Zewail et al. BMC Chemistry(2024) 18:134
https://doi.org/10.1186/s13065-024-01246-8

BMC Chemistry

RESEARCH

Open Access

Synthesis of sodium alginate / polyvinyl
alcohol / polyethylene glycol semiinterpenetrating hydrogel as a draw agent
for forward osmosis desalination
Taghreed Mohamed Mohamed Zewail1, Menatalla Ashraf Saad1*, Shrouk Medhat AbdelRazik1,
Basma Mohamed Eldakiky2 and Eman Radi Sadik2
Abstract
Typically, hydrogels are described as three-dimensional networks of hydrophilic polymers that are able tocapture a certain mass of water within their structure. Recently, hydrogels have been widely used as drawing
agents in forward osmosis (FO) desalination processes. The major aim of this study is to prepare a novelsemi-interpenetrating hydrogel by crosslinking sodium alginate (SA) and polyvinyl alcohol (PVA) by using theepichlorohydrin (ECH) crosslinker and polyethylene glycol (PEG) interpenetrated within the hydrogel’s network asa linear polymer. Based on the optimum composition of SA/PVA composite hydrogel obtained from our earlier
research, the effect of various percentages of PEG on the response of the hydrogel was investigated. The optimalcomposition of SA/PVA/PEG hydrogel was characterized by scanning electron microscopy (SEM), compression
strength testing, Fourier transform infrared spectroscopy (FTIR), and X-ray diffraction (XRD). The morphological andmechanical properties of the SA/PVA/PEG semi-interpenetrating hydrogel were also compared to those of the SA/
PVA composite hydrogel. Moreover, the performance of the optimal SA/PVA/PEG hydrogel in a FO batch unit as a
drawing agent was investigated based on the optimal operation conditions from our previous experiments. The
results showed that the optimal PEG/polymer blend mass ratio was 0.25, which increased the swelling ratio (SR)(%) of the hydrogel from 645.42 (of the neat SA/PVA hydrogel) to 2683. The SA/PVA/PEG semi-interpenetratinghydrogel was superior to the SA/PVA copolymer hydrogel in pore structure and mechanical properties. Additionally,in terms of FO desalination, the achieved water flux by SA/PVA/PEG hydrogel is higher than that accomplished by
SA/PVA hydrogel.
Keywords Polyethylene glycol, Semi-interpenetrating network hydrogel, Draw agent, Forward osmosis*Correspondence:
Menatalla Ashraf Saadmennat.ashraf@alexu.edu.eg
1
Chemical Engineering Department, Faculty of Engineering, Alexandria
University, Alexandria 21544, Egypt
2
Chemical Engineering Department, Borg Al Arab Higher Institute ofEngineering and Technology, Alexandria 21933, Egypt© The Author(s) 2024. Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use,sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) andthe source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in thisarticle are included in the article’s Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not includedin the article’s Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you willneed to obtain permission directly from the copyright holder. To view a copy of this licence, visit http://creativecommons.org/licenses/by/4.0/. The
Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available
in this article, unless otherwise stated in a credit line to the data.

Zewail et al. BMC Chemistry(2024) 18:134

Introduction
The scarcity of fresh water supplies, which cannot keep
up with the world’s population expansion, has been oneof the most prevalent problems facing human beings inrecent decades. Additionally, climate change, which produces drought in various parts of the world, made a significant contribution to this problem. Thus, by 2025, it isanticipated that nearly 60% of the population will have adrinking water shortage [1].
Nearly 97% of the water on Earth is saline water, whichmakes up the majority of the planet’s water. Desalinationis therefore one of the most commonly used methods
for creating freshwater [2, 3]. Approaches for desalination can be categorized into membrane-based and thermal approaches [4]. Nevertheless, membrane-baseddesalination processes are more energy-efficient thanthermal desalination technologies [5]. However, while
reverse osmosis (RO) is the most well-known membrane
desalination technology, forward osmosis (FO) is a growing desalination method that has been recommended
recently because of its higher water recovery, lower salt
discharge, and lower fouling propensity. In addition, theenergy consumption of seawater desalination by FO alone
without the recovery of the drawing agent is less thanthat of RO because water molecules naturally permeate
without the need for extra pressure [6, 7]. FO, which isconsidered a green desalination technique, transports
the clean water across a semipermeable membrane thatis driven by the osmotic pressure difference between thefeed solution (FS) side and the draw agent (DA) side [8,9]. The serious challenge of this technique is the chooseof an appropriate DA with higher osmotic pressure andeasy to be recovered [10].
There are two main classes of draw agents used in FO
desalination process: organic (e.g., oligomers [11]), inorganic (e.g., ammonium carbonate solution [12]), andfunctionalized nanoparticles (e.g., magnetic nanoparticles [13]). In addition, DAs can be categorized into solidmaterials (e.g., hydrogels [14]) and liquids (e.g., ionicliquids [15]). In recent years, researchers have directed
their efforts toward utilizing hydrogels as DAs for FO

Page 2 of 9desalination [16]. This is owing to the decline of their toxicity levels and reverse solute flux, and their large capacity for water absorption [17]. Hydrogels are 3-D networksof hydrophilic polymeric materials that can be synthetic
or natural [18]. Table 1 illustrates recent types of hydrogels used for FO desalination against distinct concentrations of the FS and their water fluxes.
The expression of semi-interpenetrating hydrogels canbe used when an existing crosslinked network is penetrated with another linear polymer without any chemical reaction. This design is applied in various aspects
because of its improved swelling response and desirable
mechanical properties [19]. Sodium alginate is a green
polymer that is derived from brown algae [20]. When
polyvinyl ester (typically polyvinyl acetate) is hydrolyzed,
long-chain, water-soluble polymer known as polyvinyl
alcohol (PVA) is produced. It combines the benefits ofrubber and plastic while also displaying unique qualities
like affordability, limited toxicity, superior mechanicalbehavior, and remarkable biocompatibility. Because epichlorohydrin functions as a bifunctional molecule towardhydroxyl groups in a basic solution, it was chosen as acrosslinker between SA and PVA, which are both high in
OH groups [21–23]. PEG is a synthetic polymer that has
been extensively studied and is FDA-approved for use inbiotechnology, medication delivery, tissue engineering,
and water treatment. PEG has favorable qualities such ashydrophilicity, superior mechanical characteristics, andadaptability [24–26].
This work aims to prepare a unique semi-interpenetrating hydrogel by the incorporation of PEG linear polymer
in the crosslinked network of SA and PVA, and ECH wasused as a crosslinker. In our prior work [27], we were able
to prepare the novel SA/PVA composite hydrogel andapply it as a DA in the FO desalination process. In thepresent study, we wanted to improve the water uptake
and mechanical performance of the former hydrogel byincorporating PEG to form a cutting-edge SA/PVA/PEG
semi-interpenetrating hydrogel and apply it for the firsttime as a DA in the same FO unit. Depending on the optimum composition of the SA/PVA copolymer hydrogel,

Table 1 Recent synthesized hydrogels as draw agents for forward osmosis desalination
Hydrogel
Bioartificial (Sodium alginate/polyvinyl alcohol) hydrogel
Green (Sodium alginate/flaxseed gum/polyethylene glycol) hydrogel
Thermo-responsive (deep eutectic mixture-co-N-isopropylacrylamide) hydrogel
Electro-responsive (poly(2-acrylamido-2-methyl-l-propanesulfonic acid-co-acrylamide)/
polyelectrolyte polyacrylic acid) hydrogel(polyvinyl alcohol-poly (diallyldimethylammonium chloride) hydrogel
Thermo-responsive (N-isopropylacrylamide/sewage sludge ash) hydrogel
Thermo-responsive (N-isopropylacrylamide/sewage sludge ash) hydrogel
Dual CO2 and thermo-responsive poly(N, N-dimethylallylamine) hydrogel

Feed solution
Distilled waterDistilled water
DI water
2000ppm NaCl
2 g/L NaCl

JW (LMH)0.845 (1 h)1.27 (1 h)2.38 (initial)
1.81 (initial)
2.2 (Initial)

Reference
[27]
[28]
[29]

5000 ppm NaCl
2000 ppm NaCl
DI water
1.75% NaCl

0.87 (average 6 h)
2.22(average24h)
2.33(average24h)
44 (initial)

[23]
[31]
[32]
[33]

[30]

Zewail et al. BMC Chemistry(2024) 18:134

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PVA content, and the crosslinking dose obtained fromour earlier work, the influence of various percentages of
PEG on the response of the hydrogel was investigated.
The morphological and mechanical characteristics of SA/
PVA/PEG semi-interpenetrating hydrogel were also compared to that of SA/PVA copolymer hydrogel. Moreover,the performance of the optimal SA/PVA/PEG hydrogel
as a DA in a FO batch unit was investigated dependingon the optimal operation conditions from our previous
experiments of average hydrogel particle size and feedsolution temperature.

minor variations in PEG levels, together with maintaining a constant 8% total polymer concentration (SAand PVA) for all generated samples, is imperative. Ninehours of 75 °C curing was applied to the three produced
samples. The samples of the cured hydrogel were repeatedly cleaned with heated distilled water at 60 °C until thepH approached 7. Following that, more acetone washing
was performed on the samples in order to get rid of any
remaining unreacted ECH. Lastly, to achieve a consistent
dry weight, the cleaned samples were placed in a drying
chamber set at 50 °C.

Materials and methods

Characterizations of the hydrogel

Materials

One of the most essential factors for evaluating hydrogelsis the swelling ratio (SR). In distilled water, 0.1 g of eachsample with different PEG concentration was immersed.
The weight of the swollen hydrogel was measured after 1
and 24 h to determine the optimal hydrogel’s composition, which would be further characterized. A hydrogel’s
swelling ratio (SR) is described as follows:

All the utilized materials, their specifications, and their
suppliers are defined in Table 2. All of these materials were used as they were supplied, with no further
purification.
Synthesis of the hydrogel

Depending on our earlier study, the optimal PVA content
in the crosslinked polymer blend was 25%, and the optimum ECH/total crosslinked polymer blend mass ratio
was 0.8 [27]. Thus, our present experiment was carriedout as follows:
There was a solution of sodium hydroxide (8%). It wasthen mixed with a certain amount of SA. A specified
amount of PVA was dissolved in 90 °C-heated distilledwater in the meantime. Next, a homogeneous blend isachieved by combining the two solutions. To make PEG
solution, distilled water is mixed with a specific mass of
PEG dissolved. Afterwards, the SA and PVA polymer
solution was ready, and the produced PEG solution wasadded. The combination was then mechanically mixed
for fifteen minutes. In order to produce a homogenous
paste, ECH crosslinker was next added dropwise while
being continuously stirred mechanically. For the purpose of creating three samples, the above procedures
were repeated using distinct PEG/total crosslinked polymer blend mass ratios of 0, 0.05, and 0.25. Maintaining
the ideal composition, as previously noted, with only

SR = (Ws − Wd) / Wd (1)Where Wd is the weight of the dry hydrogel, and Ws is theweight of the hydrogel after swelling at a room temperature [27].
Jeol (JSM-IT200, Japan) electron scanning microscopy was used to determine the surface morphology ofthe optimal swollen hydrogel. After one hour of swelling,
the swelled SA/PVA/PEG hydrogel sample was immediately freeze-dried under vacuum at -42 °C for three days
to ensure that all absorbed water was removed. This dry
sample was coated with gold for scanning.
Using the MultiTest-5xt (USA), the compressive
strength of the optimal swollen hydrogel was tested atvarious distances. The sample was formed into a cylindrical shape. After that, it was submerged in distilled water
for an hour. The swollen cylinders had the dimensions
represented in Table 3. At 25 °C, the swelled samples
were inserted for the compression test.

Table 2 All chemicals used in the experiments, their purity and suppliers
Material
Sodium alginate (SA)Polyvinyl alcohol (PVA)
Polyethylene glycol (PEG)
Sodium hydroxide
Epichlorohydrin (ECH)
AcetoneCellulose triacetate (CTA) membrane

Specifications
Purity (96.6%)
Degree of polymerization (1700–1800
Purity (98.99%)
Purity (99%)
Purity (92%)
Purity (99%)
Average pore diameter (1.21 nm)
Porosity (36%)
Tensile strength (33.5 MPa)
Elongation (43.8%)

Supplier
OXFORD LAB FINE CHEM LLP (India)
LOBA CHEME (India)
Sigma Aldrich (USA)
Alahram company (Egypt)
LOBA Cheme (India)
ADWIC (Egypt)
The national research center (Cairo, Egypt)

Zewail et al. BMC Chemistry(2024) 18:134

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Table 3 Dimensions of the swollen hydrogels’ samples formed
in a cylindrical shape for compressive strength test
Hydrogel
SA/PVA
SA/PVA/PEG

Surface area (cm2)
15.89
7.07

Length (cm)22

Fig. 1 Effect of PEG incorporation on the swelling response of the hydrogel in one hour (at the optimum PVA content in the crosslinked polymer
blend of 25% and ECH/crosslinked polymer blend mass ratio of 0.8)

Wide angle X-ray diffraction profiles of SA, PVA, PEG,
and the optimum SA/PVA/PEG dry hydrogel powders
were determined at room temperature with a X—ray
powder diffractometer -XRD-D2 phaser (BRUKER, GERMANY). The 2θ range for the samples was 10–100◦.
Fourier transform infrared spectroscopy (Bruker Tensor 37, Germany) was utilized for the confirmation of thechemical composition of the liquid ECH and the solid
SA, PVA, PEG, and the optimal SA/PVA/PEG dry hydrogel powders.
Forward osmosis set-up

The optimized and characterized dry SA/PVA/PEG
hydrogel was applied as a draw agent in a FO unit basedon previously determined optimal operating conditionsof average hydrogel particle size at 60 μm, FS temperature at 40 °C. The complete FO set-up was described indetails in our earlier work [27]. The achieved water flux
was calculated by Eq. (2).

Jw = (Ws ?Wd) / ρ wAt (2)Where Jw is the accomplished water flux; ws and wd are
the weight of the swollen hydrogel and the dried sample
respectively; ρw is the water density; A is the membrane’s
surface area and t is the time of each run [34].

Results and discussions
Hydrogel’s characterizations
Swelling measurements

The osmotic pressure brought on by the ionic groupdissociation and the solvation force produced by thehydrogen bonding that connects the hydrogel’s network
and water are what cause the polymer hydrogel to swell[23]. Figure 1 shows how the PEG incorporation impacts
the swelling response of the hydrogel in an hour at the
optimum PVA content and ECH dose. It is clear that
there is a significant upgrade of SR (%) by raising thecontent of PEG. By upgrading the PEG/total crosslinked
polymer blend mass ratio from 0 to 0.25, the swelling
ratio (%) approximately increased to four times its value.
Two primary reasons can be used to explain theseresults: First off, the semi-interpenetrating networkhydrogel’s structure encourages the hydrogel’s reaction towater absorption. This is carried out by enhancing water
channeling within the crosslinked network [35]. The
hydrophilicity of PEG, which is abundant in hydrophilicgroups like O group or hydroxyl terminal group, is thesecond factor. These groups can create hydrogen bonds
with water molecules, which improve the absorption ofwater [36]. There is concordance between the present
trend and the preceding study [37]. It should go without
saying that the optimal PEG/crosslinked polymer blend
mass ratio is 0.25.
SEM

The porosity affects the hydrogel’s capacity to absorb
water. Therefore, the morphology of the hydrogel microstructure is a crucial aspect [38]. Figure 2 depicts two separate images of the surface morphology of the optimum
SA/PVA/PEG and the plain SA/PVA swollen hydrogels.
Both hydrogels were examined under the same optimal
PVA content and crosslinking ratio, which are mentioned
above. This is done to investigate how the PEG interpenetration affects the hydrogel’s pore structure. After
swelling, the hydrogel was freeze-dried, revealing poresthat were originally filled with water molecules [39]. The
average pore sizes of the swollen SA/PVA and SA/PVA/PEG hydrogels were 33.48 μm and 37.09 μm, respectively.
It is quite astounding how the PEG’s presence enhances
the hydrogel’s pore structure due to its hydrophilicity.
In addition, the bulk of the hydrogel’s spherical poresare connected to one another to create an open channel
system that serves as a capillary system to quickly absorb
and expel water. This is because of the interpenetrationof PEG as a linear polymer without any chemical reaction, which enhances capillary system creation. There isconcordance between the recent trend and an older study[37].
Compressive strength test

In order to illustrate how adding PEG affects the hydrogel’s mechanical strength, the neat SA/PVA and optimal SA/PVA/PEG swollen hydrogels were conducted tocompression strength measurements. The samples wereprepared at the same PVA content and crosslinker dose.

Zewail et al. BMC Chemistry(2024) 18:134

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Fig. 2 SEM (at 200× magnification) of (a) SA/PVA and (b) SA/PVA/PEG hydrogels

Table 4 The compressive strength at 50% strain and theelasticity modulus of SA/PVA and SA/PVA/PEG hydrogels

Fig. 3 Representation of the results of the compressive strength test of
SA/PVA and SA/PVA/PEG hydrogels (at 50% strain and 25 °C)

Typically, a compression strength test is required todetermine the hydrogel’s mechanical stability by regeneration through squeezing or even another way. Actually,
a separate, postponed investigation may be carried out
for the examination of regeneration process. The resultsof the compression strength test of the SA/PVA and SA/
PVA/PEG hydrogels are shown in Fig. 3. When bothhydrogels were compressed to their half-length, the swollen neat hydrogel could withstand a compressive strengthof 20.67 KN/m2, while the optimal swollen SA/PVA/PEG
hydrogel could tolerate a compressive strength of 31.7
KN/m2.
These findings demonstrate the PEG addition’s beneficial impact on the hydrogel’s mechanical strength. This is
the result of three main factors. First of all, the design ofsemi-interpenetrating networks or even interpenetrating
networks promotes mechanical properties when compared to the basic copolymer hydrogels [35, 40]. Secondly, PEG is highly regarded in many applications due toits exceptional mechanical strength [25, 41]. Thirdly andfinally, with higher PEG dosages, physical entanglement

HydrogelCompressive strength (KN/m2)

SA/PVA
SA/PVA/PEG

20.67
31.7

Modulus ofelasticity (KN/
m2)
12.19
22.28

and hydrogen bonding effects became more evident andserved as physical crosslinking points between PEG andthe polymer blend of SA and PVA. This, subsequently,
requires higher compressive strength [42].
Table 4 displays the elastic modulus and compressive
strength of SA/PVA and SA/PVA/PEG swollen hydrogels
at a 50% strain. The term “elasticity” refers to a material’s ability to revert to its original shape and dimensions
after a load is removed. It is therefore a very significant
mechanical property to analyze because a hydrogel built
from a polymer network uses the concept of initiallydeveloped rubber elasticity [43]. The swollen SA/PVA/PEG hydrogel had an elasticity modulus that was higher
than that of the SA/PVA hydrogel. This demonstrates
how using PEG improved the hydrogel’s elasticity. Actually, our findings are consistent with earlier research thatlooked at how PEG incorporation affected the hydrogel’s
mechanical properties. In order to study how the PEG
dose affects the mechanical properties of the hydrogel,
Chan et al. synthesized a strong and semi-interpenetrating hydrogel from polyethylene glycol and collagen.
They discovered that the upgrade of PEG concentration improved the hydrogel’s elasticity and compressive
strength at 50% strain [25].
FTIR

Figure 4 shows the IR spectra of SA, PVA, ECH, PEG,
and SA/PVA/PEG hydrogel. The IR spectra of SA, PVA,
and ECH were clearly described in our previous workZewail et al. BMC Chemistry(2024) 18:134

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Fig. 4 FTIR spectrum of SA, PVA, PEG, ECH, and SA/PVA/PEG[27]. For the IR spectrum of PEG, a terminal grouphydroxyl is represented by the broad absorption peak at
3431.33 cm− 1. The peak at 2883.56 cm− 1 is associatedwith CH-stretching, while the peak at 1105.93 cm− 1 isconnected to C-O stretching [44].
Regarding the IR spectrum of SA/PVA/PEG hydrogel,there are three main points that confirm the crosslinking reaction between SA and PVA using ECH. Firstly, thepeaks corresponding to -OH stretching in SA and PVA
are shifted to 3439.05 cm− 1. Secondly, the peak associated with acetal group stretching vanished, possibly asa result of the hydrolysis side reaction during the crosslinking reaction. Finally, the epoxide functionalities of
epichlorohydrin, which are characterized by vibrations at
962 and 925 cm− 1, are no longer present. On the other
hand, the peak at 1099.41 ensures the interpenetration of
the PEG polymer chain within the network of the hydrogel without any contribution to the crosslinking reaction.
XRD

Figure 5 shows the XRD of SA, PVA, PEG, and the optimal SA/PVA/PEG hydrogel. The XRD spectra of SA andPVA were well explained in our previous study [27]. PEG
has been found to have a main XRD peak at 2Ɵ = 19°
and 23° and other minor peaks at 26°, 36°, 39.7°, and 45°
degrees, which is in agreement with findings from a priorstudy [45].
The SA/PVA/PEG hydrogel blend’s XRD pattern lacks
any distinct peaks and exhibits a broad diffraction at 2Ɵ= 20°, which suggests an amorphous structure. The sharp
and weak peaks associated with PVA and SA, respectively, have vanished, which supports the existence ofcrosslinks between these two substances. On the other
hand, PEG is present as a linear polymer and does notinteract chemically with SA and PVA, according to thehydrogel’s XRD, which nonetheless clearly shows thestrong peaks at 2Ɵ = 19.31° and 23.32° that correspondto PEG.

Fig. 5 XRD spectrums of (a) SA, (b) PVA, (c) PEG, and (d) optimal SA/PVA/PEG hydrogel

FO experiments

Depending on our previous study, the optimal FO operating conditions were adjusting the membrane orientation
at the PRO mode (active layer facing the DA), the averagehydrogel’s particle size of 60 μm, and the feed solution
temperature at 40 °C. We used those optimum conditions
in our current work to study the impact of PEG incorporation on the FO performance.

Zewail et al. BMC Chemistry(2024) 18:134

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Water flux

Figure 6 represents how distinct feed solution concentrations influence the achieved water flux by SA/PVA/PEG hydrogel as DA. In addition, this figure shows a brief
comparison between the performance of SA/PVA and
SA/PVA/PEG hydrogels as DAs in FO desalination under
the same mentioned operating conditions.
It is clear that the water flux decreases from 0.876 to
0.199 LMH as the FS concentration rises from zero to1000 ppm. The current trend can be related to the factthat as FS’s ionic strength rises, the osmotic pressure
driving force between FS and the hydrogel declines,
which leads to a decreased water flux. The current findings are consistent with earlier research [37, 46], andalso with our previous study on the SA/PVA copolymerhydrogel.
Moreover, it is obvious that the behavior of SA/PVA/PEG hydrogel was superior to that of SA/PVA neathydrogel, which consequently proves the positive impact
of PEG interpenetration on the water flux. This is due tothe enhanced pore structure of the SA/PVA/PEG hydrogel and the hydrophilicity of the PEG polymer [35, 36].
Both reasons consequently improve the hydrogel’s capability to hold the fresh water and hence the achieved
water flux.
Table 5 shows the FO performance of different semiinterpenetrating hydrogels as DAs in the FO desalination process that has been investigated in the previous
studies. In addition, the behavior of the SA/PVA bioartificial hydrogel as a DA in the FO unit at different FS’s
concentrations is also represented. Thermo-responsive
semi-interpenetrating hydrogels have been shown to beeffective as DAs in the FO desalination process by Cai
et al. They produced heat-sensitive semi-IPN hydrogels
by polymerizing MIPAM with poly(sodium acrylate)(PSA) or polyvinyl alcohol (PVA). Noteworthy is the factthat the FO procedure documented in this study started
with hydrogels that were partially swelled and had beenFig. 6 The achieved water flux by SA/PVA and the optimal SA/PVA/PEG
hydrogels at different FS concentrations in 1 h (at average hydrogel’s particle size of 60 μm and the FS temperature at 40 °C)

pre-conditioned at 40 °C. It is obvious from Table 5 thatour present hydrogel outperforms the behavior of theprevious semi-IPN hydrogels and also the composite SA/
PVA hydrogel that was prepared and applied under thesame conditions. The reasons behind that are explainedin the preceding paragraph.
Reverse solute flux

Due to the concentration gradient across the membrane,reverse solute flux (RSF), which has a detrimental impact
on the driving force in the FO process, is defined as thesolute diffusion from the draw solution side to the feedsolution side [47]. Since there is no concentration gradient in the current work’s use of a hydrogel as a draw
agent—a solid material with a high-water absorption
capacity—reverse solute flux is minimal in this study [48].
Measurements of the conductivity of the distilled waterused as the FS in the FO experiments were used to establish the RSF’s negligible value. When compared to otherfeed solutions with higher concentrations, distilled waterprovides the strongest driving force, hence conductivity
tests of this solution typically provide the most accurate

Table 5 FO performance of the present work and earlier studies
HydrogelPartially swollen (PNIPAm-IPN-PSA) (0.8 M-0.2 M)
Partially swollen (PNIPAm-IPN-PVA) (0.8 M-0.2 M)
Partially swollen (PNIPAm-IPN-PVA) (0.5 M-0.5 M)
SA/PVA

Membrane
CTA

FS
2000 ppm NaCl solution

CTA

SA/PVA/PEG (present work)

CTA

Distilled water
250 ppm NaCl solution
500 ppm NaCl solution
750 ppm NaCl solution
1000 ppm NaCl solution
Distilled water
250 ppm NaCl solution
500 ppm NaCl solution
750 ppm NaCl solution
1000 ppm NaCl solution

Water flux (LMH)
0.18 (1 h)0.12 (1 h)
0.18 (1 h)0.845 (1 h)0.399 (1 h)0.359 (1 h)0.279 (1 h)0.129 (1 h)0.876 (1 h)
0.541 (1 h)0.406 (1 h)0.374 (1 h)
0.199 (1 h)Reference
[16]

[27]

Zewail et al. BMC Chemistry(2024) 18:134

indicator of RSF. The distilled water’s conductivity wasmeasured to be 0.01 S/cm both before and after the FOrun, indicating that no RSF was achieved. These findings
are in consistency with our previous work [27, 28].

Conclusion
We prepared a semi-interpenetrating SA/PVA/PEG
hydrogel from a crosslinked blend of SA and PVA using
ECH, and PEG was interpenetrated within the hydrogel’s
network as a linear polymer. The produced hydrogel wascharacterized using swelling measurements, SEM, compressive strength tests, FTIR, and XRD. The characterized and optimized hydrogel was applied as a draw agent
in the FO desalination cell. Moreover, the performanceof the currently prepared hydrogel was compared to thatof the previously prepared SA/PVA copolymer hydrogel.
Our conclusions were that by increasing the PEG content
in the hydrogel, the swelling response of the hydrogel
would be enhanced, and SA/PVA/PEG semi-interpenetrating hydrogel was superior to SA/PVA hydrogel in thepore structure and compressive strength. In addition, in
the FO desalination cell, the SA/PVA/PEG semi-interpenetrating hydrogel achieved a greater water flux thanthe SA/PVA copolymer hydrogel. Besides, upgrading the
FS concentration had a negative impact on water flux,
and reverse solute flux was negligible.
Acknowledgements
All authors are thankful for Alexandria University.
Author contributions
Taghreed Mohamed Mohamed Zewail, Supervisor of the research point, main
contributor in results analysis and writing - Original Draft, Writing - Review& Editing, Menatalla Ashraf Saad, Characterizations and writing - Original
Draft, Writing - Review & Editing, Shrouk Medhat AbdelRazik, Preparation,
Application, writing - Original Draft, Writing - Review & Editing, Eman Radi
Sadik & Basma Mohamed Eldakiky, writing - Original Draft, Writing - Review &Editing. All authors read and approved the final manuscript.
Funding
Open access funding provided by faculty of engineering, Alexandria
University.
Open access funding provided by The Science, Technology & Innovation
Funding Authority (STDF) in cooperation with The Egyptian Knowledge Bank
(EKB).
Data availability
No datasets were generated or analysed during the current study.

Declarations
Ethics approval
Not applicable.
Consent to participate
Not applicable.
Consent for publication
Not applicable.
Competing interests
The authors declare no competing interests.

Page 8 of 9

Received: 12 December 2023 / Accepted: 11 July 2024

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