水环境中g-C3N4纳米材料的光化学转化机制及其生物效应研究

Graphitic carbon nitride (g-C3N4) has become a new research hotspot and drawn broad interdisciplinary attention due to the great application potential in visible-light photocatalysis area. g-C3N4 will be extensively produced and used, and its entry to the environment is inevitable. Such releases of g-C3N4 may cause undesired risks to human health and ecosystems. The transformation of g-C3N4 by environmental photochemical processes will change its properties and thus influence its environmental transport, fate, and toxicity, which is critical for assessing the environmental risks and safety application of g-C3N4. However, sufficient attention has not been given to the photochemical transformation of g-C3N4 in the aquatic environment. Therefore, this research project will firstly synthesis 14C-labled g-C3N4 with various structures and properties, and then investigate the transformation and degradation of 14C-labled g-C3N4 by photochemical reactions in water. The degradation kinetics and half-life will be evaluated by monitoring 14CO2 generation. The effect of the typical water quality factors and the features of g-C3N4 on its degradation kinetics will be examined. Then, the structural changes and degradation byproducts of g-C3N4 after photochemical reactions will be characterized by various instruments. Furthermore, the critical reaction oxygen species (ROS) will be identified through EPR and free radical quenching methods. Based on these results, g-C3N4 photochemical transformation pathway and mechanisms will be proposed. Finally, the toxicity and bioaccumulation of g-C3N4 photochemical reaction solutions after different reaction times will be tested using standard test organisms to probe the potential biological impacts of degraded g-C3N4, and establish the relationship between ROS, structural changes, and bio-effects changes during g-C3N4 photochemical degradation process. This research will contribute to understanding the environmental behaviors of g-C3N4, and provides a scientific basis for its risk evaluation and safety application.

极具应用价值的g-C3N4光催化材料将被大量生产使用，并释放到环境中成为新型污染物。g-C3N4在环境中的光化学转化行为能显著影响其归趋及毒性，对其环境风险评估至关重要。基于此，本项目借助14C标记技术，制备不同形貌性质的14C标记的g-C3N4。首先通过监测14CO2的生成，定量研究g-C3N4的降解动力学及半衰期，明确g-C3N4自身性质及水环境因子对其光化学转化的影响；其次表征分析g-C3N4光化学降解中间产物，揭示其光化学降解转化规律及其演变过程；并进一步识别关键反应活性自由基，阐明g-C3N4在环境光化学过程的降解转化机制；最后评价转化后g-C3N4的生物效应，建立“活性自由基-性质变化-生物效应”之间的内在联系。在此基础上，阐明光化学过程对g-C3N4在水环境中的降解转化及对其生物效应的影响。该研究可为深入认识g-C3N4的环境归趋，和评价其生态风险与合理利用提供科学依据。

g-C3N4作为近年来被广泛开发应用的光催化材料，具有极大的应用前景。但在开发应用的同时，评价g-C3N4在使用过程及环境光化学过程的降解转化尤为重要，但目前关于该方面的研究还不多。基于此，本项目主要研究了光化学反应对g-C3N4的降解转化过程及机制，并对其反应前后的环境行为和生物效应的变化进行了初步评估。主要研究内容和结果包括：（1）考察了不同形貌性质的g-C3N4光化学降解动力学，以及重要环境因素对g-C3N4光化学降解转化动力学的影响。发现紫外波段对g-C3N4的光化学降解起主要作用，且g-C3N4经氧化后其氧化程度越高、光化学降解越快；（2）探索了g-C3N4经光化学反应的降解中间产物、途径及对其降解转化起作用的关键活性基团。通过自由基猝灭实验证实•O2ˉ和•OH是g-C3N4光化学降解的关键活性自由基。借助多种仪器分析表征手段对g-C3N4反应后的固体材料表面形貌，元素组成等进行了分析，通过总有机碳（TOC）的降低、无机离子的生成，液相色谱-质谱联用仪（LC-MS）对降解生成的小分子中间产物进行了鉴别。在此基础上，推测g-C3N4经光化学反应，通过脱氨基-羟基化-脱羧基循环反应过程，逐步降解转化为小分子物质，并最终矿化为NO3-、CO2和H2O；（3）考察了经光化学反应前后g-C3N4的水体稳定性、光催化性能和对绿藻毒性的变化。借助Zeta电位测试和沉降实验，发现光化学反应光化学反应引入含O基团，g-C3N4的水稳定性增加，但结构骨架的破坏导致其对四环素降解的光催化活性大大降低。通过藻类暴露发现光化学反应增大了g-C3N4生物毒性效应。本研究系统的研究了g-C3N4的光化学降解过程和机制，并考察了光化学转化对其环境行为、生物效应的影响，可为科学评价g-C3N4的环境行为和健康风险提供依据。