Faraday Discussions最新文献

Catalyst stability is central to the viability of lignin-first biorefineries, yet conventional characterisation often fails to detect the subtle deactivation processes that govern product quality. Here, we demonstrate that ultraviolet–visible (UV–Vis) spectroscopy, when combined with gel permeation chromatography (GPC), can serve as a sensitive diagnostic tool for detecting catalyst performance decline in Reductive Catalytic Fractionation (RCF). We introduce a concentration-independent spectral index (SI₃₂₀), derived from the absorbance ratio at 280 and 320 nm, given by SI₃₂₀ = 1 – A₃₂₀/A₂₈₀. Native-like lignins show negligible absorbance at 320 nm (SI₃₂₀ ≈ 1), whereas condensation, benzylic oxidation, and extended π-conjugation depress SI₃₂₀. As a ratio, SI₃₂₀ is concentration-independent within the Beer–Lambert regime and can be profiled across the chromatogram to yield SI₃₂₀(M) profiles, with M denoting apparent molar mass. SI₃₂₀(M) profiles report directly on the formation of chromophores associated with catalyst ageing across the lignin apparent-M distribution. Utilising post-consumer cardboard as a substrate, we tracked RCF over RANEY^® Ni across multiple recycling runs. A comparative analysis of fresh and recycled catalysts revealed systematic SI₃₂₀ downshifts in oligomer fractions, indicating chromophore accumulation well before changes in bulk yield of low M products become evident. Linear regression of SI₃₂₀(M) mean values (r² = 0.95) enables a practical estimate of catalyst life. Under our conditions, it is estimated that RANEY^® Ni can sustain lignin stabilisation for up to 15 runs of catalyst use (ca. 45 h operation), after which the chromophore density approaches that of organosolv lignin. Our findings reframe UV–Vis spectroscopy from a simple detection method for GPC analysis into a diagnostic platform of lignin-first catalysis. By funnelling apparent-M-resolved spectra into a simple index, GPC–UV–Vis enables rapid, non-destructive monitoring of catalyst performance, supports optimisation of RCF conditions and recycling protocols, and highlights the stabilising action of hydrogen-transfer catalysis. In the broader context, the approach is general to diverse feedstocks, catalysts, and lignin-first modalities, offering a practical route to correlate catalyst ageing with product quality and to guide development of durable, robust catalysts for circular economy and lignin valorisation.

This article addresses current challenges in lignin chemistry by exploring four thematic areas. We begin by examining the major chemical transformations that occur in lignin and discuss the emerging structural understanding of technical lignins. The discussion then shifts to lignin fractionation strategies, which are essential for reducing its inherent heterogeneity and complexity, thereby enabling its use in practical applications. Next, we delve into the chemical and physical behavior of lignin in solution, with particular emphasis on its self-assembly processes relevant to nanoparticle formation. The supramolecular interactions driving these assemblies – such as π–π stacking, hydrogen bonding, and solvent polarity – are analyzed to identify key parameters for designing lignin-based nanomaterials. These materials show promising applications across sectors including agriculture, packaging, cosmetics, and pharmaceuticals. We then consider the broader valorization of lignin, focusing on the rheological and antioxidant properties of lignin fractions. Particular attention is given to their role in forming polymer blends with polyethylene, highlighting their influence on thermal stability and mechanical performance. Finally, we explore lignin's potential as a non-petroleum precursor for carbon fiber production. We critically assess the main barriers in this field, such as lignin's relatively low molecular weight and thermal behavior, which hinder effective fiber formation and graphitization. Strategies to address these challenges, including the integration of fractionation techniques with chemical modifications, are discussed. The article concludes with a review of recent efforts to overcome the limitations of lignin graphitization and enhance its viability as a sustainable carbon fiber source.

This work offers a side-by-side overview of the behaviour of two liquors obtained via two fractionation processes, ionosolv and organosolv, from Eucalyptus globulus wood, and how the precipitation strategy that follows may affect the final yield, morphology, and particle size of every kind of lignin nanoparticle. For lignin nanoparticle precipitation, two bottom-up techniques and two top-down approaches were employed to determine which combination of fractionation process and synthesis treatment would provide the nanoparticles with the best characteristics. The results demonstrated the importance of the fractionation process in the final lignin nanoparticle yield, as ionosolv fractionation gave enhanced yields of more than 60% lignin in the form of nanoparticles. However, sphericity, particle sizes, and non-agglomerated structures were easily obtained from organosolv liquors, in which precipitation was carried out progressively in the absence of sonication. The use of ultrasound mostly resulted in the breakage of particles into smaller and irregular pieces. However, in the case of ionosolv liquors, homogeneous spherical nanoparticles were fused, forming agglomerates of smaller particles through the top-down strategy of complete addition of the antisolvent followed by sonication. The highest precipitation yield of nanoparticles was obtained from ionosolv liquors in which the full amount of antisolvent was added in one step to precipitate lignin, and then sonication was applied. In contrast, the lignin nanoparticles (LNPs) precipitation strategy that resulted in more spherical LNPs was the bottom-up strategy of precipitation by progressive antisolvent addition, resulting in visually observed non-aggregated spherical particles with a particle size distribution of 200 nm < d_p < 500 nm, molecular weight of M_w = 14 000 g mol⁻¹, and thermal degradation property of T_10% = 310 °C.