氰基功能化介孔二氧化硅的制备与表征

doi:10.3724/SP.J.1077.2012.00134

摘要/Abstract

摘要：

以2-氰乙基三乙氧基硅烷(CTES)和正硅酸乙酯(TEOS)为硅源, 聚氧乙烯-聚氧丙烯-聚氧乙烯三嵌段共聚物(P123)为模板剂, 采用共缩聚法在酸性条件下合成了氰基功能化的介孔二氧化硅. 通过XRD、SEM、氮气吸附-脱附、FT-IR和元素分析等技术对样品的结构、形貌、孔性质和官能团等进行了表征. 研究结果表明, 硅源的混合方式对氰基的引入量和分布有一定影响, 其中以直接混合方式所得样品中基团含量最高, 其分布也最均匀. 另外, 随着氰基引入量的增加, 样品的形貌与孔结构略有变化. 当CTES加入量超过20mol%时, 材料的介孔由圆柱形的直孔道向瓶颈型的孔道结构发生转变. 同时随着材料中氰基含量增大, 样品的孔容由0.70 cm³/g降到0.22 cm³/g、表面积从666 m²/g降到312 m²/g, 孔径由4.2 nm减小到2.7 nm, 表明氰基分子占据了部分孔道空间.

关键词: 介孔材料, 二氧化硅, 功能化, 氰基

Abstract:

Cyano-functionalized mesoporous silicas were synthesized by one-pot co-condensation of tetraethoxysilane (TEOS) and 2-cyanoethyltriethoxysilane (CTES), using Pluronic P123 triblock copolymer as the structure- directing agent under strongly acidic conditions. The physicochemical properties, such as structure, morphology, pore property and cyano content were characterized by XRD, SEM, N₂ adsorption-desorption isotherm, FT-IR and elemental analysis, respectively. It was found that the order for adding the two silicon sources, namely CTES and TEOS has a profound influence on the content and distribution of cyano group. Within three mixture orders, the sample synthesized with pre-mixed TEOS and CTES as silica sources is best, with highest cyano content and uniform distribution. As cyano content increasing, surface morphology and pore properties are changed. The straight cylindrical pore structure is transformed into bottle-neck-like structure with up to 20mol% CTES loading in the synthesis mixture. Pore volume, surface area and pore size decrease from 0.70 cm³/g to 0.22 cm³/g, 666 m²/g to 312 m²/g, 4.2 nm to 2.7 nm, respectively when cyano content is increased, which maybe result from that cyano group occupies part of pore channel.

Key words: mesoporous, silica, functionalization, cyano

中图分类号:

O613
TB332

郭风, 朱桂茹, 高从堦. 氰基功能化介孔二氧化硅的制备与表征[J]. 无机材料学报, 2012, 27(2): 134-138.

GUO Feng, ZHU Gui-Ru, GAO Cong-Jie. Preparation and Characterization of Cyano-functionalized Mesoporous Silica[J]. Journal of Inorganic Materials, 2012, 27(2): 134-138.

图/表 7

Table 1 Elemental analysis of cyano-functionalized silica samples prepared by different addition way of silanes

Samples	C content/(mg·g^-1)	N content/(mg·g^-1)	CN content/(mmol·g^-1)	Average CN content/(mmol·g^-1)
M-20/CN	133.7	30.5	2.18	2.19
	124.5	31.3	2.23
	124.9	30.2	2.16
C-20/CN	197.4	42.8	3.06	2.09
	83.8	17.6	1.26
	122.9	27.4	1.96
T-20/CN	144.8	26.2	1.87	1.95
	131.3	27.3	1.95
	123.0	28.3	2.02

图1 不同氰基含量功能化介孔二氧化硅的FT-IR图谱

Fig. 1 FT-IR spectra of cyano-functionalized mesoporous silicas

图2 给出了样品的N2吸附-脱附等温线和孔径分布曲线. 从图2(A)中可以看到, 当有机官能团引入量较低时, 样品的N2吸附-脱附等温线呈现典型的Langmuir Ⅳ型, 并且伴有H1型滞后环, 说明材料具有介孔结构. 此外, 在N2相对压力P/P0为0.4~0.5处出现了一明显突跃, 这些都是具有圆柱形细长孔道结构介孔二氧化硅材料典型的N2吸附-脱附曲线. 但是随着氰基引入量的继续增加, 对于样品M-20/CN、M-30/CN和M-40/CN, 吸附-脱附等温线已经明显偏离H1型, 介孔类型也由圆柱形的直孔道向具有H2型滞后环的瓶颈型孔道结构发生转变, 这与吴宝虎等[15]、Yang等[4]的发现类似. 但与Yang等[4]在 90℃所得10mol%的样品即呈现H2型滞后环不同, 本实验所得M-10/CN仍呈现H1型滞后环, 这很有可能是陈化温度不同造成的. 另外, 从吸附-脱附曲线上还可以看出, 随着材料中氰基含量的增大, 出现突跃的相对压力稍向减小的方向移动, 说明随着氰基引入量的增加, 材料的孔径和孔体积均有所减小, 这一点也可从孔径分布曲线得到验证. 从孔径分布曲线(图2(B))可以看出, 所得氰基功能化介孔硅材料均具有较窄的孔径分布, 相关的物理化学参数列于表2. 从孔径分布曲线可以看出, 与Yang等[4]在相近条件下制备的介孔硅CN/SBA-15一致, M-10/CN具有双介孔孔道结构, 但是与之相比, 本实验所得材料的孔径较小, 孔径分布范围较窄. 由表2数据可知, 随着有机官能团引入量的增加, 材料的孔容、孔径和比表面积均有一定程度的降低, 表明功能化基团占据了部分孔道空间, 这是材料比表面积下降的主要原因. 另外, 合成过程中有机基团中烷基链的存在引起的扰动会导致胶束结构出现收缩, 同时有机基团引起的位阻效应将迫使表面活性剂的头部离开胶束, 从而导致胶束曲率增大, 降低了孔径[11].

图2 不同氰基含量功能化介孔二氧化硅的N2吸附-脱附等温线和孔径分布曲线

Fig. 2 N2 adsorption-desorption isotherms at 77K (A) and pore size distributions curves (B) of cyano-functionalized mesoporous silicas

Table 2 Physicochemical properties of cyano-functionalized mesoporous silicas

Samples	S_BET/(m²·g^-1)*	V_p /(cm³·g^-1)	D_BJH/nm**	C /(mmol·g^-1)	CN content/(mmol·g^-1)	CN /(groups·nm^-2)
M-10/CN	666	0.70	4.22	8.5	1.16	1.05
M-20/CN	533	0.39	3.00	10.7	2.33	2.63
M-30/CN	436	0.29	2.79	13.7	3.34	4.61
M-40/CN	312	0.22	2.68	16.0	4.30	8.30

图3 不同氰基含量功能化介孔二氧化硅的XRD图谱

Fig. 3 XRD patterns of cyano-functionalized mesoporous silicas

图4 不同氰基含量功能化介孔二氧化硅的SEM照片

Fig. 4 SEM images of mesoporous silica modified with different concentrations of cyano groups

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