Construction And Properties Of TiO₂ Based Micro/Nano Composite Structures On Sheet Steel Enamel Surfaces

Enamel,a substantial and artistic coating material with extreme hardness,high thermalstability,excellent anti-corrosion,easy-cleaning and easy-processing properties,has been widely used for vessels,architecture ornaments,medical instruments,water storage facilities,industrial reactors,highly thermal anti-corrosion equipments,environmental protection devices in power plants,electronic products,and art-wares.On the other hand,enamel materials with antibiotic self-cleaning,photocatalytic dissociation and super-hydrophilic properties exhibit a great potential in the application of sanitary wares and architecture ornaments etc.Design of multi-component nano-composites on the enamel surface is an efficient way to reinforce their optical,electrical and chemical properties and performance.So far,semiconductor TiO₂ is considered as a highly stable and photo-induced hydrophilic catalyst,but some drawbacks,such as its wide band gap,low utilization of sunlight,and UV irradiated photo-induced hydrophilicity,still inhibit its further application.Based on the above consideration,this paper mainly focuses on the research and development of a series of sheet steel enamels with excellent photocatalysis property and super-hydrophilicity.A new type of enameled steel materials was firstly prepared by designing optimized glaze formulas,mill-addition recipes and firing technology.The relationship between micromorphology and annealing temperature was systematically investigated.Furthermore,Enamel-TiO₂,Enamel-TiO₂-CdS,and Enamel-TiO₂-Bi composites were successfully synthesized by sol-gel and hydro-thermal methods.Their micro-structures,surface properties,and photocatalysis performance were preliminarily studied.These as-prepared enamel composites showed significant advantages in anti-fog,anti-fouling,and self-cleaning.The main results are listed in below:?1?In the first chapter,a new type of SiO₂-B₂O₃-TiO₂-R2 O enameled steel material was developed.Based on various frit formulas and mill-addition recipes,a series of enamel frits were coated on the surface of steel plates.The color of composites changed from initial transparent light-yellow to milky white after firing.The properties of enamel were improved through the modification of Ti,Si,B oxides ratio,in which the expansion coefficient is even matching to that of steel.In addition,amorphous SiO₂ was added to the enamel composites for enhancing their anti-corrosion ability and thermalstability.When 8 wt.% of SiO₂?0.8-1.5 ?m in particle size?was added at 800 ± 5 ? firing temperature,anti-corrosion level T goes up to Class A+ and the thermal shock temperature can even reach up to 300 ?.It promoted the ?-SiO₂ liquid phase migrating into [AlO₄] to form [-SiO₂-B₂O₃-Al₂O₃]network.Also,the components of enamel were quite sensitive to the firing temperature.More anatase TiO₂ emerged as the firing temperature is below 800 ?,while more rutile TiO₂ appeared when the temperature is over 900 ?.?2?In the second chapter,the micro-nanostructured enamel-TiO₂ composites were designed.A simple sol-gel method has been applied to construct enamel-TiO₂ composites on the enameled steel surface for upgrading photocatalysis property.After thermal treatment at 400 ?,enamel-TiO₂ micro/nano-structured composites were homogeneously dispersed.It showed an excellent photocatalysis over 5 ppm Rh B?degradation efficiency: 19.76 % after 80 minutes xenon lamp irradiation?and a good recyclability.It was found that the band gap of as-prepared Enamel-TiO₂ is 2.95 e V,and Al³⁺/Na⁺doping ions broadened the light absorption range and efficiency.Surface hydrophilicity of enamel-TiO₂ was depended on sintering temperature.When sintering temperature is 600 ?,after 3 hours of UV irradiation,Zero degree of water contact angle can be obtained,which can result in the great improvement of self-cleaning and anti-fog surface.This is probably due to the existence of anatase TiO₂,activated by ultraviolet light and generating a lot of hydroxyl radicals which has a strong absorption to water.?3?In the third chapter,Enamel-TiO₂-CdS composites were synthesized.Micro/Nano-structured TiO₂ was firstly coated on the surface of enamel by a hydrothermal method using Ti?SO₄?2 and CO?NH₂?₂ as precursors.After 12 hours of heating at 200 ?,Enamel-TiO₂?60¹00 nm?nanorods were obtained.The band gapwas calculated to be 3.07 e V,indicating it cannot work under visible irradiation.After80 min of xenon lamp irradiation,Rh B degradation efficiency reached around 24.9 %.We further modified the micro/nano-structured Enamel-TiO₂ surface with “one-step”and “two-step” hydrothermal methods by adding Cd?NO₃?₂·4H₂O and C₃H₇NO₂S as sensitizers.The two as-prepared Enamel-TiO₂-CdS micro/nano-structured composites promoted the Rh B degradation rate by 41.37 % and 25.95 %,respectively.Introduction of CdS increased the quantum yield of photogenerated electron-hole pairs and inhibited their recombination.Surface hydrophilicity of Enamel-TiO₂ nanorods showed almost 0 degree of water contact angle even without UV irradiation.Whereas the addition of CdS decreased hydrophilicity to 24.3 degree of water contact angle,which is probably due to the decreasing surface hydroxyl group density.After 3hours UV light irradiation,water contact angle was changed to 4.5 degree.?4?Finally,Enamel-TiO₂-Bi semiconductors were successfully constructed.Enamel-TiO₂-Bi VO4,Enamel-TiO₂-Bi OCl and Enamel-TiO₂-Bi₂WO₆micro/nano-structured composites were prepared by a two-step hydrothermal method using different kinds of precursors.Among them,Enamel-TiO₂-Bi₂WO₆ showed a rough nanorod structure which looked like “Caterpillars”.XRD and TEM analysis results confirmed that anatase TiO₂ and russellite Bi₂WO₆ phases were existing in the micro/nano-structured of Enamel-TiO₂-Bi₂WO₆ composites.UV-Vis analysis results displayed that composite exhibited the absorption from UV to visible range,and its band gap was calculated to be around 2.53 e V.When using Enamel-TiO₂-Bi₂WO₆ composite as the photocatalyst,Rh B degradation efficiency in UV and visible range reached up to 44.5 % and 23.5 %?After 80 min of irradiation?,respectively.It's probably due to the formation of Enamel-TiO₂-Bi₂WO₆ composite structure,which promotes the speratation efficiency,further increasing the lifetime and reaction chance of active species including e-,h+,so as ·OH.In addition,three kinds of Enamel-TiO₂-Bi based nano-composites exhibited an instant water spreading all surface phenomenon within 1.5 seconds,which is a quite potential application for their super-hydrophilicity.