Hydrogen-Binding-Initiated Activation of O-H Bonds on a Nitrogen-Doped Surface for the Catalytic Oxidation of Biomass Hydroxyl Compounds

Designing Strong, Tough, Fluorescent, and UV-Shielding PLA Materials by Incorporating a Phenolic Compound-Based Multifunctional Modifier

The realization of high stiffness, high extensibility, and multi-functions for polylactic acid (PLA) is a vital issue for its practical applications. Herein, hydroxyalkylated tannin acid (mTA), a phenolic compound-based modifier with plentiful flat aromatic structures and flexible isopropanol oligomers, is designed and fabricated to act as the multifunctional modifier for PLA. The mTA exhibits the capability of emitting fluorescence and blocking UV light due to the combination of flat aromatic structures and plentiful flexible chains. Besides, mTA with high grafting degree (h-mTA) shows an excellent compatibility to PLA due to the hydrogen bonding interface and the high affinity of grafted isopropanol oligomers to PLA. As a result, the as-prepared PLA/h-mTA20 composite exhibits a strikingly improved extensibility by 61.2 times while maintaining the high yield strength of PLA. Moreover, PLA/h-mTA can serve as a fluorescent material with multi-mode responsiveness as well as a UV-shielding material with high transparency. We envision that this work opens a novel yet facile way to prepare a strong, tough, and multifunctional PLA material with expanded application scopes and will promote the practical applications of phenolic compounds in polymers.

Stereo-Recognition of Hydrogen Bond and Its Implications for Lignin Biomimetic Synthesis

The hydrogen bond (H-bond) is essential to stabilizing the three-dimensional biological structure such as protein, cellulose, and lignin, which are integral parts of animal and plant cells; thus, stereo-recognition of the H-bond is extremely attractive. Herein, a methodology combining the variable-temperature ¹H NMR technique with the density functional theory was established to recognize the underlying H-bonding patterns in lignin diastereomers. This method successfully classified the intramolecular and intermolecular H-bonds with slope values varying between 50.2-201.5 and 221.9-655.4, respectively, from the natural logarithm of the hydroxyl proton chemical shift versus the inverse of the temperature plot. Moreover, this slope was found to be correlated with the interaction distance between the H-bond donor and acceptor. Finally, it was proposed that the stereo-preferential formation of the β-O-4 structure (erythro vs threo form) during lignin biomimetic synthesis was probably influenced by their intramolecular H-bonding patterns, thus making it easier to reach thermodynamic equilibrium.

Microenvironment engineering of supported metal nanoparticles for chemoselective hydrogenation

Selective hydrogenation with supported metal catalysts widely used in the production of fine chemicals and pharmaceuticals often faces a trade-off between activity and selectivity, mainly due to the inability to adjust one factor of the active sites without affecting other factors. In order to solve this bottleneck problem, the modulation of the microenvironment of active sites has attracted more and more attention, inspired by the collaborative catalytic mode of enzymes. In this perspective, we aim to summarize recent advances in the regulation of the microenvironment surrounding supported metal nanoparticles (NPs) using porous materials enriched with organic functional groups. Insights on how the microenvironment induces the enrichment, oriented adsorption and activation of substrates through non-covalent interaction and thus determines the hydrogenation activity and selectivity will be particularly discussed. Finally, a brief summary will be provided, and challenges together with a perspective in microenvironment engineering will be proposed.

Structural materials with afterglow room temperature phosphorescence activated by lignin oxidation

Sustainable afterglow room temperature phosphorescence (RTP) materials, especially afterglow RTP structural materials, are crucial but remain difficult to achieve. Here, an oxidation strategy is developed to convert lignin to afterglow materials with a lifetime of ~ 408 ms. Specifically, lignin is oxidized to give aromatic chromophores and fatty acids using H₂O₂. The aromatic chromophores are locked by a fatty acid-based matrix by hydrogen bonds, triggering enhanced spin orbit coupling and long afterglow emission. More interestingly, motivated by this discovery, an auto fabrication line is built to convert wood (natural structural materials) to wood with afterglow RTP emission (RTP wood) via in situ oxidation of naturally-occurring lignin located in the wood cell walls to oxidized lignin (OL). The as-prepared RTP wood exhibits great potential for the construction of sustainable afterglow furniture. With this research we provide a new strategy to promote the sustainability of afterglow RTP materials and structural materials.

Sustainable afterglow room temperature phosphorescence (RTP) Structural materials are difficult to achieve. Here, the authors demonstrate a wood based RTP material by oxidation of lignin to realize an afterglow RTP material with a lifetime of ~ 408 ms.

Control in Local Coordination Environment Boosting Activating Molecular Oxygen with an Atomically Dispersed Binary Mn-Co Catalyst

Activation of molecular oxygen plays a crucial role in natural organisms and the modern chemical industry. Herein, we report a Mn-Co dual-single-atom catalyst that exerts a specific synergy in boosting O₂ activation by collaboration between two distinct types of activation sites. Taking the oxidative esterification of the biomass platform 5-hydroxymethylfurfural (HMF) as the model reaction, the activation of O₂ is demonstrated through transforming O₂ into a reactive superoxide anion radical (O₂^•-) on Co-N₄ sites and, meanwhile, by reversible consumption and supplement of coordinated surface oxygen as a new type of reactive oxygen species (ROS) on N,O-coordinated single-atom Mn sites (Mn-N_xO_y). EXAFS analysis results show a longer average Mn-O bond distance at near 2.19 Å, which makes the breaking and formation of surface Mn-O bonds easier to cycle. Control experiments support that such Mn-O bonding conditions could facilitate H-elimination of C-H in HMF. The co-existence of two types of ROS effectively matches the oxidation of hydroxyl and aldehyde groups, and thus, the overall reaction is boosted in excellent yield of diester (95.8%) with an extremely high carbon balance. This study represents a rare example of taking advantage of the synergy of the diatomic catalyst for activating O₂ by two types of activation pathways.

Deep eutectic solvents coupled with (NH4)3H6CoMo6O24 trigger aerobic oxidation of 5-hydroxymethylfurfural to 5-formyl-2-furancarboxylic acid

An Anderson-type polyoxometalate (NH4)3H6CoMo6O24 in deep eutectic solvents exhibited outstanding catalytic performance for the selective aerobic oxidation of HMF to FFCA. It is potentially a promising and highly environmentally friendly...

Accelerating Selective Oxidation of Biomass-Based Hydroxyl Compounds with Hydrogen Bond Acceptors

Hydrogen-bonding-initiated self-association makes the valorization of biomass-based hydroxyl compounds a formidable challenge at high concentration. Apart from enhancing the dehydration reaction of hydroxyl compounds with the noncovalent medium effects, insights into how these effects can be exploited to optimize the oxidative reactivity of concentrated hydroxyl compounds remain unclear. Herein, we elucidate that deaggregation of hydroxyl groups with a catalytic number of hydrogen bond acceptors is essential in improving the reactivity of the aerobic oxidation of biomass-based neat aromatic alcohols over the vanadium-based catalyst. The neat 5-hydroxymethylfurfural (HMF) deaggregated with 25 mol % N,N-dimethylformamide (DMF) shows a >7-fold increase in reactivity to produce corresponding aldehydes with excellent selectivity, in stark contrast to the contrary deactivation of reaction in excessive DMF.