Photocatalytic Oxidation Of Aromatic Alcohols And Degradation Of Methylene Blue By Chip Microchannels And Paper Spray-based Microdroplets

Conventional bulk-phase reactions are generally carried out in large-volume containers,which are apt to generate a concentration bias.Such a concentration bias leads to low collision probability of reactants in the bulk solution,and finally decreases the reaction rate.For a photocatalytic reaction carried out in bulk solution,the light penetration in the large-volume container is specificly poor,so that the light energy can’t be utilized efficiently.Microreactors typically include microchannel reactors,microdroplets,membranes,etc.has advantages of extremely small amouts of reactants and solvents consumption,significant reaction rate and excellent mass transfer and heat transfer efficiencies.Microreactors have been widely used in analytical science,organic synthesis,material analysis,mechanism exploration and so on.Photocatalysis is a recent discipline particularly green and environmental frendly since it operates at room temperature by replacing catalyst’s thermo-activation by photo-activation（or replacing phonons by photons）.It can promote the degradation or synthesis process of desirable compounds once the light energy is converted into chemical energy.So photocatalytic reactions in microreactors which have both advantages of microreactors and photocatalysis become a new trend in photochemistry.In this dissertation,photocatalyzed oxidation and degradation were performed in two microreactors（microchannels in microchips and microdroplets from paper spray）in which direct oxidation of aromatic alcohols into their corresponding carboxylic acids in¹00%yields and highly efficient degradation of methylene blue（¹00%）were achieved.The specific research contents of this thesis are listed as follows:（1）The magnetic nano-Fe₃O₄@SiO₂@TiO₂ was prepared under different conditions,and the magnetic nanoparticles with good suspension and photocatalysis properties for passing into the microchannel reactor were screened.We established a microanalysis system for the on-line degradation and monitoring of high concentrations of methylene blue in a microchannel-based microreactor by ultraviolet light,in which the magnetic nanoparticles as the photocatalyst were separated by the external magnetic field before the off-channel ultraviolet-visible detection.The conditions of catalytic system,reaction temperature,sample flow rate,Fe₃O₄@SiO₂@TiO₂ concentration,H₂O₂ concentration were optimized.Under the optimal conditions,we achieved nearly 100%photocatalytic degradation of 2×10^-4 mol/L methylene blue in 15 min.（2）We established a reaction system for oxidation of aromatic alcohols to aromatic acids,in which the ultraviolet light was used as the light source,sodium hypochlorite was used as the oxidant,and the paper-based spray was used as the microreactor.We optimized illumination wavelength,voltage,distance,paper tip angle,alcohol to water ratio,paper base and solvent type,etc,in order to achieve high yields and high quantity of aromatic acid in microdroplets.In the microdroplets,the yields of all tested aromatic alcohols oxidized to aromatic acids were close to 100%（except for p-nitrobenzyl alcohol with a yield of 39%）in45 min.In the conventional bulk solution,however,the yields of aromatic acids were 1-10%with 2-50%yield of aromatic aldehyde and small amounts of a by-product.Increasing the paper spray tip number,the synthesized amounts of aromatic acids in the paper spray were enhanced to 19 mg/h.（3）We established a reaction system for photocatalyzed degradation of organic dyes（with methylene blue as the model）in a thin film and microdroplets from paper spray,in which the UV-LED array was used as the light source,and GO-TiO₂ was used as the catalyst.The initial amount of dye,the catalytic system,the amount of catalyst,the light intensity,and the spray solvent were optimized.When the supporting capacity of GO-TiO₂ on the paper surface was80μg/cm²,4.5μg methylene blue was nearly 100%degraded within 15 minutes,and the degradation rates of toluidine blue O,azure B,Congo red,methyl orange,orange II and crystal violet were 98%,97%,95%,65%,70%and 49%,respectively.Under the same conditions,when TiO₂ was used as catalyst,the catalytic efficiencies of methylene blue,toluidine blue O and azure I were 80%,91%and 71%,respectively,whereas the degradation rates of methyl orange,orange II and crystal violet were 78%,86%and 51%,respectively with comparable degradation rates of Congo red（100%）.