To explore graphene applications in various fields, the processability of graphene becomes one of the important key issues, particularly with the increasing availability of synthetic graphene approaches, because the direct dispersion of hydrophobic graphene in water is prone to forming agglomerates irreversibly. Here, a facile method is proposed to increase the dispersity of graphene through noncovalent functionalization graphene with a water-soluble aromatic electroactive dye, methylene green (MG), during chemical reduction of graphene oxide (GO) with hydrazine. Atomic force microscopic and UV-vis spectrophotometric results demonstrate that chemically reduced graphene (CRG) functionalized with MG (CRG-MG) is well-dispersed into water through the coulomb repulsion between MG-adsorbed CRG sheets. The electrochemical properties of the formed CRG-MG are investigated, and the results demonstrate that CRG-MG confined onto a glassy carbon (GC) electrode has lower charge-transfer resistance and better electrocatalytic activity toward the oxidation of NADH, in relation to pristine CRG (i.e., without MG functionalization). This method not only offers a facile approach to dispersing graphene in water but also is envisaged to be useful for investigations on graphene-based electrochemistry.

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Along with reduced graphene oxide (RGO), water soluble Prussian blue nanoparticles (PBNPs, around 6 nm) are synthesized and broadly characterized. These two types of highly stable, low-cost and chemically compatible nanomaterials are exploited as building ingredients to prepare electrically enhanced and functionally endorsed nanohybrid electrocatalysts, which are further transformed into free-standing graphene papers. PBNPs doped graphene papers show highly effi cient electrocatalysis towards reduction of hydrogen peroxide and can be used alone as fl exible chemical sensors for potential applications in detection of hydrogen peroxide or/and other organic peroxides. The as-prepared PBNPs-RGO papers are further capable of biocompatible accommodation of enzymes for development of freestanding enzyme based biosensors. In this regard, glucose oxidase is used as an example for electrocatalytic oxidation and detection of glucose. The present work demonstrates a facile and highly reproducible way to construct free-standing and fl exible graphene paper doped with electroactive catalyst. Thanks to high stability, low-cost and effi cient electrocatalytic characteristics, this kind of nanohybrid material has potential to be produced on a large scale, and offers a broad range of possible applications, particularly in the fabrication of fl exible sensing devices and as a platform for electrocatalytic energy conversion. Scheme 1 . Schematic illustration of the experimental procedures. A) Wet-chemical conversion of GO to RGO via hydrazine reduction, B) synthesis of PNBPs starting from the mixture of FeCl 3 and K 4 Fe(CN) 6 , C) preparation of PBNPs-RGO hybrid nanosheets, and D,E) processes of preparing PBNPs-RGO hybrid paper including fi ltration, drying and annealing. Not drawn to scale.

Understanding of Förster resonance energy transfer (FRET) in thin films composed of quantum dots (QDs) is of fundamental and technological significance in optimal design of QD based optoelectronic devices. The separation between QDs in the densely packed films is usually smaller than the size of QDs, so that the simple point-dipole approximation, widely used in the conventional approach, can no longer offer quantitative description of the FRET dynamics in such systems. Here, we report the investigations of the FRET dynamics in densely packed films composed of multisized CdSe QDs using ultrafast transient absorption spectroscopy and theoretical modeling. Pairwise interdot transfer time was determined in the range of 1.5 to 2 ns by spectral analyses which enable separation of the FRET contribution from intrinsic exciton decay. A rational model is suggested by taking into account the distribution of the electronic transition densities in the dots and using the film morphology revealed by AFM images. The FRET dynamics predicted by the model are in good quantitative agreement with experimental observations without adjustable parameters. Finally, we use our theoretical model to calculate dynamics of directed energy transfer in ordered multilayer QD films, which we also observe experimentally. The Monte Carlo simulations reveal that three ideal QD monolayers can provide exciton funneling efficiency above 80% from the most distant layer. Thereby, utilization of directed energy transfer can significantly improve light harvesting efficiency of QD devices.

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