Search

Ideonella sakaiensis PETase (IsPETase) is a unique polyethylene terephthalate (PET) hydrolase that displays great potential for mitigating PET waste at moderate temperatures. Although IsPETase exhibits greater specific activity towards PET, rapid activity loss limits its commercial application. Herein, semi-saturation mutation was carried out to stabilize the most flexible region in IsPETase and a thermostable S92P/D157A variant with a Tm value of 70.8 °C (ΔTm = 24.1 °C) was constructed, which enabled a 109.3-fold increase in products released from amorphous PET depolymerization at 40 °C. The further depolymerization of untreated post-consumer PET obtained 17.34 mM products (95.0% TPA). The crystal structure indicated that the "wobbling" W156 residue in IsPETaseWT was fixed in the substrate-binding conformation in the S92P/D157A variant, which contributed to an increase in thermostability and could provide steady interaction with the substrate. Previous studies emphasized that the W156 residue exhibiting a "wobbling effect" is critical to substrate binding, while the different structure–function relationship of the S92P/D157A variant indicated that the wobbling of W156 may not be a pre-requisite for efficient PET biodegradation. Instead, engineering PET hydrolases for fixing the conserved W156 residue in the substrate-binding conformation was proposed. The S92P/D157A variant exhibited a preference for PET in the gauche conformation, which is consistent with its efficiency towards the degradation of low crystallinity PET, further cementing the importance of conformation selection and providing complementary evidence for the function of the fixed W156 residue in PET binding and catalytic processes. Collectively, our results could contribute to the understanding and engineering of more effective PET hydrolases, promoting the industrial application of the enzymatic PET recycling process. [ABSTRACT FROM AUTHOR]

The reaction of cellulose with CO2 in the presence of various organic superbases resulted in a novel CO2 derivative dissolution strategy for cellulose, presenting a special solvent system for cellulose dissolution processing and derivatization. The properties of the cellulose solution are important for the preparation of particular regenerated materials via dissolution processing. Herein, properties of the cellulose solution in a CO2/1.8-diazabicyclo[5.4.0]undec-7-ene/dimethyl sulfoxide (CO2/DBU/DMSO) solvent system were first systematically studied, and it was found that the apparent viscosities of cellulose solutions were highly dependent on the cellulose type, concentration and temperature. The overlap concentrations (c*) were determined to be 2 and 0.6 wt% for the microcrystalline cellulose (MCC) and wood pulp solutions, respectively. The Cox–Merz rule was valid for cellulose solutions in the CO2/DBU/DMSO solvent system. Furthermore, taking advantage of the reversible chemistry of CO2 in this solvent system, a reversible CO2-controlled sol–gel transition of the newly achieved cellulose solution in CO2/DBU/DMSO was identified by dynamic rheology of measuring the temperature dependence of storage modulus (G′) and loss modulus (G′′). Furthermore, the interesting CO2-controlled sol–gel transition was developed via integrated thermal-induced CO2 release and anti-solvent extraction for the preparation of regenerated cellulosic gel materials and then cellulose films with a tensile strength of 44.3 MPa. Interestingly, it was found that the regenerated cellulose through this approach turned out to be a cellulose IVI crystalline structure. [ABSTRACT FROM AUTHOR]

Cellulose nanocrystals (CNC) have attracted great attention due to their excellent physical properties, abundant functional groups, and extensive use in many fields. However, how to facilely and efficiently prepare CNC and utilize the cellulosic raw materials comprehensively are still major challenges. Herein, a comprehensive utilization strategy of cellulose is implemented by facile, high-yield, controllable CNC preparation and effective enzymatic hydrolysis of the cellulosic residue. CNC with a mixed crystal form of cellulose I and cellulose II was successfully prepared through the partial dissolution of cellulose in an aqueous tetrabutylphosphonium hydroxide (TBPH) solution under mild conditions followed by regeneration, short-term ultrasonic dispersion, resulting in a high CNC yield of up to 72.2%, high crystallinity of up to 72.1%, and tunable dimensions and crystal structure of CNC. The characterization results confirmed that the present method produced a nonderivative form of cellulose and changed its crystalline structure to varying degrees, and CNC exhibited thermal stability comparable to that of the raw materials. A partial dissolution/regeneration/ultrasonic dispersion mechanism was proposed for this CNC preparation process. Cellulose residue obtained from the CNC production process led to a high enzymatic hydrolysis rate of up to 89.1%, which was twice as high as that of the raw material. The overall process finally resulted in a comprehensive cellulose utilization rate of more than 95%. The present strategy provides a candidate approach for the comprehensive utilization of cellulose through the synchronous production of advanced high-performance materials and fine chemicals. [ABSTRACT FROM AUTHOR]

Recycling spent cathodes from Li-ion batteries (LIBs) is an appealing route to address environmental issues and resource shortage, but is plagued by effective and simple recycling techniques. Current recycling technologies generally involve multi-steps such as acid leaching, precipitation, smelting, or solid-state sintering, and obtained products possess inferior electrochemical properties. The current work explores a new regeneration method for failed LiCoO2 cathode material. The electrochemical performance of LiCoO2 is fully recovered through a single thermal-chemical treatment of spent LiCoO2 in molten LiOH–KOH–Li2CO3 under air atmosphere. The molten salt mixture presents suitable dissolving capacity, homogeneous thermal circumstance, abundant Li+, and high ion diffusion rate to decompose impurities, compensate for Li+ deficiency, and repair damaged structure through a "dissolution-recrystallization" mechanism. Under the optimized reaction temperature of 500 °C, the regenerated LiCoO2 possessed similar stoichiometric composition and crystalline structure of commercial LiCoO2. Importantly, the discharge capacity of spent LiCoO2 was recovered from 68.3 mA h g−1 to 144.5 mA h g−1, reaching the original level of commercial LiCoO2. Besides, the regenerated LiCoO2 also delivered superior cycling of 92.5% capacity retention after 200 cycles and excellent rate performance. This work presents an effective and extendable approach to regenerate spent cathode materials to retrieve their electrochemical performance. [ABSTRACT FROM AUTHOR]

Selective and green conversion of chitin to levulinic acid (LA) has been realized by the catalysis of the ionic liquid (IL) 1-methyl-3-(3-sulfopropyl)imidazolium hydrogen sulfate ([C3SO3Hmim]HSO4) up to a yield of 67.0%. The relationship between the structure of IL and the yield of LA was investigated, demonstrating that both acidity and the hydrogen bonding ability of IL dictate its catalytic activity. Furthermore, by means of NMR, IR, SEM, GPC analyses and determination of the degree of acetylation (DA), two approaches of deacetylation–depolymerization to glucosamine (GlcN) and direct depolymerization to N-acetylglucosamine (GlcNAc) were proposed as chitin hydrolysis mechanisms, which occur only at the outer surface while leaving the interior crystalline chitin intact. The N-acetyl groups in chitin construct strong intramolecular and intermolecular hydrogen bond networks that contribute to the integration of the crystalline structure and building up of barriers to shield the accessibility of glycosidic linkages with the acidic catalyst. [ABSTRACT FROM AUTHOR]

The crude chitin deacetylase (a novel bacterial CDA) with a molecular mass of approximately 31 kDa was produced by culturing the bacteria of Acinetobacter schindleri MCDA01. The produced CDA was directly applied to surface deacetylation of crab shell α-chitin. For enzyme production, a maximum total enzyme activity of 150.09 ± 1.66 U mL−1 was achieved through submerged fermentation following 72 hours of incubation. Increased enzyme activity was observed with EDTA and metal ions of Fe3+, Ba2+, Sr2+, K+, Na+ and Li+, while enzyme activity was inhibited by Co2+ or Cd2+. The degree of deacetylation (DDA) was increased from 6.46% to 30.58% when the chitin was treated by 12 000 U of CDA at 30 °C and pH 7.0 for 96 h. The high crystallinity of original chitin was maintained, with yield greater than 90% after enzymatic deacetylation, indicating that the CDA deacetylation occurred on the surface of crystalline chitin fibrils without destroying the crystal structure. The chitin nanofibers (CDA-ChNs) were obtained with widths mostly between 25 and 45 nm and lengths of more than several micrometers by sonication of the CDA-treated surface-deacetylated chitin (CDA-Ch) aqueous suspensions at pH 3–4. The application of bacterial CDA on chitin provides a new path to the biorefinery of chitin nanofibers, and the resulting CDA-ChNs might exhibit advanced performance in forming multifunctional materials because of their unique fiber size and high aspect ratio. [ABSTRACT FROM AUTHOR]

The accumulation of solid waste due to rapid industrialization has a negative impact on the environment. In this study, ZnS-containing waste from the mining-metallurgy industry was utilized for the synthesis of trigonal ZnIn2S4 layered crystals by a flux method using various binary fluxes: CaCl2 : InCl3, SrCl2 : InCl3, BaCl2 : InCl3, NaCl : InCl3, KCl : InCl3, and CsCl : InCl3. Among the binary fluxes used, KCl : InCl3 was found to be the most favorable for the synthesis of phase-pure trigonal ZnIn2S4 layered crystals. The XRD and SEM results revealed that the flux-grown ZnIn2S4 crystals have a trigonal structure and a morphology composed of large stacked layers. Unexpectedly, the UV-vis diffuse reflectance spectrum exhibited the onset of the absorption edge at approximately 700 nm for trigonal ZnIn2S4 crystals. The photocatalytic activities for H2 production of the Pt-photodeposited ZnIn2S4 samples grown using CaCl2 : InCl3, NaCl : InCl3, and KCl : InCl3 fluxes were evaluated. Trigonal ZnIn2S4 crystals grown using the KCl : InCl3 flux in this study exhibited higher photocatalytic activity for H2 evolution (132 μmol h−1) than previously reported hexagonal ZnIn2S4 synthesized by a hydrothermal method due to the decreased defect density and higher crystallinity achieved by the binary flux method. The presence of secondary crystalline phases (ZnS and In2S3) in ZnIn2S4 crystals grown using NaCl : InCl3 and CaCl2 : InCl3 fluxes positively impacted the photocatalytic activity and exhibited photocatalytic H2 evolution rates of 188 and 232 μmol h−1, respectively, because of the efficient separation and transfer of photogenerated charge carriers. The decay of the transient absorption of electrons in three samples at 2000 cm−1 was monitored by transient absorption spectroscopy, confirming that the lifetime of free electrons becomes longer depending on the binary flux used: KCl : InCl3 ＜ NaCl : InCl3 ＜ CaCl2 : InCl3. The binary flux method applied in this study demonstrates that accumulated solid industrial wastes can be turned into beneficial photocatalytic materials. [ABSTRACT FROM AUTHOR]

Global phosphorus (P) should be managed more sustainably to secure food, energy, and water for a growing population. Despite the abundance of calcium in most environments, we have not fully utilized its thermodynamic stability to form calcium phosphate minerals (CaP) for aqueous P management. In this study, we showed that the energy barriers to CaP nucleation can be reduced by seeding reactive CaP nuclei in calcium alginate beads. The CaP nucleation kinetics enhanced by seeds effectively immobilized aqueous P into the macroscale beads, which can be reused as a slow-release fertilizer. Given that more developed CaP crystalline seeds have a lower solubility than does an amorphous structure, equilibrium P concentration was regulated successfully by the seed crystallinity during both the removal and release processes. A simultaneous seed nucleation during alginate gelation enabled control of the degree of the seeds’ crystallization without using any hazardous substance or additional energy input. Poorly crystalline hydroxyapatite CaP seeds effectively decreased aqueous P concentration from 200 to 22.7 μM within one day at a final pH 7.2 (96.4 mg P g−1 dry seed). After P recovery, the beads were moved to a P-deficient environment to be evaluated as a slow-release fertilizer. Utilizing the thermodynamic stability of CaP at neutral pH, this approach highlights a potential application of naturally abundant biomaterials for sustainable P management. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

The utilization of cellulose and its integration in a biorefinery concept is essential even in the near future due to the growing global shortage of crude oil. Here, we report the catalyzed one-pot hydrogenolysis of cellulosic materials to valuable bio-derived molecules, especially polyols (e.g. ethylene glycol). We demonstrate how a very promising bifunctional catalyst, Ru/W/AC, converted not only 100% of microcrystalline cellulose to polyols in repeated experiments with a maximum yield of 84% and an ethylene glycol productivity of 3.7 g (gcatalyst h)−1, but also pine-, birch-, and eucalyptus-derived materials. Moreover, we systematically investigated the problem of catalyst stability with time by studying the changes in both the catalyst structure and the liquid phase, which have often been overlooked when biomass is converted to fuels and chemicals. Control of the active sites for the conversion of cellulosic feedstocks coupled with reaction engineering and strategies to prevent catalyst deactivation, is a prerequisite to understanding how high yields of platform chemicals can be achieved. [ABSTRACT FROM AUTHOR]

In this work, we report that combination of levulinate as a renewably sourced anion with short chain alkyl ammonium as a cation yields room temperature ionic liquids that are capable of dissolving up to 10 wt% of microcrystalline cellulose. This dissolution results in a change of the cellulose crystalline structure from cellulose I to cellulose II, a pre-requisite step known to significantly improve the accessibility of cellulose to enzymes. As compared to previous methodologies, such ILs tolerate the presence of up to 18 wt% of water. Hence technical grade ILs can be used, thus avoiding the energy-consuming drying process generally required with traditional ILs before dissolution experiments. In addition, such ILs can be mixed with 20 wt% of γ-valerolactone, a renewably-sourced co-solvent, resulting in an improvement of the cellulose dissolution up to 20 wt% while concomitantly increasing the sustainability of these media. Finally, prepared ILs were proved to be biodegradable according to the OCDE 301F directive, thus opening a promising route for the pre-treatment of cellulose with a higher eco-efficiency. [ABSTRACT FROM AUTHOR]

γ-Valerolactone (GVL) and 1,4-pentanediol (1,4-PDO) are value-added chemicals that can be produced from levulinic acid/ester via hydrogenation coupled with acid/base-catalyzed reactions. In this study, we demonstrate that the Cu-based catalysts produced via the hydrotalcite precursors with tunable distribution of acidic and basic sites could, according to the requirement of the target products, effectively tune the production of GVL or to 1,4-PDO from levulinic acid/ester. The abundant Brønsted acid sites over the CuAl catalyst suppressed the opening of the ring of GVL, achieving a higher GVL selectivity while inhibiting 1,4-PDO formation. The introduction of Mg species to the catalyst significantly increased the abundance of the basic sites on the surface of the catalyst, which was essential for the selective conversion of GVL to 1,4-PDO via the opening of the ring structure of GVL, the rate-determining step in the conversion from levulinic acid/ester to 1,4-PDO. In addition, the CuMgAl catalyst showed a much superior catalytic stability to the CuMg or CuAl catalyst due to the more stable crystal structure, the more developed porous structure, the higher dispersion of the Cu species and the higher capability to suppress the growth of metallic Cu species under hydrothermal conditions. [ABSTRACT FROM AUTHOR]

We report a simple route to produce chitin films with different crystalline structures. The use of a green deep-eutectic-solvent (DES) choline chloride : urea (CCU) or hexafluoroisopropanol (HFIP) allows fine-tuning of the crystallization process to produce films with β-dihydrated- or γ-chitin structures. With the advent of a Grazing-Incidence X-Ray Diffraction (GIXD) technique, we propose a new and fully indexed structure of γ-chitin. This new γ-structure is modeled as a super-cell, in contrast to the idea of a simple physical mixture of α and β phases. The influence of purification, dissolution or dispersion media on chitin's crystallinity was investigated by FTIR, solid-state NMR and XRD. Results presented here may trigger applications in which a well-defined crystalline structure is required. [ABSTRACT FROM AUTHOR]

We report a facile, green and generalized method of endogenous growth of 2D boehmite nanosheets (ns) on a 3D network using Al-fibers through oxidation reaction between the Al metal and H2O (2Al + 4H2O = 2AlOOH + 3H2). Such Al-fiber@ns-AlOOH composites have substantial potential applications for microfibrous-structured catalysts and catalytic reactors, being verified by several hot-topic reactions such as CO oxidative coupling to dimethyl oxalate. [ABSTRACT FROM AUTHOR]