Parâmetros termodinâmicos da interação de ácido húmico com nanotubo de carbono de paredes múltiplas, argilas, óxidos e albumina soro bovina

• Autor(a) principal: Santos, Igor José Boggione
• Data de Publicação: 2013
• Tipo de documento: Tese
• Idioma: por
• Título da fonte: LOCUS Repositório Institucional da UFV
• Texto Completo: http://locus.ufv.br/handle/123456789/227
• topic: Ácido húmico; Interação; Termodinâmica; Humic acid; Interaction; Thermodynamics; CNPQ::CIENCIAS EXATAS E DA TERRA::QUIMICA::FISICO-QUIMICA

Climate changes caused by increased atmospheric concentration of CO2 have stimulated a better understanding of the global carbon cycle. Soils represent one of the largest compartments of C on Earth, with higher C content than plant biomass and atmosphere. Therefore , understanding the interaction of one of the major compounds in soil organic matter , humic acid (HA) with different surfaces and substances is extremely important, especially for countries like Brazil , once the majority of its greenhouse gases emissions come from agriculture. The aim of this work was to study the thermodynamic parameters of interaction between HA and multi wall carbon nanotube (MWCNT), clays, oxides and bovine serum albumin (BSA), to contribute to a better understanding of the factors that lead to stabilization of carbon in the soil , even with agricultural activities. For this, we investigated MWCNT-HA interaction at different pHs and ionic strength through adsorption isotherm and the technique of isothermal titration calorimetry, ITC (Chapter 1); the influence of the Hofmeister series in interaction HA- MWCNT via adsorption isotherm and ITC (Chapter 2); the interaction between HA and clay minerals at different ionic strengths via adsorption isotherms and ITC (Chapter 3) and HA-BSA interaction at different pHs and ionic strengths via fluorescence spectroscopy and ITC (Chapter 4). The thermodynamic analysis in all chapters demonstrated that the interaction of HA with different surfaces and substances is spontaneous (&#916;adsG ° < 0). On the first study (Chapter 1) we provided that MWCNT HA adsorbed mainly in the more acidic pH. Ionic strength, salt type and origin of HA influence on the adsorption process. The model that best fitted was Langmuir isotherm. Thermodynamic analysis showed that the adsorption enthalpy is favorable for all systems studied. The second study (Chapter 2) shows high xvii values of &#915;, which shows great potential of MWCNT in to adsorb HA. Moreover, it appears that the adsorption depends on the nature of the salts of the Hofmeister series and that the adsorption does not follow this series. Thermodynamic analysis shows that the process is enthalpically favorable for anionic Hofmeister series. The third chapter shows that the adsorption mechanism of HA on clay minerals depends on the nature of surface, of polyelectrolyte concentration and pH. The model that best fitted the systems studied was the Langmuir, except for montmorinollite at pH 4.0 and 6.0. The adsorption process is enthalpy and / or entropically favorable depending on the system. In chapter 4, the emission spectra showed that there is an intense BSA-HA interaction. There was an effect of ionic strength of the salt KCl in BSA-HA interaction. Entropy was positive for buffer systems 3.6 and 4.8 in the presence of 50 mM KCl, while in the first to enthalpy variation was unfavorable. The other systems, there was not a favorable entropic contribution for BSA-HA interaction, therefore, the process being driven by enthalpy.