g-C3N4 改性Bi2O3 对盐酸四环素的光催化降解
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Photocatalytic Degradation of Tetracycline Hydrochloride by g-C3N4 Modified Bi2O3
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Corresponding authors: OUYANG Erming, Tel:
Received: 2022-09-06 Revised: 2022-10-11
作者简介 About authors
任富彦,男,1996年生,硕士
使用液相沉淀法和热聚合法制备Bi2O3/g-C3N4复合催化剂,用SEM、XRD、XPS、FT-IR和紫外可见漫反射等手段对其微观形貌、晶体结构和光催化性能进行了表征。结果表明,这种Bi2O3/g-C3N4复合光催化剂的形貌较好、分布均匀,具有较高的光催化性能;复合催化剂Bi2O3/g-C3N4-30%的光催化性能最好,用300 W模拟可见光氙灯照射2 h后对盐酸四环素(TCH)的去除率为70%;捕获实验的结果表明,光催化降解盐酸四环素(TCH)的主要活性物种为超氧自由基(·O
关键词:
Composite catalysts of Bi2O3/g-C3N4 were successfully prepared by means of liquid-phase precipitation and thermal polymerization methods. The microscopic morphology, crystal structure and photocatalytic properties of the composite catalysts were characterized by SEM, XRD, XPS, FT-IR and UV-Vis diffuse reflection etc. The results show that the prepared Bi2O3/g-C3N4 composite photocatalyst has good morphology and uniformity of grains. The Bi2O3/g-C3N4 composite catalyst showed good photocatalytic performance. Among all the prepared composite catalysts, the composite catalyst Bi2O3/g-C3N4-30% had the best photocatalytic performance. The removal rate of tetracycline hydrochloride (TCH) by Bi2O3/g-C3N4-30% composite catalyst was 70%, which was 1.66 times that of pure Bi2O3 and 1.44 times that of pure g-C3N4. In addition, the photocatalytic degradation of tetracycline hydrochloride was verified by capture experiments. The main active species of (TCH) is superoxide radical (·O2-).
Keywords:
本文引用格式
任富彦, 欧阳二明.
REN Fuyan, OUYANG Erming.
Bi2O3是一种金属氧化物p型半导体[6],因具有特殊的介电、光学和离子导电特性而广泛用于制造气体传感器、光电子器件和光催化剂[7-8]。四种多晶体Bi2O3分别为单斜相α、四方β、体立方相γ和面立方相δ,其中单斜结构的Bi2O3在可见光照射下光催化性能较好[9,10]。Bi2O3的成本低、禁带宽度适当且能被可见光激发[11,12],但是纯Bi2O3中光电子的复合极快使其光催化活性降低[11]。有多种方法修饰Bi2O3以克服这一缺陷,包括半导体复合、碳引入、金属/非金属离子掺杂[13,14]和金属有机框架的构建[15]。其中半导体复合可降低光生电子-空穴的复合率,可提高材料的光催化活性[13,16]。g-C3N4是一种有机半导体光催化剂,因其稳定性高、低成本、可见光反应优异和可调节的结构[17]而广泛用于污染物降解和消毒[18]。同时,g-C3N4还具有独特的表面结构和合适的价带位置。Bi2O3/g-C3N4复合材料的分离光生电荷的效率,取决于在两种半导体之间的界面上建立异质结。而合成复合材料方法,必须促进半导体之间发生电荷转移的界面接触。根据两种半导体之间形成的接触水平,z型或p-n型异质结是Bi2O3/g-C3N4复合材料中电荷分离的机制[19,20]。在Bi2O3/g-C3N4复合材料的光催化反应过程中,产生与g-C3N4密切接触的Bi2O3纳米材料的合成方法[21~23]有利于z型异质结的构建,而p-n型异质结产生两种半导体之间较差的接触[24]。
基于以上分析,本文将g-C3N4与Bi2O3的复合制备z型异质结,以及一系列不同g-C3N4负载(10%~50%)的复合材料。用可见光照射降解TCH,研究Bi2O3/g-C3N4复合材料的光催化性能。
1 实验方法
1.1 实验用试剂和仪器
实验用试剂:五水和硝酸铋(Bi(NO3)3·5H2O,纯度高于98%)、氢氧化钠(NaOH,纯度不低于97%)、硝酸(HNO3, 69%)、碘化钾(KI,纯度不低于99%)、对苯醌(P-BQZ/C6H4O2,纯度不低于98%)、异丙醇(IPA,≥99%)、乙醇(纯度不低于99%)和双氰胺(纯度不低于99%)。
实验用仪器:扫描电镜(SEM,日立S-3400N)、X射线光电子能谱(XPS,Esca Lab 250 Xi,赛默飞)、X射线衍射仪(XRD,Rigaku D/max-Brm)、傅里叶红外光谱分析仪(FT-IR,Nicolet Nexus 470)和紫外-可见光度计(UV-3600)。
1.2 样品的制备
石墨相氮化碳(g-C3N4)的制备: 将置于氧化铝坩埚中的5 g双氰胺放入马弗炉中煅烧,以4℃/min的速率升温至550℃,保温3.5 h后冷却至室温。将煅烧产物研磨后用去离子水充分洗涤,然后烘干。
Bi2O3/g-C3N4复合材料的制备:将5.82 g的Bi(NO3)3·5H2O溶于60 mL 1.5 mol/L的HNO3溶液中,然后将其置于水浴锅中边搅拌边加热至50℃,加入适当质量的g-C3N4并搅拌30 min后,再缓慢加入溶有5.2 g NaOH的40 mL H2O溶液,继续加热搅拌2 h后停止加热,再搅拌2 h后离心分离产物,将得到的样品用水和醇充分清洗,随后放入70℃恒温鼓风干燥箱内烘干,然后再将其放置在马弗炉中以4.5℃/min的升温速率升温至400℃煅烧2 h,冷却后取出样品,记为Bi2O3/g-C3N4-X。X为g-C3N4的质量分数,分别为0%、10%、20%、30%、40%、50%。制备Bi2O3/g-C3N4复合材料的示意图如图1所示。用相同的方法不添加g-C3N4制备出光催化剂Bi2O3。
图1
图1
制备Bi2O3/g-C3N4复合材料的示意图
Fig.1
Schematic diagram of preparation of Bi2O3/g-C3N4 composites
1.3 样品性能的表征
用X射线衍射(XRD)、扫描电镜(SEM)、傅里叶红外光谱分析仪(FT-IR)、X射线光电子能谱(XPS)等手段表征样品的形貌。在下文所有表征项目中的Bi2O3/g-C3N4复合材料,均为Bi2O3/g-C3N4-30%。
用300 W长弧氙灯模拟可见光,在其照射下降解TCH,测试Bi2O3/g-C3N4复合材料的光催化性能。实验中将150 mg催化剂加入100 mL盐酸四环素中。启动氙灯前将溶液在黑暗中磁力搅拌器搅拌30 min,达到吸附-解吸平衡后启动氙灯,每隔20 min取4 mL上清液并用0.22 µm滤头去除溶液中的催化剂,然后用紫外分光光度计记录TCH的吸光度,降解效率(
式中C0和Ct 分别为TCH溶液的初始浓度和在处理时间t时刻的浓度。
2 结果与讨论
2.1 样品的形貌
图2给出了g-C3N4、Bi2O3和Bi2O3/g-C3N4材料的SEM照片。从图2a可见,g-C3N4是堆叠在一起的不规则块状结构,分布密集且表面光滑。图2b表明,用NaOH为沉淀剂制备的棒状Bi2O3分布均匀。在图2d中可见穿插在一起的块状结构和棒状结构,g-C3N4占据在棒与棒之间的空隙,Bi2O3颗粒占据在褶皱中。这有利于Bi2O3/g-C3N4复合材料的形成,并增大比表面积和提高光催化的吸附性能。用TEM分析了Bi2O3/g-C3N4复合材料的微观结构(图2c),可见Bi2O3/g-C3N4复合材料中Bi2O3/和g-C3N4紧密接触,出现一个明显的界面,证实了Bi2O3/与g-C3N4结合成功。在图2e给出的Bi2O3/g-C3N4的EDS图可观察到C、N、O和Bi元素,证明g-C3N4块与g-C3N4成功结合。
图2
图2
g-C3N4、Bi2O3和Bi2O3/g-C3N4材料的SEM图谱、Bi2O3/g-C3N4材料的TEM图谱及Bi2O3/g-C3N4的EDS图
Fig.2
SEM patterns of g-C3N4 (a), Bi2O3 (b) and Bi2O3/g-C3N4 materials (d), TEM patterns of Bi2O3/g-C3N4 materials (c) and EDS patterns of Bi2O3/g-C3N4 material (e)
2.2 材料的组成
图3给出了材料的XRD谱,可见g-C3N4、Bi2O3和Bi2O3/g-C3N4在2θ为10°~80°的所有衍射峰。位于2θ为12.94°和27.75°处的是g-C3N4的特征峰,分别属于g-C3N4的(100)和(002)晶面[25,26]。与Bi2O3的标准卡(PDF#41-1449)对比表明,所制备的单斜相Bi2O3位于2θ为27.3°、33.07°、46.30°和54.8°的特征衍射峰分别对应Bi2O3的(120)、(200)、(041)和(
图3
图3
g-C3N4、Bi2O3和Bi2O3/g-C3N4材料的XRD谱
Fig.3
XRD patterns of g-C3N4, Bi2O3 and Bi2O3/g-C3N4 materials
2.3 FT-IR分析
根据FT-IR光谱研究g-C3N4、Bi2O3和Bi2O3/g-C3N4的结构,找出两种材料之间的相互作用。如图4所示,在g-C3N4的FT-IR图中波数为3137 cm-1附近的宽峰与水分子的吸附或N-H键伸缩振动有关[28];位于1637 cm-1处的峰值是O-H基团的弯曲振动引起的[29];位于808 cm-1的强烈而尖锐的峰,可归因于s-三嗪芳族单元的典型振动;1248 cm-1~1637 cm-1之间的多个峰属于NH-C2或全三角N-C3基团[30]。与g-C3N4相比,Bi2O3的FT-IR图谱的峰较少,除了由波数为1389 cm-1处-OH(吸附H2O中)伸缩振动引起的峰,其它的峰都在400~537 cm-1,应该归因于Bi-O-Bi的伸缩振动峰和Bi-O的振动峰。Bi2O3/g-C3N4复合材料吸附水分子或N-H基团使宽峰的强度有所降低,两种材料复合后400~537 cm-1的金属-氧键峰强度和1248~1637 cm-1的g-C3N4不同峰的强度也有所降低,表明Bi2O3/g-C3N4光催化剂的特征峰与纯Bi2O3与g-C3N4相似。FT-IR光谱证实了Bi2O3/g-C3N4光催化剂的成功合成。
图4
图4
g-C3N4、Bi2O3和Bi2O3/g-C3N4材料的FT-IR谱
Fig.4
FT-IR images of g-C3N4, Bi2O3 and Bi2O3/g-C3N4 materials
2.4 XPS分析
对Bi2O3/g-C3N4复合催化剂的XRD谱和FT-IR的分析表明,催化剂中只存在Bi2O3和g-C3N4相,但是不能反映催化剂的表面结构。为此,测试XPS并分析了Bi2O3/g-C3N4材料的氧化态和表面化学组成,结果如图5所示。图5a给出了Bi2O3/g-C3N4复合催化剂的全谱图,可清晰地观察到C、N、Bi和O元素。图5b给出了复合催化剂Bi2O3/g-C3N4样品中Bi4f的高分辨率XPS光谱,其XPS曲线有两个特征峰,分别在164.06和158.76 eV处,属于Bi4f5/2和Bi4f7/2的两个轨道上的电子[31],都是Bi3+的特征峰。图5c中的O 1s峰分别位于529.26和530.28 eV处,分别属于样品中的表面羟基(Bi-O-H)和Bi-O键[32],由此可推断Bi2O3的存在。未发现与Bi其它价态相关联的其它峰,表明样品纯度比较高。在复合材料的N1s的XPS谱中,在398.24和399.41 eV处出现两个峰,表明三嗪环中sp2-N键的C-N=C和C—N基团的存在[33],在400.97 eV处观察到的N1s的小峰属于叔-(C)3族中的N。图5e中C1s光谱284.57、288.08和288.45 eV处拟合的三个特征峰,分别归属于氮化碳基体中的C—C键、芳香环中的C-N-C和与NH2基团连接的芳香环中的C-(N)3[34]。上述结果证明,合成的催化剂由铋(bi4f)、碳(c1s)、氮(N 1s)和氧(O 1s)元素组成。
图5
2.5 固体紫外-可见漫反射吸收谱分析
图6
图6
g-C3N4、Bi2O3和Bi2O3/g-C3N4材料的UV-Vis漫反射光谱和(Ahv)1/2与光子能量(hv)的关系
Fig.6
UV-Vis diffuse reflectance spectra (a) and (Ahv)1/2 versus photon energy (hv) for g-C3N4, Bi2O3 and Bi2O3/g-C3N4 materials (b)
用Kubelka-Munk函数计算其禁带宽度为[35]
其中α、h、v、A、Eg和n分别为吸光系数、普朗克常数、频率、常数、半导体禁带宽度和指数,而指数n则表征半导体光催化剂指数(间接带隙半导体n=2,直接带隙半导体n=1/2),由于Bi2O3是直接带隙半导体,所以n的值为1/2。禁带宽度由图6b曲线的直线段作切线与横轴交点确定,得到Bi2O3的禁带宽度为2.82 eV。而g-C3N4是间接带隙半导体,其禁带宽度为(Ahv)1/2对光子能量(hv)的曲线图上切线与x轴的交点,为2.49 eV。
2.6 Bi2O3/g-C3N4 复合材料的光催化性能
Bi2O3/g-C3N4复合材料的光催化性能,取决于g-C3N4的含量。因此,在可见光下降解TCH的性能,取决于Bi2O3/g-C3N4复合光催化剂中g-C3N4的含量。从图7a可以看出,纯Bi2O3和g-C3N4的光催化性能较差,对TCH的去除率分别只有53%和50%。Bi2O3/g-C3N4-10、Bi2O3/g-C3N4-20、Bi2O3/g-C3N4-30、Bi2O3/g-C3N4-40和Bi2O3/g-C3N4-50的复合材料光照120 min后对TCH的降解率分别为62.9%、67.4%、70%、65.9%和65.3%。这表明,Bi2O3/g-C3N4复合光催化剂的光催化性能优于纯Bi2O3和g-C3N4。同时,g-C3N4的含量为30%的材料去除率最高(为70%),而g-C3N4的含量提高到50%其去除率仅为65.3%。其原因是,Bi2O3棒上含量过高的g-C3N4抑制了可见光的吸收和光传输能力,造成对光催化的负面影响。而g-C3N4含量过低时没有足够的g-C3N4块插入Bi2O3棒上形成复合材料,也使可见光的利用率和折射效应降低。因此,减少电子迁移到光催化剂的表面可能使去除效率较低。
图7
图7
不同催化剂对TCH的降解效率及其反应过程中的一阶动力学拟合图
Fig.7
Degradation efficiency of TCH by different catalysts (a) and its first-order kinetic fitting diagram during the reaction process (b)
为了进一步比较样品的光催化活性,用伪一级动力学方程ln(C0/Ct )=kt描述反应动力学,其中Ct 为t时刻TCH浓度,C0为TCH初始浓度,k为速率常数,速率常数k越大表明降解速率越快。图7b工程了样品降解TCH的伪一级动力学图,Bi2O3、g-C3N4、Bi2O3/g-C3N4-10、Bi2O3/g-C3N4-20、Bi2O3/ g-C3N4-30、Bi2O3/g-C3N4-40和Bi2O3/ g-C3N4-50材料的反应速率常数分别为0.0049、0.00565、0.00631、0.00744、0.00815、0.00721和0.00691 min-1,其中Bi2O3/g-C3N4-30反应速率最大,是纯Bi2O3和g-C3N4的1.66倍和1.44倍。
2.7 材料的稳定性
为了研究Bi2O3/g-C3N4复合材料的可重用性和稳定性,通过在可见光照射下降解TCH评估Bi2O3/g-C3N4。在优化的条件下进行三次重复反应,在每一个阶段催化剂在用乙醇和水的混合物洗涤几次后被回收和重复使用。从图8可见,复合光催化剂循环使用3次后对TCH的去除率仅仅降低了5%,说明复合材料没有明显的失活。这表明,Bi2O3/g-C3N4复合光催化剂具有较高的稳定性。
图8
图8
Bi2O3/g-C3N4复合材料降解TCH的可循环性
Fig.8
Cyclability of Bi2O3/g-C3N4 composites for degradation of TCH
2.8 捕获剂对光催化降解性能的影响
图9
图9
在不同捕获剂条件下盐酸四环素的去除率及其相应的去除率柱状图
Fig.9
Removal rate of tetracycline hydrochloride (a) and its corresponding removal rate histogram (b) under different trapping agent conditions
3 结论
(1) 使用液相沉淀法和热聚合法制备的Bi2O3/g-C3N4复合催化剂其形貌较好和分布均匀,具有较好的光催化性能;
(2) 用300 W模拟可见光氙灯照射2 h复合催化剂Bi2O3/g-C3N4-30%对盐酸四环素(TCH)的去除率为70%。光催化降解盐酸四环素(TCH)的主要活性物种为超氧自由基(·O
(3) 在抗生素浓度为20 mg/L、Bi2O3/g-C3N4光催化剂的剂量为0.15 g/L的条件下,可见光照射120 min对TCH光催化降解效果很好,回收的催化剂使用三次后还有显著地降解性能。
(4) 对TCH的降解,起主要作用的是超氧自由基(·O
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Improved visible-light activities of g-C3N4 nanosheets by co-modifying nano-sized SnO2 and Ag for CO2 reduction and 2,4-dichlorophenol degradation
[J]. ,
Enhanced photocatalytic activity of direct Z-scheme Bi2O3/g-C3N4 composites via facile one-step fabrication
[J]. ,
Direct Z-scheme photocatalysts: principles, synthesis, and applications
[J]. ,
Room-temperature in situ fabrication of Bi2O3/g-C3N4 direct Z-scheme photocatalyst with enhanced photocatalytic activity
[J]. ,
Fabrication of flower-like direct Z-scheme β-Bi2O3/g-C3N4 photocatalyst with enhanced visible light photoactivity for Rhodamine B degradation
[J]. ,
Bi2O3/g-C3N4 nanocomposites as proficient photocatalysts for hydrogen generation from aqueous glycerol solutions beneath visible light
[J]. ,
Dramatic improvement of photocatalytic activity for N-doped Bi2O3/g-C3N4 composites
[J]. ,
Construction of g-C3N4/TiO2/Ag composites with enhanced visible-light photocatalytic activity and antibacterial properties
[J]. ,
Improved visible-light activities for degrading pollutants on TiO2/g-C3N4 nanocomposites by decorating SPR Au nanoparticles and 2,4-dichlorophenol decomposition path
[J]. ,
Photocatalytic activity of enlarged microrods of α-Bi2O3 produced using ethylenediamine-solvent
[J]. ,
Design of 2D-2D NiO/g-C3N4 heterojunction photocatalysts for degradation of an emerging pollutant
[J]. ,
Sulfur-doped g-C3N4/TiO2 S-scheme heterojunction photocatalyst for Congo Red photodegradation
[J]. ,
Ionic liquid assisted preparation of phosphorus-doped g-C3N4 photocatalyst for decomposition of emerging water pollutants
[J]. ,
Synthesis and characterization of Cu2O-modified Bi2O3 nanospheres with enhanced visible light photocatalytic activity
[J]. ,
In situ construction of α-Bi2O3/gC3N4/β-Bi2O3 composites and their highly efficient photocatalytic performances
[J]. ,
Synthesis of g-C3N4/Bi5O7I microspheres with enhanced photocatalytic activity under visible light
[J]. ,
Au/Pd/g-C3N4 nanocomposites for photocatalytic degradation of tetracycline hydrochloride
[J]. ,
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