通过溶胶-凝胶法在金红石型纳米二氧化钛（TiO2）表面包覆二氧化硅（SiO2）薄膜,对纳米TiO2进行表面改性。通过优化聚乙烯吡咯烷酮（PVP）用量、硅钛比、氨水的用量确定最佳制备条件为：TiO2用量为0.3 g,PVP用量为0.4 g,硅钛比为2∶1,氨水用量为5 mL,获得了粒径小,SiO2包覆层薄,单分散性好的SiO2-TiO2复合纳米粒子。应用FT-IR,XRD,SEM,TEM和UV-vis等对改性前后的粒子进行表征。结果表明：红外光谱图中出现Si-O-Ti键的振动吸收峰,改性前后的纳米TiO2均为金红石型,SEM及TEM显示改性后的粒子团聚现象减弱,其表面形成了约10 nm的SiO2薄膜。经过表面改性,SiO2成功包覆在纳米TiO2表面,复合纳米粒子的光催化活性得到有效抑制,纳米TiO2作为防晒剂的安全性大大提高。将其制成基础防晒霜后,复合纳米粒子的SPF值提高了40%,防晒性能得到明显改善。
The rutile TiO2 nanoparticles were encapsulated with silicon dioxide （SiO2） film by sol-gel method. The preparation conditions were optimized by investigating the dosage of polyvinylpyrrolidone （PVP）, the molar ratio of silicon to titanium, and the dosage of aqueous ammonia. The optimized preparation conditions are as follows: the mass of TiO2 is 0.3 g, PVP dosage is 0.4 g, the molar ratio of silicon to titanium is 2∶1, and the dosage of aqueous ammonia is 5 mL. The SiO2-TiO2 composite nanoparticles with small size, thin SiO2 coatings and good monodispersity were thus obtained. The modified nanoparticles were characterized by FT-IR, XRD, SEM, TEM and UV-Vis. The results show that, the vibration absorption peak of Si-O-Ti bond appears at 963 cm-1 in IR spectrum of SiO2-TiO2 composite nanoparticles, which confirms that the surface of TiO2 nanoparticles are coated by SiO2 though covalent binding between Si-OH and Ti-OH to form Si-O-Ti. XRD analysis indicates that, several diffraction peaks attributed to rutile TiO2 still exist after the superficial modification of TiO2 nanoparticles by SiO2, and no new diffraction peaks exist. The TiO2 nanoparticles before and after modification are both rutile type. SEM and TEM show that the modified composite nanoparticles are more regular, and the particle size is approximately 50 nm. Moreover, the agglomeration phenomenon of composite nanoparticles is weakened, and the SiO2 film of thickness of approximately 10 nm is formed on the surface. Therefore, the surface of TiO2 nanoparticles has been successfully modified by SiO2 coatings. The photocatalytic activity of TiO2 nanoparticles and SiO2-TiO2 composite nanoparticles was tested by photodegradation of methylene blue as a probe reaction. The results show that, after surface modification, the photocatalytic activity of composite nanoparticles is effectively inhibited, and the safety of SiO2-TiO2 composite nanoparticles as a sunscreen is greatly improved. The results of UV reflectance show that, after surface modification, the UV transmittance of SiO2-TiO2 composite nanoparticles has been decreased, i.e., the UV blocking ability is enhanced. After introducing the composite nanoparticles into a basic formula of sunscreen, the SPF value of SiO2-TiO2 composite nanoparticles reaches 43.76, which is increased by 40% than that by adding TiO2 nanoparticles into the basic formula of sunscreen, and the sun protection performance is significantly improved.
