Kinetically restraining aggregation of ZnS nanocrystals and the effect on photocatalysis

A common problem in the fabrication of nanostructures is their undesired aggregation due to their high surface free energy. Here we show that a combinatorial control of reaction kinetic parameters such as feeding rate of reactant and reaction temperature can effectively restrain the aggregation of ZnS nanocrystals. The restraining process is associated with a stabilization of ZnS nanocrystal surfaces. Slowing down the feeding rate of reactants allows formed ZnS nanocrystals to get enough time to stabilize their surfaces. The stabilization of ZnS nanocrystal surfaces is further improved by suitably increasing reaction temperature. As a result, well dispersed and uniform ZnS nanocrystals with diameter of 4–6 nm are obtained with a common reaction between Zn(NO3)2 and Na2S, which is normally viewed to easily cause an aggregation. The results of photocatalytic degradation of methylene blue show that the aggregation restraint can effectively improve the activity of ZnS nanocrystals.