Dynamic covalent Fe3O4 nanoparticles for dual-responsive Pickering emulsions triggered by pH and magnetism

In this study, we successfully synthesized silica coated Fe 3 O 4 nanoparticles (Fe 3 O 4 @SiO 2 NPs) and further animated their surface to create amino modified Fe 3 O 4 @SiO 2 (Fe 3 O 4 @SiO 2 -NH 2 ) NPs. By taking advantage of the pH-responsive dynamic (covalent) imine bond between the hydrophilic Fe 3 O 4 @SiO 2 -NH 2 NPs and the hydrophobic cinnamaldehyde molecule (R), we developed dynamic covalent Fe 3 O 4 @SiO 2 (Fe 3 O 4 @SiO 2 -R) NPs with switching wettability . These NPs were then utilized to form Pickering emulsions , and whose stability and pH/magnetic response were thoroughly investigated. As the NPs concentration in the emulsion increased, the emulsion stability initially improved but then subsequently slightly decreased. Emulsifiers exhibited emulsifying effect on various oil phases, with paraffin oil demonstrating the best effect. By adding Hydrochloric acid to the emulsion, we successfully broke the imine bond at a pH value of 2.8, resulting in demulsification. Applying a magnetic field also achieved demulsification. After five cycles of pH or magnetic response-induced emulsification and demulsification, a stable Pickering emulsion could still be obtained. Stimuli-responsive Pickering emulsions have been extensively studied, but there is limited research on double-responsive Pickering emulsions. This study presents a novel design of Pickering emulsions with pH/magnetic dual responsiveness, offering great potential for oil-water separation applications.