Facile synthesis of nitrogen-doped foam-like carbon materials from purslane stem as efficient metal-free catalysts for oxidative coupling of amines to imines

We synthesized foam-like carbon materials from purslane stem by soxhlet extraction and pyrolysis two steps. The results demonstrate that the solvents used in soxhlet extraction can extract different components from purslane stem and further make significant impacts on the structure and composition of the obtained carbon materials. When applied to catalytic oxidative coupling of amines to imines, the most active catalyst is the carbon material derived from the purslane stem pretreated with ethanol, which can be attributed to its high surface area, large pore size and accessible active sites. In addition, the catalyst shows good stability, which can be recycled at least six times and applicable in the large-scale catalytic reaction. Moreover, the carbon materials derived from celery stem and apricot leaf pretreated with ethanol in soxhlet extraction also show higher catalytic activity than the carbon materials pretreated with ethyl acetate and water, which implies that this simple synthetic process is generally applicable to a certain extent. Hence, this study can provide new way toward the synthesis of high-performance carbon materials from biomass.