Upcycling to Sustainably Reuse Plastics

Progress on Photo-, Electro-, and Photoelectro-Catalytic Conversion of Recalcitrant Polyethylene, Polypropylene, and Polystyrene - A Review

Recalcitrant waste plastics such a polyethylene, polypropylene, and polystyrene are difficult to recycle and are mostly disposed of in landfills and eventually leached into the environmental as micro- and nano-plastics. This review explores how photo-, electro-, and combined photoelectro-catalytic processes can assist in the degradation and upcycling of waste plastic into different chemicals and mitigate their release to the environment. In this work, we discuss how the different reaction mechanisms proceed, explore the current relevant literature, and highlight the developments needed to advance the field.

Accessing a Carboxyl-Anhydride Molecular Switch-Mediated Recyclable PECT Through Upcycling End-of-Use PET

Poly(ethylene terephthalate) (PET), with an annual production of exceeding 70 million tons, is mainly utilized in disposable fields and subsequently contribute to severe environmental pollution. Conventional chemical recycling, which typically involves depolymerizing polymer into monomers, is limited due to the intricate recycling process, excess using unrecyclable solvents and low polymer conversion. Inspired by protein's molecular switches, we propose a novel polymer-to-polymer recycling strategy based on polycondensation principles upcycling waste PET to high-value recyclable poly(ethylene-co-1,4-cyclohexanedimethanol terephthalate) derivatives containing molecular switches. Upon deactivating the molecular switch, an acidification reaction occurs within the system, leading to a rapid and controllable reduction in molecular weight due to the imbalance of reactive group. Conversely, activating the molecular switch triggers a ring-closing reaction that detaches acid anhydrides, bringing about equal molar ratio of groups and thereby facilitating an increase in molecular weight. By simply incorporating a molecular switch into condensation products based on melt polycondensation, closed-loop recycling capability is achieved without necessitating excessive organic solvents or complex depolymerization processes. The present study not only presents a novel pathway for end-of-use PET upcycling but also introduces an innovative concept of molecular switching for the closed-loop recyclability of condensation polymers, thereby demonstrating significant potential for large-scale implementation.

Impact of microplastics on the human digestive system: From basic to clinical

As a new type of pollutant, the harm caused by microplastics (MPs) to organisms has been the research focus. Recently, the proportion of MPs ingested through the digestive tract has gradually increased with the popularity of fast-food products, such as takeout. The damage to the digestive system has attracted increasing attention. We reviewed the literature regarding toxicity of MPs and observed that they have different effects on multiple organs of the digestive system. The mechanism may be related to the toxic effects of MPs themselves, interactions with various substances in the biological body, and participation in various signaling pathways to induce adverse reactions as a carrier of toxins to increase the time and amount of body absorption. Based on the toxicity mechanism of MPs, we propose specific suggestions to provide a theoretical reference for the government and relevant departments.

Cation-Vacancy Engineering in Cobalt Selenide Boosts Electrocatalytic Upcycling of Polyester Thermoplastics at Industrial-Level Current Density

The past decades have witnessed the increasing accumulation of plastics, posing a daunting environmental crisis. Among various solutions, converting plastics into value-added products presents a significant endeavor. Here, an electrocatalytic upcycling route that efficiently converts waste poly(butylene terephthalate) plastics into high-value succinic acid with high Faradaic efficiency of 94.0% over cation vacancies-rich cobalt selenide catalyst is reported, showcasing unprecedented activity (1.477 V vs. RHE) to achieve an industrial-level current density of 1.5 A cm-2, and featuring a robust operating durability (≈170 h). In particular, when combining butane-1,4-diol monomer oxidation (BOR) with hydrogen evolution using the cation vacancy-engineered cobalt selenide as bifunctional catalyst, a relatively low cell voltage of 1.681 V is required to reach 400 mA cm-2, manifesting an energy-saving efficiency of ≈15% compared to pure water splitting. The mechanism and reaction pathways of BOR over the vacancies-rich catalyst are first revealed through theoretical calculations and in-situ spectroscopic investigations. The generality of this catalyst is evidenced by its powerful electrocatalytic activity to other polyester thermoplastics such as poly(butylene succinate) and poly(ethylene terephthalate). These electrocatalytic upcycling strategies can be coupled with the reduction of small molecules (e.g., H2O, CO2, and NO3 -), shedding light on energy-saving production of value-added chemicals.

Advanced Catalysts for the Chemical Recycling of Plastic Waste

Plastic products bring convenience to various aspects of the daily lives due to their lightweight, durability and versatility, but the massive accumulation of post-consumer plastic waste is posing significant environmental challenges. Catalytic methods can effectively convert plastic waste into value-added feedstocks, with catalysts playing an important role in regulating the yield and selectivity of products. This review explores the latest advancements in advanced catalysts applied in thermal catalysis, microwave-assisted catalysis, photocatalysis, electrocatalysis, and enzymatic catalysis reaction systems for the chemical recycling of plastic waste into valuable feedstocks. Specifically, the pathways and mechanisms involved in the plastics recycling process are analyzed and presented, and the strengths and weaknesses of various catalysts employed across different reaction systems are described. In addition, the structure-function relationship of these catalysts is discussed. Herein, it is provided insights into the design of novel catalysts applied for the chemical recycling of plastic waste and outline challenges and future opportunities in terms of developing advanced catalysts to tackle the "white pollution" crisis.

Upcycling of Polyethylene Wastes to Valuable Chemicals over Group VIII Metal-decorated WO3 Nanosheets

Catalytic cracking of polyolefin wastes into valuable chemicals at mild conditions using non-noble metal catalysts is highly attractive yet challenging. Herein it is reported that 2D tungsten trioxide (2D WO3) nanosheets, after decorating with group VIII metal promoters (i.e., Fe, Co, or Ni), convert high-density polyethylene (HDPE) into alkylaromatics and olefins at low temperature and ambient pressure without using any solvent or hydrogen: 2D Ni/WO3 with abundant Brønsted acidic sites initiates HDPE cracking at a low temperature of 240 °C; 2D Fe/WO3 with low energy barrier of cyclization achieves a high HDPE conversion to 84.2% liquid hydrocarbons with a selectivity of 30.9% to aromatics at 300 °C. In-situ spectroscopic investigations and supplementary theoretical calculations illustrate that these aromatics are formed through the cyclization of alkene intermediates. These 2D catalysts also display high efficiency in the low-temperature cracking of single-use commercial polyethylene wastes such as packaging bags and bottles. This work has demonstrated the high potential of 2D non-noble metal catalysts in the efficient upcycling of waste polyolefin at mild conditions.

Photoreforming of Plastic Waste to Sustainable Fuels and Chemicals: Waste to Energy

The extensive accumulation of plastic waste has given rise to severe environmental pollution issues. Contemporary conventional recycling methods, such as incineration and landfilling, contribute significantly to pollutant emissions and carbon footprints, against the principles of sustainable development. Leveraging renewable solar energy to transform plastics into high-value chemicals and green fuels offers a more promising and sustainable approach to managing plastic waste resources. This comprehensive review centers on the recent advancements in plastic photoreforming, categorizing them based on the types of end products. Particular emphasis is placed on the evolving research landscape surrounding the conversion of plastics into high-value chemicals through photoreforming, as well as the economic considerations for large-scale photoreforming production. The analysis conducted here reveals key pathways and emerging trends that are poised to shape the trajectory of enhanced photoconversion, ultimately influencing the realization of a carbon-neutral future.

The current progress of tandem chemical and biological plastic upcycling

Each year, millions of tons of plastics are produced for use in such applications as packaging, construction, and textiles. While plastic is undeniably useful and convenient, its environmental fate and transport have raised growing concerns about waste and pollution. However, the ease and low cost of producing virgin plastic have so far made conventional plastic recycling economically unattractive. Common contaminants in plastic waste and shortcomings of the recycling processes themselves typically mean that recycled plastic products are of relatively low quality in some cases. The high cost and high energy requirements of typical recycling operations also reduce their economic benefits. In recent years, the bio-upcycling of chemically treated plastic waste has emerged as a promising alternative to conventional plastic recycling. Unlike recycling, bio-upcycling uses relatively mild process conditions to economically transform pretreated plastic waste into value-added products. In this review, we first provide a précis of the general methodology and limits of conventional plastic recycling. Then, we review recent advances in hybrid chemical/biological upcycling methods for different plastics, including polyethylene terephthalate, polyurethane, polyamide, polycarbonate, polyethylene, polypropylene, polystyrene, and polyvinyl chloride. For each kind of plastic, we summarize both the pretreatment methods for making the plastic bio-available and the microbial chassis for degrading or converting the treated plastic waste to value-added products. We also discuss both the limitations of upcycling processes for major plastics and their potential for bio-upcycling.

Cutting-edge developments in plastic biodegradation and upcycling via engineering approaches

The increasing use of plastics has resulted in the production of high quantities of plastic waste that pose a serious risk to the environment. The upcycling of plastics into value-added products offers a potential solution for resolving the plastics environmental crisis. Recently, various microorganisms and their enzymes have been identified for their ability to degrade plastics effectively. Furthermore, many investigations have revealed the application of plastic monomers as carbon sources for bio-upcycling to generate valuable materials such as biosurfactants, bioplastics, and biochemicals. With the advancement in the fields of synthetic biology and metabolic engineering, the construction of high-performance microbes and enzymes for plastic removal and bio-upcycling can be achieved. Plastic valorization can be optimized by improving uptake and conversion efficiency, engineering transporters and enzymes, metabolic pathway reconstruction, and also using a chemo-biological hybrid approach. This review focuses on engineering approaches for enhancing plastic removal and the methods of depolymerization and upcycling processes of various microplastics. Additionally, the major challenges and future perspectives for facilitating the development of a sustainable circular plastic economy are highlighted.

Toward Sustainable Polymer Materials for Rechargeable Batteries: Utilizing Natural Feedstocks and Recycling/Upcycling of Polymer Waste

The ever-increasing demand for rechargeable battery systems in the era of electric vehicles has spurred extensive research into developing polymeric components for batteries, such as separators, polymer electrolytes, and binders. However, current battery systems rely on expensive and nonrenewable resources, which potentially have a negative environmental impact. Therefore, polymer materials derived from natural resources have gained significant attention, primarily due to their cost-effective and environmentally sustainable features. Moreover, natural feedstocks often possess highly polar functional groups and high molecular weights, offering desirable electro-chemo-mechanical features when applied as battery materials. More recently, various recycling and upcycling strategies for polymeric battery components have also been proposed given the substantial waste generation from end-of-life batteries. Recycling polymeric materials includes an overall process of recovering the components from spent batteries followed by regeneration into new materials. Polymer upcycling into battery materials involves transforming daily-used plastic waste into high-value-added battery components. This review aims to give a state-of-the-art overview of contemporary methods to develop sustainable polymeric materials and recycling/upcycling strategies for various battery applications.

Photocatalytic Upcycling of Plastic Waste into Syngas by ZnS/Ga2O3 Z-Scheme Heterojunction

The photocatalytic conversion of plastic waste into value-added products using solar energy presents a promising approach for promoting environmental sustainability. Nonetheless, the emission of CO2 during the conventional photocatalytic degradation process remains a major hurdle that impedes its further development. In this study, we propose an efficient photocatalytic conversion of polyethylene plastic into syngas (CO+H2 mixtures) by using a ZnS/Ga2O3 Z-scheme heterojunction photocatalyst. It is found that the strong redox capability of photogenerated holes and electrons in the Z-scheme heterojunction photocatalyst can promote the oxidative depolymerization of PE plastic, concurrently enabling the efficient reduction of the intermediate product CO2 into syngas. Furthermore, this system also demonstrates applicability in the conversion and upcycling of other polyolefin plastics including polypropylene and polyvinyl chloride. Our findings highlight the potential of polyolefin plastics photoreforming for the production of syngas under environmentally benign conditions.

Unraveling the Impact of Oxygen Vacancy on Electrochemical Valorization of Polyester Over Spinel Oxides

Electrochemical upcycling of end-of-life polyethylene terephthalate (PET) using renewable electricity offers a route to generate valuable chemicals while processing plastic wastes. However, it remains a huge challenge to design an electrocatalyst with reliable structure-property relationships for PET valorization. Herein, spinel Co3O4 with rich oxygen vacancies for improved activity toward formic acid (FA) production from PET hydrolysate is reported. Experimental investigations combined with theoretical calculations reveal that incorporation of VO into Co3O4 not only promotes the generation of reactive hydroxyl species (OH*) species at adjacent tetrahedral Co2+ (Co2+ Td), but also induces an electronic structure transition from octahedral Co3+ (Co3+ Oh) to octahedral Co2+ (Co2+ Oh), which typically functions as highly-active catalytic sites for ethylene glycol (EG) chemisorption. Moreover, the enlarged Co-O covalency induced by VO facilitates the electron transfer from EG* to OH* via Co2+ Oh-O-Co2+ Td interaction and the following C─C bond cleavage via direct oxidation with a glyoxal intermediate pathway. As a result, the VO-Co3O4 catalyst exhibits a high half-cell activity for EG oxidation, with a Faradaic efficiency (91%) and productivity (1.02 mmol cm-2 h-1) of FA. Lastly, it is demonstrated that hundred gram-scale formate crystals can be produced from the real-world PET bottles via two-electrode electroreforming, with a yield of 82%.

Photochemical Aerobic Upcycling of Polystyrene Plastics

Although the introduction of plastics has improved humanity's everyday life, the fast accumulation of plastic waste, including microplastics and nanoplastics, have created numerous problems with recent studies highlighting their involvement in various aspects of our lives. Upcycling of plastics, the conversion of plastic waste to high-added value chemicals, is a way to combat plastic waste that is receiving increased attention. Herein, we describe a novel aerobic photochemical process for the upcycling of real-life polystyrene-based plastics into benzoic acid. A new process employing a thioxanthone-derivative, in combination with N-bromosuccinimide, under ambient air and 390 nm irradiation is capable of upcycling real-life polystyrene-derived products in benzoic acid in yields varying from 24-54 %.

High-Entropy Materials in Electrocatalysis: Understanding, Design, and Development

Electrocatalysis is a crucial method for achieving global carbon neutrality, serving as an essential means of energy conversion, and electrocatalyst is crucial in the process of electrocatalysis. Because of the abundant active sites, the multi-component synergistic effect of high-entropy materials has a wide application prospect in the field of electrocatalysis. Moreover, due to the special structure of high-entropy materials, it is possible to obtain almost continuous adsorption energy distribution by regulating the composition, which has attracted extensive attention of researchers. This paper reviews the properties and types of high-entropy materials, including alloys and compounds. The synthesis strategies of high-entropy materials are systematically introduced, and the solid phase synthesis, liquid-phase synthesis, and gas-phase synthesis are classified and summarized. The application of high-entropy materials in electrocatalysis is summarized, and the promotion effect of high-entropy strategy in various catalytic reaction processes is summarized. Finally, the current progress of high-entropy materials, the problems encountered, and the future development direction are reviewed. It is emphasized that the strategy of high flux density functional theory calculation guiding high-entropy catalyst design will be of great significance to electrocatalysis.

Plastic-Degrading Enzymes from Marine Microorganisms and Their Potential Value in Recycling Technologies

Since the 2005 discovery of the first enzyme capable of depolymerizing polyethylene terephthalate (PET), an aromatic polyester once thought to be enzymatically inert, extensive research has been undertaken to identify and engineer new biocatalysts for plastic degradation. This effort was directed toward developing efficient enzymatic recycling technologies that could overcome the limitations of mechanical and chemical methods. These enzymes are versatile molecules obtained from microorganisms living in various environments, including soil, compost, surface seawater, and extreme habitats such as hot springs, hydrothermal vents, deep-sea regions, and Antarctic seawater. Among various plastics, PET and polylactic acid (PLA) have been the primary focus of enzymatic depolymerization research, greatly enhancing our knowledge of enzymes that degrade these specific polymers. They often display unique catalytic properties that reflect their particular ecological niches. This review explores recent advancements in marine-derived enzymes that can depolymerize synthetic plastic polymers, emphasizing their structural and functional features that influence the efficiency of these catalysts in biorecycling processes. Current status and future perspectives of enzymatic plastic depolymerization are also discussed, with a focus on the underexplored marine enzymatic resources.

Recovering Valuable Chemicals from Polypropylene Waste via a Mild Catalyst-Free Hydrothermal Process

Waste polypropylene (PP) presents a significant environmental challenge, owing to its refractory nature and inert C-C backbone. In this study, we introduce a practical chemical recovery strategy from PP waste using a mild catalyst-free hydrothermal treatment (HT). The treatment converts 64.1% of the processed PP into dissolved organic products within 2 h in an air atmosphere at 160 °C. Higher temperatures increase the PP conversion efficiency. Distinct electron absorption and emission characteristics of the products are identified by spectral analysis. Fourier transform-ion cyclotron resonance-mass spectrometry (FT-ICR-MS) reveals the oxidative cracking of PP into shorter-chain homologues (10-50 carbon atoms) containing carboxylic and carbonyl groups. Density functional theory (DFT) calculations support a reaction pathway involving thermal C-H oxidation at the tertiary carbon sites in the polymer chain. The addition of 1% H2O2 further enhances the oxidation reaction to produce valuable short-chain acetic acids, enabling gram-scale recycling of both pure PP and disposable surgical masks from the real world. Techno-economic analysis (TEA) and environmental life cycle costing (E-LCC) analysis suggest that this hydrothermal oxidation recovery technology is financially viable, which shows significant potential in tackling the ongoing plastic pollution crisis and advancing plastic treatment methodologies toward a circular economy paradigm.

Co-upcycling of Plastic Waste and Biowaste via Tandem Transesterification Reactions

Polyethylene terephthalate (PET) and glycerol are prevalent forms of plastic and biowaste, necessitating facile and effective strategies for their upcycling treatment. Herein, we present an innovative one-pot reaction system for the concurrent depolymerization of PET plastics and the transesterification of glycerol into dimethyl terephthalate (DMT), a valuable feedstock in polymer manufacturing. This process occurs in the presence of methyl acetate (MA), a byproduct of the industrial production of acetic acid. The upcycling of biowaste glycerol into glycerol acetates renders them valuable additives for application in both the biofuel and chemical industries. This integrated reaction system enhances the conversion of glycerol to acetins compared with the singular transesterification of glycerol. In this approach, cost-effective catalysts, based on perovskite-structured CaMnO3, were employed. The catalyst undergoes in situ reconstruction in the tandem PET/glycerol/MA system due to glycerolation between the metal oxides and glycerol/acetins. This process results in the formation of small metal oxide nanoparticles confined in amorphous metal glycerolates, thereby enhancing the PET depolymerization efficiency. The optimized coupled reaction system can achieve a product yield exceeding 70% for glycerol acetates and 68% for PET monomers. This research introduces a tandem pathway for the simultaneous upcycling of PET plastic waste and biowaste glycerol with minimal feedstock input and maximal reactant utilization efficiency, promising both economic advantages and positive environmental impacts.

Photocatalytic Cracking of non-Biodegradable Plastics to Chemicals and Fuels

Plastic pollution is worsening the living conditions on Earth, primarily due to the toxicity and stability of non-biodegradable plastics (NBPs). Photocatalytic cracking of NBPs is emerging as a promising way to cleave inert C-C bonds and abstract the carbon atoms from these wastes into valuable chemicals and fuels. However, controlling these processes is a huge challenge, ascribed to the complicated reactions of various NBPs. Herein, we summarize recent advances in the CO2 and carbon-radical-mediated photocatalytic cracking of NBPs, with an emphasis on the pivotal intermediates. The CO2-mediated cracking proceeded with indiscriminate C-H/C-C bond cleavage of NBPs and tandem photoreduction of CO2, while carbon-radical-mediated cracking was realized by the prior activation of C-H bonds for selective C-C bond cleavage of NBPs. Catalytic generation and conversion of different intermediates greatly depend on the kinds of active species and the structure of photocatalysts under irradiation. Meanwhile, the fate of a specific intermediate is compared with small molecule activation to reveal the key problems in the cracking of NBPs. Finally, the challenges and potential directions are discussed to improve the overall efficiency in the photocatalytic cracking of NBPs.

Polyoxymethylene Upcycling into Methanol and Methyl Groups Catalyzed by a Manganese Pincer Complex

Polyoxymethylene (POM) is a commonly used engineering thermoplastic, but its recycling by conventional means, i.e., mechanical recycling, is not practiced to any meaningful extent, due to technical limitations. Instead, waste POM is typically incinerated or disposed in landfills, where it becomes a persistent environmental pollutant. An attractive alternative to mechanical recycling is upcycling, namely, the conversion of waste POM into value-added chemicals, but this has received very little attention. Herein, we report the upcycling of POM into useful chemicals through three different reactions, all of which are efficiently catalyzed by a single pincer complex of earth-abundant manganese. One method involves hydrogenation of POM into methanol using H2 gas as the only reagent, whereas another method converts POM into methanol and CO2 through a one-pot process comprising acidolysis followed by Mn-catalyzed disproportionation. The third method utilizes POM as a reagent for the methylation of ketones and amines.

Advancing Recyclable Thermosets through C═C/C═N Dynamic Covalent Metathesis Chemistry

Thermoset polymers have become integral to our daily lives due to their exceptional durability, making them feasible for a myriad of applications; however, this ubiquity also raises serious environmental concerns. Covalent adaptable networks (CANs) with dynamic covalent linkages that impart efficient reprocessability and recyclability to thermosets have garnered increasing attention. While various dynamic exchange reactions have been explored in CANs, many rely on the stimuli of active nucleophilic groups and/or catalysts, introducing performance instability and escalating the initial investment. Herein, we propose a new direct and catalyst-free C═C/C═N metathesis reaction between α-cyanocinnamate and aldimine as a novel dynamic covalent motif for constructing recyclable thermosets. This chemistry offers mild reaction conditions (room temperature and catalyst-free), ensuring high yields and simple isolation procedures. By incorporating dynamic C═C/C═N linkages into covalently cross-linked polymer networks, we obtained dynamic thermosets that exhibit both malleability and reconfigurability. The resulting tunable dynamic properties, coupled with the high thermal stability and recyclability of the C═C/C═N linkage-based networks, enrich the toolbox of dynamic covalent chemistry.

Photochemical Aerobic Upcycling of Polystyrene Plastics via Synergistic Indirect HAT Catalysis

Plastic pollution constitutes an evergrowing urgent environmental problem, since overaccumulation of plastic waste, arising from the immense increase of the production of disposable plastic products, overcame planet's capacity to properly handle them. Chemical upcycling of polystyrene constitutes a convenient method for the conversion of plastic waste into high-added value chemicals, suggesting an attractive perspective in dealing with the environmental crisis. We demonstrate herein a novel, easy-to-perform organocatalytic photoinduced aerobic protocol, which proceeds via synergistic indirect hydrogen atom transfer (HAT) catalysis under LED 390 nm Kessil lamps as the irradiation source. The developed method employs a BrCH2CN-thioxanthone photocatalytic system and was successfully applied to a variety of everyday-life plastic products, leading to the isolation of benzoic acid after simple base-acid work up in yields varying from 23-49 %, while a large-scale experiment was successfully performed, suggesting that the photocatalytic step is susceptible to industrial application.

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.

Fully Floatable Mortise-and-Tenon Architecture for Synergistically Photo/Sono-Driven Evaporation Desalination and Plastic-Enabled Value-Added Co-Conversion of H2O and CO2

Establishing an advanced ecosystem incorporating freshwater harvesting, plastic utilization, and clean fuel acquisition is profoundly significant. However, low-efficiency evaporation, single energy utilization, and catalyst leakage severely hinder sustainable development. Herein, a nanofiber-based mortise-and-tenon structural Janus aerogel (MTSJA) is strategically designed in the first attempt and supports Z-scheme catalysts. By harnessing of the upper hydrophilic layer with hydrophilic channels embedding into the hydrophobic bottom layer to achieve tailoring bottom wettability states. MTSJA is capable of a fully-floating function for lower heat loss, water supply, and high-efficiency solar-to-vapor conversion. Benefiting from the ultrasonic cavitation effect and high sensitivity of materials to mechanical forces, this is also the first demonstration of synergistic solar and ultrasound fields to power simultaneous evaporation desalination and waste plastics as reusable substrates generating fuel energy. The system enables persistent desalination with an exceptional evaporation rate of 3.1 kg m-2 h-1 and 82.3% efficiency (21 wt.% NaCl solution and 1 sun), and realizes H2, CO, and CH4 yields with 16.1, 9.5, and 3 µmol h-1 g-1, respectively. This strategy holds great potential for desalination and plastics value-added transformation toward clean energy and carbon neutrality.

Liquid-assisted grinding enables a direct mechanochemical functionalization of polystyrene waste

The plastic waste crisis has grave consequences for our environment, as most single-use commodity polymers remain in landfills and oceans long after their commercial lifetimes. Utilizing modern synthetic techniques to chemically modify the structure of these post-consumer plastics (e.g., upcycling) can impart new properties and added value for commercial applications. To expand beyond the abilities of current solution-state chemical processes, we demonstrate post-polymerization modification of polystyrene via solid-state mechanochemistry enabled by liquid-assisted grinding (LAG). Importantly, this emblematic trifluoromethylation study modifies discarded plastic, including dyed materials, using minimal exogenous solvent and plasticizers for improved sustainability. Ultimately, this work serves as a proof-of-concept for the direct mechanochemical post-polymerization modification of commodity polymers, and we expect future remediation of plastic waste via similar mechanochemical reactions.

Biodegradation of oxidized low density polyethylene by Pelosinus fermentans lipase

Polyethylene (PE) exhibits high resistance to degradation, contributing to plastic pollution. PE discarded into the environment is photo-oxidized by sunlight and oxygen. In this study, a key enzyme capable of degrading oxidized PE is reported for the first time. Twenty different enzymes from various lipase families were evaluated for hydrolytic activity using substrates mimicking oxidized PE. Among them, Pelosinus fermentans lipase 1 (PFL1) specifically cleaved the ester bonds within the oxidized carbon-carbon backbone. Moreover, PFL1 (6 μM) degraded oxidized PE film, reducing the weight average and number average molecular weights by 44.6 and 11.3 %, respectively, within five days. Finally, structural analysis and molecular docking simulations were performed to elucidate the degradation mechanism of PFL1. The oxidized PE-degrading enzyme reported here will provide the groundwork for advancing PE waste treatment technology and for engineering microbes to repurpose PE waste into valuable chemicals.

Carbon Recycling of High Value Bioplastics: A Route to a Zero-Waste Future

Today, 98% of all plastics are fossil-based and non-biodegradable, and globally, only 9% are recycled. Microplastic and nanoplastic pollution is just beginning to be understood. As the global demand for sustainable alternatives to conventional plastics continues to rise, biobased and biodegradable plastics have emerged as a promising solution. This review article delves into the pivotal concept of carbon recycling as a pathway towards achieving a zero-waste future through the production and utilization of high-value bioplastics. The review comprehensively explores the current state of bioplastics (biobased and/or biodegradable materials), emphasizing the importance of carbon-neutral and circular approaches in their lifecycle. Today, bioplastics are chiefly used in low-value applications, such as packaging and single-use items. This article sheds light on value-added applications, like longer-lasting components and products, and demanding properties, for which bioplastics are increasingly being deployed. Based on the waste hierarchy paradigm-reduce, reuse, recycle-different use cases and end-of-life scenarios for materials will be described, including technological options for recycling, from mechanical to chemical methods. A special emphasis on common bioplastics-TPS, PLA, PHAs-as well as a discussion of composites, is provided. While it is acknowledged that the current plastics (waste) crisis stems largely from mismanagement, it needs to be stated that a radical solution must come from the core material side, including the intrinsic properties of the polymers and their formulations. The manner in which the cascaded use of bioplastics, labeling, legislation, recycling technologies, and consumer awareness can contribute to a zero-waste future for plastics is the core topics of this article.

Towards carbon neutrality: Sustainable recycling and upcycling strategies and mechanisms for polyethylene terephthalate via biotic/abiotic pathways

Polyethylene terephthalate (PET), one of the most ubiquitous engineering plastics, presents both environmental challenges and opportunities for carbon neutrality and a circular economy. This review comprehensively addressed the latest developments in biotic and abiotic approaches for PET recycling/upcycling. Biotically, microbial depolymerization of PET, along with the biosynthesis of reclaimed monomers [terephthalic acid (TPA), ethylene glycol (EG)] to value-added products, presents an alternative for managing PET waste and enables CO2 reduction. Abiotically, thermal treatments (i.e., hydrolysis, glycolysis, methanolysis, etc.) and photo/electrocatalysis, enabled by catalysis advances, can depolymerize or convert PET/PET monomers in a more flexible, simple, fast, and controllable manner. Tandem abiotic/biotic catalysis offers great potential for PET upcycling to generate commodity chemicals and alternative materials, ideally at lower energy inputs, greenhouse gas emissions, and costs, compared to virgin polymer fabrication. Remarkably, over 25 types of upgraded PET products (e.g., adipic acid, muconic acid, catechol, vanillin, and glycolic acid, etc.) have been identified, underscoring the potential of PET upcycling in diverse applications. Efforts can be made to develop chemo-catalytic depolymerization of PET, improve microbial depolymerization of PET (e.g., hydrolysis efficiency, enzymatic activity, thermal and pH level stability, etc.), as well as identify new microorganisms or hydrolases capable of degrading PET through computational and machine learning algorithms. Consequently, this review provides a roadmap for advancing PET recycling and upcycling technologies, which hold the potential to shape the future of PET waste management and contribute to the preservation of our ecosystems.

Photothermal Mineralization of Polyolefin Microplastics via TiO2 Hierarchical Porous Layer-Based Semiwetting Air-Plastic-Solid Interfaces

Photo-mineralization of microplastics under mild conditions has emerged as a promising solution to plastic waste disposal. However, the inadequate contact between oxygen, water-insoluble polyolefin microplastics, and photocatalysts remains a critical issue. In this study, a TiO2 hierarchical porous layer (TiO2-HPL) photocatalyst is presented to establish air-plastic-solid triphase interfaces for the photothermal mineralization of polyolefins. The wettability of the TiO2-HPL-based triphase interface is finely controlled from plastophobic to plastophilic. High-resolution imaging and finite element simulation demonstrate the significance of a semiwetting state in achieving multidirectional oxygen diffusion through the hierarchical pore structure while maintaining sufficient contact between the plastic phase and photocatalysts. For low-density polyethylene, the TiO2-HPL achieves a photothermal mineralization rate of 5.63 mmol g-1 h-1 and a conversion of 26.3% after 20 h of continuous irradiation. Additionally, the triphase photocatalytic system with semiwetting gas-plastic-solid interfaces shows good universality for various polyolefin reagents and products, illustrating its potential in achieving efficient photothermal mineralization of non-degradable microplastics.

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.

Upcycling of Carbon Fiber/Thermoset Composites into High-Performance Elastomers and Repurposed Carbon Fibers

Recycling of carbon fiber-reinforced polymer composites (CFRCs) based on thermosetting plastics is difficult. In the present study, high-performance CFRCs are fabricated through complexation of aromatic pinacol-cross-linked polyurethane (PU-AP) thermosets with carbon fiber (CF) cloths. PU-AP thermosets exhibit a breaking strength of 95.5 MPa and toughness of 473.6 MJ m-3 and contain abundant hydrogen-bonding groups, which can have strong adhesion with CFs. Because of the high interfacial adhesion between CF cloths and PU-AP thermosets and high toughness of PU-AP thermosets, CF/PU-AP composites possess a high tensile strength of >870 MPa. Upon heating in N,N-dimethylacetamide (DMAc) at 100 °C, the aromatic pinacols in the CF/PU-AP composites can be cleaved, generating non-destructive CF cloths and linear polymers that can be converted to high-performance elastomers. The elastomers are mechanically robust, healable, reprocessable, and damage-resistant with an extremely high tensile strength of 74.2 MPa and fracture energy of 149.6 kJ m-2. As a result, dissociation of CF/PU-AP composites enables the recovery of reusable CF cloths and high-performance elastomers, thus realizing the upcycling of CF/PU-AP composites.

Cost-Effective and Scalable Solar Interface Evaporators Derived from Industry Waste for Efficient Solar Steam Generation

Interfacial solar steam generation for sustainable and eco-friendly desalination and wastewater treatment has attracted much attention. However, costly raw materials and complex preparation processes pose constant challenges to its wide promotion. Herein, a novel, cost-effective, and scalable strategy is presented for preparing solar interface evaporators using industrial waste as a raw material. Modified polyethylene foam evaporators (M-EPEs) are simply prepared by drilling and then hydrophilic modification of industrial waste (EPE-1). M-EPEs not only retain the strong mechanical properties and thermal insulating properties (0.047 W·m-1·K-1) of EPE-1 but also exhibit superhydrophilicity and strong light absorption (over 90%). M-EPEs achieve a high evaporation rate of 1.497 kg·m-2·h-1 and photothermal efficiency of up to 93.8% under 1 kW·m-2 solar illumination. Moreover, it has excellent stability and salt tolerance. Our work addresses the environmental issues of recycling polyethylene waste and provides a facile and efficient strategy for designing low-cost, large-scale solar interface evaporators for desalination.

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.

Fundamental investigation of micro-nano cellulose and lignin interaction for transparent paper: Experiment and electrostatic potential calculation

Plastic has significant negative consequences for the environment and human health, demanding greener alternatives. Lignocellulose is a sustainable biomass material, and its paper has been considered as a potential material to replace plastics. Micro-nano lignocellulose, derived from natural plants, possesses a small size and abundant hydrogen bonding capacity. However, there is no clear explanation for the interactions between lignin and micro-nano cellulose, and little understanding of how the interaction can affect the papers' structure and optical properties. Electrostatic potential calculation is a reliable tool to explain non-covalent interactions, and can explore the binding between lignin and micro-nano cellulose. In this paper, kenaf - a non-wood fiber raw material - was employed to prepare micro-nano lignocellulose. The resulting slurry facilitated the production of transparent paper via a simple casting method. The prepared transparent micro-nano paper exhibited high transparency (~90 %), UVA resistance (~80 %), and hydrophobicity (~114°). More importantly, the electrostatic potential calculation demonstrates the inherent relationship between structure and performance, providing practical knowledge for constructing film materials.

Polyurethane with β-Selenocarbonyl Structure Enabling the Combination of Plastic Degradation and Waste Upcycling

Degradable polymers offer a promising solution to mitigate global plastic pollution, but the degraded products often suffer from diminished value. Upcycling is a more sustainable approach to upgrade polymer waste into value-added products. Herein, we report a β-selenocarbonyl-containing polyurethane (SePU), which can be directly degraded under mild conditions into valuable selenium fertilizers for selenium-rich vegetable cultivation globally, enabling both plastic degradation and waste upcycling. Under oxidation condition, this polymer can be easily and selectively degraded via selenoxide elimination reaction from mixed plastic waste. The degraded product can serve as effective selenium fertilizers to increase selenium content in radish and pak choi. The SePU exhibits excellent mechanical properties. Additionally, we observed the formation of spherulites-like selenium particles within the materials during degradation for the first time. Our research offers a successful application of selenoxide elimination reaction in the field of plastic degradation for the first time, endowing plastics with both degradability and high reusable value. This strategy provides a promising solution to reduce pollution and improve economy and sustainability of plastics.

Recent advancement on photocatalytic plastic upcycling

More than 8 billion tons of plastics have been generated since 1950. About 80% of these plastics have been dumped in landfills or went into natural environments, resulting in ever-worsening contamination. Among various strategies for waste plastics processing (e.g., incineration, mechanical recycling, thermochemical conversion and electrocatalytic/photocatalytic techniques), photocatalysis stands out as a cost-effective, environmentally benign and clean technique to upcycle plastic waste at ambient temperature and pressure using solar light. The mild reaction conditions for photocatalysis enable the highly selective conversion of plastic waste into targeted value-added chemicals/fuels. Here, we for the first time summarize the recent development of photocatalytic plastic upcycling based on the chemical composition of photocatalysts (e.g., metal oxides, metal sulfides, non-metals and composites). The pros and cons of various photocatalysts have been critically discussed and summarized. At last, the future challenges and opportunities in this area are presented in this review.

Exploring g-C3N4 as a green additive for biodegradable poly(butylene adipate-co-terephthalate) film with enhanced UV shielding and mechanical properties

Typical small organic dyes exhibit excellent UV absorption capabilities and are commonly used as additives to shield plastic films from photoaging. However, their tendency to decompose easily and migrate rapidly within a polymer matrix limits their service life. Herein we prepared g-C3N4 nanosheets and fabricated g-C3N4/PBAT films to investigate the effects of g-C3N4 on UV shielding and plasticizing of a biodegradable PBAT film. Photophysical characterizations revealed that an improved UV light barrier performance was achieved on g-C3N4/PBAT films compared to pure PBAT. Furthermore, the photoaging results show that g-C3N4 can stably exist in the PBAT matrix, enabling the aged g-C3N4/PBAT films to maintain their effective UV shielding ability, whereas the aged benzophenone (UV-0)/PBAT film shows a substantial decrease in UV light absorption due to the photodecomposition of UV-0. Additionally, g-C3N4 acted as a reinforcing material for PBAT, as evidenced by the approximately 1.5-fold increase in longitudinal tear strength and 1.6-fold increase in tensile strength of g-C3N4/PBAT films compared to pure PBAT. Remarkably, even after 100 hours of photoaging, the aged g-C3N4/PBAT films retained their favorable mechanical properties. This study highlights the potential of g-C3N4 as a new type of UV shield additive for future practical applications in protecting biodegradable plastic from photoaging.

Environmental Sustainability of Solvent Extraction Method in Recycling Marine Plastic Waste

The global plastic production of 400 million tons/year has caused major catastrophes in marine environments. The current study, therefore, aimed to mitigate this challenge through the dissolution–reprecipitation method of eradicating impurities and contaminants from marine plastic debris. The results revealed that the rate of the dissolution of polyethylene (PE) outweighed polypropylene (PP) at lower temperatures. HDPE (high density polyethylene) and PP had optimal dissolution temperatures of 75 °C and 90 °C at 20 and 30 min, respectively, resulting in recovery percentages of 96.67% and 87.35% when applied to actual marine waste samples. Overall, this recycling method conserved the plastic quality and properties, making it a viable alternative for virgin plastics. The life cycle assessment (LCA) revealed that the drying stage demonstrated the greatest environmental impact within the system. The overall process, however, yielded a lower environmental impact in comparison with established findings. Conclusively, the current study has successfully restored marine plastic waste with high recovery rates and minimum chemical alterations, yielding a low environmental footprint.

Enhanced adsorption of diclofenac onto activated carbon derived from PET plastic by one-step pyrolysis with KOH

Plastic pollution is a severe threat to the health of ecosystems, and recycling plastics is recognized as a key control strategy. This study used the one-step pyrolysis assisted with KOH activation to recycle the widely used polyethylene terephthalate (PET) plastic as activated carbon (PET-AC) which was subsequently applied to adsorb diclofenac (DCF), a frequently detected emerging contaminant in water, for the first time. It was found that both the pyrolysis temperature and the addition of KOH can effectively regulate the pore sizes and volumes of PET-AC. PET-AC obtained at 700 °C demonstrated a high adsorption capacity of DCF up to 179.42 mg g-1 at 45 °C. The adsorption kinetics was conducted with both static jar and dynamic column tests and analyzed with various models. Thermodynamic results demonstrated that the adsorption of DCF was spontaneous and endothermic. The material also presented an excellent potential to adsorb other pharmaceuticals and personal care products in water. XPS and FTIR analysis indicated that the adsorption might be mainly driven by the physical forces, especially π-π interaction and hydrogen bonding. This study provided a reference for recycling waste plastic as an efficient adsorbent to eliminate organic contaminants from water.

Dual-Doped Nickel Sulfide for Electro-Upgrading Polyethylene Terephthalate into Valuable Chemicals and Hydrogen Fuel

Electro-upcycling of plastic waste into value-added chemicals/fuels is an attractive and sustainable way for plastic waste management. Recently, electrocatalytically converting polyethylene terephthalate (PET) into formate and hydrogen has aroused great interest, while developing low-cost catalysts with high efficiency and selectivity for the central ethylene glycol (PET monomer) oxidation reaction (EGOR) remains a challenge. Herein, a high-performance nickel sulfide catalyst for plastic waste electro-upcycling is designed by a cobalt and chloride co-doping strategy. Benefiting from the interconnected ultrathin nanosheet architecture, dual dopants induced up-shifting d band centre and facilitated in situ structural reconstruction, the Co and Cl co-doped Ni3S2 (Co, Cl-NiS) outperforms the single-doped and undoped analogues for EGOR. The self-evolved sulfide@oxyhydroxide heterostructure catalyzes EG-to-formate conversion with high Faradic efficiency (> 92%) and selectivity (> 91%) at high current densities (> 400 mA cm-2). Besides producing formate, the bifunctional Co, Cl-NiS-assisted PET hydrolysate electrolyzer can achieve a high hydrogen production rate of 50.26 mmol h-1 in 2 M KOH, at 1.7 V. This study not only demonstrates a dual-doping strategy to engineer cost-effective bifunctional catalysts for electrochemical conversion processes, but also provides a green and sustainable way for plastic waste upcycling and simultaneous energy-saving hydrogen production.

Electrochemical Production of Glycolate Fuelled By Polyethylene Terephthalate Plastics with Improved Techno-Economics

Electrochemical valorization of polyethylene terephthalate (PET) waste streams into commodity chemicals offers a potentially sustainable route for creating a circular plastic economy. However, PET wastes upcycling into valuable C2 product remains a huge challenge by the lack of an electrocatalyst that can steer the oxidation economically and selectively. Here, it is reported a catalyst comprising Pt nanoparticles hybridized with γ-NiOOH nanosheets supported on Ni foam (Pt/γ-NiOOH/NF) that favors electrochemical transformation of real-word PET hydrolysate into glycolate with high Faradaic efficiency (> 90%) and selectivity (> 90%) across wide reactant (ethylene glycol, EG) concentration ranges under a marginal applied voltage of 0.55 V, which can be paired with cathodic hydrogen production. Computational studies combined with experimental characterizations elucidate that the Pt/γ-NiOOH interface with substantial charge accumulation gives rise to an optimized adsorption energy of EG and a decreased energy barrier of potential determining step. A techno-economic analysis demonstrates that, with the nearly same amount of resource investment, the electroreforming strategy towards glycolate production can raise revenue by up to 2.2 times relative to conventional chemical process. This work may thus serve as a framework for PET wastes valorization process with net-zero carbon footprint and high economic viability.

Heterogenous electromediated depolymerization of highly crystalline polyoxymethylene

Post-consumer plastic waste in the environment has driven the scientific community to develop deconstruction methods that yield valued substances from these synthetic macromolecules. Electrocatalysis is a well-established method for achieving challenging transformations in small molecule synthesis. Here we present the first electro-chemical depolymerization of polyoxymethylene-a highly crystalline engineering thermoplastic (Delrin®)-into its repolymerizable monomer, formaldehyde/1,3,5-trioxane, under ambient conditions. We investigate this electrochemical deconstruction by employing solvent screening, cyclic voltammetry, divided cell studies, electrolysis with redox mediators, small molecule model studies, and control experiments. Our findings determine that the reaction proceeds via a heterogeneous electro-mediated acid depolymerization mechanism. The bifunctional role of the co-solvent 1,1,1,3,3,3-hexafluoro-2-propanol (HFIP) is also revealed. This study demonstrates the potential of electromediated depolymerization serving as an important role in sustainable chemistry by merging the concepts of renewable energy and circular plastic economy.

A facile alternative strategy of upcycling mixed plastic waste into vitrimers

Chemical depolymerization has been identified as a promising approach towards recycling of plastic waste. However, complete depolymerization may be energy intensive with complications in purification. In this work, we have demonstrated upcycling of mixed plastic waste comprising a mixture of polyester, polyamide, and polyurethane through a reprocessable vitrimer of the depolymerized oligomers. Using poly(ethylene terephthalate) (PET) as a model polymer, we first demonstrated partial controlled depolymerization, using glycerol as a cleaving agent, to obtain branched PET oligomers. Recovered PET (RPET) oligomer was then used as a feedstock to produce a crosslinked yet reprocessable vitrimer (vRPET) despite having a wide molecular weight distribution using a solventless melt processing approach. Crosslinking and dynamic interactions were observed through rheology and dynamic mechanical analysis (DMA). Tensile mechanical studies showed no noticeable decrease in mechanical strength over multiple repeated melt processing cycles. Consequently, we have clearly demonstrated the applicability of the above method to upcycle mixed plastic wastes into vitrimers and reprocessable composites. This work also afforded insights into a potentially viable alternative route for utilization of depolymerized plastic/mixed plastic waste into crosslinked vitrimer resins manifesting excellent mechanical strength, while remaining reprocessable/ recyclable for cyclical lifetime use.

Circularity in polymers: addressing performance and sustainability challenges using dynamic covalent chemistries

The circularity of current and future polymeric materials is a major focus of fundamental and applied research, as undesirable end-of-life outcomes and waste accumulation are global problems that impact our society. The recycling or repurposing of thermoplastics and thermosets is an attractive solution to these issues, yet both options are encumbered by poor property retention upon reuse, along with heterogeneities in common waste streams that limit property optimization. Dynamic covalent chemistry, when applied to polymeric materials, enables the targeted design of reversible bonds that can be tailored to specific reprocessing conditions to help address conventional recycling challenges. In this review, we highlight the key features of several dynamic covalent chemistries that can promote closed-loop recyclability and we discuss recent synthetic progress towards incorporating these chemistries into new polymers and existing commodity plastics. Next, we outline how dynamic covalent bonds and polymer network structure influence thermomechanical properties related to application and recyclability, with a focus on predictive physical models that describe network rearrangement. Finally, we examine the potential economic and environmental impacts of dynamic covalent polymeric materials in closed-loop processing using elements derived from techno-economic analysis and life-cycle assessment, including minimum selling prices and greenhouse gas emissions. Throughout each section, we discuss interdisciplinary obstacles that hinder the widespread adoption of dynamic polymers and present opportunities and new directions toward the realization of circularity in polymeric materials.

Gold-Catalyzed Precise Bromination of Polystyrene

Modification of commodity aromatic polymers is highly desirable for accessing materials with new properties. The long-standing challenge for such approaches lies in the development of catalytic methods that can functionalize the aromatic polymers with high precision while preserving the molecular weight and distribution of the starting polymers without any alteration. Herein, we report a highly efficient AuCl₃-catalyzed site-selective aromatic C-H halogenation of polystyrene. The most important feature of this method is that the degree of halogenation can be precisely controlled by simply changing the loading of the halogenating agent, thus allowing the tuning of functional group density in an accurate and predictable manner. Various functional groups, including NH₂ and Bpin, can be installed through effective derivatization of the resultant brominated polystyrene, thus making the method a valuable strategy for the synthesis of value-added materials with tailored properties.

Microbial Enzyme Biotechnology to Reach Plastic Waste Circularity: Current Status, Problems and Perspectives

The accumulation of synthetic plastic waste in the environment has become a global concern. Microbial enzymes (purified or as whole-cell biocatalysts) represent emerging biotechnological tools for waste circularity; they can depolymerize materials into reusable building blocks, but their contribution must be considered within the context of present waste management practices. This review reports on the prospective of biotechnological tools for plastic bio-recycling within the framework of plastic waste management in Europe. Available biotechnology tools can support polyethylene terephthalate (PET) recycling. However, PET represents only ≈7% of unrecycled plastic waste. Polyurethanes, the principal unrecycled waste fraction, together with other thermosets and more recalcitrant thermoplastics (e.g., polyolefins) are the next plausible target for enzyme-based depolymerization, even if this process is currently effective only on ideal polyester-based polymers. To extend the contribution of biotechnology to plastic circularity, optimization of collection and sorting systems should be considered to feed chemoenzymatic technologies for the treatment of more recalcitrant and mixed polymers. In addition, new bio-based technologies with a lower environmental impact in comparison with the present approaches should be developed to depolymerize (available or new) plastic materials, that should be designed for the required durability and for being susceptible to the action of enzymes.

Mechanochemistry Milling of Waste Poly(Ethylene Terephthalate) into Metal-Organic Frameworks

Converting poly(ethylene terephthalate) (PET) into metal-organic frameworks (MOFs) has emerged as a promising innovation for upcycling of waste plastics. However, previous solvothermal methods suffer from toxic solvent consumption, long reaction time, high pressure, and high temperature. Herein, a mechanochemical milling strategy was reported to transform waste PET into a series of MOFs with high yields. This strategy had the merits of solvent-free conditions, ambient reaction temperature, short running time, and easy scale-up for large-scale production of MOFs. The as-prepared MOFs exhibited definite crystal structure and porous morphology composed of agglomerated nanoparticles. It was proven that, under mechanochemical milling, PET was firstly decomposed into 1,4-benzenedicarboxylate, which acted as linkers to coordinate with metal ions for forming fragments, followed by the gradual arrangement of fragments into MOFs. This work not only promotes high value-added conversion of waste polyesters but also offers a new opportunity to produce MOFs in a green and scalable manner.

Synthesis, Characterization, and Gas Adsorption Performance of Amine-Functionalized Styrene-Based Porous Polymers

In recent years, porous materials have been extensively studied by the scientific community owing to their excellent properties and potential use in many different areas, such as gas separation and adsorption. Hyper-crosslinked porous polymers (HCLPs) have gained attention because of their high surface area and porosity, low density, high chemical and thermal stability, and excellent adsorption capabilities in comparison to other porous materials. Herein, we report the synthesis, characterization, and gas (particularly CO₂) adsorption performance of a series of novel styrene-based HCLPs. The materials were prepared in two steps. The first step involved radical copolymerization of divinylbenzene (DVB) and 4-vinylbenzyl chloride (VBC), a non-porous gel-type polymer, which was then modified by hyper-crosslinking, generating micropores with a high surface area of more than 700 m² g^-1. In the following step, the polymer was impregnated with various polyamines that reacted with residual alkyl chloride groups on the pore walls. This impregnation substantially improved the CO₂/N₂ and CO₂/CH₄ adsorption selectivity.