Square Wave Voltammetric Determination of Lead(II) Ions Using a Carbon Paste Electrode Modified by a Thiol‐Functionalized Kaolinite

Abstract

This work reports the electroanalysis of lead(II) in aqueous medium, using a carbon paste electrode modified by a novel thiol-functionalized clay. This later was obtained upon the grafting of 3-chloropropyltriethoxysilane onto the interlayer surfaces of kaolinite, followed by the substitution under carefully controlled conditions of chloro by thiol groups. The raw kaolinite, its dimethylsulfoxide (DMSO) intercalate used as starting material and the resulting hybrids were characterized by X-ray diffraction, thermal analysis, infrared spectroscopy and CHNS elemental analysis. These techniques demonstrated the displacement of DMSO by the organosilane molecules which were grafted on the internal hydroxyl groups located on the kaolinite surface. The final functionalized kaolinite, with approximate chemical formula Si 4 Al 4 O 10 (OH) 6 [O 2 Si(OEt)(CH 2 ) 3 SH] was evaluated as electrode modifier for lead(II) sensing. A two-step analytical procedure based on the accumulation at open circuit-detection was applied by square wave voltammetry. Various parameters affecting both the two steps were optimized: a linear response to lead(II) was obtained in the concentration range from 3 10 À7 to 10 À5 M, with a detection limit estimated at 6 10 À8 M. The interfering effect of some ions likely to influence the stripping determination of lead(II) ions was evaluated, and the proposed method applied to a real sample.

Silylation of clay mineral surfaces

“…As indicated by literature (Avila et al, 2010;Tonlé et al, 2007Tonlé et al, , 2011, temperature was an important factor for successful silylation of kaolinite. To elucidate the influence of temperature on the grafting reaction, Yang et al (2012) conducted a series of grafting reactions on kaolinite at different temperatures (175, 185, 195 and 220°C).…”

“…The existence of crystal defects (e.g., isomorphous substitution, vacancy and broken bond) can obviously increase the reactivity of the siloxane surface (Carrado et al, 2001). The hydroxyl surfaces (e.g., Al-octahedral surface in kaolinite) are excellent sites for grafting since the surface hydroxyls can condensate with alkoxyl group and/or the hydroxyls in the hydrolyzed silane (Brandt et al, 2003;Tonlé et al, 2007Tonlé et al, , 2011Detellier, 1993, 1996). Due to the high ratio of terminal surface area to the basal surface area, hydroxyl groups located at broken edges play an important role in the silane grafting reaction.…”

“…Due to lack of swelling ability for non-swelling clay minerals such as kaolinite, pre-intercalation with small polar molecules is an indispensable step in the silylation of internal surfaces. This demands rigorous conditions for successful grafting such as high reaction temperature, inert atmosphere, and so on (Brandt et al, 2003;Tonlé et al, 2007Tonlé et al, , 2011.…”

“…To achieve a successful interlayer grafting, pre-intercalation with small polar molecules, e.g., dimethyl sulfoxide (DMSO) is an indispensable step to prepare an intercalate precursor, which will be used as substrate for further organosilane intercalation and subsequent silylation. Tunney and co-workers conducted a series of pioneering work on the interlayer grafting of kaolinite (Brandt et al, 2003;Tonlé et al, 2007Tonlé et al, , 2011Detellier, 1993, 1996). A number of small-sized organics (e.g., ethylene glycol, methyl ether, 1,2-propanediol and 1,3-propanediol) were successfully applied in kaolinite grafting.…”

“…More recently, Guerra et al (2012) reported that silylated kaolinite was prepared by using APTES in the medium of dry toluene under an argon atmosphere, and the basal spacing was increased from 0.71 nm (pristine kaolinite) to 1.31 nm (silylated product). The prominent difference of the basal spacings in the silylated products indicates that the reaction conditions (e.g., reaction temperature, atmosphere and solvent) have a prominent influence on the interlayer structure of silylated products (Avila et al, 2010;Kobayashi and Matsunaga, 1991;Tonlé et al, 2007Tonlé et al, , 2011.…”