Achieving net-zero greenhouse gas emission plastics by a circular carbon economy

Self-Assembled Blossom-Shaped NiCo2S4 Nanosheets In Situ Deposited Electrodes: Possessing High Reactivity and Selectivity for Bromine-Based Flow Batteries

Bromine-based flow batteries (Br-FBs) are emerging rapidly due to their high energy density and wide potential window for renewable energy storage systems. Nevertheless, the sluggish kinetics of the Br2/Br- reaction on the electrode is considered to be the main challenge contributing to the poor performance of Br-FBs. Herein, we report self-assembled blossom-shaped NiCo2S4 nanosheets, enabling in situ growth on graphite felt (GF) via a one-step hydrothermal method. In the prepared NiCo2S4-GF, the gaps formed by the nanosheets restrict bromine diffusion, the sulfuretted blossom-shaped structure provides active sites with bromine adsorption capacity, and the synergistic effect of Ni and Co accelerates the electron transfer rate, which allow the electrode to exhibit excellent electrocatalytic activity compared to commercial GF, CoS-GF, and NiS-GF. Moreover, NiCo2S4-GF demonstrates unique selectivity for enhancing the Br2/Br- redox reaction compared to the bimetallic oxide of NiCo2O4-GF. Consequently, the zinc-bromine flow battery (ZBFB) with NiCo2S4-GF achieves an energy efficiency of 80.16%, which is 16.18% higher than that of the battery with commercialized GF at a current density of 60 mA cm-2, as well as a maximum power density of 260.75 mW cm-2 at 280 mA cm-2. The effective enhancement of the performance of ZBFB suggests that NiCo2S4-GF possesses great application potential in Br-FBs.

Sustainability synergies and trade-offs considering circularity and land availability for bioplastics production in Brazil

Alongside the concerns of waste management, plastic production represents a future problem for managing greenhouse gas emissions. Advanced recycling and bio-based production are paramount to face this challenge. The sustainability of bio-based polyethylene (bioPE) depends on the feedstock, avoiding stress on natural resources. This work discusses Brazil's potential to meet future global bioPE demand by 2050, using sugarcane as feedstock and considering environmental sustainability for production expansion. From the assessed 35.6 Mha, 3.55 Mha would be exempt from trade-offs related to land use change (dLUC), biodiversity, and water availability. The scenario with the highest circularity efficiency would require 22.2 Mha to meet the global demand, which can be accommodated in areas with positive impacts in carbon stocks, neutral impacts in water availability, and medium impacts on biodiversity. Here, we show that dropping demand is essential to avoid trade-offs and help consolidate bioPE as a sustainable alternative for future net-zero strategies.

Bimetallic Single-Atom Catalysts for Water Splitting

Green hydrogen from water splitting has emerged as a critical energy vector with the potential to spearhead the global transition to a fossil fuel-independent society. The field of catalysis has been revolutionized by single-atom catalysts (SACs), which exhibit unique and intricate interactions between atomically dispersed metal atoms and their supports. Recently, bimetallic SACs (bimSACs) have garnered significant attention for leveraging the synergistic functions of two metal ions coordinated on appropriately designed supports. BimSACs offer an avenue for rich metal-metal and metal-support cooperativity, potentially addressing current limitations of SACs in effectively furnishing transformations which involve synchronous proton-electron exchanges, substrate activation with reversible redox cycles, simultaneous multi-electron transfer, regulation of spin states, tuning of electronic properties, and cyclic transition states with low activation energies. This review aims to encapsulate the growing advancements in bimSACs, with an emphasis on their pivotal role in hydrogen generation via water splitting. We subsequently delve into advanced experimental methodologies for the elaborate characterization of SACs, elucidate their electronic properties, and discuss their local coordination environment. Overall, we present comprehensive discussion on the deployment of bimSACs in both hydrogen evolution reaction and oxygen evolution reaction, the two half-reactions of the water electrolysis process.

Environmental Benefits of Circular Ethylene Production from Polymer Waste

The linear nature of the current plastics economy and increasing demand for polymers poses a pressing global problem. In this work, we explore the environmental and economic performance of a circular alternative for polymer production through chemical plastic recycling following the waste-to-methanol-to-olefins (WMO) route. We assess the life-cycle environmental impacts and techno-economic feasibility of this novel circular production route (CPR) in 2020 and 2050, and compare them to the existing linear production route (LPR), deploying naphtha steam cracking for olefin production, and a mix of landfill and incineration as end-of-life treatment. Our results showcase that CPR could enable significant impact reductions, notably in 2050 assuming a low-carbon electricity mix based on renewables. However, the shift from linear to circular comes with burden-shifting, increasing the impacts relative to LPR on five environmental indicators in 2020 (i.e., terrestrial and freshwater eutrophication, particulate matter formation, acidification, and metal/mineral resources use). From the techno-economic viewpoint, we found that ethylene from waste polymers could become competitive with fossil ethylene when deployed at large scale. Moreover, it is significantly cheaper than its green analogs, which deploy methanol-to-olefins with green methanol from captured CO2 and electrolytic H2, showcasing the potential of implementing high-readiness level technologies to close the loop for polymers.

Structural Elucidation of a Metagenomic Urethanase and Its Engineering Towards Enhanced Hydrolysis Profiles

While plastics like polyethylene terephthalate can already be degraded efficiently by the activity of hydrolases, other synthetic polymers like polyurethanes (PUs) and polyamides (PAs) largely resist biodegradation. In this study, we solved the first crystal structure of the metagenomic urethanase UMG-SP-1, identified highly flexible loop regions to comprise active site residues, and targeted a total of 20 potential hot spots by site-saturation mutagenesis. Engineering campaigns yielded variants with single mutations, exhibiting almost 3- and 8-fold improved activity against highly stable N-aryl urethane and amide bonds, respectively. Furthermore, we demonstrated the release of the corresponding monomers from a thermoplastic polyester-PU and a PA (nylon 6) by the activity of a single, metagenome-derived urethanase after short incubation times. Thereby, we expanded the hydrolysis profile of UMG-SP-1 beyond the reported low-molecular weight carbamates. Together, these findings promise advanced strategies for the bio-based degradation and recycling of plastic materials and waste, aiding efforts to establish a circular economy for synthetic polymers.

Fully recyclable and tough thermoplastic elastomers from simple bio-sourced δ-valerolactones

While a large number of chemically recyclable thermoplastics have been developed in recent years, technologically important thermoplastic elastomers (TPEs) that are not only bio-based and fully recyclable but also exhibit mechanical properties that can rival or even exceed those petroleum-based, non-recyclable polyolefin TPEs are critically lacking. The key challenge in developing chemically circular, bio-based, high-performance TPEs rests on the complexity of TPE's block copolymer (BCP) structure involving block segments of different suitable monomers required to induce self-assembled morphologies responsible for performance as well as the control and monomer compatibility in their synthesis and the selectivity in their depolymerization. Here we demonstrate the utilization of bio-sourced δ-valerolactone (δVL) and its simple α-alkyl-substituted derivatives to produce all δVL-based polyester tri-BCP TPEs, which exhibit not only complete (closed-loop) chemical recyclability but also excellent toughness that is 2.5-3.8 times higher than commercial polyolefin-based TPEs. The visualized cylindrical morphology formed via crystallization-driven self-assembly in the new all δVL tri-BCP is postulated to contribute to the excellent TPE property.

Sustainable management of medical plastic waste through carbon dioxide-assisted pyrolysis

To address the challenges associated with medical plastic waste and to characterize its heterogeneity, non-recyclability, and potential biohazard risks, this study explored a carbon dioxide (CO2)-assisted pyrolysis process as a sustainable disposal method. Medical plastic waste typically includes polypropylene, polystyrene, and polyvinyl chloride. To experimentally evaluate the functional reactivity of CO2, we employed three pyrolysis setups (one-stage, two-stage, and catalytic processes). The technical advantages of using CO2 over inert gases such as nitrogen (N2) were demonstrated through pyrolysis tests. The results showed that energy production was enhanced under CO2 conditions, with catalytic pyrolysis generating 146% more flammable gases compared to pyrolysis in an N2 environment. The use of CO2 also led to a reduction in the formation of toxic chemicals due to improved thermal cracking. The CO2-assisted pyrolysis process exhibited net negative CO2 emissions when a catalyst was present, as a substantial amount of CO2 was consumed during the process. In conclusion, CO2-assisted pyrolysis of medical plastic waste offers a sustainable management solution that maximizes the utilization of carbon resources.

Perspective on the Development of Monomer Recovery Technologies from Plastics Designed to Last

In order to prevent the current unsustainable waste handling of the enormous volumes of end-of-use organic polymer material sent to landfilling or incineration, extensive research efforts have been devoted toward the development of appropriate solutions for the recycling of commercial thermoset polymers. The inability of such cross-linked polymers to be remelted once cured implies that mechanical recycling processes used for thermoplastic materials do not translate to the recycling of thermoset polymers. Moreover, the structural diversity within the materials from the use of different monomers as well as the use of such polymers for the fabrication of fiber-reinforced polymer composites make recycling of these materials highly challenging. In this Perspective, depolymerization strategies for thermoset polymers are discussed with an emphasis on recent advancements within our group on recovering polymer building blocks from polyurethane (PU) and epoxy-based materials. While these two represent the largest thermoset polymer groups with respect to the production volumes, the recycling landscapes for these classes of materials are vastly different. For PU, increased collaboration between academia and industry has resulted in major advancements within solvolysis, acidolysis, aminolysis, and split-phase glycolysis for polyol recovery, where several processes are being evaluated for further scaling studies. For epoxy-based materials, the molecular skeleton has no obvious target for chemical scission. Nevertheless, we have recently demonstrated the possibility of the disassembly of the epoxy polymer in fiber-reinforced composites for bisphenol A (BPA) recovery through catalytic C-O bond cleavage. Furthermore, a base promoted cleavage developed by us and others shows tremendous potential for the recovery of BPA from epoxy polymers. Further efforts are still required for evaluating the suitability of such monomer recovery strategies for epoxy materials at an industrial scale. Nonetheless, recent advancements as illustrated with the presented chemistry suggest that the future of thermoset polymer recycling could include processes that emphasize monomer recovery in an energy efficient manner for closed-loop recycling.

Region-Specific Sourcing of Lignocellulose Residues as Renewable Feedstocks for a Net-Zero Chemical Industry

Biobased chemicals, crucial for the net-zero chemical industry, rely on lignocellulose residues as a major feedstock. However, its availability and environmental impacts vary greatly across regions. By 2050, we estimate that 3.0-5.2 Gt of these residues will be available from the global forest and agricultural sectors, with key contributions from Brazil, China, India, and the United States. This supply satisfies the growing global feedstock demands for plastics when used efficiently. Forest residues have 84% lower climate change impacts than agricultural residues on average globally but double the land-use-related biodiversity loss. Biobased plastics may reduce climate change impacts relative to fossil-based alternatives but are insufficient to fulfill net-zero targets. In addition, they pose greater challenges in terms of biodiversity loss and water stress. Avoiding feedstock sourcing from biodiversity-rich areas could halve lignocellulose residues-related biodiversity loss without significantly compromising availability. Improvements in region-specific feedstock sourcing, agricultural management and biomass utilization technologies are warranted for transitioning toward a sustainable chemical industry.

In Situ Synthesis of High-Entropy (Oxy)Hydroxides Via Electrochemical Reconfiguration As Catalysts For Efficient Water Oxidation

Surface reconstruction plays a pivotal role in enhancing the activity of the oxygen evolution reaction (OER), particularly in terms of the structural transformation from metal oxides to (oxy)hydroxides. Herein, a novel (oxy)hydroxide (FeCoNiCuMoOOH) with high entropy is developed by the electrochemical reconstitution of corresponding oxide (FeCoNiCuMoOx). Significantly, the FeCoNiCuMoOOH exhibits much higher OER electrocatalytic activity and durability with an overpotential as low as 201 mV at a current density of 10 mA cm-2, and with a Tafel slope of 39.4 mV dec-1. The FeCoNiCuMoOOH/NF presents high stability when testing under a constant current at 100 mA cm-2 within 1000 h. The surface reconstruction is a process of dissolution-reprecipitation of Cu and Mo species and co-hydroxylation of five metal species, which ultimately leads to the formation of FeCoNiCuMoOOH from FeCoNiCuMoOx. This study holds great significance in the realm of designing high-entropy (oxy)hydroxides catalysts with exceptional activity and stability for OER.

Plastic recycling: A panacea or environmental pollution problem

Increasing plastic waste is a critical global challenge to ecological and human health requiring focused solutions to reduce omnipresent plastic pollution in the environment. While recycling has been touted as one solution to counter plastic waste and resource utilization, it has been largely ineffective in offsetting the impact of rising global plastic production of more than 400 million metric tonnes annually, due to low global recycling rates of only 9%. Over three decades since implementing plastic resin codes, recycling has favoured thermoplastics, neglecting thermoset plastics. There is a constant need to enhance overall recycling efficiency by exploring advanced methods, as enormous gaps exist in fully unlocking the potential of plastic recycling. We identify critical gaps associated with plastic waste recycling and its potential environmental impacts. We discuss substantial progress in recycling technology, designs-for-recyclability with controlled chemical use, and economic incentives to expand markets for recycled plastics and to curb plastic leakage into the environment. Additionally, we highlight some emerging strategies and legally binding international policy instruments, such as the Global Plastics Treaty that require further development to reduce plastic waste and improve plastic recyclability.

Fully Bio-Based 2,5-Furandicarboxylic Acid Polyester toward Plastics with Mechanically Robust, Excellent Gas Barrier and Fast Degradation

Aliphatic-aromatic copolyesters offer a promising solution to mitigate plastic pollution, but high content of aliphatic units (>40 %) often suffer from diminished comprehensive performances. Poly(butylene oxalate-co-furandicarboxylate) (PBOF) copolyesters were synthesized by precisely controlling the oxalic acid content from 10 % to 60 %. Compared with commercial PBAT, the barrier properties of PBOF for H2O and O2 increased by more than 6 and 26 times, respectively. The introduction of the oxalic acid units allowed the water contact angle to be reduced from 82.5° to 62.9°. Superior hydrophilicity gave PBOF an excellent degradation performance within a 35-day hydrolysis. Interestingly, PBO20F and PBO30F also displayed obvious decrease of molecular weight during hydrolysis, with elastic modulus >1 GPa and tensile strength between 35-54 MPa. PBOF achieved the highest hydrolysis rates among the reported PBF-based copolyesters. The hydrolytic mechanism was further explored based on Fukui function analysis and density functional theory (DFT) calculation. Noncovalent analysis indicated that the water molecules formed hydrogen bonding interaction with adjacent ester groups and thus improved the reactivity of carbonyl carbon. PBOF not only meet the requirements of the high-performance packaging market but can quickly degrade after the end of their usage cycles, providing a new choice for green and environmental protection.

Carbon capture and utilisation (CCU) solutions: Assessing environmental, economic, and social impacts using a new integrated methodology

Carbon Capture and Utilisation (CCU) technologies play a significant role in climate change mitigation, as these platforms aim to capture and convert CO2 that would be otherwise emitted into the atmosphere. Effective and economically sustainable technologies are crucial to support the transition to renewable and low-carbon energy sources by 2030 and beyond. Currently, studies exploring the financial viability of CCU technologies besides the joint analyses of life-cycle costs and environmental and social impacts are still limited. In this context, the study developed and validated an innovative and integrated methodology, called Life Cycle Cost and Sustainability Assessment (LCC-SA) which allows the joint assessment of (i) project life-cycle costs, (ii) socio-cultural and environmental externalities. This tool was validated with an application to an algal photobioreactors (PBRs) and allowed to assess the economic and environmental sustainability besides identifying the main critical issues to be addressed during the transition from pilot-scale plant to industrial application. The methodology's implementation estimated benefits in two main areas: (i) environmental, including CO2 removal and avoidance through biodiesel production instead of fossil-derived diesel; (ii) socio-cultural, encompassing new patents, knowledge spillovers, human capital formation, and knowledge outputs. The analysis returned as main result that the present value of the social externalities amounts to around EUR 550,000 and the present value of the costs to approximately EUR 60,000. The Economic Net Present Value (ENPV) is EUR 487,394, which shows the significance of the extra-financial effects generated by the research project. At full-scale application, environmental benefits include capturing 187 to 1867 tons of CO2 per year and avoiding 1.7 to 16.7 tons of CO2 annually through biodiesel production instead of fossil-derived diesel.

Unveiling the mechanism of triphos-Ru catalysed C-O bond disconnections in polymers

Ruthenium complexes with facially coordinating tripodal phosphine ligands are privileged catalysts for a broad range of (de-)hydrogenation-based transformations. Among these, C-O bond hydrogenolysis holds potential for the depolymerisation of both the biopolymer lignin and epoxy resins applied in wind turbine blades, aircrafts and more. However, this methodology is poorly understood in mechanistic terms. Here, we present a detailed investigation on the triphos-Ru catalysed C-O bond scission on a molecular level. A combination of experimental, spectroscopical and theoretical studies elucidates the reactivity of the ruthenium trimethylenemethane precatalyst, revealing the key roles of ruthenium phenolates in both catalyst activation as well as the catalytic cycle itself. Furthermore, a Ru(0)/Ru(II) oxidative addition into the C-O bond is disclosed, with a triphos-Ru(0) dihydrogen complex as entry point. With the molecular nature of the operating triphos-Ru species and the thermodynamics and kinetics of the catalysis unravelled, improvements of established methods as well as design of related transformations may become possible.

3D printed energy devices: generation, conversion, and storage

The energy devices for generation, conversion, and storage of electricity are widely used across diverse aspects of human life and various industry. Three-dimensional (3D) printing has emerged as a promising technology for the fabrication of energy devices due to its unique capability of manufacturing complex shapes across different length scales. 3D-printed energy devices can have intricate 3D structures for significant performance enhancement, which are otherwise impossible to achieve through conventional manufacturing methods. Furthermore, recent progress has witnessed that 3D-printed energy devices with micro-lattice structures surpass their bulk counterparts in terms of mechanical properties as well as electrical performances. While existing literature focuses mostly on specific aspects of individual printed energy devices, a brief overview collectively covering the wide landscape of energy applications is lacking. This review provides a concise summary of recent advancements of 3D-printed energy devices. We classify these devices into three functional categories; generation, conversion, and storage of energy, offering insight on the recent progress within each category. Furthermore, current challenges and future prospects associated with 3D-printed energy devices are discussed, emphasizing their potential to advance sustainable energy solutions.

Recommendations for life-cycle assessment of recyclable plastics in a circular economy

Technologies that enable plastic circularity offer a path to reducing waste generation, improving environmental quality, and reducing reliance on fossil feedstocks. However, life-cycle assessment (LCA) methods commonly applied to these systems fall far short of capturing the full suite of advantages and tradeoffs. This perspective highlights inconsistencies in both the research questions and methodological choices across the growing body of LCA literature for plastics recycling. We assert that conducting LCAs on the basis of tonnes of waste managed vs. tonnes of recycled plastics yields results with fundamentally different conclusions; in most cases, analyses of recyclable plastics should focus on the unit of recycled product yielded. We also offer straightforward paths to better approach LCAs for recycling processes and plastics in a circular economy by rethinking study design (metrics, functional unit, system boundaries, counterfactual scenarios), upstream assumptions (waste feedstock variability, pre-processing requirements), and downstream assumptions (closed-loop vs. open-loop systems, material substitution). Specifically, we recommend expanding to metrics beyond greenhouse gases by including fossil carbon balances, net diversion of waste from landfill, and quantity of avoided plastic waste leakage to the environment. Furthermore, we highlight the role that plastic waste plays as a problematic contaminant in preventing greater diversion of all wastes to recycling, energy recovery, and composting, suggesting that plastics may hold a shared responsibility for the system-wide greenhouse gas emissions that occur when mixed wastes are landfilled.

Bimetallic Metal Sites in Metal-Organic Frameworks Facilitate the Production of 1-Butene from Electrosynthesized Ethylene

Converting CO2 to synthetic hydrocarbon fuels is of increasing interest. In light of progress in electrified CO2 to ethylene, we explored routes to dimerize to 1-butene, an olefin that can serve as a building block to ethylene longer-chain alkanes. With goal of selective and active dimerization, we investigate a series of metal-organic frameworks having bimetallic catalytic sites. We find that the tunable pore structure enables optimization of selectivity and that periodic pore channels enhance activity. In a tandem system for the conversion of CO2 to 1-C4H8, wherein the outlet cathodic gas from a CO2-to-C2H4 electrolyzer is fed directly (via a dehumidification stage) into the C2H4 dimerizer, we study the highest-performing MOF found herein: M' = Ru and M″ = Ni in the bimetallic two-dimensional M'2(OAc)4M″(CN)4 MOF. We report a 1-C4H8 production rate of 1.3 mol gcat-1 h-1 and a C2H4 conversion of 97%. From these experimental data, we project an estimated cradle-to-gate carbon intensity of -2.1 kg-CO2e/kg-1-C4H8 when CO2 is supplied from direct air capture and when the required energy is supplied by electricity having the carbon intensity of wind.

Global discharge of microplastics from mechanical recycling of plastic waste

The increasing production of plastic products and generation of plastic waste have had increasingly negative environmental impacts. Although recycling could reduce plastic pollution, microplastics can be generated during the process of crushing plastic products during mechanical recycling. We conducted crushing tests with 13 different plastics and documented the size distribution of particles generated. We then estimated the discharge of microplastics associated with recycling and their removal in wastewater treatment plants. We estimated that the global discharge of microplastics would increase from 0.017 Mt in 2000 to 0.749 Mt in 2060. Although mechanical recycling was estimated to account for 3.1% of the total emissions of microplastics for 2017, discharges of microplastics from plastic recycling may increase, even if plastic pollution from well-known sources decreases. Non-OECD (Organization for Economic Cooperation and Development) Asia could be a major discharging region and would play a vital role in reducing discharges of microplastics. Reduction of the discharge of microplastics will require less use of plastic products and upgrading wastewater treatment in many countries.

A US perspective on closing the carbon cycle to defossilize difficult-to-electrify segments of our economy

Electrification to reduce or eliminate greenhouse gas emissions is essential to mitigate climate change. However, a substantial portion of our manufacturing and transportation infrastructure will be difficult to electrify and/or will continue to use carbon as a key component, including areas in aviation, heavy-duty and marine transportation, and the chemical industry. In this Roadmap, we explore how multidisciplinary approaches will enable us to close the carbon cycle and create a circular economy by defossilizing these difficult-to-electrify areas and those that will continue to need carbon. We discuss two approaches for this: developing carbon alternatives and improving our ability to reuse carbon, enabled by separations. Furthermore, we posit that co-design and use-driven fundamental science are essential to reach aggressive greenhouse gas reduction targets.

Photocatalytic CO2 Reduction Using CO2-Binding Enzymes

Novel concepts to utilize carbon dioxide are required to reach a circular carbon economy and minimize environmental issues. To achieve these goals, photo-, electro-, thermal-, and biocatalysis are key tools to realize this, preferentially in aqueous solutions. Nevertheless, catalytic systems that operate efficiently in water are scarce. Here, we present a general strategy for the identification of enzymes suitable for CO2 reduction based on structural analysis for potential carbon dioxide binding sites and subsequent mutations. We discovered that the phenolic acid decarboxylase from Bacillus subtilis (BsPAD) promotes the aqueous photocatalytic CO2 reduction selectively to carbon monoxide in the presence of a ruthenium photosensitizer and sodium ascorbate. With engineered variants of BsPAD, TONs of up to 978 and selectivities of up to 93 % (favoring the desired CO over H2 generation) were achieved. Mutating the active site region of BsPAD further improved turnover numbers for CO generation. This also revealed that electron transfer is rate-limiting and occurs via multistep tunneling. The generality of this approach was proven by using eight other enzymes, all showing the desired activity underlining that a range of proteins is capable of photocatalytic CO2 reduction.

Recyclable and (Bio)degradable Polyesters in a Circular Plastics Economy

Polyesters carrying polar main-chain ester linkages exhibit distinct material properties for diverse applications and thus play an important role in today's plastics economy. It is anticipated that they will play an even greater role in tomorrow's circular plastics economy that focuses on sustainability, thanks to the abundant availability of their biosourced building blocks and the presence of the main-chain ester bonds that can be chemically or biologically cleaved on demand by multiple methods and thus bring about more desired end-of-life plastic waste management options. Because of this potential and promise, there have been intense research activities directed at addressing recycling, upcycling or biodegradation of existing legacy polyesters, designing their biorenewable alternatives, and redesigning future polyesters with intrinsic chemical recyclability and tailored performance that can rival today's commodity plastics that are either petroleum based and/or hard to recycle. This review captures these exciting recent developments and outlines future challenges and opportunities. Case studies on the legacy polyesters, poly(lactic acid), poly(3-hydroxyalkanoate)s, poly(ethylene terephthalate), poly(butylene succinate), and poly(butylene-adipate terephthalate), are presented, and emerging chemically recyclable polyesters are comprehensively reviewed.

Environmental impacts of circularity strategies for social distancing plastic shields made of polymethyl methacrylate in the United States

One application of plastics that grew during the COVID-19 pandemic is for social distancing plastic shields, or protective barriers, made from polymethyl methacrylate (PMMA) such as transparent face guards. Although available for other applications, end-of-life impacts for barriers are currently lacking in the literature, and there is a need to fill in this gap to guide decisions. This study evaluated the end-of-life environmental impacts of PMMA barriers in the United States by using life cycle assessment. We evaluated five strategies including landfilling, waste-to-energy, mechanical recycling, chemical recycling and reuse. Data were sourced from literature and various life cycle inventory databases. The Tool for Reduction and Assessment of Chemicals and Other Environmental Impacts (TRACI) was used as the life cycle impact assessment method. Landfilling exhibited the highest impact in all indicators and reuse demonstrated optimal results for global warming potential. A scenario analysis was conducted to explore a combination of strategies, revealing that the most promising approach involved a mix of 40% reuse, 20% mechanical recycling and 40% chemical recycling. Circular economy recommendations are proposed for managing these sources of plastic waste in the United States.

Polyester biodegradability: importance and potential for optimisation

To reduce global CO2 emissions in line with EU targets, it is essential that we replace fossil-derived plastics with renewable alternatives. This provides an opportunity to develop novel plastics with improved design features, such as better reusability, recyclability, and environmental biodegradability. Although recycling and reuse of plastics is favoured, this relies heavily on the infrastructure of waste management, which is not consistently advanced on a worldwide scale. Furthermore, today's bulk polyolefin plastics are inherently unsuitable for closed-loop recycling, but the introduction of plastics with enhanced biodegradability could help to combat issues with plastic accumulation, especially for packaging applications. It is also important to recognise that plastics enter the environment through littering, even where the best waste-collection infrastructure is in place. This causes endless environmental accumulation when the plastics are non-(bio)degradable. Biodegradability depends heavily on circumstances; some biodegradable polymers degrade rapidly under tropical conditions in soil, but they may not also degrade at the bottom of the sea. Biodegradable polyesters are theoretically recyclable, and even if mechanical recycling is difficult, they can be broken down to their monomers by hydrolysis for subsequent purification and re-polymerisation. Additionally, both the physical properties and the biodegradability of polyesters are tuneable by varying their building blocks. The relationship between the (chemical) structures/compositions (aromatic, branched, linear, polar/apolar monomers; monomer chain length) and biodegradation/hydrolysis of polyesters is discussed here in the context of the design of biodegradable polyesters.

Pyrolysis of mixed engineering plastics: Economic challenges for automotive plastic waste

Chemical recycling of complex plastic waste via pyrolysis can reduce fossil resource dependence of the plastics value chain and greenhouse gas emissions. However, economic viability is crucial for its implementation, especially considering challenging waste streams with high shares of engineering plastics that have lower pyrolysis product quality than standard thermoplastics waste. Thus, this study conducts a techno-economic assessment determining the profitability factors of pyrolysis plants for automotive plastic waste in Germany including different plant capacities and calculating cost-covering minimum sales prices for the resulting pyrolysis oil. Main findings are that due to economies of scale, the cost-covering minimum sales prices vary between 1182 €/Mg pyrolysis oil (3750 Mg input/year) and 418 €/Mg pyrolysis oil (100,000 Mg input/year). The pyrolysis technology employed must be robust and scalable to realize these economies of scale. Large plant capacities face challenges such as feedstock availability at reasonable costs, constant feedstock quality, and pyrolysis oil quality, affecting pyrolysis oil pricing. Due to the limited yield and quality of pyrolysis oil produced from these technically demanding feedstocks, policy implications are that additional revenue streams such as gate fees or subsidies that are essential to ensure a positive business case are necessary. Depending on the assessed plant capacity, additional revenues between 720 and 59 €/Mg pyrolysis oil should be realized to be competitive with the price of the reference product heavy fuel oil. Otherwise, the environmental potential of this technology cannot be exploited.

Boosting CO2 chemical fixation over MOF-808 by the introduction of functional groups and defective Zr sites

CO2 cycloaddition has emerged as a promising approach for producing value-added cyclocarbonates and mitigating greenhouse gas emissions. Although MOF-808 serves as a stable catalyst for cycloaddition, its limited activity constrains broader applications. Through the modification with a fluoride group via a ligand exchange method, F-MOF-808-1.5 exhibits exceptional performance, achieving a 98.8% conversion with 97.8% selectivity to epichlorohydrin carbonate-marking a substantial 100% improvement compared to pristine MOF-808. The defective Zr sites and the electron-withdrawing groups synergistically promote the ring opening of epoxides. Furthermore, the catalyst demonstrates high stability over multiple reaction cycles. Notably, without adding solvents and co-catalysts, F-MOF-808-1.5 outperforms most reported MOF-based catalysts.

Depolymerization within a Circular Plastics System

The societal importance of plastics contrasts with the carelessness with which they are disposed. Their superlative properties lead to economic and environmental efficiency, but the linearity of plastics puts the climate, human health, and global ecosystems at risk. Recycling is fundamental to transitioning this linear model into a more sustainable, circular economy. Among recycling technologies, chemical depolymerization offers a route to virgin quality recycled plastics, especially when valorizing complex waste streams poorly served by mechanical methods. However, chemical depolymerization exists in a complex and interlinked system of end-of-life fates, with the complementarity of each approach key to environmental, economic, and societal sustainability. This review explores the recent progress made into the depolymerization of five commercial polymers: poly(ethylene terephthalate), polycarbonates, polyamides, aliphatic polyesters, and polyurethanes. Attention is paid not only to the catalytic technologies used to enhance depolymerization efficiencies but also to the interrelationship with other recycling technologies and to the systemic constraints imposed by a global economy. Novel polymers, designed for chemical depolymerization, are also concisely reviewed in terms of their underlying chemistry and potential for integration with current plastic systems.

Synthesis and Deconstruction of Polyethylene-type Materials

Polyethylene deconstruction to reusable smaller molecules is hindered by the chemical inertness of its hydrocarbon chains. Pyrolysis and related approaches commonly require high temperatures, are energy-intensive, and yield mixtures of multiple classes of compounds. Selective cleavage reactions under mild conditions ( Collapse

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Grants

• H2020 European Research Council

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Affiliation(s)

Simon T. Schwab Chair of Chemical Materials Science, Department of Chemistry, University of Konstanz, Universitätsstraße 10, 78464 Konstanz, Germany
Maximilian Baur Chair of Chemical Materials Science, Department of Chemistry, University of Konstanz, Universitätsstraße 10, 78464 Konstanz, Germany
Taylor F. Nelson Chair of Chemical Materials Science, Department of Chemistry, University of Konstanz, Universitätsstraße 10, 78464 Konstanz, Germany
Stefan Mecking Chair of Chemical Materials Science, Department of Chemistry, University of Konstanz, Universitätsstraße 10, 78464 Konstanz, Germany

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Upcycling Waste Plastics with a C-C Backbone by Heterogeneous Catalysis

Plastics with an inert carbon-carbon (C-C) backbone, such as polyethylene (PE), polypropylene (PP), polystyrene (PS), and polyvinyl chloride (PVC), are the most widely used types of plastic in human activities. However, many of these polymers were directly discarded in nature after use, and few were appropriately recycled. This not only threatens the natural environment but also leads to the waste of carbon resources. Conventional chemical recycling of these plastics, including pyrolysis and catalytic cracking, requires a high energy input due to the chemical inertness of C-C bonds and C-H bonds and leads to complex product distribution. In recent years, significant progress has been made in the development of catalysts and the introduction of small molecules as additional coreactants, which could potentially overcome these challenges. In this Review, we summarize and highlight catalytic strategies that address these issues in upcycling C-C backbone plastics with small molecules, particularly in heterogeneous catalysis. We believe that this review will inspire the development of upcycling methods for C-C backbone plastics using small molecules and heterogeneous catalysis.

Relationship between Composition and Environmental Degradation of Poly(isosorbide-co-diol oxalate) (PISOX) Copolyesters

To reduce the global CO2 footprint of plastics, bio- and CO2-based feedstock are considered the most important design features for plastics. Oxalic acid from CO2 and isosorbide from biomass are interesting rigid building blocks for high Tg polyesters. The biodegradability of a family of novel fully renewable (bio- and CO2-based) poly(isosorbide-co-diol) oxalate (PISOX-diol) copolyesters was studied. We systematically investigated the effects of the composition on biodegradation at ambient temperature in soil for PISOX (co)polyesters. Results show that the lag phase of PISOX (co)polyester biodegradation varies from 0 to 7 weeks. All (co)polyesters undergo over 80% mineralization within 180 days (faster than the cellulose reference) except one composition with the cyclic codiol 1,4-cyclohexanedimethanol (CHDM). Their relatively fast degradability is independent of the type of noncyclic codiol and results from facile nonenzymatic hydrolysis of oxalate ester bonds (especially oxalate isosorbide bonds), which mostly hydrolyzed completely within 180 days. On the other hand, partially replacing oxalate with terephthalate units enhances the polymer's resistance to hydrolysis and its biodegradability in soil. Our study demonstrates the potential for tuning PISOX copolyester structures to design biodegradable plastics with improved thermal, mechanical, and barrier properties.

Designing a circular carbon and plastics economy for a sustainable future

The linear production and consumption of plastics today is unsustainable. It creates large amounts of unnecessary and mismanaged waste, pollution and carbon dioxide emissions, undermining global climate targets and the Sustainable Development Goals. This Perspective provides an integrated technological, economic and legal view on how to deliver a circular carbon and plastics economy that minimizes carbon dioxide emissions. Different pathways that maximize recirculation of carbon (dioxide) between plastics waste and feedstocks are outlined, including mechanical, chemical and biological recycling, and those involving the use of biomass and carbon dioxide. Four future scenarios are described, only one of which achieves sufficient greenhouse gas savings in line with global climate targets. Such a bold system change requires 50% reduction in future plastic demand, complete phase-out of fossil-derived plastics, 95% recycling rates of retrievable plastics and use of renewable energy. It is hard to overstate the challenge of achieving this goal. We therefore present a roadmap outlining the scale and timing of the economic and legal interventions that could possibly support this. Assessing the service lifespan and recoverability of plastic products, along with considerations of sufficiency and smart design, can moreover provide design principles to guide future manufacturing, use and disposal of plastics.

The role of chemical and solvent-based recycling within a sustainable circular economy for plastics

Chemical and solvent-based recycling of plastic waste may help overcome some of the challenges faced by predominantly applied mechanical recycling techniques. This study quantifies the environmental impacts of chemical and solvent-based recycling as a function of varying process parameters and product composition using life cycle assessment. Furthermore, potential benefits and impacts on a system level are determined. To that end, a high-resolution material flow analysis is conducted for the reference system of Switzerland, covering all main plastic types and applications. In a scenario for the year 2040, we employ environmentally beneficial mechanical recycling where possible and convey suitable remaining waste streams to chemical or solvent-based recycling processes. Applying chemical or solvent-based recycling as a complement to maximum mechanical recycling, instead of thermal treatment with energy recovery, may achieve a reduction in the climate change impact of the system ranging from less than 10 % to almost 40 %. For achieving high environmental benefits, proper process choice and configuration are crucial. Dissolution or depolymerization provide higher benefits relative to other chemical recycling processes, but can only treat certain waste streams and require prior sorting into plastic types. Pyrolysis and gasification appeared to only have the ability to achieve substantial benefits over incineration if their output products can substitute high-impact chemicals and provided that efficient heat transfer and recovery is warranted when implemented on a large scale. As industrial-scale plants for chemical or solvent-based plastic recycling are still lacking, the upscaling potential and the environmental benefits achievable in practice are highly uncertain today.

The potential of emerging bio-based products to reduce environmental impacts

The current debate on the sustainability of bio-based products questions the environmental benefits of replacing fossil- by bio-resources. Here, we analyze the environmental trade-offs of 98 emerging bio-based materials compared to their fossil counterparts, reported in 130 studies. Although greenhouse gas life cycle emissions for emerging bio-based products are on average 45% lower (-52 to -37%; 95% confidence interval), we found a large variation between individual bio-based products with none of them reaching net-zero emissions. Grouped in product categories, reductions in greenhouse gas emissions ranged from 19% (-52 to 35%) for bioadhesives to 73% (-84 to -54%) for biorefinery products. In terms of other environmental impacts, we found evidence for an increase in eutrophication (369%; 163 to 737%), indicating that environmental trade-offs should not be overlooked. Our findings imply that the environmental sustainability of bio-based products should be evaluated on an individual product basis and that more radical product developments are required to reach climate-neutral targets.

Evaluating Heterodinuclear Mg(II)M(II) (M = Mn, Fe, Ni, Cu, and Zn) Catalysts for the Chemical Recycling of Poly(cyclohexene carbonate)

Polymer chemical recycling to monomers (CRM) is important to help achieve a circular plastic economy, but the "rules" governing catalyst design for such processes remain unclear. Here, carbon dioxide-derived polycarbonates undergo CRM to produce epoxides and carbon dioxide. A series of dinuclear catalysts, Mg(II)M(II) where M(II) = Mg, Mn, Fe, Co, Ni, Cu, and Zn, are compared for poly(cyclohexene carbonate) depolymerizations. The recycling is conducted in the solid state, at 140 °C monitored using thermal gravimetric analyses, or performed at larger-scale using laboratory glassware. The most active catalysts are, in order of decreasing rate, Mg(II)Co(II), Mg(II)Ni(II), and Mg(II)Zn(II), with the highest activity reaching 8100 h-1 and with >99% selectivity for cyclohexene oxide. Both the activity and selectivity values are the highest yet reported in this field, and the catalysts operate at low loadings and moderate temperatures (from 1:300 to 1:5000, 140 °C). For the best heterodinuclear catalysts, the depolymerization kinetics and activation barriers are determined. The rates in both reverse depolymerization and forward CHO/CO2 polymerization catalysis show broadly similar trends, but the processes feature different intermediates; forward polymerization depends upon a metal-carbonate intermediate, while reverse depolymerization depends upon a metal-alkoxide intermediate. These dinuclear catalysts are attractive for the chemical recycling of carbon dioxide-derived plastics and should be prioritized for recycling of other oxygenated polymers and copolymers, including polyesters and polyethers. This work provides insights into the factors controlling depolymerization catalysis and steers future recycling catalyst design toward exploitation of lightweight and abundant s-block metals, such as Mg(II).

Integrated Assessment of the Leading Paths to Mitigate CO2 Emissions from the Organic Chemical and Plastics Industry

The chemical industry is a major and growing source of CO2 emissions. Here, we extend the principal U.S.-based integrated assessment model, GCAM, to include a representation of steam cracking, the dominant process in the organic chemical industry today, and a suite of emerging decarbonization strategies, including catalytic cracking, lower-carbon process heat, and feedstock switching. We find that emerging catalytic production technologies only have a small impact on midcentury emissions mitigation. In contrast, process heat generation could achieve strong mitigation, reducing associated CO2 emissions by ∼76% by 2050. Process heat generation is diversified to include carbon capture and storage (CCS), hydrogen, and electrification. A sensitivity analysis reveals that our results for future net CO2 emissions are most sensitive to the amount of CCS deployed globally. The system as defined cannot reach net-zero emissions if the share of incineration increases as projected without coupling incineration with CCS. Less organic chemicals are produced in a net-zero CO2 future than those in a no-policy scenario. Mitigation of feedstock emissions relies heavily on biogenic carbon used as an alternative feedstock and waste treatment of plastics. The only scenario that delivers net-negative CO2 emissions from the organic chemical sector (by 2070) combines greater use of biogenic feedstocks with a continued reliance on landfilling of waste plastic, versus recycling or incineration, which has trade-offs.

Transition Metal Ion Doping on ZIF-8 Enhances the Electrochemical CO2 Reduction Reaction

The electrochemical reduction of CO2  to diverse value-added chemicals is a unique, environmentally friendly approach for curbing greenhouse gas emissions while addressing sluggish catalytic activity and low Faradaic efficiency (FE) of electrocatalysts. Here, zeolite-imidazolate-frameworks-8 (ZIF-8) containing various transition metal ions-Ni, Fe, and Cu-at varying concentrations upon doping are fabricated for the electrocatalytic CO2 reduction reaction (CO2 RR) to carbon monoxide (CO) without further processing. Atom coordination environments and theoretical electrocatalytic performance are scrutinized via X-ray absorption spectroscopy (XAS) and density functional theory (DFT) calculations. Upon optimized Cu doping on ZIF-8, Cu0.5 Zn0.5 /ZIF-8 achieves a high partial current density of 11.57 mA cm-2 and maximum FE for CO of 88.5% at -1.0 V (versus RHE) with a stable catalytic activity over 6 h. Furthermore, the electron-rich sp2 C atom facilitates COOH* promotion after Cu doping of ZIF-8, leading to a local effect between the zinc-nitrogen (Zn-N4 ) and copper-nitrogen (Cu-N4 ) moieties. Additionally, the advanced CO2 RR pathway is illustrated from various perspectives, including the pre-H-covered state under the CO2 RR. The findings expand the pool of efficient metal-organic framework (MOF)-based CO2 RR catalysts, deeming them viable alternatives to conventional catalysts.

Spatial-temporal dynamics of land use carbon emissions and drivers in 20 urban agglomerations in China from 1990 to 2019

Urban agglomerations (UAs) are the largest carbon emitters; thus, the emissions must be controlled to achieve carbon peak and carbon neutrality. We use long time series land-use and energy consumption data to estimate the carbon emissions in UAs. The standard deviational ellipse (SDE) and spatial autocorrelation analysis are used to reveal the spatiotemporal evolution of carbon emissions, and the geodetector, geographically and temporally weighted regression (GTWR), and boosted regression trees (BRTs) are used to analyze the driving factors. The results show the following: (1) Construction land and forest land are the main carbon sources and sinks, accounting for 93% and 94% of the total carbon sources and sinks, respectively. (2) The total carbon emissions of different UAs differ substantially, showing a spatial pattern of high emissions in the east and north and low emissions in the west and south. The carbon emissions of all UAs increase over time, with faster growth in UAs with lower carbon emissions. (3) The center of gravity of carbon emissions shifts to the south (except for North China, where it shifts to the west), and carbon emissions in UAs show a positive spatial correlation, with a predominantly high-high and low-low spatial aggregation pattern. (4) Population, GDP, and the annual number of cabs are the main factors influencing carbon emissions in most UAs, whereas other factors show significant differences. Most exhibit an increasing trend over time in their impact on carbon emissions. In general, China still faces substantial challenges in achieving the dual carbon goal. The carbon control measures of different UAs should be targeted in terms of energy utilization, green and low-carbon production, and consumption modes to achieve the low-carbon and green development goals of the United Nations' sustainable cities and beautiful China's urban construction as soon as possible.

Chemical Recycling of Commercial Poly(l-lactic acid) to l-Lactide Using a High-Performance Sn(II)/Alcohol Catalyst System

Poly(l-lactic acid) (PLLA) is a leading commercial polymer produced from biomass, showing useful properties for plastics and fiber applications; after use, it is compostable. One area for improvement is postconsumer waste PLLA chemical recycling to monomer (CRM), i.e., the formation of l-lactide (l-LA) from waste plastic. This process is currently feasible at high reaction temperatures and shows low catalytic activity accompanied, in some cases, by side reactions, including epimerization. Here, a commercial Sn(II) catalyst, applied with nonvolatile commercial alcohol, enables highly efficient CRM of PLLA to yield l-LA in excellent yield and purity (92% yield, >99% l-LA from theoretical max.). The depolymerization is performed using neat polymer films at low temperatures (160 °C) under a nitrogen flow or vacuum. The chemical recycling operates with outstanding activity, achieving turnover frequencies which are up to 3000× higher than previously excellent catalysts and applied at loadings up to 6000× lower than previously leading catalysts. The catalyst system achieves a TOF = 3000 h-1 at 0.01 mol % or 1:10,000 catalyst:PLLA loading. The depolymerization of waste PLLA plastic packaging (coffee cup lids) produces pure l-LA in excellent yield and selectivity. The new catalyst system (Sn + alcohol) can itself be recycled four times in different PLLA "batch degradations" and maintains its high catalytic productivity, activity, and selectivity.

Scalable electrosynthesis of commodity chemicals from biomass by suppressing non-Faradaic transformations

Electrooxidation of biomass platforms provides a sustainable route to produce valuable oxygenates, but the practical implementation is hampered by the severe carbon loss stemming from inherent instability of substrates and/or intermediates in alkaline electrolyte, especially under high concentration. Herein, based on the understanding of non-Faradaic degradation, we develop a single-pass continuous flow reactor (SPCFR) system with high ratio of electrode-area/electrolyte-volume, short duration time of substrates in the reactor, and separate feeding of substrate and alkaline solution, thus largely suppressing non-Faradaic degradation. By constructing a nine-stacked-modules SPCFR system, we achieve electrooxidation of glucose-to-formate and 5-hydroxymethylfurfural (HMF)-to-2,5-furandicarboxylic acid (FDCA) with high single-pass conversion efficiency (SPCE; 81.8% and 95.8%, respectively) and high selectivity (formate: 76.5%, FDCA: 96.9%) at high concentrations (formate: 562.8 mM, FDCA: 556.9 mM). Furthermore, we demonstrate continuous and kilogram-scale electrosynthesis of potassium diformate (0.7 kg) from wood and soybean oil, and FDCA (1.17 kg) from HMF. This work highlights the importance of understanding and suppressing non-Faradaic degradation, providing opportunities for scalable biomass upgrading using electrochemical technology.

Selective deconstruction of mixed plastics by a tailored organocatalyst

Plastic represents an essential material in our society; however, a major imbalance between their high production and end-of-life management is leading to unrecovered energy, economic hardship, and a high carbon footprint. The adoption of plastic recycling has been limited, mainly due to the difficulty of recycling mixed plastics. Here, we report a versatile organocatalyst for selective glycolysis of diverse consumer plastics and their mixed waste streams into valuable chemicals. The developed organocatalyst selectively deconstructs condensation polymers at a specific temperature, and additives or other polymers such as polyolefin or cellulose can be readily separated from the mixed plastics, providing a chemical recycling path for many existing mixed plastics today. The Life Cycle Assessment indicates that the production of various condensation polymers from the deconstructed monomers will result in a significant reduction in greenhouse gas emissions and energy input, opening a new paradigm of plastic circularity toward a net-zero carbon society.

Effect of Janus Nanosheets in Polypropylene on Rheological Properties and Autoclave Foam Performance

Our experiment revealed that the addition of Janus nanosheets to polypropylene (PP) has a significant impact on the viscoelasticity of the composite system. Specifically, when 0.10 wt% of Janus nanosheets were added, the complex viscosity of the composite system increased. However, when we added less than 0.05 wt% of Janus nanosheets, there was a reduction in complex viscosity, which is known as the non-Einstein phenomenon. The Cole-Cole plot showed that the nanosheet network structure did not have a significant effect on the viscosity of the composite system. Additionally, we used carbon dioxide as a foaming agent to autoclave foaming using modified PP from Janus nanosheets, and the results demonstrated that increasing the number of Janus nanosheets decreased the apparent density and strengthened the cell structure of foaming beads, resulting in improved closed porosity.

Effects of Circularity Interventions in the European Plastic Packaging Sector

Low levels of plastics circularity today reflect major challenges for the sector to reduce environmental impacts and a need for wider systemic change. In this work, we investigated the potential for climate and socioeconomic benefits of circular economy (CE) interventions in the plastic packaging system. By means of a mixed-unit input-output (IO) model, we performed a comparative scenario analysis for the development of demand and waste management up to 2030 within the EU-28 (EU27 + United Kingdom). We modeled the development of material flows and assessed the effects of both demand-side and end-of-life interventions. Different levels of ambition toward 2030 based on EU circular economy strategies were tested. Results showed that on reaching high levels of circularity, between 14 and 22 Mt CO₂-eq/year could be reduced by 2030 (20-30% of the total sector impact in 2018) compared to business-as-usual. Demand change (e.g., by decreasing product packaging intensities) showed similar emission-saving potential as achieving the current recycling target of 55%, which emphasizes the role of demand-side actions. Most scenarios displayed moderate employment gains and potential economic losses, pertaining to both direct and indirect activity shifts in the economy. While considering model limitations, the approach is useful in indicating potential first-order effects of system changes.

Zeolite Supported Pt for Depolymerization of Polyethylene by Induction Heating

We demonstrate that for polyethylene depolymerization with induction heating (IH), using a bifunctional (Pt- or Pt-Sn-containing zeolite) hydrocracking catalyst, we can obtain high hydrocarbon product yields (up to 95 wt % in 2 h) at a relatively low surface temperature (375 °C) and with a tunable product distribution ranging from light gas products to gasoline- to diesel-range hydrocarbons. Four zeolite types [MFI, LTL, CHA(SSZ-13), and TON] were chosen as the supports due to their varying pore sizes and structures. These depolymerization results are obtained at atmospheric pressure and without the use of H₂ and result in an alkane/alkene mixture with virtually no methane, aromatics, or coke formation. We also demonstrate how IH helps overcome diffusional resistances associated with conventional thermal heating and thereby shortens reaction times.

A disaster risk reduction framework for the new global instrument to end plastic pollution

There are many benefits to be realized by applying a disaster risk reduction framework to the context of plastic pollution, especially in regards to operationalizing the precautionary principle that is inherent in many international treaties and conventions. We explore the implications of framing plastic pollution as a 'disaster' in light of the development of the new global instrument to end plastic pollution by aligning the objectives of the United Nations (UN) Sendai Framework for Disaster Risk Reduction 2015-2030 (SF) and the UN Sustainable Development Goals (SDGs); and thereby also complementing the many climate and non-climate mandates embedded within the UN Framework Convention on Climate Change (UNFCCC). It has been proposed that the UN global instrument to end plastic pollution could be based on the guidelines of the Paris Agreement (PA), driven by national action plans, potential to offset and mandatory reporting requirements. Adding a disaster risk reduction lens to this approach will strongly complement and enhance the environmental and human health outcomes aspired for the global and legally binding treaty to end plastic pollution. We provide an overview to reinforce the mutual benefits of cooperation and coordination, linking the SF, UNFCCC and SDGs to the future international instrument.

Redesigning Carbon-Carbon Backbone Polymers for Biodegradability-Compostability at the End-of-Life Stage

Carbon-carbon backbone polymers are non-biodegradable, persistent plastics that have accumulated on land and oceans due to human activities. They degrade and fragment into microplastics and smaller particle sizes but do not biodegrade at an acceptable and practical rate. Their continual buildup in the natural environment precipitates serious detrimental impacts on human health and the environment, as extensively documented in the literature and media. Nearly 77% of global plastics produced are carbon-carbon backbone polymers. More importantly, 90% of packaging plastics (153.8 million metric tons) are non-biodegradable, persistent carbon-carbon backbone polymers. The recycling rate of these non-durable packaging plastics ranges from 0 to 4%. Re-designing carbon-carbon backbone polymers to labile ester backbone biodegradable-compostable polymers and treating them along with biodegradable organic waste (such as food, paper, and organic wastes) in managed industrial composting is environmentally responsible. Diverting 1 million metric tons of biodegradable organic wastes in MSW bound for landfills and open dumps to industrial composting results in 0.95 million metric tons CO₂ equivalents of GHG emissions reduction. This perspective paper discusses strategies and rationales regarding the redesign of carbon-carbon backbone polymer molecules. It describes the carbon footprint reductions achievable by replacing petro-fossil carbon with plant biomass carbon. Biodegradability and compostability are frequently used but misunderstood and misused terms, leading to misleading claims in the marketplace. This paper presents the fundamentals of biodegradability and compostability of plastics and the requirements to be met according to ASTM/ISO international standards.

Electrified hydrocarbon-to-oxygenates coupled to hydrogen evolution for efficient greenhouse gas mitigation

Chemicals manufacture is among the top greenhouse gas contributors. More than half of the associated emissions are attributable to the sum of ammonia plus oxygenates such as methanol, ethylene glycol and terephthalic acid. Here we explore the impact of electrolyzer systems that couple electrically-powered anodic hydrocarbon-to-oxygenate conversion with cathodic H₂ evolution reaction from water. We find that, once anodic hydrocarbon-to-oxygenate conversion is developed with high selectivities, greenhouse gas emissions associated with fossil-based NH₃ and oxygenates manufacture can be reduced by up to 88%. We report that low-carbon electricity is not mandatory to enable a net reduction in greenhouse gas emissions: global chemical industry emissions can be reduced by up to 39% even with electricity having the carbon footprint per MWh available in the United States or China today. We conclude with considerations and recommendations for researchers who wish to embark on this research direction.

Installing Controlled Stereo-Defects Yields Semicrystalline and Biodegradable Poly(3-Hydroxybutyrate) with High Toughness and Optical Clarity

Stereo-defects present in stereo-regular polymers often diminish thermal and mechanical properties, and hence suppressing or eliminating them is a major aspirational goal for achieving polymers with optimal or enhanced properties. Here, we accomplish the opposite by introducing controlled stereo-defects to semicrystalline biodegradable poly(3-hydroxybutyrate) (P3HB), which offers an attractive biodegradable alternative to semicrystalline isotactic polypropylene but is brittle and opaque. We enhance the specific properties and mechanical performance of P3HB by drastically toughening it and also rendering it with the desired optical clarity while maintaining its biodegradability and crystallinity. This toughening strategy of stereo-microstructural engineering without changing the chemical compositions also departs from the conventional approach of toughening P3HB through copolymerization that increases chemical complexity, suppresses crystallization in the resulting copolymers, and is thus undesirable in the context of polymer recycling and performance. More specifically, syndio-rich P3HB (sr-P3HB), readily synthesized from the eight-membered meso-dimethyl diolide, has a unique set of stereo-microstructures comprising enriched syndiotactic [rr] and no isotactic [mm] triads but abundant stereo-defects randomly distributed along the chain. This sr-P3HB material is characterized by high toughness (U_T = 96 MJ/m³) as a result of its high elongation at break (>400%) and tensile strength (34 MPa), crystallinity (T_m = 114 °C), optical clarity (due to its submicron spherulites), and good barrier properties, while it still biodegrades in freshwater and soil.

Sustainable Design of Structural and Functional Polymers for a Circular Economy

To achieve a sustainable circular economy, polymer production must start transitioning to recycled and biobased feedstock and accomplish CO₂ emission neutrality. This is not only true for structural polymers, such as in packaging or engineering applications, but also for functional polymers in liquid formulations, such as adhesives, lubricants, thickeners or dispersants. At their end of life, polymers must be either collected and recycled via a technical pathway, or be biodegradable if they are not collectable. Advances in polymer chemistry and applications, aided by computational material science, open the way to addressing these issues comprehensively by designing for recyclability and biodegradability. This Review explores how scientific progress, together with emerging regulatory frameworks, societal expectations and economic boundary conditions, paint pathways for the transformation towards a circular economy of polymers.