Fabrication Of SiO₂-TiO₂Composite Materials On Modified SiO₂Nanospheres Using ARGET ATRP

In this work, a tunable-void SiO2-TiO2composite materials were successfullyprepared using SiO2-polymethyl methacrylate (PMMA)-polyoligo(ethylene glycol)methyl ether methacrylate (PO(EO)nMA)(n=2,5and8) as the template and usingtetrabutyl titanate (TBT) as the titanium source. The synthetic process was carried out inthree steps. First, the halogen-functional ATRP initiators were immobilised on250nmSiO2nanoparticle surfaces prepared by the St ber method. Secondly,SiO2-PMMA-b-PO(EO)nMA microspheres were synthesized by applying activatorsregenerated by electron transfer atom transfer radical polymerization (ARGET ATRP)grafting methyl methacrylate (MMA), and oligo (ethylene glycol) methyl ethermethacrylate (O(EO)nMA) with different EO number from the surface of thehalogen-functional of SiO2. Thirdly, TBT hydrolysis using SiO2-PMMA-b-PO(EO)nMAas the template, the hydrolyzed TBT molecules can preferentially interact with thePO(EO)nMA (n=5and8) units of the amphiphilic copolymer through hydrogenbonding rather than with the PMMA blocks because of the strong stereohindrance effect.SiO2-TiO2composite materials were acquired through the calcination process to removethe polymer PMMA-b-PO(EO)nMA, and crystallization of amorphous TiO2change toanatase phase.A series of characterizations (1H NMR，XPS，TEM/SEM) indicated that theamphiphilic block copolymer PMMA-b-PO(EO)nMA were grafted onto SiO2nanoparticle surfaces. The thickness of PMMA polymer layer was about10nm, Mn=42800g mol1and the molecular weight distribution was narrow(Mw/Mn=1.32). Thethickness of the PMMA-PO(EO)nMA polymer layer were16,19and21nm when thenumber of EO were2,5and8, respectively. The resultant copolymers shifted towardhigher weight (54300,62100, and75400g mol1) with increased of EO number afterblock copolymerization of PO(EO)nMA. The titania samples existed only in the anatasephase, the presence of SiO2stabilized the anatase phase of TiO2even at hightemperatures, HRTEM and the nitrogen adsorption desorption indicated the preparedSiO2-TiO2composite materials had hierarchically nanoporous structures. The gradienthydrophilicity of the PMMA-b-PO(EO)nMA copolymer template facilitated thehydrolysis of TBT molecules along the PO(EO)nMA to PMMA segments, therebytuning the space between the core and shell. In addition, the space was about6nm when the EO number was2, and the space was about10nm when the EO numbers were5and8. The photocatalytic activity of the SiO2-TiO2materials had been tested on thephotodegradation of methyl orange, the percent degradation of methyl orange onSiO2-TiO2sample(n=2,450°C) reached93%, higher than other samples after5h. TheSiO2-TiO2samples calcinated at450°C exhibited lower photocatalytic activity thanSiO2-TiO2composite nanoparticles calcinated at800°C. This indicates that surface areaand the degree of crystallinity of TiO2are all significant factors in the photocatalyticactivity.The method and mechanism for preparing SiO2-PMMA-PO(EO)nMA andSiO2-TiO2can be extended to other tunable inter-lamellar voids of composite materialsand provided an improved method, thereby expanding its application scope.