Planar Photocatalytic Microreactor Of Metal Ion Doped Titanium Dioxide

Photocatalytic sewage purification based on TiO2is a potential environmentalprotection technology. Microreactor is one of the most important future directions ofchemical engineering development. Applying microreactor development intophotocatalytic sewage purification would remarkably enhance the photocatalyticefficiency and promote the industrial application process.In this paper, microreactor substrates of different structures were fabricated bychemical etching and coated with metal ion doped TiO2coatings by sol-gel method tofabricate planar photocatalytic microreactors. X-ray diffraction, Uv-visible diffusereflection spectrum and scanning electron microscope were used to characterize thephotocatalyst coatings. The results showed that TiO2was mostly anatase in the coatingswhen the calcination temperature was above673K and as the calcination temperaturerose, anatase gets lower integrity and larger particle size. When the calcinationtemperature reached973K, part of anatase in the coatings turned into rutile. As thedopant concentration rose (no more than0.5%), the microcracks of TiO2coating getsmaller and less and the grain size slightly increased. The micromorphology of differentmetal ion doped TiO2coatings was similar to each other. Copper ion doping wouldpromote the photoactivity of TiO2under visible light irradiation.Microreactors were tested for the degradation of methyl blue (MB) and methylorange (MO), and the manufacture conditions were optimized. A single-channelphotocatalytic microreactor with0.04%copper ion doped TiO2coating that was calcinedat673K had the best photocatalysis, in which65%MB and45%MO could be degradedwithin90seconds under a200W Xe lamp irradiation. The irradiation intensityexperiment demonstrated a better photocatalysis of metal ion doped TiO2microreactorsthan the undoped one. The solar irradiation experiment proved the excellent simulationof Xe lamp to solar light.Residence time distribution in single-channel microreactor was gained by stepchange method and demonstrated the flow pattern in microreactor was very close to plugflow. The reaction kinetics and products of MB and MO photocatalytic degradationswere investigated. The degradation of MB in undoped TiO2photocatalytic microreactorwas limited by the dissolved oxygen concentration (DOC), while the metal ion dopedTiO2would promote incomplete oxidation degradation of MB with insufficient DOCand produce various intermediate degradation products. The degradations of MO in bothdoped and undoped microreactors were incompletely oxidation and fit the kinetics of first order reaction. A comparative study of photocatalytic microreactors from literatureswith ours was preceded and verified the superiority of our metal ion doped planarmicroreactor in reaction volume and degradation rate per unit volume. Three furthermodifications of photocatalytic microreactors were suggested: proper structure design,highly efficient photocatalyst and well gas-liquid mixture.