The effect of hole localization on photocatalytic activity of Pt-tipped semiconductor nanocrystals is investigated. By tuning the energy balance at the semiconductor-ligand interface, we demonstrate that hydrogen production on Pt sites is efficient only when electron-donating molecules are used for stabilizing semiconductor surfaces. These surfactants play an important role in enabling an efficient and stable reduction of water by heterostructured nanocrystals as they fill vacancies in the valence band of the semiconductor domain, preventing its degradation. In particular, we show that the energy of oxidizing holes can be efficiently transferred to a ligand moiety, leaving the semiconductor domain intact. This allows reusing the inorganic portion of the "degraded" nanocrystal-ligand system simply by recharging these nanoparticles with fresh ligands.

Herein, a novel concept for the acid catalyzed dehydration of fructose (FRC) to 5-hydroxymethylfurfural (5-HMF) in a biphasic tubular reactor is presented. Reaction kinetic models were developed based on experiments performed in a newly developed lab-scale autoclave that enables a decoupled investigation of singlephase reaction and 5-HMF mass transfer. Our reaction kinetic models allow an accurate description of the biphasic reaction. Subsequently, we integrate the reaction kinetic models in the model-based design of a tailored reactor unit. This reactor unit employs the concept of in-situ extraction in a countercurrent flow of a monodisperse droplet swarm within a continuous aqueous phase. From reactor calculations, we obtain a maximum 5-HMF yield of 76% at full FRC conversion.Countercurrent in-situ extraction enables over 99% 5-HMF recovery in the organic phase.

Increasing the rotational speed of the internal gear pump entails addressing topics such as cavitation, overheating and filling problems of the tooth spaces. Besides the development of a tooth geometry and flow optimization, using CFD simulation is necessary. This paper discusses the design of the newly developed high speed internal gear pump. This includes a detailed description of the different parts as well as the dimensioning of the pump by using CFD simulations. The geometry of the pressure build-up groove has a significant effect of pressure build up inside the pump. Therefore, three different geometries are investigated. The calculation of the journal bearings for the internal gear as well as for the driving shaft is shown. To avoid cavitation problems, the suction pressure of the pump will be increased up to 25 bar. This paper will show the technical arrangements to reach this high suction pressure level whilst still using a radial shaft seal ring. In order to determine the efficiency of the newly developed high speed pump, a test rig was built up. The test rig allows the measurement of the volumetric efficiency as well as the hydraulic-mechanical efficiency at different operation points up to 10 000 rpm and 250 bar.

We investigate the influence of sulfate salts and sulfuric acid on the equilibrium behavior of 2-methyltetrahydrofuran (2-MTHF)/H 2 O/5hydroxymethylfurfural (5-HMF). Liquid−liquid equilibrium measurements are performed at atmospheric pressure and in a temperature range of T = (293−333) K. The compositions of the aqueous and organic phases, together with the dissociation state of the sulfate species, are determined with infrared spectroscopy and Indirect Hard Modeling. We show that the addition of the salts Na 2 SO 4 and Li 2 SO 4 results in salting out of 2-MTHF and 5-HMF from the aqueous phase. With increasing temperature, this effect gets less pronounced. In contrast, the addition of H 2 SO 4 does not result in any salting-out behavior. The investigation of the dissociation states shows that H 2 SO 4 dissociates to HSO 4 − while Na 2 SO 4 and Li 2 SO 4 dissociate completely to SO 4 2−. Parameter regression is performed to model the liquid−liquid equilibrium with the electrolyte perturbed-chain statistical associating fluid theory (ePC-SAFT) equation of state. For the analyzed salts, Na 2 SO 4 and Li 2 SO 4 , the performed parameter regression accurately predicts the measurement results. Still, we observe slight deviations between measured values and modeling when predicting the liquid−liquid equilibrium and the liquid density in the presence of sulfuric acid.

The phenomenon of current collapse is a limiting factor in the performance of AlGaN/GaN high electron mobility transistors (HEMTs), and can be ameliorated by the deposition of a silicon nitride passivation film on the surface. The effect of three types of surface cleaning prior to the application of a silicon nitride passivation layer are studied. The best results were obtained when the wafers were cleaned using an air plasma descum followed by an HCl dip prior to the deposition of the silicon nitride passivation. Auger electron spectroscopy depth profiling indicated that the degree of collapse was correlated with the amount of residual carbon contamination at the silicon nitride/AlGaN interface.