* Corresponding author. 1944-3994/1944-3986 © 2021 Desalination Publications. All rights reserved. Desalination and Water Treatment www.deswater.com doi: 10.5004/dwt.2021.27416 230 (2021) 169–183 August Facile solid-state synthesis of heterojunction CeO 2 /TiO 2 nanocomposite as an efcient photocatalyst for the degradation of organic pollutants Muhammad Zobayer Bin Mukhlish, Md. Amirul Islam, Md Anisur Rahman, Shafiul Hossain, Md. Akhtarul Islam, Md. Tamez Uddin* Department of Chemical Engineering and Polymer Science, Shahjalal University of Science and Technology, Sylhet 3100, Bangladesh, emails: mtuddin_cep@yahoo.com/mtuddin-cep@sust.edu Received 26 October 2020; Accepted 9 May 2021 abstract In this study, CeO 2 /TiO 2 nanocomposites (NCs) were synthesized by adopting a straightforward two steps method comprising, first, the synthesis of CeO 2 and TiO 2 nanoparticles by wet chemical precipitation method and second, the heterostructure CeO 2 /TiO 2 NCs by solid-state reaction process. The CeO 2 /TiO 2 NCs were characterized by X-ray diffraction, N 2 adsorption–desorption isotherm analysis, field emission scanning electron microscopy, energy-dispersive X-ray spectroscopy, and UV-vis diffuse reflectance spectroscopy. Regardless of CeO 2 content, the bandgap energies of CeO 2 / TiO 2 NCs were lower than that of pure TiO 2 . Photocatalytic activity of the synthesized photocata- lysts was assessed by degrading a model dye methylene blue under the illumination of UV light. The CeO 2 /TiO 2 NCs containing 2 wt% CeO 2 exhibited higher photocatalytic degradation efficiency compared to reference TiO 2 (P25), pure TiO 2 , and CeO 2 /TiO 2 NCs containing CeO 2 other than 2 wt%. The alkaline environment was favorable for photocatalytic decomposition of cationic dye methylene blue (MB). The enhanced degradation efficiency of CeO 2 /TiO 2 NCs was substantiated in terms of vectorial charge separation and the reduction of photogenerated charge carriers owing to the band offsets existing at the interface between CeO 2 and TiO 2 NPs. Finally, no significant change in the degradation efficiency of CeO 2 /TiO 2 NCs after successive uses evidenced the stability and reusability of the photocatalysts. Therefore, it can be concluded that the synthesized CeO 2 /TiO 2 heterostructure photocatalyst would be a promising candidate for application in wastewater treatment. Keywords: Solid state synthesis; CeO 2 /TiO 2 nanocomposites; Heterojunction photocatalyst; Degradation efficiency; Band offset 1. Introduction Safe and clean water is important for human health and pleasure, ecosystems, and also for a booming econ- omy [1]. With the rapid urbanization and industrialization, more and more toxic and harmful pollutants are entering into the water through various channels, which directly or indirectly threaten the harmonious development of the ecological environment and humanity [2]. Organic dyes are considered as one of the major contaminants discharged into the water environment from various industries like textiles, leather, food, pharmaceutical, printing, etc. [3,4]. Dyes tend to suppress photosynthetic activity in aquatic habitats by preventing the penetration of sunlight that affects the aquatic biota [5]. Moreover, azo dyes, which con- stitute about 60%–70% of the textile dyestuffs, have geno- toxic, mutagenic, and carcinogenic effects on living beings [6]. Consequently, the treatment of wastewater containing such ecotoxic dyes is of great interest to ensure the sus- tainability of the environment for future generations. The conventional techniques like coagulation, mem- brane separation, adsorption, and activated sludge process