Preparation of Fe-Cu-kaolinite for catalytic wet peroxide oxidation of 4-chlorophenol

Fe-Cu-kaolinites were prepared by co-precipitation and hydrothermal methods, and characterized by X-ray diffraction (XRD) and scanning electron microscope (SEM), where 2 wt.% natural kaolinite was dispersed, and the ratios of (Al + Fe + Cu)/clay = 10 mmol/g and Al/(Fe + Cu) = 5/1 were maintained. The effect of different drying methods (vacuum drying, ethanol exchange drying, freeze-drying, microwave drying, normal oven drying) and different Fe/Cu molar ratio (0/2, 0.4/1.6, 0.8/1.2, 1/1, 1.2/0.8, 1.6/0.4, 2/0) was also assessed. Catalytic wet peroxide oxidation (CWPO) reaction of 4-chlorophenol (4-CP) was used to probe the reactivity and activity of the materials prepared. The results showed that Fe and Cu could be successfully intercalated into the interlayer of kaolinite by hydrothermal method, where specific surface area and pore volume increased by 19 times and 7 times, respectively; the intensity of basal space (001) reflection peak was reduced by 80%, and tip width was doubly increased. The catalyst possessed higher reactivity, with 85.5% of 4-CP conversion being observed, whereas only 15.2% of 4-CP was removed over raw kaolinite. High-power microwave drying (720 W) was the best drying method, because it resulted in greater microstructure and thus higher reactivity (85.3% of 4-CP conversion), with lower active metal (Fe or Cu) leaching (3.96 mg L^-1). Fe/Cu molar ratio of 0.8-1.0/1.2-1.0 was considered as the optimum ratio in pillaring solution, for maintaining higher catalytic activity (85-90% of 4-CP conversion) and lower metal (Fe or Cu) leaching (7-9.3 mg L^-1).