Asymmetrically Functionalized Graphene for Photodependent Diode Rectifying Behavior

Abstract

As an atomically thin sheet of carbon atoms packed in a twodimensional (2D) honeycomb lattice with excellent electronic, thermal, and mechanical properties, graphene has shown great potential for a wide range of applications. Examples include the use of graphene and its derivatives as transparent conductive electrodes or active materials in solar cells, counter electrodes in dye-sensitized solar cells, electrocatalysts for oxygen reduction in fuel cells, high-performance electrodes in supercapacitors, batteries, actuators, and sensors. [1, 2] Of particular interest, Guo et al. [2f] reported a significant advancement in the development of layered graphene/quantum dots for highly efficient solar cells. Stoller et al.[1j] produced graphene-based supercapacitors free from any conducting filler with a specific capacitance of 135 F g À1 in aqueous electrolytes. We also demonstrated that N-doped graphene could act as a metal-free electrode with a much better electrocatalytic activity, long-term operational stability, and tolerance to crossover effect than platinum for oxygen reduction in alkaline fuel cells.[2b] By using graphene as a superior dimensionally compatible and electrically conductive component, Guo et al. [2g,h] further constructed a smart graphene-based multifunctional biointerface for cell growth as well as in situ selective and quantitative molecular detection. There is now a pressing need to integrate graphene sheets into multidimensional and multifunctional systems with spatially well-defined configurations, and hence integrated systems with a controllable structure and predictable performance. This requires controlled functionalization of graphene sheets at the molecular level, which is still a big challenge.The recent availability of solution-processable graphene by exfoliation of graphite into graphene oxides (GOs), followed by solution reduction, [3] has allowed the functionalization of graphene sheets through various solution reactions.[4] As far as we are aware, however, there is still no report on the asymmetric functionalization of graphene sheets by attaching different chemical moieties to their two opposite surfaces. The asymmetric functionalization, if realized, should significantly advance the self-assembling of graphene sheets into many new multidimensional and multifunctional systems with molecular-level control. Herein, we report for the first time a simple but effective asymmetric modification method for functionalizing the two opposite surfaces of individual graphene sheets with different nanoparticles (NPs) in either a patterned or nonpatterned fashion. The resultant asymmetrically modified graphene sheets with ZnO and Au NPs on their two opposite surfaces were demonstrated to show a strong photodependent diode rectifying behavior.We have previously developed a polymer masking technique for asymmetric functionalization of carbon-nanotube sidewalls by sequentially masking vertically aligned carbon nanotubes twice, with only half of the nanotube length being modified each time. [5,6]...

Selective Functionalization of Graphene Peripheries by using Bipolar Electrochemistry

“…Typically, to obtain two different metals or functionalities on the same graphene sheet, or simply for edge selective functionalization, some sort of local structuring or patterning is necessary . From a device perspective, the presence of two different metals at the two ends or two contacts breaks device symmetry, thereby allowing for different band alignments at the two contacts, which will enable the direct on‐site realization of photodiodes and photodetectors . On the other hand, the access to two different chemistries on the same graphene sheet will pave the way for the realization of novel heterogeneous catalyst supports …”

Synthesis of highly stable and high water retentive functionalized biopolymer-graphene oxide modified cation exchange membranes

“…Finally the product is dried at 60°C in vacuum for whole night. Further, APTEOS modified GO is sulfonated using concentrated sulfuric acid followed by chlorosulfonic acid [17]. Briefly, 100 mg of APTEOS modified GO is treated with 75 ml concentrated sulfuric acid at least for 1 hour and then addition of 15 ml chlorosulfonic acid is done drop wise.…”

“…The preparation of graphene oxide from graphite powder was done by modified Hummer's method reported earlier [16,17]. Now conversion of GO into MGO is done in two step process.…”

Nanostructuring Confinement for Controllable Interfacial Charge Transfer

“…Carbon nanostructures supported semiconductors intrinsically are metal‐semiconductor contacts . In contrast to common Schottky or p‐n junction based photovoltaic and rectifying behaviors, in which the formed built‐in fields can help to separate the photogenerated charge carriers ( Figure a and Figure S1, Supporting Information); in photocatalytic and photoelectrochemical applications (Figure a and Figure S1), however, the photogenerated charge carriers should overcome the built‐in fields and potential barriers to realize charge separation and display the role of the conducting channels (Figure b). The transfer of charges through the carbon‐semiconductor interface can be mainly described as thermionic emission and electron tunneling, according to the height and width of the potential barriers of the contacts .…”