HUMIC ACID/ORGANO-BENTONITES (HDTMA AND TDTMA) COMPLEXES: ADSORPTION AND CHARACTERIZATION

M. FERNANDEZ; ROSA M. TORRES SÁNCHEZ

Antalya

Congreso; Euroclay 2011; 2011

The detailed study of organoclays is a vital subject since combination of the hydrophobic nature of the organic molecule and the layered structure of the silicate leads to unique physicochemical properties which allowed them to be used in a widely industrial field (nanocomposite precursors, adsorbents for organic pollutants, etc.). In these applications, the behavior and properties of the organoclays depend on the structure and molecular environment of the organic molecules within the galleries, consequently the amount of intercalated organic molecules could affect the properties and so their applications. This study concerns the adsorption properties of organo-bentonites obtained through exchange at 100%, and 200% of the cation exchange capacity (1CEC and 2 CEC, respectively) using tetradecyl trimethylammonium bromide (TDTMA) and hexadecyl trimethylammonium bromide (HDTMA). The adsorption properties of organo-bentonites were tested using humic acid as a pollutant model. Batch kinetic and isotherm studies were conducted over the concentration range from 20 to 200 ppm at pH of 7. The modified samples: organo-bentonites and those with humic acid adsorbed (complexes) were studied by specific and total surface, Hg porosimetry and zeta potential determinations, X-ray diffraction (XRD) technique, Fourier transform infrared (FTIR) spectroscopy and the morphology changes evaluated by scanning electron microscope (SEM). A considerable increase (50%) was observed in the adsorption efficiency of 1CEC-HDTMA organo-bentonite, respect to all evaluated organo-bentonites. The specific total surface area of organo-bentonites samples decreased around 60 and 40%, while the specific surface area increase 36 and 54% with the increase amount of HDTMA and TDTMA, respectively. These different behaviors of both surface indicated, inhibition and enhancement adsorption of water and Nitrogen molecules, respectively. Hg porosimetry measurements indicated a decrease of maximum mesopore radius of 5 and 10% for 1 to 2 CEC of HDTMA and TDTMA, respectively. Zeta potential determinations of organo-bentonites showed negative surface charge values except for 1CEC-HDTMA sample. The humic acid adsorption increased the negative surface charge of all initial organo-bentonites. According to the XRD patterns for both TDTMA and HDTMA samples with 1CEC a bilayer and pseudo-trilayer formation could be indicated between the silicate layers. For the 2CEC samples in addition to the bilayer structure, an increase of the baseline at low angles would indicate the formation of a greater interlayer space generated by other arrangement of both organic cations. The IR spectra of organo-bentonites samples showed an increase of the C-H stretching vibrations bands (2918 and 2850 cm-1) and those of CH3 group vibration (1488 cm-1) with the HDTMA and TDTMA loading. SEM micrographs revealed that the organo-bentonites with 1CEC were mainly composed of curved particles, while those with 2CEC were mainly composed of regularly intercalated and flat layers. Adsorption of humic acid do not affect the further morphology of complex obtained.