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Graphical abstract Abstract A foam with high stability for the efficient decontamination of radioactive materials has been prepared by using well-dispersed mesoporous silica nanoparticles (NPs). Three different types of silica NPs were tested: solvent-extracted mesoporous silica (SMS) NPs, calcined mesoporous silica (CMS) NPs, and commercial silica (M-5) NPs. The stability and decontamination efficiency of the foam prepared using SMS NPs was higher than those using other silica NPs. The liquid volume in the foam with the SMS NPs are 10–25 times greater than those containing the CMS and M-5 NPs. The stability of the decontamination foam consisting of SMS NPs is higher because of its higher viscosity; the SMS NPs sample contains a larger number of particles per unit volume and has smaller particle sizes than the CMS and M-5 NPs samples. To investigate the dispersion-agglomeration properties of the silica NPs, the size distributions of the silica NPs in the decontamination foam solutions were determined by using dynamic light scattering. The SMS NPs are smaller than the CMS and M-5 NPs in the decontamination foam solution. For stainless steel 304 and carbon steel specimens corroded with the radionuclide 60Co, decontamination foams containing SMS NPs were found to exhibit a decontamination efficiency 20–40% greater than those of the foams containing the other silica NPs. This superior efficiency arises because the foams prepared with SMS NPs exhibit improved stability and their liquid component can hold larger amounts of the decontamination agent. [ABSTRACT FROM AUTHOR]