A porous particulate nanocomposite material includes, as determined by X-ray diffraction, an orthorhombic CaB.sub.2O.sub.4 crystalline phase; an orthorhombic Co.sub.3(BO.sub.3).sub.2 crystalline phase; an orthorhombic PbO.sub.2 crystalline phase; and, a cubic Co.sub.3O.sub.4 crystalline phase. The porous particulate nanocomposite material is in the form of particles having a matrix phase with a smooth surface and in which sharp-edged plates are embedded and protrude.