Characterisation of silver and zinc oxide nanoparticles biosynthesized using Ocimum gratissimum and Vernonia amygdalina plant leaf extracts

  • Rebecca Mfon

Student thesis: Doctoral ThesisDoctor of Philosophy (PhD)


The need to reduce environmental pollution and make planet Earth safer for her inhabitants
has led to the adoption of scientific methods which yield safer by-products.
Nanoparticles which have in the Science world recently attracted much attention, have been
synthesized and put into a wide range of applications but the main concern has been to ensure that the by- products from such processes are less toxic, and that their sizes are controlled
for specific applications. Though chemical and Physical methods can be used for their
synthesis, the biosynthesis option reported to be fast, cheap and environmentally friendly and
more recently the use of plant leaf extracts has been preferred because the plant
extracts through their inherent biomolecules do not only make the nanoparticles, they cap and can stabilize them.
In view of this, this work studied the effect of Ocimum gratissimum (Og) and Vernonia
amygdalina (Va) plant leaf extracts on the synthesis of silver and zinc oxide (ZnO)
nanoparticles. The resulting nanostructures were characterized using optical spectroscopy and
electron microscopy.
Boosting food production can make it more affordable especially to the low-income earners in any
society therefore this work also investigated the interactive effect of pH of synthesis and
concentration of colloidal solution of the ZnO nanoparticles (used as Nano fertilizer) on the
growth parameters (seedling characteristics and vegetative growth) of Amaranthus cruentus.
Amaranthus cruentus is widely eaten in my country Nigeria but is still not within the reach of the
average Nigerian. This research therefore used the zinc oxide nanofertilizer to grow this plant (A.
cruentus) and determined the plant treatments which give best seedling characteristics or enhance the vegetative growth of the plants. The critical limit for the nanoparticles used were also determined. While the Amaranth studies showed that the ZnO Nano fertilizer enhanced the growth of the plant, it was discovered that beyond 500mg/L concentration, the colloidal solution of the ZnO nanofertilizer became toxic and even resulted in chlorosis in some cases.
Furthermore, from available literature, it is obvious that not much has been done on
the electrodeposition of silver on gold in the presence of plant leaf extracts particularly the
ones listed for this research. This therefore was also explored using cyclic voltammetry
and chronoamperometry techniques and the morphology of the silver thin films from aqueous iii silver nitrate in the presence of each of the chosen two leaf extracts was examined using the Atomic Force Microscope (AFM). The electrodeposition experiment gave silver films whose thickness and grains sizes were refined and found to be plant leaf extract dependent.
Date of Award19 Mar 2019
Original languageEnglish
Awarding Institution
  • The University of Bristol
SupervisorAndrei Sarua (Supervisor) & Simon R Hall (Supervisor)

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