Mottness at finite doping and charge instabilities in cuprates

The intrinsic instability of underdoped copper oxides towards inhomogeneous states is one of the central puzzles of the physics of correlated materials. The influence of the Mott physics on the doping-temperature phase diagram of copper oxides represents a major issue that is subject of intense theoretical and experimental effort. Here, we investigate the ultrafast electron dynamics in prototypical single-layer Bi-based cuprates at the energy scale of the O-2p\u2192Cu-3d charge-transfer (CT) process. We demonstrate a clear evolution of the CT excitations from incoherent and localized, as in a Mott insulator, to coherent and delocalized, as in a conventional metal. This reorganization of the high-energy degrees of freedom occurs at the critical doping pcr 430.16 irrespective of the temperature, and it can be well described by dynamical mean field theory calculations. We argue that the onset of the low-temperature charge instabilities is the low-energy manifestation of the underlying Mottness that characterizes the p<pcr region of the phase diagram. This discovery sets a new framework for theories of charge order and low-temperature phases in underdoped copper oxides. ArXI

Spinning disk reactor technology in photocatalysis: nanostructured catalysts intensified production and applications

The use of photocatalysis in environmental remediation processes has become more important in the last decade, mainly due to the notable efforts made by researchers in this field. The photocatalytic process requires a semiconductor material (photocatalyst), usually a metal oxide, which can be activated through the energy transported by ultraviolet light or visible light waves. The activated photocatalyst generates active compounds, such as hydroxyl radicals and superoxide ion, able to degrade very recalcitrant and non-biodegradable compounds present on the catalyst surface or in the liquid medium. The efficiency of the pollutant removal process is affected by various factors related to the employed photocatalyst, such as mean dimension, size distribution, physical structure and energy required for the activation. The photocatalyst characteristics are strongly dependent on the production process, and several researchers have developed new intensified production nanostructured catalysts in a continuous Spinning Disk Reactor is discussed. The main features of Spinning Disk Reactor technology are reported and analysed, i.e. rotational velocity, disk diameter, disk surface material and roughness, focusing on the production of nanoparticles to be used in the photocatalytic application, in view of the process intensification of photocatalysis application in the field of environmental remediation. A general overview about process intensification and its application to chemical engineering is presented, and the advantages offered by Spinning Disk Reactor technology, in terms of an increase of process efficiency due to the misinformation of operative conditions in reactors, are illustrated. Basing on the Spinning Disk Reactor characteristics and operative conditions, nanoparticle production by Spinning Disk Reactor compared to conventional technologies and the current application of this technology to selected nanoparticles (titania, magnetite, MgO and hydroxyapatite), synthesis is discussed. Spinning Disk Reactor technology allows to produce active semiconductor particles, characterized by a mean size significantly below 100 nm and with a narrow unimodal distribution, improving the quality of these products in comparison with those produced through conventional processes and equipment. Finally, the application of vertical and horizontal Spinning Disk Reactor configuration to the degradation of refractory compounds by photocatalysis is reviewed, aiming at evaluating process efficiency and the produced nanoparticle characteristics, to assess the key parameters and the limiting factors of the technology