Adsorption of methylene blue as a descriptor of C-S-H nanostructure

The adsorption of methylene blue (MB) on C-S-H surfaces (C/S ratios 0.60-1.80) and its dependence on C-S-H nanostructure was investigated. UV-VIS spectroscopy was used to obtain the adsorption-desorption isotherms at 23 °C, 35 °C and 50 °C. The character of the UV-VIS spectra and the nature of the C-S-H-MB interaction are discussed. Several sorption models including those due to Langmuir, Harkins-Jura, Halsey, Henderson, and Freundlich are fitted to the data using a non-linear multiple-regression method. Factors influencing the sorption of MB by C-S-H are discussed. The results demonstrated that the adsorption of MB molecules on C-S-H strongly depends on the nanostructural characteristics of C-S-H.