张娈娈
, 廖运文
ZHANG Luanluan, LIAO Yunwen
文献标识码: 分类号 TB332 文章编号 1005-3093(2016)04-0307-07
通讯作者:
收稿日期: 2015-09-14
网络出版日期: 2016-04-25
版权声明: 2016 《材料研究学报》编辑部 《材料研究学报》编辑部
基金资助:
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摘要
在低温下, 通过溶胶-凝胶法(Sol-Gel)法成功将TiO2负载到聚两性离子液体基材料(CPAIL)表面, 获得了高性能催化剂CPAIL@TiO2。通过XRD, SEM, EDS, TEM, FT-IR, TGA, XPS和N2吸脱附(BET)等方法对其结构进行了表征。结果表明, CPAIL@TiO2为单一纯相锐钛矿结构, 包含有40%的TiO2, 且其能够均匀分布在CPAIL@TiO2中, 形成C—O—Ti键。在4次循环后, 对甲基橙(MO)和亚甲基蓝(MB)光催化降解程度分别可高达97%和55%, 表明CPAIL@TiO2具有高效的催化性能和循环性能。
关键词：
Abstract
A novel composite material CPAIL@TiO2, which exhibits high photocatalytic activity, was prepared by a sol-gel method using raw materials of tetrabutoxytitanium and cross-linked poly(amphoteric ionic liquid) (CPAIL). The prepared CPAIL@TiO2 was characterized by XRD, SEM, EDS, TEM, FT-IR, TGA and XPS. The results show that the mesoporous nanospheres of composite material CPAIL@TiO2 contains ca 40% TiO2, which is characterized as anatase. There existed chemical bands of C–O–Ti in the composite material. The CPAIL@TiO2 shows a good photocatalytic activity and cycle performance. The photocatalytic degradation efficiencies of the CPAIL@TiO2 could reach 97% and 55% of those of pure TiO2 for solutions of methyl orange (MO) and methylene blue (MB) respectively. In general, the above superiority of the composite material CPAIL@TiO2 demonstrates better prospects for applications in the field of environmental protection.
Keywords：
染料废水因有机物含量大、色度高、光照下稳定及致癌致突变性引起了人们的广泛关注, 并研究采用多种方法用来处理染料废水, 如氧化和生化处理等, 但废水脱色或矿化效果均不理想[1-3]。现今环境废水排放标准越来越严格, 开发和应用高级水处理技术具有重要意义。其中, 光催化净化技术存在以下优点: (1) 彻底的净化, 它是分解而不是吸附过程; (2) 广泛的净化, 几乎对所有污染物都存在作用; (3) 实用的净化, 常温下就可进行, 不需要额外条件; (4) 安全的净化, 无毒副产物[4]。
二氧化钛(TiO2)作为一种非常重要的半导体材料, 因其稳定的物理和化学性质, 得到了广泛应用[5-7]。又因其价格低廉、合成简单, 常常用来作为光催化剂处理废水。提高光催化效率的常用方法,一种是通过掺杂其他元素, 改变TiO2的可见光吸收范围或改变其带隙; 另一种方法是改变表面区域, 这是一个提高其分解效率最简单的方法 [8-11], 如调节氧缺陷, 改变结晶度, 表面氟化或引入新元素[12, 13], 拓宽了其在整个光区的吸收范围, 从而提高光催化性能。基于上述原理, 将磺酸两性离子咪唑液体引入TiO2复合材料中, 以提高高分子材料对光生电子的捕集能力和材料电子空穴分离效率, 可增强TiO2的光催化性能。本文重点考察复合材料CPAIL@TiO2的结构, 探讨交联聚两性离子液基材料对TiO2光催化性能的影响, 研究该复合材料在偶氮染料甲基橙(MO)和亚甲基蓝(MB)溶液中的光催化降解性能。
将一定量的1, 3-丙磺酸内酯溶于丙酮中, 其摩尔浓度为4.2 mol/L, 置于冰水中, 逐滴加入等摩尔的1-乙烯基咪唑, 室温下搅拌5 d, 得大量白色固体, 产品用丙酮洗涤数次, 室温下真空干燥, 得两性离子液体(IL)。 在250 mL的三颈烧瓶中加入上述合成的两性离子液体, 一定量的过硫酸钾为引发剂, 十二烷基磺酸钠为乳化剂, 溶于80 mL醇水溶液中, N2保护下搅拌30 min, 升温至70℃, 加入等摩尔的二乙烯苯(DVB)溶液, 继续反应10 h, 得到的乳白色液体用甲醇破乳, 离心, 真空干燥, 制得交联聚两性离子液体CPAIL。
合成的CPAIL置于20 mL无水乙醇中, 超声使其均匀分散在溶液中, 在强烈搅拌下, 逐滴加入冰乙酸, 调节溶液pH < 3, 形成A液; 取一定量的钛酸四丁酯溶于20 mL的无水乙醇中, 剧烈搅拌, 形成澄清淡黄色液体, 即B液。将B液在持续搅拌下, 滴加到A液中。滴加完毕后升温至80℃, 逐滴加入5 mL去离子水, 此过程控制滴速大约为2 mL/min。持续控温10 h, 得黄色晶状颗粒。产品用无水乙醇和去离子水洗涤数次至中性。合成过程如下:
PDVB@TiO2的制备: 除不加入IL外, 其余均与上述CPAIL@TiO2的制备过程相同。
TiO2的制备: 除不加入CPAIL外, 其余均与上述CPAIL@TiO2的制备过程相同, 得到的颗粒高温煅烧。
配制相同浓度的MB, MO溶液, 分别移取50 mL溶液于光反应器中, 加入50 mg CPAIL@TiO2粉末, 一定速率下搅拌30 min, 以达到吸脱附平衡, 以500 W可调氙灯作为光源, 每隔5 min取一次样, 样品离心, 测试上清液, 计算除去率。
从图1中可知实验室自制煅烧的纯TiO2在25.4°, 37.5°, 48.1°, 53.9°, 55.2°, 62.7°, 68.8°, 70.6°, 75.2°出现特征衍射峰[14], 其在(101)晶面的衍射峰强度很高, 通过与标准卡片对比, 其结构完全符合锐钛矿型的结构, 且不存在金红石型晶相[15] 。负载了CPAIL的TiO2只在25.5°左右出现明显的衍射峰。在 37.2°, 46.4°也存在较弱的衍射峰, 其他吸收峰不易被观察到。这是由于受到无定形态的高分子载体CPAIL影响, 使得TiO2的其它衍射峰不易被观察到。
由图2a可以看出TiO2为纳米球, 表面粗糙, 催化剂颗粒大小在50-100 nm之间。引入CPAIL后(图2b), 其形貌发生了明显变化, 不再呈现出球状结构, 这可能是由于CPAIL的引入使得TiO2颗粒在生成过程中发生了异相反应, 从而生成了不规则颗粒。EDS分析证实C、O、Ti元素的存在, 元素比例分别为(质量分数) 30.98%、50.24%和18.78%, 说明Ti被成功负载到CPAIL上。
从图3a, b可以看到, 在CPAIL@TiO2呈现良好的分散状态, HRTEM显示在样品中出现TiO2(101)晶面的晶格, 其晶格间距为0.35 nm, 在网格周围存在很多分散的物质, 非网格区域证明是非晶态的CPAIL[16]。这与XRD测试中只有TiO2的峰, 而不存在CPAIL的峰相一致。图3c为Ti元素在CPAIL@TiO2中的分布(白色部分), 元素响应信号只出现在选定区域内, Ti均匀分布在CPAIL@TiO2中。选区原子衍射(图3d)证实, CPAIL@TiO2中TiO2呈纯相结构, 这同样与测定的XRD数据相吻合。
图3 CPAIL@TiO2的TEM像
Fig.3 TEM images of CPAIL@TiO2, (a) TEM, (b) HRTEM, (c) distribution of Ti element, (d) selected area electron diffraction
图4表明, 纯的TiO2在室温-800 oC下, 大约只有1.5%的质量损失。而对于CPAIL@TiO2, 其质量损失存在3个过程: 室温-400℃, 存在明显的热分解, 但质量损失速率较慢, 大约为14%, 这可能是由于样品中ILs中官能团的降解造成的[17]; 400-600℃, 热分解速率明显加快, 这可能是CPAIL中碳骨链塌陷质量损失造成的, 此过程质量损失大约为16%; 温度高于600℃, 样品质量不再发生明显变化。
由图5a可以看出, CPAIL@TiO2中出现的元素的吸收峰有: C 1s, O 1s, N 1s, S 2p, Ti 2p。对于C 1s, 高分辨XPS的吸收峰出现在283.98 eV[18]。对于O元素, 在530.47 eV的吸收峰在高分辨谱图中可以拟合出3种吸收峰, 分别出现在529.25 eV, 531.40 eV, 531.98 eV, 对应于Ti—O—Ti, C—O—H, Ti—O—C键[19]。N的吸收峰出现在400.63 eV, 归因于C—N—键[20]。S的吸收峰出现在167.39 eV, 对应于—SO3—键[21]。对于Ti元素, 高倍XPS分析显示两种吸收峰在458.14 eV和463.93 eV, 分别对应于O—Ti—O和C—Ti—O键。这说明复合材料的制备是成功的[22]。
图5 CPAIL@TiO2的XPS谱
Fig.5 XPS analysis of CPAIL@TiO2, (a) full spectrum, (b) C 1s, (c) O 1s, (d) N 1s, (e) S 2p, (f) Ti 2p
图6为TiO2, PDVB@TiO2, CPAIL@TiO2以及催化MB和MO后的红外光谱图。在所有谱线中都存在3420 cm-1, 1628 cm-1吸收峰, 这归因于材料中的水合物[23]。比较PDVB@TiO2与TiO2的谱线, 发现670 cm-1对应苯环的特征吸收峰。2920 cm-1, 2845 cm-1处的峰归因于—CH2—的伸缩振动峰。上述结果说明PDVB成功与TiO2复合。在CPAIL@TiO2中, 1043 cm-1的吸收峰归因于—SO3H[24], 3420 cm-1的吸收峰为—NH2的吸收峰, 出现于—OH峰的缔合[23]。2962 cm-1处的吸收峰归因于—CH3的伸缩振动。这些均可以证明CPAIL@TiO2成功合成。同时比较光催化前后CPAIL@TiO2的红外分析谱(图6), 发现在750 cm-1以下吸收峰明显变宽变强, 这可能是部分染料或分解产物残留在了光催化剂上。
比表面积和孔径往往是影响材料光催化性能的重要因素。图7为CPAIL@TiO2的N2吸脱附曲线, 其比表面积达到144.99 m2/g, 孔径为4.89 nm, 远远大于文献报道的TiO2的比表面积(80 m2/g)[15]。高的比表面积可有效抑制固液催化过程中的催化剂颗粒聚集, 提高CPAIL@TiO2循环使用的效率和次数。同时, 比表面积的增加和孔径结构的变化有利于提高光生电子-空穴对从复合材料的主体向表面转移的速率, 从而提高催化效率。
图7 CPAIL@TiO2的N2吸脱附曲线和BJH曲线
Fig.7 N2 adsorption-desorption and BJH curves of CPAIL@TiO2
CPAIL@TiO2的光催化性能实验以MB和MO溶液作为模拟废水。同时, 与商用的P25进行比较。
图8为CPAIL@TiO2对溶液中MB的光催化实验结果。可以看出, 同纯相的煅烧的TiO2相比, PDVB@TiO2对MB的光催化降解效果明显增强, 在45 min内达到了33%, 而TiO2只有22%, CPAIL@TiO2实现了55%的光催化降解, 但仍低于商用的P25。但是复合材料中TiO2含量仅仅为P25的40%左右, 因此CPAIL@TiO2催化效率非常高。
图9为CPAIL@TiO2对溶液中MO的光催化实验结果。由图可知, CPAIL@TiO2对MO的降解程度达到了97%, 与商用P25的催化效果很相近, 但其在20 min内的催化速率明显要高于P25。与上文提到对MB的催化相类似, 在45 min内PDVB@TiO2对MO的光催化效果可达60%, 明显高于纯TiO2(30%)的。实验表明苯环与离子液体的引入均提高了复合TiO2的光催化性能, 这说明具有吸电子功能的苯环以及两性咪唑离子液体均有利于提高光生电子-空穴对的分离效率, 且两者产生一定的协同作用, 从而进一步提高复合材料的光催化降解性能。CPAIL@TiO2对MO和MB的催化过程中, 发现CPAIL@TiO2对偶氮染料存在良好的催化性能。但是对MB的催化性能明显要低, 这可能是由于MB的骨架结构不同于MO的线性结构, 其支链结构抑制了与苯环和离子液体之间的相互作用, 使其对MB的吸引功能下降。
为了进一步研究CPAIL@TiO2对染料的催化过程, 测试了纯相的TiO2与负载有CPAIL的TiO2的固体紫外漫反射光谱, 如图10所示。由图可知, CPAIL引入后, 样品的吸收波长向低波长方向移动。由于CPAIL中含有大量的苯环和咪唑环, 并存在大量的离域π键, 使得CPAIL与TiO2之间的作用力增强, 且材料中交联聚两性离子液体的含量较大, 从而导致紫外固体漫反射的峰值移向低波长。
图10 纯相TiO2与CPAIL@TiO2的固体紫外漫反射光谱
Fig.10 Solid UV-DRS of pure TiO2 and CPAIL@TiO2
为了验证CPAIL@TiO2光催化性能的稳定性, 对MO和MB溶液的光催化降解分别进行了4次循环实验, 如图11所示。经过4次循环, CPAIL@TiO2对MO的催化效果依然很高, 达到了90%; 而对于催化效果较差的MB, 发现随着循环次数的增加, 对MB的催化效果存在低幅的上升, 但基本保持稳定, 这可能是由于沉积在光催化剂表面的染料或分解产物对其造成了影响。光催化循环实验表明, 合成的CPAIL@TiO2的光催化性能比较稳定。
以聚两性离子液体基材料CPAIL为掺杂相, 在醇水体系中采用Sol-Gel法成功制备了CPAIL@TiO2。结果表明, TiO2被成功负载到了交联聚两性离子液体体系中, 且TiO2为纯的锐钛矿; CPAIL的引入大大提高了未煅烧的TiO2的光催化性能和光生电子-空穴对的分离效率。CPAIL掺杂的TiO2未经过煅烧, 就表现出很好的光催化性能, 从而节约了大量能源。实验表明CPAIL@TiO2是一种性能很好的光催化试剂。
The authors have declared that no competing interests exist.
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Evidence of graphitic AB stacking order of graphite oxides ,
Abstract Graphite oxide (GO) samples were prepared by a simplified Brodie method. Hydroxyl, epoxide, carboxyl, and some alkyl functional groups are present in the GO, as identified by solid-state 13C NMR, Fourier-transform infrared spectroscopy, and X-ray photoemission spectroscopy. Starting with pyrolytic graphite (interlayer separation 3.36 A), the average interlayer distance after 1 h of reaction, as determined by X-ray diffraction, increased to 5.62 A and then increased with further oxidation to 7.37 A after 24 h. A smaller signal in 13C CPMAS NMR compared to that in 13C NMR suggests that carboxyl and alkyl groups are at the edges of the flakes of graphite oxide. Other aspects of the chemical bonding were assessed from the NMR and XPS data and are discussed. AB stacking of the layers in the GO was inferred from an electron diffraction study. The elemental composition of GO prepared using this simplified Brodie method is further discussed.
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| [19] |
Structure and photocatalytic properties of TiO2-graphene oxide intercalated composite , |
| [20] |
Understanding the enhancement in photoelectrochemical properties of photocatalytically prepared TiO2-reduced graphene oxide composite , |
| [21] |
Preparation and characterization of high-surface-area titanium dioxide by sol-gel process , |
| [22] |
Study on stability of poly(3-hexylthiophene)/titanium dioxide composites as a visible light photocatalyst ,
Conjugated polymer/TiO 2 composites are promising visible light photocatalysts for solar chemical conversion processes in the field of environmental chemistry for decomposition of organic compounds in water and air. In consideration of the fact that conjugated polymers are also organic substances, particular attention must be focused on the stability of conjugated polymer/TiO 2 composites, which has not been laid enough emphasis upon so far. Poly(3-hexylthiophene)/titanium dioxide (P3HT/TiO 2 ) composites, as a representative of conjugated polymer/TiO 2 photocatalysts, were prepared by combining chemical oxidative polymerization method and physical blending technique. The stability of the composites was systematically studied by comparative analysis of the physical and chemical structure of P3HT/TiO 2 composites before and after the photocatalytic reaction. As confirmed by the results of high-resolution transmission electron microscopy (HRTEM), scanning electron microscope (SEM), ultraviolet-visible diffuse reflectance spectroscopy (UV鈥搗is DRS), Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS), the P3HT/TiO 2 composites were quite stable to 10聽h of photodegradation of methyl orange (MO) under visible light, maintaining both their physical and chemical structure.
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| [23] |
Hydrogenation with ruthenium nano particles supported on MCM-48 ,
Received 13th January, 2014Received in revised form26th February, 2014Accepted 12th March, 2014Published online 26th April, 2014
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| [24] |
Enhanced upconversion emission in Yb3+ and Er3+ codoped NaGdF4 nanocrystals by introducing Li+ ions , |
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