Adsorption of benzyldimethyldodecylammonium bromide on silica nanoparticles in water

Adsorption of the cationic surfactant benzyldimethyldodecylammonium bromide (BDDABr) on silica nanoparticles with ~ 12 and 31 nm in size (denoted as S-SiO 2 and L-SiO 2 , respectively) is investigated at various solid dosages ( C s , 10–40 g/L), pH (3–10), and temperature ( T , 298–308 K). No C s -effect is observed in the adsorption. However, it is interestingly found that, besides pH and T , the size of the silica particles has an obvious influence on the adsorption. The adsorption may show the Langmuir type (L-type), S-type, and “double plateau” type (LS-type) isotherms, depending on silica particle sizes and pH. Increasing pH may lead to a change in the isotherm types from S-type through LS-type to L-type. The S-type and LS-type isotherms can be adequately described using the one-step and two-step surface micellization models, respectively. The affinity of the S-SiO 2 toward BDDABr is lower than that of the L-SiO 2 , consistent with the dissociation tendency of their surface hydroxyl groups. Graphical abstract Adsorption of BDDABr on SiO 2 in water is affected by the size of SiO 2 particles besides pH and temperature. The affinity of small SiO 2 toward BDDABr is lower than that of large SiO 2 , which is consistent with the dissociation tendency of their surface hydroxyl groups.