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

A unique role of folate as a shape- and structure-directing agent has been found in nanosynthesis. Folate-capped Ag2O nanospheres transformed into hollow silver nanocubes (HAgNCs) having spherical void spaces during reduction with hydrazine hydrate (HH). HAgNCs with tunable plasmon peaks (λSPR) at 510, 550, 570, 590, and 630 nm were synthesized (hence named as HAgNC-510, HAgNC-550, HAgNC-570, HAgNC-590, and HAgNC-630, 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 (λSPR = 400 nm). Thus, the red-end of the visible solar spectrum displayed greater efficiency with HAgNCs as plasmonic photocatalysts.