Encapsulation Of Tiny Titanium Dioxide Within Metalorganic Framework For Photocatalytic Degradation Of VOCs

Recently,volatile organic compuunds are becoming one of the major contributions to air pollution.It brings hidden trouble to the environment and human beings.Photocatalytic oxidation is an important technology in the degration of VOCs,as it can decompose VOCs into CO₂ and H₂O under solar or ultraviolet（UV）light illumination at ambient temperature and pressure.Photocatalyst is the most important part in the photocatalytic reaction.TiO₂ has become the most frequently investigated and promising photocatalyst to use in VOCs purification due to its nontoxicity,inexpensiveness and chemical stability as well as relatively high efficiency.However,the wide band gap of TiO₂（³.2 eV）makes it show reactivity only to the UV region,which accounts for only⁴%of the total solar energy.Moreover,the easy recombination of light carriers and the small specific surface area of TiO₂ which limits their practical applications.The most common strategy involved the integration of TiO₂ with porous material have been developed to achieve this goal.Therefore,in this paper,tiny TiO₂nanoparticles incorporated metal-organic frameworks（MOFs）with large surface area and controllable structure was synthesized.The photoinduced charge separation efficiency of the composite is improved through enhancing the interface contact between MOF and TiO₂.Morever,a novel photocatalytic oxide reator was designed to better evaluate photocatalytic activity of prepared materials.Furthermore,the relationship between the structure and photocatalyst was revealed.Main contents of this part are listed as follows:To meet a better simulate the actual state of VOCs treatment,a new photocatalytic reactor with automatic sampling monitoring device with controllable temperature,humidity and concentration under continuous flow was designed.The reactor perform of stability and practicability was evaluated through the test of continuous flow without photocatalyst,with photocatalyst adsorption and photocatalytic reaction.The result of the blank test showed that the concentration of VOCs could be maintained for a long time,indicating that the photocatalytic reaction system has good stability.In addition,the testing curve of adsorption and photocatalytic degradation of styrene was greatly consistent with the trend of the general degradation of P25 photocatalysts.It implied that the photocatalytic reactor was practicability.In the second part,the NH₂-Ui O-66 encapsulated tiny TiO₂ nanoparticles composites were prepared by self-assembly of MOFs around the Zr⁴⁺pre-coordinated TiO₂ based on the hard-soft acid-base（HSAB）principle and applied to VOCs purification.Compared to bare TiO₂,the TiO₂@NH₂-UiO-66 composites exhibited significantly enhanced photocatalytic activity and anti inactivation.The mechanism study showed that the abundant interconnected3D cavities of the outer MOF allowed for VOCs to easily diffuse into the pores,producing a concentration microenvironment around the encapsulated TiO₂,which was beneficial to the photocatalytic reaction.The TiO₂@NH₂-UiO-66 composites exhibited a markedly improved photocatalytic efficiency and a good resistance to deactivation during the photocatalytic degradation of gaseous styrene under visible light illumination,which were associated with the synergetic effects between the TiO₂ and MOF.At the same time,the good interface contact and the encapsulated structure of the TiO₂@NH₂-UiO-66 composites are beneficial to the migration of photoelectron and the shortening of the distance of the photoelectron transmission,and thus the separation of the photoelectron hole pairs can be improved.