Photocatalytic Membrane Reactors Using Porous Titanium Oxide Membranes

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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.