现代化工

现代化工 ›› 2025, Vol. 45 ›› Issue (4) : 147-152. DOI: 10.16606/j.cnki.issn0253-4320.2025.04.026

科研与开发

铁基MOF/还原石墨烯复合泡沫镍降解罗丹明B的研究

高樱 ¹^,²^,^* ,
谢芳舒 ³ ,
林歆昊 ⁴ ,
朱维晃 ³

作者信息 +

Degradation of Rhodamine B by iron-based MOF/reduced graphene modified nickel foam

GAO Ying ¹^,²^,^* ,
XIE Fang-shu ³ ,
LIN Xin-hao ⁴ ,
ZHU Wei-huang ³

Author information +

文章历史 +

Received		Published
2024-07-08		2025-04-20
Issue Date	Revised Date
2025-04-14	2024-07-08

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摘要

为改善传统电芬顿氧化技术对污染物降解效率有限和添加的可溶性二价铁(Fe²⁺)导致二次污染等问题,通过水热-煅烧法构建出还原石墨烯/铁基MOF修饰的泡沫镍(rGO/MIL-88A/NF)电芬顿阴极。通过仪器分析与电化学测试确定了rGO/MIL-88A/NF的物化性能与电化学活性。以罗丹明B(RhB)为目标污染物,研究rGO/MIL-88A/NF阴极对RhB的降解性能,以及不同电位与pH条件对体系降解RhB的影响。结合淬灭实验与XPS分析,探究rGO/MIL-88A/NF降解污染物的运行机理。结果表明,rGO/MIL-88A/NF无需外界投加H₂O₂与Fe²⁺,为高效降解污染物的新型电芬顿阴极开发提供研究基础与思路。

Abstract

The traditional electro-Fenton oxidation technology has a limited efficiency in degrading pollutants,and will lead to the secondary pollution due to the addition of soluble divalent iron (Fe²⁺).In order to solve these issues,a reduced graphene/iron-based MOF modified nickel foam (rGO/MIL-88A/NF) electro-Fenton cathode is constructed via hydrothermal-calcination method.Through instrument characterization and electrochemical testing,the physicochemical properties and electrochemical activity of rGO/MIL-88A/NF are clarified.Taking Rhodamine B (RhB) as the target pollutant,the degradation performance of rGO/MIL-88A/NF cathode to RhB is studied,and the influences of different potentials and pH conditions on the degradation of RhB by the cathode are explored.Combined with the quenching experiment and XPS analysis,the operational mechanism for rGO/MIL-88A/NF in degrading pollutants is researched.It is found that rGO/MIL-88A/NF does not require external addition of H₂O₂ and Fe²⁺,which provides a research foundation and approach for the development of a novel electro-Fenton cathode that can remove pollutants efficiently.

Graphical abstract

关键词

铁基MOF / 电芬顿 / 阴极 / 还原石墨烯

Key words

iron-based MOF / electro-Fenton / cathode / reduced graphene

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染料废水是一种常见的工业废水,具有排放量大、成分复杂、难生物降解等特点。染料废水不仅对国家的生态环保、可持续发展造成威胁,还会对人类的身体健康造成危害^[1]。罗丹明B(RhB)作为三苯甲烷类染料之一,广泛应用于印染行业、有色玻璃等领域^[2]。RhB不仅刺激人类眼睛、皮肤和呼吸道,吸食后更对肾脏、肺部以及心脑血管造成危害^[3]。因此,开发高效降解RhB的方法具有重要意义。

电芬顿法主要通过阴极还原氧生成过氧化氢(H₂O₂),H₂O₂进而与Fe²⁺发生芬顿反应生成氧化还原电位高达2.8 eV的羟基自由基(OH·),实现对各类污染物无选择地深度降解^[4-5]。然而,阴极有限的H₂O₂产量与铁泥引发二次污染的问题限制着电芬顿的实际性能。针对上述问题,国内外研究学者设计出不同的改性阴极与异相H₂O₂活化剂,一定程度上解决了传统电芬顿的限制性因素^[6-7]。有机金属框架(MOF)是一系列以金属团簇或金属离子为中心,连接着有机配体的多孔晶体材料。MOF特殊的晶体结构有助于保持其活性位的稳定性,因而成为芬顿催化理想的候选材料^[8-9]。以过渡金属为中心原子的MOF系列表现出优异的H₂O₂催化分解活性^[10]。Li等^[11]发现H₂O₂经Cu(Ⅰ)-MOF活化后,对磺胺甲

唑有良好的去除效果。以MIL-53、MIL-88B与MIL-101等为代表的Fe-MOF在超声/H₂O₂环境下表现出高效的四环素降解能力,主要反应途径是Fe-MOF上配位不饱和铁位点对H₂O₂的吸附和分解效果,有助于大量强氧化自由基的生成^[12]。然而,MOF的连接配体通常是弱导电性或绝缘性的,限制着阴极表面的电子转移。还原石墨烯(rGO)由于其独特的晶体结构,能够弥补MOF配体导电性不足的缺陷,有助于改善MIL-88A-Fe修饰阴极的电荷传递效率。

因此,笔者以具有稳定活性位的MIL-88A为H₂O₂活化剂,通过rGO的修饰将MIL-88A固定于泡沫镍(NF)基底,制得同时具有自产H₂O₂/活化H₂O₂双功能阴极材料(rGO/MIL-88A/NF)。通过仪器表征、电化学测试等分析rGO/MIL-88A/NF的理化性质与电化学活性;以RhB为目标污染物,研究不同反应条件(外加电位、pH)对RhB降解率的影响;结合淬灭实验和X射线能谱(XPS)探究rGO/MIL-88A/NF阴极的微观运行机制。

1 材料与方法

1.1 试剂与仪器

石墨,青岛华泰有限公司生产;九水合硝酸铁、反丁烯二酸、叔丁醇,天津天力有限公司生产;RhB、硫酸钠,科密欧生产;对苯醌,梯希爱生产,以上试剂均为分析纯。实验用水由超纯水仪制备。

1.2 阴极制备

GO的制备:采用改进的Hummers法制备GO。

MIL-88A的制备:将140 mg反丁烯二酸溶解于20 mL水中,在70℃水浴中保持10 min。将530 mg九水合硝酸铁溶解于10 mL水中,缓慢加入上述反丁烯二酸溶液中,将混合溶液水浴搅拌10 min。将上述混合物加入聚四氟乙烯内衬的反应釜(40 mL)中,110℃下保持6 h。冷却至室温后,用乙醇洗涤沉淀物数次,在70℃下干燥12 h,得到MIL-88A。

rGO/MIL-88A/NF的制备:取2 mg MIL-88A溶于60 mL乙醇中,超声5 min后向上述溶液加入 1 mg GO与10 μL Nafion。将上述混合物均匀涂覆于NF表面(2 cm×2 cm)。在80℃干燥12 h后,得到rGO/MIL-88A/NF。

1.3 实验装置

电化学性能测试与降解性能测试的实验装置主要包括:电化学工作站(上海辰华CHI600E);rGO/MIL-88A/NF工作电极、铂对电极(213型)、银/氯化银参比电极(sat.KCl,0.195 V vs SHE)组成的三电极体系。

1.4 电化学性能测试

循环伏安曲线(CV)的扫描速率为50 mV/s,测试范围为-0.8~0.8 V。交流阻抗测试(EIS)的频率范围为100 kHz~10 mHz,使用Zsimwin软件对EIS数据进行拟合。

1.5 降解性能测试

以20 μmol/L的RhB为目标污染物、硫酸钠为电解质,采用上海辰华CHI600E型电化学工作站的i-T模式向体系施加恒电位,进行污染物降解性能测试。利用紫外分光光度计在最大吸收波长为554 nm时测定吸光度并计算降解率。

2 结果与讨论

2.1 rGO/MIL-88A/NF的表征

空白NF与rGO/MIL-88A/NF的SEM图和EDS图如图1所示。

从图1(a)、(b)中可以看出,未修饰空白NF的SEM形貌中可见空白NF有序的孔状结构,放大数倍后可清晰看到其光滑的表面。从图1(c)、(d)中可以看出,MIL-88A呈现出棒状外形,与文献[13]中的报道相吻合。此外,MIL-88A高均匀性地附着在NF表面。rGO在固化MOF时起类似粘结剂作用,在MIL-88A与NF之间形成一层薄膜,将MIL-88A均匀地固定于基底NF上,保证rGO/MIL-88A/NF的结构稳定性。从图1(e)~(h)中可以看出,rGO/MIL-88A/NF主要由元素C、O、Ni和Fe组成,其中部分C、O来源于rGO的修饰,Fe归因于MIL-88A的修饰,表明rGO与MIL-88A已经成功复合于NF表面。

空白NF与rGO/MIL-88A/NF的XPS谱图如图2所示。

从图2(a)中可以看出,rGO/MIL-88A/NF主要由C、O、Ni、Fe元素组成,与EDS的测试结果吻合。其中,rGO/MIL-88A/NF的C1s、O1s与Fe2p的峰强度高于空白NF,这与rGO和MIL-88A的修饰有关。由图2(b)可知,rGO/MIL-88A/NF的C—O与O—C=O峰面积高于空白NF,C—O与O—C=O等基团有助于改进阴极的亲水性,并提供双电子氧还原反应的表面活性位点。由图2(c)可知,不同于空白NF,rGO/MIL-88A/NF在531 eV左右出现Fe—O键,这主要归因于MIL-88A的中心原子Fe。由图2(d)可知,rGO/MIL-88A/NF的铁元素价态由Fe²⁺与Fe³⁺组成,其中Fe²⁺约占总Fe的61.1%,有利于阴极产生H₂O₂后的H₂O₂原位活化分解,保证体系中充足的OH·生成与高效的污染物降解。

2.2 rGO/MIL-88A/NF的电化学性能

通过电化学测试分析rGO/MIL-88A/NF的电催化活性与导电性能,结果如图3所示。从图3(a)中可以看出,通过Zimpwin软件对所得数据进行拟合,得到rGO/MIL-88A/NF的R_ct为534.3 Ω,相同条件下空白NF的R_ct高达6728 Ω,说明rGO能够提高NF基底的导电性能,使rGO/MIL-88A/NF阴极具有较高的电子传递速率,有助于提升阴极的H₂O₂产量。此外,MIL-88A均匀分布于rGO上,该阴极的三维结构有利于反应物与活性位点接触,利于进行高效的氧还原反应。从图3(b)中可以看出,测试所用扫描速率为50 mV/s,测试电位范围为-0.8~0.8 V。结果表明在0.51 V和0.02 V左右,rGO/MIL-88A/NF分别出现还原峰和氧化峰。而空白NF的CV谱图无明显的氧化还原峰出现,这归因于rGO/MIL-88A/NF上的Fe²⁺/Fe³⁺价态循环^[14]。此外,rGO/MIL-88A/NF的响应电流远高于空白NF,表明rGO与MIL-88A的修饰对NF电化学活性提升起到协同增效作用。其中,rGO为阴极上电子传递提供途径,增强MIL-88A的Fe²⁺/Fe³⁺价态循环。

2.3 rGO/MIL-88A/NF-电芬顿降解污染物

电芬顿体系对RhB的降解效果受到阴极材料、外加电位、溶液pH等因素影响。不同阴极材料在相同条件下的RhB降解能力对比如图4所示。从图4中可以看出,相较于其他阴极,80 min内rGO/MIL-88A/NF阴极对RhB的降解能力达到最高,这主要归因于rGO优异的导电性与MIL-88A稳定的活化作用。此外,rGO/MIL-88A/NF与空白NF体系的H₂O₂累积量对比如表1所示。从表1中可以看出,在反应进行10 min后,rGO/MIL-88A/NF与空白NF体系的H₂O₂累积量差异达到最高。然而,随着反应进行,两体系之间的差异逐渐减小,这是由于rGO/MIL-88A/NF上的活性Fe²⁺使大量H₂O₂活化分解所致。

不同外加电压(-0.3、-0.4、-0.5、-0.6 V和 -0.7 V)条件下电芬顿体系降解RhB的能力对比如图5(a)所示。从图5(a)中可以看出,当外加电压为-0.3 V时,80 min内RhB降解率达到88.0%左右。随着电压增加到-0.4 V,RhB降解率提高到93.1%左右。而当电压进一步升高,RhB降解率反而降低。这是由于过高的电压会导致H₂O₂分解或其他副反应产生,抑制强氧化自由基的高效生成,降低RhB的降解率。对RhB的降解数据进行拟合,发现符合一级反应动力学规律,如图5(b)所示。不同电位降解RhB的动力学方程及系数如表2所示,根据表2中的动力学系数k可知,在电位为-0.4 V的条件下,RhB的降解速率达到最高。

溶液pH(1.0、3.0、5.0和7.0)对污染物降解的影响如图6所示,不同pH降解RhB的动力学方程及系数如表3所示。从图6(a)中可以看出,调节溶液pH为1.0时,80 min内RhB的降解率达到89.4%;溶液pH为3.0的条件下,电芬顿体系对RhB降解率达到最高;pH为5.0和7.0时,80 min内RhB的降解率仅为80.6%和77.3%。以上实验现象主要由于溶液的pH过低时,体系中过量的H⁺导致副反应发生。H⁺消耗体系中的氧分子并生成水分子,限制阴极催化还原氧的效率^[15]。当溶液的pH过高时,阴极上铁离子的存在形式发生改变,部分具有活性的Fe²⁺由FeOOH或Fe₂O₃取代,导致H₂O₂活化效率降低。根据图6(b)及表3中的动力学系数k可知,在溶液pH为3.0的条件下,RhB的降解速率达到最高。

通过循环实验确定rGO/MIL-88A/NF阴极的催化稳定性,结果如图7所示。从图7中可以看出, 经过4次循环实验后,80 min内RhB的降解率仍然能达到90%以上,表明该rGO/MIL-88A/NF阴极具有良好的稳定性,为阴极表面的氧还原与H₂O₂活化提供持续的催化活性。

2.4 rGO/MIL-88A/NF-电芬顿的反应机理

使用叔丁醇(TBA)和对苯醌(BQ)作为自由基淬灭剂,分别用于清除反应体系中的OH·和超氧自由基(O₂·^-)。不同的淬灭剂对反应体系降解RhB的影响如图8(a)所示。从图8(a)中可以看出,当溶液中添加5 mmol/L TBA后,80 min内RhB的降解率仅为78.8%,这是由于加入TBA导致体系内的OH·被清除。而当溶液中添加5 mmol/L BQ后,80 min内RhB的降解率仅为79.6%。因此,OH·和 O₂·^-是该反应体系的主要活性自由基。

为了进一步研究rGO/MIL-88A/NF的作用机理,测试了反应前后的rGO/MIL-88A/NF的C 1s、O 1s与Fe 2p的XPS高分辨谱图,结果如图8(b)~(d)所示。从图8(b)~(d)中可以看出,反应前后rGO/MIL-88A/NF的C 1s、O 1s谱图并未出现显著变化。然而,对Fe 2p谱图数据进行分析后发现,反应后rGO/MIL-88A/NF中Fe²⁺的质量分数由61.1%转化为59.7%,同时Fe³⁺的质量分数相较反应前略微提升,表明Fe³⁺能通过阴极的还原作用转化为Fe²⁺。Zhu等^[15]发现碳基材料与含铁化合物可以发生络合作用形成C—O—Fe键。类似地,rGO/MIL-88A/NF中rGO和MIL-88A通过C—O—Fe键形成稳定的结构。因此,阴极上的电子可通过C—O—Fe键进行传输,提高了电子传递速率。这不仅保证反应体系中持续的Fe²⁺/Fe³⁺价态循环,还保持了rGO/MIL-88A/NF阴极的高催化活性,有利于RhB的高效降解。

结合淬灭实验及XPS测试结果,推断出rGO/MIL-88A/NF阴极反应机理,如图9所示。氧分子吸附于rGO/MIL-88A/NF阴极表面,经过活性位点的催化激活,与体系中的质子和电子结合后最终生成H₂O₂。rGO为rGO/MIL-88A/NF阴极提供导电性,而MIL-88A是阴极原位激活分解H₂O₂的主要原因。H₂O₂被MIL-88A的中心原子Fe²⁺活化后生成具有强氧化性的OH·,同时Fe²⁺转化为Fe³⁺。rGO/MIL-88A/NF阴极使电子快速通过C—O—Fe键,还原MIL-88A中的Fe³⁺。因此,具有高氧还原活性的双功能rGO/MIL-88A/NF阴极不仅实现芬顿体系高效原位生成H₂O₂,并能够原位活化分解H₂O₂,最终实现RhB的高效降解。

3 结论

(1)通过水热法制备出形态规则的MIL-88A,通过与rGO的共同修饰,最终制备出具有稳定形貌结构的rGO/MIL-88A/NF。经过重复性实验后,rGO/MIL-88A/NF仍保持良好的催化稳定性。

(2)相比于未修饰NF,rGO/MIL-88A/NF作用的电芬顿体系对RhB的降解性能显著提升。在电压为-0.4 V、pH为3.0的条件下,80 min内对RhB的降解率达到94%。此外,rGO与MIL-88A为阴极性能提供协同增效作用,rGO提升阴极的导电性,加快MIL-88A上Fe²⁺/Fe³⁺价态循环,实现零添加H₂O₂与Fe²⁺高效降解污染物。

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