TEM micrographs Fig of the catalysts MACHT MACS PACS
The above characterization results point to a much complex structure for the DOWC Gedunin derived sulfonated catalysts which different from the typical carbohydrate or sugar derived sulfonated carbons/sulfonated active carbons prepared by Hara et al. method . Structurally these multifunctional materials are related more to the N-doped carbons or carbon nitrides rather than amorphous or active carbons . In contrast to the typical carbohydrate or resin based sulfonated catalyst where the basic structural unit is simply a flexible aromatic carbon or graphene sheet functionalized with –OH, COOH and SO3H groups (I). The structural unit of sulfonated carbons obtained from the protein rich DOWC resembles a flexible carbon nitride sheet which has been extensively functionalized with OH, COOH, phosphates (PO4) and SO3H or PhSO3H groups. The DOWC based catalytic materials may adopt any one of the three the structures II or III or IV depending on the method of preparation (Fig. 8). The density and nature of surface acidic groups are directly affected by carbonisation conditions (temperature, use of activating agent etc.). Here, the H2SO4 treated and phosphoric acid activated DOWC (method 2) will take up structure II while the materials prepared by method 1 (4-BDS treated) will adopt structure III and the hydrothermally sulfonated and carbonised materials (method 3) will take up structure IV.