A novel and inexpensive method for producing activated carbon from waste polyethylene terephthalate bottles and using it to remove methylene blue dye from aqueous solution

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.

Black carbon derived PET plastic bottle waste and rice straw for sorption of Acid Red 27 dye: Machine learning approaches, kinetics, isotherm and thermodynamic studies

This study focuses on the probable use of PET waste black carbon (PETWBC) and rice straw black carbon (RSBC) as an adsorbent for Acid Red 27 (AR 27) adsorption. The prepared adsorbent is characterized by FE-SEM and FT-IR. Batch adsorption experiments were conducted with the influencing of different operational conditions namely time of contact (1-180 min), AR 27 concentration (5-70 mg/L), adsorbent dose (0.5-20 g/L), pH (2-10), and temperature (25-60°C). High coefficient value [PETWBC (R2 = 0.94), and RSBC (R2 = 0.97)] of process optimization model suggesting that this model was significant, where pH and adsorbent dose expressively stimulus removal efficiency including 99.88, and 99.89% for PETWBC, and RSBC at pH (2). Furthermore, the machine learning approaches (ANN and BB-RSM) revealed a good association between the tested and projected value. Pseudo-second-order was the well-suited kinetics, where Freundlich isotherm could explain better equilibrium adsorption data. Thermodynamic study shows AR 27 adsorption is favourable, endothermic, and spontaneous. Environmental friendliness properties are confirmed by desorption studies and satisfactory results also attain from real wastewater experiments. Finally, this study indicates that PETWBC and RSBC could be potential candidates for the adsorption of AR 27 from wastewater.

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.

A review on production and application of activated carbon from discarded plastics in the context of 'waste treats waste'

In the post-COVID scenario, the annual increase in plastic waste has taken an upsurge due to the disposal of plastic masks, gloves and other protective equipment. To reduce the plastic load ending up in landfills and oceans or dumped at roadsides, the potential of using plastic polymers in different sectors has been investigated over the years leading to their potential application in pavement laying, concrete industry, fuel generation and production of carbon-based compounds among which activated carbons (AC) is a prime example. As one of the most recommended adsorbents for removing contaminants from water and adsorbing greenhouse gases, AC creates a potential sector for using discarded plastic to further treat pollutants and approach closer to a circular economy for plastics. This paper analyses the production process, the effect of production parameters on AC characteristics and properties that aid in adsorption. The interdependence of these factors determines the surface area, porosity, relative micropore and mesopore volume, thereby defining the utility for removing contaminant molecules of a particular size. Furthermore, this work discusses the application of AC along with a summary of the earlier works leading to the existing gaps in the research area. Production costs, formation of by-products including toxic substances and adsorbate selectivity are the major issues that have restricted the commercial application of this process towards its practical use. Research aimed at valorization of plastic waste into ACs would minimize the solid waste burden, along with treating other pollutants.

Conversion of Plastic Waste to Carbon-Based Compounds and Application in Energy Storage Devices

At present, plastic waste accumulation has been observed as one of the most alarming environmental challenges, affecting all forms of life, economy, and natural ecosystems, worldwide. The overproduction of plastic materials is mainly due to human population explosion as well as extraordinary proliferation in the global economy accompanied by global productivity. Under this threat, the development of benign and green alternative solutions instead of traditional disposal methods such as conversion of plastic waste materials into cherished carbonaceous nanomaterials such as carbon nanotubes (CNTs), carbon quantum dots (CQDs), graphene, activated carbon, and porous carbon is of utmost importance. This critical review thoroughly summarizes the different types of daily used plastics, their types, properties, ways of accumulation and their effect on the environment and human health, treatment of waste materials, conversion of waste materials into carbon-based compounds through different synthetic schemes, and their utilization in energy storage devices particularly in supercapacitors, as well as future perspectives. The main purpose of this review is to help the targeted audience to design their futuristic study in this desired field by providing information about the work done in the past few years.

Removal of lead from aqueous solutions using three biosorbents of aquatic origin with the emphasis on the affective factors

The biosorptive potentials of three aquatics-based biosorbents, including shells of a bivalve mollusk and scales of two fish species for Pb removal from aqueous solutions were evaluated, for the first time. A Box-Behnken design with the response surface methodology was used to investigate the effects of the seven important variables (contact time, temperature, initial concentration, dosage, size, salinity and pH) on the sorption capacity of the sorbents. Among the seven studied factors, the effects of biosorbent dosage, initial concentration and pH were significant for all the response variables, while biosorbent size was not significant for any of the responses. The initial concentration was the most influential factor. The presence of Pb ions on the surfaces of the biosorbents after the adsorption was clearly confirmed by the SEM-EDX and XRF analyses. The maximum sorption capacities of the biosorbents were comparable to the literature and the descending order was as follows: scales of Rutilus kutum and Oncorhynchus mykiss and the shells of Cerastoderma glaucum. The isotherm studies revealed Langmuir model applicability for the Pb adsorption by R. kutum and O. mykiss scales, while Freundlich model was fitted to the adsorption C. glaucum shells.

Microporous activated carbon developed from KOH activated biomass waste: surface mechanistic study of methylene blue dye adsorption

In this work, sugarcane bagasse waste (SBW) was used as a lignocellulosic precursor to develop a high-surface-area activated carbon (AC) by thermal treatment of the SBW impregnated with KOH. This SBW activated carbon (SBWAC) was characterized by crystallinity, porosity, surface morphology and functional groups availability. The SBWAC exhibited Type I isotherm which corresponds to microporosity with high specific surface area of 709.3 m²/g and 6.6 nm of mean pore diameter. Further application of SBWAC as an adsorbent for methylene blue (MB) dye removal demonstrated that the adsorption process closely followed the pseudo-second order kinetic and Freundlich isotherm models. Conversely, a thermodynamic study revealed the endothermic nature and spontaneity of MB dye adsorption on SBWAC with high acquired adsorption capacity (136.5 mg/g). The MB dye adsorption onto SBWAC possibly involved electrostatic interaction, H-bonding and π-π interaction. This work demonstrates SBW as a potential lignocellulosic precursor to produce high-surface-area AC that can potentially remove more cationic dyes from the aqueous environment.

Adsorption of bisphenol A by activated carbon developed from PET waste by KOH activation

This study deals with the preparation of activated carbon (AC) from poly(ethylene terephthalate) (PET) waste and with the physicochemical characterization of AC and its use as adsorbent of bisphenol A (BPA) in aqueous solution. AC was prepared by chemical activation with KOH and by physical activation in steam. The activation with KOH was carried out by impregnation first of PET by wet and dry routes at the PET/KOH weight ratios of 1:1, 1:3, and 1:5 and by carbonization then of the resulting products at 850 °C for 2 h in N₂ atmosphere. The activation in steam was performed by heating at 900 °C for 1 h. The ACs were characterized by N₂ adsorption at - 196 °C, mercury porosity, mercury density measurements, FT-IR spectroscopy, and measurement of pH of the point of zero charge (pH_pzc). The activation yield is 58.4-49.4% with KOH in aqueous solution, 75.8-23.9% with solid KOH, and 5.9% with steam. Using solid KOH, greater developments of a more heterogeneous porosity with increasing impregnation PET/KOH ratio are achieved. For SK1:5, S_BET is 1990 m² g^-1 and the pore volumes are 0.71 cm³ g^-1, micropores; 0.81 cm³ g^-1, mesopores; and 1.77 cm³ g^-1, macropores. The data of BPA adsorption fit better to the Ho and Mckay second order kinetic model than to the Lagergren first-order kinetic model and to the Langmuir equation than to the Freundlich equation. From the kinetic and thermodynamic standpoints, the adsorption process of BPA is more favorable for SK1:5.

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.