Photocatalytic Membrane Reactors Using Porous Titanium Oxide Membranes

提出了一种新型的光催化反应体系，在该体系中，二氧化钛本身被固定为多孔膜，既能过滤又能光催化反应。该系统的优点是：（1）反应物通过对流向TiO_2膜强制输送;这对于反应物扩散限制总反应速率的稀溶液体系是相当有效的，（2）在多孔TiO_2膜的外表面和内表面上的氧化反应，其中可以预期高浓度的OH自由基，（3）通过TiO_2膜的一次渗透后，可以得到被OH自由基氧化的渗透液。此外，还可以通过控制TiO_2膜的孔径大小来实现联合收割机对反应物和产物的选择性。在污水净化系统中，透过液中的污染物在透过TiO_2膜的过程中被氧化，得到净化水，当TGE浓度约为1 ppm时，透过液中的TCE降解率可达进料液的60%，在黑光照射下。另一方面，在没有照射的情况下，没有观察到进料和渗透物之间的浓度差异。与没有过滤的反应相比，在全循环系统中证实了膜过滤的增强反应性。

A new type of photocatalytic reaction system in which the titanium dioxide itself is immobilized as a porous membrane capable of not only filtration but also photocatalytic reaction was proposed. The advantages of the system are (1) the forced transport of reactants by convection to TiO_2 membranes ; this would be quite effective for dilute-solution systems where diffusion of reactants limits the total reaction rate, (2) oxidation reaction on the outer and inner surface of porous TiO_2 membranes where high concentrations of OH radicals can be expected, and (3) the possibility to obtain permeate stream oxidized with OH radicals after one-pass permeation through the TiO_2 membranes. Moreover, it is possible to combine selectivity for reactants and products by controlled pore sizes of TiO_2 membranes. For the system of purification of polluted water, purified water would be obtained in the permeate stream by oxidation of pollutants while permeating through the TiO_2 membranes.The decomposition ratio of trichloroethylene (TCE) in permeate stream over that in feed stream was achieved to 60 %, when TGE solutions of approximately 1 ppm was fed to a porous titanium dioxide membrane, that is, the photocatalytic membrane reactor, under blacklight irradiation. On the other hand, no difference in concentration between feed and permeate was observed without the irradiation. Enhanced reactivity with membrane filtration was confirmed in a total recycle system, compared with reaction without filtration.