Photocatalytic Oxidation Of Acetone And Nitric Oxide Over TiO₂ And G-C₃N₄ Photocatalysts

Air is being heavily polluted due to the emission of industrial gases and the use of decoration materials.Recently,semiconductor photocatalysis has attracted much attention as it provides a sustainable way to oxidize/minerize organic pollutants by using of solar light and oxygen of air.Although TiO₂ and graphite carbon nitride（g-C₃N₄）are considered to be the typical UV and visible light responsive photocatalysts,respectively,their photoreactivity is not high enough for practical applications.In this thesis,high photoreactive TiO₂ and g-C₃N₄for air purification（acetone and NO oxidation）are fabricated by designing the surface/interfaces and tailoring the band structures of semiconductor photocatalysts.Detailed study is summarized as follows:Part Ⅰ:High energy TiO₂ nanocrystals（HE-TiO₂-NCs）decorated TiO₂ nanofibers（TiO₂-NFs）homojuntion.HE-TiO₂-NCs/TiO₂-NFs homojunction was fabricated by electrospinning the mixture of TiOF₂ cubes and tetrabutyl titanate（TBT）followed by calcination.It was found that 600 ^oC calcined HE-TiO₂-NCs/TiO₂-NFs sample（TF600）shows the highest photoreactivity under UV irradiation with an acetone oxidation rate of 97.2 ppmh^-1,4.2 times higher than pristine TiO₂-NFs sample（T600）that was prepared under similar conditions but without the addition of TiOF₂.The enhanced photoreactivity of HE-TiO₂-NCs/TiO₂-NFs was attributed to the formation of a direct Z-scheme homojunction between HE-TiO₂-NCs and TiO₂-NFs.Part Ⅱ:TiO₂ mesocrystals with surface oxygen vacancies（Ov-TiO₂MSC）.TiO₂MSC were fabricated by hydrothermal treatment of NH₄F-TBT mixture.We systematically studied the effect of calcination temperature on the structure and photocatalytic activity of TiO₂MSC toward acetone oxidation.It was found that 600 ^oC-calcined sample（T600）exhibits the highest photocatalytic activity with an actone oxidation rate of 80 ppmh^-1.The high photoreactivity of T600 is attributed to the combined effects of the formation of Ov and improved crystallinity of TiO₂MSC Ov can not only capture the photo-generated electrons,retarding the recombination of carriers,but also extend the light-responsive range.Part Ⅲ:Flower-like g-C₃N₄ assembly from porous nanosheets with nitrogen vacancies was prepared by calcination of melamine-cyanuric acid（MCA）supramolecular aggregates at 500^oC in air.We systematically studied the effect of calcination time on the structure,property and performance of the prepared flower-like g-C₃N₄ toward NO oxidation under visible irradiation.It was found that the sample calcined for 10 h（F10 sample）exhibits the highest NO removal rate（59.2%）,higher than that of bulk g-C₃N₄（B10 sample）with a NO removal rate of 45.6%which was prepared by polymerization of melamine at 500^oC for 10 h.The improved photocatalytic activity of flower-like g-C₃N₄ is due to the combined effects of enlarged BET surface area,formation of nitrogen vacancies,condensed interlayer stacking and breaking of intraplanar hydrogen bonds,which result in the extended visible-light-responsive range and improved separation of photo-generated carriers.