Catalytic Preparation Of Graphitic Carbon Sphere And Applied Basic Research Of Its Surface Adsorption And Wettability

Because of their excellent thermal shock,physical and chemical stability,graphitic carbon are widely used in traditional carbon-containing refractories;so in the adsorption and separation of dyes,heavy metal ions,water and oil pollutants owing to their light weight and large specific surface area.However,it also suffers from the limited reserve and poor dispersion of graphite.Therefore,in present thesis,carbon spheres?CS?with an average size of 0.4¹.0?m were prepared by hydrothermal carbonization using glucose and starch as carbon sources firstly and then the pH value of glucose solution,types of dispersants on the particle size and dispersion of CS were studied detailedly.Besides,graphitic carbon spheres?GCS?with an average size less than 2.0?m were also prepared by heating carbon spheres loaded with catalysts?Fe,Co and Ni?via hydrothermal method and isovolumetric impregnation method,the effects of heat treatment temperatures,catalyst amounts and soaking times on graphitization degree of GCS were studied.At the same time,density functional theory?DFT?was used to calculate the catalytic mechanism of three kinds of catalysts for the preparation of GCS.Based on the good sphericity and dispersion of CS and GCS,the Al₂O₃-SiC-C castables were prepared by using CS and GCS instead of flake graphite?FG?and ball pitch.The physical properties,oxidation resistance and thermal shock stability of the castables were studied.Meanwhile,because of the oxygen-containing functional groups on their surface and large specific surface area,the adsorption of methylene blue?MB?was studied.Moreover,because of the non-wettability of as-prepared GCS and water,the GCS foam was prepared,and their adsorption behavior of GCS and GCS foam on oil were studied.Finally,GCS and heptafluorodecyl triethoxysilane?FAS?co-modified mullite porous ceramics were prepared and used for water-oil separation in different environments.The results indicated that:?1?CS was prepared by hydrothermal carbonization with glucose as carbon source.The initial solution pH and dispersants had a great influence on the morphology of the product.Besides,GCS with polycrystalline structure and particle size of about 1.0-2.0?m were prepared by heat-treating CS loaded with catalysts via hydrothermal carbonization with glucose as carbon source at 1173¹573 K.The highest graphitization degree of GCS was about 52.3%,and the order of the catalytic activity of the three catalysts was Ni>Fe>Co.?2?GCS with an average particle size of 0.4?m and a maximum specific surface area of 543 m²/g could be prepared by heat-treating CS loaded with catalysts via isovolumetric impregnation method.The graphitization degree ranged from 47.7%to69.8%could be obtained by adding 1.0 wt%Fe,Co and Ni and firing at 1173-1473 K for 3 h.DFT results indicated that when Fe was used as catalyst,carbon atoms were more easily adsorbed on the surface of the catalyst,resulting in the formation of Fe-C compound,then graphitic carbon was obtained via the decomposition of the compound.For the case of Ni catalyst,some carbon atoms entered into the sub-surface layer of the catalyst,and then precipitated much easily to form graphite carbon;on the other hand,some carbon atoms reacted with Ni atoms to form Ni-C compound and then decomposed into graphitized carbon.These two factors made the catalyst the best catalytic activity.For the case of Co catalyst,one hand,Co was difficult to react with carbon to form Co-C compound;on the other hand,carbon atoms prefered to enter into the inner layer of Co catalyst,which resulted in the higher precipitation potential barrier of the former from the catalyst,these two factors lead to its poor catalytic activity.?3?Substitution of ball pitch with CS could greatly increase the self-flow value of the Al₂O₃-SiC-C castable.Compared with that sample using FG,the demanded water using GCS was greatly reduced,and the flexural strength and compressive strength after3 h firing at 1723 K was obviously increased.The thermal shock resistance of the Al₂O₃-SiC-C castable sample using GCS was comparable to that using FG,but much better than that using ball pitch,which could be at least partially attributed to the high graphitization degree and high thermal conductivity of as-prepared GCS.The sample using GCS also showed better oxidation resistance,which may be attributed to the more uniformly dispersion of GCS in the castable.?4?The maximum adsorption capacity of SDS modified GCS for MB was about681.4 mg/g,were respectively about 3.7 times of GCS and 18 times of CS.The functional groups and specific surface area were the main factors affecting the adsorption behaviour.DFT calculation results showed that when S-O functional group existed,charge transfer between O and S in SDS,S and N in MB were stronger,which made the adsorption between S-O group and MB more stable than these COOH and C-OH functional groups.?5?The graphitic carbon spheres foam prepared via foam-gelcasting method using GCS as starting materials possessed three-dimensional porous structure with pore size distribution of 25²00?m,and high porosity of 62%.The water contact angle of as-prepared foam was 130°,the adsorption capacity for oil was about 12¹5 g/g,and the continuous water oil separation rate was about 4.7×10⁴ g·m^-2·min^-1.FAS and GCS co-modified porous mullite ceramics exhibited superhydrophobicity with water contact angle of about 160°,their adsorption capacity for paraffin oil,vegetable oil and vacuum pump oil were about 0.8¹.2 g/g,and the continuous water/oil separation rates were respectively 3.4×10⁴ g·m^-2·min^-1,2.2×10⁴ g·m^-2·min^-1 and 1.3×10⁴ g·m^-2·min^-1;even after 10 cycles,the separation rate almost unchanged and the water/oil separation selectivity was still above 95%.In addition,the sample could also be used in high temperature?373K?,low temperature?77K?,acid?pH=1?,alkali?pH=13?and other harsh environments,and showed stable superhydrophobic and water/oil separation selectivity.The water/oil separation rate of modified porous ceramics in ice-water bath could be rapidly increased by self-heating process with an electric field.