Adsorption of Bromothymol Blue Dye onto Bauxite Clay

The goal of the current work is to use an inexpensive, non-toxic material with a high water absorption capacity, bauxite clay, to adsorb the bromothymol blue dye from an aqueous solution. In the production of textiles, leather, paint, food, cosmetics, and pharmaceuticals, synthetic organic compounds are used as dyes almost exclusively in modern industrial processes. Because to their harmful side effects, which include their inherent carcinogenicity, toxicity, and mutagenicity as well as the results of their biological transformation, these dyes pose a serious hazard to the environment when they are released. Clay minerals are valuable as depolluting agents due to their swelling potential, colloidal behavior, and adsorption capacity. The adsorption behavior of bromothymol blue dye from an aqueous solution was studied using bauxite clay. Different variables such as contact time, dosage, ionic strength, and temperature were studied to show the effect on bromothymol blue adsorption onto bauxite clay from an aqueous solution using the batch adsorption method. This study showed that the adsorption decreased by increasing the temperature (15–40 C) and increased by increasing the clay weight from 0.2 to 1.6 g. It also showed as the amount of time rose, the adsorption grew until it reached an equilibrium time of 155 minutes. Thermodynamic metrics including change in free energy (∆G), enthalpy (∆H), and entropy (∆S) all were assessed. A positive correlation was found between the absorbance and the range of concentrations of bromothymol blue (4–32 g/mL) with a correlation coefficient of 0.9911. The maximum wavelength was found and set to 432 nm for all measurements.


Introduction
Community water sources are negatively impacted by wastewater contamination, which can have negative health implications 1 .Large amounts of dyes are used in numerous businesses, causing the water in rivers and lakes to become contaminated.Dye products are used in a wide range of industries, including those related to paper, textiles, cosmetics, rubber, food, and medicine.Many dyes, especially synthetic dyes, have a hazardous impact on human health and may even be carcinogenic due to their complex chemical structures that resist biodegradation and enable them to persist for a long time in aqueous media 2 .For the removal, recovery, and recycling of harmful materials from wastewater, adsorption has emerged as the method of choice.Due to their affordability and simplicity, spectrophotometric approaches can be more beneficial for determining biological materials 3,4 .

Abstract
The goal of the current work is to use an inexpensive, non-toxic material with a high water absorption capacity, bauxite clay, to adsorb the bromothymol blue dye from an aqueous solution.In the production of textiles, leather, paint, food, cosmetics, and pharmaceuticals, synthetic organic compounds are used as dyes almost exclusively in modern industrial processes.Because to their harmful side effects, which include their inherent carcinogenicity, toxicity, and mutagenicity as well as the results of their biological transformation, these dyes pose a serious hazard to the environment when they are released.Clay minerals are valuable as depolluting agents due to their swelling potential, colloidal behavior, and adsorption capacity.The adsorption behavior of bromothymol blue dye from an aqueous solution was studied using bauxite clay.Different variables such as contact time, dosage, ionic strength, and temperature were studied to show the effect on bromothymol blue adsorption onto bauxite clay from an aqueous solution using the batch adsorption method.This study showed that the adsorption decreased by increasing the temperature (15-40 C) and increased by increasing the clay weight from 0.2 to 1.6 g.It also showed as the amount of time rose, the adsorption grew until it reached an equilibrium time of 155 minutes.Thermodynamic metrics including change in free energy (∆G), enthalpy (∆H), and entropy (∆S) all were assessed.A positive correlation was found between the absorbance and the range of concentrations of bromothymol blue (4-32 g/mL) with a correlation coefficient of 0.9911.The maximum wavelength was found and set to 432 nm for all measurements.https://doi.org/10.21123/bsj.2024.8962P-ISSN: 2078-8665 -E-ISSN: 2411-7986 Baghdad Science Journal The dyes are organic substances that can dissolve in water, especially the reactive, direct, basic, and acidic ones.It is challenging to get rid of them with traditional procedures because they are highly soluble in water.Due to the presence of chromophoric groups in its molecular structures, one of its characteristics is the capacity to color a certain substrate.However, the auxotrophic groups, which are polar and may interact with polar groups of textile fibers, are what give color to a material its ability to adhere to it 5 .Modern industrial processes nearly exclusively use synthetic organic chemicals as dyes in the manufacture of textiles, leather, paint, food, cosmetics, and pharmaceuticals 6,7 .It is estimated that more than 700,000 tons of synthetic organic dye are generated each year globally.A few examples of the several dye classes that can be separated based on their structure and application include reactive, acid, dispersion, vat, and azo dyes.These dyes constitute a major threat to the environment when they are released because of their negative side effects, including their inherent carcinogenicity, toxicity, and mutagenicity as well as the byproducts of their biological transformation 6.More details about the degradation structure are required in order to improve the stability of health products and determine whether the degradation and contaminants are harmful.These abrupt changes have a significant impact on how chemical compounds affect the environment and human health 8 .Clays are naturally occurring substances with a high capacity to absorb water.They are also often nontoxic.As a result, in addition to their usage for pollutant control, they are also beneficial as water adsorbents in contemporary, typically urban, applications such as pet litter, air conditioners, and tunnel sealing (to stop water leakage) 9 .These bauxites chemical, mineralogical, and physicomechanical characteristics are greatly influenced by the parent rocks composition the generation process of the locations geomorphology the amount of time that has passed since formation and the age of the bauxite 10,11 .
A multitude of operational parameters affect how the adsorption process turns out.The process must have enough time to run until the equilibrium state is reached because contact time is a vital component.Longer contact times between the adsorbent and the adsorbate are also believed to increase adsorption efficacy differently depending on the material's accessible sites 12 .The two main models used in adsorption research are Freundlich and Langmuir.The Langmuir model, which assumes that the surface has a specific number of binding sites with equal energy or heat and no lateral interactions, is one of the most basic equations of isotherm.One of the most crucial tests performed during the optimization process, the influence of contact duration, which requires significant care to produce the best results.When the thermodynamic analysis is finished, the other variables are kept constant while the adsorbent and adsorbate are subjected to interactions with one another at various temperatures.The outcomes might show a lot about the relationships between the various species.Calculations of the thermodynamic quantities free energy change (∆G°), entropy (∆S°), and enthalpy (∆H°) are based on how temperature affects the adsorption process.
While the strength of the adsorption is indicated by enthalpy, entropy refers to a change in the system's overall order 13 .There are several analytical methods for removing dyes, but adsorption is the most effective method since it is simple, generates a high yield, is easy to recover from, and allows the adsorbent to be reused.The adsorption of the dye bromothymol blue (BTB) onto four zeolitic materials was investigated by Tabti and colleagues.The outcomes demonstrated that an adsorbent had an efficiency of 83.44 % in removing dye 14 .It has been proven that Latvian sphagnum peat moss is an effective sorbent for removing BTB from aqueous solutions.The dye removal effectiveness of the solution showed significant fluctuation, with greatest removal at pH values of 7.5 and 2.5 15 .An aqueous media was treated with a mixture of used to conduct the experiment.These sorbents were also studied using infrared spectroscopy and thermogravimetric measurements.As a result, it was demonstrated that sphagnum sorbents could effectively remove both cationic and anionic dyes with little to no thermal treatment 16 .The adsorption of the Rhodamin dye on Iraqi bentonite was assessed using various concentrations of nano compounds, such as ZnO, TiO2, and Al2O3.To improve the bentonite's capacity for adsorption, rhodamin dye was taken out of aqueous solutions at a concentration of 0.01-0.1 g 17 .
The current study aims to use the adsorption method to remove the BTB dye from an aqueous solution using bauxite clay which is cheap, none-toxic, and has a high capacity to absorb water.

Apparatus
The UV-visible spectrophotometer was a double beam Shimadzu 1800 in a quartz cell with a 1 cm width from Japan.The LabTech LSB-045S thermostatic water bath shaker is produced in Korea.Germany produced the Radwag AS 220/C/1, ± 0.0001g, electronic balance, and centrifuge (6000 rpm).

Preparation of Standard Solutions
The buffer solution was prepared by mixing 10 ml of potassium phosphate 0.1 M and 11.2 ml of sodium hydroxide 0.1 M. Because the color of the dye changes to yellow when the pH changes, it was adsorbed at pH 6.A standard stock solution containing 100 mg/L of dye was created by dissolving 0.01 g of BTB dye in 100 ml of water.
The dye was diluted to a concentration of 4-32 mg/L to produce solutions of various concentrations.

Adsorption Experiments
All tests were carried out to investigate the impacts of contact time, adsorbent weight, and ionic strength.The absorption spectra and calibration curve of BTB dye are shown in Fig. 2 and Fig. 3.The optimal wavelength is 432 nm, as seen in Fig. 2. Therefore, the experimental values of solutions with concentrations ranging from 4 to 32 mg/L were measured and plotted against the BTB dye concentration.Eq. 1 and Eq. 2 were used to determine the amount of BTB dye that was adsorbed at contact times and the percentage of BTB dye that was removed by the BTB (R%) (Qe).R% = (Cₒ-∁ₑ)/Cₒ ×100 1 Qₑ =V(Cₒ-Cₑ)/W 2 Where Cо the initial concentration and Ce the equilibrium concentration in mg/L, V is the solution volume (25 ml), and W is the weight of the clay sample that was used in grams.

Effect of Weight on the Surface
The effect of adsorbent weight on the removal percentage of BTB dye adsorbed was examined using 25 ml of a 20 mg/L initial amount of BTB dye at 25 C.According to the data analysis Fig. 5, the sorption amount rises as the weight of the bauxite in the solution does. of BTB on the surface of bauxite reduces as a result of an increase in ionic strength.The Na+ and Clions will compete with the dye molecules for the active sites of the surface because their attraction to the surface is stronger compared to that of the molecules of dye, which explains why the electrolyte has an inhibitory impact on adsorption.Consequently, the surface causes a decline in adsorption.

Effect of Temperature
The effects of the temperature on the adsorption of BTB on bauxite were investigated at three different Temperatures, 15, 25, and 40 °C.The results are summarized in Table 1 and Fig. 7. Between 25 °C and 45 °C, there is a little decrease in the adsorption equilibrium capacities.Adsorption Thermodynamics Enthalpy (∆H), entropy (∆S) and free energy (∆G) changes were calculated using Eq. 3, Eq. 4, and Eq. 5 ∆H was calculated by the Eq. 4, and the slope is -∆H/2.303RT, Fig. 8.The Keq is calculated by the value of Qₑ/Cₑ according to Fig. 7 when Cₑ is constant, the Qₑ is measured at each temperature.
The results are summarized in Table 2.The characterization of bauxite samples was studied by Ghati and co-authors using atomic force microscopy (AFM) technique and shown in Table 3 18.∆G= -RTln Qₑ/ Cₑ 3 Log Keq= (-∆H)/(2.303RT) + Con. 4 ∆S= (∆H-∆G)/T 5 Where T is the absolute temperature and R is the universal gas constant (8.314J.mol-1K-1).The adsorption reaction is exothermic, as indicated by the negative value of ∆H˚.The ∆G˚ is positive value supports both the practicality of the procedure and the assertion that adsorption is not a spontaneous process.The value of ∆S˚ is negative because adsorption necessitates a more complex arrangement of order, Fig. 8.

Adsorption Model
Optimizing the design of an adsorption system for the adsorption of adsorbents requires finding the most appropriate correlation for the equilibrium curves.The equilibrium properties of adsorption have been described using a variety of isotherm equations, including those of Langmuir, Freundlich and Temkin.Eq. 6 and Eq. 7, respectively, show the linear forms of the Freundlich isotherm and the Langmuir eq.Ce/Qe = 1/(K_L q_m ) + Ce/q_m 6 Log Qe = log Kf + 1/n log Ce 7 The equilibrium dye concentration is Ce (mg/L), the amount adsorbed is Qe (mg/g), and the monolayer adsorption capacity of the adsorbent is qm (mg/g), KL is the Langmuir constant, and Kf and n are Freundlich constants.The Temkin isotherm and Temkin linear have been applied in the manners described below, respectively: Qe = RT/b ln (ACe) 8 Qe = RT/b lnA + RT/b lnCe 9 The results are displayed in Table 4, Fig. 9 and Fig. 10, which correspond to the Freundlich and Langmuir equations, which explain that when you plot log Qe versus log Ce, the slope will be 1/n and log Kf is the cross, Fig. 9 According to the Freundlich isotherm, BTB was absorbed.
Fe 2 O 3 , chitosan, and bamboo sawdust to remove the acid dye BTB(FeCBSD).With an adsorption efficiency (qm) of 217.39 mg/g over a contact period of 30 min and an adsorbent dosage of 0.5 g/L, the results most closely resembled the Langmuir adsorption isotherm.With an adsorption process of 225.13 mg/g at a flow rate of 20 mL/min and a bed level of 5 cm in column trials, the data closely matched the Thomas model.Abu Al Roos and colleagues looked into the possibility of removing the dye BTB from aqueous solutions using sphagnum sorbents that had undergone thermal treatment.Under ideal adsorption conditions, which included the proper shaking rate, equilibrium contact durations, and solution pH, these sorbents were tested for dye removal.The untreated sphagnum material was https://doi.org/10.21123/bsj.2024.8962P-ISSN: 2078-8665 -E-ISSN: 2411-7986 Baghdad Science Journal
At a constant beginning concentration of 20 mg/L of BTB dye and 0.6 g of bauxite at 25 ˚C, the effect of contact time on the adsorption of BTB dye on bauxite clay was examined.The adsorption, as shown in Fig. 4, increased as the time increased to reach an equilibrium time of 155 minutes.: January, 2024 https://doi.org/10.21123/bsj.2024.8962P-ISSN: 2078-8665 -E-ISSN: 2411-7986 Baghdad Science Journal

Figure 4 .
Figure 4. Effect of contact time on BTB adsorption to bauxite surface.

Figure 5 .
Figure 5.Effect of mass on removal of BTB on bauxite.

Figure 6 .
Figure 6.Effect of ionic strength on BTB adsorption to bauxite.

Figure 7 .
Figure 7. Effect of temperature on adsorption of BTB onto bauxite surface.