Heterogeneous Photocatalytic Oxidation of Nitrogen Oxides and Sulfur Dioxide in Aqueous Solutions in Connecton with Environmental Pollution

研究了环境空气中<NO_2^->的非均相光催化氧化与酸雨形成的关系。典型的实验是用氙灯在石英管中照射<NaNO_2>水溶液。水溶液中含有悬浮在超声速下的半导体粉末。<O_2>在水悬浮液中冒泡。在半导体粉末的照射下，<NO_2^->和<O_2>被定量氧化为<NO_3^->。该反应中的光活性半导体粉末为<TiO_2>, ZnO, <Ag_2O>, PbO, <Bi_2O_3>和CdS。在半导体粉末的存在下，研究了<SO_3^(2-)>在水中的光氧化作用。<SO_3^(2-)>在光催化过程中被氧化为<SO_4^(2-)>。<TiO_2>和<Fe_2O_3>是该反应的极活跃光催化剂。在<TiO_2>（锐钛矿）、<TiO_2>（金红石）和ZnO的水悬浮液中，精确测量了光照下<NO_2^->的非均相光氧化速率。对于<NO_2^->的浓度，反应按零阶进行。在假设的环境条件下，对<NO_2^->在云水滴中的光氧化速率进行了估算。当云水含量为0.2 g <m^(-3)>时，速率为11% <h^(-1)>。

Heterogeneous photocatalytic oxidation of <NO_2^-> was studied in connection with acid rain formation in environmental air. Typical experiments consisted of illuminating <NaNO_2> aqueous solution in a quartz tube with a xenon lamp. The aqueous solution contained semiconductor powders kept in suspension supersonically. <O_2> was bubbled into the aqueous suspensions. <NO_2^-> was quantitatively oxidized to <NO_3^-> with <O_2> under illumination in the presence of some semiconductor powders. Photoactive semiconductor powders in this reaction are <TiO_2> , ZnO, <Ag_2O> , PbO, <Bi_2O_3> , and CdS.Photooxidation of <SO_3^(2-)> in water was also studied in the presence of some semiconductor powders. <SO_3^(2-)> is oxidized to <SO_4^(2-)> in the photocatalytic process. <TiO_2> and <Fe_2O_3> are extremely active photocatalyst for this reaction. Rates of heterogeneous photooxidation of <NO_2^-> were precisely measured in aqueous suspension of <TiO_2> (anatase), <TiO_2> (rutile), and ZnO under illumination. The reaction proceeds in zero order with respect to <NO_2^-> concentration. The rate of photooxidation of <NO_2^-> in cloud water droplets was estimated with hypothetical environmental conditions. The rate amounts to 11% <h^(-1)> for cloud water content of 0.2 g <m^(-3)> .