水中石墨烯光化学转化机理的研究

The wide application of graphene leads to its release into aqueous environment. Due to unique electronic structure, graphene has strong photoreactivity exposed to light. In this project, the photochemical transformation behavior and mechanism of graphene in water will be investigated under irradiation of different light sources (xenon lamp, UV lamp, and solar). First, the generation types of reactive oxygen species (ROS) by graphene in water will be investigated. The generation mechanism of ROS based on the electronic structure of graphene will be elucidated. To propose the photochemical transformation pathway of graphene, its surface structure change and intermediates during light irradiation will be analyzed. Second, the electron and energy transfer between dissolved organic matter (DOM) and graphene will be investigated to elucidate the effect mechanism of DOM on ROS generation by graphene. Third, humic acid (HA) and fulvic acid (FA) are selected to investigate the effect of DOM component on photochemical transformation mechanism of graphene. The effect of HA and FA on the adsorption spectrum, dispersity, and photogenerated ROS of graphene will be compared. Combined with the ROS scavenger experiment, the key ROS responsible for the photochemical transformation of graphene in water will be confirmed. The intermediates and mineralization rate of graphene during light irradiation in the presence of HA or FA will be compared. Then the difference and relation between photochemical transformation pathway of graphene with HA or FA will be elucidated. This project will provide insight into the photochemical activity of graphene in aqueous environment.

石墨烯在应用的过程中能够释放到水环境，特殊的电子结构使其在光照下具有很强的光化学活性。本项目拟研究水中石墨烯在不同光源（氙灯、汞灯和太阳光）照射下的光化学转化行为和机理。首先研究石墨烯在水中光致活性氧自由基（ROS）的种类，揭示石墨烯的电子结构决定其光致ROS的机理，分析光照过程中石墨烯表面结构的变化和产生的中间物质，推测石墨烯光化学转化的途径；结合水中溶解性有机质（DOM）广泛共存的情况，研究DOM和石墨烯之间的电子转移和能量传递过程，揭示两者之间的相互作用对石墨烯光致ROS的作用机制；比较DOM两种成分腐殖酸（HA）和富里酸（FA）对石墨烯吸收光谱、分散性和光致ROS的影响，利用ROS淬灭实验判断导致石墨烯光化学转化的关键ROS，研究加入DOM不同成分后石墨烯产生的中间物质的差异，揭示HA或FA对石墨烯光化学转化途径的区别和联系。该课题将对石墨烯在水环境中的光化学行为进行有益探索。

气候因子能够影响天然河流沉积物中DOM的理化性质，可能影响天然水体中纳米材料的稳定性。本项目中，我们从中国不同气候区河流沉积物中提取了腐殖酸和富里酸，研究了不同浓度HA/FA 在NaCl溶液中对大尺寸氧化石墨烯（GO，589 nm）和小尺寸GO (200 nm) 聚集动力学的影响。研究发现，两种浓度HA/FA显著抑制了GO的聚集，归因于DOM为颗粒提供了空间位阻作用。对于大尺寸GO，HA对GO聚集的抑制作用高于FA，归因于HA更高的分子量，更长的碳链，更复杂的分子结构。有趣的是，大尺寸GO在加入0.2 HA后，来自Makou的HA由于更大的分子量，能够更加显著降低GO的聚集速率，然而来自Maqin的HA由于更小的分子量和更高的疏水性，对GO聚集的抑制作用小于来自Makou的HA。低浓度来自Tangke和Panjin的FA具有很高的极性，对大尺寸GO提供了更强的稳定性。光照下HA的空间位阻作用仍然占主导作用，因此抑制了GO聚集。FA光电离产生的电子将GO表面的含氧官能团降解，降低其表面亲水性，促进了其聚集。HA/FA与GO竞争吸收光，抑制了GO产生ROS。DLVO理论计算显示，GO颗粒之间相互接触的能量壁垒取决于DOM的理化性质和GO的尺寸。了解不同气候区沉积物DOM对GO稳定性的影响，对于预测天然系统中纳米颗粒的归趋具有重要意义。