(6cd) Photodegradation of Methylene Blue with CeO2/Al2O3 Catalysts

The constant development of new chemical products elevates people`s quality of life. On the other hand, it causes an increase of waste generation, such as dyes, which are found in the sewage of different industries. These organic compounds affect color, pH and temperature of water, which disturb the environment, causing toxicological effects on aquatic life and even in human beings. Several dyes used today are hard to be decomposed, causing damages to people`s healthy. In this way, studies that contribute to discover more efficient degradation techniques are necessary. Historically, heterogeneous catalysis has helped to clean water sewage using semiconductor materials, for example, titanium oxides. Cerium oxide is also a semiconductor material, so it presents a gap between valence and conduction band. In the presence of light, the photons reach the semiconductor surface and electrons are transferred from valence to conduction band, leaving a hole (h+) in the valence band, generating oxidative and reductive sites that are able to degrade organic compounds. The goal of this work was to study CeO₂/ɣ-Al₂O₃ catalysts, with different ratios of cerium oxides over alumina, applied to the photodegradation of methylene blue. The behaviors of the samples as well the load of ceria were investigated. Catalysts with 6, 12 and 24% of ceria over alumina were synthesized and thermal treated to stabilize their properties. Nitrogen adsorption, X ray diffraction (XRD) and Fourier Transform Infrared Spectroscopy (FTRI) were used to characterize the samples. The photocatalysis experiments were performed, under stirring, in a glass-jacketed reactor at 30^oC. The reactor was filled with 200mL of a 20 ppm methylene blue aqueous solution and 50 mg of catalyst. A 125 W mercury vapor lamp without external bulb was used as light source. The samples were collected at defined times along the experiments and analyzed by UV-Vis spectroscopy. The XRD showed the characteristics peaks of gamma-alumina and ceria fluorite phases. According to the BET results the area of the samples decreased with ceria addition, which is expected, since the ceria can block some alumina porous. The photocatalitic tests showed that the samples with 6, 24 and 12% of ceria load on alumina presented promising results in the degradation of methylene blue.