Synthesis, utilization, and recycling of graphene oxide-based nanohybrid biopolymeric hydrogels for purification of dye wastewater

The presence of dye-based goods or byproducts in wastewater has endangered people's health for a long time (Wibowo et al. 2023). They have an impact on the reproductive, neurological, respiratory, and endocrine systems (Hasan & Aljeboree 2023). Diseases can develop either directly (as in the case of asthma, motion sickness, allergies, rash, etc.) or indirectly (by the food chain, as in the case of heart issues, cancer, gene abnormalities, etc.) (Jawad et al. 2023). Acid Red 97 dye is a type of anionic dye. Due to its numerous uses in industries including nylon, fabrics, and wool, it was selected for the research (Chouaybi et al. 2022). The benzidine azo group of Acid Red 97 dye can be deadly, mutagenic, genotoxic, and carcinogenic to people and animals (Chouaybi et al. 2023). Some of the traditional techniques that have been used to remove such contaminants include phase separation, electrochemical treatment, crystallization, electrolysis, membrane filtration, advanced redox reactions, and catalyzed reduction (Rafiee 2020; Mahmoudian et al. 2023). Traditional techniques are not adequate to eliminate artificial dyes (Alsaffar et al. 2023) as these procedures are time-consuming, expensive, and ineffective (You et al. 2023). However, adsorption is significantly favored over the other methods because it can result in treated effluent of exceptionally high quality (Zhu et al. 2023). Its ease of use, minimal need for extra nutrients, high efficiency, strong renewal capacity, and potential for adsorbate regeneration are its advantages (Al-Shik et al. 2023).

Hybrid materials are the most intriguing structures because one can anticipate new qualities that are not present in any of their constituent parts (Zhao et al. 2023). An octagonal framework is formed by carbon atoms arranged in heavy, flat sheets that are sp² hybridized to form the characteristic two-dimensional structure known as graphene. This material has superior mechanical strength, exceptionally high thermal and electrical thermodynamic properties, and a considerable quantity of particular surface area (Januário et al. 2022). One of the most significant constraints of adsorption of dye on graphene oxide (GO) adsorbent is the inability to separate the functionalized adsorbent throughout the adsorption process (Khan et al. 2023b). Other disadvantages include GO particle aggregation, which decreases the efficiency of the adsorption mechanism and makes dispersal harder (Subrahmanya et al. 2022).

To overcome these drawbacks, the use of GO as a nanofiller in hydrogel (chitosan (CS), starch, or agar) has recently been proposed for the manufacturing of GO-impregnated hydrogels for improved adsorption performance (Sayed et al. 2023). Using GO as a replacement for a biopolymer substrate can increase hydrogel's stability (Kahya & Erim 2022). Chitosan (III) is a (1–4) straight polymer obtained by simply deacetylating chitin (I), -2-amino-linked-2-deoxy-d-glucopyranose (Pratap et al. 2023). CS is a polysaccharide that is positively charged, so CS is successfully used for acidic dyes removal because it carries positive charge (Huang et al. 2017). Starch is a carbohydrate polymer. When added to wastewater, starch can help to form flocs or clusters of particles, which can then be removed through sedimentation or filtration (Nasrollahzadeh et al. 2021). Agar is a biological polymer (C₁₂H₁₈O₉)n. Agarose and agaropectin are the chemical components of agar. Agaropectin produces a gel due to its heterogeneous mixture of small molecules that are present in lesser amounts (Mishra et al. 2011). Water-soluble polyvinyl alcohol (PVA) is a substance that has a lot of reactive hydroxyl groups. It has been employed in several biomaterial applications because of its biological suitability, chemical resistance, nontoxicity, and high durability (Li et al. 2019; Ahmadi & Ghorbanpour 2021). This polymer is readily coagulated and cross-linked (Fang et al. 2023). PVA can be employed as a substrate in the fabrication of hydrogel polymer composites to support the GO/CS, GO/starch, and GO/Agar macrostructure (Qamruzzaman et al. 2022) (Table 1).

The main objective of this study was to evaluate the effectiveness of dye removal, in particular Acid Red 97 dye from wastewater from different nanohybrid hydrogels functionalized with GO that is environmentally friendly and nontoxic. The varying parameters were studied that effect the adsorptive remediation of dye and optimum values were determined to yield maximum adsorption of dye. In this study, GO was initially synthesized by modified Hummer's approach, which reduces the evolution of toxic gases as by the conventional synthesis methods. In this approach, a substantial amount of KMnO₄ was added compared to lower amounts of NaNO₃, which reduces the evolution of toxic nitrate gases, sodium, and nitrate ions. Hence, this approach reduces the difficulty in the purification of water produced from the GO synthesis (Zainuri et al. 2023). After the synthesis of GO, hydrogels were synthesized by the chemical cross-linking of different polymeric materials to obtain nanohybrid polymeric hydrogels. These nanohybrid polymeric hydrogels have enhanced thermal and pH stability as compared to polymeric hydrogels without GO functionalization and can be employed for the remediation of wastewater containing dyes (Bashir et al. 2020). The applicability of PVA-based hybrid biopolymer hydrogels for the adsorption of acidic dyes, especially Acid Red 97 dye, has been scarcely explored. The uniqueness of this study lies in the utilization of environmentally favorable GO/CS–PVA, GO/starch–PVA, and GO/agar–PVA hybrid biopolymer hydrogels for the elimination of Acid Red 97 dye. To address this research gap, the present study was aimed at synthesizing PVA-based hybrid biopolymer hydrogels by incorporating GO blends with conductive polymeric materials, resulting in a triplet hybrid material with an enhanced surface area for the selective adsorption of acidic dyes. The proposed technique is currently being considered a promising technology for the adsorptive removal of acidic dyes from wastewater when compared to previous methods.

NaNO₃, KMnO₄, H₂O₂, (CH₃COOH), sulfuric acid (H₂SO₄), CS flakes, PVA (C₂H₄O)x, agar (C₁₄H₂₄O₉), starch (C₆H₁₀O₅)n, HCl, and NaOH employed in this study were purchased from Merck (Germany) and Sigma-Aldrich Chemical Co. (USA).

The stock solution of dye was prepared by dissolving 1 g of dye per 1,000 mL in doubly distilled water. A linear domain plotted between 0.05 and 12 mg/L was obtained with correlation coefficients higher than 0.992. All samples were diluted using high-purity water to fit in the calibration domain. Blank and control samples (solutions with adsorbent and solutions of the dye compounds without adsorbent) were used during the experiments. Blank samples and analytical standards were analyzed at each sample batch. All of the experiments were run in a batch mode with three duplicates. The data in this graph have a 5% percentage error. It means that the reported percentage values for adsorption can be considered accurate within a range of ±5% of the reported value.

In an orbital shaker, several kinds of batch experiments were carried out under various settings, including varying pH levels (2–11) of dye solutions and various hydrogel amounts (0.05–0.4 g/L) and using various starting dye concentrations to determine Acid Red 97 dye adsorption on the prepared hydrogels. By adopting a traditional method for the elimination of Acid Red 97 dye, critical manufacturing variables might be improved. To use for the adsorption experiment, hydrogels were divided into small pieces. A standard solution of the Acid Red 97 dye was made. It was diluted to the necessary concentration before usage. To get the desired pH of the Acid Red 97 dye solution, 0.1M NaCl and 0.1 M HCl solution were used. Conical glass flasks (250 mL) carrying 50 mL of dye solution with predetermined pH and hydrogel quantity were agitated at 120 rpm.

pH controls the strength of electrical charges on the material that adsorbs and is used to calculate acidity or basicity (Salleh et al. 2011; Gillani et al. 2023). Solution pH affects the solubility of dyes. As a consequence, the rate at which molecules are adsorbed varies with the pH. By adjusting the pH from 2 to 11 of the adsorbate and adsorbent solution, which included 0.05 g/50 mL adsorbent dose and 0.5 g/L starting concentration of dye with 120 revolutions per minute at 30 °C temp until equilibrium, the pH effect of various nanohybrid biopolymeric hydrogels was examined. Hydrochloric acid and sodium hydroxide were employed to vary the pH of the solution.

Conditions: 0.05 g/50 mL adsorbent concentration, 120 revolutions per minute shaking speed, 30 °C temperature, 1.5 h.

In an acidic environment, the ideal solution pH values for achieving the greatest elimination of acid dye were identified. With an increase in pH or under alkaline circumstances, the adsorption of acid dye was decreased (Sadaf & Bhatti 2014). The reduction of protons exhibited a repellent effect with dye carrying a negative charge, as well as the increased concentration of hydroxide ions and increased competition with anionic dyes. The findings showed that the adsorbent's zero-point charge (pHpzc) closely matched the results. In general, pH less than pHpzc promotes the elimination of acidic dyes (Gautam et al. 2015). The strongest attraction was seen in environments having pH less than 7 because of increased H⁺ ion concentration, whereas electrostatic repulsion predominated in a basic environment and decreased dye removal. At lower pH, enhanced hydrogel swelling was observed, leading to the increase in the adsorption of Acid Red 97 dye at lower pH (Hosseini et al. 2016). At low pH values, the surface of the hydrogel is surrounded by H⁺ ions and the interaction of negatively charged dye molecule ions to approach the hydrogel increases due to the increased electrostatic forces of interaction. The use of polyaniline for the removal of acid dye from dye solutions was examined. It was deduced that at lowest pH, maximal dye removal was possible. Raising the pH above 5 resulted in a decrease in dye adsorptive removal (Aliyam et al. 2023; Ashraf et al. 2023; Mustafa et al. 2024). On the contrary, a study was carried out by Bardajee et al. (2019), and it was studied that lowering the pH of the solution resulted in the decreased capabilities of swelling of hydrogels, ultimately leading to the decrease in the adsorption of methyl violet dye adsorption.

Conditions: Standard pH, 120 revolutions per minute shaking speed, 1.5 h contact time, 30 °C temperature.

The outcomes showed that the capacity for adsorption of GO/CS–PVA, GO/starch–PVA, and GO/agar–PVA for Acid Red 97 dye was decreased when the dose was raised from 0.05 to 0.40 g in 50 ml at pH (3, 2, and 3), 30 °C temperature, and 120 revolutions per minute. The minimum dosage of all adsorbents showed the maximum adsorption of acid dyes. This reduction in adsorbent adsorption capacity at larger doses might be attributed to interacting surface active location convergence, which lowered the entire surface area accessible for dye anion adsorption and extended diffusion path (Noreen et al. 2021; Hasan & Aljeboree 2023).

Another significant factor that may have reduced the adsorption ability of the adsorbent at greater dosages was the presence of fewer molecules of dye to completely adsorb readily available connecting functioning active locations on the adsorbent surface, resulting in reduced dye adsorption (Sadaf et al. 2014). Another factor contributing to the decrease in the adsorption capacity can be the aggregation of adsorbent hydrogel molecules, leading to the decline in the availability of the sites of adsorption. However, dye molecules may also aggregate around the adsorbents leading to predominance of repulsive forces, and consequently, the capacity of adsorption decreases as the dose of the adsorbent is increased (Tamer et al. 2021; Zaheer et al. 2024). The decrease in the adsorption capacity can also be attributed to the saturation of adsorptive active sites during the process of uptake of Acid Red 97 dye from the solution as the dose concentration is increased. Kumar & Ahmad (2011) showed that increasing the adsorbent dosage from 0.025 to 0.2 g resulted in a decrease in the nano polyaniline's adsorption ability for the Acid Red 14 dye. Similarly, a study conducted by Tamer et al. (2021) demonstrated that the adsorption capacity of azo dyes decreases with an increase in the dose of GO-doped hydrogels from 0.1 to 0.5 g; however, the percentage removal increases.

Conditions: Standard pH, 0.05 g adsorbent dosage, 0.5 g/L dye concentration, 120 revolutions per minute, 30 °C temperature.

The outcomes showed that the elimination of Acid Red 97 dye using various adsorbents was quick at the initial stages and thereafter reached equilibrium in 90 min. Consequently, it was shown that 90 min was the optimal contact period for the maximum removal of Acid Red 97 dye. An increased number of functional binding sites on the surface of the adsorbent in the early stages of an adsorption procedure, which were eventually occupied by adsorbate, could explain such adsorption behavior of acid dye using various adsorbents, and then adsorbate began to gently penetrate the adsorbent mass (Sadaf & Bhatti 2014).

Conditions: Standard pH, 0.05 g/50 mL adsorbent dosage, 120 revolutions per minute shaking speed, equilibrium time, 0.5 g/L starting concentration of dye.

The findings revealed that raising the temperature from 30 to 50 °C decreased the adsorption ability of GO/CS–PVA, GO/starch–PVA, and GO/agar–PVA hydrogels for Acid Red 97 dye. All of the preceding studies revealed a significant reduction in hydrogel adsorption capacity, demonstrating exothermic character adsorption processes, which can be attributed to the breakup of adsorption interactions at greater temperature. So 30 °C temperature was determined to be the optimum temperature (Asgher & Bhatti 2012). At elevated temperatures, binding active sites may be inactive, resulting in lower adsorption capabilities (Aksu & Isoglu 2006). It was also found that increasing the temperature significantly affected the Acid Blue 45 dye's removal. The most acid dye was eliminated at lower temperatures, and the amount of dye removed decreased as the solution's temperature rose (Arthy & Saravanakumar 2013). According to Bardajee et al. (2019), adsorption capacity of noxious dyes increases with an increase in the temperature, and this increase was estimated to be up to 10%.

Conditions: Standard pH, 0.05 g/50 mL adsorbent dosage, 120 revolutions per minute shaking speed, equilibrium time, 30 °C temperature.

As demonstrated in the aforementioned image, raising the original dye concentration increased the adsorption of Acid Red 97 dye, the maximum adsorption rates of GO/CS–PVA, GO/starch–PVA, and GO/agar–PVA hydrogels for Acid Red 97 dye was found at 10 mg/L solution. The justification for this tendency might be that initial dye concentration generates a large driving power to decrease the exchange barrier between adsorbent and aqueous forms (Santhi et al. 2010). The acid dye's capacity for adsorption was enhanced by raising the dye concentration in the solution. Sharma et al. (2022) suggested that increasing the dye concentration at varying temperature conditions increases the adsorption capacities of different cationic dyes using acid-based hydrogels.

Tables 1 and 2 show the parameters of adsorption isotherm models. The findings demonstrated that, in contrast to the Freundlich isotherm model, the Langmuir model for the GO/CS–PVA was well fitted, but for GO/starch–PVA and GO/agar–PVA hydrogels, the Freundlich isotherm model was the best fit.

Adsorption kinetics determination is an essential step for designing any batch adsorption system and for the creation of suitable practical operational conditions for an industrial batch setup (Aljohani et al. 2023). The suitability of various kinetic models to examine the adsorption research data employing various hydrogels to determine the adsorption process can be checked.

The degree of thickness of the outermost layer is represented by C_i, and Table 3 displays the K_pi, C_i, and R² values of adsorption techniques.

The results in Table 3 show numerous kinetic models applied to experimental kinetic adsorption data. k₁, k₂, K_pi, and C_i, values were calculated. The experimentally measured and computed q_e values were in good agreement with pseudo-second-order kinetics. The correlation coefficient revealed that the adsorption of Acid Red 97 dye on nanohybrid biopolymeric hydrogels might be better characterized by pseudo-second-order model. For all adsorbents used in the process of elimination of Acid Red 97 dye, the intraparticle diffusion model demonstrated limited efficiency with a poor correlation value (R²).

ΔG is change in Gibb's free energy. T is the absolute temperature and R is the gas constant (Tapouk et al. 2020).

ΔG was negative, indicating that reactions occurred spontaneously. The real measurements of ΔG proved that the adsorption procedure was a genuine physical reaction (Nageeb Rashed et al. 2016). The negative value of the predicted enthalpy demonstrated that the reaction was exothermic. The positive entropy change implied that randomness rises as the reaction proceeds (Ayuba et al. 2019).

The adsorption potential of nanohybrid biopolymeric hydrogels was enhanced due to ions from heavy metals in the adsorption medium, and this adsorption capacity was further increased by raising the amount of these ions. The increase in adsorption potential might be explained by the accumulation of adsorbate molecules brought, which decreased the dye solubility in the solution and raised their removal efficiency (Nawaz et al. 2023). As the Pb²⁺ content rose from 0.1 to 0.5M, the adsorption capacity of GO/CS–PVA, GO/starch–PVA, and GO/agar–PVA hydrogels for Acid Red 97 dye increased significantly from 8.5 to 9.5 mg g⁻¹, 7.6 to 9.2 mg g⁻¹ and 6.7 to 8.8 mg g⁻¹, respectively. When Cd²⁺ content increased from 0 to 0.5M, the adsorption capacity of GO/CS–PVA, GO/starch–PVA, and GO/agar–PVA hydrogels for Acid Red 97 dye increased significantly from 8.6 to 9.7 mg g⁻¹, 7.6 to 9.2 mg g⁻¹, and 6.8 to 8.9 mg g⁻¹, respectively.

According to the results, desorption was increased as sodium hydroxide concentration was increased to 0.5 N. The maximal elution (60, 55, and 58%) of adsorbed Acid Red 97 dye from GO/CS–PVA, GO/starch–PVA, and GO/agar–PVA hydrogels reached using 0.5 N NaOH. The recovery test was conducted four times. As evidenced, the adsorption efficiency of hybrid biopolymer hydrogels decreases with each successive cycle, as illustrated in Figure 19(b). These promising results indicate that hybrid biopolymer hydrogels can be repeatedly regenerated and employed for dye removal purposes. This indicates that the adsorbent can be repeatedly employed for removing dye from wastewater. The decline in adsorption efficiency results from a decrease in the number of active sites after each adsorption/desorption cycle. A comparable pattern was noticed in the reusability of the regenerated adsorbent for dye removal from wastewater. The decrease in adsorption could also be attributed to repulsion between positively charged molecules and the protonated surface of the adsorbent caused by H⁺ ions in an acidic environment (Munir et al. 2023; Maqbool et al. 2024).

Using a Bruker Tensor 27 Fourier transform infrared (FT-IR) spectrometer with KBr discs, the chemical characteristics of the selected adsorbents were examined, and the results were evaluated. Figure 13 displays the FT-IR spectra of the material GO. GO's FT-IR spectrum displays a characteristic carboxyl C = O peak at 1,730 cm⁻¹. The aromatic C = C group was identified as the source of the peak at 1,600 cm⁻¹. In synthesized GO, the C-O bond exhibits a peak at 1,077 cm⁻¹. Following the oxidation process, double bond carbon remained, represented by peak 1,630⁻ to 1,650 cm⁻¹. In GO, absorbed water is shown as significant increased from 2,885⁻ to 3,715 cm⁻¹. This indicated that GO acts as an adsorbent (Habte & Ayele 2019).

Carbon double bond oxygen vibrations at 1,734 cm⁻¹ of GO/starch–PVA decreased, suggested some little consumption of the -COOH groups. The peaks at around 1,600 and 1,376 cm⁻¹ are ascribed to C = O and C-O-H bonds. The creation of ester connections between GO and soluble starch is demonstrated by the presence of a signal at about 1,172 cm⁻¹ (Bustos-Ramírez et al. 2013). The loaded GO/starch–PVA hydrogel's FT-IR spectra revealed that the bands that were present in the 3,700–3,730 cm⁻¹ and 2,300–2,350 cm⁻¹ ranges have disappeared. This demonstrated the groups' active involvement in the binding of adsorbate molecules to adsorbent surfaces. GO/agar–PVA usually exhibits bands at 1,052 cm⁻¹ in its FT-IR spectra, which are ascribed to carbon single-bond oxygen stretching (Araújo et al. 2022). It was reported that the FT-IR spectrum of GO/agar–PVA displays the following: glycoside bonding at 1,070 cm⁻¹, C-C stretching at 1,376 cm⁻¹, hydroxyl group stretching at 3,340 cm⁻¹, carbon single-bond hydrogen stretching at 2,918 cm⁻¹, carbon double bond hydrogen stretching at 1,600 cm⁻¹, and S = O of sulphate esters at 1,256 cm⁻¹, respectively (Belay et al. 2017). The loaded GO/agar–PVA hydrogel's FT-IR spectra revealed the bands that were present in the 3,700–3,730 cm⁻¹ and 2,300–2,350 cm⁻¹ ranges vanished. The peak bifurcates at 1,723 cm⁻¹. This demonstrated the groups' active involvement in the binding of adsorbate molecules to adsorbent surfaces.

Biopolymeric nanocomposites, which combine natural polymers with nano-sized particles, consist of environmentally friendly components and have demonstrated remarkable efficacy in wastewater treatment. These materials offer crucial reusability, further enhancing their practical utility. It is suggested that nanohybrid biopolymeric hydrogel materials can not only adsorb acidic dyes but also be adapted for the removal of various dyes with minor structural adjustments. While biopolymeric nanocomposites hold significant promise for wastewater remediation, it is important to acknowledge and address certain limitations. One primary challenge lies in adapting these materials for large-scale industrial applications. Achieving scalability in synthesis methods and seamlessly integrating them into existing wastewater treatment systems presents a complex task. In addition, some biopolymeric nanocomposites may exhibit specificity in adsorption, limiting their effectiveness against certain types of contaminants. To ensure broad-spectrum applicability, it is essential to address this specificity in adsorption.

Future research endeavors should explore their potential applications in treating acidic industrial wastewater, offering the dual benefits of enhanced adsorption and environmental friendliness. In addition, these materials can effectively remove metals from industrial wastewater, with GO or other inorganic components serving as active photocatalysts. This implies that the adsorption of dyes may be accompanied by photocatalytic decomposition, positioning nanohybrid biopolymeric hydrogels as significant players in photocatalytic applications.

The applicability of adsorption is hindered by the challenge of separation post-adsorption. To address this issue, nanohybrid biopolymeric hydrogel materials incorporating magnetic components can be developed to facilitate easy magnetic separation. Furthermore, the recent emergence of conducting polymers, such as PVA, in hybrid material development presents new opportunities for various prospects. While the application of polymeric adsorbents in dye removal typically does not involve electrical conductivity, their conducting ability enables the fabrication of electrodes and deposition on non-conductive substrates, expanding their utility in electrochemistry.

Given the necessity for robust adsorbent materials for practical applications, efforts to enhance reliability should be pursued. Further investigations into different synthetic routes and modifications are essential to improve adsorption capacity and stability. Consequently, hybrid materials with enhanced properties could find applications in designing batteries, optoelectronic and electrochromic devices, biomedical materials, sensing or imaging devices, among others. In addition, exploring the use of ring-substituted polymers and various copolymers can expand the array of hybrid adsorbents, ultimately leading to the development of adsorbents with outstanding adsorption potential, exceptional stability, easy separation, remarkable recyclability, and broad generalization.

There is plenty of water on Earth, with 97% of it in the form of oceans and the remaining 2% in the form of icecaps and glaciers. The rest is available as freshwater. The supply of freshwater is drastically decreasing owing to pollution caused by escalating industrialization, excessive water usage, and rising global population. Textile industry activities create massive amounts of dirty effluent including different dyes. These dyes are produced at a rate of 1 million tons per year. Because artificial dyes contain complicated aromatic compounds that are resistant to sunlight, oxidation, temperature, and water, they are the most harmful substances in wastewater. As a result, there is an urgent need to eliminate them from wastewater. Adsorption is significantly favored over the other methods because it may result in treated effluent of exceptionally high quality. Hydrogels act effectively as an adsorbent (Dai et al. 2018). Natural polymers were used to create hydrogels that are biocompatible, nontoxic, and biodegradable. Various types of nanohybrid biopolymeric hydrogels were synthesized employing GO, biopolymers including (CS, starch, and agar) and synthetic polymers including (PVA) to boost the acidic dye adsorption. GO/CS–PVA outperformed the other hydrogels in terms of Acid Red 97 dye removal. The decline in adsorption ability of all adsorbents was examined as temperature increased. The results revealed that for GO/CS–PVA had adsorption capacity of 8.251 mg g⁻¹ with pH 3, 0.05 g/50 mL dosage, 90 min, 12 ppm Acid Red 97 dye concentration and temperature of 30 °C. GO/starch–PVA had adsorption capacity of 7.437 mg g⁻¹ with 2 pH, 0.05 g/50 mL dosage, 90 min, 12 ppm Acid Red 97 dye concentration and 30 °C and GO/agar–PVA had adsorption capacity of 6.142 mg/g with 3 pH, 0.05 g/50 mL dosage, 90 min, 12 ppm Acid red 97 dye concentration, and temperature 30 °C. The Langmuir model suited the GO/CS–PVA data better than the Freundlich isotherm model, but for GO/starch–PVA and GO/agar–PVA hydrogels the Freundlich isotherm model was the best fit. Several mathematical models were used to conduct and interpret kinetic investigations. The capacity of Acid Red 97 dye to adsorb on (GO/CS–PVA, GO/starch–PVA, and GO/agar–PVA) hydrogels was shown to be effectively described by a pseudo-second-order model, according to the correlation coefficient (R²). Acquiring knowledge of several thermodynamic variables was necessary to understand the nature and viability of the adsorption mechanism. Gibbs free energy values were negative showing that the reactions were spontaneous. The estimated negative values of enthalpy proved that reactions are exothermic. The positive values of entropy changes implied that randomness would rise at the solid/solution contact. A total of 0.5 N NaOH produced the greatest desorption (60, 55, and 58%). Characterization was carried out by FT-IR, SEM, and XRD. As a result, it was determined that these hydrogels are cost-effective, biocompatible, and biodegradable materials to eliminate acid dye from wastewater and can be employed as an efficient adsorbent hydrogel for enhanced adsorptive remediation of acid dye from wastewater.

The authors wish to thank their parental institutes for providing the necessary facilities to accomplish the present research work.

All authors have read and approved this manuscript.

Omera Sarwar: methodology, conceptualization, writing – original draft; Saima Noreen: supervision, conceptualization, writing – reviewing and editing; Ruba Munir: writing – reviewing and editing, investigation, conceptualization, and data curation; Hina Ambreen: resources and writing – review and editing; Amna Muneer: statistical analysis and writing – review and editing; Muhammad Zeeshan Bashir: execution and writing – review and editing; Maryam Sana: conceptualization and interpretation; Nageen Mushtaq: execution and writing – review and editing; Murtaza Sayed: writing – review and editing

This research did not receive any funding.

All relevant data are included in the paper or its Supplementary Information.

The authors declare there is no conflict.