The project was designed to study the adsorption of sodium dodecylsulphate (SDS) and cetyltrimethylammonium bromide (CTAB) on the active carbon cloth. Four isotherm models including the Langmuir, Freundlich, Sips and Sigmoid isotherms were used to correlate the experimental equilibrium data of the two ionic surfactants in pure water. The Sips and Sigmoid isotherms provides the best correlation with similar SSE. These two isotherms were then used to describe the equilibrium data of SDS and CTAB in the solution which is buffered at pH 7....[ Read more ]

The project was designed to study the adsorption of sodium dodecylsulphate (SDS) and cetyltrimethylammonium bromide (CTAB) on the active carbon cloth. Four isotherm models including the Langmuir, Freundlich, Sips and Sigmoid isotherms were used to correlate the experimental equilibrium data of the two ionic surfactants in pure water. The Sips and Sigmoid isotherms provides the best correlation with similar SSE. These two isotherms were then used to describe the equilibrium data of SDS and CTAB in the solution which is buffered at pH 7.

The effect of solution pH and ionic strength to the equilibrium data of SDS and CTAB were also investigated. It was found that the solid phase equilibrium concentration of SDS increased whereas CTAB decreased when the ionic strength of the solution increased from 0.05M to 0.09M. The adjustment of solution pH did not affect the solid phase equilibrium concentration of both SDS and CTAB.

The surface charge of the active carbon cloth was determined by the pH titration. The point of zero charge was found to appear at pH 5.59. The charge of the active carbon cloth become positive when the pH is smaller than 5.59 but negative when bigger than 5.59.

The adsorption kinetics of SDS and CTAB were studied as well. Four different sets of experiments were done for each surfactant in order to investigate the effect of initial concentration of surfactant, the solution pH, ionic strength and the charge built up on the active carbon cloth surface by applying current between the carbon cloth and counter electrode. The concentration profile in each case was then fitted by a surface diffusion model which utilized the Sips isotherm parameters that correlated the equilibrium data in the pH buffered solution. The external mass transfer coefficient and surface diffusivity were calculated by the model after performing optimization. The external mass transfer coefficients and surface diffusivities in each set of experiment were plotted and compared. Explanations accounted for their trends were given based on different adsorption mechanisms. The order of magnitude of external mass transfer coefficients for SDS and CTAB were 10^-3 and 10^-4 respectively. This indicated that SDS diffuses faster through the external film than CTAB. The order of magnitude of surface diffusivities were 10^-11 and 10^-12 for SDS and CTAB. Thus, SDS moves along the inner surface of the active carbon cloth at a faster rate than CTAB.