Hello, the used of chloride and sulfate salts in preparation of nanomaterials by precipitation method because, these salts can be easy removed by washing the ppt. and ensured from that by added AgNO3 to filter of chloride salt ... and added BaCl2 to filter of sulfate salt... all produce white color solution, this indicated to produce AgCle and BaSO4 respectively.
Plant leaf extract proves to be the best reducing agent. It will provide you dual action (Reducing as well as fine capping agent). For more understanding, i will recommend you to see the following.
1. Preparation of metal nanoparticles from different solution is very interesting topic. Different size can be associated with nucleation of aluminium nanoparticles from solution containing different ions. Cl- and SO42- ions can interact with surface of metal nanoparticles and growth of them is stopped. The same interaction was used to produce nanoparticles with different size (PVP, CTAB, SLS) and even kations as K+ or Na+ can change size and shape of nanoparticles (eg. rhodium nanoparticles).
2. For Al nanoparticles NaBH4 or LiBH4 will be the best reducing agents. You can try use hydrazine, but you need strong reducers to produce Al nanoparticles (for Cu, Ag, Au NPs you can use L-ascorbic acid, only PVP and temperature or even citric acid).