Synthesis, Characterization, and Sunlight Mediated Photocatalytic Activity of CuO Coated ZnO for the Removal of Nitrophenols

CuO@ZnO core–shell catalysts, coated by varying the CuO layer density ranging from 0.5% to 10%, were synthesized with the aim to enhance the photocatalytic activity of ZnO in sunlight and control its photocorrosion. Initially, the Cu²⁺ ions were impregnated on presynthesized ZnO by wet impregnation and finally converted to CuO layers by calcination. The optical and structural characterization of the synthesized powders was performed by DRS, PL, Raman spectroscopy, and XRD analysis, respectively. The homogeneity of the coated layers was explored by FESEM. The photocatalytic activity of CuO coated ZnO was investigated for the degradation of mononitrophenols (2-, 3-, and 4-nitrophenol) and dinitrophenols (2,4-, 2,5-, and 2,6-dinitrophenol) in the exposure of the complete spectrum and visible region (420–800 nm) of sunlight. The effect of the increasing density coated layers of CuO on photocatalytic activity was evaluated for the degradation of 4-NP. Compared to pristine ZnO, a substantial increase in the degradation/mineralization ability was observable for the catalysts coated with 0.5% and 1% CuO, whereas a detrimental effect was noticed for higher coating density. Prior to photocatalytic studies, as evaluated by cyclic voltammetry (CV), compared to pure ZnO, a significant suppression of photocorrosion was noticed, under illumination, for catalysts coated with lower CuO coating. The progress of the photocatalytic degradation process was monitored by HPLC while the mineralization ability of the synthesized catalysts was estimated by TOC. The estimation of the released ions and their further interaction with the excited states and the reactive oxygen was monitored by ion chromatography (IC)

Verwey Transition in Ultrasmall-Sized Octahedral Fe₃O₄ Nanoparticles

We observed Verwey transition in very small (6–14 nm) amine-coated octahedral magnetite (Fe₃O₄) nanoparticles that is not present in spherical similarly sized (4–13 nm) nanoparticles. Electron microscopy shows that octahedral nanoparticles have {111} facets with better cationic coordination symmetry as their surface. Spherical shape illustrates conventional superparamagnetic behavior; on the contrary, a characteristic Verwey transition near 120 K is prominent in field-cooled/zero-field-cooled curves of octahedral nanoparticles. Higher saturation magnetization in octahedral nanoparticles indicates lesser surface spin disorder and well-established anisotropy. Better surface coordination offers a reduced number of oxygen vacancies at the surface and, therefore, better stoichiometry results in a Verwey transition in octahedral nanoparticles. Electrical resistivity measurements show a sharp change in resistance for octahedral particles below the Verwey transition temperature which is completely hindered in spherical particles. The electrical transport characteristics indicate that these nanoparticle assemblies or thin films could be useful for future generation switching and memory devices

Assessment of the self-ignition characteristics of raw and processed biomass fuels

This paper is concerned with the self-ignition characteristics of untreated and torrefied biomass fuels and two coals. Using thermogravimetry in air, first order reaction kinetics at low temperature were derived, and the point of ignition and the maximum weight loss in air measured. In oxygen, data was obtained for the characteristic ignition temperature. Self–ignition temperatures and ignition delays were measured for two untreated and two torrefied biomass fuels for a number of different basket sizes using the European standard test method of spontaneous combustion.</p