Upcycling plastic wastes into value-added products via electrocatalysis and photoelectrocatalysis

Plastic,renowned for its versatility,durability,and cost-effectiveness,is indispensable in modern society.Nevertheless,the annual production of nearly 400 million tons of plastic,coupled with a recycling rate of only 9%,has led to a monumental environmental crisis.Plastic recycling has emerged as a vital response to this crisis,offering sustainable solutions to mitigate its environmental impact.Among these recycling efforts,plastic upcycling has garnered attention,which elevates discarded plastics into higher-value products.Here,electrocatalytic and photoelectrocatalytic treatments stand at the forefront of advanced plastic upcycling.Electrocatalytic or photoelectrocatalytic treatments involve chemical reactions that facilitate electron transfer through the electrode/electrolyte interface,driven by electrical or solar energy,respectively.These methods enable precise control of chemical reactions,harnessing potential,current density,or light to yield valuable chemical products.This review explores recent progress in plastic upcycling through electrocatalytic and photoelectrocatalytic pathways,offering promising solutions to the plastic waste crisis and advancing sustainability in the plastics industry.

Upcycling municipal solid waste to sustainable hydrogen via two-stage gasification-reforming

As global municipal solid waste(MSW)quantities continue to escalate,serious socio-environmental challenges arise,necessitating innovative solutions.Waste-to-hydrogen(WTH)via two-stage gasification-reforming(TSGR)presents an emergent technology for MSW upcycling,offering to ease waste management burdens and bolster the burgeoning hydrogen economy.Despite early initiatives to advance TSGR technology,a cohesive and critical analysis of cutting-edge knowledge and strategies to enhance hydrogen production remains lacking.This review aggregates literature on MSW upcycling to hydrogen via TSGR,with a focus on optimizing process control and catalytic efficiency.It underscores technological avenues to augment hydrogen output,curtail catalyst costs,and refine system performance.Particularly,the review illuminates the potential for integrating chemical and calcium looping into TSGR processes,identifying opportunities,and pinpointing challenges.The review concludes with a summary of the current state of techno-economic analysis for this technology,presenting outstanding challenges and future research directions,with the ultimate goal of transitioning WTH from theoretical to practical application.

Targeted regeneration and upcycling of spent graphite by defect‐driven tin nucleation

The recycling of spent batteries has become increasingly important owing to their wide applications,abundant raw material supply,and sustainable development.Compared with the degraded cathode,spent anode graphite often has a relatively intact structure with few defects after long cycling.Yet,most spent graphite is simply burned or discarded due to its limited value and inferior performance on using conventional recycling methods that are complex,have low efficiency,and fail in performance restoration.Herein,we propose a fast,efficient,and“intelligent”strategy to regenerate and upcycle spent graphite based on defect‐driven targeted remediation.Using Sn as a nanoscale healant,we used rapid heating(~50 ms)to enable dynamic Sn droplets to automatically nucleate around the surface defects on the graphite upon cooling owing to strong binding to the defects(~5.84 eV/atom),thus simultaneously achieving Sn dispersion and graphite remediation.As a result,the regenerated graphite showed enhanced capacity and cycle stability(458.9 mAh g^(−1) at 0.2 A g^(−1) after 100 cycles),superior to those of commercial graphite.Benefiting from the self‐adaption of Sn dispersion,spent graphite with different degrees of defects can be regenerated to similar structures and performance.EverBatt analysis indicates that targeted regeneration and upcycling have significantly lower energy consumption(~99%reduction)and near‐zero CO_(2) emission,and yield much higher profit than hydrometallurgy,which opens a new avenue for direct upcycling of spend graphite in an efficient,green,and profitable manner for sustainable battery manufacture.

Efficient and selective upcycling of waste polylactic acid into acetate using nickel selenide

The conversion of waste polylactic acid(PLA)plastics into high-value-added chemicals through electrochemical methods is a promising and sustainable approach.However,developing efficient and highly selective catalysts for lactic acid oxidation reaction(LAOR)and understanding the reaction process are challenging.Here,we report the electrooxidation of waste PLA to acetate at a high current density of 100 mA cm-2 with high Faraday efficiency(~95%)and excellent stability(>100 h)over a nickel selenide nanosheet catalyst.In addition,a total Faraday efficiency of up to 190%was achieved for carboxylic acids,including acetic acid and formic acid,by coupling with the cathodic CO_(2) reduction reaction.In situ experimental results and theoretical simulations revealed that the catalytic activity center of LAOR was dynamically formed NiOOH species,and the surface-adsorbed SeO_(x) species accelerated the formation of Ni~(3+)species,thus promoting catalytic activity.The mechanism of lactic acid electrooxidation was further elucidated.Lactic acid was dehydrogenated to produce pyruvate first and then formed CH_3CO due to preferential C-C bond cleavage,resulting in the presence of acetate.This work demonstrated a sustainable method for recycling waste PLA and CO_(2) into high-value-added products.

A Unifi ed View of Carbon Neutrality:Solar-Driven Selective Upcycling of Waste Plastics

With the rapid development of plastic production and consumption globally,the amount of post-consumer plastic waste has reached levels that have posed environmental threats.Considering the substantial CO_(2)emissions throughout the plastic lifecycle from material production to its disposal,photocatalysis is considered a promising strategy for eff ective plastic recycling and upcycling.It can upgrade plastics into value-added products under mild conditions using solar energy,realizing zero carbon emissions.In this paper,we explain the basics of photocatalytic plastic reformation and underscores plastic feedstock reformation pathways into high-value-added products,including both degradation into CO_(2)followed by reformation and direct reformation into high-value-added products.Finally,the current applications of transforming plastic waste into fuels,chemicals,and carbon materials and the outlook on upcycling plastic waste by photocatalysis are presented,facilitating the realization of carbon neutrality and zero plastic waste.

Upcycling of spent LiCoO_(2) cathodes via nickel- and manganese-doping

Direct recycling has been regarded as one of the most promising approaches to dealing with the increasing amount of spent lithium‐ion batteries(LIBs).However,the current direct recycling method remains insufficient to regenerate outdated cathodes to meet current industry needs as it only aims at recovering the structure and composition of degraded cathodes.Herein,a nickel(Ni)and manganese(Mn)co‐doping strategy has been adopted to enhance LiCoO_(2)(LCO)cathode for next‐generation high‐performance LIBs through a conventional hydrothermal treatment combined with short annealing approach.Unlike direct recycling methods that make no changes to the chemical composition of cathodes,the unique upcycling process fabricates a series of cathodes doped with different contents of Ni and Mn.The regenerated LCO cathode with 5%doping delivers excellent electrochemical performance with a discharge capacity of 160.23 mAh g^(−1) at 1.0 C and capacity retention of 91.2%after 100 cycles,considerably surpassing those of the pristine one(124.05 mAh g^(−1) and 89.05%).All results indicate the feasibility of such Ni–Mn co‐doping‐enabled upcycling on regenerating LCO cathodes.

Upcycling of phosphogypsum waste for efficient zinc-ion batteries

Zinc metal is a promising anode material for next-generation aqueous batteries,but its practical application is limited by the formation of zinc dendrite.To prevent zinc dendrite growth,various Zn^(2+)-conducting but water-isolating solid-electrolyte interphase(SEI)films have been developed,however,the required high-purity chemical materials are extremely expensive.In this work,phosphogypsum(PG),an industrial byproduct produced from the phosphoric acid industry,is employed as a multifunctional protective layer to navigate uniform zinc deposition.Theoretical and experimental results demonstrate that PG-derived CaSO_(4)2H_(2)O can act as an artificial SEI layer to provide fast channels for Zn^(2+)transport.Moreover,CaSO_(4)2H_(2)O could release calcium ions(Ca^(2+))due to its relatively high Kspvalue,which have a higher binding energy than that of Zn^(2+)on the Zn surface,thus preferentially adsorbing to the tips of the protuberances to force zinc ions to nucleate at inert region.As a result,the Zn@PG anode achieves a high Coulombic efficiency of 99.5%during 500 cycles and long-time stability over 1000 hours at 1 m A cm^(-2).Our findings will not only construct a low-cost artificial SEI film for practical metal batteries,but also achieve a high-value utilization of phosphogypsum waste.

From trash to treasure: Chemical recycling and upcycling of commodity plastic waste to fuels, high-valued chemicals and advanced materials

Of all the existing materials, plastics are no doubt among the most versatile ones. However, the extreme increases in plastic production as well as the difficulty of the material for degradation have led to a huge number of plastic wastes. Their recycling rate after disposal is less than 10%, resulting in a series of serious environmental and ecological problems as well as a significant waste of resources. Current recycling methods generally suffer from large energy consumption, the low utilization rate of recycled products with low added value, and produce other waste during the process. Here, we summarized recentlydeveloped chemical recycling ways on commodity plastics, especially new catalytic paths in production of fuels, high-valued chemicals and advanced materials from a single virgin or a mixture of plastic waste,which have emerged as promising ways to valorize waste plastics more economically and environmentally friendly. The new catalyst design criteria as well as innovative catalytic paths and technologies for plastic upcycling are highlighted. Beyond energy recovery by incineration, these approaches demonstrate how waste plastics can be a viable feedstock for energy use with the generation of clean H_(2), high-quality liquid fuels and materials for energy storage, and help inspiring more catalytic process on plastic upcycling to overcome the economical hurdle and building a circular plastic economy.

时尚与公益Upcycling的新玩法

通过重新思考已有事物,发现生活中的美,探索和推广Upcycling,非物质文化遗产等跨越时间和文化,连接传统与未来的生活与审美方式。用重视效率的商业运作,建立起在整个供应链和消费链基础上的社会效益链,将设计师、社会企业、商业组织等结合起来,让每一方都进步与得益。

Beyond Conventional Degradation:Catalytic Solutions for Polyolefin Upcycling

Polyolefins(POs,i.e.,polyethylenes,ethylene/α-olefin copolymers,and polypropylenes)are the most ubiquitous synthetic macromolecular materials in modern life.Their widespread use and low recovery rate after extensive usage have caused significant resource waste and environmental concerns.Chemical recycling of POs provides an efficient approach to unravelling the polymer chain to various chemicals.However,conventional chemical recycling methods,including pyrolysis,hydrocracking,and oxidation,require high-energy input(typically>500℃)and/or the use of environmentally unfriendly chemicals,leading to complex product distribution.In this minireview,based on recent representative works,we summarize and highlight catalytic strategies addressing these issues in PO recycling from two perspectives:(1)employing advanced catalysts or technique designs to overcome the challenges in conventional chemical deconstruction approaches;and(2)developing novel tandem/cascade catalytic systems for highly selective PO upcycling under relatively mild conditions.We hope that this minireview will help researchers better understand the state of the art of PO chemical recycling and inspire more innovative and efficient ideas for this fast-developing field.

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 CO_(2)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.

Upcycling of Poly(butylene adipate-co-terephthalate)into Dual Covalent Adaptable Networks through Chain Breaking-Crosslinking Strategy

Poly(butylene adipate-co-terephthalate)(PBAT),a widely studied biodegradable material,has not effectively addressed the problem of plastic waste.Taking into consideration the cost-effectiveness,upcycling PBAT should take precedence over direct composting degradation.The present work adopts a chain breaking-crosslinking strategy,upcycling PBAT into dual covalent adaptable networks(CANs).During the chainbreaking stage,the ammonolysis between PBAT and polyethyleneimine(PEI)established the primary crosslinked network.Subsequently,styrene maleic anhydride copolymer(SMA)reacted with the hydroxyl group,culminating in the formation of dual covalent adaptable networks.In contrast to PBAT,the PBAT-dual-CANs exhibited a notable Young's modulus of 239 MPa,alongside an inherent resistance to creep and solvents.Owing to catalysis from neighboring carboxyl group and excess hydroxyl groups,the PBAT-dual-CANs exhibited fast stress relaxation.Additionally,they could be recycled through extrusion and hot-press reprocessing,while retaining their biodegradability.This straightforward strategy offers a solution for dealing with plastic waste.

Upcycling PET in parallel with energy-saving H_(2)production via bifunctional nickel-cobalt nitride nanosheets

We describe here an electro-reforming strategy to upcycle polyethylene terephthalate(PET)waste with simultaneous hydrogen production by a bifunctional nickel-cobalt nitride nanosheets electrocatalyst.PET plastics are digested in alkaline solution giving an electrochemically active monomer ethylene glycol(EG).The introduction of Co in Co-Ni3N/carbon cloth(CC)promotes the redox behavior of Ni2+/Ni3+,which is beneficial for EG oxidation at an ultra-low potential(1.15 V vs.reversible hydrogen electrode(RHE))and breaks through the limitation of high catalytic potentials of simple Ni-based electrocatalysts(1.30 V).In PET hydrolysate with Co-Ni3N/CC couples,an integrated EG oxidation-hydrogen production system achieves a current density of 50 mA·cm^(−2)at a cell voltage of 1.46 V,which is 370 mV lower than the conventional water splitting.The in-situ Raman and Fourier transform infrared(FTIR)spectroscopies and density functional theory(DFT)calculations identify the catalytic mechanism and point to advantages of heterostructure engineering in optimizing adsorption energies and promoting catalytic activities for EG oxidation.

Chemical upcycling of poly(lactide) plastic waste to lactate ester,lactide and new poly(lactide) under Mg-catalysis condition

Chemical upcycling of end-of-life poly(lactide) plastics to lactide,lactate ester and new poly(lactide)has been achieved by using magnesium bis[bis(trimethylsilyl)amide][Mg(HMDS)_(2)]as promoter.Mg(HMDS)2 showed high efficiency in L-lactide polymerization and poly(lactide) depolymerization.Mg(HMDS)_(2)/Ph_(2) CHOH catalytic system displayed high ring-opening selectivity and the characteristic of immortal polymerization.Taking advantage of transesterification,depolymerizations of end-oflife poly(lactide) plastics to lactate ester (polymer to value-added chemicals) and lactide (polymer to monomer) were achieved with high yields.Besides,a new“depolymerization-repolymerization”strategy was proposed to directly transform poly(lactide) into new poly(lactide).This work provides a theoretical basis for the design of polymerization and depolymerization catalysts and promotes the development of degradable polymers.

TiO_(2) nanoparticle supported Ru catalyst for chemical upcycling of polyethylene terephthalate to alkanes

Production of fuel and chemicals from plastic waste is one of the effective ways to upcycle spent plastics,which is an interesting topic and of significance for green and sustainable development.Herein,we demonstrate a highly efficient catalyst,TiO_(2)nanoparticle supported Ru nanocatalyst(Ru/TiO_(2)),for upcycling polyethylene terephthalate(PET)to alkanes in the presence of H_(2) and water.Under the optimal conditions(200℃,60 bar H_(2),and small amount of H_(2)O),PET could completely convert into alkanes,dominated with cyclohexane and methane.It was indicated that the strong interaction between the TiO_(2)support and Ru nanoparticles made electrons flow from the TiO_(2)support to the Ru nanoparticles,which thus rendered Ru/TiO_(2)to have ability to simultaneously catalyze PET hydrolysis and intermediate hydrogenation.This work realizes the transformation of PET to alkanes,which provides a promising way to chemically upcycle PET.

Upcycling Polytetrahydrofuran to Polyester

One major remaining challenge in polymer chemistry is the development of efficient chemical recycling strategies to fully retrieve starting materials.Polytetrahydrofuran(PTHF)is widely used,but its stable ether bonds make it difficult to chemically reuse after disposal.Here,we propose a“polymer A→polymer B”strategy for one-step quantitative upcycling of PTHF to polyesters.The route undergoes a cascade process:PTHF is depolymerized to give tetrahydrofuran(THF)that then alternately copolymerizes with cyclic anhydrides in situ,thereby pushing the chemical equilibrium of“PTHF⇌THF”to the right.The protocol demonstrates facile features:the use of common and metal-free Brønsted/Lewis acid as catalyst,a favorable reaction temperature of 100℃,and no use of solvents.This method also accommodates 18 cyclic anhydrides to give a library of polyesters with alternating sequences,tunable thermal properties,and high-fidelity carboxyl terminals.This is an unprecedented strategy for chemical recycling of waste polyether.

Synergism of solar-driven interfacial evaporation and photo-Fenton Cr(Ⅵ) reduction by sustainable Bi-MOF-based evaporator from waste polyester

The integration of interfacial solar steam generation and photocatalytic degradation technology has pro-vided a promising platform to simultaneously produce freshwater and degrade pollutants.However,con-structing low-cost,multi-functional evaporators for treating Cr(Ⅵ)-polluted water remains challenging,and the synergistic mechanism on Cr(Ⅵ)reduction is fuzzy.Herein,we propose the combined strategy of ball milling and solution mixing for the sustainable production of Bi-MOF microrod from waste poly(ethylene terephthalate),and construct Bi-MOF-based solar evaporators for simultaneous photo-Fenton Cr(Ⅵ)reduction and freshwater production.Firstly,the evaporator comprised of Bi-MOF microrod and graphene nanosheet possesses high light absorption,efficient photothermal conversion,and good hydro-philic property.Attributing to the advantages,the hybrid evaporator exhibits the evaporation rate of 2.16 kg m^(-2) h^(-1) and evaporation efficiency of 87.5%under 1 kW m^(-2) of irradiation.When integrating with photo-Fenton reaction,the Cr(Ⅵ)reduction efficiency is 91.3%,along with the reaction kinetics of 0.0548 min^(-1),surpassing many advanced catalysts.In the outdoor freshwater production and Cr(Ⅵ)reduction,the daily accumulative water yield is 5.17 kg m^(-2) h^(-1),and the Cr(Ⅵ)reduction efficiency is 99.9%.Furthermore,we prove that the localization effect derived from the interfacial solar-driven evap-oration enhances H_(2)O_(2) activation for the photo-Fenton reduction of Cr(Ⅵ).Based on the result of density functional theory,Bi-MOF microrod provides rich active centers for H_(2)O_(2) activation to produce active sites such as e-or-O_(2).This study not only proposes a new strategy to construct multi-functional solar evaporators for freshwater production and catalytic reduction of pollutants,but also advances the chem-ical upcycling of waste polyesters.

Sustainable chemical upcycling of waste polyolefins by heterogeneous catalysis

The mass production of disposable polyolefin products has led to serious plastic pollution and an imbalance between manufacturing and recycling.Given these challenges,the chemical upcycling of waste polyolefins has attracted extensive attention due to its high efficiency and economic benefits.Herein,we review the development of polyolefin chemical upcycling in heterogeneous catalysis.The status quo of polyolefin recycling is first discussed.We then introduce the advanced strategies for chemical upcycling in the view of different value-added products and discuss their challenges and prospects.Our in-depth analysis centers on the catalytic mechanism and the design principle of heterogeneous catalysts.Finally,we outlook the promising directions to facilitate the degradation process via polymer and catalyst design and optimized catalytic engineering.Innovative strategies are expected to promote the chemical upcycling of polyolefins,bringing great promise for the sustainable development of society.

Upcycling 循环再生 香港新工业战记

近年出现了以下现象:一些设计企业重用废弃物料作生产,而制成品的款式、质量很有发展势头,更成功进驻潮流店铺跟"正常产品"看齐,部分甚至能以比正常货品更高的价钱出售,而且依然有价有市,令环保产品不再局限于作为慈善义卖的货色。这也似乎鼓励着各企业,原来成功研发环保产品一样可以获得经济效益……

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 upshifting d band centre and facilitated in situ structural reconstruction,the Co and Cl co-doped Ni_(3)S_(2)(Co,Cl-NiS)outperforms the singledoped 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.