Preparation of low density and high mesoporosity carbon aerogels by an organic/inorganic hybrid method
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摘要: 通过溶胶-凝胶途径,将间苯二酚-甲醛预聚物和二氧化硅溶胶混合,在碱性溶液中制备出有机/无机杂化水凝胶。水凝胶经溶剂置换、超临界干燥、裂解和氢氟酸刻蚀制备得到炭气凝胶。采用氮气吸附法研究了水凝胶向炭气凝胶转化的结构演变规律。固定间苯二酚/甲醛摩尔比为0.5,二氧化硅溶胶浓度为15g/100mL,考察了二氧化硅胶体颗粒的尺寸及间苯二酚和甲醛浓度对炭气凝胶孔隙结构的影响。结果表明:无机二氧化硅溶胶骨架有效减少了有机物在超临界干燥和裂解过程中的体积收缩。中孔率随间苯二酚和甲醛浓度的升高而增加,孔隙率随二氧化硅溶胶粒子的增大而减小。当间苯二酚和甲醛质量分数之和的达到20%时,7nm二氧化硅溶胶体系的密度低达0.22g/cm3,中孔率达到96%,12nm二氧化硅溶胶体系的密度低达0.26g/cm3,中孔率达到98%。Abstract: Carbon aerogels were synthesized by the solution-sol-gel polymerization of resorcinol (R) and formaldehyde (F) with silica colloidal nanoparticles as additives in a basic aqueous solution followed by supercritical drying, pyrolysis and HF etching. The R/F molar ratio was maintained at 0.5 and the concentration of R+F in solution was varied. The evolution of porosity from hydrogels to carbon aerogels was investigated by nitrogen adsorption. The effect of R+F concentration and size of the silica colloidal nanoparticles on porosity and mesopore ratios were investigated under the same concentration of silica colloidal nanoparticles at 15g/100mL. Results indicated that the volume shrinkage of carbon precursors during supercritical drying and pyrolysis can be reduced by the presence of silica colloidal nanoparticles. The mesopore ratio increased with increasing R+F concentration and porosity decreased with increasing size of the silica colloidal nanoparticles. When the R+F concentration was 20g/100mL, the densities of the carbon aerogels were 0.22 and 0.26g/cm3 with mesopore ratios of 96 and 98% for 7 and 12nm silica colloidal nanoparticles respectively.
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Key words:
- Sol-gel approach /
- Organic aerogels /
- Carbon aerogels /
- Porosity
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