. An acoustic fluidized bed consists of two layers: a bottom layer, comprising large agglomerates; and a top layer, comprising smaller agglomerates. SEM images indicate that the agglomerate sizes of the 5–10 nm SiO2 nanoparticles taken from the top and bottom layer is greater than that of the 5–10 nm SiO2 nanoparticles with surface modification. Therefore, the minimum fluidization velocity of 5–10 nm SiO2 nanoparticlesis greater than that of SiO2 nanoparticleswith surface modification.