RESUMO
The mechanism of stabilization of silver nanoparticles (Ag NPs) by 1-butyl-3-methylimidazolium tetrafluoroborate ionic liquid (IL) is elucidated from experimental spectroscopic investigations and density functional theory (DFT) calculations. FTIR spectrum of the synthesized IL stabilized silver nanoparticles reveals small red shift in B-F stretching frequency while C-H stretching remains unshifted. There is no shift in NMR peaks of IL before and after the synthesis of IL stabilized Ag NPs. This suggests that Ag NPs are surrounded by anions of ILs. The optimized structure obtained from density functional theory (DFT) calculations also shows the anionic part of the IL surrounding the Ag nanocluster. This is supported by the IR frequency data calculated using DFT. The calculated binding energy and interaction energy obtained between cluster and IL is considerably attractive. Density of State (DOS) calculation shows that the HOMO-LUMO gap of the Ag cluster-IL composite is significantly lesser than that of the IL alone.
RESUMO
There is little research on the visible light photocatalytic properties of the hybrids of plasmonic metals and organic molecules (OM) with the HOMO-LUMO gap in the visible range. Here, we investigate the mechanism of the visible light enhanced reduction of p-nitrophenol (PNP) by glycerol (a green reductant) at ambient temperature over curcumin functionalized Ag nanoparticles (c-AgNPs). The catalytic activity got significantly boosted under visible light irradiation. Reaction kinetics indicated that the catalytic mechanism followed under visible light and in the dark were different. DFT calculations showed that in the ground state, the HOMO resides on Ag while the LUMO is on the curcumin part of the composite. TD-DFT calculations demonstrated the transfer of charge from Ag to curcumin on photo-excitation. Based on this information, we propose a mechanism for understanding the role of curcumin in this photocatalytic phenomenon.
RESUMO
Curcumin-functionalized Ag/Ag2 O (c-Ag/Ag2 O) nanocomposites with varying proportions of curcumin and Ag/Ag2 O were prepared by a simple one pot green synthesis protocol in aqueous medium. The plasmonic band undergoes slight redshift, broadening and decrease in intensity with increase in the proportion of Ag2 O formed. These composite nanoparticles were found to be efficient visible-light photocatalysts for aerobic oxidation of methyl orange and rhodamine B (RhB). Functionalization by curcumin significantly enhanced the photocatalytic activity with good reusability. The photocatalytic oxidation rate showed super linear increase with light intensity because of localized surface plasmon resonance (LSPR)-induced strong near field. The trapping experiments confirmed that superoxide radicals were the main active species responsible for the degradation reaction. A plasmonic Z-scheme photocatalytic mechanism is proposed to explain the possible charge transfer and separation behavior of electron-hole pairs among Ag, Ag2 O and curcumin under visible-light irradiation.
