Eco-friendly polyester hydrogel from almond gum/citric acid/ PVA for efficient removal of grenoble green dye

Abstract

Hydrogels are 3D cross-linked networks that imbibe huge quantity of fluids without indissoluble. This peculiar property is due to its unique structural characteristics, which allows solutes to diffuse into the interior network of the hydrogels. The present investigation illustrates the synthesis of sustainable, superabsorbent hydrogels employing green monomers such as Almond gum, Citric acid and PVA, in an intuitive and economical manner. The synthesized hydrogels were characterized via FT-IR, XRD and SEM analysis. The results were corroborated by swelling behavior of hydrogel with respect to surface morphology. The percentage of swelling equilibrium at various pH levels, spanning from acidic to basic, has also been examined. The hydrogels reveals a rationalized swelling in basic medium over acidic medium. The bio-degradation of the sample could be attributed to the breakdown of ester linkage and hydrophilic pendant functionality found in hydrogel and it is strongly endorsed by the antibacterial investigations using gram positive and Gram negative pathogens. Grenoble green (Malachite green) was chosen as a cationic dye for removal from environmental sources via pH-sensitive bio-polymeric almond gum crosslinked with PVA and citric acid (APC) hydrogels. The results of dye removal demonstrated that APC hydrogels have an excellent dye removal efficiency. The impact of the hydrogel’s monomer composition on biodegradability, swelling and dye removal has also been critically examined. Consequently, the synthesized pH sensitive bio-polymeric hydrogels have a wider potential opening in diverse environmental and agricultural applications.

Keywords

almond gum swelling pH sensitive hydrogels dye removal

Introduction

Hydrogels are the most unusual sort of three-dimensional polymeric network, with high hydrophilic characteristics that allow them to retain massive amounts of aqueous solution or biological fluid. Polar groups such as -OH, -COOH, -NH₂, -CONH₂, and -SO₃H inside the polymer backbone offer hydrophilicity to hydrogel, whereas three-dimensional networks formed by chemical or physical cross-linking are responsible for its insoluble nature. As a result, hydrogels absorb more than 100 times their weight in water, pH solutions, and biological fluids; this aberrant behavior is known as swelling.^1,2

Hydrogels utilized for a variety of purposes, including drug delivery, enzyme immobilization, water treatment, infant diapers, agricultural, water-blocking tapes, and so on.^3–9 The physicochemical properties of smart hydrogels have demonstrated a notable responsiveness to slight variations in external stimuli, including temperature, pH, solvent composition, light, magnetic fields, and ionic strength, etc. pH-sensitive hydrogels absorb or release protons with respect to pH change,^10–12 which have many advantages including biocompatibility, high sensitivity, smart packaging, targeted and controlled drug delivery.^13–15

Numerous studies have been undertaken on the synthesis of hydrogels utilizing monomers derived from renewable resources that are suitable for antibacterial characteristics and pH sensitivity, prompting researchers to opt for natural and nontoxic monomers.^2,16,17 Natural biopolymers have been widely used in recent years to build intelligent hydrogels due to their outstanding attributes such as non-toxicity, chemical modification capability, biodegradability, and renewability. Natural polysaccharides have various noteworthy features and a great deal of study has been done on them in order to produce hydrogels.¹⁸

One of the natural polymers that emerge from the almond’s tree trunk is almond gum. This natural polysaccharide is nearly colourless (pale yellow to white), odourless, and non-toxic; it can be utilized as an additive in a variety of food systems due to its protein (2.45%), lipid (0.85%), and carbohydrate (92.36%) content. Almond gum is a heteropolysaccharide composed of uronic acid (5.97%), galactose (35.49%), and arabinose (41.83%), with trace amounts of glucose, mannose, and rhamnose. Numerous minerals, including potassium, magnesium, calcium, and iron, are rich in gum exudate. It possesses hydroxide-hydrogen bonding properties, hydrophilicity, and biocompatibility.^19–21

Almond gum possess significant features such as dietary fiber sources, thickeners, stabilizers, emulsifiers, suspending agents, adhesives and food reinforcement.²¹ Furthermore, the food Coatings,^22–24 cosmetic, and pharmaceutical industries can employ it because of its high tensile strength and low toxicity.²⁵ It is a superior emulsifier to Arabic gum and an established source of antioxidants and antimicrobials that can improve the biological and functional qualities of a variety of food formulations.^26,27 Almond gum based hydrogels are highly recommended for food^16,28 and biomedical applications.²⁹

Therefore, the goal of this research is to develop environmentally friendly and biodegradable hydrogel employing AG-CA and PVA with water as a solvent, in order to combat the usage of toxic chemicals. A multipurpose, affordable, and renewable resource-based monomer is citric acid (CA). Furthermore, it is a reactive functional monomer with a wide range of applications that can support hydrogen bonding interactions in a polyester network.^30–32 Citric acid is a non-toxic, gelling agent which is employed as a monomer as well as green cross-linker, it enhances homogeneous solution formation of Almond gum. PVA is a biodegradable film forming, synthetic polymer material that enhances the strength of hydrogel material by extensive crosslinking. PVA is less soluble in cold water and more soluble in hot water.³³

Water contamination is brought about by the dumping of dyes in waste water from textile, culinary, plastic, rubber, and pharmaceutical sectors. To combat the inadequacies of traditional approaches, removal studies often employ membrane extraction, coagulation, complexing, solvent extraction, ion-exchange and adsorption. Adsorption and ion exchange with polymeric materials and synthetic resins are commonly used in wastewater treatment to remove dyes from chemical operations.³⁴ Hydrogels, with ionic functional groups have gained interest for their ability to adsorb metal ions and dyes from waste water. Employing cost-effective and biodegradable adsorbents in environmentally conscious approaches may assist to mitigate the environmental impact of textile effluents. The hydrogel’s anionic backbone facilitates cationic dye diffusion in the interior network.³⁵

Grenoble green dye (Malachite green dye) is a dark green and crystalline solid. It is extremely harmful to a variety of aquatic and terrestrial creatures and persistent in the environment. It poses a risk to the ecosystem and major health risks to the general populace. The experimental evidence indicates that malachite green is a toxin that affects multiple organs.³⁶ The hazards of malachite green, as its impact on the immune and reproductive systems as well as its genotoxic and carcinogenic characteristics, have made it a highly contentious substance.³⁷ Due to its affordability, accessibility, and effectiveness, this dye is still used in many parts of the world even though it has been outlawed in a number of nations and has not received approval from the US Food and Drug Administration.³⁸ It is utilized in the cotton, paper, jute, leather, silk, and wool industries as a dye and as an anthelminthic and medicinal disinfectant.

Green Chemistry strives to replace harmful materials with greener alternatives, Utilizing a low-cost, biodegradable adsorbent. Thus, the present finding indicates the formation of biodegradable almond gum based hydrogel, using cost-effective, biocompatible monomers with simple methodology. Synthesized hydrogels are to be characterized by various spectral techniques like FTIR, SEM, X-ray Diffraction analysis. Furthermore, the hydrogels are to be studied for their anti-bacterial investigation using gram positive and gram negative bacteria followed by biodegradation studies using soil burial method. A token of environmental applications, removal of malachite green in varying compositions of both hydrogels and pH solutions (pH 4 to 11) is carried out with various compositions of hydrogels in this present investigation.

Experimental

Materials

Almond gum (AG) procured from the nearby market; Citric acid (CA) of reagent grade was purchased from Avra chemicals, Hyderabad (India). Polyvinyl Alcohol (PVA) were purchased from Merck (India) and Ethanol from Alfa Aesar, Chennai. Malachite green oxalate (C₅₂H₅₄N₄O₁₂) from Isochem, kochi. Distilled water was used during the synthesis. Almond gum only purified prior to use, other chemicals are used as such.

Purification of almond gum

To get rid of moisture and impurities, almond gum has been rinsed twice with distilled water followed by scorching in an oven for 2 hours.²⁶ After that, it was ground into a fine powder with a Butterfly Arrow 500W blender, sifted to produce a uniformly fine powder, and then it is immersed in distilled water followed by heating to form a thick viscous liquid. Then it became precipitated by utilizing cold ethanol. Ethanol solubilizes the polysaccharides in almond gum, departing the other contaminants intact. The ensuing white precipitate was dried at 60°C, and the purified almond gum was collected and stored.²

Methodology

The hydrogels were synthesized by blending AG, CA and PVA utilizing water as a solvent. It encompasses a straightforward process: 0.5 g of CA was dissolved in 20 ml of distilled water to generate a citric acid solution to this 0.5 g of AG was infused, while being continuously stirred at 200 rpm along with heating at 100°C for 30 min, engender a milky white viscous solution. The aforementioned solution is poured into the PVA solution (0.5 g of PVA in 10 ml of boiling water) and stirred for 45 min at 200 rpm at 90°C, concoct a homogeneous white solution. It is then poured into a petri dish and then heated for 2-3 h at 100°C in oven. After cooling, the films were gently taken off from the petri plates. The general mechanism for the hydrogel formation is represented in Figure 1. Table 1 represents TEA analysis and Table 2 provided a description of the AG, CA, and PVA based hydrogels.

Table 1.

TEA analysis.

S.No.	Monomers	Cost per 500g (in rupees)
1.	Citric acid	350
2.	Almond gum	400
3.	PVA	1500
Average cost required for the production of per gram of APC hydrogel = 90-100

Table 2.

Description and formulation of almond gum-based hydrogel series.

S.No.	Sample	Composition(g)			Observation	Solubility
S.No.	Sample	AG	CA	PVA	Observation	Solubility
1	APC	0.5	0.5	0.5	Pure white film	INSOLUBLE IN WATER AND ORGANIC SOLVENTS
2	A1PC	1	0.5	0.5	Pure white film
3	A2PC	1.5	0.5	0.5	Pure white film
4	A3PC	2	0.5	0.5	Pure white film
5	APC1	0.5	1	0.5	Colourless transparent film
6	APC2	0.5	1.5	0.5	Colourless transparent film
7	APC3	0.5	2	0.5	Colourless transparent film
8	AP1C	0.5	0.5	1	Colourless film
9	AP2C	0.5	0.5	1.5	Colourless film
10	AP3C	0.5	0.5	2	Colourless film

Characterization techniques

Fourier transform infrared spectral studies (FT-IR)

FT-IR spectrum of completely dried APC Hydrogel was recorded with a Shimatzu FT-IR-8400 S, spectrometer of scan range wavelength 4000-400 cm^-1.

X-ray diffraction studies

X-ray diffraction analysis of samples was performed using X-ray diffractometer (Burker D8 Advance, analytical X Pert3) operated using 2.2 KW cu-anode source, with silicon strip detector technology. The scanning range for 2θ values was set from 10° to 80° to cover all significant diffraction peaks of sample crystallites.

Swelling studies

Swelling behavior of APC based hydrogels have been carried out at room temperature in buffer solutions with varying pH values (2.0–11.0). The dried hydrogels were submerged in the swelling medium. At regular intervals (0.5 h), swollen hydrogels were taken out of the swelling medium, cleaned with filter paper, weighed, and then put back in the same bath. Equation (1) used to calculate the swelling equilibrium (S_eq %) of the hydrogels.

S_{e q} % = \frac{W_{e q} - W_{d}}{W_{d}} \times 100

(1)

W_eq – Weight of hydrogel at equilibrium state.

W_d – Weight of dried hydrogel.

APC hydrogel’s swelling S_eq % values were significantly impacted by variations in the swelling medium’s pH. The swelling behavior of hydrogels were gradually increases with time and reaches constant value at 2 h after 21 h the swelling of hydrogel again increases gradually and attain equilibrium at the 24^th hour afterwards there is no increase in the swelling behavior. This is owing to the gradual opening of vacant sites.

Scanning electron microscopy (SEM)

SEM analysis was carried out with a 3276 pulse density using Bruker Nano GmbH. The hydrogels underwent vacuum exposure for gold sputtering before being used. The hydrogel film has excellent resolution and has flower-like form. The scanning electron microscopy (SEM) method is widely used to verify the size, shape, surface morphology, and porous nature of materials. Using double-sided sticky tape, the APC hydrogel films were attached to aluminum stubs and then it is gold sputtered. An acceleration potential of 30 kV was used during analysis.

Antibacterial studies

The hydrogel’s antimicrobial activity was assessed using a well-diffusion method (Standards Institute Clinical Laboratory (CLSI) 2006; Pobiega et al., 2019). The bacterial strain was cultured for 24 h at 37°C on nutrient agar. The culture inoculum were made in a sterile saline (0.85% NaCl) (w/v) solution in an amount equal to 0.5 McFarland (∼1 × 108 cfu/mL). Mueller-Hinton agar (MHA) plates were sprayed with the test pathogen. The samples were sterilized in ethanol for 10 min, air dried under sterile condition and place over the agar medium. A well of diameter 6 mm was made using a sterile cork borer and loaded with required concentrations of standard antibacterial drug (Ciprofloxacin) into the well. The test plate was incubated for 24 h at 37°C. The zone of inhibition (mm in diameter) were read and taken as the activity against the test pathogens.

Biodegradation studies (soil burial method)

The biodegradability of hydrogels based on almond gum was evaluated by means of inhumation method. One special benefit of biodegradable hydrogels is that they break down naturally, eliminating the pollution after usage. The biodegradability test was conducted in soil under normal circumstances. The hydrogel of about 0.1 g by weight was submerged 30 cm below the surface. Every 7 days the sample was taken out of the ground. After being cleaned with distilled water, the sample was dried at 90°C in oven; hydrogel’s coherent weight is noticed. Equation (2) was used to determine the deterioration percentage.

Biodegradation (%) = \frac{W_{f} - W_{i}}{W_{i}} \times 100

(2)

Where, W_i - initial weight of the hydrogel, W_f - final weight after 7 days of soil burial.

Abolition of malachite green dye by utilizing APC bio-polymeric hydrogels

The Grenoble green (MGO) dye solution was removed by employing Bio-polymeric APC-based hydrogels via batch adsorption process. MGO dye solutions were generated at varying concentrations ranging from 10 to 100 ppm using stock solutions (1000 mg/L). 0.1 g of hydrogel sample was immersed in 25 mLof aqueous dye solution (100 mg/L). The aforementioned contents are swirled at 200 rpm for 2 h. Then the hydrogels were removed from the dye medium. The concentrations of these dye solutions have been established using spectrophotometric techniques. Spectrophotometric measurements were taken at room temperature with a Shimadzu 160A model at 619 nm. The equilibrium concentrations were calculated using calibrated scales.

The MGO adsorption efficiency (R %) was calculated by the underlying equation

R % = \frac{C_{0} - C_{e}}{C_{0}} \times 100

C_o and C_e symbolize the initial and equilibrium concentrations of the dye solutions (mg/L).

Results and discussion

Fourier transform infrared spectra (FT-IR) of APC hydrogels

The FT-IR spectral data manifest the evidence supporting the successful synthesis of APC hydrogels through the linkage and functional groups present in the hydrogel network. The synthesized polyester hydrogel shows a distinctive broad OH stretching peak at 3426 cm^-1 is due to H-bonded OH groups (hydrogen bonded OH at 3200-3570 cm^-1).^11,12 Low intensity symmetric vibration at 2924 cm^-1 and 2849 cm^-1 is due to –CH₂ groups between the macromolecular chain and crosslinking bridges, a prominent absorption band at 1721 cm^-1 corresponds to the C = O for ester group¹⁰ (crosslinking between carboxylic group of citric acid and OH of AG & PVA.). Carboxylate peak of uronic acid appears at 1414 cm^-139,40 peak at 1324 cm^-1 is due to C-OH of citric acid. Furthermore the ester formation is confirmed from the distinctive peaks corresponds to ester’s (C-C-O) and (O-C-C) at 1212 cm^-1, 1077 cm^-1 respectively.^2,41 The peaks recorded at 1144 cm^-1 and 1040 cm^-1 is attributed to Symmetric stretching of PVA (C-OH, C-O),in addition the peaks observed at 890 cm^-1, 818 cm^-1, 598 cm^-1 is due to presence of galactan and skeletal mode vibration of pyranose ring in Almond gum. The FT-IR spectra of APC hydrogels is represented in Figure 2.

FT-IR of pure Citric acid monohydrate shows a triple peak at 1716 cm^-1 due to (C = O), which is disappeared in the APC hydrogel, also the carbonyl stretching peak becomes more intense for cross-linked membrane than pure CA.^42,43 Furthermore the OH of CA observed 3342 cm^-1, but for APC hydrogel it appeared at 3432 cm^-1. Similarly pure Almond gum’s O-H peak appeared at 3200-3570 cm^-1, C-H vibrational mode and COOH peak occurs at 3523 cm^-1, 2909 cm^-1, 1625 cm^-1 respectively. In addition Carboxylic O-H in plane bending of AG appears at 1436 cm^-1 (which is absent in APC hydrogel film), 1,4 linkage of galactose recorded at 772 cm^-1, small band lying between 700 and 400, 800 cm^-1 is due to the presence of galactan and skeletal mode vibration of pyranose rings.^19,44 IR examination of PVA reveals the following characteristics: hydrogen bonded OH at 3200-3570 cm^-1, C-OH band at 1050-1150 cm^-1 and C-O band at 1090-1150, 1419 cm^-1 (C-H bending).³³ From the FT-IR data of APC hydrogels and its monomers (AG, CA, PVA), we conclude the successful synthesis of polyester network.

X-ray diffraction studies

Almond gum is amorphous in nature,⁴⁴ the XRD of APC hydrogel are shown in Figure 3 exhibits semi-crystalline character. This crystalline form results from the crosslinking of PVA and citric acid to the almond gum. A small orthorhombic lattice that expands with the (110) plane was visible in the dried gel, indicating the existence of a crystalline phase.⁴⁵ Intramolecular and intermolecular hydrogen bonding from functional groups caused by the crosslinking of CA and PVA with AG result in a certain amount of favorable crystal growth.^46–48

Swelling studies of hydrogels

It is believed that the multi-layered flower-like surface shown in SEM images improves the hydrogel’s hydrophilic properties, leading to an increase in the swelling behavior.¹¹ The swelling behavior of APC based hydrogels with different pH ranges are represented in Table 3.

Table 3.

Seq % of almond gum based hydrogels.

S.No.	Sample	pH solutions
S.No.	Sample	2	4	7	9.2	11
1	APC	380	260	260	340	180
2	A1PC	440	400	440	1260	1280
3	A2PC	880	1020	1300	3020	3120
4	A3PC	840	800	760	2340	2860
5	APC1	380	420	460	580	640
6	APC2	340	380	400	560	700
7	APC3	160	180	200	620	700
8	AP1C	420	460	640	660	780
9	AP2C	360	420	500	580	460
10	AP3C	300	300	180	340	380

Case-1 APC hydrogels (equimolar ratio)

To investigate the swelling behavior, APC hydrogel were placed in the solution with different pH values ranging from 2, 4, 7, 9.2, and 11, respectively. The S_eq % of APC exhibits 380, 260, 260, 340, 180 %. The APC hydrogels have low swelling among all in the series, due to the less availability of polar functional groups like carboxylate ion, hydroxyl ion present in the hydrogel network. They exhibit maximum swelling percentage 380 at pH two which is similar to that of APC1 hydrogel which is nothing but the minimum concentration of citric acid. The swelling equilibrium of APC hydrogel is pictured in Figure 4(a).

Case-2 variation of molar ratio of almond gum with fixed composition of citric acid and PVA

The amount of AG was varied from 0.5 g to 2 g in order to examine the impact of AG concentration on the water absorption ability of the APC based hydrogels. As illustrated in Figure 4(b) the swelling capacity is increased by increasing the amount of AG up to 1.5 g. This was because more hydrophilic polymer chains were added to the gel networks, which helped to improve the gel systems swelling properties. Further increasing the amount of AG (up to 2 g) causes the swelling to diminish because it increases the medium’s viscosity, which hampers ion transport.

The hydrogels was placed in solution with pH values of 2, 4, 7, 9.2, and 11, respectively, to investigate the swelling behavior of the substance. The S_eq% of A1PC exhibits 360, 400, 440, 1260, 1280%, while A2PC shows 880, 1020, 1300, 3020, 3120% and A3PC has 840, 800, 760, 2340, 2860%. It was observed that when the pH rose from 2 to 11, the quantity of swelling increased. At basic pH, the hydrogel’s maximum swelling is mostly caused by the repulsion between the –COO^- groups. At low pH, the carboxyl and hydroxyl groups of AG are efficiently suppressed from ionizing by the H+ ions in the external medium, this lowers the osmotic pressure as a result APC’s swelling capacity is reduced.² It has been concluded that the amount of Almond gum increases, swelling equilibrium of APC based hydrogels has been improved, because of rise of ionizable functionalities like COOH and OH.¹²

Case-3 variation of molar ratio of citric acid with fixed composition of almond gum and PVA

The APC1 hydrogels has swelling equilibrium values ranged from 380, 420, 460, 580, 640%, at pH 2, 4, 7, 9.2 and 11. Similarly APC2 hydrogels show 340, 380, 400, 560, 700% and APC3 hydrogels exhibit 160, 180, 200, 620, 700% of swelling. The S_eq% rose when the medium’s pH rose. This could be because the hydrogels’ ester hydrolyzed and carboxylic carrying anionic chains allowed for an increase in swelling by holding more water.^49,50 Thus, the extension of network is caused by the polymer chain that contains the COOH group. Consequently, a larger network volume created enormous holes in the gel, which raised the absorption of water. In the neighborhood of their pK_a values, hydrogel swelling was significantly altered.⁵¹ CA is recognized to be a triprotic acid with dissociation constants of pK_a1 = 2.94, pK_a2 = 4.1 pK_a3 = 5.82. The carboxylic group in CA only became ionized when the swelling medium’s pH reached a level higher than the hydrogel’s pK_a value. This allowed the polymer network to become more hydrophilic and improved water absorption. The formation of hydrogen bonds was discovered to reduce swelling at low pH.⁵⁰ The hydrogels exhibited reduced swelling at low pH due to protonation of the carboxyl group; the free movement of polymer backbone was constrained and increased swelling at high pH due to ionic repulsion of the carboxyl group.^52–56 The pH and swelling medium in the APC1, APC2, and APC3 hydrogel series were discovered to be proportionate to one another, which caused the gel to swell. All of these hydrogels had lower swelling percentages at pH 2 and 4 due to protonation of the carboxyl group, the polymer chain becomes hydrophobic.⁵⁷ Thus at low pH, APC1 compounds has better swelling, than APC2 and APC3 due to lower concentration of citric acid. Meanwhile the APC3 compounds show pronounced swelling at higher pH due to deprotonation in basic medium which cause the ionic repulsion between the polymer chains. From the above discussion we clearly ascertain that compared to acidic pH, the pronounced swelling percentage was noticeably larger at alkaline and neutral pH (represented in Figure 4(c)).

Case-4 variation of molar ratio of PVA with fixed composition of almond gum and citric acid

The swelling behavior was investigated for AP1C, AP2C, and AP3C hydrogels at different pH values between 2 and 11 were shown in Figure 4(d). AP1C hydrogels show S_eq% 420, 460, 640, 660, 780 %, AP2C hydrogels exhibit 360, 420, 500, 580, 460% and AP3C has 300, 300, 180, 340, 380 % at pH 2, 4, 7, 9.2 and 11 respectively. Hydrogels show an inverse relation with the concentration. On increasing concentration of PVA the swelling decreases gradually. This is due to the decrease in porosity of the polymer backbone. Similarly the high degree of crosslink density decreases the swelling nature of the hydrogel. On increasing the concentration of PVA the degree of crosslinking increases and the ability to uptake water is decreases.^58,59 Swelling is reduced as the crosslinking rises, and vice versa. Influence of pH from 2 to 11 shows the increased swelling at higher pH. At lower pH, the swelling equilibrium is low owing to the formation of H-Bonding (which restricts the mobility of polymer chain) between the COOH of Citric acid and OH of PVA s well as AG. On increasing the pH, the ionization of carboxylic acid facilitates COO^- ions, because these groups electrostatic repulsion makes it easier for water to diffuse, which increases swelling. The synthesized hydrogels based on almond gum were sensitive to the pH of the surrounding environment, according to equilibrium swelling tests.

SEM analysis of APC-Hydrogels

The scanning electron microscopy (SEM) technique of A2PC hydrogel is investigated due to its excellent swelling behavior which reveals the size, shape, surface morphology, and porous nature. This rough, porous surface of the APC hydrogels allowed liquids to seep into the substance. The substantial crosslinking and H-bonding between the CA, AG, and PVA in APC hydrogels creates Chinese rose and chrysanthemum flower-like (Chrysanthemum x morifolium –Tamil name Saamandhi) structures. Water or other fluid molecules separate the neighbouring layers of these flower-like structures, resulting in a highly swollen structure that is stabilized by H-bonding.¹¹ Several 3D flower-like structures can be seen in the SEM pictures of hydrogels. Each flower is composed of several thin petals, each of which has a thickness of around 1 µm and an average size of flowers ranging from 2 to 5 µm.^60,61

When considering the hydrogels’ numerous applications, their porous nature is a crucial factor; these pores might enhance the open area of networking, which would like to increase the interaction points of solvents and hydrophilic chains. As a result, hydrogels can enter water molecules more readily and stay in the pores.⁶² A2PC hydrogel’s surface morphology was shown in Figure 5(a)–(f).

Antibacterial studies

The most valuable characteristic in the realm of biomedical applications is the antibacterial activity.⁵⁶ Using the agar well diffusion method, the in vitro antimicrobial abilities of APC based hydrogels were evaluated against Gram-positive S. aureus and Gram-negative E. coli bacteria, the Ciprofloxacin has been chosen as a positive control. The zone of inhibition is represented in Table 4. A3PC, APC3, AP3C hydrogels exhibit a zone of inhibition 0 mm, 15 mm, 13 mm,18 mm around the tested substances. The results reveled good antibacterial activity against gram positive (Staphylococcus aureus) and has no activity for gram negative (Escherichia coli) bacteria as shown in Figure.6 The Standard Antibacterial test “SNV 195920-1992″ states that specimens exhibiting microbial zone inhibition of greater than 1 mm are deemed to be effective antibacterial agents.⁶³ Staphylococcus aureus is one of the four most common bacterial species found in chronic wounds; prolonged S. aureus biofilm infection in wounds impairs collagen granulation, which compromises wound tissue biomechanics. Such tissue repair deficit is expected to raise wound recidivism in clinical settings.⁶⁴ The synthesized hydrogels have good activity against S. aureus and they are highly recommended for wound healing purpose especially against this pathogen.

Table 4.

Antibacterial investigation of APC based hydrogels.

S.No	Strain	APC	A3PC	APC3	AP3C	Positive control
1	S.Aureus	-	15	13	18	32*
2	E.Coli	-	-	-	-	34*

Biodegradation studies (soil burial method)

Biodegradation is the process by which microorganisms break down compounds into simpler units. It has been noted that the hydrogel’s colour and physical appearance have changed during the soil burial test. The hydrogel’s active pendant groups and ester linkages have been thought to be the cause of biodegradation. The hydrogels interacted with the cell walls of several microorganisms, notably bacteria, fungi, protozoa, and actinomycetes. These Microorganisms excrete extracellular digestive enzymes on the labile ester groups of hydrogels, causing surface degradation and decreasing the molar mass of the polymeric backbone, leading to water-soluble intermediates. Furthermore, it leads to other metabolic pathways. As a result of aerobic decomposition of hydrogels CO₂, H₂O, CH₄ and some new biomass are generated. This makes this hydrogel as a better source for the clean and greener world. Figure 7(b) depicts the FT-IR spectra of deteriorated hydrogels, where the intensity of the ester peak has diminished. A number of variables, including pH, temperature, minerals, nutrients, and soil humidity, affect the hydrogels biodegradation.^12,62,57,65 In the APC hydrogel series, AP1C,AP2C,AP3C requires more time (54-65 days) for degradation, A1PC,A2PC,A3PC takes (42-50days), APC1,APC2,APC3 takes (35-40days) for complete degradation. The biodegradation of APC hydrogels demonstrates that the degradation gradually diminishes as the quantity of monomers increases. This is because of the extensive crosslinking and H-bonding between the molecules. It is clear from Table 5 degradation is directly proportional to the strength of hydrogel films. The amorphous materials are thought to be more vulnerable to deterioration than crystalline forms, the amorphous nature of hydrogel is reiterated by the X-ray diffraction studies. Furthermore according to antibacterial investigations, these hydrogels have no effect on E. coli (Figure 6), which is primarily responsible for the hydrogel network’s breakdown because of its extensive distribution in soils.⁶⁶ As a result, these bacteria efficiently accelerate the deterioration process. Figure 7(a) clearly shows the variation in hydrogel surface and the percentage of degradation in terms of weight loss (%) is represented in Figures 8(a)–(d). Equimolar concentration and citric acid increased composition have better degrading capacity than that of other compositions of the present investigation. From the degradation studies we declare that these hydrogels are bio-degradable and eco-friendly to environment.

Table 5.

Bio-degradation of APC based hydrogels.

S.No.	Sample code	No. of days required for complete degradation
1	APC	28 Days
2	APC1	35 Days
3	APC2	38 Days
4	APC3	40 Days
5	A1PC	42 Days
6	A2PC	45 Days
7	A3PC	50 Days
8	AP1C	54 Days
9	AP2C	58 Days
10	AP3C	65 Days

Grenoble green dye removal by APC based hydrogels with the influence of pH

APC based hydrogels show remarkable behavior on Grenoble green (Malachite green) dye adsorption. To investigate the impact of pH on Malachite green dye removal, the solution’s pH was altered from 4 to 11 (Figure 9(a)). illustrates the dye removal percentage (R %) of APC based hydrogels on different pH medium. Hydrogels comprising varying concentrations of AG, CA, and PVA via equation (3) (APC, A1PC, A2PC, A3PC, APC1, APC2, APC3, AP1C, AP2C, AP3C) all compounds demonstrated increased R (%) of Malachite green at higher pH contrasted to lower pH. A3PC hydrogels possessed the maximum dye removal throughout the series, with R (%) values of 27.5%, 75.00%, 91.5%, and 93.5% at pH 4, 7, 9, and 11.

At pH 11, the R% values for APC-based hydrogels seemed between 85 and 93.5%. Hydrogels showed a drop in R% at pH 4.0, ranging from 19.5 to 27.5%. Increasing the content of almond gum and citric acid enhances removal efficiency through raising the proportion of hydroxyl and carboxylate ions in the hydrogels surface providing better interactions between gel network and dye molecules. However, increasing the quantity of PVA limits dye adsorption due to the hydrogel’s high stiffness and reduced porosity generated by extensive crosslinking. In basic medium the deprotonation of hydroxyl and carboxyl groups generate an electric repulsion triggering the expansion of hydrogel and provide more number of active sites for the dye molecules. Additionally, an electrostatic force of attraction prevails between the anionic network of the hydrogel (OH and carboxylate anion) and cationic dye particles.^47,62 In a comparable vein at low pH, hydrogel does not ionize, resulting in restrained dye uptake by APC-based hydrogels. The dye removal efficiency of APC based hydrogels is as follows: A3PC>APC3>AP3C. The Dye adsorption mechanism of APC based hydrogel is represented in Figure 9(b).

Desorption studies

Deswelling of Malachite green dye from the hydrogel after adsorption can be achieved by utilizing alcoholic solvents such as ethanol and methanol while stirring at 500 rpm for 45 min. The elimination efficacy (%) of Malachite green dye is enhanced by more than 90% after four cycles. The results show that the regenerated biopolymeric APC based hydrogel is easily recovered and can be used for multiple adsorption cycles.

Kinetic studies

From the above discussion it is clear that among all the 10 hydrogels A3PC hydrogel show better dye adsorption behavior owing to the increased concentration of almond gum thus we investigated the kinetics and isotherm studies of A3PC hydrogel.

Pseudo-first-order kinetics

Pseudo-first-order kinetics suggests that the adsorption rate is controlled by the physical diffusion of dye molecules onto the hydrogel’s surface. This means that the dye molecules are retained to the adsorbent surface by weak forces. The kinetic data was fitted into Lagergren’s pseudo-first-order rate equation, given as.^67,68

Log (q_{e} - q_{t}) = \log q_{e} - k_{1} t

In the following formula, q_e and q_t indicate the adsorption capacities at equilibrium and time t, respectively. Whereas k₁ denotes the adsorption rate constant, q_e and k₁ values are shown in the table. The adsorption of malachite green (MG) on A3PC hydrogel follows the pseudo-first-order kinetics model since it fits better based on R², which is 0.99 illustrated in Figure 10(a). Table 6 demonstrates a good connection between experimental and calculated qe values, indicating that pseudo-first-order adsorption provides a better fit than the pseudo-second-order kinetics model.⁶⁹ This finding implies that adsorption is frequently governed physisorption, in which dye molecules bind to the hydrogel’s surface via electrostatic interactions (cationic dye and anionic hydrogel).

Table 6.

Data of kinetic models.

Kinetic model	q_e (exp)	q_e (cal)	R²	Rate constant
Pseudo first order	18.75	20.8	0.994	k₁ = 0.0279
Pseudo second order	18.75	22.4	0.8598	K₂ = 3.574498

Pseudo-second-order kinetics

The Lagergren pseudo-second order kinetics equation can be expressed as a linear form in equation.^70–73

t / q_{t} = 1 / k_{2} {q_{e}}^{2} + t / q_{e}

The pseudo-second-order model has a low R² of 0.85 (Figure 10(b)) than the pseudo-first-order adsorption. Which provide a better fit than the pseudo-second-order kinetics model based on their R² and q_e. The second order constant (k₂) measured as 3.5 gmg⁻¹ min⁻¹.

Langmuir adsorption isotherm

The Langmuir and Freundlich equilibrium models were extensively investigated to determine the relationship between hydrogel, dye molecules in liquid phase at constant temperature and dosage. The Langmuir model depicts the monolayer adsorption process. The Langmuir equation is often expressed as follows:⁷⁴

C_{e} / Q_{e} = 1 / K_{l} Q_{m} + C_{e} Q_{m}

(4)

Where Q_m is the monolayer adsorption capacity in mg/g and K_L is the Langmuir isotherm constant. Plotting C_e/Q_e versus C_e yields Q_m and K_L values (see Figure 11(a)). The Langmuir isotherm model is given by the dimensionless factor R_L,⁷⁵ which was defined by.

R_{L} = 1 / (1 + K L C o)

The R_L indicates the nature of the adsorption process. When R_l = 0, adsorption is irreversible, when 0‹ R_L ‹ 1, adsorption is favorable, and when R_L = 0 or R_L ›1, adsorption is unfavorable. In this investigation, A3PC hydrogel displays R_L of 0.02213. The R_L value indicating that the adsorption process is beneficial. The determination coefficient (R²) for A3PC hydrogel was 0.965, which is lesser than the Freundlich isotherm indicating a poor fit for monolayer adsorption.

Freundlich adsorption isotherm

The Freundlich isotherm model describes the heterogeneity of the adsorption process and is commonly used for investigating non-ideal adsorption on heterogeneous surfaces. It is expressed as.⁶⁷

q_{e} = {K_{f} C_{e}}^{1 / n}

The following equation provides the linear form of equation,

\ln q_{e} = \ln K_{f} + 1 / n \ln C_{e}

The intercept and slope of the lnq_e versus lnC_e (Figure 11(b)) can be utilized for determining K_f and 1/n, which reflect adsorption capacity and intensity respectively. The corresponding results were 0.0279 and 0.53 respectively (Table 7). The 1/n ratio is smaller than one, suggesting that adsorption is favorable and occurs readily. The Freundlich isotherm model better describes the adsorption efficiency and adsorption process for A3PC hydrogels, with a regression R² of 0.99 compared to the Langmuir isotherm model’s R².

Table 7.

Data’s of isotherm models.

Langmuir isotherm model constants			Freundlich isotherm model constants
K_L (L·mg−1)	R_L	R²	K_f (mg.g^-1)	1/n	R²
1.303	0.02213	0.96	0.027	0.503	0.99

Weber-Morris intraparticle diffusion model

The model showed viable adsorption mechanism for eliminating malachite green dye via A3PC hydrogel. The model is described with the following statement^76,77:

q_{t} = k_{i d} t^{0.5} + c

K_id (mg·g⁻¹·min^0.5) is the intra-particle diffusion constant, while c represents the thickness of the boundary layer. Plotting Q_t against √t yields a linear graph, indicating that the adsorption process involves intra-particle diffusion. The slope and intercept of a graph were used to find K_id and c values: 1.9498 mg•g⁻¹•min^0.5, −1.573 respectively. The determination coefficient (R²) for intraparticle diffusion is 0.94. The negative intercept implies both film diffusion and surface reaction process influence the adsorption process. The graph did not pass through the origin, which implies that the adsorption of malachite green dye on hydrogel was not solely controlled by intra-particle diffusion Figure 12.

Conclusion

In the current study pH-responsive APC based hydrogels were successfully synthesized. The formation of polyester network is confirmed by FT-IR spectroscopy. The hydrogels surface morphology was characterized by SEM analysis, its semi-crystalline nature is verified using XRD and antibacterial efficacy is evaluated by agar well diffusion method. From the above investigation we ascertain that.

• The approach proposed for the synthesis of APC hydrogel is simple, biocompatible, and economical, making it simple to apply in various sectors.

• The swelling equilibrium of hydrogels has shown good water retention on increasing the concentration of Almond gum over Citric acid and Polyvinyl alcohol. Additionally, hydrogels remarkable swelling properties were noted at alkaline pH levels as in contrast to acidic ones.

• SEM analysis provides strong confirmation about the porous, flower like morphology and supports the remarkable swelling behaviours of hydrogels.

• Hydrogels showing a reciprocal relationship between biodegradability and antibacterial activity. However, they exhibited excellent degradability and antibacterial activity.

• The hydrogels in the present investigation effectively removed highly toxic cationic dye (MGO) in aqueous medium. The dye removal efficacy maximum at basic pH and minimum acidic pH. A3PC hydrogels possessed the maximum dye removal throughout the series, with R (%) values of 27.5%, 75.00%, 91.5%, and 93.5% at pH 4, 7, 9, and 11

• The dye adsorption on the hydrogel network follows physisorption process on the basis of kinetic data, it better fits into pseudo first order kinetics and freundlich adsorption isotherm with higher R² value.

Based on our study emphases that APC based hydrogels are biodegradable, biocompatible, renewable and environmentally friendly. The monomers employed in present investigation not only lowers production costs but also improves their qualities. Consumption of these hydrogels might be implemented in controlled medication delivery, catalytic, agricultural, and environmental applications, rendering them a promising material for the foreseeable future.

Footnotes

ORCID iD

Guhanathan Selvam

Funding

The authors received no financial support for the research, authorship, and/or publication of this article.

Declaration of conflicting interests

The authors declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

References

Kono

Oeda

Nakamura

. The preparation, swelling characteristics, and albumin adsorption and release behaviors of a novel chitosan-based polyampholyte hydrogel. React Funct Polym 2012; 73: 97–107.

Syed Ahamed Hussain

Jaisankar

. An eco-friendly synthesis, characterization and antibacterial applications of novel almond gum–poly(acrylamide)-based hydrogel silver nanocomposite. Polym Test 2017; 62: 154–161.

Dayal

Mehta

Choudhary

, et al. Synthesis of acrylic superabsorbents. J Macromol Sci Polym Rev 1999; 39: 507–525.

Liu

Rauth

. Immobilization and bioactivity of glucose oxidase in hydrogel microspheres formulated by an emulsification–internal gelation–adsorption– polyelectrolyte coating method. Int J Pharm 2007; 339: 148–156.

Tonnesen

Karlsen

. Alginate in drug delivery systems. Drug Dev Ind Pharm 2002; 28: 621–630.

Liu

Liang

Zhan

, et al. Synthesis of a slow-release and superabsorbent nitrogen fertilizer and its properties. Polym Adv Technol 2005; 17: 430–438.

Bajpai

Giri

. Swelling dynamics of a macromolecular hydrophilic network and evaluation of its potential for controlled release of agrochemicals react. Funct. Polym 2002; 53: 2–3.

Naganagouda

Muliman

. Gelatin blends with alginate: gel fibers for a-galactosidase immobilization and its application in reduction of non-digestible oligosaccharides in soymilk. Process Biochem 2006; 41: 8.

Sheldon

. Enzyme immobilization: the quest for optimum performance. Adv Synth Catal 2007; 349: 1289–1307.

10.

Franklin

Guhanathan

. Synthesis and characterization of citric acid-based pH-sensitive biopolymeric hydrogels. Polym Bull 2014; 71: 93–110.

11.

Chitra

Franklin

Sudarsan

, et al. Indole-3-acetic acid/diol based pH-sensitive biological macromolecule for antibacterial, antifungal and antioxidant applications. Int J Biol Macromol 2017; 95: 363–375.

12.

Sudarsan

Franklin

Sakthivel

, et al. Non-toxic, antibacterial biodegradable hydrogels with pH-stimuli sensitivity: investigation of swelling parameters. Carbohydr Polym2016;148:206–215.

13.

Liaqat

Badshah

Minhas

, et al. pH- sensitive hydrogels fabricated with hyaluronic acid as a polymer for Site- specific delivery of mesalamine. ACS Omega 2024; 9: 28827–28840.

14.

Diana

Milzi

Gentile

, et al. Aversatile pH-sensitive hydrogel based on a high-performance dye: monitoring the freshness of milk and chicken meat. J Food Compos Anal 2024; 126:10666.

15.

Zhuo

Zhang

, et al. pH-Sensitive biomaterials for drug delivery. Molecules 2020; 25: 5649.

16.

Bouaziz

Helbert

Romdhane

, et al. Structural data and biological properties of almond gum oligosaccharide: application to beef meat preservation. Int J Biol Macromol 2014; 72: 472–479.

17.

Singh

Mohan

Kumar

. Synthesis of hydrocortisone containing dietary fiber almond gum-based hydrogels as sustained drug delivery carriers for use in Colon inflammation. Food Hydrocoll Health 2022; 2: 100057.

18.

Kono

Otaka

Ozaki

. Preparation and characterization of guar gum hydrogels as carrier materials for controlled protein drug delivery. Carbohydr Polym 2014; 111: 830–840.

19.

Mahfoudhi

Chouaibi

Donsì

, et al. Chemical compositionand functional properties of gum exudates from the trunk of the almond tree (Prunus dulcis). Food Sci Technol Int 2011; 18: 241–250.

20.

Bouaziz

Koubaa

Ellouz Ghorbel

, et al. Recent advances in rosaceae gum exudates: from synthesis to food and non-food applications. Int J Biol Macromol 2016; 86: 535–545.

21.

Rezaei

Nasirpour

. Encapsulation of curcumin using electrospun almond gum nanofibers: fabrication and characterization. Int J Food Prop 2018; 21: 1608–1618.

22.

Bouaziz

Koubaa

Neifar

, et al. Feasibility of using almond gum as coating agent to improve the quality of fried potato chips: evaluation of sensorial properties. Lebensm Wiss Technol 2016; 65: 800–807.

23.

Rasool

Zahoor

Ayoub

, et al. Formulation and characterization of natural almond gum as an edible coating source for enhancing the shelf life of fresh cut pineapple slices. Food Chem Adv 2023; 3: 100366.

24.

Mahfoudhi

Chouaibi

Hamdi

. Effectiveness of almond gum trees exudate as a novel edible coating for improving postharvest quality of tomato (Solanum lycopersicum L.). Fruits Food Sci Technol Int 2013; 19: 527–536.

25.

Sampath Kumar

Chitra

Sumithra

. Investigation of novel biodegradable almond gum - poly vinyl alcohol Bi-polymer blend for packaging applications. J. Environ Nanotechnol 2024; 6: 40–47.

26.

Mahfoudhi

Sessa

Chouaibi

, et al. Assessment of emulsifying ability of almond gum in comparison with gum Arabic using response surface methodology. Food Hydrocoll 2014; 37: 49–59.

27.

Bouaziz

Koubaa

Helbert

, et al. Purification, structural data and biological properties of polysaccharide from Prunus amygdalus gum. Int J Food Sci Technol 2015; 50: 578–584.

28.

Suresh

Puspharaj

Subramani

. Development of almond gum/alginate composites to enhance the shelf-life of post-harvest Solanum lycopersicum L. Food Hydrocoll Health 2022; 2: 100087.

29.

Gao

Pourramezan

Ramezan

, et al. Application of gums as techno-functional hydrocolloids in meat processing and preservation: a review. Int J Biol Macromol 2024; 268: 131614.

30.

Yang

Motlagh

Allen

, et al. Modulating expanded polytetrafluoroethylene vascular graft host response via citric acid based biodegradable elastomers. Adv Mater 2006; 18: 1493–1498.

31.

Franklin

Guhanathan

. Influence of chain length of diol on the swelling behavior of citric acid based pH sensitive polymeric hydrogels-A green approach. J Appl Polym Sci 2014; 132: 41403.

32.

Franklin

Guhanathan

. Simple, convenient, low-cost and solventless greener way to pH-responsive polymeric hydrogels: synthesis and characterization. J Appl Polym Sci 2015; 132: 41921.

33.

Iqbal

Shafiq

Khan

, et al. Novel chitosan/guar gum/PVA hydrogel:preparation,characterization and antimicrobial activity evaluation. Int J Biol Macromol 2020; 164: 499–509.

34.

Şolpan

Duran

Saraydin

, et al. Adsorption of methyl violet in aqueous solutions by poly(acrylamide-co-acrylic acid) hydrogels. Radiat Phys Chem 2003; 66: 117–127.

35.

Ekici

Işıkver

Saraydın

. Poly(Acrylamide-Sepiolite) composite hydrogels: preparation, swelling and dye adsorption properties. Polym Bull 2006; 57: 231–241.

36.

Culp

Beland

. Malachite green: a toxicological review. J Am Coll Toxicol. 1996; 15: 219–238.

37.

Rao

KVK

. Inhibition of DNA synthesis in primary rat hepatocyte cultures by malachite green: a new liver tumor promoter. Toxicol Lett 1995; 81: 107–113.

38.

Cha

Doerge

Cerniglia

. Biotransformation of malachite green by the FungusCunninghamella elegans. Appl Environ Microbiol 2001; 67: 4358–4360.

39.

Theophil Anand

Renuka

Ramesh

, et al. Green synthesis of ZnO nanoparticle using Prunus dulcis (almond gum) for antimicrobial and supercapacitor applications. Surf Interfaces 2019; 17: 100376.

40.

Vijayakumar

Chen

González-Sánchez

, et al. Anti-colon cancer and antibiofilm activities of green synthesized ZnO nanoparticles using natural polysaccharide almond gum (Prunus dulcis). J Cluster Sci 2022; 33: 1131–1146.

41.

Smith

. Infrared spectroscopy of polymers VIII: polyesters and the rule of three. Spectroscopy 2021; 36: 25–28.

42.

Tsioptsias

Panagiotou

Mitlianga

. Thermal behavior and infrared absorbance bands of citric acid. Appl Sci 2024; 14: 8406.

43.

Cai

, et al. Sustainable plant-based biopolymer membranes for PEM fuel cells. Int J Mol Sci 2022; 23: 15245.

44.

Bashir

Haripriya

. Assessment of physical and structural characteristics of almond gum. Int J Biol Macromol 2016; 93: 476–482.

45.

Zhao

Lou

, et al. Solgel-based hydrothermal method for the synthesis of 3D flower-like ZnO microstructures composed of nanosheets for photocatalytic applications. Ceram Int 2014; 40: 5507–5514.

46.

Mei

Shao

, et al. Single-step synthesis of hierarchical flower-like silver structures with assistance of gallic acid. Mater Res Express 2020; 8: 015010.

47.

Franklin

Guhanathan

. Investigationofcitricacid–glycerol based pH sensitive biopolymeric hydrogels for dye removal applications: a green approach. Ecotoxicol Environ Saf 2015; 121: 180–186.

48.

Shi

Wang

, et al. Removalofdirectdyesbycoagulation:theper-formance of preformed polymeric aluminium species. J Hazard Mater 2006; 136: 356–361.

49.

Shukla

Bajpai

. Plaster of Paris-reinforced nanocomposites of poly(2-hy- droxy ethyl methacrylate-Co-acrylamide) as alternative orthopaedic material. Polym Plast Technol Eng 2012; 51: 1450–1459.

50.

Grodzinski

. Polymeric gels and hydrogels for biomedical and pharmaceutical applications. Polym Adv Technol 2009; 20: 595–603.

51.

Tuncer

Cengiz

Omer

, et al. Equilibrium swelling behaviour of Ph and temperature-sensitive poly(N-vinyl2-pyrrolidone-g-citricacid) polyelectrolyte hydrogels. J Polym Sci, Polym Phys Ed 2000; 38: 153–160.

52.

Karadag

Uzum

Saraydin

. Swelling equilibria and dye adsorption studies of chemically crosslinked superabsorbent acrylamide maleic acid hydrogels. Eur Polym J 2002; 38: 2133–2141.

53.

Sakthivel

Franklin

Guhanathan

. pH sensitive itaconic acid based polymeric hydrogels for dye removal applications. Ecotoxicol Environ Saf 2016; 134: 427–432.

54.

Karadag

Saraydin

. Swelling of superabsorbent acrylamide/sodium acrylate hydrogels prepared using multifunctional crosslinker. J Chem 2002; 26: 547–553. https://journals.tubitak.gov.tr/chem/vol26/iss6/8

55.

Sudarsan

Selvi

Chitra

, et al. Nontoxic pH-sensitive silver nanocomposite hydrogels for Potential wound healing applications. P-PTM 2020; 9: 1786584.

56.

Sakthivel

Franklin

Sudarsan

, et al. Investigation on PH/Salt-Responsive multifunctional itaconic acid based polymericbiocompatible, antimicrobial and biodegradable hydrogels. React Funct Polym 2018; 122: 9–21.

57.

Gupta

Webster

Sinha

. Evolution of PVA gels prepared without crosslinking agents as a cell adhesive surface. J Mater Sci Mater Med 2011; 22: 1763–1772.

58.

Gupta

Pramanik

Kailath

, et al. Composition dependent structural modulations in trans-parent poly(vinyl alcohol) hydrogels. Colloids Surf, B 2009; 74: 186–190.

59.

Zheng

Huynh

, et al. Biodegradable pH- and temperature-sensitivemultiblock copolymer hydrogels based on poly(amino-ester urethane)s. Macromol Res 2010; 18: 974–980.

60.

Barker

Humphrey

. Survival of E-Coli in a soil protozoan:implications for disease. FEMS Microbiol Lett 1999; 172: 1–8.

61.

Zhu

Che

, et al. Effect of Na2CO3 on the microstructure and macroscopic properties and mechanism analysis of PVA/CMC composite film. Polymers 2020; 12: 453.

62.

Poerwono

Higashiyama

Kubo

, et al. Citric acid. Adv Pharmacol Drug Saf Eval 2001; 23: 115–124.

63.

Himawan

Anjani

Detamornrat

, et al. Multifunctional low temperature-cured PVA/PVP/citric acid-based hydrogel forming microarray patches: physicochemical characteristics and hydrophilic. Eur Polym J 2023; 185: 111836.

64.

Uyanga

Okpozo

Onyekwere

, et al. Citric acid crosslinked natural bi-polymer-based composite hydrogels: effect of polymer ratio and beta-cyclodextrin on hydrogel microstructure. React Funct Polym 2020; 154: 104682.

65.

Pollini

Russo

Licciulli

, et al. Characterization of antibacterial silver coated yarns. J Mater Sci Mater Med 2009; 20: 2361–2366.

66.

Roy

Santra

Das

, et al. Staphylococcus aureus biofilm infection compromises wound healing by causing deficiencies in granulation tissue collagen. Ann Surg 2020; 271(6): 1174–1185.

67.

Labidi

Kacemi

. Adsorption mechanism of malachite green onto activated phosphate rock: a kinetics and theoretical study. Bull Environ Stud 2016; 1: 69–74.

68.

Khope

Gawande

. Kinetic models for the adsorption of cobalt from aqueous phase using granular activated carbon. J Chem Pharmaceut Res 2015; 7: 551–556.

69.

Rabeie

Mahmoodi

. Green and environmentally friendly architecture of starch-based ternary magnetic biocomposite (Starch/MIL100/CoFe2O4): synthesis and photocatalytic degradation of tetracycline and dye. Int J Biol Macromol 2024; 274: 133318.

70.

Ahmed

Kumar

. Adsorption studies of hazardous malachite green onto treated ginger waste. J Environ Manag 2010; 91: 1032–1038.

71.

Wanyonyi

Onyari

Shiundu

. Adsorption of methylene blue dye from aqueous solutions using Eichhornia crassipes. Bull Environ Contam Toxicol 2013; 91: 362–366.

72.

Rabeie

Mahkam

Mahmoodi

, et al. Graphene quantum dot incorporation in the zeolitic imidazolate framework with sodalite (SOD) topology: synthesis and improving the adsorption ability in liquid phase. J Environ Chem Eng 2021; 9: 106303.

73.

McKay

. Pseudo-second-order model for sorption processes. Process Biochem 1999; 34: 451–465.

74.

Langmuir

. The constitution and fundamental properties of solids and liquids. J Am Chem Soc 1916; 38: 2221–2295.

75.

Chanzu

Onyari

Shiundu

. Biosorption of malachite green from aqueous solutions onto polylactide/spent brewery grains films: kinetic and equilibrium studies. J Polym Environ 2012; 20: 665–672.

76.

Kushwaha

Gupta

Chattopadhyaya

. Removal of cationic methylene blue and malachite green dyes from aqueous solution by waste materials of Daucus carota. J Saudi Chem Soc 2014; 18: 200–207.

77.

Weber

Morris

. Kinetics of adsorption on carbon from solutions. J Sanit Eng Div 1963; 89: 31–39.