The inferior thermoplastic properties have limited production of melt-spun fibers from lignin. Here we report on the controlled esterification of softwood kraft lignin (SKL) to enable scalable, solvent-free melt spinning of microfibers using a cotton candy machine. We found that it is crucial to control the esterification process as melt-spun fibers could be produced from lignin oleate and lignin stearate precursors with degrees of esterification (DE) ranging from 20-50%, but not outside this range. To fabricate a functional hybrid material, we incorporated magnetite nanoparticles (MNPs) into the lignin oleate fibers by melt blending and subsequent melt spinning. Thermogravimetric analysis and X-ray diffraction studies revealed that increasing the weight fraction of MNPs led to improved thermal stability of the fibers. Finally, we demonstrated adsorption of organic dyes, magnetic recovery, and recycling via melt spinning of the regular and magnetic fibers with 95% and 83% retention of the respective adsorption capacities over three adsorption cycles. The mechanical recyclability of the microfibers represents a new paradigm in lignin-based circular materials.

The development of bio-based materials capable of addressing multiple environmental challenges is critical for advancing sustainable materials design. Herein, we report electrospun nanofibers from unfractionated, chemically unmodified softwood kraft lignin and cellulose acetate, where cellulose acetate acts as a carrier polymer, enabling the formation of uniform precursor fibers with lignin contents of up to 80%. The resulting nanofibers enable sequential dye adsorption from water (methylene blue removal capacity of 19 mg/g) and carbon dioxide (CO2) capture (2.2 mmol/g) after carbonization. When evaluated solely for CO2 capture, the pristine carbonized materials show sorption capacities of 3.1–3.9 mmol/g, which increase as lignin content in the precursor fibers decreases, underscoring the importance of tuning carbon yield and capture performance. The sequential utilization of a single precursor material demonstrates a stepwise transformation that aligns with resource efficiency and sustainable material design. Overall, this study demonstrates a viable route for the direct valorization of industrial lignin into functional materials for both water purification and carbon capture applications.

The continuous rise in atmospheric carbon dioxide (CO₂) concentrations and its contribution to global climate change necessitates the development of sustainable CO₂ capture technologies. Enzyme-based CO₂ capture systems, particularly those using carbonic anhydrase (CA), offer high catalytic efficiency, but their practical use is limited by high enzyme costs, reduced enzyme stability and the difficulty of recovering them from water-based systems. Here, we report the immobilization of CA via straightforward adsorption onto sustainable and covalently stabilized lignin nanoparticles (sLNPs) for catalyzing aqueous-phase CO₂ capture. The immobilized enzyme exhibited slightly higher specific activity than free enzyme at technically important pH 9.0, which suggests that pH-stable sLNPs may contribute to stabilizing carbonic anhydrase within its microenvironment. The catalytic performance of the system was evaluated in a stopped-flow reactor by measuring CO₂ hydration at pH 7.1 and 9.4 across temperatures between 30−60 °C, using the colorimetric response of pH-sensitive dyes. The reaction kinetics at pH 7.1 showed an Arrhenius-type temperature dependence, while non-Arrhenius behavior was observed at pH 9.4. Enzyme immobilization enhanced aqueous absorption of CO₂, as shown by stirred-cell fall-in-pressure measurements at 40 and 60 °C. These results support the development of scalable biocatalytic systems for CO₂ capture in aqueous media using CA.

Biofouling remains a critical challenge in filtration systems, leading to reduced efficiency and lifespan of membranes and, consequently, increased operational costs. In this study, enzymatic protein hydrolysis using protease immobilized on lignin nanoparticles (LNPs) and lignin nanofibers (LNFs) was investigated as an approach to mitigate fouling. Bovine serum albumin (BSA) was selected as a model foulant. Proteolytic degradation of BSA was carried out using protease adsorbed on LNPs (Protease@LNPs) as such and further immobilized into an electrospun LNFs membrane (Protease@LNPs@LNFs). Activity assays showed that protease immobilization on LNPs, as well as on combined LNP-LNF systems, resulted in comparable activity retention. Quartz Crystal Microbalance with Dissipation monitoring (QCM-D) and Scanning Electron Microscopy (SEM) was used to study the hydrolysis process in real-time, while SDS-PAGE analysis was used to resolve the hydrolytic products from BSA. Densitometric analysis of the bands indicated a degree of hydrolysis of 84% after 30 minutes for both Protease@LNPs and Protease@LNPs@LNFs. Finally, we demonstrate a proof-of-concept biocatalytic membrane composed of protease adsorbed onto LNPs (Protease@LNPs) and further embedded within a three-dimensional network of LNFs for antifouling applications.