Preparation And Photocatalytic Properties Of Supported TiO₂ Quantum Dots Composites

Dye wastewater has the characteristics of high organic matter content,high biological toxicity and high chroma.Dye wastewater endangers people’s health directly or indirectly once it flows into the environment.In order to treat dye wastewater,a number of technologies have been developed,such as adsorption,biological treatment,and so on.Among them,photocatalysis which using semiconductor materials such as TiO₂to catalyze photoreaction is a promising method because of its simple reaction conditions and the ability to completely degrade dyes.More and more research has suggested that semiconductor materials show unique properties in quantum dot size（<10 nm）,so the preparation of semiconductor quantum dots for photocatalytic reactions has become a trend.In addition,with the advantages of renewable,abundant functional groups and fine multistage structure,biomass and biopolymer are suitable for the support of photocatalyst.Based on this background,the supported TiO₂quantum dots photocatalytic composites based on biomass and biopolymer were prepared by hydrothermal method in this thesis.The structure of the prepared photocatalytic materials were characterized by modern instrumental analysis technologies of SEM,EDS,TEM,HR-TEM,FT-IR,XRD,XPS and DRS.Photocatalytic properties of the prepared materials were studied with Methyl Orange and Rhodamine B dyes which were used as target pollutants.Specific research contents in this thesis are as follows:（1）TQDs/CC photocatalysts were prepared by hydrothermal method using tetrabutyl titanate and natural cotton cellulose as raw materials to in-situ load anatase TiO₂quantum dots on the surface of cotton.SEM and TEM displayed that the supported TiO₂quantum dots are uniformly decorated on cotton cellulose with crystal size ranging from 3 to 8 nm.TQDs/CC photocatalysts exhibited excellent photocatalytic activity and adsorption of anionic dyes,and its degraded rates for Methyl Orange and Rhodamine B were up to99.3%and 98.7%in 60 minutes,respectively.And the removal rates of Methyl Orange by TQDs/CC remained above 95%after ten recycle tests.Meanwhile,SEM-EDS confirmed that TiO₂quantum dots were still supported on cotton cellulose after recycle tests.TQDs/CC photocatalysts have stable photocatalytic properties and long-term reusable performance.（2）Using tetrabutyl titanate as titanium source,TiO₂quantum dots were supported in situ on wheat straw by hydrothermal method to prepare TQDs/WS photocatalytic materials with floating property,which were used for degradation of dye wastewater under natural light.SEM and TEM showed that the distribution of supported TiO₂quantum dots on wheat straw was uniform and the mean particle size of TiO₂quantum dots was 5 nm.The degradation rate of TQDs/WS photocatalytic materials for Methyl Orange were up to96.2%in 120 minutes,and degradation rate for Rhodamine B were up to 98.6%in 80minutes.At same time,TQDs/CC photocatalyst also has a certain adsorption effect on anionic dyes.The five recycle tests indicated that TQDs/WS photocatalytic materials have a long catalyst life.The band gap and photocatalytic degradation mechanism of TQDs/WS were also explored through DRS and reactive oxygen species inhibition experiments.The results showed that reactive oxygen species generated during the degradation process,such as·O₂^-,play an important role in the degradation of dyes.In addition,TQDs/WS photocatalytic materials showed excellent floating performance on water surface for up to a month,indicating its ability realize the natural degradation of dyes in wastewater using sunlight.