Photocatalytic Membrane Reactors Using Porous Titanium Oxide Membranes

提出了一种新型的光催化反应体系，将二氧化钛本身固定为多孔膜，既能过滤，又能进行光催化反应。该体系的优点是(1)通过对流强制将反应物输送到二氧化钛膜上；这对于稀溶液体系是非常有效的，因为反应物的扩散限制了总反应速度；(2)在多孔二氧化钛膜的内外表面发生氧化反应，预计会产生高浓度的羟基自由基；(3)通过二氧化钛膜的一次渗透后，可以获得被羟基氧化的渗透流。此外，通过控制二氧化钛膜的孔径大小，可以将反应物和产物的选择性结合起来。在污水净化系统中，污染物在透过TiO2膜的过程中被氧化，从而得到纯净水。在黑光照射下，当大约1ppm的三氯乙烯溶液进入多孔二氧化钛膜即光催化膜反应器时，渗透流中三氯乙烯(TCE)的分解率比进水流中的三氯乙烯分解率高达60%。另一方面，在没有辐照的情况下，料液和渗透液的浓度没有差别。与没有过滤的反应相比，全循环系统中膜过滤的反应活性增强。

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.