Effect of Particle Size and Mass of Longan Peel (Euphoria Longan L.) as Adsorbent on The Adsorption of Rhodamine B and Methylene Blue Dyes Using the Column Method

Dyes are a mixture of organic compounds that are synthesized in complex forms and are often used in the process of coloring products in various types of industries, so that this complex structure will be difficult to decompose naturally. Therefore, this dye will accumulate in the liquid waste. The accumulation of these dyes will cause harm to living things and the surrounding environment. Therefore, an effective method is needed to overcome this problem, a method that can be used to reduce the dye content in a simple and environmentally friendly way such as the adsorption method. In this study, the adsorption method using a column was used to absorb dyes from the cationic group, namely methylene blue and rhodamine B with adsorben derived from longan peel waste. In this study, the results obtained were the identification of longan peel containing several functional groups, namely O-H, C-H, C=O, -C-NO2, C=C, C-O-C, and C-N derived from alcohol, carboxylic acid, ester, ether, aromatic nitro compounds, and amines. By using a adsorbent particle size of 106 µm, it can absorb methylene blue and rhodamine B at 30.31 mg/g and 28.28 mg/g, respectively. The absorption of methylene blue with 0.1 gram of adsorbent resulted in an absorption capacity of 59.97 mg/g while 0.2 gram of adsorbent could absorb rhodamine B of 32.40 mg/g.


Introduction
Industrial development is currently in line with economic growth and world population.Supported by the development of increasingly sophisticated technology, increasing the number of product needs to support people's lives.Therefore, many industries want to improve the quality of their products by adding aesthetic value to the products produced so that consumers are more interested in these products and sales will increase.In the coloring process, the industry certainly wants to use dyes in small quantities but the resulting color intensity is high, durable and stable.Therefore, the use of synthetic dyes is the main choice, besides the price is quite cheap.This provides its own advantages for the industry.
Dyes or dyestuffs are usually a mixture of colored complex organic compounds that can be used to give a fairly permanent color to substrates such as fabric, paper, plastic, or leather.Dyes in general, colored substances must have a high affinity for the substrate or must be attached to the substrate to give the appearance of a permanent color, but that does not mean all substances that can produce certain colors can be dianngap as dyes.Unlike most other organic compounds, dyes can contain at least one chromophore group as well as a conjugated system and absorb light in the visible spectrum (400-700 nm) and exhibit electron resonance, and have a special color [1].
One of the most used dyes is methylene blue and rhodamine B which is classified in the group of cationic dyes by bringing the reactive element Cl in its structure.Methylene blue has the molecular formula C16H18N3SCl, which is only allowed for use within the scope of chemical laboratories and is strictly not allowed in the food industry.This dye is a dark green and blue solid, with a melting point of 190 0 C, a molecular mass of 319.89 g/mol and a pH range of 4. This methylene blue dye also has a moderate degree of solubility in water, but it is soluble in chloroform, glycerol and acetic acid, and is toxic to the environment.As for the dye Rhodamine B has the molecular formula C28H31N2O3Cl with a molecular weight of 472.02 g/mol.This substance is strictly forbidden to be used in the food industry, has the form of green crystals or reddish purple powder, this dye is poorly soluble in water and when dissolved will produce a bluish-red solution color and has a strong fluorescence.Rhodamine B is also a substance that is readily soluble in alcohol, HCl, and NaOH, in addition to water.Within the scope of the laboratory, this substance is used as a reagent for the identification of Pb, Bi, Co, Au, Mg, and Th and has a melting point of 165⁰c.
The presence of dyes in this waste comes from the dyeing process, where not all dye molecules are absorbed in the substrate.So that some of the dye molecules will be wasted into the environment along with the outgoing wastewater.Due to this complex structure, the dye is more difficult to degrade and will accumulate in the water.This accumulation of dyes will have a negative affect on living things and the surrounding environment.The presence of dyes in high concentrations makes it difficult for sunlight intensity to enter the waters and inhibits the photosynthesis process in the waters, causing health problems.
For living things will have an impact on health, dyes will enter the human body through consumed animals and plants, where animals and plants have been contaminated by methylene Blue and rhodamin B. Both dyes contain halogen compounds in the form of Cl which is known as a reactive material that reacts easily and can cause irritation when in contact with Cl.In addition, these two dyes are also unstable radical compounds, so they will try to achieve stability in the body by interacting with compounds in our body and triggering the formation of cancer in the body.
To overcome the contamination of these two substances, several methods have been carried out such as physics, chemistry, biology, filtration, coagulation, adsorption and liquid-liquid extraction.However, the most frequently applied method is the adsorption method because it has the advantages of simple and environmentally friendly equipment and processes.So far, the adsorption method that is often used is batch using a stirring process to accelerate the absorption process.However, in this study, the adsorption method was carried out by means of a column because of the lack of use of this column adsorption method.The column method is carried out by placing the adsorbent on the column and flowing the adsorbate through the column that has contained the adsorbent until the biosorption is saturated [2].
This method describes a separation process where the adsorbent is used as a stationary phase as an adsorbent medium which will then be passed by the mobile phase, namely the adsorbate solution.Thus, the solution that comes out of the column (eluent) doesn't need to be filtered again as in the batch method.This is one of the advantages of this column method, where the absorption process is simpler.
Although it has limitations in the amount of solution flowed, the results obtained are quite effective and all solutions can interact directly with the adsorbent in the column.This column method utilizes the capillarity affect, where the solution will exit the column through a number of gaps in the column.The larger the pores in the column, the easier the solution will flow out of the column.Conversely, when the density is high in the column, the pores between adsorbent particles are smaller and the solution will spread throughout the column to find a way out that can be passed so that the adsorption process is more evenly distributed in the column.
Longan is one of the most beloved fruits that has health benefits and can be found easily in all seasons.Not only the fruit, but the seeds, bark and leaves are also widely utilized.Various studies have reported that longan seeds and peel contain high amounts of bioactive compounds, such as phenolic acids, flavonoids and polysaccharides.
In this study, this column adsorption method will be applied for the absorption of cationic dyes, namely methylene blue and rhodamin B. The adsorbent used is longan peel waste activated with HNO3 as activator reagent.The use of acid activator reagent is expected to clean and bind the impurity particles that still remain on the surface and inside the adsorbent, thus minimizing the inhibition of the adsorption process.In addition, the use of acid as activator reagents also aims to bind the adsorption power of the adsorbent without changing the structure of the organic components in the adsorbent.Some adsorbents that have been used previously to overcome methylene blue and rhodamine B dyes contamination in solution are as follows from longan seeds, langsat peel, reeds, peanut shells, coffee grounds, banana peel, pineapple leaves, tamarind seeds, snail shells, eggshells, and small crab shells [3] [12].In previous research, Kurniawati [13][14] used longan fruit peel waste as a adsorbent to absorb Cu 2+ and Cd 2+ metals in solution.This is also the background of this study to find out other advantages of longan peel in the absorption of organic substances in solution.

Material and Method
The sample used in the form of waste longan fruit peel that is no longer used and obtained from the city market of Padang.The adsorption model used is the column method which utilizes the stationary phase in the form of longan peel adsorbent and the mobile phase is a solution of cationic dyes.The cationic dyes used are methylene blue and rhodamine B. This research was conducted at the Analytical Chemistry Laboratory, Department of Chemistry, Faculty of Mathematics and Natural Sciences, Padang State University.

Tool and Material
The equipment used were glassware, digital pH meter (HI2211), analytical balance (ABS 220-4), Whatman No. 42 filter paper, 20 mm diameter chromatography column, sieve (BS410) with sizes 106, 150, 250, and 425 µm, and spray bottle.The instruments used were Fourier Transform Infra Red with pectin elmer universal ALT sampling type Accesor 735 B and single beam UV-Vis Spectrophotometer.
The reagents used are methylene blue solutions with concentrations of 1000 and 600 ppm, rhodamine b solutions with concentrations of 1000 and 400 ppm, then there are NaOH solutions with various concentration variations of 0.01 M, 0.1 M and 0.5 M, as well as HNO3 solutions at various concentration variations (0.01 M, 0.1 M and 0.5 M), and finally distilled water as a solvent.

Preparation of Longan Peel Adsorbent
Clean 100 grams of longan peel with distilled water, dry without using direct sunlight, pure and sieve longan peel with sizes of 106, 150, 250 and 425 µm.Weigh each sample size as much as 20 grams.20 grams of longan peel for each size was soaked with 0.01 M HNO3 for 2 hours for the activation process.Separate the longan peel from the solution and wash it with distilled water until it reaches pH 7. Strain the longan peel and dry it.Store adsorbent in a closed container before use.
Take sufficient amount of longan peel adsorbent before and after activation for testing using FTIR.Do the same for testing longan peel adsorbent after contact.Identify functional groups and compare the FTIR spectrum obtained.

The Effect of particle size of adsorbent
Weigh and place 0.2 grams of adsorbent of each size (106, 150, 250 and 425 µm) in a vial.Weigh 0.25 grams of cotton and place it in a vial.Add 5 mL of distilled water pH 4 into a vial containing adsorbent and cotton.Insert the cotton into the column and compact it, followed by the adsorbent into the column afterwards.Rinse and discard the remaining aquades from the column.Flow 10 mL of 600 ppm mehylene blue solution (pH 4) into the column.Discard the first 5 drops and accommodate the next to the end.Furthermore, the final concentration of methylene blue solution collected in the vial bottle after flowing in the column using a UV-Vis spectrophotometer at a maximum wavelength of 664 nm.
The same procedure as the methylene blue test above was carried out for testing 25 mL of rhodamine B solution at pH 5 with a solution concentration of 400 ppm and a maximum wavelength of 554 nm on a UV-Vis spectrophotometer.

The Effect of Mass of adsorbent
Weigh and place 0.1, 0.2, 0.3, 0.4 and 0.5 grams of adsorbent at a size of 106 m in a vial.Weigh 0.25 grams of cotton and place it in a vial.Add 5 mL of distilled water pH 4 into a vial containing adsorbent and cotton.Insert the cotton into the column and compact it, followed by the adsorbent into the column afterwards.Rinse and discard the remaining aquades from the column.Flow 10 mL of 600 ppm Methylene blue solution (pH 4) into the column.Discard the first 5 drops and accommodate the next to the end.Furthermore, the final concentration of methylene blue solution collected in the vial bottle after flowing in the column using a UV-Vis spectrophotometer at a maximum wavelength of 664 nm.
The same procedure as the methylene blue test above was carried out for testing 25 mL of rhodamine B solution at pH 5 with a solution concentration of 400 ppm and a maximum wavelength of 554 nm on a UV-Vis spectrophotometer.
Measurement of the potential and capacity of adsorbate adsorbed on the adsorbent, can use the following equation: In equation ( 1) above, Co is the initial concentration and Ce is the final concentration of methylene blue and rhodamine B solution (mg/L), then W is the mass of adsorbent used (g) in the adsorption process and V is the volume of methylene blue and rhodamine B solution (L) used in the test.
Then in equation ( 2) above, E is the adsorption efficiency expressed in percentage (%), then there is Co which is the initial concentration and Ce is the final concentration after the adsorption process of methylene blue and rhodamine B solution (mg/L).

Result and Discussion
In this study, the topic to be discussed is related to efforts to overcome water pollution from liquid waste containing synthetic dye methylene blue and rhodamin B. Both pollutants are modeled in the form of a diluted solution from a parent solution concentrating 1000 ppm on each color substance to a solution concentrating 600 ppm for metylene blue and 400 ppm for rhodamin b.Both concentrations are the optimal concentrations obtained before.The research variable used is the influence of particle size and adsorbent mass on the adsorption process by using column methods for both colors.
As for the adsorbents used are peel of the long-lasting fruit activated with 0.01 M solution HNO3.To produce this adsorbent of the longan peel, some stages are done namely the stage of washing and drying of the peel from longan fruit that aims to remove impurities and reduce the water content in the peel from longan fruit.Furthermore, continued with the process of smoothing samples of the peel of the archaic fruit to enlarge the surface area of the adsorbent so that it can increase its adsorption power.Then proceed with the activation process using HNO3 as activator reagent aimed at enlarging the volume and diameter of the pore and pulling out impurities that cannot be removed in the previous washing process.
At this stage of activation is done chemically, where during the activation process, HNO3 which is an oxidizing oxidizing surface of the adsorbent, by breaking double bonds or oxidizing other elements present on the surface of the adsorbent.As a result, the surface of the adsorbent will erode and form new pores and enlarge the diameter of the pores that have been formed before.Therefore, this process can help to increase the adsorption power of adsorbent to adsorbate in solution.The last stage is the process of neutralization of adsorbents to remove residues from activator reagents and neutralize the charge on the surface of the adsorbent accompanied by re-drying to remove the residual water that can reduce the quality and absorbent adsorbent.In addition, the presence of excess water content can also increase moisture and speed up the occurrence of the decay process of adsorbents and produce fungi that can damage the adsorbent.
In this study, the solution used has its own optimum conditions.Where, the methylene blue solution has a pH of 4 with a concentration of 600 ppm and flowed as much as 10 mL on the column.While the rhodamine B solution used was 10 mL with pH 5 at a concentration of 400 ppm.For more details, the results obtained are as follows.

Characterization of Sample
The Longan peel adsorbent that has been produced in the previous sample preparation process is characterized which aims to determine the characteristics of the adsorbent produced.based on the results of the characterization found, then we will be able to see how the conditions of the adsorbent we use and can identify how effective the adsirben in overcoming contamination of methylene blue and rhodamin B dyes.The characterization process is carried out using chemical instruments in the form of FTIR (Fourier Transform Infrared).Where, FTIR is commonly used for qualitative testing on organic compounds and mixtures and can also be used for quantitative testing.
The working principle of this FTIR is the interaction between matter and energy in the form of infrared light from the wavenumber range of 800 to 4000 cm-1.The FTIR reading results are issued in the form of a spectrum that presents analyte-related information both qualitatively and quantitatively.In the qualitative analysis of the information presented is related to the functional groups of the components of organic compounds contained in the peel of longan, the determination of these functional groups based on the peak of the spectrum that is read at a certain wavenumber.
Furthermore, quantitatively indicated based on the value of the transmission percent of the peak spectrum is read.this percentage of transmission itself shows how much the content of these functional groups in organic compounds contained in the peel of longan fruit.this is according to Lambert beer's law which underlies the reading of the analysis results in spectrophotometry.where the greater the percentage of transmittance, the concentration of the analyte is smaller.conversely, the smaller the percentage of transmittance, the greater the concentration of analyte.
The following is the characterization of longan fruit peel adsorbent with FTIR that has been obtained : Based on the FTIR spectrum shown in Figure 1 above, it can be seen that there are several functional groups identified in their own wave numbers.That is, each data generated on each of the wavenumbers in the spectrum identified different functional groups.In the FTIR spectrum for longan fruit peel before activation in figure 1 (a), identified the existence of OH strain which is assumed to come from the functional group in the group of alcohols and carboxylic acids at a wavelength of 3399.95 cm -1 with a strong intensity of 65.54% T, then the presence of C-H from alkynes at a wavelength of 3226.62 cm -1 with a strong peak intensity of 62.82% T, The C=O of the ester group is read in the wave number 1613.43 cm -1 with a strong intensity of 57.83% T and the presence of-C-NO2 of aromatic Nitro functional group in the wave number 1368.68 cm -1 with an intensity of 58.95% T and usually this functional group can also appear in the wave number range 1300-1570 cm -1 in the fingerprint region of the FTIR spectrum.
At the wavenumber 1453.94cm-1, it is assumed that there is an aromatic C-H and C=C bending that can occur in the range of wavenumber 1450-1500 cm -1 and ~1600 cm -1 .Then also identified the presence of C-O-C group of ester, ether, carboxylic acid and alcohol at the wavenumber 1244.65 cm -1 which is characterized by a strong peak intensity of 51.03%T.In the wavenumber 1022.31cm -1 identified the presence of C-N from the group of amine compounds which usually also appears in the range of wavenumber 1300-1000 cm -1 with an intensity of 33.99% T.
In Figure 1 (b), is the result karakterisai of longan fruit peel after inactivated with HNO3.Based on the resulting spectrum, it can be seen that the same functional groups have been identified in the longan peel spectrum before activation, but what distinguishes them is the occurrence of waveform shifts in several functional groups, such as C=C aromatic, -C-NO2 from Nitro aromatic, C-N from Amine and C-H. the functional group derived from the alkyne group undergoes a change to the c-H stretch of the Alkane.Where the double bond contained in atom C is lost and turns into a single bond between atom C and other atoms bonded to each other.The loss of one bond on the C atom is assumed to be due to the influence of oxidation reactions that occur during the activation process.
The results of the characterization obtained in this study also resemble the results of the characterization of functional groups identified in the previous study.Where based on research conducted by Kurniawati, et all. in 2015, in the previous study, the functional group that was identified was in the form of OH streching which could be read at wavenumbers 3304.6 and 3289.63 cm-1 which came from hydroxyl groups in alcohols and carboxylic acids at wavenumbers ranging from 3600 to 3200 cm-1 in the FTIR spectrum.Then the identification of the C-H Stretching functional group at the wavenumber 2924.74 cm-1 and group of C=O streching from the ester compound group at the wavenumber 1635.02cm-1 [15] [16].Litchi peel Adsorbent is used to overcome the contamination of metal ions Cu(II) and Pb (II) in liquid waste.In Figure 3 above is the result of identification on methylene blue and rhodamin B dyes which aims as a comparison and see the functional groups identified in each dye.From the picture shown, the functional groups contained in the two compounds are OH and CH at wavenumbers above 3200 cm -1 derived from water molecules bound to the dye powder.Then there is CH Streching at wavenumbers 2923 and 2921 cm -1 .Then the presence of CO in the wavenumber 1729 cm -1 in the chemical structure of rhodamin B, and the CN functional group of the amine group in methylene blue shown in the wavenumber ranging between 1300 and 1200 cm -1 .The presence of molecules bound to these two color substances, can show that methylene blue and rhodamin B are hydrates containing water molecules in crystalline compounds or solids.

The Effect of Effect of Particle Size of Adsorbent
One of the factors that can affect the adsorption process is the particle size of the adsorbent used.The larger the surface area of the adsorbent (the smaller the adsorbent size), the greater the adsorption that occurs because the possibility of substances attached to the adsorbent surface is greater.This causes the part that originally did not function as a surface (the inside) after being crushed will function as a surface [17].
In this test, it was carried out under optimum conditions where for methylene blue, the adsorbate solution used had a concentration of 600 ppm with a pH of 4. As for the rhodamine B test, the solution had a concentration of 400 ppm with a pH of 5. Based on the graph above, it can be seen that the smallest adsorbent particle size of 106 µm can effectively absorb both adsorbates well.This can be seen from the absorption capacity value obtained which is higher than the other particle sizes, although the difference in the Qe value produced in each variation is not relatively high.With the use of 0.2 gram of longan peel adsorbent, the adsorbate of methylene blue and rhodamine B was 30.31 mg/g and 28.28 mg/g, respectively.
In addition, the small particle size can also affect the capillarity in the column.Where the smaller the particle size, the pores in the column are also getting smaller.So that this adsorbate solution will have a slightly longer contact time with the adsorbent when looking for a gap that can be passed to get out of the column.It can also increase the adsorption power of the adsorbate during the absorption process.

The Effect of Mass of Adsorbent
After obtaining the optimum size, the mass of the adsorbent is determined.where the mass of the adsorbent can also affect the adsorption capacity of the adsorbate.The higher the adsorbent mass, the lower the adsorption capacity.The decrease in adsorption capacity is caused by the active side of the adsorbent which is not all in contact with the adsorbate.
In this test, the optimum conditions used during the testing process were the same as the previous test, except that the variable that increased was the particle size used, which was 106 µm for both dye tests.Based on the data obtained, it can be seen that the smallest mass has a higher absorption capacity value.This is because the excess adsorbent mass cannot absorb the adsorbate effectively anymore.However, when viewed from the percentage of absorption, the greater the mass of the adsorbent, the higher the absorption efficiency.From the graph it can be seen that at the point with the smallest mass, 0.1 grams of longan peel adsorbent can absorb as much as 59.97 mg/g of Methylene blue particles in solution, while at 0.2 grams of longan peel adsorbent it can absorb as much as 32.40 mg/g of rhodamine B particles in a solution.
Based on these data, it can be seen that the more the number of adsorbents used in the adsorption process, the more adsorbate will be adsorbed, this is because there are many parts as a binding or adsorbed dye ions on the surface of the adsorbent and the presence of active groups that can bind dye ions to the maximum in large enough quantities [18].In addition, if the adsorbent mass used is too large, it causes a decrease in the ion content of the contaminants that can be adsorbed.This decrease was caused by the difference in the number of active groups that are able to absorb adsorbate, especially in the test process by using a larger number of adsorbents [19].This is because the amount between adsorban and adsorbate is not balanced.
From these two data, the longan peel adsorbent is more effective to absorb methylene blue dye than rhodamine B. this can be seen from the comparison of absorption results obtained, where with the use of 10 mL of 600 ppm methylene blue solution, the highest absorption capacity value is obtained almost close to the value of 60 mg/g.while in 25 mL of 400 ppm rhodamine B solution, only about 32.40 mg/g can be absorbed by the longan peel adsorbent.This illustrates that methylene blue dye is more easily absorbed than rhodamine B even though it is still in the same dye group.

Mechanism of Adsorption
In the process of absorbing the two dyes by this longan peel adsorbent, it can be assumed that the reactions that occur are as follows: 1. Ionization and Ion Exchange Process a. Ionization of functional groups Functional groups such as carboxyl, alcohol, carbonyl and nitro aromatic will be ionized to form anions and cations.This ionization is also affected by a solution that has an acidic pH which means protonation in the solution.The cations and anions formed are: H + , CO -, NO -, and O -. b.Ionization of dyes Dyes dissolved in water will also decompose into cations and anions.In this case, the cations and anions formed are: Cl -, C16H18N3S + and C28H31N2O3 + .Based on the assumptions above, it can be described that the dye cation will be bound to the anion on the surface of the adsorbent and the dye anion will be bound to the cation (Proton) in the solution.Therefore, the result that can be seen as evidence of this absorption process is the difference in the color of the solution which is very contrasting between before flowing and after flowing in the column.The absorbed dye will form red and blue colors on the adsorbent.While the filtrate is colorless with most of the components contained in it, namely HCl.

Formation of chemical bonds
After the formation of ion exchange, to bind the two ions, hydrogen, covalent and Van der Waals bonds are formed.Where the bond based on Van der Waals force is better known as physical adsorption and the chemical bond formed shows the chemical adsorption process.

Conclusion
This adsorbent derived from longan peel was identified as containing several functional groups that played a very important role in the absorption process of the two cationic dyes, namely methylene blue and methylene in solution.Several functional groups were identified, namely O-H, C-H, C=O, -C-NO2, C=C, C-O-C, and C-N derived from alcohols, carboxylic acids, esters, ethers, aromatic nitro compounds, and amines that can bind adsorbate particles.Methylene blue and rhodamine B in solution.
In this column method, the factors that affect the adsorption power are particle size and mass of the adsorbent used.The smaller the particle size, the greater the adsorption power due to the increased surface area of the adsorbent that will interact with the adsorbate, while the more mass of the adsorbent will decrease the absorption capacity because the number of active surfaces of the adsorbent is not proportional to the number of adsorbate particles.This can be seen in the Qe value obtained from each variable.In particle size, the largest Qe value was obtained when using a size of 106 µm of 30.31 mg/g for methylene blue and 28.28 mg/g for rhodamine B. Then on the mass of adsorbent, obtained with the smallest mass amount of 0.1 gram for methylene blue to produce a Qe value of 59.97 mg/g and 0.2 gram of adsorbent to absorb rhodamine B of 32.40 mg/g.From these two data, the longan peel adsorbent is more effective to absorb methylene blue dye than rhodamine B. this can be seen from the comparison of absorption results obtained, where with the use of 10 mL of 600 ppm methylene blue solution, the highest absorption capacity value is obtained almost close to the value of 60 mg/g.While in 25 mL of 400 ppm rhodamine B solution, only about 32.40 mg/g can be absorbed by the longan peel adsorbent.This illustrates that methylene blue dye is more easily absorbed than rhodamine B even though it is still in the same dye group.

Figure 1 .
Figure 1. chemical structure of dyes (a) methylene blue and (b) Rhodamine B

Figure 3 .
Figure 3. FTIR spectrum of longan peel after contact with (a) Rhodamine B Dyes and, (b) Methylene Blue

Figure 4 .Qe
Affect of Particle Size adsorbent after contact with (a) Methylene Blue, (b) Rhodamine B