| The human body receives a large amount of ultraviolet radiation for a long time,whic h can cause serious skin damage,such as erythema,immunosuppression and skin cancer.Sunscreen is a commonly used sunscreen product in summer,and its main active ingredient is titanium dioxide(TiO2).TiO2 can effectively shield ultraviolet radiation,but it has strong photocatalytic activity and can catalyze oxygen in tbe air to produce superoxide radicals with strong oxidation.Long-term application of sunscreen containing TiO2 will make people’s skin rough,resulting in erythema,cuticle hardening and so on.The chemical properties of(silica)SiO2 are stable.The surface of TiO2 is coated with SiO2 to prevent the direct contact between TiO2 and skin.It can effectively prevent the damage of TiO2 to skin in sunscreen.In this study,hollow SiO2 microspheres were synthesized by hydrolysis and polymerization of tetraethyl orthosilicate(TEOS)as silicon source,polyacrylic acid(PAA)aggregates formed in ethanol as template.The hollow SiO2 microspheres were characterized by XRD,FT-IR,DLS and TEM.The effects of reaction conditions on the morphology of hollow SiO2 microspheres were investigated by controlling the concentrations of PAA,ammonia and TEOS.The results showed that the concentration of PAA,ammonia and TEOS had a significant effect on the particle size and wall thickness of the hollow SiO2 microspheres.The concentration of PAA is a variable.As the concentration of PAA increases from 0.21 mM to 0.79 mM,the particle size of hollow TiO2 microspheres gradually increases from 110 nm to about 460 nm.When the ammonia concentration is a variable,the hollow structure of the hollow TiO2 microspheres becomes more obvious as the ammonia concentration increases.When the ammonia concentration is less than 0.40 M,solid TiO2 is obtained;when the ammonia concentration is continuously increased,the hollow TiO2 microspheres have a good hollow structure and the surface is smooth,and no secondary particles adhere to the surface;when the ammonia concentration exceeds 1.14 M,the particle size of the obtained hollow sphere becomes small.When the concentration of TEOS is a variable,the wall thickness of hollow TiO2 microspheres increases with the increase of TEOS concentration..The hollow TiO2@TiO2 microspheres were synthesized by hydrolysis and polymerization using tetrabutyl titanate(TBOT)as a titanium source.Hollow SiO2@TiO2 microspheres was characterized by XRD,TEM,DLS and solid ultraviolet spectrophotometer.The effects of calcination temperature and TBOT on the crystal shape and UV shielding properties of hollow TiO2@TiO2 microspheres were investigated.The results show that SiO2 has the effect of inhibiting the crystal transformation of TiO2.When the mass fraction of TiO2 increases,the hindrance becomes weaker.When the mass fraction of TiO2 accounts for 20%of hollow TiO2@TiO2 microspheres,the crystal form is rutile after calcination at 900℃ and the UV shielding effect is close to that of pure TiO2.Hollow TiO2@TiO2@TiO2 microspheres were synthesized by hydrolysis and polymerization using TEOS as a silicon source.It was characterized by XRD,TEM,DLS and solid ultraviolet spectrophotometer.The effect of TEOS on U V shielding performance and photocatalytic performance was investigated.The results show that the amount of TEOS does not have much influence on the UV shielding properties of hollow TiO2@TiO2@TiO2 microspheres hollow spheres,but the more coating,the more inhibiting the photocatalytic activity of hollow TiO2@TiO2@SiO2 microspheres.The hollow TiO2@TiO2@TiO2 microspheres synthesized in this study can not only shield the.ultraviolet rays,but also inhibit the photocatalytic activity of TiO2.Hollow TiO2@TiO2@SiO2 microspheres has low TiO2 content,low cost,good stability and non-toxicity,and can be widely used in the field of ultraviolet shielding. |
PDF Full Text Request