Preparation Of Graphene Based Multi-functional Catalysts For Organic Reactions

Graphenehas generated enormous excitement due to its unique two-dimensional structure,huge surface area, outstanding mechanical and electronic transfer properties that make it a promising candidate as a good support in heterogeneous catalytic processes.In this study, The synthesis and applications of multifunctionalgraphene hybrids were explored.Utilizing oxygen functional groups of graphene oxide, a strategy of covalently attachment of primary and tertiary amineson graphene oxide surfaceis explored, and primary and tertiary amines designed graphene oxide was used as bifunctional catalyst inthe classic trans-β-nitrostyrene forming reaction.The results show the primary and tertiary amines group are uniformly dispersed on the surface of graphene oxide with a loading density of 1.91 mmol g–1, and the catalyst with primaryamines : tertiary amines of 1:1shows the highest catalytic activity thatselectivityoftrans-β-nitrostyreneis 100%, and convertion ofbenzaldehydeis 99.5%. On the other hand, two sntagonistic functions of phosphotungstic acid and amine groups are attached on graphene oxide bythe electrostatic interactionbetween phosphotungstic acid andprimary amine groups. By controlling the ratio of immobilized phosphotungstic acid, only part of the primary aminewas occupied, creating the acid/base catalytic sites containing phosphotungstic acid, primary amine and tertiary amine on GO. The prepared acid/base bifunctional catalyst shows interesting acid/base synergistic catalytic performancein the one-pot deprotection–nitroaldol reaction, high conversion of benzaldehydedimethylacetal(100%) and satisfied yield of trans-β-nitrostyrene(99.2%) were obtained in the reactions when polyanions to amino ratio is 0.2:1. Meanwhile, the catalyst can be recycled after simple washing.It can not only reduce cost and waste water by saving separation/purification steps and solvents/reagents, but also increase the yield by avoiding the separation of intermediate products.Inspired by the organic bases and inorganic acids can be modified graphene together,general acid and base bifunctional graphene oxide was prepared.the general acid, ureidopropyl group, and the general base, the 3-[2-(2-aminoethylamino)ethylamino]-propyl groupare uniformly dispersed on the surface of graphene oxide with a loading density of 2.48 and 0.62 mmol g–1,respectively. When the general acid/base ratio was 1:4, the catalyst give the best performance that the TON of catalyst is124.5, and the yield of product is 88.4%. Then, the acid-base catalysis on the same molecule was studyed. L-proline convalently anchored on graphene oxide was prepared by a means of succinate spacerbetween the carboxylic acid on carbonyl modified graphene oxide and the hydroxylgroups on trans-4-hydroxy-L-proline. Systematic studies demonstrated L-proline molecules could be readily introduced to the graphene oxide sheets with homogeneous distributions. Notably, the obtained GO–Proline shows excellent catalytic performancewith the convertion towards benzaldehyde of 91.9% in the solvent free ketene forming reaction of benzaldehyde and acetone.Meanwhile, the catalyst exhibites excellent reusability, and the conversion remains unchanged after 5 runs.Graphene based catalysts are environmentally friendly and efficient reusable catalyststhat make graphene has good prospects in the field of organic reactions...