Effect of biosynthesized zinc oxide nanoparticles on the vegetative growth of Amaranthus cruentus plants

ZnO nanoparticles synthesis using Ocimum gratissimum and Vernonia amygdalina plant leaf extracts, their characterisation and use as nanofertilizer for growing black-seeded (BS) and pale-seeded (PS)Amaranthus cruentus plants is here presented. The nanoparticles (made possible by the flavones, phenols and flavonoids in the leaf extracts used) were of good crystalline structure, spherical in shape and in clusters. Their UV-vis peak absorbance occurred at 355 nm and 360 nm and their PL spectra showed a UV emission peak and a green emission peak. SEM images show nanoparticles sizes (which depended on the pH level of their synthesis solution and the type of plant leaf extract used) in the range 38 nm to 63 nm. When used as nanofertilizer for the Amaranthus cruentus growth, it was discovered that smaller nanoparticles produced taller plants and that both plant varieties tolerate nanofertilizer concentrations as high as 500 though nanofertilizer concentrations higher than this was detrimental to the plant growth. While the BS plants showed better shoot growth with broad leaves of area 60 , the PS plant variety had narrow and scanty leaves with leaf area as low as 4 The PS plants produced the highest yield of 60 % when treated with pH 10 500 Og-ZnO nanofertilizer but the lowest yield of 16 % when treated with pH 12 Og-ZnO nanofertilizer of concentration 500 . This work shows that these ZnO nanofertilizer enhanced the growth of the Amaranthus cruentus provided high concentrations of the fertilizers which could be toxic, are avoided.