Degradation and partial oxidation of waste plastic express packaging bags in supercritical water: Resources transformation and pollutants removal

Upcycling of waste disposable medical masks to high value-added gasoline fuel and surfactants products by sub/supercritical water degradation and partial oxidation

The amount of waste disposable medical masks (DMMs) and the potential environmental risk increased significantly due to the huge demand of disposable medical surgical masks. In this study, two effective and environmentally friendly processes, supercritical water degradation (SCWD) and subcritical water partial oxidation (SubCWPO), were proposed for the upcycling of DMMs. The optimal conditions for the SCWD process (conversion ratio>98 %) were 410 ℃, 15 min, and 1:5 g/mL. The oil products obtained from the SCWD process were mainly small molecule hydrocarbons (C7-C12) with a content of 86 % and could be recycled as fuel feedstock for gasoline. Alkyl radicals in the SCWD reaction formed double bonds and ring structures through hydrogen capture reactions, β-scission, and dehydrogenation reactions, and aromatic hydrocarbons were formed by olefin cyclization and cycloalkane dehydrogenation. The introduction of an oxidant (H2O2) to the reaction system could significantly reduce the reaction temperature and shorten the reaction time. At 350 ℃, 15 min, 1:20 g/mL, V(H2O2): V (H2O) of 1:1, the conversion ratio of the SubCWPO process was 88 %, which was higher than that of the SCWD process at 400 ℃ (71.49 %). Oil products produced from the SubCWPO process were rich in alcohols and esters, which could be used as raw materials for nonionic surfactant of polyol and fatty acid ester. The abundant hydroxyl radical in the SubCWPO system trapped hydrogen atoms on PP and reacted with the resulting alkyl radical to form alkanols, which was oxidized to form acids. The esterification of acids and alkanols formed high level of esters. The SCWD and SubCWPO processes proposed in this study are believed to be promising strategies for DMMs degradation and the recovery of high value-added hydrocarbons.

Association of Plastic Exposure with Cognitive Function Among Chinese Older Adults

Background

The widespread exposure to plastic products and the increasing number of individuals with cognitive impairments have imposed a heavy burden on society.

Objective

This study aims to investigate the relationship between plastic product exposure in daily life and cognitive function in older Chinese individuals.

Methods

Data were obtained from the 2023 Ningxia Older Psychological Health Cohort, comprising 4045 participants aged 60 and above. Cognitive function was assessed using the Mini-Mental State Examination scale. A population-based plastic exposure questionnaire was used to calculate plastic exposure scores (PES). Binary logistic regression was employed to analyze the relationship between PES and cognitive function, while restricted cubic splines were used to examine the dose-response relationship between PES and cognitive function. Latent profile analysis (LPA) was employed to explore the potential patterns of plastic exposure, and logistic regression was used to investigate the relationship between different exposure patterns and cognitive function. A linear regression model was utilized to investigate the relationship between PES and different dimensions of cognitive function.

Results

Among the 4045 participants, 1915 individuals were assessed with mild cognitive impairment (MCI). After adjusting for all covariates, PES (OR = 1.04, 95% CI 1.02-1.06) was significantly associated with the risk of MCI and exhibited a dose-response relationship. LPA identified two potential categories of plastic exposure, with a higher risk of MCI observed in the group using plastic utensils.

Conclusions

This study indicates a positive correlation between plastic exposure levels and MCI risk, particularly among individuals who frequently use plastic tableware.

Assessment of an eco-efficient process for the optimization of metal recovery in lithium cobalt oxide and lithium nickel manganese cobalt oxide batteries

The expansion of technology motivates the increase of global demands for critical minerals. In this context, the exploration of secondary sources of these components is expanding. End-of-life batteries can be seen as potential sources of lithium, cobalt, nickel and manganese for electric vehicles or diverse applications in electronic equipments. This paper provides a comprehensive evaluation of the recovery of metals from waste batteries with diverse chemistry composition. Lithium cobalt oxide (LCO) and lithium nickel cobalt manganese oxide (NMC) batteries were co-treated with polyvinyl chloride (PVC) channels under supercritical water, varying reaction temperature (400-600 °C) and PVC/Battery composition (0-3 m/m) in a tubular continuous reactor. Results show high recovery rates for all metals, with up to 90% percentage recovery of lithium and cobalt in all cases. Temperature and feed composition were identified as determining factors for the recovery of lithium from LCO batteries. In the case of cobalt, temperature was identified as the most important factor that affects its recovery. The selected optimal conditions for cobalt recovery in the solid products of reactions were identified for batteries LCO and NMC: temperature of 600 °C and PVC/Battery ratio of 3.0 and temperature of 500 °C and PVC/Battery ratio of 1.5, respectively. Environmental impacts, primarily Global Warming Potential (GWP), were minimal, with 4.71·10-5 kg CO2 eq., indicating the benefits of the process as an eco-efficient and promising route for the recycling of valuable metals.

Material flow analysis and statistical entropy evaluation of plastic packaging for express delivery in China

Encouraging the recycling of plastic packaging materials in express delivery is a necessary step toward environmentally friendly industrial development. In this study, we present a framework for analyzing the flow of materials in express plastic packaging, from production and manufacturing to consumption and recycling. In examining the use of recycled materials in post-consumer express plastic packaging and the destination of consumer packaging waste in 2020 and 2021, we found that 44.4% (1613.6 Gg) of the studied express plastic packaging was incinerated. Additionally, approximately 1296.6 Gg of express plastic packaging flowed into rural areas. Our calculations showed that the ΔRSE in 2020 was 15.1%, and on the condition that 25% separated collection with 80% recycling, ΔRSE would be - 0.5%. Results verified that separated collection is an important step in the recycling strategy for packaging materials. Survey data from universities in Beijing indicate that currently, 26% of college students are participating in the separate collection of packaging.

A novel subcritical water synergistic co-treatment of brominated epoxy resin and copper-based spent catalysts: debromination, phenol production, and copper recovery

In this study, a high-efficiency co-treatment strategy for brominated epoxy resin (BER) and copper-based spent catalyst (CBSC) was developed by using subcritical water (SubCW) process. Multivalent species of copper released from CBSC could accelerate the electron transfer of the SubCW system and efficiently catalyze radical reactions to promote the debromination and decomposition of BER, and had an effect on the capture and binding of bromine species. Meanwhile, the formation of HBr by the BER debromination resulted in a decrease in the system pH and markedly enhanced the leaching/recovery of Cu from CBSC. The optimal conditions of the SubCW co-treatment process were as follows: reaction temperature of 350 °C, solid-to-liquid ratio of 1:30 g/mL, BER-to-CBSC mass ratio of 10:1 g/g, and reaction time of 60 min. Under the optimal conditions, 97.12 % of the Br could be removed from BER by the SubCW co-treatment process and a high-purity phenol (64.09 %) could be obtained in the oil phase product, and 86.44 % of Cu in the CBSC could be leached and recovered. The introduction of CBSC significantly changed the decomposition path of BER. Compared to the SubCW process without CBSC, bromine-free oils products could be obtained by the co-treatment process of BER and CBSC at low-temperature. This study provided a novel understanding of resource conversion mechanism of BER and CBSC in subcritical water medium via the synergistic effect between the two different waste streams to improve treatment efficiency and synchronously recover high-value products.

Honeycomb-like biochar framework coupled with Fe3O4/FeS nanoparticles as efficient heterogeneous Fenton catalyst for phenol degradation

Achieving an efficient and stable heterogeneous Fenton reaction over a wide pH range is of great significance for wastewater treatment. Here, a pollen-derived biochar catalyst with a unique honeycomb-like structure, coupled with the dispersion of magnetic Fe3O4/FeS (Fe/S) nanoparticles, was synthesized by simple impregnation precursor, followed by pyrolysis. The prepared Fe/S-biochar catalyst demonstrated outstanding phenol degradation efficiency across a wide pH range, with 98% of which eliminated even under neutral conditions (pH 7.0). The high catalytic activity was due to the multilevel porous structure of pollen-derived biochar provided enough active sites and allowed for better electron transfer, then increases oxidation ability to promote the reaction. Moreover, the acid microenvironment formed by SO42- group from Fe/S composite extended the pH range for Fenton reaction, and S2- facilitated the conversion of Fe3+ to Fe2+, resulting in remarkable degradation efficiency. Further, biochar can effectively promote cycling stability by limiting Fe leaching. This work may provide a general strategy for designing 3D framework biochar-based Fe/S catalysts with excellent performance for heterogeneous Fenton reactions.

Experimental analysis on products distribution, characterization and mechanism of waste polypropylene (PP) and polyethylene terephthalate (PET) degradation in sub-/supercritical water

Supercritical water (SCW) treatment of plastics is a clean technology in the 'waste-to-energy' path. In this work, PP and PET plastics were processed by sub-/supercritical water. The results showed that temperature was the most important factor of the PP and PET degradation. The influence of factors on the degradation of plastics follows the following order: temperature > residence time > plastic/water ratio. These factors influenced the yield of gas products by promoting or inhibiting various reactions (such as reverse water gas shift reaction, methylation reaction, and Fischer-Tropsch synthesis reaction). Besides, the composition of liquid oil was also analyzed. The main composition of the liquid oil produced by PET was benzoic acid and acetaldehyde, which were generated from the decarboxylation of terephthalic acid (TPA) and dehydration reaction of ethylene glycol (EG). The liquid oil from PP was mainly long-chain olefins, long-chain alkanes, cycloalkanes, etc., which were formed by the interaction of various methyl, alkyl, hydroxyl, and other free radicals. This study could build fundamental theories of plastic mixture treatment.

The interactions between mixed waste from discarded surgical masks and face shields during the degradation in supercritical water

The widespread use of surgical masks made of polyolefin and face shields made of polyester during pandemics contributes significantly to plastic pollution. An eco-friendly approach to process plastic waste is using supercritical water, but the reaction of mixed polyolefin and polyester in this solvent is not well understood, which hinders practical applications. This study aimed to investigate the reaction of waste surgical masks (SM) and face shields (FS) mixed in supercritical water. Results showed that the optimal treatment conditions were 400 °C and 60 min, achieving a liquid oil yield of 823.03 mg·g-1 with 25 wt% FS. The interaction between polypropylene (PP), polyethylene terephthalate (PET), and iron (Fe) in SM and FS mainly determined the production of liquid oil products such as olefins and benzoic acid. The methyl-branched structure of PP enhanced PET hydrolysis, resulting in higher production of terephthalic acid (TPA). The degradation of PP was facilitated by the acidic environment created by TPA and benzoic acid in the reaction. Moreover, the hydrolysis of PET produced carboxylic acid, which coordinated with Fe3+ to form Fe-H that catalyzed the polymerization of small olefins, contributing to higher selectivity for C9 olefins. Therefore, this study provides valuable insights into the degradation mechanism of mixed PPE waste in supercritical water and guidance for industrial treatment.

Evaluation on hydrothermal gasification of styrene-butadiene rubber with oxidants via ReaxFF-MD simulation

Styrene-butadiene rubber (SBR) is widely used in tires, which brings great challenge to the disposal and reclaiming of the used tires. The ring-opening reaction pathways of benzene rings in hydrothermal gasification of styrene-butadiene rubber were revealed based on reactive force field molecular dynamics (ReaxFF-MD) simulation. H-abstraction reaction that OH radicals capture H atom from the vinyl group of styrene was critical to the degrading of the styrene monomers. The energy barrier of H2O2 converted to OH radicals was lower than that of O2 and pure water converted to OH radicals. The oxidants that can urge OH radical formed in reaction were beneficial to SBR degradation, which could be assigned to confirm that SBR degradation with H2O2 was better than that with oxygen at the same concentration. The addition of oxidant could be helpful for decreasing the degradation temperature of styrene monomers. At oxidant equivalent ratio (ER) of 0.1, H2 yield at 2500 K lifted after 135 ps and increased by 75% at 500 ps compared with that without oxidants. According to the chemical equilibrium analysis, the optimal ER for H2 was 0.4 between 350 and 600 °C (real temperatures). The results could provide theoretic support and experiment guidance for adding oxidants in reclaiming waste rubber products.

Facile Synthesis of Hybrid Nanoflowers Using Glycine and Phenylalanine and Investigation of Their Catalytic Activity

In the context of the proposed work, two different amino acids (Glycine, Phenylalanine) have interacted with copper ions in a phosphate buffer (PBS) in place of enzymes. This interaction resulted in the nucleation of copper phosphate crystals and the formation of flower-shaped amino acid-copper hybrid nanostructures (AA-hNFs), which grew through self-assembly. While Cu (II) ions in the structure of AA-hNFs were used as Fenton's agent for the catalytic activity. SEM, energy dispersive X-ray spectroscopy, X-ray diffraction, and Fourier transform infrared spectroscopy measurements were used to define the AA-hNFs' characterisation. The peroxidase-like activities of AA-hNFs were investigated by UV/VIS spectrophotometer. Metal nanoparticles have peroxidase-like activity. A class of enzymes known as peroxidases is able to catalyze the conversion of hydrogen peroxide into hydroxyl radicals. These radicals also take part in electron transfers with substrates, which results in color during oxidation. When cupric oxide nanoparticles are added to the peroxidase substrate while H2 O2 is present, a blue color product with a maximum absorbance at=652 nm can result, demonstrating the catalytic activity of a peroxidase. The morphology and composition of AA-hNFs were carefully characterized and the synthesized parameters were optimized systematically. Results showed that the nanoparticles were dispersed with an average diameter of 7-9 μm and indicated a uniform flower shape. The results of the investigation are anticipated to significantly advance a number of technical and scientific sectors.

Catalytic supercritical water oxidation of o-chloroaniline over Ru/rGO: Reaction variables, conversion pathways and nitrogen distribution

To ascertain the reaction variables on o-chloroaniline (o-ClA) mineralization, total nitrogen (TN) removal rate, and N-species distribution, o-ClA was subjected to catalytic supercritical water oxidation (CSCWO) in a fused quartz tube reactor (FQTR). The findings demonstrated that when the temperature, reaction time, and excess oxidant were 400 °C, 90 min, and 150%, respectively, the mineralization rate of o-ClA could reach more than 95%. Moreover, potential degradation pathways of o-ClA in supercritical water oxidation (SCWO) was proposed according to the GC-MS results. TN removal rate is significantly impacted by Ru/rGO, despite the fact that its catalytic effect on the mineralization of o-ClA was not particularly noteworthy. Compared with no catalyst, the TN removal rate of o-ClA obviously increased from 44.1% to 90.3% at 400 °C, 10 wt% Ru loading, 90 min and 200% excess oxidant. In addition, N-species distribution in SCWO and CSCWO were also investigated. Results indicated that the Ru/rGO catalyst could accelerate the oxidation of ammonia-N and convert it to nitrate-N, promoting N₂ generation. Finally, the possible N transformation pathway in CSCWO of o-ClA was proposed. As a result, this work offers fundamental information about o-ClA catalytic oxidation removal in the SCWO process.

New insight into the synergistic reactions involved in the hydrothermal co-liquefaction of synthetic polymer wastes by molecular dynamics and DFT methods

Coliquefying synthetic aliphatic and aromatic polymer wastes using supercritical water has drawn considerable research attention. However, the mechanisms of chemical reactions between different types of polymers are ambiguous. Herein, depolymerization mechanisms for individual polymers and reaction mechanisms for binary polymer mixtures were investigated using molecular dynamics and density functional theory (DFT). The innovative approach showed that the production of oil from individual polymers during HTL was hindered by (1) volatile C₁-C₄ molecules emitted from aliphatic polymers and (2) polycyclic aromatic hydrocarbons (PAHs) produced from aromatic polymers. Interestingly, synergistic reactions among these byproducts from different polymers could promote oil production during coliquefaction. Specifically, the synergistic radical-related reactions included (1) the ring-opening of PAHs caused by C₂H₂ molecules emitted from aliphatic polymers and (2) the recombination of PHA branches and short-chain aliphatics. A considerable synergy between aromatic polymers with higher benzene ring contents and aliphatic polymers with lower H/C atomic ratios was observed near the critical temperature of 649 K. This work provides new insights into the synergistic reactions involved in the coliquefaction of synthetic polymers and gives useful guidance for realizing efficient oil production from mixed organic wastes.

Resource saving and carbon footprint reduction potential of urban symbiosis strategy in express packaging waste recycling network

The booming express delivery industry corresponds to the environmental challenges caused by massive express packaging waste (EPW). An efficient logistics network is necessary link to support EPW recycling. This study, therefore, designed a circular symbiosis network for EPW recycling based on urban symbiosis strategy. The treatment of EPW in this network includes reuse, recycling and replacing. An optimization model with multi-depot collaboration combining material flow analysis and optimization methods was developed and a hybrid non-dominated sorting genetic algorithm-II (NSGA-II) was designed as technical support for designing the circular symbiosis network while quantitatively assessing the economic and environmental benefits of the network. The results show that the designed circular symbiosis option has better resource saving and carbon footprint reduction potential than both the business as usual option and circular symbiosis option without service collaboration. In practice, the proposed circular symbiosis network can save EPW recycling costs and reduce carbon footprint. This study provides a practical guideline for the application of urban symbiosis strategies to help urban green governance and the sustainable development of express companies.

Base- or acid-assisted polystyrene plastic degradation in supercritical CO2

Plastic has caused serious "white pollution" to the environment, and the highly inert characteristics of plastic bring a major challenge for degradation. Supercritical fluids have unique physical properties and have been widely used in various fields. In this work, supercritical CO2 (Sc-CO2) with mild conditions was selected and assisted by NaOH/HCl solution to degrade polystyrene (PS) plastic, and the reaction model was designed using response surface methodology (RSM). It was found that, regardless of the types of assistance solutions, the factors affecting PS degradation efficiencies were reaction temperature, reaction time, and NaOH/HCl concentration. At the temperature of 400 °C, time of 120 min, and base/acid concentration of 5% (in weight), 0.15 g PS produced 126.88/116.99±5 mL of gases with 74.18/62.78±5 mL of H2, and consumed 81.2/71.5±5 mL of CO2. Sc-CO2 created a homogeneous environment, which made PS highly dispersed and uniformly heated, thus promoting the degradation of PS. Moreover, Sc-CO2 also reacted with the degradation products to produce new CO and more CH4 and C2Hx (x=4, 6). Adding NaOH/HCl solution not only improved the solubility of PS in Sc-CO2, but also provided a base/acid environment that reduced the activation energy of the reaction, and effectively improved the degradation efficiencies of PS. In short, degrading PS in Sc-CO2 is feasible, and better results are obtained with the assistance of base/acid solution, which can provide a reference for the disposal of waste plastics in the future.

Supplementary Information

The online version contains supplementary material available at 10.1007/s42768-023-00139-1.

Challenges in Recycling Spent Lithium-Ion Batteries: Spotlight on Polyvinylidene Fluoride Removal

In the recycling of retired lithium-ion batteries (LIBs), the cathode materials containing valuable metals should be first separated from the current collector aluminum foil to decrease the difficulty and complexity in the subsequent metal extraction. However, strong the binding force of organic binder polyvinylidene fluoride (PVDF) prevents effective separation of cathode materials and Al foil, thus affecting metal recycling. This paper reviews the composition, property, function, and binding mechanism of PVDF, and elaborates on the separation technologies of cathode material and Al foil (e.g., physical separation, solid-phase thermochemistry, solution chemistry, and solvent chemistry) as well as the corresponding reaction behavior and transformation mechanisms of PVDF. Due to the characteristic variation of the reaction systems, the dissolution, swelling, melting, and degradation processes and mechanisms of PVDF exhibit considerable differences, posing new challenges to efficient recycling of spent LIBs worldwide. It is critical to separate cathode materials and Al foil and recycle PVDF to reduce environmental risks from the recovery of retired LIBs resources. Developing fluorine-free alternative materials and solid-state electrolytes is a potential way to mitigate PVDF pollution in the recycling of spent LIBs in the EV era.

Using waste poly(vinyl chloride) to synthesize chloroarenes by plasticizer-mediated electro(de)chlorination

New approaches are needed to both reduce and reuse plastic waste. In this context, poly(vinyl chloride) (PVC) is an appealing target as it is the least recycled high-production-volume polymer due to its facile release of plasticizers and corrosive HCl gas. Herein, these limitations become advantageous in a paired-electrolysis reaction in which HCl is intentionally generated from PVC to chlorinate arenes in an air- and moisture-tolerant process that is mediated by the plasticizer. The reaction proceeds efficiently with other plastic waste present and a commercial plasticized PVC product (laboratory tubing) can be used directly. A simplified life-cycle assessment reveals that using PVC waste as the chlorine source in the paired-electrolysis reaction has a lower global warming potential than HCl. Overall, this method should inspire other strategies for repurposing waste PVC and related polymers using electrosynthetic reactions, including those that take advantage of existing polymer additives.

A novel conversion strategy for organic compounds in waste liquid crystal displays based on the near/supercritical methanol process

Waste liquid crystal displays (LCD) contain a large number of organic compounds such as cellulose triacetate (CTA), poly(vinyl alcohol) (PVA), triphenyl phosphate (TPP), and liquid crystal (LC). It is important to recover organic compounds from waste LCD due to their value and environmental toxicity. However, it is challenging to recover organic compounds from waste LCD because of the heterogeneous mixture of glass, organics and metals contained therein. In this study, an environment-friendly near/supercritical methanol (NSCM) process was developed as a closed cycle technology for the conversion of organic compounds from waste LCD. The acid-base catalytic activity and nonpolar property of the NSCM could efficiently promote the conversion of organic compounds from waste LCD. TPP could be extracted below 200 °C in the NSCM process. Below 250 °C, the conversion ratio of organic compounds from waste LCD ranged from 5 % to 68 % due to the extraction or decomposition of TPP, LC, and PVA. The main products obtained at 250 °C included long-chain alcohols and alkanes with a similar composition to industrial liquid paraffin, which could be widely used in other industrial processes. Under the optimal operation parameters (300 °C, 30 min, and 1:20 g/ml), the conversion ratio of organic compounds could reach 98 % due to the efficient decomposition of CTA. The main products obtained included ketones and esters chemicals, which could be further used as a chemical feedstock. No secondary pollutant was generated in the whole process. The low-boiling methanol could easily be recycled, which could make the NSCM a clean process for the production of high value-added organic products from waste LCD.

Facile path for copper recovery from waste printed circuit boards via mechanochemical approach

Recycling copper (Cu⁰) from waste printed circuit boards (PCBs) is a prevalent challenge. Here, we propose a new pathway and reveal mechanisms for recovering Cu⁰ from waste PCBs via a mechanochemical approach. The successful application of mechanical force avoids using inorganic acid in the Cu⁰ recovery process. Our work demonstrates that ferric chloride (FeCl₃) was superior to ferric sulfate and ferric nitrate as a solid-phase reagent for Cu⁰ recovery due to chloride complexation. Under the induction of mechanical force, the Cu⁰ in the waste PCBs was oxidized by Fe³⁺ and complexed by Cl^¯ to form a meta-stable cuprous chloride, which was susceptible to leaching in an acidic liquid-phase system constructed by hydrolysis of ferric salt. Further mechanism analysis reveals that in the mechanochemical solid-phase reaction, Cu⁰, metallic impurities, metal oxides, and carbon materials from waste PCBs could also reduce Fe³⁺ to Fe²⁺. The optimum conditions for Cu⁰ recovery from waste PCB powder with FeCl₃ as a solid-phase reagent were: rotational speed of 500 rpm, Cu⁰:Fe³⁺ molar ratio of 1:20, and reaction time of 120 min, achieving the highest recovery of 99.6 wt%. This study presents a facile path for Cu⁰ recovery from waste PCBs for resource circulation.

The polymers and their additives in particulate plastics: What makes them hazardous to the fauna?

Due to the increasing concerns on global ecosystems and human health, the environmental risks posed by microplastics (MPs) and nanoplastics (NPs) have become an important topic of research. Their ecological impacts on various faunal species have been extensively researched and reviewed. However, the majority of those studies perceive these micro(nano)-plastics (MNPs) as a single entity rather than a collective term for a group of chemically distinct polymeric particulates. Each of the plastic polymers can possess unique physical and chemical behavior, which, in turn, can determine the possible environmental impacts. Furthermore, many studies explore the adsorption, absorption, and release of other environmental pollutants by MNPs. But only a handful of them explore the leaching of additives possessed by these polymers. Data on the environmental behavior and toxicity of individual additives associated with different polymer particulates are scarce. Knowledge about the leachability and ecotoxicity of the additives associated with environmental MNPs (unlike large plastic particles) remains limited. The ecological impacts of different MNPs together with their additives and the basis of their toxicity have not been explored yet. The present review systematically explores the potential implications of environmentally predominant polymers and their associated additives and discusses their physicochemical characteristics. The review ultimately aims to provide novel insights on what components precisely make MNPs hazardous to the fauna. The paper also discusses the major challenges proposed in the available literature along with recommendations for future research to throw light on possible solutions to overcome the hazards of MNPs.

Co-conversion of wood and polyvinyl chloride to valuable chemicals and high-quality solid fuel

Polyvinyl chloride (PVC)-containing waste streams are difficult to recycle due to high chlorine content in PVC. Toxic dioxins or corrosive hydrogen chloride (HCl) vapor released from improper management of PVC-containing wastes can cause severe environmental pollution and human health problems. While PVC is usually treated as contamination and burden in waste recycling, a novel recycling approach was developed in this study to leverage PVC as an asset. Specifically, red oak and PVC were co-converted in γ-Valerolactone, a green biomass-derivable solvent. During the co-conversion, PVC-derived HCl in the solvent acted as an acid catalyst to produce up to 14.4% levoglucosenone and 14.3% furfural from red oak. On the other hand, dechlorinated PVC hydrocarbons and lignin fraction of red oak reacted each other to form chlorine-free solid fuels with high thermal stability. The higher heating value of the solids was up to 36.2 MJ/kg, which is even higher than the heating value of anthracite coal. After the co-conversion, more than 80% of PVC-contained chlorine turned into chloride ion and the rest formed 5-chlorovaleric acid. 5-chlorovaleric acid crystals were further recovered from the post-reaction liquid with a purity of 91.2%.

Upcycling waste polyvinyl chloride: One-pot synthesis of valuable carbon materials and pipeline-quality syngas via pyrolysis in a closed reactor

Polyvinyl chloride (PVC) is one of the most commonly used plastics. The treatment and recycling of PVC waste is still challenging, due to its non-biodegradability, low thermal stability, high Cl content and low product value. In this study, a one-pot method was developed to upcycle PVC into valuable carbon materials, pipeline-quality pyrolysis gas and chlorides. The well-designed process included dechlorination by Cl-fixative (ZnO or KOH), carbonization of dechlorinated polyenes, and modification of carbon materials in sequence. ZnO and KOH converted 84.48% and 94.15% of total Cl into corresponding chlorides, respectively. CH₄ and H₂ accounted for 81.87-99.34 vol% of pyrolysis gas with higher heat values of 30.11-32.84 MJ m^-3, which can be used as substitute natural gas. As high as 83.13% of the C element was converted into carbon materials. The morphology, structure and property of carbon materials can be modified by different Cl-fixatives. Millimeter-scale carbon spheres with mono-dispersity and porous carbon with a high specific surface area of 1922 m² g^-1 were obtained when ZnO and KOH were added, respectively. Moreover, the reaction mechanisms of PVC with Cl-fixatives were also deciphered through thermogravimetric analysis and thermodynamic simulation.

A New Look at the Chemical Recycling of Polypropylene: Thermal Oxidative Destruction in Aqueous Oxygen-Enriched Medium

Recycling of plastic waste, in particular polypropylene, represents one of the most pressing challenges facing humanity. Despite the promise of chemical methods for recycling polypropylene, they usually require a high temperature and are energy-intensive. In this work, we investigated the oxidative thermolysis of polypropylene in aqueous media. This approach rendered it possible to carry out the decomposition of the polymer at a comparatively low temperature (150 °C). It was shown that among the tested, the most promising aqueous medium for the decomposition of polypropylene is water saturated with gaseous oxygen at an elevated pressure (14 bar) and at a temperature of 150 °C. In such an environment, polypropylene was converted mostly to acetic acid (up to 1.3 g/g acetic acid to starting polypropylene mass ratio). Moreover, methanol, formic acid, and propionic acid were also detected as the products. Finally, the applicability of the proposed recycling method to real polypropylene waste was shown.

Rapid color-fading colorimetric sensing of Hg in environmental samples: regulation mechanism from DNA dimension

It was found that dimension change of aptamer DNA significantly weakened the mimicking activity of gold nanozyme, which was contrary to previous research. Based on this, a rapid colorimetric method for the detection of low concentrations of mercury in environmental media was fabricated. It was observed that 40 nM Hg²⁺ causes color changes in solution. The detection limit of absorbance measurements was estimated to be 9.3 × 10^-11 M. The assay was fast and could complete a single test in half an hour. The detection results for real environment samples confirmed the reliability of the colorimetric analysis in practical application. The proposed assay provides an alternative method for real-time monitoring of mercury in the environment. In particular, the charge effect on the affinity of nanozyme consummated the DNA regulation mechanism for the simulated enzyme activity.