Solvent Effect on the Grafting of an Organophilic Silane Onto Smectite‐type Clay: Application as Electrode Modifiers for Pesticide Detection

Abstract

The effect of a non‐swelling (toluene) and a swelling (ethylene glycol (EG)) solvent on the grafting of an organophilic silane (octyltriethoxisilane) onto a smectitic clay was investigated. XRD patterns of the resulting materials reveals that the grafting occurred exclusively on the edges of the clay particles without intercalation, as evidenced by the non‐variability of the d‐value before and after the grafting. FTIR and TGA characterizations show that higher amount of silane was grafted when toluene was used as solvent. With EG, the clay particles were well‐dispersed and the grafting well controlled. These functionalized materials were used as carbon paste electrode modifiers to evaluate their abilities for electrochemical detection of organophilic pollutants at trace level. Carbendazim (cbz), a widely used fungicide was used as model compound. The clay functionalized in EG was the most efficient modifier, due to the combined effect of the characteristics of the pristine clay and the grafted silane. The electroanalysis experimental parameters were carefully optimized (pH 6.8, 15 min of accumulation time and 10 % of the modifier in the carbon paste). By varying cbz concentration, a 0.03 μM detection limit was obtained. The sensor provide very reproducible response but strongly affected by some metal ions interferences. By varying cbz concentration in river water, used as environmental sample model, higher detection limit was obtained (0.2 μM), due to interfering species.

New Trends in Nanoclay-Modified Sensors

“…During the past decade, works devoted to the development of electrochemical devices suitable for the detection of pesticides have gained growing interest as innovative alternatives in terms of on-site detection, sensitivity, rapid response, miniature size, and low cost. Most reported papers have been devoted to the development of CLME for the detection of herbicides (such as mesotrione, glyphosate, phenyl urea herbicides, and paraquat) [3,20,[38][39][40][41] and fungicides (such as propineb, chlorpyrifos, or carbendazim) [42][43][44].…”

“…Among the possible organic molecules intercalated in the nanoclay interlayer, cetyltrimethylammonium (SaCTA) [20], didodecyldimethyl ammonium (SaDDA) [20], acetylcholinesterase (AChE) [43], or methyl viologen (MV) [38] are the most common ones. Moreover, nanoclays grafted with silane molecules have also been proposed as CLME [39,44]. In this case, several strategies have been employed and the properties of the grafted nanoclays depended on the nature of the solvents and the silane molecule.…”

“…They found that silane grafting was more effective in ethylene glycol (swelling) as solvent compared to toluene (non-swelling). Also, Yanke et al [44] investigated the effect of these two solvents on the grafting of an organophilic silane (octyltriethoxisilane) onto a smectitic clay to evaluate their abilities for electrochemical detection of organophilic pesticide. There, the grafting occurred exclusively on the edges of the clay particles without intercalation.…”

“…Table 2 summarizes the behavior of several CLME toward fungicide determination, mainly propineb, carbendazim, and chlorpyrifos [21,[42][43][44][45]. A broad range of CLME configuration was observed, ranging from the application of raw nanoclays to advanced nanoclay composites with mainly carbon nanotubes and metal NPs.…”

“…The same situation was observed for the determination of carbendazim by Namontmorillonite [45], showing a LOD considerably higher than the rest of the nanoclay sensors shown in Table 2. This drawback can be overcome with the montmorillonite organofunctionalization (Octyltriethoxisilane-Mt/CPE and Heteropolyacid Mt/GCE), which produces a decrease in the LOD in one order of magnitude [21,44].…”