Activated carbons (AC) with excellent textural properties have been obtained for the first time from waste polystyrene foam (PF), without any previous treatment, following a simple and conventional two-step procedure (formation of char followed by chemical activation). Even considering that the PF is not a graphitizable material, the best AC produced from this precursor has a very high BET surface area larger than 2700 m 2 g-1 and a pore volume of 1.2 cm 2 g-1 , with a significant contribution of small mesopores. As a consequence, this AC reveals a surprising capacity to adsorption of relatively large molecules and a high specific capacitance when applied as a supercapacitor electrode. The maximum amount of adsorbed methylene blue obtained by batch equilibrium experiments are greater than 1g g-1. In the context of the technical difficulties and low economic return of the reuse and recycling of waste PF, this work offers a strategic destination for this environmentally unfriendly residue.

Although traditionally high-surface area carbon materials have been considered as rigid structures with a disordered three dimensional (3D) network of graphite microdomains associated with a limited electrical conductivity (highly depending on the porous structure and surface chemistry), here we show for the first time that this is not the case for activated carbon materials prepared using harsh activation conditions (e.g., KOH activation). In these specific samples a clear structural re-orientation can be observed upon adsorption of different organic molecules, the structural changes giving rise to important changes in the electrical resistivity of the material. Whereas short chain hydrocarbons and their derivatives give rise to an increased resistivity, the contrary occurs for longer-chain hydrocarbons and/or alcohols. The high sensitivity of these high-surface area carbon materials towards these organic molecules opens the gate towards their application for sensing devices.

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The mechanism of operation of a supercapacitor based on methylene blue (MB) as redox shuttle in cells containing activated carbon as electrodes and aqueous electrolyte has been studied. Attention is focused on the instability of these molecules which can undergo secondary reactions that impact negatively on the cell, generating fluctuations in its performance and reducing its cycling life. It is demonstrated that MB interacts strongly with activated carbons and modifies their structure, decreasing the resistance of the electrodes and increasing the energy density of the cell by more than 40%. It is also shown that MB is not stable in acidic electrolyte at the high potentials attained by the electrodes of the supercapacitor. Demethylation byproducts and oxidized derivates of the MB were detected after cycling by means of electrospray ionization mass spectrometry. These products were observed to cause a constant change in the equilibrium potential of the cell, substantially modifying the storage mechanism and the ranges of operation potential of the electrodes.

In this article, banknotes residues were used to prepare reinforced low‐density polyethylene (LDPE) composites. First, the banknotes residues were crushed into fibers and then it was added in the polymeric matrix using different weight ratios (1–20 wt %). The composites were prepared by melt compounding, followed by injection molding. Afterward, the composites were characterized by scanning electron microscopy, contact angle, thermogravimetric analysis, Fourier transform infrared (FTIR) spectroscopy, and tensile tests. The FTIR showed physical interaction between fibers and the polymer matrix. In comparison with pure LDPE, improved mechanical properties were achieved for the composites containing 5–20 wt % of fibers (i.e., increase of 83% when 20% of fibers were used), with an increase in the tensile strength and Young's modulus, and a decrease in the elongation percentage. The results illustrate that the banknotes residues can be used for reinforcement of hydrophobic polymers without the need of any chemical modification or addition of compatibilizing agents. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 136, 48232.

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