Real-Time Monitoring of Azo Dye Interfacial Adsorption at Silica–Water Interface by Total Internal Reflection-Induced Surface Evanescent Wave

Abstract

An interface research method based on total internal reflection induced evanescent wave (TIR-EW) is developed to monitor the adsorption behavior of azo dye at the silica-water interface. The monitoring system is constructed by employing silica optical fiber (SOF) as both charged substrate for dye adsorption and light transmission waveguide for evanescent wave production. According to the change of evanescent wave intensity and followed by Beer's law, the methylene blue (MB) adsorption behavior can be real-time monitored at the silica-water interface. Langmuir adsorption model and pseudo-first-order model are applied to obtain the related thermodynamic and kinetic data. The adsorption equilibrium constant ( K) and adsorption free energy (Δ G) of MB at the silica-water interface are determined to be (3.3 ± 0.5) × 10 M and -25.7 ± 1.7 kJ mol. Meanwhile, this method is highlighted to isolate elementary processes of adsorption and desorption under steady-state conditions, and gives adsorption rate constant ( k) and desorption rate constant ( k) of 8585 ± 19.8 min and 0.26 ± 0.0006 min for 15 r/min flow rate. The surface interaction process is revealed and adsorption mechanism is proposed, indicating MB first adsorbed on Si-O sites through electrostatic attraction and then on Si-OH sites through hydrogen bond with increasing MB concentrations. Our findings from this study provided molecular-level interpretation of azo dye adsorption at silica-water interface, and the results provide important insight into how MB adsorption can be controlled at the interface.

Recent advances on the removal of dyes from wastewater using various adsorbents: a critical review

“…It is considered to be a fast, low cost, simple, sludge-free process, having high efficiency and/or selectivity, mechanical stability, and recycling facilities. 14, [46][47][48][49][50][51] Adsorption process is widely used for the remediation of different pollutants from wastewater, including heavy metals, arsenic, and dyes. [52][53][54][55][56][57][58][59] Additionally, the pie-chart is displaying the percentage of literature available on dye removal for various adsorption techniques (Fig.…”

Tuning structural coloration through evanescent wave absorption at microscale concave interfaces

“…The penetration depth (dp) of the evanescent wave can be calculated based on the wavelength of incident light (λ), the incidence angle at the interface (θ) and the refractive index of the two materials at the interface (n1, n2). 18 𝑑 =…”

“…If an absorptive chemical species is localized within the penetration depth, it can interact with the evanescent wave and thereby modify the properties of the reflected light. The evanescent wave is thus highly sensitive to the chemical environment near the TIR interface, and this phenomenon is routinely exploited for sensing and spectroscopy applications [18][19][20][21] . For example, optical fiber sensors utilize the evanescent wave generated by each TIR event propagated along the fiber core to interact (absorption, fluorescence, Raman scattering, etc.)…”

Oscillating Electric Field Effects on Adsorption of the Methane–Water System on Kaolinite Surface

“…Water is considered ubiquitous in shale gas systems . The adsorption performances on the mineral–water interface were studied experimentally. − Experimental studies have indicated that moist equilibrated clays hinder gas adsorption on them, , and the adsorption amounts of methane would reduce about 40%–90% compared with that in the dry condition. ,, However, the related experimental data are still inadequate, especially for adsorption on pure clay minerals. In addition to experimental studies, the grand-canonical Monte Carlo (GCMC) and molecular dynamics (MD) simulations were used to study the effects of water on gas sorption in clay minerals or organic matter and to examine the underlying sorption mechanism. ,− Most researchers focus on methane adsorption on montmorillonite, kaolinite, coals, and kerogen, and effects of water content, pressure, and temperature on gas adsorption and clay swelling were studied. ,,− …”