1 Introduction

Human society and devolving industries are the two main factors generating environmental pollution. The various industries such as paints, cosmetics, food, textile, leather, mining, pharmaceutical, and chemical manufacturing release industrial effluents containing heavy metal ions, dyes, and non-biodegradable materials that deteriorate the quality of water and disturb aquatic life [1,2,3,4]. Dyes pose serious problems since 10–15% of them are lost during processing and lead to eutrophication [5, 6]. The dye concentration (> 2 ppm) in water proves to be toxic and may cause vomiting, diarrhea, gastritis, headache skin irritation and also affects the photosynthesis process by less diffusion of light in water. To protect wildlife, it is thus a worldwide issue to remove the dyes from industrial effluents [7]. Several techniques have been utilized for the treatment of industrialized effluents like chemical precipitation [8], electrocoagulation, oxidation, ozonation, reverse osmosis [9], photocatalytic degradation [10], and adsorption [11]. Therefore, there is an urgent need to develop regenerative and eco-friendly technologies to tackle environmental problems.

The most efficient technique is adsorption due to its flexibility in a wide range of dyes, simple design, low cost, easy operation, and high efficiency [12, 13]. Generally, to remove the pollutants from industrial wastewater mostly activated carbon as an adsorbent is used due to wide properties like porous high surface area and surface reactivity [14, 15]. Although, its utilization on a wide scale makes it difficult due to dispersion, cost-effectiveness, and reusability [16, 17]. Over the last decade, numerous materials like polymer resins [18], clay minerals [19], nanotubes [20], nanofibers [21], metal oxide and polymer-based nanomaterials [22] have been utilized for the treatment of industrial waste discharges. The adsorbents such as lemon peel, peach stones, coffee bean, walnut wood, and rice husk have also been reported for dye adsorption [23,24,25,26]. These described adsorbent’s sluggish kinetics make them undesirable. Biopolymer composites have drawn a lot of interest because of their distinctive qualities, including oxygen permeability, low interfacial tension, and biodegradation [27, 28]. The unmodified biopolymer materials have weak mechanical strength, lack reusability, and high solubility in water, that’s why cannot be repeatedly used as adsorbent material [29]. By grafting various monomers onto the polymer’s backbone and adding metal nanoparticles (MNPs) like Ni, Ag, Au, CNT, and graphene to increase their mechanical strength, unmodified biopolymers may be changed. MNP’s high surface energy and surface area are what cause the dye molecules to adhere to the polymer surface [30, 31].

Numerous studies have been reported against adsorbents for dye removal, guar gum (GG) natural polysaccharide grafted carbon nanotubes with an adsorption capacity of 61.92 mg/g [32,33,34], GG/poly(AA) and GG/poly(AA-in-ANI) are 167.571 and 168.577 (mg/g) [35], Chitosan/PVP/Bi2O3 nanocomposite, composite films made of chitosan-based natural products (ginger, curcumin, and cinnamon) as biomaterials, and chitosan-zinc oxide (ZnO) nanocomposite are only a few examples. Xanthan gum was grafted with acrylamide containing nano-silica [36]. The observed concentrations of the hydrogel polymer based on gg-cl-P(AAm-co-MAA) are 497.5 mg/g and 694.44 mg/g, respectively. But metallic composites like CoFe2O4@CMC/HZSM-5 are also helpful for treating wastewater [37]. The utilization of starch-grafted polymer composites (starch-PMA and Ag@starch-PMA) as an adsorbent material is so far to be explored. The AgNPs show remarkable photocatalytic dye degradation efficiency the rationale to blend with starch-PMA composite to enhance the adsorption efficiency and gained significant interest in dye removal from industrial wastewater [38]. The challenges regarding the MB removal from aqueous solution using these polymers as adsorbent is still required.

In the present work, innovative biodegradable Starch-PMA and Ag@Starch-PMA polymer composites that are eco-friendly, affordable, and biodegradable were created for the efficient removal of MB from wastewater. To our best knowledge, synthesized starch-based polymers have not been reported. In addition, the effects of pH, contact duration, dosage, adsorbent and dye concentration were examined. The adsorption of MB in an aqueous solution has also been evaluated using kinetic models and isotherms.

2 Materials and methods

2.1 Materials

Starch [M = 342.30 (C6H10O5)n, 99%, Sigma], acrylic acid (AA) (C3H4O2, 97%, DOW Chemical Company), methyl methacrylate (MMA) (C5H8O2, 98%, DOW Chemical Company), Lactic Acid (LA), (98%, DOW Chemical Company), Lutensol XL-100 (alkyl polyethylene glycol ethers, 97%, Sigma), potassium persulphate (K2S2O8, 99%, Sigma), AgNPs (97%, Sigma), distilled water and commercial Methylene blue dye (C16H18ClN3S). Analytical grade substances were used throughout the whole experimental process.

2.2 Synthesis of starch-PMA and Ag@starch-PMApolymer composite

0.5 g of starch was dissolved in 50 mL of distilled water at 85 °C in a three-necked reaction kettle with a mechanical stirrer to create a translucent solution. After 25 min, the starch solution was combined with Lutensol XL 100 (0.5 g) as an emulsifier and potassium persulphate (0.15 g) as an initiator (5 min). The initiator generates the free radicals of starch functional groups that start the polymerization reaction. Following that, a combination of pure monomers (4 mL of methyl methacrylate, 4 mL of acrylic acid, and 2 mL of polylactic acid) was added at a rate of one milliliter per minute while vigorously stirring the mixture and the temperature was maintained for one hour. Next, 0.005 g of green synthetic AgNPs were added, and the reaction was allowed to run its course for 30 min while being stirred. In the end, the reaction mixture was left over at room temperature; a very fine thin film of Starch-PMA and Ag@starch-PMA was obtained.

2.3 Characterization of starch-PMA and Ag@starch-PMA polymer composites

The presence of NPs inside the Ag@starch-PMA polymer composite is confirmed by UV–Vis absorption spectra (Shimadzu, UV-1240, Kyoto, Japan) in the range 300–700 nm at ambient temperature. To confirm the grafting of monomers on the starch backbone, the synthesis of starch-PMA and Ag@starch-PMA polymer composites and to examine their chemical composition FTIR (Midac Corporation) spectrum is recorded (4000–500 cm−1). The morphology of synthesized composite thin films is examined using SEM (Nova NanoSEM 450 field-emission) and the presence of the AgNPs was confirmed by the EDX analysis. A heating rate of 10 °C/min was used to measure the TGA/DTG (SDT Q600 V20.9) analysis.

2.4 Dye adsorption studies

2.4.1 Preparation of MB stock solution

A stock solution was made by dissolving 1 g of MB in 1 L of distilled water. Before using the stock solution to make the solutions for the adsorption research, it was diluted to the required concentration. To adjust the mixture’s pH, either 1 M NaOH or 1 M HCl was added.

2.4.2 Dye adsorption experiment

The purpose of the adsorption experiment was to examine how the MB adsorbs to starch-PMA and Ag@starch-PMA. Examined separately were the effects of contact duration, adsorbent dosage, starting dye concentration, and solution pH. Using a UV-Vis spectrophotometer (UV-1800, Shimadzu Corporation, Japan) that operates in the 400–800 nm range, the concentration of the MB aqueous solution was assessed both before and after adsorption. The MB solution (250 mL) was taken in two flasks, and 0.15 g of each adsorbent was mixed and put on a thermostat shaker at 150 rpm. After that, the sample was taken every 5 min until the disappearance of the dye color. To determine the adsorption (percent) and capacity for MB, Eqs. (1) and (2) were utilized.

$${\text{Dye adsorption}} \left( \% \right) = C_{0} - \frac{Ce}{{C_{0} }} \times 100$$
(1)
$$qt = \frac{{C_{0} - {\text{Ct}}}}{m}{ } \times {\text{V}}$$
(2)

Here, C0 (mg/L), and Ce (mg/L) were MB concentration at the initial and at time t, respectively; V(L) volume of dye solution and m (g) weight of the polymer adsorbent used.

Initially, the effect of adsorbent dose starch-PMA and Ag@starch-PMA on MB solution (1 mg/L)was first studied. 0.15 g of starch-PMA and Ag@starch-PMA were introduced to MB solution (1 mg/L) at 298 K to evaluate the influence of pH (1.4–10.4) on dye removal. Next, a 1 M NaOH and 1 M HCl solution was used to adjust the pH of the mixture. The final solution was analyzed at equilibrium after 3 h and 15 min. The kinetic study was conducted with starch-PMA and Ag@starch-PMA in 250 mL of MB solution (1 mg/L) at 298 K, pH 8.4, and an adsorbent dose (0.15 g). At 298 K and pH 8, 0.15 g of starch-PMA and Ag@starch-PMA were added to 100 mL of MB at various starting concentrations (10, 100, 200, 300, 400, and 500 ppm) to create the adsorption isotherm.

3 Results and discussion

3.1 FTIR analysis

Figure 1A illustrates the FTIR spectra and represents the various peaks of functional groups in pure starch, AA, MMA, and LA, respectively. The broadband in the range 3400–3600 cm−1 and peak at 2950 cm−1 confirms the –OH and –C–H stretching vibration [39,40,41]. The strong peak at 2150 cm−1 and 1750 cm−1 and 1125 cm−1 is correlated with the C = C, –C = O, and –C–O extending vibrations in the monomers [42, 43]. Figure 1B showed the FTIR spectra of Starch-PMA and Ag@starch-PMA and AgNPs. The broadband in the range 3400–3600 cm−1 ascribed –OH, at 3150 cm−1, –C = CH, below 3000 cm−1 –C–H, and 2150 cm−1 –C = CH stretching vibrations, respectively. Meanwhile, the distinctive peak at 1713 cm−1 appeared due to extending vibration of –C = O and ester groups. However, the FTIR spectrum of both prepared composites indicates that no additional peak was observed, and it suggests the Ag NPs interaction with polymer composites without any chemical bonding [44]. Therefore, we suggest that the AgNPs free network and anchored on the composite surface. So, these preliminary findings suggest that both composites had been manufactured.

Fig. 1
figure 1

A FTIR spectra of pure starch, monomers (PLA, AA, and MMA). B AgNPs, Starch-PMA, and Ag@starch-PMA polymer composites

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3.2 Thermogravimetric analysis

The TGA-DTG analysis curves of Ag@starch-PMA(A-1) and Starch-PMA(A-2) polymer composites are represented in Fig. 2. The weight loss of prepared polymer composites was seen in three steps. The first stage, which occurs between 100 and 250 °C, is characterized by weight loss brought on by water molecules evaporating. In the second step, rapid thermal degradation of the organic content (polysaccharides and elimination of CO and CO2) of prepared polymer composites occurs at 250–410 °C along with a small hump near 400 °C. The side chain and remaining AgNPs are degraded in the third stage, which starts at 410 °C and steadily decreases in weight until 600 °C. There is a slight difference in thermal degradation between Ag@starch-PMA (76%) and Starch-PMA (90%) at 520 °C and 500 °C, respectively, which is due to the presence of AgNPs.

Fig. 2
figure 2

a and b TGA-DTA plots of Ag@starch-PMA (A-1) and c, d Starch-PMA (A-2) polymer composite samples

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3.3 SEM analysis

The parent composite, starch-PMA, and its silver-based nanocomposite, Ag@starch-PMA, are studied using the SEM method to examine the surface morphology and compatibility of AgNPs. Figure 3A–C represents the SEM images of the starch-PMA composite and it can be seen that rough, stratified surface with few folding and voids. Moreover, the incorporation and uniform dispersion of AgNPs in starch-PMA, a significant change in the morphology of polymer composite and leads to the improvement in the surface area shown in figure (D) and (E). Due to surface modification, the adsorption site for MB was enhanced on the surface of the Ag@starch-PMA polymer composite and showed excellent adsorption efficiency at room temperature.

Fig. 3
figure 3

SEM images of starch-PMA at A 500 µm, B 4 µm, C 10 µm and Ag@starch-PMA polymer composite at D 1 µm, E 500 nm

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Figure 4a displays the X-ray diffraction patterns of starch-PMA and Ag@starch-PMA composites. All Ag@starch-PMA composites exhibit the distinctive peaks of the starch with no discernible variations from pure starch. In the Ag@starch-PMA composites, diffraction peaks at 38.11°, 44.39°, 65.06°, and 77.51° are clearly discernible. These peaks are indexed with the card number (JCPDS#00-04-0783), and they correlate to the silver’s face-centered cubic crystallographic planes (111), (200), (220), and (311). The coexistence of starch-PMA and Ag NPs as well as the construction of composites including Ag@starch-PMA were verified by XRD analysis (Fig. 4a) of the two materials. According to Fig. 4b, the BET surface areas for the starch-PMA and Ag@starch-PMA composites are 11.29 and 25.13 m2/g, respectively. It was observed that whereas Ag@starch-PMA has a large BET surface area due to its composite structure, starch-PMA has a smaller BET surface area. Ag NPs generate a porous environment for efficient material synthesis as shown by the considerable enhance in BET surface area that results from the addition of Ag to the Ag@starch-PMA composite. The number of reaction active sites increases with BET surface area, which may be beneficial for enhancing adsorption efficacy.

Fig. 4
figure 4

a XRD pattern of starch-PMA and Ag@starch-PMA and b Nitrogen adsorption–desorption isotherms of starch-PMA and Ag@starch-PMA

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3.4 Biodegradation studies

Using the soil burial technique, the biodegradation study of the polymer composites Starch-PMA and Ag@starch-PMA was investigated. Both composites underwent an 11 week burial test. Initially, the weight of both polymer composites increases due to water absorption present in the soil, and then gradually weight loss was observed. The polymer composite (Ag@starch-PMA) slightly shows less biodegradation due to the antimicrobial effect of AgNPs. The biodegradation of starch-PMA increased up to 37.79% while Ag@starch-PMA was 36.92% shown in Fig. 5.

Fig. 5
figure 5

Weight loss of Ag@starch-PMA and Starch-PMA polymer composites study by soil burial method

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3.5 Adsorption study of MB

3.5.1 Adsorption mechanism of MB dye onto polymer composites

The most feasible mechanism for MB adsorption on the surface of starch-PMA and Ag@starch-PMA polymer composites as adsorbents is shown in Fig. 6. The FTIR analysis examines the surface of composites formed of polymer materials to see whether functional groups (–OH and –COOH), which are essential to the adsorption process, are present. In the basic media of MB, both the –OH and –COOH are deprotonated [45]. A negative charge and a strong association with cationic MB are present on the polymer composite’s surface, which is absorbed on the adsorbent surface. In addition, the interactions exist between electronegative atoms of polymer adsorbents and positive atoms of MB dye shown in Fig. 6. Additionally, the AgNPs reinforced in the polymer composites increase the surface and provide surface energy to improve the likelihood that MB dye molecules will bind. Therefore, the surface of the produced adsorbent absorbs MB molecules.

Fig. 6
figure 6

Adsorption mechanism of MB on the surface of polymer composite

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3.5.2 Aqueous solution MB dye absorption is affected by pH

The pH of the MB dye solution has a major influence on the binding sites of the adsorbent in the adsorption process [46]. Throughout the adsorption process, the pH of the MB dye solution has a substantial influence on the adsorbent's binding sites [47, 48]. Therefore, the adsorption behavior of the synthesized starch-PMA and Ag@starch-PMA polymer composites for MB dye solution were studied by adjusting the pH range 1.4–12.4 at room temperature using 1 M HCl or 1 M NaOH. It is evident that an increase in pH results in an enhanced adsorption capacity for both polymer composites at equilibrium. Because MB dye is cationic and produces positive ions in an aqueous solution that stays constant up to pH12.4, it is noted that the highest adsorption of MB dye is reached at pH 7.4–8.4, as illustrated in Fig. 7. It is evident that an increase in pH results in an enhanced adsorption capacity for both polymer composites at equilibrium. Because MB dye is cationic and produces positive ions in an aqueous solution that stays constant up to pH12.4, it is noted that the highest adsorption of MB dye is reached at pH 7.4–8.4, as illustrated in Fig. 7.In acidic media (pH < 7), the polymer composite surface possesses positive charges due to the protonation of COO– to COOH groups of the polymer chain which affect the adsorbent efficiency and retards its adsorption capacity but increases in pH value (9–13), COOH group ionize to COO–, the polymer composite surface acquires a negative charge that enhances the adsorption process. As shown in Fig. 6, the electrostatic interaction between positive ions of MB dye and negative charges on the surface of the polymer composites supports the adsorption of Ag@starch-PMA and Starch-PMA on the surface of the polymer composites.

Fig. 7
figure 7

Effect of pH on MB adsorption a Ag@starch-PMA and b Starch-PMA polymer composite

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3.6 Adsorption kinetics studies

3.6.1 Effects of adsorption kinetics and contact time

The findings of the MB dye (1 mg/L) adsorption kinetics in the produced Starch-PMA and Ag@starch-PMA polymer composites are shown in Fig. 8a. According to the contact duration and MB removal for the two polymer composites, the adsorption rose quickly. The removal of dye is caused by the attachment of MB from the aqueous solution to the surface of polymer composites when shaken continuously. Comparing the results of two polymer composites, it can be observed that on equilibrium the adsorption of MB on Ag@starch-PMA is relatively higher than Starch-PMA. However, under the same adsorption condition (time 195 min and ambient temperature), the adsorption process reaches equilibrium in less time with higher adsorption on Ag@starch-PMA due to AgNPs. Following a 15 min dye adsorption procedure, all samples were collected and subjected to a UV/Vis spectrophotometer analysis between 300 and 700 nm.

Fig. 8
figure 8

a Effect of time on the amount of MB adsorbed onto Starch-PMA and Ag@starch-PMA polymer nanocomposites and b Structural stability of Starch-PMA and Ag@starch-PMA

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The MB adsorption recycling tests with Ag@starch-PMA composites were conducted three times under the same reaction conditions since the stability of Ag@starch-PMA polymer composites is essential to determining their appropriateness for practical applications. Figure 8b, c show, respectively, the XRD patterns of Ag@starch-PMA polymer composites before the reaction and after the third round of MB adsorption studies. The structural integrity of Ag@starch-PMA polymer composites is further confirmed by the absence of any visible structural changes between the time of adsorption recycling studies and the time prior. We may infer from the research above that the combination of Ag@starch and PMA polymer is a very durable and efficient adsorbent.

3.6.2 Kinetic models

Figure 9 illustrates the MB adsorption kinetics toward the starch-PMA and Ag@starch-PMA. Using pseudo-first order and pseudo-second-order, the rate constant for MB may be written as [49, 50]:

$$\log \left( {qe - qt} \right) = \log \, qe {-}\left( {\frac{{{\text{K}}1}}{2.303}} \right)t$$
(3)
$$\frac{t}{qt }= \frac{1}{K2qe2 } +\frac{t}{qe}$$
(4)

at equilibrium, qe is the adsorption of dye per unit mass (mg g−1), qt is the mass of dye adsorbed at time t, and K1 and K2 are the rate constants for pseudo-first and pseudo-second orders. In the current research, the kinetic study was carried out at different time intervals (15 min) for MB dye adsorption. Slop and linear fit graph of log(qe–qt)against (t) and t/qt against(t) for the pseudo-first-order, and pseudo-second-order to explain the adsorption models. The intercept and slopes of the linear plots were used to calculate the values of K1, K2, and qe, respectively. A high degree of linearity in the adsorption process points to a pseudo-second-order kinetic. Pseudo-second-order kinetics had a lower correlation coefficient factor (R2) value than pseudo-first-order kinetics. The pseudo-second-order mechanism may be used to deduce the best description of the adsorption of starch-PMA and Ag@starch-PMA for the MB aqueous solution. The correlation coefficient (R2) and theoretical adsorption capacity values, qe, were more in accord with the actual values, qe Table 1. Therefore, the adsorption process in Fig. 9a (Starch-PMA), R2 value 0.8619 follows the pseudo-first-order and in Fig. 9b (Ag@starch-PMA), R2 value 0.9898 pseudo-second order kinetics for 10 ppm concentration of MB dye solution. In general, electrostatic contacts, chemical bonds, hydrogen bonds, ion exchange, van der Waal forces, and a physical adsorption process were all present in the adsorption association between adsorbents and dye. But in my current work, hydrogen bonding and electrostatic interactions between MB dye and starch-PMA, and Ag@starch-PMA polymer composites were the main factors for the adsorption process. In Table 2, the starch-PMA and Ag@starch-PMA polymer composites' ability to adsorb MB was contrasted with that of other known adsorbent materials.

Fig. 9
figure 9

Pseudo-first order and pseudo-second order plots of a Starch-PMA and b Ag@starch-PMA polymer composites

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Table 1 Adsorption kinetic factors for the adsorption of Methylene blue onto Starch-PMA and Ag@Starch-PMA
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Table 2 Comparison of the maximal dye-removal adsorption capabilities of starch-PMA, Ag@starch-PMA, and other adsorbents
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3.6.3 Adsorption isotherm study

The relationship between adsorbent and adsorbate is extensively explained by the examination of adsorption isotherms. It is typical to use the Langmuir and Freundlich adsorption isotherms:

$$\frac{Ce}{qe}= \frac{Ce}{qm} +\frac{1}{RLqm}$$
(5)
$${\text{ln}}\,{\text{qe}} = \ln Kf + \frac{1}{n} \ln \,Ce$$
(6)

where Ce (mg/L), qe (mg/g), and qm (mg/g) are the concentrations of MB solution, adsorption capacity, and maximum adsorption capacity at equilibrium, respectively; RL and Kf (L/mg) are the Langmuir and Freundlich constants; and n is the heterogeneity factor and quantifies the intensity of adsorption. Both models may be used to investigate the MB dye adsorption behavior of manufactured starch-PMA and Ag@starch-PMA. The isotherm factors are listed in Table 3 and Fig. 10 displays the linear expression of Ce/qe against Ce for the Langmuir isotherm and lnqe against lnCe for the Freundlich isotherm, which are used to evaluate and corresponding parameters for both adsorbents, slop and intercepts (1/qmax (slop) and 1/qmax b). It was observed that the values of the Qmax (mg/g) for Starch-PMA (522.7834) and Ag@Starch-PMA (541.2563) and b, respectively, were calculated using the slope and intercept of the plot. With a linear correlation value of R2 = 0.994, the data for the MB dye adsorption onto Starch-PMA and Ag@starch-PMA polymer composites were fed into the Langmuir equation. According to the findings, the maximum adsorption (qmax) of MB values for Starch-PMA and Ag@Starch-PMA were 522.7834 and 541.2563, respectively.

Table 3 Langmuir adsorption isotherms parameters
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Fig. 10
figure 10

Fitting curves of Langmuir isotherm model a Langmuir isotherm model. b Freundlich isotherm model

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4 Conclusion

Novel starch-grafted polymer composites as adsorbents were successfully prepared via free radical polymerization. Spectroscopic techniques reveal the existence of hydroxyl and carboxylic groups on the surface of the adsorbents, and these groups are essential to the adsorptive removal of MB in the pH range of 7.4–9.4. The experimental results of MB adsorption on starch-PMA and Ag@starch-PMA support pseudo-first order and pseudo-second order, respectively, with correlation values (R2) of 0.8619 and 0.9898. The isotherm experimental data, which depicts a homogenous monolayer on the surface of adsorbents, is the best match for the Langmuir isotherm. Moreover, the biodegradation of the polymer composites with the biodegradability value of starch-PMA 37.79% and Ag@satrch-PMA 36.92% were also confirmed using the soil burial method.