Folate-Directed Shape-Transformative Synthesis of Hollow Silver Nanocubes: Plasmon Tunability, Growth Kinetics, and Catalytic Applications

Abstract

A unique role of folate as a shape-and structuredirecting agent has been found in nanosynthesis. Folate-capped Ag 2 O nanospheres transformed into hollow silver nanocubes (HAgNCs) having spherical void spaces during reduction with hydrazine hydrate (HH). HAgNCs with tunable plasmon peaks (λ SPR ) at 510, 550, 570, 590, and 630 nm were synthesized (hence named as respectively). The corresponding edge-lengths were 33 ± 4, 45 ± 8, 60 ± 8, 70 ± 10 and 100 ± 15 nm as determined by HRTEM and the aspect ratio (edge length/void diameter) remained constant at 2.3. The plasmon peak varied linearly while the molar extinction coefficient scaled exponentially with edge-length. The maximum red-shift was obtained with a molar ratio of 1:0.33:150 for Ag + :folate:HH at 50 °C with a stirring speed of 180 rpm. However, zero rpm synthesis yielded HAgNC-510 having lowest fwhm signifying high monodispersity. Within a short time span of 6−50 s, the particle-evolution was completed. It followed first-order kinetics with a faster reduction occurring at zero rpm. In addition, the HAgNCs were found to be good catalysts in dark as well as in sunlight, for the degradation of a model dye, methyl orange (MO). HAgNC-630 exhibited 3.3 times higher catalytic efficiency in sunlight as compared to solid silver nanospheres (λ SPR = 400 nm). Thus, the red-end of the visible solar spectrum displayed greater efficiency with HAgNCs as plasmonic photocatalysts.

Hollow Silver Nanostructures: The Role of Capping Agents in Tailoring the Shape, Structure, and Plasmonic Properties

“…AA-capping requires a temperature of 25°C while FA-capping requires a temperature of 50°C. In contrast to acetate, folate is much larger in size and has several amine and amide groups in addition to a carboxylate which can form coordinate bonds with silver ions (Pattanayak et al, 2013; Dadhich et al, 2018). The bulky nature of FA molecule coupled with enhanced binding affinity impedes the outward diffusion of Ag + ions.…”

“…Nanoparticles (NPs) are stabilized by capping agents through various mechanisms such as steric stabilization, electrostatic stabilization, stabilization by hydration forces, depletion stabilization and, stabilization using van der Waals forces, or a combination of a number of these mechanisms (Do Kim et al, 2004). Alteration of the shape and size has a direct impact on surface plasmon resonance (SPR) in plasmonic nanomaterials (Pattanayak et al, 2014; Dadhich et al, 2018). The effect is even greater if the structure is altered by hollowing out the nanocrystals.…”

“…To create a large bandwidth of applications, tunability in SPR is the key parameter. In recent years, due to enhanced plasmon tunability, hollow silver nanostructures have found applications in the areas as diverse as catalysis and theranostics (Bardhan et al, 2011; Dadhich et al, 2017, 2018). Good control over the SPR peak position is required for the aforementioned applications and this can be tailored by the change in the aspect ratio of nanoshells (Pattanayak et al, 2013; Schwartzberg & Olson, 2014).…”

“…Synthesis temperature, stirring speed, stabilizer, and reducing agent have potential to change the aspect ratio of the hollow nanostructure (Ben Moshe et al, 2011; Pattanayak et al, 2013). Priyam and co-workers have synthesized hollow silver nanospheres (HAgNSs) using citric acid and α -hydroxy acids (Pattanayak et al, 2013; Dadhich et al, 2018). Here, we have investigated the shape and structural transformation in the hollow nanomaterials by varying the molecular structure of the capping agent.…”

Quercetin loaded folate targeted plasmonic silver nanoparticles for light activated chemo-photothermal therapy of DMBA induced breast cancer in Sprague Dawley rats

“…Fig. 1D 52 These identifying peaks for both QRC and FA were found in the infrared (IR) spectral pattern of their physical mixture, with minor broadening or shi of peaks. Moreover, the synthesized nanoparticles exhibited similar spectral patterns to that of the raw ingredients with certain alterations in the vibrational frequencies.…”