Platinum group metals, such as Pd and Pt, found in three-way catalyst converters were recycled in a two-step method: hydrodynamic cavitation followed by sonoelectrochemical dissolution. High shear forces were obtained by using a convergent nozzle with a throat diameter of 0.2 mm, feeded by a plunger pump at a pressure of 60 MPa. Cavitating submerged jets acted locally on the water dispersed waste catalyst. As-obtained samples were analyzed by scanning electron microscopy and transmission electron microscopy. Electron microscopy on the initial sample showed that round shaped Pd and Pt nanoparticles were randomly distributed on the Al2O3 matrix. Cavitated samples show two zones in which Pt and Pd were partially and completely separated from the cordierite. The hydrodynamic cavitation separates the Pd and Pt from the cordierite leading to an apparent increase in Pd and Pt concentrations of 9% and 34% respectively. Conventional electrochemistry showed a dissolution of 20% in 1 h. To further accelerate the dissolution, a sonotrode operating at 20 kHz and 75 W was placed inside an electrochemical cell in order to increase the mass transport and obtain high dissolution rates. Indeed, the results showed that 40% of the available Pd and Pt can be recycled in just 1 h. In the absence of hydrodynamic cavitation and using conventional electrochemistry less than 10% of the available Pt and Pd is recovered in 1 h. The cost analysis showed that Pd and Pt can be recovered at less than 10 EUR per g which is 5 times smaller than their current market price.

Active and stable materials that utilize solar radiation for promoting different reactions are critical for emerging technologies. Two of the most common polymeric carbon nitrides were prepared by the thermal polycondensation of melamine. The scope of this work is to investigate possible structural degradation before and after photoelectrochemical testing. The materials were characterized using synchrotron radiation and lab-based techniques, and subsequently degraded photoelectrochemically, followed by post-mortem analysis. Post-mortem investigations reveal: (1) carbon atoms bonded to three nitrogen atoms change into carbon atoms bonded to two nitrogen atoms and (2) the presence of methylene terminals in post-mortem materials. The study concludes that polymeric carbon nitrides are susceptible to photoelectrochemical degradation via ring opening.

A hydrodynamic cavitation method was used to maximize the effect of destructuration of a honeycomb monolithic support of a spent Selective Catalyst Reduction (SCR) catalyst—V₂O₅-WO₃/TiO₂-type—for extracting crystalline titanium and tungsten oxides from the cordierite surface. A high relative inlet pressure of 40 MPa was applied to a divergent nozzle for obtaining high shear stresses of the submerged cavitating jets and intensive micro- and nano-jets and shock waves acting on the particle surface of the milled catalyst. Scanning Electron Microscopy (SEM) analysis indicated the compact morphology of the thin metal oxide layer at the surface of the cordierite support and the high content of Ti and W elements in the sample. Energy dispersive spectroscopy (EDAX) performed along with TEM investigations on different nano-zones from the sample established the elemental composition of WO₃-TiO₂ agglomerates separated after hydrodynamic cavitation processing and identified as independent nanocrystalline structures through Bright Field Transmission Electron Microscopy (BF-TEM) and High Resolution Transmission Electron Microscopy (HR-TEM) measurements. The tetragonal anatase phase of TiO₂ and cubic phase of WO₃ were established by both interplanar d spacing measurements and X-ray diffraction analysis. The photoelectrochemical results showed the possible second life application of automotive catalysts.

A small Savonius wind turbine of helical type was tested in an open jet wind facility for identifying the optimum position of the rotor blades aiming the maximization of static torque. The two blades of the wind turbine of U shape were twisted up to 180⁰ from bottom to top and three values for blade overlap were considered i.e. 0.35, 0.2 and 0.0. The turbine torque was measured for no load conditions and wind velocities between 2-8 m/s. In the same time the air flow through Savonius rotor was observed by using a visualization setup aiming to identify the correlation between the torque and the flow pattern inside the returning blade at rotating angles where the torque has highest values. Best results for the torque coefficient of 0.72 and power coefficient of 0.265 were obtained at a wind velocity of 5.8 m/s and low overlap ratio of 0.2. By measuring the overall torque of the rotor for each case study, the positive effect of pressure recovery was explained as a result of air flow through the blade overlap from the concave side of the advancing blade to concave side of the returning blade for a certain interval of the rotating angle a = 50-60°.

Increasing evapotranspiration in cities, derived from vegetation and water bodies, can effectively mitigate the effect of urban heat island (UHI). This paper presents a study on an urban ventilation solution for Bucharest City in Romania. The solution is based on lifting air volumes from the free surface of Dambovita River, which crosses the city center where UHI has a significant impact, to the roadway and pedestrian level by using cross-flow fans mounted on floating panels planted with vegetation, which are placed at the river banks. The electric motors of the cross-flow fans are powered by PV solar cells. The real optimal value of evapotranspiration (ETRO) was computed for the case of lucerne in order to assess the air temperature at the surface of the floating panel and a numerical study was performed in order to obtain the velocities of the air flow and the temperature field in a domain containing the free surface of the river, the floating panel surface, and the roadway surface (at pedestrian level). It was observed that, at low flow rates, the cooler air reaches the roadway surface in a compact jet due to the Coanda effect - the coherent air jet is of about 30–40 cm above the ground level. For a day with clear sky and no wind conditions a decrease in the air temperature of 4–5 °C can be obtained at the pedestrian level, within a layer of 1 m height. The study opens the possibility to approach such issues at a greater scale in order to assess the viability of appropriate solutions for cooling down the urban heat island as well.