Surface-morphology modification of ceramic-based composites for photocatalytic activity via simple chemical and heat treatments

Abstract

In this work, a potentially novel ceramic-based composite was developed for photocatalytic activity. Hot-press sintered Al₂O₃/Ti composites containing 20 vol.% of metallic Ti were treated with NaOH and heated to generate a nanometer-scale structure to induce an active surface layer for photocatalytic activity. Because NaOH treatment does not affect Al₂O₃ ceramics, to form a nano-structured titania layer over the entire surface of a composite whose surface contains both Al₂O₃ and Ti, strict control was exerted over the NaOH concentration, treatment temperature, and time. The results showed that Al₂O₃/Ti composites were fully covered by nano-structured sodium containing titanate layers after being treated with 5-M NaOH at room temperature for 3 h and at 60°C for 1 h. After HCl treatment at 25°C or water treatment at 80°C for 24 h, Na⁺ ions were sufficiently removed and a nano-porous structure of titanate remained despite a widened network. HCl treatment and heat treatment at temperatures of 400–600°C changed the surface structure from a nano-porous network to nano-plates or nanorods of titania. The photocatalytic activity of Al₂O₃/Ti composites treated with NaOH, HCl, and heat was also investigated. Samples heated at 600°C exhibited the highest Rhodamine B degradation efficiency of 35% after exposure to ultraviolet light for 12 h, implying the multifunctionality of the surface-modified ceramic/metal composites.