RESUMO
An Ag@Au bimetallic nanoparticle (BNP) formulation was developed in this work. The proposed formulation was developed using photochemical and chemical methods and non-toxic reagents, showing high reproducibility and homogeneity. The synthesized BNPs have an average size of 7 nm, a core-shell-like structure (silver core and gold shell), high colloidal and long-term stability, and superior catalytic activity under darkness and white light irradiation conditions when evaluating the reduction of 4-nitrophenol to 4-aminophenolate, with respect to the monometallic Ag and Au counterparts. Furthermore, BNP concentrations as low as 2 nM were required to reach 100% conversions in less than 30 minutes. Therefore, considering future applications, the high surface-to-volume ratio of the prepared BNPs coupled with their well-defined optical properties makes them a great candidate for developing heterogeneous catalyzer materials to be applicable under sunlight as an environmentally friendly catalytic system.
RESUMO
Photochromic solid materials based on the cationic polymer poly(decylviologen) are reported. The solids were obtained by freeze-drying colloidal suspensions of nanocomplexes obtained by mixing aqueous solutions of the polycation with different solutions of polyanions such as poly(sodium 4-styrenesulfonate) or sodium alginate, at a cationic/anionic polymeric charge ratio of 0.7. The photochromic responses of the solid materials fabricated with alginate as complementary charged polyelectrolyte of the cationic polyviologen are faster than those of the solid materials fabricated with poly(sodium 4-styrenesulfonate), achieving coloration kinetics in the order of minutes, and discoloration kinetics in the order of hours for the former. Aromatic-aromatic interactions between the latter polyanion and the polyviologen may stabilize the dicationic form of the viologen derivative, increasing the necessary energy to undergo photoreduction, thus decreasing the reduction kinetics.
