Abstract:
Release of untreated effluents from various industries into water bodies is one of the main
concerns of environmental pollution. Among many pollutants released into waterways, dyes
are one of the major contributors of water contamination. Hence, it is necessary to find more
environmentally convenient methods to remove these dyes from waste effluents. In this
research, the potential of metal oxide nanoparticles synthesized with plant extracts to remove
dyes in water media was investigated. Copper oxide nanoparticles were synthesized from dried
Kahata (Careya arborea) leaf extract using the co-precipitation method and characterized using
UV-vis spectroscopy, Fourier-transform infrared spectroscopy, scanning electron microscopy,
and X-ray powder diffraction. The synthesized nanoparticles were tested for removing
Rhodamine B (RB), a basic dye and Acid Orange 7 (AO7), an acidic azo dye under different
conditions including pH, light source, irradiation time, temperature and the amount of
nanoparticles. Highest dye removal was observed with both dyes at acidic pH (≤ 4), under
sunlight when treated for 1 h. Further, an increase in dye removal was observed at elevated
temperatures (~80 °C). Dye removal capacities were found to be 68% for RB (10 mg L-1
initial
dye concentration, 50 mg/mL of nanoparticles) and 70% for AO7 (50 mg L-1
initial dye
concentration, 20 mg/mL of nanoparticles) when treated for 1 h at pH 4 and ambient
temperature under sunlight. Similar removal capacities were observed after simple ethanol
wash, up to 2 and 3 cycles for AO7 and RB, respectively. Dye removal capacities for chemical
synthesized nanoparticles without plant extracts were ~20% and ~50% for RB and AO7,
respectively. Dye removing mechanism was studied using adsorption isotherms and both
Langmuir and Freundlich isotherms showed best fits to data indicating possibility of variable
adsorption sites due to different functional groups on nanoparticle surface. This study showed
an improved dye removal ability of green synthesized CuO nanoparticles compared to
chemically synthesized CuO nanoparticles. This could be attributed to the incorporation of
various functional groups from plant extract onto the surface of the nanoparticles in green
method.