No abstract

The aim of this research was to investigate how post treatment modification, such as those with sodium hydroxide or urea, can influence the capacity of activated carbon (AC) for phenolic compounds removal from liquid media. The ACs modification was performed using urea impregnation followed by pyrolysis at high temperature. With all ACs used, this treatment induced a pore volume increase, a mean pore size broadening, an increase in the point of zero charge and also in the basic character. The modification with sodium hydroxide brings to light the influence of the precursor nature as the achievements are really diverse. With the ACs obtained from PET, a pore volume and mean pore size reduction occurred, with the AC-cloth no textural effect was observed and with the AC obtained from cork, an enlargement of the mean pore size and an increase of the pore volume were confirmed. The difference in the acidic/basic character exhibited by the modified ACs was in agreement with the presence of acidic/basic superficial groups identified by FTIR. The textural and chemical properties of the ACs affect in a direct way the phenolic compounds removal capacity. Particularly, those modified with urea, which exhibited a superior removal capacity for both phenolic compounds.

No abstract

This work presents a first approach concerning the use of Tectona Grandis tree sawdust (from East Timor) for high activated carbon production, by physical activation with carbon dioxide at different temperatures. The activated carbons (AC) obtained exhibit a well-developed porous structure with a pore size distribution varying from micro to mesopores. Selected AC was successfully evaluated for pesticide removal, specific to 4-chloro-2-methylphenoxyacetic acid, from the liquid phase. The results presented are very promising, allowing to establish that Tectona Grandis sawdust is as an excellent precursor for the basic AC production and allow to expect good performance of theses adsorbents on the removal of a broad range of pollutants. It should also be noted that, this achievement is very relevant for developing countries, such East Timor, where Tectona Grandis sawdust is available and may constitute a source of income creating a handle to the technical and industrial development of this region.

Os carvões activados (AC) têm sido preparados a partir de uma diversidade de precursores, por activação física e química a diferentes temperaturas, permitindo a obtenção de adsorventes com volumes microporosos, tamanho médio de poros e química superficial muito diversificados. A optimização de algumas das suas propriedades reporta-se quase sempre a um aumento do volume microporoso ou a um ajuste do tamanho médio dos poros, mas raramente são consideradas outras propriedades de relevo como o aumento do rendimento de carbonização ou a estabilidade térmica.Os AC preparados a partir do PEEK (poli-éter-éter-cetona), por activação física num intervalo de temperaturas entre 873 e 1173 K, apresentavam um rendimento de carbonização superior a 50%. A caracterização textural através da adsorção de N 2 a 77 K, permitiu verificar que estes possuem um elevado volume microporoso (entre 0,33 e 1,27 cm 3 g -1 ), e um tamanho médio de poro variável (entre 0,88 e 2,17 nm). A análise termogravimétrica permitiu aferir da grande estabilidade térmica destes AC. Para uma temperatura de 1173 K, estes apresentam uma perda de massa inferior a 10%, pondo em evidencia uma possível aplicação na remoção de gases ou vapores em processos industriais que decorram a elevadas temperaturas.A activação química é quase sempre referida como possibilitando a obtenção de AC com um elevado rendimento e com uma porosidade mais larga, quando comparados com os AC preparados por activação física. No decorrer deste trabalho, os AC obtidos por activação física a partir do PEEK, com CO 2 a 1173 K, possuem um volume microporoso superior, um tamanho de poro mais largo e uma estabilidade térmica superior quando comparados com os AC preparados por activação química. p/p PK-9-0 PK-9-12 PK-9-33 PK-9-55 PK-9-65 PK-9-74

No abstract

For the activated carbon (AC) production, we used the most common industrial and consumer solid waste, namely polyethyleneterephthalate (PET), alone or blended with other synthetic polymer such polyacrylonitrile (PAN). By mixing PET, with PAN, an improvement in the yield of the AC production was found and the basic character and some textural and chemical properties were enhanced. The PET-PAN mixture was subjected to carbonisation, with a pyrolysis yield of 31.9%, between that obtained with PET (16.9%) or PAN (42.6%) separately. The AC revealed a high surface area (1400, 1230 and 1117 m g) and pore volume (0.46, 0.56 and 0.50 cm g), respectively, for PET, PAN and PET-PAN precursors. Selected ACs were successfully tested for 4-chloro-2-methylphenoxyacetic acid (MCPA) and diuron removal from the liquid phase, showing a higher adsorption capacity (1.7 and 1.2 mmol g, respectively, for MCPA and diuron) and good fits with the Langmuir (PET) and Freundlich equation (PAN and PET-PAN blend). With MCPA, the controlling factor to the adsorption capacity was the porous volume and the average pore size. Concerning diuron, the adsorption was controlled essentially by the external diffusion. A remarkable result is the use of different synthetic polymers wastes, as precursors for the production of carbon materials, with high potential application on the pesticides removals from the liquid phase.

Highly efficient low cost carbon adsorbents were prepared from synthetic polymers mixture, such as polyethyleneterephthalate (PET) and polyacrylonitrile (PAN), by chemical activation, with potassium hydroxide or potassium carbonate, at 1073 K. Mixtures polymers carbon activation is more effective with KOH than with K2CO3, since the apparent surface area and the micropore volume were always higher on those prepared with KOH. The activated carbons (ACs) obtained presented a high thermal stability, a basic character and a very high apparent surface area (between 1206 and 2828 m2 g-1), micropore volume (between 0.35 and 1.38 cm3 g-1), with mean pore sizes ranging the supermicropores region. These ACs were successfully tested on 2,4-dichlorophenoxyacetic acid (2,4-D) and 4-chloro-2-methylphenoxyacetic acid (MCPA) removals from the liquid phase. The results achieved are very promising, as the adsorption capacity of these AC is higher than that obtained with commercial AC used for this end.