新型纳米材料炭气凝胶的制备、表征及应用研究

【作者】 李文翠；

【导师】 郭树才； J Fricke；

【作者基本信息】 大连理工大学 ， 化工工艺， 2002， 博士

【摘要】 炭气凝胶是一种轻质、多孔、非晶态、块体纳米炭材料，其连续的三维网络结构可在纳米尺度控制和剪裁。源于其独特的网络结构，炭气凝胶具有导电性好，比表面积大、密度变化范围广的特点，是制备双电层电容器理想的电极材料。通常以间苯二酚和甲醛为原料，在碳酸钠催化作用下，经溶胶-凝胶过程、三氟乙酸老化、超临界干燥或常压干燥及高温炭化过程可得到炭气凝胶。目前影响炭气凝胶商业化应用的主要问题是其制备工艺复杂，制备成本偏高。 本论文开发了以新原料、新催化剂制备炭气凝胶的工艺过程，期望降低炭气凝胶的制备成本。实验采用低温N₂吸附、IR、NMR、XPS、SAXS、TEM、SEM、Raman和TG等手段研究了炭气凝胶的微结构特点；对炭气凝胶的合成机理进行了合理的推测和初步的实验证实；以所制炭气凝胶作双电层电容器电极材料，采用循环伏安法和阻抗谱实验表征了相应炭气凝胶电极的电化学行为。论文工作得到了国家自然科学基金和中科院山西煤化所煤转化重点实验室基金的资助。 以Ca（OH）₂和MgCO₃为催化剂（Cat）制备了间苯二酚（R）甲醛（F）炭气凝胶。相对以K₂CO₃和Na₂CO₃为催化剂的凝胶体系，凝胶化时间大大缩短，所得气凝胶密度降低。催化剂含量（R／Cat）和反应物浓度是影响凝胶化时间和气凝胶性质的主要因素。TEM显示Ca（OH）₂为催化剂制得的RF炭气凝胶的网络结构优于K₂CO₃、Na₂CO₃催化剂制得的炭气凝胶的网络结构。 以混甲酚（C_m）、甲醛为原料，NaOH为催化剂成功合成了低密度、块状无裂纹C_mF有机气凝胶及炭气凝胶。由于增大反应物含量，所得水凝胶强度好，不需经过三氟乙酸老化，缩短了气凝胶合成周期。目前实验条件下合成的C_mF有机气凝胶最低密度为0.062g／cm³，相应炭气凝胶密度为0.090g／cm³，所得气凝胶具有规则的网络结构。 将C_mF有机气凝胶炭化可以得到炭气凝胶，它继承了有机气凝胶的三维网络结构。采用IR分析技术跟踪C_mF气凝胶的热解过程，发现400～600℃之间样品中出现石墨化结构的红外活性振动，表明炭气凝胶的微结构中开始有乱层石墨化微晶出现。C_mF气凝胶是典型的中孔材料。随热解温度的升高，气凝胶的比表面积、微孔表面积相应增加，孔径分布变窄，孔尺寸缩小，总孔容增大。采用CVD法改性RF和C_mF炭气凝胶的微结构发现苯沉积优先发生在炭气凝胶的微孔。沉积之后，样品基本不含微孔，中孔缩小，大孔向中孔过渡，样品的孔径范围集中在纳米量级。 以间甲酚（m-C）、甲醛为原料，以NaOH为催化剂经溶胶-凝胶过程和CO₂超临界干燥可得橙红色有机气凝胶，高温炭化得炭气凝胶。论文研究了水凝胶的酸老化过程，发现间甲酸甲醛水凝胶的酸老化过程中存在一个合适的酸浓度，可以使气凝胶密度最小。初步证实醋酸、盐酸可以代替较为昂贵的三氟乙酸对水凝胶进行老化。NMR和 IR分析表明亚甲基键和亚甲基醚键是构成间甲酚气凝胶纳米网络交联结构的桥键。当m－C／Cat二3。反应物浓度为 4％，所得间甲酚有机气凝胶的最可几孔径分布为 21～3 5 nxn，具有与 RF气凝胶十当的比表面积（662 m‘／g）和极大的总孔容积（3．17cm3／g）。 以CofOHh为催化剂，固定催化剂含量（WCatX提高RF溶胶一凝胶体系的反应物浓度 （ 30％X经超临界干燥可以得到具有极大中孔容积o．53 cm3哈＞孔径分布非常集中的y炭气凝胶。高反应物浓度合成的RF凝胶可以经常压干燥得到干燥收缩率低的y炭气凝胶。省去烦琐的超临界干燥过程。 以混甲酚、间苯二酚的混合物为原料与甲醛聚合，经常压干燥可得到干燥收缩率低。机械强度高的Cmy有机气凝胶。CmRF有机气凝胶高温炭化可得到炭气凝胶。这一合成路线简化了炭气凝胶的制备工艺，显著降低了炭气凝胶的制备成本。随混甲酚用量的增加，常压干燥收缩率、有机气凝胶密度、热解损失、热解收缩及相应炭气凝胶的密度均有不同程度增加。当混甲酚用量达到 70 t％时，CmRF炭气凝胶仍具有较高的比表面积N05 thZ电X较大的孔容积O石2 Cffi3乍）和集中的孔径分布。拉曼光谱测试表明当初始溶液中添加 50～60 Wt％的混甲酚时，所得 CmRF炭气凝胶的微晶结构有序程度最高。 以CmRF炭气凝胶作双电层电容器的电极材料，循环伏安法测试结果表明在IMH仔O。电解液中 CmRF炭气凝胶电极存在稳定的电势窗口。当添加 40 t％的混甲酚时，所得CmRF炭气凝胶具有最高的质量比电容＊ F电）和体积比电容＊7 F儿m勺。当混甲酚的添加量小于 60 t％时，CmRF炭气凝胶电极的比电容值与文献报道的纯 y炭气凝胶电极的比电容值相当，甚至优于纯f炭气凝胶电极，而CmRF炭气凝胶的制备成本显著降低。更多还原

【Abstract】 Carbon aerogels are a novel, low-density, porous, non-crystalline, monolithic, nanometer carbon materials, whose continuous network structures can be controlled and tailored at the nanoscale. Due to their special network structures, carbon aerogels take on some excellent properties, such as the larger specific surface area, the good electric conductivity, and the alterable density. Therefore, using carbon aerogels as electrode materials for electrochemical double-layer capacitor is extremely attractive and promising. Normally, the polymerization of resorcinol (R) with formaldehyde (F) catalyzed by sodium carbonate results in the formation of dark red, transparent RF organic aerogels via a sol-gel process, acid aging process, and supercritical fluid drying or ambient pressure drying. Upon pyrolysis of RF organic precursors at high temperature, the monolithic RF carbon aerogels can be obtained.This dissertation has firstly developed a new technology process to prepare carbon aerogels by employing new raw materials and new catalysts The microstructures of the new developed carbon aerogels was investigated by means of low-temperature N2 adsorption, IR, NMR, XPS, SAXS, TEM, SEM, Raman spectroscopy and TG etc. The synthetic mechanism of the new carbon aerogels was rationally inferred based on the primary experimental demonstration. Furthermore, using the prepared carbon aerogels as electrode materials, the corresponding electrochemical behavior was characterized by means of cyclic volammetry and impedance spectroscopy. The dependence of capacitances and impedance on the microstructure of carbon aerogel electrodes was discussed.In the present study, both calcium hydroxide and magnesium carbonate were firstly employed as the catalyst to prepare resorcinol-formaldehyde carbon aerogels. In comparison with sol-gel system catalyzed by potassium carbonate and sodium carbonate, the gel time was markedly shortened and the densities of the prepared carbon aerogels were obviously reduced. It was shown that the gel time and RF carbon aerogels properties were mainly determined by the catalyst content (R/Cat) and reactant concentration. The network structures of carbon aerogels catalyzed by Ca(OH)2 were more regular than that of carbon areogels catalyzed by KaCOa, Na2CO3. The difference between these two types of carbon aerogels resulted from the participation of metal positive ion in the polycondensation reaction during the sol-gel process.In the presence of sodium hydrate, the polymerization of mixture cresol (Cm) with formaldehyde resulted in the formation of low-density, monolithic, free-crack CmF organic and carbon aerogels. Due to the high reactant concentration the aquagel had a good strength.Hence, the aging process can be saved and the preparing times of aerogels was shortened for this sol-gel system. TEM showed that the mixture cresol aerogel had a three-dimensional network. In present experiments, the lowest density of CmF organic aerogel is 0.062 g/cm3, the density of the corresponding carbon aerogel is 0.090 g/cm3. Meanwhile, the synthetic mechanism of CmF aerogel was deduced firstly based on the primary experimental demonstation..Carbon aerogels can be prepared upon pyrolysis of the CmF organic precursors at 900 癈,which can inherit well the 3D network of the original organic aerogels. The pyrolysis process of the CmF aerogel was investigated firstly by means of IR technique. The results showed an infrared active vibration occured in the temperature range of 400-600 "C, which was corresponding to the tubstatic graphitized structure formed hi these aerogels. With the increasing pyrolysis temperature, the specific surface area as well as micropore surface area and total volume increased accompanied with the narrower pore size distribution. The microstructure parameters calculated by the a s-plot for aerogels showed a good agreement with that obtained from the BJH method. The orthogonal experiment for carbonization process indicated that the heating rate and the final carbonization temperature showed mo更多还原