Probing the catalytic activity of porous graphene oxide and the origin of this behaviour

Abstract

Graphene oxide, a two-dimensional aromatic scaffold decorated by oxygen-containing functional groups, possesses rich chemical properties and may present a green alternative to precious metal catalysts. Graphene oxide-based carbocatalysis has recently been demonstrated for aerobic oxidative reactions. However, its widespread application is hindered by the need for high catalyst loadings. Here we report a simple chemical treatment that can create and enlarge the defects in graphene oxide and impart on it enhanced catalytic activities for the oxidative coupling of amines to imines (up to 98% yield at 5 wt% catalyst loading, under solvent-free, open-air conditions). This study examines the origin of the enhanced catalytic activity, which can be linked to the synergistic effect of carboxylic acid groups and unpaired electrons at the edge defects. The discovery of a simple chemical processing step to synthesize highly active graphene oxide allows the premise of industrial-scale carbocatalysis to be explored.

One-flow syntheses of diverse heterocyclic furan chemicals directly from fructose via tandem transformation platform

“…25 In this work, however, reduced GO (rGO) was used due to its better catalytic profile for various organic transformations against the GObased catalyst. 26 Notably, the use of rGO as a catalyst has not been reported for an efficient etherification of HMF under mild conditions. For facile immobilization of the rGO by external magnet force, magnetic Fe 3 O 4 nanoparticles were loaded on the rGO prepared by Hummer's method.…”

“…For facile immobilization of the rGO by external magnet force, magnetic Fe 3 O 4 nanoparticles were loaded on the rGO prepared by Hummer's method. 26 After the immobilization of the Fe 3 O 4 /rGO mixture catalyst inside the wall of PTFE (500-μm id, 1.6-mm od, 200-cm length and 120-μl volume), the commercial HMF and ethanol were introduced from the horizontal inlet and vertical inlet of the T-junction, respectively, into the PTFE capillary to optimize the conversion to EMF by varying the reaction conditions (50-100°C, 6-18 min, see ESI, Supplementary Figure S1). At 100°C, unstable microfluidic flow was observed, which was presumably due to the low boiling point of ethanol.…”

“…7 In this work, N-rGO was selected as a catalyst support and metal aggregation preventer because the doped N atoms of N-rGO provided preferable immobilization sites for the metal catalyst (see ESI Supplementary Figure S5). 26 Table 4 presents the performance results of a series of mono-and bimetallic catalysts on a magnetic Fe 3 O 4 /NrGO support that were tested to evaluate the efficiency and selectivity of hydrogenolysis with hydrogen gas and heterogeneous catalyst in a tube-in-tube microfluidic system. A gas-permeable inner Teflon tube (610-μm id, 750-μm od and 100-cm length of AF-2400) was positioned into the outer PTFE tube (1.2-mm id, 1.5-mm od and 100-cm length).…”

Magnetic defects in chemically converted graphene nanoribbons: electron spin resonance investigation

“…Here, we briefly review the ESR investigations reported [10][11][12][13] in the literature while probing for the spin properties of graphene-derived materials. For instance, an interesting work 10 carried out on chemically-derived graphene oxide and reduced graphene oxide through ESR spectroscopy reported on the presence of localized paramagnetic defects and discussed how these defects influence the transport properties.…”

“…This study has identified both localized and extended defects from the ribbons. In another systematic work, 12 Su and co-authors have employed ESR spectroscopy in exploring the catalytic properties of graphene oxide and illustrated the role of defects, concluded that localized spins are created at the edge of pi-electron system. In another work, 13 while exploring the spin magnetism of nano sized graphite particles, EPR spectroscopy has revealed the presence of strongly coupled localized and itinerant spins.…”