red seaweed

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Gelidiella acerosa. Agar is chemically composed of the structure comprising a repeating unit of (1,

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3) linked α-D-galactose (G) and (1, 4) linked β-L-3,6-anhydrogalactose(A).28, 29 It is available easily

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in low cost and 1-2 % w/w form a strong gel in water. Figure 1 shows the preparation of protein

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functionalised aerogel membranes (PFAMs) using hydrophilic seaweed polysaccharide “agar”.

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Crosslinker genipin used in this study is extracted from fruits, and a well known natural crosslinker

131

with primary amine functional group. In this study protein (BSA) is gifted with free amine groups,

132

which may be available for crosslinking reaction with genipin. It results in the formation of blue

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colored aerogels (Figure 1).

27 ;

and solid-state UV−vis spectra were recorded on Shimadzu UV-3101PC


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(a)

AG-BSA blend

After Freeze Drying

Agar

Genipin cross-linked AG-BSA blend

Micro porous Aerogel

BSA

(b) BSA Hydrogen bonding

Agar

Microwave

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


+ Genipin

Hydrogen bonding

Hydrogen bonding

134 135

Figure 1. (a) Schematic representation for the preparation of protein functionalised aerogel

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membranes (PFAMs) [Agar(AG) and BSA(P) were mixed (9:1 w/w ratio), and add crosslinker

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genipin to cross-link under ambient conditions hydrogel turned into blue in colour at room

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temperature and slicing cross-linked hydrogel and subjected to freeze-drying to yield protein

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functionalised aerogel membranes for separation]. The figure shows dark blue (cross-linked) and

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milky-white (non-crosslinked) aerogels to illustrate the difference and (b) Reaction mechanism for

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the crosslinked polymer.



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BSA

Genipin

MW

Freeze Agar layer

BSA wall

Drying Agar

142 143

Figure 2. A possible mechanism for the formation of protein functionalised aerogel membranes

144

(PFAMs).

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A possible mechanism of the formation of PFAMs has been given in Figure 2. In this

146

study, agar network is full of hydroxyl functional groups and help to form hydrogen bonding with

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protein and water molecules. In addition, protein is full of free primary amine functional groups and

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free to take in part in crosslinking reaction with genipin. The formation of such hydrogel network

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through hydrogen bonding and covalent bonding is suitable for the production of porous aerogel for

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sustainable separation. In this study naturally occurring crosslinker genipin covalently cross-linked

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with the primary amine group of BSA (Figure F1(b)). This could be explained on the basis of color

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changes from off-white to bluish green. Simultaneously hydroxyl groups of agar attached with protein

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through hydrogen bonding. Such types of structural arrangement within cross-linked hydrogels may

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results stable gel network suitable for potential use such as separation of the oil-water mixture. In

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addition, such crosslinked hydrogel form stable gel channel inside the genipin cross-linked BSA

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matrix on cooling. As mentioned agar a hydrophilic polymer is capable to attain high amount of water.

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The crosslinked hydrogel after 36 h was cut into slices, and this sliced hydrogel freeze by liquid

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nitrogen to generate ice crystal in the agar channel, which is mainly responsible for the formation of

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microporous aerogels. Ice channel is containing hydrogel subjected to a lyophilizer for drying.

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Sublimation of ice crystal from gel creates microporous aerogel during drying process without

161

disturbing the morphology of gel. To validate the mechanism for the formation of crosslinked aerogel


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membrane solid UV-spectra, FTIR, and TGA was analyzed for AG, BSA, AG-BSA blend and genipin

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crosslinked PFAMs.

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The appearance of dark-coloured hydrogel after crosslinking of genipin with agar-protein (AG-P)

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blend may be due to the chemical modifications or conjugation.26, 27 & 30 This types of conjugation can

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be confirmed using UV-Vis spectroscopy (Figure 3). Crosslinker genipin used in this study exhibited

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a characteristic peak at 240 nm, while protein (BSA) used as amino source showed a characteristic

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peak at 280 nm (Figure 3). Gelling polymer agar used in this study does not show any UV peak, but

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a blend of agar polymer with protein BSA (AG-P blend) shows a broad peak at 280 nm indicates the

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presence of BSA. The crosslinked Agar-BSA blend with genipin (AG-P-G) showed irregular

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broadening between 240 to 300 nm but a new clear peak obtained at 590 nm due to extended

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conjugation of genipin crosslinking in protein network. Such type of extended conjugation may be

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mainly responsible for the development of dark-colored gel materials.26, 27 & 30 1.0

0.8

240 nm

0.6

Abs.

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


280 nm 590 nm

0.4 (d)

0.2 (c) (b)

(a) 0.0 200 300

400

500

600

700

800

Wavelength (nm)

174 175

Figure 3. UV-Vis. Spectra of (a) Genipin (b) BSA protein (c) AG-P blend (d) Genipin cross-linked

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PFAMs.

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After UV-Vis analysis based on colour development indicates crosslinking of genipin with

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protein amine groups. To confirm the other possible interactions in the formation of the aerogel

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membrane were further analysed by FTIR (Figure 4). FTIR spectrum of agar polymer shows the 9 ACS Paragon Plus Environment


180

general pattern as reported in our previous study.26-27 Figure 4 shows characteristics IR peaks at 932

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cm-1 due to the presence of 3,6-anhydrogalactose linkage in agar. Additional two IR peaks in agar

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spectrum at 3445 cm-1 and 1075 cm-1 are due to the stretching of –OH functional group and vibration

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of C-O-C glycosidic linkage.28, 29 Protein (BSA) exhibit characteristics peak at 1664 cm-1 for the

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amide I band due to C=O stretching vibrations of the peptide bond. Similarly, BSA shows peaks near

185

1533 cm-1 is due to N-H bending vibration of amide II and 1386 cm-1 is due C-N stretching

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vibration.31 Crosslinker genipin used in this work exhibited the most characteristics IR peak at 1444

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cm-1 due to the ring stretching mode.26-27

1684 1623 1444

(a)

932

1075

1062 932 1082 932

1409

1640

3403 3405

(e)

1725 1637

(d)

1382

3445

(c)

1533 1386

1637 1664

(b)

%T

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4000 3500 3000 2500 2000 1500 1000

500

-1

Wavenumber (cm )

188 189

Figure 4. FTIR Spectra of (a) Genipin (b) BSA protein, (c) AG, (d) AG-P blend, (e) Genipin cross-

190

linked blend AG-P-G.

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The cross-linked aerogel (AG-P-G) membrane shows a new IR band at 1409 cm−1 revealed the

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presence of ring stretching of heterocyclic amine, in addition appearance of IR band at 1647 cm−1

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representing C=O stretch in the crosslinked AG-P-G.26, 27 Presence of additional characteristics agar

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and protein peaks in IR spectrum of aerogel (AG-P-G) product clearly indicates that the native

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backbone of pure agar and protein remained intact during crosslinking through cross-linker. FTIR

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results mainly shows noticeable change in the –OH stretching band of agar (AG) (Figure 4). As shown 10 ACS Paragon Plus Environment

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in Figure 4, -OH stretching band of AG shifted significantly from 3445 cm-1 to 3405 cm-1 on blending

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with BSA, and remained almost (3403 cm-1) unchanged on crosslinking with genipin in the product

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(AG-P-G). This result confirms that hydroxyl (−OH) groups present in agar network responsible for

200

hydrogen bonding interaction with N lone pair of the amide group of Protein. This may result a

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columnar structure of aerogel membrane in which Protein walls are coated with hydrophilic polymer

202

AG.

203 204

Figure 5. SEM images of (a & a’) AG-P blend, (b & b’) Genipin cross-linked PFAMs and (c & c’)

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after oil-water emulsion separation. 11 ACS Paragon Plus Environment


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The morphologies of AG-P blend and Genipin cross-linked AG-P-G blend were studied using

207

Scanning Electron Microscope (SEM) as shown in Figure 5. AG-P blend aerogel exhibited highly

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porous network ranging between 70-120 μm in sizes. This uncrosslinked hydrogel collapsed fully in

209

the presence of aqueous mixtures, and no separation is observed may be a less stable porous network

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in this blend uncrosslinked aerogel. SEM images of the AG-P-G samples confirmed that sizes of

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pores generated during water evaporation through lyophilisation are slightly modified and bigger in

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the range of 100-170 μm. This could be explained on the basis of network compactness through

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genipin crosslinking. In another way, agar-protein walls become more compact or thinner in the

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presence of genipin crosslinker due to the formation of the stable cross-linked network. The high flux

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rate compared to previous agarose and chitosan-based membranes due to the fabrication of larger

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porous sizes aerogel membrane in the present study. This study revealed that less expensive agar

217

seaweed polymer could be used to modify the porosity and flux rate of the cross-linked aerogel

218

membranes. Similarly, amino functional groups containing compound may be useful to design

219

desired porosity and flux rates of the resulting aerogel membranes for oil-water separation.

100

80

% Mass

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Page 12 of 23

60

(d) 46.8 (c) 33.7

40

(a) 28.7 (b) 25.4

20 50 220

150

250

350

o

450

Temperature ( C)


550

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221

Figure 6. Thermogram of (a) AG (b) BSA protein (c) AG-P blend (d) Genipin cross-linked blend

222

AG-P-G.

223

The stability of the resulting aerogel membranes was further confirmed by thermogravimetric

224

analysis (TGA) (Figure 6). TGA results are self-explanatory that aerogel formed in this study

225

becomes more thermally stable on crosslinking with genipin. This is mainly due to the formation of

226

the stable network in the cross-linked aerogel membrane as a result of genipin crosslinking with free

227

amino groups of BSA (Scheme …). The mass loss pattren was identical in all the aerogel samples.

228

Result of TGA shows that pure agar and BSA shows higher mass losses of 71.3 % and 74.6 %

229

respectively compared to uncrosslinked and cross-linked aerogel membranes. The uncrosslinked

230

aerogel membrane of agar and BSA shows improved stability compared to individual components

231

with slightly lower mass loss (66.3 %) up to 600 ⁰C (Figure 6). The minimum mass loss (53.2 %)

232

was obtained for the cross-linked aerogel membrane may be due to the formation of stable gel network

233

through hydrogen bonding (e.g. between agar (-OH) and amine (–NH2) and carboxylic (-COOH)

234

groups of BSA) as well as covalent bonding (Scheme …). The similar observation has been found in

235

the previous study on the agarose and chitosan-based membranes.27 The wettability of the aerogel

236

membranes was tested by contact angle measurement (ESI, Figure S2). Aerogel membranes shows

237

dynamic water contact angle 78.6° to 18.5° (for control AG), 89.6° to 9.3° ( for AG-P blend), and

238

71.9° to 8.9° (for PFAMs). The lowest contact angle for PFAMs indicates more hydrophilic nature

239

of the membranes after crosslinking with genipin. This may help to permeate more water content

240

through the PFAMs. The recycled PFAMs immediately absorbed water drops (contact angle was not

241

measured) may be due to improved hydrophilic nature.



600

(e) 605

543

(c’)

523 430

400

200 98.7

0

242

pill Oil-s

97.2

97.5

98.4

After 10 min.

-1

(d’)

After 10 min. Final

-2

Initial

Initial 800 Flux (L.m .h ) % Rejection

(b’)

(a’)

(d)

Initial

(C)

After 10 min. Final

(b)

After 10 min. Final

(a)

Initial Initial

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 14 of 23

er er ater wat /wat ne/w sel/ ene a e u i x l d e o T H Bio

243

Figure 7. (a) Oil-spill wastewater collected from ship breaking yard (a’) Oil-spill waste water

244

emulsion before and after separation, (b) Biodiesel/water emulsion, (b’) biodiesel/water emulsion

245

before and after separation, (c) Toluene/water, (c’) n-Hexane/water before and after separation, (d)

246

n-Hexane/water, and (d’) Toluene/water before and after separation, (e) Flux rate and % Rejection

247

for the various oil/water mixture.

248

The results of our previous studies encourage us to utilise the resulting aerogel membrane for

249

the water purification from different types of oil/water as well as organic/water mixtures. In the

250

present study, we have successfully tested the resulting aerogel membranes for the separation

251

applications at lab scale (Figure 7a-d). Figure 7 shows the laboratory setup of gravity-driven

252

separation assembly. In brief, a coin-sized (2 cm) diameter aerogel was wetted and fix in the neck of

253

glass funnel and used for the separation of different oil/water or organic/water mixtures and emulsion

254

(Figure 7a-d). Figure 7 shows different mixtures for membrane separation includes crude oil-spill

255

(Fig.7(a), collected from ship breaking yard), biodiesel/water emulsion (Fig.7(b), prepared by

256

sonication along with a surfactant), toluene/water (Fig7(c)), and n-hexane/water (Fig. 7(d)). Figure

257

7a’-d’ shows setups for separation experiments under gravity driven force for different mixtures. 14 ACS Paragon Plus Environment

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258

Figure 7(e) is shown the flux rates of the water from different oil-mixtures under identical conditions

259

at room temperature. The maximum 605 L.m -2.h-1 flux was obtained for n-hexane-water mixture

260

compared to other mixtures with >97 % water rejection. This aerogel membrane shows minimum

261

flux 430 L.m-2.h-1 for biodiesel/water emulsion with >97 % water rejection. Figure 7 (e) revealed that

262

aerogel membrane of the present study also showed excellent flux 543 L.m -2.h-1 for separation of

263

water from oil-spill with high ~99 % water rejection. The mixture of toluene/water also shows

264

excellent flux 523 L.m-2.h-1. Results of this study revealed that protein functionalised aerogel

265

membrane is suitable for separation of water from the above mixtures and emulsion with high flux

266

due to large sizes of the pores fabricated during the preparation process. This separation result showed

267

that flux rate was decreased about 20 % in water-hexane and 40 % in case of oil-water after 5 h

268

(Figure S3) may be due to the changes in the surface morphology of PFAMs (SEM images, Figure

269

5). Result of SEM analysis showed that microporous size of PFAM was decreased from 70-120 μm

270

to 46-60 μm after 3 cycles (Figure 5), which may be responsible for the lower flux rate with high

271

rejection. Weight loss of PFAM was measured and found that no weight loss was observed till 3

272

cycles of reuse. In addition, PFAMs obtained in the present study shows significantly higher swelling

273

in water and emulsion solutions compared to agarose and chitosan-based membranes reported in the

274

previous work.26-27 The swelling result revealed that PFAMs are more hydrophilic in nature, which

275

may be appropriate for the higher flux of permeate through it. PFAMs was recycled and reused for

276

successive three cycles (Figure S4). Flux was decreased slightly from 430 to 404 L.m-2.h-1 in emulsion

277

(biodiesel/water), 543 to 491 L.m-2.h-1 in oil-spill, and 605 to 555 L.m-2.h-1 in n-hexane/water

278

mixtures after 3 repeat cycles (ESI, Figure S4). The control AG aerogel membrane was tested for

279

the oil-water emulsion separation. But no proper separation takes place in the control AG membrane

280

and porous morphology was destroyed significantly (ESI, Figure S5). The result of this study

281

indicates that crosslinking with genipin generate homogeneous stable porous surface morphology of

282

PFAMs essential for separation.



283

The separation of water from the mixtures was checked by FTIR spectra (Figure 8). FTIR

284

spectrum of oil/spill shows characteristics peaks at 2925 cm -1 & 2858 cm-1 (C-H stretching), 1458

285

cm-1 (–CH2 bending). Biodiesel/water emulsion have characteristic peak at 2924 cm -1 & 2854 cm-1

286

(C-H stretching) and at 1743 cm-1 (C=O stretching). n-Hexane have characteristics peaks at 2926 cm-

287

1&

288

characteristic peak at 3029 cm-1 (C-H stretching aromatic), 2924 cm -1 (C-H stretching alkyl group)

289

and at 1500 cm-1 (C-C stretching in aromatic ring). All the characteristics peaks of oil, biodiesel, n-

290

hexane, and toluene were not obtained or disappeared in the permeate water samples obtained from

291

oil/spill, biodiesel/water emulsion, n-hexane/water and toluene/water mixtures. IR results indicate

292

efficient separation through PFAMs.

2861 cm-1 (C-H stretching) 1467 cm-1 and 1375 cm-1 (-CH2 & -CH3 bending). Toluene has a

40 30 20 10

(d) (e)

1467 1467 1375

(c)

1500

50

1743

60

2924 2852

(b)

2855

70

2924

80

1603 1458

(a)

2926 3029 2924 2861

90

1375

100

%T

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 16 of 23

(f) (g) (h)

0 4000 3500 3000 2500 2000 1500 1000

500

-1

293

Wavenumber (cm )

294

Figure 8. FTIR spectra of (a) oil-spill, (b) Biodiesel/water emulsion (c) n-Hexane, (d) Toluene, and

295

(e, f, g, and h) permeate from oil-spill/water, oil-water emulsion, n-hexane/water, and toluene/water.

296


Page 17 of 23 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


After 20 days

After 40 days

After 60 days Complete degradation 297 298

Figure 9. Biodegradation of PFAM in 60 days under normal condition in the soil.

299

As reported biodegradability and disposal of such materials including membranes in the environment

300

is another big issue. Hence, PFAMs of this study were tested for their biodegradability in soil

301

conditions (Figure 9). For soil biodegradation, the aerogel membrane placed in the soil and observed

302

at a different time interval. The weight losses of PFAM after 20 days and 40 days were ~70% and

303

~90% respectively in soil conditions. While no residue was obtained after 60 days in soil conditions

304

may be due to the complete degradation of membrane (Figure 9).

305

CONCLUSION

306

In this research paper, we have prepared protein functionalised biodegradable aerogel membranes

307

using BSA as protein. This protein functionalised aerogel membrane is highly porous and stable in

308

all the oil-water and emulsion mixtures. Use of natural crosslinker genipin makes this aerogel

309

membrane more environmentally friendly and less toxic in nature. Resulting protein functionalised

310

aerogel membranes have several potential properties with respect to their use in separation of oil-

311

water or emulsion as well as hydrocarbon-water. Protein functionalised aerogel membrane is less to

312

no toxic, easy to handle and biodegradable in soil.

313

Supporting Information

314 315

Swelling behaviour, contact angle measurement, permeate flux, recycle and reuse experiment results, oil-rejection rate with time, and SEM images of control AG.



Page 18 of 23

316

ACKNOWLEDGEMENTS: CSIR-CSMCRI registration number-110/2018. NV & RM want to

317

acknowledge SERB (DST, EMR/2016/004944), for financial support and A&ES&CIF, CSIR-

318

CSMCRI for sample analysis.

319 320

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Page 22 of 23

For Table of Contents Use Only

Oil-spill

Pure Water Gen.

BSA

AG

418 419

A simple and green process for preparation of protein functionalised biodegradable aerogel

420

membranes (PFAMs) has been described. PFAMs tested for oil-spill and oil-water emulsion

421

separation.


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Revised TOC 239x178mm (150 x 150 DPI)

ACS Paragon Plus Environment

Protein functionalised aerogel membranes (PFAMs) for gravity-driven

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