Towards the sustainable production of biomass-derived materials with smart functionality.

Biomass transformation into value-added products offers a solution to the end-up issue of agricultural and forestry wastes and provides a sustainable approach towards a circular material economy. Here we report a green fractionation technology for converting alkali lignin (AL) into graphene quantum dots (GQDs) which are glowing carbon nano-crystals as new guiding light for a spectrum of novel applications. AL is rapidly fractionated by an acid hydrotrope and recovered with an aromatic functionality as GQDs under mild conditions. In addition, the acid-hydrotrope can be easily recycled to restore its environmental sustainability. The as-prepared lignin-based GQDs (LGQDs) exhibit a nanoscopic few-layer structure, along with bright fluorescence, water solubility, long-term photostability, and excellent biocompatibility. Benefitting from these alluring properties, LGQDs are applied as sensitive fluorescence-switchable probes for detecting H₂O₂ which is a common physiological oxidant in biological systems. They exhibit bright excitonic fluorescence, along with significant fluorescence quenching in response to the presence of H₂O₂ with a concentration as low as 0.13 nM. The ultrasensitivity of LGQDs for detecting H₂O₂ is explored by density functional theory (DFT) calculations and the results show that the fluorescence mechanism of LGQDs is dominated by the intramolecular charge transfer (ICT) behavior, which is proposed for the first time and subsequently validated by a series of control experiments. This study offers a promising and sustainable approach for synthesis of S, N co-doped graphene quantum dots as ultrasensitive biosensors from low-cost biomass. In addition, the theoretical results highlight a deep understanding on the photoluminescence phenomenon of LGQDs and more generally biomass-based GQDs.

Furan-based compounds are a new class of compounds characteristic of wide abundance, feasible availability, and environmental friendliness. Presently, polyimide (PI) is the best membrane insulation material in the world, which is widely used in the fields of national defense, liquid crystals, lasers, and so on. At present, most polyimides are synthesized using petroleum-based monomers bearing benzene rings, while furan-based compounds bearing furan rings are rarely used as monomers. The production of petroleum-based monomers is always associated with many environmental issues, and their substitution with furan-based compounds seems a solution to addressing these issues. In this paper, t-butoxycarbonylglycine (BOC-glycine) and 2,5-furandimethanol, bearing furan rings, were employed to synthesize BOC-glycine 2,5-furandimethyl ester, which was further applied for the synthesis of furan-based diamine. This diamine is generally used to synthesize bio-based PI. Their structures and properties were thoroughly characterized. The characterization results showed that BOC-glycine could be effectively obtained using different posttreatment methods. And BOC-glycine 2,5-furandimethyl ester could be effectively obtained by optimizing the accelerating agent of 1,3-dicyclohexylcarbodiimide(DCC) with either 1.25 mol/L or 1.875 mol/L as the optimum value. The PIs originated from furan-based compounds were synthesized and their thermal stability and surface morphology were further characterized. Although the obtained membrane was slightly brittle (mostly due to the less rigidity of furan ring as compared with benzene ring), the excellent thermal stability and smooth surface endow it a potential substitution for petroleum-based polymers. And the current research is also expected to shed some insight into the design and the fabrication of eco-friendly polymers.