Current Applied Physics, Vol.20, No.2, 255-261, 2020
An investigation of local structures and EPR spectra for Cu2+ and VO2+ in biochar
Electron paramagnetic resonance (EPR) technology had been adopted to analyze the structures and properties of Cu2+ and VO2+ in Biochar (BG1 and BG2), but the local structural properties have not been clarified up to now. In present work, three possible structures (orthorhombically, rhombically and tetragonally elongated octahedra) are proposed for Cu2+ in BG1 and BG2 samples, and the former seems most reasonable in view of the best agreement between the theoretical EPR parameters based on the perturbation formulae and the experimental data. As for the VO2+ center, unlike the previous assignment of the tetragonally elongated [VO5](6-) cluster based on the simple formulae of EPR parameters, presently proposed tetragonally compressed [VO6](8-) cluster and the high order perturbation formulae of the EPR parameters yields good agreement with the observed values. This point is also supported by the d-d optical absorption B-2(1g ) -> B-2(2g) for tetragonally compressed octahedral 3 d(1) systems.
Keywords:BG1 and BG2 biochars;Cu2+ and VO2+;Electron paramagnetic resonance (EPR);Local structures of mixed ligands