The carbon quantum dot (CQD), a fluorescent carbon nanoparticle, has attracted considerable interest due to its photoluminescent property and promising applications in cell imaging and bioimaging. In this work, biocompatible, photostable, and sustainably sourced CQDs were synthesized from byproducts derived from a biorefinery process using one-pot hydrothermal treatment. The main components of byproducts were the degradation products (autohydrolyzate) of biomass pretreated by autohydrolysis. The as-synthesized CQDs had a size distribution from 2.0–6.0 nm and had high percentage of sp2 and sp3 carbon groups. The CQDs showed blue-green fluorescence with a quantum yield of ~13%, and the fluorescence behaviors were found to be stable with strong resistance to photobleaching and temperature change. In addition, it is found that the as-synthesized CQDs could be used for imaging of cells and tumors, which show potential applications in bioimaging and related fields such as phototherapy and imaging.

The lignin rendered soluble by lignocellulosic biorefinery pretreatment remains insufficiently understood along the lines of molecular properties and chemical composition. To procure a representative soluble lignin preparation, an aromatic-selective adsorptive resin was utilized. Approximately 90% of soluble lignin could be recovered from autohydrolysis pretreatment hydrolyzate (autohydrolyzate) produced from a hardwood and a nonwood biomass. Adsorbate compositional characterization revealed a befuddling magnitude of carbohydrate in selectively isolated lignin adsorbates. Quantitative structural analysis of the lignin by NMR suggested lignin–carbohydrate complexes (LCCs) as the cause behind the pronounced carbohydrate contents. Analyzed spectra revealed both hardwood and nonwood soluble lignin features of ∼10 total LCC per 100 aromatic rings, with each lignin bearing unique LCC profiles. In addition, native structures remained in large quantities. The improved understanding of hydrolyzate-soluble lignin granted from this work will aid biorefinery development by improving discourse around a biorefinery lignin source.

Recent techno-economic studies of proposed lignocellulosic biorefineries have concluded that creating value from lignin will assist realization of biomass utilization into valuable fuels, chemicals, and materials due to co-valorization and the new revenues beyond carbohydrates. The pretreatment step within a biorefinery process is essential for recovering carbohydrates, but different techniques and intensities have a variety of effects on lignin. Acidic and alkaline pretreatments have been shown to produce diverse lignins based on delignification chemistry. The valorization potential of pretreated lignin is affected by its chemical structure, which is known to degrade, including inter-lignin condensation under high-severity pretreatment. Co-valorization of lignin and carbohydrates will require dampening of pretreatment intensities to avoid such effects, in spite of tradeoffs in carbohydrate production.

Fractionation of Kraft lignin from black liquor is necessary to reduce its heterogeneity, which exerts negative effects upon lignin-commercial polymer composite materials. In this work, Kraft lignin was dissolved in acetic acid to get low viscosity lignin solution and fractionated into specific molecular weight fractions by sequential ultrafiltration with different molecular weight cut-offs. The fractionated lignins were characterized, and their suitability in polyethylene–lignin composites was evaluated. After ultrafiltration with 5k and 3k Da cutoff, fractionation resulted in three fractions of differing molecular weights and lower polydispersity than the original Kraft lignin (F1 (7010 g/mol), F2 (3540 g/mol), and F3 (1890 g/mol)). The results from spectroscopic characterization of lignin (31P, 13C, and 2D-HSQC NMR) and thermal stability analysis (TGA and DSC) indicated that the contents of various linkages and functional groups and the thermal properties of each fraction varied as a function of its molecular weight. Compared to F1 and F2, F3 (lowest molecular weight and high quantity of phenolic hydroxyl groups) most positively contributed to the mechanical properties of a polyethylene–lignin composite.

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