Photochemical Synthesis of Ag and Au Nanoparticles Using a Thioxanthone Substituted Chitosan as Simultaneous Photoinitiator and Stabilizer

Abstract

Silver (AgNPs) and gold (AuNPs) nanoparticles in aqueous solution were generated and stabilized using the 10-oxo-10H-dibenzene thiopyran-3-4-dicarboximide chitosan (TXICh) macrophotoinitiator. The photoinitiator and the nanoparticles in aqueous solution were characterized by UV-Vis spectroscopy and transmission electron microscopy (TEM). Pure TXICh in aqueous solution forms self-assembled particles with diameter around 30 nm. AgNPs were prepared using TXICh in the presence and absence of triethanolamine (TEOH). During irradiation, a broad band in the range of 410-415 nm was observed, corresponding to the plasmon absorption, indicating the AgNPs formation. TEM images revealed that the AgNPs had spherical shape in the absence and presence of TEOH. The synthesis of AgNPs in the presence of TEOH occurred rapidly (maximum conversion reached after 15 min), whereas in its absence 4 hours were required. The AgNPs prepared with TXICh/TEOH presented smaller and more uniform nanoparticles size. AuNPs were also prepared using TXICh as photoinitiator/stabilizer system. These nanoparticles showed an intense surface plasmon band at 530 nm and the TEM images revealed spherical particles of around 4 nm. These studies indicate that TXICh can act not only as a photoinitiator, but also as a stabilizer in the AgNPs and AuNPs formation.

Photochemical Synthesis of Gold and Silver Nanoparticles—A Review

“…Stabilizers and capping agents are of utmost importance since they are used to control the formation of homogenous metallic NPs of desired size and shape [ 89 , 90 ], prevent their agglomeration, and improve their colloidal stability [ 91 , 92 , 93 , 94 ]. Among the capping agents, polymers are excellent for trapping and protecting the NPs against their oxidation and coalescence [ 66 , 95 ].…”

“…Moreover, the different chemical structures of the polymers enable specific interactions with the metallic surface, triggering significant variations in the size and shape of the obtained metallic NPs [ 66 ]. Some studies have detailed the impact of various polymers on the characteristics of Ag NPs and Au NPs, such as poly(vinyl pyrrolidone) (PVP) [ 2 , 96 , 97 ], polymethacrylate (PMA) [ 98 ], poly-, mono-saccharides and proteins (chitosan, glucose, dextrose, gelatin) [ 41 , 89 , 94 , 96 ], sodium dodecyl sulfate (SDS) [ 99 ], and natural rubber (NR) latex [ 66 ]. Additionally, the experimental parameters determine the NP features and morphology, namely, the use and nature of the stabilizers, pH of the reaction medium, precursor concentration, exposure time, and, importantly, light source and wavelength [ 100 , 101 ].…”

“…Rheima et al irradiated an aqueous solution of glucose (C 6 H 12 O 6 ), used as both the reducing and stabilizing agent, in the presence of the precursor, silver nitrate, with a mercury UV lamp (λ = 365 nm, 125 W) for 30 min to produce highly crystalline hexagonal and spherical Ag NPs with an average size of 20 nm [ 131 ]. Besides, Valandro et al reported the use of other substances, such as 10-oxo-10H-di benzene thiopyran-3-4-dicarboximide chitosan (TXICh) and triethanolamine (TEOH), that act as both the reducing and stabilizing agent [ 94 ]. When a UV-LED (λ = 365 nm, 92 mW cm −2 ) irradiated for 4 h an AgNO 3 solution containing only TXICh, spherical, self-assembled Ag NPs of 2–24 nm in size are obtained ( Figure 4 A,B).…”

“…The reaction mixtures were irradiated using a 365 nm UV light with a power of 92 mW cm −2 . Adapted from [ 94 ]. Published by The Brazilian Chemical Society under Open Access Policy.…”