The emission of a bright blue fluorescence is a unique feature common to the vast variety of polymer carbon dots (CDs) prepared from carboxylic acid and amine precursors. However, the difficulty to assign a precise chemical structure to this class of CDs yet hampers the comprehension of their underlying luminescence principle. In this work, we show that highly blue fluorescent model types of CDs can be prepared from citric acid and ethylenediamine through low temperature synthesis routes. Facilitating controlled polycondensation processes, the CDs reveal sizes of 1-1.5 nm formed by a compact network of short polyamide chains of about 10 monomer units. Density functional theory calculations of these model CDs uncover the existence of a spatially separated highest occupied molecular orbital and a lowest unoccupied molecular orbital located at the amide and carboxylic groups, respectively. Photoinduced charge transfer between these groups thus constitutes the origin of the strong blue fluorescence emission. Hydrogen-bond-mediated supramolecular interactions between the polyamide chains enabling a rigid network structure further contribute to the enhancement of the radiative process. Moreover, the photoinduced charge transfer processes in the polyamide network structure easily explain the performance of CDs in applications as revealed in studies on metal ion sensing. These findings thus are of general importance to the further development of polymer CDs with tailored properties as well as for the design of technological applications.

We report the fabrication of flexible conductive graphene paper through a direct and gentle annealing process of graphene oxide paper. Thermal treatments at 700 ºC under argon or hydrogen atmosphere directly applied to parent graphene oxide paper lead to a significant removal of disruptive oxygen-containing functional groups, and to a considerable recovery of the sp 2 network structure. Detailed comparison of chemical and combined chemical-thermal treatments by scanning electronic microscopy (SEM), Raman, X-photoelectron spectroscopy (XPS) and conductivity measurements underline the high efficiency of the direct annealing process. The resulting highly reduced graphene oxide paper exhibits electrical conductivities as high as 8100 S/m representing an increase of 5 orders of magnitude with respect to the parent graphene oxide paper,

We report on the modification of graphene oxide (GO) with polyvinylalcohol (PVA) leading to the mechanical improvement of GO based materials. First, GO was covalently functionalised with PVA by esterification of carboxylic groups on GO with hydroxyl groups of PVA resulting in functionalised f-(PVA)GO. This was carried out for PVA of six different molecular weights. This functionalised graphene oxide could be formed into a paper-like material by vacuum filtration.Papers prepared from f-(PVA)GO showed significant increases in mechanical properties compared to those prepared with GO or with simple mixtures of GO and PVA. The best performance was achieved for PVA functional groups with molecular weights between 50 and 150 kg/mol. Improvements in Young's moduli of 60% and tensile strength of 400% were observed relative to GO-only paper. The improved mechanical properties are attributed to enhanced inter-flake stress transfer due to the covalently bonded PVA. Second, functionalised f-(PVA)GO was used as filler in

The development of ion-selective electrodes (ISEs) using solid-state transducer materials is of great interest for advanced potentiometric detection systems. At present, conducting polymers are the most used solid-state transducing materials. However, their reliability is strongly related to their chemical stability and the formation of internal water films. Here we report on the use of reduced graphene oxide (RGO) films of different thicknesses as transducer materials in potentiometric all-solidstate ISEs. First, the transduction mechanism is fully analyzed, revealing that RGO films act as asymmetric capacitors where their electron density is in contact with ions of the electrolyte solution, creating a capacitance due to the constant phase elements present in the system. Second, as a proof of concept, RGO films are used in a calcium ISE showing highly reproducible sensing responses and outstanding increased signal-to-noise ratios with drifts of only 10 μV/h. These performance parameters are among the best compared to those of other ISE transducer materials so far. With its ease of fabrication and processing into reproducible films of controlled thickness and ease for further tailoring chemical composition and tailoring electrical properties, RGO offers great promise as a reliable high-performance transducer material for solid-state ISE sensors.

Three-dimensional graphene aerogels of controlled pore size have emerged as an important platform for several applications such as energy storage or oil-water separation. The aerogels of reduced graphene oxide are mouldable and light weight, with a porosity up to 99.9%, consisting mainly of macropores. Graphene aerogel preparation by self-assembly in the liquid phase is a promising strategy due to its tunability and sustainability. For graphene aerogels prepared by a hydrothermal method, it is known that the pH value has an impact on their properties but it is unclear how pH affects the auto-assembly process leading to the final properties. We have monitored the time evolution of the chemical and morphological properties of aerogels as a function of the initial pH value. In the hydrothermal treatment process, the hydrogel is precipitated earlier and with lower oxygen content for basic pH values (∼13 wt% O) than for acidic pH values (∼20 wt% O). Moreover, ∼7 wt% of nitrogen is incorporated on the graphene nanosheets at basic pH generated by NH addition. To our knowledge, there is no precedent showing that the pH value affects the microstructure of graphene nanosheets, which become more twisted and bent for the more intensive deoxygenation occurring at basic pH. The bent nanosheets attained at pH = 11 reduce the stacking by the basal planes and they connect via the borders, hence leading eventually to higher pore volumes. In contrast, the flatter graphene nanosheets attained under acidic pH entail more stacking and higher oxygen content after a long hydrothermal treatment. The gravimetric absorption capacity of non-polar solvents scales directly with the pore volume. The aerogels have proved to be highly selective, recyclable and robust for the absorption of nonpolar solvents in water. The control of the porous structure and surface chemistry by manipulation of pH and time will also pave the way for other applications such as supercapacitors or batteries.