Titania/chitosan-lignin nanocomposite as an efficient photocatalyst for the selective oxidation of benzyl alcohol under UV and visible light

• Published in: RSC advances Vol. 11; no. 55; pp. 34996 - 351
• Main Authors: Khan, Ayesha, Goepel, Michael, Lisowski, Wojciech, omot, Dariusz, Lisovytskiy, Dmytro, Mazurkiewicz-Pawlicka, Marta, Gläser, Roger, Colmenares, Juan Carlos
• Format: Journal Article
• Language: English
• Published: England Royal Society of Chemistry 28.10.2021; The Royal Society of Chemistry
• Subjects: Benzaldehyde; Benzyl alcohol; Biodegradability; biomass; Chemistry; Chitosan; Conversion; Doping; energy; Energy gap; Functional materials; hot water treatment; Light; Lignin; Nanocomposites; Nitrogen; Oxidation; Photocatalysis; Photocatalysts; Selectivity; Sol-gel processes; Titanium dioxide; Ultraviolet radiation
• ISSN: 2046-2069; 2046-2069
• DOI: 10.1039/d1ra06500a

Developing functional materials from biomass is a significant research subject due to its unique structure, abundant availability, biodegradability and low cost. A series of chitosan-lignin (CL) composites were prepared through a hydrothermal method by varying the weight ratio of chitosan and lignin. Subsequently, these CL composites were combined with titania (T) to form a nanocomposite (T/CL) using sol-gel and hydrothermal based methods. T/CL nanocomposites exhibited improved photocatalytic performance in comparison with sol-gel and hydrothermally prepared pristine titania (SGH-TiO 2 ), towards the selective oxidation of benzyl alcohol (BnOH) to benzaldehyde (Bnald) under UV (375 nm) and visible light (515 nm). More specifically, the 75T/CL(25 : 75) nanocomposite (a representative photocatalyst from the 75T/CL nanocomposite series) showed very high selectivity (94%) towards Bnald at 55% BnOH conversion under UV light. Whereas, SGH-TiO 2 titania exhibited much lower (68%) selectivity for Bnald at similar BnOH conversion. Moreover, the 75T/CL(25 : 75) nanocomposite also showed excellent Bnald selectivity (100%) at moderate BnOH conversion (19%) under visible light. Whereas, SGH-TiO 2 did not show any activity for BnOH oxidation under visible light. XPS studies suggest that the visible light activity of the 75T/CL(25 : 75) nanocomposite is possibly related to the doping of nitrogen into titania from chitosan. However, according to UV-visible-DRS results, no direct evidence pertaining to the decrease in band-gap energy of titania was found upon coupling with the CL composite and the visible light activity was attributed to N-doping of titania. Overall, it was found that T/CL nanocomposites enhanced the photocatalytic performance of titania via improved light harvesting and higher selectivity through mediation of active radical species. Combining titania with chitosan-lignin composites results in an active and selective photocatalyst for the oxidation of benzyl alcohol to benzaldehyde under green light (515 nm).