The role of OH⁻in the formation of highly selective gold nanowires at extreme pH: multi-fold enhancement in the rate of the catalytic reduction reaction by gold nanowires

Abstract

There is a quest to understand the mechanism governing the morphology and geometry control of the particle growth of nanomaterials for their optical and catalytic applications. In the available literature, the role of OH in dictating the size and shape of Au nanowires is unknown. As one of the first examples, herein, we explore how excess OH ions in CTAB micelles play a significant role during the highly selective formation of gold nanowires having controlled diameters of ∼20-25 nm and length >1 μm, by reducing Au to Au in a one pot, simple synthesis procedure in the presence of Ag ions. At pH 4-11, the same procedure does not harvest Au NWs, but Au NPs of diameter 50-70 nm, indicating that excess OH is needed for nanowire formation. XRD, TGA, DSC, EDX, FT-IR and fluorescence spectroscopic analysis confirm that both CTAB and curcumin act as capping and stabilizing agents for Au NWs as well as Au NPs - there is no remarkable difference in the curcumin/CTAB content between Au NWs and NPs prepared in different pH environments. However, changing the CTAB micellar media to DPPC liposome media inhibits the formation of nanowires at pH ∼13; the growth of the Au NPs diminishes in DPPC liposomes, offering smaller NPs of diameter ∼25 to 30 nm, suggesting that the role of CTAB is necessary in nanowire formation. The rate of NW formation has been found to be 0.13 h and the growth mechanism advocates elongation in the [110] facet of Au [110] as opposed to the [100] or [111] facets. Curcumin capped Au nanowires serve as excellent nano-catalysts for the reduction of nitro-compounds and the rate of reduction of 4-nitrophenol, a model compound, by curcumin capped Au NWs is found to be ∼10 fold higher, compared to Au NPs, which signifies that catalytic activities can be dictated by the size and shape of Au NPs.

Solid-State Green Synthesis of Ag NPs: Higher Temperature Harvests Larger Ag NPs but Smaller Size Has Better Catalytic Reduction Reaction

“…The reduction of 4-nitrophenol was observed by measuring the change in the absorbance of 4-nitrophenol at 400 nm, and to confirm that this reduction happens a peak at 290 nm was also identified for the 4-aminophenol 25,26 . To study the effect of the curcumin conjugated Ag NPs as a catalyst on the reduction of 4-nitrophenol to 4-aminophenol, first we measured the absorbance of the reduction of 4-nitrophenol by using UV-VIS spectra without curcumin conjugated Ag NPs, and then we measured the reduction reaction in the presence of curcumin conjugated Ag NPs.…”

“…To study the effect of the curcumin conjugated Ag NPs as a catalyst on the reduction of 4-nitrophenol to 4-aminophenol, first we measured the absorbance of the reduction of 4-nitrophenol by using UV-VIS spectra without curcumin conjugated Ag NPs, and then we measured the reduction reaction in the presence of curcumin conjugated Ag NPs. In the first reaction, the absorbance of 4-nitrophenol at 400 nm decreased with time, and for complete reduction we need approximately 300 hours 25 . In the second reaction absorbance of 4-nitrophenol at 400 nm was monitored in the presence of curcumin conjugated Ag NPs with time, it was found that in the presence of curcumin conjugated Ag NPs 4-nitrophenol reduced within a few minutes (12 minutes maximum) as shown in Fig.…”

Curcumin as a novel reducing and stabilizing agent for the green synthesis of metallic nanoparticles

“…Nonetheless, El Kurdi et al have confirmed the role of curcumin as a reducing agent in acidic, neutral, and basic media in the presence of cetyltrimethylammonium bromide (CTAB) (65). The authors have tested the ability of curcumin to reduce Au 3+ to Au 0 at pH 4, 7, 8, 9, 11, and 13.…”

“…To end up, based on the formed Au NPs, several sensing nanoprobes were produced in order to detect different analytes. For example, El-Kurdi et al were able to detect uric acid (64), adenosine triphosphate (62,63), glucose (54), and alpha-tocopherol (65,68) 60) have established the role of Au NPs as an antioxidant. Hence, whatever is the procedure followed to prepare the nanoparticles, the use of curcumin enhances the activity of the Au NPs, where they have shown promising features based on their biomedical applications.…”

Green Synthesis of Curcumin Conjugated CuO Nanoparticles for Catalytic Reduction of Methylene Blue

“…El Kurdi et al have established CTAB as capping agent to produce uniform Au NPs. [23] Nowadays, organic dyes are one of the major pollutants in our environment and this is related directly to their undesirability, high visibility and recalcitrance. Organic dyes are widely used in paper, textile, pharmaceutical and food industries.…”