CO₂-responsive Pickering Emulsifier And Its Application In Heterogeneous Catalytic Reaction

Stimuli-responsive Pickering emulsion has potential applications in Pickering emulsion polymerization,catalyst recycling,cosmetic and personal care products.Functional nanoparticles designed for stabilizing emulsions and destabilizing emulsions as CO2-responsive emulsifier,and for transesterification of soybean oil with methanol as solid base catalyst.The mono-functional particles SiO2-G were synthesized by attaching guanidine onto fumed silica surface.Bi-functional particles SiO2-GCn(n=8,12,16)were obtained by attaching both guanidine and alkyl chain onto the surface of silica to further improve the wettability of the particles.SiO2-G and SiO2-GC 16 were used as emulsifier for toluene-water biphasic system.The influences of particles concentration,oil-water fraction,NaCl concentration and CO2 on Pickering emulsion properties were investigated.Although the functional particles did not decrease the surface and interfacial tensions of the air/oil-water interfaces,Pickering emulsions could be acquired.Increasing the'particles concentration reduces the emulsion droplet diameter until reaching the critical particle mass fraction(CFM).The volume fraction of the oil phase(cp)had an impact on the volume fraction of the emulsion.The volum fraction of the emulsion increased as the volume fraction of the toluene increased.But the emulsion would be unstable when ? exceeded 0.7,which indicated the maximum emulsion volume exsited at cp = 0.7.Addition of salt led to a decreasing of the zeta potential of particles and the emulsion stability increased.Additionally,phase inversion occurred for emulsions stabilized by SiO2-GC16 particles at 5000 mM salt concentration.The stabilization-destabilization cycles of the Pickering emulsion could be easily and successively controlled in several times by CO2/heating due to the protonation-deprotonation of guanidine groups on the particle surfaces.The functional particles SiO2-G and SiO2-GCn(n=8,12,16)can function as emulsifier and catalyst simultaneously for soybean oil-methanol biphasic systems.It was called Pickering Interface Catalyst(PIC).Experiments proved that the SiO2-G particles can function well as Pickering interface catalyst for the transesterification of soybean oil with methanol.SiO2-GC 16 improved emulsion stability while greatly reduced the catalytic activity.The catalytic activity of SiO2-GC8 and SiO2-GC 12 particles equaled to SiO2-G particles.