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目录 contents

    摘要

    采用水热法制备了铁酸锰(MnFe2O4)纳米球修饰的石墨相氮化碳(g-C3N4)复合光催化剂(MnFe2O4/g-C3N4),并对其光催化活化过一硫酸盐(PMS)去除内分泌干扰物双酚A(BPA)的性能进行探究。考察了PMS浓度、MnFe2O4负载量、催化剂投加量及pH对双酚A去除的影响。XRD、SEM、TEM及FT-IR等结果证明,MnFe2O4纳米球已成功负载于g-C3N4。光催化实验结果表明,与单独g-C3N4相比,MnFe2O4/g-C3N4光催化活性有明显提升。同时,PMS的加入可进一步大幅提高该复合光催化剂的光催化性能。当PMS浓度为1 mmol·L-1、MnFe2O4负载量为20%及催化剂投加量为0.5 g·L-1时,复合催化剂光催化活性最佳,反应2 h后,BPA的去除率达到98%。光电化学测试结果表明,引入MnFe2O4后可提升g-C3N4光生载流子分离能力。重复性实验结果表明该复合光催化剂具备较好的稳定性。本研究可为新型高效光催化体系的开发及其在环境污染控制领域的应用提供参考。

    Abstract

    In this work, MnFe2O4/g-C3N4 composite photocatalyst was prepared through a facile hydrothermal method and its photocatalytic activity for BPA degradation was evaluated. The effects of the operational parameters including PMS concentration, MnFe2O4 loading content, catalyst dosage, and pH on photocatalytic degradation of BPA were investigated. The characterization results of X-ray diffraction(XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and Fourier transform infrared spectroscopy (FT-IR) demonstrated that the MnFe2O4 nanospheres have been successfully loaded on the g-C3N4. Compared with bare g-C3N4, the MnFe2O4/g-C3N4 composite showed an enhanced photocatalytic activity for BPA degradation under visible light irradiation. More importantly, the as-prepared hybrids exhibited remarkably improved photocatalytic activities toward BPA degradation in the presence of PMS under visible light irradiation. Nearly 98% of BPA can be removed after 2 h irradiation by the 20% MnFe2O4/g-C3N4 with dosage of 0.5 g·L-1 under the optimal condition of 1 mmol·L-1 PMS. Photoelectrochemical data further confirmed the enhanced charge carrier separation performance of composite. The result of repeated experiments showed that MnFe2O4/g-C3N4 composite possessed an excellent photocatalytic stability. This work paves the way for the design of novel photocatalysis systems with applications in environmental remediation.

    文章栏目:水污染防治

    张明明, 李静, 龚焱, 等. 铁酸锰纳米球修饰石墨相氮化碳光催化活化过一硫酸盐去除双酚A [J]. 环境工程学报, 2019, 13(1): 9-19.

    双酚A(BPA)作为一种典型的内分泌干扰物,因其生产量大、使用范围广、污染面积大等特点引起了各国研究机构及环保部门的高度关[1,2,3]。其主要通过生产及制品使用过程进入到水体,污染水环境并对水生物及人类的健康造成极大的威[4,5,6]。目前,BPA的去除方法主要有物理[7]、生物[8]及化学氧化[9]。其中,传统的物理法和生物法在处理BPA废水时均存在不足。如物理法存在处理不彻底,生物法存在处理周期长、降解效率低的问题。化学氧化法是目前研究最为广泛的一种处理方法,其中光催化氧化法作为一种绿色高效的氧化技术被广泛地应用于BPA的去除。

    光催化氧化技术主要利用受激发半导体催化剂中光生电子与空穴产生的强氧化性自由基物种(·OH等),氧化分解污染物并最终将其矿化为CO2H2O[10,11]。其中,以石墨相氮化碳(g-C3N4)为代表的可见光光催化剂在处理难降解污染物方面引起了广泛的关[12,13,14,15]。g-C3N4具有易制备、无污染、高稳定性等优点。但其存在光生载流子分离能力不足、太阳光利用率低的问[16]。针对该问题,通过对其改性或与其他高级氧化技术结合可提高其光催化活性。近年来,基于硫酸根自由基(SO4•−)的新型高级氧化技术受到众多学者的关[17,18,19]。与·OH相比, S O 4 - 具有氧化电位高、pH适用范围广及半衰期长等优点,有利于有机物的降解。近期研究表明,光生电子可活化过一硫酸盐(PMS)产生 S O 4 - ,实现污染物的高效去[20,21,22]。因此,通过将可活化PMS的光催化剂与g-C3N4相结合,可促进体系中多种活性自由基的产生,进而提高g-C3N4的光催化降解BPA活性。近年来,以MnFe2O4为代表的尖晶石型铁氧体在活化PMS产 S O 4 - 方面展现出了良好的活[23,24,25]。如HUANG[24]制备了高度有序的介孔MnFe2O4,发现该MnFe2O4具备较好的活化PMS产 S O 4 - 能力,可高效去除水中染料。另外,ZHAO[25]通过将MnFe2O4负载于膨润土上制备了MnFe2O4/膨润土复合催化剂,该催化剂可活化PMS产 S O 4 - 实现去除二氯苯酚的效果。本研究采用水热法制备了MnFe2O4纳米球修饰的g-C3N4复合光催化剂,并对其物化性质进行表征。同时,考察其光催化活化PMS降解双酚A的性能及重复利用效果,并进一步对该催化反应的作用机理进行探讨。

  • 1 材料与方法

    1
  • 1.1 实验原料

    1.1

    过一硫酸盐(2KHSO5·KHSO4·K2SO4,PMS)购于Sigma-Aldrich西格玛奥德里奇(上海)贸易有限 公司;三聚氰胺、乙酸钠(NaAc)、聚乙烯基吡咯烷酮(PVP,K30)、硫酸锰(MnSO4·H2O)、三氯化铁 (FeCl3·6H2O)、氢氧化钠(NaOH)、无水硫酸钠(Na2SO4)、无水乙醇(CH3CH2OH)、甲醇(CH3OH)、叔丁醇(C4H9OH)、双酚A(BPA)均为分析纯,购于上海阿拉丁生化科技股份有限公司,实验用水为超纯水。

  • 1.2 催化剂制备方法

    1.2

    采用热缩聚法制备g-C3N4:称取5.00 g三聚氰胺并置于坩埚中,将其转移至马弗炉中,以5 ℃·min-1的升温速率加热至550 ℃并保温4 h。将反应后所得淡黄色g-C3N4块体研磨后备用。采用水热法制备MnFe2O4/g-C3N4复合催化剂,详细步骤为:将1 g PVP溶于40 mL乙二醇中并加入适量g-C3N4,搅拌均匀;随后向混合液中加入0.42 g MnSO4·H2O、1.35 g FeCl3·6H2O和2.46 g NaAc,并持续搅拌1 h;将溶液转移至不锈钢水热反应釜,在200 ℃下加热16 h后,自然冷却至室温;最后用超纯水及无水乙醇清洗约10次,所得固体粉末经60 ℃烘干备用。

  • 1.3 催化剂表征

    1.3

    采用X射线衍射(XRD,X/Pert PRO MPD,帕纳科分析仪器有限公司,荷兰)对催化剂的晶体结构进行表征。催化剂表面官能团信息采用傅里叶变换红外分光光度计(FT-IR,VERTEX 70,布鲁克公司,德国)采集。采用扫描电子显微镜(SEM,SU-8020,日立公司,日本)和透射电子显微镜(TEM,H7500,日立公司,日本)对催化剂的微观形貌进行分析。催化剂的光学吸收性质采用紫外可见漫反射光谱仪(DRS,Hitachi 3010,日立公司,日本)进行测试。

  • 1.4 实验与分析方法

    1.4

    采用长方形的石英反应器(54 mm×50 mm×60 mm)进行光催化降解实验。可见光光源主要由氙灯配用λ>420 nm的紫外截止滤光片提供。首先,称取一定量的催化剂加入到100 mL浓度为10 mg·L-1的双酚A溶液中并保持持续搅拌,反应过程中每隔一定时间进行取样,加等量甲醇淬灭后过0.22 μm膜,采用高效液相色谱法测定溶液中双酚A浓度,使用C18(250 mm×4.6 mm×5 μm)色谱柱和紫外检测器。流动相为超纯水和甲醇(体积比为70∶30),流速为1 mL·min-1。最大吸收波长设置为270 nm。每次反应后,采用离心分离回收反应后的催化剂,并通过多次醇洗与水洗后于60 ℃烘干,所得催化剂再进行重复光催化反应实验。

  • 2 结果与讨论

    2
  • 2.1 催化剂表征

    2.1
  • 2.1.1 XRD分析

    2.1.1

    通过XRD对所制备的g-C3N4、MnFe2O4和MnFe2O4/g-C3N4的晶体结构信息进行分析。如图1所示,在g-C3N4的XRD谱图中可观察到属于石墨相氮化碳的(100)晶面和(002)晶面的特征[12,14],证实了所制备材料为石墨相氮化碳。而由MnFe2O4的谱图可发现,2θ角分别在29.9°、35.1°、42.8°、56.5°和61.6°有明显的衍射峰,分别对应于尖晶石型MnFe2O4(JCPDS 73-1964)的(220)、(311)、(400)、(511)和(440)晶[23],说明合成的纳米球颗粒为尖晶石型MnFe2O4。从MnFe2O4/g-C3N4的XRD谱图中可观察到属于g-C3N4和MnFe2O4的特征峰,未发 现有其他杂质峰的存在,证明了该复合催化剂是由g-C3N4相与MnFe2O4相组成。同时,对比分析发现,复合催化剂中g-C3N4和MnFe2O4特征峰的出峰位置并未发生明显改变,说明MnFe2O4修饰未对g-C3N4的晶体结构造成改变,这也有利于发挥其光催化作用。

    图1
                            g-C3N4、MnFe2O4和MnFe2O4/g-C3N4的XRD图谱

    图1 g-C3N4、MnFe2O4和MnFe2O4/g-C3N4的XRD图谱

    Fig.1 XRD patterns of g-C3N4, MnFe2O4 and MnFe2O4/g-C3N4

  • 2.1.2 SEM分析

    2.1.2

    2为g-C3N4、MnFe2O4和MnFe2O4/g-C3N4的SEM图。由图2(a)可知,所制备的g-C3N4块体主要由尺寸在微米级的片层状结构堆叠组成。而水热合成的MnFe2O4呈现出纳米球颗粒结构,其尺寸均在500 nm左右(如图2(b)所示)。在合成过程中,通过添加PVP作为导向剂,可定向合成该球状MnFe2O4纳米颗粒。图2(c)为所制备的MnFe2O4/g-C3N4复合材料的SEM图,可发现MnFe2O4球状颗粒负载于g-C3N4纳米片层表面,进一步从TEM图(图2(d))中可清晰观察到有明显的球状颗粒附着于层状g-C3N4纳米片表面,表明MnFe2O4纳米球已成功地修饰于g-C3N4表面。以上结果说明,通过该水热法可合成MnFe2O4/g-C3N4复合半导体。与此同时,MnFe2O4纳米球与g-C3N4之间结合有利于二者界面处光生载流子的相互传递,从而有助于提高g-C3N4光催化活性。

    图2
                            g-C3N4、MnFe2O4、MnFe2O4/g-C3N4的SEM图及MnFe2O4/g-C3N4的TEM图

    图2 g-C3N4、MnFe2O4、MnFe2O4/g-C3N4的SEM图及MnFe2O4/g-C3N4的TEM图

    Fig.2 SEM images of g-C3N4, MnFe2O4, MnFe2O4/g-C3N4 and TEM images of MnFe2O4/g-C3N4

  • 2.1.3 FT-IR分析

    2.1.3

    g-C3N4、MnFe2O4和MnFe2O4/g-C3N4的FT-IR图谱如图3所示。对于g-C3N4,在3 100 cm-1处观察到的吸收峰归属于g-C3N4中NH2或吸附H2O,1 641 cm-1处的峰对应于C―N伸缩振动,1 242、1 322、1 405及1 563 cm-1处的峰可归属于g-C3N4结构中芳香性碳氮杂环,800 cm-1处则是g-C3N4中C―N环的面外伸展振[13,15]。从MnFe2O4的红外吸收谱图中可观察到属于MnFe2O4中Mn―O与Fe―O的特征吸收[23]。MnFe2O4/g-C3N4复合催化剂的红外谱图中可同时观察到属于g-C3N4和MnFe2O4的特征吸收峰,表明经水热处理后,MnFe2O4已成功地负载于g-C3N4上。进一步对比复合催化剂与g-C3N4和MnFe2O4的谱图发现,其特征峰的出峰位置有变化,并在FTIR图中添加500~1 500 cm-1段的放大图。从该放大图中可看到,经MnFe2O4修饰后,对应于g-C3N4结构中均三嗪结构的特征峰从806 cm-1移至799 cm-1,说明复合催化剂中g-C3N4的三嗪结构单元和MnFe2O4之间在水热过程中有相互作用,二者间有化合键形成。

    图3
                            g-C3N4、MnFe2O4和MnFe2O4/g-C3N4的FT-IR图谱

    图3 g-C3N4、MnFe2O4和MnFe2O4/g-C3N4的FT-IR图谱

    Fig. 3 FT-IR spectra of g-C3N4, MnFe2O4 and MnFe2O4/g-C3N4

  • 2.1.4 DRS分析

    2.1.4

    采用DRS对g-C3N4、MnFe2O4和MnFe2O4/g-C3N4的光学吸收性质进行研究。由图4所知,g-C3N4的吸收带边位于450 nm左右,具备一定的可见光光吸收能力,可利用波长小于450 nm的太阳光谱能量。而从MnFe2O4的吸收光谱图中可发现其对300~800 nm波段的光均有响应,说明其吸收范围较g-C3N4的广,可利用可见光谱中大部分的能量。对比单独g-C3N4的光吸收曲线可发现,MnFe2O4/g-C3N4复合催化剂的光吸收范围发生明显红移,说明经MnFe2O4修饰后可大幅拓宽g-C3N4的光吸收范围,有利于其对太阳光的利用效率。

    图4
                            g-C3N4、MnFe2O4和MnFe2O4/g-C3N4的DRS图谱

    图4 g-C3N4、MnFe2O4和MnFe2O4/g-C3N4的DRS图谱

    Fig. 4 DRS spectra of g-C3N4, MnFe2O4 and MnFe2O4/g-C3N4

  • 2.2 不同体系BPA降解效果

    2.2

    5为在不同催化剂反应体系下BPA的降解效果对比。从图5中可发现,单独可见光照射条件下,BPA浓度未发生明显变化,说明BPA在可见光条件下光解效果较弱,具有较高的 稳定性。同时,单独PMS对BPA的去除影响很小,说明PMS难以氧化BPA。在可见光照射的条件下,g-C3N4/Vis、MnFe2O4/Vis及MnFe2O4/g-C3N4/Vis光催化体系均对BPA表现出一定的可见光催化活性。其中,经2 h光照反应后,g-C3N4与MnFe2O4对BPA的降解率分别为19%和12%。与之相比,MnFe2O4/g-C3N4复合光催化剂表现出更高的光催化降解BPA的能力,其去除率达到35%。这说明通过修饰MnFe2O4可提高g-C3N4对BPA光催化活性。另一方面,对比分析不同催化剂加PMS的实验结果可发现,g-C3N4/PMS体系难以降解BPA,BPA去除率仅为8%,这主要是由于g-C3N4自身较弱的PMS活化能力所致。而在MnFe2O4/PMS与MnFe2O4/g-C3N4/PMS体系中均可观察到一定的BPA降解活性,这可能是由于MnFe2O4较好的活化PMS能力所致。很明显,在同时光照及PMS存在的条件下,g-C3N4、MnFe2O4及MnFe2O4/g-C3N4体系均表现出较好的光催化降解BPA性能。其中,MnFe2O4/g-C3N4/Vis/PMS体系光催化活性最佳,在PMS浓度为1 mmol·L-1时,经2 h光照反应后,其对BPA的去除率达到98%,同时TOC去除率达 到89%,远高于相同条件下g-C3N4/Vis/PMS与MnFe2O4/Vis/PMS体系,说明MnFe2O4/g-C3N4复合催化剂 体系具有最优的分解与矿化双酚A的能力,可将反应体系中的BPA几乎全部去除。该结果表明,经MnFe2O4改性后的MnFe2O4/g-C3N4具有极高的光催化活化PMS去除BPA的活性。

    图5
                            不同催化剂体系对BPA降解效果的对比

    图5 不同催化剂体系对BPA降解效果的对比

    Fig.5 Comparison of BPA degradation over different catalyst systems

  • 2.3 MnFe2O4掺杂量的影响

    2.3

    6为不同MnFe2O4掺杂量的复合催化剂对BPA降解活性的影响。从图6中可明显发现,MnFe2O4掺杂量对BPA去除有影响。在1 mmol·L-1 PMS条件下,催化体系对BPA的去除率随MnFe2O4掺杂量的增加呈先增强后减弱的变化趋势。其中,当MnFe2O4掺杂量由5%增至20%时,降解效果逐渐增强,并在20%时达到最好,BPA去除率为98%。而随着掺杂量由20%继续增加到50%时,降解效果衰减至72%。导致这种现象的主要原因是:随着负载于g-C3N4表面的MnFe2O4不断增多,g-C3N4表面活化PMS的位点逐渐增多,同时二者之间形成的异质结可提高g-C3N4的光生载流子分离能力,从而表现出更优异的光催化降解BPA活性能力;而当MnFe2O4增至一定量后,过多MnFe2O4覆盖于g-C3N4表面,阻碍 g-C3N4对光的吸收,不利于光生载流子的产生,从而导致其催化活性降低。

    图6
                            不同MnFe2O4掺杂量对BPA降解效果的影响及一级动力学常数

    图6 不同MnFe2O4掺杂量对BPA降解效果的影响及一级动力学常数

    Fig.6 Influence of MnFe2O4 contents on the removal efficiency of BPA and corresponding pseudo-first order constants

  • 2.4 PMS浓度的影响

    2.4

    从图5的对比实验结果可知,引入PMS后,光催化体系对BPA的降解效果得到了提升。因此,考察不同PMS浓度对BPA降解活性的影响。如图7所示,随着PMS浓度的增加,BPA的去除率呈现先增大后减小的趋势。当PMS浓度由0 mmol·L-1增至1 mmol·L-1时,BPA的降解效果得到提高,去除率从35%增加至98%。而当PMS浓度由1 mmol·L-1进一步增至2 mmol·L-1时,去除率提高有限,这主要是由于PMS浓度由1 mmol·L-1增至2 mmol·L-1时,反应体系中产生了过多 S O 4 - ,过量的 S O 4 - 自由基之间会发生自淬反应,或与 H S O 5 - 发生反应,生成氧化能力较弱的 S O 5 - 自由基,从而导致参与反应的 S O 4 - 减少,并使反应活性减弱。

    图7
                            PMS浓度对BPA降解效果的影响及一级动力学常数

    图7 PMS浓度对BPA降解效果的影响及一级动力学常数

    Fig.7 Influence of PMS concentration on the removal efficiency of BPA and corresponding pseudo-first order constants

  • 2.5 催化剂投加量的影响

    2.5

    8为不同催化剂投加量对BPA降解的影响。随着催化剂投加量的增大,BPA去除率呈现先增加后减弱的趋势。当催化剂投加量为0.1 g·L-1时,反应2 h后,BPA去除率为85%。而当催化剂投加量增至0.5 g·L-1时,BPA去除率可达到98%。进一步增加催化剂投加量至1.5 g·L-1时,BPA去除率下降至81%。这主要是由于在低浓度时,随着催化剂投加量的增大,可提供的PMS活性位点增多,体系中可产生更多的活性自由基,从而加速BPA的降解。而当催化剂投加量过多时,反应溶液的透光率逐渐下降,不利于g-C3N4对光的吸收,使其光催化活性减弱,BPA去除效果降低。

    图8
                            催化剂投加量对BPA降解效果的影响及一级动力学常数

    图8 催化剂投加量对BPA降解效果的影响及一级动力学常数

    Fig.8 Influence of catalyst dosage on the removal efficiency of BPA and corresponding pseudo-first order constants

  • 2.6 反应液pH的影响

    2.6

    从图9中可发现,反应液pH的变化对BPA降解无较大影响。其中,当pH为9时,BPA去除率最高,可达99%;而当pH为5时,BPA去除率较低,体系中93%的BPA被去除。造成该现象的原因主要是由于碱可活化PMS产生强氧化性自由基,从而提高双酚A的去除效果。而在酸性条件下,体系中的PMS主要以H2SO5的形式存在,不利于催化剂与其反应生成 S O 4 - ,导致BPA去除效果降低。

    图9
                            不同pH对BPA降解效果的影响及一级动力学常数

    图9 不同pH对BPA降解效果的影响及一级动力学常数

    Fig.9 Influence of pH on removal efficiency of BPA and corresponding pseudo-first order constants

  • 2.7 MnFe2O4/g-C3N4稳定性

    2.7
    图10
                            MnFe2O4/g-C3N4稳定性分析

    图10 MnFe2O4/g-C3N4稳定性分析

    Fig.10 Stability analysis of MnFe2O4/g-C3N4

    催化剂的稳定性是考察催化剂性能的一个重要指标。在本实验中,采用重复性实验对MnFe2O4/g-C3N4的稳定性进行考察。如图10所示,经5次重复实验后,MnFe2O4/g-C3N4催化剂对BPA的降解性能未发生明显衰减。其对BPA的去除率仍可维持在90%,表明该复合催化剂具备较高稳定性。

  • 2.8 催化机理分析

    2.8

    以上实验结果表明,通过在MnFe2O4/g-C3N4复合催化剂光催化体系中引入PMS,可大幅提高其对BPA的降解效果。为了确定体系中所产生自由基的种类,采用自由基捕获实验,考察不同自由基对反应的贡献。之前的研究结果表明,在羟基自由基(·OH)与硫酸根自由基( S O 4 - )同时存在的条件下,由于叔丁醇(TBA)与羟基自由基(·OH)反应比硫酸根自由基( S O 4 - )快,可选择性地淬灭掉体系中的·OH。而甲醇(MeOH)则可与·OH与 S O 4 - 快速反应。因此,采用MeOH与TBA作为自由基淬灭剂来考察反应体系中·OH与 S O 4 - 对BPA去除的贡献情况。另外,采用EDTA-2Na与对苯醌(p-BQ)分别作为光生空穴(h+)与超氧自由基(· O 2 - )的淬灭剂。由图11可知,当向体系中加入1 mol·L-1TBA后,BPA的去除率从98%减至89%,表明在该反应体系中·OH的贡献不大。相反,1 mol·L-1 MeOH的加入对催化活性有明显抑制作用,BPA的去除率由98%降至67%。由此可推断在该反应体系中, S O 4 - 对BPA的降解具有明显的贡献。这主要归因于MnFe2O4的引入,提高了催化体系活化PMS的能力,从而产生大量的强氧化性 S O 4 - ,加快BPA的氧化分解。另一方面,对比加入1 mol·L-1 p-BQ与EDTA-2Na的结果可知,p-BQ与EDTA-2Na对BPA的降解起到了明显的抑制作用,以上结果表明,在BPA降解过程中,体系中的活性物种为·OH、 S O 4 - h+及· O 2 - ,其中发挥主要作用的为· O 2 -

    图11
                            不同淬灭剂对降解BPA效能的影响

    图11 不同淬灭剂对降解BPA效能的影响

    Fig.11 Influence of the degradation of BPA in different radical scavengers

    同时,为考察g-C3N4中引入MnFe2O4后对其光生载流子分离效率的影响,采用瞬态光电流测试对g-C3N4和MnFe2O4/g-C3N4的光电流响应性能进行研究。如图12所示,g-C3N4和MnFe2O4/g-C3N4在光照时均具光响应性质,表明二者均产生了光生载流子。对比二者的光电流强度发现,MnFe2O4/g-C3N4光电流要明显高于单独g-C3N4,其电流数值大约是g-C3N4的2倍。这说明MnFe2O4的引入可提高g-C3N4光生电子空穴的分离效率,可促使更多的光生电子空穴参与反应,提高g-C3N4的光催化活性。

    图12
                            g-C3N4和MnFe2O4/g-C3N4的光电流响应

    图12 g-C3N4和MnFe2O4/g-C3N4的光电流响应

    Fig.12 Photocurrent profile of g-C3N4 and MnFe2O4/g-C3N4

    基于以上结果可知,经MnFe2O4纳米球改性的g-C3N4具备优异的光催化活化PMS去除BPA的能力。这主要归因于2个方面。一方面,MnFe2O4与g-C3N4形成的异质结结构有利于二者之间光生载流子分离,提高光催化活性。如图13所示,由于MnFe2O4的导带与价带位置均高于g-C3N4[26],二者结合形成异质结后,异质结界面处MnFe2O4产生的光生电子向g-C3N4导带转移,而g-C3N4产生的空穴则转移至MnFe2O4价带,从而促进g-C3N4光生载流子分离,提高其光催化活性。MnFe2O4的价带空穴可直接氧化BPA,而转移至g-C3N4导带的光生电子则可与表面吸附的O2发生反应,生成· O 2 - 活性自由基,氧化BPA。另一方面,由于MnFe2O4自身具有较好的活化PMS能力,其晶体表面的Mn(II)与Fe(III)与PMS反应生成高活性的 S O 4 - [23,27],可强化体系中活性自由基产生的种类与数量,从而大幅提高体系对BPA的去除能力。

    图13
                            MnFe2O4/g-C3N4体系光催化活化PMS降解BPA机理示意图

    图13 MnFe2O4/g-C3N4体系光催化活化PMS降解BPA机理示意图

    Fig.13 Schematic diagram of mechanism of the photocatalytic BPA degradation by MnFe2O4/g-C3N4 with PMS

  • 3 结论

    3

    1) 通过水热法合成铁酸锰(MnFe2O4)纳米球修饰的石墨相氮化碳 (g-C3N4)复合光催化剂,该催化剂具备较好的光催化活化PMS降解BPA的能力。在PMS浓度为1 mmol·L-1,2 h可见光照反应后,该MnFe2O4/g-C3N4/Vis/PMS体系对BPA的去除率达到98%。

    2) MnFe2O4掺杂量、PMS浓度及催化剂投加量对光催化降解BPA活性有较大影响,pH对BPA降解效果影响不大。其中,当MnFe2O4掺杂量为20%、PMS浓度为1 mmol·L-1及催化剂投加量为0.5 g·L-1时,该复合催化剂催化活性达到最优。

    3) 自由基捕获实验结果表明该光催化反应过程中, S O 4 - 、· O 2 - 及光生h+对BPA降解均有贡献,其中超氧自由基的贡献最大。光电流测试证实了MnFe2O4的引入可提高g-C3N4的光生载流子分离。同时,该复合催化剂具备较好的稳定性。

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张明明

机 构:

1. 河北工业大学土木与交通学院,天津 300401

2. 中国科学院生态环境研究中心,环境水质学国家重点实验室,北京 100085

Affiliation:

1. School of Civil and Transportation, Hebei University of Technology, Tianjin 300401, China

2. State Key Laboratory of Environmental Aquatic Chemistry, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing 100085, China

角 色:第一作者

Role:First author

邮 箱:zmmhbgydx@aliyun.com

第一作者简介:张明明(1993— ),女,硕士研究生。研究方向:高级氧化技术。E-mail:zmmhbgydx@aliyun.com

李静

机 构:河北工业大学土木与交通学院,天津 300401

Affiliation:School of Civil and Transportation, Hebei University of Technology, Tianjin 300401, China

龚焱

机 构:中国科学院生态环境研究中心,环境水质学国家重点实验室,北京 100085

Affiliation:State Key Laboratory of Environmental Aquatic Chemistry, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing 100085, China

李一兵

机 构:河北工业大学土木与交通学院,天津 300401

Affiliation:School of Civil and Transportation, Hebei University of Technology, Tianjin 300401, China

赵旭

机 构:中国科学院生态环境研究中心,环境水质学国家重点实验室,北京 100085

Affiliation:State Key Laboratory of Environmental Aquatic Chemistry, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing 100085, China

角 色:通讯作者

Role:Corresponding author

邮 箱:zhaoxu@rcees.ac.cnzhaoxu@rcorresponding author

作者简介:赵旭(1976— ),男,博士,研究员。研究方向:环境电化学、光催化等。E-mail:zhaoxu@rcees.ac.cn

金曙光,郑晓梅,张利田

角 色:中文编辑

Role:Editor

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图1 g-C3N4、MnFe2O4和MnFe2O4/g-C3N4的XRD图谱

Fig.1 XRD patterns of g-C3N4, MnFe2O4 and MnFe2O4/g-C3N4

图2 g-C3N4、MnFe2O4、MnFe2O4/g-C3N4的SEM图及MnFe2O4/g-C3N4的TEM图

Fig.2 SEM images of g-C3N4, MnFe2O4, MnFe2O4/g-C3N4 and TEM images of MnFe2O4/g-C3N4

图3 g-C3N4、MnFe2O4和MnFe2O4/g-C3N4的FT-IR图谱

Fig. 3 FT-IR spectra of g-C3N4, MnFe2O4 and MnFe2O4/g-C3N4

图4 g-C3N4、MnFe2O4和MnFe2O4/g-C3N4的DRS图谱

Fig. 4 DRS spectra of g-C3N4, MnFe2O4 and MnFe2O4/g-C3N4

图5 不同催化剂体系对BPA降解效果的对比

Fig.5 Comparison of BPA degradation over different catalyst systems

图6 不同MnFe2O4掺杂量对BPA降解效果的影响及一级动力学常数

Fig.6 Influence of MnFe2O4 contents on the removal efficiency of BPA and corresponding pseudo-first order constants

图7 PMS浓度对BPA降解效果的影响及一级动力学常数

Fig.7 Influence of PMS concentration on the removal efficiency of BPA and corresponding pseudo-first order constants

图8 催化剂投加量对BPA降解效果的影响及一级动力学常数

Fig.8 Influence of catalyst dosage on the removal efficiency of BPA and corresponding pseudo-first order constants

图9 不同pH对BPA降解效果的影响及一级动力学常数

Fig.9 Influence of pH on removal efficiency of BPA and corresponding pseudo-first order constants

图10 MnFe2O4/g-C3N4稳定性分析

Fig.10 Stability analysis of MnFe2O4/g-C3N4

图11 不同淬灭剂对降解BPA效能的影响

Fig.11 Influence of the degradation of BPA in different radical scavengers

图12 g-C3N4和MnFe2O4/g-C3N4的光电流响应

Fig.12 Photocurrent profile of g-C3N4 and MnFe2O4/g-C3N4

图13 MnFe2O4/g-C3N4体系光催化活化PMS降解BPA机理示意图

Fig.13 Schematic diagram of mechanism of the photocatalytic BPA degradation by MnFe2O4/g-C3N4 with PMS

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