Activation energy for charge transport, carrier concentration and recombination rate are identified to strongly affect the device characteristics.

Viscose fibers were impregnated with different concentrations of diammonium hydrogen phosphate (DAHP), carbonized, activated, and tested as high-performance electrode materials for supercapacitors. The yield of these activated carbon fibers (ACFs) could be increased by a factor of 14 by using DAHP compared to ACF without impregnation. These specific activation procedures yielded a high specific surface area of more than 2700 m2·g−1 with a pore size distribution (PSD) suitable for use as a supercapacitor electrode. The electrode materials were implemented in symmetric supercapacitors using TEMA BF4 as electrolyte and cyclic voltammetry measurements showed high specific capacitances of up to 167 F·g−1. Furthermore, the devices showed high energy densities of up to 21.4 W·h·kg−1 and high-power densities of up to 8.7 kW·kg−1. The supercapacitors featured high capacity retention (96%) after 10,000 cycles. These results show that ACFs made of viscose fibers, previously impregnated with DAHP, can be used as high-performance electrodes in supercapacitors for energy storage applications.

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BACKGROUNDThe use of non‐aqueous organic media is becoming increasingly important in many biotechnological applications in order to achieve process intensification. Such media can be used, for example, to directly extract poorly water‐soluble toxic products from fermentations. Likewise many biological reactions require the supply of oxygen, most normally from air. However, reliable online measurements of oxygen concentration in organic solvents (and hence oxygen transfer rates from air to the solvent) has to date proven impossible due to limitations in the current analytical methods.RESULTSFor the first time, online oxygen measurements in non‐aqueous media using a novel optical sensor are demonstrated. The sensor was used to measure oxygen concentration in various organic solvents including toluene, THF, isooctane, DMF, heptane and hexane (which have all been shown suitable for several biological applications). Subsequently, the oxygen transfer rates from air into these organic solvents were measured.CONCLUSIONThe measurement of oxygen transfer rates from air into organic solvents using the dynamic method was established using the solvent resistant optical sensor. The feasibility of online oxygen measurements in organic solvents has also been demonstrated, paving the way for new opportunities in process control. © 2015 The Authors. Journal of Chemical Technology & Biotechnology published by JohnWiley & Sons Ltd on behalf of Society of Chemical Industry.

PurposeIn this work, low-molecular-weight sulfoethyl chitosan (SECS) was used as a model template for the generation of silver core-shell nanoparticles with high potential as anticoagulants for medical applications.Materials and methodsSECS were synthesized by two reaction pathways, namely Michael addition and a nucleophilic substitution with sodium vinylsulfonate or sodium 2-bromoethanesulfonate (NaBES). Subsequently, these derivatives were used as reducing and capping agents for silver nanoparticles in a microwave-assisted reaction. The formed silver-chitosan core-shell particles were further surveyed in terms of their anticoagulant action by different coagulation assays focusing on the inhibition of either thrombin or cofactor Xa.ResultsIn-depth characterization revealed a sulfoalkylation of chitosan mainly on its sterically favored O6-position. Moreover, comparably high average degrees of substitution with sulfoethyl groups (DSSE) of up to 1.05 were realized in reactions with NaBES. The harsh reaction conditions led to significant chain degradation and consequently, SECS exhibits masses of <50 kDa. Throughout the following microwave reaction, stable nanoparticles were obtained only from highly substituted products because they provide a sufficient charge density that prevented particles from aggregation. High-resolution transmission electron microscopy images reveal that the silver core (diameter ~8 nm) is surrounded by a 1–2 nm thick SECS layer. These core-shell particles and the SECS itself exhibit an inhibiting activity, especially on cofactor Xa.ConclusionThis interesting model system enabled the investigation of structure–property correlations in the course of nanoparticle formation and anticoagulant activity of SECS and may lead to completely new anticoagulants on the basis of chitosan-capped nanoparticles.