The Influence of Duration of High-Temperature Exposure on the Properties of Carbon Nitride Obtained in Molten Salts

Abstract

In the present work the influence of duration of thermal treatment on the properties and photocatalytic performance of carbon nitride materials is investigated. Preparation of photocatalytic material proceeded in the eutectic molten salts KCl/LiCl mixture. This way of thermal treatment results in crystalline material with ordered structure, improved in comparison to convenient preparation methods. Duration was altered in range from 2 to 10 hours. Materials were studied by the methods of X-ray diffraction patterns, scanning electron microscopy. It was found that most ordered materials with the maximal degree of crystallinity are formed after 2–6 hours of high-temperature treatment. Elongation of thermal treatment up to 8 and 10 hours leads to less ordered material with the enhanced share o amorphous phase. Carbon nitride materials were used as photocatalysts for  the selective oxidation of benzyl alcohol to benzaldehyde and demonstrate high selectivities to target product. 2 hours of thermal treatment leads to formation of photocatalyst with the highest conversion (79.2 %) and selectivity (92.4 %) values. Less effective material is formed after 10 hours of treatment, where selecivity level retained, while conversion drops to 48.6 %. Morphology of materials has maximal effect on the photocatalytic properties – high crystallinity is the main feature of catalytically effective materials.