Please see the article

https://www.degruyter.com/view/j/gps.ahead-of-print/gps-2018-0030/gps-2018-0030.xml

The biomolecules present in the plants are act as  a reducing agent, they reduce silver nitrate and also  they act as a capping agent which favor the synthesis of size controlled nanoparticles through the biological synthesis method. The biomolecules like reducing sugars, phenolic compounds and protein molecules are reported to

aid in reduction and proteins in capping that formed nanoparticles.

Thanks sir, What is the reaction occurred in the dye solution while doing the Photocatalytic degradation in the presence of biosynthesised silver nano particles?

Yes, i agree with Ajay sir. your extract will act as a reducing and capping agent and we can not predict what are the chemical compounds are acting as a reducing and capping agent. Because your plant extract contain lot of flavonoids and alkaloids etc., We can classified the plant extract into two category. First one strong reducing agent, this type of extract will reduce the silver nitrate in room temperature. second one week reducing agent, it will be active in high temperature, and this reducing and capping nature depends on the chemicals present in extract.

I am completely agreed with Mr. Ajay and Mr. Vasi. Due to the presence of the reducing agent like the proteins, sugar molecules and also the phenolic types of molecules in the leaf extract, the extract act as a bioreducing agent. Depending on the reducing nature we have to provide heat during the reduction reaction. reduction reaction in room temperature is more efficient to generate lower sized nano particles and the particle size distribution will be narrow. because at high temperature there is a chance of agglomeration of nano particles. For the actual mechanism of reduction you can see this manuscript " Modified chitosan encapsulated core-shell Ag Nps for superior antimicrobial and anticancer activity". Have a nice day.  

Please read this paper...

Silver nanoparticles: Green synthesis and their antimicrobial activities

http://www.sciencedirect.com/science/article/pii/S0001868608001449

Plant extract contain starch and antioxidant molecules. Both bearing the OH group which acts as a reducing group to the silver nitrate from Ag+ to Ag0 (nano form). The molecule itself further acts as a stabilizing agent to the synthesized nanoparticles.

When we add the leaf extract to the  silver nitrate solution, it enhances the reduction of the compounds that are seen in leaf extract. It also helps the formation of cap around the compounds  during the synthesis of nanoparticle. Apart from this, they stabilise the reduction of compounds & stabilise the size of the particles. Thus, their diffusion across the cells can be made easy and can reach the target.    

Thanks for all your valuable answers Mr. Ajay, Mr. Vasi, Mr.Sovan, Mr.Amit , Mr.Dhinakarasamy, Mrs.Manal El-Sheikh, Mrs.Seeli Balaji and Rajabathar Jothiramalingam. This will be very useful for my research.

Please see the article

https://www.degruyter.com/view/j/gps.ahead-of-print/gps-2018-0030/gps-2018-0030.xml