**3. Results and discussion**

### **3.1 Morphology and physiochemical properties of composite photocatalyst**

**Figure 1** shows the synthesizing of cockle and mussel shells into powder form. Raw waste shells were crushed into smaller sizes that are allowable for the milling process, where CaCO3 powder was obtained, as shown in **Figure 1a** and **b**, respectively. After 4 hours of calcination at 950°C, the composite powder converted into CaO powder as shown in **Figure 1c**, and was used as an adsorbent for MB removal. The difference in color shows each shell has its appearance throughout the whole process. An investigation of mass reduction on both samples after calcination was performed, and

**Figure 1.** *(a) Raw waste shells, (b) powder shells before, and (c) after the calcination process to produce CaO.*

*Mollusk Shell Waste as Composite Photocatalyst for Methylene Blue Removal DOI: http://dx.doi.org/10.5772/intechopen.109857*

it was discovered that the mass for CCS reduced to 5.56 g from 10.06 g, while CMS depleted from 10.08 to 5.12 g, both shells proved to lose half of its mass after conversion of CaO. A similar finding was observed in a study of MgCO3 conversion to MgO, the mass loss was 50% approximately at a calcination temperature equal to or higher than 700°C, independent of the duration [19].

FT-IR analysis was performed on both shells to identify the composite formed before and after calcination as shown in **Figure 2**. Uncalcined cockle shell as proved in **Figure 2a** has a peak of C-O bond at 1438 cm−1 wavelength that comes in a group with a few bands at 1088, 861, and 714 cm−1 representing carbonate ion, CO3 2− with aragonite microstructure [20] indicating the CaCO3 presence before calcination. This result slightly corresponds to Ref. [21] with sharp bands found around 1450, 1080, 858, and 712 cm−1.

Situated at the peak of 939 and 1438 cm−1 in the calcined cockle shell band (**Figure 2b**), the C-O bonds seem to lose their former strength as the

CO3 2− presence is gradually lost in the calcination process, which causes the shifting in the mentioned peak. This discovery occurred due to dissipation in the reduced mass of the functional group associated with CO3 2− ion [22]. The same theory applied to uncalcined mussel shells concerning that both shells are one of the few types of mollusk shells.

As for the uncalcined mussel shell, as shown in **Figure 2c**, the C-O bonds were observed at 1442, 1077, 853, and 711 cm−1 peaks except there is a slight difference in the intensity of these peaks compared to **Figure 2a**, which have a stronger intensity of C-O content. The calcined cockle shell lost its C-O functional group, where the peak intensity of 924 and 1449 cm−1 is weakening (**Figure 2d**). According to Sari et al., [12], the functional group of CaO was formed starting at a temperature of 750°C, which is agreeable with this study as the CaO bond was formed at 656 cm−1 still in the range of 667.32 cm−1 from their characterization results.

The morphological structures of a mussel shell, mussel/TiO2, cockle shell, and cockle/TiO2 composite photocatalyst were examined by SEM as shown in **Figure 3**. TiO2 appeared as fine particles (**Figure 3c** and **d**), whereas the cockle and mussel shell is more prominent due to the micro-sized particles and exhibits irregular shape and size (**Figure 3a** and **b**). The particle sizes of mussel and cockle shells were bigger than mussel/TiO2 and cockle/TiO2 composite photocatalysts due to the integration of TiO2 in nanoparticles size. Besides, it has been established that the TiO2 and mollusk shell particles bonded together and formed a composite photocatalyst following the calcination process.

*SEM analysis for (a) cockle shell, (b) mussel shell (c) cockle shell/TiO2, and (d) mussel shell/TiO2 composite photocatalyst.*

*Mollusk Shell Waste as Composite Photocatalyst for Methylene Blue Removal DOI: http://dx.doi.org/10.5772/intechopen.109857*

**Figure 4.**

*(a) Normalized absorption and photocatalytic activity for (a) mussel and cockle shell, (b) for composite photocatalyst, and (c) percentage MB removal.*
