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.