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Development and characterization of activated charcoal adsorbent derived from oak for efficient removal of methylene blue: functionality vs surface area
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Abstract
The article investigates the development and characterization of activated charcoal derived from oak for the efficient removal of methylene blue, a cationic dye widely used in the textile industry. It emphasizes the importance of surface functionality in adsorption processes, demonstrating that high surface area alone is not sufficient for effective adsorption. The study reveals that sulfuric acid activation of oak charcoal significantly enhances its adsorption efficiency, achieving nearly 100% removal of methylene blue across a wide pH range. Detailed characterization studies, including Boehm titration, BET surface analysis, and FTIR spectroscopy, provide insights into the structural and chemical modifications that occur during activation. The article also presents adsorption studies that explore the effects of various parameters, such as pH, adsorbent dosage, initial dye concentration, contact time, and temperature, on the adsorption performance. The results highlight the competitive adsorption capacity of sulfuric acid-activated oak charcoal, making it a promising low-cost and functionally efficient adsorbent for wastewater treatment applications. The study concludes with a thorough analysis of adsorption isotherms and kinetic models, confirming the exothermic and spontaneous nature of the adsorption process.
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Abstract
With industrial growth, environmental and water pollution have become pressing issues, requiring effective treatment solutions. Adsorption is an economical and practical method for removing dyes from textile wastewater, making the choice of a sustainable, low-cost adsorbent crucial. Although it is clear that surface area is important in adsorption, the presence of functional groups that have adsorption ability is equally important. For this purpose, locally abundant oak-derived charcoal (MK) was selected. Due to its low adsorption capacity, the charcoal was activated using concentrated sulfuric acid at 150 °C with an acid-to-sample ratio of 5:1, producing activated charcoal (SMK). The adsorbent was characterized using SEM, BET, FTIR, Boehm titration, and pHpzc analyses. Methylene blue (MB), a cationic dye, was chosen as the target pollutant, and experiments were conducted to study the effects of solution pH, adsorbent dose, initial dye concentration, and temperature on MB removal. Isotherm and kinetic analyses showed that MB adsorption on SMK fits the Langmuir isotherm model, with an adsorption capacity of 370.85 mg/g, and follows a pseudo-second-order kinetic model. Thermodynamic analysis confirmed that the process is exothermic. While MK has a surface area of 76.8 m2/g but no affinity for dyes, SMK, with a surface area of 6.31 m2/g, was effective in MB removal, highlighting the importance of surface functionality. Therefore, SMK proved to be an efficient adsorbent for MB removal from water.
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1 Introduction
Water is the most essential substance for life, and without it, life cannot exist; in essence, water is life. However, underground and surface water resources of such critical importance are severely threatened by wastewater containing various domestic and industrial pollutants. Although preventive measures are taken against these threats, it is crucial that these measures are continuous and sustainable to address serious water-related issues that may arise in the future. Both physical, chemical, and biological pollution in water reduces the rate of water usage. For this reason, efforts to eliminate the pollution in water have gained momentum in recent years in order to find potable water for the continuation of life and to keep it clean for future generations [1‐5].
The main reasons for water pollution are the uncontrolled (untreated) release of domestic and industrial wastewater to nature. Structurally, pollutants found in water are divided into two groups: inorganic pollutants and organic pollutants [6‐9]. Heavy metals are examples of inorganic pollutants. Heavy metals such as Cd, Mn, Pb, Hg, Cu, Cr, and Zn can cause serious disturbances in water, even at trace levels [9‐11]. Phenol and phenol compounds and various anionic and cationic dyestuffs can be given as examples of organic pollutants. The introduction of dyestuffs, which have a wide area of use, to the receiving environment without any precaution (without treatment) creates dangerous pollution in terms of the environment. Due to the fact that especially dyes are colored, they prevent the light required for photosynthesis from reaching the depths of the water and prevent living things from producing food [12‐16]. Globally, approximately 7 × 107 tons of synthetic dyes are produced annually, with over 10,000 tons consumed by the textile industry. These dyes, including azo, direct, reactive, mordant, acid, basic, disperse, and sulfur dyes, are extensively used in dyeing wool, cotton, silk, polyester, polyamide, and acrylic fibers in textile manufacturing. Methylene blue is a cationic dye widely used in the textile industry, posing toxic effects when released into aquatic environments at high concentrations. It releases potentially carcinogenic aromatic amines such as benzidine and methylene, leading to a concentration-dependent decline in the growth rate, protein content, and pigment synthesis of microalgae species like S. platensis and C. vulgaris. Additionally, it inhibits chlorophyll synthesis, suppressing photosynthesis and causing adverse ecological impacts [17, 18].
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For this reason, the treatment of organic and inorganic pollution in wastewater is vital for living things and the ecosystem. Treatment methods such as adsorption, ion exchange, ozonation, biological oxidation, flotation, flocculation, coagulation, and sedimentation have been developed, and adsorption is one of the most commonly used methods due to its easy and applicable application [19‐24].
Adsorption is generally the preferred treatment method for its economic and application convenience. Adsorption is the treatment process of undesirable substances in wastewater by holding onto the surface of the solid when optimum conditions are met. Some examples of adsorbents are activated carbon, coals, clays, zeolites, and various metal sprouts, while artificial adsorbents are carbon nanotubes, molecular sieves (artificial zeolites), metal oxides, activated alumina, silica gels, and polymeric resins [25‐33].
Adsorption is the event that takes place on the surface of the adsorption layer. Therefore, it is directly proportional to the surface area. A larger surface area generally means more adsorption sites, which can enhance the material’s capacity to adsorb molecules. High surface area adsorbents, such as activated carbons or specific porous materials, are advantageous when a high adsorption capacity is needed, as they offer extensive contact sites for adsorbates. While a high surface area is desirable, it alone is not sufficient. The material must also have the right pore size and surface chemistry to effectively attract and hold target molecules. High surface area materials without suitable functionality may only weakly adsorb specific compounds. Functionality refers to the specific chemical groups (e.g., carboxyl, hydroxyl, amine) present on the surface of an adsorbent [34‐40]. These functional groups create active sites that can interact with adsorbate molecules through chemical bonding, electrostatic attraction, or hydrogen bonding. Functionalized surfaces are particularly useful for selective adsorption, where the goal is to adsorb certain types of molecules more effectively than others. Functional groups are crucial in applications like heavy metal ions and dyes removal from water. For example, oxygen-containing groups (e.g., carboxylic acids) on the surface of carbon materials can strongly attract and bind metal ions and dye molecules improving adsorption efficiency even if the surface area is moderate [37, 41‐43]. Excessive functional groups can sometimes lead to pore blockage, reducing surface area and pore volume. Furthermore, functionalization tailored for one type of adsorbate may not work for another; hence, selectivity can be a limitation if the adsorbate types vary. If a material has a high surface area but low functionality, it can adsorb a large amount of non-specific adsorbates but may lack selectivity. In contrast, a material with high functionality but limited surface area may be very selective and effective for certain target molecules but have a limited total adsorption capacity. Surface area primarily affects the total adsorption capacity, while surface functionality impacts the selectivity and strength of adsorption. Tailoring both properties to specific applications can lead to more efficient and selective adsorbents [37, 44‐48].
Using oak for activated charcoal production offers significant sustainability advantages. Oak is a widely available and renewable biomass source, making it an eco-friendly alternative to synthetic or fossil-based adsorbents. Additionally, the activation process can be optimized to utilize minimal chemicals or incorporate green activation methods, reducing environmental impact. Oak-based activated charcoal also contributes to waste valorization, as sawdust, wood scraps, or forestry residues can be repurposed, promoting a circular economy. Furthermore, its efficiency in dye removal, as demonstrated in the study, supports environmentally friendly wastewater treatment, reducing reliance on costly and hazardous chemical treatments.
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Oak charcoal was chosen for adsorption due to its naturally occurring porous structure and high carbon content, which provide a stable framework for surface modifications. Compared to other biomass sources, oak-derived charcoal offers structural integrity and thermal stability, making it suitable for chemical treatments like sulfuric acid modification without significant degradation. Additionally, its ability to develop functional groups upon activation enhances its adsorption efficiency, particularly for dye removal, demonstrating a balance between surface area and surface functionality. In this study, it was demonstrated that untreated oak charcoal, despite possessing a certain surface area, is insufficient for effective adsorption. However, oak charcoal modified with sulfuric acid—thereby imparting functional groups despite having minimal surface area—proved to be effective for dye adsorption. These findings highlight the critical role of surface functionality in adsorption processes.
2 Experimental
2.1 Materials and characterization
Methylene blue, sulfuric acid (98%), hydrochloric acid (35%), sodium hydroxide, potassium chloride, and sodium bicarbonate used in the experiments were sourced with analytical grade from Merck and applied without further purification. An Electromag oven, Heidolph magnetic stirrer, Sartorius RC (0.45 µm) syringe filter, and Biosan shaker were used during the experiments, while a Sartorius precision balance was employed for accurate weighing. Charcoal (MK), derived from oak wood and chosen as the adsorbent, was purchased from a local supplier.
For analysis, SEM imaging and SEM–EDX analysis were performed using a scanning electron microscope after being coated with a thin gold layer (JEOL, 30 kV). Infrared analysis was conducted with an ATR-FTIR spectrometer in the transmission mode between 4000 and 400 cm−1 with 4 cm−1 resolution (Perkin Elmer Spectrum Two), and absorbance measurements were obtained using a UV–Vis spectrophotometer (Hach Lange DR6000). A pH meter (WTW) was used for pH measurements, and an Elektromag centrifuge was employed for sample centrifugation. BET surface area, pore volume, and pore size were measured with the Quantachrome Autosorb-6 after the sample was further degassed for 4 h at 150 °C.
2.2 Preparation of the adsorbent
The adsorbent used in this study was applied in two forms: directly by pulverizing oak-derived charcoal (MK) obtained from the market and after activation. For the activation process, the charcoal was treated with sulfuric acid in a 1:5 ratio (MK:sulfuric acid) and heated at 150 °C for 12 h in an oven. The samples were then washed with a saturated sodium bicarbonate solution until neutralized. Following grinding, the adsorbent was sieved. The adsorbent activated with sulfuric acid was designated as SMK.
2.3 Characterization of the activated adsorbent
The characterization of the raw charcoal (MK) and the adsorbent (SMK) prepared by activating it was made using the following methods.
2.3.1 Boehm titration
Acidic and basic groups on the surface are determined by Boehm titration. For this purpose, it was determined using sodium hydroxide (0.05 M), sodium carbonate (0.05 M), sodium bicarbonate (0.05 M), and hydrochloric acid (0.05 M) to determine the amount of carboxylic, lactonic, phenolic, total acid, and total base on the surface. Twenty milliliters of the above solutions was taken, and 0.15 g of MK and SMK was added to them. After shaking for 96 h, the samples were separated by filtration, and the sodium hydroxide, sodium carbonate, and sodium bicarbonate extracts were titrated with 0.1 M HCl solution and the sodium hydroxide extract with 0.1 M HCl solution. Titrations were performed potentiometrically. Functional group amounts were calculated by subtracting the number of moles found by titration from the initial moles. The functional group amounts were calculated as mmol/g by dividing the calculated mole numbers by the initial sample masses [20].
2.3.2 Determination of the surface pH value (pHpzc) of the adsorbent
To determine the surface charge of the adsorbent, 50 mL of 0.1 M KCl solution was placed in each of ten 250-mL flasks. The pH of each solution was adjusted between 1 and 10 using 0.1 M NaOH and 0.1 M HCl solutions. Then, 0.1 g of adsorbent was added to each flask, sealed with parafilm, and shaken for 24 h. After 24 h, the mixtures were filtered, and the final pH values were measured. These procedures were performed separately for both MK and SMK, and graphs were plotted with the initial pH values on the x-axis and ΔpH (pHinitial − pHfinal) on the y-axis. The point where the curve intersects the x-axis was identified as the pHpzc value [20, 29].
2.4 Adsorption studies
Adsorption experiments were conducted in 250-mL flasks. To optimize the adsorption conditions, the parameters investigated included adsorbent dosage (0.025–0.3 g), solution pH (2–9), dye concentration (50–1000 ppm), contact time (5–300 min), stirring speed (200 rpm), and solution temperature (25–45 °C). The adsorption performance was evaluated for both MK and SMK as adsorbents. In each experiment, 50 mL of dye solution was used, and pH adjustments were made using 0.1 M NaOH or 0.1 M HCl. At the end of each experiment, the solutions were filtered through a Sartorius RC 0.45-µm syringe filter, and absorbance values at 665 nm were measured using a UV–Vis spectrophotometer. Results were given as the average of triple experiments.
The amount of dye adsorbed was calculated as mg/g based on the working calibration curve using the following equation.
Seven separate experiments were conducted to investigate the effect of adsorbent dosage on the adsorption of methylene blue (MB) onto SMK. In each experiment, 50 mL of 100 ppm MB solution was added to 250-mL flasks, with the pH adjusted to 9. Adsorbent dosages of 0.025, 0.05, 0.1, 0.15, 0.20, 0.25, and 0.30 g of SMK were added sequentially. The flasks were sealed with parafilm and stirred at 25 °C for 5 h (300 min). Subsequently, the solutions were filtered, and absorbance values were measured. Results were given as the average of triple experiments.
2.4.2 Effect of solution pH on adsorption
To examine the effect of solution pH on MB adsorption with MK and SMK, experiments were conducted across a pH range of 2 to 10. A 50 mL volume of 100 ppm MB solution was added to each 250-mL flask, and the pH was adjusted to the desired range using 0.1 M HCl and 0.1 M NaOH. An amount of 0.05 g of MK and SMK was then added to each flask, which was then sealed and stirred for 5 h. The final pH values were recorded, followed by filtration of the solutions. Absorbance values were measured using a UV–Vis spectrophotometer. Using the absorbance data and the calibration curve, the adsorption amount (Eq. 1) and percentage removal rate (Eq. 2) were calculated. Results were given as the average of triple experiments.
2.4.3 Effect of initial dye concentration on adsorption
To investigate the effect of initial dye concentration, 50 mL solutions with concentrations of 25, 50, 75, 100, 150, 200, 250, 300, 400, and 600 ppm were prepared from a 1000 ppm stock MB solution. The pH of each solution was adjusted to 9 using 0.1 M NaOH, and 0.05 g of SMK was added to each flask. The flasks were then agitated in a shaker for 5 h, followed by filtration of the solutions. Absorbance values were measured with a UV–Vis spectrophotometer, and the amount of adsorption (Eq. 1) and percentage removal rate (Eq. 2) were determined using the calibration curve. Results were given as the average of triple experiments.
2.4.4 Effect of contact time on adsorption
To study the effect of contact time, solutions of MB at concentrations of 100 and 200 ppm were prepared, and 0.05 g of adsorbent was added to each 50-mL flask. The pH was adjusted to 9 with 0.1 M NaOH. Samples were collected from these solutions at intervals of 5, 10, 15, 20, 30, 40, 50, 60, 70, 80, 90, 120, 150, 180, 240, and 300 min. After each interval, solutions were filtered and absorbance values were measured with a UV–Vis spectrophotometer. Using these absorbance values and the calibration curve, the adsorption amount (Eq. 1) and percentage removal rate (Eq. 2) were calculated. Results were given as the average of triple experiments.
2.4.5 Effect of temperature on adsorption
To investigate the effect of temperature on adsorption, solutions of MB at 100, 200, and 300 ppm were adjusted to pH 9 using 0.1 M NaOH. The solutions were agitated at 25, 35, and 45 °C in a water bath at 200 rpm for 5 h. The solutions were then filtered, and absorbance values were recorded using a UV–Vis spectrophotometer. Using the absorbance data and the calibration curve provided, the adsorption amount (Eq. 1) and percentage removal rate (Eq. 2) were calculated. Results were given as the average of triple experiments.
3 Results and discussion
3.1 Characterization study results of MK and SMK
3.1.1 Neutral charge point (pHpzc) study results
With the determination of the surface neutral charge point called pHpzc, an idea can be obtained about the pH range of the adsorbent to adsorb. The graphic obtained as a result of the experiment performed with the pH drift method [20] to determine the pHpzc point for MK and SMK is given in Fig. 1.
As can be seen from the graph, the surface neutral load points of MK and SMK were determined as 8.2 and 7.8. Acid activation slightly altered the pHpzc value of the MK surface. While the adsorbent surface is positively charged at values lower than this pH value, the adsorbent surface is negatively charged at pH values greater than this pH. In other words, it can be said that it can be used as adsorbent against anionic pollutants below these values and against cationic pollutants above these values. In our previous study, the pHpzc values for walnut shell treated with hydrochloric acid, sulfuric acid, and phosphoric acid were determined as 4.00, 6.07, and 4.00, respectively, indicating that sulfuric acid did not have a significant effect on the pHpzc [49]. In contrast, in our other study, it was determined that pHpzc decreased to 4 with the activation of hawthorn kernel seed with sulfuric acid [20]. Wang et al. [50] also determined the pHpzc as 6.7 and 3.0 when they treated activated carbon with hydrochloric acid and nitric acid.
3.1.2 Boehm titration results
The results of Boehm titration performed to determine the functional groups that are acidic and basic on the surface of MK and SMK, and the determined acidic and basic group amounts are given in Table 1.
Table 1
Results of MK and SMK Boehm titration
Carboxylic (mmol/g)
Lactonic (mmol/g)
Phenolic (mmol/g)
Total acid (mmol/g)
Total base (mmol/g)
MK
0.167
0.833
0.333
1.333
0.933
SMK
0.667
0.5
0.233
1.4
0.4
When the Boehm titration results given in Table 1 are examined, the amount of carboxylic, lactonic, phenolic, and basic groups on the surface of the activated MK after treatment with sulfuric acid has changed [20]. After the activation of MK, the number of carboxylic groups effective in adsorption increased approximately four times, while a decrease in phenolic and lactonic groups occurred. The total amount of acid on the surface increased by about 10%. According to these results, it was seen that while acid activation caused an increase in the total acid amount of bio-adsorbate, it caused a decrease in the number of basic groups. It can be said that the partial increase in the total acid amount and the partial decrease in the pHpzc value are similar. Higher total acid capacity may indicate more proton donors on the surface, which generally increases the capacity of acidic surfaces to adsorb basic dyes such as MB [51, 52].
3.1.3 BET surface analysis study results
BET analyses were carried out to determine the surface area, pore volume, and pore size effective in adsorption. BET surface analysis results of MK and SMK are given in Table 2.
Table 2
BET analysis results of MK and SMK
BET SA (m2/g)
PV × 102(cm3/g)
PS (nm)
MK
76.8
7.51
25.0
SMK
6.31
4.58
31.3
SA surface area, PV pore volume, PS pore size
As can be seen from Table 2, the surface properties of charcoal activated with sulfuric acid have changed considerably. When MK and SMK were examined in terms of pores, it was observed that they had meso-porosity [53, 54]. It was determined that surface area and pore volume decreased but pore size increased after activation. In the literature, it has been reported that biomass treated with sulfuric acid tends to show a decrease in surface area, especially when high temperatures or high acid concentrations are used. This is due to the fact that acid treatment may fill some of the pores in the biomass structure or disrupt the pore structure as organic components dissolve. Also, mesoporous adsorbents are more efficient during adsorption [36, 55, 56].
3.1.4 SEM surface analysis results
SEM images obtained from the analysis of MK, SMK, and SMK-MB (MB-loaded SMK) samples are presented in Fig. 2. As shown in Fig. 2, the surface of MK exhibits a porous structure and coarse particles. However, when examining the SEM images of SMK following acid activation, it can be observed that the porous structures are diminished, and the coarse particles have fragmented into smaller sizes. This finding aligns with the higher surface area of MK due to its porous structure, while a decrease in surface area is observed in SMK. This structural change suggests that while the surface area is reduced, the introduction of functional groups through sulfonation may enhance adsorption sites and adsorption capacity. The surface images of SMK-MB are also given in Fig. 2e and f. As seen from the images, the pores and particles appear covered as a result of MB loading. This observation is further supported by the SEM-EDAX analysis results (Fig. 3). According to SEM-EDAX analysis, MK contains carbon (C), oxygen (O), and calcium (Ca), whereas the sulfur (S) element is introduced into the structure as a result of activation with sulfuric acid, indicating sulfonation of the MK. The presence of sodium (Na) in the structure is likely due to incomplete removal of Na ions following neutralization with sodium bicarbonate. Additionally, the SEM-EDAX analysis of SOC-MB shows the presence of nitrogen (N), absent in SMK, which serves as evidence for the adsorption of MB onto SMK.
Fig. 2
SEM images for MK (a) × 1000, b × 2000 SMK, c × 1000, d × 2000 SMK-MB, e × 1000, and (f) × 2000
FTIR analyses are conducted to determine the molecular bond characterization of the adsorbent. These analyses have been made for both MK and SMK, and FTIR graphics are given in Figs. 4 and 5.
As observed in the FTIR spectra in Fig. 3, it is evident that MK underwent chemical modification as a result of activation. New bands appear in the spectrum of SMK, which are absent in MK. Upon examining the spectra of MK and SMK, it is suggested that the broad band between 3500 and 2500 cm−1 arises from the cellulosic structure or O–H stretching vibrations of carboxylic acids. The carbonyl (C = O) band at 1700 cm−1 in the SMK spectrum indicates the presence of carboxylic acids or their derivatives. The bands at 1212 and 1032 cm−1 are attributed to C–C stretching, while the band at 1149 cm−1 corresponds to C-O ether stretching. Additionally, bands observed at 1440, 1310, and 874 cm−1 are likely due to S–O and S = O groups formed as a result of sulfonation [57‐59]. In the FTIR spectrum of SMK-MB (Fig. 4), bands at 884, 1329, and 1598 cm−1 are associated with C-N and N–H stretching vibrations characteristic of methylene blue. When considered alongside SEM-EDAX results, the FTIR analysis of SMK-MB confirms that methylene blue was successfully adsorbed onto SMK [20, 60, 61]. These structural modifications correlate with improved adsorption performance by increasing the number of active sites and enhancing electrostatic interactions with MB molecules, as further evidenced by FTIR spectral shifts indicating functional group interactions.
3.2 Adsorption study results
Methylene blue was utilized as a cationic dye in adsorption studies conducted on both MK and SMK. During the pH scan for MB adsorption (100 ppm) on MK, it was observed that dye removal was not quantitative at any of the examined pH values (see Table S1). Consequently, SMK, obtained by activating MK with concentrated sulfuric acid, was employed in subsequent adsorption studies. The adsorption studies of the cationic dye on SMK were conducted using methylene blue, investigating the effects of pH, adsorbent dosage, initial dye concentration, contact time, and temperature on MB adsorption. Studies with the anionic dye Congo red were discontinued because the dye precipitated at pH = 1 and pH = 2 and quantitative results were not obtained at other pHs for both adsorbents.
3.2.1 Effect of solution pH on adsorption
The results of the study, in which 50-mL samples of 100 ppm and 300 ppm methylene blue solutions were adjusted to pH values ranging from 2 to 10 and mixed with 0.1 g of SMK, were conducted by shaking at 200 rpm for 5 h at 25 °C. These results are presented in the graph in Fig. 6.
Fig. 6
pH effect on MB adsorption on SMK (Ci = 100 ppm (a), 300 ppm (b); T = 25 °C, t = 5 h, V = 50 mL, m = 0.1 g)
As illustrated in Fig. 6a, nearly 100% dye removal was achieved across the entire pH range studied at a concentration of 100 ppm. In Fig. 6b, the effect of pH on adsorption for a 300 ppm methylene blue solution was examined. It was observed that there was almost quantitative removal of MB even at pH values of 2 and 3, while complete dye removal was achieved at pH values above this range. According to the pHpzc graph presented in Fig. 1, the pHpzc value for SMK was determined to be 7.8. In the adsorption studies of MB, a cationic dye, on SMK, it is inferred that the pH of the solution should be maintained above 7.8 for optimal adsorption [62]. The nearly 100% adsorption observed at pH values below 7.8 may be attributed to the influence of other mechanisms (such as diffusion, π-π interactions, and hydrophobic interactions) in the adsorption process. For subsequent studies, a pH value of 9 was selected as the appropriate condition [63, 64].
3.2.2 The effect of the amount of adsorbent on adsorption
To investigate the effect of adsorbent dosage on the adsorption process in a 100 ppm methylene blue solution, varying amounts of SMK (0.025, 0.05, 0.1, 0.15, and 0.2 g) were added to 50 mL of the solution, which was then adjusted to pH 9. The mixture was shaken at 200 rpm for a duration of 5 h. The results obtained for the conditions of initial concentration (Ci) = 100 ppm, temperature (T) = 25 °C, contact time (t) = 5 h, volume (V) = 50 mL, and pH = 9 are presented in Table 3.
Table 3
The effect of adsorbent amount on MB adsorption
Amount (g)
0.025
0.05
0.10
0.15
0.20
DR (%)
99.28
99.63
99.68
99.67
99.63
As can be seen from Table 3, dye removals close to 100% were obtained in all the studied adsorbent amounts. In the next adsorption studies, the appropriate amount of adsorbent was determined as 0.05 g.
3.2.3 Effect of initial dye concentration on adsorption
For the adsorption studies with SMK, different concentrations of MB are prepared, and the graphics drawn against the adsorption amount (Q) and DR% are given in Fig. 7a.
Fig. 7
a Effect of MB initial concentration on SMK (pH = 9, T = 25 °C, t = 5 s, V = 50 mL, m = 0.05 g). b Effect of time on MB adsorption on SMK (Ci = 100 and 200 ppm, pH = 9, T = 25 °C, V = 50 mL, m = 0.05 g). c Effect of temperature on MB adsorption on SMK (Ci = 100 and 200 ppm, pH = 9, t = 5 s, V = 50 mL, m = 0.05 g)
As illustrated in Fig. 7a, the adsorption capacity reached saturation at a concentration of 600 ppm, with no further increase in Q observed at higher concentrations. The adsorption capacity of SMK was determined to be Q = 370.85 mg/g. Additionally, the graph shows that dye removals approached nearly 100% up to 400 ppm, followed by a decrease in removal efficiency beyond this concentration. These results suggest that SMK is a suitable adsorbent for methylene blue and similar dyes across a broad concentration range.
Methylene blue studies with various adsorbents have been investigated, and the removals found in the literature are given in Table 4. As can be clearly seen from the table, adsorption capacities are not only proportional to surface areas, but also functionality is an important feature. SMK demonstrates a competitive adsorption capacity (370.85 mg/g) compared to many adsorbents listed in Table 4, despite its relatively low surface area (6.31 m2/g). This suggests that the high adsorption efficiency of SMK is driven more by its functional properties, particularly the sulfonation process, rather than just surface area. Unlike high surface area adsorbents such as corncob-to-xylose residue (2249 mg/g, 2025 m2/g), SMK provides a cost-effective alternative, as its activation with H2SO4 is relatively simple and scalable. Additionally, the nearly 100% removal efficiency up to 400 ppm indicates that SMK is highly effective within practical dye concentrations, making it a promising low-cost and functionally efficient adsorbent for wastewater treatment applications.
Table 4
Comparison of the Qm values in the literature of the adsorption of MB
In order to investigate the effect of the adsorption time of SMK on methylene blue adsorption, two different concentrations of 100 ppm and 200 ppm have been studied and are given in Fig. 7b. As can be seen in the graph, it was observed that the dye removal for 100 ppm concentration in the adsorption of MB on SMK occurred very rapidly with approximately 92% in the first 5 min. It was observed that the adsorption was almost completed in about 30 min, and in SMK adsorption of 200 ppm MB, the dye removal increased rapidly until the first 90 min, and there was almost 100% dye removal in 180 min.
3.2.5 Temperature effect on adsorption
In order to investigate the effect of temperature, adsorption studies of MB on SMK were conducted at initial concentrations of 100 ppm and 200 ppm at 25, 35, and 45 °C, with the results presented in Fig. 7c. At the specified temperatures, almost 100% dye removal was achieved in studies with an initial concentration of 100 ppm, indicating that temperature change had no effect on removal efficiency. However, in studies conducted at an initial concentration of 200 ppm, dye removal was found to be influenced by temperature, with removal efficiency decreasing as temperature increased.
3.3 Adsorption isotherms of MB on SMK
The adsorption capacity and behavior of MB on SMK were investigated using the Langmuir [72], Freundlich [73], and Temkin isotherms [74], employing the equations provided below (Eqs. 3, 4, and 5, respectively). The Langmuir isotherm plot, constructed with Ce versus Ce/qe values, is presented in Fig. S1. The Freundlich isotherm plot, using lnCe versus lnqe values, is shown in Fig. S2, and the Temkin isotherm plot, with lnCe values against qe values, is provided in Fig. S3. The isotherm constants calculated from the Langmuir, Freundlich, and Temkin models are summarized in Table 5.
concentration of the substance remaining in solution at equilibrium (mg/L)
qe
amount of adsorbed substance at equilibrium (mg/g)
n
Freundlich constant related to adsorption intensity
$$Q_e=B\ln A+B\ln C_e$$
(5)
where:
\(B=RT/b\)
A
Temkin isotherm constant (L/g)
R
gas constant (8.314 J/mol K)
T
absolute temperature (K)
b
Temkin adsorption constant (J/mol)
These models aid in elucidating the adsorption mechanism and quantifying the adsorption capacity of MB on SMK.
The isotherm model results in Table 5 indicate that the Langmuir model provides the best fit for describing the adsorption of MB on SMK, as evidenced by the high correlation coefficient (R2 = 0.9999). This suggests that the adsorption process likely follows monolayer coverage on a homogeneous surface, with a maximum adsorption capacity (Qm) of 370.4 mg/g and a binding energy constant (KL) of 0.375 L/mg. In contrast, the Freundlich model shows a lower correlation coefficient (R2 = 0.7989), indicating a less favorable fit and suggesting that adsorption does not strictly follow the multilayer adsorption model on a heterogeneous surface. The Freundlich constant (KF = 135.4) and the value of 1/n = 0.1939 imply moderate adsorption intensity. For the Temkin model, the moderate correlation coefficient (R2 = 0.9453) indicates a reasonable fit, suggesting that the adsorption is influenced by indirect adsorbate–adsorbate interactions, as reflected in the heat of adsorption parameter (B = 37.488 kJ/mol). The Temkin isotherm constant (AT = 74.87 L/mg) further supports this interaction effect. Overall, the Langmuir model’s high R2 value implies it is the most suitable for describing MB adsorption on SMK under the studied conditions [75, 76].
3.4 Kinetic study results for MB adsorption on SMK
The graphs of the kinetic study results for MB adsorption on SMK are given in Fig. S4, Fig. S5, and Fig. S6, and the kinetic data obtained from these graphics are given in Table 6.
Table 6
Kinetic data for MB adsorption on SMK
Kinetic model
Pseudo first order
Ci (ppm)
qexp (mg/g)
qtheo (mg/g)
k1 (min−1)
R2
100
99.8
2.56
0.0445
0.8749
200
196.5
297.70
0.0184
0.7922
Kinetic model
Pseudo second order
Ci (ppm)
qexp (mg/g)
qtheo (mg/g)
k2 (g mg−1 min−1)
R2
100
99.8
100.0
0.0278
1.000
200
196.5
238.1
1.46 × 10−4
0.9925
Kinetic model
Intra-particle diffusion model
Ci (ppm)
qexp (mg/g)
kint (mg g−1 min−1/2)
R2
100
99.8
0.4202
0.5800
200
196.5
15.023
0.9187
The kinetic study results for MB adsorption on SMK, summarized in Table 6, demonstrate that the adsorption process is best described by the pseudo-second-order kinetic model, based on the high correlation coefficients (R2 = 1.000 for 100 ppm and R2 = 0.9925 for 200 ppm). The experimental adsorption capacities (qexp) closely align with the theoretical values (qtheo), indicating that the adsorption process is likely governed by chemisorption involving electron-sharing or electron-transfer mechanisms between MB and SMK.
The pseudo-first-order model, with lower correlation coefficients (R2 = 0.8749 for 100 ppm and R2 = 0.7922 for 200 ppm), shows a weaker fit to the experimental data, suggesting it does not adequately describe the adsorption dynamics. Additionally, the intra-particle diffusion model provides a moderate fit (R2 = 0.5800 for 100 ppm and R2 = 0.9187 for 200 ppm), indicating that while intra-particle diffusion contributes to the adsorption process, it is not the sole rate-limiting step.
These results collectively suggest that the adsorption of MB on SMK is likely controlled by chemisorption, as reflected in the pseudo-second-order kinetic model, with minor contributions from intra-particle diffusion [64, 75‐77].
3.5 Thermodynamic study results
In order to determine the thermodynamic parameters using the graph in Fig. 7c, the lnK − 1/T graph given in Fig. 8 was drawn, and the thermodynamic parameters were calculated. Calculated results for thermodynamic parameters are given in Table 7.
The thermodynamic analysis of MB adsorption on SMK, as shown in Table 7, reveals that the adsorption process is exothermic, with an enthalpy change (ΔH) of − 129.3 kJ/mol. This negative enthalpy value suggests that the adsorption is driven by heat release, with a tendency toward decreased adsorption efficiency as temperature rises, aligning with typical exothermic behavior.
The entropy change (ΔS) of − 0.40 kJ/mol K indicates a trend toward decreased randomness at the solid–liquid interface during adsorption, suggesting an ordered adsorption layer formation on the SMK surface. Additionally, the Gibbs free energy (ΔG) values, which are negative across all temperatures studied (− 10.1 kJ/mol at 298 K, − 6.1 kJ/mol at 308 K, and − 2.1 kJ/mol at 318 K), confirm that the adsorption process is spontaneous under the experimental conditions. However, the reduction in ΔG values with increasing temperature suggests a decreased thermodynamic favorability at higher temperatures, reinforcing that adsorption is less effective as temperature rises [75, 76, 78].
4 Conclusions
This study investigates the adsorption properties of oak charcoal activated by sulfuric acid (SMK) for removing cationic and anionic pollutants. Initial attempts with untreated oak charcoal yielded no effective adsorption results. However, sulfuric acid activation significantly enhanced the material’s adsorption efficiency for methylene blue (MB). SMK achieved nearly 100% MB removal across a wide pH range at 100 ppm. pH 9 was selected as the optimum, aligning with SMK’s pHpzc of 7.8. The optimal SMK amount for MB removal was identified as 0.05 g. SMK demonstrated efficient dye removal up to 400 ppm and a saturation adsorption capacity of 370.85 mg/g, a competitive result among similar adsorbents. Nearly 100% MB removal was achieved within 30 min at 100 ppm and 90 min at 200 ppm. Temperature studies indicated stable adsorption at 100 ppm but a decline at 200 ppm with increasing temperatures, confirming the process’s exothermic nature. Characterization analyses showed a reduction in pore structure upon acid activation and the formation of sulfonyl groups, enhancing MB adsorption. Isotherm modeling revealed strong agreement with the Langmuir model, indicating monolayer adsorption with a capacity of 370.85 mg/g. Kinetic studies best fit a pseudo-second-order model, suggesting chemisorption as the primary mechanism. Thermodynamic parameters confirmed spontaneous and exothermic adsorption. In summary, sulfuric acid-activated oak charcoal (SMK) demonstrated high efficacy as a low-cost, versatile adsorbent for MB and potentially other cationic pollutants across diverse pH levels and concentrations. Especially as seen from the BET analysis results, it was clearly seen that the adsorption properties were significantly improved thanks to the effectiveness of the functionality, despite the decrease in surface area.
Acknowledgements
The authors gratefully thank the financial support provided by the Scientific Research Projects Unit of Yozgat Bozok University (Grant no. 6601a-FBE/19-258).
Declarations
Conflict of interest
The authors declare no competing interests.
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Development and characterization of activated charcoal adsorbent derived from oak for efficient removal of methylene blue: functionality vs surface area
Rathi BS, Kumar PS (2021) Application of adsorption process for effective removal of emerging contaminants from water and wastewater. Environ Pollut 280:116995. https://doi.org/10.1016/j.envpol.2021.116995CrossRef
3.
Badran AM, Utra U, Yussof NS, Bashir MJK (2023) Advancements in adsorption techniques for sustainable water purification: a focus on lead removal. Separations 10(11):565CrossRef
4.
Abdulhameed AS, Al Omari RH, Bourchak M, Abdullah S, Abualhaija M, Algburi S (2024) Bio-sourced multifunctional adsorbent of chitosan and adipic acid activated-dragon fruit peels for organic dye removal from water: eco-friendly management and valorization of biomass. Biomass Bioenerg 190:107414. https://doi.org/10.1016/j.biombioe.2024.107414CrossRef
5.
Aydin D, Gübbük İH, Ersöz M (2024) Recent advances and applications of nanostructured membranes in water purification. Turk J Chem 48(1):1–20. https://doi.org/10.55730/1300-0527.3635CrossRef
6.
Khader EH, Mohammed TJ, Mirghaffari N, Salman AD, Juzsakova T, Abdullah TA (2022) Removal of organic pollutants from produced water by batch adsorption treatment. Clean Technol Environ Policy 24(2):713–720. https://doi.org/10.1007/s10098-021-02159-zCrossRef
7.
Tee GT, Gok XY, Yong WF (2022) Adsorption of pollutants in wastewater via biosorbents, nanoparticles and magnetic biosorbents: a review. Environ Res 212:113248. https://doi.org/10.1016/j.envres.2022.113248CrossRef
8.
Arora C, Bharti D, Soni S, Patel A, Singh R (2023) Chapter 20 - Adsorptive removal of hazardous dyes from industrial waste using activated carbon: an appraisal. In: Singh P, Verma P, Singh R, Ahamad A, Batalhão ACS (eds) Waste Management and Resource Recycling in the Developing World. Elsevier, pp 455–483
9.
Gautam RK, Mudhoo A, Lofrano G, Chattopadhyaya MC (2014) Biomass-derived biosorbents for metal ions sequestration: adsorbent modification and activation methods and adsorbent regeneration. J Environ Chem Eng 2(1):239–259. https://doi.org/10.1016/j.jece.2013.12.019CrossRef
10.
Isam M, Baloo L, Chabuk A, Majdi A, Al-Ansari N (2024) Optimization and modelling of Pb (II) and Cu (II) adsorption onto red algae (Gracilaria changii)-based activated carbon by using response surface methodology. Biomass Convers Biorefinery 14(15):16799–16818. https://doi.org/10.1007/s13399-023-04150-8CrossRef
11.
Uzun I, Güzel F (2000) Adsorption of some heavy metal ions from aqueous solution by activated carbon and comparison of percent adsorption results of activated carbon with those of some other adsorbents. Turk J Chem 24(3):291–298
12.
Sarioz N, Isik B, Cakar F, Cankurtaran O (2024) Valorization of the performance of novel and natural sodium alginate/pectin/Portulaca oleracea L. ternary composites in the adsorption of toxic methylene blue dye from the aquatic environment. Int J Biol Macromol 282:136867. https://doi.org/10.1016/j.ijbiomac.2024.136867CrossRef
Loura N, Rathee K, Dhull R, Singh M, Dhull V (2024) Carbon nanotubes for dye removal: a comprehensive study of batch and fixed-bed adsorption, toxicity, and functionalization approaches. J Water Process Eng 67:106193. https://doi.org/10.1016/j.jwpe.2024.106193CrossRef
George G, Ealias AM, Saravanakumar MP (2024) Advancements in textile dye removal: a critical review of layered double hydroxides and clay minerals as efficient adsorbents. Environ Sci Pollut Res 31(9):12748–12779. https://doi.org/10.1007/s11356-024-32021-wCrossRef
17.
Al-Tohamy R, Ali SS, Li F, Okasha KM, Mahmoud YAG, Elsamahy T et al (2022) A critical review on the treatment of dye-containing wastewater: ecotoxicological and health concerns of textile dyes and possible remediation approaches for environmental safety. Ecotoxicol Environ Saf 231:113160. https://doi.org/10.1016/j.ecoenv.2021.113160CrossRef
18.
Dutta S, Adhikary S, Bhattacharya S, Roy D, Chatterjee S, Chakraborty A et al (2024) Contamination of textile dyes in aquatic environment: adverse impacts on aquatic ecosystem and human health, and its management using bioremediation. J Environ Manage 353:120103. https://doi.org/10.1016/j.jenvman.2024.120103CrossRef
19.
Veluchamy A, Jeyabalan J, Singh A, Narayanasamy S, Verma A (2024) A review on recent insights of azoreductases mediated dye degradation: a sustainable approach for bioremediation of industrial wastewater. J Water Process Eng 68:106403. https://doi.org/10.1016/j.jwpe.2024.106403CrossRef
20.
Akköz Y, Coşkun R, Delibaş A (2019) Preparation and characterization of sulphonated bio-adsorbent from waste hawthorn kernel for dye (MB) removal. J Mol Liq 287:110988. https://doi.org/10.1016/j.molliq.2019.110988CrossRef
21.
Nahar K, Hedayati Marzbali M, Gbolahan Hakeem I, Sharma A, Chiang K, Surapaneni A et al (2024) Hydrothermal processing of primary, waste-activated, and digested sewage sludge: products characterisation, fate of heavy metals and nutrients, and process integration. J Ind Eng Chem. https://doi.org/10.1016/j.jiec.2024.10.047CrossRef
22.
Xu X, Li Y, Vo P, Shukla P, Ge L, Zhao C (2024) Electrochemical advanced oxidation of per- and polyfluoroalkyl substances (PFASs): development, challenges and perspectives. Chem Eng J 157222. 10.1016/j.cej.2024.157222
23.
Nam H, Lee H, Kim S, Bae J, Shah NS, Al-Anazi A et al (2024:) Removal of contaminants in paper dyeing wastewater by Fenton and photo-Fenton processes with biological treatment. Appl Catal O: Open 196:207015. https://doi.org/10.1016/j.apcato.2024.207015CrossRef
24.
Cai C-H, Then CK, Lin Y-L, Shih C-C, Li C-C, Yang T-S (2024) Associative analysis of sludge microbiota and wastewater degradation efficacy within swine farm sludge systems. Heliyon 10:e39997. https://doi.org/10.1016/j.heliyon.2024.e39997CrossRef
25.
Abbas M, Trari M (2024) Adsorption behavior of methylene blue onto activated coconut shells: kinetic, thermodynamic, mechanism and regeneration of the adsorbent. Dose-Response 22(4):15593258241290708. https://doi.org/10.1177/15593258241290708CrossRef
26.
Martínez RJ, Vela-Carrillo AZ, Godínez LA, Pérez-Bueno JdJ, Robles I (2023) Competitive adsorption of anionic and cationic molecules on three activated carbons derived from agroindustrial waste. Biomass Bioenergy 168:106660. https://doi.org/10.1016/j.biombioe.2022.106660CrossRef
27.
Gupta VK, Kumar R, Nayak A, Saleh TA, Barakat MA (2013) Adsorptive removal of dyes from aqueous solution onto carbon nanotubes: a review. Adv Coll Interface Sci 193–194:24–34. https://doi.org/10.1016/j.cis.2013.03.003CrossRef
28.
Zenasni M, Benyoucef A, Sabantina L (2023) Development and characterization of novel hybrid materials formed from poly(2-aminophenyl disulfide)@silica gel for dye adsorption application. Eng Proc 56(1):281
Munawwar H, Munir R, Muneer A, Zaheer F, Bashir MZ, Sayed M et al (2024) Synthesis and applications of zinc oxide nanorods, copper-doped zinc oxide nanorods, nickel hydroxide/zinc oxide nanorods, iron (III) oxide/zinc oxide nanorods and zinc oxide/graphene oxide nanorods for batch adsorption, fixed-bed column study, and degradation of cationic dye (Blue Tur-XGB B-3) from wastewater. Catal Surv Asia. https://doi.org/10.1007/s10563-024-09441-2CrossRef
32.
Ciğeroğlu Z, El Messaoudi N, Şenol ZM, Başkan G, Georgin J, Gubernat S (2024) Clay-based nanomaterials and their adsorptive removal efficiency for dyes and antibiotics: a review. Mater Today Sustain 26:100735. https://doi.org/10.1016/j.mtsust.2024.100735CrossRef
33.
Agustin SF, Kusdiana A, Rahmah W, Rusli H, Kadja GTM (2024) Zeolite-based core–shell adsorbent for the removal of toxic pollutants from aquatic environment: current challenges and opportunities. J Nanopart Res 26(5):94. https://doi.org/10.1007/s11051-024-05996-3CrossRef
34.
Cecen F, Aktas Ö (2011) Activated carbon for water and wastewater treatment: integration of adsorption and biological treatment. Wiley
35.
Jain A, Balasubramanian R, Srinivasan MP (2015) Production of high surface area mesoporous activated carbons from waste biomass using hydrogen peroxide-mediated hydrothermal treatment for adsorption applications. Chem Eng J 273:622–629. https://doi.org/10.1016/j.cej.2015.03.111CrossRef
36.
Asasian Kolur N, Sharifian S, Kaghazchi T (2019) Investigation of sulfuric acid-treated activated carbon properties. Turk J Chem 43(2):663–675. https://doi.org/10.3906/kim-1810-63CrossRef
37.
Manyangadze M, Chikuruwo NHM, Chakra CS, Narsaiah TB, Radhakumari M, Danha G (2020) Enhancing adsorption capacity of nano-adsorbents via surface modification: a review. S Afr J Chem Eng 31(1):25–32. https://doi.org/10.1016/j.sajce.2019.11.003CrossRef
38.
Badsha MAH, Khan M, Wu B, Kumar A, Lo IMC (2021) Role of surface functional groups of hydrogels in metal adsorption: from performance to mechanism. J Hazard Mater 408:124463. https://doi.org/10.1016/j.jhazmat.2020.124463CrossRef
39.
Bell JG, Zhao X, Uygur Y, Thomas KM (2011) Adsorption of chloroaromatic models for dioxins on porous carbons: the influence of adsorbate structure and surface functional groups on surface interactions and adsorption kinetics. J Phys Chem C 115(6):2776–2789. https://doi.org/10.1021/jp1099893CrossRef
40.
Li Y, Du Q, Liu T, Peng X, Wang J, Sun J et al (2013) Comparative study of methylene blue dye adsorption onto activated carbon, graphene oxide, and carbon nanotubes. Chem Eng Res Des 91(2):361–368. https://doi.org/10.1016/j.cherd.2012.07.007CrossRef
Xie R, Jin Y, Chen Y, Jiang W (2017) The importance of surface functional groups in the adsorption of copper onto walnut shell derived activated carbon. Water Sci Technol 76(11):3022–3034. https://doi.org/10.2166/wst.2017.471CrossRef
43.
Yang X, Wan Y, Zheng Y, He F, Yu Z, Huang J et al (2019) Surface functional groups of carbon-based adsorbents and their roles in the removal of heavy metals from aqueous solutions: a critical review. Chem Eng J 366:608–621. https://doi.org/10.1016/j.cej.2019.02.119CrossRef
44.
Hotová G, Slovák V, Zelenka T, Maršálek R, Parchaňská A (2020) The role of the oxygen functional groups in adsorption of copper (II) on carbon surface. Sci Total Environ 711:135436. https://doi.org/10.1016/j.scitotenv.2019.135436CrossRef
45.
Gorbounov M, Halloran P, Masoudi Soltani S (2024) Hydrophobic and hydrophilic functional groups and their impact on physical adsorption of CO2 in presence of H2O: a critical review. J CO2 Utilization 86:102908. https://doi.org/10.1016/j.jcou.2024.102908CrossRef
Youk S, Hofmann JP, Badamdorj B, Völkel A, Antonietti M, Oschatz M (2020) Controlling pore size and pore functionality in sp 2-conjugated microporous materials by precursor chemistry and salt templating. J Mater Chem A 8(41):21680–21689CrossRef
48.
Zhao Y, Feng C, Tian C, Li Z, Yang Y (2022) Enhanced adsorption selectivity of bisphenol analogues by tuning the functional groups of covalent organic frameworks (COFs). Sep Purif Technol 297:121489. https://doi.org/10.1016/j.seppur.2022.121489CrossRef
49.
Coskun R, Yildiz A, Delibas A (2017) Removal of methylene blue using fast sucking adsorbent. J Mater Environ Sci 8(2):398–409
50.
Wang S, Zhu ZH, Coomes A, Haghseresht F, Lu GQ (2005) The physical and surface chemical characteristics of activated carbons and the adsorption of methylene blue from wastewater. J Colloid Interface Sci 284(2):440–446. https://doi.org/10.1016/j.jcis.2004.10.050CrossRef
51.
Fidel RB, Laird DA, Thompson ML (2013) Evaluation of modified boehm titration methods for use with biochars. J Environ Qual 42(6):1771–1778. https://doi.org/10.2134/jeq2013.07.0285CrossRef
52.
Schönherr J, Buchheim JR, Scholz P, Adelhelm P (2018) Boehm Titration Revisited (Part II): A comparison of Boehm titration with other analytical techniques on the quantification of oxygen-containing surface groups for a variety of carbon materials. C. 4(2):22
Liu F, Xu Z, Wan H, Wan Y, Zheng S, Zhu D (2011) Enhanced adsorption of humic acids on ordered mesoporous carbon compared with microporous activated carbon. Environ Toxicol Chem 30(4):793–800. https://doi.org/10.1002/etc.450CrossRef
55.
Pak S-H, Jeon M-J, Jeon Y-W (2016) Study of sulfuric acid treatment of activated carbon used to enhance mixed VOC removal. Int Biodeterior Biodegradation 113:195–200. https://doi.org/10.1016/j.ibiod.2016.04.019CrossRef
56.
Angın D, Altintig E, Köse TE (2013) Influence of process parameters on the surface and chemical properties of activated carbon obtained from biochar by chemical activation. Biores Technol 148:542–549. https://doi.org/10.1016/j.biortech.2013.08.164CrossRef
57.
Müller F, Ferreira CA, Franco L, Puiggalí J, Alemán C, Armelin E (2012) New sulfonated polystyrene and styrene–ethylene/butylene–styrene block copolymers for applications in electrodialysis. J Phys Chem B 116(38):11767–11779. https://doi.org/10.1021/jp3068415CrossRef
58.
Lee W-J, Jung H-R, Lee MS, Kim J-H, Yang KS (2003) Preparation and ionic conductivity of sulfonated-SEBS/SiO2/plasticizer composite polymer electrolyte for polymer battery. Solid State Ionics 164(1):65–72. https://doi.org/10.1016/S0167-2738(03)00298-4CrossRef
59.
Hassan MIu, Taimur S, Khan IA, Yasin T, Ali SW (2019) Surface modification of polypropylene waste by the radiation grafting of styrene and upcycling into a cation-exchange resin. J Appl Polym Sci 136(10):47145CrossRef
60.
El-Shafie AS, Karamshahi F, El-Azazy M (2023) Turning waste avocado stones and montmorillonite into magnetite-supported nanocomposites for the depollution of methylene blue: adsorbent reusability and performance optimization. Environ Sci Pollut Res 30(56):118764–118781. https://doi.org/10.1007/s11356-023-30538-0CrossRef
61.
Nambiar AP, Pillai R, Sanyal M, Vadikkeettil Y, Shrivastav PS (2023) A starch based sustainable bio-hybrid composite for surface assimilation of methylene blue: preparation, characterization, and adsorption study. Environ Sci: Adv 2(6):861–876. https://doi.org/10.1039/D2VA00274DCrossRef
62.
Karagöz S, Tay T, Ucar S, Erdem M (2008) Activated carbons from waste biomass by sulfuric acid activation and their use on methylene blue adsorption. Biores Technol 99(14):6214–6222. https://doi.org/10.1016/j.biortech.2007.12.019CrossRef
63.
Jawad AH, Abdulhameed AS, Mastuli MS (2020) Acid-factionalized biomass material for methylene blue dye removal: a comprehensive adsorption and mechanism study. J Taibah Univ Sci 14(1):305–313. https://doi.org/10.1080/16583655.2020.1736767CrossRef
64.
Jawad AH, Razuan R, Appaturi JN, Wilson LD (2019) Adsorption and mechanism study for methylene blue dye removal with carbonized watermelon (Citrullus lanatus) rind prepared via one-step liquid phase H2SO4 activation. Surf Interfaces 16:76–84. https://doi.org/10.1016/j.surfin.2019.04.012CrossRef
65.
Yağmur HK, Kaya İ (2021) Synthesis and characterization of magnetic ZnCl2-activated carbon produced from coconut shell for the adsorption of methylene blue. J Mol Struct 1232:130071. https://doi.org/10.1016/j.molstruc.2021.130071CrossRef
66.
Sayğılı H, Güzel F (2016) High surface area mesoporous activated carbon from tomato processing solid waste by zinc chloride activation: process optimization, characterization and dyes adsorption. J Clean Prod 113:995–1004. https://doi.org/10.1016/j.jclepro.2015.12.055CrossRef
67.
Yu Y, Wan Y, Shang H, Wang B, Zhang P, Feng Y (2019) Corncob-to-xylose residue (CCXR) derived porous biochar as an excellent adsorbent to remove organic dyes from wastewater. Surf Interface Anal 51(2):234–245. https://doi.org/10.1002/sia.6575CrossRef
68.
Çağlar E, Donar YO, Sinağ A, Biroğul İ, Bilge S, Aydincak K et al. (2018) Adsorption of anionic and cationic dyes on biochars, produced by hydrothermalcarbonization of waste biomass: effect of surface functionalization and ionicstrength. Turk J Chem 42(1):86–99
69.
Senthil Kumar P, Fernando PSA, Ahmed RT, Srinath R, Priyadharshini M, Vignesh AM et al (2014) Effect of temperature on the adsorption of methylene blue dye onto sulfuric acid–treated orange peel. Chem Eng Commun 201(11):1526–1547. https://doi.org/10.1080/00986445.2013.819352CrossRef
70.
Gokce Y, Aktas Z (2014) Nitric acid modification of activated carbon produced from waste tea and adsorption of methylene blue and phenol. Appl Surf Sci 313:352–359. https://doi.org/10.1016/j.apsusc.2014.05.214CrossRef
71.
Jawad AH, Surip SN (2022) Upgrading low rank coal into mesoporous activated carbon via microwave process for methylene blue dye adsorption: Box Behnken design and mechanism study. Diam Relat Mater 127:109199. https://doi.org/10.1016/j.diamond.2022.109199CrossRef
72.
Langmuir I (1918) The adsorption of gases on plane surfaces of glass, mica and platinum. J Am Chem Soc 40(9):1361–1403CrossRef
73.
Freundlich HMF (1906) Over the adsorption in solution. J Phys chem 57(385471):1100–1107
74.
Tempkin M, Pyzhev V (1940) Kinetics of ammonia synthesis on promoted iron catalyst. Acta Phys Chim USSR 12(1):327
75.
Marnani NN, Tezel FH, Basu OD (2024) Adsorptive removal of dyes: a comparison of graphene oxide to granular activated carbon and zeolite NaY. Appl Sci 14(21):9811CrossRef
76.
Nguyen Thi HP, Cao PA, Han DL, Nguyen VH, Nguyen DD, La DD (2024) Cost-effective approach for fabrication of high-quality expanded vermiculite for alizarin red S removal from aqueous media. ChemistrySelect 9(40):e202403256. https://doi.org/10.1002/slct.202403256CrossRef
77.
Aracagök YD, Torun M, Kabalak M (2023) A study on the removal of reactive black 5 with Tenebrio molitor adult chitin chemically modified with cetyltrimethylammonium bromide. Biomass Convers Biorefinery 13(14):13279–13290. https://doi.org/10.1007/s13399-023-04701-zCrossRef
