A negatively charged nanoparticle cannot deposit upon a surface that itself is negatively charged. The net charge upon the graphene oxide nanoparticle must be positive if it has deposited upon a negative surface. The case you are mentioning might be due to deposition of a positively charged reducing/stabilizing agent upon the negatively charged graphene oxide nanoparticle during nanoparticle synthesis and as such the attraction forces between the positively charged agent bonded to graphene oxide nanoparticle might be responsible for its deposition upon negatively charged surface.

Dear syed salman

can you explain more? what means positively charged stabilizing agent? I should add we donot use any agent.

as I read in defferent papers, reducing potential of graphen oxide is about 1.2 eV. It is suggested to keep GO2 at this level of potential to get better performance. knowing this, my question is why deposition occures while there is repulsing forces between them.

thank you in advance for your kind help.

Dear Zahra Bagheri

As you must know that there are a variety of methods used for synthesizing NPs, most of them use stabilizing/reducing agents that prevents NPs from binding to each other. It depends upon the mechanism you use for NP synthesis. During the synthesis step, constituents used may bind to the NPs to enhance their stability and can be both positive or negative.

Now the answer to your question is "No, with repulsion forces, there wont be any deposition"

Deposition would only occurs if both the surfaces have opposite charges. Having said that, since your question was a generalized one, I gave a hypothetical answer previously about how the deposition might have occurred.