Colorimetric sensing of imidacloprid in cucumber fruits using a graphene quantum dot/Au (III) chemosensor

The current research presents a very simple method for the colorimetric detection of imidacloprid using a graphene quantum dot/Au (III) chemosensor. The results demonstrated that there is an interaction between Au³⁺ ions and the imidazole group of the pesticide toward reduction of Au³⁺ to Au⁰ in the presence of graphene quantum dots. This phenomenon changes the color of gold nanoparticles from yellow to grey or red, and causes a shift in the peak of localized surface plasmon resonance (LSPR) as gold nanoparticles are formed or aggregated based on the concentration of imidacloprid. Imidacloprid was determined by the developed sensor in a linear area of 0.01–1 ppm with a detection limit of 0.007 ppm. Therefore, a simple, quick, and sustainable sensor has been developed for the determination of the investigated analyte. Moreover, the sensor was applied to determine imidacloprid in the real cucumber samples fairly successful.

Adsorption of textile dyes using an activated carbon and crosslinked polyvinyl phosphonic acid composite

Activated carbon is one of the most studied materials for the adsorption of textile dyes. The adsorptive properties of this material are a result of its high specific surface area and some of the functional groups acquired during the chemical activation. This work reports the preparation of a composite material using CarZN400 activated carbon and polyelectrolyte poly(VPA-co-TEGDMA). The adsorptive properties of the material obtained are a result of the combination of the high specific surface area of the carbon and the ionic exchange capability of the polyelectrolyte. The covering of the surface of activated carbon with poly(VPA-co-TEGDMA) allowed to obtain a composite material (CarZN400C) with greater adsorption capacity for cationic dyes compared to the carbon. The adsorption isotherms of the dyes fit Langmuir's model, and the adsorptive capacities for cationic dyes for CarZN400C ranged between 222 and 416 mg/g. The kinetic study showed that the adsorption of basic and acid dyes fit the pseudo-second order kinetic model. CarZN400C also exhibited the ability to adsorb textile dyes present in wastewater. It was observed that, when making a previous treatment of the wastewater using coagulation-flocculation followed by adsorption using CarZN400C, it was possible to obtain removal percentages of color close to 100%. The wastewaters treated by coagulation-flocculation and adsorption improved their quality by decreasing the value for COD.