Carbonization: A feasible route for reutilization of plastic wastes

Environmental toxicology of microplastic particles on fish: A review

The increase in plastic debris and its environmental impact has been a major concern for scientists. Physical destruction, chemical reactions, and microbial activity can degrade plastic waste into particles smaller than 5 mm, known as microplastics (MPs). MPs may eventually enter aquatic ecosystems through surface runoff. The accumulation of MPs in aquatic environments poses a potential threat to finfish, shellfish, and the ecological balance. This study investigated the effect of MP exposure on freshwater and marine fish. MPs could cause significant harm to fish, including physical damage, death, inflammation, oxidative stress, disruption of cell signalling and cellular biochemical processes, immune system suppression, genetic damage, and reduction in fish growth and reproduction rates. The activation of the detoxification system of fish exposed to MPs may be associated with the toxicity of MPs and chemical additives to plastic polymers. Furthermore, MPs can enhance the bioavailability of other xenobiotics, allowing these harmful substances to more easily enter and accumulate in fish. Accumulation of MPs and associated chemicals in fish can have adverse effects on the fish and humans who consume them, with these toxic substances magnifying as they move up the food chain. Changes in migration and reproduction patterns and disruptions in predator-prey relationships in fish exposed to MPs can significantly affect ecological dynamics. These interconnected changes can lead to cascading effects throughout aquatic ecosystems. Thus, implementing solutions like reducing plastic production, enhancing recycling efforts, using biodegradable materials, and improving waste management is essential to minimize plastic waste and its environmental impact.

Sustainable valorization of waste plastic into nanostructured materials for environmental, energy, catalytic and biomedical applications: A review

The extensive production and utilization of plastic products are inevitable in the current scenario. However, the non-degradable nature of waste plastic generated after use poses a grave concern. Comprehensive efforts are being made to find viable technological solutions to manage the escalating challenge of waste plastic. This review focuses on the progress made in transformation of waste plastic into value-added nanomaterials. An overview is provided of the waste plastic issue on a global level and its ecological impacts. Currently established methodologies for waste plastic management are examined, along with their limitations. Subsequently, state-of-the-art techniques for converting waste plastic into nanostructured materials are presented, with a critical evaluation of their distinct merits and demerits. Several demonstrated technologies and case studies are discussed regarding the utilization of these nanomaterials in diverse applications, including environmental remediation, energy production and storage, catalytic processes, sensors, drug delivery, bioimaging, regenerative medicine and advanced packaging materials. Moreover, challenges and prospects in the commercial level production of waste plastic-derived nanomaterials and their adoption for industrial and practical usage are highlighted. Overall, this work underscores the potential of transforming waste plastic into nanostructured materials for multifaceted applications. The valorization approach presented here offers an integration of waste plastic management and sustainable nanotechnology. The development of such technologies should pave the way toward a circular economy and the attainment of sustainable development goals.

Recycling and reuse of waste agricultural plastics with hydrothermal pretreatment and low-temperature pyrolysis method

Recycling and reuse of agricultural plastics is an urgent worldwide issue. In this work, it is shown that low-density polyethylene (PE) typically used in mulch films can be converted into high-capacity P and N adsorbents through a two-step method that uses hydrothermal pretreatment (180 °C, 24 h) followed by pyrolysis at 500 °C with Ca(OH)2 additive. CaPE@HC500 materials prepared with the proposed two-step method were found to have high adsorption capacities for phosphate (263.6 mg/g) and nitrogen (200.7 mg/g) over wide ranges of pH (3-11). Dynamic adsorption of phosphate by CaPE@HC500 material in a packed-bed had a half-time breakthrough of 210 min indicating the feasibility of continuous systems. Material stability, cost, environmental-friendliness, and recyclability of the CaPE@HC500 material were determined to be superior to literature-proposed Ca-containing adsorbents. The two-step method for converting waste agricultural plastic mulch films into adsorbents is robust and highly-applicable to industrial settings.

Carbon Dots: A Bright Future as Anticounterfeiting Encoding Agents

Counterfeit products and data vulnerability present significant challenges in contemporary society. Hence, various methods and technologies are explored for anticounterfeiting encoding, with luminescent tracers, particularly luminescent carbon dots (CDs), emerging as a notable solution. CDs offer promising contributions to product security, environmental sustainability, and the circular economy. This critical review aims to highlight the luminescence responsiveness of CDs to physical and chemical stimuli, achieved through nanoengineering their chemical structure. The discussion will delve into the various tunable luminescence mechanisms and decay times of CDs, investigating preferential excitations such as up-conversion, delayed fluorescence, fluorescence, room temperature phosphorescence, persistent luminescence, energy and charge transfer, as well as photo-chemical interactions. These insights are crucial for advancing anticounterfeiting solutions. Following this exploration, a systematic review will focus on the research of luminescent CDs' smart encoding applications, encompassing anticounterfeiting, product tracing, quality certification, and information encryption. Finally, the review will address key challenges in implementing CDs-based technology, providing specific insights into strategies aimed at maximizing their stability and efficacy in anticounterfeiting encoding applications.

A multifunctional solution to enhance capacity and stability in lithium-sulfur batteries: Incorporating hollow CeO2 nanorods into carbonized non-woven fabric as an interlayer

Lithium-sulfur batteries (LSBs) hold promise as the next-generation lithium-ion batteries (LIBs) due to their ultra-high theoretical capacity and remarkable cost-efficiency. However, these batteries suffer from the serious shuttle effect, challenging their practical application. To address this challenge, we have developed a unique interlayer (HCON@CNWF) composed of hollow cerium oxide nanorods (CeO2) anchored to carbonized non-woven viscose fabric (CNWF), utilizing a straightforward template method. The prepared interlayer features a three-dimensional (3D) conductive network that serves as a protective barrier and enhances electron/ion transport. Additionally, the CeO2 component effectively chemisorbs and catalytically transforms lithium polysulfides (LiPSs), offering robust chemisorption and activation sites. Moreover, the unique porous structure of the HCON@CNWF not only physically adsorbs LiPSs but also provides ample space for sulfur's volume expansion, thus mitigating the shuttle effect and safeguarding the electrode against damage. These advantages collectively contribute to the battery's outstanding electrochemical performance, notably in retaining a reversible capacity of 80.82 % (792 ± 5.60 mAh g-1) of the initial value after 200 charge/discharge cycles at 0.5C. In addition, the battery with HCON@CNWF interlayer has excellent electrochemical performance at high sulfur loading (4 mg cm-2) and low liquid/sulfur ratio (7.5 µL mg-1). This study, thus, offers a novel approach to designing advanced interlayers that can enhance the performance of LSBs.

Enhanced UV protection in silk fibroin based electrospun fabrics realized via orientation induced high efficiency of azobenzene isomerization

Due to the poor UV protection capability, natural silk fabrics not only suffer from easy damage by sunshine but also induce possible sunburn in the human body. Efficient azobenzene isomerization and enhanced UV shielding are realized by replacing the natural silk with natural protein silk fibroin (SF) and electrospinning together with light-responsive copolymer P(MEO2-co-OEG300-co-AHMA). Compared to a solution cast film, the absorption peak intensity at 355 nm is 60 % higher in UV-Vis spectra of the electropsun SF/P(MEO2-co-OEG300-co-AHMA) fabrics. This improvement is related to the highly oriented chains, inducing more space and higher efficiency for azobenzene isomerization. Only exposure to visible light for 20 min, the absorption peak corresponding to the trans- state at 355 nm recovers to 92.5 % in the electrospun fabrics, which is at least 100 % faster than that in the solution cast film (50 min). It is related to the zip effect of the isomerization in the oriented chain structure. Thus, not only the absorption of UV radiation, but also the isomerization rate is enhanced. Based on these unique absorption and recovery capabilities, the SF based electrospun fabrics can be used to replace the natural silk fabrics for UV shielding in summer, especially for cyclic use.

A review on value-addition to plastic waste towards achieving a circular economy

Plastic and mixed plastic waste (PW) has received increased worldwide attention owing to its huge rate of production, high persistency in the environment, and unsustainable waste management practices. Therefore, sustainable PW management and upcycling approaches are imperative to achieve the objectives of the United Nations Sustainable Development Goals. Numerous recent studies have shown the application and feasibility of various PW conversion techniques to produce materials with better economic value. Within this framework, the current review provides an in-depth analysis of cutting-edge thermochemical technologies such as pyrolysis, gasification, carbonization, and photocatalysis that can be used to value plastic and mixed PW in order to produce energy and industrial chemicals. Additionally, a thorough examination of the environmental impacts of contemporary PW upcycling techniques and their commercial feasibility through life cycle assessment (LCA) and techno-economical assessment are provided in this review. Finally, this review emphasizes the opportunities and challenges accompanying with existing PW upcycling techniques and deliver recommendations for future research works.

Polymer Waste Valorization into Advanced Carbon Nanomaterials for Potential Energy and Environment Applications

The rise in universal population and accompanying demands have directed toward an exponential surge in the generation of polymeric waste. The estimate predicts that world-wide plastic production will rise to ≈590 million metric tons by 2050, whereas 5000 million more tires will be routinely abandoned by 2030. Handling this waste and its detrimental consequences on the Earth's ecosystem and human health presents a significant challenge. Converting the wastes into carbon-based functional materials viz. activated carbon, graphene, and nanotubes is considered the most scientific and adaptable method. Herein, this world provides an overview of the various sources of polymeric wastes, modes of build-up, impact on the environment, and management approaches. Update on advances and novel modifications made in methodologies for converting diverse types of polymeric wastes into carbon nanomaterials over the last 5 years are given. A remarkable focus is made to comprehend the applications of polymeric waste-derived carbon nanomaterials (PWDCNMs) in the CO2 capture, removal of heavy metal ions, supercapacitor-based energy storage and water splitting with an emphasis on the correlation between PWDCNMs' properties and their performances. This review offers insights into emerging developments in the upcycling of polymeric wastes and their applications in environment and energy.

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.

Recent advancements in the use of plastics as a carbon source for carbon nanotubes synthesis - A review

Plastics, which majorly consist of polypropylene (PP), polyethylene (linear low-density polyethylene (LLDPE), low-density polyethylene (LDPE) and high-density polyethylene (HDPE)), polystyrene (PS), polyvinyl chloride (PVC), polyethylene terephthalate (PET), etc., are the most abundant municipal solid wastes (MSW). They have been utilized as a cheap carbon feedstock in the synthesis of carbon nanotubes (CNTs) because of their high hydrocarbon content, mainly carbon and hydrogen, especially for the polyolefins. In this review, the detailed progress made so far in the use of plastics (both waste and virgin) as cheap carbon feedstock in the synthesis of CNTs (only) over the years is studied. The primary aim of this work is to provide an expansive landscape made so far, especially in the areas of catalysts, catalyst supports, and the methods employed in their preparations and other operational growth conditions, as well as already explored applications of plastic-derived CNTs. This is to enable researchers to easily access, understand, and summarise previous works done in this area, forging ahead towards improving the yield and quality of plastic-derived CNTs, which could extend their market and use in other purity-sensitive 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.

Sustainable Polyvinyl Chloride-Derived Soft Carbon Anodes for Potassium-Ion Storage: Electrochemical Behaviors and Mechanism

Soft carbon is a promising anode material for potassium-ion batteries due to its favorable properties such as low cost, high conductivity, stable capacity, and low potential platform. Polyvinyl chloride, as a white pollutant, is a soft carbon precursor that can be carbonized at varying temperatures to produce soft carbons with controllable defect and crystal structures. This work investigates the effect of carbonization temperature on the crystalline structures of the obtained soft carbons. In situ Raman spectroscopy was used to elucidate the adsorption-intercalation charge storage mechanism of potassium ions in soft carbons. Soft carbons prepared at the temperature of 800 °C have a defect-rich, short-range ordered structure, which provides optimal intercalation and adsorption sites for potassium ions, resulting in a satisfactory capacity of 302 mAh g-1 . This work presents new possibilities for designing soft carbon materials from recycling plastics for potassium-ion batteries.

Impact of PVC microplastics on soil chemical and microbiological parameters

Microplastics (MPs) are emerging pollutants whose occurrence is a global problem in natural ecosystems including soil. Among MPs, polyvinyl chloride (PVC) is a well-known polymer with remarkable resistance to degradation, and because its recalcitrant nature serious environmental concerns are created during manufacturing and waste disposal. The effect of PVC (0.021% w/w) on chemical and microbial parameters of an agricultural soil was tested by a microcosm experiment at different incubation times (from 3 to 360 days). Among chemical parameters, soil CO₂ emission, fluorescein diacetate (FDA) activity, total organic C (TOC), total N, water extractable organic C (WEOC), water extractable N (WEN) and SUVA₂₅₄ were considered, while the structure of soil microbial communities was studied at different taxonomic levels (phylum and genus) by sequencing bacterial 16S and fungal ITS2 rDNA (Illumina MiSeq). Although some fluctuations were found, chemical and microbiological parameters exhibited some significant trends. Significant (p < 0.05) variations of soil CO₂ emission, FDA hydrolysis, TOC, WEOC and WEN were found in PVC-treated soils over different incubation times. Considering the structure of soil microbial communities, the presence of PVC significantly (p < 0.05) affected the abundances of specific bacterial and fungal taxa: Candidatus_Saccharibacteria, Proteobacteria, Actinobacteria, Acidobacteria and Bacteroides among bacteria, and Basidiomycota, Mortierellomycota and Ascomycota among fungi. After one year of experiment, a reduction of the number and the dimensions of PVC was detected supposing a possible role of microorganisms on PVC degradation. The abundance of both bacterial and fungal taxa at phylum and genus level was also affected by PVC, suggesting that the impact of this polymer could be taxa-dependent.

Porous carbon tubes from recycling waste COVID-19 masks for optimization of 8 mol% Y2O3-doped tetragonal zirconia polycrystalline nanopowder

Disposable polypropylene medical masks are widely used to protect people from injury caused by COVID-19 worldwide. However, disposable medical masks are non-biodegradable materials, and the accumulation of waste masks can pollute the environment and waste resources without a reasonable recycling method. The aims of this study are to transform waste masks into carbon materials and to use them as a dispersant in preparing high-quality 8 mol% Y₂O₃-doped tetragonal zirconia nanopowders. The waste masks were carbonized to get a carbon source in the first step, then KOH was used to etch the carbon source creating a micropores structure in the carbon material after the carbon-bed heat treatment method. The resulting carbon material is a porous tube structure with a high specific surface area (1220.34 m²/g) and adsorption capacity. The as-obtained porous carbon tubes were applied as a dispersant to produce 8 mol% Y₂O₃-doped tetragonal zirconia nanopowders, and the resulting nanopowders owned well-dispersed and had the smallest particle size than that prepared by activated carbon as a dispersant. Besides, the sintered 8 mol% Y₂O₃-doped tetragonal zirconia ceramic possessed high density, which resulted in higher ionic conductivity. These findings suggest that waste face masks can be recycled to prepare high-added-value carbon materials and provide a green and low-cost method to reuse polypropylene waste materials.

Activated carbons derived from polyethylene terephthalate for coin-cell supercapacitor electrodes

We successfully prepared activated carbon derived from polyethylene terephthalate (PET) via carbonization and subsequent activation under various conditions and applied it as active material for supercapacitors. In the activation, we used CO2 for physical activation or KOH for chemical activation and varied the activation temperature from 600 °C to 1,000 °C. We found that CO2 activation is unsuitable because of insufficient pore formation or low activation yield. Interestingly, PET-derived activated carbon obtained using KOH (PETK) at 700 °C-900 °C exhibited higher specific surface areas than YP50f, which is a commercial activated carbon. Furthermore, some PETKs even displayed a dramatic increase in crystallinity. In particular, the PET-derived activated carbon prepared at 900 °C with KOH (PETK900) had the highest retention rate at a high charge-discharge rate and better durability after 2500 cycles than YP50f. Furthermore, employing the same process that we used with the PET chips, we successfully converted waste PET bottles into activated carbon materials. Waste PET-derived activated carbons exhibited good electrochemical performance as active material for supercapacitors. We thus found chemical activation with KOH to be an appropriate method for manufacturing PET-derived activated carbon and PETKs derived both from PET chips and waste PET have considerable potential for commercial use as active materials for supercapacitors.

Electronic Supplementary Material

Supplementary material is available for this article at 10.1007/s11814-023-1466-3 and is accessible for authorized users.

A Versatile Sulfur-Assisted Pyrolysis Strategy for High-Atom-Economy Upcycling of Waste Plastics into High-Value Carbon Materials

With the overconsumption of disposable plastics, there is a considerable emphasis on the recycling of waste plastics to relieve the environmental, economic, and health-related consequences. Here, a sulfur-assisted pyrolysis strategy is demonstrated for versatile upcycling of plastics into high-value carbons with an ultrahigh carbon-atom recovery (up to 85%). During the pyrolysis process, the inexpensive elemental sulfur molecules are covalently bonded with polymer chains, and then thermally stable intermediates are produced via dehydrogenation and crosslinking, thereby inhibiting the decomposition of plastics into volatile small hydrocarbons. In this manner, the carbon products obtained from real-world waste plastics exhibit sulfur-rich skeletons with an enlarged interlayer distance, and demonstrate superior sodium storage performance. It is believed that the present results offer a new solution to alleviate plastic pollution and reduce the carbon footprint of plastic industry.

On the use of plastic precursors for preparation of activated carbons and their evaluation in CO2 capture for biogas upgrading: a review

In circular economy, useful plastic materials are kept in circulation as opposed to being landfilled, incinerated, or leaked into the natural environment. Pyrolysis is a chemical recycling technique useful for unrecyclable plastic wastes that produce gas, liquid (oil), and solid (char) products. Although the pyrolysis technique has been extensively studied and there are several installations applying it on the industrial scale, no commercial applications for the solid product have been found yet. In this scenario, the use of plastic-based char for the biogas upgrading may be a sustainable way to transform the solid product of pyrolysis into a particularly beneficial material. This paper reviews the preparation and main parameters of the processes affecting the final textural properties of the plastic-based activated carbons. Moreover, the application of those materials for the CO₂ capture in the processes of biogas upgrading is largely discussed.

Upcycling face mask wastes generated during COVID-19 into value-added engineering materials: A review

Billions of disposable face masks (i.e., single-use masks) are used and discarded worldwide monthly due to the COVID-19 outbreak. The immethodical disposal of these polymer-based wastes containing non-biodegradable constituents (e.g., polypropylene) has provoked marked and severe damage to the ecosystem. Meanwhile, their ever-growing usage significantly strains the present-day waste management measures such as landfilling and incineration, resulting in large quantities of used face-covering masks landing in the environment as importunate contaminants. Hence, alternative waste management strategies are crucially demanded to decrease the negative impacts of face mask contamination. In this venue, developing high-yield, effective, and green routes toward recycling or upcycling face mask wastes (FMWs) into value-added materials is of great importance. While existing recycling processes assist the traditional waste management, they typically end up in materials with downgraded physicochemical, structural, mechanical, and thermal characteristics with reduced values. Therefore, pursuing potential economic upcycling processes would be more beneficial than waste disposal and/or recycling processes. This paper reviews recent advances in the FMWs upcycling methods. In particular, we focus on producing value-added materials via various waste conversion methods, including carbonization (i.e., extreme pyrolysis), pyrolysis (i.e., rapid carbonization), catalytic conversion, chemical treatment, and mechanical reprocessing. Generally, the upcycling methods are promising, firming the vital role of managing FMWs' fate and shedding light on the road of state-of-the-art materials design and synthesis.

Porous Carbon-Carbon Composite Materials Obtained by Alkaline Dehydrochlorination of Polyvinyl Chloride

Porous carbon-carbon composite materials (PCCCM) were synthesized by the alkaline dehydrochlorination of polyvinyl chloride solutions in dimethyl sulfoxide containing the modifying additives of a nanostructured component (NC): graphite oxide (GO), reduced graphite oxide (RGO) or nanoglobular carbon (NGC), with subsequent two-step thermal treatment of the obtained polyvinylene-NC composites (carbonization at 400 °C and carbon dioxide activation at 900 °C). The focus of the study was on the analysis and digital processing of transmission electron microscopy images to study local areas of carbon composite materials, as well as to determine the distances between graphene layers. TEM and low-temperature nitrogen adsorption studies revealed that the structure of the synthesized PCCCM can be considered as a porous carbon matrix in which either carbon nanoglobules (in the case of NGC) or carbon particles with the "crumpled sheet" morphology (in the case of GO or RGO used as the modifying additives) are distributed. Depending on the features of the introduced 5-7 wt.% nanostructured component, the fraction of mesopores was shown to vary from 11% to 46%, and S_BET-from 791 to 1115 m² g^-1. The synthesis of PCCNC using graphite oxide and reduced graphite oxide as the modifying additives can be considered as a method for synthesizing a porous carbon material with the hierarchical structure containing both the micro- and meso/macropores. Such materials are widely applied and can serve as adsorbents, catalyst supports, elements of power storage systems, etc.

From polyvinyl chloride waste to activated carbons: the role of occurring additives on porosity development and gas adsorption properties

Conversion of waste plastic to carbon materials has been considered as a potential approach for plastic recycling. In this study, polyvinyl chloride (PVC) plastic, one of the most widely used polymers, was used as a single precursor to prepare porous carbons via chemical activation process. The results showed that KOH activation followed by acid washing was an effective strategy to recover all calcium- and up to 92% of titanium-based compounds, the main metal additives in PVC, in the form of soluble salt. Those metal additives in PVC acted as a type of hard template, which benefit the development of microporosity and carbon dioxide (CO₂) adsorption. Textural characterization demonstrated that the prepared carbons possessed high surface area and pore volume of up to 2507 m²/g and 1.11 cm³/g, respectively. At 0 °C and 100 kPa, the PVC-derived carbon, PH_73, which has highest ultra-micropore volume among all samples, exhibited excellent CO₂ adsorption capacity of 6.90 mmol/g and high CO₂/N₂ selectivity. Converting the non-degradable PVC into high-quality porous carbon materials could be considered as a potential strategy for plastic waste recycling.

Recent Advances in Carbon-Silica Composites: Preparation, Properties, and Applications

The thermal catalytic conversion of biomass is currently a prevalent method for producing activated carbon with superb textural properties and excellent adsorption performance. However, activated carbon suffers severely from its poor thermal stability, which can easily result in spontaneous burning. In contrast, silica material is famed for its easy accessibility, high specific surface area, and remarkable thermal stability; however, its broader applications are restricted by its strong hydrophilicity. Based on this, the present review summarizes the recent progress made in carbon-silica composite materials, including the various preparation methods using diverse carbon (including biomass resources) and silica precursors, their corresponding structure–function relationship, and their applications in adsorption, insulation, batteries, and sensors. Through their combination, the drawbacks of the individual materials are circumvented while their original advantages are maintained. Finally, several bottlenecks existing in the field of carbon-silica composites, from synthesis to applications, are discussed in this paper, and possible solutions are given accordingly.

Cost-effective carbon fiber precursor selections of polyacrylonitrile-derived blend polymers: carbonization chemistry and structural characterizations

Blending polyacrylonitrile (PAN) with plastic wastes and bio-based polymers provides a convenient and inexpensive method to realize cost-effective carbon fiber (CF) precursors. In this work, PAN-based blend precursors are investigated using ReaxFF reactive molecular dynamics simulations with respect to the formation of all-carbon rings, the evolutions of oxygen-containing and nitrogen-containing species, and the migration of carbon atoms to form turbostratic graphene. From these simulations, we identify that PAN/cellulose (CL) blend manifests the highest carbon yield and the most substantial all-carbon ring formation. This ReaxFF-based finding is confirmed by Raman and TEM experiments indicating high crystallinity for PAN/CL-derived blend CFs. We trace the pathway of gasification and carbonization of PAN/CL to elaborate the mechanism of the formation of all-carbon ring networks. We discover that the acetals of CL can catalyze the cyclization of the blend precursor, allowing for the search for CL derivatives or the other kinds of bio-based polymers with similar functionalities as alternative blends. In addition, we examine the structural characteristics using the carbon-carbon (C-C) radial distribution functions, C-C bond length distributions, and sp² C atom ratios for the four representative precursors, i.e., PAN, oxidized PAN, PAN/nylon 6,6, and PAN/CL. Our simulation results show the most extensive all-carbon ring cluster and graphitic structure growths for PAN/CL. Therefore, we propose PAN/CL as a cost-effective alternative CF precursor, since (a) CL is naturally abundant and eco-friendly for production, (b) the blend precursor PAN/CL does not require oxidation treatment, (c) PAN/CL has a high carbon yield with substantial all-carbon ring formation, and (d) PAN/CL based CFs potentially provide a mechanical property enhancement.

Challenges and opportunities in sustainable management of microplastics and nanoplastics in the environment

The accumulation of microplastics (MPs) and nanoplastics (NPs) in terrestrial and aquatic ecosystems has raised concerns because of their adverse effects on ecosystem functions and human health. Plastic waste management has become a universal problem in recent years. Hence, sustainable plastic waste management techniques are vital for achieving the United Nations Sustainable Development Goals. Although many reviews have focused on the occurrence and impact of micro- and nanoplastics (MNPs), there has been limited focus on the management of MNPs. This review first summarizes the ecotoxicological impacts of plastic waste sources and issues related to the sustainable management of MNPs in the environment. This paper then critically evaluates possible approaches for incorporating plastics into the circular economy in order to cope with the problem of plastics. Pollution associated with MNPs can be tackled through source reduction, incorporation of plastics into the circular economy, and suitable waste management. Appropriate infrastructure development, waste valorization, and economically sound plastic waste management techniques and viable alternatives are essential for reducing MNPs in the environment. Policymakers must pay more attention to this critical issue and implement appropriate environmental regulations to achieve environmental sustainability.

Application of Slow Pyrolysis to Convert Waste Plastics from a Compost-Reject Stream into Py-Char

There is growing recognition that the degradation of plastics in the environment is a serious problem. This study investigated and reported on the feasibility of removing end-of-life plastics from circulating in the environment. The specific example focuses on non-recyclable plastics found in a waste diversion program for compostable materials, known as the Green Bin Program. The purpose of this study was to identify and quantify the types of polymers in this stream, as well as to determine if it could be successfully turned into char without separation of its components. The measurements show that polyethylene (72 wt.%), polypropylene (14 wt.%) and polyethylene terephthalate (12 wt.%) are the main constituents of this stream, with minor contributions from polybutylene adipate terephthalate (PBAT), polyvinyl alcohol (PVA), poly methyl methacrylate (PMMA), polystyrene (PS), Nitrile rubber and Nylon. Samples of the as-received waste containing plastics and fibrous material were subjected to a slow pyrolysis process. The yield of the char product depended on the conditions of the pyrolysis and a strong synergistic effect was noted when both the plastic and fibrous materials were co-pyrolyzed. The study of variable pyrolysis conditions, along with DTA-TGA-MS studies on the mechanism of the char formation, indicate that the positive effect results from enhanced interaction of plastics with air, in the presence of fibrous material, during the initial/pre-treatment step.

Enhanced Stability and Mechanical Properties of a Graphene–Protein Nanocomposite Film by a Facile Non-Covalent Self-Assembly Approach

Graphene-based nanocomposite films (NCFs) are in high demand due to their superior photoelectric and thermal properties, but their stability and mechanical properties form a bottleneck. Herein, a facile approach was used to prepare nacre-mimetic NCFs through the non-covalent self-assembly of graphene oxide (GO) and biocompatible proteins. Various characterization techniques were employed to characterize the as-prepared NCFs and to track the interactions between GO and proteins. The conformational changes of various proteins induced by GO determined the film-forming ability of NCFs, and the binding of bull serum albumin (BSA)/hemoglobin (HB) on GO’s surface was beneficial for improving the stability of as-prepared NCFs. Compared with the GO film without any additive, the indentation hardness and equivalent elastic modulus could be improved by 50.0% and 68.6% for GO–BSA NCF; and 100% and 87.5% for GO–HB NCF. Our strategy should be facile and effective for fabricating well-designed bio-nanocomposites for universal functional applications.

Automated SEM-EDS Analysis of Transition Metals and Other Metallic Compounds Emitted from Incinerating Agricultural Waste Plastic Film

Illegal open burning, which is criticized as a leading source of air pollutants among agricultural activities, currently requires constant effort and attention from countries around the world. A speciation analysis method is required to examine the harmful effects of particulate matter generated by incineration on the human body. In this study, to simulate open-air incineration, infrastructure for incineration tests complying with US EPA method 5G was built, and a large-area analysis was conducted on the particulate matter through automated SEM-EDS. For test specimens, waste mulching LDPE collected by Korea Environment Corporation Dangjin Office was used. To raise the identifiability of analyzed particles, the specimen was sampled on a plate made of Ag, which has a high atomic number, three times. Metal particulate matter showed a high reaction to C and C-O. The ratio of metal particulate matters that reacted to C and C-O was in the order of Cu (94.1%) > Fe (83.3%) > Al (79.7%). In this study, it was verified that waste mulching adsorbs metal chemicals originating from the soil due to its properties and deterioration, and that when it is incinerated, it emits particulate matter containing transition metals and other metals that contribute to excessive ROS production and reduction.

Preparation of high-performance supercapacitors from waste polyurethane-based hierarchical porous carbon

The specific surface area and pore structure of carbon materials significantly impact their electrochemical performance.

Science-society-policy interface for microplastic and nanoplastic: Environmental and biomedical aspects

The global concern over the possible consequences of the downsizing of plastic to microplastics (MPs) and nano plastics (NPs) needs to be addressed with a new conceptual framework. The transformation of plastics to MPs and NPs can be discussed in terms of fundamental physics principles applicable to micro and nanophase matter and colloidal science principles. Further, accurate and reliable detection and characterization of MPs and NPs are crucial for an extensive understanding of their environmental and ecological impacts. The other decisive factor that can classify MPs and NPs as hazardous to existing nanomaterials is discussing the cytotoxicity study on human cell lines. The human health risk assessment that might arise from the ingestion of MPs and NPs can be addressed about contrast agents used for medical imaging. However, the lack of standard analytical techniques for MPs and NPs measurement is an emerging challenge for analytical scientists due to their complex physicochemical properties, especially in environmental samples. This review article navigates readers through the point of origin of MPs and NPs and their interdisciplinary aspects. Biomedical applications of plastics and concerns over the toxicity of MPs and NPs are further analyzed. Moreover, the analytical challenges of MPs and NPs have been discussed with critical inputs. Finally, the worldwide efforts being made for creating a common platform of discussion on a different aspect of plastic pollution were taken into account.

Upcycling Plastic Waste into High Value-Added Carbonaceous Materials

Even though plastic improved the human standard of living, handling the plastic waste represents an enormous challenge. It takes more than 100 years to decompose discarded or buried waste plastics. Microplastics are one of the causes of significantly pervasive environmental pollutants. The incineration of plastic waste generates toxic gases, underscoring the need for new approaches, in contrast to conventional strategies that are required for recycling plastic waste. Therefore, several studies have attempted to upcycle plastic waste into high value-added products. Converting plastic waste into carbonaceous materials is an excellent upcycling technique due to their diverse practical applications. This review summarizes various studies dealing with the upcycling of plastic waste into carbonaceous products. Further, this review discusses the applications of carbonaceous products synthesized from plastic waste including carbon fibers, absorbents for water purification, and electrodes for energy storage. Based on the findings, future directions for effective upcycling of plastic waste into carbonaceous materials are suggested.

Strategic Approach Towards Plastic Waste Valorization: Challenges and Promising Chemical Upcycling Possibilities

Plastic waste, which is one of the major sources of pollution in the landfills and oceans, has raised global concern, primarily due to the huge production rate, high durability, and the lack of utilization of the available waste management techniques. Recycling methods are preferable to reduce the impact of plastic pollution to some extent. However, most of the recycling techniques are associated with different drawbacks, high cost and downgrading of product quality being among the notable ones. The sustainable option here is to upcycle the plastic waste to create high-value materials to compensate for the cost of production. Several upcycling techniques are constantly being investigated and explored, which is currently the only economical option to resolve the plastic waste issue. This Review provides a comprehensive insight on the promising chemical routes available for upcycling of the most widely used plastic and mixed plastic wastes. The challenges inherent to these processes, the recent advances, and the significant role of the science and research community in resolving these issues are further emphasized.

Review of the valorization options for the proper disposal of face masks during the COVID-19 pandemic

The COVID-19 pandemic has affected not only human health and economies but also the environment due to the large volume of waste in the form of discarded personal protective equipment. The remarkable increase in the global usage of face masks, which mainly contain polypropylene, and improper waste management have led to a serious environmental challenge called microplastic pollution. Potential practices for waste management related to waste valorization of discarded face masks as the major type of waste during the COVID-19 pandemic are explored in this study. Recommendations based on governmental practices, situation of state facilities, and societal awareness and engagement applicable to emergency (including COVID-19 pandemic) and postpandemic scenarios are offered while considering potential solutions and available waste management practices in different countries during emergency conditions. However, multicriteria decision making for a country must determine the optimal solution for waste management on the basis of all affecting factors. Awareness of scientific, governments, and communities worldwide will successfully eradicate this important environmental issue.

Potential Chemicals from Plastic Wastes

Plastic is referred to as a “material of every application”. From the packaging and automotive industries to the medical apparatus and computer electronics sectors, plastic materials are fulfilling demands efficiently. These plastics usually end up in landfills and incinerators, creating plastic waste pollution. According to the Environmental Protection Agency (EPA), in 2015, 9.1% of the plastic materials generated in the U.S. municipal solid waste stream was recycled, 15.5% was combusted for energy, and 75.4% was sent to landfills. If we can produce high-value chemicals from plastic wastes, a range of various product portfolios can be created. This will help to transform chemical industries, especially the petrochemical and plastic sectors. In turn, we can manage plastic waste pollution, reduce the consumption of virgin petroleum, and protect human health and the environment. This review provides a description of chemicals that can be produced from different plastic wastes and the research challenges involved in plastic waste to chemical production. This review also provides a brief overview of the state-of-the-art processes to help future system designers in the plastic waste to chemicals area.

Upcycling of plastic waste into fluorescent carbon dots: An environmentally viable transformation to biocompatible C-dots with potential prospective in analytical applications

The profitable impact on ecological system made the upcycling of plastic waste as one of the captivating issues in scientific world. The current work highlights the sustainable approach to transform the plastic waste comprises of bottles, used cups and polyethylene bags via simple heating to fluorescent carbon dots (C-dots). The obtained C-dots have displayed the absorption peaks around at 260 nm with size ranging between 5 and 30 nm. The upcycling has produced the structural changes in plastic waste and affected the optical properties of C-dots. The three types of used plastic waste as precursor have displayed excellent emission properties with peak positioned around 422 nm and quantum yield (QY) values ∼62, 65 and 64% for C-dots generated from plastic polybags, cups and bottles (P-CDs, C-CDs and B-CDs) respectively. The toxicity profiling of C-dots has been successfully tested by employing multi-assay biocompatible activities i.e. antibacterial and antifungal activities. The potential prospective of C-dots derived from plastic waste have further been explored in analytical applications involving selective copper metal ion sensing in aqueous media. The outcomes of the current studies have highlighted the potential accomplishment in preserving environment fate and giving response towards the budding social hitch of plastic waste.

Single-use plastics: Production, usage, disposal, and adverse impacts

Single-use plastics (SUPs), invented for the modern "throwaway society," are intended to be used only once. They are being increasingly produced and used globally, most notably as packaging or consumables, such as SUP shopping bags or disposable tableware. We discuss how most SUPs are landfilled or incinerated, which causes pollution, consumes valuable land, and squanders limited natural resources. Only relatively small amounts are currently recycled, a hindrance to the concept of a circular economy. Moreover, SUP litter aggregation in the natural environment is a major concern. This article briefly reviews SUP contamination in various environmental media including soil, rivers, lakes and oceans around the world. In the face of mounting evidence regarding the threat posed to plant growth, soil invertebrates and other land animals, (sea) birds, and marine ecosystems, there is a growing push to minimize SUPs. Regulatory tools and voluntary actions to reduce SUP usage have been put forward, with some suggestions for minimizing SUP waste.

A review of smart electrospun fibers toward textiles

Electrospinning as a versatile technology has attracted a large amount of attention in the past few decades due to the facile way to produce micro- and nano-scale fibers featuring flexibility, large specific surface area and high porosity. Stimuli-responsive polymers are a class of smart materials that are capable of sensing surround environment and interacting with them. Therefore, the combination of electrospinning and smart materials could have a great deal of benefits over the development of smart fibers. In this review, it offers a comprehensive understanding of smart electrospun fibers toward textile applications. Firstly, the definition of smart fibers and the differences between interactive fibers and passive interactive fibers are briefly introduced. Then some interactive fibers made from temperature-, pH-, light-, electric field/electricity-, magnetic field-, multi-responsive polymers, as well as some polymers featuring piezoelectric and triboelectric effect which are suitable flexible electrics, are emphasized with their applications in the form of electrospun fibers. Afterwards, some passive and hybrid smart electrospun fibers are introduced. Finally, associated challenges and perspectives are summarized and discussed.

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Understanding of passive smart electrospun fibers and interactive smart electrospun fibers.

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The recent progress in flexible electronics from electrospun fibers.

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The recent progress in stimuli-responsive polymers applied in interactive smart electrospun fibers.

An efficient strategy for the enhancement of adsorptivity of microporous carbons against gaseous formaldehyde: Surface modification with aminosilane adducts

In an effort to develop a cost-effective mitigation tool for volatile organic compounds, particularly formaldehyde (FA), microporous activated carbon (AC) was modified into three different forms of AC-1, AC-2, and AC-3 using a raw commercial AC product (AC-0). First, AC-1 and AC-2 were produced by the modification of AC-0 with N/S heteroatoms using identical mixture of dicyandiamide and thiourea precursors through either solvothermal (AC-1) or microwave-assisted calcination (AC-2) synthesis. Second, aminosilane-functionalized AC (AC-3) was prepared solvothermally using N-[3-(Trimethoxysilyl)propyl]ethylenediamine reagent. The relative adsorption performances for gaseous FA (1 ppm) in terms of 10% breakthrough volume (BTV10: L atm g^-1) at near-ambient conditions (25 °C and 1 atm) were AC-3 (132) > AC-2 (66.5) > AC-1 (14.2) > AC-0 (10.4). In a comparison based on partition coefficients (mole kg^-1 Pa^-1) at BTV10, AC-3 outperformed AC-0 by a factor of 214, while the adsorption performance of AC-2 was 36-times higher than AC-1. The enhanced performance of AC-2 over AC-1 reflected the effect of the microwave synthesis protocol on the improvement of surface chemistry (e.g., N/S doping) and texture (e.g., surface area and pore volume) of AC-based adsorbents as compared to conventional solvothermal method. Further, the prominent role of surface chemistry (e.g., relative to textural properties), as observed with the increases in the amount of doped functional elements (including N:C and silicon:C ratios), is supported by the apparent dependence of performance on the selected modification procedures. Based on kinetic and X-ray photoelectron spectroscopy analyses, the superiority of aminosilylated AC-3 can be attributed to a synergistic effect between physisorption (e.g., pore diffusion) and chemical interactions of the FA carbonyl (C=O) group with amine and silica functionalities (via Mannich coupling [Schiff base] and cycloaddition reaction mechanisms, respectively). This confirms the significance of surface chemistry, relative to pore diffusion, in achieving maximum adsorption of gaseous FA molecules.

Release kinetics as a key linkage between the occurrence of flame retardants in microplastics and their risk to the environment and ecosystem: A critical review

The widely occurring debris of plastic materials, particularly microplastics, can be an important source of flame retardants, which are one of the main groups of chemicals added in the production of plastics from polymers. This review provides an overview on the use of flame retardants in plastic manufacturing, the kinetics of their releases from microplastics, the factors affecting their releases, and the potential environmental and ecosystem risk of the released flame retardants. The releases of flame retardants from microplastics typically involve three major steps: internal diffusion, mass transfer across the plastic-medium boundary layer, and diffusion in the environmental medium, while the overall mass transfer rate is commonly controlled by diffusion within the plastic matrix. The overall release rates of additive flame retardants from microplastics, which are dependent on the particle's geometry, can often be described by the Fick's Law. The physicochemical properties of flame retardant and plastic matrix, and ambient temperature all affect the release rate, which can be predicted with empirical and semi-empirical models. Weathering of microplastics, which reduces their particle sizes and likely disrupts their polymeric structures, can greatly accelerate the releases of flame retardants. Flame retardants could also be released directly from the microplastics ingested by aquatic organisms and seabirds, with physical and chemical digestion in the bodies significantly enhancing their release rates. Limited by the extremely slow diffusion in plastic matrices, the fluxes of flame retardants released from microplastics are very low, and are unlikely to pose significant risk to the ecosystem in general. More research is needed to characterize the mechanical, chemical, and biological processes that degrade microplastics and accelerate the releases of flame retardants and to model their release kinetics from microplastics, while efforts should also be made to develop environmentally benign flame retardants to ultimately minimize their risk to the environment and ecosystem.

Rational synthesis of silicon into polyimide-derived hollow electrospun carbon nanofibers for enhanced lithium storage

Flexible energy devices with high energy density and long cycle life are considered to be promising applications in portable electronics. In this study, silicon/carbon nanofiber (Si@CNF) core–shell electrode has been prepared by the coaxial electrospinning method. The precursors of polyimide (PI) were for the first time used to form the core–shell structure of Si@CNF, which depicts outstanding flexibility and mechanical strength. The effect of doping concentrations of silicon (Si) nanoparticles embedded in the fiber is investigated as a binder-free anode for lithium-ion batteries. A 15 wt% doped composite electrode demonstrates superior performance, with an initial reversible capacity of 621 mA h g−1 at the current density of 100 mA g−1 and a high capacity retention up to 200 cycles. The excellent cycling performance is mainly due to the carbonized PI core–shell structure, which not only can compensate for the insulation property of Si but also has the ability to buffer the volume expansion during the repeated charge–discharge process.

Reaction pathway of poly(ethylene) terephthalate carbonization: Decomposition behavior based on carbonized product

Char, a solid product obtained from carbonization of waste Poly(Ethylene) Terephthalate (PET), has high potential to solve the current plastic waste problem through the synthesis of new carbon-based adsorbents. However, thermal degradation reaction of polymer involves multiple series of complex reaction pathways and the formation of char is not clarified. In this study, the phase behavior of PET carbonization and the mechanism of char formation was studied in detail. Based on the van Krevelen diagram, it is evident that rapid thermal decomposition of PET occurs through decarbonylation to form char and decarboxylation to form wax. Based on the analysis of cross-linking behavior, a correlation between the degree of cross-linking as a function of CO and CO₂ and dependent parameters based on the experimental operation was obtained. The findings validified the assumption that scission of CO bond in the ester group through decarbonylation and decarboxylation to release CO and CO₂ leads to the formation of char. The cross-linking behavior was further clarified by studying the distribution of cross-linking structure in char and wax. It was confirmed that decarbonylation reaction to release CO is highly associated with the formation of cross-linking to form char in the solid residue, whereas decarboxylation reaction to release CO₂ is highly associated with the formation of cross-linking to form aromatic compounds in the wax residue.