新型Fe_3O_4@α-MnO_2活化过一硫酸盐降解水中偶氮染料

Novel Fe_3O_4@α-MnO_2 activated peroxymonosulfate degradation of azo dyes in aqueous solution

采用两步水热法制备了新型磁性纳米Fe_3O_4@α-MnO_2复合材料作为催化剂,用于活化过一硫酸盐(PMS)产生强氧化性的硫酸根自由基(SO4-·)氧化降解偶氮染料活性黑5(RBK5).采用透射电子显微镜(TEM),X射线粉末衍射仪(XRD)和振动样品磁强计(VSM)对制备的催化剂进行表征,证明成功合成了纳米α-MnO_2包覆Fe_3O_4形态的Fe_3O_4@α-MnO_2催化剂,催化剂的饱和磁化强度为39.89emu/g.Fe_3O_4@α-MnO_2催化剂活化PMS与单一的Fe_3O_4和α-MnO_2活化PMS相比,具有更高的催化效率,说明铁锰双金属存在协同作用.同时研究了催化剂的投加量、PMS的浓度和初始pH值等各种因素对RBK5的降解效率以及反应动力学的影响.实验结果表明,Fe_3O_4@α-MnO_2催化剂活化PMS降解RBK5的过程符合准一级反应动力学,在催化剂投加量为1.2g/L,PMS的浓度为4mmol/L,初始pH值为7.0,反应时间为60min的情况下,浓度为30mg/L的RBK5的降解效率可达到91%,此时RBK5的降解速率常数也达到最高值0.023min^(-1).此外,通过加入自由基淬灭剂甲醇、叔丁醇和硝基苯判断了Fe_3O_4@α-MnO_2/PMS体系中起主要氧化降解作用的活性物种为SO4-·.

The degradation of reactive black 5, an azo dye, in aqueous solutions was investigated using novel magnetic nano-Fe3O4@α-MnO2 catalyst, which prepared by two step hydrothermal method. The catalyst was characterized by transmission electron microscope（TEM）, X-ray diffraction（XRD） and vibration sample magnetometer（VSM）. TEM and XRD results of as-synthesized catalyst showed the nano-α-MnO2 coated Fe3O4 was successfully prepared. VSM indicated the saturation magnetization of nano-Fe3O4@α-MnO2 was reach up to 39.89 emu/g. As all the Fe3O4, α-MnO2 and nano-Fe3O4@α-MnO2 was applied to assess the individual and interaction effects of metals, the higher catalytic efficiency of nano-Fe3O4@α-MnO2 implied the synergistic effect between Fe and Mn. Several operating parameters（catalyst dosage, PMS concentration and initial p H value） on the treatment efficiency and reaction kinetics of RBK5 were also studied. As results, the RBK5 degradation process via Fe3O4@α-MnO2 activated PMS is consistent with the pseudo-first-order reaction. The degradation efficiency of RBK5（30 mg/L） could reach 91% within 60 min under the condition of the catalyst dosage was 1.2 g/L, the PMS concentration was 4 mmol/L, and the initial p H value was 7.0. Under this situation, the degradation rate constant of RBK5 also reached the highest value of 0.023 min^-1. Moreover, the main active species in RBK5 degradation in Fe3O4@α-MnO2/PMS system was identified as SO4-· by adding radical quencher such as methanol, tert-butanol and nitrobenzene.