Time Dependence of the Spectra of Methylene Blue−Clay Mineral Suspensions

Abstract

Aqueous dispersions of different smectite-type clay minerals were probed by ion-exchange of methylene blue (Mb). The evolution of the absorption spectra with time demonstrates the importance of the strength of the Mb−clay surface interaction, which is affected by the colloidal nature of the suspension and typical clay characteristics. A strong Mb−surface interaction is observed for clay minerals with tetrahedral substitution and a large basal surface area. Mb species adsorb in a more polar environment and show well-resolved bands. Their mobility is small. When the Mb−surface interaction is weaker, Mb−Mb interactions and interactions among the clay particles dominate. This is the case for octahedrally substituted clays with a large edge surface. Mb species experience the influence of the surrounding water phase and of neighboring Mb molecules. They remain mobile, even for longer aging periods. The absorption spectra evidence a less polar, “undefined” adsorption environment.

Effect of the exchangeable cations on the spectral properties of methylene blue in clay dispersions

“…In other works, this band was assigned to J-aggregates with a head-to-tail intermolecular association [21,22]. However, J-dimers, which absorbed light at 690 nm, were identified on the surface of quartz [23].…”

“…(2) MB + cations are acidified on the clay surface, forming divalent MBH 2+ cations [6,7,21,22,26,27]. The latter interpretation is based on the observation that strongly acidic solutions of MB absorb light at 750 nm.…”

In vitro investigation of methylene blue-bearing, electrostatically assembled aptamer–silica nanocomposites as potential photodynamic therapeutics

“…A few studies [12,13] have used specific tumor-targeting molecules to functionalize the nanocar- wavelength region enable penetration to deeper tissue sections [23]. Methylene blue (MB) is an attractive candidate PS for PDT because of its hydrophilicity, cost effectiveness, strong absorption at 550-700 nm, and high singlet oxygen quantum yield ( D ≈ 0.5) [24,25]. Furthermore, MB has been approved by the United States Food and Drug Administration for the treatment of methemoglobinemia [26].…”

Adsorção do corante azul de metileno em partículas de argilominerais: análise dos tamanhos das partículas

“…Diversos estudos mostraram que ocorre uma variação espectral de corantes adsorvidos em argilas no meio aquoso. 24,25,30,31 Diversos autores propuseram alguns eventos prováveis que poderiam ocorrer, principalmente através de estudos de suspensões com a argila SWy-1, uma montmorilonita proveniente de Wyoming, Estados Unidos. Os resultados sugerem que no momento em que o corante é adicionado à suspensão de argila, ocorre inicialmente uma adsorção preferencial nas superfícies externas dos tactoides em suspensão.…”