Adsorption of Methylene Blue By Graft Copolymer Acrylamide Onto Pineapple Peel Cellulose With The Addition of Activated Carbon Microwave-Assisted

Cationic dyes such as methylene blue are among the most widely used dye in the textile and paper industry. The dye waste produced causes environmental pollution and is harmful to human health. Thus, wastewater treatment becomes an important aspect of reducing this problem. Adsorption is a very effective method for treating various wastewaters due to its high selectivity and capacity. This study aims to prepare an adsorbent from graft copolymer acrylamide onto cellulose with the addition of activated carbon microwave-assisted and to test its performance as an adsorbent for methylene blue. The adsorbent synthesis was carried out using a microwave-assisted graft copolymer technique. The graft of acrylamide onto cellulose with the addition of activated carbon was carried out at various times (3, 4, and 5 minutes). Based on the FTIR spectra characterization of the adsorbent, the functional groups are C=O and N-H, and SEM analysis shows that the surface forms an interconnected network. At 3, 4, and 5 minutes of irradiation, grafting ratios were 329.72, 128.00, and 150.12, with grafting efficiency of 99.74, 72.94, and 78.02%. Following the Langmuir isotherm model and pseudo second order kinetics, the maximum adsorption capacities of the adsorbent on methylene blue were, respectively, 14.00, 6.04, and 9.97 mg/g. The experimental results show that the adsorbent can effectively remove or eliminate methylene blue in an aqueous solution.


Introduction
Cationic dyes such as methylene blue are among the most widely used dye in the textile and paper industry (Makhado et al., 2018). The resulting dye waste causes environmental pollution and is a hazard to human health. This dye is difficult to remove due to its complicated molecule and low biodegradability (Freitas et al., 2015). Therefore, wastewater treatment is an important aspect to reduce or eliminate this problem. Synthetic dyes have been removed from wastewater use a variety of techniques. Wastewater treatment can be carried out by several techniques, such as coagulation, flocculation, oxidation, adsorption, electrochemistry, and membrane filtration (Fakhre and Ibrahim, 2018). Among these methods, adsorption is very effective for treating various wastewater due to its high selectivity and capacity (Asadollahzadeh et al., 2020).
Biopolymer-based adsorbents have received more attention due to their non-toxicity and biodegradability (Oladoja et al., 2015). Cellulose is a biopolymer polysaccharide which is usually utilized because it has abundant hydroxyl groups. Most cellulose can be utilized from agricultural waste because it is available in large quantities, renewable, and easy to obtain. In Indonesia, pineapple (Ananas comosus (L). Merr) is one of the most abundant fruits. According to BPS (2019), the total production of pineapples in 2018 was around 1,805,506 tons. Utilization of pineapple peel as a raw material for the manufacture of adsorbents is an environmentally friendly approach to overcome the problem of disposal. A small portion of the pineapple peel produced is used as animal feed and fertilizer (Ketnawa et al., 2012). However, most of it is burned as waste, causing environmental pollution (Gnanasekaran et al., 2021). The cellulose content in pineapple peel is around 20-25% (Hu et al., 2013). However, the strong intramolecular and intermolecular hydrogen makes it difficult for cellulose to depend on other compounds. The characteristics and qualities of cellulose can be improved with this grafting approach.
Polymer modification using microwaves is one of the successful techniques used in graft copolymerization.
Microwave irradiation causes selective excitation, producing free radical just on the polymer (Sen et al., 2013). Most studies have focused on binary systems that use biopolymer and graft monomer. The combination of grafted acrylamide onto cellulose and the addition of activated carbon allows for the creation of hybrids with both properties and new properties as a result of their interactions. So that the presence of activated will enhance the adsorbent's ability to handle complicated dye effectively. The purpose of this study is to fabricate adsorbents from acrylamide graft copolymers on cellulose with the addition of activated carbon, and then use microwave irradiation to test their effectiveness against methylene blue.

Materials
Pineapple peel (Tangkit, Jambi), acrylamide (Merck, Germany), and activated carbon (Technical) are used as raw materials in the graft copolymer synthesis process. 30% hydrogen peroxide (Merck, Germany) and potassium hydroxide (Merck, Germany) were used for the cellulose isolation process. Sodium hydroxide (Merck, Germany) and urea (Merck, Germany) were used for the cellulose solubility test. Selenium (Merck, Germany), 95-97% sulfuric acid (Merck, Germany), 3% boric acid (Merck, Germany), and hydrochloric acid (Merck, Germany) were used for the test for nitrogen content. Methylene blue (Merck, Germany) was used for performance tests.

Isolation of Pineapple Peel Cellulose
Pineapple peel cellulose isolation refers to the method (Hu et al., 2013) and the delignification (Cahyani., 2013). Pineapple peel was washed and dried in an Pineapple peel was cleaned before being dried in a 60 °C oven. After that, it was ground up and put through an 80 mesh sieve. 50 g of pineapple peel powder were mixed in 1000 mL of distilled water for two hours at 80 °C. At 80 to 90 °C for 2, 3, and 3 hours, 5% hydrogen peroxide solution (4% sodium hydroxide solution, pH 12) was used to delignify the insoluble residue. After becoming cleaned with distilled water, the residue was dried for 16 hours at 50 °C. To remove the hemicellulose, 10% potassium hydroxide solution was added and left on for 10 hours. Following a wash with distilled water to neutral the pH, the residue was dried at 50 °C for 24 hours, and filtered through an 80 mesh sieve.

Determination of Cellulose, Hemicellulose, and Lignin Levels
Testing the analysis of cellulose, hemicellulose, and lignin refers to the method (Datta. 1981). A sample of 1 g was put into a beaker and 150 mL of distilled water was added. The sample was heated for 2 hours at 100 °C. The sample was then filtered, cleaned with distilled water, and the residue material was dried in an oven at 105°C until the weight remained constant (a). After being heated at 100 °C for 2 hours, the dried residue was dissolved in 150 mL of 1 N H2SO4. The residue material was then filtered and cleaned with distilled water. The residue material was dried to a constant weight and weighed (b). The dry residue was then immersed in 10 mL of 72% H2SO4 for 4 hours, diluted by adding 150 mL of 1 N H2SO4, and heated at 100 °C for 2 hours. After that, the sample was filtered and cleaned using distilled water. The residue material was dried to a constant weight and weighed (c). The residue was ashed for 6 hours at 600 °C. Determination of hemicellulose, cellulose, and lignin content can be calculated using Equation 1 -3.

Adsorbent Synthesis
4 g of acrylamide was mixed into distilled water. Cellulose and activated carbon are to the add for 24 hours at room temperature. The blend was microwave irradiated for 3, 4, and 5 minutes at 750 W while being dried at 60 °C. Microwave power and exposure time refer to (Bai et al., 2018;Huang et al., 2018). The graft ratio and efficiency were determined by Equation 4 and 5 (Mas'ud et al., 2013).

Infrared Fourier Transform Analysis
A sample of 0.005 g was mixed with 0.1 g KBr, made into pellets with a pressure of 1 atm (Shimadzu -A21004200562 LP, Japan), which were then measured at wavenumbers range from 4000 to 500 cm -1 at a scanning speed of 72 payar/min.

The morphology of Adsorbent
The morphology of the adsorbent was characterized by using a scanning electron microscopy (SEM, Thermo Scientific, United States of America). The scellulose isolate and adsorbent were attached to the top of the set holder, then coated with gold metal in a vacuum. Observations of morphology were made at a voltage of 20 kV and a magnification range of 10.000x-100.000x.

Methylene Blue Adsorption
Adsorbent much as 0.125 g was put into 20 mL of methylene blue solution at time intervals (30,60,90,120,150,180,210,240,270, and 300 minutes) and concentration (25, 50, 75, 100, and 125 ppm). Utilizing a UV-Vis spectrophotometer with a 665 nm wavelength, the absorbance was measured each time the solution was obtained. Equation 6 can be used to calculate and measure the adsorption capacity. Q =

Cellulose from pineapple peel
The delignification process using alkaline hydrogen peroxide is one of the efficient processes because besides being able to break the bond of structural molecules between carbohydrates and lignin. Hydrogen peroxide is dissociated into hydrogen cations and hydroperoxyl anions. The pH condition is one of the most important things to encourage the formation of hydroperoxyl anions (HOO -). The anion then reacts with the remaining peroxide to form a very reactive hydroxyl radical that attacks the lignin structure. The following is the result of analysis of the chemical components of pineapple peel can be seen in Table 1.
The concentration of cellulose, hemicellulose, and lignin in pineapple peel are 75.46%, 7.23%, and 0.53%. According to Dai and Huang (2017a), the levels of cellulose, hemicellulose, and lignin found in pineapple skin are 23.67%, 15.61%, and 6.87% respectively. This indicates that hemicellulose and lignin have been successfully separated during the process.

Adsorbent
The adsorbent was carried out through a graft copolymerization reaction using microwaves. Microwave irradiation causes selective excitation, forming multiple free radical sites on the polymer backbone. This results in a higher percentage of grafting and homogeneous heating of the material (Aldahri et al., 2017). Cellulose isolate served as the main framework grafted with acrylamide monomer. The reaction mechanism of the graft copolymer is shown in Figure 1.
The synthesis process begins when microwave irradiation affects the formation of free radicals in the cellulose backbone. When larger molecules are subjected to microwave irradiation, rotation of the whole molecule is extremely difficult or even impossible. Under these conditions, the microwaves will be absorbed by the polar bonds (O-H) in the polysaccharides and the bonds will undergo partial rotation. This partial rotation causes the breaking of polar bonds and the formation of free radicals. Meanwhile, water molecules only carry on the irradiation energy so that the acrylamide double bond breaks and produces free radicals due to radiation exposure (Mishra et al., 2012). The success of the adsorbent can be seen from the percentage grafting shown in Figure 2. The adsorbent showed that the percentage of grafts produced decreased with the length of the irradiation time. The grafting ratio (GR) and grafting efficiency (GE) decreased as the number of acrylamide monomers in the system decreased. In addition, the high concentration of acrylamide monomers causes free radicals to bind to each other between monomers to form homopolymers (Dey et al., 2017). The homopolymer formation inhibits the rate of monomer molecules entering the free radicals, resulting in a low grafting percentage. The optimum time for grafting occurred in minute 3 with a grafting ratio and efficiency of 329.72 and 99.74%, respectively.

Adsorbent Functional Group
The success of grafting on the adsorbent can be done by comparing the functional groups between the cellulose isolate and the adsorbent using an FTIR spectrophotometer. The FTIR spectra of cellulose isolate, adsorbent, and after adsorption of methylene blue were analyzed in the 4000 to 500 cm -1 region, as shown in Figure 3. The polysaccharide group's C-H stretching vibrations may be seen in the absorption peak at 2920 cm -1 . In addition, the cellulose isolates showed a significant decrease in band intensity at the absorption peaks of 1432 cm -1 and 1374 cm -1 which came from the C-H deformation of cellulose and hemicellulose. A typical structure of βglycosidic cellulose between sugar units is represented by the sharp absorption peak in the 897 cm -1 regions. These results are consistent with the study of Hu et al (2010) which stated that cellulose isolate was characterized by absorption peaks of 3400, 2900, 1053, and 1436 cm -1 showing O-H, N-H, C-O-C stretching vibrations, and C-H bending vibrations, respectively. At 3, 4, and 5 minutes, the adsorbent spectra showed significant absorption peaks at 1675, 1672, and 1676 cm -1 , indicating C=O stretching vibrations, respectively. Furthermore, there are three absorption peaks for the N-H stretching vibration at 1608, 1611, and 1612 cm -1 . Grafted acrylamide molecules showed O-H, N-H, C=O, and N-H bending vibrations at wave numbers of 3400, 3200, 1650, and 1600 cm -1 , respectively (Mas'ud et al., 2013). The adsorbent after methylene blue adsorption (Figure 3e) indicated that the OH groups were reduced. This is indicated by the presence of a peak that is not too wide. Furthermore, there was a shift in the absorption peak in the range of 600-1000 cm -1 .

Adsorbent Surface Morphology
SEM analysis of cellulose isolates showed that the surface looked smoother by forming long bands (Figure 4a). This result is different from the surface of the adsorbent, which forms an interconnected network. The network formed shows the presence of crosslinks that occur between polymer chains. The surface of cellulose isolates shows structural changes and physical deformations, such as rough, fractured, and porous fibers (Phitsuwan et al., 2016). This change is brought on by the degradation of lignin and hemicellulose.
The results of the minute 3 grafting ( Figure  4b) showed a more homogeneous pore surface. However, when the irradiation time was extended (Figures 4c and 4d), the surface of the adsorbent showed an uneven graft distribution, and there were still surfaces that did not form a polymer network. In general, activated carbon has a porous surface which can lead to increased adsorption of methylene blue by producing a high removal capacity (Inyinbor et al., 2016).

Adsorption Kinetics
The adsorption of a material by the adsorbent is described as a function of time in adsorption kinetics. To determine the adsorption mechanism and rate constant, a kinetic model method is required. As shown in Figure 5 and Table 2, these results can be described by adsorption kinetics using the two kinetic models pseudo first order and pseudo second order. The adsorption kinetics of methylene blue more closely follow the pseudo second order model, which is indicated by the coefficient of determination (R 2 ) greater than the pseudo first order. Based on the interaction between adsorbent and adsorbate molecules, the results show that the adsorption mechanism formed is chemical adsorption. Chemical adsorption generally involves coordination bonds as the sharing of electron pairs by the adsorbate and adsorbent molecules (Rahmawati and Santoso, 2012). isotherms against methylene blue on adsorbent 3 minutes, 4 minutes, and 5 minutes

Adsorption Isotherm
The adsorption isotherm shows the temperature-dependent adsorption interaction between the adsorbent and adsorbate. The adsorption isotherm can be used to determine the methylene blue adsorption model. The model's use can be shown by the adsorption isotherm in Figure 6 and Table 3. Table 3. A dsorption isotherm parameter results after adsorption of methylene blue Based on Table 3, the adsorption process of methylene blue on the surface of the adsorbent more closely follows the Langmuir isotherm, which is indicated by a higher coefficient of determination (R 2 ) than the Freundlich isotherm. The adsorption process can be assumed that the active surface sites of the three types of adsorbents are homogeneous, where one methylene blue molecule occupies one active site.

Conclusion
Based on the research results, methylene blue adsorbent has succeeded in forming graft copolymers at the optimum time of 3 minutes. The synthesized adsorbent showed that the length of irradiation time could reduce the grafting percentage. The adsorbent's maximum methylene blue adsorption capacities were 14.005, 6.042, and 9.970 mg/g, respectively. Methylene blue dye adsorption isotherm and kinetics model were in accordance with the pseudo second order model and Langmuir isotherm. The experimental results show that the adsorbent can effectively remove or eliminate methylene blue dye.