Optical determination of Cr(VI) using regenerable, functionalized sol–gel monoliths

Abstract

Transparent, pyridine-functionalized sol-gel monoliths have been formed and their use in Cr(VI) sensing applications is demonstrated. The monoliths were immersed in acidic Cr(VI)-containing solutions, and the Cr(VI) uptake was monitored using UV-vis and atomic absorption spectroscopies. At concentrations at the ppm level, the monoliths exhibit a yellow color change characteristic of Cr(VI) uptake, and this can be measured by monitoring the absorption change at about 350 nm using UV-vis spectroscopy. Concentrations at the ppb level are below the limit of detection using this wavelength of 350 nm for measurement. However, by adding a diphenylcarbazide solution to monoliths that have been previously immersed in ppb-level Cr(VI) solutions, a distinct color change takes place within the gels that can be measured at about 540 nm using UV-vis spectroscopy. Concentrations as low as 10 ppb Cr(VI) can be measured using this method. The monoliths can then be regenerated for subsequent sensing cycles by thorough washing with 6.0M HCl. The factors affecting monolith uptake of Cr(VI) have been explored. In addition, the gels have been characterized using X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and Brunauer-Emmett-Teller (BET) measurements.

Optical and electrochemical sol-gel sensors for inorganic species

“…Another metal ion of intense interest to our group is the oxo anion chromate (CrO 4 2− or HCrO 4 − ) [26,32,67] . Cr(Ⅵ) is known to be carcinogenic and a toxic environmental pollutant while at the same time Cr(Ⅲ) is an essential trace element in mammals, important for the processing of glucose [68] .…”

“…Many sensing techniques that are capable of portability are electrochemical in nature [60,61] , but some optical techniques have also been reported [25] . We have explored the use of ligand grafted sol-gel monoliths for the detection of Cu 2+ and chromate ions using optical signal transduction [23,24,26] . The determination of Cu 2+ ions is based on the formation of Cu 2+ -amine complexes between the Cu 2+ ions and amine ligands that are imprint-grafted on sol-gel monoliths [62][63][64][65] .…”

“…One of the most important features for optical sensing is that they are transparent in the visible region [13] . Sol-gels have found applications in the optical monitoring of pH [3,5,8,9,[14][15][16][17][18][19][20][21][22] , metal ions [23][24][25][26][27] , and various other analytes [28][29][30] . Sol-gels have also found use in electrochemical [31 -38] and spectroelectrochemical [39] sensing applications.…”

The preparation of sol–gel materials doped with ionic liquids and trialkyl phosphine oxides for Yttrium(III) uptake

“…In recent years, doping of functional molecules in sol-gels has been attracted much attention due to potential applications in numerous areas such as optics, sensors, catalysis and separations [1][2][3][4][5][6]. The use of functionalized solid support extractants to separate metal ions and organic compounds from aqueous media is gaining popularity [7].…”

Fluorescent-Dye Doped Thin-Film Sensors for the Detection of Alcohol Vapors

“…The optical sensors have also been designed to function in a multianalyte platform for the simultaneous detection of multiple gas analytes. The studies here follow our earlier work in the development of optical sensors for chemicals in both liquid and gas phases [35]- [39].…”