Synthesis

characterization of Co

3

O

4

and Ag-Co

3

O

4

composites and evaluation of their photo-catalytic activities towards photo-degradation of aqueous solution of rhodamine B dye under irradiation of visible light have been described in this paper. Co

3

O

4

was prepared by solid phase mechano chemical process using Co(NO

3

)

2

·6H

2

O and NH

4

HCO

3

as precursor materials. Ag was deposited on Co

3

O

4

from AgNO

3

using Calotropis gigantea extract as reducing agent. XRD

SEM and FTIR were used for characterization of prepared composites. Photo-catalytic efficiencies of as-prepared Co

3

O

4

and Ag-Co

3

O

4

were evaluated for aqueous phase photo-degradation of rhodamine B. It was found that deposition of Ag on Co

3

O

4

highly enhanced the photo-catalytic activity of Co

3

O

4

. Photo-catalytic degradation followed the Eley-Rideal mechanism. About 100% and 91% photo-degradation of 40 ml dye solution achieved at 313 K in 90 and 120 min over 0.05 g of Ag-Co

3

O

4

as photo-catalyst using 100 and 200 mg·L

-1

as initial concentration of dye respectively.