基于生物原细胞模型的凝聚层半导体光催化体系研究

Weak adsorption of organic pollutants on the surface of semiconductor photocatalyst, and the quick recombination of photo-generated electron-hole pairs, are main reasons responsible for the low quantum efficiency of semiconductor photocatalysis. Coacervate micro-droplets, as one of the protocell models, show higher efficiency in (bio-)chemical reactions due to the efficient sequestration of catalyst and substrate from the external water phase into the droplets. In this proposal, photo reaction was further introduced into the coacervate, and the study based on photocatalysis in coacervate system was therefore put forward. The aim of the proposal is to establish the photocatalysis model based on coacervate system by study the effect of the coacervate structure on the aggregation state of the semiconductor photocatalyst and the corresponding behaviors of photophysics and photochemistry. The photocatalysis system based on coacervate is predicted to have high quantum yield due to the high efficient sequestration of semiconductor photocatalyst and organic pollutants into the coacervate micro-droplets. In addition, the special environment of coacervate, such as strong internal electric field, will facilitate the separation of photo-generated electron-hole pairs (supression of the recombination). The study of the proposal will not only promote the development of colloidal science and semiconductor photocatalysis, but also provide new ideas in solving the increasingly serious problems in environment and energy.

有机污染物在催化剂表面的吸附弱以及光生载流子容易复合，是导致半导体光催化效率不高的主要原因。基于生物原细胞模型的凝聚层微反应器，因为可以高倍富集分散于水相中的催化剂和反应物小分子，而显示出比水相更高的反应效率。本项目拟进一步将光引入到凝聚层中，开展基于凝聚层的半导体光催化体系研究。通过考察凝聚层结构对半导体光催化纳米粒子聚集态行为及其光物理和光化学性能的影响，建立基于凝聚层体系的半导体光催化反应模型。凝聚层的富集作用，可以大大提高半导体催化剂周围模型污染物的浓度；凝聚层特殊的微环境（内电场）也有利于半导体光生载流子的分离（抑制复合）。因此，可以预测基于凝聚层体系的半导体光催化，将具有更高的量子效率。本项目的研究，不仅会推动胶体科学和半导体光催化理论的发展，也将为日益严峻的环境与能源问题的解决，提供新的思路。

作为最具代表性的半导体光催化材料，TiO2存在环境污染物吸附弱和降解缺乏选择性的问题。本项目利用环境污染物在凝聚层/水两相中的分配系数不用，开发基于TiO2/凝聚层的半导体光催化体系。基于生物原细胞模型的凝聚层微反应器，因为可以高倍富集分散于水相中的催化剂和反应物小分子，而显示出比水相更高的反应效率。我们系统研究了两种稳定凝聚层（PDDA/ATP和PDDA/KPSE）的构建、光催化剂和模型污染物（MO, MB, RhB, SRhB和X3B等）在凝聚层中的分配与光催化选择性降解行为。结果发现（1）PDDA/ATP和PDDA/KPSE都按照摩尔比3:1的比例混合，可以得到稳定的凝聚层；（2）高能面TiO2纳米片因为其表面高极性，在凝聚层中具有很大的分配系数（在PDDA/ATP凝聚层的分配系数高达6000），非常容易进入凝聚层相；（3）因为分子结构不同，凝聚层对染料模型污染物的富集能力有所差异。RhB难以进入凝聚层，而MO, MB和X3B等染料易于进入凝聚层；（4）通过凝聚层对RhB的屏蔽作用，成功实现混合染料的选择性光催化降解。MB/RhB混合染料在TiO2水溶液中的降解没有选择性，但是MB在TiO2/PDDA/ATP和TiO2/PDDA/KPSE这两种凝聚层中的光催化降解选择性分别高达16.3和9.6；（5）意外发现染料/凝聚层体系存在光致褪色（PDDA/ATP）和光致浑浊（PDDA/KPSE）等光敏现象，有望用于防伪等实际应用领域。本项目的研究，不仅会推动胶体科学和半导体光催化理论的发展，也为日益严峻的环境与能源问题的解决，提供了新的思路。