BIOTEMPLATED SYNTHESIS OF NANOSTRUCTURED ZnO WITH ENHANCED VISIBLE LIGHT PHOTOCATALYTIC ACTIVITY

Cotton wool was used as a biotemplate for the synthesis of nanostructured ZnO with enhanced visible light photocatalytic activity. Zn(II+) complexes were introduced into the structure of cotton fibers via evaporation of ammonia solution containing dissolved ZnO powder. Thermal decomposition of Zn(II+) impregnated biotemplate at 500 degrees C, 600 degrees C and 700 degrees C provides yellowish ZnO fine powder which retains the morphology of cotton wool fibers. The photocatalytic activities of both starting and biotemplated ZnO powders were evaluated from the time dependency of degradation of Methyl Violet 2B under the UV (lambda similar to 365 nm) and visible light (lambda similar to 400 nm and lambda similar to 425 nm) irradiation. Measurements were carried out online in UV-Vis spectrometer using a homemade cuvette holder housing equipped with an LED diode The degradation rate constant for biotemplated ZnO under visible light irradiation was 8 times higher than that of the starting ZnO. The significantly enhanced photocatalytic activity of biotemplated ZnO under visible light irradiation can be attributed to the intimate contact of the ZnO crystalline phase with residual carbonaceous species.