Polymers obtained from biomass are promising alternatives to petro-based polymers owing to their low cost, biocompatibility, and biodegradability. Lignin, a complex aromatic polymer containing several functional hydrophilic and active groups including hydroxyls, carbonyls, and methoxyls, is the second most abundant biopolymer in plants. In particular, sustainable lignin-based gels are emerging as an appealing material platform for developing energy- and sensing-related applications owing to their attractive and tailorable physiochemical properties. This study describes the preparation strategies of lignin-based gels according to previously reported methods, with significant attention on the diverse performance of lignin-derived gel materials. Additionally, a detailed review of lignin-based gels utilized as an important resource in diverse fields is provided. Finally, a future vision on challenges and their possible solutions is presented.

Highly efficient photon-to-electron conversion is crucial for achieving photocatalytic conversion. In this study, oxygen-doped carbon nitride nanocages (O@CNNCs) were engineered via dual strategies of morphology-controlled heteroatom doping, which was successfully used in the photocatalytic selective oxidation of xylose/xylan to xylonic acid. The nanocage-shaped O@CNNCs had a larger surface area, which was 4.02 times of carbon nitride (CN). Furthermore, with the assistance of morphology regulation and O-doping, O@CNNCs exhibit highly efficient photon-to-electron conversion, enhanced visible-light utilization, high photocurrent, low resistance, and fast separation/migration of electron-hole pairs. Correspondingly, the photocatalytic oxidation of xylose to xylonic acid using O@CNNCs was successfully achieved under mild reaction conditions with a yield of 83.4%. O@CNNCs have excellent recyclability, in which the yield of xylonic acid in the 5th cycle was 98.2% of its initial use. The O@CNNC photocatalytic system was also suitable for macromolecular xylan, and a xylonic acid yield of 77.34 mg was obtained when 100 mg xylan was used. The oxidation-active species captured experiments indicated that holes were crucial for the selective oxidation of xylose to xylonic acid. Overall, this study provides a new strategy for the preparation of photocatalysts with excellent photon-to-electron conversion and selective oxidation of biomass-derived feedstocks to xylonic acid.

Developing efficient catalysts for organic pollutants degradation is crucial for remediating the current severe water environment, yet remains a great challenge. Herein, we report silver nanoparticles immobilized on an amine-functionalized metal-organic framework (MOFs) (Ag/UiO-66-NH₂) as a robust catalyst for the reduction of 4-nitrophenol (4-NP). The fabricated Ag/UiO-66-NH₂ catalyst exhibits the merits of superior activities (high turnover frequency (TOF) 3.2 × 10⁴ h^–1 and k value 6.9 × 10^–2 s^–1), cost-effectiveness under the lowest NaBH₄ concentration (n_[NaBH4]/n_[4-NP], 200), outstanding cyclability (10 recycling runs), and observable long-term durability, significantly outperforming previously reported catalytic system. The excellent degradation efficiency is ascribed to the favorable microenvironment modulation of unique MOF structure, which regulates the intrinsic properties of active sites and improves the electron-transfer process. Notably, the Ag/UiO-66-NH₂ also promotes the catalytic degradation of several organic pollutants at room temperature and hence could find a broad application for water remediation. This work offers a new avenue for the development of high-performance MOF-based catalysts with excellent activity and durability.