A seedless, one pot,
green and selective synthesis of triangular
gold nanoplates (NPs) by the reduction of chloroauric acid using Aegle marmelos gum (bael fruit derived gum; BG),
with control over size is reported. The size of the NPs is found to
be dependent critically on the concentration of the BG with triangular,
triangular with truncation at the apex and hexagonal plates being
the predominant shapes over a wide concentration range, at room temperature.
At very high concentration of BG and at room temperature, the shape
of the particles is spherical. A fine-tuning of the temperature, at
a particular concentration of BG, results in the formation of perfect
triangular NPs. Increasing the temperature of reduction to 90 °C
and especially above a particular BG concentration, Au nanoparticles
that are elongated spheres are obtained as the major product. The
possible mechanism for the Au NPs formation is investigated using
techniques such as HR-TEM, SEM, XRD and UV–visible spectroscopy.
The formation of single and polycrystalline Au seeds and fused particles
along with multiple twinning suggest that a particular well-faceted
seed might not be the prerequisite for the formation of NPs but rather
a critical rate of formation of Au(0). A schematic diagram is also
presented representing the concentration and temperature regime over
which anisotropic and especially triangular NPs can be synthesized
with bael gum.