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Sensing with Graphene
Published in Sunipa Roy, Chandan Kumar Sarkar, MEMS and Nanotechnology for Gas Sensors, 2017
Sunipa Roy, Chandan Kumar Sarkar
A novel graphene oxide paper-like material possessing a unique layered structure has been developed by directed-flow assembly method in which each graphene oxide sheets are interlocked mutually in a near-parallel fashion. The average modulus of graphene oxide paper was found to be 32 GPa [114]. The conventional Hummers’ method developed in 1957 using KMnO4 has been modified by the pre-exfoliation of the graphite by microwave heating. Vacuum filtration of colloidal dispersions of graphene oxide sheets through an Anodisc membrane filter yielded free-standing graphene oxide paper with thicknesses ranging from 1 to 30 mm after drying. The average elastic modulus and the fracture strength were found to be 32 GPa and 120 MPa, respectively. The mechanical properties of this ‘graphene oxide paper’ have been improved by chemical cross-linking between individual platelets by the use of divalent ions [115] and polyallylamine [116]. A self-assembled graphene oxide paper was also made at a liquid/air interface by evaporating the hydrosol of graphene oxide [117]. After annealing, its stiffness and tensile strength increased to such a value which is not reported till date. Graphene oxide prepared by a ‘bottom-up’ approach (Tang–Lau method) is much more affable compared to traditional ‘top-down’ method, in which strong oxidizers are involved. In ‘bottom-up’ approach, the precursor is glucose; the advantage of this process is that the thickness can be controlled more easily. Graphene oxide reduction with hydrazine has been reported [118] earlier.
Near-UV light assisted green reduction of graphene oxide films through l-ascorbic acid
Published in International Journal of Smart and Nano Materials, 2021
Jaime Regis, Sebastian Vargas, Andrea Irigoyen, Elsa Bramasco-Rivera, Jose L. Bañuelos, Luis C. Delfin, Anabel Renteria, Ulises Martinez, Tommy Rockward, Yirong Lin
It is shown in the literature that graphene oxide paper/films can rapidly desorb around 80% of the adsorbed moisture using wrinkle-like tunnels such as those shown in (Figure 2(B))[81]; however, other factors affect the moisture desorption of the reduced graphene oxide film. As Boukhalov et al. have demonstrated through simulation, the interlayer distance between graphene sheets plays a crucial role in the water-permeation mechanism [87]. The decrease in interlayer distance from the reduction of the graphene oxide can make the membrane 100 times less permeable to water and create blockage when the interlayer spacing drops to around 4 Å, as demonstrated experimentally by Nair et al. [88]. While it is suggested that the formation of percolated capillaries from unoxidized or reduced regions assists the flow of water [87], the probability of lenticular pores forming between impermeable passages which would essentially seal water in cannot be discarded. Due to the modest heat applied during the vacuum drying to limit the influence on reduction, it is unlikely that lenticular pores would be ruptured. In addition, intercalated water in the films can restrict the movement of other molecules, in this case, glucuronic acid and oxalic acid whose presence near the films’ surface can influence the XPS readings. Due to the impermeability to molecules other than water, chemical approaches are not suggested as appropriate methods to reduce graphene oxide stacked structures such as films, membranes, or papers.