Tetrasulfide‐Functionalized Mesoporous Silica on Nanowire Ring Resonators for Detection of Aqueous Lead, Pb(II). (16th October 2018)

• Record Type: Journal Article
• Authors: Chen, Hao; Saunders, John E.; Borjian, Sogol; Wu, Xiaowei; Crudden, Cathleen M.; Xu, Dan‐Xia; Loock, Hans‐Peter
• Is Part Of: Advanced sustainable systems. Volume 3:Number 1(2019)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2018-10-16
• Subjects: absorption kinetics -- detection -- lead -- mesoporous silica -- microphotonics -- Pb(II) -- silicon photonics; Sustainable living -- Periodicals; Sustainability -- Periodicals; Green technology -- Periodicals; Periodicals; 628
• DOI: 10.1002/adsu.201800084
• Languages: English
• ISSNs: 2366-7486

Abstract

Abstract: Silicon‐on‐insulator (SOI) microring resonators coated with tetrasulfide‐functionalized mesoporous silica (MPS) (S4 ‐MPS) are reported as sensors to detect Pb(II) ions in aqueous solutions from 10 ppb to 1 ppm. The sensors are based on the interaction of the evanescent field of the guided light with the functionalized mesoporous silica films. Upon absorption of metal ions, the resonant wavelengths of the microresonators shift due to the increased refractive index of the film. The sensors are exposed to aqueous solutions of Pb(II) ions at different concentrations and time‐resolved absorption–desorption curves are obtained. The concentrations of Pb(II) ions are determined using the Lorentz–Lorenz model. It is found that two distinct binding sites with different affinities for Pb(II) are present in the S4 ‐MPS silica films, corresponding to tetrasulfide groups and, likely, silanol groups. The number of available binding sites corresponds to 1/25 of the total number of S4 ‐groups. Equilibrium constants for absorption of Pb(II) to both binding sites are obtained from the rate constants for the absorption and desorption processes. The initial absorption rates depend linearly on the concentration of Pb(II) and are used to determine the 3σ limit of detection as 58 ppbm in deionized water and 350 ppbm in tap water. Abstract : Microphotonic tandem ring resonators are coated with tetrasulfide‐functionalized mesoporous silica films to create remarkably sensitive and specific sensors for lead, Pb(II) in water. Using simply additivity rules for material polarizability, the refractive index changes of the films can be quantified. Rate constants, equilibrium constants, and binding energies for Pb(II) adsorbing to tetrasulfide sites and to silanol sites can be obtained.