Laboratoire Chimie de la Matière Condensée de Paris, UMR UPMC-Collège de France-CNRS 7574, Collège de France, 11 place Marcelin Berthelot, 75231 Paris, France.
J Am Chem Soc. 2012 Jul 4;134(26):10761-4. doi: 10.1021/ja303170h. Epub 2012 Jun 20.
Spectroscopic ellipsometry was utilized to follow in situ photodegradation of organic species in the vicinity of TiO(2) nanoparticles during UV irradiation. Stacked layers composed of TiO(2), mesoporous SiO(2), and mixed mesoporous SiO(2)/TiO(2) nanocomposites with controlled thickness and porosity were used as model materials. Lauric acid molecules and poly(vinyl chloride) (PVC) layers were used as model mobile and immobile pollutants, respectively. The local photocatalytic activity was deduced by monitoring the variation of the thickness and refractive index of each independent layer. We show that the photocatalyzed degradation of an organic pollutant takes place only when the latter is located in close vicinity to the TiO(2) nanoparticle surface or can naturally diffuse toward it. As a result, the reaction efficiency is directly related to the organic pollutant diffusion. We also show that the distance of photocatalysis efficiency (d(s)) at which radical intermediates are still present and active is <10 nm from the TiO(2) surface under the conditions of the experiments. This was confirmed by the fact that an immobile condensed organic phase such as PVC was protected from the photocatalytic degradation when separated from the TiO(2) by a 20 nm layer of mesoporous silica.
光谱椭圆偏振法被用于在紫外光照射下，跟踪 TiO(2)纳米粒子附近的有机物种的原位光降解。使用堆叠层，该堆叠层由 TiO(2)、介孔 SiO(2)和具有受控厚度和孔隙率的混合介孔 SiO(2)/TiO(2)纳米复合材料组成，用作模型材料。月桂酸分子和聚氯乙烯(PVC)层分别用作模型可移动和不可移动污染物。通过监测每个独立层的厚度和折射率的变化，推断出局部光催化活性。我们表明，只有当有机污染物位于 TiO(2)纳米粒子表面附近或可以自然扩散到表面时，才会发生光催化降解。因此，反应效率与有机污染物的扩散直接相关。我们还表明，在实验条件下，仍存在和活跃的自由基中间体的光催化效率距离(d(s))<10nm，这一点得到了证实，因为当不可移动的凝聚有机相，如 PVC，通过 20nm 厚的介孔硅层与 TiO(2)分离时，它不会受到光催化降解的影响。
