Synthesis of activated carbon from banana peels for dye removal of an aqueous solution in textile industries: optimization, kinetics, and isotherm aspects

Environmental degradation has become worse in recent years as a result of the release of numerous industrial effluents. Untreated solid and liquid sewage is recklessly discharged in large quantities into rivers and streams, particularly those that run through cities, towns and various production areas (Koyachew 2016). As a result, the water body has become heavily contaminated with several pollutants. Moreover, pollution raises the price of water purification and reduces the volume of available water. Thus, it is advocated that all wastewater types that are most likely to be released into the environment be treated to prevent pollution (Afrad et al. 2020).

Major water contaminants include a variety of organic and inorganic substances such as heavy metals and industrial compounds. They have the potential to harm human health and obstruct industrial or agricultural water use (Akpor & Muchie 2011). When the level of a pollutant in the water supply exceeds an acceptable threshold for certain water usage, such as drinking or industrial water supply, the water is termed unsafe (Sharma & Bhattacharya 2017; Bodini et al. 2021).

Dyes are organic pollutants that are made up of synthetic aromatic organic chemicals that bind to textiles or surfaces to give them color. Synthetic dyes are common water contaminants due to their high solubility, and they are frequently detected in trace amounts in industrial wastewater (Ziarani et al. 2018). Industries such as textile, cosmetics, food and paper sectors utilize dyes. However, if dyes are not properly disposed of after usage in these sectors, they can be harmful to the environment (Sarkar et al. 2017). Dyes may have a major impact on photosynthetic activity in aquatic life because of the presence of aromatic metals, chloride and other chemicals. One of the most problematic aspects of dye treatment is that the majority of dyes used in industry are resistant to light, oxidation and aerobic digestion. Dyes, on the other hand, are typically synthetic and have a complex aromatic molecular structure that makes them more stable, making them non-biodegradable (Chen & Zhao 2009). Because of their high chemical and biological oxygen demands, suspended particles, turbidity and hazardous components, dyes in wastewater undergo biological and chemical transformations, which deplete dissolved oxygen (Singh & Arora 2011).

Chemical-based textile dyes, in contrast to natural dyes, have become increasingly popular in the textile and dyeing sectors due to their cost-effectiveness and great stability toward many parameters such as high temperature and light. As a result, extremely contaminated effluents are discharged from those sectors (Bhatia et al. 2017). The color and organic content of wastewater from textile dyeing and finishing activities are often high. The effluent from the textile sector is known to be brightly colored, contains a significant number of suspended particulates, has a wide pH range, is hot and has a high chemical oxygen demand (Saini 2017). If dyes are left untreated, they can survive in the aquatic environment for a long time due to their great thermal and light stability. Water-soluble textile dyes have had a significant impact on the fragile ecosystems surrounding industries, and they pose serious environmental issues. A relatively little amount of dye in water is extremely visible and limits light penetration in water systems, causing photosynthesis to suffer (Carmen & Daniela 2010; Gulnaz et al. 2011).

The reason for this is that dyes are generally colored and so can tint surface water. It is well acknowledged that the color of water has a significant impact on the public impression of its quality. Color is the first contaminant to be detected in wastewater. Water with very small quantities of colors (less than 1 ppm for some colors) is very visible and unpleasant (Ardila-Leal et al. 2021).

Chemical and physical treatment methods for dyes in effluent include adsorption, coagulation, precipitation, filtration, membrane separation and oxidation. Dye-containing wastewaters are difficult to treat because the dyes are refractory molecules (especially azo dyes), resistant to aerobic digestion, durable to oxidizing agents and may be present in small amounts. Traditional color removal processes may be cost-prohibitive and/or technically challenging (Chatzisymeon et al. 2006; Nahiun 2021). As a result, an effective treatment of wastewater containing dyes is required. Chemical reduction, ion exchange, evaporation, reverse osmosis and chemical precipitation are some of the methods for treating wastewater containing colors. The drawbacks of utilizing these approaches include the high capital and operating costs, as well as the disposal of leftover sludge (Kumar et al. 2012). The bio-adsorption technique with optimum conditions is an appealing option for treating contaminated water, especially if the adsorbent is affordable and does not require any extra processing prior to use. There are a number of articles and review papers researched before year to year. Reviewing different articles in the literature, four parameters considered to affect the adsorption processes mostly were found to be adsorption time, pH, adsorbent dose and initial dye concentration. However, optimization of the adsorption process variables and studying the adsorption mechanism should be adapted to reduce labor and costs. This study aimed to synthesize and determine the banana peel's adsorptive capacity for removing reactive dye (reactive blue) and to investigate the adsorption process and effect of operating parameters such as adsorption time, pH, adsorbent dose and initial dye concentration on the removal of reactive dye from aqueous solutions. Banana peel is a waste product that can be found in great quantities. In addition to treating the dye effluent, converting scrap banana peel into usable bio-adsorbent reduces the amount of home garbage.

The material used in this study was the banana peel to prepare an activated banana peel bio-adsorbent. The reactive blue dye was chosen as a model pollutant (adsorbate) obtained from Bahir Dar textile industry wastewater. Chemicals (H₂SO₄, HCl, NaOH all with 99% purity) were used to activate the banana peel adsorbent and to adjust the desired level of pH during the experiments.

The raw banana peel was collected from a local juice house in Bahir Dar, Ethiopia. The banana peel was washed with distilled water to remove the remaining dust materials. The size of the peel was reduced from 1 to 2 cm to accelerate the drying process. After all the dripping water was sun-dried, the peel was placed in an oven (Cooper technology, TD-1315/v/c, 2016) for 24 h at 105 °C to remove the moisture content. The dried peel was powdered using an attrition mill. The powdered banana peel was sieved (IC-205/EV) and the particle size below 125 μm was retained. It was then weighed and packed in an air-tight plastic bag.

A two-stage activation process was conducted; a physical activation succeeded by a chemical action. These two action methods would result in an enhanced porosity and hence produce an activated banana peel bio-adsorbent with a relatively large surface area. The physical activation particularly was a thermal treatment to vent out volatile components that leave vacant space on the precursor (banana peel) (Jjagwe et al. 2021). For this process, 20 g of the sample was subjected to 350 °C at a rate of 10 °C/min for 3 h in a furnace under an N₂ environment, based on the method adopted by Zamora-Ledezma et al. (2021). After being cooled and size reduced to 125 μm, the sample was further activated chemically at different operating conditions. The bio-adsorbent passed a subsequent physical (under 350 °C temperature and inert environment) and acid activation with variation in acid concentration, temperature and activation time. Acid activation is one of the most common chemical treatments and has been used to increase the specific surface area and the number of acidic centers, modify the surface functional group and obtain solids with high porosity (Kumar et al. 2013; Shuma et al. 2019). The parameters considered for the activation process are acid (sulfuric acid) concentration, activation temperature and activation time (Table 1). These parameters were studied in a range of different levels to scrutinize the respective effect and to see at which operating conditions can the bio-adsorbent best be synthesized.

Proximate analysis: the proximate studies (moisture content, volatile matter, fixed carbon and ash content all in percent) of the activated banana peel were determined using ASTM standard procedures as used in many studies (Shuma et al. 2019; Kassahun et al. 2022).

pH of point of zero charge determination: Point zero charge is when the net charge on the adsorbent surface is zero (Saruchi & Kumar 2019). The surface charge of the adsorbent depends on the pH of the solution and its pH of point zero charges, pH_pzc (Liu et al. 2010; Bakatula et al. 2018). The adsorbent surface will be negatively charged when pH > pH_pzc and positively charged if the pH < pH_pzc (Belachew & Hinsene 2020). A 1.5-g of adsorbent was added to 45 mL of 0.1 N KNO₃ solution in the pH range of 2–14. The pH solution was adjusted by adding drops of 0.1 N NaOH and HCl solutions. Each flask was sealed and shaken thoroughly for 48 h at room temperature. Finally, the pH was measured and recorded. The net charge (ΔpH) on acid- and base-activated banana peel surfaces was determined by the difference between initial pH and pH after 48 h.

Scanning electron microscopy (SEM): the morphology of a synthesized activated banana peel bio-adsorbent was studied by plating the activated banana peel on an aluminum stub coated with carbon conductivity tape sample holder and put into SEM (FEI, INSPCT-F50, Germany). The operating conditions used to observe the SEM image were 20 kV, 16 mm working distance, more than 5,000x magnification, 20 μm scale and vacuum pressure (Birhanu et al. 2020).

Brunauer–Emmett–Teller (BET) surface area analyzer: A 0.4 g of sample was weighed and added into the preparation unit of the surface analyzer (Horiba 96000 series) where the sample was subjected to a temperature of 150 °C for 2 h to remove (degas) the moisture content. The methods and procedures employed for measuring BET surface area were followed and adopted by many authors (Naderi 2015). Based on the single nitrogen molecule surface area and the nitrogen adsorbed–desorbed of the multipoint data, the surface area of the sample was determined.

Fourier-transform infrared spectroscopy (FTIR): Functional groups of an activated banana peel bio-adsorbent were analyzed using FTIR (Thermo Scientific iS50 ABX) instrument equipped with ATR (attenuated total reflection) accessory, Potassium bromide (KBr) beam splitter and detector. After the background was taken, the samples were placed on the sample holder and an IR light source was applied to collect data at 32 resolution and 16 scans. The infrared solution was analyzed in the range of 4,000 and 400 cm⁻¹ wavenumber (Turki et al. 2018).

Thermal gravimetric analyses (TGAs): 20 g of an activated banana peel bio-adsorbent sample was weighed and placed into a ceramic sample holder separately. The samples were then put into a temperature-controlled TGA cell (DTG-60H) and were set to decompose from ambient temperature to 800 °C. The percentage of mass loss as function temperature was recorded and analyzed (Saadatkhah et al. 2020).

Batch adsorption experiments: this was carried out to achieve the optimum operating conditions for the removal of the selected dye from the aqueous solution (Banerjee et al. 2013). A reactive blue dye 19 (C₂₂H₁₆N₂Na₂O₁₁S₃, 99% pure) solution with a concentration of 1,000 mg/L was prepared as a stock solution. To know the maximum wavelength absorbency of reactive blue dye, 25 mg/L of the dye solution was taken and scanned using a UV–Vis spectrophotometer (DR 5000). The maximum wavelength (λ-max) and absorbance of the dye were taken and scanned from 300 to 700 nm using a UV/VIS spectrometer and it was found at 660 nm. Also, a series of batch experiments were made by diluting this solution. Reactive blue dye solutions with concentrations ranging from 0 to 100 mg/L were prepared by dilution of the stock solution.

The optimization and interaction effects of the variables on the adsorption processes were studied using response surface methodology followed by central composite design (RSM-CCD).

Individual parameter effect: The influence of each parameter on the dye adsorption uptake capacity of an acid-activated banana peel bio-adsorbent was studied based on one variable at a time approach. Therefore, adsorption time ranging from 20 to 140 min, pH from 1 to 7, the adsorbent dose from 1.0 to 4.0 g/L, and initial dye concentration from 20 to 80 mg/L have been considered. The parameters considered along the level studied are shown in Table 2.

Interaction effects and model evaluation using RSM-CCD: To investigate the adsorption process other than individual effects, consideration of the interactive effect of parameters on the process makes logical sense. The interaction effect and optimization of parameters were performed using RSM. The levels of each parameter for this study are given in Table 3.

Isotherm models show the equilibrium amount of adsorbate available in the solution and the amount of adsorbate available on the surface of adsorbent. Langmuir and Freundlich are the most robust models used to mathematically predict equilibrium adsorption processes. Adsorption isotherm experiments were conducted by adding 2 g/L of adsorbent to 500 mL of different initial concentrations of 25, 45, 65, 85, 105 and 125 mg/L of the adsorbate to be adsorbed, with pH of 3.0 and the adsorption process was agitated by a mechanical stirrer for 4 h of time. After each adsorption was finished, the adsorbent was filtered, the equilibrium concentrations were determined using UV-spectroscopy and the corresponding amount of adsorbate at equilibrium (q_e) was calculated.

Several adsorption and desorption processes had been made to test the reusability of the activated banana peel bio-adsorbent over the adsorption of dye molecules (Dahiru et al. 2018). A 2 g/L of the adsorbent was allowed to adsorb 40 mg/L of dye molecules at ambient temperature for 4 h and shacked at 500 rpm. The precipitate was added to 500 mL of 0.1 M NaOH solution and shacked for 12 h and then washed several times using distilled water until the pH became neutral. The supernatant solution was analyzed and the removal capacity was determined. The adsorption–desorption process was repeated 10 times until the capacity of the adsorbent fell below 50%.

As can be seen Figure 1(b), at a fixed acid concentration of 1.5 M and 3 h of activation time, the removal efficiency of the adsorbent increased with the activation temperature. In a similar pattern, the removal efficiency of the adsorbent as a function of activation time at an acid concentration of 1.5 M and at an activation temperature of 70 °C is depicted in Figure 1(c). It increased rapidly from 56.2 to 89% when the activation time changed from 1 to 3 h. However, the efficiency does not change substantially despite the time increasing to 5 h. As illustrated in the graph, an activation time of 3 h seems an ideal operating condition along the optimum acid concentration and activation temperature. As a result, it appears on the surface that acid concentration of 1.5 M, activation temperature of 70 °C and activation time of 3 h are favorable conditions to get an activated banana peel that fulfills the requirements of the adsorbent.

The moisture content, volatile matter, ash and fixed carbon content of the raw banana peels and activated banana peel bio-adsorbent are shown in Table 4. The parameters of the bio-adsorbent improved owing to the preparation and activation processes as compared to the raw banana peel. According to the study by Hammouda & Mihoubi and Kramarenko et al., the moisture content of the prepared raw banana peel is between 7 and 10% and that of activated is about 5–7% (Hammouda & Mihoubi 2014; Kramarenko et al. 2016).

Surface area is a paramount characteristic of adsorbents as the adsorption process is a surface phenomenon. As is the case with all adsorbents, the activated banana peel produced by the physical and chemical processes is assumed to have enough surface to qualify for dye adsorption. The BET results showed that surface areas of the raw banana peel and activated banana peel bio-adsorbent to be 75 and 432 m²/g, respectively. Sinto et al. reported surface area of activated banana peels to be 426 m²/g using different techniques (Sinto et al. 2018).

Effect of adsorption time: The graph of removal efficiency rapidly increased from 48.6 to 87.6% as the adsorption time varied from 20 to 60 min at a fixed pH of 3, adsorbent dose of 2 g/L and initial dye concentration of 40 mg/L as depicted in Figure 6(a). When the adsorption time further increased to 140 min with the interval shown, the removal efficiency of the bio-adsorbent for dye adsorbate slightly increases and shortly after that tends to remain almost constant at 92%. The increment of removal efficiency as a function of time implies that adsorption requires time to take place. According to Zheng et al. (2021) study, the adsorption mass transfer phenomenon involves three main steps: external diffusion, internal diffusion, and attachment to the active site. As a result, it demands a certain period to adsorb a given amount of adsorbate and of course until all the surface available is taken up or equilibrium is attained. Dwivedi et al. (2016) discussed 90 min to remove about 84% of cyanide contaminant. The adsorption time sufficient to remove most of the adsorbate may be short or long depending on the type of adsorbent and adsorbate the behavior of adsorption (Deng et al. 2014).

Effect of pH: The dyes are complex organic compounds with different functional groups and unsaturated bonds, so they show different levels of ionization at different pHs. In this regard, the biosorption of reactive blue dye solutions was carried out by varying pH of 1–7, with bio-adsorbent dose, initial dye concentration and adsorption time kept constant at 2 g/L, 40 mg/L and 60 min, respectively, and presented in Figure 6(b). The removal capacity of the adsorbent below pH of 3 was found to be around 90% and sharply falls all the way down to 40% as the pH increases to 7. It can be deduced that the solution pH was directly related to the availability of positively charged active sites on the surface of the bio-sorbent to bind with the dye molecules. Since the point zero charge of this particular adsorbent surface is 4.7, it assumes a positively charged surface below a pH of 4.7, as a consequence, adsorption of the anionic dye molecules becomes more favorable at low pH than high ones. The positive ions (H+) provide an electrostatic attraction between the adsorbent surface and the dye molecules leading to maximum adsorption. Some studies reported that the amount of dye uptake decreases with increasing the pH solutions from 2.5 up to 6 (Fernandes et al. 2008; Elkady et al. 2011; Gulnaz et al. 2011).

Effect of adsorbent dose: Adsorbent dose is among the essential parameters that strongly affect the adsorption process as observed in Figure 6(c). The removal efficiency of the adsorbent increases from 64.4 to 91.5% as the adsorbent dose increases from 1 to 2 g/L and appears almost constant thereafter. For a given dye concentration of 40 mg/L, it seems at high doses (say 3 g/L and above) the amount of adsorbate molecules available are already taken and the removal efficiency tends to remain constant.

Effect of initialdye concentration: The removal efficiency of the activated banana peel bio-adsorbent as a function of initial dye concentration of 20–80 mg/L at a fixed adsorption time of 60 min, pH of 3 and adsorbent dose of 2 g/L is demonstrated in Figure 6(d). As can be observed from the graph, the removal efficiency lightly changes from 92.2 to 88.2% as the initial dye concentration varies from 20 to 40 mg/L. when the initial dye concentration increases to 80 mg/L, however, the removal efficiency sharply declines to 37.4%. It is apparent that the dye's initial concentration radically affects the removal efficiency for a given adsorbent of 2 g/L. Increasing the dye concentration (molecules) at this fixed adsorbent amount would mean a small surface area for adsorption.

The interaction of the effect of adsorption time and pH on the removal efficiency of the bio-adsorbent at a given adsorbent dose of 2 g/L and initial dye concentration of 40 mg/L is illustrated in Figure 8(a). It can be seen from the graph that the removal efficiency rapidly increases from 62.8 to 91.8% as the adsorption time increases from 40 to 66 min and pH decreases from 4 to 2.8. Thereafter, the removal efficiency slowly increases as adsorption time increases to 80 min and pH decreases to 2. The increment of removal efficiency at these given operating conditions may attribute to a favorable condition that the adsorption time and pH conduce for mass transfer to take place rapidly. Moreover, it seems that the activated bio-adsorbent provided relatively enough surface area to adsorb the dye molecules at first and then tends to approach equilibrium where the adsorption process is about to stop. The removal efficiency, thus, was found to be almost constant (Padmavathy et al. 2016).

Likewise, Figure 8(b) demonstrates removal efficiency as a function of adsorption time and adsorbent dose at pH of 3 and 40 mg/L of initial dye concentration. It reveals the increment of the removal efficiency from 64.1 to 90.8% when the adsorption time varied from 40 to 64 min and the adsorbent dose varied from 1.5 to 2.1 g/L. Up next, the removal efficiency slightly increases to 92.5% despite the adsorption time and adsorbent dose increases to 80 min and 2.5 g/L, respectively.

The increase in removal efficiency with both adsorbent dose and adsorption time is due to the availability of surface area as the adsorbent amount increases and sufficiently enough time for adsorption (Manoj et al. 2015). Figure 8(c) clearly depicted how the removal efficiency of the activated bio-adsorbent varies with the variation of adsorption time and initial dye concentration at pH 3 and 2 g/L of adsorbent dose. The graph unfolds the increment of the removal efficiency at a considerable rate from 58 to 91.8% when the adsorption time increases from 40 to 64 min and the initial dye concentration decreases from 60 to 38 mg/L. As the model predicted, the removal efficiency shows a slow increase to 96.6% as adsorption time further varied to 80 min and the initial concentration decreased to 30 mg/L. It appears that initial dye concentration played a significant role in the removal efficiency. High efficiency at low concentrations would mean that the activated bio-adsorbent assumed more room for adsorption relative to the molecules of dye. On the other hand, higher dye concentration outnumbers the available surface and causes the removal efficiency to decline sharply (Padmavathy et al. 2016).

Figure 8(d) described the surface plots of response removal efficiency of dye adsorption process by the activated bio-adsorbent drawn with the variable's pH and adsorbent dose at a constant adsorption time of 60 min and initial dye concentration of 40 mg/L. It can clearly be observed from the graphs that the removal efficiency of the bio-adsorbent in terms of adsorbing dye molecules has an increment pattern with the adsorbent dose and a decrement pattern with pH. As such, when the adsorbent amount varied from 1.5 to 2 g/L and the pH changed from 4 to 2.8, the efficiency was found to change from 73.8 to 90% at a noticeable rate. It, however, remains constant, give or take, even though the adsorbent increases to 2.5 and pH further decreases to 2. It can thus be concluded that the cumulative effect of both variables to have a sound removal efficiency is in the vicinity of 2 g/L of adsorbent dose and pH of 3 for a given initial dye concentration of 40 mg/L for an adsorption time of 60 min. It also seems that the increase of the adsorbent amount allows more room for the adsorption of dye molecules till the process tends toward equilibrium. At a high-pH dye solution, the adsorption competes with other molecules which causes the efficiency of dye removal to decline rapidly.

The interaction effect of pH and initial concentration on the removal efficiency of the activated bio-adsorbent in the event of dye molecules adsorption is given in Figure 8(e). As would be expected, the removal efficiency is more pronouncedly dependent on the dye concentration for a constant adsorption time of 60 min and an adsorbent dose of 2 g/L. The efficiency was found to go up to 94% when the dye concentration was reduced to 30 mg/L. While the adsorbent amount is kept at 2 g/L, it is crystal clear that the removal efficiency declines with concentration and the reverse holds true. Apparently, since adsorption is a surface phenomenon, higher dye concentration would outnumber the available surface present in the 2 g/L adsorbent and as consequence, some dye molecules remain adsorbed or not removed from the synthetic solution. It is, therefore, imperative that the dye concentration should be proportional to the adsorbent dose which in this case is 2 g/L to 40 mg/L to get about 90% of the dye removed, putting other factors aside.

Figure 8(c) presented the removal efficiency of activated bio-adsorbent concerning adsorbent dose and initial dye concentration at a fixed adsorption time of 60 min and pH of 3. The model equation pretty well predicts the removal efficiency to increase from 70 to 94% based on the variation of adsorbent dose from 1.5 to 2.0 and initial dye concentration from 50 to 30 mg/L. As is so often the case, the removal efficiency tends to increase with the adsorbent dose and decrease with the dye's initial concentration (Al-senani & Al-fawzan 2018). All told, the removal efficiency of activated bio-adsorbent used to adsorb synthetic dye solution was found to be dependent on the four parameters, namely adsorption time, pH, adsorbent dose and initial dye concentration. On top of that, adsorption time and adsorbent dose were found to have a positive effect, and pH and initial dye concentration negative effect on the removal efficiency. It appears on the surface that 90% or so of the dye molecules can be removed at favorable operating conditions of the variables without some extended levels considered (Mohan et al. 2006; Padmavathy et al. 2016).

Parameter optimization: the indication of the need for optimization that compromises level parameters and yields an acceptable level of removal efficiency. The optimization gives no lower nor higher but in-between values of variables and responses based on the criteria set. The optimum operating conditions of the dye adsorption process were found to be an adsorption time of 60 min, pH of 3, an adsorbent dose of 2 g/L, and an initial dye concentration of 40 mg/L from the RSM-CCD numerical optimization. The optimum operating condition found was validated with triplicated experimental data and the deviation between the experimental result and that of the model predicted was 1.3%.

The two well-known isotherm models, Langmuir and Freundlich adsorption isotherm models were used to study the adsorption mechanism. The coefficient of determination (R²) was used to indicate the isotherm model that best fits with experimental data. The R² values and the model parameters or coefficients are presented in Table 6. The adsorption behavior of the dye molecules on bio-adsorbent is best described mathematically using the Langmuir isotherm model since the R² value is 0.9996. Furthermore, it can be inferred that the dye molecules formed a monolayer on the surface of the adsorbent.

This study looked into the bio-adsorption of reactive blue dye onto the activated banana peel. Thermal and chemical surface modifications were done to the bio-adsorbent to boost its ability to absorb the anionic dye, reactive blue. With the surface modification, the change in the surface charges of adsorbent materials was aimed. The characterization methods of the activated banana peel such as proximate analysis, BET, TGA, SEM, XRD, and FTIR gave reliable and guaranteed results for the adsorption of dye from the aqueous solution or textile effluent. The activated banana peel bio-adsorbent was allowed to adsorb the dye molecules at different operating conditions. The operating conditions were optimized and this optimum condition can remove most of the dye molecules from the synthetic solution. From the kinetics and isotherm model study, it can be concluded that the rate at which the dye molecules are being adsorbed and the behavior of adsorption follow pseudo-second-order and Langmuir isotherm models. The regeneration test suggested that the activated banana peel bio-adsorbent can be used four times and repeated before its removal performance falls <80%. To sum it up, activated banana peels can be a good candidate for adsorbent material to mitigate wastewater problems to a considerable extent. Using banana peel as a means to treat wastewater has two-fold advantages: (1) turning a waste material into a useful adsorbent and (2) it is relatively cheap and easy to prepare.

The authors would like to thank the Department of Chemical Engineering, College of Food and Chemical Engineering, Wollo University, Kombolcha Institute of Technology, Kombolcha, Ethiopia; Bahir Dar University, Bahir Dar, Ethiopia; and Addis Ababa Science Technology University, Addis Ababa, Ethiopia for their collaboration during the laboratory work.

M.K. conceptualized the study, prepared the methodology, did formal analysis, investigated the study, collected resources, and did data curation; T.S. did software analysis, validated the study, wrote and prepared the original draft; B.G. wrote, reviewed and edited the article, T.T. visualized and supervised the study. All authors have read and agreed to the published version of the manuscript.

All relevant data are included in the paper or its Supplementary Information.

The authors declare there is no conflict.