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 [VO 5 ]6− cluster based on the simple formulae of EPR parameters, presently proposed tetragonally compressed [VO 6 ]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 2B 1g →2B 2g for tetragonally compressed octahedral 3 d1 systems. • Local structure of amorphous biochar is investigated for Cu2+ and V4+. • Based on the analysis of experimental work, several improved discussions are completed. • High concentration of O in biochar may induce strong distortion along C 4 axis. • Cu2+ and VO2− in BG1 and BG2 form orthorhombically elongated octahedra and tetragonally compressed octahedra, respectively. [ABSTRACT FROM AUTHOR]