This work reports
an environmentally friendly and economically
feasible green synthesis of monometallic oxides (SnO2and
WO3) and their corresponding mixed metal oxide (SnO2/WO3–x) nanostructures
from the aqueousPsidium guajavaleaf
extract for light-driven catalytic degradation of a major industrial
contaminant, methylene blue (MB).P. guajavais a rich source of polyphenols that acts as a bio-reductant as
well as a capping agent in the synthesis of nanostructures. The chemical
composition and redox behavior of the green extract were investigated
by liquid chromatography–mass spectrometry and cyclic voltammetry,
respectively. Results acquired by X-ray diffraction and Fourier transform
infrared spectroscopy confirm the successful formation of crystalline
monometallic oxides (SnO2and WO3) and bimetallic
SnO2/WO3–xhetero-nanostructures
capped with polyphenols. The structural and morphological aspects
of the synthesized nanostructures were analyzed by transmission electron
microscopy and scanning electron microscopy coupled with energy-dispersive
X-ray spectroscopy. Photocatalytic activity of the synthesized monometallic
and hetero-nanostructures was investigated for the degradation of
MB dye under UV light irradiation. Results indicate a higher photocatalytic
degradation efficiency for mixed metal oxide nanostructures (93.5%)
as compared to pristine monometallic oxides SnO2(35.7%)
and WO3(74.5%). The hetero-metal oxide nanostructures
prove to be better photocatalysts with reusability up to 3 cycles
without any loss in degradation efficiency or stability. The enhanced
photocatalytic efficiency is attributed to a synergistic effect in
the hetero-nanostructures, efficient charge transportation, extended
light absorption, and increased adsorption of dye due to the enlarged
specific surface area.