Influence of Stainless-Steel Catalyst Substrate Type and Pretreatment on Growing Carbon Nanotubes from Waste Postconsumer Plastics

Recent Progresses in Pyrolysis of Plastic Packaging Wastes and Biomass Materials for Conversion of High-Value Carbons: A Review

The recycling of plastic packaging wastes helps to alleviate the problems of white pollution and resource shortage. It is very necessary to develop high-value conversion technologies for plastic packaging wastes. To our knowledge, carbon materials with excellent properties have been widely used in energy storage, adsorption, water treatment, aerospace and functional packaging, and so on. Waste plastic packaging and biomass materials are excellent precursor materials of carbon materials due to their rich sources and high carbon content. Thus, the conversion from waste plastic packaging and biomass materials to carbon materials attracts much attention. However, closely related reviews are lacking up to now. In this work, the pyrolysis routes of the pyrolysis of plastic packaging wastes and biomass materials for conversion to high-value carbons and the influence factors were analyzed. Additionally, the applications of these obtained carbons were summarized. Furthermore, the limitations of the current pyrolysis technology are put forward and the research prospects are forecasted. Therefore, this review can provide a useful reference and guide for the research on the pyrolysis of plastic packaging wastes and biomass materials and the conversion to high-value carbon.

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.

Self-Supported Spray-Coated NiFe-LDH Catalyst on a Stainless Steel Substrate for Efficient Oxygen Evolution Reaction

In the quest for more efficient and cost-effective electrocatalytic systems, careful selection of catalysts and substrates plays a pivotal role. This study introduces an approach by synthesizing and depositing NiFe-layered double hydroxide (NiFe-LDH) catalysts on commercial AISI 304 substrates by using a low-temperature spray-coating technique. Through systematic investigations, the influence of processing conditions, such as the synthesis, ultrasonic power for having a stable nanoparticle's dispersion, and spray cycle optimization on the electrochemical and morphological properties of the coatings, is thoroughly explored. The results showcase exceptional catalytic performance, achieving an overpotential of 230 mV at 10 mA/cm2, with enhanced stability even at high current densities of 500 mA/cm2. The study highlights the significance of meticulous processing optimization and presents a scalable methodology that holds great potential for developing catalysts for oxygen evolution reactions (OER) and facilitates their integration into industrial processes.

Transforming Cl-Containing Waste Plastics into Carbon Resource for Steelmaking: Theoretical Insight

The accumulation of waste plastics poses a significant environmental challenge, leading to persistent pollution in terrestrial and aquatic ecosystems. A practical approach to address this issue involves the transformation of postconsumer waste plastics into industrially valuable products. This study focuses on an example of harnessing the carbon content in these polymers for carbon-demanding industrial processes, thereby reducing waste plastics from the environment and alleviating the demand for mined carbon resources. Employing quantum simulations, we examine the viability of polychloroprene as a carburizing agent in the steelmaking process. Our simulations reveal that polychloroprene exhibits excellent carbon diffusivity in molten iron, with a theoretical diffusion coefficient of 8.983 × 10-5cm2 s-1. This value competes favorably with that of metallurgical coke and surpasses the carbon diffusivity of other polymers, such as polycarbonate, polyurethane, and polysulfide. Additionally, our findings demonstrate that the chlorine content in polychloroprene does not permeate into molten iron but instead remains confined to the molten iron and slag interface.

Structure-oriented conversions of plastics to carbon nanomaterials

The accumulation of waste plastics has caused serious environmental issues due to their unbiodegradable nature and hazardous additives. Converting waste plastics to different carbon nanomaterials (CNMs) is a promising approach to minimize plastic pollution and realize advanced manufacturing of CNMs. The reported plastic-derived carbons include carbon filaments (i.e. carbon nanotubes and carbon nanofibers), graphene, carbon nanosheets, carbon sphere, and porous carbon. In this review, we present the influences of different intrinsic structures of plastics on the pyrolysis intermediates. We also reveal that non-charring plastics are prone to being pyrolyzed into light hydrocarbons while charring plastics are prone to being pyrolyzed into aromatics. Subsequently, light hydrocarbons favor to form graphite while aromatics are inclined to form amorphous carbon during the carbon formation process. In addition, the conversion tendency of different plastics into various morphologies of carbon is concluded. We also discuss other impact factors during the transformation process, including catalysts, temperature, processing duration and templates, and reveal how to obtain different morphological CNMs from plastics. Finally, current technology limitations and perspectives are presented to provide future research directions in effective plastic conversion and advanced CNM synthesis.

The impact factors in transforming plastics into carbon nanomaterials are reviewed.

The carbon morphology tendency from different plastics is revealed.

Directions for future research on plastic carbonization are presented.

Sustainable management of plastic wastes in COVID-19 pandemic: The biochar solution

To prevent the COVID-19 transmission, personal protective equipment (PPE) and packaging materials have been extensively used but often managed inappropriately, generating huge amount of plastic waste. In this review, we comprehensively discussed the plastic products utilized and the types and amounts of plastic waste generated since the outbreak of COVID-19, and reviewed the potential treatments for these plastic wastes. Upcycling of plastic waste into biochar was addressed from the perspectives of both environmental protection and practical applications, which can be verified as promising materials for environmental protections and energy storages. Moreover, novel upcycling of plastic waste into biochar is beneficial to mitigate the ubiquitous plastic pollution, avoiding harmful impacts on human and ecosystem through direct and indirect micro-/nano-plastic transmission routes, and achieving the sustainable plastic waste management for value-added products, simultaneously. This suggests that the plastic waste could be treated as a valuable resource in an advanced and green manner.

Upcycling Plastic Wastes into Value-Added Products by Heterogeneous Catalysis

Plastics are playing essential roles in the modern society. The majority of them enter environment through landfilling or discarding after turning into wastes, causing severe carbon loss and imposing high risk to ecosystem and human health. Currently, physical recycling serves as the primary method to reuse plastic waste, but this method is limited to thermoplastic recycling. The quality of recycled plastics gradually deteriorates because of the undesirable degradation in the recycling process. Under such background, catalytic upcycling, which can upgrade various plastic wastes into value-added products under mild conditions, has attracted recent attention as a promising strategy to treat plastic wastes. This Review highlights recent advances in the development of efficient heterogeneous catalysts and useful strategies for upcycling plastics into liquid hydrocarbons, arene compounds, carbon materials, hydrogen, and other value-added chemicals. The functions of catalysts and the reaction mechanisms are discussed. The key factors that influence the catalytic performance are also analyzed.

Carbon Graphitization: Towards Greener Alternatives to Develop Nanomaterials for Targeted Drug Delivery

Carbon nanomaterials have attracted great interest for their unique physico-chemical properties for various applications, including medicine and, in particular, drug delivery, to solve the most challenging unmet clinical needs. Graphitization is a process that has become very popular for their production or modification. However, traditional conditions are energy-demanding; thus, recent efforts have been devoted to the development of greener routes that require lower temperatures or that use waste or byproducts as a carbon source in order to be more sustainable. In this concise review, we analyze the progress made in the last five years in this area, as well as in their development as drug delivery agents, focusing on active targeting, and conclude with a perspective on the future of the field.

Upcycling Waste Polyethylene into Carbon Nanomaterial Via A Carbon-Grown-On-Carbon Strategy

Upcycling waste plastics (e.g., polyethylene (PE)) into value-added carbon products is regarded as a promising approach to address the increasingly serious waste plastic pollution and simultaneously achieve carbon neutrality. However, developing new carbonization technology routes to promote the oxidation of PE at low temperature and construct the stable crosslinking network remains challenging. Here, we propose a facile carbon-grown-on-carbon strategy using carbon black (CB) to convert waste PE into core/shell carbon nanoparticles (CN) in high yields at low temperature. The yield of CN remarkably rises when the heating temperature decreases or the dosage of CB grows. The obtained CN displays turbostratic structure and closely aggregated granular morphology with a size of ca. 80 nm. It is found, prior to the oxidation and carbonization of PE, CB forms a 3D network architecture in the PE matrix. More importantly, CB not only catalyzes the partial oxidation of PE to form PE macromolecular radicals and introduce oxygen-containing groups at low temperature in the early stage, but also favors for the construction of a stable crosslinking network in the latter stage. This work offers a facile sustainable strategy for chemical upcycling of PE into value-added carbon products without post-treatments or usage of metallic catalysts. This article is protected by copyright. All rights reserved.

Ocean plastics: environmental implications and potential routes for mitigation - a perspective

This review provides a current summary of the major sources and distribution of ocean plastic contamination, their potential environmental effects, and prospects towards the mitigation of plastic pollution. A characterization between micro and macro plastics has been established, along with a comprehensive discussion of the most common plastic waste sources that end up in aquatic environments within these categories. Distribution of these sources stems mainly from improper waste management, road runoff, and wastewater pathways, along with potential routes of prevention. The environmental impact of ocean plastics is not yet fully understood, and as such, current research on the potential adverse health effects and impact on marine habitats has been discussed. With increasing environmental damage and economic losses estimated at $US 1.5 trillion, the challenge of ocean plastics needs to be at the forefront of political and societal discussions. Efforts to increase the feasibility of collected ocean plastics through value-added commercial products and development of an international supply chain has been explored. An integrative, global approach towards addressing the growing ocean plastic problem has been presented.

Pyrolytic Conversion of Plastic Waste to Value-Added Products and Fuels: A Review

Plastic production has been rapidly growing across the world and, at the end of their use, many of the plastic products become waste disposed of in landfills or dispersed, causing serious environmental and health issues. From a sustainability point of view, the conversion of plastic waste to fuels or, better yet, to individual monomers, leads to a much greener waste management compared to landfill disposal. In this paper, we systematically review the potential of pyrolysis as an effective thermochemical conversion method for the valorization of plastic waste. Different pyrolysis types, along with the influence of operating conditions, e.g., catalyst types, temperature, vapor residence time, and plastic waste types, on yields, quality, and applications of the cracking plastic products are discussed. The quality of pyrolysis plastic oil, before and after upgrading, is compared to conventional diesel fuel. Plastic oil yields as high as 95 wt.% can be achieved through slow pyrolysis. Plastic oil has a heating value approximately equivalent to that of diesel fuel, i.e., 45 MJ/kg, no sulfur, a very low water and ash content, and an almost neutral pH, making it a promising alternative to conventional petroleum-based fuels. This oil, as-is or after minor modifications, can be readily used in conventional diesel engines. Fast pyrolysis mainly produces wax rather than oil. However, in the presence of a suitable catalyst, waxy products further crack into oil. Wax is an intermediate feedstock and can be used in fluid catalytic cracking (FCC) units to produce fuel or other valuable petrochemical products. Flash pyrolysis of plastic waste, performed at high temperatures, i.e., near 1000 °C, and with very short vapor residence times, i.e., less than 250 ms, can recover up to 50 wt.% ethylene monomers from polyethylene waste. Alternatively, pyrolytic conversion of plastic waste to olefins can be performed in two stages, with the conversion of plastic waste to plastic oil, followed by thermal cracking of oil to monomers in a second stage. The conversion of plastic waste to carbon nanotubes, representing a higher-value product than fuel, is also discussed in detail. The results indicate that up to 25 wt.% of waste plastic can be converted into carbon nanotubes.

Kinetics of Carbon Nanotubes and Graphene Growth on Iron and Steel: Evidencing the Mechanisms of Carbon Formation

Carbon formation on steel has recently become an active research area with several important applications, using either carbon nanotubes (CNTs) or graphene structures. The production of vertically aligned CNT (VACNT) forests with combined metals has been explored with important results. Detailed kinetics is the best approach to understand a mechanism. The growth behavior seems complex but can be simplified through the knowledge of the three more common alternative reaction mechanisms/routes. The time required to optimize the production and properties might be reduced. The mechanistic proposal reported in 1971 was better explained recently. The volcano shape Arrhenius plot reported is observed only when Fe, Co, and Ni are used as reaction catalysts. Other metals are catalytically active at higher temperatures, following a different route, which does not require surface catalysis decomposition of the reactive gas. C₂H₂ and low olefins react well, but CH₄ is not reactive via this surface catalysis route. Optimizing production of CNTs, research work is usually based on previous experience, but solid-state science-based studies are available.

Beyond Mechanical Recycling: Giving New Life to Plastic Waste

Increasing the stream of recycled plastic necessitates an approach beyond the traditional recycling via melting and re-extrusion. Various chemical recycling processes have great potential to enhance recycling rates. In this Review, a summary of the various chemical recycling routes and assessment via life-cycle analysis is complemented by an extensive list of processes developed by companies active in chemical recycling. We show that each of the currently available processes is applicable for specific plastic waste streams. Thus, only a combination of different technologies can address the plastic waste problem. Research should focus on more realistic, more contaminated and mixed waste streams, while collection and sorting infrastructure will need to be improved, that is, by stricter regulation. This Review aims to inspire both science and innovation for the production of higher value and quality products from plastic recycling suitable for reuse or valorization to create the necessary economic and environmental push for a circular economy.