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全球纺织业每年的染料总消耗量超过10 000 t,并且每年约有100 t的染料被排放到自然水体中[1]。染料废水具有色度高、毒性大、成分复杂且难生物降解的特点,对环境和人体都有危害。罗丹明B(RhB)是一种在轻工业中广泛使用的阳离子型染料,具有致癌性。
处理染料废水的常用方法包括物理法、化学法和生物法[2]。近年来,随着新能源的开发与利用,具有绿色环保特征的光催化技术备受人们的关注[3]。光催化降解有机染料被认为是一种清洁高效的染料废水处理方法,该方法能够高效地将多种污染物转化为毒性较小的中间产物,或是将其彻底降解为CO2和H2O,达到无害化处理的要求。
近年来,金属有机框架(MOF)材料在光催化领域受到越来越多的关注[4-7]。MOF材料是一类由金属离子(簇)和有机配体配位而成的杂化材料[8],具有稳定性高[9]、比表面积大、孔隙度高以及结构灵活可调的典型特征[10-12]。MOF材料在异相催化等领域均有优异的表现[13-14],其出众的吸附性能[15]与异相催化潜力为传统的染料废水处理提供了新的解决方案[16]。但是,大多数 MOF材料的宽带隙只能吸收紫外光,而对可见光吸收率低[17],并且纯MOF材料存在光生电子-空穴对复合快的问题[18],导致其光催化活性并不理想。因此,许多研究致力于采用配体修饰[19-20]、掺杂金属[21-22]等方法对MOF材料进行改性,以提升其光催化活性。目前,氨基修饰是增强MOF材料可见光吸收的一种常用方法[23-25]。
本研究评估了氨基修饰Fe/Cu-MOF对RhB的光催化降解性能,考察了非氨基配体/氨基配体的配比、初始条件对催化效果的影响,并基于以上结果提出了氨基修饰Fe/Cu-MOF光催化降解RhB的反应机制,包括光捕获和电子转移路径,以及主要活性物种的生成过程。
氨基修饰增强的Fe/Cu-MOF对罗丹明B的光催化降解性能及相关机理
Performance and mechanism of amino modification enhanced photocatalytic degradation of Rhodamine B by Fe/Cu-MOF
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摘要: 利用溶剂热合成法合成了氨基修饰的Fe/Cu-MOF-NH2,分别采用XRD、SEM、N2吸附-脱附、UV-vis、EA等检测方法进行了表征分析,并将其用于RhB的光催化降解,考察了RhB的初始质量浓度、催化剂质量浓度和pH对光催化降解的影响。结果表明,氨基的引入显著提升了催化剂的可见光响应性能;在合成Fe/Cu-MOF-NH2时,当含氨基配体与不含氨基配体的摩尔比为1∶1、RhB初始质量浓度为300 mg·L−1、催化剂质量浓度为1 mg·mL−1、pH为4.2时,光照4 h后,催化剂对RhB的去除率达到99.53%。活性物种淬灭实验结果表明,·OH、h+分别是Fe/Cu-MOF-NH2和Fe/Cu-MOF在催化降解过程中的主要活性物种。以上结果可为探究Fe/Cu-MOF-NH2光催化降解RhB的机制提供参考。Abstract: An amino-modified Fe/Cu-MOF-NH2 was synthesized by solvothermal method for photocatalytic degradation of RhB. And this composite was characterized by XRD, SEM, N2 adsorption-desorption, UV-vis and EA. The effects of RhB initial concentration, catalyst concentration and pH on the photocatalytic degradation of RhB were investigated. The result showed that the visible light response of the catalyst increased greatly after amino modification. When the molar ratio of the amino ligand to the non-amino ligand was 1∶1 during Fe/Cu-MOF-NH2 synthesis, the removal rate of RhB reached 99.53% for 300 mg·L−1 RhB after 4 hours of irradiation at Fe/Cu-MOF-NH2 dosage of 1 mg·mL−1 and pH=4.2. The quenching experiments of active species showed that ·OH and h+ were the main active species in the catalytic degradation of Fe/Cu-MOF-NH2 and Fe/Cu-MOF, respectively. The above results can provide a reference for exploring the mechanism of photocatalytic degradation of RhB by Fe/Cu-MOF-NH2.
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表 1 Fe/Cu-MOF与Fe/Cu-MOF- NH2的比表面积、孔容与孔径
Table 1. Specific surface area, pore volume and average pore size of Fe/Cu-MOF and Fe/Cu-MOF-NH2
样品 比表面积/(m2·g−1) 孔容/(cm3·g−1) 平均孔径/nm Fe/Cu-MOF 248.3 0.211 3.401 Fe/Cu-MOF-NH2 21.11 0.120 22.805 表 2 Fe/Cu-MOF和Fe/Cu-MOF-NH2的元素含量分析
Table 2. Elemental analysis of Fe/Cu-MOF and Fe/Cu-MOF-NH2
% 样品 N C H Fe/Cu-MOF 1.21 30.67 4.696 Fe/Cu-MOF-NH2 4.02 31.59 5.511 表 3 不同温度下煅烧的Fe/Cu-MOF-NH2的比表面积、孔容与孔径
Table 3. Specific surface area, pore volume and average pore size of Fe/Cu-MOF-NH2 calcined at different temperatures
样品 比表面积/(m2·g−1) 孔容/(cm3·g−1) 孔径/nm Fe/Cu-MOF-NH2 21.11 0.120 22.805 Fe/Cu-MOF-NH2-200 ℃ 18.369 0.091 23.373 Fe/Cu-MOF-NH2-300 ℃ 15.626 0.114 24.898 -
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