*3.8.3 Effect of contact time*

The effect of contact time on the grafted pine magnetite composite with acrylamide for the adsorption of methylene blue is shown in **Figure 8**. The adsorption experiment was done at 100 mg/L concentration. The adsorption rate of the grafted composite on the removal of MB is faster from the beginning which might be influenced by the grafted composite with higher specific gravity which makes them better in dispersity and more efficient contact with MB. The adsorption capacity of the grafted composite is higher due to its high surface area.

equilibrium at constant temperature [24, 25]. To successfully obtain the adsorptive behaviour of any substance from the liquid to the solid phase, it is important to have a satisfactory description of the equilibrium state between two phases composing the adsorption system. Langmuir and Freundlich isotherms are the well-known isotherms which have been used to describe the equilibrium of adsorption systems. Typically, the Langmuir model describes the monolayer sorption on a surface containing a limited number of sites and predicting a homogeneous distribution of sorption energies [25]. Freundlich describe the heterogeneity distribution. The results of the MB concentration dependence study were subjected to analyses by

*Characterization of Grafted Acrylamide onto Pine Magnetite Composite for the Removal…*

*DOI: http://dx.doi.org/10.5772/intechopen.92114*

The theoretical Langmuir isotherm is represented by the following equation:

where *qe* is the amount of dye adsorbed at the equilibrium time (mg/g), *Ce* is the

empirical constant. The parameters of the isotherm models are calculated from the

**Table 2**. The results show *R*<sup>2</sup> values for the Langmuir are higher than those of Freundlich isotherm model. This implies that the equilibrium adsorption data comply with the Langmuir isotherm, suggesting that the adsorption process occurs in a homogeneous surface. Also, it can be stated that the results demonstrate no interaction and transmigration of dyes in the plane of the neighboring surface [26].

(mg/g) and *KL* is the Langmuir adsorption equilibrium constant (dm3

where *KF* is the equilibrium adsorption coefficient (dm3

experimental data and the values of correlation coefficient (*R*<sup>2</sup>

*Ce=qe* ¼ 1*=qmKL* þ *Ce=qm* (1)

Log *qe* ¼ log *KF* þ 1*=n* log *Ce* (2)

/mg), *qm* is the maximum adsorption capacity

/mg).

) are demonstrated in

/mg) and 1/*n* is an

using Langmuir and Freundlich isotherm models.

*Effect of contact time at 100 mg/L on the MB adsorption of the GACA.*

Freundlich linear expression was represented by:

equilibrium dye concentration (dm<sup>3</sup>

**Figure 8.**

**167**

### **3.9 Adsorption isotherms**

The adsorption isotherm explains the relationship between an adsorbate in the liquid phase and the adsorbate adsorbed on the surface of the adsorbent at

**Figure 7.** *Effect of adsorbent dose on the adsorption of MB.*

*Characterization of Grafted Acrylamide onto Pine Magnetite Composite for the Removal… DOI: http://dx.doi.org/10.5772/intechopen.92114*

**Figure 8.** *Effect of contact time at 100 mg/L on the MB adsorption of the GACA.*

equilibrium at constant temperature [24, 25]. To successfully obtain the adsorptive behaviour of any substance from the liquid to the solid phase, it is important to have a satisfactory description of the equilibrium state between two phases composing the adsorption system. Langmuir and Freundlich isotherms are the well-known isotherms which have been used to describe the equilibrium of adsorption systems. Typically, the Langmuir model describes the monolayer sorption on a surface containing a limited number of sites and predicting a homogeneous distribution of sorption energies [25]. Freundlich describe the heterogeneity distribution. The results of the MB concentration dependence study were subjected to analyses by using Langmuir and Freundlich isotherm models.

The theoretical Langmuir isotherm is represented by the following equation:

$$\mathbf{C}\_{\epsilon}/q\_{\epsilon} = \mathbf{1}/q\_{m}K\_{L} + \mathbf{C}\_{\epsilon}/q\_{m} \tag{1}$$

where *qe* is the amount of dye adsorbed at the equilibrium time (mg/g), *Ce* is the equilibrium dye concentration (dm<sup>3</sup> /mg), *qm* is the maximum adsorption capacity (mg/g) and *KL* is the Langmuir adsorption equilibrium constant (dm3 /mg). Freundlich linear expression was represented by:

$$\text{Log}\,q\_{\epsilon} = \log K\_F + \mathbf{1}/n \text{ log C}\_{\epsilon} \tag{2}$$

where *KF* is the equilibrium adsorption coefficient (dm3 /mg) and 1/*n* is an empirical constant. The parameters of the isotherm models are calculated from the experimental data and the values of correlation coefficient (*R*<sup>2</sup> ) are demonstrated in **Table 2**. The results show *R*<sup>2</sup> values for the Langmuir are higher than those of Freundlich isotherm model. This implies that the equilibrium adsorption data comply with the Langmuir isotherm, suggesting that the adsorption process occurs in a homogeneous surface. Also, it can be stated that the results demonstrate no interaction and transmigration of dyes in the plane of the neighboring surface [26].

With increasing pH, the number of hydrogen ions i solution was reduced and the

competitive effect, repulsive interaction weakened, lead to an increase in the removal rate. The MB removal rate became stable when the pH reached 12, where the higher percentage removal for MB was observed in comparison to other pH

**Figure 7** shows the effect of adsorbent dose on the percentage removal and amount of dye that was adsorbed. This effect was necessary in order to observe how the novel adsorbent used impacted on the adsorption stoichiometry. It also gave an idea of the propensity of dye molecules to be adsorbed with the smallest amount of adsorbent. When the mass of the adsorbent was 0.5 g, the percentage adsorption removal increased rapidly, which contributed to the increased surface area of the adsorbent which in turn increased the number of binding sites [23]. The adsorption capacity decreased as the amount of adsorbent GACA increased because more active sites were available for the adsorption of dye, which resulted in more interactions between dye and adsorbent thus increasing the MB percentage removal.

The effect of contact time on the grafted pine magnetite composite with acrylamide for the adsorption of methylene blue is shown in **Figure 8**. The adsorption experiment was done at 100 mg/L concentration. The adsorption rate of the grafted composite on the removal of MB is faster from the beginning which might be influenced by the grafted composite with higher specific gravity which makes them better in dispersity and more efficient contact with MB. The adsorption capacity of

The adsorption isotherm explains the relationship between an adsorbate in the

liquid phase and the adsorbate adsorbed on the surface of the adsorbent at

At mass 0.5 g the highest percentage removal of 99.8% was achieved.

the grafted composite is higher due to its high surface area.

values.

*3.8.2 Effect of adsorbent dose*

*Waste in Textile and Leather Sectors*

*3.8.3 Effect of contact time*

**3.9 Adsorption isotherms**

**Figure 7.**

**166**

*Effect of adsorbent dose on the adsorption of MB.*


as the desorbing agent. Observation showed that there was a gradual reduction from 29.8% to 14.03% after cycle 4. The results explain that the higher adsorption capac-

*Characterization of Grafted Acrylamide onto Pine Magnetite Composite for the Removal…*

The study showed that acrylamide was successfully grafted onto pine magnetite composites. FT-IR, BET, SEM, TEM and XRD characterization provided sufficient evidence to demonstrate the incorporation and distribution of the iron oxide nanoparticles within the polymer matrix. GACA nanocomposites were shown to be effective in the adsorption of methylene blue at a pH of 12. The role of adsorbent dose and contact time demonstrated excellent results in the adsorption of methylene blue due to the increased surface area and high rate of the adsorption were achieved. The adsorption data was adequately interpreted by Langmuir and Freundlich isotherm models respectively. It was found that Langmuir isotherm

ity proves the adsorbent to be a good adsorbent for the removal of MB.

We are grateful to Prof E.N. Nxumalo and Mr S.A. Zikalala for their contributions on the study. Vaal University of Technology and National Research

Kgomotso N.G. Mtshatsheni\*, Bobby E. Naidoo and Augustine E. Ofomaja Department of Chemistry, Vaal University of Technology, Vanderbijlpark,

© 2020 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ by/3.0), which permits unrestricted use, distribution, and reproduction in any medium,

\*Address all correspondence to: kgomotsom@vut.ac.za

provided the original work is properly cited.

Foundation of South Africa are thanked for financial support.

**3.11 Conclusions**

model gave the best equilibrium fit.

*DOI: http://dx.doi.org/10.5772/intechopen.92114*

**Acknowledgements**

**Author details**

South Africa

**169**

**Table 2.**

*Isotherm parameters for methylene blue dye adsorption on GACA.*

Higher *Kf* value for GACA indicates a higher adsorption capacity for methylene blue and a value of *n* > 1 indicates favorable adsorption conditions [27, 28].

### **3.10 Desorption and regeneration**

The main goal of desorption studies is the competitiveness of adsorbents reusability in the multiple adsorption or desorption cycles and their beneficial potential in practical and economical applications. Desorption studies were performed with 0.01 M, 0.05 M and 0.1 M HCl. Typically, 1 g of PMC saturated with 100 mg/L of MB was placed in different desorption solutions and constantly stirred in a water bath at 200 rpm for 2 h. The adsorbent solutions were centrifuged and analysed using UV-VIS spectrophotometer. **Figure 9(a)** demonstrates the effect of eluent concentrations on MB dye desorption efficiency. It was observed that desorption efficiency increased with increase in the eluent concentration even though the shift is small in percentage. The maximum desorption percentage was found at 0.1 M HCl (99.8%) whereby 0.01 M HCl showed the minimum desorption efficiency (98.8%). An increase in HCl concentration resulted in an increase in H<sup>+</sup> ions concentration which led to a subsequent increase in dye desorption efficiency.

Regeneration shows the competitiveness of the adsorbent where it expresses the good reusability and recycling abilities. **Figure 9(b)** demonstrates the possibility of regeneration and reusability of the grafted pine magnetite composite with acrylamide. Adsorption-desorption reaction cycles were repeated 4 times using 0.1 M HCl

*Characterization of Grafted Acrylamide onto Pine Magnetite Composite for the Removal… DOI: http://dx.doi.org/10.5772/intechopen.92114*

as the desorbing agent. Observation showed that there was a gradual reduction from 29.8% to 14.03% after cycle 4. The results explain that the higher adsorption capacity proves the adsorbent to be a good adsorbent for the removal of MB.
