The adsorption mechanism of hydrogen sulfide (H2S) molecules on pristine and Pt-decorated graphene sheets was studied using density functional theory calculations based on local density approximation and generalized gradient approximation methods. Our calculations show that a Pt-decorated graphene system has much higher binding energy, higher net charge transfer values and shorter connecting distances than pristine graphene due to chemisorption of the H2S molecule. Furthermore, the calculated density of states show that orbital hybridization is visible between the H2S and Pt-decorated graphene sheets, while there is no evidence for hybridization between the H2S molecule and the pristine graphene sheet. Interestingly, we find that up to seven H2S molecules can stably bind to a Pt atom on each side of the graphene sheet with desirable binding energy. (C) 2012 Elsevier B. V. All rights reserved.