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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.

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Using a combination of a mild stabilizer and a mild reductant, sodium citrate and hydrazine hydrate, anisotropic silver nanocrystals (NCs) were synthesized with tunable plasmon peaks at 550 nm, 700 nm, 800 nm, 900 nm and 1010 nm (the samples are named Ag-550, Ag-700, Ag-800, Ag-900 and Ag-1010, respectively). TEM investigations revealed that Ag-550 NCs were pentagonal nanoplates while the other four samples were nanopyramids with a pentagonal base with the edge length varying between 15 and 30 nm. The non-linear optical (NLO) properties of these NCs were studied by the Z-scan technique using the CW He-Ne laser (632.8 nm, 15 mW). The shape change from 2D nanoplates (Ag-550) to 3D nanopyramids (Ag-700) resulted in sign reversal of the non-linear refractive index, n, from a negative (-3.164 × 10 cm W) to a positive one (1.195 × 10 cm W). This corresponds to a change from a self-defocussing effect to a self-focussing one. Besides shape, the size effect is also prominently observed. Amongst nanopyramids, as the edge length increases, n increases linearly and reaches a maximum of 3.124 × 10 cm W. Doubling the edge length from 15 nm to 30 nm resulted in 162% increase in n. On moving from Ag-550 to Ag-900 NCs, with the increasing plasmon wavelength, the non-linear absorption (NLA) coefficient increased exponentially to a high value of 8.52 × 10 cm W. However, Ag-1010 showed 29% decrease in NLA which is attributed to twinning present in the crystal structure as seen in the HR-TEM images. Due to the tunable NLO properties, these anisotropic Ag NCs hold great potential for applications in optical limiting, switching and data storage.