Study On Fe-Doped Nano-TiO₂ Photocatalytic Air Purifying Inorganic Coatings

Indoor air quality has an important impact on human health.In daily life,many household products and interior decoration materials are the main way to produce formaldehyde,which has a wide source,long latent period and long emitting time,and always affects people’s health.Photocatalysis is a new green technology with mild reaction,low cost and no pollution,which can oxidize formaldehyde in the air into clean substances that are harmless to human body such as titanium dioxide and water.Due to the outstanding features of TiO₂photocatalysts such as non-toxicity,high catalytic efficiency,stable performance and low cost,it has become the most widely researched material in the field of photocatalysis.The most widely used interior wall coatings on the market are mostly organosilicon emulsions,benzene propylene emulsions,etc.These coatings themselves release formaldehyde and other harmful gases,and most organic coatings often face the problem of being degraded themselves when combined with photocatalytic components.Most importantly,organic coatings have a dense structure and only the surface can realize photocatalytic reaction,while the microporous structure of inorganic coatings can give full play to the overall photocatalytic performance of the coatings.It is important to combine photocatalysts with coatings to prepare a functional coating with automatic air pollution cleaning.Therefore,this thesis investigates the synthesis of nanometer titanium dioxide photocatalyst,the preparation of metakaolin-based inorganic coating,and the combination of both to study the work of photocatalytic air cleaning inorganic functional coatings,and the specific research contents and conclusions are as follows:（1）The nano-Fe-TiO₂ photocatalytic powder was prepared by sol-gel method using titanium tetrachloride solution,iron nitrate,deionized water,anhydrous ethanol and ammonia.The nanometer Fe-TiO₂ composite photocatalysts with the best performance were screened under natural light conditions with photocatalytic activity as the index,and their structures were characterized in relation.The results show that the crystalline form of nano-TiO₂ is anatase at the calcination temperature of 600℃,and the crystal shape is similar to spherical shape,and the distribution is more uniform,with only a few agglomerates.（2）Fe concentration doping amount at n（Fe）:n（Ti）=0.3%,the structure is still similar to spherical shape,the particle size distribution is around 10 nm,which is nanoscale,the spectral response range of TiO₂is broadened,the wavelength of absorbed light produces obvious red shift,and the absorption wavelength in visible region reaches 600 nm.by photocatalytic degradation of organic solution rhodamine B,the doping amount at n（Fe）:n（Ti）=0.3%,its efficiency of photocatalytic degradation of rhodamine B under LED lamp for 72 h reached86%.（3）High performance green inorganic coatings were prepared by using metakaolin as the base material,modified water glass as the binder,sodium hexametaphosphate as the dispersant,sodium dodecyl sulfonate surfactant and carboxymethyl fiber as the emulsifier.The research results show that the coating can be well coated on the substrate surface with a surface drying time of 1.8h and a hardness of 9 H when the water glass ratio is 0.75 and the modulus is m=1.8.The adhesion can reach grade 1 when tested with a lattice knife scribe,and the macroscopic morphology is smooth and flat without defects such as pits,cracks and peeling after being soaked in water and alkaline solution for 168h respectively.（4）The air-purifying inorganic coatings were prepared by two preparation processes.The degradation efficiency and macroscopic morphology of the photocatalytic coatings for formaldehyde were investigated separately.The results showed that the formaldehyde degradation efficiency of the coatings prepared by the In-situ growth method was 87%,which was significantly higher than that of the coatings prepared by the mechanical blending method,and the surface of the coatings prepared by the mechanical blending method had a large number of agglomerated small particles and poor macroscopic coating performance.（5）The formaldehyde degradation efficiency,stability and its comprehensive physical properties of the air-purifying inorganic coating prepared by in situ growth method were investigated.The results show that the air-purifying inorganic coating prepared by 5%additive photocatalyst has a removal rate of 87%for formaldehyde at a concentration of 1.8mg/m³after 7 d of light exposure;the formaldehyde degradation efficiency of the coating is only reduced by 9%through 4 cycles of formaldehyde degradation experiments,and the stability is good;the macroscopic morphology is smooth and flat,without defects such as pits,cracks and peeling.