材料工程  2017, Vol. 45 Issue (10): 12-17   PDF    
http://dx.doi.org/10.11868/j.issn.1001-4381.2015.000498
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文章信息

刘阳龙, 郑玉婴, 曹宁宁, 王翔
LIU Yang-long, ZHENG Yu-ying, CAO Ning-ning, WANG xiang
水热法合成铁掺杂的硫化镉及光催化性能
Synthesis and Photocatalytic Activity of Iron Doped CdS by Hydrothermal Method
材料工程, 2017, 45(10): 12-17
Journal of Materials Engineering, 2017, 45(10): 12-17.
http://dx.doi.org/10.11868/j.issn.1001-4381.2015.000498

文章历史

收稿日期: 2015-04-27
修订日期: 2016-10-13
水热法合成铁掺杂的硫化镉及光催化性能
刘阳龙1, 郑玉婴2 , 曹宁宁2, 王翔2    
1. 福州大学 石油化工学院, 福州 350108;
2. 福州大学 材料科学与工程学院, 福州 350108
摘要: 以硝酸镉、硝酸铁和硫脲为原料,水为溶剂,通过水热法一步合成铁掺杂的硫化镉。产物经SEM,XRD,EDS和XPS等技术进行表征,以亚甲基蓝的光催化降解为目标反应,评价其光催化活性。结果表明:水热温度对硫化镉的形貌影响较大,不同反应温度可分别得到球状、花状、簇状和棒状的硫化镉,其中花状硫化镉的光催化性能最高。XRD分析表明,160℃反应时,所得掺铁的硫化镉均为六方晶体结构。光催化实验表明,铁掺杂能进一步提高硫化镉的催化活性,当Fe和Cd的掺杂比为1:10时,催化效果最佳。
关键词: 硫化镉    水热法    形貌    铁掺杂    光催化   
Synthesis and Photocatalytic Activity of Iron Doped CdS by Hydrothermal Method
LIU Yang-long1, ZHENG Yu-ying2 , CAO Ning-ning2, WANG xiang2    
1. School of Chemical Engineering, Fuzhou University, Fuzhou 350108, China;
2. College of Materials Science and Engineering, Fuzhou University, Fuzhou 350108, China
Abstract: Fe-doped cadmium sulfide was prepared by hydrothermal method in aqueous solution using cadmium nitrate, ferric nitrate and thiourea as raw materials. The samples were characterized by SEM, XRD, EDS and XPS. The photocatalytic degradation of methylene blue (MB) in aqueous solution was used as a target reaction to evaluate their photocatalytic activity. The experimental results show that the reaction temperature has a great effect on the morphology of cadmium sulfide, and spherical, flowerlike, clustered and rodlike cadmium sulfide are obtained in various reaction temperatures. Among them, the photocatalytic activity of flowerlike CdS is observed to be better than other CdS materials. The XRD indicates that Fe-doped cadmium sulfide is hexagonal crystal structure when the reaction temperature is 160℃. The experimental results also indicate that Fe-doped can obviously improve the photocatalytic activity of cadmium sulfide and when the doping ratio of Fe to Cd is 1:10, the photocatalytic effect is the best of all.
Key words: CdS    hydrothermal method    morphology    iron doping    photocatalytic   

随着人类社会的快速发展,环境污染问题的日益严重,半导体光催化技术越来越受到人们的重视[1, 2]。半导体光催化技术是利用太阳能,在常温常压下深度降解空气和水中多种挥发性有机物质,在此过程中极少产生二次污染[3, 4]。其中硫化镉(CdS)作为一种典型的Ⅱ-Ⅵ族n型半导体材料,其禁带宽度为2.42eV,能吸收波长小于520nm的紫外光和可见光,具有介电常数小,激子效应大等特点,在太阳能转化、非线性光学、光电调节器、光敏电阻、传感器、光电子、光催化、生物检测等领域具有广泛的应用前景[5-9],因而备受人们的关注。但CdS的光催化效率低、易发生光腐蚀,明显限制了CdS的使用。

研究表明,通过沉积贵金属、嵌入层状化合物、与宽禁带半导体复合、离子掺杂等[10-14]方法,对纯CdS进行改性,能极大地改善材料的光催化活性。其中采用过渡金属离子掺杂[15]的方法可以抑制光生电子和空穴的复合,从而有效地提高光生载流子的分离效率,增大光的利用效率,减缓光腐蚀的发生,有助于延长CdS的使用寿命。

近年来,各种形貌的CdS,如树枝状、棒状、花状、球状等[16-19]均被合成出来,合成方法主要有溶剂共热法、沉淀法、溶胶-凝胶法、水热法等[20-23]。其中水热法更为简单,成本较低,而且反应是在密闭的高压釜中进行,更易控制。如赵荣祥等[24]利用离子液辅助水热法合成了树枝状硫化镉,钱留琴等[25]通过添加表面活性剂PVP,水热法制得了玉米棒状和花状硫化镉。但以水为溶剂,通过一步水热合成的方法,制备铁掺杂的硫化镉晶体,至今鲜见报道。

本工作以硝酸镉为镉源、硝酸铁为铁源、硫脲为硫源,采用水热法制得铁掺杂的硫化镉晶体。与以往很多文献[26-28]不同的是,重点研究了不同温度对硫化镉晶体形貌的影响,不同形貌的硫化镉晶体的光催化性能以及铁的掺杂量对催化活性的影响。

1 实验 1.1 试剂

硫脲((NH2)2CS);无水乙醇(CH3CH2OH);硝酸镉(Cd(NO3)2);九水合硝酸铁(H18FeN3O18),国药集团化学试剂有限公司,AR;去离子水。

1.2 水热法制备CdS

称取3.2g的硫脲、2.5g的硝酸镉、不同量的硝酸铁与70mL去离子水混合,磁力搅拌使其完全溶解后,转移至内衬聚四氟乙烯的高压反应釜中,放入烘箱中在不同温度下恒温反应12h后取出,经自然冷却,将反应后的溶液,经去离子水和乙醇交替洗涤、离心,在60℃下干燥12h后,即可得硫化镉晶体。

图 1 制备掺铁硫化镉的流程图 Fig. 1 Flow diagram showing the preparation process of iron doped CdS
1.3 样品表征

采用FE-SEM,Supra-55型场发射扫描电子显微镜观察样品的微观形貌。X射线衍射源为铜靶,狭缝为0.3nm,工作管电压40kV,工作管电流100mA,扫描速率为4(°)/min,扫描范围2θ为10°~80°。X射线光电子能谱(XPS)测试在ESCALAB250型能谱仪上完成。光催化降解亚甲基蓝实验在光催化反应仪上进行,以500W的氙灯为光源,吸光度测试采用UV-1800型紫外可见分光光度计。

1.4 光催化实验

以500W的氙灯为光源,称取0.1g自制样品分散于浓度为1.8×10-5mol/L的100mL亚甲基蓝溶液中,置于光催化反应仪内,在打开氙灯之前,电磁搅拌0.5h以达到吸附平衡,再在氙灯冷光源模拟太阳光照射下,每隔0.5h取5mL的亚甲基蓝,离心分离取上层清液测定亚甲基蓝溶液的吸光度。在实验浓度范围内,亚甲基蓝溶液的吸光度与浓度成正比,以吸光度代替浓度计算催化效率,即公式η=C/C0=A/A0,式中CC0AA0分别表示为降解后浓度、初始浓度、降解后的吸光度和初始吸光浓度。

2 结果与分析 2.1 形貌分析及光催化活性比较

图 2为140,160,180℃和200℃下反应12h得到CdS的SEM图。从图 2可知,反应温度对晶体的形貌影响较大,随着水热温度的升高,硫化镉晶体的形状依次为球状、花状、簇状和棒状。图 3是不同形貌硫化镉样品对亚甲基蓝的光催化降解曲线。从图 3可以看出,催化活性顺序为花状>簇状>球状>棒状。因为相比于其他形貌,花状硫化镉具有更大的比表面积,催化活性更高,与文献[29, 30]报道相符。所以可知水热反应的最佳温度为160℃。

图 2 不同水热反应温度合成CdS的SEM图 (a)140℃; (b)160;(c)180℃; (d)200℃ Fig. 2 SEM images of CdS obtained from different reaction temperatures be hydrothermal method (a)140℃; (b)160;(c)180℃; (d)200℃
图 3 不同形貌的硫化镉对亚甲基蓝的光催化降解曲线 Fig. 3 Photocatalytic degradation curves of MB to different morphology CdS
2.2 铁掺杂的花状硫化镉的XRD表征

图 4是水热温度为160℃时不同掺铁量的硫化镉XRD图。从图 4可以看出,掺铁的硫化镉,与未掺杂的硫化镉相比,结构没有发生明显的变化,这与文献[31]报道一致。其中不同掺铁量的样品的衍射峰分别出现在2θ=24.7°,26.4°,28°,36.5°,43.6°,47.6°和51.8°的附近,与六方相CdS(JCPDS crad NO.41-1049) 对应的(100),(002),(101),(102),(110),(103),(112) 特征峰一致,没有出现Cd,CdO或其他镉化合物的杂质峰,且衍射峰尖锐,说明所得的样品均为纯净的六方纤锌矿,结晶程度较高。

图 4 不同掺铁量的CdS的XRD图 Fig. 4 XRD patterns of CdS with different Fe doping concentrations
2.3 铁掺杂的花状硫化镉的EDS表征

为了确定合成样品的化学元素成分,特对其进行了EDS分析。图 5为样品(Fe:Cd=1:10) 的EDS谱图。从能谱中可以看出,Cd和S的吸收峰强度很大,说明Cd和S是样品中的主要元素,经图谱积分计算,其化学计量比接近1:1,说明所制备的硫化镉纯度较高。图谱中除了Cd和S两种元素的主要特征峰以外,还有Fe,C和O的峰位,其相对百分比含量较小,说明铁离子已经成功掺杂到硫化镉样品中,其中C和O元素可能是用去离子水和无水乙醇对样品进行洗涤过程中引入的。

图 5 硫化镉样品(Fe:Cd=1:10) 的EDS谱图 Fig. 5 EDS spectrum of CdS sample(Fe:Cd=1:10)
2.4 铁掺杂的花状硫化镉的XPS表征

图 6为样品(Fe:Cd=1:10) 的XPS谱图。由图 6(a)可见,除C,O,S,Cd,Fe等元素特征能谱峰外,无其他元素能谱峰,表明样品有较高的纯度。其中C的1s和O的1s轨道结合能分别为284.64eV和531.58eV,略大于标准数据中的C1s(285.0eV)和O1s(531.8eV)的电子结合能。图 6(b)为Cd的3d轨道结合能,Cd的3d5/2和3d3/2结合能分别为404.95eV和411.65eV,图 6(c)为S的2p轨道结合能,结合能为161.41eV,其结果与文献[32]基本一致。图 6(d)为Fe的2p轨道结合能,结合能为710.68eV,大于标准数据中的Fe2p(706.7eV)的电子结合能,说明Fe3+的微区环境发生了变化,可能是由于部分铁离子进入硫化镉晶体内部,导致Fe3+周围的电子云密度发生变化所致。同时根据XPS的定量分析结果可得,Fe,Cd和S元素的原子个数比近似为1:10:10,说明样品的纯度较高,掺杂效果较好。

图 6 硫化镉样品(Fe:Cd=1:10) 的XPS谱图 Fig. 6 XPS spectra of CdS sample(Fe:Cd=1:10)
2.5 铁掺杂的花状硫化镉的光催化活性表征

图 7是不同掺铁量的花状硫化镉对亚甲基蓝的降解活性比较。从图 7可以看出,催化活性顺序为CdS(Fe:Cd=1:10)>CdS(Fe:Cd=1:5)>CdS(Fe:Cd=1:25)>CdS(Fe:Cd=1:1)>CdS(Fe:Cd=0:1),说明掺杂适量的Fe3+,可以显著地提高材料的光催化活性。当Fe和Cd的掺杂比为1:10时,CdS的催化活性最高,进一步增加掺杂量,催化活性反而降低,导致上述现象的原因主要是由于过渡金属铁离子的引入能有效地提高电子和空穴的分离效率,从而提高其催化活性,但当掺杂的Fe3+过量时,就会成为光致电子和空穴的复合中心,反而使其催化活性降低。

图 7 不同掺铁量的样品对亚甲基蓝的光催化降解曲线 Fig. 7 Photocatalytic degradation curves of MB to different Fe doping concentrations samples
3 结论

(1) 采用硝酸镉,硝酸铁和硫脲为原料,以水为溶剂,通过水热法一步合成铁掺杂的硫化镉,在不同的水热反应温度下,可分别得到球状、花状、簇状和棒状硫化镉。

(2) 不同形貌硫化镉的催化活性顺序为花状>簇状>球状>棒状,主要是因为花状硫化镉具有更大的比表面积,其光催化性能明显高于其他形貌的硫化镉,因此最佳水热温度为160℃。

(3) 适量的铁掺杂能进一步提高花状硫化镉的催化活性,当Fe和Cd的掺杂比为1:10时,光催化效果最佳,进一步增加掺杂量,催化活性反而降低。

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