Hydrothermal modification and characterization of bentonite for reactive adsorption of methylene blue: An ESI-MS study

Reactive adsorption of methylene blue (MB), a cationic dye, using pretreated (hydrothermally modified) bentonite clay was investigated. The modified clay showed high efficacy for MB removal via, reactive adsorption, which is supported by electrospray ionization mass spectrometry (ESI-MS) study. The modified clay was characterized by Fourier transform infra-red spectroscopy (FTIR), field emission scanning electron microscopy coupled with energy dispersive spectroscopy (FE-SEM with EDS), transmission electron microscopy (TEM) and BET surface area analysis. The results indicated that the crystalline structure of raw bentonite upon hydrothermal treatment transformed into amorphous nature. Pretreatment increased the concentration of OH surface functional groups pointing toward increased reactive behavior. Pretreated bentonite completely removed the MB dye rendering the solution colorless. Furthermore, ESI-MS analysis showed reactive degradation of MB molecule by oxidation via hydroxylation of reaction intermediates. The degradation products of MB were found environmentally benign.