Studies on solubilization of thiram by surfactants and interactions with adsorbents in the presence of surfactant micelles

Studies on reduction of negative impacts of pesticides have attracted considerable attention due to their importance in human life and environment. Thiram, poorly water soluble pesticide, is commonly used in agricultural applications. The solubilization of thiram was studied in micellar solutions of two different anionic and cationic surfactants possessing the same hydrocarbon tail but different hydrophilic head groups, namely sodium dodecyl sulphate and dodecyl trimethyl ammonium bromide. Adsorption of thiram onto different activated carbons (positively charged; PAC and negatively charged; NAC) has been also studied in the presence of this surfactant micelles. Solubilization experiments of thiram which was chosen as a model are important for both pesticide formulations and agricultural applications. Thiram surfactant interaction studies are also important in many areas such as waste water treatment plants, surface and ground water. It was considered that investigation of adsorption on activated carbon using surfactant containing solution is necessary for both removal of toxic effects effectively from environment and clarifying of adsorption mechanism. This study aimed to investigate solubilization of a poorly water soluble organic substance with different surfactant micelles and solubilization of surfactans on the solid-liquid interface as a result of adsorption. It is also aimed to investigate the interaction of this substance with different adsorbents in the presence of these surfactant micelles has been investigated. The results showed that solibility of thiram increased with increasing surfactant concentration. It is found that SDS solubilizing capacity is higher than DTAB solubilizing capacity and hydrophobic interaction is the most important factor for thiram binding to the surfactant micelles. Adsorption kinetic data were modeled using the Lagergren first order and the pseudo second order kinetic equations. Intraparticle diffusion graphics were also plotted. The data obtained from all kinetic studies are fitted to the pseudo-second order kinetic equation better than the Lagergren first order kinetic equation for both negative and positive activated carbons. It was determined that intraparticle diffusion mechanism played important role for all adsorption experiments. The Giles isotherms were used to understand the adsorption mechanism of thiram Isotherms plotted appear to fit L-type according to Giles isotherm classification. Our results showed that the adsorption capacity of positively charged activated carbon for thiram was higher than the adsorption capacity of negatively charged activated carbon in the aqueous solutions. Presence of micelles diminished the adsorption of thiram or totally inhibited depending on their structures. Inhibitory effect of micelles on the adsorption of thiram can be explained as a result of incorporation of thiram to micelles.