The Preparation Of Photocatalytic TiO₂ Crystals Using Atmospheric Pressure Plasma Jet Driven By Dual-frequency Power Sources And Its Doping Modification

In recent years,low temperature atmospheric pressure plasma jet has been widely used in several fields such as material surface treatment,plasma medicine and nano science and technology.The most significant advantage is that it can discharge without chamber and vacuum equipment,so that non equilibrium plasma can be generated in open space rather than narrow gap.The dual-frequency?DF?generated to atmospheric pressure cold plasma jet,which combines the advantages of long plasma plume,low gas temperature,high electron density and strong chemical activity compared to single frequency of low frequency?LF?or radio frequency?RF?driven plasma jet.So it is used as a tool for the preparation of nanoparticles,and it has a higher crystallinity and efficiency.Based on the advantages,this paper designed dual-frequency?50 kHz/110 MHz and 100 kHz/100 MH?driven atmospheric pressure non equilibrium plasma jet deposition system.Titanium tetrachloride?TiCl₄?and isopropyl titanate?TTIP?were used as titanium source.One step method of preparing TiO₂ nanopowders and nitrogen or carbon doped TiO₂ photocatalyst was developed for the first time,which using atmospheric pressure plasma jet driven by dual-frequency power sources.The main work includes the following three parts:1.Mixed-phase TiO₂ nanopowders with different ratios of anatase and rutile have been successfully synthesized using atmospheric pressure plasma jet driven by dual-frequency power sources.These results indicated that samples possessed anatase and rutile structure,in addition,the crystallinity of the TiO₂ nanopowders increased and the chlorine contamination decreased with discharge RF power increasing.The TiO₂ nanopowders which were produced at the discharge RF power of 110 W had the highest photocatalytic activity.Optical emission spectroscopy?OES?was used to detect various excited species in the plasma jet.The results indicate that the various RF power significantly changes the intensities of emission lines(Ar,Ar⁺,Ti,Ti⁺,Ti²⁺,Ti³⁺and O),which results in the TiO₂ nanopowders have mixed phases of anatase and rutile.2.In this work,nitrogen-doped TiO₂ nanofibers films with mixed phases of anatase and rutile have been prepared by using atmospheric pressure dual-frequency plasma jet in one step for the first time.The XRD and Raman analysis showed that the nitrogen-doped TiO₂ nanofibers films have highly crystallinity.The UV-vis spectra further illustrates that nitrogen-doped TiO₂ nanofiber films can be deposited in one step.This indited that the samples have the weak absorption of the visible light region and narrower band gap.Finally,the conductivity of as-deposited nitrogen-doped TiO₂films were evaluated by I-V measurement,the result showed that the films exhibits the higher conductivity.3.A novel method of synthesizing Ti³⁺doped TiO₂ was proposed.By using atmospheric pressure plasma jet generated by dual-frequency power sources under normal temperature,we prepared Ti³⁺doped TiO₂ hollow spheres by different thickness of carbon Shell.The as-synthesized Ti³⁺doped TiO₂ hollow microspheres were characterized by XRD parttern,SEM images,HRTEM images,Raman spectra,XPS and UV-Vis spectra.The results indicated that these samples were mixed phases of anatase and rutile and the structure of hollow sphere varied by different thickness of carbon shell.The connection between the TiO₂ hollow sphere and carbon layer was via Ti-O-C chemical bond.Amount of Ti³⁺ions were found,which were accompanied with the formation of oxygen vacancies.Meantime,the as-synthesized catalysts also display strong absorption in the visible light region and a narrower band energy gap.Optical emission spectroscopy?OES?was used to observe different excited species in the discharge area.The results showed that the oxygen content had a significant impact on the preparation of Ti³⁺doped TiO₂ hollow spheres with different content of oxygen vacancies.Finally,the photocatalytic activities of as-prepared samples were evaluated by decomposition of Rhodamine B aqueous solution,which showed better photocatalytic activity under UV-vis light irradiation.