The fabrication and self-flocculation effect of hybrid TiO ₂ nanoparticles grafted with poly(N-isopropylacrylamide) at ambient temperature via surface-initiated atom transfer radical polymerization

This article reports on the fabrication of hybrid titanium dioxide (TiO ₂) nanoparticles grafted with thermoresponsive poly(N-isopropylacrylamide) (PNIPAM) and their self-flocculation effect caused by the thermal phase transition and entanglement behavior of PNIPAM. Surface-initiated atom transfer radical polymerization (ATRP) of N-isopropylacrylamide (NIPAM) was conducted rapidly (within a few minutes) in aqueous solution at ambient temperature by using CuBr/N,N,N′, N′′,N′′-pentamethyldiethylenetriamine (PMDETA) as the catalysts and started from the surface of TiO ₂ nanoparticles derivatized with ATRP initiators. Without purifying the inhibitor, the grafted PNIPAM gives low molecular weights (M _n < 3000) and a narrow molecular weight distribution (PDI < 1.1) determined by GPC detection, which gives the hybrid TiO ₂-PNIPAM both a self-flocculation effect with rapid response to temperature, and a temperature-controlled switching effect of the degradation of Rhodamine B in solution. Moreover, the hybrid TiO ₂-PNIPAM exhibits a particular dispersion effect at ambient temperature in aqueous solution caused by the hydrophilicity and the entanglement interaction of the grafted PNIPAM. These effects for hybrid TiO ₂-PNIPAM provide a new way to re-use TiO ₂ nanoparticles for pollutant degradation systems and to avoid secondary pollution effectively due to the thermal phase transition and entanglement behavior.