Interaction of sodium dodecylbenzenesulfonate with chrysotile fibers. Adsorption or catalysis?

Sodium dodecylbenzenesulfonate (SDBS) aqueous solutions in contact with chrysotile fibers show a concentration reduction up to 53% (C-0 = 3.0 x 10(-3) mol 1(-1), above critical micellar concentration (CMC)) and 90% (C-0 = 0.15 x 10-3 moll-1, below CMC) after 4 h contact with the fibers at room temperature, when air bubbling is used as an oxygen supplier. Adsorption/desorption experiments with 3.0 x 10(-3) mol 1(-1) solution show that only 6% of the surfactant is recovered after successive washing steps in water. Experiments in open and closed stirred flasks show that the surfactant depletion is lower. In non-aerated systems, pseudo-equilibrium is achieved after 4 h. When air bubbling is used, the amount of SDBS removed keeps rising at least for 24 h. The calculated Gibbs pseudo-surface concentration indicates the formation of 2-10 monolayers onto the chrysotile surface. These results are inconsistent with a solely adsorptive process. One degradation product was identified and quantified (CO2), rendering a turnover number of 1500. A mechanism for a catalytic process is proposed. (C) 2002 Elsevier Science B.V. All rights reserved.