Tartrate-gel synthesized BaFe12-xCuxO19 (0 ≤ x ≤ 1) nanoceramics: Magnetic and catalytic properties

Abstract

Magnetic catalysts present distinct advantages over their non-magnetic counterparts, primarily due to their ease of recovery from the reaction mixture through magnetic separation. Herein, magnetic and catalytic properties of Cu-substituted barium hexaferrite (BaFe12-xCuxO19, 0 ≤ x ≤ 1) nanoceramics, synthesized via a tartrate-gel method, are evaluated. Using XRD, FTIR, Raman, SEM, XPS, and VSM techniques, the synthesized compositions were characterized. The powder XRD analysis revealed that all samples predominantly consisted of hexaferrite phase, with small impurity phases, α-Fe2O3, CuO and BaFe2O4. The structural parameters (a, b, c), extracted from Rietveld refinement analysis, increased with ‘x’, primarily due to substitution of smaller Fe3+ cation by larger Cu2+ cation. The FTIR and Raman spectra of the samples exhibited characteristic bands corresponding to the M-type hexaferrite. A red-shift occurred in these bands as the Cu amount increased in the Ba-hexaferrite lattice, owing to increase in metal-oxygen bond length. Due to sintering aid nature of copper, considerable increase in the particle size is observed with inclusion of Cu. XPS spectral analysis indicated the oxygen defects in the Cu-substituted sample. The magnetic parameters (MS, HC, and K1) are found to decrease upon incorporation of Cu ions into the Ba-hexaferrite crystal structure. Conversely, the Curie temperature (TC) showed a slight increase with Cu content ‘x’. The unsubstituted sample (x = 0) exhibited no catalytic activity in the reduction of nitrophenol, whereas both Cu-substituted samples displayed enhanced activity with comparable rate constants (0.02 min−1). This activity was attributed to the presence of Cu ions at the octahedral sites (2a or 4f2). Additionally, a magnetic separation process followed by a reusability test was conducted for the x = 0.5 sample over five successive cycles. The consistent activity observed in each cycle underscored the robustness of the engineered magnetic catalyst.