Giannis Mpourmpakis, Center for Catalytic Science and Technology, Department of Chemical Engineering, University of Delaware, Colburn lab, 150 Academy Street, Newark, DE 19716 and Dion Vlachos, Director of Center for Catalytic Science and Technology (CCST), University of Delaware, Newark, DE 19716.
First principle calculations have been performed to examine the growth mechanisms of silver nanoparticles (NPs) in the presence of citrate. Through suitable energy relations, we show that the carboxyl groups preferentially interact with specific crystallographic planes of NPs and solvent effects can be significant. As the charge of the NP approaches zero, electrostatic interactions gradually decrease, and this affects binding and the role of citrate. Further reduction of the citrate-silver NP complex decreases the binding energy of the citrate. This decrease is related to the symmetry of the NP via the latter's electron affinity value. We found out that hydrogen bonds among citrate molecules play a key-step in the growth mechanism. Our results explain for the first time the effect of pH and citrate concentration on the morphology of silver NPs and provide evidence that it is possible to unravel and control NP size and shape.