RSC sustainability最新文献

We present the use of an ultraporous permanently polarized hydroxyapatite (upp-HAp) catalyst for continuous and highly efficient production of formic acid (predominant) and acetic acid using wet CO₂ (i.e. CO₂ bubbled into liquid water) as a reagent. In all cases, reactions were conducted at temperatures ranging from 95 to 150 °C, using a CO₂ constant flow of 100 mL s⁻¹, and without applying any external electric field and/or UV radiation. Herein, we study how to transfer such a catalytic system from batch to continuous reactions, focusing on the water supply (proton source): (1) wet CO₂ or (2) liquid water in small amounts is introduced in the reactor. In general, the reduction of CO₂ to formic acid predominates over the C–C bond formation reaction. On the other hand, when liquid water is added, two interesting outcomes are observed: (1) the yield of products is higher than in the first scenario (>2 mmol g_c⁻¹·min⁻¹) while the initial liquid water remains largely available due to the mild reaction temperature (95 °C); and (2) a high yield of ethanol (>0.5 mmol g_c⁻¹·min⁻¹) is observed at 120 °C, as a result of the increased efficiency of the C–C bond formation. Analysis of kinetic studies through temporal and temperature dependence shows that CO₂ fixation is the rate limiting step, ruling out the competing effect of proton adsorption on the binding sites and confirming the crucial role of water. The activation energy for the CO₂ fixation reaction has been determined to be 66 ± 1 kJ mol⁻¹, which is within the range of conventional electro-assisted catalysts. Finally, mechanistic insights on the CO₂ activation and role of the binding sites of upp-HAp are provided through isotopic-labeling (¹³CO₂) and near-ambient pressure X-ray photoelectron spectroscopy (NAP-XPS) studies.

Different lignins, differing in their botanical origin or the extraction method, were subjected to aerobic catalytic depolymerisation in basic aqueous media using a copper-based catalyst (CuO/TiO₂) towards aromatic compounds. Lignins were obtained from different kinds of biomass, including hardwood, softwood and wheat straw, and using different extraction methods such as kraft, soda or organosolv. Extensive characterization (elemental analysis; ¹H, ¹³C, ³¹P and HSQC NMR; FTIR-ATR; DLS and SEC) revealed structural differences between lignin samples. For example, organosolv softwood lignin shows a higher degree of β-O-4 linkages, while organosolv wheat straw lignin presents higher structural degradation. These changes resulted in differences during the catalytic aerobic depolymerisation. The structural properties were correlated with the reaction results. Thus, the average molecular weight is directly related to the observed degree of conversion, and the β-O-4 content is correlated with the yields of aromatic compounds obtained. It was also observed that the catalytic effect of the CuO/TiO₂ catalyst is more pronounced when the non-catalytic reaction shows low yields of aromatics. Finally, despite higher reactivity, hardwood lignin did not produce high yields of aromatic compounds due to the rapid degradation of the products.

Much research is currently focused on designing functional materials derived from sterculia gum (SG) for sustainable development. Herein, poly(vinylsulfonic acid) (poly(VSA) and poly(vinyl pyrrolidone) (PVP) was grafted onto SG to form semi-interpenetrating network (semi-IPN) hydrogels for use in a drug-delivery (DD) system for doxycycline and in hydrogel wound dressings (HWDs). The hydrogels were characterized using FESEM, EDS, AFM, FTIR spectroscopy, ¹³C-NMR, and XRD. A range of biomedical properties were assessed by evaluating the interactions of the hydrogels with blood, mucosal tissues, and drugs. In the FTIR analysis, bands were observed at 1288 and 1149 cm⁻¹ due to asymmetric and symmetric stretching of SO₂ of poly(VSA) along, while in the ¹³C-NMR analysis, a peak at 63.21 ppm was noted due to a carbon attached to a sulfonic acid group of poly(VSA), confirming the polymerization reactions. The hydrogels were found to be biocompatible (hemolysis analysis = 2.54 ± 0.02%) and mucoadhesive (detachment force = 91.0 ± 8.0 mN). The semi-IPN HWDs exhibited antioxidant and antimicrobial properties. The dressings were permeable to oxygen and water vapor but impermeable to microbes. The diffusion mechanism of doxycycline from the dressings was found to follow a non-Fickian mechanism. The release profile could be best described by the Higuchi kinetic model. Overall, these properties revealed that the drug-encapsulating hydrogels could be applied as materials for DD and wound dressing.

Effective pretreatment of ligno-hemicellulosic biomass has emerged as a pre-requisite for its efficient conversion into biogas through the anaerobic digestion (AD) process. Assessment of various pre-treatment methods shows microbial pretreatment to be the most promising, economically viable, and environment-friendly option. Microbial pretreatment offers the advantages of low energy consumption and minimal pollution generation, thus making it a promising avenue for enhancing biogas yields from biomass. Fungi and bacteria, along with their enzymes, play pivotal roles in this method. Fungal pretreatment, involving cellulose and lignin-degrading species like brown-rot and white-rot fungi, have shown improved biogas yield. Bacterial and enzymatic pretreatments offer quicker results, making them attractive options for shortening the reaction time. Microbial consortia have shown remarkable efficiency in biomass degradation and its anaerobic digestion under thermophilic conditions. Physical pretreatment methods, such as mechanical size reduction, have shown potential to increase biomass accessibility and enhance biogas production. However, due to its energy-intensive nature and for improving biogas yields, further research is needed to develop more cost-effective approaches. The combination of physical and biological pretreatment methods offers a promising approach to effectively pretreat ligno-hemicellulosic biomass for improved biogas production.

The efficiency of hydrogen production from solar water splitting can be substantially increased by adding natural lignocellulosic feedstock as a sacrificial agent in the process. However, the efficiency of the hydrogen yield from photoreforming (PR) natural lignocellulosic feedstock is still far from that of model compounds. In this paper, we report a new pathway for boosting H₂ yield by simply applying a commercial SrTiO₃ catalyst in PR processes following thermo-alkaline hydrolysis acidizing (TAH-A), thermo-alkaline hydrolysis reversed-phase (TAH-RP) filtration, and two-stage thermo-alkaline hydrolysis (TS-TAH) pretreatment. The efficiency of the hydrogen yield from PR natural lignocellulosic feedstock was significantly improved through all the pretreatments. The greatest enhancement was found for TS-TAH corn stover, where the hydrogen yield reached 4.7 μmol, which is 2.3 times higher than that of TAH-RP filtration. The advantage was attributed to the elimination of most of the lignin from the corn stover following the TS-TAH. This greatly restrained the light-absorbing effect of lignin from the lignin-TAH-PR system, and more light energy was applied to excite the catalyst for H₂ evolution. This featured finding potentially provides a feasible method for in-depth utilization of natural lignocellulosic feedstocks in PR hydrogen production technology.

Efforts towards developing biobased chemicals primarily focus on generating molecules chemically analogous to those derived from petroleum. The compositional uniqueness of biomass can also be leveraged to reinvigorate the chemical industry with novel multifunctional molecules. We demonstrate the value and potential of these new compounds in the case of Nylon-66, a commodity polyamide that suffers from poor flame resistance. The conventional route to inhibit flammability involves blending the polymer with additives, which improves flame retardance but has mechanical property trade-offs. Herein, we address these limitations through the synthesis of a novel multifunctional comonomer derived from renewably sourced trans-3-hexenedioic acid (t3HDA). t3HDA was subjected to a one-pot isomerisation and functionalisation strategy where the alkene migrates to render this molecule active for phospha-Michael-addition (MA) with 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO), a halogen-free flame-retardant (FR). This DOPO-functional counit was polymerised into Nylon-66 copolymers and compared with physical blends of DOPO and Nylon-66 using a suite of thermomechanical techniques; analysis revealed comparable crystallinity, flame retardance, and thermomechanical properties for the DOPO-functionalised bio-advantaged polyamides. The synthesis strategy presented herein can be extended to a variety of functional groups and novel properties, a platform for creating bespoke bio-advantaged polymers.

This study presents the successful synthesis and characterization of five novel zinc oxide quantum dots @ bis MPA polyester-64-hydroxyl dendrimer nanostructures with tuneable hydrophilicity. A unique feature of these ZnO quantum dots @ bis MPA polyester-64-hydroxyl dendrimer nanostructures is the functionalization of the bis MPA polyester-64-hydroxyl dendrimer with five different varying numbers of surface hydroxyl functional groups with zinc oxide quantum dots. The surface groups varied from 1, 5, 10, 20 and 40 zinc oxide quantum dots in ZnO-QDs @ bis MPA polyester-64-hydroxyl dendrimer nanostructures, respectively. The highly water-dispersible ZnO quantum dots @ bis MPA polyester-64-hydroxyl dendrimer nanostructures G4-R(ZnO-QDs)₁, G4-R(ZnO-QDs)₅, G4-R(ZnO-QDs)₁₀, G4-R(ZnO-QDs)₂₀ and G4-R(ZnO-QDs)₄₀ were chemically synthesized. The ZnO-QDs @ bis MPA polyester-64-hydroxyl dendrimer nanostructures were characterized using techniques such as UV-vis-NIR spectroscopy, atomic force microscopy, dynamic light scattering, attenuated total reflectance Fourier transform infrared spectroscopy, and Raman spectroscopy. Notably, these ZnO quantum dots @ bis MPA polyester-64-hydroxyl dendrimer nanostructures exhibited high water-dispersibility. A significant finding is that the unique feature of ZnO quantum dots @ bis MPA polyester-64-hydroxyl dendrimer nanostructures demonstrated synergistic antibacterial activity against Gram-positive bacteria. This research contributes to the growing field of nanotechnology by providing a method to tune the hydrophilicity, optical properties, molecular vibration, size and toxicity of nanostructures, which could have broad impacts on various scientific and technological domains.

For extremely efficient bioethanol production, simultaneous pretreatment, saccharification, and fermentation in the same reaction pot (called a one-pot process) is necessary. Thermotolerant yeast Kluyveromyces marxianus can ferment at around 50 °C and is thus suitable for this process. We have developed cellulose-dissolving zwitterionic liquids, which are suitable pretreatment solvents to enable a one-pot process. On the other hand, there are no studies of the toxicity to yeasts including Kluyveromyces marxianus. We here studied the toxicity after establishing the screening methods applicable to high temperature. The zwitterion was confirmed to be low-toxic in most cases, compared to the most famous cellulose-dissolving ionic liquid. We further subjected two natural zwitterions, trimethylglycine and L-carnitine, to the same screening. Trimethylglycine, especially, was low-toxic, while it does not dissolve cellulose. The inhibition of growth and fermentation depended on the ion species, concentration, microorganism species, and temperature.

Renewable polyesters with a good balance between impact strength and elastic modulus (stiffness) are not very common, especially when combined with high glass transition temperature (T_g). Achieving such high performance properties would enable the substitution of high performance polymers like ABS and polycarbonate with chemically recyclable polyesters from bio-based or recycled sources. One of the challenges in developing these materials is to select the right composition of the right monomers/comonomer ratios and making these materials with high molecular weight, which can be challenging since some of the most promising rigid diols, such as isosorbide, are unreactive. This study comprises aromatic polyesters from (potentially) renewable monomers, using bio-based isosorbide as a means to increase their T_g and to inhibit their crystallization, while using flexible co-diols to improve impact strength. To incorporate a high amount of isosorbide into the targeted polyesters, we used the synthesis method with reactive phenolic solvents previously developed in our group. The selected compositions display high T_g's (>90 °C) and high tensile modulus (>1850 MPa). We show that more polar monomers such as the stiffer 2,5-furandicarboxylic acid (FDCA) and diethylene glycol cause high stiffness but decreased impact strength (<5 kJ m⁻²). Combining terephthalic acid and isosorbide with more flexible diols like 1,4-butanediol, 1,4-cyclohexanedimethanol (CHDM) and 1,3-propanediol provides a better balance, including the combination of high tensile modulus (>1850 MPa) and high impact strength (>10 kJ m⁻²).

Chemical recycling is of paramount importance to minimise the environmental impact of plastic waste. Polyethylene terephthalate (PET) is a polar thermoplastic widely used in fibres and packaging and is amenable to chemical depolymerisation. Recent efforts are devoted to its degradation via glycolysis. Even though it requires milder conditions than hydrolysis, catalysts are still necessary. In this case, ionic liquids (ILs) come into play to catalyse the reaction. In particular, we focus on choline-based liquids due to their low toxicity and cost compared to imidazolium-based ones. However, due to the complexity of the process, detailed information on the operating mechanism is scarce, which hinders the progress towards a rational design of new and more efficient systems. Herein, we present a computational study to address the role of IL catalysts during PET glycolysis under realistic catalytic conditions, i.e., considering time, concentration, and temperature. We perform classical molecular dynamics (MD) simulations on several systems, including a complex ternary mixture formed by ethylene glycol (EG), PET oligomers, and the [Ch]₃[PO₄] catalyst. By means of radial/spatial distribution functions, H-bond analysis, and domain count, we present a detailed solvation scenario of the catalytic system. Our findings suggest that the IL anion (and the IL cation to a lesser extent) does participate in the nucleophilic activation of EG, while the IL cation does not play a significant role in the electrophilic activation of PET.