Coffee-waste templated CeOx/TiO2 nanostructured materials for selective photocatalytic oxidations

• Published in: Chemosphere (Oxford) 2023-01, Vol.311, p.136672-136672, Article 136672
• Main Authors: Solís, Rafael R., Rodríguez-Padrón, Daily, Martín-Lara, María Ángeles, Calero, Mónica, Luque, Rafael, Muñoz-Batista, Mario J.
• Format: Article
• Language: English
• Subjects: Benzaldehyde; Cerium; Coffee-templated; Green synthesis; Photocatalysis; Solvent-free; Titania
• ISSN: 0045-6535; 1879-1298
• DOI: 10.1016/j.chemosphere.2022.136672

An environmentally friendly solvent-free approach was tested using spent coffee as a biomass sacrificial template for the preparation of TiO2 modified with CeOx. The use of coffee as a template pursues the preparation of a nanostructured heterojunction without the need for a solvent. Two variables were optimized in the synthesis process, i.e. calcination temperature and proportion of CeOx. Firstly, bare coffee-template titania was prepared to explore the effect of the calcination temperature, within 500–650 °C. The anatase phase was obtained up to 600 °C. Higher temperatures, i.e. 650 °C, led to the appearance of rutile (10%) and efficient removal of the sacrificial agent (0.6% residue). The maximum photocatalytic activity in terms of conversion, in the oxidation of benzyl alcohol, was achieved employing the bare coffee-template TiO2 at 650 °C, and it was found comparable to the benchmarked P25. The incorporation of ceria in the solvent-free approach considerably improved photocatalytic benzaldehyde production. No changes in the XRD pattern of TiO2 were appreciated in the presence of ceria due to the low amount added, within 1.5–6.0%, confirmed by XPS as superficial Ce3+/Ce4+. The UV–visible absorption spectra were considerably redshifted in the presence of Ce, reducing the bandgap values of bare titania. An optimum amount of ceria in the structure within 3-0% was found. In this case, the selectivity towards benzaldehyde was ca. 75%, 3 times higher than the selectivity value registered for the benchmarked P25 or the bare prepared TiO2. [Display omitted] •Use of coffee as a sacrificial template for the preparation of nanostructured CeOx-TiO2.•The optimum temperature for template removal and crystalline anatase was 600 °C.•CeOx presence increases the selectivity reaction of benzyl alcohol to benzaldehyde.•CeOx reduces the recombination effect and redshifts the radiation absorption spectrum.•Bands alignment proposal with electron caption by Ce vacant and action by holes.