Ecotoxicological evaluation of chitosan biopolymer films particles in adult zebrafish (Danio rerio): A comparative study with polystyrene microplastics

To mitigate the environmental impact of microplastics (MPs), the scientific community has innovated sustainable and biodegradable polymers as viable alternatives to traditional plastics. Chitosan, the deacetylated form of chitin, stands as one of the most thoroughly investigated biopolymers and has garnered significant interest due to its versatile applications in both medical and cosmetic fields. Nevertheless, there is still a knowledge gap regarding the impact that chitosan biopolymer films (CBPF) may generate in aquatic organisms. In light of the foregoing, this study aimed to assess and compare the potential effects of CBPF on the gastrointestinal tract, gills, brain, and liver of Danio rerio against those induced by MPs. The findings revealed that both CBPF and MPs induced changes in the levels of oxidative stress biomarkers across all organs. However, it is essential to note that our star plots illustrate a tendency for CBPF to activate antioxidant enzymes and for MPs to produce oxidative damage. Regarding gene expression, our findings indicate that MPs led to an up-regulation in the expression of genes associated with apoptotic response (p53, casp3, cas9, bax, and bcl2) in all fish organs. Meanwhile, CBPF produced the same effect in genes related to antioxidant response (nrf1 and nrf2). Overall, our histological observations substantiated these effects, revealing the presence of plastic particles and tissue alterations in the gills and gastrointestinal tract of fish subjected to MPs. From these results, it can be concluded that CBPF does not represent a risk to fish after long exposure.

Upcycling plastic waste into fully recyclable composites through cold sintering

Plastics have substantial societal benefits, but their widespread use has led to a critical waste management challenge. While mechanical recycling dominates the reuse of post-consumer plastics, it is limited in efficacy, especially for composites. To address this, we propose a direct reprocessing approach that enables the creation of hybrid, long-lasting, and durable composites from difficult-to-recycle plastics. This approach utilizes cold sintering, a process that consolidates inorganic powders through fractional dissolution and precipitation at temperatures far below conventional sintering; these temperatures are compatible with plastic processing. We show that this process can create inorganic-matrix composites with significant enhancements in tensile strength and toughness over pure gypsum, which is commonly found in construction waste. These composites can be recycled multiple times through direct reprocessing with the addition of only water as a processing promoter. This approach to recycling leads to composites with orders of magnitude lower energy demand, global warming potential, and water demand, when compared against common construction products. Altogether, we demonstrate the potential for cold sintering to integrate waste into high-performance recyclable composites.

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.

Photo-electrochemical activation of persulfate for the simultaneous degradation of microplastics and personal care products

The recent widespread use of microplastics (MPs), especially in pharmaceuticals and personal care products (PPCPs), has caused significant water pollution. This study presents a UV/electrically co-facilitated activated persulfate (PS) system to co-degrade a typical microplastic polyvinyl chloride (PVC) and an organic sunscreen p-aminobenzoic acid (PABA). We investigated the effect of various reaction conditions on the degradation. PVC and PABA degradation was 37% and 99.22%, respectively. Furthermore, we observed alterations in the surface topography and chemical characteristics of PVC throughout degradation. The possible degradation pathways of PVC and PABA were proposed by analyzing the intermediate products and the free radicals generated. This study reveals the co-promoting effect of multiple mechanisms in the activation by ultraviolet light and electricity.

Bridged Bicyclic Lactam Enables Chemically Recyclable Nylon

Nylon, a widely-used high-performance thermoplastic, boasts exceptional durability and resistance to various solvents and weak acids, making it indispensable across diverse applications. However, its nonbiodegradable nature has led to alarming environmental pollution in land and oceans. Chemical recycling to monomers (CRM) stands as a crucial strategy for establishing a circular plastic economy, but the CRM of nylon remains largely unexplored. Herein, we introduce the bridged bicyclic lactam 5-azabicyclo[2.2.1]octan-6-one (5/6-LM), evolved from δ-valerolactam and pyrrolidone, to solve the trade-off in depolymerizability and performance. Notably, 5/6-LM exhibits nearly 95 % conversion in mild polymerization conditions and efficient depolymerization catalyzed by lewis acids. This compound is synthetically accessible from commercially available chemicals in a single step at room temperature, demonstrating high efficiency and scalability up to 50 g in laboratory. Furthermore, the resulting polyamide displays remarkable attributes including high crystallinity and thermostability up to 283 °C, significantly broadening the scope of chemically recyclable nylons.

Chloride and Hydride Transfer as Keys to Catalytic Upcycling of Polyethylene into Liquid Alkanes

Transforming polyolefin waste into liquid alkanes through tandem cracking-alkylation reactions catalyzed by Lewis-acid chlorides offers an efficient route for single-step plastic upcycling. Lewis acids in dichloromethane establish a polar environment that stabilizes carbenium ion intermediates and catalyzes hydride transfer, enabling breaking of polyethylene C-C bonds and forming C-C bonds in alkylation. Here, we show that efficient and selective deconstruction of low-density polyethylene (LDPE) to liquid alkanes is achieved with anhydrous aluminum chloride (AlCl3) and gallium chloride (GaCl3). Already at 60 °C, complete LDPE conversion was achieved, while maintaining the selectivity for gasoline-range liquid alkanes over 70 %. AlCl3 showed an exceptional conversion rate of 5000g L D P E m o l c a t - 1 h - 1 ${{{\rm g}}_{{\rm L}{\rm D}{\rm P}{\rm E}}{{\rm \ }{\rm m}{\rm o}{\rm l}}_{{\rm c}{\rm a}{\rm t}}^{-1}{{\rm \ }{\rm h}}^{-1}}$ , surpassing other Lewis acid catalysts by two orders of magnitude. Through kinetic and mechanistic studies, we show that the rates of LDPE conversion do not correlate directly with the intrinsic strength of the Lewis acids or steric constraints that may limit the polymer to access the Lewis acid sites. Instead, the rates for the tandem processes of cracking and alkylation are primarily governed by the rates of initiation of carbenium ions and the subsequent intermolecular hydride transfer. Both jointly control the relative rates of cracking and alkylation, thereby determining the overall conversion and selectivity.

From Polyester Plastics to Diverse Monomers via Low-Energy Upcycling

Polyester plastics, constituting over 10% of the total plastic production, are widely used in packaging, fiber, single-use beverage bottles, etc. However, their current depolymerization processes face challenges such as non-broad spectrum recyclability, lack of diversified high-value-added depolymerization products, and crucially high energy consumption. Herein, an efficient strategy is developed for dismantling the compact structure of polyester plastics to achieve diverse monomer recovery. Polyester plastics undergo swelling and decrystallization with a low depolymerization energy barrier via synergistic effects of polyfluorine/hydrogen bonding, which is further demonstrated via density functional theory calculations. The swelling process is elucidated through scanning electron microscopy analysis. Obvious destruction of the crystalline region is demonstrated through X-ray crystal diffractometry curves. PET undergoes different aminolysis efficiently, yielding nine corresponding high-value-added monomers via low-energy upcycling. Furthermore, four types of polyester plastics and five types of blended polyester plastics are closed-loop recycled, affording diverse monomers with exceeding 90% yields. Kilogram-scale depolymerization of real polyethylene terephthalate (PET) waste plastics is successfully achieved with a 96% yield.

Coupled conversion of polyethylene and carbon dioxide catalyzed by a zeolite-metal oxide system

Zeolite-catalyzed polyethylene (PE) aromatization achieves reduction of the aromatic yield via hydrogenation and hydrogenolysis reactions. The hydrogen required for CO2 hydrogenation can be provided by H radicals formed during aromatization. In this study, we efficiently convert PE and CO2 into aromatics and CO using a zeolite-metal oxide catalyst (HZSM-5 + CuZnZrOx) at 380°C and under hydrogen- and solvent-free reaction conditions. Hydrogen, derived from the aromatization of PE over HZSM-5, diffuses through the Brønsted acidic sites of the zeolite to the adjacent CuZnZrOx, where it is captured in situ by CO2 to produce bicarbonate and further hydrogenated to CO. This favors aromatization while inhibiting hydrogenation and secondary hydrogenolysis reactions. An aromatic yield of 62.5 wt % is achieved, of which 60% consisted of benzene, toluene, and xylene (BTX). The conversion of CO2 reaches values as high as 0.55 mmol gPE-1. This aromatization-hydrogen capture pathway provides a feasible scheme for the comprehensive utilization of waste plastics and CO2.

Hydrogenolysis of Poly(Ethylene-co-Vinyl Alcohol) and Related Polymer Blends over Ruthenium Heterogeneous Catalysts

The hydrogenolysis of polymers is emerging as a promising approach to deconstruct plastic waste into valuable chemicals. Yet, the complexity of plastic waste, including multilayer packaging, is a significant barrier to handling realistic waste streams. Herein, we reveal fundamental insights into a new chemical route for transforming a previously unaddressed fraction of plastic waste - poly(ethylene-co-vinyl alcohol) (EVOH) and related polymer blends - into alkane products. We report that Ru/ZrO2 is active for the concurrent hydrogenolysis, hydrogenation, and hydrodeoxygenation of EVOH and its thermal degradation products into alkanes (C1-C35) and water. Detailed reaction data, product analysis, and catalyst characterization reveal that the in-situ thermal degradation of EVOH forms aromatic intermediates that are detrimental to catalytic activity. Increased hydrogen pressure promotes hydrogenation of these aromatics, preventing catalyst deactivation and improving alkane product yields. Calculated apparent rates of C-C scission reveal that the hydrogenolysis of EVOH is slower than low-density polyethylene. We apply these findings to achieve hydrogenolysis of EVOH/polyethylene blends and elucidate the sensitivity of hydrogenolysis catalysts to such blends. Overall, we demonstrate progress towards efficient catalytic processes for the hydroconversion of waste multilayer film plastic packaging into valuable products.

Recyclable, Malleable, and Strong Thermosets Enabled by Knoevenagel Adducts

Plastic recycling is critical for waste management and achieving a circular economy, but it entails difficult trade-offs between performance and recyclability. Here, we report a thermoset, poly(α-cyanocinnamate) (PCC), synthesized using Knoevenagel condensation between terephthalaldehyde (TPA) and a triarm cyanoacetate star, that tackles this difficulty by harnessing its intrinsically conjugated and dynamic chemical characteristics. PCCs exhibit extraordinary thermal and mechanical properties with a typical Tg of ∼178 °C, Young's modulus of 3.8 GPa, and tensile strength of 102 MPa, along with remarkable flexibility and dimensional and chemical stabilities. Furthermore, end-of-life PCCs can be selectively degraded and partially recycled back into one starting monomer TPA for a new production cycle or reprocessed through dynamic exchange aided by cyanoacetate chain-ends. This study lays the scientific groundwork for the design of robust and recyclable thermosets, with transformative potential in plastic engineering.

Polymer Waste Recycling of Injection Molding Purges with Softening for Cutting with Fresnel Solar Collector-A Real Problem Linked to Sustainability and the Circular Economy

A plastic injection waste known as "purge" cannot be reintegrated into the recycling chain due to its shape, size, and composition. Grinding these cannot be carried out with traditional mills due to significant variations in size and shape. This work proposes a process and the design of a device that operates with solar energy to cut the purges without exceeding the degradation temperature. The size reduction allows reprocessing, revalorization, and handling. The purges are mixtures of processed polymers, so their characterization information is unavailable. Some characterizations were conducted before the design of the process and after the cut of the purges. Some of the most representative purges in a recycling company were evaluated. The flame test determines that all material mixtures retain thermoplasticity. The hardness (Shore D) presented changes in four of the purges being assessed, with results in a range of 59-71 before softening and 60-68 after softening. Young's modulus was analyzed by the impulse excitation technique (IET), which was 2.38-3.95 GPa before softening and 1.7-4.28 after softening. The feasibility of cutting purges at their softening temperature was evaluated. This was achieved in all the purges evaluated at 250-280 °C. FTIR allowed for corroboration of no significant change in the purges after softening. The five types of purges evaluated were polypropylene-ABS, polycarbonate-ABS-polypropylene, yellow nylon 66, acetal, and black nylon 66 with fillers, and all were easily cut at their softening temperature, allowing their manipulation in subsequent process steps.

Cu Promoted the Dynamic Evolution of Ni-Based Catalysts for Polyethylene Terephthalate Plastic Upcycling

Upcycling plastic wastes into value-added chemicals is a promising approach to put end-of-life plastic wastes back into their ecocycle. As one of the polyesters that is used daily, polyethylene terephthalate (PET) plastic waste is employed here as the model substrate. Herein, a nickel (Ni)-based catalyst was prepared via electrochemically depositing copper (Cu) species on Ni foam (NiCu/NF). The NiCu/NF formed Cu/CuO and Ni/NiO/Ni(OH)2 core-shell structures before electrolysis and reconstructed into NiOOH and CuOOH/Cu(OH)2 active species during the ethylene glycol (EG) oxidation. After oxidation, the Cu and Ni species evolved into more reduced species. An indirect mechanism was identified as the main EG oxidation (EGOR) mechanism. In EGOR, NiCu60s/NF catalyst exhibited an optimal Faradaic efficiency (FE, 95.8%) and yield rate (0.70 mmol cm-2 h-1) for formate production. Also, over 80% FE of formate was achieved when a commercial PET plastic powder hydrolysate was applied. Furthermore, commercial PET plastic water bottle waste was employed as a substrate for electrocatalytic upcycling, and pure terephthalic acid (TPA) was recovered only after 1 h electrolysis. Lastly, density functional theory (DFT) calculation revealed that the key role of Cu was significantly reducing the Gibbs free-energy barrier (ΔG) of EGOR's rate-determining step (RDS), promoting catalysts' dynamic evolution, and facilitating the C-C bond cleavage.

The Overlooked Potential of Sulfated Zirconia: Reexamining Solid Superacidity Toward the Controlled Depolymerization of Polyolefins

Closed-loop recycling via an efficient chemical process can help alleviate the global plastic waste crisis. However, conventional depolymerization methods for polyolefins, which compose more than 50% of plastics, demand high temperatures and pressures, employ precious noble metals, and/or yield complex mixtures of products limited to single-use fuels or oils. Superacidic forms of sulfated zirconia (SZrO) with Hammet Acidity Functions (H0) ≤ - 12 (i.e., stronger than 100% H2SO4) are industrially deployed heterogeneous catalysts capable of activating hydrocarbons under mild conditions and are shown to decompose polyolefins at temperatures near 200 °C and ambient pressure. Additionally, confinement of active sites in porous supports is known to radically increase selectivity, coking and sintering resistance, and acid site activity, presenting a possible approach to low-energy polyolefin depolymerization. However, a critical examination of the literature on SZrO led us to a surprising conclusion: despite 40 years of catalytic study, engineering, and industrial use, the surface chemistry of SZrO is poorly understood. Ostensibly spurred by SZrO's impressive catalytic activity, the application-driven study of SZrO has resulted in deleterious ambiguity in requisite synthetic conditions for superacidity and insufficient characterization of acidity, porosity, and active site structure. This ambiguity has produced significant knowledge gaps surrounding the synthesis, structure, and mechanisms of hydrocarbon activation for optimized SZrO, stunting the potential of this catalyst in olefin cracking and other industrially relevant reactions, such as isomerization, esterification, and alkylation. Toward mitigating these long extant issues, we herein identify and highlight these current shortcomings and knowledge gaps, propose explicit guidelines for characterization of and reporting on characterization of solid acidity, and discuss the potential of pore-confined superacids in the efficient and selective depolymerization of polyolefins.

Functional upcycling of waste PET plastic to the hybrid magnetic microparticles adsorbent for cesium removal

Accumulation of mismanaged plastic in the environment and the appearance of emerging plastic-derived pollutants such as microplastics strongly demand technologies for waste plastic utilization. In this study, polyethylene terephthalate (PET) from waste plastic bottles was directly utilized to prepare a matrix of an adsorbent for cesium (Cs+) removal. The organic matrix of PET-derived oligomers obtained by aminolysis depolymerization was impregnated with bentonite clay and magnetite nanoparticles (Fe3O4 NPs), playing the roles as a major adsorptive medium for Cs+ removal and as a functional component to primarily provide efficient separation of the hybrid adsorbent from aqueous system, respectively. The obtained hybrid composite microparticles were next tested as an adsorbent for the removal of Cs+ cation from aqueous solutions. The adsorption process was characterized by fast kinetics reaching ca. 60% of the equilibrium adsorption capacity within 5 min and the maximum adsorption capacity toward Cs+ was found to be 26.8 mg/g. The adsorption process was primarily dominated by the cationic exchange in bentonite, which was not significantly affected by the admixture of the competing mono- and divalent cations (Na+, K+, and Mg2+). The proposed approach here exploits the sustainable utilization scenario of plastic waste-derived material to template complex multifunctional nanocomposites that can find applications for pollution cleaning and environmental remediation.

Grave-to-cradle photothermal upcycling of waste polyesters over spent LiCoO2

Lithium-ion batteries (LIBs) and plastics are pivotal components of modern society; nevertheless, their escalating production poses formidable challenges to resource sustainability and ecosystem integrity. Here, we showcase the transformation of spent lithium cobalt oxide (LCO) cathodes into photothermal catalysts capable of catalyzing the upcycling of diverse waste polyesters into high-value monomers. The distinctive Li deficiency in spent LCO induces a contraction in the Co-O6 unit cell, boosting the monomer yield exceeding that of pristine LCO by a factor of 10.24. A comprehensive life-cycle assessment underscores the economic viability of utilizing spent LCO as a photothermal catalyst, yielding returns of 129.6 $·kgLCO-1, surpassing traditional battery recycling returns (13-17 $·kgLCO-1). Solar-driven recycling 100,000 tons of PET can reduce 3.459 × 1011 kJ of electric energy and decrease 38,716 tons of greenhouse gas emissions. This work unveils a sustainable solution for the management of spent LIBs and plastics.

Chitinous Bioplastic Enabled by Noncovalent Assembly

Natural polymeric-based bioplastics usually lack good mechanical or processing performance. It is still challenging to achieve simultaneous improvement for these two usual trade-off features. Here, we demonstrate a full noncovalent mediated self-assembly design for simultaneously improving the chitinous bioplastic processing and mechanical properties via plane hot-pressing. Tannic acid (TA) is chosen as the noncovalent mediator to (i) increase the noncovalent cross-link intensity for obtaining the tough noncovalent network and (ii) afford the dynamic noncovalent cross-links to enable the mobility of chitin molecular chains for benefiting chitinous bioplastic nanostructure rearrangement during the shaping procedure. The multiple noncovalent mediated network (chitin-TA and chitin-chitin cross-links) and the pressure-induced orientation nanofibers structure endow the chitinous bioplastics with robust mechanical properties. The relatively weak chitin-TA noncovalent interactions serve as water mediation switches to enhance the molecular mobility for endowing the chitin/TA bioplastic with hydroplastic processing properties, rendering them readily programmable into versatile 2D/3D shapes. Moreover, the fully natural resourced chitinous bioplastic exhibits superior weld, solvent resistance, and biodegradability, enabling the potential for diverse applications. The full physical cross-linking mechanism highlights an effective design concept for balancing the trade-off of the mechanical properties and processability for the polymeric materials.

Corrosion Engineering of Part-Per-Million Single Atom Pt1/Ni(OH)2 Electrocatalyst for PET Upcycling at Ampere-Level Current Density

The plastic waste issue has posed a series of formidable challenges for the ecological environment and human health. While conventional recycling strategies often lead to plastic down-cycling, the electrochemical strategy of recovering valuable monomers enables an ideal, circular plastic economy. Here a corrosion synthesized single atom Pt1/Ni(OH)2 electrocatalyst with part-per-million noble Pt loading for highly efficient and selective upcycling of polyethylene terephthalate (PET) into valuable chemicals (potassium diformate and terephthalic acid) and green hydrogen is reported. Electro-oxidation of PET hydrolysate, ethylene glycol (EG), to formate is processed with high Faraday efficiency (FE) and selectivity (>90%) at the current density close to 1000 mA cm-2 (1.444 V vs RHE). The in situ spectroscopy and density functional theory calculations provide insights into the mechanism and the understanding of the high efficiency. Remarkably, the electro-oxidation of EG at the ampere-level current density is also successfully illustrated by using a membrane-electrode assembly with high FEs to formate integrated with hydrogen production for 500 h of continuous operation. This process allows valuable chemical production at high space-time yield and is highly profitable (588-700 $ ton-1 PET), showing an industrial perspective on single-atom catalysis of electrochemical plastic upcycling.

Do industrial solid waste recycling and technological innovation promote low-carbon development in China? New insights from NARDL approach

Recycling waste is crucial for consolidating resources and promoting sustainable development, serving a pivotal role in achieving the objectives of carbon peak and carbon neutrality. Nonetheless, most existing research has primarily focused on municipal solid waste (MSW) recycling, often neglecting the significant volume of industrial solid waste (ISW). This study aims to explore the asymmetric effects of industrial solid waste recycling and technological innovation on the low-carbon development. To this end, this study selects GDP and carbon intensity as indicators representing economic growth and environmental quality. A variable that can enhance GDP growth while reducing carbon intensity signifies its contribution to low-carbon development. By collecting data from China over the period of 1985-2020, non-linear autoregressive distributed lag (NARDL) models of GDP and carbon intensity are established to discover whether the low-carbon development can be achieved by enacting ISW recycling and technological innovation. The results show the asymmetric shocks of ISW recycling and technological innovation on economic growth and environmental quality. In the long run, both ISW recycling and technological innovation promote low-carbon development. In the short run, technological innovation proved to be detrimental to economic growth and environmental quality. This paper also highlights the inhibitory effect of the labor force on economic growth. The "pollution haven hypothesis" is supported by the finding that foreign direct investment reduces carbon intensity. Additionally, the Granger test revealed the direction of the variables' causality. Based on empirical findings, policymakers can protect the environment and create economic value simultaneously through waste recycling and technological innovation, thereby realizing low-carbon development.

Transforming polypropylene waste into transparent anti-corrosion weather-resistant and anti-bacterial superhydrophobic films

The global pollution crisis arising from the accumulation of plastic in landfills and the environment necessitates addressing plastic waste issues. Notably, polypropylene (PP) waste accounts for 20% of total plastic waste and holds promise for hydrophobic applications in the realm of recycling. Herein, the transparent and non-transparent superhydrophobic films made from waste PP are reported. A hierarchical structure with protrusions is induced through spin-casting and thermally induced phase separation. The films had a water contact angle of 159° and could vary in thickness, strength, roughness, and hydrophobicity depending on end-user requirements. The Bode plot indicated enhanced corrosion resistance in the superhydrophobic films. Antibacterial trials with Escherichia coli and Staphylococcus aureus microbial solutions showed that the superhydrophobic film had a significantly lower rate of colony-forming units compared to both the transparent surface and the control blank sample. Moreover, a life cycle assessment revealed that the film production resulted in a 62% lower embodied energy and 34% lower carbon footprint compared to virgin PP pellets sourced from petroleum. These films exhibit distinctiveness with their dual functionality as coatings and freestanding films. Unlike conventional coatings that require chemical application onto the substrate, these films can be mechanically applied using adhesive tapes on a variety of surfaces. Overall, the effective recycling of waste PP into versatile superhydrophobic films not only reduces environmental impact but also paves the way for a more sustainable and eco-friendly future.

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.

From Soy Waste to Bioplastics: Industrial Proof of Concept

The global plastic waste problem is pushing for the development of sustainable alternatives, encouraged by stringent regulations combined with increased environmental consciousness. In response, this study presents an industrial-scale proof of concept to produce self-standing, transparent, and flexible bioplastic films, offering a possible solution to plastic pollution and resource valorization. We achieve this by combining amyloid fibrils self-assembled from food waste with methylcellulose and glycerol. Specifically, soy whey and okara, two pivotal protein-rich byproducts of tofu manufacturing, emerge as sustainable and versatile precursors for amyloid fibril formation and bioplastic development. An exhaustive industrial-scale feasibility study involving the transformation of 500 L of soy whey into ∼1 km (27 kg) of bioplastic films underscores the potential of this technology. To extend the practicality of our approach, we further processed a running kilometer of film at the industrial scale into transparent windows for paper-based packaging. The mechanical properties and the water interactions of the novel film are tested and compared with those of commercially used plastic films. By pioneering the large-scale production of biodegradable bioplastics sourced from food byproducts, this work not only simultaneously addresses the dual challenges of plastic pollution and food waste but also practically demonstrates the feasibility of biopolymeric building block valorization for the development of sustainable materials in real-world scenarios.

Strain Engineering of Cd0.5 Zn0.5 S Nanocrystal for Efficient Photocatalytic Hydrogen Evolution from Wasted Plastic

The challenge of synthesizing nanocrystal photocatalysts with adjustable lattice strain for effective waste-to-energy conversion is addressed in this study. Cd0.5 Zn0.5 S (CZS) nanocrystals are synthesized by a simple solvothermal method, regulation of the ratio between N, N-dimethylformamide, and water solvent are shown to provoke expansion and contraction, inducing an adjustable lattice strain ranging from -1.2% to 5.6%. With the hydrolyzed wasted plastic as a sacrificial agent, the 5.6% lattice-strain CZS exhibited a robust hydrogen evolution activity of 1.09 mmol m-2  h-1 (13.83 mmol g-1  h-1 ), 4.5 times that of pristine CZS. Characterizations and density functional theory calculation demonstrated that lattice expansion increases the spatial distance between the valence band maximum and conduction band minimum, thus reducing carrier recombination and promoting charge transfer. Additionally, lattice expansion induces surface S vacancies and adsorbed OH groups, further enhancing redox reactions. This study focuses on the synchronous regulation of crystal structure, charge separation/transport, and surface reactions through lattice strain engineering, which providing a reference for the rational design of new photocatalysts for effective waste-to-energy conversion.

Waste to energy: Trending key challenges and current technologies in waste plastic management

Due to the 'forever' degrading nature of plastic waste, plastic waste management is often complicated. The applications of plastic are ubiquitous and inevitable in many scenarios. Current global waste plastics production is ca. 3.5 MMT per year, and with the current trend, plastic waste production will reach 25,000 MMT by 2040. However, the rapid growth in plastic manufacture and the material's inherent nature resulted in the accumulation of a vast amount of plastic garbage. The current recycling rate is <10 %, while the large volumes of discarded plastic waste cause environmental and ecological problems. Recycling rates for plastic vary widely by region and type of plastic. In some developed countries, the recycling rate for plastics is around 20-30 %, while in many developing nations, it is much lower. These statistics highlight the magnitude of the plastic waste problem and the urgent need for comprehensive strategies to manage plastic waste more effectively and reduce its impact on the environment. This review critically analyses past studies on the essential and efficient techniques for turning plastic trash into treasure. Additionally, an attempt has been made to provide a comprehensive understanding of the plastic upcycling process, the 3Rs policy, and the life-cycle assessment (LCA) of plastic conversion. The review advocates pyrolysis as one of the most promising methods of turning plastic trash into valuable chemicals. In addition, plastic waste management can be severely impacted due to uncontrollable events, such as Covid 19 pandemic. Recycling and chemical upcycling can certainly bring value to the end-of-life plastic. However, the LCA analysis indicated there is still a huge scope for innovation in chemical upcycling area compared to mechanical recycling. The formulation of policies and heightened public participation could play a pivotal role in reducing the environmental repercussions of plastic waste and facilitating a shift towards a more sustainable future.

Acid-Cleavable Aromatic Polymers for the Fabrication of Closed-Loop Recyclable Plastics with High Mechanical Strength and Excellent Chemical Resistance

Although closed-loop recycling of dynamic covalent bond-based plastics does not require catalysts, their mechanical strength and chemical stability remain a major concern. In this study, closed-loop recyclable poly(aryl imine) (PAI) plastics with high mechanical strength and excellent chemical resistance are fabricated by copolymerizing aromatic amines and aromatic aldehydes through dynamic imine bonds. The resulting PAI plastic with a tensile strength of 58.2 MPa exhibits excellent chemical resistance and mechanical stability in acidic and basic aqueous solutions and various organic solvents. The PAI plastics can be depolymerized in a mixed solvent of tetrahydrofuran (THF)/HCl aqueous solution through the dissociation of imine bonds, and the monomers can be facilely recovered with high purity and isolated yields due to the solubility difference between the aromatic amines and aromatic aldehydes in selective solvents. The efficient closed-loop recycling of the PAI plastic can also be realized through monomer conversion because the hydrolysis of the aromatic aldehydes generates aromatic amines. The recovered monomers can be used to re-fabricate original PAI plastics. This PAI plastic can be selectively recovered from complicated mixed polymer waste streams due to the mild depolymerization conditions of the PAI plastic and its high stability in most organic solvents.

Next-Generation Vitrimers Design through Theoretical Understanding and Computational Simulations

Vitrimers are an innovative class of polymers that boast a remarkable fusion of mechanical and dynamic features, complemented by the added benefit of end-of-life recyclability. This extraordinary blend of properties makes them highly attractive for a variety of applications, such as the automotive sector, soft robotics, and the aerospace industry. At their core, vitrimer materials consist of crosslinked covalent networks that have the ability to dynamically reorganize in response to external factors, including temperature changes, pressure variations, or shifts in pH levels. In this review, the aim is to delve into the latest advancements in the theoretical understanding and computational design of vitrimers. The review begins by offering an overview of the fundamental principles that underlie the behavior of these materials, encompassing their structures, dynamic behavior, and reaction mechanisms. Subsequently, recent progress in the computational design of vitrimers is explored, with a focus on the employment of molecular dynamics (MD)/Monte Carlo (MC) simulations and density functional theory (DFT) calculations. Last, the existing challenges and prospective directions for this field are critically analyzed, emphasizing the necessity for additional theoretical and computational advancements, coupled with experimental validation.

Biobased, biodegradable and compostable plastics: chemical nature, biodegradation pathways and environmental strategy

Increasing pollution of plastic waste is one of the major global environmental threats, deteriorating our land, water and air. The shift towards biobased, biodegradable and compostable plastics is considered a green alternative to petroleum-based plastic due to its renewable source or biodegradability. However, there is a misconception about biodegradable plastics and their degradability and behaviour after service life. Biobased, biodegradable and compostable plastics offer various benefits such as less carbon footprint, energy efficiency, independence and eco-safety. On the other hand, there are some disadvantages such as higher cost, limited recycling, misuse of terms and lack of legislation. Also, there is an urgent need for comparable international standard methods to define these materials as biodegradable material, or biocompostable material. There are some standards currently available, however, an in-depth detail and explanation of these standards is still missing. This review outlines the basic definition and chemical structure of biobased, biodegradable and compostable plastics; describes the degradation pathways of biodegradable and compostable plastics; and summarises current key applications of these materials together with possible future applications in different industries. Finally, strategies are developed for minimising the environmental impacts and the need for future research is proposed.

Selective poly(vinyl ether) upcycling via photooxidative degradation with visible light

Poly(vinyl ethers) (PVEs) have many applications, such as adhesives, lubricants, and anticorrosive agents, thanks to their elastic, nonirritating, and chemically inert properties. The recycling of PVEs remains largely underexplored, and current methods lack generality towards other polymer classes. Thus, the chemical upcycling of PVE into small molecule feedstocks would provide an alternative approach to combat these current issues. Here, we report a visible light-mediated method of upcycling poly(isobutyl vinyl ether) (PIBVE) into small molecules via photooxidative degradation using chlorine or bromine radicals. PIBVE can be degraded to low molecular weight oligomers within 2 h, producing good yields of alcohols, aldehydes, and carboxylic acids. Mechanistic studies suggest that hydrogen atom transfer (HAT) from the backbone or the side chain leads to small molecule generation via oxidative cleavages. Additionally, this protocol was applied to a copolymer of poly(methyl acrylate-co-isobutyl vinyl ether) to demonstrate the preference for the degradation of polymers bearing more electron-rich C-H bonds through a judicious choice of abstraction agent. Ultimately, we show that photooxidative degradation enables the selective chemical upcycling of PVEs as a method of plastic waste valorization.

Solar reforming as an emerging technology for circular chemical industries

The adverse environmental impacts of greenhouse gas emissions and persistent waste accumulation are driving the demand for sustainable approaches to clean-energy production and waste recycling. By coupling the thermodynamically favourable oxidation of waste-derived organic carbon streams with fuel-forming reduction reactions suitable for producing clean hydrogen or converting CO2 to fuels, solar reforming simultaneously valorizes waste and generates useful chemical products. With appropriate light harvesting, catalyst design, device configurations and waste pre-treatment strategies, a range of sustainable fuels and value-added chemicals can already be selectively produced from diverse waste feedstocks, including biomass and plastics, demonstrating the potential of solar-powered upcycling plants. This Review highlights solar reforming as an emerging technology that is currently transitioning from fundamental research towards practical application. We investigate the chemistry and compatibility of waste pre-treatment, introduce process classifications, explore the mechanisms of different solar reforming technologies, and suggest appropriate concepts, metrics and pathways for various deployment scenarios in a net-zero-carbon future.

Degradation Product-Promoted Depolymerization Strategy for Chemical Recycling of Poly(bisphenol A carbonate)

The accumulation of waste plastics has a severe impact on the environment, and therefore, the development of efficient chemical recycling methods has become an extremely important task. In this regard, a new strategy of degradation product-promoted depolymerization process was proposed. Using N,N'-dimethyl-ethylenediamine (DMEDA) as a depolymerization reagent, an efficient chemical recycling of poly(bisphenol A carbonate) (BPA-PC or PC) material was achieved under mild conditions. The degradation product 1,3-dimethyl-2-imidazolidinone (DMI) was proven to be a critical factor in facilitating the depolymerization process. This strategy does not require catalysts or auxiliary solvents, making it a truly green process. This method improves the recycling efficiency of PC and promotes the development of plastic reutilization.

A robust depolymerization route for polysiloxanes

A versatile, robust, and stable tetrabutylammonium difluorotriphenylsilicate (TBAT) catalyst has been deployed for efficient depolymerization of silicones. This catalyst is soluble in a variety of organic solvents and is stable up to 170 °C, enabling a wide range of reaction conditions under which F--catalysed siloxane bond cleavage can be initiated. This effort offers significant advancement overcoming the traditional limitations of silicone depolymerization, such as high catalyst loading, storage and handling, and few viable reaction media.

Recent Advancements in Pyrolysis of Halogen-Containing Plastics for Resource Recovery and Halogen Upcycling: A State-of-the-Art Review

Plastic waste has emerged as a serious issue due to its impact on environmental degradation and resource scarcity. Plastic recycling, especially of halogen-containing plastics, presents challenges due to potential secondary pollution and lower-value implementations. Chemical recycling via pyrolysis is the most versatile and robust approach for combating plastic waste. In this Review, we present recent advancements in halogen-plastic pyrolysis for resource utilization and the potential pathways from "reducing to recycling to upcycling" halogens. We emphasize the advanced management of halogen-plastics through copyrolysis with solid wastes (waste polymers, biomass, coal, etc.), which is an efficient method for dealing with mixed wastes to obtain high-value products while reducing undesirable substances. Innovations in catalyst design and reaction configurations for catalytic pyrolysis are comprehensively evaluated. In particular, a tandem catalysis system is a promising route for halogen removal and selective conversion of targeted products. Furthermore, we propose novel insights regarding the utilization and upcycling of halogens from halogen-plastics. This includes the preparation of halogen-based sorbents for elemental mercury removal, the halogenation-vaporization process for metal recovery, and the development of halogen-doped functional materials for new materials and energy applications. The reutilization of halogens facilitates the upcycling of halogen-plastics, but many efforts are needed for mutually beneficial outcomes. Overall, future investigations in the development of copyrolysis and catalyst-driven technologies for upcycling halogen-plastics are highlighted.

Multi-Functional Organofluoride Catalysts for Polyesters Production and Upcycling Degradation

The production and degradation of polyesters are two crucial processes in polyester materials' life cycle. In this work, multi-functional organocatalysts based on fluorides for both processes are described. Organofluorides were developed as catalysts for ring-opening polymerization of lactide (lactone). Compared with a series of organohalides, organofluoride performed the best catalytic reactivity because of the hydrogen bond interaction between F- and alcohol initiator. The Mn values of polyester products could be up to 72 kg mol-1 . With organofluoride catalysts, the ring-opening copolymerization between various anhydrides and epoxides could be established. Furthermore, terpolymerization of anhydride, epoxide, and lactide could be constructed by the self-switchable organofluoride catalyst to yield a block polymer with a strictly controlled polymerization sequence. Organofluorides were also efficient catalysts for upcycling polyester plastic wastes via alcoholysis. Mixed polyester materials could also be hierarchically recycled.

Solvent-Promoted Catalyst-Free Recycling of Waste Polyester and Polycarbonate Materials

Polymeric materials are indispensable in our daily lives. However, the generation of vast amounts of waste polymers poses significant environmental and ecological challenges. Instead of resorting to landfilling or incineration, strategies for polymer recycling offer a promising approach to mitigate environmental pollution. Pioneering studies have demonstrated the alcoholysis of waste polyesters and polycarbonates; however, these processes typically require the use of catalysts. Moreover, the development of strategies for catalyst removal and recycling is crucial, particularly in some industrial applications. In contrast, we present a catalyst-free method for the alcoholysis of common polyester and polycarbonate materials into small organic molecules. Certain polar organic solvents exhibit remarkable efficiency in polymer degradation under catalyst-free conditions. Employing these polar solvents, both polymer resins and commercially available products could be effectively degraded via alcoholysis. Our design contributes a straightforward route for recycling waste polymeric materials.

Polyethylene upcycling to aromatics by pulse pressurized catalytic pyrolysis

To address the challenging issues of waste plastic pollution and petroleum shortage, we report herein a pulse pressurized catalytic pyrolysis process where polyethylene is continuously converted into aromatics using HZSM-5 catalyst incorporated with hydrated SiO2. Pressurization improves the activity of single-pulse pyrolysis of polyethylene by 14.42%. In contrast to the linear decrease of BTEXS relative yield with a K value of - 0.23 under non-pressurized conditions, pressurization results in a notable stability in the latter stage, characterized by a K value of only - 0.063. Comprehensive catalyst characterization demonstrates that pressurization promotes the release of water from hydrated SiO2, enabling HZSM-5 to effectively undergo dealumination and obtain suitable acidity and pore structure, and ultimately enhancing the resistance to carbon deposition. In summary, pressurization improves both pyrolysis activity and catalysis stability, offering a promising strategy for the high-value utilization of waste plastics.

3D Oleophilic Sorbent Films Based on Recycled Low-Density Polyethylene

Recycling low-end, one-time-use plastics-such as low-density polyethylene (LDPE)-is of paramount importance to combat plastic pollution and promote sustainability in the modern green economy. This study valorizes LDPE waste by transforming it into 3D oleophilic swellable thin films through a process involving dissolution, phase separation, and extraction. These films are subsequently layered using a customized polypropylene (PP) based nonwoven fabric separator and securely sealed in a zigzag pattern. The zigzag-shaped seal enhances the adhesion of pollutants to the sorbent by providing wire curvatures that increase retention time and uptake capacity. As a result, the sorbent exhibits impressive oil uptake capacities, with immediate and equilibrium values of 120 g/g and 85 g/g, respectively. Notably, the as-prepared sorbent demonstrates low water retention and high selectivity for oil, outperforming commercially available oil sorbents. The unique design involving a 3D-film structure, superposed films, and a zigzag-shaped seal offers a sustainable and value-added solution to the issues of LDPE waste and oil spills on water surfaces.

Copolymerization Involving Sulfur-Containing Monomers

Incorporating sulfur (S) atoms into polymer main chains endows these materials with many attractive features, including a high refractive index, mechanical properties, electrochemical properties, and adhesive ability to heavy metal ions. The copolymerization involving S-containing monomers constitutes a facile method for effectively constructing S-containing polymers with diverse structures, readily tunable sequences, and topological structures. In this review, we describe the recent advances in the synthesis of S-containing polymers via copolymerization or multicomponent polymerization techniques concerning a variety of S-containing monomers, such as dithiols, carbon disulfide, carbonyl sulfide, cyclic thioanhydrides, episulfides and elemental sulfur (S8). Particularly, significant focus is paid to precise control of the main-chain sequence, stereochemistry, and topological structure for achieving high-value applications.

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.

Rapid Polyolefin Hydrogenolysis by a Single-Site Organo-Tantalum Catalyst on a Super-Acidic Support: Structure and Mechanism

The novel electrophilic organo-tantalum catalyst AlS/TaNpx (1) (Np=neopentyl) is prepared by chemisorption of the alkylidene Np3 Ta=CHt Bu onto highly Brønsted acidic sulfated alumina (AlS). The proposed catalyst structure is supported by EXAFS, XANES, ICP, DRIFTS, elemental analysis, and SSNMR measurements and is in good agreement with DFT analysis. Catalyst 1 is highly effective for the hydrogenolysis of diverse linear and branched hydrocarbons, ranging from C2 to polyolefins. To the best of our knowledge, 1 exhibits one of the highest polyolefin hydrogenolysis activities (9,800 (CH2 units) ⋅ mol(Ta)-1  ⋅ h-1 at 200 °C/17 atm H2 ) reported to date in the peer-reviewed literature. Unlike the AlS/ZrNp2 analog, the Ta catalyst is more thermally stable and offers multiple potential C-C bond activation pathways. For hydrogenolysis, AlS/TaNpx is effective for a wide variety of pre- and post-consumer polyolefin plastics and is not significantly deactivated by standard polyolefin additives at typical industrial concentrations.

High-Molecular-Weight and Light-Colored Disulfide-Bond-Embedded Polyesters: Accelerated Hydrolysis Triggered by Redox Responsiveness

Disulfide bonds have attracted considerable attention due to their reduction responsiveness, but it is crucial and challenging to prepare disulfide-bond-based polyesters by melt polycondensation. Herein, the inherently poor thermal stability of the S-S bond in melting polycondensation was overcome. Moreover, poly(butylene succinate-co-dithiodipropionate) (PBSDi) with a light color and high molecular weights (Mn values up to 84.7 kg/mol) was obtained. These polyesters can be applied via melt processing with Td,5% > 318 °C. PBSDi10-PBSDi40 shows good crystallizability (crystallinity 56-38%) and compact lamellar thickness (2.9-3.2 nm). Compared with commercial poly(butylene adipate-co-terephthalate) (PBAT), the elevated mechanical and barrier performances of PBSDi make them better packaging materials. For the degradation behavior, the disulfide monomer obviously accelerates the enzyme degradation but has a weaker effect on hydrolysis. In 0.1 mol/L or higher concentrations of H2O2 solutions, the oxidation of disulfide bonds to sulfoxide and sulfone groups can be realized. This process results in a stronger nucleophilic attack, as confirmed by the Fukui function and DFT calculations. Additionally, the greater polarity and hydrophilicity of oxidation products, proved by noncovalent interaction analysis, accelerate the hydrolysis of polyesters. Moreover, glutathione-responsive breakage, from polymers to oligomers, is confirmed by an accelerated decline in molecular weight. Our research offers fresh perspectives on the effective synthesis of the disulfide polyester and lays a solid basis for the creation of high-performance biodegradable polyesters that degrade on demand.

Biodegradation of low-density polyethylene (LDPE) through application of indigenous strain Alcaligenes faecalis ISJ128

The resiliency of plastic products against microbial degradation in natural environment often creates devastating changes for humans, plants, and animals on the earth's surface. Biodegradation of plastics using indigenous bacteria may serve as a critical approach to overcome this resulting environmental stress. In the present work, a polyethylene degrading bacterium Alcaligenes faecalis strain ISJ128 (Accession No. MK968769) was isolated from partially degraded polyethylene film buried in the soil at plastic waste disposal site. The biodegradation studies were conducted by employing various methods such as hydrophobicity assessment of the strain ISJ128, measurement of viability and total protein content of bacterial biofilm attached to the polyethylene surface. The proliferation of bacterial cells on polyethylene film, as indicated by high growth response in terms of protein content (85.50 µg mL-1) and viability (1010 CFU mL-1), proposed reasonable suitability of our strain A. faecalis ISJ128 toward polyethylene degradation. The results of biodegradation assay revealed significant degradation (10.40%) of polyethylene film within a short period of time (i.e., 60 days), whereas no signs of degradation were seen in control PE film. A. faecalis strain ISJ128 also demonstrated a removal rate of 0.0018 day-1 along with half-life of 462 days. The scanning electron microscope (SEM) and Fourier transform infrared (FTIR) spectroscopy studies not only displayed changes on polyethylene surface but also altered level of intensity of functional groups and an increase in the carbonyl indexes justifying the degradation of polyethylene film due to bacterial activity. In addition, the secondary structure prediction (M fold software) of 16SrDNA proved the stable nature of the bacterial strain, thereby reflecting the profound scope of A. faecalis strain ISJ128 as a potential degrader for the eco-friendly disposal of polyethylene waste. Schematic representation of methodology.

Concentration-Dependent Photocatalytic Upcycling of Poly(ethylene terephthalate) Plastic Waste

Photocatalytic plastic waste upcycling into value-added feedstock is a promising way to mitigate the environmental issues caused by the nondegradable nature of plastic waste. Here, we developed a MoS2/g-C3N4 photocatalyst that can efficiently upcycle poly(ethylene terephthalate) (PET) into valuable organic chemicals. Interestingly, the conversion mechanism is concentration-dependent. For instance, at a low ethylene glycol (EG) concentration (7.96 mM), acetate is the main product. Unexpectedly, the conversion of PET water bottle hydrolysate with only 7.96 mM ethylene glycol (EG) can produce a 4 times higher amount of acetate (704.59 nmol) than the conversion of 300 mM EG (174.50 nmol), while at a higher EG concentration (300 mM), formate is the dominant product. Herein, a 40 times higher EG concentration (300 mM compared to 7.96 mM) would produce only ∼3 times more formate (179 nmol compared to 51.86 nmol). In addition, under natural sunlight conditions, comparable amounts of liquid and gaseous products are produced when commercial PET plastics are employed. Overall, the photocatalytic PET conversion process is quite efficient under a low concentration of EG in PET hydrolysate, indicating the enormous potential of this photocatalysis strategy for real plastics upcycling.

Synthesis of Clean Hydrogen Gas from Waste Plastic at Zero Net Cost

Hydrogen gas (H2 ) is the primary storable fuel for pollution-free energy production, with over 90 million tonnes used globally per year. More than 95% of H2 is synthesized through metal-catalyzed steam methane reforming that produces 11 tonnes of carbon dioxide (CO2 ) per tonne H2 . "Green H2 " from water electrolysis using renewable energy evolves no CO2 , but costs 2-3× more, making it presently economically unviable. Here catalyst-free conversion of waste plastic into clean H2 along with high purity graphene is reported. The scalable procedure evolves no CO2 when deconstructing polyolefins and produces H2 in purities up to 94% at high mass yields. The sale of graphene byproduct at just 5% of its current value yields H2 production at a negative cost. Life-cycle assessment demonstrates a 39-84% reduction in emissions compared to other H2 production methods, suggesting the flash H2 process to be an economically viable, clean H2 production route.

An LCA answer to the mixed plastics waste dilemma: Energy recovery or chemical recycling?

The study focuses on mixed plastics waste (MPW), whose complex and unpredictable composition (due to high polymer heterogeneity, additives, and contaminants) makes its valorisation a true technical, environmental, economic, and regulatory challenge. Chemical recycling by means of advanced thermochemical treatments (ATT) could be a successful strategy, able to support the transition from a carbon intensive to a carbon negative sector, and alternative to the current treatments of energy recovery or mechanical downcycling. Some of these ATTs provide an efficient recovery of valuable resources, such as fuels and chemicals, but their role is mainly limited by time necessary to complete the process optimization and implement the required infrastructures. A reliable identification of the best alternatives is thus crucial. A specific LCA approach quantifies the environmental performances of a selected set of ATT technologies for resource recovery from MPW. It includes plastics-to-energy, by combustion or gasification; plastics-to-methane and plastics-to-hydrogen, by gasification; and plastics-to-oil, by thermal pyrolysis. The results highlight the crucial role of carbon capture and storage (CCS) units, which partially reduces that of the specific thermochemical treatment. The best performances, particularly for Climate Change category, are those of the MPW-to-hydrogen by gasification, followed by those of MPW-to-energy by combustion or gasification, all equipped with CCS. The sensitivity analysis considers the evolution of the European energy mix, characterised by a larger utilisation of renewable energy sources, and highlights the corresponding increased sustainability of chemical recycling by ATTs. This suggests that the MPW dilemma should be definitively solved in a close future.

Mechanistic Understanding of Efficient Polyethylene Hydrocracking over Two-Dimensional Platinum-Anchored Tungsten Trioxide

Chemical upcycling of polyethylene (PE) can convert plastic waste into valuable resources. However, engineering a catalyst that allows PE decomposition at low temperatures with high activity remains a significant challenge. Herein, we anchored 0.2 wt.% platinum (Pt) on defective two-dimensional tungsten trioxide (2D WO3 ) nanosheets and achieved hydrocracking of high-density polyethylene (HDPE) waste at 200-250 °C with a liquid fuel (C5-18 ) formation rate up to 1456 gproducts  ⋅ gmetal species -1  ⋅ h-1 . The reaction pathway over the bifunctional 2D Pt/WO3 is elucidated by quasi-operando transmission infrared spectroscopy, where (I) well-dispersed Pt immobilized on 2D WO3 nanosheets trigger the dissociation of hydrogen; (II) adsorption of PE and activation of C-C cleavage on WO3 are through the formation of C=O/C=C intermediates; (III) intermediates are converted to alkane products by the dissociated H. Our study directly illustrates the synergistic role of bifunctional Pt/WO3 catalyst in the hydrocracking of HDPE, paving the way for the development of high-performance catalysts with optimized chemical and morphological properties.

A Model Ensemble Approach Enables Data-Driven Property Prediction for Chemically Deconstructable Thermosets in the Low-Data Regime

Thermosets present sustainability challenges that could potentially be addressed through the design of deconstructable variants with tunable properties; however, the combinatorial space of possible thermoset molecular building blocks (e.g., monomers, cross-linkers, and additives) and manufacturing conditions is vast, and predictive knowledge for how combinations of these molecular components translate to bulk thermoset properties is lacking. Data science could overcome these problems, but computational methods are difficult to apply to multicomponent, amorphous, statistical copolymer materials for which little data exist. Here, leveraging a data set with 101 examples, we introduce a closed-loop experimental, machine learning (ML), and virtual screening strategy to enable predictions of the glass transition temperature (Tg) of polydicyclopentadiene (pDCPD) thermosets containing cleavable bifunctional silyl ether (BSE) comonomers and/or cross-linkers with varied compositions and loadings. Molecular features and formulation variables are used as model inputs, and uncertainty is quantified through model ensembling, which together with heavy regularization helps to avoid overfitting and ultimately achieves predictions within <15 °C for thermosets with compositionally diverse BSEs. This work offers a path to predicting the properties of thermosets based on their molecular building blocks, which may accelerate the discovery of promising plastics, rubbers, and composites with improved functionality and controlled deconstructability.

Plastic degradation by insect hexamerins: Near-atomic resolution structures of the polyethylene-degrading proteins from the wax worm saliva

Plastic waste management is a pressing ecological, social, and economic challenge. The saliva of the lepidopteran Galleria mellonella larvae is capable of oxidizing and depolymerizing polyethylene in hours at room temperature. Here, we analyze by cryo-electron microscopy (cryo-EM) G. mellonella's saliva directly from the native source. The three-dimensional reconstructions reveal that the buccal secretion is mainly composed of four hexamerins belonging to the hemocyanin/phenoloxidase family, renamed Demetra, Cibeles, Ceres, and a previously unidentified factor termed Cora. Functional assays show that this factor, as its counterparts Demetra and Ceres, is also able to oxidize and degrade polyethylene. The cryo-EM data and the x-ray analysis from purified fractions show that they self-assemble primarily into three macromolecular complexes with striking structural differences that likely modulate their activity. Overall, these results establish the ground to further explore the hexamerins' functionalities, their role in vivo, and their eventual biotechnological application.

Chemoenzymatic Photoreforming: A Sustainable Approach for Solar Fuel Generation from Plastic Feedstocks

Plastic upcycling through catalytic transformations is an attractive concept to valorize waste, but the clean and energy-efficient production of high-value products from plastics remains challenging. Here, we introduce chemoenzymatic photoreforming as a process coupling enzymatic pretreatment and solar-driven reforming of polyester plastics under mild temperatures and pH to produce clean H2 and value-added chemicals. Chemoenzymatic photoreforming demonstrates versatility in upcycling polyester films and nanoplastics to produce H2 at high yields reaching ∼103-104 μmol gsub-1 and activities at >500 μmol gcat-1 h-1. Enzyme-treated plastics were also used as electron donors for photocatalytic CO2-to-syngas conversion with a phosphonated cobalt bis(terpyridine) catalyst immobilized on TiO2 nanoparticles (TiO2|CotpyP). Finally, techno-economic analyses reveal that the chemoenzymatic photoreforming approach has the potential to drastically reduce H2 production costs to levels comparable to market prices of H2 produced from fossil fuels while maintaining low CO2-equivalent emissions.

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.

Electrochemical Wastewater Refining: A Vision for Circular Chemical Manufacturing

Wastewater is an underleveraged resource; it contains pollutants that can be transformed into valuable high-purity products. Innovations in chemistry and chemical engineering will play critical roles in valorizing wastewater to remediate environmental pollution, provide equitable access to chemical resources and services, and secure critical materials from diminishing feedstock availability. This perspective envisions electrochemical wastewater refining─the use of electrochemical processes to tune and recover specific products from wastewaters─as the necessary framework to accelerate wastewater-based electrochemistry to widespread practice. We define and prescribe a use-informed approach that simultaneously serves specific wastewater-pollutant-product triads and uncovers a mechanistic understanding generalizable to broad use cases. We use this approach to evaluate research needs in specific case studies of electrocatalysis, stoichiometric electrochemical conversions, and electrochemical separations. Finally, we provide rationale and guidance for intentionally expanding the electrochemical wastewater refining product portfolio. Wastewater refining will require a coordinated effort from multiple expertise areas to meet the urgent need of extracting maximal value from complex, variable, diverse, and abundant wastewater resources.

Modular Alcohol Click Chemistry Enables Facile Synthesis of Recyclable Polymers with Tunable Structure

The facile synthesis of chemically recyclable polymers derived from sustainable feedstocks presents enormous challenges. Here, we develop a novel, modular, and efficient click reaction for connecting primary, secondary, or tertiary alcohols with activated alkenes via a bridge molecule of carbonyl sulfide (COS). The click reaction is successfully applied to synthesize a series of recyclable polymers by the step polyaddition of diols, diacrylates, and COS. Diols and diacrylates are common chemicals and can be produced from biorenewable sources, and COS is released as the industrial waste. In addition to sustainable monomers, the approach is atom-economical, wide in scope, metal-free, and performed under mild conditions, affording unprecedented polymers with nearly quantitative yields. The produced polymers also possess predesigned and widely tunable structure owing to the versatility of our method and the broad variety of monomers. The in-chain thiocarbonate and ester polar groups can play as breakpoints, allowing these polymers to be easily recycled. Overall, the polymers have broad prospects for green materials given their facile synthesis, readily available feedstocks, desirable performance, and chemical recyclability.