# Optimization Study for the Desorption of Methylene Blue Dye from Clay Based Adsorbent Coating

^{1}

^{2}

^{3}

^{*}

## Abstract

**:**

## 1. Introduction

## 2. Materials and Methods

#### 2.1. Chemicals and Solution Used

_{2}, which were present in half amount to that of SiO

_{2}present in bentonite. The percentage of calcium carbonate was higher in the binder and also considered as a major content [15].

#### 2.2. Adsorption Study

_{e,sorption}(mg/g) = V(Ci − Ce)/M,

#### 2.3. Desorption Study

_{H}; Equation (4)) and chemical regeneration (Q

_{C}; Equation (5)) method are given below:

_{e,desorp}(mg/g) = V(C

_{f}/M),

_{H}% = (W

_{AA}− W

_{AR})/(W

_{AA}− W

_{BA}) × 100,

_{C}% = (Q

_{e, desorp}/q

_{e,sorption}) × 100,

_{f}is the MB concentration in the solvent (mg/L), W

_{AA}is the weight after adsorption (g), W

_{AR}is the weight after heating (g) and W

_{AB}is the weight before adsorption (g). The desorption efficiency is defined as the amount of dye desorbed from per gram of spent adsorbent at equilibrium.

#### 2.4. Optimization Study

_{1}), concentration (x

_{2}) and contact time (x

_{3}) and their interaction was studied using response surface methodology (RSM). RSM is a statistical method that uses quantitative data from appropriate experiments to determine regression model equations and operating conditions. The optimization process involves three process; conducting a statistically designed experiment, determining mathematical model coefficients and prediction of the response value and to check the adequacy of the developed model. The range and variable of the experiment is given in Table 1.

_{o}+ β

_{1}x

_{1}+ β

_{2}x

_{2}+ β

_{3}x

_{3},

_{o}+ β

_{1}x

_{1}+ β

_{2}x

_{2}+ β

_{3}x

_{3}+ β

_{11}x

_{1}

^{2}+ β

_{22}x

_{2}

^{2}+ β

_{33}x

_{3}

^{2}+ β

_{12}x

_{1}x

_{2}+ β

_{13}x

_{1}x

_{3}+ β

_{23}x

_{2}x

_{3},

_{1}, x

_{2}and x

_{3}are the coded values of three variables and β

_{o}, β

_{1}, β

_{2}, β

_{3}, β

_{11,}β

_{22,}β

_{32,}β

_{12}, β

_{13}and β

_{23}are the regression coefficient constants of the developed model, respectively. Fitting of the polynomial equation was determined using the R

^{2}value. The model terms were also determined from p-values with a 95% confidence level. The optimization of factors and their interaction was carried out using a main effect, interaction, Pareto charts, surface and contour plots.

#### 2.5. Characterization

## 3. Results and Discussion

#### 3.1. Desorption Study

#### 3.2. Optimization Study

_{1}), concentration (x

_{2}) and contact time (x

_{3}). The polynomial first order and interactive regression model equation was developed using the Minitab software. Therefore, model equations are shown in Equations (8) and (9).

_{1}+ 0.108x

_{2}+ 0.0574x

_{3}(R

^{2}= 0.973, p = 0.001),

_{1}+ 0.171x

_{2}+ 0.0062x

_{3}− 0.000060x

_{2}x

_{3},

^{2}= 0.982, p = 0.004).

_{1}

^{2}, x

_{2}

^{2}, x

_{3}

^{2}) and interactive terms (x

_{1}x

_{2}, x

_{1}x

_{3}) were insignificant (p > 0.05) and therefore removed from equation 7. This model describes that the concentration of MB (x

_{2}) had a great effect on the desorption efficiency of the dye followed by the temperature (x

_{1}), time (x

_{3}) and concentration–time interaction (x

_{2}.x

_{3}). According to Equation (9), the interaction of concentration–time (x

_{2}.x

_{3}) had a negative effect on the desorption efficiency whereas temperature (x

_{1}), concentration (x

_{2}) and time (x

_{3}) had a positive effect. The ANOVA table of the fitted model (Table 5) shows that the regression was with a p = 0.004, which thereby, confirms that the data model fits the experimental data.

#### 3.2.1. Main Effects

_{3}) between the solvent (HCl) and adsorbent coating had a great effect on the desorption of the dye, as is evident by the longer vertical line. However, the temperature (x

_{1}) of the solvent also plays an important role in the desorption process. Since the interaction between the dye and adsorbate coating is an electrostatic interaction (strongly bonded), therefore the dye cannot be able to desorb at a lower temperature, which resulted in a lower desorption efficiency. Whereas, the desorption efficiency at a higher temperature increases, which showed that the solubility and distribution coefficient of MB in the solvent increased. Moreover, increment in the desorption efficiency with respect to the concentration (x

_{2}) showed a high driving force for the mass transfer from the solid to liquid phase. Furthermore, the dye molecules tended to form an aggregate during the adsorption process, which resulted in a higher desorption efficiency.

#### 3.2.2. Interaction Plots

_{1}.x

_{2}, x

_{1}.x

_{3}, x

_{2}.x

_{3}) is shown in Figure 5. The interaction of concentration and time (x

_{2}.x

_{3}) were found to be statistically significant for the determination of Qe as compared to the temperature–concentration and temperature–time interaction. The effect of the interaction of concentration–time was found to be more significant at a lower temperature. However, the temperature–concentration and temperature–time interaction were more significant at a higher temperature and resulted in higher desorption efficiency (Qe).

#### 3.2.3. The Pareto Chart

_{1}), time (x

_{3}) and concentration (x

_{2})) and the interaction of concentration–time (x

_{2}x

_{3}) was found to be more significant at the 0.05 level. Whereas temperature–time (x

_{1}x

_{3}), temperature–concentration (x

_{1}x

_{2}) and temperature–concentration–time (x

_{1}x

_{2}x

_{3}) had a smaller effect and were not significant for desorption of MB from the adsorbent coating.

#### 3.2.4. Contour and Surface Plots

#### 3.3. Characterization

#### 3.4. Desorption Mechanism

## 4. Conclusions

## Author Contributions

## Funding

## Conflicts of Interest

## References

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**Figure 2.**Effect of solvents on the desorption of methylene blue dye (MB) from the clay adsorbent coating.

**Figure 3.**(

**a**) Predicted values vs. the experimental values for the desorption of MB from the clay adsorbent coating while (

**b**) Normal probability plot of the standardized residual.

**Figure 4.**Main effects plots (of temperature, concentration and time) for Qe for the desorption of MB from the clay adsorbent coating.

**Figure 5.**Interaction plots (of temperature–concentration, temperature–contact time, concentration–contact time) for the desorption of MB from the clay adsorbent coating.

**Figure 9.**Scanning electron micrograph of the (

**a**) adsorbent before adsorption, (

**b**) adsorbent after adsorption of MB and (

**c**) adsorbent after desorption of MB.

Factors | Low Level (–1) | High Level (+1) |
---|---|---|

(x_{1}) Temperature (°C) | 30 | 60 |

(x_{2}) Concentration (mg/L) | 50 | 100 |

(x_{3}) Contact time (min) | 15 | 150 |

Heating Temperature (°C) | Desorption Efficiency (%) |
---|---|

150 | 8.03 ± 1.07 |

160 | 8.14 ± 0.5 |

170 | 8.39 ± 0.67 |

190 | 8.99 ± 1.12 |

Experiment | Coded Values | Real Values | Desorption Efficiency (mg/g) | Predicted Values | ||||
---|---|---|---|---|---|---|---|---|

x_{1} | x_{2} | x_{3} | x_{1} | x_{2} | x_{3} | |||

1 | 1 | −1 | −1 | 60 | 30 | 15 | 10.293 | 10.016 |

2 | −1 | −1 | −1 | 30 | 30 | 15 | 2.302 | 2.606 |

3 | 1 | −1 | 1 | 60 | 30 | 150 | 10.493 | 10.610 |

4 | −1 | −1 | 1 | 30 | 30 | 150 | 3.293 | 3.200 |

5 | 1 | 1 | −1 | 60 | 100 | 15 | 23.169 | 21.923 |

6 | 1 | 1 | 1 | 60 | 100 | 150 | 20.560 | 21.950 |

7 | −1 | 1 | 1 | 30 | 100 | 150 | 15.965 | 14.540 |

Predictor | Coef | SE Coef | T | p |
---|---|---|---|---|

Constant | −10.031 | 2.499 | −4.10 | 0.026 |

x_{1} | 0.247 | 0.0364 | 6.78 | 0.007 |

x_{2} | 0.171 | 0.0246 | 6.96 | 0.006 |

x_{3} | 0.0062 | 0.017 | 0.36 | 0.007 |

x_{2 − }x_{3} | −0.000060 | 0.00023 | −0.26 | 0.011 |

Source | Seq SS | DF | Adj SS | Adj MS | F Value | p Value |
---|---|---|---|---|---|---|

Main effects | 381.740 | 3 | 381.740 | 127.247 | 53.29 | 0.004 |

Two-way interactions | 0.163 | 1 | 0.163 | 0.163 | 0.07 | 0.008 |

Regression | 381.903 | 4 | 381.903 | 95.476 | 39.99 | 0.006 |

Residual error | 7.163 | 3 | 7.163 | 2.388 | ||

Total | 389.066 | 11 |

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**MDPI and ACS Style**

Momina; Rafatullah, M.; Ismail, S.; Ahmad, A.
Optimization Study for the Desorption of Methylene Blue Dye from Clay Based Adsorbent Coating. *Water* **2019**, *11*, 1304.
https://doi.org/10.3390/w11061304

**AMA Style**

Momina, Rafatullah M, Ismail S, Ahmad A.
Optimization Study for the Desorption of Methylene Blue Dye from Clay Based Adsorbent Coating. *Water*. 2019; 11(6):1304.
https://doi.org/10.3390/w11061304

**Chicago/Turabian Style**

Momina, Mohd Rafatullah, Suzylawati Ismail, and Anees Ahmad.
2019. "Optimization Study for the Desorption of Methylene Blue Dye from Clay Based Adsorbent Coating" *Water* 11, no. 6: 1304.
https://doi.org/10.3390/w11061304