X-ray Absorption Near-Edge Structure (XANES) at the O K-Edge of Bulk Co₃O₄: Experimental and Theoretical Studies

We combine theoretical and experimental X-ray absorption near-edge spectroscopy (XANES) to probe the local environment around cationic sites of bulk spinel cobalt tetraoxide (Co3O4). Specifically, we analyse the oxygen K-edge spectrum. We find an excellent agreement between our calculated spectra based on the density functional theory and the projector augmented wave method, previous calculations as well as with the experiment. The oxygen K-edge spectrum shows a strong pre-edge peak which can be ascribed to dipole transitions from O 1s to O 2p states hybridized with the unoccu- pied 3d states of cobalt atoms. Also, since Co3O4 contains two types of Co atoms, i.e., Co3+ and Co2+, we find that contribution of Co2+ ions to the pre-edge peak is solely due to single spin-polarized t2g orbitals (dxz, dyz, and dxy) while that of Co3+ ions is due to spin-up and spin-down polarized eg orbitals (dx2−y2 and dz2 ). Furthermore, we deduce the magnetic moments on the Co3+ and Co2+ to be zero and 3.00 μB respectively. This is consistent with an earlier experimental study which found that the magnetic structure of Co3O4 consists of antiferromagnetically ordered Co2+ spins, each of which is surrounded by four nearest neighbours of oppositely directed spins

Characterisation of Congolese Aquatic Biomass and Their Potential as a Source of Bioenergy

This study assesses the bioenergy potential of two types of aquatic biomass found in the Republic of Congo: the green macroalgae Ulva lactuca (UL) and Ledermanniella schlechteri (LS). Their combustion behaviour was assessed using elemental and biochemical analysis, TGA, bomb calorimetry and metal analysis. Their anaerobic digestion behaviour was determined using biochemical methane potential (BMP) tests. The average HHV for LS is 14.1 MJ kg−1, whereas UL is lower (10.5 MJ kg−1). Both biomasses have high ash contents and would be problematic during thermal conversion due to unfavourable ash behaviour. Biochemical analysis indicated high levels of carbohydrate and protein and low levels of lipids and lignin. Although the lipid profile is desirable for biodiesel production, the levels are too low for feasible extraction. High levels of carbohydrates and protein make both biomasses suitable for anaerobic digestion. BMP tests showed that LS and UL have an average of 262 and 161 mL CH4 gVS−1, respectively. The biodegradability (BI) of LS and UL had an average value of 76.5% and 43.5%, respectively. The analysis indicated that these aquatic biomasses are unsuitable for thermal conversion and lipid extraction; however, conversion through anaerobic digestion is promisin

Effect of oxygen contamination on structural and magnetic properties of MnPd bilayer grown on Fe/MgO(001): Ab initio study

We present a detailed study of oxygen contamination on the structural and magnetic properties for both Fe/MgO(001) substrate and MnPd bilayer grown on Fe/MgO(001) by using a plane wave self consistent field (PWscf) method based on DFT and DFT+U approaches, where a generalized gradient correction for exchange-correlation potential is taken into account. For the clean ($$\hbox {Mn}_{0.5}$$$$\hbox {Pd}_{0.5}$$)$$_{2}$$ bilayer grown on Fe/MgO(001) substrate, we have found that the c(2x2)-MnPd/c(2x2)-MnPd arrangement, where the magnetic moments of the Mn (Pd) atoms belonging to the surface and subsurface of 4.61 (0.05 $$\mu _{B}$$) and -4.03 (0.21 $$\mu _{B}$$), is lowest in energy than the c(2x2)-MnPd/p(1x2)-MnPd, p(1x2)-MnPd/MnPd-c(2x2) and p(1x2)-MnPd/p(1x2)-MnPd arrangements. A ripple is obtained at the surface (subsurface) plane. The contamination by O (1-ML coverage) on top for both Fe/MgO(001) and MnPd/Fe(100) multilayers increases interlayer distances between the surface and subsurface layers, with a preferential adsorption of oxygen atoms on the fourfold hollow sites when both DFT and DFT+U approaches are used. Similar magnetic ordering is obtained for Fe/MgO(001) and O/Fe/MgO(001) as well as for (MnPd)$$_{n}$$/Fe(100) and O/(MnPd)$$_{n}$$/Fe(001) sytems, where n=1-2, taking into account both approaches. The DFT+U approach produces an enhancement of the magnetic moments but does not modify the magnetic ground states of those systems. Here, we found that one half of oxygen atoms is pushed out-of-plane while the other half penetrates the MnPd (Fe) surface, giving rise to the MnO (FeO) oxide surface, in agreement with available experimental data

Characterisation of Congolese Aquatic Biomass and Their Potential as a Source of Bioenergy

This study assesses the bioenergy potential of two types of aquatic biomass found in the Republic of Congo: the green macroalgae Ulva lactuca (UL) and Ledermanniella schlechteri (LS). Their combustion behaviour was assessed using elemental and biochemical analysis, TGA, bomb calorimetry and metal analysis. Their anaerobic digestion behaviour was determined using biochemical methane potential (BMP) tests. The average HHV for LS is 14.1 MJ kg−1, whereas UL is lower (10.5 MJ kg−1). Both biomasses have high ash contents and would be problematic during thermal conversion due to unfavourable ash behaviour. Biochemical analysis indicated high levels of carbohydrate and protein and low levels of lipids and lignin. Although the lipid profile is desirable for biodiesel production, the levels are too low for feasible extraction. High levels of carbohydrates and protein make both biomasses suitable for anaerobic digestion. BMP tests showed that LS and UL have an average of 262 and 161 mL CH4 gVS−1, respectively. The biodegradability (BI) of LS and UL had an average value of 76.5% and 43.5%, respectively. The analysis indicated that these aquatic biomasses are unsuitable for thermal conversion and lipid extraction; however, conversion through anaerobic digestion is promising