Hybrid TiO₂Porous Films And Superhydrophilicity Without UV Irradiation

In order to obtain TiO2superhydrophilic surface without induced and sustained by ultraviolet light, the research are carried out based on various constructing approaches of superhydrophilic surface. By doping transition metal Ag and adding soft templates to adjust chemical component and constructing special micro structure on the surface, the two methods work together to overcome the disadvantages of single modification method which could not abtain TiO2films with prompt wetting properity and long-last superhydrophilicity.Ag-TiO2sols were prepared by sol-gel method using titanium-n-butoxide as TiO2precursor, silver nitrate as silver source, poly (ethylene glycol)(PEG), Tween80, PEO-PPO-PEO (P123) as structure directing agent, and corresponding Ag-TiO2films were prepared by dip-coating method. Due to the differences in mechanism of hydrolysis-condensation reaction of TBOT and exisiting form of Ag ions in alkaline and acidic system, two kinds of sol system were employed using triethanolamine (TEA) and acetic acid (HAc) as hydrolysis controlling agent, respectively. And the influences of Ag-doping, H2O content, addition of soft templates, aging time and calcination temperature on Ag-TiO2films were investigated.As-prepared composite films were characterized by X-ray diffraction, X-ray photoelectronic spectroscopy, scanning electron microscopy and atom force microscopy. The hydrophilicity of Ag-TiO2films were comprehensively evaluated in terms of static water contact angle, wetting time and long-term stability by contact angle measuring device.The result shows that proper Ag-doping could change the photocatalytic reaction mechanism on TiO2surface and suppress agglomeration of TiO2particles and phase transformation from highly reactive anatase phase to stable rutile phase so as to increase dynamic wetting rate and response to visible light. At the same time, Ag doping films could exibit potential antibacterial property. H2O content in TiO2sols plays an important part in the formation of porous microstructure of corresponding TiO2films and their hydrophilic property. Sol aging time and calcination temperature have a connection with TiO2particle size and crystal phase in TiO2films.The optimal H2O content, aging time and calcination temperature differ in alkaline and acidic system. By adjusting technical parameters, porous TiO2films with reactive anatase phase could be obtained which possess better superhydrophilic effect. By comparison, alkaline sol system has higher stability, and corresponding films have smaller TiO2particle size, higher specific surface area and a more uniform dispersion of Ag particles. Transition temperature from anatase to rutile phase is lowered. TiO2films derived from alkaline system exibit rough and porous microstructure and better hydrophilic property.Compared with pure TiO2films, hydrophilicity level of those prepared by soft template method was improved. The rough surface with porous microstructure favors long-term superhydrophilicity in dark. The type and additive amount of soft templates can directly affect surface morphology and hydrophilic property of TiO2films. PEG2000could effectively achieve pore-forming function, and as-prepared TiO2films exibit fast wetting property less that0.08s. Tween80could result in macroporous morphology with low roughness which shows comparatively poor superhydrophilicity. P123addition forms mesoporous size, and surface depth and roughness are greatly improved which induce outstanding superhydrophilicity in dark.Ag-doping and addition of soft templates have synergistic influence on superhydrophilic property of TiO2films without ultraviolet light. Ag-TiO2films showed excellent superhydrophilic property under natural light conditions. Water droplets could fully spread on the surface within0.08second with static water contact angle of0°. Superhydrophilicity could last for more than30days when the films were stored in dark place. Superhydrophilic properties were enhanced when the films were irradiated under visible light. The composite Ag-TiO2films showed excellent anti-fogging effect.