Microstructural Modification And The Adsorptive Desulfurization Performances Of G-C₃N₄

With more stringent legislative control towards the sulfur content in fuel oil,more efficient and low cost adsorption desulfurization technology has been highlighted in recent years.In this dissert,g-C₃N₄,a new type of green material with unique ring of N₆ and graphite-like crystalline structure as well as non-toxic properties,is applied as desulfurization adsorbent.In order to promote its adsorptive performances,we prepared various types of g-C₃N₄ to disclose the relationship between the microstructures and its adsorptive performances.The details are listed as follows:1.The bulk g-C₃N₄ was intercalated by different concentration of H₂SO₄ solution（Wt%is 50%,75%,90%,98%）and the intercalation compounds were named as CNS50,CNS75,CNS90 and CNS98respectively.The samples were intercalated except CNS50 successfully by the results of XRD,EDS and XPS.The process of intercalation included several orders and the most was three-order intercalation.Thus,the specific surface was improved a lot,and CNS75 has the biggest specific surface area of 33.37 m²/g,which is higher 3.7 times than bulk g-C₃N₄.Even though the specific surface area of CNS98 is only 10.58m²/g,it has best absorption capacity of 32.49 mgS/g to thiophene and good selectivity in benzene.According to the absorption kinetics,the protonation effect and polar functional groups after intercalating reactions affect its absorption and the inserted layer structure has an influence on transfer of sulfocompounds and the time of equilibrium.2.The colloidal SiO₂ was used as hard template to synthesize mesoporous g-C₃N₄ at different calcination temperature（500℃,550℃and 600℃）,and were named as CN-500,CN-550 and CN-600respectively.The methods of TEM and BET proved the existence of the mesoporous.The results of UV-vis and XPS indicated that the calcination temperature has an influence on ring of heterocycle of the mesoporous g-C₃N₄.The structure of CN-600 is mainly heptazine ring structure,and the CN-500 is mainly triazine ring structure.The heptazine ring structure of mesoporous g-C₃N₄ can promote absorption in model fuel.The CN-600 is the best absorbent and has a good selectivity in the aromatic solution.The adsorbents have a best absorption capacity of thiophene among different sulfocompounds and the adsorption capacity of CN-600 toward thiophene is up to 40.82 mgS/g.Due to Steric effect and molecular size and so on,the adsorption order ofsulfocompounds is that:thiophene>trimethylthiophene>dimethylthiophene>2,5-dimethylthiophene>benzothiophene>dibenzothiophene.3.The dicyandiamide was treated at 200℃hydrothermally and growed into macromolecular structure.Calcinating freeze-drying-assembled can obtain some special hexagon tubular structure of g-C₃N₄,and there has not been recorded now.According to temperature curve and documents,we speculate the growth mechanism:the cyanamide molecular crystallize in the tube wall preferentially and the molecular inside of the tube volatilize because of hysteresis of the heat transfer.The samples have poor crystalline by the results of XRD and FTIR.The wall of hexagon tube was composed by thin layer and some mesopores.The hollow tube can provide open entrance for sulfocompounds and help to decrease the time to reach absorption equilibrium.