Desenvolvimento de novos materiais baseados em argilas e carvões para aplicações como catalisadores e adsorventes em remediação ambiental

Abstract

Two classes of microporous materials based on pillared clay and activated carbon composite were studied in view to check their applicability in environmental remediation. The pillared clay was utilized in three processes: (i) as a catalyst on the oxidation of organiccontaminants; (ii) in the production of magnetic adsorbents to eliminate metallic cations contaminants of water and (iii) in the production of monolith catalysts to be used in the treatment of liquid etHuent. The activated carbon was used: (i) on the preparation of magneticcomposites to adsorb organic contaminants and (ii) as contaminants oxidizer in aqueous medium with H2O2. The pillared montmorillonite with keggiji, Alu, was characterized with powder X-ray diffraction (XRD), N2 adsorption/desorption, infrared spectroscopy (IR), emperature-programmed reduction (TPR) and X-ray photoelectronic spectroscopy (XPS). The pillarization process highly increases the specific area of the clay, from 22 to 217 m^g"', mainly due to the microporous formation. Tests of thermal stability show that the pillarstructure collapses only at 800 ''C in air. Catalysts were also prepared by impregnating the pillared clay with aqueous solution of Fe, Co, Mn, Cr and Pd. These catalysts were characterized with XRD, N2 adsorption/desorption and TPR, The impregnation with Fe or Pdcollapsed the pillar structure and caused a strong decrease of the specific area. This structure collapsing was less evident for pillars impregnated with Ni, Cr, Mn or Co and the specific areas in these cases were only slightly smaller. The catalysts were tested on the chlorobenzene oxidation. It was observed the following order of catalytic activity, according to the impregnating metal: Pd > Cr > Co > Fe > Mn > Ni, The catalyst with Pd showed the highest activity on the chlorobenzene oxidation, but some formation of byproducts was observed in thiscase. The catalysts with Cr or Co completely promoted the oxidation of the chlorobenzene. It is was also observed that the catalysts with Cr and Co were completely deactivated after 12 h, but the Pd-catalyst kept its activity for 72 h. Tests with xylene led to a partial deactivation of thecatalyst with Cr, certainly due to the presence of H2O vapor and coke deposition. Monolith catalysts of clay were impregnated with iron oxide (10, 20 and 30 mass%). These monoliths were thermally treated under a H2 atmosphere at 200, 300 or 400 T for 1 h. This treatment led to the formation of a Fe7Fe304 composite on the monolith surface. These catalysts were characterized with XRD and ^^Fe Mossbauer spectroscopy. The materials were then tested in two reactions: (i) H2O2 decomposition and (ii) Drimaren red dye oxidation. Tlie clay was alsoused to prepare the magnetic composite clay/iron oxide at ratios 1/1, 1/2 and 1/3, being the composites characterized with saturation magnetization measurements, XRD, "^^Fe Mossbauer spectroscopy, N2 adsorption, TPR and SEM and tested as adsorbents of the metallic ions Ni"', Zn^\ Cu^^ and Cd^' in aqueous medium. They were also prepared magnetic composites based on activated carbon/iron oxide at ratios 1/1, 1/2 and 1/3, which were characterized with saturation magnetization measurements, XRD, Mossbauer spectroscopy, N2 adsorption, TPR and SEM. These materials showed high capacity to adsorb Drimaren red dye, phenol, chloroform and chlorobenzene. The activated carbon/iron oxide composites were treated with H2 at 300, 500, 700 and 800 and their activities on the decomposition of organic compounds with H2O2 were verified. Data of magnetization, XRD and ""^^Fe Mossbauer spectroscopy showed that, for the samples treated at 300 or 500 "C, maghemite and magnetite were formed on the surface of the activated carbon particles, A similar study was carried out with pure activated carbon. In this case, the H2O2 decomposition and the dye oxidation tests showed that the pure activated carbon present higher catalytic activity than the composite with iron, presumably due to the creation of reduction sites, after thermal treatment under H2.