Synthesis, characterization and photocatalytic activities of carbon fiber based tungsten catalysis

In the last decades, the lack of clean water sources have become an important issue due to the rapid growth of industrialization and population growth. Therefore, various practical methods such as extraction, oxidation, adsorption, biodegradation and photocatalytic degradation have been developed. The photocatalytic systems ‒in which semiconductors are used‒ decompose the organic pollutants into biodegradable compounds and in the end transform them into harmless carbon dioxide and water. Titanium dioxide (TiO2) is a known efficient photocatalyst which has high activity under UV light and high photo-corrosion resistance. However, the utilization of TiO2 is limited because of the wide band gap of TiO2 which requires ultraviolet radiation to become active. Owing to these reasons, new type of semiconductors have been developed that can be an alternative to TiO2 by reducing band gap and increasing photocatalytic performance. Tungsten trioxide (WO3) is a novable alternative for TiO2 photocatalyst because of its narrow band gap (2.4‒2.8), non-toxicity, photosensitivity, resilience to photocorrosion and inexpensiveness. Also, while TiO2 absorbes just 5% of solar radiation, WO3 absorbes 30% of solar radiation. In this study, the degradation efficiency of the industrial dye Orange II was investigated by carbon fiber based tungsten trioxide (WO3) and bismuth tungstate (Bi2WO6) catalysts. Carbon fiber (CF) based WO3 and Bi2WO6 catalysts were produced by solvothermal and hydrothermal methods, respectively. For comparison, raw WO3/TiO2 and Bi2WO6 catalysts were also synthesized and the most efficient catalyst was determined. Characterization of catalysts was examined by SEM, XPS, Raman and FTIR analyses. Photocatalytic experiments were investigated under two different wavelengths (UV-A, Visible) and were also performed in the dark conditions. Catalysts with different carbon fiber ratios were synthesized and the effect of CF addition on the photocatalytic performance was investigated. The experimental data were applied to the Langmuir‒Hinshelwood kinetic model and the kinetic constants of each catalysts were calculated. Then, the effects of different parameters (initial concentration of organic contaminant, amount of catalyst, pH) on the efficiency of photocatalytic removal were examined and optimum conditions were determined for the photocatalytic degradation. According to results, the optimum CF ratios were determined as 5% and 15% for WO3/TiO2/CF and Bi2WO6/CF, respectively. When the effect of catalytic removal of initial pollutant concentration was investigated, for both catalysts, the percentage of catalytic removal decreased as the initial pollutant concentration increased. It was observed that the catalytic degradation efficiency increased with the increase in the amount of catalyst to a certain level. According to the pH effect studies, WO3/TiO2/CF exhibited high catalytic efficiency in acidic medium; while Bi2WO6/CF catalyst showed high photocatalytic performance in the alkaline medium. Keywords: Photocatalysis, carbon fiber, tungsten, bismuth, water purification, Orange II