Synthesis And Photocatalysis Of Titanium Dioxide Nanocomposites

In order to solve the two major problems?energy crisis and environmental degradation?in the 21st century,photocatalytic technology,as one of the green and sustainable countermeasures,has received extensive attention from experts and scholars at home and abroad.It uses photocatalyst as a medium to convert solar energy into electrical energy or chemical energy to achieve clean energy production or environmental purification.As one of the most popular semiconductor photocatalysts,titanium dioxide?TiO₂?with its excellent properties has been initially industrialized and applied.However,the photocatalytic performance of TiO₂ can be further improved both in the absorption range of sunlight and in the conversion efficiency of solar energy.In this dissertation,based on the photocatalytic mechanism and performance influencing factors of TiO₂,TiO₂ was composited with porous supports to realize the nano-crystallization of TiO₂ particles,and at the same time,the problems of easy agglomeration and difficult separation of nanoparticles were solved.Moreover,the adsorption of the carriers led to improved photocatalytic performance and purification ability.Futhermorethe,TiO₂ nanoparticles were combined with another semiconductor catalyst to form heterojunctions,which could inhibit the rapid recombination of photogenerated carriers to enhance the catalytic activity.The main contents are as follows:?1?A series of TiO₂/SBA-15 nanocomposites were successfully prepared by loading TiO₂ nanoparticles on hydrothermally synthesized mesoporous silica?SBA-15?via a multistep impregnation method.The results showed that the anatase TiO₂ nanoparticles were mainly distributed in the two-dimensional hexagonal mesopores of SBA-15,and mesopores restricted the growth of TiO₂ crystals.With the increase of the loading,the specific surface area,total pore volume,and average pore size of TiO₂/SBA-15 nanocomposites decreased in turn.Compared with the pure TiO₂?4-TiO₂?prepared by removing SBA-15,the TiO₂/SBA-15 nanocomposite still had a large specific surface area?about 3-4 times that of 4-TiO₂?.Therefore,TiO₂/SBA-15nanocomposites presented excellent adsorption properties,which made the photocatalytic performance of TiO₂/SBA-15 better than that of 4-TiO₂.The TiO₂/SBA-15 nanocomposites prepared by the three-step impregnation method revealed the best photocatalytic activity in the degradation of methylene blue?MB?dyes.?2?A series of TiO₂/AC nanocomposites were successfully prepared by loading TiO₂ nanoparticles on commercial activated carbon?AC?via a multistep impregnation method.The results showed that the anatase TiO₂ nanoparticles with uniform particle size were distributed on the surface of AC.The TiO₂ nanoparticles obtained by removing the AC were still anatase phase,and the average grain size did not significantly increase,which was much smaller than that of the pure TiO₂?0-TiO₂?prepared without adding AC.0-TiO₂ contained two crystal phases of anatase and rutile,and the crystal particles are severely compacted,so that the specific surface area was smaller than that of TiO₂ which is burned out of AC and much smaller than that of TiO₂/AC nanocomposites.TiO₂/AC nanocomposites exhibited excellent removal of MB molecules.The photocatalytic tests of TiO₂ nanoparticles obtained by removing the AC and 0-TiO₂ showed that the TiO₂ nanoparticles on TiO₂/AC nanocomposites had much higher photocatalytic activity than that of 0-TiO₂.?3?A series of Bi₂O₃/TiO₂ nanocomposites with different Bi₂O₃ contents were successfully prepared by loading Bi₂O₃ nanoparticles on the TiO₂ nanoparticles?prepared by removing the AC in?2??via a impregnation method.The results showed that the extremely small particles of Bi₂O₃ nanoparticles were highly dispersed and supported on anatase TiO₂ nanoparticles with a particle size of about 8.5 nm.In the synthesis process of nanocomposites,the phase transition of TiO₂ in the anatase phase did not occur,and the grain size did not increase significantly.The Bi₂O₃/TiO₂nanocomposite particles exhibited a certain extent of agglomeration,so that their structural parameters?specific surface area and total pore volume?decreased with the increase of Bi₂O₃ content.After the photocatalytic degradation test of MB solution,the adsorption performance of Bi₂O₃/TiO₂ nanocomposites to MB was lower than that of pure TiO₂,but due to the presence of heterojunctions in the nanocomposite,the separation of photogenerated electrons or holes could be effectively achieved,thus Bi₂O₃/TiO₂ nanocomposites exhibited better photocatalytic activity than pure TiO₂.