Polyethylene terephthalate (PET), as the most widely utilized polyester, causes global environmental problems due to its massive and durable accumulation in natural environments. The glycolysis of PET is an attractive alternative to mechanical recycling, but there remains a strong demand for efficient, convenient, and inexpensive catalysts. Herein, we present a spray-drying-assisted way to construct magnetic hollow micro-sized nanoaggregates (HMNAs) by assembling composite metal oxide nanoparticles to depolymerize PET synergistically. The as-prepared ZnO–Fe3O4 HMNAs completely depolymerized PET with a high monomer yield of 92.3% in a short period of 30 min at 190 °C, far above individual ZnO and Fe3O4 nanoparticles (NPs). The composite HMNAs can be magnetically separated in a few minutes and maintain a high activity for 5 cycles. DFT study reveals that the HMNAs effectively facilitated glycolysis by the high content of Lewis acid sites as well as the stronger adsorption between PET and the catalyst owing to the structural synergy effect of ZnO–Fe3O4 HMNAs. Furthermore, this spray drying strategy as a versatile and scalable methodology is extended to fabricate other HMNAs, exhibiting a similarly enhanced efficiency of glycolysis. The HMNAs are expected to open up avenues for the design of catalysts for upcycling of discarded plastics.
The use of sunlight to initiate free radical polymerization under air is a key challenge. Due to the associated low light intensity, usual or commercial photoinitiators are characterized by a low efficiency. In this work, seventeen carbazole-fused coumarin-based oxime esters were developed as monocomponent and photocleavable (Type I) initiators of polymerization displaying excellent light absorption properties in the visible range. Compared to the benchmark photoinitiator (diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide), some of them (namely OXE-1 and OXE-5) could show photoinitiation performance similar to or better than the reference compound upon irradiation with a LED at 405 nm. The photoinitiation mechanism of these photoinitiators is proposed, supported by theoretical calculations; the detection of CO2 during photopolymerization was performed by means of Fourier transform infrared spectroscopy and the detection of radical species was performed by electron spin resonance analysis. Through direct laser writing, different objects exhibiting an excellent spatial resolution could be obtained. Parallel to the photoinitiating ability, the different photoinitiators also showed a thermal initiation behavior, meaning that these structures can serve both as thermal and photo-initiators on demand. Due to the high sensitivity of these structures to sunlight, OXE-1 and OXE-5 were also investigated as solar photoinitiators (reactive also in Central Europe during winter) and excellent monomer conversions could be obtained within one hour using a multifunctional acrylate monomer (Ebecryl 605). To the best of our knowledge, these two oxime esters constitute the first examples of sunlight activable oxime esters ever reported in the literature.
Hemoproteins have recently emerged as attractive biocatalysts for catalyzing carbene-mediated cyclopropanation, a synthetically valuable reaction not found in nature. In this study, we present a hemoglobin-catalyzed strategy for the highly stereoselective synthesis of nitrile-substituted cyclopropanes. This method offers efficiency and environmental friendliness by utilizing an asymmetric olefin cyclopropanation reaction catalyzed by wild-type Vitreoscilla hemoglobin in the presence of in situ generated diazoacetonitrile. A diverse range of nitrile-substituted cyclopropanes could be synthesized in water with exceptional stereoselectivity, achieving up to 99.9% de and ee and high turnover numbers of up to 3232. By employing this sustainable approach, not only can various chiral nitrile-substituted cyclopropanes be efficiently obtained, but also the practical application of hemoglobin in organic synthesis can be expanded.
Green and nano-structured catalytic media are vital for biocatalysis to attenuate the denaturation tendency of biocatalysts under severe reaction conditions. Hydrotropes with multi-faceted physiochemical properties represent promising systems for sustainable protein packaging. Herein, the ability of adenosine-5′-triphosphate (ATP) and cholinium salicylate ([Cho][Sal]) ionic liquid (IL) to form nano-structures and to nano-confine Cytochrome c (Cyt c) enhanced the stability and activity under multiple stresses. Experimental and computational analyses were undertaken to explain the nano-structured phenomenon of ATP and IL, structural organizations of nano-confined Cyt c, and site-specific interactions that stabilize the protein structure. Both ATP and IL form nano-structures in aqueous media and could cage Cyt c via multiple nonspecific soft interactions. Remarkably, the engineered molecular nano-cages of ATP (5–10 mM), IL (300 mg mL−1), and ATP + IL surrounding Cyt c resulted in 9-to-72-fold higher peroxidase activity than native Cyt c with exceptionally high thermal tolerance (110 °C). The polar interactions with the cardiolipin binding site of Cyt c, mediated by hydrotropes, were well correlated with the increased peroxidase activity. Furthermore, higher activity trends were observed in the presence of urea, GuHCl, and trypsin without any protein degradation. Specific binding of hydrotropes in highly mobile regions of Cyt c (Ω 40–54 residues) and enhanced H-bonding with Lys and Arg offered excellent stability under extreme conditions. Additionally, ATP effectively counteracted reactive oxygen species (ROS)-induced denaturation of Cyt c, which was enhanced by the [Sal] counterpart of IL. Overall, this study explored the robustness of nano-structured hydrotropes to have a higher potential for protein packaging with improved stability and activity under extreme conditions. Thus, the present work highlights a novel strategy for real-time industrial biocatalysis to protect mitochondrial cells from ROS-instigated apoptosis.
Flexible screen-printing technology combined with the use of a nano/material coating for improving electrode functionalities boosted the manufacturing of highly sensitive electrochemical sensors addressing the need for fast and easy-to-handle tests in different application fields. However, due to the large-scale production and disposable and single-use nature of these devices, their environmental footprint should be taken into careful consideration. Herein, the innovative reuse of post-consumer polyethene terephthalate (PET) plastics as an alternative substrate coupled with biochar as an environmentally friendly and cost-effective modifier is described as a sustainable alternative for the production of robust electrochemical sensors. The good printability of reused plastics with graphite inks despite the chemical heterogeneity, different crystallinity, and surface roughness was demonstrated using atomic force microscopy and attenuated total reflection Fourier transform infrared spectroscopy. Functionalization with brewers’ spent grain biochar enabled the fabrication of highly performing electrochemical sensors for nitrite detection in water having a limit of detection and a limit of quantification of 3.3 nM and 10.3 nM, respectively, with a linear range spanning from 0.01 to 500 μM, and good reproducibility (RSD% 8%). The innovative intervention of the biochar-multilayer system markedly enhanced the electron transfer process at the electrode interface while simultaneously serving as an absorptive material for the investigated analyte. This work lays a foundation for repurposing end-of-life plastics for the electronics industry and presents a customizable reuse strategy aimed to keep the value of plastics in the economy and reduce waste and leakage into the natural environment.
Chitin, particularly α-chitin, is the most abundant and highly recalcitrant form, fortified by an intricate network of hydrogen bonds. Efficient valorization of α-chitin requires mild pre-treatment and enzymatic hydrolysis. Streptomyces spp. secrete chitin-active CAZymes that can efficiently tackle the recalcitrant problem of chitin biomass. To better understand the potential of Streptomyces spp., a comparative analysis was performed between the novel isolate, Streptomyces sp. UH6 and the well-known chitin degraders, S. coelicolor and S. griseus. Growth studies and FE-SEM analysis revealed that all three Streptomyces spp. could utilize and degrade both α- and β-chitin. Zymogram analysis showed expression of 5–7 chitinases in the secretomes of Streptomyces strains. The chitin-active-secretomes produced by Streptomyces sp. UH6 and S. griseus were optimally active at acidic pH (pH 4.0 and 5.0) and 50 °C. Time-course degradation of α- and β-chitin with the secretomes generated N-acetyl-D-glucosamine (GlcNAc) and N,N-diacetylchitobiose [(GlcNAc)2] as the predominant products. Further, the highly crystalline α-chitin was subjected to pre-treatment by ball-milling, which reduced the crystallinity from 88% to 56.6% and increased the BET surface area by 3-folds. Of note, the activity of all three Streptomyces secretomes was improved by a mild pre-treatment, while Streptomyces sp. UH6 secretome displayed improved GlcNAc and (GlcNAc)2 yields by 14.4 and 9.6-folds, respectively. Overall, our results suggest that the Streptomyces chitin-active-secretomes, particularly Streptomyces sp. UH6, can be deployed for efficient valorization of chitin biomass and to establish an economically feasible and eco-friendly process for valorizing highly recalcitrant α-chitin.
Polystyrene plastic is a widely used artificial material, but there is still no efficient, economic or environmentally friendly recycling method for waste polystyrene plastic, which has caused serious environmental pollution and a waste of resources. Herein, the method of nitric acid oxidative upgrade is used to convert polystyrene plastic into a high-value chemical raw material, benzoic acid. The yield can reach nearly 90% at 180 °C within 3 h, and the purity of the product is more than 95%. In this process, nitric acid is decomposed by heat to generate nitrogen dioxide and oxygen, which react with the carbon-centered radicals formed at weak sites on the long chain of polystyrene and further generate peroxy radicals and hydroxyl radicals. The formation of oxygen-containing functional groups promoted the fracture of the C–C bond and eventually formed benzoic acid. In addition, this method also has good treatment effects on real-life polystyrene plastic products. This research provides a new method for the recycling and high-value utilization of waste polystyrene plastics. The intrinsic material value of polymers can be maintained by recycling functional chemicals through oxidative upgrade.
The production of advanced biofuels represents a near-term opportunity to decarbonize the heavy vehicle transportation sector. However, important barriers must be overcome and successful deployment of these technologies will require (i) catalyst and process development to reduce cost and improve carbon utilization and (ii) industry-relevant validation of operability to de-risk scale-up. Herein, we seek to address these challenges for an integrated two-step process involving catalytic fast pyrolysis (CFP) followed by co-hydrotreating of bio-oil with refinery streams. Technoeconomic and lifecycle analysis based on the data presented herein reveal the potential to generate low-carbon transportation fuels and chemical co-products with a modelled selling price of $2.83 gasoline gallon equivalent (2016$) and a 78% reduction in greenhouse gas emissions compared to fossil-based pathways. The feedstock for this research was a blend of 50 wt% loblolly pine and 50 wt% waste forest residues, and the CFP step was performed using an ex situ fixed bed of Pt/TiO2 with co-fed H2 at atmospheric pressure. Compared to previous state-of-technology benchmarks, advancements in catalyst design and synthesis methodology enabled a four-fold reduction in Pt loading and a 400% increase in time on stream without negatively impacting upgrading performance. Additionally, a first-of-its-kind integrated assessment of waste gas adsorption showed near quantitative recovery of acetone and 2-butanone, which collectively represent approximately 5% of the biomass carbon. The valorization of these co-products opens opportunities to support decarbonization of the chemical sector while simultaneously improving the overall process carbon efficiency to >40%. After condensation, the CFP-oil was co-hydrotreated with straight run diesel (10 : 90 vol%) to achieve 95% biogenic carbon incorporation. The oxygen content of the hydrotreated oil was below detection limits, and the diesel fraction exhibited a cetane number and cloud point suitable for a finished fuel. This manuscript concludes by highlighting remaining research needs associated with improving thermal management during catalyst regeneration, mitigating catalyst deactivation due to inorganic deposition, and demonstrating the durability of biomass feeding systems when operated in hydrogen-rich environments.