Upcycling waste polyethylene terephthalate (PET) bottles into high-performance activated carbon for electrochemical desalination

Upcycling waste polyethylene terephthalate (PET) bottles has attracted intensive research interests. This simultaneously alleviates plastic pollution and achieves a waste-to-resource strategy. Waste PET water bottles were used to fabricate value-added activated carbon (AC) electrodes for capacitive deionization (CDI). The KOH activation temperature (greater than 700 °C) prominently affected the physi-chemical properties and desalination performance of PET-derived activated carbons (PET-AC). Profiting from a large Brunauer-Emmet-Teller specific surface area (1448 m2 g-1) with a good mesoporous structure (the ratio of the mesopore volume to the total pore volume was 41.3%), PET-AC-1000 (activated at 1000 °C) possessed a huge specific capacitance of 108 F g-1 for capacitive ion storage. Moreover, when utilized as the electrode material in single-pass CDI, PET-AC-1000 exhibited a maximum electrosorption capacity of 10.82 ± 0.11 mg g-1 and a low level of energy consumption (0.07 kWh mol-1), associated with good electrochemical charging-discharging cyclic stability. The results provide a promising facile approach to tackle the challenge of plastic pollution and promote the advancement of electrode materials for economic affordable and energy-efficient electrochemical desalination process, which meets the United Nations (UN) sustainable development goals (SDGs).

A waste-to-wealth conversion of plastic bottles into effective carbon-based adsorbents for removal of tetracycline antibiotic from water

Currently, plastic waste and antibiotic wastewater are two of the most critical environmental problems, calling for urgent measures to take. A waste-to-wealth strategy for the conversion of polyethylene terephthalate (PET) plastic bottles into value-added materials such as carbon composite is highly recommended to clean wastewater contaminated by antibiotics. Inspired by this idea, we develop a novel PET-AC-ZFO composite by incorporating PET plastic-derived KOH-activated carbon (AC) with ZnFe2O4 (ZFO) particles for adsorptive removal of tetracycline (TTC). PET-derived carbon (PET-C), KOH-activated PET-derived carbon (PET-AC), and PET-AC-ZFO were characterized using physicochemical analyses. Central composite design (CCD) was used to obtain a quadratic model by TTC concentration (K), adsorbent dosage (L), and pH (M). PET-AC-ZFO possessed micropores (d ≈ 2 nm) and exceptionally high surface area of 1110 m2 g-1. Nearly 90% TTC could be removed by PET-AC-ZFO composite. Bangham kinetic and Langmuir isotherm were two most fitted models. Theoretical maximum TTC adsorption capacity was 45.1 mg g-1. This study suggested the role of hydrogen bonds, pore-filling interactions, and π-π interactions as the main interactions of the adsorption process. Thus, a strategy for conversion of PET bottles into PET-AC-ZFO can contribute to both plastic recycling and antibiotic wastewater mitigation.

Application of Infrared Pyrolysis and Chemical Post-Activation in the Conversion of Polyethylene Terephthalate Waste into Porous Carbons for Water Purification

In this study, we compared the conversion of polyethylene terephthalate (PET) into porous carbons for water purification using pyrolysis and post-activation with KOH. Pyrolysis was conducted at 400-850 °C, followed by KOH activation at 850 °C for samples pyrolyzed at 400, 650, and 850 °C. Both pyrolyzed and post-activated carbons showed high specific surface areas, up to 504.2 and 617.7 m2 g-1, respectively. As the pyrolysis temperature increases, the crystallite size of the graphite phase rises simultaneously with a decrease in specific surface area. This phenomenon significantly influences the final specific surface area values of the activated samples. Despite their relatively high specific surface areas, pyrolyzed PET-derived carbons prove unsuitable as adsorbents for purifying aqueous media from methylene blue dye. A sample pyrolyzed at 650 °C, with a surface area of 504.2 m2 g-1, exhibited a maximum adsorption value of only 20.4 mg g-1. We propose that the pyrolyzed samples have a surface coating of amorphous carbon poor in oxygen groups, impeding the diffusion of dye molecules. Conversely, post-activated samples emerge as promising adsorbents, exhibiting a maximum adsorption capacity of up to 127.7 mg g-1. This suggests their potential for efficient dye removal in water purification applications.

Application of Activated Carbons Obtained from Polymer Waste for the Adsorption of Dyes from Aqueous Solutions

Plastic waste disposal is a major environmental problem worldwide. One recycling method for polymeric materials is their conversion into carbon materials. Therefore, a process of obtaining activated carbons through the carbonization of waste CDs (as the selected carbon precursor) in an oxygen-free atmosphere, and then the physical activation of the obtained material with CO2, was developed. Dyes such as methylene blue (MB) and malachite green (MG) are commonly applied in industry, which contaminate the water environment to a large extent and have a harmful effect on living organisms; therefore, adsorption studies were carried out for these cationic dyes. The effects of the activation time on the physicochemical properties of the activated materials and the adsorption capacity of the dyes were investigated. The obtained microporous adsorbents were characterized by studying the porous structure based on low-temperature nitrogen adsorption/desorption, scanning electron microscopy (SEM-EDS), elemental analysis (CHNS), Raman spectroscopy, X-ray powder diffraction (XRD), infrared spectroscopy (ATR FT-IR), thermal analysis (TG, DTG, DTA), Boehm's titration method, and pHpzc (the point of zero charge) determination. Moreover, adsorption studies (equilibrium and kinetics) were carried out. The maximum adsorption capacities (qm exp) of MB and MG (349 mg g-1 and 274 mg g-1, respectively) were identified for the obtained material after 8 h of activation. The results show that the use of waste CDs as a carbon precursor facilitates the production of low-cost and effective adsorbents.

Conversion of polyethylene terephthalate waste into high-yield porous carbon adsorbent via pyrolysis of dipotassium terephthalate

A method for conversion of polyethylene terephthalate (PET) waste into porous carbon material is proposed. The recycling of PET bottle waste includes the stages of low-temperature hydrolysis of the polymer and subsequent pyrolysis at 800 °C. To provide PET hydrolysis at ∼150 °C and atmospheric pressure, the polymer was pre-dissolved in dimethyl sulfoxide and then an aqueous solution of potassium hydroxide was added. The potassium terephthalate formed as a result of the alkaline hydrolysis of PET allows the carbon-containing precursor to be preserved for further activation to temperatures beyond 600 °C. The proposed method leads to the formation of a porous carbon material, increasing the yield of carbon residue to 25 wt%, which is higher compared to the yield of carbon residue in the direct pyrolysis of PET. The obtained porous carbon is characterized by graphite-like structure and specific surface area of ∼1100 m² g^-1. It has been shown that PET-derived carbon material can be used to remove pollutants from aqueous media. The adsorption properties of the carbon material were demonstrated by adsorption of methylene blue from an aqueous solution. The capacity of the carbon material was found to be 443 mg g^-1.

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.

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.

3,5-Dinitrosalicylic Acid Adsorption Using Granulated and Powdered Activated Carbons

Some nitroaromatic compounds are found in wastewater from industries such as the weapons industry or the wine industry. One of these compounds is 3,5-dinitrosalicylic acid (DNS), widely used in various tests and frequently found as an emerging pollutant in wastewater and to which the required attention has not been given, even though it may cause serious diseases due to its high toxicity. This study investigated the adsorption of DNS using granulated activated carbon (GAC) and powdered activated carbon (PAC) at different temperatures. The results show that in equilibrium, the adsorption takes place in more than one layer and is favorable for the removal of DNS in both GAC and PAC; The maximum adsorption capacity was obtained at 45 °C, with values of 6.97 mg/g and 11.57 mg/g, respectively. The process is spontaneous and exothermic. In addition, there was a greater disorder in the solid-liquid interface during the desorption process. The predominant kinetics using GAC (7.14 mg/g) as an adsorbent is Elovich, indicating that there are heterogeneous active sites, and when PAC (10.72 mg/g) is used, Pseudo-second order kinetics predominate, requiring two active sites for DNS removal. External mass transfer limitations are only significant in GAC, and ATR-FTIR studies in PAC demonstrated the participation of functional groups present on the adsorbent surface for DNS adsorption.

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.

Activated Carbons and Their Evaluation in Electric Double Layer Capacitors

This review presents a summary of the manufacturing of activated carbons (ACs) as electrode materials for electric double layer capacitors. Commonly used techniques of open and closed porosity determination (gas adsorption, immersion calorimetry, X-ray and neutrons scattering) were briefly described. AC production methods (laboratory and industrial) were detailed presented with the stress on advantages and drawbacks of each ones in the field of electrode materials of supercapacitor. We discussed all general parameters of the activation process and their influence on the production efficiency and the porous structure of ACs. We showed that porosity development of ACs is not the only factor influencing capacity properties. The role of pore size distribution, raw material origin, final carbon structure ordering, particles morphology and purity must be also taken into account. The impact of surface chemistry of AC was considered not only in the context of pseudocapacity but also other important factors, such as inter-particle conductivity, maximal operating voltage window and long-term stability.

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.

Carbonization: A feasible route for reutilization of plastic wastes

Plastics not only bring convenience and color to human life, but also bring endless troubles and disaster to our environment. Reutilization of plastic wastes is in favor of energy conservation and emission reduction, thereby is a significant pathway of plastic wastes disposal. Carbonization is an effective way of converting polymer precursors to valuable carbon materials for use in fields of energy conversion and storage, environmental protection and restoration. Here, we present a systematic multi-perspective overview of carbonization as a feasible route of reutilization of plastic wastes. A brief summary of conventional routes for plastic wastes is followed by a brief introduction of carbonization for converting plastics to carbon materials. Special emphasis is paid on the carbonization pathways and mechanisms of common plastics. Finally, the feasibility, application prospect and challenge of carbonization as one method of reutilization of plastic wastes are proposed. By presenting a consolidated information source on different carbonization mechanisms, this review provides a valuable guideline for reutilization of plastic wastes by carbonization.

Effect of bifunctional acid on the porosity improvement of biomass-derived activated carbon for methylene blue adsorption

Activated carbon (AC) with high specific surface area was prepared by using bifunctional H₃PO₄ agent, which led to dehydrating and activation effects through hydrothermal pretreatment and subsequent pyrolysis process. N₂ adsorption and desorption isotherms of AC showed a high BET surface area of 2434 m² g^-1 and a total volume of pores (V_T) of 2.0447 m³ g^-1 for AC. The morphology and the chemical components of hydrochar and AC were characterized by scanning electron microscopy and Fourier transform infrared spectroscopy, which indicated that H₃PO₄ was benefitting for the formation of porous structure of AC. Subsequently, the effect of H₃PO₄ in hydrothermal pretreatment and activation process was investigated by comparative experiments. The removal and adsorption of methylene blue (MB) dye with different concentrations onto the AC were studied. The monolayer equilibrium adsorption capacity was 644 mg g^-1, showing that AC has good adsorption qualities for methylene blue (MB). The adsorption balance data of MB on AC was best fitted to the Redlich-Peterson model. The adsorption kinetic data fit better to the pseudo-first-order model at low MB concentration, and the pseudo-second-order and Elovich models fit better when the MB concentration was rising.