Abu Jafar Mahmood

Synthesis and characterization of ZnO-TiO2 nanocomposites and their application as photocatalysts

Nanocomposite ZnO-TiO2 powders of varying ZnO/TiO2 molar ratios have been prepared from their salt/compound by heating at 600°C and 900°C and characterized using scanning electron microscope and X-ray diffraction techniques. The nanosized powders can decolorize/degrade brilliant golden yellow (BGY), an azo dye extensively used in textile industries, in water under solar irradiation. The effects of various parameters such as photocatalyst loading, molar ratio of ZnO/TiO2, pH of the solution, initial dye concentration, and irradiation time on the photodecolorization have been investigated. ZnO-TiO2 nanocomposite (6 g/L) in the molar ratio of 1:1 or 3:1, prepared at 900°C, can efficiently decolorize about 98% of 20 mg/L BGY at pH of about 7 by 2-h illumination in sunlight. The initial dye decolorization follows pseudo-first-order kinetics. Finally, trial experiments were done using real textile wastewater to find out the effectiveness of the photocatalysts to a more complex system.

Photocatalytic decolorization of crystal violet in aqueous nano-ZnO suspension under visible light irradiation

Nanosized ZnO was prepared through hydrothermal process and characterized by scanning electron microscopy, X-ray diffraction and laser-induced breakdown spectra measurement techniques. The as-prepared nanosized ZnO was used to investigate the decolorization/degradation of crystal violet, a cationic dye which is extensively used in dyeing/textile industries, under visible light through adsorption studies of the dye solution with ZnO in the dark. The results show that the adsorption of CV on ZnO takes about 200 min to reach equilibrium, and the equilibrium time at a certain concentration of the dye seems to be independent of temperatures that are used for the preparation of ZnO samples. The adsorption data follow the pseudo-first-order kinetic model (Lagergren), and the adsorption pattern follows the Langmuir model.Prepared ZnO (300°C) was found to be a more efficient photocatalyst among others including pristine ZnO, to decolorize/degrade the dye. The decolorization rate is increased with the decreasing of the initial dye concentration and reached at a limiting value. The catalyst loading also influences the decolorization/degradation of the dye, and decolorization rate is increased with increasing the catalyst loading and reached at a limiting value. ZnO was found to be stable under visible light irradiation at solution pH = 6. The photocatalytic degradation of the dye followed zero-order kinetics, and the Langmuir-Hinshelwood mechanism was found to be valid.

Zinc oxide-mediated photocatalytic decolorization of Ponceau S in aqueous suspension by visible light

ZnO, comprising nanosize particles (approximately 40 nm) has been prepared by heating (300°C) ZnCO3, which was obtained as precipitate by mixing ZnSO4 and (NH4)2CO3 solutions. The prepared ZnO was characterized by X-ray diffraction, scanning electron microscopy (SEM), laser-induced breakdown spectroscopy, and adsorption studies. It has been used to catalyze the decolorization of Ponceau S (PS), a model diazo dye, in an aqueous suspension under visible light (I ≈ 1.8 × 10−4 W cm−2). This ZnO was found to be more efficient as a photocatalyst compared to pristine ZnO. ZnO samples with higher temperatures (500°C and 700°C) show less catalytic activity. SEM images show that the particle size of ZnO increases with the increase in calcined temperature of ZnO through agglomeration, resulting in a decrease in surface area. Photodecolorization of PS is affected by its and ZnO concentrations, but unaffected by the initial pH of the solutions in the range of 4 to 7. Illumination for a sufficiently long time completely mineralizes the dye, but no Zn2+ can be detected in the clear solution.Photodegradation kinetics in the ZnO suspension obeys the Langmuir-Hinshelwood equation, and some activation of the ZnO surface by light is indicated.