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不同前驱体制备g-C3N4光催化性能及稳定性

第47卷第3期2018年3月

应 用 化 工Applied Chemical Industry

Vol.47No.3Mar.2018

收稿日期:2017-06-27 修改稿日期:2017-07-21基金项目:国家科技重大专项项目(2016ZX05040003)

作者简介:刘宗梅(1991-),女,河南商丘人,中国石油大学(华东)在读硕士研究生,师从赵朝成教授,主要从事光催化处

理污水的研究三电话:156********,E -mail:liuzongmei 1118@http://www.wendangku.net/doc/4f889e87a66e58fafab069dc5022aaea988f4158.html

通讯联系人:赵朝成,博士生导师,硕士三E -mail:zhaochch0821@http://www.wendangku.net/doc/4f889e87a66e58fafab069dc5022aaea988f4158.html

科研与开发

不同前驱体制备g-C 3N 4光催化性能及稳定性

刘宗梅,李玲艳,朱诗月,林飞飞,郭锐,赵朝成

(中国石油大学(华东)化学工程学院,山东青岛 266580)

摘 要:分别以硫脲二二氰二胺二三聚氰胺和尿素为前驱体,550?条件下热聚合法合成了g-C 3N 4,样品经扫描电镜(SEM)二X 射线衍射(XRD)二傅里叶变换红外光谱(FTIR)二紫外-可见漫反射(UV-Vis)二N 2吸附二元素分析等一系列方法进行了表征,可见光条件下降解亚甲基蓝来评价g-C 3N 4的光催化性能三结果表明,以尿素为前驱体合成的g-C 3N 4有着最佳的光学吸收特性二最大的比表面积和最高的C /N 摩尔分数,且其显示了最佳的光催化活性,4种前驱体合成的g-C 3N 4均有着较好的稳定性三关键词:不同前驱体;g-C 3N 4;光催化;亚甲基蓝

中图分类号:TQ 319;TQ 209;X 703 文献标识码:A 文章编号:1671-3206(2018)03-0421-04

Photocatalytic activity and stability of g-C 3N 4synthesized by

different precursors

LIU Zong-mei ,LI Ling-yan ,ZHU Shi-yue ,LIN Fei-fei ,GUO Rui ,ZHAO Chao-cheng

(College of Chemical Engineering,China University of Petroleum(East China),Qingdao 266580,China)

Abstract :g-C 3N 4was synthesized by thermal polymerization at 550?,use thiourea,dicyandiamide,melamine and urea as precursors,respectively,and the samples were characterized by scanning electron microscopy (SEM),X-ray diffraction(XRD),Fourier transform infrared spectroscopy(FTIR),UV-Vis diffuse reflectance,N 2adsorption and elemental analysis.The photocatalytic activity of g-C 3N 4was evaluated by degradation of methylene blue under visible light conditions.The results show that g-C 3N 4synthesized use urea as precursor has the best optical absorption properties,maximum surface area and highest C/N molar fraction,and it shows

the best photocatalytic activity.g-C 3N 4was synthesized by four precursors all have a good stability.Key words :different precursor;graphite carbon nitride;photocatalysis;methylene blue 能源危机和环境污染已经成为当今社会最迫切需要解决的两大问题,半导体光催化技术在太阳能转换和环境治理方面发挥着巨大的潜能[1-3]三近年来,一种新的可见光催化材料g-C 3N 4(2.7eV),有着独特的半导体能带结构二优异的化学稳定性和热稳定性[4-5],且价格低廉,制备简单,可由多种前驱体如尿素[6-7]二硫脲[8-9]二二氰二胺[10-11]二三聚氰胺[12-13]等通过一步聚合法直接制得三

有研究表明,不同前驱体制得的g-C 3N 4光催化

活性存在差异三Xin [14]分别用单氰胺二双氰胺和三聚氰胺在同一实验条件下制得g-C 3N 4,结果表明,

前驱体为双氰胺的g-C 3N 4光催化活性最好三Wang

和其他合作者[15-17]采用含硫性物质,硫脲二硫氰酸

胺二S8作为前驱体和反应介质,对g-C 3N 4的热聚合过程进行调控,从而提高了其对污染物的降解活性三尿素价廉易得,现有研究很少以尿素为前驱体和以

其他材料为前驱体来比较他们在可见光下的光催化活性,基于此,本文采用尿素二硫脲二二氰二胺二三聚氰胺4种前驱体热聚合法制备g-C 3N 4,分别考察其在可见光条件下的光催化活性和稳定性三

1 实验部分

1.1 试剂与仪器

硫脲二三聚氰胺二尿素二亚甲基蓝二二氰二胺均为分析纯三

万方数据

应用化工第47卷

QSXL-1008型马弗炉;XPA-7型光催化反应仪; TU-1901型紫外可见分光光度计;JEM-2100型扫描电镜;XRD-6100型X射线衍射仪;S400型傅里叶变换红外光谱仪;U3010型UV-Vis漫反射光谱; ASAP2010物理吸附仪三

1.2 催化剂的制备

分别称取10.0g的尿素二硫脲二二氰二胺二三聚氰胺固体,溶于10mL去离子水中,混合搅拌均匀,然后80?条件下烘干,将烘干后的固体置于带盖的坩埚中,氮气气氛条件下马弗炉中煅烧2h,保持煅烧温度550?,升温速率5?/min,自然冷却到室温后,将得到的黄色固体研磨成粉末备用,分别将以硫脲二二氰二胺二三聚氰胺二尿素为前驱体制得的系列催化剂命名为g1-C3N4,g2-C3N4,g3-C3N4,g4-C3N4三1.3 光催化活性评价

光催化活性评价使用XPA光催化反应仪,采用1000W氙灯,用滤光片滤去>420nm的紫外光,保证实验在可见光下进行三实验时,称取催化剂0.05g,以10mg/L的亚甲基蓝为目标污染物,反应溶液100mL,将催化剂与溶液超声混合均匀三反应开始前,先将催化剂与亚甲基蓝溶液于磁力搅拌条件下暗反应30min,以达到催化剂对反应底物的吸附-脱附平衡,然后打开光源,预热5min后开始计时,此后每隔30min取样2mL,用0.45μm的滤头滤去催化剂,稀释1倍后在664nm处测其吸光度,整个反应过程持续3h三

2 结果与讨论

2.1 光催化性能测试

不同前驱体制备的g-C3N4光催化性能见图1三

图1 不同前驱体制备的g-C3N4光催化性能Fig.1 Photocatalytic performance of g-C3N4prepared by

different precursors

由图1可知,以硫脲二二氰二胺二三聚氰胺二尿素为前驱体制得的g-C3N4在可见光条件下对亚甲基蓝的降解率存在差异,其中,g4-C3N4对亚甲基蓝的降解率最高,3h达到了61.8%,g1-C3N4,g2-C3N4,g3-C3N4也分别达到了39%,53%和47%,所以,尿素为前驱体制得的g-C3N4,其光催化活性最佳,其次是二氰二胺,硫脲为前驱体时降解率最低三这一方面可能是由于尿素在热聚合过程中的聚合度最高,另一方面是因为尿素制得的g-C3N4有着较大的比表面积和孔体积,表面活性位点增加,因此催化效率最高三

2.2 SEM分析

对4种样品的形貌进行了SEM表征,结果见图2三

图2 g1-C3N4(a)二g2-C3N4(b)二

g3-C3N4(c)和g4-C3N4(d)的SEM图Fig.2 SEM images of g1-C3N4,g2-C3N4,g3-C3N4and g4-C3N4由图2可知,(a),(b)和(d),这三种前驱体合成的g-C3N4有着相似的外貌结构,都呈现出层状二卷曲状二薄片状堆积的结构,类似石墨结构,(c)呈块状堆积结构三由(d)可看出尿素合成的g-C3N4有着较多的孔道结构,推测其比表面积较大,这一推测在N2吸附表征中得到了验证三

2.3 XRD分析

不同前驱体制备的g-C3N4的XRD图谱见图3三

图3 g1-C3N4(a)二g2-C3N4(b)二g3-C3N4(c)和

g4-C3N4(d)的XRD图谱

Fig.3 XRD patterns of g1-C3N4,g2-C3N4,g3-C3N4and g4-C3N4由图3可知,所有样品都具有g-C3N4典型的两特征峰,表明成功的合成了g-C3N4,两峰位置分别位于2θ=13?和2θ=27.4?处,晶面指数对应g-C3N4的(100)和(002)[18-19]三其中2θ=13?的衍射峰对应的是g-C3N4中均三嗪结构单元的特征峰,其晶面间距约为0.681nm;较强的衍射峰2θ=27.4?对应的

224

万方数据

第3期刘宗梅等:不同前驱体制备g-C3N4光催化性能及稳定性是g-C3N4中共轭芳香杂环堆积结构,其晶面间距约

为0.327nm三此外,可以看出,g1-C3N4的峰相对较

低,聚合度不高,而g4-C3N4的衍射峰强度最高,峰

形相比也比较尖锐,说明以尿素为前驱体制得的

g-C3N4结晶度最好,这和光催化性能实验的结果一

致,在相同时间内,g4-C3N4的光催化活性最高三

2.4 FTIR分析

不同前驱体制备的g-C3N4粉末的FTIR光谱见

图4三

图4 g1-C3N4(a)二g2-C3N4(b)二g3-C3N4(c)和

g4-C3N4(d)的FTIR图谱

Fig.4 FTIR spectra of g1-C3N4,g2-C3N4,g3-C3N4and g4-C3N4由图4可知,图中几个典型的吸收峰值显示了C二N间化学键特征振动模式三在810cm-1处的吸收峰值对应三嗪单元的特征呼吸模型,位于1250~ 1580cm-1之间的几个较强的吸收区域可归因于C N杂环的拉伸模式[20-21],吸收峰值约1336cm-1处归因于C N键,且1641cm-1处来自C=N的拉伸模式[12,22-23]三3100~3300cm-1处较宽的吸收带来自伯胺和仲胺的拉伸模式及其分子间氢键的相互作用三约3000cm-1的吸收峰可能是由于吸附的水分子产生的O H三实际上,有报道称,残留的氢原子可能来自类石墨C N片的边缘上的C NH2形式和2个C NH键中的H[21]三

2.5 UV-Vis分析

为了研究样品的光学吸收特性对光催化活性的影响,对4种样品进行了UV-Vis漫反射光谱表征,结果见图5三

由图5可知,g1-C3N4,g2-C3N4和g3-C3N4有着相似的吸收特性,光吸收边界在475nm左右,而g4-C3N4的光吸收特性最强,对可见光的吸收边界也显示出明显的红移现象三这也就解释了为什么以尿素为前驱体合成的g-C3N4在可见光条件下的光催化活性最好三此外,在各样品的吸收尾部存在微弱的吸收现象,这可能会改善材料对可见光的吸收,产生这种现象的原因可能由于样品在热聚合过程中引起的结构缺陷三

图5 g1-C3N4(a)二g2-C3N4(b)二g3-C3N4(c)

和g4-C3N4(d)的UV-Vis图谱

Fig.5 UV-Vis diffuse reflection spectra of g1-C3N4,

g2-C3N4,g3-C3N4and g4-C3N4

2.6 N2吸附

图6为4种前驱体合成的g-C3N4在常温下的N2吸附-脱附等温线三

图6 g1-C3N4二g2-C3N4二g3-C3N4和

g4-C3N4的N2吸附-脱附等温线Fig.6 N2adsorption-desorption isotherms of g1-C3N4,

g2-C3N4,g3-C3N4and g4-C3N4

由图6可知,4种样品都呈现出典型的Ⅳ型曲线,说明合成的g-C3N4均具有介孔结构三g1-C3N4二g2-C3N4二g3-C3N4和g4-C3N4四种样品的比表面积分别为8.14,24.08,11.17,82.50m2/g,可以看出,以尿素为前驱体合成的g-C3N4,其比表面积最大,远远大于以硫脲二二氰二胺和三聚氰胺为前驱体合成的g-C3N4,其次为g2-C3N4,g1-C3N4的比表面积最小,这和光催化性能测试的结果是一致的三这也就解释了g4-C3N4光催化活性最佳的部分原因,较大的比表面积有助于样品对污染物的吸附和反应三2.7 元素分析

为了考察各样品元素含量对光催化活性的影响,对各样品做了元素分析,结果见表1三

由表1可知,不同前驱体合成的g-C3N4元素含量存在差异,g1-C3N4二g2-C3N4二g3-C3N4和g4-C3N4 4种样品的H含量相同,C/N摩尔分数分别是65.4%,66.2%,65.9%和66.9%,均低于理论值75%三以尿素为前驱体合成的g-C3N4,其C/N摩尔分数最高,光催化性能测试也显示最佳,因此我们推

324

万方数据

应用化工第47卷

测,较高的C/N摩尔分数有助于提高g-C3N4的光催化活性三

表1 g1-C3N4二g2-C3N4二g3-C3N4和g4-C3N4的各元素含量Table1 The content of each element of g1-C3N4,

g2-C3N4,g3-C3N4and g4-C3N4

样品名称H/%C/%N/%C N/% g1-C3N4 1.8534.4661.4565.4 g2-C3N4 1.8534.7761.2666.2 g3-C3N4 1.8534.6361.3365.9 g4-C3N4 1.8534.9861.0266.9

注:表中的H二C二N元素含量以质量分数计,C/N以摩尔分数计三2.8 重复性和稳定性评价

图7考察了不同前驱体制备的g-C3N4样品的稳定性情况,相同实验条件下,将各催化剂循环使用4次三

图7 不同前驱体制备的g-C3N4重复性实验

Fig.7 Repeated experiment of g-C3N4prepared by

different precursors

由图7可知,以硫脲二二氰二胺二三聚氰胺二尿素为前驱体制得的g-C3N4降解率从初始的39.8%, 53%,47%,61.8%降为33.4%,46.6%,41.2%和55.6%,略微有所下降,这可能是由于各样品在光反应过程中吸附了少量有机物,导致其表面的活性位点减少,但总的来说,这4种前驱体制得的g-C3N4都有着较好的稳定性三

3 结论

(1)本文分别以硫脲二二氰二胺二三聚氰胺和尿素为前驱体,550?条件下热聚合法成功合成了g-C3N4,结果表明,所有样品都呈现出相似的晶相结构,以尿素为前驱体合成的g-C3N4聚合度最高,光学吸收特性最佳,比表面积最大为82.5m2/g,C/N 摩尔分数最高为66.9%三

(2)光催化性能结果表明,以尿素为前驱体制得的g-C3N4光催化活性最佳,3h内对亚甲基蓝的降解率达到了61.8%三对4种前驱体制成的g-C3N4进行了重复性实验,结果表明,相同实验条件下,各样品都保持着较高的稳定性三参考文献:

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