Kinetic and Theoretical Study of Removal Gentian Violet from Aqueous Solution Using Stachy Plant

: The main parameters and methods influencing the removal of Gentian Violet (GV) dye from aqueous media were investigated using a stachy plant in this study. The surface of the stachy plant was determined using FTIR spectra. Adsorption is influenced by the adsorbent's characteristic groups. The research took into account the usual conditions for GV dye adsorption by the stachy plant, such as the impact of contact time. Mass dosage , after 0.3 g the amount of adsorbed dye declines. Study pH and ionic strength, the results obtained showed that at pH 3 the largest adsorption of (GV) was seen, while at pH 9, the lowest adsorption was observed at 298 K, the adsorption kinetics and equilibrium constants were achieved


Introduction:
Textiles, paper, printing, leather, food, cosmetics, and other sectors that utilize dyes to color their end product consume a lot of water. Dyecontaining wastewater is very difficult to handle since the dyes are recalcitrant organic molecules that are resistant to aerobic digestion and light stability. Dyes, even at very low concentrations, are highly visible and cause environmental harm because they are harmful to marine life 1 . Suspended elements, mineral solutes, organic solutes, dissolved gases, and microbes are only a few of the most prevalent types of water pollutants. Because of their commercial and societal importance, the effects and toxicity of important dyes discharged into the atmosphere have been intensively investigated 2 . Synthetic dyes are particularly harmful to all forms of life since they contain sulfur, colors, nitrates, acetic acid, surfactants, enzymes, chromium compounds, and heavy metals like copper, arsenic, silver, cadmium, mercury, nickel, cobalt, and a few more substances. Violet 3 (Basic) the synthetic cationic dyes, gentian violet, and methyl violet 10B all belong to the triarylmethane group. This dye is commonly used to dye cotton, wool, silk, and nylon in the textile industry, as well as in the creation of printing inks and as a dermatological agent in biological stains and veterinary medicine 3 . Gentian violet (GV) is toxic and it can cause discomfort when absorbed through the skin, as well as inhalation and ingestion. It can cause kidney failure and eye inflammation, which can lead to permanent blindness and cancer in serious cases 4 . As a result, removing GV from wastewater is extremely important. Inhalation, ingestion, and direct contact with the skin are all ways that gentian violet dye (GV) can affect humans, causing cancer and extreme eye irritation 5 .
Adsorption is one of the most efficient dye removal methods, less expensive and harmless absorbent materials should be used in the adsorption process. Many low-cost adsorbents derived from agricultural wastes and natural materials have recently been investigated for dye removal from aqueous solutions 6 . Researchers have published a study that focuses on low-cost adsorbents that are mostly obtained from agricultural waste and industrial leftovers since they are abundant in nature and require minimal processing. Plant waste is cheap because it has no or very little economic value. This has led many workers to search for the use of cheap and efficient alternative materials. As a result, many employees are looking for low-cost, high-efficiency alternatives 7 . Spent corncob substrate 8 , sunflower seed shells 9 , palm kernel fiber 10 , Luffa cylindrical fibers 8 , olive pomace 11 , Biologically Active Plants 12 , wheat shells 31 and pomelo (Citrus grandis) peel. The aim of this research is to determine the stachys plant's static adsorption ability of Gentian Violet (G).

Materials and Methods: Adsorbent
The plant Stachys was used in this analysis, distilled water was used to clean the plant leaves. The plant leaves were then filtered before being dried in a 60°C oven for 4 hours to remove any remaining moisture and leave it for a week at room temperature. The dried materials were ground and sieved to a size of 150 microns to make powder. The stachys plant sample that has been prepared.

Adsorbate
To make the stock solution, 0.1 g of (GV) was dissolved in 1 L distilled water. It was slowly soaked to ensure that all of the (GV) powder was dissolved in distilled water. The experimental solutions were made by accurately diluting the dye stock solution to various initial concentrations ranging from (1-5 ) ppm, with a maximum wavelength of 590 nm for (GV). This dye's structure is listed in Fig. 1.

The effect of different parameters of adsorption processes of GV:
The influence of contact time Adsorption equilibrium trials using 0.3 g of adsorbent in 75 mL of dye at a concentration of 5 ppm are carried out at 25°C for 5, 10, 15, 20, and 25 minutes.

The Effect of mass dosage
The effect of mass dose was examined by agitating in different masses (0.1, 0.2, 0.3, 0.4, and 0.5 g) at 25 °C, 100 rpm, and 75 mL of (GV) dye concentration 5 ppm.

The Effect of pH
At 25 °C, 100 rpm, and 75 mL of dye concentration 5 ppm. At various pH levels, the influence of pH on the rate of color loss was examined (3, 5, 7, and 9). 0.1 N NaOH and 0.1 N HCl solutions were used to adjust the pH using a pH meter with a composite pH electrode.

The Effect of ionic strength
Adsorption studies were performed at 25 °C using 75 mL of dye with a 5 ppm concentration and varied KCl concentrations (0.01, 0.001, 0.0001) M.

Surface Characterizations
The adsorbent deposit of Stachys was investigated using Fourier Transform Infrared spectroscopy (FTIR), with spectra taken before and after Gential Violet concentration 5 ppm adsorptions shown in Figs. 2 and 3. We can see absorption bundles from the OHhydroxyl groups in the range (3429.43-3417.86 cm -1 ) and the appearance of absorption bundles at (3082.25-3074.53 cm -1 ) after adsorption returns to the aromatic CH groups in the dye and C = C groups at (1647.21 cm -1 ), C = O groups at (1680-1630 cm -1 ) in the FTIR spectrum the CH-groups on the surface of the stachys powder, as well as the active N-H group within the range, account for the absorption in this range (2924.04-2920.23 cm -1 ) (1249.78 cm -1 ). These groups are important sites for adsorption since they have the ability to shape chemical or physical bonds and can include a pair of electronic or electrostatic changes that can be involved in the formation of physical links or chemical bonds 14 . Figure 4 depicts the influence of contact time on the adsorption of (GV) onto stachys. The results show that the adsorption process reached equilibrium in 25 minutes, and that the amount of dye removed at equilibrium increased as contact time increased. After 15 minutes, the changes in equilibrium adsorption became more stable, and equilibrium was reached in 25 minutes. The adsorbent's ability gradually depleted over time as the few remaining vacant surface sites became difficult to occupy due to repulsive forces between the solute molecules on the solid and bulk phases, and the high removal rate at the start of the contact period was due to the large amount of surface area available for dye adsorption during the initial stage. 12  Figure 5 shows the adsorption of dye GV as a function of adsorbent dosage. The amount of adsorbed dye increases as the adsorbent dose is increased, but the adsorption quantity decreases after 0.3 g. It is self-evident that raising the adsorbent dose increases the number of usable adsorption sites, resulting in an increase in the amount of adsorbed material dye 35 . The decrease in adsorption density as the adsorbent dose is increased is due to the fact that adsorption sites remain unsaturated during the adsorption reaction, while the number of adsorption sites available increases as the adsorbent dose is increased 16 . The adsorption isotherm can be used to define the dye distribution between the solid phase and the solution at a specific temperature once equilibrium has been attained. The Langmuir, Freundlich, and Temkin models were employed to fit the equilibrium data. Fig. 6 shows that the adsorption of GV dye on the surface of the stachy follows the pattern (S3), and the orientation of the adsorbed molecules on the adsorbing surface is in an oblique or vertical manner.

Langmuir Isotherm
The Langmuir isotherm theory assumes that the adsorbate is coated in a monolayer on a   Fig. 7. Table 1 shows the values of Qm and kL calculated from the slope and intercepts (1).

Freundlich Isotherm
The Freundlich isotherm is an empirical equation that applies to adsorption on heterogeneous surfaces and is not restricted to the generation of monolayers. The amount of adsorbate adsorbed on the adsorbent surface is thought to increase as the adsorbate concentration rises. The Freundlich isotherm can be represented in its linear form as follows 18 .: log Qe = log Kf + 1/n log Ce 4 where Qe is the total amount of Gentian violet dye adsorbed (mg/g), Ce is the equilibrium dye concentration in solution (mg/L), and Kf and 1/ n are constants that integrate the adsorption ability and strength, respectively. The adsorption of (GV) dye is shown by linear plots of log Qe versus log Ce. Fig. 8 shows the Freundlich adsorption isotherm. The values of Kf and 1/n given in Table 1.

Temkin Isotherm
Temkin and Pyzhev looked into the impact of specific indirect sorbate/adsorbate interactions on adsorption isotherms, proposing that as a result of these interactions, the heat of adsorption of all molecules in the layer will drop linearly with coverage 19 . The Temkin isotherm was used in the following applications: qe  RT / b ln ( K T Ce) 5 KT stands for the equilibrium binding constant (L/g), b for the heat of adsorption (J/mol), R for the universal gas constant (8.314J/mol K), and T for the absolute temperature (K), As shown in table 1 . Fig.  9 shows the Temkin adsorption isotherm. When plotting qe against ln Ce, the values of the constants b, kT are obtained from the slope and intercept values.  Through the results of Table 1, it was found that the adsorption of GV dye is in great agreement with an equation Temkin.

The Effect of pH:
The effect of pH on the adsorption of (GV) was examined at pH 3, 5, 7, and 9. At pH 3, the largest adsorption of (GV) was seen, while at pH 9, the lowest adsorption was observed (see Fig. 10). As the pH of the solution increased 20, 21 , the adsorption of (GV) decreased. This was due to the extinction of the positive hydrogen ions, which encouraged electrostatic repulsion between the negative charges of the dye surface 22 . The carboxylic groups are the most prevalent at an acidic pH 23 . The surface charge of stachys becomes more positively charged at pH 3, boosting (GV) adsorption via electrostatic attraction. Fig.10 shows the results of the pH effect on Gentian violet elimination. The increase in adsorption with increased ionic strength could be due to compression of the thickness of the diffused double layer. The reason this is due to the fact that the interactions between the solvent molecules and KCl ions are higher than the interactions of the dye which leads to an increase in the solubility of the dye in the aqueous solution, and thus leads to an increase in the solubility of the dye in the aqueous solution in the ability to be adsorbed on the surface. The adsorbent particle and adsorbate species may be aided in approaching each other more closely as a result of the compression, resulting in considerable attractive forces and enhanced adsorption 24 . Fig. 11 shows the Effect of ionic strength on removal of Gentian Violet. The kinetics of adsorption is crucial for controlling the efficiency of a process. Various kinetic models, including pseudo-first-order and pseudo-secondorder models, have been studied by various researchers. The kinetics of adsorption is significant because it regulates the efficiency of the process. Lagergren's pseudo-first-order rate equation is roughly defined by the following equation 16 : log (qe-qt) = loq qe -( k / 2.303 t ) 6 qe is the total amount of dye adsorbed at equilibrium in mg/g. Plotting log (qe -qt) versus t for various dye concentrations yielded the value of k. . Fig. 12 shows the Pseudo -first order plot for (GV) dye adsorption.

Figure 12. Pseudo -first order plot for (GV) dye adsorption.
The pseudo-second-order kinetic model the following equation 16 : t/ q = 1 / k2 qe 2 + t/ qe 7 A linear relationship is obtained by plotting t/q vs t, where k2 is the second-order rate constant (g/mg min). The k2 and qe values the intercept and slope of the plots of t/q versus t is determined. Fig. 13 shows the Pseudo-second order plot of (GV) dye adsorption. Figure 13. Pseudo-second order plot of (GV) dye adsorption.
In this study, the adsorption of Gentian Violet by stachy plants was explained using the pseudosecond order model. The second-order kinetic model had higher correlation coefficients than the first-order kinetic model 25 .
Theoretical Studies: a) Theoretical electrostatics ( potential energy ) (E.P) The electron distribution is important for locating reaction sites in a molecule because it determines the electrostatic potential of molecules and specifies the interaction of the molecular system's energy with a positive point charge. A molecule having a substantially negative electrostatic charge is more likely to be attacked by positively charged species 26 . To examine the reactive sites of the molecules, the (E.P) of Gentian Violet dye was measured and plotted as a 2D and 3D contour, fig. 14.