Boosting 5-Hydroxymethylfurfural Electrooxidation by Porous Biochar via Loading Numerous Surface-Exposed Cobalt Phosphonates

The electrooxidation of 5-hydroxymethylfurfural (HMF) into 2,5-furandicarboxylic acid (FDCA) demonstrated its unique superiority, not only in reducing overpotential and improving energy conversion efficiency for green hydrogen production but also in utilizing abundant biomass resources and producing high-value-added chemicals. However, designing highly efficient electrocatalysts for HMF electrooxidation (HMF-EOR) with low cost and high performance for large-scale production remained a huge challenge. Herein, we introduced an easy one-step activation process to produce P-doped porous biochar loaded with multiple crystal surfaces exposed to CoP2O6 catalysts (CoP2O6@PC), which exhibited outstanding electrooxidation performance. To achieve a current density of 50 mA cm-2, only a low overpotential of 200 mV was needed for the electrooxidation of HMF in 1.0 M KOH + 10 mM HMF. This performance far surpassed that of other similar materials. CoP2O6@PC exhibited outstanding HMF-EOR performance with high conversion (nearly 100%), selectivity (97.1%), faradaic efficiency (95.3%), and robust stability. This work represents a promising strategy to fabricate macroscale and low-cost HMF-EOR electrocatalysts and achieve potential industrial applications of HMF-EOR.

Rapid and Selective Photo-degradation of Polymers: Design of an Alternating Copolymer with an o-Nitrobenzyl Ether Pendant

The development of polymers with on-demand degradability is required to alleviate the current global issues on polymer-waste pollution. Therefore, we designed a vinyl ether monomer with an o-nitrobenzyl (oNBn) group as a photo-deprotectable pendant (oNBnVE) and synthesized an alternating copolymer with an oNBn-capped acetal backbone via cationic copolymerization with p-tolualdehyde (pMeBzA). The resultant alternating copolymer could be rapidly degraded into lower-molecular-weight compounds upon simple exposure to UV irradiation without any reactants or catalysts, while it was sufficiently stable toward heat and ambient light. This degradation proceeds via cleavage of the hemiacetal structure generated upon photo-deprotection of the oNBn pendant. The oNBn-peculiar degradability allowed the exclusive photo-degradation of the oNBnVE/pMeBzA segments in a diblock copolymer composed of oNBnVE/pMeBzA and benzyl vinyl ether (BnVE)/pMeBzA segments.

Towards Upcycling Biomass‐Derived Crosslinked Polymers with Light

Photodegradable, recyclable, and renewable, crosslinked polymers from bioresources show promise towards developing a sustainable strategy to address the issue of plastics degradability and recyclability. Photo processes are not widely exploited for upcycling polymers in spite of the potential to have spatial and temporal control of the degradation in addition to being a green process. In this report we highlight a methodology in which biomass‐derived crosslinked polymers can be programmed to degrade at ≈300 nm with ≈60 % recovery of the monomer. The recovered monomer was recycled back to the crosslinked polymer.

Electroreforming of Biomass for Value-Added Products

Humanity's overreliance on fossil fuels for chemical and energy production has resulted in uncontrollable carbon emissions that have warranted widespread concern regarding global warming. To address this issue, there is a growing body of research on renewable resources such as biomass, of which cellulose is the most abundant type. In particular, the electrochemical reforming of biomass is especially promising, as it allows greater control over valorization processes and requires milder conditions. Driven by renewable electricity, electroreforming of biomass can be green and sustainable. Moreover, green hydrogen generation can be coupled to anodic biomass electroforming, which has attracted ever-increasing attention. The following review is a summary of recent developments related to electroreforming cellulose and its derivatives (glucose, hydroxymethylfurfural, levulinic acid). The electroreforming of biomass can be achieved on the anode of an electrochemical cell through electrooxidation, as well as on the cathode through electroreduction. Recent advances in the anodic electroreforming of cellulose and cellulose-derived glucose and 5-hydrooxylmethoylfurural (5-HMF) are first summarized. Then, the key achievements in the cathodic electroreforming of cellulose and cellulose-derived 5-HMF and levulinic acid are discussed. Afterward, the emerging research focusing on coupling hydrogen evolution with anodic biomass reforming for the cogeneration of green hydrogen fuel and value-added chemicals is reviewed. The final chapter of this paper provides our perspective on the challenges and future research directions of biomass electroreforming.

The Increasing Value of Biomass: Moving From C6 Carbohydrates to Multifunctionalized Building Blocks via 5-(hydroxymethyl)furfural

Recent decades have been marked by enormous progress in the field of synthesis and chemistry of 5-(hydroxymethyl)furfural (HMF), an important platform chemical widely recognized as the "sleeping giant" of sustainable chemistry. This multifunctional furanic compound is viewed as a strong link for the transition from the current fossil-based industry to a sustainable one. However, the low chemical stability of HMF significantly undermines its synthetic potential. A possible solution to this problem is synthetic diversification of HMF by modifying it into more stable multifunctional building blocks for further synthetic purposes.

Aerobic Oxidation of 5-Hydroxymethylfurfural to 2,5-Furandicarboxylic Acid over Holey 2 D Mn2 O3 Nanoflakes from a Mn-based MOF

The aerobic oxidation of 5-hydroxymethylfurfural (HMF) to 2,5-furandicarboxylic acid (FDCA), a promising renewable monomer to produce bio-based polymers such as polyethylene furanoate (PEF), has recently emerged as the subject of increasing interest. Here, holey 2 D Mn₂ O₃ nanoflakes were obtained by a facile thermal treatment of a Mn-based metal-organic framework (MOF) precursor. The structural and morphological properties of the nanoflakes were characterized by powder XRD, FTIR, SEM and TEM to explore the formation process. It was inferred that the linker loss in the MOF precursor and the oxidation of the Mn cation induced by the heat-treatment in air were responsible for the formation of holey 2 D Mn₂ O₃ nanoflakes. The specific morphology and redox cycle of the Mn cation on the surface endowed the synthesized nanoflakes with promising performance on the selective oxidation. The obtained nanoflakes calcined at 400 °C (M400) afforded over 99.5 % yield of FDCA at complete conversion of HMF, which is superior to the catalytic activity of commercial Mn₂ O₃ and activated MnO₂ . To our knowledge, Mn₂ O₃ exhibiting such a high performance on the aerobic oxidation of HMF to FDCA has not yet been reported. Based on the investigation of the experimental parameters, a plausible reaction mechanism was proposed.

When Will 5-Hydroxymethylfurfural, the "Sleeping Giant" of Sustainable Chemistry, Awaken?

Bring on the subs! Biorefining will be realized by using two different approaches: the production of new biobased molecular targets or sustainable access to traditional base and commodity chemicals. Awakening of 5-hydroxymethylfurfural (HMF) can be expected with different probabilities, depending on the approach chosen to create a sustainable future.

Lipase-Catalyzed Synthesis of Furan-Based Oligoesters and their Self-Assembly-Assisted Polymerization

We investigate the synthesis of bio-based hydrophilic and hydrophobic oligoesters, which in turn are derived from easily accessible monomers from natural resources. In addition to the selection of renewable monomers, Novozyme 435, an immobilized lipase B from Candida antarctica was used for the oligomerization of monomers. The reaction conditions for oligomerization using Novozyme 435 were established to obtain a moderate-to-good yield. The average number of repeating units and the molecular weight distribution of hydrophilic and hydrophobic oligoester were identified by using NMR spectroscopy, gel-permeation chromatography, and MS. The oligoester derived from a hydrophilic monomer self-assembled to form a viscous solution, which upon further heating resulted in the formation of a polymer by the intermolecular Diels-Alder reaction. The viscosity of the solution and the assembly of oligoester to form a fibrous structure were investigated by using rheological studies, XRD, and SEM. The molecular weight of the cross-linked polymer was identified by using matrix-assisted laser desorption/ionization-MS. The thermal properties of the bio-based polymers were investigated by using thermogravimetric analysis and differential scanning calorimetry. For the first time, the self-assembly-assisted polymerization of an oligoester is reported using the intermolecular Diels-Alder reaction, which opens a new avenue in the field of polymer science.

Ruthenium Supported on High-Surface-Area Zirconia as an Efficient Catalyst for the Base-Free Oxidation of 5-Hydroxymethylfurfural to 2,5-Furandicarboxylic Acid

Several ZrO₂ -supported ruthenium catalysts were prepared and utilized in the oxidation of 5-hydroxymethylfurfural (HMF) to 2,5-furandicarboxylic acid (FDCA) under base-free conditions. Full conversion of HMF and almost perfect selectivity towards FDCA (97 %) were achieved after 16 h by using pure O₂ as an oxidant and water as a solvent. The catalytic tests show that the size of the Ru particles is crucial for the catalytic performance and that the utilization of high-surface-area ZrO₂ leads to formation of very small Ru particles. Superior activity was obtained for catalysts based on ZrO₂ that had been synthesized by a surface-casting method and has high surface areas up to 256 m²  g^-1 . In addition to good activity and selectivity, these catalysts show also high stability and constant activity upon recycling, confirming the suitability of Ru/ZrO₂ in the base-free oxidation of HMF.

Photocaged Competitor Guests: A General Approach Toward Light-Activated Cargo Release From Cucurbiturils

A general approach toward the light-induced guest release from cucurbit[7]uril by means of a photoactivatable competitor was devised. An o-nitrobenzyl-caged competitor is photolyzed to generate a competitive guest that can displace cargo from the host macrocycle solely based on considerations of chemical equilibrium. With this method the release of terpene guests from inclusion complexes with cucurbit[7]uril was demonstrated. The binding of the herein investigated terpenes, all being lead fragrant components in essential oils, has been characterized for the first time. They feature binding constants of up to 10⁸  L mol^-1 and a high differential binding selectivity (spanning four orders of magnitude for the binding constants for the particular set of terpenes). By fine-tuning the photoactivatable competitor guest, selective and also sequential release of the terpenes was achieved.

Smart, Sustainable, and Ecofriendly Chemical Design of Fully Bio-Based Thermally Stable Thermosets Based on Benzoxazine Chemistry

A smart synthetic chemical design incorporating furfurylamine, a natural renewable amine, into a partially bio-based coumarin-containing benzoxazine is presented. The versatility of the synthetic approach is shown to be flexible and robust enough to be successful under more ecofriendly reaction conditions by replacing toluene with ethanol as the reaction solvent and even under solventless conditions. The chemical structure of this coumarin-furfurylamine-containing benzoxazine is characterized by FTIR, (1) H NMR spectroscopy and two-dimensional (1) H-(1) H nuclear Overhauser effect spectroscopy (2D (1) H-(1) H NOESY). The thermal properties of the resin toward polymerization are characterized by differential scanning calorimetry (DSC) and the thermal stability of the resulting polymers by thermogravimetric analysis (TGA). The results reveal that the furanic moiety induces a co-operative activating effect, thus lowering the polymerization temperature and also contributes to a better thermal stability of the resulting polymers. These results, in addition to those of natural renewable benzoxazine resins reviewed herein, highlight the positive and beneficial implication of designing novel bio-based polybenzoxazine and possibly other thermosets with desirable and competitive properties.

Synthesis of Bis(hydroxylmethylfurfuryl)amine Monomers from 5-Hydroxymethylfurfural

We report the synthesis of bis(hydroxylmethylfurfuryl)amine (BHMFA) from 5-hydroxymethylfurfural (5-HMF) by reacting 5-HMF with primary amines in the presence of homogeneous Ru(II) catalysts having sterically strained ligands. BHMFA is a group of furan-based monomers that offer great potential to form functional biopolymers with tunable properties. A range of primary amines, such as aliphatic and benzyl amines, are readily converted with 5-HMF to form the corresponding BHMFA in good yields. The reaction proceeds through reductive amination of 5-HMF with primary amine to form secondary amine, followed by reductive amination of 5-HMF with in situ generated secondary amine to produce BHMFA.