Impact of the use of co-adjuvants agents during chemical activation on the performance of activated carbons in the removal of 4-chloro-2-methyl-phenoxyacetic acid

The present work discusses the influence of additives, designated as co-adjuvants agents of the chemical activation, containing nitrogen on their structure, on the activated carbons (ACs) produced from waste of polyethylene terephthalate (PET) and cork by chemical activation, with KOH, at 973 K. The co-adjuvants agents used were urea, 2-chloro-4,6-diamino-1,3,5-triazine, (2-hydroxyethyl) urea and polyethylenimine. The ACs, produced from PET, only activated with KOH presented a porous volume of 0.53 cm3 g-1. The chemical activation of PET with KOH and urea, or 2-chloro-4,6-diamino-1,3,5-triazine or (2-hydroxyethyl) urea allows obtaining ACs with a porous volume upper than 0.91 cm3g-1. The same improvement (porous volume higher than 0.93 cm3g-1) was achieved with cork, with urea or polyethylenimine. On all ACs produced with the four co-adjuvants agents, an increment in the nitrogen content was very noticeable. The high thermal stability of these ACs allows inferring, that the nitrogen was directly connected to the ACs array, and not only retained on the surface. These ACs were successfully tested on 4-chloro-2-methyl-phenoxyacetic acid (MCPA) removals from the aqueous medium, with removal percentages ranging from 65% in solutions containing 2.50 mmol L-1 to 100% in solutions with concentrations lower than 0.25 mmol L-1. Five ACs had an MCPA adsorption capacity greater than 3.7 mmol g-1, meanwhile, the highest value found in the literature was 2.99 mmol g-1 on the commercial AC-GAB (Spaltro et al., 2018)

Adsorption of pesticides onto activated carbons from wood composites

A series of activated carbon was produced from particleboard and medium-density fibreboard monoliths, which are waste originated from the industry, and then characterized and evaluated for potential application for phenoxyacetic acids removals, such 2,4-dichlorophenoxyacetic acid (2,4-D), 2-methyl-4-chlorophenoxy acetic acid (MCPA) and 3-(3,4-dichlorophenyl)-1,1-dimethylurea (diuron), from the liquid phase. All AC retain the shape of the precursor, and displays a microporous structure well-developed, reaching 0.58 cm 3 g -1. The adsorption isotherms for three pesticides were obtained in the optimal conditions and the AC with high superficial area and micropore volume exhibited better performance, allowing to state that, this AC could be a great substitute of those habitually used for this purpose. The pesticides adsorption data were linearized using the Langmuir and Freundlich equation, being the first a very good fit to the experimental data

Designing activated carbons from natural and synthetic raw materials for pollutants adsorption

Over the last decades the literature has shown the possibility of producing activated carbons (AC) from a wide variety of raw materials, and to use them as one of the most environmentfriendly solutions for waste disposal [1]. Simultaneously, it has been shown that the adsorption of pollutants from different sources by activated carbons is one of the most efficient techniques for remediating or solving this kind of problem [2]. In this context, phenolic compounds represent one of the most important classes of pollutant present in the environment [3]. In this perspective, we present a study involving the production of AC from cork (Quercus suber L.), PEEK (polyetheretherketone) wastes or granulated recycled PET (polyethyleneterephthalate) and their applicability for the adsorption of phenolic compounds from the liquid phase. All samples were characterised in relation to their structural properties and chemical composition, by different techniques, including nitrogen adsorption at 77 K, elemental analysis (C, H, N, O and S) and point of zero charge (PZC). The activated carbons produced demonstrated high adsorption capacities both in the gas and liquid phase as exemplified by N2 and phenolic compounds adsorption experiments. Based on the structural and chemical properties, and on the kinetic and equilibrium studies of liquid phase adsorption, it is possible to conclude that it is the porous volume of the ACs that predominantly controls the process of phenolic compounds adsorption

Using Different Co-Adjuvant Activating Agents to Improve Activated Carbon Adsorption Capacities

Activated carbon (AC) has proved to be an effective adsorbent for the removal of an assortment of organic and inorganic pollutants from aqueous or gaseous media. However, the pursuit for more effective and cheaper AC is still very active and a diversity of textural and chemical treatments are described as a way to expand their applications. It is well known that the surface area and surface chemistry of AC strongly affect their adsorption capacity [1-3]. In particular, an increase in the nitrogen content has been related to an increase of the basic character and also to the development of the porous structure. In most published work this was achieved through an AC post treatment, including either a reaction with nitrogen containing reagents, such as ammonia, nitric acid, or a diversity of amines. However, the AC prepared directly from a nitrogen rich precursor through a physical or chemical activation is referred to as presenting the best characteristics, namely high nitrogen content, high basic character, low nitrogen leaching and also a good thermal stability [4]. To improve the AC adsorption capacities for acidic pesticide removal from the aqueous phase, we intend to improve the porous structure and introduce nitrogenated groups directly into the AC matrix, using different co-adjuvant activating agents as a nitrogen source, by chemical activation, with potassium hydroxide, of cork or poly(ethyleneterephthalate) (PET) precursors

Activated Carbons Prepared from Natural and Synthetic Raw Materials with Potential Applications in Gas Separations

A carbon molecular sieve for the purification of a gas mixtures containing O2, N2 and CO2, CH4 was produced from a waste granulated PET by means of a single carbonisation step at 973 K. Activated carbon materials presenting good adsorption capacity and some selectivity for O2/N2 and CO2/CH4 were prepared from granulated PET and cork oak with pore mouth narrowing using CVD from benzene. The diffusion coefficients of O2, N2, CO2 and CH4 in these materials were calculated and are comparable to published values determined on Takeda 3A and on a carbon molecular sieve prepared from PET textile fibres by means of carbonisation and subsequent CVD with benzene. However, the selectivities were not quite as good as those given by Takeda 3A. However, taking into account that this is a first attempt at producing CMS from PET, the results are encouraging, and it is to be expected that further development of the experimental procedure will result in new materials with improved performanc

Hydrothermal stability of ordered mesoporous titanosilicate materials prepared at room temperature

A study of hydrothermal stability, performed in boiling water under static conditions, of MCM-41 materials containing different titanium content, prepared by direct synthesis at ambient temperature and pressure, using tetraethoxysilane, titanium ethoxide and octadecyltrimethylammonium bromide is presented. The behaviour is compared with pure silica grades prepared by a similar procedure. The samples were characterised by X-ray diffraction, adsorption of nitrogen at 77K and diffuse reflectance UV–Vis spectroscopy. It was found that the stability improves as the amount of titanium increases and that Ti-MCM-41 samples prepared with Si/Ti≤50 are significantly stable. After 12h in boiling water the pore size uniformity was practically maintained and only a small decrease in pore volume (5-9%), total surface area (2-7%) and mesopore width (3%) and a slight increase in pore wall thickness (3-6%) occurred. In contrast, some degradation of the MCM- 41 structure for the pure silica and the lower Ti content (Si/Ti=100) samples was observed with the effect being less pronounced for the latter. The higher hydrothermal stability of titanium substituted samples is probably correlated with a higher degree of polymerisation of the pore walls and with the presence of extra framework titanium

Porosity of clay catalysts for biomass conversion: a comparative study

A detailed description of the porosity, in particular of microporosity, was reported and allowed a clear comparison of the effects on the porosity of chemical treatments on clays from the Source Clays Repository (USA) and SD clay from Porto Santo (Portugal)

Stability of clay-based catalysts in contact with water vapour

The search for cleaner processes is one of the major challenges in modern chemical industries. In this context clay derived materials are environmentally friendly catalysts that can be easily tailored to optimize their catalytic activity for a precise reaction of interest. Furthermore, clay-based catalysts can be easily separated, recovered and reused and their versatility, low cost, high catalytic activity and/or selectivity render them very attractive materials. Considering that the stability towards water vapour is a crucial aspect for catalytic performance and reuse of the catalysts, we present a study of the pore structure stability, in the presence of water vapour, of clay catalysts prepared by acid activation with HCl solutions and ion-exchange with sodium, aluminium and iron, from a natural clay collected at Serra de Dentro (Porto Santo Island, Portugal) [1]. For elucidating the influence of water vapour on the pore structure stability, water vapour adsorption- -desorption isotherm, at 298 K, was determined on each sample by gravimetric method as well as n-pentane adsorption−desorption isotherms, at 298 K, which were determined before and after the corresponding water adsorption-desorption isotherms. Prior to the measurements, the samples were outgassed during 5 h at 473 K and the adsorptives were outgassed by repeated freeze–thaw cycles. The results to be reported in the communication allow us to state that, upon contact with water vapour, the less acid activated catalysts suffered some reduction in pore volume reflecting changes in the pore structure, while the more acid activated catalysts and those prepared by ion-exchange presented excellent stability upon one cycle of water vapour adsorption-desorption. The results are corroborated by nitrogen adsorption-desorption isotherms determined, at 77 K, before and after the water and n-pentane adsorption-desorption measurements

Use of dirty plastic waste as precursors for activated carbon production – a contribution to the circular economy

The production of activated carbons (ACs) from dirty plastic wastes derived from the mechanical/biological treatment of urban solid wastes, disposable plastics and plastics used in agriculture is reported. The use of these precursors is innovative and contributes to the circular economy by the valorization of dirty plastics that are usually disposed in landfills. ACs were produced by physical activation, with air or CO2, and chemical activation, with KOH or K2CO3. ACs presented a BET (N2) area and pore volume up to 723 m2/g and 0.32 cm3/g. Selected samples were tested for the 2,4-dichlorophenoxyacetic acid (MCPA) and 4-chloro-2-methyl-phenoxyacetic acid (2,4-D) removal from the liquid phase. PB-K2CO3-1:1–700 presented an apparent maximum adsorption capacity of 245 and 289 mg g−1 for MCPA and 2,4-D, respectively.Fundo Ambiental Portuguê

Dealing with plastic waste from agriculture activity

The increase in agricultural production and food quality has forced the growing useof plastics in various activities. The plastic wastes are partially recycled in or outside Portugal;nevertheless, the contaminated wastes are sent to landfill. It is crucial to consider new models fortheir valorization at a regional level and from a circular economy perspective. In the scope of the Placarv õ es project, a study was elaborated, which included the types and quantities of plastics used in the irrigation area of the Alqueva Dam, in southern Portugal. The crops that use the most plastic are intensive olive groves, almonds, and table grapes, which represent more than 91% of total plastic waste. The production of activated carbons (ACs) is a solution to avoid plastics landfill. ACs wereproduced from plastic used on food packaging (PB-Samples) and sheeting film (PS-Samples) byactivation with K 2 CO 3 . ACs presented well-developed textural properties (PB-K 2 CO 3 -1:1–700 andPS-K 2 CO 3 -1:1–700 exhibited a volume of 0.32 and 0.25 cm 3 g − 1 and an apparent surface area of 723 and 623 m 2 g − 1 , respectively). Both ACs performed very well concerning four pesticide removals from the liquid phase. This solution is very promising, such these ACs could be applied in effluent treatments on a large scale