*3.5. E*ff*ect of Water Content*

Water content plays an important role in the hydrothermal synthesis of zeolites. It not only serves as a solvent during the crystallization process, but also regulates the formation of possible precursors of zeolite frameworks [34]. Hence, the crystallization of K-MER zeolite was studied at 180 ◦C for 14 h by varying the molar ratio of water from 100 to 280 (Table 1). At low water content (H2O/Al2O3 = 100: W-14), LTL crystalline phase was co-crystallized with the MER crystalline phase (Figure 9a). This observation could also be confirmed by the AAS spectroscopy results where the Si/Al ratio of solid was 2.82 indicating the mixing of both high silica (LTL) and low silica (MER) zeolites. The results were further supported by FESEM analysis where cylindrical nanorods of ca. 350 <sup>×</sup> 970 nm2, which were characteristic of LTL-type zeolite, were observed and grown together with the K-MER nanocrystals (Figure 10a). The LTL crystalline phase, however, slowly disappeared with increasing water content, indicating the direct influence of water on the crystallization of LTL-type zeolite. At higher H2O/Al2O3 ratios (196–280), zeolites of pure MER crystalline phase with different crystallite sizes and morphologies were obtained. As shown, the bundle-like MER-type zeolite particles made up of nanorod primary crystals (205 <sup>×</sup> 40 nm2) were captured at H2O/Al2O3 <sup>=</sup> <sup>196</sup> (Figures 9c and 10c: W-3). The nanocrystals grew further, and larger secondary crystals with wheatsheaf morphology were formed when the water content was further increased to H2O/Al2O3 = 280 (Figures 9d and 10d: W-16). The change of morphology and increment in particle size could be explained by the dilution of nutrient when the water content increased. As a result, the low concentration of nutrients in the synthesis medium favors the crystal growth more than nucleation process. Hence, particles with larger size and different morphology are formed [35].

**Figure 9.** XRD patterns of (**a**) W-14, (**b**) W-12, (**c**) W-3 and (**d**) W-16 samples prepared from an aluminosilicate precursor hydrogel with a composition of 7SiO2: 1Al2O3: 3.5K2O: *z*H2O with *z* = 100, 130, 196 and 280, respectively. All samples were heated at 180 ◦C for 14 h. The \* marks in (**a**,**b**) indicate the presence of the LTL crystalline phase.

**Figure 10.** FESEM images of (**a**) W-14, (**b**) W-12, (**c**) W-3 and (**d**) W-16 samples solids prepared using a gel precursor of 7SiO2:1Al2O3:3.5K2O: *z*H2O at 180 ◦C for 14 h where *z* = 100, 130, 196 and 280, respectively.
