Besides, nearly all the peaks observed on Acid-B–SBA–K moved to the lower
wavernumbers, which indicated that the surface of B–SBA–K had
been modified by unsaturated groups, and revealed that the
oxidation of HNO3 produced marked chemical modifications on
B–SBA–K. The change in the surface, in particular the unsaturated
groups, contributed to the increased adsorption capacity of metal
ions.