# Effect of the pH on the synthesized nanoparticles [closed]

I have synthesized gold nanoparticles in water through the seed-mediated thermal method by cationic additive $\ce{Ag+}$ as an assisted growth procedure [article]. The pH of the nanoparticles solution is about 2. I would like to reach the pH of the solution to 5.I found that when I use NaCl solution or buffer (such as sodium acetate) for adjasting pH, it cause the aggregation of nanoparticles.
How to increase the pH without any aggregation in the nanoparticles solution?