| Coating material can be applied on the surface of products,which can impart special functionality to the product.Self-cleaning coating materials can facilitate the dirt remove on surface of product by the assistance of external environment.Nano TiO2 has been widely used for crafting self-cleaning coatings due to its good chemical stability and photocatalytic activity.The self-cleaning function of coating mainly relies on photocatalytic decomposition of organic pollutants.However,in the case of TiO2-based coatings,low self-cleaning efficiency and easy degradation of the coating are commonly found.Porous TiO2 exhibits relatively high photocatalytic performance due to its large specific surface area.Recently,researches on the preparation of porous TiO2 using biomass as a template have attracted much attention.The presence of biotemplate can suppress coating degradation induced by the photocatalytic effect of TiO2.Casein is a natural protein with microcluster-like micelle structure,which makes it a good candidate for preparing porous nanoparticle,meanwhile,it also can be used as coating materials.In this dissertation,casein micelles were employed as templates to produce porous TiO2 nanospheres(temp-TiO2)with tunable structure.Based on this,ZnO(ZnO QDs)and Cs2AgBiBr6 perovskite quantum dots(PQDs)were separately loaded into temp-TiO2 to obtain TiO2-based composites.Subsequently,temp-TiO2 and its composites were separately integrated with modified casein emulsion to fabricate self-cleaning coating materials.In addition,stability and film-forming mechanism of the composite emulsion,as well as self-cleaning mechanism of the composite coatings were further discussed and proposed.The main results are shown as follows.(1)Temp-TiO2 was designed via hydrothermal method using casein micelles as the template and butyl titanate(TBOT)as a precursor.The structure and properties of temp-TiO2 were optimized by tuning the type and particle size of template,TBOT dosage and hydrothermal reaction parameters to obtain correlations between the structure and its properties.The morphology,crystal structure and porosity of temp-TiO2 were characterized by transmission electron microscopy(TEM),scanning electron microscopy(SEM),X-ray diffractometry(XRD)and specific surface area analyzer.The results confirm that porous temp-TiO2 has been successfully prepared.The crystal form of temp-TiO2 is anatase and its particle size is approximately 500 nm.The specific surface area and average pore size of temp-TiO2 are 172 m2/g and 7.49 nm,respectively.When caprolactam-modified casein micelles were used as template,TBOT dosage was 0.06%,hydrothermal temperature was 120℃,and reaction time was 10 h,temp-TiO2 with mesoporous structure and good photocatalytic performance was obtained.Mesoporous structure not only increased the reactive area between TiO2 and pollutants,but also enhanced the light absorption capacity of TiO2.Photocatalytic results showed 98.9%Rhodamine B(RhB)was degraded under UV irradiation for 240 min using temp-TiO2 as a catalyst.The degradation efficiency was only reduced by 0.5%after 5 cycles of use.Fitting and calculation results indicate that the photocatalytic reaction of temp-TiO2 is a first-order reaction.Application of temp-TiO2 in casein-based coating suggested nearly no degradation.Accordingly,its photocatalytic mechanism involving pollutant absorption and the degradation caused by·OH and ·O2-was discussed and established.(2)Temp-TiO2/ZnO QDs composite was obtained by introducing ZnO QDs into as-prepared temp-TiO2.Since ZnO QDs possess more negative conduction band position,the effective separation of electrons(e-)and holes(h+)can be realized,and the carrier lifetime is prolonged,thus improving the photocatalytic performance of temp-TiO2.The effects of mixing way,ZnO QDs surface ligand and its dosage,stirring time on the structure and properties of composites were investigated.Firstly,the optical properties of ZnO QDs were detected by UV-Vis spectrophotometer and fluorescence spectrometer.Then the microstructure and crystal structure of temp-TiO2/ZnO QDs composites were characterized by TEM,SEM,XRD and specific surface area analyzer.Results showed that ZnO QDs with high crystallinity were obtained using oleic acid as ligand,and their average particle size was approximately 8 nm.Temp-TiO2/ZnO QDs composite with good photocatalytic properties was obtained via blending method,when weight content of ZnO QDs was 1.5%.The composite possessed mesoporous structure with high specific surface area of 240 m2/g,and its pore size is approximately 3.97 nm.The photocatalytic results showed that the photocatalytic reaction of temp-TiO2/ZnO QDs was a first-order reaction.The required time for complete degradation of RhB was shortened by approximately 60 min compared with that of temp-TiO2.At the same time,the composite material also showed good reusability and weak degradation effect on coatings during the photocatalytic process.Accordingly,the photocatalytic mechanism was discussed and established.The introduction of ZnO QDs into temp-TiO2 facilitates the separation efficiency of e--h+ pairs,thus improving the photocatalytic performance of temp-TiO2/ZnO QDs.(3)PQDs were introduced into temp-TiO2 to obtain temp-TiO2/PQDs composites.Combining with narrow-band PQDs can not only enhance the separation efficiency of e-and h+ in temp-TiO2,but also expand its absorption to the visible region,thus achieving visible light-induced photocatalysis.Due to the ionic structural characteristics of PQDs,their stability is relatively poor.Therefore,in this dissertation,effects of PQDs dosage,light wavelength,and air humidity on the stability and photocatalytic performance of temp-TiO2/PQDs composite were investigated to estimate the possibility of its practical use.The optical properties,stability and photocatalytic properties of PQDs were firstly detected by UV-Vis spectrophotometer and fluorescence spectrometer.The microstructure and crystal structure of temp-TiO2/PQDs composite were then investigated by TEM,SEM,XRD and specific surface area analyzer.Results confirmed that the obtained PQDs not only possessed good stability,but also showed excellent photocatalytic performance.By incorporating PQDs within temp-TiO2 could further improve the stability of PQDs.The optimal photocatalytic performance of temp-TiO2/PQDs composite was achieved,when the volume content of PQDs was 40%.The composite exhibited mesoporous structure with specific surface area of 155 m2/g and average pore size of 3.64 nm.99.85%of RhB was degraded after 150 min’ UV irradiation using temp-TiO2/PQDs as a catalyst,and the photocatalytic reaction was a first-order reaction.Compared with temp-TiO2,the required time for complete degradation of RhB was shortened by 90 min.Furthermore,the obtained composite showed nearly no degradation effects on coatings.In addition,temp-TiO2/PQDs could not only be used for visible light-induced photocatalytic degradation,but also showed photocatalytic activity in absolute water system or environment with high air humidity.However,reusability of the composite in water system was relatively poor.Degradation efficiency was reduced by 9.55%after 5 cycles of use.Accordingly,based on the results,photocatalytic mechanism of the composite in different conditions was discussed.When water content in the environment is relatively low,the presence of PQDs is conducive to improving the separation efficiency of e--h+ pairs,and accelerating the charge transfer between temp-TiO2 and PQDs,so as to improve the photocatalytic activity of the composite.When the water content is relatively high,PQDs in the composite may be partially hydrolyzed,and generate BiOBr,which is also conducive to improving separation efficiency of e--h+ pairs in the composite,and further improving its photocatalytic performance.(4)Temp-TiO2,temp-TiO2/ZnO QDs and temp-TiO2/PQDs composites were added into modified casein emulsion to obtain a series of film-forming composite emulsion.The composite emulsion was applied in leather finishing to endow leather surface with good self-cleaning behavior.Firstly,stability of the composite emulsion was investigated.The stability mechanism was explored by combining the results of emulsion stability and zeta potential of each component in the emulsion.Furthermore,the composite emulsion was casted into films.Structural evolution of composite emulsion during the film-forming process was observed by AFM and SEM.Accordingly,the film-forming mechanism was revealed.The properties of composite film were investigated.The composite emulsion was also applied in leather finishing.Performance of the finished leather was investigated.Results showed that the composite emulsion containing temp-TiO2,temp-TiO2/ZnO QDs or temp-TiO2/PQDs was more stable than emulsion containing template-free TiO2.The good stability of composite emulsion mainly depends on the electrostatic repulsive force between modified casein latex particles and TiO2 nanoparticles.The results verified the self-cleaning function of composite film was mainly based on the hydrogen peroxide and superoxide radicals drived oxidative decomposition of pollutants and antifouling activity of the superhydrophilic layer formed on the coating surface under UV irradiation.Related mechanism models were also proposed.Application results showed that the composite film and composite emulsion finished leather exhibited good self-cleaning behaviors to soy sauce,chili oil and coffee stains.Meanwhile,compared to modified casein emulsion finished leather,the antibacterial and air permeability properties of composite emulsion finished leather were improved.It was noted that composite emulsion containing temp-TiO2/PQDs endowed leather with excellent self-cleaning behavior and antibacterial property. |
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