Facile synthesis and characterisation of novel Sn/Si mixtures for the efficient removal of methylene blue and crystal violet dyes from aqueous media

ABSTRACT In this work, novel mixtures based on silicon and tin materials were synthesised via reaction of 2.407, 5.247, 7.195, or 9.59 g of tin chloride dihydrate with 6 g of sodium metasilicate pentahydrate. The samples, which were synthesised using 2.407, 5.247, 7.195, and 9.59 g, are abbreviated as T1, T2, T3, and T4, respectively. XRD confirmed that these mixtures consist of amorphous Sn/Si, sodium tin silicate, tin oxide, and sodium silicate. The average crystallite size of T1, T2, T3, and T4 samples is 5.23, 8.13, 12.26, 15.72 nm, respectively. The synthesised mixtures were used as adsorbents for the removal of methylene blue and crystal violet dyes from aqueous media. 15 min, pH 6, and 298 Kelvin are regarded as the optimum conditions for the removal of studied dyes using T1, T2, T3, and T4 samples. The adsorption process of crystal violet or methylene blue dyes was fitted well with the Langmuir equilibrium isotherm and pseudo-second-order kinetic model. The thermodynamic parameters confirmed that the removal of crystal violet and methylene blue dyes is chemical, spontaneous, and exothermic. The maximum adsorption capacity of T1, T2, T3, and T4 samples towards crystal violet dye is 34.81, 36.83, 29.46, and 11.98 mg/g, respectively. Also, the maximum adsorption capacity of T1, T2, T3, and T4 samples towards methylene blue dye is 30.13, 29.33, 17.09, and 13.43 mg/g, respectively. HCl: butanol (1:3) can efficiently desorb the dyes for three cycles of adsorption/desorption. Hence, the adsorbents can be used successfully several times for the removal of crystal violet and methylene blue dyes.


Introduction
With the growth of mankind, the need for water for versatile purposes is the main requirement.Among the drawbacks of this rapid growth is the environmental disorder associated with the pollution problem.One of the important classes of the pollutants is organic dyes which are considered serious water pollutants and their existence in water makes it no longer good and sometimes difficult to be CONTACT Ehab A. Abdelrahman dr.ehabsaleh@yahoo.com;ehab.abdelrahman@fsc.bu.edu.egSupplemental data for this article can be accessed here.
treated.This difficulty is attributed to the fact that organic dyes have a synthetic origin and a complex molecular structure which makes them more stable and difficult to be biodegraded [1].
The colouring textile industry is known as an important industry and indicates the rate of development in countries around the world.However, the wastewater of these industries is considered a harmful source of pollution for creatures due to the variety of dyes present in it.Mutagenic and carcinogenic effects of some dyes have been ascertained [1,2].Dysfunction of the kidney, liver, brain, reproductive system, and central nervous system are correlated to the effect of dyes on human beings [3].Therefore removal of dyes from wastewater is of important consideration.Researchers are looking for low-cost methods to remove these dyes from the aquatic environment.It is estimated that textile industries release approximately 100 tons of dyes and pigments to the water streams annually [4,5].
Recently, different physical, chemical, and biological tools were used such as ultrafiltration, reverse osmosis, ion exchange, and surface adsorption to activated carbon, charcoal, wood chips, and silica gel for colour removal from effluent, which is relatively successful in the applicability of COD [6,7].Adsorption has gained supreme importance for environmental protection by removing textile dyes from disposed water.Some of the adsorbents are effective in removing dyes and various pollutants, but some are not.That is why, new effective adsorbents are needed, noticing the cost-effectiveness, energy efficiency, design flexibility, besides biodegradability and availability.Characteristics that can affect the removal of contaminations are adsorption capacity, specific surface area, pore volume, grain size, and pore size distribution.They are so important because if they change, the efficiency of removal change too [8].Removal of dyes from wastewater has made it an ideal alternative to other expensive treatment methods.
For the removal of dyes, a wide variety of adsorbents has been used, of them, the most common are zeolites, alumina, silica gel besides activated carbon which is the oldest well-known adsorbent and is usually prepared from coconut shell, lignite, wood, coal, and so on.Zeolites are highly porous and their charges are negative.Application of 3A zeolite to remove Rhodamine B is common and this adsorbent can remove ~90% of this contaminant from industrial wastewater [9].Alumina is an especial crystalline product that is synthesised in various sizes and its appearance is granule with a surface area of 200-300 m 2 /g.Alumina is a great adsorbent for the removal of disperse dyes from water [10].Silica gel is a porous, non-crystalline granule.The surface area of it booms expeditiously rather than alumina and reaches 900 m 2 /g and is prepared by the coagulation of colloidal silicic acid [11].There are numerous articles about removing dyes and other pollutants by activated carbon.Furthermore, surface area in activated carbon is quite high (near 200 m 2 /g) [12,13].Despite that this adsorbent is very effective, it is not selective.It is ideal for all of the adsorbents to be regenerated after being used and became saturated.
Organic dyes such as methylene blue and crystal violet are considered harmful pollutants.These dyes are used in several chemical industries like silk, paper, and printing.Unfortunately, these dyes are known for their stability, toxicity, and their high resistance to degradation.First, they cause serious problems in human health like irritation, high blood pressure, respiratory difficulties, and kidney failure.Second, they affect and threaten aquatic life by leaking the penetration of light due to their colour intensity even if they are present in small concentrations.Third, they also affect the life of animals [14][15][16][17][18][19][20][21][22][23][24][25][26][27].So it is very essential to treat water and get rid of these dyes.
Nowadays geopolymer a porous non-crystalline powder is widely used especially for the removal of methylene blue and crystal violet due to its low cost, easy to use, high adsorption capacity, and reusability.It is known that the synthesis of geopolymer undergoes three steps.First, the dissolving of silica and aluminium.Second, formation of -Si-O-Al-O-monomer by condensation.Third, formation of a gel by repeating units of -Si-O-Al-O-.So, in this paper, new amorphous materials similar to geopolymers were synthesised through the replacement of aluminium with other metals such as tin The repeating unit in our products is Si-O-Sn-O.Also, the products were characterised using various instrumental techniques, for example, XRD, FT-IR, FE-SEM, EDS, and BET.Besides, the synthesised amorphous materials were tested as adsorbents for removing methylene blue and crystal violet dyes from aqueous media after optimising several factors such as contact time, the dose of adsorbents, concentration of dye, pH, temperature of dye solution, and reusability of adsorbents [28][29][30][31][32].
Finally, it is worth mentioning that Ehab et al [33] synthesised novel adsorbents composed of silicon and other metal like zinc, nickel, and chromium with high adsorption capacity ranging from 36.5 to 53.7 mg/g.Also, Khalifa et al [34] synthesised mesoporous silica nanoparticles modified by dibenzoylmethane and used them as a novel composite for the removal of Cu(II), Hg(II), and Cd(II) ions from aqueous media with a high capacity ranging from 25.17 to 35.37 mg/g.

Synthesis of mixtures
First, solution A was prepared as follows: 2.407 g of tin chloride dihydrate was dissolved in 50 mL of distilled water and 1 mL of concentrated HCl.Other A solutions were prepared as previously described using different amounts of tin chloride dihydrate (5.247 g, 7.195 g, and 9.59 g).Solution B was prepared as follows: 6 g of sodium metasilicate pentahydrate was dissolved in 50 mL of distilled water.After that, solution B was added drop by drop to solution A with continuous stirring for 30 min.Besides, the precipitate was filtrated, washed several times using distilled water, and dried in a desiccator over anhydrous CaCl 2 .The samples, which were synthesised using 2.407, 5.247, 7.195, and 9.59 g, are abbreviated as T1, T2, T3, and T4, respectively.

Characterisation
The X-ray diffraction (XRD) pattern of the T1, T2, T3, and T4 samples was gotten using a Bruker diffractometer (D8 Advance) with K α Cu radiations have wavelength (λ) equals 0.15 nm.Also, the Fourier transform (FT-IR) spectra of the T1, T2, T3, and T4 samples, on KBr pellets, was obtained at room temperature using a Nicolet single beam spectrometer in the range from 400 to 4000 cm −1 .Additionally, BET surface area (m 2 /g), average pore radius (nm), and total pore volume (cc/g) of the T1, T2, T3, and T4 samples were determined from nitrogen isotherms at −196 °C using Quantachrome analyser (Nova 2000 series).Besides, the surface morphology of the T1, T2, T3, and T4 samples was investigated using JSM5410 JEOL field emission scanning electron microscopy (FE-SEM).Furthermore, the high-resolution scanning electron microscopy (HR-TEM) images of the T1, T2, T3, and T4 samples were measured using a transmission electron microscope (JEOL 2100) at a speeding voltage equals to 200 kV.

Removal of methylene blue and crystal violet dyes from aqueous media
Typical batch experiments for the removal of methylene blue and crystal violet dyes from aqueous media by the T1, T2, T3, and T4 samples were accomplished as the following: 0.05 g of the T1, T2, T3, or T4 sample was added to 25 mL of 50 mg/L of methylene blue or crystal violet aqueous solution which was adjusted at the wanted pH value using 0.1 M NaOH and HCl.Then, the mixture was agitated using a magnetic stirrer at 355 rpm for several times (1-60 min) and temperatures (298-328 kelvin).Besides, the suspensions were centrifuged then the concentration of methylene blue or crystal violet dyes, which exists in the filtrate, was determined using a UV-Vis spectrophotometer.
The mass of the adsorbed methylene blue or crystal violet dyes per gram of the T1, T2, T3, or T4 sample (Q, mg/g) was determined using Eq.(1).Also, the % removal (% R) of methylene blue or crystal violet dyes using the T1, T2, T3, or T4 sample was calculated using Eq. ( 2).
where, C o (mg/L) is the initial concentration of methylene blue or crystal violet dyes whereas C e (mg/L) is the equilibrium concentration of methylene blue or crystal violet dyes.Besides, V (L) is the volume of methylene blue or crystal violet aqueous solution whereas m (g) is the utilised amount of the T1, T2, T3, or T4 sample.

Characterisation of the synthesised products
Figure 1(a-d) represents the XRD patterns of the T1, T2, T3, and T4 samples, respectively.All the samples consist of amorphous Sn/Si, sodium tin silicate, tin oxide, and sodium silicate.Broad peaks in the 2Ɵ range from 10° to 40° confirm the presence of amorphous Sn/Si [33].Peaks at 2Ɵ (hkl) equals 12.06 (110), 16.79 (200) [37].The average crystallite size of T1, T2, T3, and T4 samples is 5.23, 8.13, 12.26, 15.72 nm, respectively.The surface textures (average pore radius, BET surface area, and total pore volume) of the samples was determined by studying the N 2 gas adsorption and desorption behaviour at 77 K as shown in Table S1. Figure S1A-D represents the N 2 adsorption/desorption isotherms of the T1, T2, T3, and T4 samples, respectively.The results proved that the isotherms can be classified as type IV [38,39].

Effect of pH
The effect of pH on the % removal of crystal violet dye by the T1, T2, T3, and T4 samples was accomplished in the pH range of 2-8 and the data are displayed in Figure 5(a).The results showed that the % removal of crystal violet dye increased with increasing pH from 2 to 6 where it reached 98, 97.40, 76, and 27.6% at pH 6 in the case of T1, T2, T3, and T4 samples, respectively.Thereafter, the % removal of crystal violet dye stayed approximately constant when the pH altered from 6 to 8. Also, the effect of pH on the adsorption capacity of the T1, T2, T3, and T4 samples towards crystal violet dye was accomplished in the pH range of 2-8 and the data are displayed in Figure 5(b).The results showed that the adsorption capacity of the T1, T2, T3, and T4 samples towards crystal violet dye increased with increasing pH from 2 to 6 where it reached 24.50, 24.35, 19, and 6.90 mg/g at pH 6 in the case of T1, T2, T3, and T4 samples, respectively.Hence, 6 is regarded as the optimum pH for the removal of crystal violet dye using T1, T2, T3, and T4 samples.The effect of pH on the % removal of methylene blue dye by the T1, T2, T3, and T4 samples was accomplished in the pH range of 2-8 and the data are displayed in Figure 6(a).The results showed that the % removal of methylene blue dye increased with increasing pH from 2 to 6 where it reached 96.76, 96, 55.49, and 20.80% at pH 6 in the case of T1, T2, T3, and T4 samples, respectively.Thereafter, the % removal of methylene blue dye stayed approximately constant when the pH altered from 6 to 8. Also, the effect of pH on the adsorption  capacity of the T1, T2, T3, and T4 samples towards methylene blue dye was accomplished in the pH range of 2-8 and the data are displayed in Figure 6(b).The results showed that the adsorption capacity of the T1, T2, T3, and T4 samples towards methylene blue dye increased with increasing pH from 2 to 6 where it reached 24.19, 24.00, 13.87, and 5.20 mg/g at pH 6 in the case of T1, T2, T3, and T4 samples, respectively.Hence, 6 is regarded as the optimum pH for the removal of methylene blue dye using T1, T2, T3, and T4 samples.

Effect of time
The effect of time on the % removal of crystal violet dye by the T1, T2, T3, and T4 samples was accomplished in the time range of 1-60 min and the data are displayed in Figure 7(a).The results showed that the % removal of crystal violet dye increased with increasing time from 1 to 15 where it reached 98.10, 97.50, 77.20, and 28.8% in the case of T1, T2, T3, and T4 samples, respectively.Thereafter, the % removal of crystal violet dye stayed approximately constant when the time altered from 15 to 60 min.Also, the effect of time on the adsorption capacity of the T1, T2, T3, and T4 samples towards crystal violet dye was accomplished in the time range of 1-60 min and the data are displayed in Figure 7(b).The results showed that the adsorption capacity of the T1, T2, T3, and T4 samples towards crystal violet dye increased with increasing time from 1 to 15 min where it reached 24.53, 24.38, 19.30, and 7.20 mg/g in the case of T1, T2, T3, and T4 samples, respectively.Hence, 15 min is regarded as the optimum time for the removal of crystal violet dye using the T1, T2, T3, and T4 samples.The effect of time on the % removal of methylene blue dye by the T1, T2, T3, and T4 samples was accomplished in the time range of 1-60 min and the data are displayed in Figure 8(a).The results showed that the % removal of methylene blue dye increased with increasing time from 1 to 15 min where it reached 98.80, 91.20, 50.40, and 23.32% in the case of T1, T2, T3, and T4 samples, respectively.Thereafter, the % removal of methylene blue dye stayed approximately constant when the time altered from 15 to 60 min.Also, the effect of time on the adsorption capacity of the T1, T2, T3, and T4 samples towards methylene blue dye was accomplished in the time range of 1-60 min and the data are displayed in Figure 8(b).The results showed that the adsorption capacity of the T1, T2, T3, and T4 samples towards methylene blue dye increased with increasing time from 1 to 15 min where it reached 24.70, 22.80, 12.60, and 5.83 mg/g in the case of the T1, T2, T3, and T4 samples, respectively.Hence, 15 min is regarded as the optimum time for the removal of methylene blue dye using T1, T2, T3, and T4 samples.The kinetic experimental data were performed and examined to calculate the rate constant of adsorption utilising pseudo-first-order (Eq.( 3)) and pseudo-second-order Eq. ( 4)) equations [33,[38][39][40][41][42][43][44].
where, q e (mg/g) is the uptake capacity of the T1, T2, T3, and T4 samples towards crystal violet or methylene blue dyes at the equilibrium.Besides, q t (mg/g) is the uptake capacity of the T1, T2, T3, and T4 samples at the time t.Moreover, K 2 (g/mg.min)and K 1 (1/min) are the rate constants of the pseudo-second-order and pseudo-first-order models, respectively.The plots of the pseudo-first-order and pseudo-second-order results in the case of crystal violet dye were clarified in Figure S2A-B, respectively.Also, the plots of the pseudofirst-order and pseudo-second-order results in the case of methylene blue dye were clarified in Figure S3A-B, respectively.The results show that the adsorption process of crystal violet or methylene blue dyes was fitted well with the pseudo-second-order kinetic model as elucidated in Tables S2 and S3.

Effect of temperature
The effect of temperature on the % removal of crystal violet dye by the T1, T2, T3, and T4 samples was accomplished in the temperature range of 298-328 kelvin and the data are displayed in Figure S4A.The results showed that the % removal of crystal violet dye decreased with increasing temperature where it reached 90.80, 87.50, 30.00, and 8.00% at 328 kelvin in the case of the T1, T2, T3, and T4 samples, respectively.Also, the effect of temperature on the adsorption capacity of the T1, T2, T3, and T4 samples towards crystal violet dye was accomplished in the temperature range of 298-328 kelvin and the data are displayed in Figure S4B.The results showed that the adsorption capacity of the T1, T2, T3, and T4 samples towards crystal violet dye decreased with increasing temperature where it reached 22.70, 21.88, 7.50, and 2.00 mg/g at 328 kelvin in the case of the T1, T2, T3, and T4 samples, respectively.Hence, 298 kelvin is regarded as the optimum temperature for the removal of crystal violet dye using the T1, T2, T3, and T4 samples.The effect of temperature on the % removal of methylene blue dye by the T1, T2, T3, and T4 samples was accomplished in the temperature range of 298-328 kelvin and the data are displayed in Figure S5A.The results showed that the % removal of crystal violet dye decreased with increasing temperature where it reached 74.88, 73.00, 13.20, and 2.92% at 328 kelvin in the case of the T1, T2, T3, and T4 samples, respectively.Also, the effect of temperature on the adsorption capacity of the T1, T2, T3, and T4 samples towards methylene blue dye was accomplished in the temperature range of 298-328 kelvin and the data are displayed in Figure S5B.The results showed that the adsorption capacity of the T1, T2, T3, and T4 samples towards methylene blue dye decreased with increasing temperature where it reached 18.72, 18.25, 3.30, and 0.73 mg/g at 328 kelvin in the case of the T1, T2, T3, and T4 samples, respectively.Hence, 298 kelvin is regarded as the optimum temperature for the removal of methylene blue dye using the T1, T2, T3, and T4 samples.The thermodynamic parameters such as change in the entropy (ΔS o ), change in enthalpy (ΔH o ), and change in free energy (ΔG o ) were calculated utilising Eqs. ( 5) and ( 6) [33,[38][39][40][41][42][43].
where, T (kelvin), K d (L/g), and R (KJ/mol K) are the temperature, distribution constant, and gas constant, respectively.Besides, the distribution constant (K d ) was calculated utilising Eq. (7).
Figure S6A-B displays the plot of lnK d versus 1/T in the case of crystal violet and methylene blue dyes, respectively.Also, the thermodynamic parameters in the case of crystal violet and methylene blue dyes are listed in Tables S4 and S5, respectively.The data showed that the removal of crystal violet and methylene blue dyes is chemical due to negative sign of ∆H o .Besides, the removal of crystal violet and methylene blue dye is exothermic because ∆H o is negative and more than 40 KJ/mol.Furthermore, the removal of crystal violet and methylene blue dyes is spontaneous because of the negative sign of ΔG o .Moreover, the removal of crystal violet and methylene blue dyes takes place in a disordered way at the solution boundary/adsorbent owing to the positive sign of ΔS o as presented in Tables S4 and S5.

Effect of adsorbent dosage
The effect of adsorbent dosage on the % removal of crystal violet and methylene blue dyes by the T1, T2, T3, and T4 samples was accomplished in the dosage range of 0.025-0.10g and the data are displayed in Figure S7A-B, respectively.The results showed that the % removal of crystal violet and methylene blue dyes increased with increasing dosage range from 0.025 g to 0.05 g.Besides, the % removal of crystal violet and methylene blue dyes stayed approximately constant when the dosage altered from 0.05 g to 0.10 g due to the blocking of the active sites of adsorbents by the adsorbed dye molecules.Hence, 0.05 g is regarded as the optimum dosage for the removal of crystal violet and methylene blue dyes using the T1, T2, T3, and T4 samples.

Effect of concentration
The effect of concentration on the % removal of crystal violet dye by the T1, T2, T3, and T4 samples was accomplished in the concentration range of 25-150 mg/L and the data are displayed in Figure S8A.The results showed that the % removal of crystal violet dye decreased with increasing concentration where it reached 46.67, 48.67, 38.00, and 13.33% at 150 mg/L in the case of the T1, T2, T3, and T4 samples, respectively.Also, the effect of concentration on the adsorption capacity of the T1, T2, T3, and T4 samples towards crystal violet dye was accomplished in the concentration range of 25-150 mg/L and the data are displayed in Figure S8B.The results showed that the adsorption capacity of the T1, T2, T3, and T4 samples towards crystal violet dye increased with increasing concentration where it reached 35.00, 36.50, 28.50, and 10 mg/g in the case of the T1, T2, T3, and T4 samples, respectively.The effect of concentration on the % removal of methylene blue dye by the T1, T2, T3, and T4 samples was accomplished in the concentration range of 25-150 mg/L and the data are displayed in Figure S9A.The results showed that the % removal of methylene blue dye decreased with increasing concentration where it reached 40.00, 38.67, 21.33, and 12.00% at 150 mg/L in the case of the T1, T2, T3, and T4 samples, respectively.Also, the effect of concentration on the adsorption capacity of the T1, T2, T3, and T4 samples towards methylene blue dye was accomplished in the concentration range of 25-150 mg/L and the data are displayed in Figure S9B.The results showed that the adsorption capacity of the T1, T2, T3, and T4 samples towards methylene blue dye increased with increasing concentration where it reached 30.00, 29.00, 16.00, and 9.00 mg/g in the case of the T1, T2, T3, and T4 samples, respectively.The equilibrium experimental data were examined utilising Langmuir (Eq.( 8)) and Freundlich Eq. ( 9)) equations [33,[38][39][40][41][42][43].
The plots of the Langmuir and Freundlich results in the case of crystal violet dye were clarified in Figure S10A-B, respectively.Also, the plots of the Langmuir and Freundlich results in the case of methylene blue dye were clarified in Figure S11A-B, respectively.The results show that the adsorption process of crystal violet or methylene blue dyes was fitted well with the Langmuir equilibrium isotherm as elucidated in Tables 1 and 2. The maximum adsorption capacity of the T1, T2, T3, and T4 samples towards crystal violet dye is 34.81, 36.83, 29.46, and 11.98 mg/g, respectively.Also, the maximum adsorption capacity of the T1, T2, T3, and T4 samples towards methylene blue dye is 30.13,29.33, 17.09, and 13.43 mg/g, respectively.The adsorption performance of the T1, T2, T3, and T4 samples was evaluated by comparing its adsorption capacity (Q max) with that of other adsorbent materials in the literature such as kaolin modified with graphene oxide, mordenite, magnetic multi-wall carbon nanotube, and titanate nanotube as clarified in Table 3 [44][45][46][47][48][49][50][51][52][53].Obviously, the T1 and T2 samples outperformed most of the materials because it has the highest adsorption capacity value.

Effect of reusability
The T1, T2, T3, and T4 samples have been regenerated for reusability for three cycles of adsorption/desorption.For this purpose, the dye-loaded adsorbent was stirred with 25 mL of HCl: butanol (1:3) for 30 min.After that, the adsorbent was separated, washed several times with distilled water, and dried at 60 °C.Then, the regenerated adsorbent was utilised as previously described in the experimental part for three cycles of adsorption/ desorption.The results showed that the % removal (% R) or adsorption capacity (Q) towards crystal violet and methylene blue dyes changes slightly as shown in Tables 4 and  S6, respectively.Hence, this confirms the possibility of using these adsorbents successfully several times for the removal of crystal violet and methylene blue dyes.

Conclusions
Novel mixtures rely on tin and silicon substances were synthesised by the reaction of 6 g of sodium metasilicate pentahydrate with 2.407, 5.247, 7.195, or 9.59 g of tin chloride dihydrate.The samples, which were synthesised using 2.407, 5.247, 7.195, and 9.59 g, are abbreviated as T1, T2, T3, and T4, respectively.The mixtures were characterised using different tools such as XRD, FT-IR, FE-SEM, BET, and HR-TEM.The mixtures can efficiently remove methylene blue and crystal violet dyes from aqueous media.The maximum adsorption capacity of T1, T2, T3, and T4 samples towards crystal violet dye is 34.81, 36.83,29.46, and 11.98 mg/g, respectively.Also, the maximum adsorption capacity of T1, T2, T3, and T4 samples towards methylene blue dye is 30.13,29.33, 17.09, and 13.43 mg/g, respectively.

Figure 5 .
Figure 5.The effect of pH on % removal (a) and adsorption capacity (b) in the case of crystal violet dye.

Figure 6 .
Figure 6.The effect of pH on % removal (a) and adsorption capacity (b) in the case of methylene blue dye.

Figure 7 .
Figure 7.The effect of time on % removal (a) and adsorption capacity (b) in the case of crystal violet dye.

Figure 8 .
Figure 8.The effect of time on % removal (a) and adsorption capacity (b) in the case of methylene blue dye.

Table 1 .
Constants of the applied equilibrium isotherms in the case of crystal violet dye.

Table 2 .
Constants of the applied equilibrium isotherms in the case of methylene blue dye.

Table 3 .
Comparison between adsorption capacity of our adsorbents with others in the literature.