Elaine Gabutin Mission

Natural biopolyesters in the form of suberin could be a promising resource for the synthesis of a wide array of chemicals, fuels and materials. However, access to this molecule is limited by a chemical-intensive and laborious work-up procedure based on alkaline hydrolysis or methanolysis. Herein, we propose the ultrafast supercritical hydrolysis as a novel and scalable approach for the facile access to suberin from cork. Supercritical water (SCW) with high or low ionic properties (pK_w of 13 and 15) would allow the liquefaction of lignocellulosic materials while avoiding the hydrolysis of ester linkages. Therefore, extractives and carbohydrates partition in aqueous products while suberin and lignin are enriched in the solid products. Suberin yield reached as high as 66.6% of the dry cork at 386 °C and 1.27 s (pK_w = 13), owing to the removal of up to 94.7% of polysaccharides content of the original cork biomass. The occurrence of repolymerization reaction, however, was observed under this condition, including an increase in Klason lignin presumably due to pseudo-lignin formation. Meanwhile, lower repolymerization products accompanied by a 77.1% polysaccharides and 14% lignin removal was achieved when working at 395 °C and 0.25 s (pK_w = 15), at the expense of lower suberin yield of 59.8%. It appears that even a longer reaction time of 1.27 s would not lead to hydrolysis of ester linkages in suberin but influences the extent of liquefaction of the lignocellulosic matrix and the formation of repolymerization products. A lower ion product and a reaction time of less than 1 s would be preferable to strike a balance between maximum polysaccharides removal and minimum repolymerization products generation. This study has contributed towards the development of a new sustainable process to access valuable molecules from cork and has highlighted the importance of obtaining high quality and highly functionalized biopolymers as a source of new building blocks.

Water electrolysis is an environment-friendly process of producing hydrogen with zero-carbon emission. Herein, we studied the water vapor electrolysis using a proton-conducting membrane composed of graphene oxide (GO) nanosheets intercalated with cations (Al³⁺ and Ce³⁺). We examined the effect of cation introduction on the physical and chemical structures, morphology, thermal and chemical stabilities, and the proton conductivity of stacked GO nanosheet membranes by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), X-ray photoemission spectroscopy (XPS), Raman spectroscopy, atomic force microscopy (AFM), dynamic light scattering (DLS), thermogravimetric-differential thermal analysis (TG-DTA), and electrochemical impedance spectroscopy (EIS). Concentration cell measurements revealed that the cation-modified membranes are pure proton conductors at room temperature. The proton conductivity of a GO membrane was much improved by cation modification. The cation-modified GO membranes, sandwiched with Pt/C electrodes as the cathode and anode, electrolyzed humidified air to produce hydrogen at room temperature, indicating the feasibility of this carbon-based electrochemical device.

Biomass valorization involves breaking down naturally occurring long chain polysaccharides into their constituent monomers. The polysaccharide chain consists of monomers adjoined via C (carbon)–O (oxygen) glycosidic linkages that are typically cleaved via hydrolytic scission. In this study, we aimed to recover fucose from the polysaccharide fucoidan, which can be extracted from seaweed biomass. We investigated the depolymerisation behavior of fucoidan sourced from two different species of seaweeds, namely Undaria pinnatifida (F-UP) and Fucus vesiculosus (F-FV). Catalytic depolymerisation experiments were performed using four different carbon-based catalysts – graphene, multiwalled carbon nanotubes (MWCNT), graphene oxide (GO), and reduced graphene oxide (rGO) – under microwave (MW) irradiation. Our results showed that the depolymerisation of fucoidan was best achieved using GO, which was attributed to the abundance of oxygen functionalities on its surface. Furthermore, based on gel permeation chromatography analyses, the depolymerisation of fucoidan was found to follow a two-step process: (1) random scission leading to the production of short-chain oligosaccharides and (2) acid-catalysed hydrolysis of the oligosaccharides to fucose. Because of the longer chain length of F-UP (61 kDa), the highest fucose yield of 17.4% using this species was obtained at a higher temperature of 120 °C in a closed vessel. Meanwhile, in the case of F-FV (1.1 kDa), the highest yield of 54.0% was obtained under reflux conditions at a lower temperature of 104 °C. Our mechanistic study based on semi-empirical quantum calculations also revealed that the recovery of fucose from F-FV is more energetically favoured than from F-UP as a result of their structural differences.

Catalyst design and surface chemistry have long been regarded as the major foundations for the catalytic activity of carbon-based catalysts. However, surface modification of carbon-based catalysts typically involves huge quantities of strong acids that eventually leach into the solution contaminating the target compounds. We have previously demonstrated that the mixture of reduced graphene oxide (rGO) and residual cellulose would generate additional glucose after the first cycle by simply elevating the temperature. In this study, we sought to understand how rGO under microwave (MW)-subcritical water (subH₂O) facilitates the depolymerization of cellulose. It was found out that the MW sensitizing properties of rGO improved, enhancing the electronic transport properties. The partial removal of functional groups has resulted into much smaller particles and formation of nanopores and nanovoids which facilitated the precise cleaving of the glycosidic bonds with glucose yields reaching up to 66 ± 4 wt% in as short as 5 min. The yield highly correlates with the H₃O⁺/OH⁻ concentration and hugely depends on the rGO structure that varies according to the synthesis method, preferably in the absence of water. The depolymerization mechanism takes place via random scission. This study indicates that rGO, in spite of having fewer functionalities than pristine graphene oxide (GO), can still be used for catalysis even without surface modification in combination with MW and subH₂O.

The abundance in hydroxyl groups neighboring the hydrolytic site (β-1,4 glycosidic bonds) in cellulose forms a tightly packed crystalline structure, and hence, is a major challenge in cellulose depolymerization into fermentable sugars. Herein, we report on the synergistic effect of the carbocatalyst, graphene oxide (GO) and microwave irradiation (MW) on cellulose depolymerization in the absence of pretreatment. Results showed that microcrystalline cellulose (MCC) can be effectively depolymerized into glucose in as short as 30 s at 473 K (800 W). Generated yields without pretreatments were as high as 61 ± 4% within 60 min (200 W and 453 K), which has never been reported before to the best of our knowledge. The synergy of GO and MW was demonstrated by high heating rates and which allowed for the activation of in situ crystalline-to-amorphous transformations and suppressed immediate formation of degradation products. The activity of GO under MW was much higher than those of other solid acid catalysts such as Amberlyst 15, sulfated zirconia, and phosphotungstic acid due to the variety of surface functionalities and its high microwave absorptivity. The depolymerization mechanism was also discussed in terms of surface attrition of MCC as observed via scanning electron microscopy. On this basis, the proposed process offers an important strategy for cellulose depolymerization.