| Carbon aerogels are low-density porous materials with a unique three-dimensional nano-network. So far carbon aerogel is the only kind of aerogel that is electronically conductive. Carbon aerogels had been applied to electrodes for supercapacitors, advanced catalyst supports, chromatographic packing, adsorbents and so on, owing to their unique microstructures and properties. Up to now, most carbon aerogels were prepared by supercritical CO2 drying, which is time-consuming and wastes substantial liquid CO2 during the process. Therefore, carbon aerogels are expensive as compared with other materials for a given application, which limits their commercial viability.Porous carbons begin to be oxidized at 370℃in air, leading to an apparent weight loss and as a result, their electric resistivity and porosity increase and mechanical properties decrease, which greatly limit their applications in catalytical fields. Antioxidation must be done to improve their reliability, safety and service life in catlytical fields. Antioxidation is realized by active point inhibition, coating inhibition and matrix inhibition for porous carbons.In this paper resorcinol-formaldehyde (RF) carbon aerogels were derived by ambient drying method. P-doped and B-doped phenol-furfural (PF) carbon aerogels were derived with the addition of H3BO3 and H3PO4. And the possibility of ambient pressure drying method was investigated. In the end of the paper, the CVD and liquid-phase impregnation method were used to modify the oxidation resistance of carbon aerogels. The main results and conclusions are as follows:1. RF carbon aerogels rich in macopores were prepared by ambient pressure drying method by using resorcinol and formaldehyde as raw materials,Na2CO3 as catalyst. Sol-gel and solvent exchange process were performed prior to the drying. The ratio of macropores can reach up to 89%,Brunauer-Emmett-Teller(BET) surface areas can be 510m2/g.And the carbonization yield is in the range of 50%～60%,which is higher than the similar RF aerogels at ambient pressure dring.2. B-doped carbon aerogels rich in macropores were prepared by the sol-gel polycondensation of phenol, m-cresol and furfural by an acid catalyst in a 1-propanol solution, followed by supercritical n-hexane drying and pyrolysis. The effects of amounts of H3BO3 additive and reactant concentrations on properties of the B-doped carbon aerogels were investigated. When the amounts of H3BO3 additive is fixed, the partical size of the aerogels decreased with the increased reactant concentration and at the same time the BET surface areas increased from 1 m2/g to 370m2/g.It can be deduced that with the racatant concentration the micropores of carbon aerogel increased. 3. P-doped carbon aerogels rich in macropores were prepared by the sol-gel polycondensation of phenol m-cresol and furfural by an acid catalyst in a 1-propanol solution, followed by supercritical n-hexane drying and pyrolysis. The carbon aerogels were characterized by infrared spectroscopy,N2 adsorption,mercury intrusion method and scanning electron microscopy. The BET surface areas can reach up to 455m2/g and the ratio of macropores can reach up to 99%. The effects of amounts of H3PO4 additive and reactant concentrations on properties of the P-doped carbon aerogels were investigated.4. Surface coating, liquid-phase impregnation and CVD method were applied to surface modification of carbon aerogels. Aluminium phosphate, aluminium dihydrogen phosphate and tetraethoxysilane were used in these methods. And the oxidation resistance of the modified carbon aerogels was evaluated by the self-assemblied gravimetric equipment. The oxidation weight loss of carbon aerogels after modified can reduce 10 to 35 percent. |
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