Preparation Of Photocatalytic Material SiO₂/N-TiO₂ And Its Application In Cement-based Materials

Photocatalytic materials can degrade organic pollutants under light conditions,and the reaction products are non-toxic and harmless,and do not cause secondary pollution.It is usually used with building materials by spraying and mixing to adsorb and degrade gas pollutants and harmful organic matter in natural environment.However,the band gap of Ti O₂（3.2e V）is large,electron-hole closed extremely easily,cause its catalytic effect is poorer in visible light,Nano Ti O₂ has a large specific surface area,which is easy to condense and difficult to separate,in addition,When photocatalytic material is applied to the surface of building material by spraying,The caking property is poor,and fall off easily,The photocatalytic performance cannot be maintained for a long time.To solve the above problems,a core-shell nanocomposite Si O₂/N-Ti O₂（NST）with high visible light catalytic activity was prepared in this paper,and the application of photocatalytic materials in cement-based materials was studied by surface spraying and mixing.The main innovative work of the paper includes:The preparation of core-shell nanocomposite NST with high visible light catalytic activity was studied.Using nano-Si O₂ microspheres as the core and nano-Ti O₂ as the shell,the core-shell nanocomposite NST with controllable size was synthesized by solvothermal method.The core-shell nanocomposite NST was bounded by Ti-O-Si bond steadily.Nitric acid not only acts as N source,but also provides H⁺as a stabilizer,which controls the reaction speed and makes the whole reaction process more gentlely and controllable.When the volume ratio of nitric acid to tetramethyl titanate was1:6,the photocatalytic performance was the best,the degradation rate of Rh B solution with mass concentration of 10 mg/L reached more than 99%in 30 min.The interaction mechanism between NST and cement-based material surface was studied,and the optimal spraying process parameters were proposed.The results show that NST reduces the water absorption of cement-based materials by more than 10%（more than 13%at 1 day;more than 20%at 3 day,）;Compared with P25（Ti O₂with average particle size of 25 nm）,the photocatalytic durability of NST on the surface of cementitious materials is improved by 20%（standard curing for 28 days,washing for5 days）.The mechanism is that the pozzolanic reaction occurs between NST and CH（calcium hydroxide）,and C-S-H gel with low polymerization degree is formed.The photocatalytic performance of NST on the surface of cement-based materials is significantly affected by the natural environment,and the order of the specific influence degree is:light intensity>temperature>humidity,and the influence of light intensity and temperature（in a certain range）on the catalytic efficiency is positively correlated.When the ambient temperature is 20℃,the ambient humidity is 50%,the spraying amount of NST on the surface of cement-based material is 20.83 g/m²,and curing under standard conditions for 28 days,the photocatalytic performance is best.The effect of NST on the properties of cement-based materials was studied.The results show that NST can accelerate the exothermal peak of cement hydration by more than 0.5 h,promote the formation of cement hydration products,optimize the early pore structure of cement paste,and significantly improve the early mechanical properties（1-day compressive strength and flexural strength increased by 30%and 5%respectively）and chloride ion erosion resistance of cement paste.The optimum content of NST in cement is 1.5%of cement mass.