Fluidization Characteristics And Coating Properties Of Atomic Layer Deposition Reactor Based On TiO₂ Nanoparticles

Atomic layer deposition（ALD）has the advantages such as good uniformity,high conformity and good compactness.Therefore,ALD can accurately control the coating thickness and composition of particles,and effectively change the surface and interface properties of particles.The traditional static vacuum ALD reactor is mainly used the modification of flat substrate.It is difficult to achieve the modification of batch nanoparticles,and the device is expensive to manufacture.Therefore,it is necessary to explore an ALD reactor for micro-nano particle modification.Particle fluidization is a relatively mature method for treating particles.However,micro-nano particles have the characteristics of small particle size,high specific surface energy and easy agglomeration,which is difficult to fluidize under conventional conditions.In this paper,vibration-assisted particle fluidization is introduced,and the atmospheric pressure vibration fluidized ALD equipment is built autonomously.And it can achieve the uniform fluidization and deposition modification of large micro-nano particles.TiO₂ nanoparticles are widely used in the fields of photocatalyst,coating,papermaking due to stable chemical properties,non-toxicity and low cost.Therefore,this thesis focuses on modified the surface of TiO₂ nanoparticles for different application scenarios to improve or shield the photocatalytic activity.And debugging and verifying the best operating conditions and performance of the self-made ALD fluidized bed reactor.The specific research contents are as follows:（1）The preparation of Cu_xO/TiO₂ nanoparticles and its photocatalytic activity:In order to broaden the optical response range and reduce the recombination rate of electron-hole pairs of TiO₂,Cu_xO/TiO₂ photocatalysts with different Cu_xO loadings were prepared by liquid-phase deposition.The photocatalytic performance of the Cu_xO/TiO₂ photocatalyst was investigated by the degradation of Rhodamine B.The optimized 0.08-Cu_xO/TiO₂ photocatalyst showed the excellent Rhodamine B degradation performance,which was 7.5 times that of commercial TiO₂ nanoparticles.After calcination at 450°C,the light response range of the Cu_xO/TiO₂ photocatalyst was expanded and the recombination rate of photogenerated electron-hole pairs was reduced,but its photocatalytic activity was greatly reduced.It may be that calcination will cause part of the Cu₂O on the surface of the photocatalyst to be converted into Cu O,which is not conducive to the degradation of Rh B.At the same time,calcination will reduce the specific surface area of the Cu_xO/TiO₂ nanoparticles and cause a decrease in catalytic activity.The free radical capture experiment showed that for the Cu_xO/TiO₂ photocatalyst,the degradation of Rhodamine B mainly through the oxidation of hydroxyl radicals,and the direct oxidation of some of the holes also take part of the Rhodamine B degradation.（2）Fluidization characteristics of micro-nano particles in a vibrating fluidized bed reactor at atmospheric pressure:In order to investigate the fluidization performance of micro nano particles in the atmospheric ALD vibration fluidized bed,the fluidization characteristics of resin particles,TiO₂ and Si O₂ nanoparticles with different particle sizes and properties were studied to determine the optimal fluidization conditions.The experimental fluidized bed is a quartz glass tube with an inner diameter of 26 mm and a height of 350 mm.The two terminals of the glass tube are composed of quartz sand cores with a pore size of 150-178μm.The particles with difference of density,size and viscosity,its fluidization quality will be affected.When the initial bed height of resin particles is 30 mm,the gas velocity is 8.16 cm/s,and the optimum fluidization amplitude is 0.66 mm.When the initial bed height of TiO₂ nanoparticles is 5 mm,the gas velocity is 5.65 cm/s,and the optimum fluidization amplitude is 1.16 mm.When the initial bed height of Si O₂ nanoparticles is 10 mm,the gas velocity is 5.02 cm/s,and the optimum fluidization amplitude is 0.66 mm.Under the amplitude of 1.16 mm,the bed height of TiO₂ particles is 10 mm,the better fluidization quality can be achieved when the gas velocity is 6.91 cm/s.Tracer fluidization experiments and microscopes were used to investigate the changes of particle aggregates during fluidization.After a period of time,dyed particles and unstained particles were uniformly mixed.The results show that the aggregates were in a dynamic fragment-agglomeration behavior during fluidization,and the device can achieve uniform fluidization of nanoparticles.（3）Surface modification of TiO₂ nanoparticles by amorphous TiO₂ via atomic layer deposition:To validate the modification effect of self-made atmospheric vibration fluidized ALD reactor on nanoparticles,commercial TiO₂ was modified to inhibit its photocatalytic activity and improve the weatherability of TiO₂ coating.Amorphous TiO₂ film were deposited on the surface of commercial TiO₂ from Ti Cl₄ and H₂O at 80°C.The online mass spectrometer was used to monitor the reaction process and reaction products in time.The results showed that HCl was the main signal sources when each precursor entered the reactor.The signal shows the same trend in each cycle,indicating that the device conforms to the ALD process.The inhibitory effect of coating cycles on the photocatalytic activity of TiO₂ was investigated by degradation of methylene blue.The results show that the photocatalytic activity of commercial TiO₂decreases with the increase of the number of cycles.After UV irradiation for 120 min,the photocatalytic activity of 10-cycles samples was inhibited by 50%compared with commercial TiO₂.It can obtain a uniform and dense TiO₂ film,and the film thickness increases at a rate of0.373 nm per cycle by TEM.Deposition experiments show that the self-made device can realize the coating modification of nanoparticles.