Effect of pH on the structural characteristics of in situ synthesized Ni-incorporated SBA-15 magnetic composites

Ni-incorporated SBA-15 magnetic composites were two-stage hydrothermal synthesized from initial strong acidic media through a pH-adjusting method. The structure, morphology, surface area and pore size distribution of the samples were systematically characterized by using XRD, FT-IR, SEM, TEM and N-2 physical adsorption techniques. It was found that, when pH was adjusted to 7, the obtained sample still could exhibit hexagonal mesostructure, very similar to that of the pristine SBA-15 except for a slightly reduced long-range ordering and surface area. However, an increase in the unit cell and wall thickness of the samples suggested the more Ni species were incorporated into the framework of SBA-15. A further increase in pH to 9 produced deterioration of long-range ordering of the sample, possibly resulting from the blocking of some mesopores. Thus, the pH-adjusting method played an important role on the structure of Ni-SBA-15 composites. Measurements taken with increasing applied field revealed the samples having superparamagnetic behaviors. Furthermore, the saturation magnetization values were increased with the more Ni species transforming into magnetic nanoparticles by the increasing pH.