Preparation of Composite Derived from Banana Peel Activated Carbon and MgFe 204 as Magnetic Adsorbent for Methylene Blue Removal H )

Received: 25th November 2020 Revised: 13th January 2021 Accepted: 31th January 2021 Online: 31 January 2021 Methylene blue (MB) is one of the dyes used often by the textile industry. Therefore, MB residual is contained in the textile industry waste. MB can irritate, leading to permanent eye and animal injuries; therefore, the textile industry waste concentration must be degraded before disposed to the environment. MB residual in textile industry waste can be treated with activated carbon adsorption. However, the adsorption method is less effective because the deposition takes a long time. This research aims to make activated carbon composites from banana peels and magnesium ferrite (BPAC/MgFe204) using the coprecipitation method to obtain activated carbon with magnetic properties (magnetic adsorbent). The obtained composite was characterized using X-Ray Diffraction (XRD), Scanning Electron Microscope (SEM), Energy Dispersive X-Ray (EDX), and Surface Area Analyzer. The adsorption performance of methylene blue on composites was evaluated with variations in pH, concentration, contact time, determination of adsorption isotherms, and kinetics of adsorption. XRD analysis results showed the composite has a cubic crystal structure with a crystallite size of 7.69 nm. SEM analysis results show the surface morphology has pores with irregular shapes. EDX analysis results showed that the composition of activated carbon composite was 65.56% carbon, 2.28% Mg, 5.50% Fe, and 26.66% 0. The results surface area analysis showed a composite surface area of 88.134 m2/g. Composite adsorption performance showed maximum results at pH 7, variations in concentration at 10 ppm, and contact time 180 minutes with adsorption capability of 99.26%. Determination of the adsorption isotherm follows the Freundlich adsorption isotherm model with a pseudo-second-order adsorption kinetics model. The obtained BPAC/MgFe204 composite can potentially be a magnetic adsorbent capable of adsorbing methylene blue in an aqueous solution.


Introduction
The textile industry has a significant role in Indonesia. The industrial sector plays an essential role in promoting economic growth, poverty alleviation , and creating job opportunities to reduce high levels of unemployment [1]. Nevertheless, behind the positive impact that the textile industry has, there are negative The types of dyes used in the textile industry today are very diverse. Therefore, textile waste handling becomes very complicated and requires several steps until it is entirely safe to be released into the aquatic can be used as a bleaching agent (dye remover), gas absorber, and metal absorber [ 4 ]. The adsorption method using adsorbents alone turned out to be less effective because the deposition only relies on the force of gravity alone. In recent years research has developed on adsorbent composites with magnetic materials that can be easily separated from the dye waste solution in the adsorption process by utilizing an external magnetic field. Magnetic separation has become one of the most promising water purification techniques in the environment. Its nature does not produce contaminants such as flocculants and can filter or separate large amounts of waste in a short time [ 5 ].
Banana is a fruit that is easy to grow in tropical countries such as Indonesia. Therefore, a banana is one of the fruits abundant in Indonesia. After harvesting bananas, 80% of the peels, stems, and leaves are removed without further processing. This has resulted in an immense enough potential for banana peel waste so that it is necessary to overcome the banana peel to have more use value [6]. LFX et al [ 7 ] has conducted previous research that banana peels can be used as adsorption on azo dyes. produced 30.6 emu / g [ 15 ], ceramic method plus mechanical milling produced 36 emu / g [16], one-step mechanochemical route produced 50 emu / g [ 17 ], and ultrasonic wave assisted ball milling produced 54.84 emu / g [12].
Although magnesium ferrite can adsorb pollutants in an aqueous solution , this adsorbent ' s development prepares its composite with a common adsorbent such as activated carbon (AC). Kaur et al [18] reported that a nanocomposite of MgFe 204 -loaded activated charcoal was prepared in a sol-gel approach with a high Cr(VI) sorption capacity of 500 mg / g at pH 2.0. Based on our literature research, there is still a lack of information toward synthesis and characterization of AC from banana peels (BPAC) and magnesium ferrite composite, also its performance as an adsorbent for methylene blue (MB) removal. In this work, we reported a simple method in preparation BPAC / MgFe 204 composites and its adsorption performance study (optimum condition, isotherm, and kinetic) as an adsorbent for MB removal in an aqueous solution.

Methodology
This research went through several experimental stages using the equipment and materials described as follows.

Equipment / Tool / Material.
The equipment used includes glassware, porcelain cups, analytical balances, hot plate, magnetic stirrer , oven , furnace, 100 mesh size sieve, and external magnet. The banana peel was washed first and cut into small pieces, then dried under the sun for three days. Furthermore, the dried banana peel was burned in a furnace at 300°C for 15 minutes. Banana peel that has become carbon cooled in a desiccator then sieved with a 100-mesh sieve. Carbon from the banana peel was chemically activated using 1% NaCl solution, stirring for 120 minutes using a 500 -rpm magnetic stirrer at 8o°C. Then filtered and washed to a neutral pH and dried at 105 .
In recent years, the spinel ferrite (SFs) nanoparticles have been a fascinating research object and have become the focus of many kinds of research for both scientific and technological interests. The SFs nanoparticles have the structural formulaMFe 204 (M is a divalent metal ion, such as Ni, Co, Cu, Mn, Mg, Zn , Fe) with a cubic spinel crystal structure [8]. Magnesium ferrite nanoparticles attract many researchers ' attention due to their low toxicity [ 9 ], high chemical stability [10], and high saturation magnetization value [11,12]. Spinel ferrite is commonly used as a magnetic adsorbent for any kind of pollutants such as ion metals, dyes, and other such as phenol, tetracycline, and phosphorous compounds [ 13 ]. Tang et al [ 14 ] reported that doping 10% magnesium into -Fe 203 could increase the specific surface area from 162 m 2 / g to 438 m 2 / g, which is 2.7 times higher. Therefore, increase the adsorption performance of particles toward As(III) and As(V) from aqueous solutions. Substitution of a lighter metal ionMg 2+ into heavy Fe 3+ in -Fe 203 induces internal and surface defects / pores, lead to increasing the surface area of Mg 0.27 Fe 2.5o04 . The magnetic properties of MgFe 204 depend on its structure, such as particle size, crystallinity, crystallite size, and cation distribution.  of BPAC / MgFe 204 composites. Then stirred at a speed of 300 rpm using a magnetic stirrer, carried out for 60 minutes to find an optimum condition in adsorbate concentration, pH, and contact time. After stirring using a magnetic stirrer, it is stored on an external magnet to separate the composite within 2 minutes. The absorbance was measured using the UV Vis Spectrophotometer.
Methylene blue, whose absorbance has been measured using a UV Vis spectrophotometer at 663 nm wavelength, was entered into a linear regression of the calibration curve for methylene blue ' s standard solution.
Then the percentage of removal was obtained by entering the concentration of methylene blue into equation (1 The primary solution was made of methylene blue in 100 ppm, then diluted to produce a series of standard MB solutions consist of 5 ppm, 10 ppm, 20 ppm, 30 ppm, 40 ppm, and 50 ppm. The absorbance was then measured using a spectrophotometera standard curve by plotting the concentration against the absorbance. Figure 1 showed the linear regression of the standard curve of MB solutions.
= Initial concentration of methylene blue = Equilibrium concentration of methylene blue

. Result and Discussion
Characterization of BPAC / MgFe 204 composites and the adsorption performance of BPAC / MgFe 204 composites against methylene blue was carried out using UV-Vis Spectrophotometry with various tests. The variations made were variations in pH, contact time, and MB concentration. The adsorption isotherms were determined using Langmuir isotherm and Freundlich isotherms, then determined adsorption kinetics using pseudo-first-order and pseudo-second-order.

. Magnetic Properties of Composites BPAC / MgFe 204
The BPAC / MgFe 204 composites ' magnetic properties were tested using an external magnet. This was done to determine how strongly the composite can respond or be attracted by a magnet.  (20 ppm) was varied with three different pH which are 5 , 7 , and 9 representatives for acid, neutral, and base environment, respectively. For contact time variation, decreasing MB concentration was monitored for 3 hours of contact with composite while stirred using a magnetic stirrer.
The data collection process began by preparing 20 mL of methylene blue into a beaker and adding 0.01grams magnet for 2 minutes approximately ( Figure 3 ). In this separation process, the filtration process can be minimized using filter paper.
sample are ( 511 ) and ( 440 ), which crystallize in the cubic crystal system. These results were consistent with those reported by Suharyadi et al. [20]  where D is crystallite size, = 0.154060 nm is the Cu-K X-ray wavelength, Maximum (FWHM) value of each characterization peak, is diffraction angle, and = 0.9 is a constant [21]. The crystallite size obtained (Table 1) was following the percentage of crystallinity obtained. The percentage of crystallinity ( %crystallinity) obtained was 10.9 %, and the amorphous percentage was 80.9 %.The %crystallinity (or ratio of crystalline to non-or nano-crystalline species in a material) is evaluated by evaluating the baseline to peak separation in an extended scan range. The small crystallite size was obtained due to the addition of activated carbon. According to Aflahannisa and Astuti [ 22], research is reported as a decrease in crystallite size and an increase in carbon mass.  Figure   5 a that the sample ' s surface morphology has pores with irregular shapes. In Figure 5 b, it can be seen that the sample was heterogeneous or non-uniform.
The X-ray diffraction pattern shown in Figure   the adsorbent and the dyes determine the adsorption capacity [ 27 ].

Surface Area Analyzer (SAA)
The surface area of the BPAC / MgFe 204 composite was analyzed using SAA. The results of the characterization of the surface area were 88.134 m 2 / g. The surface area obtained was lower than the surface area of standard activated carbon , which has a surface area ranging from 300 -3500 m 2 / g [ 23 ]. The presence of MgFe 204 crystal probably blocking the pores of activated carbon leading to the lower surface area.
The surface area of the BPAC / MgFe 204 composite was higher than the surface area of the activated carbon of the Kepok banana peel reported by [ 24 ] of 16.53 m 2 / g, higher than the surface area of nanomagnesium ferrite (n-MgFe 204 ) of 53.83 m 2 / gconducted by Srivastava eta /. [ 25 ], and higher than that conducted by Rigo et al. [26 ] in a study of Nickel Ferrite / Carbon Nanotube composites with a surface area of 54 m 2 / g. Figure 7 shows that the percentage of methylene blue adsorption by the composite BPAC / MgFe 204 has increased from pH 5 ( 83.05 %) and achieved optimum adsorption at pH 7 ( 85.03 %), and then decreased again at pH 9 (80.16%). The decrease in adsorption was caused by the exchange between the adsorbent and the adsorbate.

.1. pH Optimization of Methylene Blue
The adsorbent ' s surface area and the interaction between  The adsorption rate was high below 50 minutes and decelerated after 50 minutes due to the equilibrium state system.

. 3 . Result of Concentration Variations
where qe are the adsorbate amount adsorbed per unit weight at equilibrium; Ce is the equilibrium concentration of adsorbate (mg / L); KL is Langmuir constant; is maximum monolayer Langmuir sorption capacity; KF is Freundlich constant, which is related to adsorption capacity (mg / g), and l / n describes the adsorption intensity.
Determination of the type of adsorption isotherm in this study using various concentrations, namely 10 , 15   Based on Figure 9 , The percentage of removal was not significantly changed in the range of MB concentration 10-30 ppm. Commonly, increasing the adsorbate concentration will increase the percentage of removal until it reaches maximum equilibrium adsorption capacity (qe) and then decrease [28]. Therefore, there is an optimal concentration of adsorbate, which could not be observed yet from these data. For further observation, increasing the MB concentration range until 100 ppm perhaps will get the optimum concentration and maximum qe.

. Determination of Adsorption Isotherms
According to the mechanism , the change in adsorbate concentration in the adsorption process can be studied by determining the adsorption isotherm. The adsorption isotherm type can be used to determine the adsorbent ' s adsorption mechanism against the adsorbate. Liquid, solid-phase adsorption usually follows the Langmuir and Freundlich type isotherm [   Based on Figure10, it can be seen that the correlation coefficient ( R 2 ) of the adsorption of methylene blue dye by the BPAC / MgFe 204 composite shows R 2 = 0, 96 for the Langmuir isotherm and the Freundlich isotherm R 2 = 0, 98 . The R 2 value obtained from the Freundlich isotherm model was more significant than the Langmuir isotherm model, so the adsorption that occurs tends to follow the Freundlich isotherm model, which means that the adsorption of methylene blue dye occurs physically (physical adsorption) [ 29 ].
The Qmax value in the Langmuir isotherm model will always be constant after reaching a particular equilibrium concentration. In the Freundlich isotherm model, the adsorption capacity increases with increasing equilibrium concentration. This indicates that the Freundlich isotherm model is not limited to single-layer adsorption so that even though the adsorbent has reached its saturation point, the adsorption process can take place at a particular stage [ 19 ]. This study ' s KF value was 5.30 mg / g, more significant than the KF carried out by [ 30 ], which was 2.85 mg / g in a study using banana peel adsorbent for methylene blue dye.
The Freundlich approach assumes that the adsorbent surface was heterogeneous, and the adsorption forms multiple (multilayer) adsorption layers that take place physically (physisorption) , where each molecule has different adsorption potentials. However, the adsorbate is not firmly attached to the adsorbent. The adsorbate can move from one part of the adsorbent surface to another, and the surface left by the adsorbate can be replaced by other adsorbates [ 31 ]. This is also in accordance with the results of SEM characterization, which showed that the BPAC / MgFe 204 composite was heterogeneous or nonuniform with irregular pores.

. Determination of Adsorption Kinetics
There are two models for studying adsorption kinetics: the pseudo-first-order Lagergren model and the pseudo-second-order model [ 13 ]. The adsorption kinetics of methylene blue by BPAC / MgFe 204 composites were evaluated based on the firstorder (Eq. 5 ) and second-order (Eq. 6) pseudo reaction equations at variations in contact time ranging from 5 to 180 minutes and variations in concentrations of 10 ppm, 20 30 Based Table 3 that the R 2 value in each kinetics model, at a concentration of 10 ppm, 20 ppm and 30 ppm the values were R 2 0, 6871 ; 0, 9491 ; 0, 9551 for pseudofirst-order and R 2 value for pseudo-second-order concentrations of 10 ppm, 20 ppm and 30 ppm were 0.9960 ; 0.9996 ; 0.9999 . To determine the order used , it is seen based on the R 2 value close to 1. Based on the data obtained and shown in Table 3 of the two kinetics models, the pseudo-second-order kinetics model gives a greater R 2 than the pseudo-first-order kinetics model. It can be interpreted that the kinetics model, which is suitable to describe the adsorption kinetics model of BPAC / MgFe 204 composites against methylene blue, was the pseudosecond-order kinetics. This kinetics model shows that the adsorption process, both adsorbent, and adsorbate influence each other ' s adsorption kinetics [ 32 ]. Pseudosecond-order adsorption kinetics assumes that the adsorbing capacity is proportional to the total surface adsorbent and depends on the adsorbent ' s ability to adsorb dyes [ 29 ]. This is consistent with the determination of the adsorption isotherm of BPAC / MgFe 204 composites, which more closely follows the Freundlich adsorption isotherm, which states that each molecule has different adsorption potentials.

. Conclusion
Based on the research results on making BPAC / MgFe 204 composites as a magnetic adsorbent for methylene blue removal, it can be concluded that the preparation of BPAC / MgFe 204 composites was successfully carried out by the coprecipitation method, the composites could adsorb methylene blue. The BPAC / MgFe 204 composite characteristics indicated that activated carbon content was amorphous and contained Mg and Fe. The sample's surface morphology has pores with irregular shapes and heterogeneous or non-uniform characteristics. The surface area of the composites was 88.132 m 2 / g. The adsorption performance of BPAC / MgFe 204 composites showed maximum results at pH 7 ,10 ppm concentration of adsorbate, and180 minutes of contact time with a percentage of MB removal 99.26 %. Furthermore, the adsorption isotherm follows the Freundlich isotherm equation with a correlation coefficient ( R 2 ) of 0.98 , with the adsorption kinetics model following the pseudo-secondorder equation.