**3.7 Point zero charge (pHpzc)**

To further investigate the effects of modifications on the suitability of the synthesized materials for adsorption, the isoelectric point or point of zero charge (pHpzc) was determined. The solution pH is an important parameter for dye adsorption because it does not only change the surface charge of the adsorbent but also it affects the molecular structure of the dye. As MB is a cationic dye, it can easily form positively charged species over a wide pH range. The solid addition method was used to determine the pHpzc of the pine cone composite. To a series of 100 cm<sup>3</sup> volumetric flasks, 45 cm<sup>3</sup> of 0.01 mol/dm<sup>3</sup> KNO3 solution were transferred. The pHi values of the solutions were roughly adjusted between pH 2 and 12 by the addition of either 0.1 mol/dm3 HCl or NaOH on a pH meter with constant stirring. The total volume of the solution in each flask was made up to 50 cm3 by the addition of KNO3 solution of the same strength. The pHi of the solutions was accurately noted, and 0.1 g of pine cone composite were added to each volumetric flask, which was then immediately closed. The suspensions were allowed to equilibrate for 48 h on a shaker operating at 200 rpm. The pHf values of the supernatant were accurately noted and the difference between the initial and final pH values (ΔpH = pHf – pHi) were plotted against the pHi. The solution pH is an important parameter for


**Table 1.**

*BET surface area and pore characteristics for synthesized materials.*

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

dye adsorption because it does not only change the surface charge of an adsorbent, but it also reflects the molecular structure of the dye.

Changes in the point of zero charge values within the sample can be attributed by the difference in types and amounts of surface functional groups present on the surface of the adsorbent. pHpzc is observed when modification on the suitability of the synthesized materials is determined. It is known to be the pH at which the amount of positive charges on a biosorbent surface equals the amount of the negative charge, i.e., the pH at which the biosorbent surface has net electrical neutrality [21, 22]. Methylene blue is a cationic dye and can easily form positively charged species over a wide pH range. The pHpzc of pine magnetite composite was found to be 8.56 and grafted pine magnetite with acrylamide was found to be 6.2. The decrease in the pHpzc is attributed to the modification of the surface area.

### **3.8 Adsorption studies**

because of the graft copolymerization process and incorporation iron oxide magnetite. Supporting information showed the granular smooth surface. Roughness of the surface increased after modification, better matrix coherence was achieved after incorporation of the iron oxide magnetite nanoparticles. All the observations confirmed that grafting pine magnetite composite with acrylamide allows better compatibility. The presence of the Fe peak in the EDX of the nanocomposite showed successful incorporation of iron oxide composite in the polymer matrix **Figure 5(c)**.

A surface property of an adsorbent describes the effect of modification on the surface area of the adsorbent. **Table 1** shows comparison of the effect of modification on the surface area of the materials. The pure pine magnetite nanoparticles

25.86 nm. On the other hand, the NaOH treated pine had a surface area of 2.25 m<sup>2</sup>

pine cone structure which was found to be important for the improvement of mass diffusion and adsorptive capacity. An increase in surface area, pore volume and pore size confirmed that GACA can adsorb MB more efficiently than the PMC. The

To further investigate the effects of modifications on the suitability of the synthesized materials for adsorption, the isoelectric point or point of zero charge (pHpzc) was determined. The solution pH is an important parameter for dye adsorption because it does not only change the surface charge of the adsorbent but also it affects the molecular structure of the dye. As MB is a cationic dye, it can easily form positively charged species over a wide pH range. The solid addition method was used to determine the pHpzc of the pine cone composite. To a series of 100 cm<sup>3</sup> volumetric flasks, 45 cm<sup>3</sup> of 0.01 mol/dm<sup>3</sup> KNO3 solution were transferred. The pHi values of the solutions were roughly adjusted between pH 2 and 12 by the addition of either 0.1 mol/dm3 HCl or NaOH on a pH meter with constant stirring. The total volume of the solution in each flask was made up to 50 cm3 by the addition of KNO3 solution of the same strength. The pHi of the solutions was accurately noted, and 0.1 g of pine cone composite were added to each volumetric flask, which was then immediately closed. The suspensions were allowed to equilibrate for 48 h on a shaker operating at 200 rpm. The pHf values of the supernatant were accurately noted and the difference between the initial and final pH values (ΔpH = pHf – pHi) were plotted against the pHi. The solution pH is an important parameter for

> **NaOH treated pine**

Ave. pore size (nm) 25.86 10.17 23.10 17.33

/g) 113.60 2.25 54.80 57.77

/g) 0.6321 0.0177 0.1522 0.1591

**Pine magnetite composite (PMC)**

**Grafted acrylamide**

23.10 nm. Grafted acrylamide reflected the surface area of 57.77 m<sup>2</sup>

distinct pore structure size enables fast transportation of particles.

/g, pore volume of 0.6321 cm<sup>3</sup>

/g, pore volume of 0.1522 cm3

/g and pore size of 17.33 nm. The higher surface area was due to the

/g and pore size of 10.17 nm. Pine magnetite composite

/g and pore size of

/g and pore size of

/g, pore volume

/g,

**3.6 BET (surface area) analyses**

*Waste in Textile and Leather Sectors*

showed a surface area of 113.60 m<sup>2</sup>

exhibited surface area of 54.80 m<sup>2</sup>

**3.7 Point zero charge (pHpzc)**

**Properties Pure magnetite**

Surface area (m2

Pore volume (cm<sup>3</sup>

**Table 1.**

**164**

**composite**

*BET surface area and pore characteristics for synthesized materials.*

pore volume of 0.0177 cm<sup>3</sup>

of 0.1591 cm<sup>3</sup>

#### *3.8.1 Effect of solution pH*

The adsorption experiments were carried out using batch equilibration techniques. Various methylene blue (MB) solutions with different pH range, initial concentrations and mass dosage were prepared by diluting 1000 mg/dm<sup>3</sup> . Equilibrium experiments, to determine the adsorption capacity of pine magnetite composite were conducted using 250 cm<sup>3</sup> bottles. 0.1 g of PMC and 100 cm<sup>3</sup> of the MB solution were added and shaken for 2 h at 26°C. Thereafter, absorbance was determined using UV-VIS spectrophotometer at the wavelength corresponding to the maximum absorbance (*λ*max = 665 nm) as determined from the plot. This wavelength was used for measuring the absorbance of residual concentration of MB. pH of the solution was adjusted using 0.1 M HCl and 0.1 M NaOH. **Figure 6** showed the effect of pH on the adsorption of MB. An increase in pH showed an increase in percentage removal. When the pH was 2.0 and 4.0, the removal rate of MB was 99.4 and 99.5%, respectively. This indicated that the lower adsorption of MB at acidic pH was due to the presence of excess H<sup>+</sup> ions. The influence of low pH to MB adsorption was that H<sup>+</sup> ions could occupy the binding sites; this was not favorable for the adsorption of MB. Furthermore, MB possessed positive surface charges and could be repulsed by H+ ions to prevent MB adsorption onto grafted pine magnetic composite.

**Figure 6.** *Effect of pH on the adsorption of MB.*

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 values.
