Micelles Cascade Assembly to Tandem Porous Catalyst for Waste Plastics Upcycling.

Catalytic upcycling of polyolefins into high-value chemicals represents the direction in end-of-life plastics valorization, but poses great challenges. Here, we report the synthesis of a tandem porous catalyst via a micelle cascade assembly strategy for selectively catalytic cracking of polyethylene into olefins at a low temperature. A hierarchically porous silica layer from mesopore to macropore is constructed on the surface of microporous ZSM-5 nanosheets through cascade assembly of dynamic micelles. The outer macropore arrays can adsorb bulky polyolefins quickly by the capillary and hydrophobic effects, enhancing the diffusion and access to active sites. The middle mesopores present a nanoconfinement space, pre-cracking polyolefins into intermediates by weak acid sites, which then transport into zeolites micropores for further cracking by strong Brønsted acid sites. The hierarchically porous and acidic structures, mimicking biomimetic protease catalytic clefts, ideally match the tandem cracking steps of polyolefins, thus suppressing coke formation and facilitating product escape. As a result, light hydrocarbons (C1-C7) are produced with a yield of 443 mmol gZSM-5 -1, where 74.3 % of them are C3-C6 olefins, much superior to ZSM-5 and porous silica catalysts. This tandem porous catalyst exemplifies a superstructure design of catalytic cracking catalysts for industrial and economical upcycling of plastic wastes.

Selective Photoreforming of Waste Plastics into Diesel Olefins via Single Reactive Oxygen Species.

The accumulation of plastic waste poses a pressing environmental challenge. Catalytic conversion stands out as an ideal approach for plastics upcycling, particularly through solar-driven plastics photoreforming. However, due to the common effects of multiple reactive oxygen species (ROS), selectively generating high-value chemicals becomes challenging. In this study, we developed a universal strategy to achieve >85 % selective production of diesel olefins (C15-C28) from polyolefin waste plastics via single ROS. Using tetrakis (4-carboxyphenyl) porphyrin supramolecular (TCPP) with different central metals as an example to regulate single ROS generation, results show Ni-TCPP facilitates triplet exciton production, yielding 1O2, while Zn-TCPP generates ⋅O2 - due to its strong built-in electric field (IEF). 1O2 directly dechlorinates polyvinyl chloride (PVC) due to the electro-negativity of chlorine atoms and the low dissociation energy of C-Cl bonds, while ⋅O2 - promotes direct dehydrogenation of polyethylene (PE) due to the electro-positivity of hydrogen atoms and the high dissociation energy of C-H bonds. This method is universally applicable to various single ROS systems. Installation experiments further affirm the application potential, achieving the highest diesel olefin production of 76.1 µmol h-1. Such a universally adaptive approach holds promise for addressing the global plastic pollution problem.

Polymer Multi-Block and Multi-Block+ Strategies for the Upcycling of Mixed Polyolefins and Other Plastics.

Due to a continued rise in the production and use of plastic products, their end-of-life pollution has become a pressing global issue. One of the biggest challenges in plastics recycling is the separation of different polymers. Multi-block copolymers (MBCPs) represent an efficient strategy for the upcycling of mixed plastics via induced compatibilization, but this approach is limited by difficulties associated with synthesis and structural modification. In this contribution, several synthetic strategies are explored to prepare MBCPs with tunable microstructures, which were then used as compatibilizer additives to upcycle mixtures of polyolefins with other plastics. A multi-block+ strategy based on a reactive telechelic block copolymer platform was introduced, which enabled block extension during the in situ melt blending of mixed plastics, leading to better compatibilizing properties as well as better 3D printing capability. This strategy was also applicable to more complex ternary plastic blends. The polymer multi-block strategy enabled by versatile MBCPs synthesis and the multi-block+ strategy enabled by in situ block extension show exciting opportunities for the upcycling of mixed plastics.

Tandem chemical deconstruction and biological upcycling of poly(ethylene terephthalate) to ß-ketoadipic acid by Pseudomonas putida KT2440.

Poly(ethylene terephthalate) (PET) is the most abundantly consumed synthetic polyester and accordingly a major source of plastic waste. The development of chemocatalytic approaches for PET depolymerization to monomers offers new options for open-loop upcycling of PET, which can leverage biological transformations to higher-value products. To that end, here we perform four sequential metabolic engineering efforts in Pseudomonas putida KT2440 to enable the conversion of PET glycolysis products via: (i) ethylene glycol utilization by constitutive expression of native genes, (ii) terephthalate (TPA) catabolism by expression of tphA2IIA3IIBIIA1II from Comamonas and tpaK from Rhodococcus jostii, (iii) bis(2-hydroxyethyl) terephthalate (BHET) hydrolysis to TPA by expression of PETase and MHETase from Ideonella sakaiensis, and (iv) BHET conversion to a performance-advantaged bioproduct, ß-ketoadipic acid (ßKA) by deletion of pcaIJ. Using this strain, we demonstrate production of 15.1 g/L ßKA from BHET at 76% molar yield in bioreactors and conversion of catalytically depolymerized PET to ßKA. Overall, this work highlights the potential of tandem catalytic deconstruction and biological conversion as a means to upcycle waste PET.

Gene amplification, laboratory evolution, and biosensor screening reveal MucK as a terephthalic acid transporter in Acinetobacter baylyi ADP1.

Microbial terephthalic acid (TPA) catabolic pathways are conserved among the few bacteria known to turnover this xenobiotic aromatic compound. However, to date there are few reported cases in which this pathway has been successfully expressed in heterologous hosts to impart efficient utilization of TPA as a sole carbon source. In this work, we aimed to engineer TPA conversion in Acinetobacter baylyi ADP1 via the heterologous expression of catabolic and transporter genes from a native TPA-utilizing bacterium. Specifically, we obtained ADP1-derived strains capable of growing on TPA as the sole carbon source using chromosomal insertion and targeted amplification of the tph catabolic operon from Comamonas sp. E6. Adaptive laboratory evolution was then used to improve growth on this substrate. TPA consumption rates of the evolved strains, which retained multiple copies of the tph genes, were ~0.2 g/L/h (or ~1 g TPA/g cells/h), similar to that of Comamonas sp. E6 and almost 2-fold higher than that of Rhodococcus jostii RHA1, another native TPA-utilizing strain. To evaluate TPA transport in the evolved ADP1 strains, we engineered a TPA biosensor consisting of the transcription factor TphR and a fluorescent reporter. In combination with whole-genome sequencing, the TPA biosensor revealed that transport of TPA was not mediated by the heterologous proteins from Comamonas sp. E6. Instead, the endogenous ADP1 muconate transporter MucK, a member of the major facilitator superfamily, was responsible for TPA transport in several evolved strains in which MucK variants were found to enhance TPA uptake. Furthermore, the IclR-type transcriptional regulator DcaS was identified as a repressor of mucK expression. Overall, this work presents an unexpected function of a native protein identified through gene amplification, adaptive laboratory evolution, and a combination of screening methods. This study also provides a TPA biosensor for application in ADP1 and identifies transporter variants for use in metabolic engineering applications focused on plastic upcycling of polyesters.

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

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

An Integrated Plasma-Photocatalytic System for Upcycling of Polyolefin Plastics.

Nondegradable polyolefin plastics, which account for >60 % of total plastic waste, trigger severe global concerns and thus demand effective management technologies. However, owing to the chemical inertness of non-polar C-C backbones in the polyolefin structure, efficient upcycling of polyolefin plastics under ambient conditions remains a great challenge. This study introduces an integrated plasma-photocatalytic technology, coupling plasma treatment with solar-driven reforming under mild conditions, for the efficient upcycling of polyolefin plastics into value-added hydrogen and gaseous fuels. The first plasma step grafts oxygenated groups, such as -OH, O-C=O, and C=O, onto the polyolefin chains, which leads to the formation of a polar and hydrophilic polymer that facilitates the subsequent reforming in the photocatalytic step. Therefore, high hydrogen production activity with a benchmark efficiency of >100 µmol g-1 h-1 was achieved. Moreover, the integrated process also demonstrates high versatility in upcycling different polyolefin plastics including polyethylene, polypropylene and polyvinyl chloride. The findings provide a new avenue for plastic upcycling in an efficient and sustainable way.

Hydrogenolysis-Isomerization of Waste Polyolefin Plastics to Multibranched Liquid Alkanes.

Upcycling of waste polyolefin plastics still meets with economic and technological challenges in practice. In this work, the catalytic hydrogenolysis-isomerization of nondegradable polyolefin plastic waste to high-value gasoline, diesel, and light lubricants with highly branched chain is achieved over a bifunctional Rh/Nb2 O5 catalyst under relatively mild conditions. Owing to the high efficiency of metallic Rh active sites, the dehydrogenation/hydrogenation of long carbon chains of polyolefins is enhanced. With the assistance of strong Brønsted acidity of Nb2 O5 , the cleavage of C-C bonds, skeletal rearrangements, as well as the ß-scission of alkylcarbenium ions occurs, which boosts the one-step solvent-free catalytic hydrogenolysis and isomerization of polyolefins. In addition, the preliminary economic analysis shows that this technology is economical, feasible, and has great potential in accelerating the transition to a circular plastics economy for sustainable development.

Templating of catalytic gold and silver nanoparticles by waste plastic PET-derived hydrogel playing a dual role of a reductant and a matrix.

The progressive accumulation of discarded plastic in the environment demands further development of waste management of plastic waste and conversion technologies of such waste to value-added materials. Recently, the conversion of plastic waste to functional materials via chemical recycling has attracted considerable attention. In this report, plastic waste (PET) was utilized for the preparation of a hydrogel-based catalyst via a cross-linking reaction of PET-derived oligo(terephthalamide)s followed by the electroless metallization. The polymeric matrix of PET-derived hydrogel plays multiple roles of (i) an adsorption media for noble metal ions such as Au3+ and Ag+, (ii) a reducing agent of Au3+ and Ag+ ions to Au0 and Ag0, and (iii) a matrix for the controlled growth of Au and Ag nanoparticles (AuNPs and AgNPs). The obtained hybrid hydrogels after metallization contained well-dispersed AuNPs and AgNPs of 6.1 ± 3.7 nm or 6.1 ± 1.4 nm size, respectively. The catalytic activities of the hybrid hydrogels with metal nanoparticles were studied in a model system of p-nitrophenol reduction in an aqueous solution. The hybrid materials of both Au@hydrogel and Ag@hydrogel were catalytically active for the reduction of p-nitrophenol, obeying the first-order kinetics. Importantly, the AuNPs or AgNPs in the hydrogel matrix preserved the original catalytic activity after multiple p-nitrophenol reduction reactions, showing a promising reusability of the catalysts. The proposed here approach aims to broaden the scope of conversion routes of plastic waste to value-added materials as well as to develop new types of polymeric matrices for templating and growth of metal nanoparticles for catalytic applications.

Upcycling to Sustainably Reuse Plastics.

Plastics are now indispensable in daily lives. However, the pollution from plastics is also increasingly becoming a serious environmental issue. Recent years have seen more sustainable approaches and technologies, commonly known as upcycling, to transform plastics into value-added materials and chemical feedstocks. In this review, the latest research on upcycling is presented, with a greater focus on the use of renewable energy as well as the more selective methods to repurpose synthetic polymers. First, thermal upcycling approaches are briefly introduced, including the redeployment of plastics for construction uses, 3D printing precursors, and lightweight materials. Then, some of the latest novel strategies to deconstruct condensation polymers to monomers for repolymerization or introduce vulnerable linkers to make the plastics more degradable are discussed. Subsequently, the review will explore the breakthroughs in plastics upcycling by heterogeneous and homogeneous photocatalysis, as well as electrocatalysis, which transform plastics into more versatile fine chemicals and materials while simultaneously mitigating global climate change. In addition, some of the biotechnological advances in the discovery and engineering of microbes that can decompose plastics are also presented. Finally, the current challenges and outlook for future plastics upcycling are discussed to stimulate global cooperation in this field.

Temperature-dependent synthesis of multi-walled carbon nanotubes and hydrogen from plastic waste over A-site-deficient perovskite La0.8Ni1-xCoxO3-δ.

Thermochemical conversion of plastic wastes into carbon nanotubes (CNTs) and hydrogen is a promising management option to eliminate their hazardous effect. The yields and morphologies of CNTs strongly depend on the catalyst design and reaction conditions. To boost the efficiency, tuning of bimetallic nanoparticles as catalyst is an effective approach. For that reason, A-site-deficient perovskite La0·8Ni1-xCoxO3-δ (LN1-xCx, x = 0.15, 0.5, 0.85) was developed and used as a catalyst precursor to achieve in situ formation of bimetallic Ni-Co nanoparticles. At an optimized Ni-to-Co ratio, the LN0.5C0.5 exhibited the highest yields of multi-walled CNTs, namely 840 and 853 mg/gcatalyst from high density polyethylene and polypropylene, respectively. This could be attributed to the higher catalytic capability of LN0.5C0.5 catalyst for the decomposition of hydrocarbons into hydrogen and carbon. In both cases, multi-walled CNTs had regular shapes when the reaction temperature was 700 °C. At higher reaction temperatures, the morphological changes of carbon products were observed from multi-walled CNTs to carbon nano-onions. The Raman spectra showed that compared with the commercial multi-walled CNTs, the as-prepared multi-walled CNTs had a lower degree of defects.

Current Developments in the Chemical Upcycling of Waste Plastics Using Alternative Energy Sources.

The management of plastics waste is one of the most urgent and significant global problems now. Historically, waste plastics have been predominantly discarded, mechanically recycled, or incinerated for energy production. However, these approaches typically relied on thermal processes like conventional pyrolysis, which are energy-intensive and unsustainable. In this Minireview, some of the latest advances and future trends in the chemical upcycling of waste plastics by photocatalytic, electrolytic, and microwave-assisted pyrolysis processes are discussed as more environmentally friendly alternatives to conventional thermal reactions. We highlight how the transformation of different types of plastics waste by exploiting alternative energy sources can generate value-added products such as fuels (H2 and other carbon-containing small molecules), chemical feedstocks, and newly functionalized polymers, which can contribute to a more sustainable and circular economy.