Heterogeneous catalytic activation of peroxymonosulfate for efficient degradation of organic pollutants by magnetic Cu^0/Fe_3O_4 submicron composites

亚微米级Cu^0/Fe_3O_4复合物多相催化过一硫酸盐降解有机污染物（英文）

Magnetic Cu^0/Fe3O4 submicron composites were prepared using a hydrothermal method and used as heterogeneous catalysts for the activation of peroxymonosulfate（PMS） and the degradation of organic pollutants.The as-prepared magnetic Cu^0/Fe3O4 submicron composites were composed of Cu^0 and Fe3O4 crystals and had an average size of approximately 220 nm.The Cu^0/Fe3O4 composites could efficiently catalyze the activation of PMS to generate singlet oxygen,and thus induced the rapid degradation of rhodamine B,methylene blue,orange Ⅱ,phenol and 4-chlorophenol.The use of0.1 g/L of the Cu^0/Fe3O4 composites induced the complete removal of rhodamine B（20 μmol/L） in15 min,methylene blue（20 μmol/L） in 5 min,orange Ⅱ（20 μmol/L） in 10 min,phenol（0.1mmol/L） in 30 min and 4-chlorophenol（0.1 mmol/L） in 15 min with an initial pH value of 7.0 and a PMS concentration of 0.5 mmol/L.The total organic carbon（TOC） removal higher than 85%for all of these five pollutants was obtained in 30 min when the PMS concentration was 2.5 mmol/L.The rate of degradation was considerably higher than that obtained with Cu^0 or Fe3O4 particles alone.The enhanced catalytic activity of the Cu^0/Fe3O4 composites in the activation of PMS was attributed to the synergistic effect of the Cu^0 and Fe3O4 crystals in the composites.Singlet oxygen was identified as the primary reactive oxygen species responsible for pollutant degradation by electron spin resonance and radical quenching experiments.A possible mechanism for the activation of PMS by Cu^0/Fe3O4 composites is proposed as electron transfer from the organic pollutants to PMS induces the activation of PMS to generate ^1O2,which induces the degradation of the organic pollutants.As a magnetic catalyst,the Cu^0/Fe3O4 composites were easily recovered by magnetic separation,and exhibited excellent stability over five successive degradation cycles.The present study provides a facile and green heterogeneous catalysis method for the oxidative removal of organic pollutants.

过一硫酸盐催化活化技术因其可产生强氧化性活性氧化物种,可快速氧化降解并矿化有机污染物的优异性能而备受关注.本文成功制备了亚微米级Cu^0/Fe_3O_4复合物,发现其能多相催化过一硫酸盐产生单线态氧降解有机污染物.首先,以CuCl_2·2H_2O,FeCl_2·4H_2O和FeCl_3·6H_2O为铜源和铁源,水合肼为还原剂,采用水热法在180℃反应24 h制备了亚微米级磁性Cu^0/Fe_3O_4复合物.表征结果显示,所制材料为Cu^0和Fe_3O_4的复合物,颗粒大小约为220 nm;单一相Cu^0和Fe_3O_4晶体粒径分别为33.8和106.2 nm,而Cu^0/Fe_3O_4复合物中Cu^0和Fe_3O_4晶体粒径分别减为20.8和31.9 nm.这表明Cu^0和Fe_3O_4复合降低了Cu^0和Fe_3O_4晶体粒径,有利于Cu^0和Fe_3O_4的分散.BET测试结果表明,Cu^0/Fe_3O_4复合物比表面积为4.6 m^2/g,与Cu^0颗粒的(4.2 m^2/g)相当,但远小于Fe_3O_4的(15.6 m^2/g).制备的Cu^0/Fe_3O_4复合物可有效催化过一硫酸盐产生单线态氧降解罗丹明B、亚甲基蓝、金橙Ⅱ、苯酚和对氯酚.当Cu^0/Fe_3O_4复合物的用量为0.1 g/L,过一硫酸盐浓度为0.5 mmol/L和初始pH为7时,Cu^0/Fe_3O_4复合物可在30 min内完全降解20μmol/L的罗丹明B、亚甲基蓝、金橙Ⅱ以及0.1 mmol/L的苯酚和对氯酚.对比试验显示,在相同条件下,Cu^0和Fe_3O_4颗粒分别可以降解28%和20%的罗丹明B.这表明Cu^0/Fe_3O_4复合物中的Cu^0和Fe_3O_4晶体在催化过一硫酸盐降解污染物的反应中具有协同作用,这主要来源于Cu^0/Fe_3O_4复合物中Cu^0和Fe_3O_4的晶体粒径变小和更好的分散.采用分光光度法测定了降解反应液中铜和铁离子的溶出量.当Cu^0/Fe_3O_4复合物的用量为0.1 g/L,过一硫酸盐浓度为0.5 mmol/L和初始pH为7时,反应60 min后,降解液中铜和铁离子的浓度分别为0.22和0.1 mg/L,仅占复合物中总铜和总铁量的1.1%和0.2%,表明Cu^0/Fe_3O_4复合物具有较强的化学稳定性.所制Cu^0/Fe_3O_4复合物具有超顺磁性,借助磁场实现快速分离回收,可循环利用五次,表明其优越的催化稳定性.通过加入乙醇和叠氮化钠,考察了Cu^0/Fe_3O_4复合物催化活化过一硫酸盐体系中的活性氧化物种.发现100 mmol/L乙醇的加入对污染物的降解无明显影响,而加入同等量的叠氮化钠可完全抑制污染物的降解,表明Cu^0/Fe_3O_4复合物催化活化过一硫酸盐产生的主要活性氧物种为单线态氧.采用电子顺磁共振谱进一步证实了单线态氧的生成.基于以上研究,Cu^0/Fe_3O_4复合物催化活化过一硫酸盐的机理为Cu^0/Fe_3O_4作为一个电子媒介加速过一硫酸盐和污染物之间的电子转移,从而导致污染物被快速降解.该反应机理不同于常见的金属催化过一硫酸盐产生硫酸根和羟自由基的反应机理.我们推测,电导性优良的Cu^0在此催化反应中起着关键性作用.本催化方法可作为一种绿色的氧化技术用于环境污染物的氧化降解处理.