Emulsion templated hydrophilic polymethacrylates. Morphological features, water and dye absorption

Journal Pre-proof Emulsion templated hydrophilic polymethacrylates. Morphological features, water and dye absorption

Doris Golub, Peter Krajnc PII:

S1381-5148(19)30998-8

DOI:

https://doi.org/10.1016/j.reactfunctpolym.2020.104515

Reference:

REACT 104515

To appear in:

Reactive and Functional Polymers

Received date:

20 September 2019

Revised date:

28 January 2020

Accepted date:

30 January 2020

Please cite this article as: D. Golub and P. Krajnc, Emulsion templated hydrophilic polymethacrylates. Morphological features, water and dye absorption, Reactive and Functional Polymers (2019), https://doi.org/10.1016/j.reactfunctpolym.2020.104515

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© 2019 Published by Elsevier.

Journal Pre-proof Emulsion templated hydrophilic polymethacrylates. Morphological features, water and dye absorption Doris Golub, Peter Krajnc* University of Maribor, Faculty of Chemistry and Chemical Engineering, PolyOrgLab, Smetanova 17, 2000 Maribor, Slovenia *corresponding author: [email protected]

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Abstract

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Emulsions with high volume fraction of droplet phase were used to prepare macroporous polymers (polyHIPEs) of dimethylaminoethyl methacrylate (DMAEMA) and 2-hydroxyethyl

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methacrylate (HEMA) crosslinked with various amounts of ethylene glycol dimethacrylate

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(EGDMA) and N,N'-methylene bisacrylamide (MBAA), respectively. Monoliths with cellular interconnected porous structure were obtained. Up to 6 times of water (weight/weight) was

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absorbed by the materials while no apparent change in volume was found suggesting that the main mechanism of water absorption was primary pore filling. Prepared materials were used for the removal of dyes methylene blue (MB) and methyl orange (MO) from their aqueous

Keywords:

emulsion

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solutions; in 120 minutes 6.5 mg g-1 of MB and 1.6 mg g-1 of MO were removed.

templating;

polyHIPE;

dimethylaminoethyl

methacrylate;

2-

1.

Introduction

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hydroxyethyl methacrylate; dye removal

Application of high internal phase emulsion templating (emulsions with droplet volume share typically over 74 %) [1] was first reported in 1960’s and patented in 1980’s [2,3]. Such porous polymers have several advantageous properties, like open cellular structure, high porosity, high permeability, good interconnectivity and low density, and these properties can be customized to chosen application [4-6]. A large variety of porous polymers, also known as polyHIPEs, have been synthesized, where high internal phase emulsions (HIPEs) were used as templates for the porous structure. PolyHIPEs have a unique morphology, which is the result of the formation of micrometer-sized pores created by the droplets of the internal phase emulsion. These pores are typically connected with interconnecting channels, resulting in a 1

Journal Pre-proof highly porous interconnected material. Because of their unique properties, they are applicable in numerous applications, such as filter media [7,8], ion exchange modules [9], protein purification [8], separation membranes [7,10], water purification [11], tissue engineering [12,13], agriculture applications [14,15] and even for extinguishing fires [16]. Most of the polyHIPEs reported so far are based on hydrophobic polymers and are synthesized from water-in-oil (w/o) emulsions, although direct high internal phase emulsions [17] and multiple emulsions [18] can be prepared. Such polyHIPEs exhibit poor water absorption, which is, for various applications, a critical requirement. Thus, hydrophilic polyHIPEs can be prepared directly within oil-in-water (o/w) emulsions, where the external

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phase contains hydrophilic monomers that are dissolved in water. Another approach for

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preparation of more hydrophilic polyHIPEs can take advantage of the stability of w/o emulsion. In this approach, the hydrophobic polyHIPE is synthesized within a w/o emulsion

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and is then altered to enhance hydrophilicity. Alterations can be obtained through the addition

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of a hydrophilic co-monomer or crosslinker to a HIPE based on the hydrophobic monomer [14-16,19,20]. Such prepared hydrophilic hydrogels can absorb large amounts of water. The

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ability of a hydrogel to absorb water is based on the presence of hydrophilic groups (like amino, hydroxyl and carboxyl groups) in the polymeric structure, while the crosslinking

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among the polymer chains prevents their dissolution [21,22]. In recent years, more attention has been paid to the hydrogels, of which properties can

such

hydrogels,

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change under the influence of pH, temperature and solvent component. For the preparation of poly(2-hydroxyethyl

methacrylate)

or

poly(HEMA)

and

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poly(dimethylaminoethyl methacrylate) or poly(DMAEMA), two functional polyelectrolytes, which contain ionizable groups, can be used. Poly(HEMA) contains a hydroxyl functional group which makes it hydrophilic and also has high mechanical strength and resistance to chemical and microbial decomposition. Preparation of polyHIPEs based on HEMA has already been reported [21-25]. On the other hand, poly(DMAEMA) is a weak polyelectrolyte that contains tertiary amino groups and shows both pH and temperature sensitive behaviour [26]. At a low pH, the amino groups in DMAEMA are protonated, the charge repulsion promotes water absorption and the hydrogels are able to increase up to 6 times their weight [26,27]. The crosslinker content in the polymer network structure dictates a number of polymer hydrogel properties, such as mechanical strength, swelling behaviour and hydrophilicity [28]. While polyHIPE material from methacrylic acid [29] and some methacrylates, e.g. methyl methacrylate [30] and glycidyl methacrylate [31], are well established; there are no reports on 2

Journal Pre-proof polyHIPEs from DMAEMA and very few on polyHIPEs from HEMA [21,23-25]. The aim of this study was to prepare and test the hydrophilic polyHIPE materials with sufficient crosslinking, to prevent any volume change of the monoliths, while still keeping the capacity for aqueous solutions uptake at a reasonably high degree. Therefore, the targeted prevailing mechanism of water uptake should be the cavity filling.

2.

Experimental

2-(dimethylamino)ethyl methacrylate

(DMAEMA,

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Monomers

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2.1. Materials

98%,

Sigma-Aldrich),

2-

ethylhexyl acrylate (EHA, 98%, Sigma-Aldrich), 2-hydroxyethyl methacrylate (HEMA, 97%,

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Sigma-Aldrich) and ethylene glycol dimethylacrylate (EGDMA, 98%, Sigma-Aldrich) were

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flushed twice through an aluminum oxide (Al2 O 3 , 99%, Acros Organics) column before use to remove the inhibitors. Azobis(isobutyronitrile) (AIBN, 98%, Sigma-Aldrich) was purified by

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recrystallization in methanol (99.9%, Carlo Erba Reagents). N,N'-methylenebisacrylamide (MBAA, ≤ 99, Fluka), ammonium peroxodisulfate (APS, 98%, Fluka), N,N,N’,N’-

poly(ethylene

99%,

glycol)-block-poly(ethylene glycol)-block-poly(propylene

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poly(propylene

(TEMED,

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tetramethylethylenediamine

Fluka),

glycol)

poly(ethylene

(Pluronic® L-121,

glycol)-block-poly(ethylene

glycol)-blockSigma-Aldrich),

glycol)

(Pluronic

F68, Sigma-Aldrich), calcium chloride hexahydrate (CaCl2 ×6H2 O, 98%, Sigma-Aldrich),

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cyclohexane (99.5%, Carlo Erba Reagents), isopropanol (99.7%, Carlo Erba Reagents), methylene blue (MB, ≤ 96%, Kemika), methyl orange (MO, ≤ 96%, Kemika) and buffer solutions (Sigma-Aldrich) were all used as received.

2.2. Preparation of poly(DMAEMA-co-EGDMA) polyHIPEs from w/o emulsion

For the preparation of continuous phase of emulsion, monomer DMAEMA, crosslinker EGDMA, surfactant PEL 121 and initiator AIBN (4 wt.% based on monomers) were mixed and placed into a two-neck round-bottom reactor, equipped with an overhead stirrer with a Dshaped paddle. While stirring at 300 rpm, the aqueous phase, consisting of 1.79 g CaCl2 × 6H2 O dissolved in 100 mL of degassed deionized water, was added dropwise. After the addition of all the aqueous phase, stirring was continued for 60 min to obtain homogenous, white water-in-oil (w/o) emulsion. The emulsion was transferred to polypropylene mould and 3

Journal Pre-proof cured in convection oven at 60 °C for 24 h. The polyHIPE monoliths were purified by Soxhlet extraction, first 24 h with water and next 24 h with isopropanol. After purification, the polyHIPE monoliths were air-dried. Composition data for all DMAEMA polyHIPE monoliths (labelled with letter D) are in Table 1.

2.3. Preparation of poly(HEMA-co-MBAA) polyHIPE from o/w emulsion

Deionized water, monomer HEMA, crosslinker MBAA, initiator APS (2 wt.% based on monomer) and surfactant Pluronic® F68 (20 wt.% of water phase) were placed in a two-

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necked round bottom flask. Cyclohexane was added dropwise to the monomer solution while

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stirring with an overhead stirrer at 280 rpm. After the addition of all cyclohexane, stirring was continued for another 60 min to form a homogenous, white oil-in-water (o/w) emulsion.

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Stirring rate was reduced to 50 rpm and the reducing agent TEMED (60 μL) was added. The

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emulsion was transferred to the polypropylene mould and cured in convection oven at 50 °C for 24 h. The polyHIPE monoliths were purified via Soxhlet extraction, first 24 h with water

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and next 24 h with isopropanol and then air-dried. Composition data for HEMA polyHIPE

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monoliths (labelled with letter H) are in Table 2.

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2.4. Characterization of polyHIPEs

FTIR spectra were recorded on an IR Affinity-1 (Shimadzu Corporation, Japan) spectrometer

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in the wave number region 4000 – 600 cm-1 . SEM images were taken on a scanning electron microscope Philips XL-30 SEM, operating at 20 kV. Each sample was coated with a thin layer of palladium prior scanning analysis. Cavity size distribution was determined by SEM image

analysis,

by

measuring

the

diameter

of

at

least

50

cavities.

Nitrogen

adsorption/desorption measurements were taken on a Micromeritics TriStar II 3020 porosimeter (Micromeritics, USA) using BET model for surface area evaluation. The change in methylene blue

and methyl orange concentrations was monitored using UV-VIS

spectrometer Lambda 2 (Perkin Elmer, Germany).

2.5. Water absorption studies of prepared polyHIPE monoliths

Water absorption studies were performed in buffer solutions with various pH values at various temperature using approximately 0.05 g of dry polymer. Totally dried pieces were weighed 4

Journal Pre-proof and then immersed in the buffer solutions. The monolithic pieces were periodically withdrawn from the solution and weighed, after removing the excess surface water by filter paper, until the hydrated weight reached a constant value. The water absorption ratio (Sr, weight/weight) was calculated using the following Equation 1: W

Sr = W s

(1)

d

where Ws and Wd are the weight of swollen and dry material respectively. 2.6. Adsorption studies

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Procedure for adsorption studies were performed according to literature [32,33]. Briefly, methylene blue and methyl orange were used as adsorbents and were not purified prior to use.

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To study the effect of pH on the adsorptive removal of dyes, aqueous solutions of 50 mg L-1 of dyes were prepared. Approximately 0.05 g of dry samples were immersed in the dye

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solutions (20 mL) contained in glass vessels at pH 4, 7 and 9. Samples were withdrawn at different time intervals (15, 30, 45, 60, 75, 90, 105 and 120 min) and the amount of residual

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dye in solutions was determined using UV/VIS spectrometer at λmax = 663 nm for MB and at

Qt =

( c 0 −c t) ∗V m

(2)

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Equation 2:

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λmax = 464 nm for MO. The amount of adsorbed dye was calculated using the following

where Q t is the rate of adsorbed dye per mass unit of the adsorbent (mg g-1 ), c0 is initial dye

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concentration (mg L-1 ) and ct is dye concentration (mg L-1 ) at time t, V is the volume of the solution added (L) and m is the amount of dry samples (g) taken for adsorption measurements.

We were also interested in the comparison of the results for the adsorptive removal of dyes between the dry samples and the samples in equilibrium, therefore the second part of the experiments were performed. In these experiments, 0.05 g pieces of dry samples D2 were immersed in buffer solution with pH 4, 7 and 9 for 20 h, to achieve the absorption equilibrium, prior to the dye adsorption. When the absorption equilibrium was reached, the swollen samples were immersed in the 20 mL of prepared dye solution with concentration 50 mg L-1 at pH 4, 7 and 9. The amount of residual dye in solutions was determined at different time intervals (same as for dry hydrogel) using UV/VIS spectrometer and the amount of adsorbed dye was calculated using the following Equation 3: 5

Journal Pre-proof Qe =

( c 0−c et ) ∗V

(3)

m

where Q e is the equilibrium rate of adsorbed dye per mass unit of the adsorbent (mg g-1 ), c0 is initial dye concentration (mg L-1 ) and cet is dye concentration (mg L-1 ) of equilibrium sample at time t, V is the volume of the solution added (L) and m is the weight of swollen material (g) taken for adsorption measurements.

3.

Results and discussion

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3.1. PolyHIPE characterization

Two different hydrophilic monomers were used for the preparation of polyHIPE monoliths,

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namely DMAEMA, and HEMA. Despite significant hydrophilicity of monomers, water-in-oil emulsions proved more suitable for the polymer preparation than oil-in-water. We have

e-

shown previously that in the case of HEMA, both type of emulsions can be used for the preparation of polyHIPE monoliths while besides the functional monomer, the crosslinker

high

internal phase

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also plays a role in this process [24]. PolyDMAEMA polyHIPEs were prepared using w/o emulsion

precursors,

as

shown in Scheme

1.

The chemical

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characterization of prepared samples was measured with FTIR spectroscopy, which confirmed the chemical composition of prepared polyDMAEMA polyHIPEs exhibiting the signals for C-

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H group at 2949 cm-1 , for ester carbonyl group C=O at 1724 cm-1 , for CH3 and CH2 vibrations

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at 1452 cm-1 and for the symmetric stretching vibration of C-N band and C-O-C stretching at 1145 cm-1 (Figure 1a). The chemical composition of polyHEMA polyHIPEs, prepared using o/w high internal phase emulsion precursors, was confirmed with signals for hydroxyl group O-H at 3368 cm-1 , acrylate ester carbonyl group C-C=O at 1722 cm-1 , amide carbonyl group N-C=O at 1654 cm-1 and amide N-H bending vibration at 1529 cm-1 (Figure 1b). Using 80 vol% of droplet phase in the emulsion resulted in polyHIPE monoliths with interconnected, open-cell, porous morphology as observed by scanning electron microscopy (SEM) (Figure 2). For polyDMAEMA sample D1 (40 % crosslinked), cavities (primary pores) with diameters between 4.7 and 9.3 μm were formed. Very few interconnecting pores can be observed, suggesting the formation of a thicker polymer film between the droplets of water phase. In order to obtain the materials with a more interconnected porous structure, crosslinker content and the amount of surfactant were varied. The average cavity diameter size, together with 6

Journal Pre-proof average diameter of interconnecting pores for all polyDMAEMA samples are recorded in Table 3. As can be seen from the results, the decrease in crosslinker content (from 40 % to 30 %) and increase in surfactant concentration (from 20 % to 25 %) resulted in the decrease in average cavity diameter, which is very likely due to increased emulsion stability. These results show that the surfactant concentration significantly affects the cavity diameters. Furthermore, for samples with the lowest crosslinker content (20 %) and same amount of surfactant concentration (20 %), larger cavity diameters were expected, since the crosslinker content also affects the pore sizes. This expectation was confirmed, as results in Table 3 clearly show that the samples with lower crosslinker content have larger average cavity

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diameter sizes. For polyHEMA polyHIPEs (Figure 3), the same observations regarding

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average cavity diameter sizes can be seen. From Table 3 it can be observed that an increase in crosslinker content resulted in a decrease in average cavity diameter size.

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Nitrogen adsorption/desorption measurements were performed in order to determine

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the specific surface area of prepared polyHIPEs. Results for polyDMAEMA samples with lower crosslinker content resulted in average BET surface area between 2.5 m² g-1 and 7.5 m²

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g-1 . The specific surface area of polyHIPEs is highly dependent on the concentration of the crosslinking agent. Typically, when the crosslinker content is increased, the specific surface area also increases and vice-versa [34]. In the case of sample D1 (40 % crosslinked) the BET

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surface area was 23.4 m² g-1 , which coincides with the expected results. The BET surface area

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for polyHEMA samples are between 2.9 m² g-1 and 10.1 m² g-1 . This, relatively low surface areas are typical for polyHIPEs with the relatively large pore size, while no meso and micro

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pores are present in the dry state of polymer. The BET surface areas for samples are summarized in Table 3.

3.2. Water absorption studies

The water absorption of prepared polyHIPEs was studied by immersing the obtained polyHIPEs in buffer solutions of various pH values (4, 7 and 9). The water uptake of the material was calculated using Equation 1. The water absorption of polyHIPE was fast at the beginning (in first 30 min) and then became slower until the samples reached their absorption equilibrium. The polyHIPEs can absorb large amounts of water when they have high porosity and a hydrophilic surface, thus crosslinking agent EGDMA was used to help to increase the hydrophilic properties of the polyDMAEMA polyHIPEs. For most polyDMAEMA samples, 7

Journal Pre-proof it was observed that the decrease in EGDMA content resulted in the higher water absorption capacity (Figure 4). Higher crosslinked polyHIPEs are more stable and more compact, which resulted in reduced water absorption capacity. However, the decrease in water absorption with increased crosslinking content is not always seen. For e.g. polyDMAEMA sample D1, the water absorption capacity was relatively high in spite of the high concentration of the crosslinking agent. The water absorption capacity depends on a number of factors, such as monomer, co-monomer and crosslinker reactivity, the structure of crosslinker and different porosity due to different composition of reaction mixture. As observed from Figure 4, polyDMAEMA polyHIPEs were able to increase up to 6 times their weight with no apparent

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change in the monoliths volume. In addition, the highest water uptake of prepared

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polyDMAEMA polyHIPEs was observed in the buffer solution with pH 4. This can be due to the fact that amino groups in DMAEMA are protonated when the pH of solution is acidic, and

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the charge repulsion facilitates the water absorption.

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On the other hand, the increase in crosslinker content resulted in lower water absorption capacity for HEMA/MBAA polyHIPEs, as can be seen from Figure 5. The

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HEMA/MBAA polyHIPEs were able to increase up to 9 times their weight with no apparent change in the monoliths volume. In addition, HEMA/MBAA polyHIPEs do not exhibit

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significant changes in water absorption when the pH of solution varies, but an increase in water absorption with increasing the pH of solution was observed, with the highest water

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uptake in buffer solution with pH 9.

In the case of some polyHIPE monoliths prepared previously the water uptake was

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described as the result of the existence of three absorption mechanisms within polyHIPEs [35]. First mechanism is most likely due to the filling of the primary pores (cavities), second is the absorption within the polyHIPE walls through interaction with the hydrophilic polymer and third is the filling of relatively large volume, which is the result of the hydrogel swelling void expansion. In our case, the targeted prevailing mechanism of water absorption for prepared polyHIPEs was the cavity filling, which was successfully achieved, as our prepared polyHIPEs increased their weight with no change in the overall monoliths volume, suggesting that the polyHIPE network structure facilitated first mechanism and partially second.

3.3. Adsorption studies

The wastewater from paper, textile and other industries is often contaminated with different pollutants, mostly heavy metals and synthetic organic dyes, which represents a serious issue 8

Journal Pre-proof in the global ecosystem. Synthetic dyes are usually non-biodegradable and can be toxic, mutagenic and carcinogenic and can accumulate in the living organisms, where they can cause different respiratory issues, allergic reactions, like skin irritations and dermatitis, and other diseases [36-38]. The removal of dyes thus represents a necessity and one of the many available methods for the removal of dyes is adsorption. The behaviour of functional groups present in the adsorbent molecules and in polyHIPEs, is one that plays a major role in the process of dye adsorption from dye solutions with different pH values. pH value can reduce or increase the dye adsorption, which is attributed to changes in the charge of the adsorbent surface with the change in the pH value

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[33,39]. The effect of pH on adsorption of cationic dye methylene blue and anionic dye

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methyl orange was studied at pH 4, 7 and 9 at room temperature and at initial dye concentration of 50 mg L-1 for chosen samples. It is apparent from the Figure 6 and Figure 7a

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that as the pH of the MB dye solution increases, adsorption of MB also increases. In aqueous

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solution, cationic dye MB carries a positive charge due to the presence of amine groups. When the solution becomes alkaline, the deprotonation of amine functional groups in

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DMAEMA polyHIPEs occurs, which results in the elevated electrostatic attraction force between the negatively charged surface and positively charged MB, thereby resulting in an

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increased MB adsorption.

On the other hand, the anionic dye MO carries a negative charge, when dissolved in

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water, due to the presence of sulphonate groups. When the solution pH becomes acidic, the amine functional groups in DMAEMA polyHIPEs get protonated and the elevated

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electrostatic attraction force between the positively charged surface and negatively charged MO resulting in an increased MO adsorption, as can be observed from Figure 7b and Figure 8. When the pH of MO dye solution is increased and solution becomes alkaline, the surface carries a negative charge, there by resulting in a decreased MO adsorption. The second part of experiment was performed for the comparison of the adsorptive removal of dyes between the dry samples and the samples in equilibrium. As can be seen from Figure 9, the equilibrium adsorption values of wet samples are lower than the values of dry samples. This adsorption decrease is due to the lack of active sites, which are already occupied with water molecules. For binding of the dye molecule to the active site, the water molecule must first be excluded, resulting in the slow diffusion of the dye molecule into the polymer chain, thereby the adsorption values are lower.

4.

Conclusions 9

Journal Pre-proof

We have shown that emulsion templating, utilizing both water-in-oil and oil-in-water high internal phase emulsions, can be a good method for the preparation of hydrophilic cellular polymers with an interconnected porous morphology. Both 2-hydroxyethyl methacrylate and dimethylaminoethyl methacrylate were used to prepare monolithic crosslinked material. With a relatively high crosslinking degree, volume stability has been achieved and no volume change after absorption of aqueous solutions occurred, making the materials useful for applications where large volume changes of typical hydrogels are not desired. Adsorption of both cationic (methylene blue) and anionic (methyl orange) dyes from aqueous solutions was

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achieved rapidly with the novel materials.

Acknowledgements

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The financial support of the Slovenian Research Agency by Program No. P2-006 is gratefully

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acknowledged.

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hydroxyethyl methacrylate-based polyHIPEs: Effect of the leaving group. React. Funct. Polym. 109 (2016) 99-103. https://doi.org/10.1016/j.reactfunctpolym.2016.10.008.

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[26] G. Gürdag, S. Cavus, Synthesis and swelling behaviour of poly(2-dimethylaminoethyl methacrylate-co-N-hydroxymethyl acrylamide) hydrogels. Polym. Adv. Technol.17 (2006) 878–883. https://doi.org/10.1002/pat.846. [27] R. Paris, I. Quijada-Garrido, Temperature- and pH-responsive behaviour of poly(2-(2methoxyethoxy)ethyl

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hydrogels.

Europ. Polym. J. 46 (2010) 2156-2163. https://doi.org/10.1016/j.eurpolymj.2010.09.004. [28] J. E. Elliott, M. Macdonald, J. Nie, C. N. Bowman, Structure and swelling of poly(acrylic acid) hydrogels: effect of pH, ionic strength, and dilution on the crosslinked polymer structure. Polymer 45 (2004) 1503-1510. https://doi.org/10.1016/j.polymer.2003.12.040. [29] U. Sevšek, P. Krajnc, Methacrylic acid microcellular highly porous monoliths: Preparation

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functionalization.

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https://doi.org/10.1016/j.reactfunctpolym.2012.02.007.

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Journal Pre-proof [30] S. Huš, P. Krajnc, PolyHIPEs from Methyl methacrylate: Hierarchically structured microcellular polymers with exceptional mechanical properties. Polymer 55 (2014) 44204424. https://doi.org/10.1016/j.polymer.2014.07.007. [31] S. Jerenec, M. Šimić, A. Savnik, A. Podgornik, M. Kolar, M. Turnšek, P. Krajnc, Glycidyl methacrylate and ethylhexyl acrylate based polyHIPE monoliths: Morphological, mechanical and chromatographic properties. React. Funct. Polym. 78 (2014) 32-37. https://doi.org/10.1016/j.reactfunctpolym.2014.02.011. [32] D. Şolpan, M. Şen, Z. Kölge, M. Torun, O. Güven, Adsorption of Some Dyes on Cationic Poly(N,N-Dimethyl Amino Ethylmethacrylate) Hydrogels. Hacettepe J. Biol. &

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Chem. 37 (2009) 233-240.

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[33] A. R. Hernandez-Martínez, J. A. Lujan-Montelongo, C. Silva-Cuevas, J. D. MotaMorales, M. Cortez-Valadez, A. Jesus Ruíz-Baltazar, M. Cruz, J. Herrera-Ordonez, Swelling methylene

adsorption

hydrogel.

React.

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poly(N,N-dimethylacrylamide-co-2-hydroxyethyl

Funct.

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122

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75-84.

e-

methacrylate)

blue

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and

https://doi.org/10.1016/j.reactfunctpolym.2017.11.008.

Polymer

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[34] S. Mane, S. Ponrathnam, N. Chavan, Effect of Chemical Crosslinking on Properties of Review.

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https://doi.org/10.13179/canchemtrans.2015.03.04.0245.

Emulsion

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[35] S. Kovačič, M. S. Silverstein, Superabsorbent, High Porosity, PAMPS-Based Hydrogels Rapid

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[36] J. Z. Yi, L.M. Zhang, Removal of methylene blue dye from aqueous solution by adsorption onto sodium humate/polyacrylamide/clay hybrid hydrogels. Biores. Technol. 99 (2008) 2182-2186. https://doi.org/10.1016/j.biortech.2007.05.028. [37] H. Kasgöz, A. Durmus, Dye removal by a novel hydrogel-clay nanocomposite with enhanced

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https://doi.org/10.1002/pat.1045. [38] H. Kasgöz, New sorbent hydrogels for removal of acidic dyes and metal ions from aqueous solutions. Polym. Bull. 56 (2006) 517-528. https://doi.org/10.1007/s00289-0060515-5. [39] M. T. Yagub, T. K. Sen, S. Afroze, H. M. Ang, Dye and its removal from aqueous solution

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Figure captions

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Scheme 1. PolyHIPE synthesis using water-in-oil high internal phase emulsion.

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Figure 1. FTIR spectra of polyHIPEs a) D1, D4 and D7; b) H1 and H2.

Figure 2. SEM images of polyHIPE samples a) D1, b) D2, c) D3 d) D4, e) D5, f) D6, g) D7

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and h) D8.

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Figure 3. SEM image of polyHIPE samples a) H1, b) H2, c) H3, d) H4 and e) H5.

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crosslinker content.

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Figure 4. Water absorption studies of polyDMAEMA polyHIPE samples as a function of

Figure 5. Water absorption studies of polyHEMA polyHIPE samples as a function of crosslinker content.

Figure 6. Adsorption capacity of MB on the polyHIPEs at different pH: a) D1, b) D2, c) D4, d) D7, e) H2, f) H3 and g) H5.

Figure 7. PolyHIPEs samples after adsorption of a) MB and b) MO.

Figure 8. Adsorption capacity of MO on the polyHIPEs at different pH: a) D1, b) D2, c) D4, d) D7, e) H2, f) H3 and g) H5.

Figure 9. Adsorption capacity of sample D2 in equilibrium for a) MB and b) MO. 14

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Scheme 1.

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Pr

e-

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Schemes and Figures

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Figure 1. 16

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Figure 2. 17

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Figure 3.

18

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Pr

e-

Figure 4.

Figure 5.

19

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Figure 6.

20

Pr

e-

pr

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Figure 7.

21

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Pr

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Figure 8.

22

Figure 9.

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Journal Pre-proof Tables

Table 1. Emulsion composition data for polyDMAEMA polyHIPEs. Crosslinker Sample

a)

content

[g]

[%]

[g]

wt% surfactant

[g]

VH2O c) [mL]

PEL121

40

3.02

-

2.52

20

22.5

D2

30

3.15

0.62

1.99

20

24

D3

30

3.15

0.62

2.01

25

24

D4

20

3.67

0.63

1.34

25

23.5

D5

20

3.02

-

0.96

D6

20

3.69

0.63

1.34

D7

20

2.11

-

1.34

20

24

D8

20

1.83

0.63

1.33

20

24

Mol % in relation to monomers;

b)

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16.5

20

23.5

pr

20

10 wt% based on monomer DMAEMA;

c)

all samples

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have 80 % pore volume.

f

D1

e-

a)

mDMAEMA mEHAb) mEGDMA

Sample

a)

content

a)

VCH b)

[g]

[g]

[mL]

2.22

0.140

5.24

22

2.22

0.402

5.22

22

2.23

0.657

5.25

22

M MBAA

[g]

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[%]

mH2O

mHEMA

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Crosslinker

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Table 2. Emulsion composition data for polyHEMA polyHIPEs.

H1

5

H2

13

H3

20

H4

30

2.27

1.191

5.22

22

H5

40

2.22

1.763

5.24

22

Mol % in relation to monomer;

b)

all samples have 75% pore volume.

24

Journal Pre-proof Table 3. Specific surface area of samples with average cavity diameter size. Crosslinker Sample

content

surface area

diameter size

[m2 g-1 ]

[µm]

Average diameter of interconnecting pores [µm]

40

20

23.4

6.2

**

D2

30

20

6.5

3.9

1.0

D3

30

25

7.5

3.6

0.9

D4

20

25

5.1

4.3

1.1

D5

20

20

2.5

5.0

1.1

D6

20

20

2.9

8.4

1.3

D7

20

20

5.5

5.6

1.3

D8

20

20

3.2

4.5

1.0

H1

5

20

2.9

8.1

2.3

H2

13

20

3.7

5.6

2.1

H3

20

20

4.6

5.1

1.8

H4

30

20

8.2

4.5

2.3

H5

40

20

10.1

4.3

1.4

pr

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** – no interconnecting pores.

f

D1

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[%]

Average cavity

e-

[%]

Surfactant

Specific

25

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Journal Pre-proof Highlights Highly crosslinked macroporous networks of 2-hydroxyethy methacrylate and dimethylaminoethyl methacrylate were prepared using high internal phase emulsions as precursor colloidal templates. Monoliths were able to absorb water filling the cavities of the macroporous network while no overall monolith volume change appeared.

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Materials were able to adsorb methylene blue and methyl orange from aqueous solutions quickly and efficiently.

27