Progress and perspectives for the use of pillared clays as adsorbents for organic compounds in aqueous solution

The world is faced with several problems as regards water pollution. This is due to several factors, including the discharge of effluents into the environment with no prior treatment. This wastewater, therefore, contains significant levels of pollutants, including numerous toxic organic contaminants and others that are similarly undesirable. Several studies have attempted to find ways of removing wastewater contaminants using pillared interlayered clays (PILC) as adsorbents. In this work, we present a summary of those studies that have used PILC as adsorbents for the removal of organic compounds from aqueous solutions while simultaneously illustrating their potential for this purpose. A general overview is provided so that the reader can acquire a basic understanding of the PILC and their modified counterparts that have been used, and some of the characteristics that can directly affect their adsorption behavior, especially their textural and surface properties.

Adsorption of Supranol Yellow 4 GL from aqueous solution by surfactant-treated aluminum/chromium-intercalated bentonite

The aim of this paper is to study the adsorption of the acid dye Supranol Yellow 4 GL (S.Y. 4 GL) from aqueous solution on an inorgano-organo clay. Bentonite is naturally occurring clay with good exchanging ability. By exchanging its interlamellar cations with cetyltrimethylammonium bromide (CTAB) and hydroxyaluminic or chromium polycations, the properties of natural bentonite can be greatly improved. Batch adsorption tests of Supranol Yellow 4 GL were carried out at 20 degrees C and constant pH 6.5. To investigate the adsorption mechanisms, the simplified kinetic models, such as pseudo-first-order, pseudo-second-order, Elovich equation and intraparticle diffusion are tested. The results show that adsorption follows second-order rate kinetic. The correlation coefficients obtained for second-order kinetics model are greater than 0.998 indicating a better fitting of this equation. The experimental data are analysed by Langmuir, Freundlich and Elovich isotherms. The equilibrium adsorption capacity of anionic dye is determined from the Langmuir equation and found to be 142, 85 and 128, 20mg/g (standard deviation; Deltaq (%)=3.52 and 18.51) for CTAB-Cr-B and CTAB-Al-B, respectively.

Adsorption of vapor-phase VOCs (benzene and toluene) on modified clays and its relation with surface properties

A mexican bentonite was used to prepare three modified clays: an organoclay (OC–CPC) by intercalating cetylpyridinium chloride (CPC), an aluminum-pillared clay (Al-PILC), and an inorganic–organic clay (IOC–CPC) prepared from Al-PILC intercalating CPC. The infrared and thermogravimetric analyses enabled us to differentiate between the structures obtained. Interlayer distance was assessed through X-ray diffraction; the OC–CPC was the clay that showed the highest value (12.4 Å). The natural clay’s specific area was 43.5 m2/g, increasing to 157.2 m2/g for Al-PILC. The OC–CPC and IOC–CPC specific areas were 13.27 m2/g and 14.5 m2/g, respectively. Al-PILC was a microporous material; whereas natural clays, OC–CPC and IOC–CPC were non-porous materials. Toluene and benzene adsorption on OC–CPC was higher than in IOC–CPC and Al-PILC. Natural clay showed no adsorption capacity for these compounds. Comparison of the GC retention times for non polar and low-polarity compounds (octyne and benzene) in columns packed with OC–CPC and a commercial non polar column (squalene) showed that the OC–CPC possessed a higher organophilic (non polar) nature than squalene. This explains the higher benzene and toluene adsorption capacity of the OC–CPC compared with the other modified clays. The toluene and benzene adsorption isotherm for OC–CPC was well-described by the GAB (Guggenheim–Anderson–De Boer) model for the whole range of relative pressure used in this work (0–0.9) describing multilayer adsorption and capillary condensation.Key words: organoclay, inorgano–organo clay, vapor phase VOC’s adsorption, clay surface properties.

Preparation of a porous clay heterostructure and study of its adsorption capacity of phenol and chlorinated phenols from aqueous solutions

A porous clay heterostructure (PCH) from a Mexican clay was prepared and characterized, and its aqueous phenol and dichlorophenols (DCPs) adsorption capacities were studied using a batch equilibrium technique. The PCH displayed a surface area of 305.5 m2/g, 37.2 A average porous diameter, and a basal space of 23.2 A. The adsorption capacity shown by the PCH for both phenol and DCPs from water (14.5 mg/g for phenol; 48.7 mg/g for 3,4-DCP; and 45.5 mg/g for 2,5-DCP) suggests that the PCH has both hydrophobic and hydrophilic characteristics, as a result of the presence of silanol and siloxane groups formed during the pillaring and calcination of the PCH. The values of maximal adsorption capacity for dichlorophenols were higher than those reported for aluminum pillared clays and some inorgano-organo clays and comparable with some ionic exchange resins.

Comparison of modified montmorillonite adsorbents. Part I: Preparation, characterization and phenol adsorption

This study concerns with the development of modified montmorillonites as adsorbents for water treatment. Polymeric aluminium and iron intercalated forms of montmorillonites have been prepared in the absence and presence of an alkylammonium cationic surfactant (Hexdecyl-trimethyl-ammonium bromide, HDTMA). Montmorillonites intercalated with polymeric Al, Fe, Fe/Al (2:1 Fe to Al ratio in solution), possess large N2 Brunauer-Emmett-Teller (BET) surface areas. XRD data also shows trace amounts of illite and plagioclase within the clay materials. Montmorillonites intercalated with HDTMA, polymeric Fe/HDTMA, polymeric Al/HDTMA and polymeric Fe/Al/HDTMA (1:1 metal to surfactant molar ratio in solution) undergo some losses of N2 BET surface areas. Preliminary adsorption studies on phenol have shown that polymeric Al/HDTMA- and HDTMA-only-modified montmorillonites possess a good affinity for phenol, whereas the polymeric Al/Fe modified- and starting montmorillonites have little affinity for phenol adsorption.