Removal of Direct Yellow 50 from aqueous solutions using chitosan-iso-vanillin derivatives chelating polymers

Background Water contamination has increasingly become a significant problem affecting the welfare of living organisms perceived to be aquatic beneficiaries. The nature and origin of the contaminant always determines the purification techniques. The most common contaminants in wastewater include organic compounds such as dyes that must be eliminated to enhance water purity and safety. The results indicate that the removal of DY50 by the modified chitosan was affected by the solution pH, sorbent dosage, initial DY50 concentration, contact time, and temperature. The experimental data were fitted to the Langmuir, Freundlich, and Temkin isotherms, and Langmuir isotherm showed the best fit. The kinetic data were fitted to the pseudo-first-order and pseudo-second-order rate equations. The removal rate was 97.9% by chemisorption components after the three hours at about 0.05 g of sorbent dose and 100 ppm of the Direct Yellow 50 dye initial concentration. The adsorption behavior of the modified chitosan for the removal of DY50 was well-21 described using the pseudo-second-order kinetic model, Intraparticle diffusion analysis was also conducted. The thermodynamic properties such as free energy (∆G), enthalpy (∆H), and entropy (∆S), in addition to the intra-23 particle diffusion rate were similarly defined. in This study examined the application of cost-effective chitosan-iso-vanillin compound in the elimination of Direct Yellow 50 dye from wastewater. The research conducted numerous symmetric exercises to regulate the kinetic and thermodynamic factors. A chitosan-iso-vanillin polymer was used to eliminate the Direct Yellow 50 dye impurities from the wastewater. The pollutant elimination efficiency, adsorption capacity, and sorption mechanism of the aqueous DY50 dye by the chitosan-iso-vanillin were determined.

. The compounds acetone and ethanol were used to wash and filter the obtained material through the Soxhlet   the elimination of dye [11,12]. Similarly, additional practical was performed at varying DY50 dye concentration 82 and temperature, for example, 20, 30, 40, 50, 70, 100, and 150 mg. L-1 and 20 °C, 30 °C, 50 °C, and 70 °C 83 parameters, respectively. The polymer enhanced elimination of metal ion [13]. Similarly, various weights of 0.01, 84 4 0.05, 0.1, 0.2, and 1.0 g of the dehydrated adsorbent were used to examine the impact of the polymer present. After 85 that, solutions were filtered to obtain the DY50 concentration remains [1,14,15]. The UV-Vis spectroscopy was 86 applied to determine the quantity. The quantity of DY50 ions in equilibrium denoted by (Q e ) was calculated, as 87 shown in the Eq. (1): Similarly, C o and C e denote both initial and equilibrium dye concentration (mg. L -1 ), W is polymer quantity (g),

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and V represents the volume of the dye (L).

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At every time interval, the quantity of DY50 remains were eliminated by the Eq. (2): Whereby C t denotes the DY50 solution concentrations (mg. L -1 ) at various period intervals (t).

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Chitosan is among the most readily available biopolymer. The compound has various behavioral characteristics 95 such as the capability to form mechanical membranes, non-toxicity nature, antimicrobial activity, and 96 biocompatibility, thus influencing its massive food engineering application. The technique has helped in water 97 purification, food preservation, and fruit juice isolation, among other activities [16][17][18]. Similarly, the polymer can 98 be used in an organized delivery system through the microsphere/ionosphere method. The polymer involves cross-99 linking to advance the reacting agents' specific and time frame activities like glutaraldehyde, formaldehyde, and 100 glyoxal. Additionally, both the bean and orchid vanilla were also applied to purify and flavoring nutrients due to 101 their safety. The substance also displays additional bioactive properties [2,19,20]. The combination of both the

Effect of pH on DY50
107 The solution's pH influence on the DY50 sorption was between 3.0 to 10.0pH. DY50 solution's pH value plays 108 a significant role in adsorption as it influences functional groups' dissociation both on the active sites and 109 adsorbent's surface charge and the DY50 solution's chemistry [21]. As the pH value increased, the amount of DY50 110 adsorbed by chitosan-iso-vanillin decreased. The optimum level of adsorption (97.3%), mass 0.05g, was recorded 111 at a pH value of 3.0. Previous study reports that other studies found that when chitosan-iso-vanillin is used as an 112 adsorbent, optimum pH ranged between 3 to 6 [2]. As Fig 3. illustrates, the adsorbent used was able to remove  shows that an increase in the initial DY50 concentration leads to an increased dye adsorption 120 capacity onto chitosan-iso-vanillin. The initial amount of molecules in the dye over the available adsorption sites 121 decreased at low concentrations. As a result, more adsorption sites became known to the dye molecules. The 122 adsorption rate was affected by the initial DY50 concentration that also influenced the sorbent adsorption capacity 123 [21,23]. The impact was induced by a rise in a concentration gradient that resulted in a similar surge in initial 124 DY50 concentration. However, the number of adsorption sites reduced at high initial dye concentration due to a 125 rise in dye molecules concentration [24,25]. It can be summarized that the ratio of adsorption areas to the dye 126 molecules' initial quantity was equal at low concentration [26]. The anionic dye adsorption level was increased by 127 protonation. The figure below graphically demonstrates the impact of the initial concentration.

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This can be summarized by the fact that at low concentrations, the ratio of the initial number of dye molecules to 129 the available adsorption sites is low; therefore, more adsorption sites are available for the dye molecules, and the 130 removal rate increases. However, at higher concentrations, the ratio of the initial number of available adsorption 131 sites to the dye molecules is low; therefore, the number of available adsorption sites becomes lower, and the dye 132 removal decreases. Proton effectively improved the adsorption of the anion dye onto chitosan [27].

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The adsorption of DY50 onto chitosan-iso-vanillin was explained using a linear plot of the Langmuir, Freundlich,

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and Temkin isotherm models. The current study demonstrated the distribution method of the adsorbed molecules 135 in the equilibrium state between both the solid and liquid phases, which is referred to as isotherm adsorption.

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The Langmuir isotherm model is shown by Eq. (3): 6 C e /Q e = 1/ (Q 0 K L ) + C e /Q 0 (3) K L and Q o were the coefficients of the Langmuir adsorption model, and they are related to sorption energy (L/mg) 138 and adsorption capacity (mg/g), respectively.

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Furthermore, R L , a dimensional constant separation factor, was used to express those basic properties of the 140 Langmuir isotherm model and was defined as Eq. (4): The isotherm can be estimated based on the value of R L , where if R L = 1, the isotherm is linear, if greater than 142 one is unfavorable, either (0 <R L <1) is favorable or (R L = 0) is irreversible.

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The Freundlich model, which is acceptable at low concentrations and heterogeneous surfaces, is expressed by Eq.

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The Temkin model includes the effects of indirect adsorption/desorption reactions on the adsorption temperature.

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The hypothesis of this model is based on the fact that the adsorption process decreases the adsorption heat of all 150 molecules linearly. The Temkin isotherm can be calculated by Eq. (6): = (-∆H), A is the Temkin equilibrium, and the adsorption (maximum) capacity is Q 0 [28,29].

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A and b from the intercept and the slope of plot q e against plot ln C e are shown in Table 1. The isotherm parameters 155 R 2 of the Langmuir, Freundlich, and Temkin models were 0.9886, 0.9779, and 0.9771, respectively. Also, the 156 adsorption coefficient (K L ) was 0.2259 and the maximum removal capacity Q 0 was 250 mg.g -1 . The constant K F 7 of the Freundlich isotherm, which reflects the capacity of the adsorption, was 43.7219 mg/g. Also, the adsorption 158 was measured using the Temkin isotherm model, which suggests that the energy of the adsorption decreases 159 because of the increase in the surface coverage by the DY50 ions by the regular distribution of the binding energies 160 to a maximum; the sorption process can be visualized based on this model. In this study, the Langmuir isotherm 161 was a favorable model that most suitable the equilibrium data across the adsorption isotherm [30].

Effect of Adsorbent Dosage. 163
The dosage test was also conducted in the study to determine the adsorption rate of the DY50. The was also noted to have risen probably due to the molecules' clumping or intersection. Similarly, it is employed to 168 treat acute cadmium infections [26]. The impact of adsorbent dosage on DY50 results was obtained and graphically 169 demonstrated, as shown in Table 2 and Fig. 5, respectively. Table 2 shows a change in the absorbent dose from 170 0.01g to 0.3g and its effect on the removal of DY50. As observed from Table 2, the lowest removal rate of DY50,   The kinetic data were processed via two adsorption patterns: the pseudo-first and second kinetic orders shown in

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Eq. (7) and Eq. (8), respectively. The models of the pseudo-first and second kinetic orders could better describe 187 the adsorption of dye on different sorbents [2].
The observed (Q e ) experimentally observed at 39.19 mg/L, the equilibrium was reached at 180 min, reflecting the R ) of the pseudo-first order (0.9798) in Table 3. The adsorption of DY50 191 by chitosan-iso-vanillin approached balance rapidly, and the adsorption surface was densely covered.

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Subsequently, the surface was gradually blocked by the dye molecules, which increased the time needed to reach 193 balance. These results are consistent with [15], in which the authors reported that the greater the concentration, the 194 greater the time needed to reach equilibrium; that is, there is a direct relationship between these two parameters.

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The rate constant was calculated via Eq. (9) to examine the adsorption mechanism as follows: 196 q t = k id t 1⁄2 + c (9) where q t the mass of DY50 in contact time t (min), k id (mg.g -1 .min -½ ) is the intra-particle diffusion rate constant 197 and c is the boundary layer effect of adsorption. Fig 7. shows the linear plot q t versus t 1/2 for DY50. The mechanism 198 of intra-particle diffusion, which was not dominant in the rate-determining step, was illustrated using the 199 correlation coefficient (R 2 = 0.9785) of the Weber-Morris model. Additionally, the adsorption occurs by diffusion 200 in both the surface and intra-particles. In this study, the kinetic model of the pseudo-second order was dominant 201 and, therefore, there was a direct adsorption rate control in the total kinetics of the sorption; this corroborated [32].

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This result indicated that the electron exchange was controlled between adsorbates and adsorbents via chemical 203 adsorption [33].

Influence of Temperature and Thermodynamic Investigation 205
The effect of temperature on the adsorption of DY50 by chitosan-iso-vanillin at pH=3 and the thermodynamic 206 study are illustrated in Fig. 8 The removal of DY50 was studied at four different temperatures (20,30,50, and 70 207 9 °C). The adsorption process was influenced by temperature; i.e., a change in temperature can change the 208 equilibrium capacity of the adsorbent to adsorb a specific compound. An increase in temperature decreases the 209 adsorption of the dye, representing the exothermic nature of the adsorption reaction, whereas a decrease in 210 temperature represents its endothermic nature. The physical bonding between both organic compounds, including 211 dyes and the active sites of adsorption, was weakened with increasing temperature, in addition to the low 212 temperature of the adsorbed species and few available active sites [34,35]. However, the effect of temperature was 213 negligible. This behavior was consistent with [36], in which the authors found that the removal of pigments may 214 not be affected by a change in the temperature of wastewater. Therefore, temperature has a distinct effect on 215 adsorption altering the adsorption equilibrium amplitude to adsorb certain compounds.

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Thermodynamic factors like entropy(ΔS), enthalpy (ΔH), and free energy (ΔG) were employed to define the 217 adsorption process changes the results are shown in shows that the adsorption is exothermic. These parameters have been used to deduce the mechanism of adsorption 220 Table 4 shows that all ∆G values were negative, which indicated that the sorption was spontaneous and rapid at 221 the four applied temperatures. Also, an increasing in temperature followed by an increase in the absolute value of 222 ΔG may facilitate the adsorption process.

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The exothermic or endothermic nature of the adsorption is based on the value of ΔH, which here is negative; this 224 suggests that the adsorption was exothermic. Conversely, a positive ΔH value suggests another type of reaction,

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which is lined to heat. Consequently, positive values of entropy quantity (ΔS) may have been an indication of an 226 enhanced disorder rate at the solid and liquid interface [37].   355 Table 1. Results of fitting the DY50 removal data to the Langmuir, Freundlich, and Temkin isotherms.
356 Table 2. Effect of adsorption dosage of chitosan-iso-vanillin on DY removal at pH 3.
358 Table 4. Thermodynamic parameters for DY removal on chitosan-iso-vamillin at different temperatures.