Functionalization of bentonite nano clayThe FTIR analysis of Bentonite nano-clay’s functionalization revealed significant changes in the clay’s vibrational modes and absorption bands, indicating the effective attachment of functional groups, as shown in Fig. 1. These findings demonstrate the efficiency of the functionalization method in improving the clay’s surface qualities and reactivity, which is crucial for industrial applications like adsorption, catalysis, and nano-composite materials.Figure 1FTIR of Functionalization of Bentonite Nano clay.Hydrogel characterizationFourier transform infrared spectroscopy (FTIR)-testThe study used Fourier Transform Infrared Spectroscopy (FTIR) to investigate the surface functionalization and chemical properties of nano-composite films made of Carrageenan-based hydrogel, Bentonite Nano-clay, and Polyvinyl Alcohol (PVA) as shown in, Table 2 and Fig. 2. Interestingly, almost all the hydrogels have exhibited prominent peaks around 3690 cm−1 indicating O–H stretching. These hydroxyl groups on the designed hydrogels can form hydrogen bonding with hydroxyl and amine groups present in OTC pollutant. Therefore, it is anticipated that the designed gydrogels will have higher adsorption capacity due to the presence of these bonding sites. In addition, the carboxyl groups (C=O) at 1581.6 cm−1 and 1352.1 cm−1, alcohol groups (C–O) present at at 1382.9 cm−1 and 1027.4 cm−1 and siloxane groups (Si–O) present at around 1004.9 cm−1 and 914.2 cm−1 can also form hydrogen bonding or van der Waal interactions with OTC, thereby providing more active sites for the adsorption.
Table 2 K-carrageenan-based hydrogel nano-composite with significant FTIR peaks.Figure 2FTIR analysis of hydrogel at magnifications (a) KPB-1 (b) KPB-2 (c) KPB-3 (d) KPB-4 (e) KPB-5 (f) KPB-6.SEM analysis of hydrogelThe study used Scanning Electron Microscopy (SEM) to analyze the surface shape of hydrogel films, as shown in Fig. 3, which affects their adsorption capacity. The hydrogel’s higher surface area allows for better interactions with contaminants. The addition of nano fillers increased the mechanical strength of the nano-composite films, demonstrating the power of hydrogen bonding between oxygen-containing groups and hydroxyl groups of chitosan and polyvinyl alcohol. Findings of our study are crucial for applications like adsorption, medication administration, and tissue engineering.Figure 3SEM images of hydrogel at magnifications ((a) X 1/4 3000 for KPB-1 (b) X 1/4 15,000), for KPB-2 (0.05) at magnifications ((c) X 1/4 3000 for KPB-3 (0.1) (d) X 1/4 15,000) for KPB-4 (0.15) at magnifications ((e) X 1/4 3000 for KPB-5(0.2) (f) X 1/4 15,000) for KPB-6.Hydrogel X-ray diffraction analysisThe X-ray Diffraction (XRD) technique was used to evaluate the crystallinity of K-carrageenan (KC)-based hydrogel. The results showed a semi-crystalline structure, with higher crystallinity correlated with higher intensities, as shown in Fig. 4. Modifications with Nano clay and cross-linker reduced crystallinity, affecting the material’s crystalline structure. As crystallinity increases, these characteristics also tend to increase.Figure 4X-Rays Diffraction of hydrogel (a) KPB-1 (b) KPB-2 (c) KPB-3 (d) KPB-4 (e) KPB-5 (f) KPB-6.Properties of hydrogelSwelling behavior of K-carrageenan (KC) hydrogel in distilled waterHydrogels grow gradually over time, with swelling occurring at later periods. Increased PVA concentrations increase swelling percentages, indicating PVA’s water-absorbing ability, as shown in Fig. 5. Stability and equilibrium occurs after 70–80 min, allowing hydrogels to absorb as much water as possible. Understanding these tendencies is crucial for modifying hydrogel properties. Table 3 displays the swelling behavior of K-carrageenan hydrogel in distilled water at different time intervals and polyvinyl alcohol concentrations. The swelling percentage, indicates water absorption and is crucial for evaluating its effectiveness in drug delivery and tissue engineering applications.Figure 5Comparative analysis of swelling ratio of K-carrageenan hydrogel after equal interval of time.Table 3 The swelling ratio after equal interval of time.Figure 5 shows the equilibrium swelling, which stabilizes after 70–80 min, indicating that the hydrogel has decomposed. This information assists the researchers in better understanding the kinetics and properties of the hydrogel’s swelling behavior, which is useful for applications like as medication delivery, wound dressings, and tissue engineering. Overall, the Table 3 is useful for comprehending the swelling behavior of kappa carrageenan hydrogels and their prospective applications in various disciplines.Table 3 shows the swelling ratio (Ws–Wd) of kappa carrageenan KC hydrogel with time compared to distilled water. The table comprises columns for time intervals (minutes) and distinct KC hydrogel compositions, each with differing PVA concentrations or formulations. The table’s key findings include time-dependent swelling, which normally rises with time, and the influence of PVA concentration on swelling ratios. Larger PVA concentrations result in larger swelling ratios, demonstrating that PVA improves the hydrogel’s ability to absorb water.Effect of pH on adsorption capacityThe effect of pH on the adsorption capacity of KC hydrogel is shown in the Fig. 6. The ability of a material to attract and hold molecules or chemicals from its surroundings is referred to as its adsorption capacity. The ideal pH range for maximizing KC hydrogel adsorption capability is typically near-neutral to slightly alkaline (about pH-6 to pH-8). KPB-1, for instance, has greater adsorption capability at pH-6 and pH-8 than at pH-2 and pH-4. This behaviour can be explained by swelling behavior of KPB-1 hydrogel which might swell at higher pH i.e. 6 to 8. This excessive swelling increases the surface area and active sites for adsorption.Figure 6Variation in pH at various concentration of K-carrageenan hydrogel.The reaction to pH changes is also concentration dependent, depending on the starting concentration of KC hydrogel. Understanding these pH-dependent adsorption properties is critical for optimizing the hydrogel performance in various applications such as water treatment, drug delivery, and adsorption of pollutants from aqueous solutions.Figure 7 shows that pH has a substantial impact on the OTC adsorption capacity of KC hydrogel. The adsorption capability across multiple pH levels, the hydrogel, especially KC/PVA/0.05, consistently outperforms other hydrogel formulations.Figure 7Effect of pH on adsorption capacity of OTC.Effect of initial concentration on K-carrageenan hydrogelThe ideal adsorbent dose is 0.05 g with a pH of 6 over 120 min on a magnetic stirrer at 35 °C. At an initial concentration of 40 mg/L, the KC/PVA/0.1 (H) Bentonite Nano clay nano-composite adsorbent displays outstanding capacity to adsorb OTC, with an excellent adsorption of 99%. The adsorbent’s effectiveness rises as the initial oxytetracycline concentration increases. The adsorbent still has 98% adsorption capacity at a lower starting concentration of 20 mg/L.However, Fig. 8 shows that when the initial OTC concentration rises to 40 mg/L, the adsorbent reaches its maximum potential, obtaining a adsorption capacity of more than 95%. This is due to the fact because initially at higher OTC concentrations, the driving force is maximum and more active sites are available for adsorption. As the adsorption proceeds, the gydrogel has reached its maximum potential and the active sites are nearly fully occupied by OTC molecules.Figure 8Variation in adsorption capacity at different concentration of Kappa carrageenan/Polyvinyl alcohol/Bentonite Nano clay Hydrogel.Overall removal of OTC from hydrogelThe removal efficiency for OTC from pharmaceutical wastewater by kappa carrageenan/ polyvinyl alcohol/ bentonite nanoclay (KPB) hydrogel was evaluated under various conditions and the results are demonstrated in Fig. 9. It was observed that removal effectiveness of most adsorbent compositions drecreases, as the initial OTC content increases. Thus, the adsorbent composition greatly influence adsorption capacity, with KPB-3 consistently demonstrating the best removal percentages, even at increasing OTC concentrations. This result can be explained by the fact that KPB-3 hydrogel had the optimum composition and it had provided synergistic effect of kappa carrageenan, polyvinyl alcohol, and bentonite nanoclay. Moreover, at initial concentrations, the hydrogel’s adsorption sites are abundantly available that make it suitable for handling higher OTC loads. The best performance of KPB-3 hydrogel can be explained by excellent swelling behaviour of the hydrogels that provide excessive surface area and active sites for adsorption.Figure 9Overall % removal of OTC from pharmaceutical wastewater by Kappa carrageenan/ Polyvinyl alcohol/ Bentonite Nano clay Hydrogel.Significant differences and correlationThe ANOVA test revealed that pH and concentration significantly influence OTC adsorption by a hydrogel (Table 4). The adsorption capacity of OTC is marginally higher than 0.054, suggesting that pH and concentration are more important. The sum of squares for pH fluctuations affecting OTC adsorption is 8.867, with a p-value of 0.01.
Table 4 ANOVA test on the properties of hydrogel, including pH and concentration and removal of OTC.ANOVA test revealed that pH and concentration significantly influence the hydrogel’s efficacy in removing OTC. The F-statistic is 6.697, with a p-value of 0.01, and the SS for OTC removal efficacy is 3.585, indicating some difference but not substantial, as shown in Table 4. Therefore, pH and concentration have a greater influence on OTC adsorption. In summary, the ANOVA findings show that pH and concentration have a greater influence on OTC adsorption by the hydrogel.The offered correlation (Table 5) demonstrates the links between several factors associated with KC/ PVA/ BNC hydrogel. The degree and direction of a linear link between two variables are measured by correlation.
Table 5 Correlation between the properties of Kappa carrageenan/Polyvinyl alcohol/Bentonite Nano clay Hydrogel.The study found no significant relationships between pH, temperature, contact time, or swelling. Initial concentration had strong positive correlations with pH, temperature, and contact time, indicating weak positive linear associations.Reaction kinetics modelAdsorption is a crucial process used in environmental remediation and wastewater treatment. Researchers used OTC solutions in a mixture of Kappa-carrageenan, polyvinyl alcohol, and Bentonite clay (Table 6).
Table 6 Different parameters of the kinetic model.Comparative analysisEnvironmental concerns have led to a growing demand for biodegradable polymers, such as Carrageenan, a flexible polymer from Irish Moss. Pharmaceutical products (PPs) are ubiquitous in environmental compartments, making efficient removal strategies difficult to identify8. A composite material with a cadmium adsorption capacity of 20.6 mg/g is selective in removing lead ions. Clay minerals, the oldest and least expensive adsorbents, potentially extract pharmaceutical products from wastewater effluents32. Research gaps exist in determining the full potential of clay-based adsorbents33,34. A recent research aims to develop biocompatible aerogel microparticles using commercial carrageenan as a precursor. Supercritical carbon dioxide extraction transform the gel into an aerogel, with analyzed FTIR, SEM, particle density and particle size distribution26. Three different carrageenans were used to create biodegradable aerogel micro-spherical particles with varying surface areas and average pore volume and size. The surface area varied from 33 to 174 m2/g, with an average pore volume and size of 0.35 0.11 cm3/g and 12.34 3.24. The porous material can be used in medication delivery applications26. Hybrid aerogel monoliths from alginate and -carrageenan were created by heating a carrageenan solution to 90 °C and adding a KSCN solution as a cross-linker. Cylindrical -carrageenan aerogels were created by gently dripping a -carrageenan solution into a -carrageenan solution35. Contact time is an important factor in oxytetracycline removal from pharmaceutical wastewater, with extended contact duration from 20 to 120 min, improving removal effectiveness with a 0.05 g adsorbent dosage.Researchers are exploring the economic viability of applying kappa carrageenan hydrogels in wastewater treatment and other applications by utilizing conditions, such as temperature, different pH levels and desorbing agents. The reusability of kappa carrageenan hydrogel combined with nano-composites has been explored and significant adsorption capabilities have been found36. A study on a specific contaminant showed a remarkable reusability of the hydrogel-nanocomposite with up to 90% retention of initial capacity even after five to ten cycles37. The adsorption process was endothermic, and the hydrogel was more reusable after five cycles and with over 70% clearance rate37,38. This study presented a novel carrageenan hydrogel for removing cationic methylene blue (MB) from aqueous solutions. PG hydrogel with reactive function groups enhanced the hydrogels adsorption capacity and stability. The adsorption was well-fitted using the Langmuir isotherm and the pseudo-second order model39. The beads could be easily regenerated and reused for at least five cycles efficiently. The material demonstrated excellent adsorption ability in various pH ranges, with a maximum capacity of 80.28 mg g−1 at 45 °C. Thermal, chemical, and pH level changes can be used to renew Kappa carrageenan hydrogel, with the effectiveness of regeneration determined by the adsorbate and applied technique40.Research on the economic feasibility of kappa carrageenan hydrogels for water treatment and other applications suggests possible cost effective methods of wastewater treatment. Studies on the reusability of nano-composites mixed with kappa carrageenan hydrogel showed strong adsorption capacities across several cycles. By using these nanocomposites in water purification systems, the requirement for single-use materials can be decreased, improving sustainability initiatives. The results highlight the vital significance that accurate pH management plays in optimizing the adsorption capacity for pollutants in pharmaceutical wastewater treatment regimens. The study also emphasizes the wider significance of OTC removal efficiency in adsorption processes and its implications for public health and environmental protection. In recent years, numerous different plant extracts, including Azadirachta indica leaf extract, have been utilized to remediate industrial effluent. Plant-based remediation has gained popularity for the efficient cleanup of polluted water41,42. Recent breakthroughs in materials science and green chemistry have resulted in the production of nanomaterials with large specific surface areas and diverse functionalities, making them effective in removing heavy metals from wastewater. According to the research, the most efficient, effective, clean, and sustainable technique for removing heavy metals from wastewater is by the adsorption of these metals onto green nanomaterials derived from plant extracts43,44,45.
Removal of oxytetracycline from pharmaceutical wastewater using kappa carrageenan hydrogel
