Suchergebnisse

Chitosan-derived N-doped carbon materials are attractive candidates for the preparation of catalysts with a wide range of applications. Chitosan is a nitrogen rich (∼7 wt %) renewable biomass resource derived from seafood waste. Nitrogen-containing functional groups (amine and acetamide) of chitosan make it a suitable precursor for the synthesis of N-doped carbon materials. This perspective provides an overview on various techniques for the preparation and characterization of chitosan-based N-doped carbon materials and their application in the field of electrocatalysis and photocatalysis. Additional doping with nitrogen imparts greater electrochemical stability and basic character to the material due to the ability of nitrogen atoms to accept electrons. Nevertheless, each type of C–N bonding configuration has unique potential for catalytic reactions attributed to different electronic structure and catalytically active sites. The ability to acquire desired N-bonding states during the process of doping will provide a better control over the material application. The promising performance of chitosan-based N-doped carbon materials in electrocatalytic and photocatalytic reactions is attributed to their improved electronic structure and charge transfer properties. Moreover, research trends toward the design of chitosan-based N-doped carbons materials with required features for electrocatalytic and photocatalytic applications have also been identified. ; This publication is part of a project that has received funding from the European Union's Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie Grant Agreement No. 711859 and from the financial resources for science in the years 2017-2021 awarded for the implementation of an international cofinanced project. Roger Gläser and Michael Goepel gratefully acknowledge support from the Leipzig Graduate School of Natural Sciences, Building with Molecules and Nano-objects, as well as from the Research Academy Leipzig.

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-TiO2), 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-TiO2 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-TiO2 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. ; This publication is part of a project that has received funding from the European Union's Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement no. 711859 and from the financial resources for science in the years 2017–2021 awarded for the implementation of an international co-financed project. Juan Carlos Colmenares would like to acknowledge the support from the National Science Centre, Poland, within OPUS-20 project number 2020/39/B/ST5/00076. Roger Gläser and Michael Goepel gratefully acknowledges support from the Leipzig Graduate School of Natural Sciences: Building with Molecules and Nano-objects (BuildMoNa) as well as from the Research Academy Leipzig.

Solar energy-driven processes for biomass valorization are priority for the growing industrialized society. To address this challenge, efficient visible light-active photocatalyst for the selective oxidation of biomass-derived platform chemical is highly desirable. Herein, selective oxidation of 5-hydroxymethylfurfural (HMF) to 2,5-diformylfuran (DFF) was achieved by visible light-driven photocatalysis over titania. Pristine titania is photocatalytically inactive under visible light, so an unconventional approach was employed for the visible light (λ=515 nm) sensitization of titania via a formation of a visible light-absorbing complex of HMF (substrate) on the titania surface. Surface-complexation of HMF on titania mediated ligand-to-metal charge transfer (LMCT) under visible light, which efficiently catalyzed the oxidation of HMF to DFF. A high DFF selectivity of 87 % was achieved with 59 % HMF conversion after 4 h of illumination. The apparent quantum yield obtained for DFF production was calculated to be 6.3 %. It was proposed that the dissociative interaction of hydroxyl groups of HMF and the titania surface is responsible for the surface-complex formation. When the hydroxyl groups of titania were modified via surface-fluorination or calcination the oxidation of HMF was inhibited under visible light, signifying that hydroxyl groups are decisive for photocatalytic activity. ; This publication is part of a project that has received funding from the European Union's Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement No. 711859 and from the financial resources for science in the years 2017–2021 awarded for the implementation of an international co-financed project. Roger Gläser and Michael Goepel gratefully acknowledges support from the Leipzig Graduate School of Natural Sciences: Building with Molecules and Nano-objects as well as from the Research Academy Leipzig. Adam Kubas acknowledges support from the National Science Centre, Poland, grant number 2018/30/E/ST4/00004. Access to high performance computing resources was provided by the Interdisciplinary Centre for Mathematical and Computational Modelling in Warsaw, Poland, under grant GB79-5.