Biofouling Control Using Nano Silicon Dioxide Reinforced Mixed

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Biofouling control using nano silicon dioxide reinforced mixed-charged zwitterionic hydrogel in aquaculture cage nets AHANA MOHAN, and P Muhamed Ashraf Langmuir, Just Accepted Manuscript • DOI: 10.1021/acs.langmuir.8b04071 • Publication Date (Web): 28 Feb 2019 Downloaded from http://pubs.acs.org on March 5, 2019

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Biofouling control using nano silicon dioxide reinforced mixed-charged zwitterionic hydrogel in aquaculture cage nets. Ahana Mohan and P Muhamed Ashraf * ICAR – Central Institute of Fisheries Technology Cochin 682 029, India.

*Corresponding author P Muhamed Ashraf Ph D Fishing Technology Division ICAR Central Institute of Fisheries Technology Matsyapuri PO Cochin 682 029, Kerala India. Phone: +91 484 2412300 +91 9746236477 Email: [email protected] Fax: +91 484 2668212

ACS Paragon Plus Environment

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Biofouling control using nano silicon dioxide reinforced mixed-charged zwitterionic hydrogel in aquaculture cage nets. Ahana Mohan and P Muhamed Ashraf* ICAR – Central Institute of Fisheries Technology Cochin 682 029, India. Abstract: Biofouling in aquaculture cages negatively affects the farm productivity and it requires huge sums of money and labour for its management. Super hydrophilic pseudo zwitterionic hydrogel, N-isopropylacrylamide (NIPA) + [2-(methacryloyloxy)ethyl]trimethylammonium (TMA) + 3-sulfopropyl methacrylate (SA) co-polymer, is considered as a potential antifouling agent. The present study aimed to synthesize nano silicon oxide reinforced NIPA-TMA-SA mixed-charged zwitterionic hydrogel over polyaniline coated polyethylene aquaculture cage nets through situ microwave reaction and to test its biofouling resistance. The study highlighted the formation of stable coating over polyethylene, four different treatments and their effective inhibition of fouling compared to untreated one. Six month’s immersions of treated nettings in the estuarine environments demonstrated that the biofouling inhibition by nano silicon oxide reinforced zwitterionic hydrogel coated polyethylene were unable to satisfy the industrial standards but free from hard shelled fouling organisms compared to untreated controls. More research is needed to improve the quality of the coatings. The mixed-charged zwitterionic hydrogel with nano silicon oxide showed medium hydrophilic nature. FTIR, SEM and spectroscopic evaluation showed the successful formation of hydrogel over the aquaculture cage net. Nano silicon oxide reinforced in the matrix through a hydrogen and co-ordination bonding between NH2 and carbonyl of the polymeric chain respectively. Keywords: Biofouling, zwitterionic hydrogel, aquaculture cages, nano silicon, INTRODUCTION Fish production through aquaculture farming is considered as an alternative cheap protein source for growing populations in the world. Biofouling is a major problem and the submerged aquaculture cage nets were highly susceptible to biofouling eventually ended with increased economic burdens [1]. Frequent replacement of cage nets or manual / mechanical cleaning need to be undertaken to get rid of the biofouling [2]. Copper oxide coated aquaculture cage nets are


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extensively used to combat biofouling and the major disadvantages are less effective against foulers, increased weight of the cages and the fear of excessive copper leaching into the environment, thereby pollution [3]. The biocide coating must be light in weight, more toxic to the foulers and adhered strongly over the net. The aquaculture cage nets are generally fabricated using polyethylene, which is non polar in nature. Surface modification of polyethylene needs to be done with suitable polar molecule to incorporate biocides. Polyaniline, a conductive polymer, is in situ synthesized over the polyethylene cage nettings and effectively employed as a platform to incorporate biocides [4]. The biocide may either be a nano metal oxide or organic hydrophilic hydrogel [4, 5]. Hydrogel based materials against biofouling have been investigated extensively. Since the hydrogel is not having surface energy difference with surrounding waters and requires only minimum thermodynamic driving force for irreversible binding. Cowei et al [6] developed colourless poly(hydroxyl-ethylmethacrylate) hydrogel for inhibiting fouling on optical windows of submerged sensors. Rasmussen et al., [7] tested the settlement of barnacles on different non solid hydrogels. The materials exhibit lower settlement with difference in different gels. Ekblad et al. [8] investigated the protein resistant poly(ethyleneglycol) (PEG) hydrogel against biofouling. PEG has poor stability as PEG macromolecular chains can rapidly autoxidise and degrades during storage and handling at room temperature, especially by transition metal ions, which exists in most biological related solution [9]. Significant effort has been invested in the search for an alternative antifouling materials with stability higher than PEG. Zwitterionic polymers are just perfect alternatives for PEG. Zwitterionic polymers refer to a family of materials that have the same number of cations and anions along their polymer chains. Zwitterionic polymers are super hydrophilic due to the presence of abundant ions and subsequent strong hydration layer. Zwitterionic polymers usually synthesised using sulphur or carboxy or phosphor betaines [10-14]. These betaine pendent structures resist the attachment of proteins, or microorganisms. Zwitterionic based hydrogels and films may partially lose their antifouling property when the surface chemistry is modified in order to add a supplementary bioactive function through the implementation of the additional conjugate [15]. Now the research is focussed on synthesis of mixed-charged copolymers which can exhibit the biofouling resistance similar to zwitterionic polymers [15-17]. Mixed charged copolymer of 2(methacryloyloxy)ethyl]trimethylammonium (+vely charged) and 3-sulfopropyl methacrylate (-vely charged) showed biofouling resistance on plasma

proteins [18]. Poly(N-

isopropylacrylamide) (NIPA) + [2-(methacryloyloxy)ethyl]- trimethylammonium (TMA) + 3-


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sulfopropyl methacrylate (SA) hydrogel was synthesised by Venault et al [19] and the hydrogel showed excellent biofouling resistance. These super hydrophilic copolymers may exhibit lower efficiency in biofouling resistance under marine environment. Since the hydrophilic polymer inhibits protein adsorption, but is less efficient in resisting the degradation and the attack of microorganisms. Introduction of copper oxide along with PEG hydrogel exhibited excellent biofouling resistance in aquaculture cage nets and also inhibited the attack of microorganisms on PEG hydrogel [5]. In view of the above an attempt was made to synthesise a metal oxide incorporated poly (NIPA-co-TMA/SA) hydrogel in situ over a polyaniline coated polyethylene aquaculture cage net. Experiments were conducted to synthesize nano copper oxide incorporated NIPA-co-TMA/SA hydrogel through microwave reaction, but it was failed to form the hydrogel. The nano silicon dioxide (SiO2) is considered as an environment friendly ceramic oxide with excellent antibacterial property [20]. The nano SiO2 incorporated NIPAco-TMA/SA hydrogel through microwave method was successfully synthesized and the same was used for the present study. The present study aimed to synthesize nano sized SiO2 incorporated poly(NIPA-co-TMA/SA mixed-charged zwitterionic polymeric hydrogel in situ over a polyethylene aquaculture cage netting material treated with polyaniline. The treated net was evaluated for biofouling resistance in the estuarine environments. Materials and methods 2.1. Materials used The chemicals N-Isopropylacrylamide (NIPA), Ammonium persulfate (APS), N,N,N′,N′tetraethylmethylenediamine (TEMED), N,N′- methylenebis(acrylamide) (MBAA) and 3Sulfopropyl methacrylate potassium salt (SA) were sourced from Sigma-Aldrich. Trimethylamine (TMA), Hydrochloric acid (HCl) and Aniline were procured from Merck India. Nano silicon dioxide from Reinste Nano Ventures, New Delhi, India and high density Polyethylene nettings (PE) were purchased from Matsyafed Net factory, Government of Kerala, India. Millipore type I water was used through out the study. 2.2. Synthesis and Standardisation of Nano SiO2 Mixed-Charged Zwitterionic Hydrogel The mixed-charged zwitterionic hydrogel was synthesised by modifying the method described by Venault et al [19]. NIPA (20 wt%) and TMA/SA mixture (TMA - 40 wt%, 20 wt% HCl and 40 wt% SA) was dissolved in 5 ml of millipore water containing 1.6 wt% MBAA. The monomer mixture was sonicated in a bath sonicator for 10 min to make the solution


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homogenous. 8.0 mg each of the APS and TEMED (1:2 molar ratio) were added to initialise the copolymerisation reaction. The monomer mixture is taken in a silica crucible and optimised the microwave assisted reaction conditions using Milestone ETHOS Plus microwave digestion system with IR sensor. The microwave digestion system programmed in such a way that the microwave heating from room temperature to 45oC within 2 min and then allowed to vent 15 min to reach room temperature. The mixed-charged zwitterionic hydrogel (PZH) was formed and the process was repeated by incorporating varying concentrations of nano SiO2 (nSiO). The formed hydrogel exhibited characteristics of zwitterionic hydrogel. 2.3. Implementation of Nano SiO2 Mixed-Charged Zwitterionic Hydrogel over PE-PANI Polyaniline was coated over PE nettings according to the method described in Ashraf et al., [4] (Supplementary Fig S1). The required amounts of NIPA, TMA, SA, MBAA, APS, TEMED and varied concentrations of nano SiO2 were taken in a beaker. The mixture was sonicated and the PE-PANI coated cage netting was immersed in the solution for 5 min. Taken out and spread over a petri plate. The microwave reaction was performed as described in the section 2.1. The nano SiO2 (weight / volume basis) treatment details was given in Table 1 and Supplementary Fig S2. Table 1: Treatment details of nano incorporated PZH Symbol

Treatment details

Conc. of SiO2 (%)

AN0

PE

0

AN1

PE-PANI

0

AN2

PE-PANI PZH + nano SiO2

0.01

AN3

PE-PANI PZH + nano SiO2

0.02

AN4

PE-PANI PZH

0

2.4. Field Exposure Studies The pre weighed and tagged net samples were tied over a square heavy duty PVC frame as shown in the supplementary Fig S3. The PVC racks were immersed at 2 m depth (1 m below the low tide depth) from the surface in the test site of Cochin Estuary for 6 months. 2.5. Characterisation of hydrogel


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Pre weighed quantities of nano SiO2 incorporated zwitterionic hydrogel (PZH-nSiO) and zwitterionic hydrogel were taken separately in a quartz crucible and filled with water. Every day the water in the crucible was drained and the excess water, wiped with filter paper (Whatman No 1). The weight of the hydrogel was noted and continued the process till 5 days. Hydrogel formation was analysed by using Shimadzu 2450 double beam UV-Vis spectrophotometer fitted with integrating sphere accessory. The samples to be analysed were dropped over Whatman GF/F 25 mm filter paper and scanned from 800 to 200 nm at 1nm interval. Thermo Nicolet iS10 Fourier transform infrared (FTIR) spectrometer was used for the characterization of hydrogel molecule. The PE nettings, PE-PANI and PE-PANI with PZHnSiO hydrogel were analysed directly using diffusive reflectance accessory fitted with FTIR. The sample scanned from 4000 to 400 cm-1 and the data was processed through OMNIC software. Leica MZ 16A stereo microscope was used for the evaluation of hydrophilicity of the material. Polyethylene sheets were treated with PANI, PZH-nSiO as per treatment described in the section 2.3. PE sheets (both treated and untreated) i.e., PE, PE-PANI, PEPANI PZH and PE-PANI PZH-nSiO were analysed under a stereo microscope by adding 5µl of water droplet and viewed under 25x magnification. Scanning Electron micrographs of cage nettings were analyzed using JEOL 6390LV after treating it with low vacuum gold sputtering. 3. Results and Discussion. 3.1 Characterisation The mixed-charged zwitterionic hydrogel was synthesised according to the procedure mentioned in the section 2.2. The standardisation of the method was carried out by trial and error method, finally the method was standardised and the formed hydrogel was shown in supplementary Fig S4. The nano SiO2 concentration (wt/vol basis) in hydrogel was 0.01% and 0.02% in AN2 and AN3 respectively. 3.1.1. UV-Vis Spectrophotometeric Studies UV-Visible spectroscopic analysis will provide information on the changes in the characteristic absorption of molecules due to different treatments. The UV-Visible spectroscopic evaluation of PZH and PZH-nSiO was shown in Figure 1. The absorption of PZH was shown at 204, 208, 213, 218, 220, 223 and 228 nm. Nano SiO2 incorporated hydrogel exhibited intense peaks at 203 nm and 214 nm [21, 22]. This was due to the presence of nano SiO2 in the matrix. Other absorption peaks were shown at 207, 209, 218, 221, 224 and 229 nm. All the peaks were shifted


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slightly towards the red side compared to the hydrogel matrix and it was due to the formation of PZH-nSiO hydrogel. When SiO2 was incorporated in the matrix there was an appearance of low intensity peaks at 747 nm and 782 nm. These results showed that nano SiO2 was successfully incorporated into the matrix. It may have interacted with the oxygen of carbonyl and amine functional groups present in the mixed-charged zwitterionic moiety through hydrogen bonding. 0.6 0.5 Absorbance

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0.4 0.3 0.2 0.1 0 200

250

300

350 Wavelength nm

PZH + nano SiO2

400

450

500

PZH

Figure 1: UV-Vis spectra of PZH and PZH + nano SiO2 from 200 to 500 nm analysed by using integrating sphere accessory. The samples to be analysed were dropped over Whatman GF/F 25 mm filter paper and scanned from 800 to 200 nm. 3.1.2. Hydrophilicity of treated nettings Hydrophilicity study of hydrogel coated over PE was difficult in PE netting because of its shape (cylindrical shape). Thus, the experiment was repeated over PE sheets instead of PE nettings. The PE sheets were subjected to the following treatments viz., PE-PANI, PE-PANI-PZH and PE-PANI-PZH-nSiO. 5 µl of water droplet added over the above treated and untreated PE sheets and were analysed under stereomicroscope by viewing at 25x magnification (Supplementary Fig S5). The untreated hydrophobic control PE film exhibited spherical droplet


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with 3.011 mm diameter. The 5 µl water droplet over PE-PANI film showed the average diameter of 3.107 mm. The water droplet diameters were 5.861 and 4.012 mm respectively in PE-PANI-PZH and PE-PANI-PZH-nSiO. The PZH coating over PE –PANI film showed increased hydrophilicity than PE and PE-PANI. Introduction of nano SiO2 along with PZH made the coating became semi hydrophilic characteristics, with less hydrophilicity but it is not purely hydrophobic. The semi hydrophilic nature expected to enhance the antifouling capability due to the combined effect of less protein absorption and also prevented the attack of microorganism due to the presence of nano SiO2 [23]. 3.1.3. Water absorption capacity of hydrogel To study the water absorption capacity of the PZH and PZH-nSiO was studied for 7 days and the results were shown in Figure 2. Considerable amounts of water were absorbed by the hydrogels [24]. Water absorption steadily increased up to six days later it reduced. Water absorption capacity of PZH is higher than the water absorption capacity of PZH-nSiO. Thus, it can be concluded that PZH-nSiO was not as hydrophilic as PZH, it’s in semi hydrophilic nature. The results were correlated with the findings of hydrophilicity of hydrogel. amount of water absorbed per gram of gel (g)

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14 12 10 8 6 4 2 0 Day 1

Day 2

Day 3 PZH

Day 4

Day 5

Day 6

Day 7

PZH+nano SiO2

Figure 2: Graph showing the amount of water absorbed per gram by PZH and PZH-nSiO for 7 days.


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3.1.4. Fourier transform infrared (FTIR) spectrometer The characteristics of PZH and PZH-nSiO hydrogel was studied using FTIR and the results were shown in Figure 3. FTIR spectral bands of PE, PE-PANI, PE-PANI-PZH and PE-PANIPZH-nSiO were analysed and presented in Table 2. The standard peak of polyethylene in PE at 726 cm-1 was shifted to 718 cm-1, 719 cm-1 and 718 cm-1 in PE-PANI, PE-PANI PZH and PE-PANI PZH-nSiO respectively. This shift was due to the interaction between PE and PANI. Similarly, there is a shift in –CH2 twisting vibration at 1299 cm-1 in PE to 1310 cm-1 in PEPANI and 1308 cm-1 in PE-PANI PZH and PE-PANI PZH-nSiO. The –CH2 bending vibration of PE (1473 cm-1, 1463 cm-1) was shifted to 1481 cm-1 and 1468 cm-1 in PE-PANI. The absorption at 1468 cm-1 in PE-PANI was shifted to 1458 cm-1 in PE-PANI PZH, indicating the interaction of polyaniline with –CH2 group of polyethylene in PE. The standard peak of polyaniline at 1159 cm-1 and 1504 cm-1 in PE-PANI was shifted to 1165 cm-1 and 1508 cm-1 in PE-PANI PZH and PE-PANI- PZH-nSiO. This shift indicates the interaction of polyaniline and zwitterionic polymer at Quinoid, NH4+ and Benzenoid ring of PE-PANI. There is a shift in the standard quinoid peak of polyaniline in PE-PANI PZH-nSiO. The absorption at 1031 and 1560 cm-1 in PE-PANI PZH was shifted respectively to 1036 cm-1 and 1575 cm-1 in PE-PANI PZH-nSiO. This shift was due to the interaction of nano SiO2 at the Quinoid ring of the PZH. The standard peak of zwitterionic polymer of PE-PANI PZH at 1720 cm-1 gets shifted to 1735 cm-1 in PE-PANI PZH-nSiO. This shift indicated the interaction of nano SiO2 over a C=O group of zwitterionic polymer. This further affirms that the change in C=O vibration in PEPANI-PZH-nSiO. FTIR results confirmed that zwitterionic polymer of the hydrogel interact with Quinoid, NH4+ of polyaniline and nano SiO2 was incorporated at oxygen of a C=O group of zwitterionic polymer. The results showed that nano SiO2 was successfully incorporated in the hydrogel matrix. The probable orientation SiO2 in the polymer matrix was shown in Figure 4.


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Figure 3. FTIR spectra of PE, PE-PANI, PE-PANI PZH, PE-PANI PZH+ nano SiO2 from 400cm-1 – 4000 cm-1

Table 2. FTIR characteristics of PE, PE-PANI, PE-PANI PZH and PE-PANI PZH + nano SiO2 Standard

FTIR absorption (wavenumber cm -1) showed in the

FTIR

present study

absorption

PE

PE-PANI

peak

PE-PANI

PE-PANI

PZH

PZH+ nano

(wavenumber

Description

SiO2

cm-1) Polyethylene [4] 731, 720

726

718

719

718

CH2 rocking deformation

1176

1180

1200

1198

1198

CH2 wagging deformation


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1306

1299

1310

1308

1308

CH2 twisting

1351, 1366

1350, 1364

1351, 1368

1353, 1367

1351, 1368

CH2 wagging deformation

1473, 1463

1473, 1463

1481, 1468

1473, 1458

1479, 1465

CH2 bending

2851

2837

2840

2845

2845

CH2 symmetric

2919

2925

2910

2908

2908

CH2 asymmetric

-

858

857

858

Quinoid ring out of

Polyaniline [4] 829

plane 1027

-

1030

1031

1036

Quinoid ‚ NH4+

1141

-

1159

1165

1163

Quinoid ‚ NH+

1300

-

1310

1308

1308

v (C-N) 2° aromatic amine

1500

-

1504

1508

1509

Benzenoid ring

1585

-

1559

1560

1575

Quinoid ring

Zwitterionic Polymer [19, 25-26] 607

-

-

608

608

C=C=O vibration

1045

-

-

1050

1052

SO3- symmetric stretching

1650

-

-

1653

1653

NH-C=O vibration

1718

-

-

1720

1735

C=O vibration

3300

-

-

3301

3300

NH stretching

-

-

-

456

Si-O-Si flexural

Nano SiO2 [27-28] 456

libration vibration 795

-

-

-

789

Si-O symmetric vibration


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950

-

-

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-

992

Si-OH asymmetric vibration

1090

-

-

-

1082

Si-O asymmetric vibration

Figure 4. Possible structure of (a) PZH (details described in ref [19]) and (b) nano SiO2 incorporated PZH 3.5. Scanning Electron Microscopy:


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PE

PE PANI

AN2

AN3

AN 4 Figure 5. Scanning electron micrographs of untreated polyethylene, polyaniline coated polyethylene, 0.01% nano SiO2 reinforced mixed-charged zwitterionic hydrogel coated polyethylene, 0.02% nano SiO2 reinforced mixed-charged zwitterionic hydrogel coated polyethylene and zwitterionic hydrogel alone coated polyethylene.


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Scanning electron micrographs of PE, PE-PANI, PE-PANI-PZH and PE-PANI-PZH-nSiO was shown in Figure 5. PANI nano rods were formed and covered the entire matrix of the polyethylene uniformly. PZH treatment over PANI has exhibited a uniform coverage over the PANI with fine flake like structures. Incorporation of nano SiO2 made the coating more compact, continuous and uniformly covered the entire PANI present. The nano SiO2 was seen in the matrix. The incorporation of nano SiO2 in the hydrogel improved the surface characteristics of the cage net and this might have influenced the antifouling property of PZH complex. 3.2. Field Evaluation One month

Two month

Three month

AN0

AN1

AN2


Six month

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AN3

AN4 Figure 6. Microscopic images of the aquaculture cage nets exposed 1, 2, 3, 6 months in the estuary. The samples were retrieved after 1, 2, 3 and 6 months and their microscopic images were shown in Figure 6. The control without any treatment exhibited hydroid accumulation up to 2 months. Third month onwards thick coating of polymeric substances like coating were formed and six month sample the twines were accumulated with a heavy coat of calcareous shelled foulers. AN1 to AN4 showed increased accumulation of hydroids in the first month and it was lowest in AN3 in the second month sample. Third month also showed increased fouling attack. In six month sample all the treated and control netting material accumulated different types of fouler community. The fouling density was highest in AN4. Probably the PZH might be degraded due to the attack of microorganisms and the metal ions present in the sea water [8]. Control samples accumulated hard shelled foulers whereas green algae or similar types of foulers were accumulated in treated samples. Hydroids are common foulers in the region and its accumulation was not shown in the PZH-nSiO treated nettings except first months. The results showed that the treatment was effective to prevent biofouling completely up to two months. The study area was in tropical region with an average rainfall of 3000 to 4000 mm per year. The region has 3 seasons, viz. Summer (February to May), Monsoon (June to September) and Post monsoon (October to January). The samples exposed in estuary on 20th February 2018, which roughly coincides with the onset of summer season in the study area. In the middle of the third month the area experienced with pre monsoon showers and this might have sloughed off the foulers from the aquaculture cage nets. During six month’s exposure, the samples


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experienced the summer and monsoon season, this might have influenced the settlement pattern of the fouling community with different species. The results highlighted that long term exposed samples with different treatments accumulated different types of foulers. This shows the PZH and PZH-nSiO treatment over the aquaculture cage nets, effective in preventing the foulers with hard shells. The biomass accumulation over the cage nettings during the six month exposure period was shown in Figure 7. The two month exposed samples accumulated the biomass 583 g kg-1, 396 g kg-1, 350 g kg-1, 344 g kg-1 and 518 g kg-1 of netting respectively in AN0, AN1, AN2, AN3 and AN4. The lowest accumulation of biomass was shown by PE-PANI PZH-nSiO (AN3). The highest accumulation of biomass was showed by PE (AN0). We could see a considerable decrease in the biomass accumulation when compared with 1 month sample. This may probably due to changes in weather conditions. There was an incessant rain in the month of April and this may result in low salinity and hence the foulers might be sloughed off from the netting. On microscopic evaluation growth of hydroids were found in PE (AN0), PE-PANI (AN1) and PE-PANI PZH (AN4). On examining the knot (not shown in Figure) and mesh of AN3 i.e., 0.02% SiO2 treated PE-PANI PZH-nSiO sample, the growth of hydroids was very less than other treated samples. Three and six month long exposed sample exhibited more fouling on treated samples than control. This shows the treatment was effective upto two months. The monsoon season in the region sloughed off the accumulated foulers and the experiment failed to give a proper conclusion on effectiveness. 1400 Biomass per kg of net (g)

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1200 1000 800 600 400 200 0 AN0 AN1 AN2AN3 AN4 1 mon th

AN0 AN1 AN2AN3 AN4 2 Mon th



Figure 7: Graph showing the amount of biomass in g per kg of net accumulated in sample in 1 month, 2 month and 3 month


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The mechanism of adsorption of polyaniline over polyethylene was described in details elsewhere [5]. All hydrogels have a hydrophilic nature. It may favour nano biofouling [19]. NIPA is already known low-biofouling biocide and it exhibits a low protein adsorption level [18]. The combination of electropositive TMA and electronegative SA segments gives rise to a pseudo zwitterionic structure. Copolymerisation of NIPA with equimolar TMA and SA gives a hydrophilic protein resistant pseudo zwitterionic hydrogel [19]. The water trapped between the electropositive and electronegative groups form a hydration layer between the electric charges prevent attachment of protein and cells. Introduction of nano SiO2 along with the NIPA and TMA+SA during copolymerisation yields a mixed-charged zwitterionic hydrogel having improved surface structure and hydrophilic characteristics. Silica incorporated hydrogels exhibited reduced fibrinogen adsorption [11]. Reinforcement of silica not only improve the protein resistance and acted as a biocide to resist the attack of bacteria to degrade the hydrogel. The scanning electron micrographs showed the more ordered structure in PZH-nSiO hydrogel compared to PZH hydrogel (See Table of Content Graphics). This has prevented the approach of protein over the matrix and improved the efficiency in biofouling resistance. Conclusion

Nano SiO2 reinforced mixed-charged zwitterionic hydrogel was coated over polyaniline surface modified polyethylene aquaculture cage nets. The hydrogel formed was compact and uniformly covered the matrix. The hydrogel exhibited medium hydrophilic nature, which made the hydrogel protein and bacteria resistant. The SiO2 reinforced in the PZH were interacted with CO and NH groups of the PZH polymer evidenced by FTIR. The field exposure studies of the PZH-SiO hydrogel exhibited biofouling resistance up to two months, but was not up to the standard of industrial application. Further studies are required to make the composite more efficient in biofouling resistance under marine environment. Acknowledgement The author sincerely thanks to the Director, ICAR - Central Institute of Fisheries Technology for providing facilities and the technical staff of the Fishing Technology Division of ICAR - CIFT. Thanks are also due to Dr. Leela Edwin, Head, Fishing Technology Division, Dr MM Prasad, Head, MFB Division and Sophisticated Technology Instrumentation Centre, CUSAT for extending support and guidance, FTIR and SEM facilities respectively. Funding Source


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This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.

Declarations of interest The authors report no declarations of interest.

Supporting Information Available The following figures are available in supplementary file. 

Fig S1: Polyethylene netting (a) without treatment (PE) (b) Polyaniline treated (PEPANI)

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Fig S2: (a) 0.01% nano SiO2 incorporated PZH coated over PE-PANI (b) 0.02% nano SiO2 incorporated PZH coated over PE-PANI (c) PZH coated over PE-PANI

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Fig S3: Sample rack

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Fig S4: PZH with (a) 0.01% nano SiO2 (b) 0.02% nano SiO2

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Fig 5: Microscopic evaluation of hydrophilicity (a) PE (b) PE-PANI (c) PE-PANI PZH (d) PE-PANI PZH + nano SiO2 by adding 5µl of water droplet and viewed under 25x magnification except in c) where 20x magnification used.

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Biofouling Control Using Nano Silicon Dioxide Reinforced Mixed

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