SYNTHESIS OF SILVER NANOPARTICLES USING UV IRRADIATION AND THEIR APPLICATION IN HERBICIDE DETECTION

In this research, silver nanoparticles were synthesized by exposing the mixture of silver nitrate and stabilizer solutions to 8 watts of UV-irradiation for one hour. Five stabilizers including tannic acid (TA), poly(methacrylic acid, sodium salt) (PMA), carboxymethyl cellulose sodium salt (CMC), chitosan (CS) and humic acid sodium salt (HA) were used. Initial pH of the stabilizer solution was varied from 5.0, 6.0, 7.0, 8.0 to 9.0 and the molar ratio of stabilizer to silver ions (MR) was varied from 10:1, 1:1 to 1:10 in order to study the effects of these parameters on the synthesis process. The results showed that all five stabilizers acted as reducing agents and UV irradiation assisted the reduction process. All TEM images showed that the sizes of all synthesized particles were less than 50 nm. They exhibited the characteristic peaks of UV-Vis absorption in the wavelength of 350-430 nm depending on the type, the amount and the pH of the stabilizer. The synthesized silver nanoparticles colloids mostly had yellow color with spherical particles. However, the colloids of silver nanoparticles synthesized using CS at MR of 1:10 with pH of 5.0 and using PMA at MR of 1:10 with pH of 6.0 exhibited purple color with spherical and rod-like particles. In addition, the mixture of the particles having spherical and trigonal shapes was found in the colloids of CMC-stabilized silver nanoparticles synthesized using MR of 1:10. The suitable conditions for synthesizing the silver nanoparticles based on their stability after one month storage and their characteristics of being silver nanoparticles such as color and size were at pH of 6.0 when TA was used as a stabilizer at MR of 1:1 and at pH of 6.0 when PMA was used as a stabilizer at MR of 1:10. Finally, the ability for herbicide detection of the synthesized silver nanoparticles was investigated. The silver nanoparticles that exhibited highest sensing abilities to pyrazosulfuron-ethyl and paraquat herbicides were the samples synthesized in the presence of TA with MR of 1:1 at pH of 6.0 and the sample synthesized in the presence of PMA with MR of 1:10 at pH of 6.0, respectively.