Depolymerization of plastics by means of electrified spatiotemporal heating

Hydrogenation of the benzene rings in PET degraded chemicals over meso-HZSM-5 supported Ru catalyst

Chemical upcycling of waste polyethylene terephthalate (PET) to value-added products can reduce the emission of CO2, microplastics and toxic chemicals. In this work, mesoporous H-type Zeolite Socony Mobil-5 (HZSM-5) supported Ru catalyst (Ru/m-HZSM-5) was synthesized and tested in the hydrogenation of PET degraded chemicals (bis(2-hydroxyethyl) terephthalate, dimethyl terephthalate, diethyl terephthalate, and terephthalic acid). Characterizations disclosed that Ru/m-HZSM-5 catalyst possesses mesopores (a dominant channel of 5.32 nm), enlarged specific surface area (404 m2·g-1), and Ru NPs dispersed highly (40.6 %) compared to that of Ru/HZSM-5. And also, it was found that Ru/m-HZSM-5 was capable for the hydrogenation of benzene rings in these PET degraded chemicals with large sizes (1.09-1.82 nm). In particular, the conversion of BHET and the selectivity of BHCD over Ru/m-HZSM-5 reached 95.5 % and 95.6 % at 120 °C within 2 h. And Ru/m-HZSM-5 could be recycled at least five times without obvious loss of activity and selectivity.

Catalyst- and Solvent-Free Upcycling of Poly(Ethylene Terephthalate) Waste to Biodegradable Plastics

Poly(ethylene terephthalate) (PET) is an important polymer with annual output second only to polyethylene. Due to its low biodegradability, a large amount of PET is recycled for sustainable development. However, current strategies for PET recycling are limited by low added value or small product scale. It is urgent to make a breakthrough on the principle of PET macromolecular reaction and efficiently prepare products with high added value and wide applications. Here, the catalyst- and solvent-free synthesis of biodegradable plastics are reported through novel carboxyl-ester transesterification between PET waste and bio-based hydrogenated dimer acid (HDA), which can directly substitute some terephthalic acid (TPA) units in PET chain by HDA unit. This macromolecular reaction can be facilely carried out on current equipment in the polyester industry without any additional catalyst and solvent, thus enabling low-cost and large-scale production. Furthermore, the product semi-bio-based copolyester shows excellent mechanical properties, regulable flexibility and good biodegradability, which is expected to substitute poly(butylene adipate-co-terephthalate) (PBAT) plastic as high value-added biodegradable materials. This work provides an environmental-friendly and economic strategy for the large-scale upcycling of PET waste.

Electrothermal mineralization of per- and polyfluoroalkyl substances for soil remediation

Per- and polyfluoroalkyl substances (PFAS) are persistent and bioaccumulative pollutants that can easily accumulate in soil, posing a threat to environment and human health. Current PFAS degradation processes often suffer from low efficiency, high energy and water consumption, or lack of generality. Here, we develop a rapid electrothermal mineralization (REM) process to remediate PFAS-contaminated soil. With environmentally compatible biochar as the conductive additive, the soil temperature increases to >1000 °C within seconds by current pulse input, converting PFAS to calcium fluoride with inherent calcium compounds in soil. This process is applicable for remediating various PFAS contaminants in soil, with high removal efficiencies ( >99%) and mineralization ratios ( >90%). While retaining soil particle size, composition, water infiltration rate, and cation exchange capacity, REM facilitates an increase of exchangeable nutrient supply and arthropod survival in soil, rendering it superior to the time-consuming calcination approach that severely degrades soil properties. REM is scaled up to remediate soil at two kilograms per batch and promising for large-scale, on-site soil remediation. Life-cycle assessment and techno-economic analysis demonstrate REM as an environmentally friendly and economic process, with a significant reduction of energy consumption, greenhouse gas emission, water consumption, and operation cost, when compared to existing soil remediation practices.

Sustainable Plastics with High Performance and Convenient Processibility

Designing and making sustainable plastics is especially urgent to reduce their ecological and environmental impacts. However, it remains challenging to construct plastics with simultaneous high sustainability and outstanding comprehensive performance. Here, a composite strategy of in situ polymerizing a petroleum-based monomer with the presence of an industrialized bio-derived polymer in a quasi-solvent-free system is introduced, affording the plastic with excellent mechanical robustness, impressive thermal and solvent stability, as well as low energy, consumes during production, processing, and recycling. Particularly, the plastic can be easily processed into diverse shapes through 3D printing, injection molding, etc. during polymerization and further reprocessed into other complex structures via eco-friendly hydrosetting. In addition, the plastic is mechanically robust with Young's modulus of up to 3.7 GPa and tensile breaking strength of up to 150.2 MPa, superior to many commercially available plastics and other sustainable plastics. It is revealed that hierarchical hydrogen bonds in plastic predominate the well-balanced sustainability and performance. This work provides a new path for fabricating high-performance sustainable plastic toward practical applications, contributing to the circular economy.

Recent advances in oxidative degradation of plastics

Oxidative degradation is a powerful method to degrade plastics into oligomers and small oxidized products. While thermal energy has been conventionally employed as an external stimulus, recent advances in photochemistry have enabled photocatalytic oxidative degradation of polymers under mild conditions. This tutorial review presents an overview of oxidative degradation, from its earliest examples to emerging strategies. This review briefly discusses the motivation and the development of thermal oxidative degradation of polymers with a focus on underlying mechanisms. Then, we will examine modern studies primarily relevant to catalytic thermal oxidative degradation and photocatalytic oxidative degradation. Lastly, we highlight some unique studies using unconventional approaches for oxidative polymer degradation, such as electrochemistry.

Closed-Loop Polymer-to-Polymer Upcycling of Waste Poly (Ethylene Terephthalate) into Biodegradable and Programmable Materials

Poly(ethylene terephthalate) (PET), extensively employed in bottles, film, and fiber manufacture, has generated persistent environmental contamination due to its non-degradable nature. The resolution of this issue requires the conversion of waste PET into valuable products, often achieved through depolymerization into monomers. However, the laborious purification procedures involved in the extraction of monomers pose challenges and constraints on the complete utilization of PET. Herein, a strategy is demonstrated for the polymer-to-polymer upcycling of waste PET into high-value biodegradable and programmable materials named PEXT. This process involves reversible transesterifications dependent on ester bonds, wherein commercially available X-monomers from aliphatic diacids and diols are introduced, utilizing existing industrial equipment for complete PET utilization. PEXT features a programmable molecular structure, delivering tailored mechanical, thermal, and biodegradation performance. Notably, PEXT exhibits superior mechanical performance, with a maximal elongation at break of 3419.2 % and a toughness of 270.79 MJ m-3. These characteristics make PEXT suitable for numerous applications, including shape-memory materials, transparent films, and fracture-resistant stretchable components. Significantly, PEXT allows closed-loop recycling within specific biodegradable analogs by reprograming PET or X-monomers. This strategy not only offers cost-effective advantages in large-scale upcycling of waste PET into advanced materials but also demonstrates its enormous prospect in environmental conservation.

Recycling polyolefin plastic waste at short contact times via rapid joule heating

The chemical deconstruction of polyolefins to fuels, lubricants, and waxes offers a promising strategy for mitigating their accumulation in landfills and the environment. Yet, achieving true recyclability of polyolefins into C2-C4 monomers with high yields, low energy demand, and low carbon dioxide emissions under realistic polymer-to-catalyst ratios remains elusive. Here, we demonstrate a single-step electrified approach utilizing Rapid Joule Heating over an H-ZSM-5 catalyst to efficiently deconstruct polyolefin plastic waste into light olefins (C2-C4) in milliseconds, with high productivity at much higher polymer-to-catalyst ratio than prior work. The catalyst is essential in producing a narrow distribution of light olefins. Pulsed operation and steam co-feeding enable highly selective deconstruction (product fraction of >90% towards C2-C4 hydrocarbons) with minimal catalyst deactivation compared to Continuous Joule Heating. This laboratory-scale approach demonstrates effective deconstruction of real-life waste materials, resilience to additives and impurities, and versatility for circular polyolefin plastic waste management.

Lifecycle Management for Sustainable Plastics: Recent Progress from Synthesis, Processing to Upcycling

Plastics, renowned for their outstanding properties and extensive applications, assume an indispensable and irreplaceable role in modern society. However, the ubiquitous consumption of plastic items has led to a growing accumulation of plastic waste. Unreasonable practices in the production, utilization, and recycling of plastics have led to substantial energy resource depletion and environmental pollution. Herein, the state-of-the-art advancements in the lifecycle management of plastics are timely reviewed. Unlike typical reviews focused on plastic recycling, this work presents an in-depth analysis of the entire lifecycle of plastics, covering the whole process from synthesis, processing, to ultimate disposal. The primary emphasis lies on selecting judicious strategies and methodologies at each lifecycle stage to mitigate the adverse environmental impact of waste plastics. Specifically, the article delineates the rationale, methods, and advancements realized in various lifecycle stages through both physical and chemical recycling pathways. The focal point is the attainment of optimal recycling rates for waste plastics, thereby alleviating the ecological burden of plastic pollution. By scrutinizing the entire lifecycle of plastics, the article aims to furnish comprehensive solutions for reducing plastic pollution and fostering sustainability across all facets of plastic production, utilization, and disposal.

Upcycling of polyethylene to gasoline through a self-supplied hydrogen strategy in a layered self-pillared zeolite

Conversion of plastic wastes to valuable carbon resources without using noble metal catalysts or external hydrogen remains a challenging task. Here we report a layered self-pillared zeolite that enables the conversion of polyethylene to gasoline with a remarkable selectivity of 99% and yields of >80% in 4 h at 240 °C. The liquid product is primarily composed of branched alkanes (selectivity of 72%), affording a high research octane number of 88.0 that is comparable to commercial gasoline (86.6). In situ inelastic neutron scattering, small-angle neutron scattering, solid-state nuclear magnetic resonance, X-ray absorption spectroscopy and isotope-labelling experiments reveal that the activation of polyethylene is promoted by the open framework tri-coordinated Al sites of the zeolite, followed by β-scission and isomerization on Brönsted acids sites, accompanied by hydride transfer over open framework tri-coordinated Al sites through a self-supplied hydrogen pathway to yield selectivity to branched alkanes. This study shows the potential of layered zeolite materials in enabling the upcycling of plastic wastes.

Recent Progresses and Challenges in Upcycling of Plastics through Selective Catalytic Oxidation

Chemical upcycling of plastics provides an important direction for solving the challenging issues of plastic pollution and mitigating the wastage of carbon resources. Among them, catalytic oxidative cracking of plastics to produce high-value chemicals, such as catalytic oxidation of polyethylene (PE) to produce fatty dicarboxylic acids, catalytic oxidation of polystyrene (PS) to produce benzoic acid, and catalytic oxidation of polyethylene terephthalate (PET) to produce terephthalic acid under mild conditions has attracted increasing attention, and some exciting progress has been made recently. In this article, we will review recent progresses on the catalytic oxidation upcycling of plastics and provide our understanding on the current challenges in catalytic oxidation upcycling of plastics.

Oil recovery from microwave co-pyrolysis of polystyrene and polypropylene plastic particles for pollution mitigation

Addressing the mounting environmental challenge of non-degradable polymeric waste, the world grapples with escalating production driven by population growth, modernization, and industrialization. Pyrolysis has emerged as a promising and strategic solution for transforming non-degradable polymeric waste into valuable fuels and other chemical products. This study detailed the high-quality oil recovery from microwave co-pyrolysis of polystyrene (PS) and polypropylene (PP) mixtures. The effects of PS/PP ratio (30:0, 10:20, 15:15, 20:10, and 30:0 g), microwave power (400, 500, 600, 700, and 800 W), and pyrolysis temperature (450, 500, 550, 600, and 650 °C) on oil yield and components were studied, and the synergistic effect, higher heating value (HHV) and thermal efficiency were also detailed. The results revealed that the highest oil yield was 93.84 wt% when PS/PP ratio, microwave power, and pyrolysis temperature were adjusted at 20:10 g, 600 W, and 550 °C, respectively. And the maximum higher heating value and thermal efficiency were 45.67 MJ/kg and 56.53%, respectively. The contents of aromatic hydrocarbons, cyclic hydrocarbons, and oxygenated hydrocarbons varied in the ranges of 1.92-58.88 area%, 10.47-41.76 area%, and 5.06-24.36 area%, respectively. The contents of the major carbon numbers were C8 and C9, and they varied in 2.51-43.66 area% and 7.31-20.09 area%, respectively. The results presented in this study showed that high-quality oil can be recovered from polystyrene and polypropylene plastics by using microwave irradiation, contributing to cleaner ways for plastics recycling.

Flash heating process for efficient meat preservation

Maintaining food safety and quality is critical for public health and food security. Conventional food preservation methods, such as pasteurization and dehydration, often change the overall organoleptic quality of the food products. Herein, we demonstrate a method that affects only a thin surface layer of the food, using beef as a model. In this method, Joule heating is generated by applying high electric power to a carbon substrate in <1 s, which causes a transient increase of the substrate temperature to > ~2000 K. The beef surface in direct contact with the heating substrate is subjected to ultra-high temperature flash heating, leading to the formation of a microbe-inactivated, dehydrated layer of ~100 µm in thickness. Aerobic mesophilic bacteria, Enterobacteriaceae, yeast and mold on the treated samples are inactivated to a level below the detection limit and remained low during room temperature storage of 5 days. Meanwhile, the product quality, including visual appearance, texture, and nutrient level of the beef, remains mostly unchanged. In contrast, microorganisms grow rapidly on the untreated control samples, along with a rapid deterioration of the meat quality. This method might serve as a promising preservation technology for securing food safety and quality.

Distributed electrified heating for efficient hydrogen production

This study introduces a distributed electrified heating approach that is able to innovate chemical engineering involving endothermic reactions. It enables rapid and uniform heating of gaseous reactants, facilitating efficient conversion and high product selectivity at specific equilibrium. Demonstrated in catalyst-free CH4 pyrolysis, this approach achieves stable production of H2 (530 g h-1 L reactor -1) and carbon nanotube/fibers through 100% conversion of high-throughput CH4 at 1150 °C, surpassing the results obtained from many complex metal catalysts and high-temperature technologies. Additionally, in catalytic CH4 dry reforming, the distributed electrified heating using metallic monolith with unmodified Ni/MgO catalyst washcoat showcased excellent CH4 and CO2 conversion rates, and syngas production capacity. This innovative heating approach eliminates the need for elongated reactor tubes and external furnaces, promising an energy-concentrated and ultra-compact reactor design significantly smaller than traditional industrial systems, marking a significant advance towards more sustainable and efficient chemical engineering society.

Hydrodeoxygenation of Oxygen-Containing Aromatic Plastic Wastes into Cycloalkanes and Aromatics

Chemical recycling and upcycling offer promising approaches for the management of plastic wastes. Hydrodeoxygenation (HDO) is one of the appealing ways for conversion of oxygen-containing plastic wastes, including polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polycarbonate (PC), polyphenyl ether (PPO), and polyether ether ketone (PEEK), into cyclic alkanes and aromatics in high yields under mild reaction conditions. The challenge lies in achieving C-O activation while preserving C-C bonds. In this review, we highlight the recent advancements in catalytic strategies and catalysts for the conversion of these oxygen-containing plastic wastes into cycloalkanes and aromatics. The reaction systems, including multi-step routes, direct HDO and transfer HDO methods, are exemplified. The design and performance of HDO catalysts are systematically summarized and compared. We comprehensively discuss the functions of the catalysts' components, reaction pathway and mechanism to gain insights into the HDO process for efficient valorization of oxygen-containing plastic wastes. Finally, we provide perspectives for this field, with specific emphasis on the non-noble metal catalyst design, selectivity control, reaction network and mechanism studies, mixed plastic wastes management and product functionalization. We anticipate that this review will inspire innovations on the catalytic process development and rational catalyst design for the HDO of oxygen-containing aromatic plastics to establish a low-emission circular economy.

Continuous and low-carbon production of biomass flash graphene

Flash Joule heating (FJH) is an emerging and profitable technology for converting inexhaustible biomass into flash graphene (FG). However, it is challenging to produce biomass FG continuously due to the lack of an integrated device. Furthermore, the high-carbon footprint induced by both excessive energy allocation for massive pyrolytic volatiles release and carbon black utilization in alternating current-FJH (AC-FJH) reaction exacerbates this challenge. Here, we create an integrated automatic system with energy requirement-oriented allocation to achieve continuous biomass FG production with a much lower carbon footprint. The programmable logic controller flexibly coordinated the FJH modular components to realize the turnover of biomass FG production. Furthermore, we propose pyrolysis-FJH nexus to achieve biomass FG production. Initially, we utilize pyrolysis to release biomass pyrolytic volatiles, and subsequently carry out the FJH reaction to focus on optimizing the FG structure. Importantly, biochar with appropriate resistance is self-sufficient to initiate the FJH reaction. Accordingly, the medium-temperature biochar-based FG production without carbon black utilization exhibited low carbon emission (1.9 g CO2-eq g-1 graphene), equivalent to a reduction of up to ~86.1% compared to biomass-based FG production. Undoubtedly, this integrated automatic system assisted by pyrolysis-FJH nexus can facilitate biomass FG into a broad spectrum of applications.

Do medical devices contribute to sustainability? The role of innovative polymers and device design

Sustainability of a medical device has not yet become a major issue in public discussions compared to other topics with impact to material performance, clinical application, production economy and environmental pollution. Due to their unique properties, polymers (plastics) allow for multiple, flexible applications in medical device technology. Polymers are part of the majority of disposable and single use medical device and contribute with 3% to the worldwide production of plastics. The global medical polymer market size was valued 19.9 billion US-$ in 2022 and its value projection for 2023 is expected to reach 43.03 billion US-$ Here, a wider concept of related sustainability is introduced for medical devices and their polymer components. A close look on medical device specification reveals that additional properties are required to provide sustainability, such as biodegradability, quality by device design (QbD), as well as an inbuild performance service for patients, healthcare professionals and healthcare providers. The increasing global numbers for chronic and non-communicable diseases require a huge demand for single use medical devices. A careful look at polymer specification and its performance properties is needed, including possible chemical modifications and degradation processes during waste disposal. Bioengineers in charge of design and production of medical devices will only be successful when they apply a holistic and interdisciplinary approach to medical device sustainability.

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.

Post-Consumer Carpet Fibers in Concrete: Fiber Behavior in Alkaline Environments and Concrete Durability

The widespread use of carpets in residential and commercial buildings and their relatively short life span result in large volumes of carpet being landfilled. A potential solution to this problem is the use of post-consumer carpet fibers in concrete. To this end, this paper systematically identifies the common fiber types in a typical post-consumer carpet fiber bale and evaluates their durability under exposure to varying levels of alkalinity. The tensile strengths and toughness of the fibers belonging to the nylon and polyethylene terephthalate (PET) families (the dominant fibers in most post-consumer carpets) are reduced by up to 50% following exposure to extreme alkalinity, the reasons for which are determined using spectroscopic and microscopic evaluations. The chloride ion transport resistance of concretes (~40 MPa strength) containing 2.5% carpet fibers by volume (~25 kg of fibers per cubic meter of concrete) is comparable to that of the control mixture, while mortar mixtures containing the same volume fraction of carpet fibers demonstrate negligible enhancement in expansion and loss of strength when exposed to 1 N NaOH. This study shows that moderate-strength concretes (~40 MPa) for conventional building and infrastructure applications can be proportioned using the chosen volume of carpet fibers without an appreciable loss of performance. Consideration of low volume fractions of carpet fibers in low-to-moderate-strength concretes thus provides a sustainable avenue for the use of these otherwise landfilled materials in construction applications.

Low-Temperature Upcycling of Polypropylene Waste into H2 Fuel via a Novel Tandem Hydrothermal Process

Plastic waste is a promising and abundant resource for H2 production. However, upcycling plastic waste into H2 fuel via conventional thermochemical routes requires relatively considerable energy input and severe reaction conditions, particularly for polyolefin waste. Here, we report a tandem strategy for the selective upcycling of polypropylene (PP) waste into H2 fuel in a mild and clean manner. PP waste was first oxidized into small-molecule organic acids using pure O2 as oxidant at 190 °C, followed by the catalytic reforming of oxidation aqueous products over ZnO-modified Ru/NiAl2 O4 catalysts to produce H2 at 300 °C. A high H2 yield of 44.5 mol/kgPP and a H2 mole fraction of 60.5 % were obtained from this tandem process. The entire process operated with almost no solid residue remaining and equipment contamination, ensuring relative stability and cleanliness of the reaction system. This strategy provides a new route for low-temperature transforming PP and improving the sustainability of plastic waste disposal processes.

A general strategy for recycling polyester wastes into carboxylic acids and hydrocarbons

Chemical recycling of plastic wastes is of great significance for sustainable development, which also represents a largely untapped opportunity for the synthesis of value-added chemicals. Herein, we report a novel and general strategy to degrade polyesters via directly breaking the Calkoxy-O bond by nucleophilic substitution of halide anion of ionic liquids under mild conditions. Combined with hydrogenation over Pd/C, 1-butyl-2,3-dimethylimidazolium bromide can realize the deconstruction of various polyesters including aromatic and aliphatic ones, copolyesters and polyester mixtures into corresponding carboxylic acids and alkanes; meanwhile, tetrabutylphosphonium bromide can also achieve direct decomposition of the polyesters with β-H into carboxylic acids and alkenes under hydrogen- and metal-free conditions. It is found that the hydrogen-bonding interaction between ionic liquid and ester group in polyester enhances the nucleophilicity of halide anion and activates the Calkoxy-O bond. The findings demonstrate how polyester wastes can be a viable feedstock for the production of carboxylic acids and hydrocarbons.

Chemical recycling of plastic wastes with alkaline earth metal oxides: A review

Plastics have been widely used in daily life and industries due to their low cost and high durability, leading to huge production of plastics and tens of millions of plastic wastes every year. Chemical recycling can recycle contaminated and degraded plastics (that mechanical recycling cannot deal with) to obtain value-added products, which potentially solves the environmental problems caused by plastics and realizes a circular economy. Alkaline earth metal oxides, as a category of cost-effective and multi-functional materials, have been widely used in chemical recycling of common plastics, acting as three roles: catalyst, template, and absorbent. Among five commercial plastics, polyethylene terephthalate is suitable for pyrolysis and solvolysis. Polyethylene and polypropylene, which are ideal precursors for synthesis of carbon nanotubes, could be combined with biomass for co-pyrolysis. Polyvinyl chloride needs to be pretreated to reduce chloride content prior to pyrolysis. Depolymerization of polystyrene into monomers is attractive. This review summarized the chemical recycling approaches of commercial plastics and the strategies with alkaline earth metal oxides for the development of efficient recycling processes. It will aid understanding of the advances and challenges in the field and promote the future research.

Sustainable ethylene production: Recovery from plastic waste via thermochemical processes

The concept of monomer recovery from plastic waste has recently gained broad interest in industry as a powerful strategy to reduce the environmental impacts of chemical production and plastic waste pollution. Herein, we focus on the ethylene recovery from plastic waste via thermochemical pathways, such as pyrolysis, gasification, and steam cracking of pyrolysis oil derived from plastic waste. Ethylene recovery performance of different thermochemical conversion processes is evaluated and compared with respect to plastic waste types, process types, ethylene recovery yields, and process operating conditions. Based on the analysis of available data in earlier literature, future research is recommended to further enhance the viability of the thermochemical ethylene recovery technologies. This review is expected to offer a meaningful guideline on developing efficient platforms for the value-added monomer recovery from plastic waste through thermochemical conversion routes. It is also hoped that this review serves as a preliminary step to encourage the widespread adoption of thermochemical conversion-based ethylene recovery from plastic waste by industries.

Closed-Loop Recyclable Silica-Based Nanocomposites with Multifunctional Properties and Versatile Processability

Most plastics originate from limited petroleum reserves and cannot be effectively recycled at the end of their life cycle, making them a significant threat to the environment and human health. Closed-loop chemical recycling, by depolymerizing plastics into monomers that can be repolymerized, offers a promising solution for recycling otherwise wasted plastics. However, most current chemically recyclable polymers may only be prepared at the gram scale, and their depolymerization typically requires harsh conditions and high energy consumption. Herein, it reports less petroleum-dependent closed-loop recyclable silica-based nanocomposites that can be prepared on a large scale and have a fully reversible polymerization/depolymerization capability at room temperature, based on catalysis of free aminopropyl groups with the assistance of diethylamine or ethylenediamine. The nanocomposites show glass-like hardness yet plastic-like light weight and toughness, exhibiting the highest specific mechanical strength superior even to common materials such as poly(methyl methacrylate), glass, and ZrO2 ceramic, as well as demonstrating multifunctionality such as anti-fouling, low thermal conductivity, and flame retardancy. Meanwhile, these nanocomposites can be easily processed by various plastic-like scalable manufacturing methods, such as compression molding and 3D printing. These nanocomposites are expected to provide an alternative to petroleum-based plastics and contribute to a closed-loop materials economy.

Mixed Plastics Wastes Upcycling with High-Stability Single-Atom Ru Catalyst

Mixed plastic waste treatment has long been a significant challenge due to complex composition and sorting costs. In this study, we have achieved a breakthrough in converting mixed plastic wastes into a single chemical product using our innovative single-atom catalysts for the first time. The single-atom Ru catalyst can convert ∼90% of real mixed plastic wastes into methane products (selectivity >99%). The unique electronic structure of Ru sites regulates the adsorption energy of mixed plastic intermediates, leading to rapid decomposition of mixed plastics and superior cycle stability compared to traditional nanocatalysts. The global warming potential of the entire process was evaluated. Our proposed carbon-reducing process utilizing single-atom catalysts launches a new era of mixed plastic waste valorization.

Facile H2PdCl4-induced photoreforming of insoluble PET waste for C1-C3 compound production

Plastic pollution has emerged as a pressing global concern, driven by the extensive production and consumption of plastic, resulting in over 8 billion tons of plastic waste generated to date. Conventional disposal methods have proven inadequate in effectively managing polymer waste, necessitating the exploration of novel techniques. Previous research has demonstrated the successful application of photoreforming (PR) in converting water-soluble oligomer fragments of plastics into valuable chemicals. However, an unresolved challenge remains in dealing with the insoluble oligomer fragments characterized by complex chemical structures and larger molecular sizes. In this study, we propose a facile approach that involves H2PdCl4-induced activation on PET substrate for PR of PET bottles. Remarkably, this method enables the production of C1-C3 compounds without the reliance on sacrificial reagents or photocatalysts. The significant findings of this study offer a practical solution to address the most formidable aspect of plastic PR, specifically targeting the insoluble oligomer fragments. Moreover, this research contributes to the advancement of effective strategies for the sustainable management of plastic waste.

Understanding Rapid PET Degradation via Reactive Molecular Dynamics Simulation and Kinetic Modeling

As the demand for PET plastic products continues to grow, developing effective processes to reduce their pollution is of critical importance. Pyrolysis, a promising technology to produce lighter and recyclable components from wasted plastic products, has therefore received considerable attention. In this work, the rapid pyrolysis of PET was studied by using reactive molecular dynamics (MD) simulations. Mechanisms for yielding gas species were unraveled, which involve the generation of ethylene and TPA radicals from ester oxygen-alkyl carbon bond dissociation and condensation reactions to consume TPA radicals with the products of long chains containing a phenyl benzoate structure and CO2. As atomistic simulations are typically conducted at the time scale of a few nanoseconds, a high temperature (i.e., >1000 K) is adopted for accelerated reaction events. To apply the results from MD simulations to practical pyrolysis processes, a kinetic model based on a set of ordinary differential equations was established, which is capable of describing the key products of PET pyrolysis as a function of time and temperature. It was further exploited to determine the optimal reaction conditions for low environmental impact. Overall, this study conducted a detailed mechanism study of PET pyrolysis and established an effective kinetic model for the main species. The approach presented herein to extract kinetic information such as detailed kinetic constants and activation energies from atomistic MD simulations can also be applied to related systems such as the pyrolysis of other polymers.

Chemical upcycling of polyethylene, polypropylene, and mixtures to high-value surfactants

Conversion of plastic wastes to fatty acids is an attractive means to supplement the sourcing of these high-value, high-volume chemicals. We report a method for transforming polyethylene (PE) and polypropylene (PP) at ~80% conversion to fatty acids with number-average molar masses of up to ~700 and 670 daltons, respectively. The process is applicable to municipal PE and PP wastes and their mixtures. Temperature-gradient thermolysis is the key to controllably degrading PE and PP into waxes and inhibiting the production of small molecules. The waxes are upcycled to fatty acids by oxidation over manganese stearate and subsequent processing. PP ꞵ-scission produces more olefin wax and yields higher acid-number fatty acids than does PE ꞵ-scission. We further convert the fatty acids to high-value, large-market-volume surfactants. Industrial-scale technoeconomic analysis suggests economic viability without the need for subsidies.