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Adsorpcja czerwieni kwasowej 114 i fuksyny zasadowej z roztworów wodnych na mezoporowatych materiałach węglowych

Jedynak K., Repelewicz M.

Inżynieria i Ochrona Środowiska

2016

T. 19, nr 2

227--239

In this work the adsorption of basic fuchsin and acidic red on mesoporous carbon materials C-KS and C-KC was examined. Carbon materials were obtained applying softtemplating method in environment of hydrochloric acid and citric acid. For examined adsorbents low-temperature nitrogen adsorption isotherms were determined, used next for porous structure parameters calculations. Obtained isotherms can be categorized as IV type according to IUPAC classification. Studied adsorbents have large surface area SBET: 650 m2/g (C-KS) and 760 m2/g (C-KC); large total pore volume Vt: 0.59 cm3/g (C-KC) and 0.89 cm3/g (C-KS). Mesopores participation in total porosity of examined carbons is 83% for C-KS and 71% for C-KC. This confirms that examined carbons are mesoporous materials with significant advantage of mesoporosity over microporosity. Mesopores dimension, for maximum of distribution function (in the mesopores range) were estimated using Kruk- Jaroniec-Sayari (KJS) method. Mesopores dimension for C-KC carbon is 6 nm and for C-KS carbon is 8.7 nm. Adsorbates concentrations, before and after adsorption, were estimated using spectrophotometric method. Adsorption studies were carried out at 25°C. The adsorption equilibrium for studied mesoporous systems: carbon material - dye solution, was achieved after 8 hours. Studies of the adsorption process kinetics showed that in three cases adsorption kinetics proceeded in compliance with model of apparent II order of reaction: C-KC (acidic red 114) and C-KS (basic fuchsin and acidic red 114). In one case adsorption kinetics proceeded in compliance with model of apparent I order of reaction: C-KC (basic fuchsin). Obtained adsorption isotherms were applied to Langmuir and Freundlich equations. Adsorption process of fuchsin on both examined carbons and adsorption of acidic red on C-KC carbon was carried out in agreement with adsorption model described by Langmuir equation. However, acidic red adsorption on C-KC carbon is better described by Freundlich adsorption model. Adsorption abilities, of examined mesoporous carbon materials, are significantly higher in relation to fuchsin than to acidic red 114; e.g. for C-KS adsorbent, it is 1.289 mg/g (acidic red 114) and 10.661 mg/g (fuchsin). Applying K constant value from Langmuir equation, free enthalpy >G was calculated. Obtained values change in range of –25 to –34 kJ/mol. Negative values of >G show that studied adsorption process is spontaneous.

Celem pracy było zbadanie kinetyki adsorpcji oraz wyznaczanie izoterm adsorpcji czerwieni kwasowej 114 i fuksyny zasadowej z roztworów wodnych na zsyntezowanych metodą miękkiego odwzorowania mezoporowatych materiałach węglowych C-KS oraz C-KC. W trzech przypadkach kinetyka adsorpcji przebiegała zgodnie z modelem pseudo II - rzędu: C-KC (czerwień kwasowa 114) oraz C-KS (czerwień kwasowa 114 i fuksyna zasadowa), w jednym zgodnie z modelem pseudo I - rzędu: C-KC (fuksyna zasadowa). Równowaga adsorpcyjna ustaliła się we wszystkich badanych przypadkach po 8 h. Adsorpcja w warunkach równowagowych została opisana za pomocą równań Langmuira i Freundlicha. W trzech przypadkach adsorpcja barwników zachodziła zgodnie z modelem Langmuira, w jednym opisana została przez równanie Freundlicha - C-KC (czerwień kwasowa 114).

Mezoporowate węgle : synteza i właściwości

Choma J., Jaroniec M., Zawiślak A.

Wiadomości Chemiczne

2008

[Z] 62, 5-6

373-402

Porous carbonaceous materials are widely used in everyday life and industry because they possess very high surface area, pore volume and unique physicochemical properties, including high adsorption capacity for many organic molecules. Porous carbons have been prepared for hundreds of years, however traditional methods used for their preparation allow rather for a limited control of pore sizes and volumes of micropores and mesopores, which in fact results in a broad distribution of pore sizes. The most common applications of porous carbons include adsorption, catalysis, gas storage, purification of air and water and electrochemical applications [1,2]. This article presents a survey of literature devoted to new methods of synthesis and characterization of mesoporous carbonaceous materials. One of the major topics reviewed in this article is the synthesis of ordered mesoporous carbons (OMC) with a help of ordered mesoporous silicas (OMS) (Fig. 1) [7, 25], colloidal silica (Fig. 2 and 3) [11, 29, 40, 59] and colloidal silica crystals as hard templates [57]. In addition to the synthesis of OMC, this paper presents an overview of physicochemical properties of OMC, especially adsorption properties. The exemplary characteristics, which include BET surface area, pore volume and pore size distribution, are provided for selected carbon materials [29]. A special emphasis was placed on the method, which employs monolithic siliceous templates obtained by pressing colloidal silica followed by their impregnation with oxalic acid (catalyst), resorcinol and formaldehyde (carbon precursors), polymerization of carbon precursors, carbonization and template removal (Fig. 4) [60]. This method affords carbons with uniform spherical mesopores as well as carbon composites with inorganic nanoparticles (e.g., silver), which after additional activation (e.g., with KOH) give micro and mesoporous carbons with superior structural characteristics. A set of basic parameters for one of these carbons includes: the diameter of spherical pores of 26,8 nm, the BET surface area of 1300 m2/g and the single-point (total) pore volume of 4,3 cm3/g; however, only 0,19 cm3/g of the total pore volume belongs to micropores. After KOH activation the volume of micropores increased to 0,8 cm3/g, the BET surface area increased to 2300 m2/g, but the volume of mesopores was reduced to 1,8 cm3/g [60]. Another important topic reviewed in this article is the synthesis of mesoporous carbons from thermosetting polymers (e.g., phenolic resins) used as carbon precursors in the presence of block copolymers used as soft templates (Fig. 5) [29, 78, 79]. This new synthetic strategy affords mesoporous carbons in the form of monoliths, fibers and films and permits to scale up this process. Additional activation of the resulting carbons with KOH (Fig. 7) affords micro and mesoporous carbons with high surface area and large volumes of both types of pores, improving significantly their adsorption properties. A set of basic parameters for one of the soft-templated carbons includes: the BET surface area of about 500 m2/g, the total pore volume of 0,7 cm3/g and the pore width of about 9,7 nm. After KOH activation the BET surface area increased to about 900 m2/g, the total pore volume and the volume of micropores increased to 0,9 cm3/g and 0,22 cm3/g, respectively [79]. Novel ordered mesoporous carbons are not only attractive materials for various advanced applications but also for the development of accurate methods for characterization of porous solids. This article shows that in addition to such important characterization methods as transmission electron microscopy (TEM), scanning electron microscopy (SEM), and powder X-ray diffraction (XRD), adsorption of nitrogen, argon and other adsorbates (Fig. 8) is one of the key methods for the pore structure analysis, especially for the assessment of global properties of porous materials.