Abstract:

MnSO₄ and (NH₄)₂S₂O₈ were used as the raw materials for the hydrothermal synthesis of MnO₂, which is an inexpensive, low toxic and effective adsorbent. The structure, morphology and adsorption performance of the obtained MnO₂ were studied by X-ray diffraction (XRD), scanning electron microscopy (SEM) and adsorption experiments, respectively. Moreover, the structure-active relationship was studied. The results showed that burr spherical MnO₂ with three different crystal phases (α, β and γ), β-MnO₂ with spheroidic and needle-like morphologies could be prepared by changing the hydrothermal temperature and hydrothermal time. Among them, the adsorption capacity of burr spherical γ-MnO₂ on methylene blue (MB) could reach 19.33mg/g. The burr spherical like γ-MnO₂ was synthesized at hydrothermal temperature of 80℃ and hydrothermal time of 12h. Burr spherical MnO₂ can be obtained under either of the following situation: ① when the hydrothermal time is 12h, and the hydrothermal temperatures are between 50℃ and 110℃. ② hydrothermal temperature is 80℃ with various hydrothermal time(4h, 8h, 24h). The adsorption of MB is influenced by the crystal phase and morphology of MnO_2. The adsorption performance of burr spherical MnO₂ with various crystal phases is in the order of β<α<γ. Moreover, the adsorption performance of β-MnO₂ with different morphologies is in the order of needle-like2. The adsorption performance of burr spherical γ-MnO₂ on MB was improved by changing the pH of MB solution from 10.00 to 1.00. The adsorption process was accompanied by chemical reaction, and can be described by the Langmuir isothermal model. The result provides a basis for the study of the mechanism and the structure-activity relationship of MnO₂ for adsorbing dye.

Key words: manganese dioxide, adsorption property, methylene blue, morphology, crystal phase, structure-active relationship

摘要：

以MnSO₄和(NH₄)₂S₂O₈为反应原料，采用水热法制备廉价低毒的MnO₂吸附剂。借助X射线粉末衍射（XRD）、扫描电镜（SEM）和静态吸附实验，探究材料的结构、形貌、吸附性能以及构效关系。结果表明，通过改变水热温度、反应时间，可以得到毛刺球状α、β、γ三种晶型MnO₂以及类球状和针状β-MnO₂。其中水热温度80℃、反应12h时得到的毛刺球状γ-MnO₂吸附亚甲基蓝（MB）效果最好，达到19.33mg/g。当水热温度在50～110℃反应12h以及水热温度为80℃反应4h、8h、24h，所得到的产品的形貌均为毛刺球状。晶型和形貌对MnO₂吸附MB能力均有影响。不同晶型的MnO₂毛刺球对MB吸附性能的影响为β＜α＜γ；不同形貌的β-MnO₂却对吸附效果影响较大，为针状＜类球状＜毛刺球形。随着MB溶液的pH从10.00减少到1.00时，毛刺球状γ-MnO₂对MB的吸附量呈上升趋势，吸附过程还伴随着化学反应，且吸附的过程符合Langmuir等温模型。本文将为MnO₂吸附染料的机制和构效关系研究提供依据。

关键词: 二氧化锰, 吸附能力, 亚甲基蓝, 形貌, 晶型, 构效关系