Synthesis, characterization and magnetic behavior of Co/MCM-41 nano-composites

• Co species as isolated Co2+, oxide clusters and Co3O4 nano-particles were detected.
• For higher Co loads were detected, by XRD, Co3O4 particles on the external surface.
• The confining of Co species inside the mesopores was achieved by increasing Co load.
• Paramagnetism from oxide clusters/nano-particles becomes dominant for higher Co loads.
• Superparamagnetism can be assigned to Co species of small size and finely dispersed.

Synthesis, structure and magnetic properties of Co/MCM-41 as magnetic nano-composites have been investigated. Mesoporous materials with different degrees of metal loading were prepared by wet impregnation and characterized by ICP, XRD, N2 adsorption, UV–vis DRS, TPR and EPMA-EDS. Cobalt oxide clusters and Co3O4 nano-particles could be confined inside the mesopores of MCM-41, being this fact favored by the Co loading increasing. In addition, larger crystals of Co3O4 detectable by XRD also grow on the surface when the Co loading is enhanced. The magnetic characterization was performed in a SQUID magnetometer using a maximum magnetic applied field µ0Ha=1 T. While the samples with the higher Co loadings showed a behavior typically paramagnetic, a superparamagnetic contribution is more notorious for lower loadings, suggesting high Co species dispersion.

Room temperature hysteresis loops as a function of the Co content. Figure optionsDownload as PowerPoint slide