Characteristics Of A Gas-Liquid-Solid Photocatalytic Mini-Fluidized Bed And Heterojunction Catalysts

Gas-liquid-solid photocatalytic mini-fluidized bed reactors have significant application prospects in the chemical,energy and environmental industries.However,relevant literatures haven't been reported at domestic and abroad.This paper designed and manufactured a gas-liquid-solid photocatalytic mini-fluidized bed with hydraulic diameter of 6 mm and a test system.Fe-TiO₂ as catalyst coated on the outer surface of glass beads and inner surface of the reactor.Photocatalytic degradation of MB was used as a model reaction.The degradation rates,mixing and mass transfer characteristics under different flow rates of air,MB flow rates,initial bed heights,Xe lamp powers and initial concentrations were investigated.The mass transfer coefficient and the radiation flux were measured by benzoic acid dissolution method and potassium ferrioxlate actitometer,respectively.Under the conditions of the gas and liquid Reynolds number of this experimental?0.23?Re_G?0.37,33.47?Re_L?60.25?the Thiele modular was 0.0429 and the Dak?hler number Da was much less than 0.1.Therefore,the internal and external mass transfer resistance of the three-phase mimi-fluidized bed can be neglected.The mass transfer coefficient increased on account of that the resistances of mass transfer among the phases decreased.The mass transfer coefficient k_m,MB,MB of the gas-liquid-solid photocatalytic mimi-fluidized bed was32.09×10-5 m s^-1,which was 4.42 times higher than liquid-solid mini-fluidized bed and2.89 times higher than gas-liquid mini-bubble column under the same operation conditions,respectively.The apparent quantum efficiency of the three-phase photocatalytic mini-fluidized bed was 0.19%-0.44%,indicating that it had higher quantum efficiency comparing to photocatalytic plate microchannel reactor.Subsequently,a coupled model based on radiation transfer and reaction kinetics was constructed in mini-fluidized bed with optimized structure of light source.In the development of the coupled model,the effective spectra in this system were discretized into 5 nm interval,assuming that the optical properties of Xe lamp,actinometer and the catalyst were constant over the interval;the polychromatic characteristic of Xe lamp was taken into consideration to obtain the total absorbed photons of the reaction process;a non-uniform radiative flux field due to scattering and absorption of radiation by the solid particles and bubbles in the direction of radiation propagation was established.A novel visible-light response heterojunction catalyst was also developed.The fragmented O-g-C₃N₄ discontinuously coated on the surface of Fe-TiO₂,which exhibited excellent photocatalytic degradation and photocatalytic stability under visible light.Compared with prinstine O-g-C₃N₄ and Fe-TiO₂,the photocatalytic degradation efficiency of O-g-C₃N₄@Fe-TiO₂ was 1.32 and 1.65 times than that of the former two,respectively.Compared with the electrically neutral Fe-TiO₂,the electronegative O-g-C₃N₄ demonstrated excellent adsorption capacity for the cation MB⁺.The proper band structure of the element-doped O-g-C₃N₄ and Fe-TiO₂ catalysts ensured the absorption ability of visible light by O-g-C₃N₄@Fe-TiO₂,at the same time,the Z-scheme transfer mechanism of photogenerated carriers in O-g-C₃N₄@Fe-TiO₂ was constructed.