The Preparation Of TiO₂ Photocatalyst Composites And The Mechanism For The Removal Of Nitrogen Oxidation

TiO₂ semiconductor is one of the most potential photocatalytic materials for large-scale environmental application in real life,due to its good stability,high economical,non-toxic and high photocatalytic activity.However,some drawbacks of the TiO₂ semiconductor photocatalyst largely impair its application: a.The TiO₂ photocatalyst can only absorb UV light?wavelength shorter than 386 nm?because of its wide band gap?3.2 eV?,which limit the utilization of sunlight energy.b.The the low photoproduction carrier separation efficiency of TiO₂ photocatalyst resulting in low quantity yield.c.The photocatalytic reaction is a surface chemical reaction,so the adsorption capacity is a key to of TiO₂ photocatalytic reaction.It is a challenge to improve the adsorption capacity of TiO₂ photocatalyst over the gaseous pollutants.To solve these problems,the paper evaluated the nitrogen oxidation?NO_x?removal of as prepared samples under the simulated sunlight and visible light,respectively.The chemical and physical properties of the materials were researched by X-ray diffraction?XRD?,Infrared spectrum testing?FTIR?,X-ray photoelectron spectroscopy?XPS?,Raman spectroscopy test?RS?,Scanning electron microscope?SEM?,Transmission electron microscope?TEM?,Ultraviolet-visible diffuse reflection spectrum?DRS?,Temperature programmed stripping?TPD?.The photoelectric properties of the materials were tested by electrochemical workstation.At the same time by electron spin resonance?ESR?spectrum and capture experiment speculated the photocatalytic mechanism of materials.In this paper,the main research results showed in the followings:1.The titania/hydroxyapatite?TiO₂/HAp?composites were synthesized by a facile hydrothermal method.It was found that the photocatalytic activities of 75% TiO₂/HAp?mass ratios of TiO₂: HAp = 3:1?composites were dramatically improved as compared with the pristine components and other composites under the simulated solar light irradiation.Moreover,the toxic intermediate NO2 production was significantly inhibited over TiO₂/HAp.The high surface area of TiO₂/HAp composites can provide more active sites to promote the reaction rate.The results from temperature programmed desorption?TPD?confirmed that the 75% TiO₂/HAp sample had stronger chemisorption for NO.The photocurrent tests and electrochemical impedance spectroscopy?EIS?show that 75% of TiO₂/HAp possess high separation efficiency and faster transferring of the photo-generated charge carriers.These phenomena may be attributed to the surface of HAp is rich in hydroxyl groups and PO43-groups.On the one hand,the surface OH groups of HAp played a key role in the NO_x adsorption.On the other hand,the surface OH groups due to the hydrogen bond can adsorbed H2 O molecules,which can react with the holes to produce hydroxyl?·OH?radicals.what's more,the electron state change of the PO43-groups in the surface of HAp result in the generation oxygen defect level,which can promote the holes and electrons separation and effectively improve the TiO₂ photocatalytic removal efficiency.2.In this study,we report a very simple carbon doping method to obtain C-doped TiO₂ using the glucose as C source,then C-TiO₂ is hybridized with graphene oxide using hydrothermal method to obtain C-TiO₂/GO,which shows a good visible light catalytic performance and good stability.The NO_x removal rate of C-TiO₂/GO?0.11%?composites is up to 40.5%.The TPD results show that the NO adsorption quantity and bond energy with NO of the C-TiO₂/GO?0.11%?are higher than one component?C-TiO₂?,which may be because the GO surface contains a lot of oxide groups is advantageous to the adsorption of NO.In addition,the photocurrent tests and electrochemical impedance spectroscopy?EIS?have proved that C-TiO₂/GO composites have high photocatalysis activity because of higher the photocurrent density and faster migration rate.The ESR test and capture experiments have proved that ·O2-and ·OH radicals were the major species involved for NO removal over C-TiO₂/GO composites.And it is not a traditional composite photocatalytic mechanism.The introduction of GO leads to the generation of Z-scheme mechanism for C-TiO₂/GO composites that has the high the carrier separation and migration efficiency,and strong oxidation reduction ability.