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

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

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

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

Ordered mesoporous silica materials for protein adsorption

Lysozyme and BSA were used, as model proteins of considerably different dimensions, in order to evaluate the influence of the distinct pore structural characteristics of three types of ordered mesoporous silica materials (MCF, SBA-15 and MCM-41) on protein adsorption. Characterisation by X ray diffraction and nitrogen adsorption at 77K revealed the typical pore structural features of each type of material. The maximum of the pore size distributions indicated that the width of the windows of MCF (2) (mesitylene/P123 of 2) was larger than the pore diameter of the unidirectional tubular pores of SBA-15. All the materials presented similar small external surface areas but high pore volumes, with that of MCF (2) being the highest. The adsorption of lysozyme at pH=8 increased in the order MCM-41<< SBA-15< MCF (2), and the uptakes were well above those of BSA at pH=5. Although BSA is not completely excluded from the mesopores of SBA-15 and MCF (2), as happens with MCM-41, the adsorption occurs to a very limited extent. The overall behaviour of these SBA-15 and MCF (2) samples was not significantly different and both revealed potential for the separation of these proteins

Adsorption of MCPA on different activated carbons

Pesticides play an important role in the success of modern farming and food production but their use increases the residue levels in soils and waters and has been a public concern because of the potential risk to human health and the environment. Pesticides are generally applied in larger amounts than those needed for the pest control and they are swept away by transport processes such as leaching. Liquid phase adsorption is one of the mechanisms which decrease solute mobility and thus could be suitable for assessing the capacity of materials to adsorb pollutants. Several treatment processes are available to remove inorganic and organic pollutants (including herbicides) from aqueous or gaseous phase, with adsorption on activated carbons being often considered to be highly efficient, easy to use and one of the most economical [1]. In particular, the concentration of compounds belonging to the phenoxyacid group has increased and a worrying fact is that these compounds are more often detected in both superficial and underground waters. MCPA was selected because it is considered highly carcinogenic, its biological degradation is very slow and it has been detected in natural and drinking waters with contamination levels up to 0.4 µg/L [2]. In Portugal, for example, permitted levels have been decreased to only 0.1 µg/L for any one pesticide or a total of 0.5 µg/L for all [3]

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

Loop Quantum Gravity: An Inside View

This is a (relatively) non -- technical summary of the status of the quantum dynamics in Loop Quantum Gravity (LQG). We explain in detail the historical evolution of the subject and why the results obtained so far are non -- trivial. The present text can be viewed in part as a response to an article by Nicolai, Peeters and Zamaklar [hep-th/0501114]. We also explain why certain no go conclusions drawn from a mathematically correct calculation in a recent paper by Helling et al [hep-th/0409182] are physically incorrect.Comment: 58 pages, no figure