木质素基水凝胶负载纳米颗粒对稻田镉的吸附消减机理

Cadmium pollution of rice fields in China is serious, but it is lack of effective means to eliminate cadmium in soil. Nanoparticles are an excellent adsorbent due to its strong affinity for cadmium sorption. However, nanoparticle application in soil remediation are greatly restricted because they are easily aggregated, potentially toxic and difficult to be recovered in the environment. This study plans to use environmentally-stable hydrogel to support nanoparticles in order to solve the above problems. This study will choose nanoparticle-lignin based hydrogel composites as the research object. Firstly, regulation mechanism of nanoparticle size and mechanical strength will be studied by exploring the responses of nanoparticle distribution and hydrogel tensile property to the reaction conditions such as time and temperature. Secondly, the interface reaction mechanism and influencing factors of cadmium adsorption will be clarified by correlating the physicochemical properties of the composites with the cadmium adsorption thermodynamics and kinetics. The effects of application method and water holding capacity on elimination process of cadmium in paddy field and degradation/mineralization process of the composites will be investigated via soil incubation experiments. The cadmium -removing performance of the composites will be evaluated as well. The proposed study will provide a theoretical basis for establishment of a new nanoparticle-based method to remove cadmium from paddy soil and is of great significance for the restoration of polluted soil and the food security.

我国稻田镉污染问题突出，但有效的净化手段匮乏。纳米颗粒具有特殊的反应活性，能与镉强力结合，是一种优良吸附剂。但纳米颗粒在环境中具有易团聚性、潜在毒性，且难以回收，极大限制了其在稻田镉污染修复中的应用。本研究拟通过环境稳定型水凝胶负载纳米颗粒的方式解决上述问题，以木质素基水凝胶负载纳米颗粒复合材料为研究对象，通过探索纳米颗粒赋存形态和材料拉伸性能对温度、时间等反应条件的响应，阐明交联程度对纳米粒径和机械强度的调控机制；通过耦合镉的吸附热力学和动力学行为与材料的理化性质，阐明材料吸附镉的界面反应机制和影响因素；在此基础上，通过土壤培养实验，探讨施用方式、持水量对水田镉的消除过程和材料降解矿化过程的影响，评价复合材料消减水田镉的性能，为建立一种基于纳米颗粒消减水田镉的新方法提供科学依据。本研究对于修复污染水田、保障粮食安全具有重要意义。

稻田土壤镉污染问题突出，目前尚缺乏稻田镉污染切实有效的消减途径。针对水田环境特点，申请人提出构筑稳定型纳米复合水凝胶用于稻田土壤Cd高效消除。项目优选采用木质素与丙烯酰胺自由基共聚以及原位负载策略，制备了一种兼具高效Cd吸附和稳定机械性能的负载纳米FeS的木质素水凝胶复合材料（FeS@LH）。通过改变木质素和丙烯酰胺单体的比例，调控水凝胶聚合程度，进而实现FeS纳米颗粒的尺寸和负载含量的调控。通过FTIR、SEM、XRD、XPS等对FeS@LH的结构进行表征，通过TG-DTA、降解实验、压缩实验评估FeS@LH的热稳定性能和机械强度，批吸附实验表明FeS@LH对水体中镉的吸附符合准二级吸附动力学和Langmuir吸附热力学模型。耦合分析结果表明，沉淀反应是吸附镉的主要机理，占比84.06%；其次是水凝胶络合反应、水凝胶溶胀、纳米粒子表面吸附。土壤培养实验表明，表层施用的方式、3 cm覆水土壤，动态条件可取得FeS@LH的最大去除效果；FeS@LH纳米复合材料可有效消除中轻度和重度污染稻田土壤中Cd，消减率可达49.6%和22.4％；大田实验结果显示，应用30天后FeS@LH回收率可达96.8%，保留有较强的机械强度，对土壤中和空心菜中的Cd含量最大消除率分别达37.6%和34.5%；FeS@LH的应用降低了空心菜中Pb、Cu等的含量，提高了土壤中TN和有机质的含量，可重建土壤优势菌群。本研究完成了从土壤Cd消减水凝胶的构建, 并系统化验证了水体、土壤和大田实验中镉消除效果，为Cd污染农田修复提供了新材料、新策略以及数据支撑。